Sulfur-rich Surface Research Articles

Enhancing photocatalytic H2 evolution of Cd0.5Zn0.5S with the synergism of amorphous CoS cocatalysts and surface S2− adsorption

Designing surface phase is an efficient strategy to facilitate charge separation and photocatalytic H2-evolution performance. In this work, CoS cocatalysts were intimately anchored on Cd0.5Zn0.5S (denoted as CZS) photocatalyst via in-situ precipitate transformation in S2−/SO32− solution with cobaltous phosphate (CoPi) as a precursor, meanwhile, S2− ions were adsorbed on the CZS to form a sulfur-rich surface (denoted as CZS-S). The photocatalytic H2-evolution rate of CoS/CZS-S is 2.02 mmol·g−1·h−1 in 0.1 M Na2S/Na2SO3 sacrificial agent system. In addition, CoS/CZS-S exhibits excellent stability in both Na2S/Na2SO3 and lactic acid system. The theoretical calculations (DFT) and experimental results reveal that amorphous CoS can work as a highly effective cocatalyst for H2 evolution reaction and the intimate contact between CZS and CoS facilitates the photoelectrons transfer from CZS to CoS. The adsorbed S2− ions mainly work as effective hole acceptors. As a result of the synergism of CoS and adsorbed S2− ions, the boosted separation and immigration of photoelectrons and photoholes and high photocatalytic H2-evolution performance of CoS/CZS-S are realized. The present work highlights simultaneous reinforcing reduction and oxidation half-reaction dynamics via a facile and economic surface strategy to achieve efficient solar H2-evolution from H2O splitting.

Fabrication of multiwall carbon nanotubes decorated with MoS2 nanoflowers for adsorption of Ag(I) from aqueous solution

In this work, a facile solvothermal method was employed to fabricate multiwall carbon nanotubes (MWCNTs) decorated with MoS2 nanoflowers (MoS2/MWCNTs) nanohybrid using carboxylation multiwall carbon nanotubes (MWCNTs-COOH) as skeleton for MoS2 in-situ growth, and the MoS2/MWCNTs nanohybrid was used as a novel sorbent to adsorb Ag(I) from aqueous solution. The structures and components of the obtained samples before and after adsorption were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), zeta potential analyzer and N2 adsorption-desorption isotherms. Meanwhile, the effect of solution pH, initial concentrations of Ag(I), contact time and temperature on the adsorption performance of the MoS2/MWCNTs nanohybrid for Ag(I) in aqueous solution were explored by batch experiments. The results show that MoS2 was decorated on MWCNTs in nanoflower-like structure, which could avoid agglomeration of MWCNTs and MoS2, expose as much of the sulfur-rich surface as possible, and provide abundant adsorption sites and transport channels for Ag(I) ions. The specific surface area of the MoS2/MWCNTs nanohybrid was 4.5 times that of pure MoS2. At the optimal adsorption conditions, the maximum adsorption capacity of the MoS2/MWCNTs nanohybrid for Ag(I) was 601.97 mg/g. The formation of Ag2S was main contribution for the adsorption, besides that, there was electrostatic adsorption. Based on the advantages of the simple synthesis method and high adsorption capacity, the MoS2/MWCNTs nanohybrid could be a promising candidate material for Ag(I) removal from wastewater.

Activating and optimizing the MoS2@MoO3 S-scheme heterojunction catalyst through interface engineering to form a sulfur-rich surface for photocatalyst hydrogen evolution

