Search

• Water was able to leach 21 % of Co and 37 % of Ni due to weathering of sulphides. • All dissolved Co leached from oxidized phases via chemical leaching mechanism. • Electrochemical leaching enhanced Ni yield up to 63 %. • Water leaching adjusts pH inherently and results in industrially attractive PLS. Energy transition from fossil- to a material-intensive energy system is highly dependent on the availability of Co and Ni. This has increased interest towards non-traditional raw material streams such as mining waste. In this work, leaching experiments were conducted on historical flotation tailings with low concentrations of Co (0.081 wt%), Ni (0.055 wt%), Cu (0.15 wt%) and Zn (0.17 wt%). This low grade may challenge the feasibility of industrial operation, and therefore water, and commonly used mineral acids, were investigated as lixiviants for the process. The electrochemical leaching behaviour was studied using various oxidants (O 2 , Cu2+, Fe3+ and H 2 O 2). The results showed that a substantial amount of Co (21 %) and Ni (37 %) could be leached using water, with no additional oxidants or pH adjustment (80 °C, 5 min). In water leaching, the system stabilized inherently to pH =3.7 and the redox potential to E h < 0.3 V vs Ag/AgCl. This indicates that during the 32–67 years of piling, the weathering conditions had caused natural oxidation of Co– and Ni-bearing minerals such as pyrrhotite and pentlandite. The leaching yields of Co and Ni were slightly increased (5 % units for Co, 10 % units for Ni) by introducing additional acid (1 M) into the leaching system. Further addition of oxidants did not increase the leaching yield of Co, suggesting that the dissolution of Co-bearing minerals followed the chemical leaching mechanism. In contrast, some of the Ni leaching was found to be electrochemical in nature, as extraction increased up to 63 % with the use of strong oxidative (cupric chloride) conditions – most likely due to partial chalcopyrite or pentlandite leaching. Undissolved Co and Ni remained in refractory minerals such as chalcopyrite or pyrite. In addition to Co and Ni, 52 % of Zn and 37 % of Cu were also found to be soluble under acidic conditions. When considering the use of historical flotation tailings as a feed stream in hydrometallurgical processing, direct water leaching may provide an attractive and robust leaching strategy, with spontaneous inherent pH adjustment. An increase in solid-to-liquid ratio or solution circulation (higher acidity) could increase percentual Co and Ni yield and enable enrichment of the target metals in the pregnant leach solution (PLS). If flotation is considered for concentration of Co– and Ni-bearing minerals, water leaching prior to flotation is recommended, to improve both the flotation performance and overall flotation and metal recovery. [ABSTRACT FROM AUTHOR]

• Water miscible organic solvents significantly enhanced Sc elution efficiency. • 4 M H 2 SO 4 in 50 vol% 1-PrOH eluted 98 % of Sc from VP OC 1026 (shake flask). • >97 % Sc on TP 272 could be eluted with 6 M H 2 SO 4 in 50 vol% 2-PrOH (shake flask). • 10 vol% 2-PrOH in 2 M H 2 SO 4 increased [Sc] max from 167.0 to 532.6 mg/L (continuous). Scandium is a strategic element with exceptional applications however, its widespread application has been limited mainly due to its high price which itself originates from lack of enriched primary reserves. Mineralized waste materials and mine tailings collected from various mining activities often contain low amounts of Sc and rare earth elements (REE), along with much higher levels of contaminants such as Si, Fe and Al. Ion exchange resins, especially phosphorus containing solvent impregnated ones, show extremely high selectivity for quantitative adsorption of Sc from pregnant leach solutions. However, efficient and economical elution of Sc from these types of resins is still a challenge. In this study, a series of water miscible organic solvents including methanol, ethanol, 1-propanol, 2-propanol and acetone are explored with sulfuric acid in elution of Sc at room temperature (25 °C). With the proposed binary solvent system in this study, 98% of the adsorbed Sc was eluted from VP OC 1026 (impregnated with D2EHPA) with 4 M H 2 SO 4 in 50 vol.% 1-propanol while negligible amount of Sc could be recovered with 2 M H 2 SO 4 even at high temperatures. Also, exceeding 97% of the loaded Sc on TP 272 (impregnated with Cyanex 272) could be successfully eluted with 6 M H 2 SO 4 containing 50 vol.% 2-Propanol. Nevertheless, the elution efficiency of Sc from TP 272 was notably constrained, falling below 20 %, when 2 M H 2 SO 4 was employed as the eluent. The added organic solvents also significantly increased the performance of H 2 SO 4 in elution of Sc from the resins in columns. The addition of just 10 vol.% 2-propanol to 2 M H 2 SO 4 led to significant increase in the elution of Sc from TP 272. The maximum concentration of Sc in the eluted fractions increased by over threefold, going from 167.0 mg/L to 532.6 mg/L, when compared to using 2 M H 2 SO 4 under similar elution conditions. [ABSTRACT FROM AUTHOR]

• Copper anode slime (CAS) is a valuable mining waste due to its critical metal content. • A revision of the metal and mineral composition of CAS is performed. • Operational conditions of CAS treatment for extracting metals were analyzed. • Ionic liquids and deep eutectic solvents are new leachants for green CAS treatment. • A conceptual flowchart for the green CAS processing is proposed. Copper anode slime (CAS) is a valuable residue produced during the refining of metallic copper. Although it contains toxic elements such as As, Sb, and Cd, CAS is also a source of various valuable metals, including Au, Ag, platinum group metals, Se, Te, Sn, Cu, Ni, and Pb, among others. However, processing CAS is difficult due to the various mineralogical phases present. To improve the efficiency of valuable metal recovery, many researchers have explored different alternatives, including the gradual replacement of potentially toxic reagents with more environmentally friendly options that produce physically and chemically stable residues. Additionally, the use of green solvents that partially or totally replace water in the CAS processing have been increasingly proposed. This article provides a detailed review of the various hydrometallurgical options available for processing anodic copper slimes. It also highlights optimum conditions reported by researchers for achieving good recoveries of different slime components. The information presented can serve as a helpful guide for those interested in exploring new methods of processing anodic slimes and designing experiments. In addition, the article proposes two conceptual designs for processing CAS, which integrate different selectivity and compatibility criteria in reactivity. These designs have demonstrated higher recoveries of each element per stage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quantitative reconciliation of mineralogical data with leachate dynamic. • Investigation of mine waste rock water content on weathering. • Decrease in leachate pH at lower water saturation. • Carbonate phase size reduction with increase in water saturation. Water content plays a critical yet ambivalent role in the physical and geochemical stability of mine tailings and waste rock, but its effects on individual chemical weathering reactions (dissolution and precipitation) and bulk water quality remain poorly understood. We experimented with synthetic waste rock to quantitatively reconcile modal and textural mineralogical parameters (mineral size, association, and liberation) with leachate quality at different water saturation levels (5–100%). Leachate pH consistently decreased from a 13-week average of 6.14 at 100% saturation to 5.37 at 5% saturation. Simultaneously, mineralogical analyses revealed a reduction in the size of carbonate phases over the course of weathering, decreasing from 200 µm to 145 µm as water saturation increased from 5% to 100%, which could be a contributing factor to more alkaline pH in samples with higher water saturation. Total concentrations of iron (Fe) and copper (Cu) in solution increased with lower moisture, with Cu concentrations increasing 24-fold in samples at 5% saturation compared to full saturation. In contrast, arsenic (As) concentration increased with higher moisture levels, which we attribute to reduced galvanic protection of As-bearing pyrite from oxidation. Multivariate statistical evaluation allowed us to uncover correlations between water chemistry and mineralogical data (i.e., sulfide associations or phase perimeters) and to explain chemical differences between samples, particularly those at 100% and 5% water saturation. Our findings underscore the importance of conducting quantitative mineralogical investigations on mine waste materials and considering their stored water content in the formulation of mine waste management strategies. [ABSTRACT FROM AUTHOR]

