Oxidation Of Metal Sulfides Research Articles

Remediation of AMD based on hydrogeochemical zonation: A typical metal mine in China

Mining activities disrupt the natural oxidative balance underground, increasing the oxidation of metal sulfides like pyrite. This process leads to the formation of highly acidic mine drainage (AMD) with elevated concentrations of iron (Fe) and sulfate (SO42−). However, generic plugging and backfilling methods, when applied without considering the specific post-mining oxidative environments of different metal mines, often yields minimal results. To clarify the distribution of the underground redox environment after mining of a metal mine in Dexing, China, fifteen water samples from flood and dry periods, as well as fifteen borehole samples, were collected for hydrogeological and chemical analysis. For the first time, the study proposed that the redox zone could be identified and delineated through vertical analysis of water storage media, mineral composition, and hydrochemical characteristics. A hydrogeochemical cause model was constructed, revealing that AMD formation primarily occurs in oxidative and transition zones. Based on the redox zone characteristics of the study area, actual engineering sealing was performed on the oxidation and transition zones of cavity No. 23. As a result, the pH increased from 2.5 before remediation to 4.5, indicating a reduction in acidity. The concentrations of SO42− and Fe significantly decreased, reducing from 1360.0 mg/L and 147.0 mg/L before treatment to 726.0 mg/L and 23.6 mg/L after treatment; the total decrease amounting to 46.6 % and 84.0 %, respectively. The concentrations of Mn and Cu similarly, decreased by 10.7 % and 15.6 %, respectively. This study provides a novel approach and valuable reference for the refined identification and classification of redox zones after metal mine exploitation, as well as for the targeted plugging and treatment of cavities that produce AMD.

Alunogen from the sulfate efflorescence of the Stone Town Nature Reserve in Ciężkowice (the Outer Carpathian Mountains, Poland)

Alunogen (Al2(SO4)3∙17H2O), a rare secondary mineral, has been found in the efflorescence on sandstones from the Stone Town Nature Reserve in Ciężkowice, southeastern Poland. This is probably the first find of this salt on such rocks in Poland. Alunogen forms in various geological environments, but mainly from the oxidation of pyrite and other metal sulfides in ore deposits and Al-rich Earth materials under low-pH conditions. Its crystallization at this particular site depends on a set of necessary physicochemical (pH, concentration), climatic (season, temperature, humidity), site-related (location and protection of efflorescence), and mineralogical (the presence of pyrite) conditions. This paper presents the mineralogical and geochemical characteristics of the alunogen from the Stone Town Nature Reserve (based on SEM-EDS, XRPD, EPMA and Raman spectroscopy methods) as well as of the efflorescence itself (based on XRPD and STA coupled with QMS and FTIR for the analysis of gas products). Crystals of alunogen take the shape of flakes, often with a hexagonal outline, clustered in aggregates forming a cellular network. Its calculated formula is (Al1.96Fe3+0.01)Σ1.97(SO4)3∙17H2O (based on 12 O and 17 H2O). The unit-cell parameters refined for the triclinic space group P1 are: a = 7.423 (1) Å, b = 26.913 (5) Å, c = 6.056 (1) Å, a = 89.974 (23)°, b = 97.560 (25)°, g = 91.910 (22)°. The Raman spectra (SO4) bands are: intensive 995 cm−1 (ν1); low-intensive 1069, 1093 and 1127 cm−1 (ν3); low-intensive 419 and 443; medium-intensive 470 cm−1 (ν2); and medium-intensive 616 cm−1 (ν4). Those at 530, 312 and at 338 cm−1 are assigned to water vibrations and those at 135, 156, 180 cm−1 to the lattice modes. Although the efflorescence contained an admixture of other minerals (pickeringite, gypsum and quartz), the predominant alunogen is almost chemically pure and the above parameters are consistent with the values reported in the literature for alunogen from different locations and of various origins.