As a crucial part of artificial photosynthesis, the design of the catalyst is important essential. Among them, the interface engineering between semiconductors and the construction of surface-active sites play a vital role in generating and transporting light-excited electrons, which can ultimately accelerate water decomposition. Therefore, the MoS2@MoO3 step (S)-scheme heterojunction photocatalyst was prepared by in-situ partial sulfidation. The excellent interface engineering of MoS2@MoO3 nanomaterials achieves a high surface reaction rate. The in-situ vulcanization strategy gradually corrodes from the outside to the inside. The introduction of sulfur atoms can replace oxygen atoms to build a sulfur-rich surface and generate molybdenum sulfide. The amount of thioacetamide is adjusted to control vulcanization and optimizing the experimental conditions, the best hydrogen production rate is 12416.8 µmol h−1 g−1. An in-situ irradiation XPS experiments and DFT calculations provide a deeper understanding of the S-scheme electron transport mechanism in MoS2@MoO3. MoS2@MoO3 interface interaction has penetrating electron channels and a strong interface interaction force, which effectively promotes the charge transfer between interfaces. This gradual surface vulcanization strategy provides new ideas for introducing synergistic surface-active sites and optimizing interface engineering photocatalyst projects.

Simultaneous realization of sulfur-rich surface and amorphous nanocluster of NiS1+x cocatalyst for efficient photocatalytic H2 evolution

Transition-metal sulfides have been proved to be a favorable candidate for high-efficiency cocatalyst for photocatalysts, but the major bottlenecks remains lacking sufficient active sites for interfacial H2-generation reactions. In this article, the sulfur-rich NiS1+x nanoclusters with abundant active unsaturated S sites are homogeneously anchored on TiO2 particles by a facile S2O32−-mediated photodeposition route. The as-synthesized NiS1+x/TiO2(1 wt%) photocatalyst achieves the boosted H2 evolution rate of 264.42 μmol h-1 as well as shows an outstanding stability and repeatability. The sulfur-rich NiS1+x nanoclusters can not only act as an outstanding cocatalyst to effectively accelerate the electron migration from TiO2 to NiS1+x nanoclusters, but also provide numerous active unsaturated S sites to promote interfacial H2-generation reaction, thereby promoting the photocatalytic H2-production rate of the NiS1+x/TiO2 photocatalysts. Particularly, the present method can be extended to construct other metal sulfides (AgSx, CoSx or CuSx) to evidently promote the photocatalytic H2-evolution activity.

Ultrahigh efficient and selective adsorption of Au(III) from water by novel Chitosan-coated MoS2 biosorbents: Performance and mechanisms

The design and synthesis of high-performance materials for the recovery of gold are of paramount importance to alleviate its high consumption and protect the environment. Herein, three different ratios biosorbents (CS-MoS2-1, 2, 3) were successfully synthesized by embeding MoS2 into the crosslinking chitosan to recover gold ions from solution. These materials not only inherit the excellent properties of chitosan, but also possess the sulfur-rich surface of MoS2, making that the maximum adsorption capacity of CS-MoS2-1, 2 and 3 were 2012.46, 2611.32 and 3108.79 mg/g, respectively. Besides, these biosorbents show outstanding selectivity for gold ions in the presence of coexisting ions, and demonstrate attractive reusability after four cycles. Adsorption mechanism of the three biosorbents to Au(III) was mainly electrostatic attraction and coordination. With the easy synthesis, environmental-friendly and ultra-efficient performance, CS-MoS2-1, 2, 3 are expected to be a promising candidate for Au(III) adsorption from aqueous media.

Competition of Hg2+ adsorption and surface oxidation on MoS2 surface as affected by sulfur vacancy defects

