Methodology to Prioritize Chilean Tailings Selection, According to Their Potential Risks

Evaluation of the geochemical background of soil in a hyper-arid zone using a multivariate statistical methodology: The case of the city of Antofagasta in the Atacama Desert

This study investigates the geochemical background and factors influencing the variability of 19 environmentally relevant elements in the soils of Antofagasta, Chile, a region known for its extensive mining activities. Employing robust multivariate statistical techniques on a dataset of 94 soil samples, we identified four main factors explaining 70% of the total variance in elemental concentrations. These four factors reflect the influence of Jurassic volcanic rocks, intrusive rocks, marine sediments, and mafic to intermediate intrusive rocks. Cluster analysis revealed three distinct geochemical populations, each reflecting a unique combination of natural and anthropogenic influences. We established background concentrations for each element within these clusters using robust statistical methods. Geostatistical analysis, employing inverse distance weighted interpolation, produced factor distribution maps that, when integrated with geological data, provided insights into lithological and anthropogenic influences on soil geochemistry. Our findings highlight the complex interplay between natural geological processes, the region's unique arid climate, and anthropogenic activities in shaping the geochemical landscape of Antofagasta. This study contributes to the understanding of geochemical backgrounds in mining-intensive, arid regions and provides a methodological framework applicable to similar environments worldwide.

Characterization and utilization potential of typical molybdenum tailings in Shaanxi Province, China

Shaanxi Province is located in the most important molybdenum ore district in the world, but a lot of molybdenum tailings have been released, polluting the environment and wasting resources seriously. Taking eleven tailing samples collected at the main molybdenum tailings ponds in Shaanxi Province as the research object, the physical, chemical, and mineralogical characteristics were studied through scanning electron microscope, X-ray fluorescence, X-ray diffraction, inductively coupled plasma mass spectrometer, and others. The ecological risk and utilization potential of molybdenum tailings were investigated through leaching test, geo-accumulation index, potential ecological risk assessment, and other methods. The results demonstrated that the main chemical and mineralogical composition of various molybdenum tailings in Shaanxi Province is similar, and the predominant mineral composition is muscovite, quartz, microcline, and calcite. The potential ecological risk of heavy metals in six molybdenum tailings is high, while Pb and Cd are the main pollution risk elements. Molybdenum tailings contain considerable amounts of critical minerals with huge potential economic value, and molybdenum tailings with high environmental hazards could be converted into a possible source for critical minerals by recovering the critical minerals and repurposing the secondary tailings as an additive or cement substitute. This study provides an innovative idea for the pollution treatment of molybdenum tailings and indicates the prospect of molybdenum tailings as a secondary source for critical minerals.

MICP mediated by indigenous bacteria isolated from tailings for biocementation for reduction of wind erosion

In this study, native ureolytic bacteria were isolated from copper tailings soils to perform microbial-induced carbonate precipitation (MICP) tests and evaluate their potential for biocement formation and their contribution to reduce the dispersion of particulate matter into the environment from tailings containing potentially toxic elements. It was possible to isolate a total of 46 bacteria; among them only three showed ureolytic activity: Priestia megaterium T130-1, Paenibacillus sp. T130-13 and Staphylococcus sp. T130-14. Biocement cores were made by mixing tailings with the isolated bacteria in presence of urea, resulting similar to those obtained with Sporosarcina pasteurii and Bacillus subtilis used as positive control. Indeed, XRD analysis conducted on biocement showed the presence of microcline (B. subtilis 17%; P. megaterium 11. 9%), clinochlore (S. pasteurii, 6.9%) and magnesiumhornblende (Paenibacillus sp. 17.8%; P. megaterium 14.6%); all these compounds were not initially present in the tailings soils. Moreover the presence of calcite (control 0.828%; Paenibacillus sp. 5.4%) and hematite (control 0.989%; B. subtilis 6.4%) was also significant unlike the untreated control. The development of biofilms containing abundant amount of Ca, C, and O on microscopic soil particles was evidenced by means of FE-SEM-EDX and XRD. Wind tunnel tests were carried out to investigate the resistance of biocement samples, accounted for a mass loss five holds lower than the control, i.e., the rate of wind erosion in the control corresponded to 82 g/m2h while for the biocement treated with Paenibacillus sp. it corresponded to only 16.371 g/m2h. Finally, in compression tests, the biocement samples prepared with P. megaterium (28.578 psi) and Paenibacillus sp. (28.404 psi) showed values similar to those obtained with S. pasteurii (27.102 psi), but significantly higher if compared to the control (15.427 psi), thus improving the compression resistance capacity of the samples by 85.2% and 84.1% with respect to the control. According to the results obtained, the biocement samples generated with the native strains showed improvements in the mechanical properties of the soil supporting them as potential candidates in applications for the stabilization of mining liabilities in open environments using bioaugmentation strategies with native strains isolated from the same mine tailing.

