How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data

Rudolf Suppes; Soraya Heuss-Aßbichler

doi:10.3390/resources10110110

Suppes, Rudolf;Heuss-Aßbichler, Soraya

2021-10-29 00:00:00

resources Article How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data 1 , 2 , 3 Rudolf Suppes * and Soraya Heuss-Aßbichler Institute of Mineral Resources Engineering (MRE), RWTH Aachen University, Wüllnerstr. 2, 52064 Aachen, Germany CBM GmbH—Gesellschaft für Consulting, Business und Management mbH, Horngasse 3, 52064 Aachen, Germany Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstr. 41, 80333 Munich, Germany; soraya@min.uni-muenchen.de * Correspondence: rudolf.suppes@rwth-aachen.de or suppes@cbm-ac.de Abstract: A sustainable raw materials (RMs) recovery from waste requires a comprehensive genera- tion and communication of knowledge on project potentials and barriers. However, a standardised procedure to capture sustainability aspects in early project development phases is currently missing. Thus, studies on different RM sources are not directly comparable. In this article, an approach is Citation: Suppes, R.; presented which guides its user through a practical interpretation of on-site exploration data on Heuss-Aßbichler, S. How to Identify tailings compliant with the United Nations Framework Classiﬁcation for Resources (UNFC). The Potentials and Barriers of Raw development status of the overall project and the recovery of individual RMs are differentiated. To Materials Recovery from Tailings? make the assessment results quickly comparable across different studies, they are summarised in a Part II: A Practical UNFC-Compliant heat-map-like categorisation matrix. In Part I of this study, it is demonstrated with the case study Approach to Assess Project tailings storage facility Bollrich (Germany) how a tailings mining project can be assessed by means of Sustainability with On-Site remote screening. In Part II, it is shown how to develop a project from ﬁrst on-site exploration to a Exploration Data. Resources 2021, 10, decision whether to intensify costly on-site exploration. It is concluded that with a UNFC-compliant 110. https://doi.org/10.3390/ assessment and classiﬁcation approach, local sustainability aspects can be identiﬁed, and a commonly resources10110110 acceptable solution for different stakeholder perspectives can be derived. Academic Editors: Andrea Thorenz and Armin Reller Keywords: anthropogenic raw materials; sustainability assessment; tailings recycling Received: 31 July 2021 Accepted: 15 October 2021 Published: 29 October 2021 1. Introduction A growing world population, the growth of emerging economies, and the global Publisher’s Note: MDPI stays neutral transition to a decarbonised energy supply lead to an increasing demand for mineral raw with regard to jurisdictional claims in materials (RMs) [1–4]. For more than a century, the annual average increase in global published maps and institutional afﬁl- mineral RM demand is reported to be 3% [1], and a 2- to 3-fold increased global demand iations. for Al, Cu, Fe, Mn, Ni, Pb and Zn is expected between 2010 and 2050 [5,6]. Due to net stock additions and low recycling rates, the primary mining industry is expected to remain an important supplier of RMs in the foreseeable future [6,7]. In mining, valuable RMs are extracted from ores by separating wanted from unwanted Copyright: © 2021 by the authors. minerals. A common method to do so is froth ﬂotation, which requires the ores to be ﬁnely Licensee MDPI, Basel, Switzerland. ground to a particle size of typically 10–200 m [8]. The unwanted minerals are rejected as This article is an open access article tailings, and they are usually stored in tailings storage facilities (TSFs). The global annual distributed under the terms and tailings production is estimated to lie in the range of 5–14 Gt [9], and it is estimated that conditions of the Creative Commons in China alone some 12,000 TSFs exist [10]. Globally, ore grades are decreasing and ore Attribution (CC BY) license (https:// complexities are increasing [11] so that the amount of produced tailings and energy spent creativecommons.org/licenses/by/ per unit of produced commodity are increasing. 4.0/). Resources 2021, 10, 110. https://doi.org/10.3390/resources10110110 https://www.mdpi.com/journal/resources Resources 2021, 10, 110 2 of 48 Despite continuous improvements in the construction and management of TSFs, they can be regarded as legacies with long-lasting environmental impacts, such as the occupation of large surface areas, and high external costs [12–16]. Risks associated with TSFs comprise the contamination of soil and water with acidic leachates or heavy metals, especially in the case of sulphidic tailings [13,17–19]. Other risks include dam stability issues which, on average, cause 2 to 3 annual TSF failures, leading to a contamination of large areas and threatening human lives [20,21]. The environmental impact of TSFs has increased public pressure on the primary mining industry to act more environmentally friendly [6,22,23]. At the same time, tailings contain usable RMs due to former processing inefﬁciencies or an emerging demand for RMs which were not exploitable in the past [24]. The active promotion of sustainability in RM sourcing in the past decade by institutions such as the European Commission (EC) has initiated a paradigm shift so that formerly regarded waste is now becoming interesting for valorisation [25–27]. Scientists have investigated the recovery of metalliferous or industrial minerals from tailings [28–30], or an alternative valorisation, e.g., in construction materials [31–33] or glass making [34–36]. A comprehensive exploration is required to identify if tailings can be valorised. How- ever, conventional case studies under consideration of the Committee for Mineral Reserves International Reporting Standards (CRIRSCO) classiﬁcation principles from the primary mining industry usually target single RMs and neglect other contained RMs (cf., Ref- erences [37–39]). Hence, the knowledge on their RM potential is incomplete. Usually, economic aspects are mainly considered in the primary mining industry [8,40], while environmental and social aspects of RMs recovery are mostly neglected or ignored; only recently have sustainability aspects been given greater attention [41]. The United Nations Sustainable Development Goals aim at a worldwide sustainable extraction of natural RMs [42]. Therefore, the prospects of mineral RMs recovery requires environmental and social aspects to be regarded as equal to economic ones. As a result, these aspects must be assessed concurrently with geological, technological, and legal aspects to obtain comprehensive exploration results [43]. This is possible when applying the United Nations Framework Classiﬁcation for Resources (UNFC) principles, which are based on the 3 categories: degree of conﬁdence in the estimates (G category), technical feasibility (F category), and environmental-socio-economic viability (E category) [44]. In this way, decision-makers in RM management can get an overview of the potentials and barriers of mineral RMs recovery from tailings and its competitiveness across different RM sources. In mineral RM exploration in the primary mining industry, a mineral deposit is ﬁrst identiﬁed with remote techniques [8,45]. It is then investigated on site with intensiﬁed tech- niques to obtain data for a ﬁrst techno-economic assessment, termed a scoping study [8,45]. Despite the many recent case studies on anthropogenic RMs developed in analogy to natural RMs [46], a standardised procedure is missing. Existing case studies provide a snapshot of a speciﬁc stage of project development in the RMs recovery chain [47], e.g., the remote exploration [48]. Hence, there is a research gap in the development of case studies which outline the progression of RMs recovery project development [47]. This study addresses the lack of a standardised procedure to explore tailings as anthro- pogenic RMs. It is the ﬁrst to demonstrate how a UNFC-compliant tailings mining project assessment and classiﬁcation can evolve from a ﬁrst remote TSF screening (Part I [43]) to a consecutive interpretation of on-site exploration data (Part II). In this article, a systematic and practical UNFC-compliant approach is developed for a very preliminary assessment and classiﬁcation of tailings mining projects based on on-site exploration data. It is tested to what extent an overview of project potentials and barriers can be obtained. The research questions are: (1) is it possible to reconcile different stakeholder interests with a UNFC- compliant approach or must different perspectives be considered on their own merits? (2) which aspects should be considered in very preliminary UNFC-compliant assessments? (3) can a UNFC-compliant approach be used to identify site-speciﬁc project potentials and barriers? Resources 2021, 10, 110 3 of 48 The approach focuses on metalliferous tailings from industrial processes. A project’s development status is differentiated in terms of geological, technological, economic, envi- ronmental, social, and legal aspects. Beside the rating of the overall project, each contained RM is rated individually as a separate subproject. The rating is performed in a categorisa- tion matrix in a heat map-like style. In this way, driving factors as well as barriers can be identiﬁed quickly. The approach is tested with the case study TSF Bollrich (Germany) from a public decision-maker ’s perspective, considering the interests of local environmental non-governmental organisations (NGOs), private investors, and the city administration of Goslar. The TSF was chosen since it is a potential source of economically highly relevant RMs, it is situated in a complex environment with several stakeholders, and there is a potential to relieve the burden on the environment and society [43]. The article is structured as follows: (i) outline of the frame conditions for the further development of the case study Bollrich, (ii) proposal of a UNFC-compliant anthropogenic RMs assessment and classiﬁcation approach, (iii) development of a categorisation matrix for a UNFC-compliant rating of the overall project and subprojects for individual RMs, (iv) case study application, and (v) discussion of the developed approach. 2. Terms and Methods 2.1. Key Words and Deﬁnitions TSF: physical structure for tailings storage. Deposit: potential RM source. Target minerals: minerals wanted for valorisation. Other minerals: unwanted minerals. Recovery: physical extraction process. Material recovery: extraction of minerals to be used in con- struction materials. Tailings mining: process from exploration, recovery, and processing to rehabilitation. A very preliminary study is regarded as an analogue to a scoping study from the primary mining industry [45] (p. 31), and it is deﬁned as follows: it is the ﬁrst quantiﬁca- tion of a tailings mining project’s potentials and barriers with respect to geological, technological, economic, environmental, social, and legal aspects. The degree of uncertainty in the estimates is high. The study is based on directly generated project data, for instance from on-site exploration or information from other sources such as from the literature and model assumptions based on similar projects. Technological considerations are based on conceptual foundations. 2.2. Considerations for the Development of the Case Study TSF Bollrich This case study is based on the screening results from Reference [43], where the following potentials are identiﬁed: an economic interest in the TSF is justiﬁed due to its size and the presumably contained critical raw materials (CRMs) BaSO and In, as well as the highly economically relevant RMs Ag, Au, Cu, Pb, and Zn. The development costs are expected to be low since buildings, transportation, and utilities infrastructure are present in the near vicinity. As Germany has a high rating on the ease of doing business ranking, favourable regulatory conditions for an investment can be assumed. The TSF’s environment is vulnerable to a potential TSF failure: the nearest human settlement is located ~400 m downstream of the TSF, and the high score on the Human Footprint Index indicates that land-use-related social tension with competing interests can be expected in the area. Therefore, a removal of the TSF would reduce the potentially severe risks of a TSF failure. The following barriers are identiﬁed [43]: the TSF is located in a challenging envi- ronment with a potential for social conﬂicts due to agricultural, forest, industrial and commercial, nature and water protection, recreation, and residential areas in the near vicin- ity. A diverse and socially active stakeholder group of a minimum of 18 parties could be identiﬁed, which may potentially form a strong base for a project rejection. Amongst others, these include environmental NGOs, the Development Association Cultural Heritage Ore Mine Rammelsberg, and the Air Sports Community Goslar. The geological knowledge on the deposit is limited due to unknown RM quantities and qualities. Furthermore, poten- tially contained RMs are presumed based on literature on mined ores and their processing. Knowledge on the TSF’s geomechanical stability is missing. Valuable ecosystems with Resources 2021, 10, x FOR PEER REVIEW 4 of 47 Mine Rammelsberg, and the Air Sports Community Goslar. The geological knowledge on Resources 2021, 10, 110 4 of 48 the deposit is limited due to unknown RM quantities and qualities. Furthermore, poten- tially contained RMs are presumed based on literature on mined ores and their pro- cessing. Knowledge on the TSF’s geomechanical stability is missing. Valuable ecosystems with protected species have formed as a result of ecological succession. To overcome these protected species have formed as a result of ecological succession. To overcome these barriers, on-site exploration and evaluating techno-economic feasibility is required; local barriers, on-site exploration and evaluating techno-economic feasibility is required; lo- stakeholders’ environmental, social, and economic interests must be considered; and ad- cal stakeholders’ environmental, social, and economic interests must be considered; and vantages and disadvantages of RMs recovery need to be weighed against each other. advantages and disadvantages of RMs recovery need to be weighed against each other. 2.3. UNFC-Compliant Anthropogenic Raw Materials Assessment and Classiﬁcation Approach 2.3. UNFC-Compliant Anthropogenic Raw Materials Assessment and Classification Approach The assessment and classiﬁcation approach from Heuss-Aßbichler et al. [47] (p. 17) The assessment and classification approach from Heuss-Aßbichler et al. [47] (p. 17) was adopted and modiﬁed by adding sub-steps and assigning assessment methods. The was adopted and modified by adding sub-steps and assigning assessment methods. The modiﬁed approach consists of 3 phases (cf., Figure 1), which can be reiterated when addi- modified approach consists of 3 phases (cf., Figure 1), which can be reiterated when addi- tional information is required or when new information on preceding steps is generated: tional information is required or when new information on preceding steps is generated: 1. Deﬁnition of project and generation of information. 1. Definition of project and generation of information. 2. Assessment of project’s development status. 2. Assessment of project’s development status. 3. UNFC-compliant categorisation of criteria and project classiﬁcation. 3. UNFC-compliant categorisation of criteria and project classification. selected TSF for very preliminary (re-)assessment 1) definition of project & generation of information other research (literature, on-site exploration public data bases, etc.) compilation of knowledge base: • basic information (location, deposition, history, etc.) • mineral- & material-centric information setting objectives of the project model assumptions scenario modelling 2) assessment of projec t’s development status techno-economic assessment environmental assessment material flow analysis [MFA] social assessment economic assessment legal assessment (discounted cash flow [DCF]) sensitivity & uncertainty analysis 3) UNFC-com pliant categorisation of criteria & project classification interpretation of assessment results placing results in categorisation matrix for: • overall project • subprojects for individual raw materials [RMs] project classification inventory for future study proceed with preliminary study Figure 1. Practical UNFC-compliant approach for a systematic assessment and classification of min- Figure 1. Practical UNFC-compliant approach for a systematic assessment and classiﬁcation of eral RMs recovery from tailings at very preliminary level. The leftwards arrow over rightwards mineral RMs recovery from tailings at very preliminary level. The leftwards arrow over rightwards arrow indicates mutual influence, and the dotted circles indicate possible reiteration steps. arrow indicates mutual inﬂuence, and the dotted circles indicate possible reiteration steps. Resources 2021, 10, 110 5 of 48 2.4. Case Study Assessment Methods 2.4.1. Environmental Assessment TSF-related risks can have a great inﬂuence on the classiﬁcation result of a tailings mining project [49]. Based on data from scientiﬁc literature, publicly accessible sources, and observations on Google Earth [50], a status quo risk assessment is performed. The TSF’s stability and its impacts on the surrounding environment is assessed, including the following subjects of protection (adopted from Reference [51]): air, ﬂora and fauna, ground, groundwater, human health, landscape, and surface water. 2.4.2. Social Assessment Investors are recognising that ignoring social aspects in project development can create barriers to RMs recovery [6]. Amongst others, it is therefore important to consider the attitudes of local stakeholders such as communities towards a possible RMs recovery. From the stakeholders identiﬁed in Reference [43], this study focused on administrative bodies, industry, and local environmental NGOs as proxies for concerned citizens. Due to a lack of data, only basic tendencies on stakeholder attitudes are assessed. The assessment is based on an internet search and the study of Bleicher et al. [52] who interviewed stakeholders on a potential RMs recovery from mine waste in the Harz region including the TSF Bollrich. They focused on stakeholders from non-speciﬁed local and regional environmental NGOs, industry, administrative bodies, and scientiﬁc institutions, and they considered secondary sources such as public media. 2.4.3. Material Characterisation and Material Flow Analysis The drill core sampling campaigns on the TSF Bollrich for tailings characterisation are described in References [53,54]. 