Two dimensional molybdenum disulfide (2D-MoS2) has been recently developed to be used as superb adsorbents for removing heavy metals from water due to its huge sulfur-rich surface area. In this work, single adsorption and co-adsorption performances of H2O, Hg2+ and O2 on MoS2 surface with and without S-vacancy defects have been theoretically studied to explore the Hg2+ adsorption and surface oxidation through density function theory (DFT) calculations. Moreover, the Hg2+ adsorption and surface oxidation have experimentally studied through atomic force microscopy (AFM) to verify the theoretical calculation results. It has been found that S-vacancy defects make MoS2 surface more reactive, leading to the much stronger adsorption energy of H2O, Hg2+ and O2 on defective MoS2 surface. O2 can only be physically adsorbed on the perfect MoS2 surface, while it bonds to the unsaturated Mo atoms at the vacancy site on defective MoS2 surface. Besides, co-adsorption results illustrate that Hg2+ have priority to react with MoS2 surface than O2 due to the much stronger binding affinity, and surface oxidation occurs only when there are enough reaction sites for the Hg2+ adsorption and surface oxidation simultaneously. These theoretical co-adsorption results are consistent with the experimental Hg2+ adsorption and surface oxidation results obtained by AFM. These findings in this study are of great significance for the development and utilization of MoS2-based nanomaterials as a heavy metal adsorbent.

Structural Evolution and Chemical Bonding in Bi-nuclear Niobium Sulfide Clusters: Nb2S n −/0 (n = 4–7)

Geometric and electronic structures of a series of bi-nuclear niobium sulfide clusters, Nb2S /0 (n = 4–7), were investigated by the theoretical calculations. Vertical detachment energies were estimated based on the generalized Koopmans’ theorem and were used to simulate the anionic photoelectron spectra. The structural evolution behaviors were found to be present in the sequential sulfidation of Nb2S −/0 . Concretely, the additional sulfur atoms tended to occupy the bridging sites of Nb2S /0 (n = 4, 5) clusters. Then varied poly-sulfur ligands (i.e., bridging S 2 2 , terminal S 2 2 and bridging S 3 2 ) began to emerge in the Nb2S /0 (n = 6, 7) clusters. Frontier molecular orbitals were analyzed to understand the chemical bonding. It was found that the highest occupied molecular orbital of Nb2S cluster, even the sulfur-rich Nb2S 7 cluster, still retained the Nb–Nb bonding features. The results were compared with the analogs Mo2S /0 (n = 4–7) clusters. The findings in structures and chemical bonding may provide insight into the properties of niobium sulfides, especially for the sulfur-rich surfaces.

Achieving high-performance PbS quantum dot solar cells by improving hole extraction through Ag doping

PbS quantum dot solar cells are promising candidates for low-cost and highly efficient light harvesting devices owing to their solution processability and bandgap tunability. The p-type ethanedithiol (EDT) treated PbS quantum dot film plays an important role in PbS quantum dot solar cells with an n-i-p junction device structure. However, despite their sulphur-rich surface the EDT-treated PbS quantum dot film still have a relatively low carrier concentration. Higher carrier concentrations in this layer are desirable to extend depletion regions and improve hole extraction. Also imbalances in the charge mobility between the intrinsic layer and the p-type layer may lead to charge build-up at this interface. These obstacles limit further improvement of the device performance. Herein, we utilize EDT-treated Ag-doped PbS quantum dots as a p-type layer to fabricate PbS quantum dot photovoltaic cells. The carrier carrier concentration, mobility and band extrema as well as Fermi energy levels of Ag doped PbS quantum dot film can be tailored by tuning the Ag/Pb mole ratio from 0.0% to 2.0% during fabrication. The device performance has been significantly improved from 9.1% to 10.6% power conversion efficiency largely due to improvements in carrier concentration in the PbS-EDT layer through the incorporation of silver impurities.

Two-dimensional molybdenum disulfide as adsorbent for high-efficient Pb(II) removal from water

Two-dimensional (2D) molybdenum disulfide might be highly capable of lead removal from wastewater due to the huge sulfur-rich surface area. An attempt was made to explore the feasibility of using 2D molybdenum disulfide as a super adsorbent in water in this work. Adsorption isotherm and kinetics and SEM-EDS were conducted to investigate Pb(II) adsorption capacity at the interface of 2D molybdenum disulfide/water, and XPS was used to study the adsorption mechanism. The results indicated that 2D molybdenum disulfide had a dramatic efficiency for Pb(II) removal from water with a 1479mg/g adsorption capacity. The adsorption followed the Freundlich isotherm model and fitted well with both the pseudo-first-order and pseudo-second-order kinetics models. The adsorption might be attributed to the chemical adsorption due to the complexation of Pb(II) with intrinsic S or O atoms exposed on 2D molybdenum disulfide surfaces, together with electrostatic adsorption.

