Mineral-water Interface Research Articles

A review of cadmium sorption mechanisms on soil mineral surfaces revealed from synchrotron-based X-ray absorption fine structure spectroscopy: Implications for soil remediation

ABSTRACT The sorption of cadmium (Cd) is one of the most important chemical processes in soil, affecting its fate and mobility in both soil and water and ultimately controlling its bioavailability. In order to fundamentally understand the sorption/desorption of Cd in soil systems, X-ray absorption fine structure spectroscopy (XAFS) has been applied in numerous studies to provide molecular-level information that can be used to characterize the surface adsorption and precipitation reactions that Cd can undergo. This information greatly improves our current knowledge of the possible chemical reactions of Cd in soil. This paper critically reviews the mechanisms of Cd sorption/desorption at the mineral-water interface based on XAFS studies performed over the past twenty years. An introduction to the basic concepts of sorption processes is provided, followed by a detailed interpretation of XAFS theory and experimental data collection and processing, ending finally with a discussion of the atomic/molecular-scale Cd sorption mechanisms that occur at the soil mineral-water interface. Particular emphasis is placed on literature that discusses Cd adsorption and speciation when associated with iron, manganese, and aluminum oxides and aluminosilicate minerals. Multiple sorption mechanisms by which Cd is sorbed by these minerals have been found, spanning from outer-sphere to inner-sphere to surface precipitation, depending on mineral type, surface loading, and pH. In addition, the application of complementary techniques (e.g., 113Cd nuclear magnetic resonance (NMR) and molecular dynamics simulation) for probing Cd sorption mechanisms is discussed. This review can help to develop appropriate strategies for the environmental remediation of Cd-contaminated soils.

Pb Sorption at the Barite (001)–Water Interface

Sorption of ions at the mineral-water interface is an important factor that determines the fate of toxic metals in the environment. Here we use barite as a model substrate to understand the interac...

Influence of Surface Compositions on the Reactivity of Pyrite toward Aqueous U(VI).

Pyrite plays a significant role in governing the mobility of toxic uranium in an anaerobic environment via an oxidation-reduction process occurring at the mineral-water interface, but the factors influencing the reaction kinetics remain poorly understood. In this study, natural pyrites with different impurities (Pb, As, and Si) and different surface pretreatments were used to react with aqueous U(VI) from pH ∼3.0 to ∼9.5. Both aqueous and solid results indicated that freshly crushed pyrites, which do have more surface Fe2+/Fe3+ and S2- sites that were generated from breakage of Fe(S)-S bonds during ball milling, exhibited a much stronger reactivity than those treated with acid washing. Besides, U(VI) reduction which involves the possible intermediate U(V) and the formation of hyperstoichiometric UO2+x(s) was found to preferentially occur at Pb- and As-rich spots on the pyrite surface, suggesting that the incorporated impurities could act as reactive sites because of the generation of lattice defects and galena- and arsenopyrite-like local configurations. These reactive surface sites can be removed by acid washing, leaving a pyrite surface nearly inert toward aqueous U(VI). Thus, reactivity of pyrite toward U(VI) is largely governed by its surface compositions, which provides an insight into the chemical behavior of both pyrite and uranium in various environments.

Macroscopic and spectroscopic characterization of U(VI) sorption on biotite

Knowledge of the geochemical behavior of uranium is critical for the safe disposal of radioactive wastes. Biotite, a Fe(II)-rich phyllosilicate, is a common rock-forming mineral and a major component of granite or granodiorite. This work comprehensively studied the sorption of U(VI) on biotite surface with batch experiments and analyzed the uranium speciation with various spectroscopic techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and time-resolved fluorescence spectra (TRFS). Our results indicated that uranyl ions could penetrate into the interlayer of biotite, this ion-exchange process was pH-dependent and only favorable under acidic condition. Instead of precipitation or reduction to uraninite, the TRFS results strongly suggests U(VI) forms surface complexes under the neutral and alkaline condition, though the number and structure of surface species could not be identified accurately. Besides, the oxidation of biotite with peroxide hydrogen showed that structural Fe(II) would have a very low redox reactivity. With leaching experiments, zeta potential analysis and thermodynamics calculation, we discussed the possible reasons for inhibition of U(VI) reduction at the biotite-water interface. Our results may provide insight on interaction mechanism of uranium at mineral-water interface and help us understand the migration behavior of uranium in natural environments.