Gallionella and Sulfuricella populations are dominant during the transition of boreal potential to actual acid sulfate soils

Acid sulfate soils release metal laden, acidic waters that affect the environment, buildings, and human health. In this study, 16S rRNA gene amplicons, metagenomes, and metatranscriptomes all demonstrated distinct microbial communities and activities in the unoxidized potential acid sulfate soil, the overlying transition zone, and uppermost oxidized actual acid sulfate soil. Assembled genomes and mRNA transcripts also suggested abundant oxidized acid sulfate soil populations that aligned within the Gammaproteobacteria and Terracidiphilus. In contrast, potentially acid tolerant or moderately acidophilic iron oxidizing Gallionella and sulfur metabolizing Sulfuricella dominated the transition zone during catalysis of metal sulfide oxidation to form acid sulfate soil. Finally, anaerobic oxidation of methane coupled to nitrate, sulfate, and ferric reduction were suggested to occur in the reduced parent sediments. In conclusion, despite comparable metal sulfide dissolution processes e.g., biomining, Gallionella and Sulfuricella dominated the community and activities during conversion of potential to actual acid sulfate soils.

Microbial diversity response to geochemical gradient characteristics on AMD from abandoned Dashu pyrite mine in Southwest China.

The formation and release of acid mine drainage (AMD) have caused extremely serious pollution in the environment around many mining areas. The biological oxidation of metal sulfide minerals causes the production and release of AMD. To understand the interaction mechanism between microbial and AMD, the study uses Southwest Dashu pyrite as an example to investigate the geochemical gradient characteristics and microbial diversity response on AMD from abandoned mine. Through collecting and testing the water samples, the geochemical parameters such as physical and chemical indexes, main ion composition and microbial community composition of seven mine drainage points were obtained. The results showed that the geochemical and microbial community structure the decrease of AMD pollution in the study area with the decrease of altitude has obvious gradient characteristics. Although AMD has the distribution of acid-resistant iron and sulfur bacteria oxidizing bacteria, the microbial community diversity has obvious gradient characteristics. The categories with a relative abundance of > 5% include Proteobacteria, Actinobacteriota, Firmicutes, WPS-2, Chloroflexi, Bacteroidota, and Acidobacteriota. Actinobacteriota, which was common in the AMD, was distributed throughout the samples. The correlation analysis between water quality parameters and microbial community showed that the microbial community structure was affected by environmental factors. With the increase of acidity and metal ion content, the diversity of microbial community decreased, and the content of acid-resistant iron and sulfur oxidizing bacteria increased. The results showed that pH, dissolved oxygen (Do), the total iron (Fe) content (TFe), SO42-, and Al3+ were the five parameters that most affected microbiological diversity and interaction. Hydrogeochemistry and major ions analysis revealed that AMD in the study area mainly comes from the biological oxidation of metal sulfides and the dissolution and cation exchange of other minerals around the deposit. The degree of AMD pollution is related to the hydrogeochemical conditions in the mine. The higher the mine's water level, the lower the pollutants, and the less AMD is produced and released. The findings confirmed that geochemical gradients significantly changed the biota of the mine water and enriched the related microbial diversity adapted to different environmental factors. Therefore, the findings provide strong support for mine containment to inhibit oxidation and lay the foundation for prevention and control strategies of AMD pollution sources.

Genesis of the Daping Gold Deposit in the Middle Xuefeng Mountain Area, Southern China: Constraints from Geochemistry, Fluid Inclusion, and H-O-S Isotope

The medium-sized Daping gold deposit is located in the middle Xuefeng Mountain area of Southern China with gold ores hosted in sericite phyllite, sericitolite, and mylonite. The auriferous quartz-carbonate-sulfide veins and adjacent alteration rocks are structurally controlled within the NE (northeast) shear zone with NE, NNE (north-east-east), and NW (northwest) trending at high inclination angles. The petrogeochemistry analysis results show that the gold ores are characterized by high content values of SiO2, S, and As and low content values of Al2O3 and Na2O and display strong enrichment of LREE with δEu values ranging from 0.54 to 0.75. Four stages of mineralization/alteration were identified: the first stage has mineral assemblages of quartz+pyrite+arsenopyrite±carbonate minerals, the second stage has mineral assemblages of quartz+polymetallic sulfide minerals (pyrite, arsenopyrite, chalcocite, galena, chalcopyrite, tetrahedrite)±chlorite±carbonate minerals, the third stage has mineral assemblages of quartz and carbonate minerals, and the supergene stage is characterized by limonite±patina which were formed by the oxidation of metal sulfides. Among them, the first stage and the second stage are the main gold mineralization stages. The ore-forming fluid inclusions in quartz are mainly composed of liquid phase (H2O) and gas phase (H2O and CO2), and based on the microthermometric analysis, the first metallogenic stage and second metallogenic stage yielded average homogenization temperature of 184.5 and 255.8°C and average salinity of 7.64 wt.% NaCl eqv. and 11.35 wt.% NaCl eqv., respectively. Thus, the ore-forming fluids belong to H2O-CO2-NaCl, medium-low temperature, and medium-low salinity fluid. The δ D H 2 O and δ 18 O H 2 O values of auriferous quartz are from -51‰ to 62‰ and from -1.44‰ to 5.42‰, respectively, indicating that the ore-forming fluids may belong to mixing fluids of the magmatic fluid and meteoric hydrothermal fluid. The values of δ34S of metal sulfides range from -0.94‰ to 1.98‰ (-0.131‰ in average), implying that sulfur may source from the concealed granite and/or basement metamorphic strata. The Daping gold deposit formed in the Indosinian period under the tectonic environment of compression between the Cathaysian plate and Yangtze plate and may belong to orogenic gold deposits.