Adsorption and aggregation of Cu2+ on carboxymethylated sugarcane bagasse: Adsorption behavior and mechanism

Abundant biomass resources provide us with sufficient material basis, while a large amount of bio-waste is also produced and the high-value utilization of bio-waste is still highly desirable. Herein, we reported a facile one-pot fabrication approach towards efficient utilization of sugarcane bagasse via carboxymethylation to adsorb and recycle Cu2+ ions. The modified sugarcane bagasse possessed outstanding adsorption efficiency, with a maximum capacity of 263.7 mg g-1, owing to the functional groups such as carboxyl and hydroxyl groups, as well as aromatic structure. It was noted that the carboxymethylated sugarcane bagasse (MSB40) swelled rapidly when suffering Cu2+ ions solution, and more adsorption sites were available since the physical diffusion barrier was removed, thereby enhancing the absorption capacity. Interestingly, Cu2+ ions could induce the aggregation of MSB40 due to the Cu2+ ions compress colloid double layer, neutralizes surface charges, which benefited the following separation process. Ultimately, copper oxide was recovered and the purity reached 97.9%. Additionally, in the presence of both Ca2+ and Mg2+ ions, MSB40 exhibited excellent selectivity for the adsorption of Cu2+ ions. This strategy offers a facile and novel clue for the high-value utilization of bio-waste and the recovery of copper for biomaterial and environmental applications.

Assessment of environmental pollution and human health risks of mine tailings in soil: after dam failure of the Córrego do Feijão Mine (in Brumadinho, Brazil)

The dam failure of the Córrego do Feijão Mine (CFM) located in Minas Gerais State, Brazil, killed at least 278 people. In addition, large extensions of aquatic and terrestrial ecosystems were destroyed, directly compromising the environmental and socioeconomic quality of the region. This study assessed the pollution and human health risks of soils impacted by the tailing spill of the CFM dam, along a sample perimeter of approximately 200 km. Based on potential ecological risk and pollution load indices, the enrichments of Cd, As, Hg, Cu, Pb and Ni in soils indicated that the Brumadinho, Mário Campos, Betim and São Joaquim de Bicas municipalities were the most affected areas by the broken dam. Restorative and reparative actions must be urgently carried out in these areas. For all contaminated areas, the children's group indicated an exacerbated propensity to the development of carcinogenic and non-carcinogenic diseases, mainly through the ingestion pathway. Toxicological risk assessments, including acute, chronic and genotoxic effects, on people living and working in mining areas should be a priority for public management and mining companies to ensure effective environmental measures that do not harm human health and well-being over time.

Spatial distribution and pollution evaluation in dry riverbeds affected by mine tailings

