Mechanisms Of Pyrite Oxidation Research Articles

Electrochemical Oxidation Mechanism of Pyrite in a Copper(II)-Citrate-Sodium Thiosulfate Composite System

Pyrite is an important gold carrier during gold leaching, but it is readily oxidized, which causes environmental problems such as acidic mine drainage. Thus, it is necessary to study the oxidation mechanism of pyrite in a gold-leaching electrolyte. The surface oxidation reaction of pyrite is a multi-electron transfer electrochemical oxidation process. Based on this, electrochemical technology was used to explore the electrochemical oxidation mechanism of pyrite in a Cu2+-Cit3−-S2O3 2− system. The surface oxidation products of the pyrite were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The experiments showed that the thiosulfate concentration did not change the oxidation mechanism of pyrite at 0.30 V under the conditions of this experiment. Increasing the concentration and potential of thiosulfate accelerated the oxidation rate of pyrite. The electrochemical oxidation of pyrite in the Cu2+-Cit3−-S2O3 2− system occurred in two stages. At low potentials in a passivated state, the process was diffusion-controlled, and the surface oxidation rate was slow. When the potential exceeded 0.50 V, the passivation film on the surface was penetrated, allowing the oxidation reaction on the surface of pyrite to continue. The results of this experiment are useful for deepening the understanding of the oxidation mechanism of pyrite in electrolytes.

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.

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.

The genesis of an extremely acidic perched aquifer within roasted pyrite waste in a fully urbanized area (Zaragoza, Spain)

Contaminated groundwater is a serious problem in developed countries. The abandonment of industrial waste may lead to acid drainage affecting groundwater and severely impacting the environment and urban infrastructure. We examined the hydrogeology and hydrochemistry of an urban area in Almozara (Zaragoza, Spain); built over an old industrial zone, with pyrite roasting waste deposits, there were acid drainage problems in underground car parks. Drilling and piezometer construction, and groundwater samples revealed the existence of a perched aquifer within old sulfide mill tailings, where the building basements interrupted groundwater flow, leading to a water stagnation zone that reached extreme acidity values (pH < 2). A groundwater flow reactive transport model was developed using PHAST to reproduce flow and groundwater chemistry, in order to be used as a predictive tool for guiding remediation actions. The model reproduced the measured groundwater chemistry by simulating the kinetically controlled pyrite and portlandite dissolution. The model predicts that an extreme acidity front (pH < 2), coincident with the Fe (III) pyrite oxidation mechanism taking dominance, is propagating by 30 m/year if constant flow is assumed. The incomplete dissolution of residual pyrite (up to 18 % dissolved) predicted by the model indicates that the acid drainage is limited by the flow regime rather than sulfide availability. The installation of additional water collectors between the recharge source and the stagnation zone has been proposed, together with periodic pumping of the stagnation zone. The study findings are expected to serve as a useful background for the assessment of acid drainage in urban areas, since urbanization of old industrial land is rapidly increasing worldwide.

H2O2 mediated oxidation mechanism of pyrite (0 0 1) surface in the presence of oxygen and water

Pyrite (FeS2) is the most common metal sulfide in nature. The oxidation mechanism of the pyrite has attracted intensive research attentions. It has been determined that this process involves multi-step electron transfer reactions between the FeS2 surface and the adsorbed O2 and H2O. In this process, sulfoxide (such as S2O32−, SO42−) and ferrous (Fe2+) are released into solution, and intermediate by-products, such as hydrogen peroxide (H2O2) and other reactive oxygen species (ROS), are produced. However, our understanding of the formation and transformation of these transient species is still limited. In this study, oxidation pathways by O2 and H2O on the pyrite (001) surface are explored by means of density functional theory (DFT) simulation. The oxidation pathway including the H2O2 forms as the intermediate is reported for the first time. It is found that the H2O2 molecule forms with low activation energy barriers when the O2 and H2O are co-absorbed on the pyrite surface. The H2O2 dissociates and releases the O atom to promote the sulfur oxidation. The product distribution resulted by the H2O2 mediated oxidation pathway agrees with the isotopic composition experiment that a minor amount of O2 is permanently incorporated into SO42– during pyrite oxidation (O in SO42– is mainly derived from water).