• E-waste is one of the fastest-growing solid wastes in the globe. • E-waste co-processing with ore minerals and their products is feasible. • Some e-waste is co-processed in integrated pyro-hydrometallurgical facilities. • Niche e-waste co-processing based on leaching can be developed with further studies. E-waste generation has been exponential due to technological advancements, urbanisation and modern lifestyles, reduced replacement intervals of consumer electronics, lack of design-for-environment components in electrical and electronic equipment, lack of repairs and high costs of repairs. 62 million tonnes of e-waste was generated in 2022, equivalent to 7.8 kg of e-waste per person per year. E-waste management has also been challenging, and a significant fraction ends up in landfills despite the presence of precious, base and critical metals. In addition, another substantial fraction is processed by the informal sector employing sub-standard methods without considering approved environmental, health and safety aspects. Since only 22.3 % of e-waste has been collected and properly recycled, extensive e-waste recycling frameworks, including niche methods, are needed. E-waste co-processing with ore minerals, including mine waste, and metal concentrates and other waste materials in smelters, is thus identified as a promising area to address the e-waste management and value recovery challenge. This is supported by the availability of low-grade ores to produce critical metals and copper and mine tailing management requirements. Integrated pyro-hydrometallurgical facilities in developed countries already process some e-waste with metal concentrates and other waste materials. However, niche e-waste co-processing techniques utilising heap leaching, tank leaching and acid-generating mine tailings are needed since the best available techniques depend on local socio-techno-economic considerations. This study on e-waste co-processing with natural resources and their products could be beneficial to developing the relatively unexplored research area with future studies. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) are critical for the energy transition; however, their 'green' credentials are at odds to the environmental damage as part of mining, recovery and processing. Opportunities may exist to recover REEs from uranium tailings as part of the 'economic rehabilitation' of tailings storage facilities. [Display omitted] • Water leach able to extract rare earth elements (REEs) from tailings. • More than 10,000 t of REEs could be recovered using an in situ water leach. • REEs recovery using water leach potential exceeds the uranium recovery during initial mining. • Water leaching and recovery of REEs from tailings allows for economic rehabilitation. • In situ extraction from tailings allows for low water, low energy recovery. The global energy transition from fossil fuels to renewable sources poses substantial challenges to increase metal production, including industry-critical rare earth elements (REEs). Environmental and social concerns obfuscate the production of these 'green' metals and only ∼1% of REE demand is met from recycling. This work highlights the potential for the 'economic rehabilitation' of the Mary Kathleen Mine, a relinquished uranium (U) mine with very high (∼3 wt%) total REE concentrations within the tailings storage facility (TSF). Leaching of the tailings revealed that approximately 5% of the REEs are water-soluble, suggesting the possibility for in situ extraction. Using an in situ water leach, the projected total REE recovery is >10,000 t, which would exceed the total amount of U recovered (7,532 t) during the initial mining operation. The proposed in situ recovery would offer a truck-free mine, using solar energy and water recycling technologies to recover REEs from a waste source, reducing environmental contamination. [ABSTRACT FROM AUTHOR]

Dense medium separation circuits use a dense medium to separate low density waste material from high density valuable minerals. Since the dense medium is an expensive consumable, it is recovered after separation of the valuable minerals from waste. A dynamic nonlinear model of a dense medium separation circuit of an iron ore plant in South Africa is developed to track the flow of medium in the circuit. An extended Kalman filter is designed for estimating observable but unmeasured states. The model is validated using online plant data. This paper serves as a precursor for further work to detect and mitigate expensive medium losses in the circuit. • A dense medium separation circuit is modelled from first principles. • Each unit process model is evaluated for state observability. • The states are estimated from industrial data using an extended Kalman filter. • The results indicate how the estimates can be used to detect medium losses. [ABSTRACT FROM AUTHOR]

[Display omitted] • It is possible to use sustainable methods for Cu recover from mining wastes. • Glycine leaching of mining wastes can recover 100 % of Cu at pH = 9.5. • Proposed technology is a selective method for Cu extraction over As or Fe. • Glycine/H 2 O 2 leaching generates phytostimulant post-leaching residues. • Post-leaching residues has a potential use for mining areas restauration. Finding strategies that promote sustainability in the recovery of metals with industrial applications is imperative to reduce costs and mitigate environmental impacts. The use of environmentally friendly reagents such as glycine is being widely investigated due to the benefits that its application entails from an industrial, economic, and environmental perspective. We sought through this study to advance in the application of glycine leaching systems for the recovery of copper from different wastes and minerals while determining the optimal conditions for its recovery. Experimental results showed that among the 3 feedstocks tested (two mining wastes and one sulfide mineral) under the established operating conditions (room temperature and different alkaline pHs), the best copper recovery was obtained with the most oxidized waste at pH 9.5, which allowed a 100% of copper recovery along with low leaching of Fe and As. Furthermore, the characterization of its final post-leaching residue showed phytostimulant properties. Unfortunately, these selected conditions did not yield favorable results for the sulfide mineral and the less oxidized wastes. In this case, further research will be necessary to achieve higher metal recoveries. [ABSTRACT FROM AUTHOR]

• Study is first transform acid mine drainage (AMD) waste into ferric ammonium sulfate (FAS) • AMD was used as complex matrix to test boundaries for FAS formation. • FAS formation by controlled crystallisation was highly selective. • FAS was formed as major product when AMD Fe concentration was greater than 2500 mg/L. Green and sustainable production of secondary products from waste sources is needed for a global circular economy. The primary aim of this work was to produce ferric ammonium sulfate (FAS) from acid mine drainage (AMD). AMD with a Fe content of approximately 240 mg/L was used as a matrix to model FAS formation under different solution concentrations of Fe and S (as ferric sulfate and sulfuric acid). This approach offered the benefit of identifying boundary conditions for FAS synthesis from wastes, so that the results of this study can be applied to many different AMD compositions. Results showed that increased Fe concentrations were associated with higher crystal yields and more selective crystallisation. Fe, S, and Al were more selectively incorporated over other elements present in AMD, however, XRD analysis did not show additional Al-bearing alum products. FAS was produced for AMD solutions where Fe was above 2500 mg/L, which demonstrates that FAS could be formed from iron-rich waste solutions. [ABSTRACT FROM AUTHOR]

• Sample preparation procedures within automated mineralogy are discussed. • This step is as essential as the initial sample collection or the subsequent analysis. • Failure to get it right undermines the quality of the work, particularly with agglomerations. • Resolving agglomerations leads to significant lost time in post-processing. • A case study is presented of typical poor-quality sample preparation and comparisons against best practise. The use of automated mineralogy has been critical in understanding all stages of a mine cycle including; identification of potential ore phases for exploration projects; routine composites for monthly mineralogy trends including liberation of target phases plus identification of penalty phases; for mine closure; and the potential of reactions like carbon sequestration from mine waste in order to ensure efficient remediation. Whilst automated mineralogy is clearly a key technique, the quality of the data and how 'automated' the actual automated mineralogy process is, is driven by the accuracy and efficiency of sample preparation techniques. The need for on-site operational mineralogy is growing with the need for rapid turnaround of data to drive processing plants. This paper discusses the effects of poor sample preparation on the quality of automated mineralogy data outputs including liberation metrics, mineral abundance and grain size. Potential sources for error from preparation techniques include; inefficient cleaning of all utensils and the block itself; poor screening, deagglomeration and polishing of the sample; and the pressure to streamline these preparation techniques for optimisation of mine site laboratories in order to rapidly generate data to monitor daily processing plant activity. A further discussion touches on how automated is automated mineralogy, establishing that a large percentage of the process depends on the efficiency and accuracy of sample preparation and that research should be focused on optimising this stage of the process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phosphate mine waste rock contains non-negligible amounts of residual phosphate. • Indured phosphate constituted 25 wt% of the total sample, with 18 wt% P 2 O 5. • DE-XRT sorting technology can be an effective technique to recover the lost phosphate. • PMWR piles are a suitable resource for the application of SBS technology. • Materials sorting can reduce the environmental footprint of PMWR piles. Phosphate extraction and processing generates large volumes of phosphate mine waste rock (PMWR) that still contains non-negligible amounts of residual phosphate. Due to the increasing demand for phosphorous (P), in particular by the fertilizer industry, PMWR can become a potential resource for P beneficiation if cost-effective methods are applied. The main objectives of this study are to: i) characterise PMWR from the Ben Guerir mine site (Morocco); ii) evaluate the efficiency of hand- and sensor-based sorting (SBS) to recover the lost phosphate; and. iii) upgrade the P 2 O 5 content in the concentrate. Samples were collected from different locations in the PMWR piles and divided into two main fractions: >30 mm and < 30 mm. The coarse fraction (>30 mm) was sorted using three main SBS technologies to separate phosphate from gangue materials: dual energy X-ray transmission (DE-XRT), near-infrared combined with color (NIR/color), and color technologies. The fine fraction was processed with the conventional flowsheet used by the mine. Chemical and mineralogical characterisation showed that the composite sample contained up to 17.5 wt% P 2 O 5 , with an abundance of fluorapatite, calcite, quartz, and dolomite. The hand sorting demonstrated that >50 wt% of the PMWR within the coarse fraction (>30 mm) was in the form of indured phosphate (IndP). The remaining lithologies were represented by phosphated flint, flint, silexite, limestone, and marl. In terms of sorting efficiency, the tests highlighted the performance of DE-XRT for materials characterised with a difference in atomic density. The use of DE-XRT allowed a P 2 O 5 recovery of 70 wt%, with an increase of the P 2 O 5 content from 13.5 wt% to 18.5 wt%. The remaining lithologies were successfully separated using SBS technologies. Materials sorting is an interesting technology that can reduce the environmental footprint of PMWR by recovering the lost phosphate and valorising the remaining lithologies for civil engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Continuous Fe(II) biooxidation can be operated at very extreme [Fe] and pH. • No biological inhibition is observed when liquors with [Fe] up to 57 g/L are biooxidized. • At pH 0.44 and 40 g/L of [Fe] stability of biofilm is feasible. • The decrease in biooxidation rate can be caused by salting-out effect. • FPBB is a suitable design for operating at [Fe] < 57 g/L and 2 > pH > 0.44. The utility of ferrous iron biooxidation is to regenerate Fe(III) at required rates and conditions in specific hydrometallurgical contexts, such as metal extraction from ores/concentrates and mining and electronic waste. In these applications, considerable kinetics improvements can be achieved by increasing [Fe(III)], but pH must be decreased to avoid precipitation of this oxidant. Information about continuous biooxidation operation is limited to [Fe] < 20 g/L and 2.3 > pH > 1, therefore, it is interesting to test wider ranges for these parameters. A 1L flooded packed-bed bioreactor (30 cm in height), inoculated with Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, was operated 60 days in continuous mode without interruptions at [Fe] up to 57 g/L and pH up to 0.44. Total Fe(II) conversion was achieved when operating at [Fe] = 57 g/L and pH = 1.2. The maximum biooxidation rate reached was 3.5 g/L·h for [Fe] = 40 g/L and 1 h of hydraulic retention time. Biooxidation rate decreases by 32 % when pH decreases from 1.2 to 0.44. Nevertheless, the biofilm remained stable at this low pH and steady state was achieved. When comparing the relative decreases in biooxidation rate and oxygen solubility, the drop of efficiency can be explained by aeration limitations and salting out effect. [ABSTRACT FROM AUTHOR]

