Major recent failures in Brazilian mine waste containment facilities, current cases of maximum emergency level and imminent risk of rupture, and a brief sustainability analysis.

Waste is the materials left over after the processing of ores. Significant disasters involving waste disposal structures have occurred in Brazil in recent years and caused severe damage by contaminating soil, rivers and coastal areas, destroying native fauna and flora, interrupting the water supply and compromising its potability, putting the population's health, livelihoods and economy at risk, as well as causing 289 irreparable human deaths. Regulatory laws have become stricter, and since 2019, after the tailings dam tragedies occurred in 2015 and 2019 in Mariana and Brumadinho, in Minas Gerais, the operation of  upstream-raised tailings dams has been prohibited in Brazil. In 2022, a waste slide from a sterile pile at the Pau Branco Mine in Nova Lima promoted a dike overflow. There was the death of five people whose car was buried by a landslide on a hillside. New strategies and technologies, such as reprocessing and recycling, can be tested to ascertain whether they can help improve practices in tailings management. Indeed, mining companies' corporate responsibility and sustainability practices need to be evaluated to verify whether they better match expectations. On the other hand, more specific and detailed regulations and resolutions are required to ensure the safe monitoring and management of sterile waste piles. This paper presents a review of the facts, a discussion of the literature (mainly on recent tailings dam disasters), the current situation of mining-containing waste structures in Brazil, a brief sustainability analysis and perspectives aimed at preventing/minimising catastrophes in the future.

When another one bites the dust: Environmental impact of global copper demand on local communities in the Atacama mining hotspot as registered by tree rings.

Assessing the impact of mining activity on the availability of environmental pollutants is crucial for informing health policies in anticipation of future production scenarios of critical minerals essential for the transition to a net-zero carbon society. However, temporal and spatial monitoring is often sparse, and measurements may not extend far enough back in time. In this study, we utilize variations of chemical elements contained in tree-rings collected in local villages from an area heavily affected by copper mining in the Atacama Desert since the early 20th century to evaluate the temporal distribution of pollutants and their relationship with local drivers. By combining time-varying data on local drivers, such as copper production and the dry tailings deposit area, we show how the surge in copper production during the 1990s, fueled by trade liberalization and increased international demand, led to a significant increment in the availability of metal(loid)s related to mining activities on indigenous lands. Our findings suggest that the environmental legislation in Chile may be underestimating the environmental impact of tailing dams in neighboring populations, affecting the well-being of Indigenous Peoples from the Atacama mining hotspot region. We argue that future changes in production rates driven by international demand could have negative repercussions on the environment and local communities. Therefore, mining emissions and the management of tailing dams should be carefully considered to anticipate their potential negative effects on human and ecosystem health.

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).

Blending bauxite residues with multiple byproducts improves capping materials for tailings storage facilities.

Amelioration and management of large volumes of tailings resulting from alumina refining is a major challenge owing to the high alkalinity and salinity of residues. Blended byproduct caps are a potential new and more cost-effective approach to tailings management, where tailings are blended with other local byproducts in order to reduce pH, salinity and toxic elements. Here, alkaline bauxite residue was blended with four byproducts (waste acid, sewage water, fly ash and eucalypt mulch) to create a range of potential capping materials. We leached and weathered materials in the glasshouse with deionized water over nine weeks to investigate if byproducts on their own or in combination improved cap conditions. Combining all four byproducts (10 wt % waste acid, 5 wt % sewage water, 20 wt % fly ash and 10 wt % eucalypt mulch) achieved lower pH (9.60) compared to any byproduct applied individually, or un-remediated bauxite residue (pH 10.7). Leaching decreased EC by dissolving and exporting salts and minerals from the bauxite residue. Fly ash addition increased organic carbon (likely from non-combusted organic material) and nitrogen, while eucalypt mulch increased inorganic phosphorus. Addition of byproducts also decreased the concentration of potentially toxic elements (e.g., Al, Na, Mo and V) and enhanced pH neutralisation. Initial pH with single byproduct treatments was 10.4-10.5, which decreased to between 9.9-10.0. Further lowering of pH and salinity as well as increased nutrient concentrations may be possible through higher addition rates of byproducts, incorporation of other materials such as gypsum, and increasing leaching/weathering time of tailings in situ.