Electrochemical investigation of the oxidation of pyrite in neutral solutions

Pyrite, as the most common sulfide on the Earth's surface, is of central importance in a devastating environmental issue known as acid mine drainage (AMD). Although the oxidation of pyrite under neutral conditions is related to numerous environmental issues and industrial processes, its puzzling chemistry is largely unknown. Here, we analyzed the behavior and mechanism of pyrite oxidation in neutral solutions using a combination of electrochemical techniques. The oxidation of pyrite under neutral conditions followed a two-step oxidation law, i.e., below 0.4 V oxidation of iron occurred mainly, and oxidation of sulfur occurred above 0.4 V. Below 0.7 V, a typical passivation behavior of pyrite oxidation existed and can be eliminated with anodic potential higher than 0.7 V. In situ Fourier-transformed electrochemical impedance spectroscopy showed that the surface layer formed during oxidation in neutral conditions was mainly from iron oxidation products rather than sulfur oxidation products. These results indicated that the passivation of pyrite does not originate from the surface sulfur film, but should be explained by the semiconductor properties of pyrite.

Mechanism of pyrite oxidation in copper(II)-ethylenediamine-thiosulphate gold leaching system

Although the Cu2+–ethylenediamine–S2O32− system is a promising alternative to cyanide-based gold leaching systems because of its low cost, nontoxicity, and environmental friendliness, its performance is strongly affected by the presence of pyrite. Therefore, a deep understanding of the mechanism of pyrite oxidation in this system is of high practical importance. Herein, this mechanism was probed to demonstrate the occurrence of rapid reactions on the pyrite surface at high S2O32− concentrations and reveal that the dissolution of bulk pyrite was most favoured at a certain optimal S2O32− concentration, i.e., S2O32− ions strongly affected the surface properties of pyrite. Anodic processes occurring in active, passive, and transpassive dissolution regions were studied by linear sweep voltammetry, with additional insights into the properties of pyrite electrodes and the related electrochemical reactions obtained by electrochemical impedance spectroscopy and equivalent circuit fitting. With increasing potential at range of 0.20 to 0.80 V, the reactions on the pyrite surface accelerated, and its roughness significantly increased. The products of pyrite surface oxidation were identified by Raman spectroscopy and X-ray photoelectron spectroscopy, and a corresponding mechanism was proposed. Thus, this work provides a theoretical basis for the regulation and control of gold leaching reagents in the Cu2+–ethylenediamine–S2O32− system.

New Insights into the Oxidation Mechanism of Pyrite in Copper-Containing Sulfuric Acid: An Electrochemical, AFM, Raman Spectroscopy and XPS Investigation

The oxidation of pyrite in copper-containing sulfuric acid has been the subject of intense research yet has no comprehensive research on electrochemistry and surface species. In this study, pyrite’s electrochemical oxidation mechanism was systematically elucidated in copper-containing sulfuric acid by using electrochemical techniques. Anodic processes occurring in active, passive, and transpassive dissolution regions were studied by linear sweep voltammetry. The corresponding equivalent electrochemical circuits were fitted for these three regions with the potential of ranging from 0.40 V to 0.80 V vs SCE, and the results of fittings were used to clarify the characteristics of electrodes and electrochemical reactions in copper-containing sulfuric acid. With increasing potential, the reactions on the pyrite surface accelerated, and its roughness significantly increased. In addition, the interfacial transfer of electrons is dominated by surface charge transfer. The products of pyrite surface oxidation were identified by Raman spectroscopy and X-ray photoelectron spectroscopy. Based on the results of the electrochemical methods and surface analysis techniques, the mechanism of pyrite oxidation can be clarified and the specific course of the reaction can be described in detail. These results provided further insight into a better understanding of the pyrite oxidation mechanism in the presence of copper ions.

High redox potential promotes oxidation of pyrite under neutral conditions: Implications for optimizing pyrite autotrophic denitrification

Pyrite autotrophic denitrification (PAD) represents an important natural attenuation process of nitrate pollution and plays a pivotal role in linking nitrogen, sulfur, and iron cycles in a variety of anoxic environments. However, there are knowledge gaps about the oxidation mechanism of pyrite under anaerobic neutral conditions. This study explored the performance of PAD in the presence of EDTA and revealed the mechanism of anaerobic pyrite oxidation and microbial mineral transformation. It was demonstrated that ~200 mV was the electrochemical threshold for converting pyrite into bioavailable forms in PAD conditions, and accelerated pyrite oxidation by Fe3+-EDTA complexes can improve the performance of PAD effectively. Furthermore, genus related to sulfur and nitrogen cycle (Sulfurimonas, Denitrobacter) were found at higher abundances in cultures containing EDTA. The analysis of metagenomic binning showed that the microbial community in PAD culture with EDTA addition exhibited higher levels of functional diversity and redundancy. These results will further the understanding of the oxidation mechanism of pyrite under anaerobic neutral conditions and the corresponding microbial activities, and provide insights into the practical application of PAD.

