Sulfidic Tailings Research Articles

Bioleaching of cobalt from sulfide tailings generated by vanadium-titanium-magnetite ore beneficiation

Cobalt-bearing sulfide tailings are one of the most important by-products in the beneficiation process of vanadium titanium-magnetite in China’s Panxi area, which can produce acid mine drainage (AMD) due to the release of heavy metal elements. The efficient and comprehensive recovery of the tailings associated with vanadium titanium magnetite is of great strategic significance for environmental protection and the sustainable and healthy development of cobalt resources. In this study, bioleaching of cobalt from the sulfide tailing was investigated using mesophilic bacteria (Acidithiobacillus ferrooxidans) and moderately thermophilic bacteria (Sulfobacillus thermosulfidooxidans), respectively, accompanied with leaching residues analysis. Leaching tests indicated that 54.69 % of cobalt was leached by A. ferrooxidans after 29 days, whereas the cobalt extraction could be up to 77.14 % at day 29 in the presence of S. thermosulfidooxidans. As XRD, SEM and XPS analysis of residues showed, the surface of the tailing was covered by jarosite after bioleaching, which hindered the further leaching of the tailing and prevented AMD production. In contrast, during abiotic leaching, the surface of the tailing was dominated by the continuous accumulation of elemental sulfur, indicating a limited leaching capacity by acid. Additionally, most nickel was recovered simultaneously from the tailing by bioleaching, but the extractions of copper and titanium were rather low. This study offers new insights into the utilization of cobalt-bearing sulfide resources that are associated with vanadium-titanium magnetite ores. It also holds significance for guiding the treatment of other cobalt-bearing sulfide tailings.

An Electrochemical Study of the Effect of Sulfate on the Surface Oxidation of Pyrite.

Pyrite is one of the most abundant metal sulfide tailings and is susceptible to oxidation, yielding acidic mine drainage (AMD) that poses significant environmental risks. Consequently, the exploration of pyrite surface oxidation and the kinetic influencing factors remains a pivotal research area. Despite the oxidation of pyrite producing a significant amount of sulfate (SO42-), a comprehensive investigation into its influence on the oxidation process is lacking. Leveraging pyrite's semiconducting nature and the electrochemical intricacies of its surface oxidation, this study employs electrochemical techniques-cyclic voltammetry (CV), Tafel polarization, and electrochemical impedance spectroscopy (EIS)-to assess the effect of SO42⁻ on pyrite surface oxidation. The CV curve shows that SO42- does not change the fundamental surface oxidation mechanism of pyrite, but its redox peak current density decreases with the increase in SO42-, and the surface oxidation rate of pyrite decreases. The possible reason is attributed to SO42- adsorption onto pyrite surfaces, blocking active sites and impeding the oxidation process. Furthermore, Tafel polarization curves indicate an augmentation in polarization resistance with elevated SO42- concentrations, signifying heightened difficulty in pyrite surface reactions. EIS analysis underscores an increase in Weber diffusion resistance with increasing SO42⁻, indicating that the diffusion of Fe3+ to the pyrite surface and the diffusion of oxidized products to the solution becomes more difficult. These findings will improve our understanding of the influence of SO42- on pyrite oxidation and have important implications for deepening the understanding of surface oxidation of pyrite in the natural environment.

Accumulated Copper Tailing Solid Wastes with Specific Compositions Encourage Advances in Microbial Leaching

