Pyrite Oxidation Process Research Articles

Regional characteristics of groundwater sulfate source and evolution in the multi-layer aquifer system of the northern Shaanxi coal mine base, northwestern China: Evidence from geochemical and isotopic fingerprints

Groundwater sulfate contamination in mining areas has attracted widespread attention. However, deciphering the source and evolution of sulfate in large-scale mining areas remains a challenge due to intense anthropogenic influences and complex hydrogeological conditions. In this study, 94 groundwater samples were analyzed by a combination of self-organizing maps, MixSiar model, multi-isotope analyses (δ34S, δ18OSO4, δD and δ18Owater) and hydrogeochemical methods to investigate the regional characteristics of groundwater sulfate source and evolution in China's largest coalfield (the Shenfuyu Coalfield). The results showed that the source and evolution of groundwater sulfate were controlled by human activities (mining and agricultural activities) and hydrogeological conditions. The groundwater sulfate primarily originated from pyrite oxidation, gypsum dissolution and human inputs. For the mining districts with shallow mining depths, pyrite oxidation and fertilizer contributed to groundwater sulfate. In addition, the ground cracks and abandoned mines controlled the BSR and pyrite oxidation processes. In contrast, the gypsum dissolution and cation exchange dominated the sulfate evolution in the mining districts with deep mining depths due to slow groundwater circulation. This study provided new insights into the source and evolution of groundwater sulfate in large coalfields, as well as references for regional water resource utilization and protection.

Pyrite-activated persulfate to degrade 3,5,6-trichloro-2-pyridyl in water: Degradation and Fe release mechanism

TCP (3,5,6-trichloro-2-pyridinol), the main recalcitrant degradation product of chlorpyrifos, poses a high risk to human health and ecological systems. This study provided a comprehensive exploration of the pyrite-activated persulfate (PS) system for the removal of TCP in water and placed particular emphasis on the pyrite oxidation process that releases Fe. The results showed that the pyrite-activated PS system can completely degrade TCP within 300 min at 5.0 mmol/L PS and 1000 mg/L pyrite at 25 °C, wherein small amounts of PS (1 mmol/L) can effectively facilitate TCP removal and the oxidation of pyrite elements, while excessive PS (>20 mmol/L) can lead to competitive inhibitory effects, especially in the Fe release process. Aimed at the dual effects, the evident positive correlation (R2 > 0.90) between TCP degradation (kTCP) and Fe element release (kFe), but the value of k (0.00237) in the pyrite addition variable experiment was less than that in the PS experiment (k = 0.00729), further indicating that the inhibition effect of excessive addition consists of PS but not notably pyrite. Moreover, the predominant free radicals and non-free radicals produced in the pyrite/PS system were tested, with the order of significance being •OH < Fe (Ⅳ) < SO4•- < •O2− < 1O2, wherein 1O2 emerged as the principal player in both TCP degradation and Fe release from the pyrite oxidation process. Additionally, CO32− can finitely activate PS but generally slows TCP degradation and inhibit pyrite oxidation releasing Fe process. This study provides a theoretical basis for the degradation of TCP using pyrite-activated PS.

Pyrite oxidation: Characteristics of (FeS2O)12 species, a possible reaction intermediate

We evaluated by quantum calculations the properties of pyrite-oxygen species (FeS2O)12 that can appear in the first stages of the oxidation process of pyrite with dissolved oxygen. The calculations were made with the Amsterdam Density Functional software. The obtained results suggest that (FeS2O)12 can be formed only after the dissociation of the oxygen molecule into much more reactive species.