Two-Dimensional Molybdenum Disulfide as a Superb Adsorbent for Removing Hg2+ from Water

One feature of two-dimensional (2D) molybdenum disulfide nanosheets is the huge sulfur-rich surface area, which might lead to the strong adsorption of Hg2+ in water, because the sulfur on the surfaces could strongly bind to Hg2+. In this work, the adsorption of Hg2+ on 2D molybdenum disulfide sheets in water has been studied in order to develop a novel and efficient adsorbent for removing Hg2+ from water. The study was performed through the measurements of adsorption isotherm and kinetics, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The partially oxidized 2D molybdenum disulfide sheets with less than five S–Mo–S layers were prepared through the exfoliation of natural molybdenite. AFM observations illustrated a fast and multilayer Hg2+ adsorption on the surface of 2D molybdenum disulfide. The results of adsorption tests and SEM-EDS have indicated that 2D molybdenum disulfide was a superb adsorbent. The ads...

Atomistic Modeling of Sulfur Vacancy Diffusion Near Iron Pyrite Surfaces

Through density functional calculations, we investigated the diffusion of isolated sulfur vacancies (VS) from the bulk of iron pyrite (cubic FeS2) to the (100) and (111) surfaces. The influence of vacancy depth on the vacancy formation energy and the activation energy for vacancy diffusion are discussed. Significantly, we find that VS defects tend to migrate toward stoichiometric and sulfur-rich surfaces through sequential “intra-dimer” and “inter-dimer” hops. We find a pre-exponential constant (D0) of 9 × 10–7 m2 s–1 and an activation energy (E) of 1.95 eV for sulfur vacancy diffusion in bulk pyrite, corresponding to a vacancy diffusion coefficient DV = D0 exp(−E/kT) = 9 × 10–40 m2 s–1 at 25 °C and 5 × 10–18 m2 s–1 at 600 °C. The activation energy is smaller near the surface (e.g., E = 1.5 eV near the stoichiometric (100) surface), resulting in faster vacancy diffusion near the surface than in the bulk. Using the formation enthalpy of VS at the (100) surface, E = 2.37 eV, we find a sulfur diffusivity in bulk pyrite DS = 7 × 10–47 m2 s–1 at 25 °C and 2 × 10–20 m2 s–1 at 600 °C. The calculated DS values are in reasonable agreement with experiment only at intermediate temperatures (∼275–625 °C). Our results show that bulk and near-surface sulfur vacancies can be healed in sulfur-rich conditions at reasonably high temperatures. The mechanism of vacancy diffusion presented here should be useful in managing VS defects during the fabrication of high-quality pyrite samples for solar energy conversion applications.

Photophysical Properties of CdSe/CdS core/shell quantum dots with tunable surface composition

We report the synthesis and optical characterization of core/shell CdSe/CdS quantum dots (QDs) with controlled surface composition. Using secondary phosphine chalcogenide and cadmium carboxylate precursors in an alternating layer-by-layer synthetic approach, the elemental surface composition of the quasi-type-I CdSe/CdS core/shell QDs can be repeatedly tuned from predominately cadmium to predominantly sulfur, as measured by X-ray photoelectron spectroscopy (XPS). Similar to CdS and CdSe core-only QDs, the surface composition has a significant effect on the photoluminescence (PL) quantum yield: sulfur terminated QDs exhibit quenched PL, while cadmium terminated QDs have relatively bright PL. Density-functional tight-binding calculations on CdSe/CdS core/shell clusters suggest that PL quenching for sulfur-rich surfaces is the result of a high density of hole surface states in the QD bandgap. Time-resolved PL measurements confirm the QDs’ nonradiative recombination rates are strongly sensitive to the surface composition.

