Pyrite Oxidation Research Articles

Hydrogeochemical Behavior of Shallow Groundwater around Hancheng Mining Area, Guanzhong Basin, China

A total of 18 samples of shallow groundwater around the Hancheng mining area in the Guanzhong Basin were collected from 1–4 May 2018. According to the analysis of hydrochemical data, the Gibbs semi-logarithmic diagram and Piper diagram were used to research the hydrogeochemical behavior of shallow groundwater around the Hancheng mining area in the Guanzhong Basin. The results of the groundwater hydrochemical analyses shown on the Gibbs and Piper plots are as follows: The chemical composition analysis showed that the main cation components were Mg2+, Ca2+, Na+, and K+, the anion components were HCO3−, Cl−, and SO42−. A measure of 89% of the groundwater samples in this area were freshwater, the HCO3− were mainly dolomite, calcite, and gypsum dissolved precipitation resulted. Na+ and Cl− came from the dissolution of halite. Most of the groundwater was of the SO4·Cl-Ca·Mg type, accounting for 61.1%. The main ion chemistry of the shallow groundwater in this area is controlled by rock weathering, and pyrite oxidation is a significant factor affecting the SO42− concentration. These research results will help analyze the formation mechanism of chemical components and provide some basic data for the evolution of mine water in this area in the future.

New insights into the mechanism of pyrite oxidation in copper(II)–ammonia–thiosulfate gold leaching system: An Electrochemical, AFM, Raman spectroscopy and XPS investigation

The nontoxicity, low cost, and environmental friendliness of the Cu2+–NH3–S2O32− gold leaching system make it a viable alternative to cyanide-based systems. However, the strong influence of certain sulphide minerals (e.g., pyrite) on the performance of the former system complicates its compositional regulation. Herein, the mechanism of electrochemical pyrite oxidation in the Cu2+–NH3–S2O32− system is probed by electrochemical techniques combined with surface analysis techniques. The results indicate that the anodic oxidation of pyrite can be assigned to active, passive, or transpassive regions, depending on the applied potential, with high potentials accelerating the reactions on the pyrite surface. Thiosulphate concentration is shown to influence the surface properties and the rate of surface reactions of pyrite. AFM images indicated that the morphological changes on the pyrite electrode surface became much rougher with increasing potential. Moreover, Raman spectroscopy and XPS provided strong evidence for the analysis of the surface species of pyrite surface oxidation. Our work will further explain and provide a mechanism for the oxidation of pyrite in the Cu2+–NH3–S2O32− system. More importantly, this study is expected to be able to provide a theoretical basis for guiding the regulation and control of gold leaching reagent in the Cu2+–NH3–S2O32− system.

Geochemical and petrological studies of high sulfur coal and overburden from Makum coalfield (Northeast India) towards understanding and mitigation of acid mine drainage

Opencast coal mining produces trash of soil and rock containing various minerals, that are usually dumped nearby the abandoned sites which causes severe environmental concern including the production of acid mine drainage (AMD) through oxidation pyrite minerals. The current study entailed assessing the potential production of AMD from an opencast coal mining region in Northeast part of India. In order to have a comprehensive overview of the AMD problem in Makum coalfield, the physico-chemical, geochemical, and petrological characteristics of the coal and overburden (OB) samples collected from the Makum coalfield (Northeast India) were thoroughly investigated. The maceral compositions reveal that coal features all three groups of macerals (liptinite, vitrinite, and inertinite), with a high concentration of liptinite indicating the coal of perhydrous, thereby rendering it more reactive. Pyrite (FeS2) oxidation kinetics were studied by conducting the aqueous leaching experiments of coal and (OB) samples to interpret the chemical weathering under controlled laboratory conditions of various temperature and time periods, and to replicate the actual mine site leaching. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was operated to detect the disposal of some precarious elements from coal and OB samples to the leachates during our controlled leaching experiment. The Rare earth element (REE) enrichment in the samples shows the anthropogenic incorporation of the REE in the coal and OB. These experiments reveal the change in conductivity, acid producing tendency, total dissolved solid(TDS), total Iron(Fe) and dissolved Sulfate(SO42−) ions on progress of the leaching experiments. Moreover, the discharge of FeS2 via atmospheric oxidation in laboratory condition undergoes a significant growth with the rise of temperature of the reaction systems in the environment and follows pseudo first order kinetics. A bio-remediative strategies is also reported in this paper to mitigate AMD water by employing size-segregated powdered limestone and water hyacinth plant in an indigenously developed site-specific prototype station. Apart from neutralisation of AMD water, this eco-friendly AMD remediation strategy demonstrates a reduction in PHEs concentrations in the treated AMD water.

