Control Acid Mine Drainage Research Articles

Passivation of metal sulfides by a marine bacterium for acid mine drainage control

Acid mine drainage originates from metal sulfides oxidation, which results in acidic metal-rich leachate. In this study, a novel and environmentally friendly approach was demonstrated to passivate pyrite and lead-zinc tailings, respectively. The key to this approach is to develop biofilms of the marine bacterium Qipengyuania flava S1. Biofilms can induce biomineralization, thereby isolating metal sulfides from air and water. The stability and biological toxicity of the bio-passivation layers were evaluated by leaching bio-passivated pyrite or tailings in initially acidic H2O2 solutions with shaking for 180 days and then cultivating Brassica chinensis and Allium cepa with the leachates. Our results showed that after passivation, the amount of iron released by pyrite decreased by at least 99.2 ± 0.2 (in wt%). For lead-zinc tailings after passivation, the released metal ions (Fe+Al+Pb+Zn) decreased by at least 52.0 ± 3.2 (in wt%). The bio-passivation layers also maintained the pH of the leachate in the range of 7.5–8.0. Before bio-passivation, compared with mineral water, the pyrite leachate significantly inhibited the growth of the two plants, and the tailings leachate significantly inhibited the growth of A. cepa, whereas the bio-passivated pyrite or tailings leachate did not show any inhibitory effect.

Applewood Biochar at Different Smoldering Conditions Passivates Pyrite by Promoting the Formation of Jarosite.

To control acid mine drainage (AMD) from the source, a new environmentally and green passivator (biochar) has been introduced to passivate pyrite. To reduce the difficulty of biochar preparation and cost, and improve its production scale, in-situ pyrolysis of applewood by smoldering to produce biochar. Here, particle size, moisture content and gas flow rate were selected to prepare biochar by smoldering through orthogonal combination, and the pyrite was passivated with different conditions and biochar concentrations (2g/L, 3g/L, 4g/L). The results revealed that when the particle size is 200mm×200mm×20mm, the water content is 20-30%, and the gas flow rate is 0.4L/m3, the biochar yield is the highest. Biochar promotes the formation of passivating layer (jarosite), inhibits the release of metal ions. Increasing biochar concentration can promote the formation of jarosite and enhance the passivation effect on pyrite.

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.

Modeling the influence of forest vegetation and climate change on the long-term performance of a cover with capillary barrier effects used to control acid mine drainage: the Lorraine case study

ABSTRACT The Lorraine mine site in Témiscamingue region (Québec, Canada) was reclaimed with a cover with capillary barrier effects (CCBE) to limit acid mine drainage generation. The main objective of this study is to predict the long-term hydrogeological behaviour of the CCBE at Lorraine site, including the influence of vegetation and climate change (CC). Numerical simulations showed that performance of the CCBE is: (1) not affected by forest vegetation and CC in the saturated zone in the north of the Lorraine site and (2) more sensitive to vegetation in the unsaturated zone in the south where the phreatic level is low.

Effect of Freeze–Thaw and Wetting–Drying Cycles on the Hydraulic Conductivity of Modified Tailings

Mine tailings have shown viability as the fine–grained layer in a capillary barrier structure for controlling acid mine drainage in a circular economy. Their saturated hydraulic conductivities (ksat) under wetting–drying cycles and freeze–thaw cycles remain unexplored. In this study, modified tailings with a weight ratio of 95:5 (tailings/hydrodesulfurization (HDS) clay from waste–water treatment) and an initial water content of 12% were used. The ksat of specimens was measured after up to 15 wetting–drying cycles, each lasting 24 h, with a drying temperature of 105 °C. The ksat for wetting–drying cycles decreased from 3.9 × 10−6 m/s to 9.5 × 10−7 m/s in the first three cycles and then stabilized in the subsequent wetting–drying cycles (i.e., 5.7 × 10−7 m/s–6.3 × 10−7 m/s). Increased fine particles due to particle breakage are the primary mechanism for the ksat trend. In addition, the migration of fines and their preferential deposition near the pore throat area may also promote this decreasing trend through the shrinking and potentially clogging–up of pore throats. This could be explained by the movement of the meniscus, increased salinity, and, subsequently, the shrinkage of the electrical diffuse layer during the drying cycle. Similar specimens were tested to measure ksat under up to 15 freeze–thaw cycles with temperatures circling between −20 °C and 20 °C at 12 h intervals. Compared to the untreated specimen (i.e., 3.8 × 10−6 m/s), the ksat after three freeze–thaw cycles decreased by 77.6% (i.e., 8.5 × 10−7 m/s) and then remained almost unchanged (i.e., 5.6 × 10−7 m/s–8.9 × 10−7 m/s) in subsequent freeze–thaw cycles. The increased fine grain content (i.e., 3.1%) can be used to explain the decreased ksat trend. Moreover, the migration of fines toward the pore throat area, driven by the advancing and receding of ice lens fronts and subsequent deposition at the pore throat, may also contribute to this trend.