Obtaining elemental sulfur for Martian sulfur concrete

A potential candidate material for the construction of Mars habitats is concrete made from the Martian regolith and sulfur extracted from the regolith itself. Sulfur concrete, which has excellent mechanical properties, can be prepared at a low temperature (<150 °) and without water (unlike Portland-cement concrete). The surface of Mars has a much higher concentration of sulfur than those of the Earth, the Moon, or the asteroids. Sulfur on Mars, however, exists not as elemental sulfur—which is needed in concrete production—but as sulfates (usually hydrated) and sulfides. This paper surveys thermochemical and electrochemical methods that might be used to produce elemental sulfur from its compounds contained in the minerals on Mars. Possible methods include chemical or electrochemical oxidation or decomposition of sulfides, which include sulfides that exist naturally on Mars as well as sulfides that are produced via chemical or electrochemical reduction of sulfates. Some of the methods to obtain elemental sulfur—such as chemical or electrochemical oxidation or decomposition of metal sulfides or hydrogen sulfide—have already been demonstrated. The methods of producing elemental sulfur from sulfur-containing minerals on Mars will have the added benefit of generating byproducts (e.g. water, hydrogen, oxygen, and metals) that are useful for explorations of the Red Planet. In the future, chemical processes for the production of elemental sulfur may also have important industrial applications on Earth.

Acceleration of acid mine drainage generation with ozone and hydrogen peroxide: Kinetic leach column test and oxidant propagation modeling

Uncovered mine tailings may result in environmental stresses such as severe acidification and heavy metal discharge to adjacent watercourses. These problems originate in metal sulfide oxidation, which results in acidic metal-rich leachate, known as acid mine drainage (AMD) that persists over time. Sulfides in mine tailings can persist for centuries. Thus, accelerating the sulfur oxidation process can help mitigate this problem. In this study, the use of ozone and hydrogen peroxide to increase the leaching of coal mine tailings was investigated in detail. One of the biggest challenges when using oxidizers is determining the acting plume. To this end, the decomposition kinetics of oxidants were studied when contacting mine tailings. Additionally, a mathematical model was developed to predict the subsurface propagation of the oxidizers used. In the group where ozone was applied, there was a 62% reduction in sulfur content, while the corresponding reduction in the control group was only 18%. The results indicated that ozone and hydrogen peroxide increased metal leaching, and decreased ecotoxicity compared to a control group. The kinetic rates were dependent on the saturation of coal mine tailings. Furthermore, the spread model contributed to oxidation plume determination. For ozone, it was observed that for a kinetic rate of -0.2669∙CO30.7899 mol·m−3·s−1, a 60% increase in pressure causes the ozone plume to increase the effective transport distance by 30%. This paper presents an innovative strategy for mitigating AMD.