Oxidation mechanism of pyrite in a thiosulfate solution: electrochemical impedance (EIS) and in situ Raman spectroscopy

Ammoniacal thiosulfate has been used lately as an alternative lixiviant for leaching gold from sulfides ores which are not amenable for cyanidation. However, the oxidation of the sulfide minerals generates products that inhibit the dissolution of gold and can promote the degradation of the leaching solution. The complexity of the ammoniacal thiosulfate leaching system has prevented the unification and clarification of the mechanisms of oxidation of sulfide ores used for gold extraction.In this study, a method combining polarization curves, Electrochemical impedance spectroscopy (EIS), and in situ Raman spectroscopy was implemented to investigate the oxidation process of high-purity pyrite. Pyrite samples were dispersed in carbon paste electrode (CPE-Py). The polarization curves of CPE-Py exhibited an increase in current values for overpotentials greater than 0.1 V, indicating the initiation of mineral oxidation processes. Subsequently, a maximum current was observed initially, followed by subsequent decrease, indicating the occurrence of passivation processes on the electrode surface. Hydrodynamic polarization curves demonstrated that the overpotential at which the passivation process occurs is independent of mass transport, suggesting that the passivation products were formed through solid-state transformation.Impedance spectra revealed that at overpotentials below 0.1 V, a partially resolved capacitive semicircle was observed, which was associated with the resistance encountered when charge was transferred between the solution and the surface layer interface. This resistance decreased as the polarization overpotential increased, implying a decrease in charge transfer kinetics. At higher overpotentials (0.3 V–0.4 V), a second capacitive semicircle appeared, linked to the oxidation of one or several species present in the mineral.In situ Raman spectroscopy was utilized to identify the oxidation species of pyrite in ammonia-thiosulfate ((NH4)2S2O3) leaching solution at a pH = 10.2. The composition of the species varied depending on the applied anodic potential. At low anodic potentials (0.1 V), Fe(OH)2 and thiosulfate (S2O32−) were formed, while at high anodic potentials (0.4 V), iron products such as Fe3O4 and γ-FeOOH, as well as sulfide species including thiosulfate, tetrathionates and sulfates (S2O32−, S4O6−2 and SO42−) were formed.

Study on Electrochemical Behavior of Oxidized Pyrite in Alkaline Electrolyte

Nowadays, refractory gold ore production around the world accounts for about 30% of total gold production, and the low leaching rate of such gold concentrate seriously limits the efficient utilization of gold resources. The alkaline preoxidation process can improve the leaching rate of this kind of gold deposit and has good development and application prospects. Therefore, it is of great significance to study the oxidation and dissolution behavior of pyrite in an alkaline environment. In this paper, the oxidation process of gold-bearing pyrite in an alkaline electrolyte was studied using electrochemical techniques, and the oxidation products of a pyrite electrode in an alkaline solution were characterized using XPS, SEM, and other analytical methods. The results show that the optimum pH for pyrite electrochemical oxidative dissolution is about 12, and the oxidation potential of pyrite should be above 0.8 V. In the process of alkaline oxidative dissolution of pyrite, part of the S element enters the electrolyte in the forms of Sx2−, S2O32−, SO32−, and SO42−, and a small amount of the S element is adsorbed on the surface of the electrode in the form of S0 and becomes a part of the passive layer. The Fe element is adsorbed on the surface of the electrode in the forms of Fe(OH)2, Fe2O3, and Fe2(SO4)3, which become the main components of the passivation layer. This study provides a theoretical basis and reference data for the chemical preoxidation treatment of gold-bearing sulfide ores.

Experimental Study on the Oxidation Reaction of Coal-Pyrite and Mineral-Pyrite with the Participation of Fe(III) and Bacteria under Acidic Conditions