Alumina inhibits pyrite oxidative dissolution by regulating solid film passivation layer and S, Fe, and Al speciation transformation

The oxidation of pyrite results in the formation of a solid film passivation layer on its surface. This layer effectively hinders the direct interaction between H2O, O2, and the pyrite surface, thereby impeding the oxidation dissolution of pyrite. There are few studies on whether alumina (Al2O3), a common aluminum-containing oxide, affects the formation of a solid film passivation layer on the surface of pyrite and inhibits the oxidation dissolution of pyrite. This research investigates the impact of Al2O3 incorporation on the speciation transformation of S, Fe, and Al on the surface of pyrite during oxygen pyrite process. The oxidation of pyrite followed the “polysulfide-thiosulfate” complex oxidation pathway. When <1.5 g/L Al2O3 was introduced, it increase pyrite oxidation, whereas ≥1.5 g/L Al2O3 prevented pyrite oxidation. The process of Al2O3 dissolution results in the consumption of H+ and the subsequent release of Al3+. This, in turn, facilitates the hydrolysis of Fe3+ and Al3+ to generate a secondary mineral layer on the pyrite surface. As a result of the accumulation of S promotes the formation of polysulfide chemical (FeSn) or iron deficiency sulfide (Fe1-xS), resulting in the formation of a solid film passivation layer composed of sulfur film and secondary mineral layer. The results demonstrated that Al2O3 can promote the formation of a solid film passivation layer on the surface of pyrite, which has significant implications for controlling the oxidation dissolution process of pyrite and offers a new perspective for the source control of acid mine drainage.

Inputs and transport of acid mine drainage-derived heavy metals in karst areas of Southwestern China

Heavy metal pollution caused by acid mine drainage (AMD) is a global environmental concern. The processes of migration and transformation of heavy metals carried by AMD are more complicated in karst areas where carbonate rocks are widely distributed. Water, suspended particulate matter (SPM), and sediments are the crucial media in which heavy metals migrate and it is important to elucidate the geochemical behavior of AMD heavy metals in these environments. This study tracked AMD heavy metals from release to migration and transformation in a natural river system in a karst mining area. AMD directly impacted the hydrochemical composition of the karst water environment, but the carbonate rock naturally neutralized the acidity of the AMD. AMD heavy metal concentrations decreased gradually after the tributaries from the mining area entered the main river, with the metals tending to accumulate in SPM and sediments. The forms in which heavy metals were present were influenced by pH and their relative concentrations. Raman spectroscopy and transmission electron microscopy of sediments from the mining area suggested that the presence of an iron phase plays an important role in the fate of AMD-derived heavy metals. It is, therefore, necessary to elucidate the mechanisms of iron phase precipitation from sediments in order to control AMD-derived heavy metals in karst mining areas. This study improves our understanding of the geochemical behavior of heavy metals in karst environments and provides direction for the prevention and control of AMD in affected areas.

A strategy for source control of acid mine drainage by intelligent management of mine wastes

For mine site management, the release of acid and heavy metal ions from sulfur-containing waste rock or tailings (principally chalcopyrite and pyrite) under natural deposit conditions is a major environmental problem. In this study, the interaction between chalcopyrite and pyrite at different mass ratios under a simulated acid mine drainage environment was investigated. The dissolution experiments showed that a low proportion of pyrite promotes chalcopyrite dissolution, while a high proportion inhibits dissolution. However, this phenomenon is weakened by the presence of microorganisms. In addition, the combined characterization by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy indicated that a high ratio of pyrite incorporation facilitated the formation of passivation layers on the chalcopyrite surface. Scanning electron microscopy results show that many oxidation etching pits are found on the surface of the chalcopyrite residues surface in a low ratio of pyrite addition, whereas numerous islands are observed and tightly wrapped around the surface of the chalcopyrite residues surface in a high ratio of pyrite addition. The current work presents a viable, practical approach to tailings stacking that reduces the release of the heavy metal ions copper and acid through the appropriate proportioning of ores.