Against the backdrop of the increasing copper demand in a low-carbon economy, this work statistically forecasted the distribution of China’s copper tailings for the first time, and then characterized them as finely crushed and low-grade mining solid wastes containing copper mainly in the form of chalcopyrite, bornite, covelline, enargite and chalcocite based on available research data. China is the globally leading refined copper producer and consumer, where the typical commercial-scale bioleaching of copper tailings is conducted in the Dexing, Zijinshan and Jinchuan mining regions. And these leaching processes were compared in this study. Widely used chemolithoautotrophic and mesophilic bacteria are Acidithiobacillus, Leptospirillum, Acidiphilium, Alicyclobacillus and Thiobacillus with varied metal resistance. They can be used to treat copper sulfide tailings such as pyrite, chalcopyrite, enargite, chalcocite, bornite and covellite under sufficient dissolved oxygen from 1.5 to 4.1 mg/L and pH values ranging from 0.5 to 7.2. Moderate thermophiles (Acidithiobacillus caldus, Acidimicrobium, Acidiplasma, Ferroplasma and Sulfobacillus) and extreme thermophilic archaea (Acidianus, Metallosphaera, Sulfurococcus and Sulfolobus) are dominant in leaching systems with operating temperatures higher than 40 °C. However, these species are vulnerable to high pulp density and heavy metals. Heterotrophic Acidiphilium multivorum, Ferrimicrobium, Thermoplasma and fungi use organic carbon as energy to treat copper oxides (malachite, chrysocolla and azurite) and weathered sulfides (bornite, chalcocite, digenite and covellite) under a wide pH range and high pulp density. We also compared autotrophs in a planktonic state or biofilm to treat different metal sulfides using various sulfur-cycling enzymes involved in the polysulfide or thiosulfate pathways against fungi that produce various organic acids to chelate copper from oxides. Finally, we recommended a bioinformatic analysis of functional genes involved in Fe/S oxidization and C/N metabolism, as well as advanced representation that can create new possibilities for the development of high-efficiency leaching microorganisms and insight into the mechanisms of bioleaching desired metals from complex and low-grade copper tailings.

Studying the process of metals and non-metals transfer in a low-temperature gas flow over sulfide tailings materials

ABSTRACT A large number of publications have been devoted to the study of aerosol atmospheric transport, but the low-temperature transfer of metals and metalloids as a part of gas flow remains poorly understood. The present work is devoted to the study of gas stream composition using an approach based on the collection of nascent condensate upon cooling of the air flow formed over the surface of contaminated sites. A special laboratory unit was designed to collect the condensate followed by the study of its composition using atomic emission and mass spectrometry. The main novelty of this work consists of the application of the single-particle ICP‒MS technique to obtain qualitative information concerning the state of the elements in the condensates. Gold and silver are most likely present in the samples as nanoparticles; arsenic, selenium, tin and lead are present both as nanoparticles and as soluble forms; and barium and mercury are present only in soluble forms. The condensed phase contains As, Hg, Au, Ag, Pb and Sn at the ppb level, while the main elements of the tailings material (Fe, Ba, Cu, Zn and others) are present at the ppm level, which exceeds the background concentration.

Mechanism investigation of food waste compost as a source of passivation agents for inhibiting pyrite oxidation

Pyrite oxidation causes the generation of acid mine drainage (AMD), posing significant challenges in the management of sulfide tailings. Passivation agents such as humic acid have been tested to prevent pyrite oxidation. The potential of using humate rich food waste compost as a source of passivation agents to suppress pyrite oxidation was explored in this study. Batch leaching tests were conducted at room temperature, involved oxidatively leaching a pure pyrite and a pyrite-containing coal refuse sample, respectively, with and without adding the compost at acidic pH. The involved passivation mechanisms were investigated by solution leaching tests and spectroscopic (XPS) and microscopic (SEM) analysis of the pure pyrite sample and its leaching residues. Compared to the control, adding the compost led to the increases in solution pH, removal of the Fe2+/Fe3+ ions from the solutions by adsorption, and remarkable decreases (≥58 %) in sulfur concentration in both samples. Both SEM and XPS analysis indicated that a coating layer was successfully established on pyrite surface after being leached in the presence of the compost. The coating layer comprised a mixture of organic species (e.g., O-CO and N-H/C groups) and phosphate, potentially improving the likelihood of providing antioxidant protection over acidic pH. As a low-cost material, food waste compost can benefit the source control of AMD not only in terms of its surface passivation, but also its intrinsic alkalinity, metal immobilization, and low environmental risk.