As one of the crucial factors contributing to coal spontaneous combustion, the oxidation of pyrite is a complex process involving multiple reactions, particularly in the presence of oxidants (Fe3+ and O2) and bacteria. However, experimental results based on mineral-pyrite are not entirely applicable to coal-pyrite due to their differences in formation environments and compositions. This study selected two types of coal-pyrite and one type of mineral-pyrite as research to conduct oxidation experiments with the participation of oxidant (Fe3+) and bacteria (Acidithiobacillus ferrooxidans), respectively, to obtain the following conclusions. Under natural conditions, the chemical oxidation rate of pyrite is slow, but the addition of oxidant Fe3+ and bacteria can significantly accelerate the oxidation rate. The promotion effect of oxidant Fe3+ on the oxidation reaction is stronger than that of bacteria. Under the same conditions, the oxidation rate of coal-pyrite samples is slightly higher than that of mineral-pyrite, due to the relatively higher impurities content, poorer crystal structure, and humic acid in the coal seams. Additionally, different compositions of coal-pyrite samples can lead to various oxidation degrees under different conditions. Therefore, the oxidation process and mechanism of pyrite in coal seams are complex and affected by many factors, which need further study to prevent coal spontaneous combustion accurately and effectively.

The use of biogenic Fe3+ and H2SO4 generated from pyrite waste to enhance bornite bioleaching: A potential utilization of acid mine drainage

The huge amount of pyrite wastes not only occupy a lot of lands, but its oxidation also releases considerable amounts of ferric iron and acid into the environment to form acid mine drainage (AMD). On the other hand, ferric iron and acid are ideal leaching agents for copper sulfides such as bornite (Cu5FeS4). In this study, the influence of biogenic Fe3+ and H2SO4 generated from pyrite bioleaching on the extraction of copper from bornite was investigated using a two-stage method combining the two bioleaching processes (first pyrite oxidation, then bornite leaching). In the pyrite oxidation process, pyrite bioleaching leachate (PBL) with varying pH and iron concentrations was collected at different times for subsequent bornite bioleaching. The result showed that the bioleaching of bornite was significantly improved in PBL, and the copper extraction of bornite was increased by almost 75 % after bioleaching in PBL with pH of 1.25 and total iron concentration (TFe) of 4 g/L. The results of XRD, SEM and XPS proved that the increase of solution pH during bornite bioleaching would cause the precipitation of iron to form jarosite or schwertmannite on the surface of bornite. Besides, natural acid mine drainage could also improve bornite bioleaching to a certain extent. The finding can provide an important guide for the bioleaching of low-grade copper sulfides as well as the potential utilization of AMD.

Redox Behavior of Secondary Solid Iron Species and the Corresponding Effects on Hydroxyl Radical Generation during the Pyrite Oxidation Process.

During the pyrite oxidation process, aqueous ferrous/ferric ions (Fe2+/Fe3+), as well as surface-adsorbed Fe2+/Fe3+, have been widely recognized to dominate hydroxyl radical (•OH) generation, while this study reveals that the secondary solid iron species also play non-negligible roles. Based on the different forms and the presence of sites, the secondary solid iron species were classified as Fecoat (iron-containing coating on the pyrite surface) and Fedep (ex situ-deposited iron (oxyhydr)oxide that is not in contact with pyrite). Instead of participating in building a stubborn passivation layer on the pyrite surface, Fecoat is easy to fall off from the pyrite surface as the oxidation of pyrite deepens, while large fractions of Fedep and Fecoat are found to be extractable with nitrilotriacetic acid (NTA). Achieved by cyclically oxidizing pyrite within different NTA levels (0/0.1/10 mM), Fecoat and Fedep were proved to have distinct redox behavior during the pyrite oxidation process. Amorphous Fedep, originated from the hydrolyzation of dissolved Fe3+, accelerates the nonradical decay of hydrogen peroxide (H2O2); as a result, the accumulation of Fedep always decreases the •OH production during the pyrite oxidation process. However, part of Fedep adsorbs on the pyrite surface through electrostatic attraction and converts into Fecoat. The electron conduction between Fecoat and pyrite was verified, which accelerates the oxidative dissolution of pyrite, produces reactive Fe(II), and therefore favors •OH generation. This study improves our understanding of the redox behavior of pyrite in complex media such as natural processes and practical engineering systems.