Dredging and deposition of metal sulfide rich river sediments results in rapid conversion to acid sulfate soil materials

Sediments along the Baltic Sea coast can contain considerable amounts of metal sulfides that if dredged and the spoils deposited such that they are exposed to air, can release high concentrations of acid and toxic metals into recipient water bodies. Two river estuaries in western Finland were dredged from 2013 to 2018 and the dredge spoils were deposited on land previously covered with agricultural limestone to buffer the pH and mitigate acid and metal release. In this study, the geochemistry and 16S rRNA gene amplicon based bacterial communities were investigated over time to explore whether the application of lime prevented a conversion of the dredge spoils into acid producing and metal releasing soil. The pH of the dredge spoils decreased with time indicating metal sulfide oxidation and resulted in elevated sulfate concentrations along with a concomitant release of metals. However, calculations indicated only approximately 5% of the added lime had been dissolved. The bacterial communities decreased in diversity with the lowering of the pH as taxa most similar to extremely acidophilic sulfur, and in some cases iron, oxidizing Acidithiobacillus species became the dominant characterized genus in the deposited dredge spoils as the oxidation front moved deeper. In addition, other taxa characterized as involved in oxidation of iron or sulfur were identified including Gallionella, Sulfuricurvum, and Sulfurimonas. These data suggest there was a rapid conversion of the dredge spoils to severely acidic soil similar to actual acid sulfate soil and that the lime placed on the land prior to deposition of the spoils, and later ploughed into the dry dredge spoils, was insufficient to halt this process. Hence, future dredging and deposition of dredge spoils containing metal sulfides should not only take into account the amount of lime used for buffering but also its grain size and mixing into the soil.

Genesis of the Daping Gold Deposit in the Middle Xuefeng Mountain Area, Southern China: Constraints from Geochemistry, Fluid Inclusion, and H-O-S Isotope

The medium-sized Daping gold deposit is located in the middle Xuefeng Mountain area of Southern China with gold ores hosted in sericite phyllite, sericitolite, and mylonite. The auriferous quartz-carbonate-sulfide veins and adjacent alteration rocks are structurally controlled within the NE (northeast) shear zone with NE, NNE (north-east-east), and NW (northwest) trending at high inclination angles. The petrogeochemistry analysis results show that the gold ores are characterized by high content values of SiO2, S, and As and low content values of Al2O3 and Na2O and display strong enrichment of LREE with δEu values ranging from 0.54 to 0.75. Four stages of mineralization/alteration were identified: the first stage has mineral assemblages of quartz+pyrite+arsenopyrite±carbonate minerals, the second stage has mineral assemblages of quartz+polymetallic sulfide minerals (pyrite, arsenopyrite, chalcocite, galena, chalcopyrite, tetrahedrite)±chlorite±carbonate minerals, the third stage has mineral assemblages of quartz and carbonate minerals, and the supergene stage is characterized by limonite±patina which were formed by the oxidation of metal sulfides. Among them, the first stage and the second stage are the main gold mineralization stages. The ore-forming fluid inclusions in quartz are mainly composed of liquid phase (H2O) and gas phase (H2O and CO2), and based on the microthermometric analysis, the first metallogenic stage and second metallogenic stage yielded average homogenization temperature of 184.5 and 255.8°C and average salinity of 7.64 wt.% NaCl eqv. and 11.35 wt.% NaCl eqv., respectively. Thus, the ore-forming fluids belong to H2O-CO2-NaCl, medium-low temperature, and medium-low salinity fluid. The and values of auriferous quartz are from -51‰ to 62‰ and from -1.44‰ to 5.42‰, respectively, indicating that the ore-forming fluids may belong to mixing fluids of the magmatic fluid and meteoric hydrothermal fluid. The values of δ34S of metal sulfides range from -0.94‰ to 1.98‰ (-0.131‰ in average), implying that sulfur may source from the concealed granite and/or basement metamorphic strata. The Daping gold deposit formed in the Indosinian period under the tectonic environment of compression between the Cathaysian plate and Yangtze plate and may belong to orogenic gold deposits.

Mechanistic insights into trace metal mobilization at the micro-scale in the rhizosphere of Vallisneria spiralis

Mobilization of trace metals in the rhizosphere of macrophytes is controlled by root-driven chemical changes, especially the steep gradients of O2 and pH from the rhizosphere to bulk sediments. Here, the O2 and pH dynamics, and the distribution of trace metal, in the rhizosphere of Vallisneria spiralis were obtained using planar optodes and diffusive gradients in thin films, respectively. Radial O2 loss (ROL) and acidification occurred on all visible roots of V. spiralis and exhibited highly spatiotemporal dynamics depending on the root growth and various environmental conditions. Trace metals showed different mobilization mechanisms in the rhizosphere. ROL and produced Fe(III) (oxyhydr)oxides decreased the mobility of Fe, As, Co, V and W in the rhizosphere. However, Mn, Ni and Cu exhibited greater mobility in the rhizosphere than bulk sediments as a result of the oxidation of metal sulfide and proton-induced dissolution of minerals. In particular, Co and Ni presented increased activity at the interface between rhizosphere and bulk sediment, which was attributed to the redox dissolution processes of Fe and Mn as a result of ROL and rhizosphere acidification. These results provide new insights into the roles of macrophyte root-induced O2 and pH changes in controlling trace metal mobility in sediments.