Characterization and Pollution Assessment of Potentially Toxic Metals (PTMs) in the Sulfide Tailings from Boudoukha Abandoned Mine (Zn–Pb–Cu), NE Algeria

Characterization and Pollution Assessment of Potentially Toxic Metals (PTMs) in the Sulfide Tailings from Boudoukha Abandoned Mine (Zn–Pb–Cu), NE Algeria

Valorisation of sulphide tailings: A novel dilute reagents-based Mn extraction process

The surging demand for manganese (Mn) and the concomitant scarcity of its primary resources have ignited interest in the extraction of this pivotal metal from unconventional sources, notably mining tailings. This study delves into the efficacy of dilute reagents as a judicious and discerning method for extracting Mn from sulphide tailings, concurrently offering environmental amelioration and substantial economic advantages. Specifically, the investigation concentrates on the adept and selective leaching of Mn from rhodochrosite (MnCO3) mineral under optimized conditions. Under the optimized conditions of 5 % HCl, a liquid-to-solid ratio of 5, a 90-minute leaching period, and a temperature at 50 °C, an exemplary 95 % leaching of MnCO3 was achieved while incurring a modest 12 % leaching of Fe, the principal impurity in the sample. Subsequent to the leaching process, MnO was efficiently extracted from the solution, exhibiting a purity surpassing 96 %, facilitated by the introduction of a diluted ammonium hydroxide solution (0.1 M NH4OH) at a solution pH of 9.8 and a temperature of 48 °C. The proposed methodology for reprocessing sulphide tailings offers numerous benefits, including cost-effective recovery and extraction, resulting from dilute reagents used and promoting a circular economy in mining. This research substantiates a significant stride towards the sustainable utilization of mining by-products, concurrently addressing both economic and environmental imperatives.

Study on strengthening of sulfide tailings high-efficiency solid-liquid separation using water reducing admixtures

The global focus on refined mineral processing and environmental protection has led to stricter requirements for tailings disposal processes. The complex composition and chemical environment of tailings pose challenges in sedimentation and pipeline transportation. This research developed a new additive that is suitable for disposing of copper-lead-zinc sulfide tailings. This additive not only improves sedimentation efficiency and concentration, but also enhances the flowability of high-concentration slurry. This study investigated the effects of four typical water reducing admixtures on the settling and rheological properties of tailings. However, the combination of lignin/PCE and NPAM had a synergistic effect, further improving settling and rheological performance. The addition of PCE increased settling rate by over 2 times, increased sediment concentration by 6.71%, and significantly reduced slurry viscosity and yield stress. The study also used FBRM to analyze the changes in particle/floc size distribution over time. The results showed that the addition of PCE captured more fine particles during flocculation and formed larger flocs. These findings can be used as a reference for the use and optimization of additives in tailings disposal engineering.

Research on resource comprehensive utilization of granite-type sulfide mine tailings

In order to recover and utilize mica and quartz from the tailings of a granite-type sulfide ore in Jiangxi Province, the technique of separating mica and quartz from the tailings by flotation without acid was investigated. Pyrite flotation was performed on a 500 g tailing sample to remove pyrite. And the middlings were acquired by desliming of the unfloated products. Finally mica and quartz was separated from the middlings in the mechanical flotation cell. Under conditions of pH=10.3 with a pulp concentration of 35% and a collector concentration of 180 g/t, a yield of 12.89% mica and 42.73% quartz was obtained, with silica grades as high as 71.50% in the quartz. The mica and quartz products can be used in construction ceramics and construction sand, respectively. It is believed that the outcomes of this work could provide ideas for comprehensive utilization of sulfide tailings.

Environmental compliance assessment for the desulfurization of sulfide mine waste tailings: A case study of Ok Tedi Mine, Papua New Guinea

The effective management of sulfide mine waste tailings is a complex task because of the potential for acid rock drainage to harm aquatic ecosystems. Although previous research has explored the environmental consequences of sulfide mine waste tailings and the potential advantages of desulfurization method, there is a lack of studies examining the environmental compliance of desulfurization efforts. To bridge this knowledge gap, a study was conducted at the Ok Ted Mine to evaluate the environmental compliance of the implemented desulfurization process. Ninety samples of sulfide tailing, desulfurized tailing, and sulfide concentrate were collected and analyzed for geochemical and physical properties. The acid-generating capacities were assessed using the Sobek's static test, whereas the particle size, pH, and recovery were evaluated for the overall performance of the desulfurization process. These findings indicated that the desulfurization process significantly reduced the acid-generating capacity and heavy metal concentrations of the sulfide tailings below the regulatory threshold levels. Therefore, the desulfurization approach employed at the Ok Ted Mine comply with the environmental regulaotry requirments. For further assessment, a study is recommended to evaluate the impact of desulfurization on the ecosystem to predict full extent of biodiversity recovery after mine life.