Theory analysis and vestigial information of surface relaxation of natural chalcopyrite mineral crystal

X-ray diffraction was used to measure the unit cell parameters of chalcopyrite crystal. The results showed that the chalcopyrite crystal is perfect, and the arrangement of its atoms is regular. A qualitative analysis of molecular mechanics showed that surface relaxation causes the chalcopyrite surface to be sulfur enriched. Atomic force microscope (AFM) was used to obtain both a microscopic three-dimensional topological map of chalcopyrite surface and a two-dimensional topological map of its electron cloud. The AFM results revealed that the horizontal and longitudinal arrangements of atoms on the chalcopyrite surface change dramatically compared with those in the interior of the crystal. Longitudinal shifts occur among the copper, iron and sulfur atoms relative to their original positions, namely, surface relaxation occurs, causing sulfur atoms to appear on the outermost surface. Horizontally, AFM spectrum showed that the interatomic distance is irregular and that a reconstruction occurs on the surface. One result of this reconstruction is that two or more atoms can be positioned sufficiently close so as to form atomic aggregates. The lattice properties of these models were calculated based on DFT theory and compared with the experimental results and those of previous theoretical works. On analyzing the results, the atomic arrangement on the (001) surface of chalcopyrite is observed to become irregular, S atoms move outward along the Z-axis, and the lengths of Cu—S and Fe—S bonds are enlarged after geometry optimization because of the surface relaxation and reconstruction. The sulfur-rich surface and irregular atomic aggregates caused by the surface relaxation and reconstruction greatly influence the bulk flotation properties of chalcopyrite.

Partitioning of dissolved organic matter-bound mercury between a hydrophobic surface and polysulfide-rubber polymer

This study investigated the role of dissolved organic matter on mercury partitioning between a hydrophobic surface (polyethylene, PE) and a reduced sulfur-rich surface (polysulfide rubber, PSR). Comparative sorption studies employed polyethylene and polyethylene coated with PSR for reactions with DOM-bound mercuric ions. These studies revealed that PSR enhanced the Hg-DOM removal from water when DOM was Suwannee River natural organic matter (NOM), fulvic acid (FA), or humic acid (HA), while the same amount of 1,3-propanedithiol-bound mercuric ion was removed by both PE and PSR-PE. The differences for Hg-DOM removal efficiencies between PE and PSR-PE varied depending on which DOM was bound to mercuric ion as suggested by the PE/water and PSR-PE/water partition coefficients for mercury. The surface concentrations of mercury on PE and PSR-PE with the same DOM measured by x-ray photoelectron spectroscopy were similar, which indicated the comparable amounts of immobilized mercury on PE and PSR-PE being exposed to the aqueous phase. With these observations, two major pathways for the immobilization reactions between PSR-PE and Hg-DOM were examined: 1) adsorption of Hg-DOM on PE by hydrophobic interactions between DOM and PE, and 2) addition reaction of Hg-DOM onto PSR by a complexation reaction between Hg and PSR. The percent contribution of each pathway was derived from a mass balance and the ratios among aqueous mercury, PE-bound Hg-DOM, and PSR-bound Hg-DOM concentrations. The results indicate strong binding of mercuric ion with both dissolved organic matter and PSR polymer. The FT-IR examination of Hg-preloaded-PSR-PEs after the reaction with DOM corroborated a strong interaction between mercuric ion and 1,3-propanedithiol compared to Hg-HA, Hg-FA, or Hg-NOM interactions.