Model-Based Analysis of Reactive Transport Processes Governing Fluoride and Phosphate Release and Attenuation during Managed Aquifer Recharge.

In water-scarce areas, the reclamation of wastewater through advanced water treatment and subsequent reinjection into depleted aquifers is an increasingly attractive water management option. However, such injection can trigger a range of water-sediment interactions which need to be well understood and quantified to ensure sustainable operations. In this study, reactive transport modeling was used to analyze and quantify the interacting hydrogeochemical processes controlling the mobilization of fluoride and phosphate during injection of highly treated recycled water into a siliciclastic aquifer. The reactive transport model explained the field-observed fluoride and phosphate transport behavior as a result of the incongruent dissolution of carbonate-rich fluorapatite where (i) a rapid proton exchange reaction primarily released fluoride and calcium, and (ii) equilibrium with a mineral-water interface layer of hydrated dibasic calcium phosphate released phosphate. The modeling results illustrated that net exchange of calcium on cation exchange sites in the sediments postbreakthrough of the injectant was responsible for incongruent mineral dissolution and the associated fluoride and phosphate release. Accordingly, amending calcium chloride into the injectant could potentially reduce fluoride and phosphate mobilization at the study site. Insights from this study are broadly applicable to understanding and preventing geogenic fluoride mobilization from fluoride-bearing apatite minerals in many other aquifers worldwide.

A brief review of the correlation between electrical properties and wetting behaviour in porous media

Wettability is a critical interface property for two-phase flow and reactive transport process in porous media. Wettability alteration is considered as the dominated mechanism for enhanced oil recovery during low salinity waterflooding. The conventional characterization of wettability by contact angle at a single substrate and Amott method at core are limited. In this minireview, we introduce recent improvements in characterization of the electrochemical properties of an interfacial layer formed at the mineral-water interface, and review the application of surface potential (i.e., zeta potential) as an invasive and reliable technique to characterise the wetting behaviour of sample core across different geochemistry conditions. In order to resolve the puzzle of the wettability alteration in an oil-brine-rock system, experimental studies combined with numerical simulations across multiscale and variable geochemistry conditions are required for the future investigation. Cited as : Li, S., Hou, S. A brief review of the correlation between electrical properties and wetting behaviour in porous media. Capillarity, 2019, 2(3): 53-56, doi: 10.26804/capi.2019.03.02

Crystal habit-directed gold deposition on pyrite: Surface chemical interpretation of the pyrite morphology indicative of gold enrichment

The occurrence of the {2 1 0} shape of pyrite crystals has been used as an empirical indicator for gold enrichment in ore deposits. Such indicating, also called ‘typomorphism’ in ore mineralogy, was conventionally attributed to environmental factors such as sulfur fugacity and temperature and pressure conditions in the ore-forming hydrothermal fluid. Here we show that the crystal-face specific redox reactivity of pyrite is also an important governing potency that drives gold enrichment in the pyrite crystals with particular shapes. This conclusion was drawn from data compiled from chemical analysis of field samples, laboratory testing of gold deposition on natural pyrite crystals, as well as theoretical calculations. Kinetic measurements of gold reductive deposition first revealed the highest precipitation rate on the {2 1 0} faces, particularly when pyrite crystals are enclosed by complex forms containing {2 1 0}. Corroborating with the experimental observations, density functional theory (DFT) calculations further indicated that the {2 1 0} possesses a high adsorption energy for gold, a high energy state of the highest occupied molecular orbital and consequently a low Eh. These results afford evidence supporting the view that the face specific reactivity, an intrinsic property of crystal, plays an important role in the gold concentration in pyrite and the occurrence of specific pyrite shapes. Our findings not only provide a surface chemical view for understanding the empirical prospecting method but also exemplified the significance of crystal face specific-reactivity in understanding crystallographic orientation related geochemical processes. The crystal face specific reactivity may be a critical factor controlling geochemical reactions at mineral-water interface, such as prebiotic synthesis on pyrite surfaces and mineral-water interface controlled kinetic isotope fractionation.