Inhibition of pyrite oxidation through forming biogenic K-jarosite coatings to prevent acid mine drainage production

This study proposes a novel method by forming biogenic K-jarosite coatings on pyrite surfaces driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) to reduce heavy metal release and prevent acid mine drainage (AMD) production. Different thicknesses of K-jarosite coatings (0.7 to 1.1 μm) were able to form on pyrite surfaces in the presence of A. ferrooxidans, which positively correlated with the initial addition of Fe2+ and K+ concentrations. The inhibiting effect of K-jarosite coatings on pyrite oxidation was studied by electrochemical measurements, chemical oxidation tests, and bio-oxidation tests. The experimental results showed that the best passivation performance was achieved when 20 mM Fe2+ and 6.7 mM K+ were initially introduced with a bacterial concentration of 4 × 108 cells·mL−1, reducing chemical and biological oxidation by 70 % and 98 %, respectively (based on the concentration of total iron dissolved into the solution by pyrite oxidation). Similarly, bio-oxidation tests of two mine waste samples also showed sound inhibition effects, which offers a preliminary demonstration of the potential applicability of this method to actual waste rock. This study presents a new perspective on passivating the oxidation of metal sulfide tailings or waste and preventing AMD.

Atmospheric leaching of Ni, Co, Cu, and Zn from sulfide tailings using various oxidants

The growing demand for nickel and cobalt increases the interest in extracting metals from secondary sources, such as flotation tailings. A preferential strategy for the processing of the complex and/or low-grade secondary sources may be material integration into existing primary processes. In this research, a robust sulfuric acid leaching treatment was studied for metal extraction from sulfidic flotation tailings (Ni 0.45 %, Co 0.80 %, Cu 0.20 %, Zn 0.58 %). The impact of leaching parameters on metals extraction was studied; oxygen gas (1–2 L/min), ferric ions (0.05–0.3 M), and hydrogen peroxide (0.5–0.8 M), temperature (30–90 °C), sulfuric acid concentration (0.2–2 M), and solid–liquid ratio (50–100 g/L). It was found that after 30-minutes 20.0 % of nickel, 5.6 % of cobalt, and 33.0 % of the main impurity iron were extracted using oxygen as oxidant. Increasing temperature and sulfuric acid concentration were shown to have a positive effect on extraction. Also, with the further addition of ferric ions, cobalt extraction could be slightly increased (from 6.2 % to 8.3 %) whereas both nickel and cobalt could be increased with hydrogen peroxide (nickel 22.9 %, cobalt 14.2 %). However, the use of H2O2 can be challenging due to its high environmental footprint as well as partial decomposition by ferric ions, increasing H2O2 consumption further. The results suggest that the mineralogy of the investigated tailings limited feasible metals extraction using atmospheric conditions up to ≈ 20 % for nickel and ≈ 10 % for cobalt, with nickel distributing stronger into non-refractory minerals while cobalt reported more to pyrite. For other base metals, zinc extraction from sphalerite was shown to be efficient (up to ≈ 90 %) whereas copper extraction was limited (up to ≈ 30 %). In future, such atmospheric sulfuric acid leaching may provide a robust recovery route for non-refractory minerals present in the tailings, while full valorization of sulfide tailings matrix will require higher intensity processing with technologies such as pressure oxidation (POX), concentrated chloride leaching, bioleaching, roasting-leaching or very fine milling of the raw material prior to atmospheric leaching.

Tools to improve mine closure: 10 years of research in integration of environment in the mine life cycle

Abstract Mine closure can be approached by several points of view, from the technical, engineering, ecological, up to social and governance aspects. The definition of a good mine closure should cover most, if not all, of these aspects. This article provides a review of technical and engineering-oriented research work as a partial answer to the question ‘what is good mine closure’. The article presents a ten-year research program realized in the framework of a Canada Research Chair in integration of environment in the mine life cycle. Research projects aimed at better planning mine closure and mine site reclamation from the early stages of a mining project life cycle are exposed as possible steps to strive for optimal mine waste management. At the exploration stage, geo-environmental characterization and modeling are proposed as tools to improve mine waste management planification. During mine operations, environmental desulfurization is suggested as a method to reduce environmental risks associated with sulfidic tailings and waste rock. Indeed, research has shown that acid mine drainage and metal leaching can be significantly limited via desulfurization. At the closure stage, desulfurized tailings can be used to replace at least part of natural materials used for reclamation cover systems. Research work done on other types of mine waste, such as waste rock and water treatment sludge, also show good potential for their reuse as closure material. All these tools can be integrated into the mine life cycle to better plan for closure, which ultimately will make mine closure more sustainable.