Source control on the acid mine drainage produced by the oxidation of pyrite and sulfur-containing uranium tailings based on the microbially induced carbonate precipitation technology

Large quantities of acid mine drainage (AMD) generated through the oxidation of sulfide-bearing minerals, particularly pyrite, pose a significant global environmental challenge. The implementation of efficient and fundamental governance methods is crucial as current conventional approaches fail to address the root cause of this problem. To investigate the technique of controlling AMD at its source, a 10-day static experiment was conducted in order to examine the inhibitory effect of Sporosarcina pasteurii (S. pasteurii) on oxidative acid production from pyrite under varying redox potentials (Eh) and Ca2+ concentrations. Additionally, a 180-day dynamic column experiment was carried out to assess the long-term stability of its inhibition and heavy metal fixation. The results of both short-term and long-term analysis indicate that the metabolic activity of S. pasteurii has beneficial effects on the control of AMD through sulfur oxidation, even in the presence of strong oxidants such as H2O2 and FeCl3. 1. It stabilizes pH within the neutral to alkaline range; 2. It maintains Eh at a low potential reducing environment; 3. It promotes an increase in SO42− concentration, followed by a decline and stabilization at lower concentrations; 4. It supplies carbonate for pyrite oxidation, maintaining a balance between acid production and consumption. Additionally, SEM, XRD, and XPS results demonstrated that the mineral surface appeared flat without prominent characteristic peaks of oxidation products, indicating effective inhibition of pyrite oxidation by S. pasteurii. The immobilization experiments for heavy metals showed that Cd exhibited the highest fixation effect with a rate of 94%; Mn, Cu, Zn, and Co had the second best fixation effect with ion concentrations decreasing by 82%, 83%, 87%, and 88% respectively; Ni and U(VI) decreased by rates of 75% and 69% respectively. These experimental findings suggest that S.pasteurii can effectively inhibit pyrite oxidation as well as sulfur-containing uranium waste rock oxidation while providing long-term stabilization for heavy metal immobilization.

The geochemical processes affecting the mobility of Cu, Pb, Zn during phytostabilization on sulfidic mine tailings revealed by a greenhouse study

Sulfidic mine tailings have the potential to release toxic metals into the surrounding environment. Phytostabilization can stabilize these toxic metals in the rhizosphere, providing a sustainable method for mine reclamation. However, previous research has not examined the inorganic geochemical processes in the rhizosphere that are significant for controlling acid mine drainage. Therefore, a greenhouse study was conducted to explore the geochemical processes affecting the mobility of Cu, Pb, and Zn through the establishment of phytostabilization on sulfidic mine tailings. The mineralogy of substrates before and after experiments and the changes in metal concentrations and pH of the drainage were analyzed. The results showed that at the end of the experiments, pH of pot substrates with plants became acidic (pH ranging from 2.59 to 3.77), the concentrations of Cu, Pb, and Zn in the drainage increased (up to 20.14 mg/L of Cu, 2.28 mg/L of Pb, and 3199.87 mg/L of Zn), leading to the generation of acid mine drainage. It was concluded that, in addition to the sulfide oxidation, two other acidification processes played a role: the decomposition of organic matter and the release of roots exudates, in decreasing pH and increasing metal concentrations in the drainage from amended tailings. The acidity in the rhizosphere was neutralized sequentially through the following geochemical processes: (1) dissolution of carbonates, (2) dissolution of Al&Fe (oxy)hydroxide, and (3) silicates weathering. The long-term reliability of phytostabilization can be achieved by re-applying amendments to initiate these neutralization processes. This research has filled the research gap regarding the geochemical mechanisms controlling the migration of metals in the rhizosphere during phytostabilization with two grass species (Pascopyrum and Lolium multiflorum). It provides a valuable reference for designers and engineers when considering metal immobilization in sulfidic mine tailings through the technique of phytostabilization during mine reclamation and closure stage.