Geochemical processes during hydraulic fracturing in a tight sandstone reservoir revealed by field and laboratory experiments

The application of hydraulic fracturing has transformed tight sandstone gas into a very important global unconventional resource. The accurate description of geochemical processes during hydraulic fracturing can provide essential information for improving tight gas production. In this study, field fracturing and laboratory water-rock interaction experiments were designed and performed in conjunction with geochemistry, isotope, XRF, XRD and SEM techniques to reveal the prevalent geochemical processes. Sixty-five flowback fluid samples were collected from a hydraulic fracturing well and a tight sandstone sample was drilled from gas reservoir to perform water-rock interaction experiments. The results indicate that hydraulic fracturing flowback fluid is a complex mixture, with high TDS values (0.93–33.04 g/L) and heavy isotopes (e.g., mean δ18O of −5.35‰, mean 87Sr/86Sr of 0.714651). Geochemistry and isotope data reveal that the mixing process between fracturing fluid and formation water exerts an important influence on the flowback fluid chemistry, while water-rock and fluid-fluid interactions are also variably important during the hydraulic fracturing process. Pyrite oxidation process is confirmed during hydraulic fracturing in the tight sandstone reservoir, while the addition of gel breaker makes the process prominent. Due to high clay mineral contents (24%), ion exchange and adsorption/desorption are critical factors affecting the stability of the clay minerals during the entire fracturing and flowback processes. Approximately, 20%-43% of the strontium was removed from the solution by ion exchange between the 8 and 44 h intervals of the flowback process. The fractures derived from fracturing connect different types of high salinity formation water, leading to potential mineral precipitation (e.g., barite and calcite). The analysis of formation water needs to be taken into consideration during hydraulic fracturing operations.

Pyrite activated peroxymonosulfate combined with as a physical-chemical conditioner modified biochar to improve sludge dewaterability: analysis of sludge floc structure and dewatering mechanism.

In this study, we proposed an advanced oxidation process of pyrite (FeS2) and peroxymonosulfate (PMS) and prepared a modified polyaluminum chloride biochar (P-BC). The motivation is to use the combination of FeS2 + PMS + P-BC to improve waste activated sludge (WAS) dewaterability. The method to improve the sludge dewatering effect with the combination of FeS2 + PMS + P-BC is as follows: in the first step, pour 0.75 g/g TSS FeS2 and 0.6 g/g TSS PMS into the sludge, and stir for 15 min. Then, add P-BC and stir for 5 min; complete the entire WAS processing process. The vacuum filtration test was used to evaluate the dehydration effect. The water content (Wc) and specific resistance to filtration (SRF) of the raw sludge can be reduced from the original values of 92% and 2.36 × 1013 m/kg to 67% and 9.89 × 1011 m/kg, respectively. The results showed that the combination of FeS2 + PMS + P-BC can effectively improve the sludge dewatering effect through oxidation. A laser particle size analyzer is used to observe changes in sludge particle size. The median diameter of sludge particles increased from 55.37 to 64.56 μm. A zeta analyzer to is used observe changes in sludge zeta potential. The zeta potential of sludge particles increased from − 15.8 to 0.4 mV. In the analysis of extracellular polymeric substances (EPS) of sludge, it was found that protein (PN) and polysaccharide (PS) in EPS decreased significantly. To further analyze the phenomenon of PN and PS drop, excitation-emission-matrix spectra (3D-EEM) was used. To observe the changes of sludge functional group, X-ray photoelectron spectroscopy was used. It was found that FeS2 + PMS + P-BC can destroy the functional groups of sludge, such as O–H, C–C, and O═C—NH– related to proteins and polysaccharides.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-022-21074-4.