3 scenarios are developed: no RMs recovery (NRR0), con- ventional RMs recovery (CRR1), and enhanced RMs recovery (ERR2). The amount and com- position of generated commodities and residues are evaluated with a material ﬂow analysis (MFA) according to Reference [55] under consideration of available recovery technologies: 1. Scenario deﬁnition and selection of relevant processes and mass ﬂows. 2. Mass ﬂow quantiﬁcation with published and estimated data, and model assumptions for unavailable data. 3. Mass ﬂow visualisation with Sankey diagrams. 2.4.4. Economic Assessment The economic viability is assessed with a discounted cash ﬂow (DCF) analysis to determine the net present value (NPV) before taxes, considering internal costs and revenues. The NPV is estimated with the open-source software R (www.r-project.org, accessed on 16 January 2021) after N PV = I + I /(1 + r) , (1) 0 å i i=1 where I is the initial investment [ ] in year 0, I is the net cash ﬂow [ ] in the i-th year, r is 0 i the discount rate [-], and t is the project’s duration [a]. Given estimated ﬁgures for target mineral masses, prices and recovery rates are rounded down; they are rounded up for costs to estimate conservatively as per CRIRSCO [45]. 2.4.5. Sensitivity and Uncertainty Analysis To increase the reliability of the assessment, sensitivity and uncertainty analyses is performed [56]. The sensitivity analysis is performed by varying input factors to determine how the outputs depend on them. The uncertainties are assessed with dynamic price forecasts by applying autoregressive functions to historical price data of metals, minerals, diesel, and electric energy (cf., Supplementary Materials, Figures S1–S9). Resources 2021, 10, 110 6 of 48 2.4.6. Legal Assessment The legal aspects right of mining, environmental protection, and water protection are considered. Due to a lack of data, the state of development of legal aspects are assessed by making basic considerations based on data from Reference [53]. 2.5. Development of a Categorisation Matrix for a UNFC-Compliant Project Rating In the categorisation matrix, the overall project and subprojects for individual RMs are differentiated. The UNFC’s G, F, and E categories are addressed. The E category is subdivided into economic (a), environmental (b), social (c), and legal (d) aspects, the latter being deﬁned as a distinct subcategory in this article. For the project categorisation and classiﬁcation, an exemplary 35 factors for the rating of the overall project and 9 factors for the rating of the subprojects for individual RMs are assessed. They are adapted and modiﬁed after a literature search on established assessment factors from the primary mining industry, literature on sustainability in mining, case studies, and our own reasoning. Table 1 provides an overview of the chosen factors, their allocation to groups, and the rationale for choosing them based on their inﬂuence on a project. A proposal is made for a UNFC-compliant rating with descriptive indicators to describe a state and performance indicators to quantitatively compare the status quo with target values. For better legibility, the categorisation matrix is divided into separate tables (cf., Appendix A, Tables A1–A10). With the above nomenclature, an exemplary rating in the social subcategory might look like E3.1c or E1c. Factors with high uncertainty remain in the 3rd UNFC subcategorisation (3.1, 3.2, 3.3), while more developed factors can be rated as high as in the 1st UNFC category (1, 2, 3). For a quick overview of project potentials and barriers, an individual colour is assigned to each rating. In the discussion in Section 4.1, the rating results are presented in a heat-map-like style for a quick overview. Table 1. Categorisation matrix: assessed factors and rationale behind their application based on their inﬂuence on a project. Category & Factor Inﬂuence on UNFC Axis overall project rating geological conditions (relevant for project development) (1) quantity, (2) quality, (3) homogeneity potential proﬁtability, mine planning, overall uncertainty G TSF condition & risks (relevant for project development) (4) ordnance exploration costs, overall project safety F mine planning considerations (relevant for project execution) (5) mine/operational design, (6) metallurgical testwork, reliability of the ﬁnancial analysis, efﬁciency of the operation, F (7) water consumption environmental footprint infrastructure (relevant for project development) (8) real estate, (9) mining & processing, (10) utilities, project viability, ramp-up time F (11) transportation & access post-mining state (relevant for future impacts) (12) residue storage safety, (13) rehabilitation necessary aftercare measures, public acceptance F microeconomic aspects (relevant for project development) (14) economic viability, (15) economic uncertainty potential returns, investor interest E a ﬁnancial aspects (relevant for project development) (16) investment conditions, (17) ﬁnancial support potential returns, investor interest, security of investment E a environmental impacts during project execution (18) air emission, (19) liquid efﬂuent emission, (20) noise mine planning, local population, local ecosystems E b emission environmental impacts after project execution (21) biodiversity quality of ecosystem after the project E b (22) land use land which can be repurposed (23) material reactivity aftercare measures, local ecosystems social impacts during project execution (24) local community, (25) health & safety, (26) human rights & social acceptance, peace & wellbeing, (unforeseeable) costs for E c business ethics compensation Resources 2021, 10, 110 7 of 48 Table 1. Cont. Category & Factor Inﬂuence on UNFC Axis social impacts due to project execution (27) wealth distribution, (28) investment in local human capital social peace & wellbeing, employment of local population, E c (29) degree of RM recovery, (30) RM valorisation valuable legacy for workers & society after mine closure Resources 2021, 10, x FOR PEER REVIEW 8 of 47 amount of new residues, ecological risks, effort for & efﬁciency of future RMs recovery social impacts after project execution (31) aftercare, (32) landscape social risks, social wellbeing, external costs E c (7) no losses & dilution of tailings occur during mining & transport. legal situation (relevant for project development) (8) the processing plant produces 3 types of products: (i) a pure industrial mineral concentrate (BaSO4), (ii) a (33) right of mining, (34) environmental protection,(35) water project feasibility, social acceptance, effort for formal project E d mixed sulphide concentrate (CuFeS2, PbS, ZnS) including all high-technology metals (Co, Ga, In), & (iii) mixed protection planning residues due to inefficiencies in mineral processing. subproject for individual RMs rating geological conditions (relevant for project (9 development) ) smelters pay for the recoverable Co, Ga, & In content in the mixed sulphide concentrate based on a recov- (36) quantity, (37) quality, (38) homogeneity potential proﬁtability, mine planning, RM uncertainty G ery with ammonia leaching as specified in Reference [60]. mine planning considerations (relevant for project execution) (10) a discount rate of 15% is chosen to reflect a high risk investment [8]. (39) recoverability efﬁciency of the operation, amount of new residues F Above-ground landfill for contaminated but non-hazardous waste such as pre-treated domestic microeconomic aspects (relevant for project development) waste or commercial mineral waste. Geological base and surface sealing is required. (40) demand, (41) RM criticality, (42) price development project viability, investor interest, overall project risk E a impacts after project execution (43) solid matter, (44) eluate environmental risks of new deposition, aftercare measures E b 3.1.2. Setting Objectives of the Project a: economic aspects, b: environmental aspects, c: social aspects, d: legal aspects. Based on current research, the TSF Bollrich offers the potential for action by a public decision-maker at national level seeking a sustainable solution at reasonable costs. Based 3. Results on the stakeholder assessment (cf., Section 3.2.2), 3 relevant stakeholder perspectives are 3.1. Deﬁnition of the Project and Generation of Information considered: NGOs with environmental concerns due to TSF-related risks, private inves- 3.1.1. Knowledge Base on the Case Study Deposit tors seeking economic opportunities, and the city administration of Goslar seeking an op- The tailings deposit Bollrich (cf., Figure 2) near Goslar was part of the Rammels- portunity to create high-value jobs and to establish a regional recycling industry. berg mining operation [57]. It contains BaSO , Co, Ga, and In, which are CRMs in the The selected scenarios’ objectives are: no RMs recovery (NRR0)—a physically and European Union (EU), and the elements Cu, Pb, and Zn, which are economically highly chemically stable, maintenance-free structure is created. Environmental and social risks important in the EU [58]. The deposit is nationally relevant as it is one of the few possible are minimised by preventing the release of contaminants due to recovery and by avoiding CRM sources [59]. The ﬁrst exploration with a focus on geological aspects took place in the transport of hazardous material in a vulnerable region. The environment is rehabili- 1983 before its abandonment in 1988 after ca. 50 years of operation [54]. In the 2010s, tated, and the current landform is retained. RMs recovery (CRR1)—application of conven- the exploration’s main focus was on mineral processing. Geological, technological, en- tional technologies with off-site residue disposal. The original landform is restored, and vironmental, legal, [53] and social aspects [52] were also investigated. A comprehensive the area is rehabilitated. RMs recovery (ERR2)—the same processes as in CRR1 but the assessment of a potential tailings mining project has not been carried out. produced residues are sold to a local recycling company. Figure 2. Schematic illustration of the TSF Bollrich’s near environment: (a) marks the main dam, (b) Figure 2. Schematic illustration of the TSF Bollrich’s near environment: (a) marks the main dam, (b) the middle dam, (c) the water retention dam, (d) the disused processing plant, (e) a glider airfield, the middle dam, (c) the water retention dam, (d) the disused processing plant, (e) a glider airﬁeld, and (f) the disused landfill Paradiesgrund. The neutralisation sludge between the dams (b,c) is yel- and (f) the disused landﬁll Paradiesgrund. The neutralisation sludge between the dams (b, c) is lowish. The white dotted line marks the disused railway connection from Oker to the processing yellowish. The white dotted line marks the disused railway connection from Oker to the processing plant, (i) the stream of neutralised mine water, (ii) the connection between the pond Gelmketeich plant, (i) the stream of neutralised mine water, (ii) the connection between the pond Gelmketeich and and the water retention pond, and (iii) the river Gelmke. Adapted after Google Earth [50]. the water retention pond, and (iii) the river Gelmke. Adapted after Google Earth [50]. 3.1.3. Scenario Modelling In the rehabilitation scenario (NRR0), a leachate collection system is installed, the TSF is stabilised by in-situ concrete injection, its surface is sealed, and leachates are captured and treated on site in a 5-year closure phase. In a 30-year aftercare phase, emissions and the TSF’s stability are monitored. Reference data is used for the techno-economic assess- ment (cf., Tables A12 and A13). No historical data is available for a price forecast. Resources 2021, 10, 110 8 of 48 In this study, the deposit in its current condition is assessed and classiﬁed from a sustainability viewpoint, considering the area around the TSF within a radius of 10 km. Information was derived from the existing scientific studies on the deposit in Refer- ences [52–54,60] and from publicly available data sources. The knowledge base on the deposit is summarised in Table A11. The material ﬂows and economics are evaluated quantitatively based on published data and model assumptions for unavailable data (cf., Table 2). Table 2. Summary of model assumptions for the case study TSF Bollrich. Model Assumption (1) for in-situ rehabilitation, TSF abandonment is performed as for DK II class landﬁlls under the German Landﬁll Regulation (DepV) [61]. (2) mass of dam material is neglected in mineral RMs recovery scenarios alongside its further treatment. (3) freight costs for commodities & residues to downstream processes are neglected. (4) all equipment can be used over the whole life of mine (LOM) without renewal except for the pipelines & pumps, which are exchanged in year 6 of the mining operation due to abrasive wear. (5) processing plant Bollrich: assets can be used (for operation, administration, etc.), processing machinery can be reactivated, & the BaSO concentrate can be conditioned on site; basic infrastructure is in place. (6) experimental tailings recovery rates from lower pond applicable to tailings from upper pond, neglecting the inﬂuence of neutralisation sludge on processing. (7) no losses & dilution of tailings occur during mining & transport. (8) the processing plant produces 3 types of products: (i) a pure industrial mineral concentrate (BaSO ), (ii) a mixed sulphide concentrate (CuFeS , PbS, ZnS) including all high-technology 4 2 metals (Co, Ga, In), & (iii) mixed residues due to inefﬁciencies in mineral processing. (9) smelters pay for the recoverable Co, Ga, & In content in the mixed sulphide concentrate based on a recovery with ammonia leaching as speciﬁed in Reference [60]. (10) a discount rate of 15% is chosen to reﬂect a high risk investment [8]. Above-ground landﬁll for contaminated but non-hazardous waste such as pre-treated domestic waste or commercial mineral waste. Geological base and surface sealing is required. 3.1.2. Setting Objectives of the Project Based on current research, the TSF Bollrich offers the potential for action by a public decision-maker at national level seeking a sustainable solution at reasonable costs. Based on the stakeholder considerations (cf., Section 3.2.2), 3 relevant stakeholder perspectives are considered: NGOs with environmental concerns due to TSF-related risks, private investors seeking economic opportunities, and the city administration of Goslar seeking an opportunity to create high-value jobs and to establish a regional recycling industry. The selected scenarios’ objectives are: no RMs recovery (NRR0)—a physically and chemically stable, maintenance-free structure is created. Environmental and social risks are minimised by preventing the release of contaminants due to recovery and by avoiding the transport of hazardous material in a vulnerable region. The environment is rehabilitated, and the current landform is retained. RMs recovery (CRR1)—application of conventional technologies with off-site residue disposal. The original landform is restored, and the area is rehabilitated. RMs recovery (ERR2)—the same processes as in CRR1 but the produced residues are sold to a local recycling company. 3.1.3. Scenario Modelling In the rehabilitation scenario (NRR0), a leachate collection system is installed, the TSF is stabilised by in-situ concrete injection, its surface is sealed, and leachates are captured and treated on site in a 5-year closure phase. In a 30-year aftercare phase, emissions and the Resources 2021, 10, 110 9 of 48 Resources 2021, 10, x FOR PEER REVIEW 9 of 47 TSF’s stability are monitored. Reference data is used for the techno-economic assessment (cf., Tables A12 and A13). No historical data is available for a price forecast. Figure 3 outlines the general project for CRR1 and ERR2 from a material ﬂow per- Figure 3 outlines the general project for CRR1 and ERR2 from a material flow per- spective. Geotechnical and mine planning considerations are conceptual. The low mineral spective. Geotechnical and mine planning considerations are conceptual. The low mineral content estimated in Reference [53] is adopted to estimate conservatively (cf., Table A11). content estimated in Reference [53] is adopted to estimate conservatively (cf., Table A11). A homogeneous deposit is assumed. The tailings are mined in a dredging operation (cf., A homogeneous deposit is assumed. The tailings are mined in a dredging operation (cf., Figure S10) and processed on site in the existing processing plant at a constant rate over a Figure S10) and processed on site in the existing processing plant at a constant rate over a 10-year period, followed by a 1-year rehabilitation period. The products leave the system 10-year period, followed by a 1-year rehabilitation period. The products leave the system boundaries at the mineral processing plant’s outlet where the reference point is set. The boundaries at the mineral processing plant’s outlet where the reference point is set. The target minerals are extracted with a multi-stage froth ﬂotation as speciﬁed by Roemer [60] target minerals are extracted with a multi-stage froth flotation as specified by Roemer [60] (cf., Table A16) based on a sampling campaign on the lower pond [53]. A pure industrial (cf., Table A16) based on a sampling campaign on the lower pond [53]. A pure industrial mineral concentrate (BaSO ), a mixed sulphide concentrate containing base metals (Cu, Pb, mineral concentrate (BaSO4), a mixed sulphide concentrate containing base metals (Cu, Zn) and high-technology metals (Co, Ga, In), and mixed residues are produced. Tailings, Pb, Zn) and high-technology metals (Co, Ga, In), and mixed residues are produced. Tail- commodity, and residue masses are estimated as dry matter. ings, commodity, and residue masses are estimated as dry matter. saleable quantities recovery of market / reference point (commodities) extractable quantities: downstream source of treatment: dredging processes anthropogenic raw mineral non-saleable materials: tailings processing quantities (residues) disposal Figure 3. Tailings mining project Bollrich for the mineral RMs recovery scenarios (CRR1, ERR2) Figure 3. Tailings mining project Bollrich for the mineral RMs recovery scenarios (CRR1, ERR2) from from a material flow perspective. The light grey and dark grey shaded fields illustrate the spatial a material ﬂow perspective. The light grey and dark grey shaded ﬁelds illustrate the spatial and and mineral processing system boundaries, respectively. mineral processing system boundaries, respectively. The database with fixed and variable parameters for the techno-economic assessment The database with ﬁxed and variable parameters for the techno-economic assessment is