Oxidation mechanism of pyrite concentrates (PCs) under typical circulating fluidized bed (CFB) roasting conditions and design principles of PCs’ CFB roaster

The circulating fluidized bed (CFB) roasting process is a promising way to utilize pyrite concentrates (PCs) which are byproducts in nonferrous metal production processes. The oxidation mechanism of PCs was investigated under typical CFB roasting conditions with the temperature of 850 °C and oxygen concentration of 1–21% on a drop tube furnace. The oxidation reaction pathway and products of PCs are strongly coupled with particle morphology evolution, which affects the oxygen diffusion from the particle surface to the core. A reaction path model of PC oxidation coupled with particle morphology evolution under CFB roasting conditions was proposed. The initial relatively slow oxidation of the porous particle structure followed by the relatively fast oxidation for complete oxidation was demonstrated to be the ideal reaction path for the CFB roasting operation of PCs. The critical issue for PCs roasting in the CFB reactor is to inhibit the particle temperature rise in dense phase region to avoid the formation of compact solid spheres. The flow and reaction behaviors of PC particles in CFB reactor naturally follow the ideal reaction path and make the CFB roasting technology feasible. Finally, the design principles of PCs CFB roasting process were suggested.

Triple oxygen isotope insight into terrestrial pyrite oxidation

The mass-independent minor oxygen isotope compositions (Δ'17O) of atmospheric O2 and [Formula: see text] are primarily regulated by their relative partial pressures, [Formula: see text]/[Formula: see text] Pyrite oxidation during chemical weathering on land consumes [Formula: see text] and generates sulfate that is carried to the ocean by rivers. The Δ'17O values of marine sulfate deposits have thus been proposed to quantitatively track ancient atmospheric conditions. This proxy assumes direct [Formula: see text] incorporation into terrestrial pyrite oxidation-derived sulfate, but a mechanistic understanding of pyrite oxidation-including oxygen sources-in weathering environments remains elusive. To address this issue, we present sulfate source estimates and Δ'17O measurements from modern rivers transecting the Annapurna Himalaya, Nepal. Sulfate in high-elevation headwaters is quantitatively sourced by pyrite oxidation, but resulting Δ'17O values imply no direct tropospheric [Formula: see text] incorporation. Rather, our results necessitate incorporation of oxygen atoms from alternative, 17O-enriched sources such as reactive oxygen species. Sulfate Δ'17O decreases significantly when moving into warm, low-elevation tributaries draining the same bedrock lithology. We interpret this to reflect overprinting of the pyrite oxidation-derived Δ'17O anomaly by microbial sulfate reduction and reoxidation, consistent with previously described major sulfur and oxygen isotope relationships. The geologic application of sulfate Δ'17O as a proxy for past [Formula: see text]/[Formula: see text] should consider both 1) alternative oxygen sources during pyrite oxidation and 2) secondary overprinting by microbial recycling.

AFM Study of Pyrite Oxidation and Xanthate Adsorption in the Presence of Seawater Salts

The effect of seawater ions presents a great challenge to theories about mechanisms of pyrite oxidation, collector adsorption, and surface reactions. As the use of seawater is key to the sustainability of the mining industry in regions without fresh water, there is a need to study the surfaces of minerals and products that are formed in the presence of seawater salts. In this study, atomic force microscopy (AFM) was used to analyze the topography of pyrite surfaces subjected to treatments, including oxidation and exposure to xanthate and solutions of seawater salts and xanthate, at pH 8.5. Topographic details were related to surface products. The results showed that xanthate was adsorbed without hindrance on oxide-free pyrite which validated one well-known model. The results also showed that pyrite oxidized forming a structure of interconnected pillars and that xanthate was adsorbed on the top and skirt of these pillars; the experimental evidence on the increase in the height and width of these pillars validated another well-known model. In the presence of seawater salts, the cations covered the surface of the pyrite, suppressing collector adsorption regardless of the dose. The results are expected to help in decisions about the flotation of sulfide minerals in water with limited metallurgical quality.