Inhibition of Microbial Pyrite Oxidation by PropS-SH for the Control of Acid Mine Drainage

Inhibition of Microbial Pyrite Oxidation by PropS-SH for the Control of Acid Mine Drainage

A clay-coal fly ash based dual hydraulic-reactive liner for controlling acid mine drainage.

Hydraulic liners are used to restrict hazardous leachates such as acid mine drainage (AMD) from entering the hydrogeological system. In this study, we hypothesized that: (1) a compacted mix ratio of natural clay and coal fly ash with a hydraulic conductivity of at most 1 × 10- 8 ms- 1 can be achieved, and (2) mixing clay and coal fly ash in the right proportion can result in increased contaminant removal efficiency of a liner system. The effects of adding coal fly ash to clay on the mechanical behavior, contaminant removal efficiency, and saturated hydraulic conductivity of the liner were investigated. All clay:coal fly ash specimen liners with less than 30% coal fly ash had significantly (p < 0.05) lower cohesion stress values, and were discarded without further tests. Saturated hydraulic conductivity values showed no significant effect (p > 0.05) on the results of clay:coal fly ash (7:3) specimen liners and compacted clay liner. The clay:coal fly ash mix ratios of 8:2 and 7:3 significantly (p < 0.05) reduced the leachate concentration of Cu, Ni, and Mn. The pH of AMD increased from an average of 2.14 to 6.80 after permeating through a compacted specimen of mix ratio 7:3. Overall, the 7:3 clay to coal fly ash liner showed superior pollutant removal capacity and its mechanical and hydraulic properties were comparable to compacted clay liners. This laboratory scale investigation emphasizes potential limitations with column scale evaluation of liners and provides new information on the application of dual hydraulic reactive liners for engineered hazardous waste disposal systems.

Hydrophobic modification of pyrite with a composite of sodium oleate and SiO2 nanoparticles to inhibit its oxidation for controlling acid mine drainage

The formation of acidic mine drainage (AMD) is mainly due to the oxidation of pyrite in the presence of water. In this study, the environmentally friendly Sodium oleate (SO) was used as hydrophobic agent and SiO2 nanoparticles were added as a filler material to modify pyrite. Na-oleate and nano-SiO2 nanoparticles form a hydrophobic passivation film directly on the pyrite surface in a very simple process.Excellent antioxidant capacity was achieved with the addition of 6% SO and 1 wt% SiO2 at a reaction temperature of 70 °C. Chemical leaching experiments and electrochemical experiments were used to characterise the antioxidant properties of this hydrophobic passivated film. The results showed that the pH of the leachate could be maintained above 5.7, a 2.6 increase over raw pyrite. In addition, the reduction rate of SO42- and total Fe concentration could reach over 83.69% and 97.91%, respectively. SO-SiO2-treated pyrite exhibits lower oxidation rates in electrochemistry and an increased contact angle of 70.1° compared to pristine pyrite. Finally, this paper details the mechanism of the action of SO-SiO2 on the surface of pyrite by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The results show that sodium oleate can combine with iron ions to form iron oleate wrapped on the surface of pyrite, while silica nanoparticles attach to pyrite by physical adsorption, filling the pores on the surface of hydrophobic film layer and effectively protecting pyrite from oxidation.

Performance and mechanisms of PropS-SH/Ce(dbp)3 coatings in the inhibition of pyrite oxidationtion for acid mine drainage control