Erratum to: Surface oxidation of transition metal sulfide and phosphide nanomaterials

Erratum to: Surface oxidation of transition metal sulfide and phosphide nanomaterials

Metal contamination pathways of a restored marshland in an industrial estuary

Contaminated surface sediments were removed from a coastal marsh and replaced with clean engineered sediments before marsh vegetation was replanted and the site was reopened to the tide. Differences in trace metal concentrations (Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn) were monitored for 11 years at different sediment depths, under two types of engineered sediments (with and without compost), and at three marsh surface elevations. Except for Hg and Cd, all others followed the patterns of Fe and Mn of decreasing concentration during drought years and increasing concentration during wet years. Metals in deep sediments (> 25 cm) are always higher than on the surface. Surfaces higher in the terrain had fewer metal concentrations compared to lower elevations. The compost treatment had no insignificant effect on metal concentration. The main pathways involved in remobilization from the buried legacy sediments are organic metal complexation, reductive dissolution, and oxidation of metal sulfides. Hg showed an enrichment pattern throughout the study period suggesting atmospheric deposition as the main pathway. Similarly, sources of Cd are most likely from atmospheric wet deposition since most of the Cd variation is explained by changes in the amounts of rain. Metal concentration in the sediments decreased up to 50% from pre-restoration conditions; the only exceptions were Hg and Cd which continue to accumulate. Increasing dry periods and storm frequencies from changing global weather patterns have the potential to create conditions for greater bioavailability of metals from this and similar world estuaries.

Release and fate of pyritic sulfur in chemical looping combustion

Chemical-looping combustion (CLC) technology is an attractive solution for efficient fuel conversion with inherent separation of the greenhouse gas CO2. Sulfur is a major consideration in coal utilization, and pyrite is the major inorganic sulfur contaminant in most coals, therefore the release and fate of pyritic sulfur in the CLC process was investigated. A natural iron ore, and two synthetic materials (CuO/SiO2 and NiO/Al2O3) produced by the impregnation method were selected as oxygen carriers to investigate the effect of oxygen carrier on the sulfur distribution. Results showed that SO2 was the major sulfurous gas released, and a small amount of H2S and CS2 was escaped from the reactor in the reduction stage. The fractions of sulfur converted to gaseous substances in this stage were 90.38%, 82.22%, and 78.00% when using iron ore, CuO/SiO2, and NiO/Al2O3 respectively. Part of sulfur was stored in the oxygen carrier, and the presence of metal sulfides was confirmed by X-ray diffractometer (XRD). In the reoxidation stage, SO2 was produced by the oxidation of metal sulfides. The fraction of sulfur converted to gaseous species in this stage reached 2.26%, 11.84%, and 15.42% for iron ore, CuO/SiO2, and NiO/Al2O3 respectively. The accumulation of sulfur on the surfaces of three oxygen carriers was all detected by the Energy dispersive X-ray spectroscopy (EDX).

Characterization of an acid rock drainage microbiome and transcriptome at the Ely Copper Mine Superfund site.

The microbial oxidation of metal sulfides plays a major role in the formation of acid rock drainage (ARD). We aimed to broadly characterize the ARD at Ely Brook, which drains the Ely Copper Mine Superfund site in Vermont, USA, using metagenomics and metatranscriptomics to assess the metabolic potential and seasonal ecological roles of microorganisms in water and sediment. Using Centrifuge against the NCBI “nt” database, ~25% of reads in sediment and water samples were classified as acid-tolerant Proteobacteria (61 ± 4%) belonging to the genera Pseudomonas (2.6–3.3%), Bradyrhizobium (1.7–4.1%), and Streptomyces (2.9–5.0%). Numerous genes (12%) were differentially expressed between seasons and played significant roles in iron, sulfur, carbon, and nitrogen cycling. The most abundant RNA transcript encoded the multidrug resistance protein Stp, and most expressed KEGG-annotated transcripts were involved in amino acid metabolism. Biosynthetic gene clusters involved in secondary metabolism (BGCs, 449) as well as metal- (133) and antibiotic-resistance (8501) genes were identified across the entire dataset. Several antibiotic and metal resistance genes were colocalized and coexpressed with putative BGCs, providing insight into the protective roles of the molecules BGCs produce. Our study shows that ecological stimuli, such as metal concentrations and seasonal variations, can drive ARD taxa to produce novel bioactive metabolites.