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.

Stabilization of potentially toxic elements contained in mine waste: A microbiological approach for the environmental management of mine tailings.

Metals are key materials extensively employed in several industries to produce technological and daily-life products. The mining industry that produces such commodities generates Tons of waste that if not remediated can be transferred to the surrounding environment, thus representing a water, air, and soil pollution threat. In this work, we evaluated the feasibility of microbial sulfate reduction (SR) as a management strategy for this waste. Mine tailings were sampled from two abandoned mining sites located in Sonora (northwestern Mexico) and treated in anaerobic microcosms under SR conditions using anaerobic sludge as the inoculum at two different tailing:inoculum ratios (TIR). Major TIR's were found to be the triggering factor for the highest SR activities observed (73.6 ± 8.8 mg SO42- L-1 day-1). This stimulation was linked to the dissolution of sulfate bearing minerals (anglesite, jarosite, and gypsum) which provided additional sulfate for microbial activity. However, under this condition, longer lag phases for SR were observed, which was potentially due to pH inhibition at early incubation stages (pH ~3.7). Despite this, all biologically SR performing treatments presented important sulfide precipitation which was associated to changes in the mineralogy of the mine tailings. Metals of environmental concern such as As, Cd, Co, Cr and, Pb were detected to have shifted from the aqueous extractable phase to the bound to Fe and Mn oxides and residual phases. This finding was in accordance with the non-detectable concentrations of these metals in the aqueous phase by the end of the biological treatment which proved the effectiveness of this approach. This study provides insights into the promising potential of anaerobic microbes for the environmental management of mine tailings.

Cyanide Contamination of the Puyango-Tumbes River Caused by Artisanal Gold Mining in Portovelo-Zaruma, Ecuador.

PURPOSE OF REVIEW: To examine cyanide (CN-) contamination of a large river in southeastern Ecuador that has been severely impacted by the indiscriminate discharge of untreated gold processing effluents. RECENT FINDINGS: Poor environmental stewardship of cyanide (CN-) use by 87 gold processing centers in Portovelo-Zaruma in southern Ecuador to leach residual gold from Hg-contaminated tailings has resulted in high CN- contamination of the Puyango-Tumbes River downstream from the centers. Free CN- concentrations were high in river surface waters for 50 km below the processing plants, with the highest concentration 9088 times above the CCME standard of 5 µg/L and 1136 times above the 24-h LC50 concentration of 40 µg/L free CN- for some fish species. Due to cyanidation of mercury-contaminated tailings, the formation of Hg-CN complexes is a grave concern, as these complexes have been shown to be highly bioavailable. Preliminary tests conducted in a laboratory using bioassays with Danio rerio sp. and varying concentrations of synthetic Hg(CN)2 salt have shown significant THg bioaccumulation in muscle and kidney fish tissues exposed to concentrations >0.12 mg/L. Furthermore, low MeHg results in fish tissues demonstrated little occurrence of methylation and that the bulk of the total mercury content was in the form of inorganic mercury. Although construction of a communal tailings facility (CTF) in Portovelo is a positive development to reduce riverine pollution, the requirement to truck tailings up to the CTF likely results in inadequate compliance of environmental regulations that are poorly enforced.

Potential Effect of Porosity Evolution of Cemented Paste Backfill on Selective Solidification of Heavy Metal Ions.