Inhibition of tailings oxidation could availably control the generation of acid mine wastewater from its source. Organosilanes serving as a high-efficiency inhibitor of the oxidation of pyrite, bring some problems including safety hazards caused by large amounts of organic solvents, difficult high-temperature curing, poor long-term properties, and so on. In our work, the PropS-SH/Ce (dbp)3 (PS/Ce (dbp)3) passivator with excellent passivation performance and self-healing properties was prepared by choosing 3-mercaptopropyltrimethoxysilane (PropS-SH) and dibutyl phosphate (Ce (dbp)3) as the main passivating agent and the repair agent, respectively. We reduced the ratio of ethanol to water by adjusting the pH of the organosilane condensation and also achieved room-temperature curing by extending the curing time. Electrochemical and chemical leaching experiments results showed that the most appropriate addition of Ce (dbp)3 was 0.2 wt% for enhancing the passivation performance of the passivated coating. In a 6-month chemical leaching experiment, the PS/Ce (dbp)3-0.2 passivation coating cured at room temperature showed a better passivation effect and maintained 90.55% and 78.54% of total Fe and SO42− passivation efficiencies. The passivation and self-healing mechanisms were investigated by FT-IR, XPS, 29Si NMR, and other characterization methods, which were as follows: silane formed a cross-linked mesh structure by Si–O–Si bonding, in which Ce (dbp)3 was physically filled. And the Si–OH on the surface of the passivation film formed Fe–O–Si bonds with the hydroxyl groups on the surface of the pyrite, thus attaching to the surface of the pyrite and isolating the oxidation medium. When the passivation coating was locally damaged, the oxidation reaction caused a change in pH, which accelerated the dissolution of Ce (dbp)3 in the passivation layer. Ce3+ underwent a valence change and formed a CeO2 precipitate, while dbp− could form a complex with Fe2+ on the pyrite surface, both of which worked together to repair the broken passivation coating and prevent the oxidation reaction.

Suppression of pyrite oxidation by co-depositing bio-inspired PropS-SH-tannic acid coatings for the source control acid mine drainage

In previous works, both tannic acid (TA) and organosilane-based passivators have been proven to possess good inhibition effects on pyrite oxidation, which could effectively prevent acid mine drainage (AMD) generation at the source. However, the hydrophilicity of TA passivation film and the complex coating process of organosilane-based passivators (high temperature conditions were required during the process carried out) may limit their further practical use. Therefore, to achieve the purpose of better coating treatment of pyrite under mild conditions, TA and γ-mercaptopropyltrimethoxysilane (PropS-SH) were introduced to synergistically passivate pyrite in this work. Electrochemistry tests and chemical leaching experiments both confirmed that PropS-SH-TA coated pyrite had better oxidation resistance than raw pyrite and single PropS-SH or TA coated pyrite. Additionally, the analyses of scanning electron microscopy (SEM) measurements and static water contact angle tests demonstrated that a scaly coating was formed on PropS-SH-TA coated pyrite surface, which may be the reason for the significant improvement of its surface hydrophobicity. Finally, the study on the film-forming mechanism of PropS-SH-TA composite passivator displayed that the benzoquinone derivatives formed by TA could copolymerize with PropS-SH through Michael addition or Schiff base reaction, which constructed a dense hydrophobic film on pyrite surface. The newly formed composite film could provide a better oxidation barrier for pyrite based on TA passivation film.

Straw Biochar at Different Pyrolysis Temperatures Passivates Pyrite by Promoting Electron Transfer from Biochar to Pyrite

To control acid mine drainage (AMD) at source, biochar, a new green and environmentally friendly passivator has been introduced to passivate pyrite. However, the raw material and pyrolysis temperature largely determine the physical and chemical properties of biochar, the causal relationship between biochar and pyrite and the underlying mechanism are still unknown. Here, biochar materials (rice-straw biochar (RSB) and sugarcane bagasse biochar (SBB)) at different pyrolysis temperatures (300–600 °C) were utilized for the passivation of pyrite. The results of our investigations revealed that the passivation ability of RSB was superior to that of SBB. The addition of RSB with higher pyrolysis temperatures could greatly enhance the passivation efficiency of pyrite. RSB-500 (produced at a pyrolysis temperature of 500 °C) achieved the best passivation effect on pyrite. RSB can form Fe-O bonds through C=O bonding with pyrite. Moreover, the addition of RSB created a reducing environment in the mixture system because of its strong electron-donation capacity (EDC) and altered the energy-band structure of pyrite, which promoted the transfer of electrons from biochar to pyrite. On the contrary, the addition of SBB did not result in the formation of Fe-O bonds with pyrite. In addition, the EDC of SBB was also lower than that of RSB and it had almost no effect on the band structure of pyrite. Hence it did not alter the direction of the electron migration. These findings shed light on the mechanism of biochar passivation of pyrite and provide a theoretical foundation for selecting suitable biochar materials for AMD prevention at source.