given in Tables A14–A16. Energy flows are considered for tailings recovery and pro- is given in Tables A14–A16. Energy ﬂows are considered for tailings recovery and pro- cessing. Initial and intermediate investment costs for mining and processing equipment, cessing. Initial and intermediate investment costs for mining and processing equipment, and infrastructure, are included in the capital expenditure (CAPEX). Variable costs for and infrastructure, are included in the capital expenditure (CAPEX). Variable costs for mining, processing, electric and mechanical maintenance, administration, and general ser- mining, processing, electric and mechanical maintenance, administration, and general vices are included in the operating expenditure (OPEX). Revenues are realised immedi- services are included in the operating expenditure (OPEX). Revenues are realised imme- ately. In ERR2, the mixed residues are sold to a recycling company for an application in diately. In ERR2, the mixed residues are sold to a recycling company for an application construction materials. Mine site preparation costs are estimated to be low due to the sim- in construction materials. Mine site preparation costs are estimated to be low due to the ple mine plan, good mine site accessibility by road, and the availability of buildings for simple mine plan, good mine site accessibility by road, and the availability of buildings for the processing plant and the operation’s administration. Mine site rehabilitation costs the processing plant and the operation’s administration. Mine site rehabilitation costs such such as for revegetation and environmental monitoring are considered. Assets and ma- as for revegetation and environmental monitoring are considered. Assets and machinery chinery are liquidated at the operation’s end at a residual value of 10%. are liquidated at the operation’s end at a residual value of 10%. Certain relevant aspects are out of the scope of this study: costs for preventing emis- Certain relevant aspects are out of the scope of this study: costs for preventing sions during development, mining, transport and processing, for renewing the railway emissions during development, mining, transport and processing, for renewing the railway access, for removing roads and railway at mine closure, for treating and disposing of wa- access, for removing roads and railway at mine closure, for treating and disposing of water ter from mining and processing, and downstream processing. from mining and processing, and downstream processing. The uncertainty analysis comprises 3 price forecasts: pessimistic (p), mean (m), and The uncertainty analysis comprises 3 price forecasts: pessimistic (p), mean (m), and optimistic (o), after which the respective scenarios are named (CRR1p, CRR1m, etc.). The optimistic (o), after which the respective scenarios are named (CRR1p, CRR1m, etc.). The pessimistic pessimistic and and optimistic optimistic for forec ecasts asts re refer fer to to the the l lower ower a and nd upper upper limits limits of of the the 95% 95% conf conﬁ-i- dence dence interval, interval, r respectively espectively. CuFeS . CuFeS , 2, PbS, and PbS, and ZnS ZnS co concentrate ncentrate prices prices are estim are estimated ated [62]. [62]. Prices Pricesfor forselling sellingand andcosts costsfo for r disposing disposing o of fr esidues residuesar are e ﬁxed fixed due due to to a a lack lack of of data. dataThe . The mean price forecast (m), representing the most realistic case, is focussed. Material ﬂow mean price forecast (m), representing the most realistic case, is focussed. Material flow uncertainties uncertainties ar are n e neglected eglected as as t the he dependence dependence on p on price rice and and cost cost variations variations is is focussed. focussed. 3.2. Case Study Assessment 3.2. Case Study Assessment 3.2.1. Environmental Assessment: Status Quo Risks 3.2.1. Environmental Assessment: Status Quo Risks The area around the TSF is contaminated with heavy metals such as As, Cd, and Pb, The area around the TSF is contaminated with heavy metals such as As, Cd, and Pb, which partially exceed the concentration threshold values for soil in parks and recreational which partially exceed the concentration threshold values for soil in parks and recrea- areas in Germany [63,64]. However, the source of pollution could also be the former tional areas in Germany [63,64]. However, the source of pollution could also be the former transport of ores via the Bollrich area to smelters in Oker [65]. Hence, the TSF’s contribu- tion to the pollution is unknown. Resources 2021, 10, 110 10 of 48 transport of ores via the Bollrich area to smelters in Oker [65]. Hence, the TSF’s contribution to the pollution is unknown. No data is available on the TSF’s impact on human health, local ﬂora and fauna, and surface and groundwater as there currently is no monitoring in place [53]. Dust emissions from the TSF can be excluded due to the wet tailings storage. The neutralisation sludge is unlikely to emit dust as it hardens when being exposed to air [54]. Heavy-metal-laden seepage is collected at the foot of the dam and returned into the TSF [53]. However, the unsealed TSF base constitutes a risk for the release of contaminants [53]. A general safety concern is that the TSF is freely accessible (observed on Google Earth [50]), and there are several trails around the TSF (https://regio.outdooractive.com/oar-goslar/de/ touren/#ﬁlter=r-fullyTranslatedLangus-,sb-sortedBy-0&zc=15,10.46323,51.90085, accessed on 16 January 2021). Hence, people who are not familiar with the area may come in direct contact with the TSF. The main dam’s stability in its current state and in the case of extreme rainfalls could be conﬁrmed by conservative calculations [66]. However, 2 sinkholes in karstiﬁed zones in near vicinity to the TSF were reported [53]. The knowledge on the karstiﬁed zones is limited [53] so that the long-term risk for the TSF’s stability is currently unknown. 3.2.2. Social Assessment: Stakeholder Considerations The Harz region has an ore mining history ranging from the Middle Ages to the 1980s [52]. Today, the region is facing the challenges of demographic change, young peo- ple’s emigration, a weak economy, and environmental burdens from former mining [52,65]. A particularity is the Goslar community’s and city administration’s strong awareness of the region’s mining history, which is regarded as a cultural heritage and an important factor for tourism [52,65]. This can be observed in public social media such as the Goslar Tales forum: the category Mines and Smelters has 70 topics from 2011 to 2019 with 925 contribu- tions (http://www.goslarer-geschichten.de/forum.php, accessed on 26 September 2020). The TSF’s history, basic knowledge, opinions, and safety concerns on water quality are discussed, and photos and videos are shared. The results of Bleicher et al. [52] are summarised: generally, RMs recovery from mine waste is regarded as a development opportunity for the Harz region, and the trust in scientists and the industry is shared by public media. Scientiﬁc institutions and the industry are identiﬁed as the current regional drivers of CRMs recovery from mine waste. All interviewed stakeholders were in favour of developing knowledge and technologies for mine waste valorisation, with the exception of minor criticism from an environmental activist about the presumption of scientists that good ideas are approved by everyone. However, environmental NGOs see RMs recovery from mine waste as an opportunity to at least partially rehabilitate the environment. The city’s administration is interested in RMs recovery from mine waste since the establishment of a recycling industry might attract highly skilled workers, and the possible knowledge transfer with scientiﬁc institutions and the opportunity to test novel technologies is seen as one of the region’s strengths. 3.2.3. Techno-Economic Assessment: Material Flow Analysis No material ﬂow takes place in NRR0 due to in-situ stabilisation. Figure 4 depicts the speciﬁc material ﬂows for the RMs recovery scenarios (CRR1, ERR2) (cf., Figure A1 for a detailed production breakdown). Over a 10-year period, 7.1 million t of tailings are mined and processed. In CRR1, 2.7 million t of commodities (i.e., 38 wt% of total tailings), and 4.4 million t of mixed mineral residues are produced. The commodities consist of an industrial mineral and a mixed sulphide concentrate. In ERR2, all tailings are valorised. The commodities (CRR1, ERR2) leave the system boundaries for off-site conditioning. Resources 2021, 10, 110 11 of 48 Resources 2021, 10, x FOR PEER REVIEW 11 of 47 CRR1 / ERR2 ∑ commodities + residues = 7,100,000 t industrial mineral concentrate commodities 1,300,000 t recovery of 2,700,000 t extractable quantities: reference point market / dredging mixed sulphide concentrate source of treatment: downstream anthropogenic raw 7,100,000 t mineral 1,400,000 t processes materials: tailings processing residues mixed residues 4,400,000 t 4,400,000 t disposal (CRR1) sales (ERR2) Figure 4. Material flow systems and 5-year material flows for the mineral RMs recovery scenarios Figure 4. Material ﬂow systems and 5-year material ﬂows for the mineral RMs recovery scenarios (CRR1, ERR2). The light grey and dark grey shaded fields illustrate the spatial and mineral pro- (CRR1, ERR2). The light grey and dark grey shaded ﬁelds illustrate the spatial and mineral processing cessing system boundaries, respectively. All figures were rounded to the sixth digit. system boundaries, respectively. All ﬁgures were rounded to the sixth digit. 3.2.4. Techno-Economic Assessment: Discounted Cash Flow Analysis 3.2.4. Techno-Economic Assessment: Discounted Cash Flow Analysis Table 3 summarises the results of the DCF analysis (cf., Figures S15–S17). Generally, Table 3 summarises the results of the DCF analysis (cf., Figures S15–S17). Generally, mineral RMs recovery is economically viable (CRR1m, ERR2m) under the project’s cur- mineral RMs recovery is economically viable (CRR1m, ERR2m) under the project’s current state rent state of asses of assessment. sment. The DCF analy The DCF analysis yields sis yielpositive ds positiv NPVs e NPV in s iERR2 n ERRr 2egar rega dless rdless of of the the price price for forec ecast. ast. The The NPV NPV in inCRR1 CRR1 bec becomes omes n negative egative in in the pe the pessimistic ssimistic for forec ecast ast(CRR1p). (CRR1p). The NPVs of NRR0, CRR1m, and ERR2m are EUR 124.5 million, EUR 73.9 million, and The NPVs of NRR0, CRR1m, and ERR2m are EUR −124.5 million, EUR 73.9 million, and EUR EUR 172.5 172.5 m million, illion, re respectively spectively. . 98% 98% of of all all cost costss in in t the he rehabi rehabilitation litation scenar scenario io ( (NRR0) NRR0)ar ar ee attributed to the 5-year closure and leachate phase. In the mineral RMs recovery scenarios attributed to the 5-year closure and leachate phase. In the mineral RMs recovery scenarios (CRR1m, ERR2m), the largest share of revenues is attributed to BaSO with a 49% and (CRR1m, ERR2m), the largest share of revenues is attributed to BaSO4 with a 49% and 47% 47% contribution, respectively, and a share of the total commodity masses of 64.4 wt% and contribution, respectively, and a share of the total commodity masses of 64.4 wt% and 24.5 24.5 wt%, respectively. The second highest revenues are attributed to Zn with a contribution wt%, respectively. The second highest revenues are attributed to Zn with a contribution of 27% and 25%, respectively, and a ZnS share of the total commodity masses of 5.5 wt% of 27% and 25%, respectively, and a ZnS share of the total commodity masses of 5.5 wt% and 2.1 wt%, respectively. The high-technology metals Co, Ga, and In contribute least and 2.1 wt%, respectively. The high-technology metals Co, Ga, and In contribute least to to the revenues from RMs sales with a combined share of ca. 2% of total revenues and a the revenues from RMs sales with a combined share of ca. 2% of total revenues and a combined share of total commodity mass of 0.6% and 0.02%, respectively. combined share of total commodity mass of 0.6% and 0.02%, respectively. Residue disposal is the highest cost factor in CRR1m with a share of 62% of total costs. Table 3. Results of the DCF analysis. The rehabilitation scenario (NRR0) has a project duration of The OPEX is the second highest cost factor in CRR1m and the highest in ERR2m with a 35 years. The RMs recovery scenarios (CRR1, ERR2) has a project duration of 11 years. The left share of total costs of 21% and 58%, respectively. In both scenarios, the smallest cost factor column shows cost and revenue factors of the NPVs. Figures are given in millions of EUR. is electric energy consumption with a share of 0.8% and 2.4%, respectively. Scenarios Table 3. Results of the DCF analysis. The rehabilitation scenario (NRR0) has a project duration of 35 NRR0 CRR1p ERR2p CRR1m ERR2m CRR1o ERR2o years. The RMs recovery scenarios (CRR1, ERR2) has a project duration of 11 years. The left column NPV Factor shows cost and revenue factors of the NPVs. Figures are given in millions of EUR. total NPV 124.6 16.6 82.0 73.9 172.5 164.4 263.1 Scenarios costs NRR0 CRR1p ERR2p CRR1m ERR2m CRR1o ERR2o CAPEX - 14.6 14.6 14.6 14.6 14.6 14.6 NPV Factor OPEX - 29.1 29.1 29.1 29.1 29.1 29.1 total NPV −124.6 −16.6 82.0 73.9 172.5 164.4 263.1 diesel - 3.4 3.4 5.1 5.1 6.9 6.9 electric ener costs gy - 1.2 1.2 1.2 1.2 1.2 1.2 residue disposalCAPEX - - 87.7 −14.6 - −14.6 87.7−14.6 - −14.6 87.7−14.6 -−14.6 rehabilitation - 4.0 4.0 4.0 4.0 4.0 4.0 OPEX - −29.1 −29.1 −29.1 −29.1 −29.1 −29.1 closure & leachate phase 122.0 - - - - - - diesel - −3.4 −3.4 −5.1 −5.1 −6.9 −6.9 aftercare phase 2.6 - - - - - - electric energy - −1.2 −1.2 −1.2 −1.2 −1.2 −1.2 residue disposal - −87.7 - −87.7 - −87.7 - revenues BaSOrehabilitation - - 92.1 −4.0 92.1 −4.0 106.2−4.0 106.2−4.0 120.4−4.0 120.4−4.0 Cu - 9.4 9.4 14.9 14.9 20.3 20.3 closure & leachate phase −122.0 - - - - - - Pb - 14.1 14.1 30.5 30.5 47.0 47.0 aftercare phase −2.6 - - - - - - Zn - 6.1 6.1 58.2 58.2 110.2 110.2 revenues Co - 0.7 0.7 2.6 2.6 4.6 4.6 BaSO4 - 92.1 92.1 106.2 106.2 120.4 120.4 Ga - 0.3 0.3 0.7 0.7 1.0 1.0 Cu - 9.4 9.4 14.9 14.9 20.3 20.3 In - 0.2 0.2 2.1 2.1 4.1 4.1 Pb - 14.1 14.1 30.5 30.5 47.0 47.0 asset liquidation - 0.1 0.1 0.1 0.1 0.1 0.1 Zn - 6.1 6.1 58.2 58.2 110.2 110.2 residue sales - - 11.0 - 10.9 - 10.9 Co - 0.7 0.7 2.6 2.6 4.6 4.6 p: pessimistic price forecast (lower limit of 95% conﬁdence interval), m: mean price forecast, o: optimistic price Ga - 0.3 0.3 0.7 0.7 1.0 1.0 forecast (upper limit of 95% conﬁdence interval). In - 0.2 0.2 2.1 2.1 4.1 4.1 asset liquidation - 0.1 0.1 0.1 0.1 0.1 0.1 Resources 2021, 10, 110 12 of 48 Residue disposal is the highest cost factor in CRR1m with a share of 62% of total costs. The OPEX is the second highest cost factor in CRR1m and the highest in ERR2m with a share of total costs of 21% and 58%, respectively. In both scenarios, the smallest cost factor is electric energy consumption with a share of 0.8% and 2.4%, respectively. 3.2.5. Techno-Economic Assessment: Sensitivity and Uncertainty Analysis The NPV is most sensitive to BaSO price variations (cf., Figures A2 and A3). In CRR1m and ERR2m, a decreased BaSO price by 69% and 100% yields an NPV decrease of 100% and 62%, respectively. In CRR1m, decreased Pb and Zn prices by 100% yields an NPV decrease of 42% and 79%, respectively. In ERR2m, a decreased Zn price by 100% yields an NPV decrease of 34%. The NPV is relatively insensitive to other price variations. Residue disposal was the most inﬂuential cost factor in CRR1m, with a price increase of 84% yielding an NPV of zero. CAPEX and OPEX increases of 504% and 253% (CRR1m), respectively, and 1178% and 592% (ERR2m), respectively, yields NPVs of zero. 3.2.6. Legal Assessment: Basic Considerations The legal aspects for a possible project execution have not been considered so far. The TSF is still monitored under Mining Law (State Ofﬁce for Mining Energy and Geology (LBEG), personal communication, 16 September 2020). As for the right of mining, it needs to be assessed if the mining or waste legislation applies [67]. Goldmann et al. [53] rate the legal aspects for environmental protection as follows: strict legal restrictions and high efforts to achieve legal consent are expected since heterogeneous and high-quality ﬂora and fauna ecosystems were identiﬁed during preliminary on-site inspections. It is likely that an environmental impact study and a concept to protect the ecosystems and/or to remediate impacts upfront are necessary. Potential impacts on the surrounding protected natural areas and landscapes need to be assessed. As for water protection, potential impacts on the river Gelmke in near vicinity (cf., Figure 2) and the nearby Ammentalbach need to be assessed. Potential impacts on groundwater are unclariﬁed. 