Old Sulfidic Ore Tailing Dump: Ground Features, Mineralogy, Biodiversity—A Case Study from Sibay, Russia

The Urals (Russia) are among the largest mining areas in the world, with millions of tons of mine waste deposited. An old sulfidic tailing dump formed over decades of mining activities at the Sibay ore-processing plant is a typical cause of acid mine drainage (AMD) formation, posing a threat to ecosystems of neighboring environments. In this study, the formation of oxidized surface soil layers in four zones of the Sibay tailing dump was revealed, and their chemical–mineralogical and physical–mechanical characteristics were analyzed. According to the results of the metabarcoding of hypervariable regions of the 16S rRNA genes, oxidation in soil layers was associated with the activity of sulfur- and iron-oxidizing acidophiles represented by a few genera: Ferroacidibacillus, Sulfoacidibacillus, Sulfobacillus, and Ferroplasma. The structure of the microbial communities in soil layers differed depending on the zone and depth of sampling. In the samples characterized by the weak oxidation of sulfide minerals, microbial communities were dominated by bacteria of the genus Pseudomonas. The data obtained in this research are of importance to predict the oxidation/leaching processes in mine wastes and their negative environmental impacts in the mining region, as well as to develop technologies for processing these raw materials.

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., “circular” shaped in the talc group, “fine-grained” shaped in the chlorite group, and “donut” shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

A combined compost, dolomite, and endophyte addition is more effective than single amendments for improving phytorestoration of metal contaminated mine tailings

Background and aimsRe-vegetation of mining-impacted landscapes reduces transport of toxic elements while improving soil fertility. This study evaluated whether the planting of a native perennial grass with a consortium of diazotrophic microbial endophytes and municipal waste compost—alone and in combination—enhanced plant growth while stabilizing metal(loids) in dolomite-amended tailings from a historically mined polymetallic mineral deposit.MethodsWe grew Bouteloua curtipendula seedlings in tailings with hazardous concentrations of As, Cd, Pb, Mn, and Zn. We evaluated how plant growth, organic matter accumulation, and major, minor, and trace element mobilization and phytostabilization responded to microbial endophyte and/or compost amendments after the 45-day growth experiment.ResultsAlthough most of the added endophytes were not uniquely identified, the best plant growth and fertility outcomes were achieved with a combination of amendments: dolomite to reduce acidity, compost to increase nitrogen, and a mixed consortium endophyte seed coating to synergistically increase organic carbon and grass biomass yields. Compost reduced shoot and root concentrations—but not yields—of contaminant metals. Endophytes increased foliar Cd, Co, Mn, and Pb yields but mobilized Pb and Zn from the tailings. Root stabilization of Cd, Co, Mn did not require amendments.ConclusionThe most effective means of revegetating these acidic, polymetallic tailings with the native B. curtipendula is with a simultaneous dolomite, compost, and endophyte seed treatment. Due to potential phosphate solubilization and siderophore production by this consortium of endophytes, strategies to capture solubilized metal(loids) may be needed for sulfidic tailings with metal(loids) associated with mobile mineral phases.

Performance of mortar and concrete containing artificial aggregate from cold-bonded sulphidic mine tailings

Repurposing sulphidic tailings in construction products offers a sustainable solution for this mining waste. Aggregates (1–4 mm and 2–8 mm) were produced at pilot scale using cold granulation with minimal cement content (6 wt% CEM III/B + 94 wt% tailings). Superplasticizer dose was optimized in mortar and concrete mixes replacing 17 % and 32 % of natural aggregates. The concretes benefit from the additional buffering capacity from cement hydrates in granules (relevant for carbonation and chloride penetration), but their increased porosity lower freeze–thaw resistance. Cement-based mixes offer a sustainable solution for this waste in applications with moderate or non-structural requirements.