Microbial succession during the transition from active to inactive stages of deep-sea hydrothermal vent sulfide chimneys

BackgroundDeep-sea hydrothermal vents are highly productive biodiversity hotspots in the deep ocean supported by chemosynthetic microorganisms. Prominent features of these systems are sulfide chimneys emanating high-temperature hydrothermal fluids. While several studies have investigated the microbial diversity in both active and inactive sulfide chimneys that have been extinct for up to thousands of years, little is known about chimneys that have ceased activity more recently, as well as the microbial succession occurring during the transition from active to inactive chimneys.ResultsGenome-resolved metagenomics was applied to an active and a recently extinct (~ 7 years) sulfide chimney from the 9–10° N hydrothermal vent field on the East Pacific Rise. Full-length 16S rRNA gene and a total of 173 high-quality metagenome assembled genomes (MAGs) were retrieved for comparative analysis. In the active chimney (L-vent), sulfide- and/or hydrogen-oxidizing Campylobacteria and Aquificae with the potential for denitrification were identified as the dominant community members and primary producers, fixing carbon through the reductive tricarboxylic acid (rTCA) cycle. In contrast, the microbiome of the recently extinct chimney (M-vent) was largely composed of heterotrophs from various bacterial phyla, including Delta-/Beta-/Alphaproteobacteria and Bacteroidetes. Gammaproteobacteria were identified as the main primary producers, using the oxidation of metal sulfides and/or iron oxidation coupled to nitrate reduction to fix carbon through the Calvin-Benson-Bassham (CBB) cycle. Further analysis revealed a phylogenetically distinct Nitrospirae cluster that has the potential to oxidize sulfide minerals coupled to oxygen and/or nitrite reduction, as well as for sulfate reduction, and that might serve as an indicator for the early stages of chimneys after venting has ceased.ConclusionsThis study sheds light on the composition, metabolic functions, and succession of microbial communities inhabiting deep-sea hydrothermal vent sulfide chimneys. Collectively, microbial succession during the life span of a chimney could be described to proceed from a “fluid-shaped” microbial community in newly formed and actively venting chimneys supported by the oxidation of reductants in the hydrothermal fluid to a “mineral-shaped” community supported by the oxidation of minerals after hydrothermal activity has ceased. Remarkably, the transition appears to occur within the first few years, after which the communities stay stable for thousands of years.8HEoUqvqhha4gXuyieWpP_Video

Unraveling Polymorphic Pyrrhotite Electrochemical Oxidation by Underlying Electronic Structures

Metal sulfide oxidation is a common, yet poorly understood, phenomenon that significantly affects surface properties. In this paper, we studied the electrochemical oxidation of polymorphic pyrrhotites (Fe1–xS) to gain insights into the relationship between their electrochemical oxidation rate and electronic structures. Surface composition of oxidized pyrrhotites, as shown by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS), suggested that one key step for pyrrhotite oxidation is the outward diffusion of metal cations to form polysulfide and oxides. This diffusion process involves the rupture of Fe–S bonds and, hence, depends on the Fe–S bond strength. According to the ToF-SIMS, the Fe–S bond strength in the defective layer (>100 nm), the layer right underneath the polysulfide layer (∼20 nm), was modified by the incorporation of oxygen atoms, which mainly existed in the form of OH– and H2O. It was found that oxygen anions are much more abundant in the def...

DFT + U and Low-Temperature XPS Studies of Fe-Depleted Chalcopyrite (CuFeS2) Surfaces: A Focus on Polysulfide Species

The initial release of cations upon oxidation of metal sulfides commonly produces a metal-deficient surface and undersurface layers, which should greatly affect the properties of materials but are still poorly understood. We employed density functional theory + U simulation of chalcopyrite (012) and (110) surfaces with up to a half of surface iron removed together with X-ray photoelectron spectroscopy (XPS) of fast-frozen chalcopyrite oxidized in aqueous solutions. It was calculated that the centers comprising tri- or pentasulfide anions or tri- and disulfide complexes have the negative formation energy of 1.2–1.5 eV per one extracted Fe atom, while defects with disulfide anions are disadvantageous. The surfaces are typically “metallic” with comparable densities of S sp and Cu 3d states at the Fermi level. Upon performing cryo-XPS studies, it was found that sulfide surfaces depleted in iron but not in copper, and polysulfide anions Sn2– with n ≥ 5 arose. As oxidation progresses, a deficit of Cu occurs, an...

