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This paper presents the results of an investigation of the incorporation of Au within pyritic ore from the Qiucun epithermal Au deposit, China. The new data provide insights into the mode of occurrence of Au during fluid-rock interactions within epithermal systems. The distribution and mode of occurrence of Au within arsenian pyrite were investigated using a chemical and structural characterization-based approach combining laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace element analysis, megapixel synchrotron X-ray fluorescence analysis (MSXRF), and atom probe tomography (APT). The resulting data indicate that invisible Au is present at elevated concentrations in the form of a homogeneous solid solution within As-rich pyrite domains, which yields Au concentrations that positively correlate with As. Arsenic-induced lattice defects, such as stacking faults and the expansion of the pyrite unit cell, provide evidence of the effect of As on the incorporation of Au into pyrite. The nucleation and crystallization of electrum preferentially occurred at the fluid-pyrite reaction interface or along fractures and grain boundaries within the pre-existing pyrite. This study indicates that changes in physicochemical conditions (e.g., temperature, pH, and sulfur fugacity) during fluid-pyrite interactions are key controls on the development of nanometer- or micrometer-scale clusters of gold. The systematic compositional and textural observations documented in this study provide new insights into the mechanisms responsible for the different modes of occurrence of Au (ionic vs. particulate) and enable us to further understand the processes involved in the formation of Au mineralization.

A Raman spectroscopic study on the nature of As-S substitution in natural arsenian pyrite [Fe(S,As)2] is presented, covering a compositional range of 0.01–4.6 at% As. Three Raman-active modes were identified in the Raman spectrum of a nearly pure pyrite: Eg (344 cm−1), Ag (379 cm−1), and Tg(3) (432 cm−1). The Raman vibrational modes exhibit one-mode behavior, and the wavenumbers of optical modes vary approximately linearly with As content, correlating with the change in bond constants with increasing substitution of As for S. The linewidth of the Ag mode increases with increasing As substitution, which may be attributed to the increase in lattice strain associated with the substitution of As for S. This study provides experimental evidence for As-induced structural evolution of pyrite from being stable to metastable before decomposing into other phases. Our results, together with those of another Raman study of arsenian pyrite whose As substitution is more complex, indicate that one cannot use Raman band shifts to determine As content, but for a given As content, can characterize the nature of As substitution, i.e., As for S or As for Fe or both.

The dissolution of silicate minerals has been largely examined under steady state conditions. The primary aim of this study was to understand the potential of the non-steady state dissolution of silicate minerals in treatment of acid and metalliferous drainage (AMD) resulting predominantly from pyrite oxidation. To this end, flow-through dissolution cell experiments were carried out using selected silicate minerals (biotite, chlorite, olivine and K-feldspar), all commonly found in AMD environments, under various pH and flow rate conditions, for comparison to pyrite dissolution carried out under the same conditions. Both acid generation rate (pyrite) and steady-state and non-steady state acid neutralisation rates (silicates) were calculated and compared. Results showed that the non-steady state acid neutralisation rates due to silicate dissolution were greater than the steady-state neutralisation rates and that all silicate minerals investigated in this study, except K-feldspar, can provide acid neutralisation rates to match the acid generation rate due to pyrite dissolution under certain conditions.

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.

The aim of this study was to determine the combined effect of galvanic interaction and silicate addition on the dissolution of pyrite, the major contributor to acid and metalliferous drainage (AMD). Single (pyrite, sphalerite, and galena)- A nd bi-sulfide (pyrite-sphalerite and pyrite-galena) batch dissolution experiments were carried out with addition of 0.8 mM dissolved silicate for comparison to previously published data. The pyrite dissolution rate was reduced by 98% upon silicate addition at pH 7.4 with little effect at pH 3.0 and 5.0. The effect of galvanic interaction on reducing pyrite dissolution decreased with increasing pH and was greater in the presence of sphalerite than galena. In contrast, the effect of silicate addition increased with increasing pH and was greater in the presence of galena than sphalerite. The greatest combined effect was at pH 7.4, with

Selenium (Se) has been mobilised by leaching from coal and associated waste rock exposed by mining activities in Western Canada, with deleterious impact on aquatic wildlife. Waste rock characterisation indicates that up to 7% of the Se, as Se(IV), may be associated with organic matter, with ≈9%, as Se(0), associated with euhedral pyrite. Small 1−2 µm mineral particles with average Se concentration of 1.0 ± 0.4 wt% account for the remaining Se with the largest components likely to be associated with Fe oxide/hydroxide/carbonate as Se(0) and framboidal pyrite as Se(IV) and Se(0). No evidence was found for the presence of Se(−I), Se(−II) or Se(VI). In the first 8 weeks of leaching Se release was not correlated to the addition of aqueous silicate, added to aid pyrite passivation, but was reduced by approximately one third when the waste was treated with manure. This suggests the primary initial source of leached Se was not pyrite. Added organic C results in increased microbial numbers, particularly aerobic microbes, and promotes the formation of extensive coating of extracellular polymeric substances resulting in depletion of O2 at particle surfaces, reducing oxidation of Se(IV) and therefore reducing the leach rate of Se. Subsequent to 8 weeks of leaching the rates of release of Se from the treated wastes were similar regardless of treatment strategy but were reduced as compared to the untreated waste rock, suggestive of partial framboidal pyrite geochemical and microbial passivation. Se leaching was not correlated to S leaching, but the source(s) of the leached S was not known as approximately half of the S within the waste rock was non-sulfidic. These results indicate that utilisation of local organic carbon-containing wastes for coverage of coal waste rock may be a cost-effective strategy to reduce Se leaching to acceptable rates of release regardless of whether the Se is associated with framboidal pyrite or organics Refereed/Peer-reviewed