Polyphosphate Adsorption and Hydrolysis on Aluminum Oxides.

The geochemical behaviors of phosphate-containing species at mineral-water interfaces are of fundamental importance for controlling phosphorus mobility, fate, and bioavailability. This study investigates the sorption and hydrolysis of polyphosphate (a group of important long-chained phosphate molecules) on aluminum oxides in the presence of divalent metal cations (Ca2+, Cu2+, Mg2+, Mn2+, and Zn2+) at pH 6-8. γ-Al2O3 with three particle sizes (5, 35, and 70 nm) was used as an analogue of natural aluminum oxides to investigate the particle size effect. All metal cations enhanced polyphosphate hydrolysis at different levels, with Ca2+ showing the most significant enhancement, and the difference in the enhancement might be due to the intrinsic affinity of metal cations to polyphosphate. In the presence of Ca2+, the hydrolysis rate decreased with increasing mineral particle size. Solid-state 31P nuclear magnetic resonance spectroscopy (NMR)revealed the main surface P species to be amorphous calcium phosphate precipitates, phosphate groups in polyphosphate that formed direct bonds with the mineral surface as inner-sphere complexes, and phosphate groups in polyphosphate that were not directly bonded to the mineral surfaces. Our results reveal the critical roles of mineral-water interface processes and divalent metal cations on controlling polyphosphate speciation and transformationand phosphorus cycling.

Kinetics of neptunium sorption and desorption in the presence of aluminum (hydr)oxide minerals: Evidence for multi-step desorption at low pH

Kinetics analyses of sorption and desorption provide important insight into reaction mechanisms occurring at the mineral-water interface. They are also needed to determine when equilibrium is achieved, identify intermediate chemical species, and inform models describing neptunium mobility. Neptunium sorption to and desorption from four different aluminum (hydr)oxides - bayerite (α-Al(OH)3), gibbsite (γ-Al(OH)3), corundum (α-Al2O3), and γ-alumina (γ-Al2O3) - were investigated as a function of mineral concentration (5 – 170 m2 L−1), neptunium concentration (10−9 – 10−7 M), and pH (5.5 – 10.5). Neptunium sorption was characterized by a two-step reaction with an initial fast sorption step occurring within minutes followed by a slower equilibrium process, which was attributed to initial sorption of neptunium to a small number of strong sorption sites followed by sorption of neptunium to a larger number of weak sorption sites. The kinetics data were modeled using the linear and non-linear forms of the pseudo-first and pseudo-second order rate equations and the goodness of fit parameters were compared. Non-linear pseudo-second order rate constants described neptunium sorption to aluminum (hydr)oxides most accurately and were used to determine the reaction orders with respect to mineral concentration and [H+]. Neptunium desorption experiments demonstrated that the desorption mechanism changed as a function of pH and that the forward and reverse reactions were not equivalent. At pH ≥ 7.5, desorption reached steady-state within an hour and was accurately described by the non-linear pseudo-second order rate equations. A desorption plateau was observed at pH 5.5 that could not be described by either pseudo-first or –second order kinetics, suggesting the possibility of a multi-step desorption reaction. The comparatively slow desorption kinetics observed here suggests that sorbed neptunium could be slowly released back into the aqueous phase and act as a continuous source of contamination to the environment.