Microbial oxidation of metal sulfides and its consequences

Microbial oxidation of metal sulfides and its consequences

Selected trace elements and metals in groundwater within Permian sediments near Olkusz (Zn-Pb ore mining region, S Poland)

The extensive mining of Zn-Pb ores in the Olkusz region resulted in significant changes of both water table level and chemical composition of water in all aquifers in the area. This was caused by intensive dewatering of mining excavations and development of a thick aeration zone reaching 150 m in a central part of the area. That created favorable conditions for oxidation of metal sulfides occurring in the ore-bearing dolomites (Middle Triassic) and started the process of forming readily soluble hydroxysulphates which then migrated to lower aquifers, including the Permian. As a result of those processes, various metals and other elements toxic to the water environment appeared in leaks observed in mine galleries. Changes in concentrations of selected elements (Fe, Mn, Zn, Pb, Cu, Ba, Ni, Co, As, Cr, Hg, Tl, Ag, Cd, B) in mine waters over the period of the last nearly 50 years were described. Water samples were collected from exploratory boreholes, piezometers, and wells located in investigated area inflows and seepages occurring in shafts and drifts excavated in Permian conglomerates. Mean concentrations of metals (Pb, Cd, Cr, Hg, Tl) and other toxic elements were surprisingly low; Pb, 3.94 μg/L; Cd, 0.2 μg/L; Cr, up to 2.26 μg/L; Hg, 0.25 μg/L; Tl, 3.59 μg/L; and As, 6.31 μg/L. However, the observed concentrations varied significantly over time, reaching respectively up to 190 μg Pb/L, 60 μg Cd/L, 15.6 μg Cr/L, 2.67 μg Hg/L, 81.3 μg Tl/L, and 155 μg As/L.

Collaborative effects of Acidithiobacillus ferrooxidans and ferrous ions on the oxidation of chalcopyrite

In recent decades, the bioleaching of chalcopyrite has been successfully developed and employed in copper hydrometallurgy. Understanding the decomposition mechanism of chalcopyrite is also of great significance for environmental remediation because the microbial oxidation of metal sulfides in mining waste and outcrop rocks commonly causes serious environmental contamination. This study investigates the influence of Acidithiobacillus ferrooxidans (A. ferrooxidans) and added Fe2+ ions on the oxidation of chalcopyrite. The results show that A. ferrooxidans and added Fe2+ ions can collaboratively promote the recovery of Cu from chalcopyrite. In the bioleaching system with added Fe2+ ions, A. ferrooxidans prefer to oxidize soluble Fe2+ ions rather than decompose chalcopyrite to acquire energy, which inhibits the release of Cu at the first stage but enhances the growth of A. ferrooxidans. After reacting for 18 days, however, the produced Fe3+ ions greatly promote decomposition and release more Cu than the bioleaching system free of Fe2+, which remained in the rest experiments. Both the oxidation of chalcopyrite and the release of Cu in the bioleaching system are greater than what occurs in the chemical leaching system. Chalcocite, covellite, bornite, and elemental sulfur were identified as intermediate products, and a sulfur transforming route of S2−/S22− → Sn2−/S0 → SO32− → SO42− can be recognized by X-ray photoelectron spectroscopy. As the principle end product, jarosite covered the chalcopyrite grains and consequently inhibited further oxidation. It is noteworthy that the released Cu2+ ions barely suppressed the growth of A. ferrooxidans because they tended to be enriched only in extracellular polymeric substance (EPS), while Fe3+ ions could be found on both the cell surfaces and the EPS, which implies a potential mechanism for the survival of cells in a high Cu2+ solution. Collectively, an integrated model of chalcopyrite oxidation, collaborated by both chemical and microbial oxidation, has been proposed to elucidate the bioleaching mechanisms and to give a perspective on its hydrometallurgical and environmental applications.