The objective of this study was to evaluate the level of pollution, sources and potential risk of heavy metals (Zn, Cu, Mn, Cd, Cr, Ni, Fe and Pb) and arsenic (As) in four dry riverbeds affected by mine tailing, which drain into one of the biggest coastal lagoon of Europe (Mar Menor). El Beal, La Carrasquilla, Las Matildes and Ponce dry riverbeds sediments were sampled along its course (20, 18, 13, 19 samples were collected, respectively), and total/soluble metal(loid)s, water soluble ions, nitrogen, and organic/inorganic carbon contents were analyzed. Spatial distribution, principal component analysis (PCA), hierarchical cluster analysis (HCA), contamination factor (Cf), pollution load index (PLI) and potential ecological risk index (RI) were used to identify the possible sources of metal(loid)s and to assess the sediment pollution status. The results showed that the mean total concentrations of As, Cu, Cd, Mn, Zn and Pb exceeded the natural background levels of the study area, with the highest values located close to the mining areas. Correlation and cluster analysis identified that Cd and Zn were associated mainly with anthropogenic activities for all riverbeds, while Cr and Ni come from parent. PLI graded the four riverbeds as contaminated by heavy metals, while RI manifested that 100% of samples located in El Beal, La Carrasquilla and Las Matildes had a significantly high ecological risk. Therefore, this study suggests that mine wastes are the main source of metal(loids) contamination in the dry riverbeds, which results can be used to design actions and measures to reduce the environmental impact of metal(loid)s in the Mar Menor coastal lagoon.

Characteristic curve modeling of plant species behavior in soils with heavy metals

Many vegetal species can accumulate great amounts of metallic elements in their tissues. For this reason, they are called metal hyperaccumulators. An indicator of great interest in environmental sciences is the bioconcentration factor because it is recognized for establishing the potential accumulation of chemicals in organisms. Particularly in soil phytoremediation processes, it measures the capacity of a certain plant to capture metals, in terms of soil concentration. According to their behavior, four types of plants can be distinguished regarding soil concentration increase: indicator, excluder, accumulator, and hyperaccumulator. This study proposes a new model to categorize plants according to their behavior related to soil concentration increase, using several characteristic curves obtained from 1288 experimental measurements collected from different bibliographic sources. The metals analyzed were Cu, Fe, Pb, and Zn. The proposed model is obtained through linear regression and nonlinear transformations to model the expected behavior of plants in high concentration conditions. In particular, the basic equation of the model has three key components to represent the expected concentration in the plant root given the final soil concentration level, the type of species, and specific metal: a linear factor that determines the growth for low concentration values, an exponential factor that determines its decrease for high concentration values, and a logarithmic factor that limits the maximum value that can be reached in practice and influences the decay for high concentration values. After fitting the experimental data using linear regression, the proposed model has a 0.084 R2 determination coefficient and all of its parameters are considered significant. Furthermore, it shows that 60 of the 257 species assessed behave as accumulators and 10 of them as hyperaccumulators. The main contribution of this model is its ability to handle soils with high concentrations, where it would be hard for plants to achieve concentrations similar to or higher than the substrate containing them. Thus, the conventional criterion of the bioconcentration factor would incorrectly categorize a plant as an excluder. In contrast, this new model allows assessing plant effectiveness in a phytoremediation process of highly concentrated affected sites, such as mine tailings.

Socio-Environmental Risks Linked with Mine Tailings Chemical Composition: Promoting Responsible and Safe Mine Tailings Management Considering Copper and Gold Mining Experiences from Chile and Peru

There is a need to define mine tailings in a clear, precise, multidisciplinary, transdisciplinary, and holistic manner, considering not only geotechnical and hydraulic concepts but also integrating environmental and geochemical aspects with implications for the sustainability of mining. This article corresponds to an independent study that answers questions concerning the definition of mine tailings and the socio-environmental risks linked with mine tailings chemical composition by examining the practical experience of industrial-scale copper and gold mining projects in Chile and Peru. Definitions of concepts and analysis of key aspects in the responsible management of mine tailings, such as characterization of metallic-metalloid components, non-metallic components, metallurgical reagents, and risk identification, among others, are presented. Implications of potential environmental impacts from the generation of acid rock drainage (ARD) in mine tailings are discussed. Finally, the article concludes that mine tailings are potentially toxic to both communities and the environment, and cannot be considered as inert and innocuous materials; thus, mine tailings require safe, controlled, and responsible management with the application of the most high management standards, use of the best available technologies (BATs), use of best applicable practices (BAPs), and implementation of the best environmental practices (BEPs) to avoid risk and potential socio-environmental impact due to accidents or failure of tailings storage facilities (TSFs).