An SFG spectroscopy study of the interfacial water structure and the adsorption of sodium silicate at the fluorite and silica surfaces

Sodium silicate (SS) is often used as a depressant or a dispersant to improve the selectivity of froth flotation. The depressing ability of SS changes with its concentration and the solution pH. However, the depressing mechanism is unclear. In this paper, sum frequency generation spectroscopy was used to investigate the water structure at the mineral-water interface to provide a molecular understanding of SS adsorption and its role in flotation. Our study shows that a significant amount of silicate species adsorbs at the fluorite-water and silica-water interfaces in a wide range of pH, independently of the surface potential. The adsorption layer of silicate species on the fluorite surface can be removed at low pH (acidic condition), but its removal becomes difficult at high pH (basic condition). On the contrary, the adsorption of silicate species at the silica surface is so strong that the adsorbed species cannot be removed at the whole pH range. This finding agrees with flotation results showing that SS can be used as a dispersant for fluorite at pH = 6–8, but it behaves like a depressant at higher pH. Also, SS effectively depresses the silica floatability at the whole range of pH due to its strong interaction with the mineral surface. This work provides the molecular details about the SS adsorption onto the mineral surface which is complementary to the previous macroscopic studies such as FTIR, zeta potential, and XPS measurements.

Calcium-Facilitated Aggregation and Precipitation of the Uranyl Peroxide Nanocluster U60 in the Presence of Na-Montmorillonite.

The unique and diverse features of uranyl peroxide nanoclusters may contribute to the enhanced mobility of uranium in the environment. This study examines the sorption of the uranyl peroxide nanocluster [UO2(O2)(OH)]6060- (U60) to Na-montmorillonite (SWy-2), plagioclase (anorthite), and quartz (SiO2) as a function of time, U60 concentration, and mineral concentration. SWy-2 was studied in both its untreated form as well as after two different pretreatments, denoted as partially treated SWy-2 and fully treated SWy-2. U60 was removed (∼99%) from solution in the presence of untreated and partially treated SWy-2. However, U60 was not removed from suspensions containing anorthite, quartz, or fully treated SWy-2, even after several months. The removal of U60 from suspensions containing untreated SWy-2 is promoted in part by the exchange of Li+ counter-ions, normally weakly associated with U60 in solution, for Ca2+ ions naturally present in the clay. In solution, Ca2+ ions induce the aggregation of nanoclusters, which precipitate on the surface of SWy-2. Ca-rich U60 aggregates associated with SWy-2 were identified and characterized by scanning electron microscopy with energy dispersive spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. This research enhances our understanding of the molecular-scale processes controlling U60 behavior at the mineral-water interface.

Role of Cations in Adsorption of Supercritical Carbon Dioxide at Smectite Mineral–Water Interfaces: Molecular Dynamics and Adaptive Biasing Force Simulation Studies

The microscopic understanding of uptake and retention of supercritical carbon dioxide by expandable layered aluminosilicate minerals is of central importance for large-scale geological sequestration of CO2. At the molecular scale, the interlayer charge-balancing cations (CBCs) play a crucial role in CO2 adsorption by these cost-effective and environmentally friendly materials. This article investigates the influence of CBCs on the structure, dynamics, and energetics of CO2–H2O mixtures nanoconfined in four different montmorillonites with different CBCs (Cs+, K+, Na+, and Ca2+) using molecular dynamics and enhanced sampling simulations. The results reveal that both CO2 and H2O coexist in a single layer at the center of the interlayer, that CO2 molecules orient parallel to the basal surface and form two-dimensional percolation paths that facilitate their lateral diffusion, and that the near-neighbor CO2 molecules preferentially adopt a distorted slipped-parallel geometry in all of these systems. The calculated activation barriers for CO2 and H2O to diffuse away from the first coordination shells of cations show that Cs+–CO2 and Ca2+–H2O affinities are relatively higher than those of the other cations. The residence times in the cation coordination shells, relative orientations, and diffusion constants of intercalates are also quantified. The presented results can be useful for rational design of engineered layered minerals with improved CO2 retention capacity.

Nonenzymatic RNA Oligomerization at the Mineral–Water Interface: An Insight into the Adsorption–Polymerization Relationship

Nonenzymatic RNA polymerization, a major challenge in understanding the origins of life on early Earth, was previously achieved in the presence of montmorillonite clay and high magnesium concentrat...