Highlights • Advanced separation techniques used for recovery of iron from bauxite residue. • Coal dust, most effective reducer amongst sugar cane bagsse, spent spot lining. • Reduction roasting is not a good alternative. • Best option is Hydrocyclone & magnetic separation with 70% Fe 2 O 3 and 80% recovery. Abstract In the Bayer process, bauxite is digested with sodium hydroxide solution at high temperature and pressure producing alumina and generating the waste known as 'red mud' or 'bauxite residue' in large quantity. After the process, the residue which is alkaline in nature has pH of 10.5–13 and is disposed of in red mud ponds. It contains undigested alumina along with a substantial quantity of iron in it (about 35–55%). Keeping in view, the environmental concerns related to red mud, metal recovery remains one of the promising areas. Iron recovery from the bauxite residue would be an alternative for utilization and remediation of hazardous red mud. Using physical methods, iron-rich bauxite residue can be separated and may be utilized as low-grade iron ore. In the paper, advanced physical recovery techniques such as multistage magnetic separation, use of carbon-containing wastes as reducing agents and separation using hydro cyclone have been discussed. A comprehensive study on % recovery and iron present in the desired fraction has been examined. The processes have been discussed using flow diagrams. Comparison of chemical, particle size analysis and scanning electron microscopy of red mud samples in hydro cyclone studies have been studied. Iron content is raised to 70% Fe 2 O 3 from 52% Fe 2 O 3 in the original red mud with the recovery of about 80% by adopting hydro-cyclone and magnetic separation route and this seems to be the most appropriate one. Consequently, this article would be immensely useful in deciding the best implementable method for recovery of iron from the bauxite residue and for better waste management. [ABSTRACT FROM AUTHOR]

Highlights • Kinetics and mechanism of cerium leaching from weathered residual rare earth ore investigated. • Cerium dissolution was strongly increased by planetary ball milling of ore. • Planetary ball milling changed rate-determining process from chemical reaction to diffusion control. • Chemical reaction rate constant was higher diffusion rate constant. • Main mechanism of enhanced cerium leaching was mechanochemical reduction of tetravalent cerium. Abstract This study addressed the enhancement of cerium dissolution from weathered residual rare earth ore by mechanochemical activation by planetary ball milling. The activation mechanism was elucidated using cerium L III -edge x-ray absorption fine structure (XAFS) analysis to evaluate the effect of planetary ball milling on the crystal structure of the cerium minerals and phase composition of the ore. Leaching experiments were performed to investigate the influence of mechanochemical activation on leaching kinetics and extent of cerium dissolution. The leaching kinetics were performed using the shrinking core model in conjunction with an innovative approach based on cerium L III -edge XAFS analysis to resolve the independent leaching curves of tri- and tetravalent cerium. Planetary ball milling induced reduction of tetra- to trivalent cerium and resulted in increased cerium dissolution from weathered residual rare earth ore. Leaching results and specific surface area measurements highlighted that cerium dissolution was enhanced not only by the increase in surface area of the ore, but also by mechanochemical reaction. When the ore was grinding by planetary ball mill, the rate-determining process of leaching changed from chemical reaction to diffusion control and the leaching rate constants decreased, indicating the main mechanism of enhancement of cerium dissolution was reduction of tetravalent cerium. [ABSTRACT FROM AUTHOR]

Highlights • Reductive decomposition of waste calcium arsenate via a simple route. • Obtaining elemental arsenic of commercial value. • Simultaneously regenerating CaO containing a few impurities. • Minimization and reclamation of waste calcium arsenate are realized. Abstract Roasting waste calcium arsenate with charcoal powder was studied, serving the purpose of minimizing and/or reclaiming the waste by obtaining elemental arsenic of commercial value while regenerating recyclable CaO. Exploratory experiments were carried out to confirm the feasibility of the suggested process, in which elemental arsenic reaching the grade of 94.5% was obtained. Effects including roasting temperature, dosage of charcoal powder and roasting time were then investigated. The results showed that about 99.0% arsenic could be extracted by volatilization after the sample was roasted at 900 °C for 150 min with 14% charcoal powder, leaving the roasting residue, mainly consisting of CaO, containing arsenic as low as 0.42%. Thermodynamic calculations with respect to equilibrium compositions of the reaction system are diagramed and discussed. Attempts were made to determine and explain the mechanism by comprehensively analyzing the results of Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that As (V) in the waste calcium arsenate was reduced to As (III) before its conversion into the elementary state. [ABSTRACT FROM AUTHOR]

Highlights • Valuable metals (W, Zn, Cu) in Cabeço do Pião tailings disposal were assessed. • Multivariate Statistical Analysis proved to be a useful planning tool for tailings re-mining. • Geostatistics corroborated the results of Principal Component Analysis. Abstract The present work was developed in the scope of ERA-MIN/0007/2015 REMinE project, aiming recover of valuable metals through reprocessing of abandoned mine waste deposits. Cabeço do Pião site, the Portuguese case study in this project, is an old tailings disposal whose property was transferred from Panasqueira Mine to the Municipality of Fundão. The material deposited in the dam constitutes a risk to the environment, in particular to Zézere's river that flows close to the bottom of the tailings pile and is a relevant contributor for the supply of drinking water. The study area was sampled at two different depths according to a regular grid. About fifty samples were collected and analyzed by X-ray fluorescence. The multivariate analysis of the chemical and the particle size data, allowed to establish mineralogical associations, proving to be a useful planning tool in a future selective re-mining of the tailings pile. Information extracted from the results of the principal component analysis was corroborated by the results of the geostatistical techniques applied to the analytical data. [ABSTRACT FROM AUTHOR]

The mining industry generates large amounts of tailings every year. The most common destination for the tailings is deposition in tailings storage facilities (TSFs), which can have enormous dimensions. The management and storage of such large volumes of material pose many challenges in terms of dam stability and immobilization of hazardous contaminants that represent human-health and environmental risks, particularly for sulfide-containing materials. In addition, considerable amounts of precious and base metals can be lost in the tailings. Due to the economic value and growing industrial demand for precious and base metals, tailings may therefore be potential sources of secondary raw materials. This contribution investigates the flotation of pyrite-rich tailings, containing residual chalcopyrite, galena, and sphalerite, and high amounts of ultrafine particles. Flotation was used to recover the sulfide minerals and generate tailings with low sulfur content. The Cu-Pb-Zn-rich product could go to further treatment (e.g. (bio)hydrometallurgy) to recover the metals, while the low sulfur fraction could be used in the civil construction industry. Automated mineralogy (MLA) was used to provide quantitative mineralogical and textural data. Bench-scale experiments were performed by combining classic flotation and floc flotation (flotation of flocs of targeted minerals). Flotation of the material as received, as well as after classification into two fractions was performed. The samples as received and the coarser fraction (+37 µm) underwent classic flotation, while the finer fraction (−37 µm) was processed either by using the classic or the floc flotation approach. The flotation of the coarser particles provided higher sulfide recoveries, higher combined Cu-Pb-Zn grades in the concentrate (3.66 %), cleaner residues (1.6 % S), faster flotation rates, and reduced reagent consumption. Likewise, the results from the fine particle flotation allowed lower S content in the residues (3.4 % S) as compared to the flotation of the original material. The results of the use of floc flotation for the finer fraction show an increase in the mass pull with a slight increase in the recovery of sulfides. Overall, the development of a route to process the tailings proved to be promising and the use of a two-route approach indicates advantages as compared to a single route. [ABSTRACT FROM AUTHOR]