4. Discussion 4.1. Interpretation of the Case Study Results The rating results are summarised in the categorisation matrix in Tables 4 and 5. The justiﬁcation for the rating is given in Tables A17–A26. As no RMs are recovered in the rehabilitation scenario (NRR0), only the overall project is rated. The lowest rating in a category is chosen for the rating of the overall category (cf., Reference [68] (p. 37)). For NRR0, the categorisation matrix shows that the knowledge on the TSF’s geology has medium conﬁdence (G2). The rehabilitation scenario’s state of technological develop- ment has a low overall rating (F3) due to the uncertainty regarding possible ordnance, the conceptual operational design, the unclariﬁed usability of TSF water, and the unclariﬁed long-term storage safety. The infrastructural conditions (F1–F2) and rehabilitation planning (F2) are rated high. As only costs are incurred and as there currently is no knowledge on a potential ﬁnancial support, the economics are rated low (E3.3a). As for the environmental aspects, the unclariﬁed potential dust emission and in-situ cementation of reactive material lead to a low rating (E3.3b). As for the social aspects, only the retained landscape is rated positively (E2c). The legal aspects are generally underdeveloped (E3.3d). In CRR1m and ERR2m, the project can be expected to be economically viable (E3.1a). However, the NPV in the pessimistic forecast for CRR1 is negative. ERR2 is more resilient in this respect due to the sales of the new residues. The favourable economics of ERR2 are highlighted in the overall category rating (E.3.1a) as opposed to CRR1 (E3.3a) due to the higher uncertainty in the pessimistic price forecast. The driving revenue factor is the BaSO sales due to its relatively high grade (24.5 wt%), its high price compared to the other commodities, its high recovery rate (74%), and the forecasted price increase. The BaSO price is relatively stable, with the largest price drop being ca. 17% in the past 20 years (cf., Figure S3). CRR1m is relatively insensitive to BaSO price variations with the NPV 4 Resources 2021, 10, 110 13 of 48 becoming negative at a decreased BaSO price by 69%. ERR2 is more resilient with a BaSO 4 4 price drop to EUR 0, leading to a decreased NPV of 38%. In general, the presence of real estate, transportation, and utilities infrastructure reduces the mine development costs. Residue disposal is the greatest cost factor in CRR1 with 64% of all costs, and it is the greatest economic risk with a price increase of 93% leading to a negative NPV. A price increase is possible if a further conditioning is necessary to meet the criteria of disposal sites. Regarding CAPEX and OPEX, CRR1m and ERR2m are relatively insensitive to cost variations, and they are regarded as economically viable given that the estimates are in the accuracy and contingency range for scoping studies of 50% and 30%, respectively [45]. For the upper pond, there is high uncertainty regarding geological knowledge on the neutralisation sludge, as well as the Co, Ca, and In contents (G3). The TSF’s volume, and the BaSO and base metal contents are well known (G2). Metallurgical testwork on the tailings from the upper pond is missing (F3), and it is unknown if the neutralisation sludge could be valorised in ERR2. These tailings might be difﬁcult to process due to the high sulphate ion content [54]. If they need to be disposed of too, the disposal costs would increase in both scenarios (CRR1, ERR2). RMs recovery has a higher rating regarding environmental aspects as compared to rehabilitation only (NRR0). However, planning considerations such as the resettlement of rare ﬂora and fauna still requires fundamental work (E3.3d), and the RMs efﬁciency (E3.3c) and preservation of RMs for future generations (E3.2c) in CRR1 could be improved. In contrast, the complete tailings valorisation (E1c) and high RM efﬁciency (E3.1c) are positively highlighted in the categorisation matrix. The development status of social aspects is generally low, just as for legal aspects (E3.3d). For the individual RMs, a clear distinction in the geological and technological cate- gories between the development status for BaSO (G2F2), base metals (G2F2), FeS (G2F1), 4 2 and inert material (G2F1) can be seen as compared to the high-technology metals (G3F3). The development status for economic and environmental aspects is heterogeneous. Most RMs have a high economic importance or are CRMs in the EU, and all except for FeS and inert material have a clear demand. The mean RM price forecast yields increasing BaSO , Co, and In prices (E3.1a); stagnant Pb and Zn prices (E3.2a); and decreasing Cu and Ga prices (E3.3a). For the new residues, the Pb solid matter content and dissolved Pb in leachate impede a disposal as inert waste (DK 0 class) (E3.2b) [61]. On the extreme ends, Ga and FeS has the lowest (G3F3E3.3a) and highest (G2F1E3.2a) rating, respectively. In sum, all 3 scenarios are rated equally in the overall rating in terms of the degree of conﬁdence in the geological estimates and technical feasibility (G2F3). The scenarios differ in the economic performance with rehabilitation incurring costs only, and CRR1 having a higher uncertainty as compared to ERR2. Considering the proposed differentiation of the E category, the scenarios are categorised as G2/F3/E3.3a/E3.3b/E3.3c/E3.3d (NRR0), G2/F3/E3.3a/E3.2b/E3.3c/E3.3d (CRR1), and G2/F3/E3.1a/E3.2b/E3.3c/E3.3d (ERR2). The conversion into the current ofﬁcial UNFC categorisation yields G2F3E3 for all 3 sce- narios. There is currently no class for this categorisation [44]. In comparison to the categorisation of G4F3E3 in the preceding screening study [43], only the G category could be improved. Resources 2021, 10, 110 14 of 48 Table 4. Categorisation matrix for the overall project rating of the rehabilitation scenario (NRR0) and the mineral RMs recovery scenarios (CRR1, ERR2). Scenario Factor NRR0 CRR1 ERR2 UNFC G Category geological conditions (relevant for project development) (1) quantity G2 G2 G2 (2) quality G2 G2 G2 (3) homogeneity G2 G2 G2 UNFC F Category TSF condition & risks (relevant for project development) (4) ordnance F3 F3 F3 mine planning considerations (relevant for project execution) (5) mine/operational design F3 F3 F3 (6) metallurgical testwork - F3 F3 (7) water consumption F3 F1 F1 infrastructure (relevant for project development) (8) real estate F1 F1 F1 (9) mining & processing - F3 F3 (10) utilities F2 F2 F2 (11) transportation & access F2 F2 F2 post-mining state (relevant for future impacts) (12) residue storage safety F3 F3 F3 (13) rehabilitation F2 F2 F2 UNFC E Category microeconomic aspects (relevant for project development) (14) economic viability E3.3a E3.1a E3.1a (15) economic uncertainty - E3.3a E3.1a ﬁnancial aspects (relevant for project development) (16) investment conditions - E3.1a E3.1a (17) ﬁnancial support E3.3a E3.1a E3.1a environmental impacts during project execution (18) air emission E3.3b E3.1b E3.1b (19) liquid efﬂuent emission E3.1b E3.1b E3.1b (20) noise emission E3.2b E3.2b E3.2b environmental impacts after project execution (21) biodiversity E3b E3b E3b (22) land use E3.2b E3.2b E3.2b (23) material reactivity E3.3b E3.1b E3.1b social impacts during project execution (24) local community E3.3c E3.2c E3.2c (25) health & safety E3.3c E3.3c E3.3c (26) human rights & business ethics E3.3c E3.3c E3.3c social impacts due to project execution (27) wealth distribution E3.3c E3.3c E3.3c (28) investment in local human capital E3.3c E3.3c E3.3c (29) degree of RM recovery E3.3c E3.2c E1c (30) RM valorisation E3.3c E3.3c E3.1c social impacts after project execution (31) aftercare E3c E1c E1c (32) landscape E2c E1c E1c legal situation (relevant for project development) (33) right of mining E3.3d E3.3d E3.3d (34) environmental protection E3.3d E3.3d E3.3d (35) water protection E3.3d E3.3d E3.3d G2 G2 G2 F3 F3 F3 E3.3a E3.3a E3.1a total rating E3.3b E3.2b E3.2b E3.3c E3.3c E3.3c E3.3d E3.3d E3.3d a: economic aspects, b: environmental aspects, c: social aspects, d: legal aspects. Resources 2021, 10, 110 15 of 48 Table 5. Categorisation matrix for the subproject rating for individual RMs (CRR1, ERR2). Subprojects for RMs Factor BaSO Cu Pb Zn Co Ga In FeS Inert Material 4 2 UNFC G Category geological conditions (relevant for project development) (36) quantity G2 G2 G2 G2 G3 G3 G3 G2 G2 (37) quality G2 G2 G2 G2 G3 G3 G3 G2 G2 (38) homogeneity G2 G2 G2 G2 G3 G3 G3 G2 G2 UNFC F Category mine planning considerations (relevant for project execution) (39) recoverability F2 F2 F2 F2 F3 F3 F3 F1 F1 UNFC E Category microeconomic aspects (relevant for project development) (40) demand E3.1a E3.1a E3.1a E3.1a E3.1a E3.1a E3.1a E3.2a E3.3a (41) RM criticality E1a E2a E2a E2a E1a E1a E1a E2a E3a (42) price development E3.1a E3.3a E3.2a E3.2a E3.1a E3.3a E3.1a - - impacts after project execution (43) solid matter - E3.1b E3.2b E3.1b - - - - E1b (44) eluate E3.1b E3.1b E3.2b E3.1b - - - - E1b G2 G2 G2 G2 G3 G3 G3 G2 G2 F2 F2 F2 F2 F3 F3 F3 F1 F1 total rating E3.1a E3.3a E3.2a E3.2a E3.1a E3.3a E3.1a E3.2a E3.3a E3.1b E3.1b E3.2b E3.1b - - - - E1b 1 2 Wissenbach shales & ankerit. a: economic aspects, b: environmental aspects, c: social aspects, d: legal aspects. 4.2. Reconciliation of Stakeholder Perspectives with an Application of the UNFC Principles Environmental NGOs’ perspective: the TSF Bollrich constitutes an ecological burden in a sensitive environment with high potential long-term environmental and social risks [43]. Indeed, the TSF’s current geomechanical state is stable, but it requires constant maintenance such as the removal of large trees and assuring seepage in the main dam [66]. The TSF is an upstream dam type, which is the most vulnerable type [16,20]. The lacking knowledge on the karstiﬁed zones in the area and the former occurrence of sinkholes near the TSF are currently rated as non-problematic [53]. However, for a conservative approach, the risk must be rated high due to the uncertainty. A sudden release of the contained masses and toxic elements would cause widespread environmental destruction and social issues, and would threaten human lives [43]. Therefore, the long-term physical and chemical risks and associated legacy costs are regarded as a necessity to act. Hence, early actions are preferable, and the rehabilitation costs (NRR0) can be seen as external costs borne by society to prevent harm. As the TSF is integrated well into the landscape, being visible only from nearby hills or from close up, the beneﬁt of NRR0 is that the current landscape is mostly retained. On top, NRR0 has a relatively short duration of perceptible works on the TSF of 5 years. Hence, negative environmental and social impacts due to project execution are kept at a minimum as compared to RMs recovery (CRR1, ERR2). However, stabilising the tailings impedes a future RMs recovery. On top, rehabilitation incurs costs only so that a combination with RMs recovery (CRR1, ERR2) is preferable. Since the new residues in CRR1 consume land due in a disposal site and since future emissions cannot be excluded as the storage conditions are currently unclear, ERR2 is preferable. Private investors’ perspective: TSF rehabilitation (NRR0) generates relatively high revenues. However, the TSF Bollrich is an economically viable source of important RMs. Since a domestic RMs recovery can contribute to reducing RM supply risks by diversifying the sourcing of CRMs on a national level, a private company could beneﬁt from a positive public perception when engaging in RMs recovery. As CRR1 and ERR2 include environ- mental rehabilitation, they reduce the anthropogenic footprint. As the highest revenues of all scenarios are generated in ERR2, and as there is a certain economic risk in CRR1 shown with the pessimistic price forecast, ERR2 is preferable economically. Goslar city administration’s perspective: NRR0 is in line with the city development goals [65] by restoring the recreational qualities of the TSF area in a relatively short period. Resources 2021, 10, 110 16 of 48 However, the anthropogenic footprint is not reduced and the tailings’ long-term stability is unclear [69] so that future measures might be necessary. With RMs recovery (CRR1, ERR2), the city administration saves rehabilitation expenses. An intensiﬁed interaction of industry and scientiﬁc institutions could strengthen the region in the long run. However, the short duration of active works (CRR1) thwart the goal to establish long-term high-quality jobs and to attract investors who seek long-term opportunities [65]. Such opportunities are created in ERR2 so that the Harz region’s challenge of a weak economic structure and emigration of young people can be tackled [52], and an innovative recycling industry can be established [65]. Dealing with the region’s environmental legacy from former mining is seen by the city administration of Goslar as a key challenge for a sustainable development [65] so that negative impacts of new residues must be avoided (ERR2). Résumé: with the application of the UNFC-principles, the advantages and disad- vantages of all 3 scenarios could be made visible for all 3 stakeholders. The overview of all factors shows that all 3 stakeholder interests are best fulﬁlled with the RMs recovery scenario ERR2 in which most beneﬁts are generated, namely, environmental rehabilitation, economic revenues, and long-term regional development. In the assessed constellation, the city administration of Goslar would be a particularly eligible main project driver under compulsory consideration of the enablers environmental NGOs and private investors. 4.3. Path Forward for the Case Study Bollrich For the RMs recovery scenarios (CRR1, ERR2), a higher rating of the project as poten- tially viable (G2F2E2) requires the following aspects to be addressed: the extent of karstiﬁed zones needs to be investigated to better assess the risk of a potential damage to the TSF. The amount of dam material, and the amount, composition, distribution and valorisability of neutralisation sludge need to be investigated. Furthermore, a solution is required for the discharge of the Rammelsberg mine water, preferably with a recovery of RMs such as Zn. The costs for residue disposal (CRR1) and conditioning for an application in construction materials (ERR2) needs to be investigated. To enhance RM efﬁciency, a potential concen- trate buyer needs to be willing to valorise the FeS and to recover the high-technology metals. It should be investigated if all residues in ERR2 can be valorised. The recoverability of As, Cd, Cr, Ni, and Tl needs to be investigated as they are important in high-technology applications, e.g., robotics or decarbonised energy production [70]. A milestone is the determination of site-speciﬁc processing costs for which reference values are used in this article. An economic estimation after taxes and other governmental charges are required to make it comparable across country borders [71]. An uncertainty analysis on tailings mass could account for errors in the geological estimates. In terms of legal aspects, fundamental work must be carried out such as the estimation of costs and the duration of clarifying legal barriers, the engagement of authorities, and the drafting of applications. As for environmental aspects, the present ﬂora and fauna needs to be inventoried in detail; measures for the compensation of environmental impacts need to be drafted; and rehabilitation, environmental monitoring, and post-closure land use plans need to be conceptualised. For the endorsement of a project plan, a disposal site for residues needs to be determined, and a transportation concept must be developed. A comprehensive systematic stakeholder assessment is required. The process should be transparent and clearly structured to enable a fact-based discussion at all times. For all scenarios, the TSF’s long-term risks need to be weighed against the temporary dis- turbance of local nature and communities, potential long-term regional beneﬁts such as environmental rehabilitation, and the local recruitment of workforce. 4.4. Integrating Sustainability Aspects into Raw Materials Classiﬁcation RMs recovery from tailings can have certain beneﬁts: processing the already ground tailings is less energy-intense than processing ores under similar conditions [72]. The potential savings are high since ore crushing and grinding are the most energy-intense processes with ca. 40% of a mine’s energy consumption [73,74]. Moreover, it is increasingly Resources 2021, 10, 110 17 of 48 acknowledged that aspects other than the RMs have to be considered in present-day RMs assessments [52]. RMs recovery from tailings offers the opportunity to rehabilitate the environment [12,75], which can reduce environmental and social risks. Hence, tailings can be regarded as a secondary RM source with a lower social conﬂict potential than ores [11]. The challenge is to identify and communicate these potential beneﬁts, especially for environmental and social aspects [46]. Indeed, geological and techno-economic aspects can be assessed with established methods from the conventional CRIRSCO classiﬁcation [45], but it is unsuitable for capturing sustainability aspects [43,49]. In contrast, the UNFC recognises environmental and social aspects as potential driving factors, integrating them into the classiﬁcation [44]. Current shortcomings of the UNFC are its lacking practica- bility [8], user guidance [43,49], speciﬁcation of knowledge which must be generated in very preliminary studies [49], and standardised assessment and classiﬁcation template for anthropogenic RMs including key factors which must be considered [47,49]. This article demonstrates how one can be guided through a practical UNFC application. Established methods from the conventional mineral RMs classiﬁcation are combined with methods to account for environmental and social beneﬁts. With the following aspects, the developed approach supports the integration of sustainability aspects into RMs classiﬁcation: First, the report of on-site exploration data by Goldmann et al. [53] on the TSF Bollrich documents relevant aspects extensively but it lacks a frame for an overall rating. In their report, a techno-economic classiﬁcation of the tailings in terms of conventional resources or reserves as well as the determination of cut-off grades was not possible due to the geological uncertainties [53]. Environmental and legal aspects are discussed separately, but they do not contribute to the classiﬁcation. This is common in current classiﬁcation practice, which focusses on economic aspects [16,40]. Therefore, current practice cannot fully reﬂect a project’s potentials. In contrast, the presented UNFC-compliant assessment and classiﬁcation approach provides a comprehensive framework to communicate the development status of the TSF Bollrich case study by considering all relevant geological, technological, and environmental-socio-economic aspects on site during exploration. Second, mining companies worldwide are increasingly recognising that their economic interests need to be aligned with social values for long-term success [6,23,76]. However, the reinterpretation of waste as a RM source requires a change of mindset [52]. In this context, a challenge is to create a common understanding of sustainable acting as local stakeholders’ perspectives on sustainable mining often diverge [77]. Hence, the sustainable prospects of a potential project need to be communicated transparently to local communities in the project development phase to create a common understanding. Thus, the developed assessment and classiﬁcation approach offers the opportunity to integrate a stakeholder assessment in the decision-making process. The needs of local stakeholders are particularly addressed in terms of impacts related to land use, the environment, and health. Third, the example of the Harz region highlights the importance of including social aspects such as involving local communities in the development of RMs recovery projects and transparently communicating potential long-term impacts on former contaminated sites: although the Mansfeld area is comparable to the Goslar area, the local population is sceptical about RMs recovery due to dishonest communication and selﬁsh behaviour of potential project developers in the past [52]. Especially in densely populated areas, social conﬂicts can arise. The inclusion of local values, such as those expressed by the town council as the elected representative of local citizens, can help to improve the sustainability of a project and inﬂuence a project assessment in terms of enhancing the common good [77]. Fourth, the developed categorisation matrix addresses several issues: in the classiﬁca- tion of tailings with conventional practice, the RM potential beside the target RM potential is usually not captured, e.g., References [37–39]. This means that part of the RM potential remains unassessed. The distinct classiﬁcation of the individual RMs in the categorisation matrix highlights the potentials of and barriers to their recovery. The heat map-like visu- alisation of the categorisation enables a quick comparison of all aspects with each other, promoting a transparent communication of the assessment results. For instance, in each of Resources 2021, 10, 110 18 of 48 the scenarios, the impairment of local ecosystems around the TSF Bollrich are captured in the categorisation matrix. Consequently, a project developer is required to comment on how further measures can be taken to overcome the scenario-speciﬁc barriers. As another example, even a longer duration of the RMs recovery scenarios (CRR1, ERR2) could be con- sidered more favourable than the relatively short impairment caused by the rehabilitation scenario (NRR0) due to the long-term beneﬁts resulting from the risk reduction associated with the removal of the tailings. In a stakeholder assessment, all relevant stakeholders can question the factors considered in order to reach a mutually agreed decision. In the course of the study, consensus building can be documented and evaluated. Fifth, the case study shows how the application of the UNFC principles can reconcile 3 different stakeholder perspectives: the TSF-related long-term risks are identiﬁed as the main project drivers. Considering the remediation costs as external costs borne by society enables a comparison of the monetary impacts of the TSF in case of rehabilitation (NRR0) with those of the other scenarios (CRR1, ERR2). Scrutinising the considered stakeholder perspectives leads to the following common values: minimisation of physico-chemical risks associated with the TSF, minimisation of emissions to the environment during any operation, achievement of a long-term aftercare-free state after project execution, and the preservation of the area’s recreational value and ecosystem quality. On this basis, the RMs recovery scenario ERR2 should be prioritised since it addresses all common values. 