Defects and their behaviors in mineral dissolution under water environment: A review

Mineral dissolution is a spontaneous process that takes indispensible role in the determination of water quality in a specific water body. Deep insights into defects as a result of characterization technique development have greatly improved our understanding of their significances and behaviors in the dissolution within the mineral-water interface. Based on the progresses from previous decades, this review attempts to re-elaborate the molecular-scale process of dissolution. Material flow within the mineral/water interface is updated, with emphasis on the function of defect sites. A brief introduction of defect properties is presented, including the microscopic appearances and typical physicochemical characteristics. Feasible strategies that have been adopted to increase the defect abundance are inferred, which maybe enlightening for hydrometallurgy. The merits and drawbacks of the techniques that could be employed for the qualitative and quantitative determination of defect presence are introduced, although relatively satisfactory performances are noted. With the aid of these techniques, it is concluded that screw dislocation is the main defect type responsible for surface topography evolution as a result of dissolution. Finally, this review identifies the current knowledge gaps and future research needs for comprehensively identifying the significance of defects in mineral dissolution.

Facet-Mediated Adsorption and Molecular Fractionation of Humic Substances on Hematite Surfaces.

Interactions between dissolved organic matter (DOM) and iron oxyhydroxides have important environmental and geochemical implications. The present study employed two hematite nanocrystals to investigate the adsorption and molecular fractionation of two typical humic substances (HSs) using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Hematite with a predominant exposure of {100} facets induced more pronounced adsorption and molecular fractionation of HSs than {001} facets, indicating that the interfacial adsorptive fractionation process of HSs was mediated by exposed facets of hematite. Further exploration of the surface OH groups of the two hematite nanocrystals confirms that the facet-mediated molecular fractionation of HSs was attributable to the abundance of singly iron-atom coordinated -OH sites on the hematite surfaces. Molecules with a high oxidation state and high aromaticity such as oxidized black carbon, polyphenol-like, and tannic-like compounds preferentially formed ligand-exchange complexes with singly coordinated -OH groups on the hematite surfaces, inducing the selective binding and molecular fractionation of HSs at the mineral-water interface. These results demonstrate that singly iron-atom coordinated -OH sites determine DOM adsorption and mediate molecular fractionation on hematite surfaces, and this contributes substantially to our understanding of the molecular mechanisms of iron oxyhydroxide-mediated molecular exchange of DOM in soils and/or sediments.

Kinetics of europium sorption to four different aluminum (hydr)oxides: Corundum, γ-alumina, bayerite, and gibbsite

Kinetic studies can improve our understanding of the environmental mobility of radionuclides by providing insight into sorption mechanisms occurring at the mineral-water interface. While nearly identical equilibrium europium sorption edges are obtained for gibbsite (γ-Al(OH)3), bayerite (α-Al(OH)3), corundum (α-Al2O3), and γ-Al2O3, differences in surface acidity and crystal structure result in distinct reaction rates. Batch kinetic experiments were performed to investigate europium sorption to four aluminum (hydr)oxide minerals as a function of time (10–120 min), mineral concentration (0.5–50 m2 L−1), pH (5–7), and europium concentration (10−8–10−6 M). Linear and non-linear pseudo-first and pseudo-second order rate equations were used to fit the data. The overall reaction rates and reaction orders with respect to proton concentration, mineral concentration, and europium concentration were determined, leading to a governing rate law for each mineral system. Europium sorption is characterized by a two-step reaction with a fast initial sorption step followed by a slower sorption or aging process. The pseudo-second order equations resulted in better model fits of the data. Using the non-linear pseudo-second order rate constants, it was observed that the reaction orders for each mineral system were similar but resulted in different overall reaction rates following the trend bayerite ∼ γ-Al2O3 > corundum > gibbsite. However, the calculated reaction orders are similar to those previously reported for plutonium(IV/V) interactions with iron (oxyhydr)oxide minerals, suggesting that these binary systems share similar elementary reactions.