Block and panel caving mines are increasingly being proposed for the excavation of massive ore-bodies located at depth. The lack of selectivity associated with the mining methods results in both ore and waste being caved and transported through material handling systems to the surface for processing and waste rock disposal. Sensor-based sorting systems provide an opportunity to automate the discrimination between ore grades and rock types, providing an enhanced level of selectivity for ore control and thereby improving mine productivity. To evaluate the potential to add value to a caving operation, a sensor-based ore sorting study, incorporating bulk and particle sorting systems, was carried out for the New Afton block cave mine. Results showed that rock from the copper-gold porphyry deposit is amenable to prompt gamma neutron activation analysis, and to X-ray fluorescence sensors. A conceptual flowsheet, where both technologies are used as separate unit operations, was evaluated. Test samples of varying copper head grades allowed an ore value calculation method to be developed based on the integration of continuous bulk sorting and particle sorting. The calculation method can be applied to block models of a future cave at New Afton and used to evaluate the change in the economic footprint. It was found that the concept demonstrated an improvement in the net smelter return of excavated material. [ABSTRACT FROM AUTHOR]

The extraction of ore minerals from fine-grained flotation tailings is a commercially interesting but technologically challenging endeavor that needs to be supported by a full technical and economic feasibility study. A novel approach to such an assessment is introduced here. It is illustrated by the example of a historic tailing storage facility containing on average 0.2 wt% of Sn as cassiterite. Mineral processing test work identified flotation as a suitable technology route to recover this cassiterite. The viability of flotation was attributed to three material parameters, namely grade, liberation and particle size of cassiterite. These parameters were quantified for a set of ten exploration drill cores by chemical assay and mineral liberation analysis. For each of the three relevant parameters a suitable weighting function was defined that was applied to the entire data set. The data was then geo-referenced and combined to construct a 3D model illustrating a depreciated grade, i.e., the amount of cassiterite-bound tin that can realistically be recovered from the tailings. Results of the case study illustrate the importance of combining chemical grade data with quantitative mineralogical and microfabric information in any effort to objectively assess the residual value contained in industrial tailings or any other residue considered for re-processing. [ABSTRACT FROM AUTHOR]

Prediction of the geoenvironmental characteristics of mine waste materials typically relies on the static and kinetic testing of individual waste units. In reality, waste rock piles are heterogeneous landforms containing potentially acid forming (PAF) units juxtaposed with non-acid forming (NAF) units. Despite this, predictive geoenvironmental test work programs rarely characterise blends of waste materials. Through undertaking laboratory-based blended static testing and mineralogical assessments, a first insight into the leachate chemistry of a waste landform can be ascertained. This was tested using three waste units (Type A – alkaline, B – neutral and D – PAF; n = 31) obtained from the Savage River mine, Western Tasmania. Seven daughter blend types (1–7; n = 42) were prepared using different ratios of the individual waste types, and characterised by acid base accounting and mineralogical techniques. Blend types were NAF when a maximum of 20% of Type D was used, with daughter blend 4 (90% Type A + 10% Type D) the most inert when screened against ANZECC (2000) aquatic protection trigger values. This study demonstrates that through first-pass static blended testing, opportunities exist to improve waste-rock handling practices and design NAF waste piles once field trials, involving a range of particle sizes, have been conducted. [ABSTRACT FROM AUTHOR]

The environmental legacies of metal mining are often dominated by large waste facilities, which can be sources of acid and metalliferous drainage, resulting in both local pollution and irreversible loss of some of the soluble minerals. Whether a material is treated as waste or ore depends on a wide variety of factors and circumstances. Three critical aspects – time, the extractive strategy and the economic context - are discussed in this paper. The authors argue that the fine line between waste and ore requires a mine waste management (MWM) hierarchy that properly considers waste as a potential future resource. This hierarchy exhibits four main levels: reduce, reprocess & stockpile, downcycle and dispose, which are illustrated by a review of both academic research and public data on industrial practices. The authors conclude that to generate the most successful outcomes the hierarchy must operate across all levels and is a core component of an overall mine sustainability framework. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) is often treated using active lime treatment, which generates a significant amount of sludge that contains mainly metal hydroxide precipitates, calcium sulfate, and unreacted lime. Previous work showed that sludge may have interesting geotechnical and geochemical properties to be used, in combination with a silty soil, as a part of covers (oxygen barriers) to prevent AMD generation from waste rock and tailings impoundments. The reuse of sludge can reduce the volume of natural soil required for site reclamation. Mixtures of sludge and a natural silty soil were tested in the laboratory (for over 500 days) and in field experiments (4 years) as an oxygen barrier cover placed over acid-generating tailings and waste rock. Data from the testwork include monitoring of leachate geochemical parameters (e.g. pH, conductivity, metal and sulfate content) and hydrogeological parameters (water content, suction, effluent flowrate). Results indicate that soil-sludge mixture is an efficient oxygen barrier. [ABSTRACT FROM AUTHOR]

Process water from mineral processing plants may contain a significant amount of dissolved metal ions, which may be recycled as process water, or discharged into the environment as effluent. If they are discharged into the environment they may cause significant problems for the local flora and fauna. One method of removing metal ions from aqueous systems, which has generated considerable interest over recent years, is the emulsion liquid membrane (ELM) technique, which incorporates solvent extraction and stripping. This work details the use of design of experiments applied to an ELM process for removing copper ions from a dilute aqueous solution. Initially, a fractional factorial design was used to screen out the most important factors; this was followed by a central composite design to obtain optimal operating conditions. The extraction percentage of copper was obtained as more than 99% under these conditions. [ABSTRACT FROM AUTHOR]

Resource efficiency is both, a scientific concept in sustainability assessment and a policy concept that aims to achieve maximum extraction of resource materials from a mineral deposit at minimum waste production. Presently, established proxies for resource efficiency use weight-based measures of a system’s materials consumption However, such proxies are not directly applicable to mining operations. This study introduces a new method and associated techniques for the evaluation and quantification of resource efficiency in mining operations. This approach considers intensities in land, water, energy and mineral deposit consumption (i.e. specific resource consumption to produce one unit of output). Applying this new methodology, resource intensities have been assessed and quantified for 22 major copper mines. Results have allowed relative ranking of these mines in terms of resource efficiency. This work also demonstrates that deposit properties and its geographic location impact on resource efficiency. Consequently, political measures, needed to promote resource efficiency in mining, should focus on region-specific aspects and the properties of the mined ore deposit. [ABSTRACT FROM AUTHOR]

The oil sands industry generates large quantities of mineral waste, such as fluid fine tailings (FFT), whose disposal is often challenging. The use of planar electrokinetic geocomposites (eGCPs) in FFT disposal areas could improve in-situ dewatering by allowing water to drain after it is expulsed during consolidation and by permitting the use of electro-osmosis (EO) to displace a significant portion of the remaining water. Four dewatering experiments involving mature fine tailings (MFT) are presented here: in three of them increasing normal stresses are applied on the MFT followed by EO; in the fourth test, EO is applied before the normal stress is increased. The results show that eGCPs adequately filter MFT; the particles did not clog or blind the filter. MFT were significantly dewatered under an applied normal stress followed by EO. EO was very efficient at extracting the more tightly bound water that remained after mechanical dewatering. In one configuration, a significant improvement of the shear strength from nearly 0 kPa to a mean value of 25 kPa was obtained, which is significantly higher than the 10 kPa required by Alberta regulations. The final solids content in that case was about 70%, starting from an initial solids content of 45%. The energy required for that test was 10.6 kW h per dry tonne. [ABSTRACT FROM AUTHOR]

This study examines mechanical activation as the pre-treatment method for ultramafic mine waste containing olivine and serpentine. Specific surface area, microstructure and carbonation conversion in a direct aqueous carbonation process were measured to test the effects of mechanical activation. It was found that, as a result of the grinding energy input on materials, surface area was increased, crystallite size was reduced and microstrain was accumulated, carbonation conversion was enhanced. With the presence of serpentine content, the formation of new surface area was promoted and the disordering of forsterite structure was prevented. Forsterite makes up the majority of the content and contributes to CO 2 sequestration under selected carbonation conditions. For the purposes of mineral carbonation, the mechanical activation of mine waste is preferable to simply grinding pure olivine. [ABSTRACT FROM AUTHOR]