A new organosilane passivation agent prepared at ambient temperatures to inhibit pyrite oxidation for acid mine drainage control

Acid mine drainage (AMD) is a significant environmental problem caused by the oxidation of pyrite and other metal sulfide ores. Organosilane passivation is an effective strategy to inhibit pyrite oxidation. However, synthetic organic silane passivation agents generally require temperatures of 50–80 °C, resulting in high energy consumption and high synthesis cost. In this study, a 3-aminopropyltrimethoxysilane -methyltrimethoxysilane (APS-MTMS) coatings was successfully prepared at ambient temperatures of 15–40 °C as a passivation agent to inhibit pyrite oxidation. Chemical leaching tests were used to study the inhibition performance of APS-MTMS for pyrite oxidation. The experimental results showed that the release of the total Fe from APS-MTMS-coated pyrite was 11.31 mg/L after chemical oxidation for 7 hours, and the passivation rate can reach 77.78%. The contact angle of the APS-MTMS-coated pyrite was significantly larger (140.4°) than that of the bare pyrite (58.8°), indicating that APS-MTMS prompted the formation of a superhydrophobic surface of pyrite, improving the oxidation resistance. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied to probe the interaction mechanism of APS-MTMS with pyrite. The results indicated that APS accelerated the Si–O–Si formation by amino protonation and enriched a crosslinked network of Si–O–Si and Fe–O–Si on the pyrite surface to prevent pyrite oxidation. This study provides a novel method for preparing organosilane passivation materials at ambient temperatures for AMD control.

An integrated management strategy for acid mine drainage control of sulfidic 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 CaCO3/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.

Alternative flotation collectors for the environmental desulfurization of gersdorffite (NiAsS) bearing mine tailings: Surface chemistry

Environmental desulfurization by froth flotation is a promising technique for the control of acid mine drainage (AMD) and has already been applied in a wide variety of mining operations to prevent environmental risks. This paper aims to address the flotation challenges of gersdorffite for environmental purposes. Gersdorffite, a Ni-As-sulfosalt (NiAsS) frequently encountered in many gold mine wastes, is a major source of contamination. Gersdorffite surface characterization was conducted using diffuse reflectance infrared fourier transform (DRIFT) spectroscopy and optical microscopy, to gain a better understanding of the physicochemical evolution of the mineral surface. The main parameters evaluated were the impact of air-oxidation (aging) and the effect of pH at different values using different reagents (soda ash (NaOH) and lime (CaO)) on the mineral surface chemistry. Collector adsorption behavior was also studied using four collector types as alternatives to xanthate, mainly based on dithiophosphates (DTP) and mercaptobenzothiazole (MBT). Dry grinding of the gersdorffite generated a thin and heterogeneous particle coating mainly composed of arsenic oxides (arsenite and arsenate) and nickel sulfates (NiSO4), with minor elemental sulfur. Hydroxylated Ni species (Ni-OH) were also observed. MBT molecules were found to be the most active compound responsible for the adsorption of the collectors as demonstrated by the adsorption isotherms and the DRIFT spectra. The results of this study have led to a better understanding of gersdorffite surface chemistry before and after the collector adsorption, which should impact its flotation behavior.

Effects of abandoned coal mine on the water quality

ABSTRACT Improving effective strategies to control acid mine drainage (AMD) in abandoned mine areas is a significant challenge because of water quality issues. AMD is a serious water pollution problem. The water in the area where the mine is located acquires an acidic character, the pH level of the environment decreases, the concentration of heavy metals increases with their dissolution in the acidic environment, and can cause serious environmental pollution by creating a toxic effect for all living things. However, acidic characteristics are not observed in the waters at high pH levels; a basic environment is formed; the heavy metal dissolution slows down; and the precipitation of minerals begins. In such an environment, it is not possible to observe AMD formation and heavy metal pollution. If AMD source is characterized, the most effective strategies can be developed to control the acidic effluents. The main aim of this work was to investigate the potential impact of Ovacik abandoned, coal mine (Cankiri, Turkey) on the water quality in the areas around the mine. Water samples were collected along the open pit area (abandoned), dump sites and coal storage area. Effluent characterizations were investigated for the better evaluation of the water contamination level to develop the successful treatment strategies. In the studies conducted in the same field in 2010–2011, it was determined that the water pH changes between 6.64 and 8.13. Similarly, in this study, the results showed that the pH values of water streams in the abandoned mine were measured between 7.28 and 8.94 with no heavy metal contamination. Although the coal deposit exhibits AMD source minerals, the rock formations which have alkaline content prevented AMD in the considered site.