Mineral–Water Interface Structure of Xenotime (YPO4) {100}

Crystal truncation rod (CTR) measurements and density functional theory (DFT) calculations were performed to determine the atomic structure of the mineral–water interface of the {100} surface of xenotime (nominally YPO4). This mineral is important, because it incorporates a variety of rare earth elements (REEs) in its crystal structure. REEs are critical materials necessary for a variety of renewable and energy efficient technologies. Current beneficiation techniques are not highly selective for REE ore minerals, and large amounts go to waste; this is a first step toward designing more efficient beneficiation. Evidence is found for minor relaxation of the surface within the topmost monolayer with little or no relaxation in subsurface layers. Justification for ordered water at the interface is found, where water binds to surface cations and donates hydrogen bonds to surface phosphates. The average bond lengths between cations and oxygens on water are 228 pm in the best fit to the CTR data, versus 243 and 2...

Study on the Law of Membrane Efficiency of Unsaturated Shale and Its Application

The microscopic interaction mechanism between working fluids and shale reservoirs is the key basic issue for the efficient development of shale gas. The initial water saturation of clay-rich shale is low, and the water absorption through strong chemical osmosis is an important factor for the wellbore instability of the drilling fluid filtration loss and the low flowback rate of hydraulic fracturing. Membrane efficiency is a key parameter in evaluating the mechanical-chemical coupling of shale-fluid interaction. Because microcracks develop in reservoir shale, pressure transfer experiments are no longer capable of obtaining membrane efficiency value. In this paper, the characteristics of shale water saturation are considered. The model calculating membrane efficiency is obtained, and the shale membrane efficiency of the reservoir studied, based on the triple-layer model of clay mineral-water interface electrochemistry. Membrane efficiency of unsaturated shale depends on the excess charge density of the surface of the solid in different water saturations. The analysis of factors influencing shale membrane efficiency in unsaturated reservoirs shows that the shale membrane efficiency decreases with the increase of water saturation under unsaturated conditions. The partition coefficient of counterion in the Stern layer, cation exchange capacity, and solute concentration in pore fluid will affect the membrane efficiency of unsaturated shale. The membrane efficiency of the reservoir section shale in Fuling area is calculated and analyzed, and the water-absorbing capacity by chemical osmosis of the reservoir interval shale is evaluated based on the membrane efficiency model of unsaturated shale.

A comprehensive predictive model for sulfate adsorption on oxide minerals

This article presents a set of equations that enables the prediction of sulfate adsorption behavior on all oxide minerals over a wide range of pH, ionic strength, sulfate concentration, and solid/water ratio based on the extended triple-layer model (ETLM). Although surface complexation models including the ETLM have been frequently applied to describe sulfate–surface interactions on oxides, the proposed adsorption stoichiometries and equilibrium constants have been mutually inconsistent even in a specific sulfate–oxide system. Here, we show that the outer-layer capacitance (C2), a TLM parameter that has been traditionally set to 20 µF cm−2, has a significant impact on the model prediction of sulfate adsorption. With the capacitance value being the same as the inner-layer one (i.e., C2 = C1), which is a theoretically and spectroscopically reasonable assumption, our ETML calculation adequately represents all adsorption, surface titration, and proton co-adsorption data for various sulfate–oxide systems reported in the literature (i.e., oxides; goethite, ferrihydrite, γ-alumina, gibbsite, and hematite) and those obtained in the present study (i.e., oxide; anatase). The combination of a monodentate-mononuclear inner-sphere (MMin) and a bidentate-binuclear outer-sphere (BBout) surface complex was found to explain all experimental data. Analysis of the retrieved equilibrium constants for the two surface species with the Born solvation theory led to the development of predictive equations for sulfate adsorption constants on all oxides. Considering the ubiquity of sulfate in natural environments, our proposed model should significantly contribute to a better understanding of the geochemical processes occurring at the mineral–water interface.

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.