• Bioleaching is an important technique for the reprocessing of sulfidic mine wastes. • Acidophilic microbial consortium can simultaneously recover both valuable and hazardous elements from pyrite-rich waste rock and tailings. • XRD and SEM/MLA reveal mineralogical transformations after microbial-leaching. • Jarosite was the main secondary mineral formed after bioleaching. • Potential for revenue generation and environmental risk reduction at the Neves Corvo mine, Portugal. Sulfidic mine waste usually contains elevated amounts of valuable and hazardous metal(loid)s, which may pose environmental risks but can also provide opportunities for resource recovery. Reprocessing of mine waste can offer both economic and environmental benefits by supplying some of the ever-growing global demand for valuable metals, as well as reducing environmental risks. The present study aimed to simultaneously recover both valuable and hazardous metal(loid)s from two sulfidic mine waste samples (waste rock (NC_01) and tailings (NC_02)) from the Neves Corvo mine, Portugal, using a novel acidophilic consortium dominated by iron-oxidizing Leptospirillum genus and Acidiphilium sp. Bioleaching results showed that over 70% of the total Zn, Co, In, As, and Cd contents of NC_01 and NC_02 were leached within 21 days, while 55%–62% Mn was leached. Copper behaved in a refractory manner, as only 33% and 21% Cu were leached from NC_01 and NC_02, respectively. X-ray diffraction (XRD) and Scanning electron microscope-based automated image analyses (SEM/MLA-GXMAP) of the bioleached residues revealed an almost complete absence of residual pyrite in NC_01 and a reduction of pyrite in NC-02, as well as the formation of secondary minerals, especially jarosite. In most cases, the biogenic jarosite co-precipitated some of the leached elements again, e.g., Cu and Pb. In conclusion, a synchronized method for bioleaching valuable and hazardous metal(loid)s was developed using a novel acidophilic consortium, thereby demonstrating the potential for the generation of economic value and environmental risk reduction for sulfidic mine waste samples. [ABSTRACT FROM AUTHOR]

The consequence of a strong economic growth in emerging countries combined with the rise of the world population is an increase in the demand for raw materials, leading to growing concern regarding their availability and the global efficiency of the supply chain. These tensions reinforce the need to associate the development of the recycling industry to the identification of new resources which could be used for the recovery of valuable materials. The purpose of this study is to develop a novel biological co-processing approach for the recovery of strategic metals in both sulfidic mining wastes and post-consumer wastes (WEEE). The principle of this treatment is based on two steps: mine wastes are biologically oxidized, resulting in the production of a ferric iron-sulfuric acid lixiviant solution which is used to leach base and other soluble metals contained in e-scraps. Batch tests were carried out using flotation tailings wastes containing 60% of pyrite and grinded Printed Circuit Boards (PCB < 750 μm) with a solid load of 2.5%. Two series of tests were conducted in order to study the influence of the ferric iron concentration and of the bacterial activity on metals dissolution. Results showed that a higher ferric iron concentration led to an increase in the dissolution rate of copper which is the main metal contained in the PCBs. Moreover, a dissolution yield of 98.3% was reached for copper after 2 days when bacterial activity was observed, corresponding to an increase of about 20% compared to the tests without bacterial activity. Finally, this study highlights the importance of the availability of ferric iron and of the bacterial oxidation of ferrous iron for the feasibility of this bioleaching process dealing with the recycling of PCBs. [ABSTRACT FROM AUTHOR]

• Feasibility of environmental desulfurization and cemented paste backfill. • Leaching behavior of cemented paste backfill. • Environmental benefits of cemented paste backfill. • Environmental and economical benefits of integrated management strategy of mine tailings. The oxidation of sulfide minerals releases acidic leachate enriched in sulfate, iron, and toxic metals and metalloids (e.g., As, Sb, Cu, Pb, Cd, Zn, Hg, etc.) known as acid mine drainage (AMD). This eco-hydrological hazard is imminent when mineralogical and geochemical analysis indicates that acid-generating (sulfides) overcome the acid-neutralizing (carbonate) minerals in the ore and mining waste. AMD represents a multifaceted problem faced by the mining industry. The most widespread management technique is to store the tailings into engineered impoundments and actively neutralize the acidity produced by the oxidation of the sulfide minerals by adding alkaline chemical agents. However, this method involves a constant and long-term commitment, elevated operational costs, and several geotechnical and environmental drawbacks. In a pre-mining stage, geological, geochemical, mineralogical, and textural characterization of the mine waste could guide proper and site-specific mining waste management. In this paper, we present an integrated strategy to reduce the acid mine drainage (AMD) potential of the Dundee Precious Metals Chelopech (DPM-Ch) tailings through a combination of environmental desulfurization and cemented paste backfill (CPB) – the latter one being already practiced on-site. In the proposed scenario, a desulfurization plant would be installed downstream to re-float the non-valuable reactive pyrite. The reactive pyrite concentrate would be combined with the CPB material, whereas the remaining tailings would be discharged at the tailings management facility (TMF). The lack of neutralizing gangue (NP of untreated tailings < 8 kg CaCO 3 /t) precludes converting the tailings into non-acid generating. However, reducing nearly six times the amount of lime required to neutralize the acidity produced by pyrite oxidation was feasible without substantially increasing operational costs. Supporting the environmental benefits of combining desulfurization and backfill, an X-ray mapping of the CPB material revealed that this approach effectively encapsulates the reactive gangue, ultimately avoiding pyrite oxidation and leaching of heavy metals. [ABSTRACT FROM AUTHOR]

• In-depth characterisation of different mine waste materials from the same tailing pond. • Sources of metals of interest (Pb and Zn) are different mineral and slag phases. • Low abundance of Pb/Zn phases causes a nugget effect. • The chemical heterogeneity of slags exacerbates the nugget effect. • The approach is applicable to different mine waste deposits around the globe. The exploitation of mine waste materials as secondary resources requires in-depth mineralogical analyses, with metal deportment being of particular relevance for metal recovery. Using a combination of the Scanning Electron Microscope (SEM)-based Mineral Liberation Analyser (MLA) and Electron Probe Micro-Analyser (EPMA) methods, the deportment of lead and zinc in the historic Plombières mine site (East Belgium) was investigated. The mine site comprises four different materials: soil, metallurgical waste, brown and yellow tailings. The integration of the MLA and EPMA data allowed the identification and quantification of Pb- and Zn-bearing phases, including minerals present in low abundances as well as slag phases. Different slag types and Pb oxides phases are the main sources of lead in Plombières mine waste samples. These phases host 65 to 99 % of the Pb, the rest is distributed between cerussite (0 to 37 %), and/or anglesite (0 to 17 %). Approximately 95 % of Zn is hosted by different types of slags or by fraipontite, with minor amounts contributed by sphalerite (0.1 to 3 %), gahnite (1.0 to 2.4 %), willemite (0.1 to 2.9 %), and bannisterite (0 to 3 %). The MLA/EPMA measurements were validated by comparing calculated Pb and Zn grades with bulk grades measured by X-ray fluorescence spectroscopy. The coefficients of correlation between the measured and calculated values were found to be 0.89 for lead and 0.80 for zinc. Uncertainties on the metal deportments were estimated by bootstrap resampling and are typically low. The highest uncertainties are observed when the metal-bearing phases are present in low abundances, which is particularly noticeable in the yellow tailings. Considering the promising results, the integrated approach applied in this study should be applicable to other metals and waste deposits across the globe. [ABSTRACT FROM AUTHOR]

Highlights: [•] Worldwide availability of mining wastes for ex situ mineral carbonation. [•] Direct aqueous mineral carbonation with mechanical exfoliation. [•] High carbonation yield for serpentinised materials without heat activation. [•] Life cycle analysis for comparison of aqueous mineral carbonation processing routes. [ABSTRACT FROM AUTHOR]