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.

Formation processes of groundwater in a non-ferrous metal mining city of China: Insights from hydrochemical and strontium isotope analyses.

Tongling is a significant non-ferrous metal mining city in China, which produces waste that negatively impacts the area's water environment. It is essential to comprehend the hydrochemical properties and formation processes of groundwater to safeguard and utilize it efficiently. We explored major ions, strontium, and its isotopes in water and river-bottom samples from the northern (i.e., A-A' section) and southern (i.e., B-B' section) areas. The hydrochemical facies show the mining activities have a greater impact on surface water than on groundwater. Groundwater hydrochemical formation results from several factors, with water-rock interaction and ion exchange being primary. Additionally, the dissolution of calcite, dolomite, and feldspar, oxidation of pyrite, and hydrolysis of carbonate minerals also impact the formation of groundwater chemistry. Our analysis of strontium and its isotopes indicates that carbonate dissolution primarily occurred in the recharge area; the runoff from the recharge to the discharge area results in the dissolution of certain silicate rocks; calcite dissolution sources account for > 70% contribution in both surface water and groundwater water-rock interactions, whereas silicate rock dissolution sources and dolomite dissolution sources account for < 30%. Due to changed order of dissolved carbonate and silicate minerals during groundwater flow, the distribution of strontium and its isotopes in the A-A' section is opposite to that in the B-B' section. The findings provide a basis for developing, utilizing, managing, and protecting groundwater resources, especially in similar mining areas.

Hydrogeochemical modelling of pyrite oxidation ion mobility in unsaturated mine waste rock piles

Hydrogeochemical modelling of pyrite oxidation ion mobility in unsaturated mine waste rock piles

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

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

Identifying sources of acid mine drainage and major hydrogeochemical processes in abandoned mine adits (Southeast Shaanxi, China).

Acid mine drainage (AMD) has resulted in significant risks to both human health and the environment of the Han River watershed. In this study, water and sediment samples from typical mine adits were selected to investigate the hydrogeochemical characteristics and assess the environmental impacts of AMD. The interactions between coexisting chemical factors, geochemical processes in the mine adit, and the causes of AMD formation are discussed based on statistical analysis, mineralogical analysis, and geochemical modeling. The results showed that the hydrochemical types of AMD consisted of SO4-Ca-Mg, SO4-Ca, and SO4-Mg, with low pH and extremely high concentrations of Fe and SO42-. The release behaviors of most heavy metals are controlled by the oxidation of sulfide minerals (mainly pyrite) and the dissolution/precipitation of secondary minerals. Along the AMD pathway in the adit, the species of Fe-hydroxy secondary minerals tend to initially increase and later decrease. The inverse model results indicated that (1) oxidative dissolution of sulfide minerals, (2) interconversion of Fe-hydroxy secondary minerals, (3) precipitation of gypsum, and (4) neutralization by calcite are the main geochemical reactions in the adit, and chlorite might be the major neutralizing mineral of AMD with calcite. Furthermore, there were two sources of AMD in abandoned mine adits: oxidation of pyrite within the adits and infiltration of AMD from the overlying waste rock dumps. The findings can provide deeper insight into hydrogeochemical processes and the formation of AMD contamination produced in abandoned mine adits under similar mining and hydrogeological conditions.

Rare earth element behaviors of groundwater in overlying aquifers under the influence of coal mining in northern Ordos Basin, China.