Mechanical activation for sulfidic tailings treatment by tailings: Environmental aspects and cement consumption reduction

Sulfidic mine tailings are one of the massive hazardous solid wastes, containing large amounts of toxic heavy metals. Poor management of tailings can lead to the production of acid mine drainage and the heavy metal transfer emissions into the environment. Thus, in this study, mechanical activation was used to reuse a combination of carbonate tailings (TC) and sulfidic tailings (TS) for concrete construction purposes and to effectively immobilize heavy metals. The results showed that after tailings treatment, the heavy metal leaching rate was significantly below the allowed criteria based on the toxicity characteristic leaching procedure (TCLP). The mercury intrusion porosimetry (MIP) test results on the specific surface area and porosity after the activation pointed out increase and reduction, respectively. In the concrete sample containing 20 % cement-replacing activated tailings, the critical pore diameter after 28 curing days was 60 nm, which was less than that of the control sample with a critical pore diameter of 150 nm. According to X-ray diffraction (XRD) and scanning electron microscopy (SEM), ettringite and calcium silicate hydrate gel acted as hosts for heavy metals ions and played an inevitable role in stabilizing metal pollutants. Results revealed that the compressive strength of the sample containing 20 % of the activated tailings after 28 curing days was 31.2 MPa, which was higher than the strength of the control sample (26.99 MPa). Overall, it was concluded that the combined mechanically activated mine tailings can be a viable substitute for cement (up to 40 %) for constructing concrete samples. The utilized combined approach led to diminish adverse effect of sulfide content in concrete samples besides the cement consumption reduction.

Metals recovery from polymetallic sulfide tailings by bioleaching functional bacteria isolated with the improved 9K agar: Comparison between one-step and two-step processes

Due to the characteristics of simple process, environmental friendliness and low operating costs, biometallurgy has become a popular technology for metals recovering from low-grade ores and tailings. In order to enhance the efficiency of bioleaching functional bacteria acquisition, the 9K agar was optimized by adjusting the ratio of two solutions to achieve better and faster solidification for the functional bacteria growth and isolation. By using the improved 9K agar, six functional stains within genera of Acidithiobacillus ferriphilus, A. ferrooxidans and Leptospirillum ferrooxidans were isolated from the enrichment of acid mine drainage. After the Fe2+ oxidation ability evaluation, three strains of WT1-1, XT2-2, and YT3-1 within the three genera were selected and employed as the individual inoculum for the bioleaching from polymetallic sulfide tailings. Eventually, a maximum leaching efficiency of 58.37% Cu, 53.14% Al, 80.09% Mg, and 76.95% Zn were observed by A. ferriphilus WT1-1 after 28 d. To further improve the bioleaching efficiency, the three strains were mixed proportionally as the inoculum in both one-step and two-step bioleaching processes. Comparing to the pure cultures, the leaching efficiencies of Cu and Mg were significantly enhanced in both one- and two-steps, while no significant change in Zn. By comparing the one- and two-step processes, leaching efficiencies of Al, Mg, and Zn were higher in the one-step process, whereas Cu was observed to be higher in the two-step process. Therefore, the selection on leaching process of one or two steps should be determined based on tailings composition and target metals.

Seasonal hydrology and gas transport in a composite cover on sulfide tailings

This study presents the field performance of a five-layer composite cover to mitigate acid mine drainage in legacy sulfide tailings in northern Ontario, Canada. Installed in 2008, this cover comprised sand, clay, geosynthetic clay liner, sand, and waste rock layers. To evaluate the effectiveness of the cover in reducing water and oxygen ingress, groundwater and vadose zone hydrological characterization, stable water isotope analysis, pore-gas measurements, oxygen flux calculations, and variably saturated flow modeling were conducted. The results indicate that the clay layer stayed nearly saturated in the spring, fall, and winter, but temporary desiccation occurred during the summer. Compared to uncovered tailings, the cover significantly lowered diffusive oxygen flux. In the summer, fall, and winter, the capillary barrier effect of the cover functioned effectively and inhibited percolation. Atmospheric pore-gas oxygen concentrations at one out of the three monitoring locations indicate potential cover imperfections that enabled oxygen transport into the tailings. In the spring and early summer, snowmelt infiltration resulted in percolation that compromised the capillary barrier effect, as well as lateral drainage. The resulting increase in water saturation in the cover limited oxygen transport. Despite potential cover imperfections, this composite cover reduced oxygen and water ingress a decade after installation.