Cemented paste backfill (CPB) is a common environmentally friendly mining approach. However, it remains undetermined whether CPB pollutes underground mine water. Tank leaching analysis of a CPB mass in distilled water was performed for 120 d, and water quality was tested in situ for a long-term pollution assessment. Computerized tomography was also used to determine the CPB micro-pore structure and ion-leaching mechanism. The dissolved Zn2+, Pb2+ and As5+ concentrations in the leachate peaked at 0.56, 0.11 and 0.066 mg/L, respectively, whereas the Co2+ and Cd2+ concentrations were lower than the detection limit. The CPB porosity decreased from 46.07% to 40.88% by soaking, and 80% of the pore diameters were less than 13.81 µm. The permeability decreased from 0.8 to 0.5 cm/s, and the quantity, length, and diameter of the permeate channels decreased with soaking. An in-situ survey showed novel selective solidification. The Zn2+ concentration in the mine water was 10-20 times that of the background water, and the Pb2+ concentration was 2-4 times the regulated value. Although the Pb2+ content decreased significantly with mining depth, there remains a serious environmental risk. Mine water pollution can be reduced by adding a solidifying agent for Pb2+ and Zn2+, during CPB preparation.

Geochemical behavior and environmental risks related to the use of abandoned base-metal tailings as construction material in the upper-Moulouya district, Morocco.

In some developing countries, base-metal residues that were abandoned in tailing ponds or impoundments are increasingly used as construction material without any control, engineering basis, or environmental concern. This uncontrolled reuse of mine tailings may constitute a new form of pollution risks for humans and ecosystems through metal leaching. Therefore, the aim of the current study is to assess mine drainage, metal mobility, and geochemical behavior of two abandoned mine tailings commonly used in the upper-Moulouya region (eastern Morocco) as fine aggregates for mortar preparation. Their detailed physical, chemical, and mineralogical properties were subsequently evaluated in the context of developing appropriate alternative reuses to replace their conventional disposal and limit their weathering exposure. The obtained results showed that both tailings contain relatively high quantities of residual metals and metalloids with lead (ranging between 3610 and 5940 mg/kg) being the major pollutant. However, the mineralogical investigations revealed the presence of abundant neutralizing minerals and low sulfide content which influence mine drainage geochemistry and subsequently lower metals mobility. In fact, leachate analyses from weathering cell kinetic tests showed neutral conditions and low sulfide oxidation rates. According to these results, the tailings used as construction material in the upper-Moulouya region have very low generating potential of contaminated effluents and their reuse as aggregates may constitute a sustainable alternative method for efficient tailing management.

Oil sands thickened froth treatment tailings exhibit acid rock drainage potential during evaporative drying.

Bitumen extraction from oil sands ores after surface mining produces different tailings waste streams: 'froth treatment tailings' are enriched in pyrite relative to other streams. Tailings treatment can include addition of organic polymers to produce thickened tailings (TT). TT may be further de-watered by deposition into geotechnical cells for evaporative drying to increase shear strength prior to reclamation. To examine the acid rock drainage (ARD) potential of TT, we performed predictive analyses and laboratory experiments on material from field trials of two types of thickened froth treatment tailings (TT1 and TT2). Acid-base accounting (ABA) of initial samples showed that both TT1 and TT2 initially had net acid-producing potential, with ABA values of -141 and -230 t CaCO3 equiv. 1000 t(-1) of TT, respectively. In long-term kinetic experiments, duplicate ~2-kg samples of TT were incubated in shallow trays and intermittently irrigated under air flow for 459 days to simulate evaporative field drying. Leachates collected from both TT samples initially had pH~6.8 that began decreasing after ~50 days (TT2) or ~250 days (TT1), stabilizing at pH~2. Correspondingly, the redox potential of leachates increased from 100-200 mV to 500-580 mV and electrical conductivity increased from 2-5 dS m(-1) to 26 dS m(-1), indicating dissolution of minerals during ARD. The rapid onset and prolonged ARD observed with TT2 is attributed to its greater pyrite (13.4%) and lower carbonate (1.4%) contents versus the slower onset of ARD in TT1 (initially 6.0% pyrite and 2.5% carbonates). 16S rRNA gene pyrosequencing analysis revealed rapid shift in microbial community when conditions became strongly acidic (pH~2) favoring the enrichment of Acidithiobacillus and Sulfobacillus bacteria in TT. This is the first report showing ARD potential of TT and the results have significant implications for effective management of pyrite-enriched oil sands tailings streams/deposits.