4.5. Development Potential of the Assessment and Classiﬁcation Approach A comparison of the classiﬁcation result from the screening of the TSF Bollrich (G4F3E3) in Reference [43] to the result from this article (G2F3E3) shows that the im- provements in the E and F categories are not reﬂected in the overall rating. This can be explained with the selected factors and indicators to measure the development status, especially for the social and legal aspects. A comparison of the factors and indicators applied in this study with other case studies could show if they all suit the scope of a very preliminary study or if some of them should be applied in more developed studies. Additionally, the low rating in the E and F categories can be explained with the procedure to choose the lowest rating in a category as the overall rating. An example is the rating of economic aspects for the RM Cu: despite the favourable rating of the demand (E3.1a) and RM criticality (E2a), the low rating of the forecasted decreasing price development (E3.3a) is determinant. This issue could be resolved by weighting factors for instance. It is worth noting that there is currently no class deﬁned for a rating as G2F3E3. A proposal is made for a possible description: based on very preliminary results, a prospective project has been identiﬁed as a potential source of RMs for which further studies are required to justify further development. Factors related to the impact on global warming are not considered in this study. This could be remediated by performing a life cycle assessment (LCA). It enables the consideration of external costs, and it was also used in conjunction with the UNFC [78]. Another advantage is that it allows for a comparison to projects from primary mining [78]. Regarding tailings, the LCA has been used to assess aspects such as environmental impacts in early phases of mine planning [79], and TSF site management and closure scenarios [80]. For RMs recovery from tailings, an LCA should provide decision-makers with information on environmental impacts which could be compared with primary mining. In general, the LCA requires site-speciﬁc data for a detailed analysis of processes and their impacts [81]. The LCA performed by Goldmann et al. [53] for the conceptualised dredging system shows that an LCA in very preliminary studies can be applied to assess different mining options. The use of LCAs in early project development phases on aspects such as mineral processing and a possible contribution to the classiﬁcation must yet be examined. 5. Conclusions and Recommendations To recapitulate, the deposition of tailings in TSFs impacts the environment and local communities and can even threaten human health [16]. These impacts could be aggravated Resources 2021, 10, 110 19 of 48 in the future due to a climate-change-induced increased likelihood of extreme weather occurrences [20]. At the same time, the global tailings production is increasing due to an increasing demand for highly important RMs, which are forecasted to at least double between 2010–2050 [4,5]. The increasing RM demand could partially be met by using the RM potential of tailings: 10–20% of all technospheric metal RMs are estimated to be deposited in landﬁlls and TSFs; metal grades in tailings can be as high as in ores [40]. Technological advancements enable the exploitation of the residual metals content [29,82] or the valorisation in construction materials [83,84]. RMs recovery from tailings can also be an opportunity to reduce the environmental and social impacts of TSFs [75]. For the re-interpretation of tailings as a source of RMs, the potential beneﬁts of and barriers to their exploitation need to be captured and assessed holistically. The assessment shows that the TSF Bollrich is an economically interesting source of BaSO ; the base metals Cu, Pb, and Zn; and the high-technology metals Co, Ga, and In. Removing the TSF has positive long-term environmental impacts. However, there is high uncertainty regarding geological knowledge and technological extractability of the CRMs. An issue is that the applied social and legal factors are generally underdeveloped. The research questions are answered: (1) the tailings deposit Bollrich is an exam- ple of a RMs recovery project which takes place in a complex environment where the inﬂuence of various site-speciﬁc stakeholders needs to be considered. With a UNFC- compliant approach, different stakeholder perspectives can be addressed in order to derive a commonly acceptable solution. In the case study, the enhanced mineral RMs recovery scenario ERR2 aligns the interests of environmental NGOs, private investors, and the city administration of Goslar: environmental rehabilitation to protect the TSF’s vulnerable environment, the generation of proﬁts, and a long-term regional development. It can therefore be concluded that a UNFC-compliant assessment is suitable for identifying areas of conﬂict between economic, environmental and social interests, and for achieving a generally acceptable solution. (2) It is suggested that for very preliminary studies, aspects relevant for project development and execution, impacts due to project execution, and impacts after project execution should be considered. Furthermore, the availability of primary on-site exploration data and secondary research data could be regarded as a prerequisite for a very preliminary study on tailings. As tailings usually contain multiple RMs, a comprehensive overview of the RM potential with differentiation of individual RMs is required. The data must allow for an initial assessment of the following aspects: (i) characterisation and quantiﬁcation of the total and individual RM content, (ii) laboratory investigation of processability, (iii) technological conceptualisation of project execution and aftercare measures, (iv) DCF analysis, (v) inventory on present rare ﬂora and fauna, (vi) status quo environmental risk assessment, and (vii) identiﬁcation of relevant stakehold- ers. After a clariﬁcation of these aspects, a project can be advanced to a preliminary study. (3) The identiﬁcation and communication of sustainability aspects in RMs classiﬁcation poses a challenge. Despite a project’s impact on its local environment and communities, related site-speciﬁc project potentials and barriers are usually not considered. The example of the Harz region demonstrates that, in addition to conventional economic interests, a site-speciﬁc approach is essential from the beginning of project development. The example of the tailings deposit Bollrich shows that an integration of local sustainability aspects into the assessment, represented by the development goals of the city administration of Goslar, can give a strong impulse for project development: strengthening the regional industrial role, creating high-value jobs, and developing tourism. The developed UNFC-compliant categorisation matrix captures the development status of speciﬁed factors and communi- cates the results in a quickly understandable manner in a heat-map-like style. Hence, it enables a point-by-point comparison of different scenarios so that the individual potentials and beneﬁts become clear. In this way, the most auspicious option can be quickly identiﬁed, and its development can be justiﬁed. Recommendations made: as for the case study TSF Bollrich, enhance the geological knowledge on the metalliferous CRMs; investigate the processability of the neutralisation Resources 2021, 10, 110 20 of 48 sludge; assess the recoverability of As, Cd, Cr, and Tl; and consider a direct valorisation of RMs in the Rammelsberg mine water. If the RMs recovery project is executed, the city administration’s tax revenues could be used to rehabilitate other contaminated areas from former mining activities. In this way, the local community hosting the mining activity can beneﬁt directly from it, which is uncommon in current practice [77]. Thus, RMs recovery from the TSF Bollrich could serve as a role model for a sustainable development of the Harz region. As for the developed approach, investigate if all selected factors and indica- tors, especially those for social and legal aspects, are suitable for very preliminary studies. Correspondingly, determine which factors are necessary and which are optional in very preliminary studies. Since the overall rating does not properly reﬂect the improvements made and deﬁcits encountered in the course of several studies, introduce a reporting to support decision-making. As for the development of an anthropogenic RMs management, a database for the assessment of the global anthropogenic RM potential needs to be estab- lished. For this, waste producers could be obligated by law to report on all contained RMs in their wastes. Lastly, UNFC-compliant case studies on anthropogenic RMs are currently very labour-intensive due to a lack of experience. More UNFC-compliant case studies are needed to derive a reference base of project potentials and barriers. This would provide future studies with a benchmark for a quick recognition of a project’s prospects of reaching the next level of maturity. Supplementary Materials: Figure S1: Results of autoregressive electric energy price forecast based on yearly historical data from 2014 to 2020 from Statista [85]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S2: Results of autoregressive diesel price forecast based on yearly historical data from 1950 to 2020 from Statista [86]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S3: Results of autoregressive BaSO4 price forecast based on yearly historical data from 2011 to 2020 from the USGS [87–90]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S4: Results of autoregressive Co price forecast based on yearly historical data from 1996 to 2020 from the USGS [87,89–93]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S5: Results of autoregressive Cu price forecast based on monthly historical data from 1999 to 2021 from IndexMundi [94]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S6: Results of autoregressive Ga price forecast based on yearly historical data from 1999 to 2020 from the USGS [87,89–93]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S7: Results of autoregressive In price forecast based on yearly historical data from 1999 to 2020 from the USGS [87,89–93]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S8: Results of autoregressive Pb price forecast based on monthly historical data from 1999 to 2021 from IndexMundi [95]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S9: Results of autoregressive Zn price forecast based on monthly historical data from 1999 to 2021 from IndexMundi [96]. The blue line on the right-hand side depicts the mean price forecast, and the blue and grey areas represent the 95% and 75% conﬁdence intervals, respectively, Figure S10: Conceptual mine plan and processing schematic. The light grey shaded ﬁeld indicates the spatial system boundaries and the dark grey shaded ﬁelds indicate products (adapted after Goldmann et al. [53]), Figure S11: Results of the sensitivity analysis of the conventional mineral RMs recovery scenario (CRR1p) with pessimistic price forecast and a discount rate of 15%, Figure S12: Results of the sensitivity analysis of the conventional mineral RMs recovery scenario (CRR1o) with optimistic price forecast and a discount rate of 15%, Figure S13: Results of the sensitivity analysis of the enhanced mineral RMs recovery scenario (ERR2p) with pessimistic price forecast and a discount rate of 15%, Figure S14: Results of the sensitivity analysis of the enhanced mineral RMs recovery scenario (ERR2o) with optimistic price forecast and a discount rate of 15%, Figure S15: Comparison Resources 2021, 10, 110 21 of 48 of costs, revenues and NPVs for the mean price forecast of the 3 scenarios with no mineral RMs recovery (NRR0), conventional mineral RMs recovery (CRR1m) and enhanced mineral RMs recovery (ERR2m). With a discount rate of 15%, NRR0 is discounted over a period of 35 years, and CRR1m and ERR2m over a period of 11 years, Figure S16: Comparison of costs, revenues and NPVs for the pessimistic price forecast of the 3 scenarios with no mineral RMs recovery (NRR0), conventional mineral RMs recovery (CRR1p) and enhanced mineral RMs recovery (ERR2p). With a discount rate of 15%, NRR0 is discounted over a period of 35 years, and CRR1p and ERR2p over a period of 11 years, Figure S17: Comparison of costs, revenues and NPVs for the optimistic price forecast of the 3 scenarios with no mineral RMs recovery (NRR0), conventional mineral RMs recovery (CRR1o) and enhanced mineral RMs recovery (ERR2o). With a discount rate of 15%, NRR0 is discounted over a period of 35 years, and CRR1o. Author Contributions: Conceptualisation, R.S.; methodology, R.S.; validation, R.S., S.H.-A.; re- sources, R.S.; writing—original draft preparation, R.S.; writing—review and editing, R.S., S.H.-A.; visualisation, R.S.; project administration, R.S.; funding acquisition, R.S., S.H.-A. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the German Ministry of Research and Education (BMBF) as part of the research project ADRIANA (Client II programme), grant agreement number 033R213A-D. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: This research used publicly available data available in the referenced sources. The database can be found in the Appendix A and supplementary materials. Acknowledgments: The authors are thankful to Bernd G. Lottermoser for his comments and to Jonas Krampe for providing the R code. In addition, the authors would like to express their deep gratitude to two anonymous reviewers who helped to improve the manuscript. Conﬂicts of Interest: The authors declare no conﬂict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. Abbreviations Abbreviation/Unit Description Ag lat. argentum (silver) Al aluminium Au lat. aurum (gold) BaSO barium sulphate (barite) Cd lat. cadmia (cadmium) Co cobalt Cu lat. cuprum (copper) CuFeS copper iron disulphide (chalcopyrite) Fe lat. ferrum (iron) FeS iron disulphide (pyrite) Ga lat. gallia (gallium) In indium Mn manganese Mo molybdenum Ni nickel Pb lat. plumbum (lead) PbS lead sulphide (galena) Tl lat. tellus (tellurium) Zn zinc ZnS zinc sulphide (sphalerite) ADRIANA Airborne spectral Detection of Reusable Industry mAterials in tailiNgs fAcilities Resources 2021, 10, 110 22 of 48 BMBF German Ministry of Research and Education CAPEX capital expenditure CL:AIRE Contaminated Land: Applications in Real Environments CRM Critical Raw Material DCF discounted cash ﬂow E East EC European Commission EU European Union LOM Life of Mine N North NPV net present value OPEX operating expenditure Qty. quantity RM raw material TSF tailings storage facility UNECE United Nations Economic Commission for Europe UNFC United Nations Framework Classiﬁcation for Resources UNFC E category represents environmental-socio-economic viability UNFC F category represents technical feasibility UNFC G category represents degree of conﬁdence in the geological estimate USGS U.S. Geological Survey W West C degree Celsius (unit of temperature on the Celsius scale) -6 m micrometre (unit of length, equivalent to 10 metres) a year km kilometre (unit of length, equivalent to 10 metres) kW kilowatt (SI-derived unit of power) kWh kilowatt-hour (SI-derived unit of energy) -3 3 l litre (SI-derived unit of volume, equivalent to 10 m ) m metre (SI unit of length) m square metre (SI-derived unit of surface) m cubic metre (SI-derived unit of volume) -3 mm millimetre (unit of length, equivalent to 10 metres) t metric tonne (unit of weight, equivalent to 1000 kilograms) Appendix A Table A1. Degree of conﬁdence in the geological estimates (G) for the overall project rating with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Geological conditions (relevant for project development) degree of geological certainty: ore quality, former high (G1) (1) quantity amount of target RMs processing efﬁciency, [45] medium (G2) deposit volume low (G3) degree of geological certainty: physico-chemical high (G1) former processing, storage (2) quality [45] properties of target RMs medium (G2) conditions low (G3) degree of geological certainty: distribution of target RMs manner of former high (G1) (3) homogeneity [24] inside the deposit deposition medium (G2) low (G3) Resources 2021, 10, 110 23 of 48 Table A2. Technical feasibility (F) for the overall project rating with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating TSF condition & risks (relevant for project development) degree of knowledge: regional history, former non-existence proven (F1) unexploded ordnance (4) ordnance searching activities existence proven (F2) from armed conﬂicts unclariﬁed (F3) Mine planning considerations (relevant for project execution) geological knowledge on level of detail of planning: optimising RMs recovery (5) mine/operational deposit, project planning extended (incl. detailed under consideration of [45] phase, quality of model design operational factors) (F1) strategic goals & assumptions, legal advanced (incl. pit conﬁguration restrictions restrictions & processing scheme) (F2) basic (conceptual) (F3) degree of research on mineral investigation of possible sampling techniques, processability: (6) metallurgical testwork methods for mineral representativeness of test [45] industrial scale (F1) processing feed, testing techniques pilot scale (F2) laboratory scale (F3) percentage of recycled water: demand of fresh water available water resources, high (>80%) (F1) (7) water consumption supply for mining & water efﬁciency of mining [13,97,98] medium (50–80%) (F2) processing system low (<50%) (F3) Infrastructure (relevant for project development) condition of infrastructure: former mine closure, availability of land & highly developed (fully reusable) (8) real estate current land use, time [45] reusability of buildings (F1) lapsed after abandonment acceptable (usable after upgrade) (F2) bleak (requires (re-)construction) (F3) condition of equipment: reusability of equipment former mine closure, highly developed (fully reusable) (9) mining & processing related to general services, current land use, time [45] (F1) mining & processing lapsed after abandonment acceptable (usable after upgrade) (F2) bleak (requires new acquisition) (F3) mine closure & time condition of infrastructure: lapsed after abandonment, access to utilities supply highly developed (full access) (10) utilities [45] current land use, lines (e.g., electricity) (F1) proximity to human acceptable (access after upgrade) settlements (F2) bleak (requires (re-)construction) (F3) topography, former mine condition of infrastructure: access to mine & markets closure, current land use, highly developed (fully reusable) (11) transportation & via air, road, railway, or [45] time lapsed after mine (F1) access waterway abandonment, proximity acceptable (usable after upgrade) to human settlements (F2) bleak (requires (re-)construction) (F3) Post-mining state (relevant for future impacts) suitability of new disposal site ability of new storage amount of new residues, for safe storage: facility to safely store new topography, type of (12) residue storage safety high degree of safety proven (F1) [13,98–100] residues for an indeﬁnite construction, climate, preliminary assertion of safety time period regional seismic activity (F2) unsafe or unclariﬁed (G3) residue characteristics, level of detail of planning: process of recontouring, local ecosystem, concrete (F1) (13) rehabilitation [101] revegetating, & restoring landscape, environmental conceptual (F2) the water & land values laws, local climate none (F3) Resources 2021, 10, 110 24 of 48 Table A3. Economic viability (E a) for the overall project rating with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Microeconomic aspects (relevant for project development) discounted cash ﬂow over mine planning, RMs projected LOM: prices, costs of input (14) economic economic returns from project [45,97] positive (NPV >> 0 ) viability factors (labour, energy, (E3.1a) materials), payments to neutral (NPV~0 ) (E3.2a) public sector (e.g., taxes) negative (NPV << 0 ) (E3.3a) uncertainty of cash ﬂow in pessimistic scenario: degree of detail in (15) economic overall uncertainty of economic estimates low (NPV >> 0 ) (E3.1a) planning, data quality of [45] uncertainty medium (NPV~0 ) (E3.2a) economic estimate high (NPV << 0 ) (E3.3a) Financial aspects (relevant for project development) country rank on the conditions concerning taxes, royalties, & country-speciﬁc ease-of-doing-business regulations, condition of other ﬁnancial regulations, which are a index: (16) investment [45,68] precondition for decision makers with ﬁnancial market, social country rank < 75 (E3.1a) conditions considerations, respect to location & investment country rank 75–125 environmental (E3.2a) considerations country rank > 125 (E3.3a) probability of approval: ﬁnancial support from political institutions (17) ﬁnancial active socio-political high (E3.1a) for innovative projects such as loans, [102] support support medium (E3.2a) equity ﬁnancing, or guarantees can low (E3.3a) incentivise RMs from mineral waste Table A4. Environmental viability (E b) for the overall project rating with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Environmental impacts during project execution risk of dust emission: particle size, TSF cover, local low (<80%) (E1b) risk of tailings being eroded by wind climate, wind conditions, pit (18) air emission [13,98] medium (50–80%) (E2b) conﬁguration high (>50%) (E3b) risk of groundwater soil liner, drainage system, contamination: wet tailings storage, local (19) liquid efﬂuents from tailings can contaminate soil & [13,98] low (E1b) environment, tailings’ efﬂuent emission surface water medium (E2b) chemical properties high (E3b) noise & vibrations during mining; transport & expected degree of impact: mine planning, protective processing can cause disturbances of local low (E1b) (20) noise measures, topography, [97] communities determined by individual & medium (E2b) emission proximity to human collective perception high (E3b) settlements Environmental impacts after project execution total number of protected species that are affected by mining activities & that will local ecosystem, mining be resettled on post-mining (21) biodiversity inﬂuence on habitats & species [97] system, landscape, land: rehabilitation measures all (100%) (E1b) some (1–99%) (E2b) none (0%) (E3b) freely available post-mining amount of new residues, type land: of disposal, rehabilitation, (22) land use land requirement after mine closure [97] most (>80%) (E1b) land development some (50–80%) (E2b) opportunities little (<50%) (E3b) reduction of reactive material’s mass: (23) material target minerals, concentration capability of contained minerals to produce [13,103] high (>80%) (E1b) reactivity of sulphidic minerals AMD medium (50–80%) (E2b) low (<50%) (E3b) Resources 2021, 10, 110 25 of 48 Table A5. Social viability (E c) for the overall project rating with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Social impacts during project execution probability of approval communication with stakeholders, commitment beyond formal regulatory through active commitment: proximity to human urban, protected, (24) local requirements, the recognition of diverse [68,97,104] high (>80%) (E3.1c) or culturally relevant areas, community values, & the right to be informed about medium (50–80%) (E3.2c) participation of local communities in issues & conditions that inﬂuence lives decision-making low (>50%) (E3.3c) total number of complaints or prosecutions for mining system, local health & safety protection of workers & local non-compliance in planning (25) health & standards, corporate values for the communities from injuries & diseases, & phase: [97] safety establishment of a safe work environmentalpollution none (plans have been environment & lively safety culture communicated publicly) (E3.1.c) more than 1 (plans have been communicated publicly) (E3.2c) none (plans have not been communicated publicly) (E3.3c) total number of complaints or prosecutions for wages, right to organise trade unions, non-compliance in planning degree to which a mining company bribery & corruption, violation of (26) human rights phase: [97] values ethically correct behaviour human rights, forcefully gained control & business ethics none (plans have been over land, a country’s governance communicated publicly) (E3.1.c) more than 1 (plans have been communicated publicly) (E3.2c) none (plans have not been communicated publicly) (E3.3c) Social impacts due to project execution total number of complaints or prosecutions for distribution of earning between mining a country’s governance, choice of non-compliance in planning (27) wealth company, local communities, & suppliers, & contractors; percentage of [97] phase: distribution government locally hired workers; wages none (plans have been communicated publicly) (E3.1.c) more than 1 (plans have been communicated publicly) (E3.2c) none (plans have not been communicated publicly) (E3.3c) percentage of employees sourced from local percentage of locally hired workers, (28) investment in fostering personal skill development & communities: offering higher education & training & local human capacity-building of employees by [97] high (>80%) (E3.1c) transferable skill development; degree capital education & skill development medium (50–80%) (E3.2c) to which work is contracted out low (<50%) or unclariﬁed (E3.3c) residue disposal: complete residue valorisation disposal of new residues, mineral (29) degree of RM RMs can become inaccessible for recovery (E1c) processing, residue stabilisation, recovery for future generations separate disposal (E3.1c) residue characteristics mixed disposal (E3.2c) sterilisation (E3.3c) total mass reduction as percentage of original tailings target minerals, maturity of utilising a RM in a sustainable manner to mass: (30) RM valorisation technologies, potential [97] limit the impact of its recovery on the high (>80%) (E1c) valorisation markets, RMs prices environment medium (50–80% (E2c) low (<50%) (E3c) Social impacts after project execution duration of aftercare measures: level of commitment & necessary land management, national (31) aftercare short-term (<5 years) (E1c) measures on post-mining land regulations, rehabilitation measures mid-term (5–30 years) (E2c) long-term (>30 years) (E3c) impact on the environment: mining activities can cause a visual topography, local ecosystem, mine positive (E1c) (32) landscape [97] impact by transforming landscapes planning, local climate neutral (E2c) negative (E3c) Resources 2021, 10, 110 26 of 48 Table A6. Legal viability (E d) for the overall project rating with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Legal situation (relevant for project development) state of development: regulations affecting supranational, national, & application in development (33) right of mining [45] project planning & regional laws & rules (E3.1d) realisation authorities engaged (E3.2d) application not begun or unclariﬁed (E3.3d) state of development: regulations affecting (34) environmental supranational, national, & application in development [45,53,97] project planning & protection regional laws & rules (E3.1d) realisation authorities engaged (E3.2d) application not begun or unclariﬁed (E3.3d) state of development: regulations affecting supranational, national & application in development (35) water protection project planning & [45] regional laws & rules (E3.1d) realisation authorities engaged (E3.2d) application not begun or unclariﬁed (E3.3d) Table A7. Degree of conﬁdence in the geological estimates (G) for the rating of individual RMs with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Geological situation (relevant for project development) degree of geological ore quality, former certainty: (36) quantity amount of target RMs processing efﬁciency, [45] high (G1) deposit volume medium (G2) low (G3) degree of geological certainty: physico-chemical former processing, (37) quality high (G1) [45] properties of target RMs potential revenues medium (G2) low (G3) degree of geological certainty: mine planning, mineral distribution of target RMs (38) homogeneity [45] high (G1) feed grade, timing of inside the deposit medium (G2) revenues low (G3) Table A8. Technical feasibility (F) for the rating of individual RMs with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Mine planning considerations (relevant for project execution) percentage of RM which is technological development, state extracted from the tailings: ability to extract a wanted of metallurgical testing, (39) recoverability - high (>80%) (F1) RM from the tailings equipment availability, state of medium (50–80%) (F2) target RM low (<50%) (F3) Resources 2021, 10, 110 27 of 48 Table A9. Economic viability (E a) for the rating of individual RMs with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Microeconomic aspects (relevant for project development) favourable conditions for existence of a current practical use for the market, price, available RM extraction: RM & absence of geological, technological, (40) demand technology, public yes (E3.1a) economic, environmental, social, &/or acceptance, regulations conditionally (E3.2a) legal objections against its recovery no (E3.3a) allocation to EC’s economic importance, criticality assessment: (41) RM importance of a RM in an industry or supply risk, CRM (E1a) [59] criticality economy substitutability high economic importance or supply risk (E2a) no criticality (E3a) forecasted mean price development over the demand, supply risk, (42) price project’s duration: forecasted RM price behaviour - quality, & quantity of development positive trend (E3.1a) historical data stagnant trend (E3.2a) negative trend (E3.3a) Table A10. Environmental viability (E b) for the rating of individual RMs with the UNFC-compliant categorisation matrix. Factor Explanation Dependence on Modiﬁcation after Indicator & UNFC Rating Impacts after project execution concentration of RM solid matter in new residues to qualify for class DK 0 (inert waste) according to German a RM’s potential to harm concentration, toxicity, Landﬁll Regulation DepV [61]: (43) solid matter [13,105,106] human health, ﬂora, &/or valorisation path non-hazardous material (E1a) fauna threshold value not exceeded (E3.1a) threshold value exceeded (E3.2a) unclariﬁed (E3.3a) concentration of RM in eluate from new residues to qualify for class DK 0 (inert waste) according to German concentration, toxicity, a RM’s potential to harm Landﬁll Regulation DepV [61]: (44) eluate valorisation path, [13,105,106] human health, ﬂora, &/or non-hazardous material (E1a) solubility fauna threshold value not exceeded (E3.1a) threshold value exceeded (E3.2a) unclariﬁed (E3.3a) Table A11. Knowledge base on the Bollrich tailings deposit for project deﬁnition. The dark grey shaded ﬁelds indicate data associated with high uncertainties, while the light grey shaded ﬁelds indicate data associated with moderate uncertainties, and the dashes indicate factors for which no information is available. Category & Factor Data Sources UNFC Axis (A) type of study very preliminary study - (B) basic information (a) geography 0 00 0 00 Goslar district, Lower Saxony (Germany) (51 54 8.97 N, 10 27 47.31 E), (i) location 270 m above mean sea level nearest human settlement ~400 m E air-line [50] distance downstream of main dam (ii) topography at the foot of Harz mountain range, up to 1141 m altitude with deep valleys [107] folded & faulted Paleozoic rocks of the Harz Mountains are uplifted & thrust over younger Mesozoic rocks of the Harz foreland along the Northern Harz Boundary fault leading to steeply tilting & partly inverted (iii) local geology Mesozoic strata; Mesozoic rocks are largely composed of Triassic to [108] Cretaceous sedimentary rocks of varying composition (i.e., mostly impure limestones, clastic sandstones (greywackes) & shales); younger Quaternary sediments are rare & locally limited Resources 2021, 10, 110 28 of 48 Table A11. Cont. Category & Factor Data Sources UNFC Axis in near vicinity: agricultural, forest, industrial & commercial, & recreation & observed on Google (iv) land use residential areas Earth [50] Four small rivers observed downstream of TSF within a 1.5 km radius observed on Google (v) surface waters (Abzucht, Ammentalbach, Gelmke & Oker) Earth [50] moderately warm, temperature 0.7 to 16.3 C (average 7.2 C), average (vi) climate [109,110] rain precipitation 911 mm/a, average climatic water balance 366 mm/a (b) geogenic deposit two strongly deformed lens-shaped main ore bodies (high & low grade), sedimentary exhalative deposit (SedEx), ﬁne grained (10–30 m) principle sulphide minerals sphalerite ((Zn,Fe)S) & pyrite (FeS ), less amounts of (i) mineralisation galena (PbS) & chalcopyrite (CuFeS ), Ag, Au, (average estimated grades [50,107,111] 14 wt% Zn, 6 wt% Pb, 2 wt% Cu, 140 g/t Ag & 1 g/t Au), barite (BaSO ) (average grade 20 wt%)—additionally ca. 30 trace elements such as Co, Ga, & In, hosted by Middle Devonian Wissenbach shales underground mine, closed for economic reasons in 1988 after >1000 years of (ii) former mining operation, now UNESCO World Heritage site located ~3 km W air-line [50,107,111] distance from second processing plant Bollrich & TSF (c) tailings deposit (i) data collection scientiﬁc publications or publicly accessible data, assumptions based on methods scientiﬁc publications, &/or own reasoning was in operation for ~49 years, decommissioned in 1987; supplied by processing plants Rammelsberg (into upper pond, 1938–1987) & Bollrich (ii) history [53,57,107] (into lower pond, 1956–1987); course of river Gelmke was changed several times (iii) recoverability target minerals previously & non-previously mined minerals - G 3 3 quantity & V = 2,030,000 m , m = 7,100,000 t, r = 3.5 t/m (weighted mean tailings dry [53,54] quality value), r = 2.3 t/m neutralisation sludge exploration of deposit: (i) 10 drill cores (17–28 m) taken in upper pond along main dam & parallel to main dam in the middle of the pond, analysis [53] G of 16 elements; (ii) 90 water depth metering points 26 drill cores taken in upper & lower ponds, analysis of 4 elements & [54] 3 minerals low degree of alteration associated with oxidation [53] valley impoundment, estimated surface area 315,000 m consists of 3 ponds: (i) lower pond (west, 74 vol% of TSF, r = 3.0 t/m , max. water depth 4 m, average water depth 2 m), (ii) upper pond (middle, [53,66], Ruler Tool [50], average water depth 26 vol% of TSF, r = 3.7 t/m , max. water depth 0.5 m, average water depth TSF structure 0.4 m), (iii) water retention pond (East) estimated with data consists of 3 dams: (i) main dam (max. 33 m height, max. 18 slope, raised from Reference [53] 6 times, up-stream), (ii) middle dam (max. 19 m height), (iii) water retention dam (max. 8 m height) drill core data of upper pond shows relatively homogeneous deposit with slightly increasing Ba grades with depth; deposit modelled based on homogeneity [53] G, F historical & current terrain models, water depth measurements, historical & current core data; validation by comparison to production records dam stability: occurrence of sinkhole at northern part of TSF documented in 1986 & several sinkholes near TSF reported in the past, which are associated safety with karstiﬁed geological structures nearby; expertise from 1986 concludes [53] F considerations that TSF is not imminently threatened; conﬁrmed by current calculations; unexploded ordnance: existence of WWII ordnance cannot be excluded based on historical data so it needs to be investigated prior to mining [53], observed on not rehabilitated, left to ecological succession, no signs of AMD or erosion (iv) rehabilitation observable Google Earth [50] Resources 2021, 10, 110 29 of 48 Table A11. Cont. Category & Factor Data Sources UNFC Axis (v) assessment status maturity level research work - characterisation complete for lower pond [53] partial for upper pond; not all elements/minerals analysed; amount, composition, & shape of deposition of mine water neutralisation sludge in upper & lower pond roughly estimated evaluation partial - classiﬁcation prospective project (E3F3G4) [43] (vi) economics BaSO , Co, Ga, & In are CRMs in EU with very high economic importance; RM criticality [112] E a Cu, Pb, & Zn have high economic importance in EU further industrial & metalliferous minerals of interest, use of residues in - E a valorisation construction materials conceivable (vii) social impacts no apparent imminent hazards known; negative impacts through dermal health protection [53] E c contact, ingestion or inhalation not given; risk assessment not performed [53,54], www.cutec.de/ ﬁleadmin/Cutec/ ﬁrst scientiﬁc exploration shortly in 1983 before TSF abandonment in 1988; documents/cutec- one recent research project (REWITA) with focus on mineral RMs recovery scientiﬁc interest news/2020/new58_ E c (2015–2018); proposal for follow-up project (REMINTA) on material dezember2020.pdf extraction submitted (accessed on 24 February 2021) 4 positive perception of project idea by administrative bodies, environmental SLO [52] E c NGOs, & scientists local population’s perception of project idea unknown - (viii) environmental impacts possible negative impacts unknown; disused landﬁll “Paradiesgrund” pollution located 250 m N air-line distance from TSF; possible inﬂuence on landﬁll [53] E b when mining the TSF needs to be investigated TSF’s base not sealed & in direct contact with tailings integrated into landscape (visible only from up close or from hills); environment has been adapting through natural succession; active gilder landscape cf., Figure 2 E b airﬁeld ~100 m N air-line distance from TSF; hiking trails next to TSF & biking Euroroute R1 near TSF on-site inspection of the TSF showed that rare ﬂora, & aerial & soil fauna current status [53] E b colonise the site conservation areas & protected landscapes nearby, protected species of ﬂora protected areas [53] E b & fauna sighted in area around TSF since 1966, neutralised mine water from the Rammelsberg mine has been secondary use discharged into the TSF (mainly upper pond, currently ~450,000 to [54] E b 900,000 m /a); overlay of tailings and neutralisation sludge Resources 2021, 10, 110 30 of 48 Table A11. Cont. Category & Factor Data Sources UNFC Axis (d) technology (i) mine planning mine planning considerations on conceptual basis (dredging) - F extraction of BaSO , Co, Cu, Ga, In, Pb, Zn, & inert residues evaluated in discontinuous laboratory experiments on tailings from lower pond, processing sequences: (i) sulphide separation together with contaminants (rougher+cleaner+leaching), (ii) BaSO separation (rougher+cleaner+scavenger+conditioning); (ii) processing [60] F recovery rates (tested on material from lower pond; ammonia leaching route for sulphides): BaSO (74%), Co (12%), Cu (74%), Ga (2%), In (26%), Pb (65%), Zn (72%) & inert material (93%) processing tests on tailings from upper pond not performed; precipitation of SO ions in multiple stages necessary to recover metals (e) infrastructure (i) real estate buildings & land from former processing available [53] F (ii) mining & former processing plant available ~550 m E air-line distance from TSF [53] processing based on observation (iii) utilities access to public electricity, gas, & water grid assumed F on Google Earth [50] dirt roads, federal highway B6 ~1.6 km N air-line distance from TSF & (iv) transportation & public railway ~500 m E air-line distance from TSF; disused railway tracks [53], observed on access from processing plant Bollrich to public network (estimated abandonment Google Earth [50] in 1988) (f) politics (i) political willingness - - E c (g) legislation/licensing (i) ownership Bergbau Goslar GmbH (address: Bergtal 18, 38640 Goslar, Germany) [53] E d (ii) legal exploration currently supervised under German Federal Mining Act (BBergG) [53] E d framework (iii) legal mining - - E d framework (iv) operating license - - E d (v) contracts - - E d (C) mineral- & material-centric information (a) chemical & mineralogical composition Ba (14.4), Cu (0.15), Fe (12.5), Pb (1.2), Zn (1.3) [mean, wt%]; Ag (-), As (700), (i) elements [53] G Cd (30), Co (185), Ga (23), In (5.9), Tl (70) [mean, g/g] (ii) minerals G main mineral silica-based: Al, Si, K, Ni, Ga groups (& carbonate: Ca, Mn, Fe, (Mg), (Co) [53,54] associated sulphidic: Fe, Co, Cu, Zn, Pb, As, Cd, In, Tl elements) sulphate: Ba, Ca estimated cumulated minerals content (total dry mass/share of tailings’ quantities: [53] mass) BaSO 1,739,000 t/24.5 wt% (monomineralic) CuFeS 31,000 t/0.44 wt% FeS 1,086,000 t/15.3 wt% (7.1 wt% Fe in tailings) PbS 85,000 t/1.2 wt% ZnS 149,000 t/2.1 wt% Resources 2021, 10, 110 31 of 48 Table A11. Cont. Category & Factor Data Sources UNFC Axis Wissenbach 2,350,000 t/33.1 wt% shales ankerit 1,611,000 t/22.7 wt% main minerals in neutralisation masses unknown; high & low concentrations of Zn & BaSO , respectively [54] sludge: carbonate CaCO clay minerals Al O 2 3 zinc hydroxide Zn(OH) quartz SiO gypsum CaSO 2 H O 4 2 (b) physico-chemical properties tailings: very ﬁne, 90% of particles < 60 m, predominantly 2–60 m & particle size partially >20% below 3 m, analysed with 4 samples from 2 drill [53,54] G distribution coresneutralisation sludge: very ﬁne, ~80% of particles < 20 m geomechanical classiﬁed into geomechanical category GK III according to DIN 1054: highly [113] G properties difﬁcult regarding the interaction of structure & subsoil abrasiveness expected to be abrasive (30 wt% abrasive material in tailings) [53] G water content 29 wt%, estimated mean water content [53] G no valorisation as soil possible due to heavy metal concentration (As, Cd, Cr, Cu, Hg, Ni, Pb, Tl, & Zn) according to guideline “LAGA TR Boden” toxic elements (note: tailings are not soil per deﬁnition); classiﬁed as DK IV hazardous [53,114] G waste according to Landﬁll Regulation DepV; As, Cd, & Tl mainly associated with sulphides (As mainly with FeS & Cd mainly with ZnS) 1 2 3 econ.: economic aspects, env.: environmental aspects, soc.: social aspects, leg.: legal aspects. WWII: Word War II. AMD: acid mine drainage. SLO: social license to operate. Table A12. Basic data for the in-situ rehabilitation scenario NRR0. Parameter Unit Value Source Remarks surface area m 315,000 estimated with Google Earth [50] - leachate emission constant; inﬂux assumed duration of closure & following scenario B in Reference [51] only to occur in closure phase until in-situ a 5 leachate phase (p. 104) stabilisation is completed & inﬂux of rainwater or groundwater is phase neglected minimum duration according to Landﬁll duration of aftercare phase a 30 Landﬁll Ordinance DepV [61] Ordinance DepV [61] average water depth for lower & upper ponds calculated based on 82 out of average emission of based on the assumption of a constant leachate m /a 39,000 90 measurements taken from Reference leachate ﬂow & that only the standing water is drained [53]; visible water surface measured with Google Earth [50] leachate treatment - - assumption active on-site treatment unit Resources 2021, 10, 110 32 of 48 Table A13. Economic parameters for closure and aftercare in the in-situ stabilisation and rehabilitation scenario NRR0. A conversion rate GBP-EUR of 0.9 is assumed as per 14 August 2020 [115] and rounded up. From the referenced sources, the maximum values are chosen for a conservative approach. Parameter Unit Value Source Remarks In-situ Stabilisation & Surface Sealing ﬁnal surface cover including infrastructure 100 [51] closure & leachate phase /m concrete injection /m 68 [69] (p. 77) closure & leachate phase Leachate treatment active on-site treatment /m 50 [51] closure & leachate phase Other Costs maintenance & repair of leachate collection system /(a m ) 0.6 [51] closure & leachate phase monitoring of leachates /(a m ) 0.4 [51] closure & leachate phase monitoring of groundwater 0.3 [51] closure & leachate phase /(a m ) insurances /(a m ) 0.4 [51] closure & leachate phase maintenance of surface sealing /(a m ) 1.0 [51] aftercare phase maintenance of infrastructure 0.6 [51] aftercare phase /(a m ) monitoring of settlement /(a m ) 0.1 [51] aftercare phase monitoring of environment including weather /(a m ) 0.2 [51] aftercare phase aftercare management, reports, & documentation 0.6 [51] aftercare phase /(a m ) Table A14. Fixed economic and technological parameters for the techno-economic assessment of the mineral RMs recovery scenarios CRR1 and ERR2. A conversion rate USD–EUR of 0.85 is assumed as per 4 August 2020 [116]. Parameter Unit Value Source Remarks Qty. CAPEX Mining [117] (p. SU 12), www.cat.com/en_US/ 230 kW ship engine (d) , 272 kW products/new/power-systems/ dredger (including cutterhead (d–e) , Caterpillar 1,579,000 marine-power- systems/commercial- 1 cutterhead) C18 ACERT engine used as propulsion-engines/18493267.html reference (accessed on 14 March 2021) www.cat.com/en_US/products/new/ equipment/excavators/medium- CAT 320 GC, 1 m bucket capacity, excavator 160,000 1 excavators/1000032601.html (accessed (d) on 14 March 2021) wheel loader 269,000 [117] (p. SU 22) 157 kW (d), 3.8 m bucket capacity 1 bulldozer (with 145,000 [117] (p. SU 28) - 1 ripper) 6x6 traction, 15 m loading capacity, dump truck 384,000 [117] (p. SU 34) 1 (d) rubber boat (incl. www.marine-sales.de (accessed on transport of crew & light material to 4800 2 engine) 14 March 2021) dredger, (d) ensuring continuous processing plant feed & contingency for feed twin silo (2 810 m ) 343,000 [117] (p. Misc 92) stream disruptions; integrated 1 stirring function assumed to keep tailings suspended 3 3 41 kW (e) , 40 m head @ 90 m /h, slurry pump 24,000 [117] (p. misc 56) 6 redundant system foreseen Resources 2021, 10, 110 33 of 48 Table A14. Cont. Parameter Unit Value Source Remarks Qty. 300 mm nominal diameter, assumed to be suitable for offshore & onshore pipeline /m 1350 [118] (p. 42) application; 800 m one-way, 267 redundant system foreseen; water recirculation included longest distance to cover from ﬂoating bodies for landing site at northern part of 8750 [118] (p. 46) 40 pipeline middle dam to bottom right corner of lower dam (480 m) Processing low value is chosen since assets & processing plant 6,000,000 [119] (p. 13) machinery were assumed to be in - reactivation place & reusable Infrastructure mine site low value chosen due to simple development (paving 1,300,000 [119] (p. 13) mine plan, good mine site - roads, reactivating accessibility & available buildings railway, etc.) reclamation - removal of assets, mean value assumed due to surface rehabilitation, /t 2 [101] (p. 117) relatively small reclamation area & - tailings & environmental off-site residue disposal monitoring Other Fixed Economic Parameters low value chosen to reﬂect very discount rate % 15 [8] (p. 297) - high risk accounts for required non-speciﬁed contingency factor % 30 [45] (p. 58) - assets applied to assets & machinery liquidating value % 10 [120] (p. 16) under mining to estimate residual - value reclamation & asset liquidation only mine life a 11 estimated with Taylor ’s Rule [62] (p. 80) - in year 11 run-of-mine (ROM) t/h 170 assumption - - working days d/a 260 assumption - - administration working days mining d/a 260 assumption - - working days d/a 365 assumption - - processing shift system mining shifts/d 2 assumption 8 h per shift - shift system shifts/d 3 assumption 8 h per shift - processing working hours h/d 8 assumption - - administration working hours h/d 16 assumption - - mining working hours h/d 24 assumption - - processing percentage of net smelter return for %-NSR (Europe) % 65 [62] (p. 75) - Cu Cu percentage of net smelter return for %-NSR % 65 [62] (p. 75) - Pb Pb percentage of net smelter return for %-NSR % 50 [62] (p. 75) - Zn Zn Resources 2021, 10, 110 34 of 48 Table A14. Cont. Parameter Unit Value Source Remarks Qty. Technological Parameters low value chosen for conservative tailings mass t 7,100,000 [53] (p. AP1/75) - approach pump head m 55 [53] (p. AP5/19) - - r % 74 [60] (p. 254) - - Ba for ammonia leaching path of r % 12 [60] (p. 254) - Co sulphides r % 74 [60] (p. 176) - - Cu r % 87 [60] (p. 176) - - FeS2 for ammonia leaching path of r % 2 [60] (p. 254) - Ga sulphides for ammonia leaching path of r % 26 [60] (p. 254) - In sulphides r % 93 [60] (p. 254) - - inert material r % 68 [60] (p. 176) - - Pb r % 70 [60] (p. 176) - - Zn 1 2 3 4 (d): diesel engine. (d–e) diesel-electric engine. (e): electric engine. r: recovery rate. Table A15. Variable economic parameters for the techno-economic assessment of the mineral RMs recovery scenarios CRR1 and ERR2. A conversion rate USD–EUR of 0.85 are assumed as per 4 August 2020 [116]. Data adopted from Reference [117] if not stated otherwise. Energy Consumption Energy Consumption Maintenance & Overhaul Machine/Item Remarks [l /h] [kW ] [ /h] diesel electricity fuel consumption @ 502 kW approximated based on speciﬁcation sheet & CAT engine assumed to constantly dredger 125 - 112 deliver 502 kW, http://s7d2.scene7.com/ is/content/Caterpillar/ LEHM0004-00 (accessed on 15 March 2021) excavator 13 - 13 - wheel loader 24 - 20 - bulldozer (with ripper) 21 - 16 - dump truck 15 - 13 - no data could be retrieved rubber boat (including for maintenance & 2 - - engine) overhaul, negligible due to expected low value twin silo (2 810 m ) - - 5.8 - slurry pump - 41 3.2 - Resources 2021, 10, 110 35 of 48 Table A16. Variable economic parameters for the techno-economic assessment of the mineral RMs recovery scenarios CRR1 and ERR2. A conversion rate USD–EUR of 0.85 is assumed as per 4 August 2020 [116] if not stated otherwise. Parameter Unit Value Source Remarks Qty. OPEX mining machine operating costs /h 200 derived from Reference [117] overhaul, maintenance, lubricants, & wear - diesel consumption l/h 202 derived from Reference [117] - - electric energy kW 246 derived from Reference [117] - - consumption shift supervisor /(a person) 78.4 based on Reference [120] including assumed employers’ share of 40% 2 machine driver /(a person) 58.8 based on Reference [120] including assumed employers’ share of 40% 10 metal worker /(a person) 70.0 based on Reference [120] including assumed employers’ share of 40% 2 processing processing costs /t 7.2 [119] - - metal recovered machine operating costs /t 10.7 [119] electric energy only - metal recovered shift supervisor /(a person) 78.4 [120] including assumed employers’ share of 40% 3 control panel operator /(a person) 58.8 [120] including assumed employers’ share of 40% 3 machine operator /(a person) 58.8 [120] including assumed employers’ share of 40% 3 metal worker /(a person) 70.0 [120] including assumed employers’ share of 40% 3 services & administration general services /d 5210 [119] - - administrative services /d 1310 [119] - - RM prices forecast based on yearly average prices in electricity /kWh cf., Figure S1 raw data from Reference [85] Germany for commercial customers from - 2014–2019 forecast based on yearly average prices in diesel /l cf., Figure S2 raw data from Reference [86] - Germany from 1950–2020 forecast based on yearly BaSO prices from BaSO /t cf., Figure S3 raw data from References [87–90] - 4 tailings 1 2011–2020 raw data from References forecast based on yearly Co prices from Co /t cf., Figure S4 - tailings 1 [87,89–93] 1996–2020 forecast based on monthly Cu prices from November 1999–March 2021 & price per Cu /t cf., Figure S5 raw data from Reference [94] - tailings tonne tailings estimated after Wellmer et al. [62] (p. 47 ff.) raw data from References forecast based on yearly Ga prices from Ga /t cf., Figure S6 - tailings 1 [87,89–93] 1999–2020 raw data from References forecast based on yearly In prices from In /t cf., Figure S7 - tailings 1 [87,89–93] 1999–2020 forecast based on monthly Pb prices from November 1999–March 2021 & price per Pb /t cf., Figure S8 raw data from Reference [95] - tailings tonne tailings estimated after Wellmer et al. [62] (p. 74 ff.) forecast based on monthly Zn prices from November 1999–March 2021 & price per Zn /t cf., Figure S9 raw data from Reference [96] - tailings tonne tailings estimated after Wellmer et al. [62] (p. 74 ff.) intended valorisation as ﬁller in construction materials; reference value for high-quality sand in Goslar is EUR 19.5 residue sales /t 5.0 assumption (www.recyclingpark.de/startseite.html, - accessed on 2 June 2021); lower price assumed to estimate conservatively due to lack of information on effort to condition residues residue disposal /t 40.0 [53] (p. AP7-9/58) high value chosen to estimate conservatively - under consideration of monthly/yearly USD–EUR conversion rates. batteries, corrosion weighting agent alloys, electrical disposal (CRR1) construction protection, photo- for drilling fluids appliances, etc. disposal sales (ERR2) material voltaics, etc. high-technology inert contaminants base metals industrial mineral sulphides inert material metals material industrial mineral mixed sulphide concentrate mixed residues concentrate reference point Resources 2021, 10, 110 36 of 48 Resources 2021, 10, x FOR PEER REVIEW 35 of 47 BaSO 1,287,000 t CuFeS 23,000 t PbS 199,000 t 68,000 t ZnS 108,000 t Co 1,300 t Ga 1,503 t 163 t In 40 t FeS 946,000 t As 4,970 t 951,680 t Cd 213 t Tl 497 t Wissenbach shales 165,000 t 278,000 t ankerit 113,000 t BaSO 453,000 t 453,000 t CuFeS 8,000 t FeS 142,000 t 228,000 t PbS 31,000 t ZnS 47,000 t Wissenbach shales 2,188,000 t 3,687,000 t ankerit 1,499,000 t Figure A1. Detailed production breakdown of 10-year material flows for the RMs recovery scenarios Figure A1. Detailed production breakdown of 10-year material ﬂows for the RMs recovery scenarios (CRR1, ERR2). (CRR1, ERR2). Resources 2021, 10, x FOR PEER REVIEW 36 of 47 Resources 2021, 10, x FOR PEER REVIEW 36 of 47 Resources 2021, 10, 110 37 of 48 Figure A2. Results of the sensitivity analysis of the conventional mineral RMs recovery scenario Figure A2. Results of the sensitivity analysis