[Display omitted] • This review focuses on the extractive metallurgy of mining and processing wastes. • The extractive metallurgy of mining wastes largely relies on established methods. • Seven processes for critical metal extraction from mining wastes are explored. • Bioleaching shows great potential for critical metal extraction from mining waste. The transition to low-carbon economies, advancements in high-tech and rapid uptake of electronic equipment will see increased demand over the coming decades for so-called "critical" metals: metals considered important to society and that are vulnerable to supply disruption. Consequently, there is now a global drive to find and develop critical metal resources. Significant concentrations of critical metals have reported to mining and processing wastes over time due to a range of factors, including unfavourable economics and unsuitable processing infrastructure. With expanding scope and scale of markets, mining and processing wastes now represent a largely un-tapped resource of critical metals. The reclamation of critical metals from solid mining and processing wastes involves mineral processing, metal extraction, and metal recovery. Metal extraction involves the separation of metals from a metal-bearing material using chemical reactions. Metal extraction from solid mining and processing wastes largely relies on established processing techniques. However, the overall process configuration can differ greatly from conventional primary production methods, and there is often an opportunity to streamline the reprocessing of wastes where the original production process has already done some of the required physical or chemical work. This review provides an overview of seven technologies: atmospheric leaching, pressure leaching, bioleaching, resin-in-pulp, pyrometallurgy, phytomining and solvometallurgy, that are suitable for extracting specific critical metals from solid mining and processing wastes. Eleven critical metals are considered in this review: cobalt, gallium, germanium, indium, lithium, nickel, rhenium, tellurium, tin, tungsten, and vanadium. The approaches discussed are important for the extraction of critical metals from mining and processing wastes now and into the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mine tailings samples from Chile were bioleached in stirred tank reactors with 2 L and 20 L volume. • Moderate thermophiles showed a higher bioleaching performance than mesophiles. • Up to 74% of Co and almost 100 % Cu were extracted. • Cu was mainly acid leached and Co bioleached. • Low Fe dissolution (<14%) favors the downstream processing for Cu and Co recovery. Metals from low-grade sulfide ores, electronic waste and mine tailings can be recovered using biohydrometallurgy. In this study, acidophilic microbial consortia of mesophiles and moderate thermophiles were applied in shake flasks as well as in stirred tank reactors (STR) to bioleach cobalt and copper from mine tailings in Chile. The mine tailings near Taltal contained considerable amounts of copper (∼5000 ppm) and cobalt (∼115 ppm). After adaptation of the mesophilic consortium, 38% of Co and 86% of Cu were recovered in 2-L STR at 10% solid load after 12 days bioleaching at 30 °C. In a mini-pilot test in 20-L STR at 15% solid load, Co and Cu extraction reached 49% and 83%, respectively. Improved metal recovery was obtained by using a moderate thermophilic microbial consortium at 42 °C, reaching 74% of Co and almost 100 % Cu in 2-L STR at 10% solid load. Low Fe dissolution below 14% for all tests was observed which may favor the downstream processing of Cu and Co. Together with the results from chemical leaching, the data indicated that Cu was mainly leached by sulfuric acid (acid leaching) while a high Co extraction required Fe(II)-oxidizing microbial activity (bioleaching). [ABSTRACT FROM AUTHOR]

• Impacts associated with tailings releases are poorly quantified in LCA. • Comparison of different approaches to account for releases from tailings. • Generic inventory datasets may overestimate tailings releases to environment. • Interdisciplinarity is key to develop more complete models to be applied in LCA. Extracting mineral ores to produce mineral concentrates and finally metals that enter the value chains of different sectors is a waste intensive activity. In particular, mineral processing activities generate yearly and globally several billion tons of wastes called tailings. Tailings storage is associated with significant environmental risks due to different sources such as releases to groundwater. Yet, these environmental impacts are poorly taken into account in the environmental life cycle assessment of a concentrate or metal production, in particular due to a lack of representative data in the inventory. This paper aims at coupling geochemical modelling geochemical modelling with life cycle assessment to quantify releases from tailings and the associated environmental impacts. In the present work, reactive transport modelling was implemented to quantify more accurately short-term (100-year timeframe) and long-term (10,000 year-timeframe) tailings releases. Reactive transport modelling allows modelling and estimating the distributions in space and in time of chemical reactions occurring in a specific environment. The resulting tailings releases are compared with those calculated through the approach, based on a first order law of kinetics, used in the ecoinvent database. The results from the ecoinvent approach are calculated both with generic and site-specific parameters. These different approaches are applied on the case-study of a polymetallic sulphidic ore from a mine in Northern Europe. The tailings releases obtained through the different approaches differ. Overall, the reactive transport model leads to quantities released at both short-term and long-term timeframes being smaller than those calculated with the ecoinvent approach. As a result, the impacts on ecotoxicological and toxicological categories show differences between two to eight orders of magnitude. Each approach used to model the tailings releases differ in the nature and amount of data needed as well as in the sophistication of the model used. While the approach based on reactive transport modelling is exhaustive and presumably provides a more accurate prediction for the releases from tailings, it also requires massive computational resources and much larger volumes of data, some of which being difficult to obtain on-site. Consequently, a consensus has to be found between the complexity of the model used, the data availability and the expected reliability of the results. [ABSTRACT FROM AUTHOR]

• Potential for copper slag waste as global resource for circular economy is examined. • Comprehensive review given of amount generated in the last 20 years worldwide. • Assessed is the global demand and supply risks for copper and cobalt. • Estimated are production rate and remaining reserves and benefits of reprocessing. The mining industry faces a number of challenges that include rapid depletion of high-grade deposits, high energy cost for metal production, and growing environmental concerns associated with mining waste disposal. Copper slag is one of the mining wastes that is raising growing concern due to the huge volumes being produced and dumped annually worldwide. These huge quantities of slag not only cause environmental pollution and space problems for disposal, but they also waste valuable copper and cobalt. This is increasingly important due to the growing demand for these metals in emerging technologies, potentially resulting in a supply deficit from conventional mining production. To address these challenges, recycling and repurposing of copper slag waste using innovative technologies should be considered, creating a resource for a circular economy. This paper presents a review of copper slag production and its potential as a world resource for cobalt and copper metals. An overview of copper and cobalt production from ore reserves, and of global demand and supply risks for these metals is presented. The potential benefits of reprocessing copper slag waste using the circular economy model are discussed. This paper demonstrates that applying the circular economy principles to the copper slag waste has the potential to create additional economic value, improve the energy efficiency of the metal production, increase the supply of critical metals, and reduce the impacts of metal production on the environment. [ABSTRACT FROM AUTHOR]

Highlights: [•] We propose improvements to mine waste assessment. [•] We advocate use of a flowsheet analogous to the process mineralogy of ore. [•] Integration of mineralogy techniques with kinetic testwork requires further work. [•] We present three case studies of the use of mineralogy within mine waste assessment. [ABSTRACT FROM AUTHOR]

The world is entering a new era of exploring and exploiting outer space. The revolution in small, low-cost satellites, the recent initiatives from some countries to establish a legal framework, the increasing demand for technology metals and advances in space additive manufacturing have renewed the interest in space mining. Biomining, the use of microorganisms to extract and recover valuable metals from minerals and wastes, could be used as alternative ISRU technology for harnessing space resources. This paper reviews in situ resources available on the Moon, Mars, and Near-Earth Asteroids (NEAs) for implementing biomining processes in space, the effects of the space environment on biomining microbes, and space-based bioreactor designs that will enable leaching of metals from regoliths. A comparison between terrestrial and space biomining will also be presented, focusing on the differences in the composition of minerals on Earth and space, the types of microorganisms used for leaching, and the parameters that need to be optimised in the space biomining processes. Next steps to mature biomining approaches by combining knowledge from synthetic biology, systems biology, geomicrobiology and process engineering for space applications will also be explored. Through an integrative effort of these fields, biomining processes commonly employed on Earth can be harnessed for sustainable space exploration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Physical separation techniques could be used to desulfurize mine wastes. • Physical separation techniques can achieve the same performance as flotation. • Physical separation techniques are efficient, less expensive, and ecofriendly. • Suitable technique depends on mineralogy, texture and particle size of waste. • Combinations of techniques including flotation improve desulfurization efficiency. Management of mine wastes (e.g., waste rock and tailings) is becoming an increasing global environmental concern for mining industries around the world. With environmental regulations becoming more restrictive, there is a continuously growing need to develop efficient and clean integrated techniques to sustainably manage mine wastes. Mines wastes often contain acid-forming minerals, such as sulfides and sulfosalts that are responsible for generating contamination. Environmental desulfurization using non-selective flotation has recently been implemented as an integrated management approach for mine tailings. Furthermore, physical separation techniques, commonly used in mineral processing and offering a remarkable potential for sulfur and valuable minerals enrichment, are rarely used to manage mine wastes. The separation methods for sulfides and sulfosalts, which are based on the physical properties of the minerals, can achieve the same performance as flotation. These physical properties are mainly related to: i) the particle size distribution, ii) the difference in density between the targeted minerals (i.e., sulfides and sulfosalts) and those of the gangue minerals, iii) the magnetic properties, iv) the electrical attributes, and v) the response to specific sensing. Based on the discrepancy between mineral properties, various methods are proposed, including sieving/screening, hydrodynamic classification, gravity concentration, dense medium separation, magnetic and electrical separation, and sensor-based sorting. These techniques could be considered to be more efficient, less expensive, and more respectful of the environment than flotation. This critical review aims to evaluate the suitability of these physical separation techniques, other than the widely used flotation, to mine waste environmental desulfurization. The paper includes a brief description of these techniques, a discussion of their advantages, and their limitations for the removal of the most common sulfides and sulfosalts (mainly responsible for contaminated mine drainage). Indeed, the application of one or more of these mineral processing techniques requires specific conditions, which depend on the size-by-size mineralogical characterization of each mine waste. The specific requirements for the application of each technique are explored. [ABSTRACT FROM AUTHOR]