Heavy metal pollution index calculation in geochemistry assessment: a case study on Playa Las Petroleras

This work is aimed to assess potential risk associated with the presence of metals and metalloids in soil at "Playa Las Petroleras" sector, located in Antofagasta (Chile). The zone under study has been affected by four oil spill events. This sector is located in an urban area by the sea. So, it has a great social and environmental relevance. The concentrations of 15 elements in soil samples were assessed, four of them presenting potential ecological risk: As, Co, Cu, and Pb. Nine pollution indices were applied to data: four single pollution indices and five integrated pollution indices to assess soil pollution. The single pollution indices show that the site bears potential ecological and environmental risk due to the presence of Cu, the site being classified as highly contaminated owing to a severe enrichment of this metal. For Co, all the indices allow classifying the site as little or uncontaminated, while the level of As and Pb pollution could be considered as ranging from uncontaminated to moderately contaminated. The integrated pollution indices show that average concentrations are highly contaminated mainly owing to the presence of Cu.

Simultaneous removal of lead, manganese, and copper released from the copper tailings by a novel magnetic modified biosorbent

Potentially toxic elements including lead (Pb), manganese (Mn), and copper (Cu) released from copper tailings would cause severe long-term environmental risks and potential threats to human health. To prevent these negative effects caused by the release of the metals, a novel magnetic carboxyl groups modified bagasse with high adsorption affinity and strong magnetism was synthesized through an in-situ precipitation method and used to simultaneously remove Pb, Mn, and Cu from the eluate of copper tailings. Results showed that release of Pb, Mn, and Cu from the copper tailings was pH, time, and particle size dependent, and maximum concentrations of them released in the eluate was 1.7, 1.9, and 4.1 mg L^-1 under weak acid conditions. Batch adsorption experiment showed that the as-synthesized magnetic modified bagasse could selectively absorb Pb, Mn, and Cu from a complex solution with adsorption capacity of 137.3, 13.1, and 90.0 mg g^-1, respectively. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy-mapping (EDS-mapping) demonstrated that Pb, Mn, and Cu interacted with the magnetic modified biosorbent mainly through coordination and ion exchange. Column experiments showed that higher than 99.5% of the released Pb, Mn, and Cu could be simultaneously removed by the magnetic modified bagasse, and the maximum concentrations of them released in the eluate of the copper tailings were all decreased to lower than 0.01 mg L^-1, which reached the discharge standards. After recycled by a magnet, the magnetic modified bagasse could be collected easily and used repeatedly. Because of the high efficiency and easy recovery, the used method had great practical application value in removal of potentially toxic elements released from metallic tailings.

Past, Present, and Future of Copper Mine Tailings Governance in Chile (1905-2022): A Review in One of the Leading Mining Countries in the World

How mine tailings storage facilities (TSF) are managed reflects the history, regulatory framework, and environment of a country and locale of the mine. Despite many attempts to find an environmentally friendly strategy for tailings management and governance that balances the needs of society and the ecosystem, there is no worldwide agreement regarding the best practices for tailings management and governance. This article reviews the evolution of copper tailings management and governance in Chile, current practices, and changes that could be or may need to be made to improve practices in response to local environmental conditions and local tolerance for risk. The progress to date in developing a holistic tailings management strategy is summarized. This article also describes recent proposals for the best available technologies (BATs), case histories of Chilean TSF using conventional technology, thickened tailings, paste tailings, filtered tailings, water use reduction, tailings reprocessing to obtain rare earth elements (REEs), circular economy, submarine deep-sea tailings disposal, and ways to avoid failure in a seismic region. Finally, the Chilean tailings industry's pending issues and future challenges in reducing the socioenvironmental impacts of tailings are presented, including advances made and lessons learned in developing more environmentally friendly solutions.