Resonant soft X-ray reflectivity as a sensitive probe to investigate polished zinc sulphide surface

Resonant soft X-ray reflectivity measurements at and near the L 3 absorption edge of sulphur have been performed on mechanically polished zinc sulphide using Indus-1 synchrotron source. A sulphur rich surface (∼15 nm thick) consisting of two layers with gradient electron density distribution was uniquely determined. As compared to bulk ZnS, the top layer has ∼30–50% less electron density whereas, the intermediate layer has ∼10–18% less electron density. Conventional hard X-ray reflectivity measurement at Cu Kα wavelength also indicates low electron density (sulphur rich) surface of ZnS but the technique was found insensitive for unique determination of electron density distribution. Optical constants of ZnS in the soft X-ray region (100–250 eV) have been reported for the first time and were in good agreement with the theoretically reported values.

Quantum Dot Photovoltaics in the Extreme Quantum Confinement Regime: The Surface-Chemical Origins of Exceptional Air- and Light-Stability

We report colloidal quantum dot (CQDs) photovoltaics having a approximately 930 nm bandgap. The devices exhibit AM1.5G power conversion efficiencies in excess of 2%. Remarkably, the devices are stable in air under many tens of hours of solar illumination without the need for encapsulation. We explore herein the origins of this orders-of-magnitude improvement in air stability compared to larger PbS dots. We find that small and large dots form dramatically different oxidation products, with small dots forming lead sulfite primarily and large dots, lead sulfate. The lead sulfite produced on small dots results in shallow electron traps that are compatible with excellent device performance; whereas the sulfates formed on large dots lead to deep traps, midgap recombination, and consequent catastrophic loss of performance. We propose and offer evidence in support of an explanation based on the high rate of oxidation of sulfur-rich surfaces preponderant in highly faceted large-diameter PbS colloidal quantum dots.

Rate law for galena dissolution in acidic environment

A dissolution rate law for galena in acidic environment was derived from the steady-state dissolution rates using flow-through experiments. The influence of temperature, dissolved oxygen concentration and pH between 1 and 3 was assessed. This rate law can be used for predicting galena dissolution behavior in a wide range of conditions analogous to Acid Rock Drainage. For pH below 2, the dissolution rate law can be expressed as: R Gn , pH < 2 = 10 − 5.7 ± 0.4 e − 23 ± 3 RT a H + 0.43 ± 0.05 where R Gn is the galena dissolution rate (mol m − 2 s − 1 ), R is the gas constant (kJ mol − 1 K − 1 ) , T is the temperature (K) and a H + is the activity of hydrogen ion in the solution. Galena dissolution rate law for pH between 2 and 3 can be expressed as: R Gn , pH = 2 − 3 = 10 − 8.5 ± 0.4 e − 15 ± 2 RT a H + − 0.78 ± 0.04 a O 2 ( aq ) 0.30 ± 0.03 where a O 2 ( aq ) is the activity of dissolved oxygen. XPS (X-ray Photoelectron Spectroscopy) examination of the reacted galena samples shows the formation of a lead-deficient and sulfur-rich surface layer, consistent with the observed non-stoichiometry between dissolved sulfur and lead in all the studied solutions. Based on the S/Pb ratio observed in solution and the reacted surfaces and the pH and dissolved oxygen dependence of the rates, two possible reactions for galena dissolution in acidic aqueous solution are proposed; (1) at pH ≤ 2 the rate seems to be determined by the protonation of surface sulfur atoms, and (2) at pH ≥ 2 the rate seems to be controlled by the attachment of oxygen to surface sulfur atoms. The values obtained for the activation energies (15 ± 2 kJ mol − 1 at pH 3 and 23 ± 3 kJ mol − 1 at pH 1) suggest that galena dissolution is controlled by diffusion processes or mixed-controlled by diffusion of reactants and products between the bulk solutions and the reacting surfaces.