The role of Acidithiobacillus ferrooxidans in Fe(II) oxidation of pyrite in bioleaching processes

AbstractBACKGROUNDMicrobial leaching is an emerging ore extraction technology, especially for low‐grade ores. In sulfide and oxide ore bioleaching systems, Acidithiobacillus ferrooxidans is becoming a widely applied microorganism for mineral processing. Many studies are currently focusing on the vital role of A. ferrooxidans in facilitating the efficiencies of sulfur and iron species transformation for sulfide ore bioleaching. Existing research usually investigates the composite action of A. ferrooxidans and Fe(III) for ore bioleaching, the effect of A. ferrooxidans alone being investigated to a lesser extent. An important effect is the role of A. ferrooxidans in the oxidative conversion of Fe(II) in pyrite bioleaching.RESULTSThe oxidative dissolution of pyrite in an imitated A. ferrooxidansbioleaching system was investigated in this work, particularly concerning the effects of bacteria on Fe(II) oxidation of the pyrite. Results of the dissolution performance test, cyclic voltammetry and polarization analysis indicated that the preceding oxidation of Fe(II) has control over the pyrite dissolution rate in the imitated bioleaching system. The semiconductor properties and carrier density of the passivation films of pyrite formed under a variety of conditions indicated that the oxidative leaching of ferrous disulfide is subject to the movement of the holes of the Fe2+species and the oxygen vacancy of H2O at the interface. Acidithiobacillus ferrooxidans promotes pyrite bioleaching by accelerating the preferential oxidation of Fe(II) caused by movement of the electron hole of Fe2+ to H2O at the solid–liquid interface.COCLUSIONThe oxidation process of pyrite in this study turns out to involve hole movement. © 2022 Society of Chemical Industry (SCI).

Study on the Alkaline Oxidation Process of Pyrite

Study on the Alkaline Oxidation Process of Pyrite

Secondary Sulfate Minerals from Thallium Mineralized Areas: Their Formation and Environmental Significance

Thallium is a highly toxic metal and is predominantly hosted by sulfides associated with low-temperature hydrothermal mineralization. Weathering and oxidation of sulfides generate acid drainage with a high concentration of thallium, posing a threat to surrounding environments. Thallium may also be incorporated into secondary sulfate minerals, which act as temporary storage for thallium. We present a state-of-the-art review on the formation mechanism of the secondary sulfate minerals from thallium mineralized areas and the varied roles these sulfate minerals play in Tl mobility. Up to 89 independent thallium minerals and four unnamed thallium minerals have been documented. These thallium minerals are dominated by Tl sulfosalts and limited to several sites. Occurrence, crystal chemistry, and Tl content of the secondary sulfate minerals indicate that Tl predominantly occurs as Tl(I) in K-bearing sulfate. Lanmuchangite acts as a transient source and sink of Tl for its water-soluble feature, whereas dorallcharite, Tl-voltaite, and Tl-jarosite act as the long term source and sink of Tl in the surface environments. Acid and/or ferric iron derived from the dissolution of sulfate minerals may increase the pyrite oxidation process and Tl release from Tl-bearing sulfides in the long term.

Probabilistic Prediction of Acid Mine Drainage Generation Risk Based on Pyrite Oxidation Process in Coal Washery Rejects-A Case Study

In this paper, we investigate a probabilistic approach in order to predict how acid mine drainage is generated within coal waste particles in NE Iran. For this, a database is built based on the previous studies that have investigated the pyrite oxidation process within the oldest abandoned pile during the last decade. According to the available data, the remaining pyrite fraction is considered as the output data, while the depth of the waste, concentration of bicarbonate, and oxygen fraction are the input parameters. Then the best probability distribution functions are determined on each one of the input parameters based on a Monte Carlo simulation. Also the best relationships between the input data and the output data are presented regarding the statistical regression analyses. Afterward, the best probability distribution functions of the input parameters are inserted into the linear statistical relationships to find the probability distribution function of the output data. The results obtained reveal that the values of the remaining pyrite fraction are between 0.764% and 1.811% at a probability level of 90%. Moreover, the sensitivity analysis carried out by applying the tornado diagram shows that the pile depth has, by far, the most critical factors affecting the pyrite remaining

Deep abiotic weathering of pyrite.