• Thermodynamic basis for NaOH-facilitated acid leaching was demonstrated. • Neodymium was thermodynamically most favorable for the extraction process. • Theoretically, crystallinity of LREE phosphates could impact the conversions from phosphates to hydroxides. • Organic acids performed as well as inorganic acids. Caustic soda (NaOH) treatment has enhanced rare earth element (REE) extraction from monazite. This study examined the effectiveness of caustic soda for RE-phosphates with lower concentrations for extraction from coal overburden, an alternative feedstock derived from mining waste. Pourbaix (Eh-pH) diagrams were constructed for La, Ce, Nd, Eu, and Y-PO 4 -H 2 O systems to understand the thermodynamics of NaOH-facilitated acid leaching for low-concentration RE-phosphates and oxides and to elucidate the difference in recoveries among individual REEs. The Eh-pH diagrams indicated that low crystallinity is beneficial for extraction. Nd was thermodynamically most favorable for the extraction process among the five elements examined, and Y was the least promising. Experiments were conducted using three Pennsylvania coal overburden samples to validate the effect of caustic soda on rare earth leaching. The experimental results showed that for NaOH (6 M), a leaching time of 2 h at 125 °C was sufficient to obtain twice the recovery values compared to those without the NaOH treatment. After implementing the caustic soda treatment, a high total REE recovery (>60%), especially for Nd and Pr, could be achieved with diluted HCl and more environmentally friendlier citric acid. The results were similar for both coarse and fine particles. This novel approach is likely to improve the feasibility of REE extraction from coal-associated feedstock in a more environmentally benign manner. [ABSTRACT FROM AUTHOR]

[Display omitted] • Six ion exchange resins were screened for selective recovery of Sc from coal fly ash. • VP OC 1026 and TP 272 showed high capacity and selectivity for Sc at low pH. • TP 272 adsorbs only Sc and no REES from coal fly ash PLS. • <1% of coal fly ash's Fe and Al content were eluted with Sc. • Elution with 2 M NH 4 F resulted in high Sc recovery (91%) from VP OC 1026. • High elution (85%) of Sc was achieved with 6 M HNO 3 from TP 272. Global demand for rare earth elements (REEs) has been on the rise due to recent rapid technological advancements. Even though most REEs are mainly recovered from rich ores and mineral deposits, recovery of REEs from secondary sources has attracted attention. However, low metal concentration, complex matrices and high levels of other impurities in mine wastes and tailings have remained the toughest challenges to overcome. The presence of low amount of valuable metals such as Sc requires utilization of very selective separation techniques such as ion exchange. A series of ion exchange resins (chelating, solvent impregnated and strongly acidic) were studied in the recovery of Sc from synthetic and actual pregnant leach solutions obtained from acid-leaching of coal fly ash. To the best of our knowledge, this paper exhibits the first attempt in selective recovery (from other REEs as well as major Fe and Al contaminations) of Sc in coal fly ash using ion exchange separation technique. With maximum capacity of ∼24 mg Sc/g resin, Sc was adsorbed quickly on phosphorus containing Lewatit® VP OC 1026 and TP 272 resins even in the presence of high levels of potentially interfering Fe3+ and Al3+ ions. Full elution of the adsorbed REEs from VP OC 1026 was achieved with 5 M H 2 SO 4 , with only minor Sc removal. While elution of Sc from these chelating resins has been reported to be challenging, Sc could be eluted almost completely with 2 M NH 4 F. Recovery of REEs with 5 M H 2 SO 4 from TP 272 resulted in co-elution of only 7% of the adsorbed Sc while the rest could be eluted efficiently with 6 M HNO 3. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bioreactor was operated for 172 days with different metal loads. • Addition of tailings leachate increased the bioreactor efficiency up to ~ 85% • Metal removal reached values close to 100%, except for Mn, Ca and Mg. • The inoculum shifted to a functional SRB community dominated by Desulfovibrionaceae. • The addition of metals enhanced the activity of the methanogens in the bioreactor. This study demonstrated the adaption of a sulfidic microbial community to mixed metal mine wastes, i.e., tailings leachate solutions, while maintaining bioreactor performance. This overall process occurred using a sulfate reducing bioreactor operated in continuous mode for 172 days with ethanol as electron donor and, at first, a synthetic mine solution and then, tailings leachate solutions. Remarkably, the addition of a succession of leachates increased the sulfate removal efficiency, which reached values around 84.7 ± 6.9% after the sulfate adaptation period. This increase was also in line with an increase in the soluble chemical oxygen demand removal efficiency and with a slight increase in the pH of the reactor. This high activity supported metal removal efficiencies close to 100% for most metals, except Mn, Ca and Mg whose precipitation was lower (80, 50 and 38%, respectively). The bacterial community in the bioreactor was initially diverse but evolved to be dominated by SRB, in particular Desulfovibrionaceae. Interestingly, the addition of the tailings leachates enriched for the presence of methanogens in the bioreactor, consistent with the consumption of the accumulated acetate. [ABSTRACT FROM AUTHOR]

• Arsenic and sulfur release from orpiment were lower than from amorphous As 2 S 3. • Arsenic release from crystalline orpiment was a mixed-controlled reaction. • Arsenic was first released as arsenite and subsequently oxidized to arsenate. • Sulfur was first released as thiosulfate and converted to sulfate via two pathways. • Sulfur-enriched product layer was partially responsible for reduced leaching rate. Arsenic trisulfide (As 2 S 3), in both amorphous and crystalline form, is a significant arsenic-containing compound naturally occurring in mine waste rock or generated as metallurgical waste. It is typically unstable in the enviroment, especially under alkaline and oxidizing conditions, which is a significant barrier to fixation of arsenic present in metallurgical waste streams in the form of arsenic trisulfide. Our previous study has shown the effect of different factors on the kinetics and mechanisms of arsenic and sulfur release from amorphous As 2 S 3. To assess the effect of crystallinity on the stability of arsenic trisulfide, a series of laboratory leaching tests were performed with crystalline orpiment under fully controlled conditions. The experimental results showed that the release of arsenic and sulfur increased with pH, dissolved oxygen concentration, and temperature, but the release rates were much slower than those of amorphous arsenic trisulfude. The speciation analyses indicated that arsenic was present in the leachates as arsenite, which was subsequently oxidized to arsenate to different extents; thiosulfate was the main soluble sulfur species, which was converted to sulfate via oxidation and disproportionation pathways. The kinetic modeling suggested that the arsenic release process is a mixed-control reaction, in which the surface chemical reaction and the diffusion of dissolved oxygen through a product layer control the arsenic release rate. The solid surface characterization supported the presence of an arsenic-deficient phase enriched in elemental sulfur on the solid surfaces. The product layer acted as a barrier to the diffusion of reagents, as evidenced by the leaching being sensitive to the removal of elemental sulfur. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfide-based tailings from mineral processing were tested as sorbents, searching for reutilization schemes. • The tailings tested are able to remove copper and dichromate from synthetic solutions, but they may simultaneously release other metals such as zinc and lead. • With respect to the sample before mineral processing, tailings have a greater surface area and a higher alkalinity, which promotes the removal of metals from water. • This study concludes that the sorption ability of tailings needs to be contrasted with their capacity for releasing metals. Sustainable schemes favor the reutilization of waste over direct disposal. In the case of mine waste from mineral processing (tailings), the reutilization of such waste as sorbents of contaminants in water can be advantageous, considering that tailings have already a plan for disposal. In this article, a methodology to evaluate the convenience of using residual minerals as sorbents is presented. The sorption ability of pyrite-based tailings using synthetic solutions containing copper ions (Cu+2) is followed and contrasted to the sorption ability of minerals before processing (feed). In the case of as-received samples, tailings show a higher capacity for copper removal in batch tests (1.3 vs. 0.4 mg Cu/g for tailings and feed, respectively). This large difference is associated with (a) the smaller particle size distribution for tailings, and (b) the ability of tailings to increase the pH and favor precipitation of metals. Interestingly, tailings were found also to release smaller amounts of undesired elements such as arsenic and cadmium. Tests using defined particle sizes for feed and tailings demonstrate that copper removal was around 0.45 mg Cu/g in batch experiments and 0.68 mg Cu/g in recirculation experiments. In all cases, copper sorption follows pseudo-second-order kinetics, suggesting a mechanism where copper is chemisorbed, forming copper sulfides according to X-ray photoelectron spectroscopy (XPS) measurements. More importantly, sorption experiments were complemented with simultaneous measurements of metal ion release from the minerals into solution. The metals released during batch sorption are mainly Pb and Zn, in the respective amounts of 0.79 and 0.32 mg/g (feed) and 0.75 and 2.19 mg/g (tailing). Thus, even though the use of mineral residues as sorbents is possible, the metal release should be considered to determine the overall convenience of the process. [ABSTRACT FROM AUTHOR]