Experimental study on oxidation mechanism of pyrite under acidic conditions

In this study, pyrite samples from the Yankan Coal Mine near the Shandi River in Yangquan City were studied in an oxidation dissolution experiment. Pyrite was studied at different solid-liquid ratios (1:100, 1:50, and 1:20), and the oxygen concentration used was equal to the value in the ambient environment, about 20.95% of the air volume. The pH, oxidation-reduction potential (Eh), and soluble salt concentration (EC), total iron concentration, and SO42− concentration in the solution at different reaction times were measured with respect to time. The oxidation reaction rate of pyrite was calculated using the SO42− concentration and the factors influencing the oxidation rate at different conditions were discussed. The experimental results showed that, after pyrite was oxidized and dissolved at solid-liquid ratios of 1:20, pyrite decrease from acid generation of the SO42−formation, then the pH of the solution increased, at solid-liquid ratios of 1:100, 1:50, and 1:20, the overall Eh and EC values decreased. No matter what solid-liquid ratio is adopted for the reaction, the Fe2+ concentration is higher than Fe3+ concentration, and the Fe2+ and total iron concentration all increase with the increase of solid-liquid ratio, while Fe3+ gradually increases, reaching a trend of relatively stable and slowly decreasing. The average apparent release rate of Fe was proportional to the different solid-liquid ratios. The oxidation reaction rate of pyrite under acidic conditions was directly related to the concentration of reactants, and a faster oxidation rate was observed at higher concentrations due to the larger reaction contact area.

UK and Irish locations from which geological or palaeontologcal specimens are known to be prone to pyrite oxidation

Pyrite oxidation (or pyrite decay) has been a problem in museum collections for many years. The damage to specimens can include total loss of the object and its label. There is no cure: the changes cannot be reversed but the process can be halted. Preventing pyrite oxidation in the first place is obviously preferable but maintaining the appropriate environmental conditions in a large storage area can be very difficult to achieve and monitoring the whole collection regularly for signs of pyrite decay may not be practicable. Therefore it would be useful for curators to know which specimens in their collection are most likely to suffer from pyrite decay. Whilst there is a great deal of literature published on the mechanisms of pyrite oxidation and its treatment, there has been very little describing which sorts of specimens are prone to the process. Alist of sites in the UK and Ireland from which problematic material is known is presented, with indications of what specimens from these sites are likely to suffer the most. This data has been crowd-sourced from curators, conservators, collectors and enthusiasts from around the UK and further afield. It is not definitive but is a starting point and can be added to over time. The most important specimens from sites identified on this list can be stored in appropriate environmental conditions and/or regularly monitored. They can also be digitally imaged or physically replicated through casting or 3D printing to preserve a record in case the worst should happen in the future.

Evidence For In Vitro and In Situ Pyrite Weathering By Microbial Communities Inhabiting Weathered Shale

Microbial pyrite oxidation is an important driver of biological weathering within shale, making a significant contribution toward biogeochemical cycling, bedrock expansion, and soil formation. These processes are of global importance, both within natural systems and in anthropogenic environments. Despite its significance, there is a lack of research that directly investigates microbe– pyrite interactions within shale. In this study, we use both field and laboratory approaches to inspect microbial pyrite oxidation in weathered shale environments within North Yorkshire, UK. Incubation of polished pyrite samples within iron-oxidizing enrichment cultures in vitro resulted in extensive colonization and surface pitting, demonstrating the weathering potential of shale microbial communities. Mineral samples were buried for 1 year within the floor of a shale rock mine, to explore pyrite bioweathering in situ. Image analysis revealed the formation of dissolution channels by microbial filaments, a novel mechanism of pyrite oxidation that broadens the taxonomic range of known microbe-pyrite interactions in weathered shale.

Pyrite oxidation mechanism in aqueous medium

The mineral pyrite is considered the most common form of the sulfide minerals. Its oxidation is a very important process in nature, which involves in the redox recycling of iron. However, because of the growing need for the industrial production, sulfide oxidation produces more and more acid mine (or rock) drainage. This acid drainage has become a heavy economic and environmental problem. This review describes the oxidation mechanism of pyrite in an aqueous medium, including general oxidation and microbial oxidation, where sulfate, ferrous ion, S0, polysulfides, iron[III], and some intermediate species are formed. Also included is recent evidence on the electrochemical oxidation determined using the electrochemical method, X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and other techniques. In addition, the factors that influence the oxidation and dissolution rate, and the descriptive approaches for different species are discussed.