Geochemical stability of potentially toxic elements in porphyry copper-mine tailings from Chile as linked to ecological and human health risks assessment

The geochemical stability, in terms of potential mobility and derived ecological and human health risks of potentially toxic elements (PTEs), of diverse fresh and old porphyry Cu-mine tailings from Chile was assessed through an integrated methodology comprising four interrelated investigation levels: (1) chemical composition and contamination degree of tailings by PTEs, (2) mineralogical characterization by X-ray diffraction and quantitative automated mineralogy analysis by scanning electron microscopy (QEMSCAN^®), (3) partitioning and potential mobility of PTEs within the tailings by a sequential extraction procedure (SEP) and leaching tests, and (4) ecological risk assessment (ERA) and human health risk assessment (HHRA). According to pollution indices, Cu, As, Pb, and Mo are most concerning PTEs present in the tailings. SEP shows that major portion of the PTEs are strongly fixed as residual fraction, and thus are poorly mobilizable and bioavailable. Among the PTEs, Cu, As, and Mo were identified as the PTEs most prone to mobilization. Leaching tests show that a low fraction of PTEs is water-leachable. Seawater enhances Mn and As leaching, while process water increases the leaching of Cu, Mn, and Mo. Phosphate particularly promotes leaching of As and Cu, whereas it does not mobilize or even immobilize Pb in the tailings. ERA suggests that mainly old tailings pose a very high potential risk for ecological receptors (PERI = 663-3356), mostly due to Cu and As. HHRA indicates that the old tailings pose higher potential non-carcinogenic and carcinogenic health risks, while the risk decreases in the order ingestion > dermal > inhalation for both children and adults. Non carcinogenic and carcinogenic HHRA points to As as the main PTE of concern via ingestion pathway in the tailings. Overall, the results revealed that particularly old tailings, containing mixed slag-tailings, pose considerable risks to the environment and human health due to potential PTEs mobilization and this aspect requires scrutiny for proper tailings management, including storage, sealing, and eventual tailings reprocessing and/or site rehabilitation after closure.

Evaluation of copper tailing amendments through poultry waste and ammonium nitrate

In this study, two amendments, poultry waste and ammonium nitrate, were evaluated to condition and stabilize a mine tailing and thus help the vegetation cover settle. Individually, ammonium nitrate was tested as a nitrogen source and chicken bone ash as a phosphate source. For this, laboratory tests were made on soil columns from the area to be remediated. The mobility and availability of metals and nutrients were determined by analyzing their leachates chemically. The results showed that the use of chicken bone ash decreases soluble metal concentrations, particularly in Fe and soluble Mn. On the other hand, experimental conditions proved that the acidification produced by ammonium nitrate nitrification does not significantly increase the lechate metal content. Therefore, its use for fertilization does not involve phytotoxicity risks. Regarding the availability of macronutrients as well as trace elements, the results showed that the concentrations lie within the ranges suitable for plant nutrition. So, the treatments are effective both for fertilization and phytoremediation.

Feasibility of re-processing mine tailings to obtain critical raw materials using real options analysis

The re-processing of mine tailings to obtain critical raw materials (CRMs) could reduce the mining of new deposits as well as ensure the profitable use of the waste materials. Though, it requires large scale industrial installations and the development of specialized technologies to obtain CRMs. New investment in mining activities is an operation, engaging for considerable financial resources involved. The scale of such an endeavor makes a new mining activity a high-risk operation due to several uncertainties present. Therefore, there is an acute need to use new tools to assess the risk associated with the planning and development of new mining activities. This study introduces a framework to evaluate the economic risk related to the re-processing of mine tailings to obtain CRMs. The framework, based on real options analysis (ROA), and sensitivity and uncertainty analysis, was applied to analyze the profitability of using mine tailings as a source of CRMs in the Chilean mining industry. The novelty of this approach consists in enabling the investment decision making including the uncertainties related to a novel investment mining project. RESULTS: show that tailing storage facilities in Chile have some stocks of CRMs, like scandium, whose extraction could be profitable. For the data used, the results of uncertainty and sensitivity analyses show that capital expenditure has a more significant influence than the other variables. Therefore, for the case of mine tailings re-processing, it is essential to develop processes and technologies that enable lower capital expenses.