Rare earth elements (REEs) have been used as tracers to reveal the hydrochemical sources and processes in groundwater systems that are usually modified by anthropogenic inputs. However, the REE behaviors in groundwater affected by mining activities have yet to be fully understood. In combination of REE geochemistry with general hydrochemical and isotopic (δ2H and δ18O) methods, this study investigated the concentration and fractionation of REEs in alkaline groundwater from two coal mines with similar aquifer lithology but different mining histories in the Northern Ordos Basin. One of the coal mines started mining in March 2009 (Ningtiaota coal mine, NTT), while the other started mining in December 2018 (Caojiatan coal mine, CJT). Results show that the primary hydrochemical type is HCO3-Ca in NTT groundwater with pH value ranging between 7.68 and 8.60, while CJT groundwater was dominated by the HCO3-Na type with higher pH of 9.09-10.00. The average values of ΣREEs were lower, and the NASC-normalized pattern reflected more intense fractionation in NTT groundwater than those in CJT groundwater. The evident differences are caused by the distinctions in water-rock interaction, complexation of inorganic species, and adsorption of REEs in NTT and CJT groundwater. Furthermore, these processes were closely related to the pH of groundwater that was different in two coal mines, which is likely linked to the different durations of coal mining activities that led to differences in development of rock fractures and pyrite oxidation. It is expected that REEs, combined with other indicators such as pH, can be used to trace and help better understand the hydrochemical changes in groundwater caused by mining.

Geochemical evolution of geothermal waters in the Pearl River Delta region, South China: Insights from water chemistry and isotope geochemistry

The Pearl River Delta (PRD) region in South China is abundant of geothermal water resources whereas geochemical evolution of the geothermal water is still poorly understood. In this study, geothermal water is sampled to investigate the provenance of CO2 and sulphate, residence time, recharge elevation, circulation depth, and water-interaction processes by analyzing chemistry of major ions and isotope geochemistry. The range of δ13C and content of bicarbonate reveal multiple sources of soil CO2, carbonate rocks, and small amounts of mantle CO2. The δ34S ratio and sulphate concentration are attributed to evaporites dissolution, input of atmospheric sulphur, seawater intrusion, and oxidation of pyrite. The residence time of up to 21.01 ka for geothermal water likely suggests the earliest precipitation recharge during the Late Pleistocene. Mountains or/and hills at an altitude of 300–760 m in north PRD region are currently the major recharge areas for the geothermal water which can circulate at the depths of up to 3000–4800 m along regional structures. The isotopic and hydrochemical analysis confirms that extensive water interaction with silicate rock, carbonate rock and evaporite, evaporation-crystallization process, and cation exchange are the key mechanisms that control the geochemical evolution of geothermal water in the PRD geothermal system.

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.

Thermodynamic Behavior of Pyrite and Arsenopyrite in Preoxidation for Chlorination Leaching of Refractory Gold Concentrate

Recently, preoxidation is an effective pretreatment method of refractory gold ore, which has been widely used due to the high desulfurization, arsenic removal, low environmental pollution, and rapid reaction rate. In this paper, we describe the thermodynamic considerations of preoxidation of pyrite and arsenopyrite, the main minerals of the refractory gold ore, and the effect of the pressure oxidation, one of the preoxidation processes on the chlorination leaching. The thermodynamic results indicated that arsenopyrite under acidic conditions is easier to oxidize compared to pyrite and the oxidation decomposition of pyrite and arsenopyrite-type gold ore can be considered mainly for pyrite. The experiment has shown that the arsenic removal rate was higher than the desulfurization rate; it is confirmed that the thermodynamic conclusion of the oxidation of pyrite and arsenopyrite was correct. Comparing the XRD, SEM, and EDX analyses of gold concentrate and pressurized oxidation residue, it can be seen that the surface of pressurized oxidation residue is a fine porous structure and the dense and durable structure of sulfide ore is mainly destroyed.

New insights into the effect of EDTA on pyrite oxidation and N2O emission during pyrite autotrophic denitrification

Pyrite autotrophic denitrification (PAD) is crucial for removing nitrate in groundwater and advanced wastewater treatment. While disulfide is typically seen as the electron donor, the role of iron in pyrite oxidation is often ignored. In this study, Ethylene Diamine Tetraacetic Acid (EDTA) had been proven to have the potential to facilitate pyrite oxidation by promoting the solubility of iron in solution, thereby enhancing the kinetics of pyrite autotrophic denitrification. Firstly, EDTA could improve PAD performance, i.e. the nitrate removal rate at EDTA addition of 5 mM was 0.69 mg N/L•h and twice that of the control. However, high concentrations of EDTA inhibited the activity of the nitrous oxide reductase, resulting in the maximum accumulation of N2O reaching 13.26 mg N/L with an EDTA concentration of 15 mM. Furthermore, the X-ray Photoelectron Spectroscopy (XPS) result indicated that the EDTA addition promoted the production of bioavailable sulfur, with the concentration of S0 at 15 mM EDTA being more than twice higher than that of the control. Transmission electron microscopy (TEM) analysis indicated that EDTA could relieve the damage of iron encrustation on cell activity because it was difficult for EDTA-chelated ferrous iron to penetrate the cell membrane. Microbial community analyses showed an increase abundance of iron oxidizing bacteria, suggesting that EDTA addition promoted the bioavailability of iron for Fe(II) autotrophic denitrification. Overall, this study will provide insights into the understanding of oxidation mechanism of PAD process and the practical application for efficient nitrogen removal and N2O mitigation.