Surface structure-dependent pyrite oxidation in relatively dry and moist air: Implications for the reaction mechanism and sulfur evolution

Pyrite oxidation not only is environmentally significant in the formation of acid mine (or acid rock) drainage and oxidative acidification of lacustrine sediment but also is a critical stage in geochemical sulfur evolution. The oxidation process is always controlled by the reactivity of pyrite, which in turn is controlled by its surface structure. In this study, the oxidation behavior of naturally existing {1 0 0}, {1 1 1}, and {2 1 0} facets of pyrite was investigated using a comprehensive approach combining X-ray photoelectron spectroscopy, diffuse reflectance Fourier transform infrared spectroscopy, and time-of-flight secondary-ion mass spectrometry with periodic density functional theoretical (DFT) calculations. The experimental results show that (i) the initial oxidation rates of both pyrite {1 1 1} and {2 1 0} are much greater than that of pyrite {1 0 0}; (ii) the initial oxidation rate of pyrite {2 1 0} is greater than that of pyrite {1 1 1} in low relative humidity, which is reversed in high relative humidity; and (iii) inner sphere oxygen-bearing sulfur species are originally generated from surface reactions and then converted to outer sphere species. The facet dependent rate law can be expressed as: r{hkl}=k{hkl}haP0.5(t+1)-0.5, where r{hkl} is the orientation dependent reaction rate, k{hkl} is the orientation dependent rate constant, h is the relative humidity, P is the oxygen partial pressure, and t is the oxidation time in seconds. {1 1 1} is the most sensitive facet for pyrite oxidation. Combined with DFT theoretical investigations, water catalyzed electron transfer is speculated as the rate-limiting step. These findings disclose the structure–reactivity dependence of pyrite, which not only presents new insight into the mechanism of pyrite oxidation but also provides fundamental data to evaluate sulfur speciation evolution, suggesting that the surface structure sensitivity should be considered to estimate the reactivity at the mineral–water interface.

Density functional theory study of oxygen atom adsorption on different surfaces of pyrite

We discussed the oxidation differential and mechanisms on different planes of pyrite. The experimental results show that the oxidation priority is: (222) plane> (200) plane> (200) plane, and there is no direct correlation between the crystal plane index, the atom numbers, and the oxidation priority. However, with more exchanged charge among atoms, the oxidation could be conducted more easily, and the distribution rule of the electric charge conforms with the variation trend of adsorption energy, which will provide more overall cognition on the oxidation mechanism of pyrite from the atomic scale.

Oxidation Mechanism of Arsenopyrite in the Presence of Water

Arsenopyrite is commonly present in mining tailings and, together with pyrite, is responsible for acid rock drainage (ARD) phenomenon. The mineral undergoes oxidation in contact with oxygen and water producing a solution containing acid and heavy metals and, hence, causing important environmental impacts. Density functional/plane wave calculations were carried out to investigate the oxidation of arsenopyrite aiming to understanding its intricate mechanism at a molecular level. Molecular oxygen is dissociatively adsorbed in the Fe–O–As adsorption sites leading to the oxidation of arsenic and iron sites in good agreement with the available experimental data. It avoids the many steps observed for the pyrite oxidation mechanism. The presence of water is extremely important for the next steps of the oxidation mechanism similarly to the oxidation mechanism of pyrite. The present work reinforces the fact that the removal of the humidity can inhibit the oxidation of the arseno(pyrites) in an aerobic condition.

Stability, Structure, and Electronic Properties of the Pyrite/Arsenopyrite Solid–Solid Interface–A DFT Study

Pyrite is the most common sulfide in the Earth. In the presence of arsenopyrite its oxidation is delayed, and instead, the arsenopyrite increases its oxidation rate, releasing As(III) and As(V) species in the medium. DFT/plane waves calculations were performed on pyrite/arsenopyrite interface models to understand the stability, structure, and electronic properties of the interface. This is the first step to understand the influence of the inlaid arsenopyrite in the pyrite oxidation mechanism. The interface is slightly stressed with minor changes in the bond lengths and lattice parameters with respect to the pure phases. The work of adhesion and the formation energy indicate that the miscibility of the two phases is not favorable, explaining the presence of large domains of either pyrite or arsenopyrite forming bulk granular regions. The valence band of the pyrite/arsenopyrite interface has large contributions from the pyrite phase, while the conduction band has large contributions from the arsenopyrite. T...