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In order to unravel the oxidation mechanism(s) of chalcopyrite (CuFeS 2 ) surfaces, the surface anisotropy of CuFeS 2 was investigated under both dry and aqueous atmospheres through a fundamental density functional theory (DFT) study. Results showed that the CuFeS 2 (112) surface was the preferred cleavage surface, rather than the commonly-assumed (001) surface. Iron oxides were formed when contacting with either molecular O 2 or dissociated O atoms, but sulfoxy species were only formed in the presence of dissociated O atoms, exposing Cu atoms on the S-terminated (001) and (112) surfaces. This indicates that strong oxidation conditions are beneficial to CuFeS 2 oxidation and the release of metals into solution. In addition, CuFeS 2 was preferentially oxidized by O 2 prior to the adsorption of H 2 O under an aqueous condition with both H 2 O and O 2 . The H 2 O adsorbed on the O-oxidized surface further promoted CuFeS 2 oxidation, resulting in the formation of a hydrophilic surface, rather than the naturally hydrophobic surface. This study has unveiled, for the first time, the mechanisms of the oxidation of the most stable and reactive CuFeS 2 (112) and (001) surfaces under both dry and aqueous environments at an atomic level, with potential applications in CuFeS 2 flotation and leaching processes.

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.

Trace elements bound in quartz lattice are efficiently removed by KCl-doping calcination and pressure leaching. Removal rate of lattice Al reaches 73.5% when 70.4% of lattice-bound trace elements are removed from quartz sand at optimum conditions. The lattice-bound trace elements in quartz are activated by high-temperature calcination, released during phase transformation from α-quartz to cristobalite, diffused to quartz surface by surface enrichment, and removed by oxidation, chlorination and pressure leaching.

Anatase (TiO2) has been widely used in photocatalysis. However, it can only absorb near-ultraviolet light with a wavelength below approximately 388 nm due to a wide band gap. Therefore a modification should be made for anatase to increase its capability in utilizing more abundant visible light. We investigated the doped anatase with the most promising 3d transition metal elements, and the results showed that the visible light absorption intensity was increased significantly due to the reduced band gap and the cavitation effects. As compared to other 3d transition metals, Cu was found to be the most effective one in improving anatase photocatalytic effects. In addition, greater Cu concentration doped in the anatase increased the photocatalysis effects but reduced the anatase stability, therefore, an optimized Cu concentration should be considered to optimize the anatase photocatalysis activity.

In order to better understand the floatability of molybdenite (MoS2), the anisotropic properties of MoS2 faces and edges were investigated, followed by the adsorption of H2O on the fresh and oxidized surface through a fundamental density functional theory (DFT) study. Results show that no new bonds were formed on any surface during the relaxation process. The surface energies of MoS2 edges (i.e. (1 0 3), (1 0 5), (1 0 0) and (1 1 0) surfaces) were nearly 10 times as to MoS2 face (i.e. (0 0 1) surface), indicating a preferential cleavage surface of (0 0 1) face. The fresh MoS2 face tends to exhibit hydrophobic properties, in contrast to edges. Further energy calculation indicates that MoS2 particles tend to be hydrophobic when edge to face ratio is less than 0.56 based on the adsorption of monolayer H2O. MoS2 surfaces are preferentially oxidized by O2, or disassociated O rather than H2O, from hydrophobic to hydrophilic, indicating a detrimental role of oxidation to its flotation process. This study therefore demonstrates, for the first time, the anisotropic properties of MoS2 face and edges at an atomic level, as well as the wettability of fresh and oxidized surfaces, suggesting that the edges to faces ratio of MoS2 dominate the floatability of MoS2.