Microbially-mediated aerobic oxidation of trace element-bearing pyrite in neutral-pH sandstone aquifer sediments

Disseminated pyrite grains in sandstone aquifer sediments are subject to microbially-accelerated reaction with dissolved oxygen, leading to more rapid decline in pH and release of trace elements to solution compared to abiotic reaction pathways.

Rock Pigeon Cave, Colorado: development and mineralogy

The late Cretaceous Mancos Shale in western Colorado contains several vadose caves developed entirely within the shale. The largest of these, Rock Pigeon Cave, is over 300 m in length and contains a seasonal stream. The cave, and others like it, is hypothesized to develop as a result of the oxidation of disseminated pyrite in the shale by descending meteoric water with resulting sulfate ions reacting with the carbonate component of the shale to produce gypsum. The gypsum pries apart the shale, increasing its secondary porosity, and allows flowing water to remove shale particles via corrasion. As these particles are removed, they are transported down-gradient to an outlet, allowing continuous openings (cave passages) to develop. Extensive sulfate mineralization is observed within the cave and takes several forms: soft globular deposits on rocks at water level, a white to tan crust on shale surfaces, dry crusts on the passage floor following evaporation of pools, and needle and hair-like extrusions on passage walls. Powder X-ray diffraction (XRD) indicates that these deposits are a mixture of thenardite and blodite with lesser amounts of gypsum, hexahydrite, and konyaite. Na+, Mg2+, and SO4 2- ions in the entering stream are the source of the sulfate minerals at stream level and on the wetted slopes above. These come out of solution as the cave stream and pools evaporate with sulfates precipitating as saturation is reached. Fibrous, needle-like sulfates on walls above the wetted zone are a result of crystallization by evaporation: fluids containing sulfate ions are extruded and evaporate at the rock/air interface. Other minerals, e.g., deposits containing goethite and jarosite, are seen on passage walls as reaction products from oxidation of pyrite in the shale.

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.

Reactive transport modelling of tailings hydrogeochemistry under a composite cover

Quantitative forecasts of acid mine drainage (AMD) production are important for remediation planning. Reactive transport simulations corresponding to a detailed sampling location at a covered legacy tailings impoundment in northern Ontario, Canada, were conducted to quantitatively assess the predominant hydrogeochemical reactions. The simulations span the period from the end of tailings deposition (circa 1970) to early 2020, 12 years after remediation by a five-layer composite cover. The conceptual model of uncovered tailings weathering and subsequent geochemistry of the covered tailings system was implemented in 1D using the multi-component reactive transport code MIN3P. Transient monthly infiltration, post-cover boundary condition changes, and a dynamic temperature regime were incorporated. The shrinking core model, including parallel O2(aq) and Fe3+ oxidation reactions for the waste rock in the cover and the underlying tailings, was implemented to simulate the oxidation of As-bearing pyrite, chalcopyrite, and sphalerite. Primary carbonate and aluminosilicate host minerals promoted acid-neutralization reactions. Precipitation of secondary phases and sorption/desorption of Cu, Zn, and arsenite were incorporated into the model. The overall agreement between key simulated and field-measured post-cover aqueous geochemical parameters suggests that the conceptual model captured the primary hydrogeochemical processes in the covered tailings. A lack of reliable data on initial tailings mineralogy and pre-cover hydrogeochemistry increased simulation uncertainty. Simulated reaction rates indicate that where intact, the cover decreased sulfide oxidation rates by both O2(aq) and Fe3+ and improved pore-water quality over time. Simulation results indicate that elevated concentrations of Zn and As are likely to persist in the tailings regardless of cover performance, whereas concentrations of Cu and Al are the parameters most sensitive to cover effectiveness.

Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Restoration of open-pit mines may utilize waste rock for landscape reconstruction, which can include the construction of backfill aquifers. Weathering and contaminant transport may be different in backfill aquifers compared to the surrounding aquifer because of newly available mineral surfaces and transportable nano- to micro-scale particles generated during mining. Waste rock from the Cordero Rojo open-pit coal mine in the Powder River Basin was exposed to benchtop leachate experiments for 20 weeks at temperatures of 5 °C and 20 °C. Collected leachate was analyzed for Eh, pH, specific conductance, alkalinity, and cation and anion concentrations as unfiltered and 0.45-μm and 0.2-μm filtered concentrations. During the experiment, leachate Eh and pH substantially varied during the first 55 days, which corresponds to a period of high specific conductance (&gt;1000 µS/cm) and alkalinity (&gt;200 mg/L). Correspondingly, anion and cation concentrations were the largest during this early weathering stage, and the filter fractions indicated multiple forms of transported elements. After this early weathering stage, column leachate evolved towards a weathering equilibrium of neutral, oxidizing, and low solute conditions indicated by positive Eh values, pH near 7, and specific conductance &lt;500 μS/cm. This evolution was reflected in the decline and stabilization or non-detection of metal(loid) concentrations reflective of a shift to primarily bulk aluminosilicate weathering when coal- and salt-associated elements, such as arsenic, cadmium, and selenium, were not detected or at minimal concentrations. Over the course of the experiment, the solute trend of certain elements indicated particular weathering processes—cadmium and nanoparticle transport, selenium and salt dissolution, and arsenic and pyrite oxidation. The mining of overburden formations and use of the waste rock for backfill aquifers as part of landscape reconstruction will create newly available mineral surfaces and nanoparticles that will weather to produce solute concentrations not typically found in groundwater associated with the original overburden.

Facet-Dependent Productions of Reactive Oxygen Species from Pyrite Oxidation.

Reactive oxygen species (ROS) are widespread in nature and play central roles in numerous biogeochemical processes and pollutant dynamics. Recent studies have revealed ROS productions triggered by electron transfer from naturally abundant reduced iron minerals to oxygen. Here, we report that ROS productions from pyrite oxidation exhibit a high facet dependence. Pyrites with various facet compositions displayed distinct efficiencies in producing superoxide (O2• -), hydrogen peroxide (H2O2), and hydroxyl radical (•OH). The 48 h •OH production rates varied by 3.1-fold from 11.7 ± 0.4 to 36.2 ± 0.6 nM h-1, showing a strong correlation with the ratio of the {210} facet. Such facet dependence in ROS productions primarily stems from the different surface electron-donating capacities (2.2-8.6 mmol e- g-1) and kinetics (from 1.2 × 10-4 to 5.8 × 10-4 s-1) of various faceted pyrites. Further, the Fenton-like activity also displayed 10.1-fold variations among faceted pyrites, contributing to the facet depedence of •OH productions. The facet dependence of ROS production can greatly affect ROS-driven pollutant transformations. As a paradigm, the degradation rates of carbamazepine, phenol, and bisphenol A varied by 3.5-5.3-fold from oxidation of pyrites with different facet compositions, where the kinetics were in good agreement with the pyrite {210} facet ratio. These findings highlight the crucial role of facet composition in determining ROS production and subsequent ROS-driven reactions during iron mineral oxidation.

Experimental timing of pyrite oxidation under various leaching conditions: consequences for rates of weathering in geological profiles

Pyrite (FeS2) is one of the most abundant sulfides on Earth and has already been studied in numerous ways for decades because of its rapid oxidation and the associated environmental impacts. This study proposes a new experimental physico-chemical approach (air, tridistilled water and water drip exposure) to determine the oxidation rate of pyrite using surface and depth data via XPS (X-ray Photoelectron Spectroscopy) analyses. Our experimental study of almost pure pyrite reveals a maximum oxidation rate of 11.7 ± 1.8 nm day−1 for drip exposure with precipitation of sulfates or Fe-oxides depending on the experimental condition. The oxidation rates obtained under various experimental conditions may be extrapolated to weathering rates of different zones of supergene profiles/ores (leached zone, saprolite and cementation zone). The extrapolation suggests a maximum rate of 4.3 ± 0.6 m Ma−1, which is consistent with data obtained by isotope dating of weathering profiles. Under geological conditions however, the oxidation rate of pyrite may be influenced by additional parameters, such as the nature of the host rock, its porosity/permeability, the climate, the influence of an oxidizing environment, and the mineralization of secondary minerals.