Succession of Internal Sulfur Cycles and Sulfur-Oxidizing Bacterial Communities in Microaerophilic Wastewater Biofilms

The succession of sulfur-oxidizing bacterial (SOB) community structure and the complex internal sulfur cycle occurring in wastewater biofilms growing under microaerophilic conditions was analyzed by using a polyphasic approach that employed 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization, microelectrode measurements, and standard batch and reactor experiments. A complete sulfur cycle was established via S(0) accumulation within 80 days in the biofilms in replicate. This development was generally split into two phases, (i) a sulfur-accumulating phase and (ii) a sulfate-producing phase. In the first phase (until about 40 days), since the sulfide production rate (sulfate-reducing activity) exceeded the maximum sulfide-oxidizing capacity of SOB in the biofilms, H(2)S was only partially oxidized to S(0) by mainly Thiomicrospira denitirificans with NO(3)(-) as an electron acceptor, leading to significant accumulation of S(0) in the biofilms. In the second phase, the SOB populations developed further and diversified with time. In particular, S(0) accumulation promoted the growth of a novel strain, strain SO07, which predominantly carried out the oxidation of S(0) to SO(4)(2-) under oxic conditions, and Thiothrix sp. strain CT3. In situ hybridization analysis revealed that the dense populations of Thiothrix (ca. 10(9) cells cm(-3)) and strain SO07 (ca. 10(8) cells cm(-3)) were found at the sulfur-rich surface (100 microm), while the population of Thiomicrospira denitirificans was distributed throughout the biofilms with a density of ca. 10(7) to 10(8) cells cm(-3). Microelectrode measurements revealed that active sulfide-oxidizing zones overlapped the spatial distributions of different phylogenetic SOB groups in the biofilms. As a consequence, the sulfide-oxidizing capacities of the biofilms became high enough to completely oxidize all H(2)S produced by SRB to SO(4)(2-) in the second phase, indicating establishment of the complete sulfur cycle in the biofilms.

Acid leaching and dissolution of major sulphide ore minerals: processes and galvanic effects in complex systems

AbstractThe kinetics and mechanisms of dissolution of the major base metal sulphide minerals, pyrite, chalcopyrite, galena and sphalerite in acidic (chloride) media have been investigated. Minerals were ground in air, then dissolved in air-equilibrated solutions at pH 2.5, while monitoring the redox potential. Solution samples were analysed by ICP-AES and HPLC, and surfaces of residual sulphides analysed using XPS. Dissolution of aerial oxidation products on pyrite particles in the first 15 min apparently led to a sulphur-rich surface, and was followed by slower dissolution of pyrite itself, driven by oxygen reduction, and resulting in net production of protons. Chalcopyrite dissolution resulted in a Cu, S-rich (near) surface layer, accompanied by net consumption of protons. Apparently incongruent dissolution of galena and sphalerite may reflect the formation of elemental S at the surface. The rates of dissolution of chalcopyrite, galena and sphalerite in the presence of pyrite were determined, respectively, as 18, 31 and 1.5 times more rapid than in single-mineral experiments. These data were consistent with galvanically-promoted mineral oxidation of the other sulphides in the presence of pyrite. In the case of galena, the experimental data suggested extensive release of Pb ions and development of a sulphur-rich surface during galvanically-promoted dissolution.

Oxidation of Synthetic and Natural Samples of Enargite and Tennantite: 1. Dissolution and Zeta Potential Study

The oxidation of synthetic and natural samples of tennantite and enargite is compared by measuring the dissolution and the zeta potential of these minerals. The changes in zeta potential with pH and oxidizing conditions are consistent with the presence of a copper hydroxide layer covering a metal-deficient sulfur-rich surface and with the extent of this copper hydroxide coverage increasing with oxidation conditions. Analysis of the zeta potential data reveals that during the acid titration of the minerals, dissolution of the surface copper hydroxide layer occurs at neutral pH values, whereas precipitation of copper hydroxide on the mineral surface is observed during the base titration. Hysteresis between the zeta potential acid and base titration curves is only observed in oxidizing conditions and is attributed to the dissolution of copper from the mineral lattice at acidic pH values. Arsenic does not appear to contribute to the mineral oxidation; in particular, its dissolution is much less than that of c...