Pyrite is a ubiquitous iron sulfide mineral that is oxidized by trace oxygen. The mineral has been largely absent from global sediments since the rise in oxygen concentration in Earth's early atmosphere. We analyzed weathering in shale, the most common rock exposed at Earth's surface, with chemical and microscopic analysis. By looking across scales from 10-9 to 102 meters, we determined the factors that control pyrite oxidation. Under the atmosphere today, pyrite oxidation is rate-limited by diffusion of oxygen to the grain surface and regulated by large-scale erosion and clast-scale fracturing. We determined that neither iron- nor sulfur-oxidizing microorganisms control global pyrite weathering fluxes despite their ability to catalyze the reaction. This multiscale picture emphasizes that fracturing and erosion are as important as atmospheric oxygen in limiting pyrite reactivity over Earth's history.

Getting rid of fool's gold

Geochemistry Pyrite, also called fool's gold, is an iron sulfide mineral that is very commonly found in rock but is almost nonexistent in sediments today. Pyrite oxidizes quickly and is a major source of sulfur to the ocean, but it is also a proxy for the oxygen content historically in Earth's atmosphere. Gu et al. conducted a set of detailed observations of the pyrite oxidation process in a shale unit. The authors found that erosion tied to fracturing is just as important as the oxygen content for the dissolution process. They developed a model that helps determine the conditions in Earth's past for which pyrite might have been stable and the role of microorganisms in the oxidation process. Science , this issue p. [eabb8092][1] [1]: /lookup/doi/10.1126/science.abb8092

Origins and mixing contributions of deep warm groundwater in a carbonate-hosted ore deposit, Sichuan-Yunnan-Guizhou Pb-Zn triangle, southwestern China

Sichuan-Yunnan-Guizhou (SYG) carbonate-hosted Pb-Zn triangle is a world-class metallogenic belt and classified as Mississippi Valley-Type (MVT), which provides the greatest ore production in China. However, little is known about the effects of water-rock interactions involving the ore deposits and the modern hydrologic system. Measured chemical and isotopic compositions of the deep groundwater are used to evaluate water origins, potential circulation depth, reaction temperatures, and mixing process with shallow groundwater to assess possible linkages between regional hydrogeology and ore deposits. Within the Maoping sub-deposit, deep groundwater is warmer (21.2–32.0 °C), has lower pH, higher HCO3− and SO42− concentrations, higher average 87Sr/86Sr ratio (0.7148) and Sr concentration (4.1 mg/L), more positive δ13CDIC values (−4.5 to −4.2‰), and lighter average isotopic value (δD = −98 and δ18O = −13.7‰) relative to shallow groundwater, suggesting an origin distinct from modern surface recharge. The light isotopic composition of the deep warm water indicates recharge at a cooler temperature in the past, perhaps during the Last Glacial Maximum. The δ13CDIC values reflect isotopic equilibrium between deep groundwater and surrounding rocks along with a possible deep source of CO2. The oxidation process of sulfides, including H2S and pyrite linked to the ore-forming processes, could produce sulfuric acid that enhances carbonates dissolution and generates elevated HCO3− and SO42− concentrations. Reaction temperatures for the deep groundwater appear to have been around 50–65 °C based on quartz geothermometers and given a regional geothermal gradient of 24.1 °C/km suggest reactions occurred at depths ~1900 m below the land surface. Elevated Sr concentrations with radiogenic Sr isotope ratios reflect reaction with basement rocks and carbonates during the deep circulation. Sr concentration and isotope mixing models demonstrate different recharge sources and suggest the contribution of deep warm groundwater captured in mine drainage. These results reflect the importance of deep groundwater circulation and reactions in a large ore deposit that may improve understanding of potential effects of these important ore bodies on regional water compositions in the SYG triangle and other MVT ore deposits.