of the conventional mineral RMs recovery scenario (CRR1m) with mean price Figure A2. Results of the sensitivity analysis of the conventional mineral RMs recovery scenario (CRR1m) with mean price forecast and a discount rate of 15%. forecast and a discount rate of 15%. (CRR1m) with mean price forecast and a discount rate of 15%. Figure A3. Results of the sensitivity analysis of the enhanced mineral RMs recovery scenario (ERR2m) with mean price forecast and a discount rate of 15%. Table A17. Overall project rating with the UNFC-compliant categorisation matrix of the degree of confidence in the geo- logical estimates (G). Factor Indicator UNFC Rating Justification Source Geological conditions (relevant for project development) degree of geological certainty: G2 NRR0, CRR1, & ERR2: deposit modelled based on direct data on 10 drill cores from lower pond, and pre-processed historical data on 14 & 12 drill cores from (1) quantity lower & upper pond, respectively. Model was validated with historical production Figure A3. Results of the sensitivity analysis of the enhanced mineral RMs recovery scenario (ERR2m) with mean price medium Figure A3. Results of the sensitivity analysis of the enhanced mineral RMs recovery scenario [53] data. Extension & volume of TSF known with medium confidence. Overall forecast and a discount rate of 15%. (ERR2m) with mean price forecast and a discount rate of 15%. knowledge on mineral quantity with medium confidence in both ponds. Knowledge gap on quantity of neutralisation sludge & other dumped material. Table A17. Overall project rating with the UNFC-compliant categorisation matrix of the degree of confidence in the geo- degree of geological logical estimates (G). certainty: (2) quality NRR0, CRR1, & ERR2: physico-chemical properties known with medium confi- Factor Indicator UNFC Rating Justification Source medium G2 [53] dence. Geological conditions (relevant for project development) degree of geological degree of geological certainty: certainty: (3) homogeneity medium G2 NRR0, CRR1, & ERR2: mineral distribution in lower pond known with medium [53,54] G2 NRR0, CRR1, & ERR2: deposit modelled based on direct data on 10 drill cores confidence. Knowledge gap on distribution of tailings & neutralisation sludge in from lower pond, and pre-processed historical data on 14 & 12 drill cores from both ponds. (1) quantity lower & upper pond, respectively. Model was validated with historical production medium [53] data. Extension & volume of TSF known with medium confidence. Overall knowledge on mineral quantity with medium confidence in both ponds. Knowledge gap on quantity of neutralisation sludge & other dumped material. degree of geological certainty: (2) quality NRR0, CRR1, & ERR2: physico-chemical properties known with medium confi- medium G2 [53] dence. degree of geological certainty: (3) homogeneity medium G2 NRR0, CRR1, & ERR2: mineral distribution in lower pond known with medium [53,54] confidence. Knowledge gap on distribution of tailings & neutralisation sludge in both ponds. Resources 2021, 10, 110 38 of 48 Table A17. Overall project rating with the UNFC-compliant categorisation matrix of the degree of confidence in the geological estimates (G). UNFC Factor Indicator Justiﬁcation Source Rating Geological conditions (relevant for project development) degree of geological certainty: NRR0, CRR1, & ERR2: deposit modelled based on direct data on G2 10 drill cores from lower pond, and pre-processed historical data on [53] medium 14 & 12 drill cores from lower & upper pond, respectively. Model (1) quantity was validated with historical production data. Extension & volume of TSF known with medium conﬁdence. Overall knowledge on mineral quantity with medium conﬁdence in both ponds. Knowledge gap on quantity of neutralisation sludge & other dumped material. degree of geological certainty: (2) quality NRR0, CRR1, & ERR2: physico-chemical properties known with medium G2 [53] medium conﬁdence. degree of geological certainty: NRR0, CRR1, & ERR2: mineral distribution in lower pond known (3) homogeneity medium G2 [53,54] with medium confidence. Knowledge gap on distribution of tailings & neutralisation sludge in both ponds. Table A18. Overall project rating with the UNFC-compliant categorisation matrix for the technical feasibility (F). UNFC Factor Indicator Justiﬁcation Source Rating TSF condition & risks (relevant for project development) degree of knowledge: NRR0, CRR1, & ERR2: existence cannot be excluded based on (4) ordnance F3 [53] unclariﬁed historical data. Requires clariﬁcation. Mine planning considerations (relevant for project execution) level of detail of (5) mine/ planning: operational design basic F3 NRR0, CRR1, & ERR2: conceptual planning. - degree of research on mineral processing: (6) metallurgical - - NRR0: factor not applicable. - testwork F3 CRR1 & ERR2: extraction of BaSO , Co, Cu, Ga, In, Pb, Zn, & inert laboratory scale material (Wissenbach shales, ankerit) evaluated in discontinuous [60] laboratory experiments on tailings from lower pond. percentage of recycled water: (7) water F1 CRR1 & ERR2: water recirculated in dredging operation. Processing consumption high (>80%) [53] water can be recirculated, too. unclariﬁed F3 NRR0: unclear if TSF water can be used for making concrete. - Resources 2021, 10, 110 39 of 48 Table A18. Cont. UNFC Factor Indicator Justiﬁcation Source Rating Infrastructure (relevant for project development) condition of infrastructure: (8) real estate NRR0, CRR1, & ERR2: buildings & land from former processing highly developed F1 [53] available. condition of equipment: (9) mining & NRR0: not applicable since specialised non-mining equipment is - - - processing required. bleak F3 CRR1 & ERR2: unclariﬁed. - condition of infrastructure: NRR0, CRR1, & ERR2: access to public electricity, gas, & water based on (10) utilities acceptable F2 observation grid assumed. on Google Earth [50] condition of infrastructure: (11) transportation NRR0, CRR1, & ERR2: dirt roads, federal highway B6 ~1.6 km N acceptable F2 [53], observed & access air-line distance from TSF & public railway ~500 m E air-line on Google distance from TSF, disused railway tracks from processing plant Earth [50] Bollrich to public network (estimated abandonment in 1988). Post-mining state (relevant for future impacts) suitability of new disposal site for safe (12) residue storage storage: safety F3 NRR0: predicting long-term stability might be difﬁcult. unclariﬁed [69] CRR1 & ERR2: new disposal site unknown. level of detail of (13) rehabilitation planning: conceptual F2 NRR0, CRR1, & ERR2: conceptual planning. - Table A19. Overall project rating with the UNFC-compliant categorisation matrix of the economic viability (E a). UNFC Factor Indicator Justiﬁcation Source Rating Microeconomic aspects (relevant for project development) discounted cash ﬂow over projected LOM: (14) economic viability CRR1m & ERR2m: NPVs of EUR 73 mio. & EUR 172 mio., positive (NPV >> 0 ) E3.1a - respectively, with mean price forecast. negative (NPV << 0 ) E3.3a NRR0: costs of EUR 125 mio. incurred. - uncertainty of cash ﬂow in pessimistic scenario: - - NRR0: no forecast performed. - low (NPV in pessimistic (15) economic E3.1a ERR2p: NPV = EUR 73 mio. - scenario >> 0 ) uncertainty high (NPV in pessimistic scenario << E3.3a CRR1p: NPV = EUR 17 mio. - 0 ) Resources 2021, 10, 110 40 of 48 Table A19. Cont. UNFC Factor Indicator Justiﬁcation Source Rating Financial aspects (relevant for project development) country rank in the ease-of-doing-business (16) investment Index. conditions - - NRR0: not applicable since company works on assignment basis. - CRR1 & ERR2: country rank 22 (Germany). Good investment high (<75) E3.1a [121] conditions assumed. probability of approval: CRR1 & ERR2: research on TSF was funded publicly & positive high E3.1a - (17) ﬁnancial results give rise to the assumption that follow-up project proposal support REWIMET might be accepted. no ﬁnancial support E3.3a NRR0: no ﬁnancial support scheme known at the moment. - scheme available Table A20. Overall project rating with the UNFC-compliant categorisation matrix for the environmental viability (E b). UNFC Factor Indicator Justiﬁcation Source Rating Environmental impacts during project execution risk of dust emission: E3.3b NRR0: unclarified if TSF needs to be drained prior to concrete unclariﬁed (18) air emission injection, which could lead to wind erosion of the tailings. CRR1 & ERR2: complete submersion of tailings in dredging high (>80%) E3.1b - operation. risk of groundwater (19) liquid contamination: efﬂuent low E3.1b NRR0, CRR1, & ERR2: status quo is expected to be retained. - emission expected degree of impact: medium E3.2b NRR0, CRR1, & ERR2: constant noise emission from TSF in based on (20) noise 2 working shifts from Mondays to Fridays. Noise is expected observa- emission tion on to be audible, especially in the surrounding mountain area & Google areas on the same plane. It is possible that the noise would Earth [50] not be audible in residential areas to topography. CRR1 & ERR2: the processing plant is to be soundproofed. Environmental impacts after projection execution total number of protected species that are affected by mining activities & (21) biodiversity that will be resettled on post-mining land: none (0%) E3b NRR0, CRR1, & ERR2: protected ﬂora & fauna species were [53] sighted during an on-site inspection. Capturing the exact types & number of species is required for planning a resettlement or other compensation measures. freely available post-mining land: some (50–80%) E3.2b NRR0: surface area of current wet cover is made available - for reuse. (22) land use CRR1 & ERR2: original topography is restored. NRR0, CRR1, & ERR2: it is expected that a solution for the collection & further treatment of the neutralisation sludge requires a permanent land use. reduction in reactive material’s mass: high (>80%) E3.1b - CRR1: 84 wt% of sulphides leave the system boundaries as (23) material commodities. ERR2: all tailings are valorised. reactivity E3.3b NRR0: factually, reactive materials remain in place. [69] low (<50%) Long-term stability difﬁcult to predict. Resources 2021, 10, 110 41 of 48 Table A21. Overall project rating with the UNFC-compliant categorisation matrix for the social viability (E c). UNFC Factor Indicator Justiﬁcation Source Rating Social impacts during project execution probability of approval through active commitment: (24) local E3.2c CRR1 & ERR2: ﬁrst indication of positive prospects by [52] community medium (50–80%) stakeholder assessment (local government, industry, university, & environmental NGOs). Local population’s opinion unknown. unclariﬁed E3.3c NRR0: no data available. - total number of complaints or prosecutions for (25) health & non-compliance in safety planning phase: NRR0, CRR1, & ERR2: plans have not been communicated none E3.3c - publicly. total number of complaints or prosecutions for (26) human rights non-compliance in & business ethics planning phase: NRR0, CRR1, & ERR2: plans have not been communicated none E3.3c - publicly. Social impacts due to project execution total number of complaints or prosecutions for (27) wealth non-compliance in distribution planning phase: NRR0, CRR1, & ERR2: plans have not been communicated none E3.3c - publicly. percentage of employees sourced from local (28) investment in communities: local human E3.3c NRR0: it can be expected that an external contractor must be hired capital unclariﬁed due to the special character of the required services. Aftercare measures could be carried out by local workers. CRR1 & ERR2: unclarified how many local workers could be employed. residue disposal: complete residue E1c ERR2: no loss since all tailings are valorised. - valorisation mixed disposal E3.2c CRR1: it is assumed that the site for the disposal of new (29) degree of RM recovery residues has no option to store different residues separately. NRR0: access to RM potential for future generations with sterilisation E3.3c - reasonable effort prevented. total mass reduction as percentage of original tailings mass: (30) RM high (>80%) E3.1c ERR2: all tailings are valorised. - valorisation NRR0: no valorisation takes place. CRR1: 38 wt% of tailings are low (<50%) E3.3c - valorised. Social impacts after project execution duration of aftercare measures: short-term (up to E1c CRR1 & ERR2: aftercare assumed to be complete after 1 year - (31) aftercare 5 years) long-term (more than NRR0: long-term behaviour difﬁcult to predict & long-term E3c [69] 30 years) monitoring might be necessary. impact on the environment: E1c CRR1 & ERR2: former topography is restored. - (32) landscape non-perceptible E2c NRR0: is expected to be well integrated into landscape with an partially perceptible according surface design. Main dam remains perceptible. Resources 2021, 10, 110 42 of 48 Table A22. Overall project rating with the UNFC-compliant categorisation matrix for the legal viability (E d). UNFC Factor Indicator Justiﬁcation Source Rating Legal situation (relevant for project development) state of development: (33) right of mining application not begun or E3.3d NRR0, CRR1, & ERR2: no concrete activities initiated. - unclariﬁed (34) environmental state of development: protection application not begun or E3.3d NRR0, CRR1, & ERR2: no concrete activities initiated. - unclariﬁed state of development: (35) water protection application not begun or E3.3d NRR0, CRR1, & ERR2: no concrete activities initiated. - unclariﬁed Table A23. Rating of individual RMs with the UNFC-compliant categorisation matrix for the degree of conﬁdence in the geological estimates (G). UNFC Factor Indicator Justiﬁcation Source Rating Geological conditions (relevant for project development) degree of geological certainty: CRR1 & ERR2: knowledge on BaSO , Cu, FeS , Pb, Zn, & inert G2 4 2 [53,54] medium material (Wissenbach shales, ankerit) with medium conﬁdence in both (36) quantity ponds. CRR1 & ERR2: knowledge on Co, Ga, & In with medium conﬁdence low G3 [53] in lower pond. Co, Ga, & In quantity in upper pond inferred. degree of geological certainty: CRR1 & ERR2: knowledge on BaSO , Cu, FeS , Pb, Zn, & inert G2 4 2 [53,54] medium material (Wissenbach shales, ankerit) with medium conﬁdence in both (37) quality ponds. CRR1 & ERR2: knowledge on Co, Ga, & In with medium conﬁdence low G3 [53] in lower pond. Co, Ga, & In quantity in upper pond inferred. degree of geological certainty: CRR1 & ERR2: knowledge on the distribution of BaSO , Cu, FeS , Pb, G2 4 2 [53,54] medium (38) homogeneity Zn, & inert material (Wissenbach shales, ankerit) with medium conﬁdence. CRR1 & ERR2: knowledge on the distribution of Co, Ga, & In with low G3 [53] medium conﬁdence in lower pond. Knowledge on Co, Ga, & In in upper pond inferred. Table A24. Rating of individual RMs with the UNFC-compliant categorisation matrix for the technical feasibility (F). UNFC Factor Indicator Justiﬁcation Source Rating Mine planning considerations (relevant for project execution) percentage of RM which is extracted from the tailings: CRR1 & ERR2: FeS (87 wt% recovered in mixed sulphide F1 2 high (>80%) [60] (39) recoverability concentrate), inert material (Wissenbach shales, ankerit) (93 wt% are recovered with the new residues). CRR1 & ERR2: BaSO (74 wt%), Cu (74 wt%), Pb (68 wt%), Zn medium (50–80%) F2 [60] (70 wt%). low (>50%) F3 CRR1, ERR2: Co (12 wt%), Ga (2 wt%), In (26 wt%). [60] Resources 2021, 10, 110 43 of 48 Table A25. Rating of individual RMs with the UNFC-compliant categorisation matrix for the economic viability (E a). UNFC Factor Indicator Justiﬁcation Source Rating Microeconomic aspects (relevant for project development) favourable conditions for RM extraction: yes E3.1a [122] CRR1 & ERR2: there is a demand for BaSO , Cu, Pb, Zn, Co, Ga, & In conditionally E3.2a CRR1 & ERR2: Fe & H SO could theoretically be produced 2 4 (40) demand [123] from CuFeS & FeS . 2 2 CRR1 & ERR2: residues theoretically usable in construction E3.3a materials, but experiments are necessary. Currently, there is per se - no not a demand for residues so that a potential application of the inert fraction (Wissenbach shales, ankerit) of the new residues needs to be clarified. allocation to EC’s criticality assessment: CRM E1a CRR1 & ERR2: BaSO , Co, Ga, & In. [112] high economic (41) RM criticality importance or supply E2a CRR1 & ERR2: Cu, Pb, S (from CuFeS & FeS ), & Zn. [112] 2 2 risk no criticality E3a CRR1 & ERR2: inert material (Wissenbach shales, ankerit). forecasted mean price development over the project’s duration: - CRR1 & ERR2: FeS is recovered as a non-paid co-product, & no - - price forecast was performed for the inert material (Wissenbach (42) price shales, ankerit). development Figures S3, positive trend E3.1a CRR1 & ERR2: BaSO , Co, In. S4 and S7 Figures stagnant trend E3.2a CRR1 & ERR2: Pb, Zn. S8 and S9 Figures negative trend E3.3a CRR1 & ERR2: Cu, Ga. S5 and S6 Table A26. Rating of individual RMs with the UNFC-compliant categorisation matrix for the environmental viability (E b). UNFC Factor Indicator Justiﬁcation Source Rating Impacts after project execution concentration of RM solid matter in new residues to qualify for class DK 0 (inert waste) according to German Landﬁll Regulation DepV [61]: NRR0: not applicable since no new residues are produced. - - (43) solid matter ERR2: not applicable since no new residues are disposed of. non-hazardous material E1b CRR1 & ERR2: inert material (Wissenbach shales, ankerit). - threshold value not exceeded E3.1b CRR1: Cu, Zn. [60] threshold value exceeded E3.2b CRR1: Pb. [60] concentration of RM in eluate from new residues to qualify for class DK 0 (inert waste) according to German Landﬁll Regulation DepV [61]: NRR0: not applicable since no new residues are produced. - - (44) eluate ERR2: not applicable since no new residues are disposed of. non-hazardous material E1b CRR1 & ERR2: inert material (Wissenbach shales, ankerit). - threshold value not exceeded E3.1b CRR1: Ba, Cu, Zn. 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How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data

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Published: Oct 29, 2021

Keywords: anthropogenic raw materials; sustainability assessment; tailings recycling

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How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data

How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data

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How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data

How to Identify Potentials and Barriers of Raw Materials Recovery from Tailings? Part II: A Practical UNFC-Compliant Approach to Assess Project Sustainability with On-Site Exploration Data

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