Chalcopyrite flotability were investigated in four common chloride salts. The results indicated that NaCl, KCl, CaCl2 increased chalcopyrite recovery while MgCl2 decreased its recovery. The monovalent salts played an insignificant role while divalent salts apparently decreased the contact angle of chalcopyrite, regardless of the presence of collectors. Furthermore, the zeta potential was increased in divalent salts and even changed from negative to positive values in MgCl2, highly due to Mg(OH)2 precipitation on chalcopyrite surface. In addition, molecular dynamics simulation indicated that Mg(OH)2 precipitates on chalcopyrite (112) surface stabilized the liquid layer and formed a hydrophilic barrier to inhibit SBX adsorption Refereed/Peer-reviewed

Sea water has been used in flotation plants, showing a promising way to save fresh water usage. Previous studies indicated that divalent salts in sea water played negative roles in chalcopyrite flotation, but not much work have been conducted to understand the eliminating mechanisms. This study systematically investigated the effects of divalent cations of Ca2+ and Mg2+ on natural flotability of chalcopyrite in the absence of collectors and frothers. The reduced recovery was mainly due to the adsorption of Mg and Ca hydroxyl complexes and precipitation on chalcopyrite surfaces, giving rise to a less hydrophobic surface. The addition of sodium hexametaphosphate (SHMP), however, significantly improved chalcopyrite recovery. Species calculation, contact angle, zeta potential, FTIR and XPS analyses were conducted to understand the influencing mechanisms of divalent ions and the beneficial effects of SHMP on chalcopyrite recovery. The primary mechanism was that SHMP prevented the adsorption of positively charged Mg and Ca compounds or precipitation with hydrophilic properties such as Mg(OH)2 on chalcopyrite surfaces, confirmed by the Derjguin-Landau-Verwey-Overbeek (DLVO) theory. Secondly, SHMP reacted with Mg2+ and Ca2+ to form dissolvable complexes, thereby declining the formation of insoluble Mg2+ and Ca2+ compounds or precipitation.

Chalcopyrite leaching process is hindered predominantly due to the passivation layers formed on its surface. The impurity salts normally present in the leaching systems may influence chalcopyrite leaching process. In this work, density functional theory (DFT) was carried out to investigate the influence of Mg 2+ and Ca 2+ on chalcopyrite (0 0 1)-S surface using Materials Studio. The results indicated that the presence of CaSO 4 contributed to the breakage of S–S bonds on chalcopyrite (0 0 1)-S surface. Although Ca 2+ was not found to bond with any of the S atoms derived from broken S 2 2− bond, a stable structure of Ca–SO 4 –Fe was formed. Similarly, the adsorption of MgSO 4 on chalcopyrite (0 0 1)-S surface contributed to the breakage of S 2 2− bond, forming a complex and stable structure of S–Mg–SO 4 –Fe as new passivation layers due to the bonding effects between Mg 2+ and a S atom from the broken S 2 2− bond. The formation of these new structures covered on chalcopyrite (0 0 1)-S surface, further reducing chalcopyrite leaching rates. This study, therefore for the first time, reveals the influencing mechanisms of Mg 2+ and Ca 2+ sulfates on chalcopyrite leaching at an atomic level.

To better understand chalcopyrite leach mechanisms and kinetics, for improved Cu extraction during hydrometallurgical processing, chalcopyrite leaching has been conducted at solution redox potential 750 mV, 35-75 °C, and pH 1.0 with and without aqueous iron addition, and pH 1.5 and 2.0 without aqueous iron addition. The activation energy (Ea) values derived indicate chalcopyrite dissolution is initially surface chemical reaction controlled, which is associated with the activities of Fe3+ and H+ with reaction orders of 0.12 and -0.28, respectively. A surface diffusion controlled mechanism is proposed for the later leaching stage with correspondingly low Ea values. Surface analyses indicate surface products (predominantly Sn2- and S0) did not inhibit chalcopyrite dissolution, consistent with the increased surface area normalised leach rate during the later stage. The addition of aqueous iron plays an important role in accelerating Cu leaching rates, especially at lower temperature, primarily by reducing the length of time of the initial surface chemical reaction controlled stage. Refereed/Peer-reviewed