Effect of electrochemical oxidation of pyrite on coal spontaneous combustion

ABSTRACT In order to study the effect of electrochemical oxidation of pyrite in high-sulfur coal on coal spontaneous combustion, the electrochemical oxidation reaction of pyrite in coal was promoted by electrolysis experiments. The FTIR test results show that the content of active groups -OH and -CH2 increases after electrolysis of high sulfur coal. According to the ignition activation energy theory, which can determine the difficulty of spontaneous combustion of coal, the activation energy of coal samples before and after electrolysis was calculated by TG curve. The ignition activation energy of high-sulfur coal after electrolysis treatment is reduced to 0.85 times that of raw coal, and the ignition activation energy of low-sulfur coal remains basically unchanged. The electrochemical oxidation process of pyrite promotes the enhancement of coal polarization and promotes the development of reactive groups, thereby enhancing the activity of coal and promoting the spontaneous combustion of coal. In addition, compared with raw coal, the shortest ignition time of high sulfur coal after electrolysis was shortened by 14 hours, which indicates that the electrochemical oxidation process of pyrite effectively promoted the low temperature oxidation reaction of coal.

Application of lime and compost on the newly established field with acid sulfate soil type in the Belandean experimental field, South Kalimantan for agricultural cultivation

The use of acid sulfate soils for agricultural cultivation is constrained by due to the oxidation process of pyrite (FeS), increasing the solubility of Al and Fe, which causes the pH to be more acidic. The specific strategy needed to utilize acid sulfate soil is through calcification technology combined with in situ organic materials. This study used lime at dose determined by the incubation method and organic materials from composted grey sedge plants, rice straw, and cow dung. The aim of this study was to determine the effect of organic matter on improving the chemical properties of acid sulfate soils. This research was arranged in a completely randomized design with four treatments and three replications. The treatments consisted of control (K0), lime without organic matter (K1), lime and organic matter (K2), and organic matter without lime (K3). The results showed that the application administration of organic matter combined with lime was able to increase the pH and available cations. The highest pH was 4.79 obtained after 14 days of incubation, and the lowest pH was observed in the control treatment, which was 3.47. The highest electrical conductivity (EC) value (76.50 μS) was observed in the K2 treatment, and the lowest EC value was observed in the K0 treatment (92.40 μS). The highest Eh value was found in the K0 treatment, reaching 274.5 mV, and the lowest was observed in K3 treatment, reaching 157.1 mV. There was a positive correlation between pH and EC and a negative correlation between pH and Eh with a value of r = 0.77 ** and r = -0.69 *, respectively.

Oxidation Characteristics of the Reactivity Between Pyrite and Aqueous Arsenate

Natural pyrites contain high levels of adsorbed and structurally incorporated arsenic (As), which may simultaneously result in the release of As and affect the oxidation process of pyrite. However, the oxidation and electrochemical behaviors of As on the oxidation reactivity of pyrites are still not clear. In this study, pyrite was prepared by a hydrothermal method and applied to study the oxidation mechanism between pyrite and aqueous arsenate. Analyses of X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy demonstrate that the as-prepared sample is an octahedron-like pyrite with high purity and crystallinity. The interaction between As(V) and pyrite as well as the electrochemical behaviors of pyrite oxidation in the presence of aqueous arsenate were investigated under acidic conditions by an ion analysis method, cyclic voltammetry (CV), Tafel, and electrochemical impedance spectroscopy (EIS). The results of the chemical reaction indicate that electrons are transferred from S22− to dissolved oxygen with the formation of SO42− in the initial As(V) concentration range of 0–0.3 mmol/L. In the initial As(V) concentration range of 0.4–1.2 mmol/L, electrons are transferred from S22− to As(V) with the formation of elemental S0 and As(III). The CV, the Tafel plot and EIS analyses indicate that aqueous arsenate in an electrolyte promotes oxidation reactivity and passivation of the pyrite electrode. Moreover, the electron transfer rate increases with increasing aqueous arsenate concentration in the electrolyte.