• Flotation of sphalerite tailings allows obtaining a Zn commercial concentrate. • pH and reagents as those used for low-grade primary sulphides. • Repeated cleaning or scavenging compensate for the low starting grades. • Re-circulations and multi-stage cleaning allow achieving high flotation efficiencies. • Retreatment by flotation allows downgrading environmental risk of sphalerite tailings. Sphalerite tailings are the most important type of waste in the mining district of Sardinia. This situation justifies the interest in the applicability of flotation as a remediation technique by which declassify the tailings (reducing the concentration of heavy metals). The flotation of mine tailings represents a novelty if aimed at environmental remediation. Instead, it is a widespread industrial practice for recovering secondary raw materials. In this case, the scientific aspects are rarely explored: this situation explains the limited number of cases examined, the review of which, however, represents a necessary premise for the research undertaken. Furthermore, the availability of industrial case demonstrates reprocessing is not only a technically possible process but also of economic interest. After an overview of the environmental problem in abandoned mining areas, the paper recalls the fundamental elements useful for developing a comparison between the main operating methods adopted in the flotation of Pb and Zn sulphides, both as primary ores (high and low Zn content) and as tailings. The case history also includes the treatment of Zn oxidized compounds. The comparison demonstrates that the treatment of sphalerite tailings can follow the same approach as that of low-grade primary ores, but with evident economic advantages, and allows achieving those, far greater, of the multiple environmental effects. [ABSTRACT FROM AUTHOR]

• Sustainable tailings management strategies are needed to address mining waste. • Secondary mining of tailings for industrial materials is a viable remediation option. • DES is a powerful tool to assess and mitigate operational risk in mining systems. • Alternate modes of operation are critical to developing effective DES frameworks. • Geostatistical heterogeneity can be suitably integrated into geometallurgy via DES. Discrete event simulation (DES) is a computational tool capable of simulating the interplay of important variables and processes within complex mining systems that are subject to geological uncertainty. Alternate modes of operation are fundamental to the development of effective DES frameworks to model and monitor system performance in response to unexpected changes (e.g. ore feed attributes). The decision to switch between modes is governed by operational policy and is triggered as critical thresholds are crossed. Hundreds of operating days can be simulated to identify potential deficiencies, bottlenecks, or other operational risks. DES is thus useful to support strategic decision-making in the design, development and sustained operation of any mining system. Based on current mining trends, tailings storage facilities are growing in both size and number, resulting in alarming tailings accumulations worldwide. Coupled with a large number of abandoned legacy mines and artisanal mining operations, tailings and other waste materials pose a significant threat to human health and safety, as well as the environment. Cost-effective tailings management strategies to mitigate these risks through site remediation are required. Research on potential uses for discarded tailings is divided between secondary metallurgical processing for extractive purposes, and incorporation into industrial materials. The current framework has been adapted to integrate geostatistical variability into DES in order to assess the potential operational risks related to secondary mining of tailings for a conceptual cement production operation. A case study loosely based on data from a tailings dam in Taltal, northern Chile, is presented. Sample calculations are provided that demonstrate the framework as a valuable tool to evaluate and mitigate potential risk factors in the development of tailings retreatment applications. [ABSTRACT FROM AUTHOR]

• The LIBs market is forecasted to reach at least US$221 B by 2024 using 20–25% CAGR. • Li production growth within the next five years will lag that of demand. • Major Li resources are found in Argentina, Australia, USA, Chile, Bolivia & China. • Current technologies for end-of-life LIBs recycling remain inefficient. • Waste streams, clays and geothermal brines are promising future Li resources. The demand for lithium has skyrocketed in recent years primarily due to three international treaties—Kyoto Protocol, Paris Agreement and UN Sustainable Development Goals—all of which are pushing for the integration of more renewable energy and clean storage technologies in the transportation and electric power sectors to curb CO 2 emissions and limit the adverse effects of CO 2 -promoted climate change. Over 60% of lithium produced in 2019 were utilised for the manufacture of lithium-ion batteries (LIBs), the compact and high-density energy storage devices crucial for low-carbon emission electric-based vehicles (EVs) and secondary storage media for renewable energy sources like solar and wind. In 2019, the global market value of lithium reached around US$213 B and is forecasted to grow by around 20–25% until 2025. In this review, the current state of global lithium resources, global lithium material flow, and forecasts of future lithium supply–demand dynamics are discussed. Persistent challenges in mining, processing and industrial-scale recycling operations are also examined and recent innovations to address these issues are introduced. Finally, unconventional lithium sources like submarine/deep-sea ferromanganese (Fe-Mn) nodules and crusts, industrial wastes (e.g., desalination brines, geothermal brines and coal fly ashes), mining wastes and effluents, and extra-terrestrial materials are explored. [ABSTRACT FROM AUTHOR]

• Fe in oxidized tailings was transformed to magnetite through low-T magnetization. • Cu and Ni contaminants accumulate in the magnetic fraction. • Ni behaves as structurally incorporated into magnetite, while Cu is loosely bound. • The final waste volume is reduced and has lower potential for metals leaching. Low-temperature magnetization using reducing gas derived from biomass pyrolysis is being explored as an option to recover Fe from oxidized waste generated during Ni extraction from bio-leaching of pyrrhotite-rich tailings. The study investigates the potential sequestration of the main transition metal contaminants - Cu and Ni - into the magnetic phases. In the original oxidized pyrrhotite tailings, Ni and Cu were associated with goethite. Magnetization at 460 °C led to full conversion of goethite and jarosite into magnetite through solid-state transformation. 93% of the magnetite was recovered in the magnetic fraction by magnetic separation. Nickel and Cu accumulation was respectively 4 times and 2 times greater in the magnetic than nonmagnetic fraction, indicating that the magnetic fraction acted as a sink for these transition metals. Metal fractionation of the magnetic fraction showed that a greater proportion of total Ni resided with the crystalline and refractory phases compared to Cu (47% of total Ni vs. 29% of total Cu). The greater affinity for Ni to incorporate into magnetite was further demonstrated using magnetized goethites co-precipitated with 100 mmol Cu or Ni kg−1: most Ni was associated with the amorphous and crystalline Fe whereas 60% of total Cu was extracted as a sorbed/exchangeable species. The greater Cu mobility during sequential extraction of magnetite is likely attributable to its monovalent state in this reducing system. Low-temperature magnetization coupled with biomass pyrolysis may represent a viable option to manage iron and leftover transition metals in oxidized, (bio)leached pyrrhotite wastes as a way to produce much smaller volumes of inert wastes. [ABSTRACT FROM AUTHOR]

• Brazilian phosphates are rich in rare earth oxides. • A concentrate phosphate fraction was separated by mini-hydrocyclones. • The influences of geometrical and operational variables were investigated. • Experimental design and response surface methodology were applied. Rare earth elements comprise of lanthanides plus yttrium and scandium. They have several applications and are produced by a limited number of countries. Brazil has an estimated reserve of 22 million metric tons and most of the minerals are associated with phosphate. In the fertilizer industry, ores containing rare earth elements are combined with phosphates, fluorides, silica, limestone, titanium and gypsum. As a result, rare earth oxides (REOs) are lost with sterile dump and mining waste or are applied to the soil together with fertilizers. In this scenario, the composition and granulometry of raw and sterile materials from a phosphate producing unit were evaluated. Considering the concentration of REOs, equal to 1.56 wt% in the Catalão (GO) phosphate concentrate and the increase in concentration with the decrease in size, the objective of the present work was to separate the fraction smaller than 25 μm with a new mini- hydrocyclone. The variables such as cone angle, length of the cylindrical region, underflow orifice diameter and feed pressure influenced the following responses: capacity, underflow- to- throughput ratio, total efficiency and concentration of REOs in the overflow stream. The separator capacity was found to range from 881.5 to 1449.0 kg/h while the underflow-to-throughput ratio was between 9 and 40% and the total separation efficiency remained at around 96%. The lowest concentration of rare earth oxides obtained in the overflow stream was 79.5% higher than the concentration in the feed, corroborating the choice of hydrocyclone as a method of concentration of REOs. [ABSTRACT FROM AUTHOR]

• More than 70% of amorphous content was obtained after 16-min grinding. • Thermal properties of all ground samples were detailed. • Schematic model of the collapsed phlogopite was proposed. • Particles morphology was analysed based on Mineral Liberation Technique. The alkali activation of mine tailings is of interest to diminish the impoundment storage of large waste stream from mining industry. However, most of the mine tailings, like phosphate mine tailings generated in Finland, are rather inert and need pre-treatment to induce the reactivity for alkali activation. In this work, mechanochemical treatment was conducted to improve the reactivity of phosphate mine tailings. The ground specimens were subjected to the crystal structural analysis of X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermal analyses by Thermogravimetry/Differential Thermal Analysis (TG/DTA), showing the increment of amorphous content and structural degradation as a function of grinding time. The subsequent alkaline reactivity test illustrated incremental alkaline dissolution of Si, Al and K and a schematic diagram of altered phlogopite structure (sources of aluminosilicates in tailings) was also proposed. Additionally, the mineralogical composition of individual particles was carried out by mineral liberation analysis (MLA), thereby evaluating the influence of pre-treatment on the mineralogy of tailings. The results indicate profound micromorphological changes and structural cleavage of the precursor due to grinding, which strongly increase alkaline reactivity. [ABSTRACT FROM AUTHOR]