Potential of Tailing Deposits in Chile for the Sequestration of Carbon Dioxide Produced by Power Plants Using Ex-Situ Mineral Carbonation

In this study, the potential of copper tailing deposits in Chile for the sequestration of carbon dioxide (CO2) via ex-situ mineral carbonation integrating the recovery of valuable metals was assessed. An inventory of tailing deposits and CO2 sources existing in Chile was constructed to determine the most suitable site for the installation of a future mineral carbonation plant and to evaluate the technical, economic, and environmental feasibility of CO2 capture, separation, and transport from the source to the mineral carbonation plant. The data of the inventory of tailings deposits in Chile were obtained from the National Service of Geology and Mining. For the thermoelectric plants installed in Chile, data of energy production were obtained from the Energy National Commission. Through the use of the technique for order preference by similarity to ideal solution (TOPSIS) method and sensitivity analysis, the optimum location in the region of Antofagasta to install a mineral carbonation plant was identified. In addition, the results show that in the region of Antofagasta five tailing deposits have the potential to sequester between 66 to 99 Mt of CO2. Meanwhile, thermoelectric plants in 2018 produced about 9.4 Mt of CO2 that is available to be sequestered, with a maximum generation potential of 21.9 Mt of CO2eq per year. The methodology and the study presented can be considered as a preliminary study to identify tailings that require further analysis.

Heavy metal pollution and ecological risk assessment of tailings in the Qinglong Dachang antimony mine, China

The pollution of heavy metals and their harm to human health and the ecological environment have caused widespread concern. In this research, we collected Qinglong antimony mine tailings (8-meter deep) and then analyzed the content changes, geochemical behavior, and ecological risk assessment of 7 heavy metals (Sb, As, Cr, Cd, Cu, Zn, Pb) in the tailing profile, providing a theoretical basis for strengthening the source control and risk control of heavy metals. In addition, the chemical forms of Sb and As were analyzed, and the relationship between their forms and their physical and chemical properties was analyzed by redundancy analysis (RDA). The results showed that the concentrations of Sb (671.97-13896.62 mg/kg), As (287.38-657.36 mg/kg), Cu (27.61-74.48 mg/kg), and Cd (0.49-1.76 mg/kg) in the tailings greatly exceeded their background values, those of Pb (15.67-125.74 mg/kg) and Cr (22.69-185.88 mg/kg) moderately exceed their background values, while that of Zn (41.66-94.48 mg/kg) was slightly below its background value. Among the chemical forms of Sb and As, the residual fraction (F4) had the highest concentration. RDA showed that the pH and tailing particle size were significantly correlated with the chemical species content of Sb and As (p < 0.05). The improved Igeo analysis showed that the tailings were extremely polluted with Sb; highly polluted with As; uncontaminated to moderately polluted with Cd, Cu, and Pb; and uncontaminated with Zn and Cr, and the average Igeo values were in the following order: Sb >As > Pb > Cd > Cu > Zn > Cr. The potential environmental risk index showed that Sb and As imposed a serious risk and Cr, Cd, Cu, Pb, and Zn imposed a low risk, which was basically consistent with the results of the improved Igeo values. This research provides comprehensive theoretical approaches to better understand the source control and risk control of heavy metals in tailing ponds.

A Methodology Based on Magnetic Susceptibility to Characterize Copper Mine Tailings

This paper intends to validate the application of magnetic techniques, particularly magnetic susceptibility, as sampling tools on a copper tailings terrace, by correlating them analytically. Magnetic susceptibility was measured in both the field and laboratory. Data obtained allowed for designing spatial magnetic susceptibility distribution maps, showing the horizontal variation of the tailings. In addition, boxplots were used to show the variation of magnetic susceptibility and the concentration of the elements analyzed at different depths of the copper tailings terrace. The degree of correlation between magnetic and chemical variables was defined with coefficient R2. The horizontal and vertical variations of magnetic susceptibility, the concentration of elements, and the significant correlations between them show a relationship between magnetic susceptibility and the chemical processes occurring in the tailing management facility, such as pyrite oxidation. Thus, the correlation functions obtained could be used as semiquantitative tools to characterize tailings or other mining residues.