Chalcopyrite, galena, and sphalerite commonly coexist with pyrite in sulfidic waste rocks. The aim of this work was to investigate their impact, potentially by galvanic interaction, on pyrite oxidation and acid generation rates under simulated acid and metalliferous drainage conditions. Kinetic leach column experiments using single-minerals and pyrite with one or two of the other sulfide minerals were carried out at realistic sulfide contents (total sulfide 47% for galena vs

The fast degradation and consequent loss of mechanical integrity is a major problem of biodegradable Mg alloy, which limits its clinical viability. This paper presents the influence of a synergistic approach combining burnishing and hydroxyapatite (HA) coating on biomechanical integrity, degradation and immune response of Mg alloy (AZ31B). The burnishing resulted in smooth surface topography, increased hardness from 0.87 to 1.45 GPa and induced microstructural disturbances with deformation twins/twin bands, which enabled formation of a dense and compact platelet-like crystals HA coating of 110 μm thickness. Compared to the untreated and burnished specimens, the burnished + HA coated surface provided remarkably higher corrosion resistance as indicated by lower corrosion current density and smaller mass loss. HA coating and surface integrity enhancement by burnishing were predominantly responsible for improved corrosion resistance. HA coating on the burnished surface exhibited hydrophilic properties and adequate bonding strength. While the modified surfaces promoted cell growth, the burnished + HA surface outperformed in exhibiting less pro-inflammatory and high anti-inflammatory cytokines, demonstrating that the treated surfaces were not posing any threat to immune cells. The findings indicate that the synergistic surface treatment can be a viable means to enhance corrosion resistance and immune response of Mg alloys implants. Refereed/Peer-reviewed

Acid and metalliferous drainage (AMD) is a major environmental issue resulting largely from exposure to weathering of mine wastes containing pyrite (FeS2). At-source strategies to reduce the rate of formation of AMD have potential to be more cost-effective and sustainable than post-generation downstream treatments. The objective of this study was to examine the efficacy of geochemical and microbial treatments for at-source control through pyrite surface passivation. Six kinetic leach columns (KLCs), using a mine waste containing 3.8 wt% pyrite, were subjected to various treatments: 1) untreated, 2) blended calcite, and applications of 3) calcite-saturated water, 4) lime-saturated water followed by calcite-saturated water, 5) biosolids extract water (providing a source of organic carbon to promote microbial growth) and 6) biosolids extract in calcite-saturated water. The untreated KLC leachate pH was on average 5.7 for the first 12 weeks, followed by a gradual decrease to pH 4.5 at week 52. This slow pH decrease is attributed to neutralisation released upon Mg-siderite dissolution. The leachate pH from all treated KLCs was near-neutral at the end of the tests. Pyrite was surface-passivated and leaching supressed by all treatments except for calcite-saturated water. Leaching of Mn and Zn from the untreated waste identified the potential for adverse environmental impact. No evidence was found for surface passivation of Zn- or Mn-containing minerals in the treated KLCs. Blended calcite addition and lime-saturated water followed by calcite-saturated water were most effective at reducing release of Zn and Mn, likely due to precipitation as hydroxides/carbonates Refereed/Peer-reviewed

The presence of latent acidity in the form of the jarosite-alunite mineral group complicates assessment of the rates of acid and metalliferous drainage (AMD) generation from potentially acid-forming waste rocks and tailings.To enable better prediction of the contributions from these secondary sulfate minerals, the relationships between pH and the rate of dissolution for natrojarosite and alunite, for comparison with pyrite, have been determined.In single mineral unstirred systems, the dissolution rates of natrojarosite and alunite in the pH range 2–7 were in the range of 10⁻¹⁴ to 10⁻¹³ molm⁻² s⁻¹ and were found to be slowest at pH 3.4 and 5.5, respectively. At pH above these respective minima, alunite and natrojarosite dissolution results in acid release. The surface area normalised dissolution rates of both minerals were 2–3 orders of magnitude slower than that of pyrite under the same conditions, and were 2–4 orders of magnitude slower than the rates of stirred dissolution of syntheticjarosite and alunite reported in the literature. In mixed mineral mini-column dissolution tests, pyrite oxidation proceeded at almost the same rate in the longer term (> 50 days), regardless of the presence or absence of natrojarosite or alunite. As the presence of these secondary sulfate minerals does not impact significantly onpyrite oxidation, their contributions to AMD can be taken into account separately enabling accurate calculation of the neutralisation rates needed to effectively manage AMD. Refereed/Peer-reviewed

Drinking water treatment sludge (DWTS) can be recycled into low-strength concrete blocks for construction use. The sodium sulfate resistance and leaching behaviours of the DWTS-derived blocks are investigated in this study. The experimental results show that the addition of DWTS degrades the sodium sulfate resistance of the concrete blocks, however CO

Acid rock drainage (ARD) is generated when mineral sulfides, primarily pyrite (FeS2), are exposed to weathering. Pyrite oxidation and dissolution may also result in the precipitation of secondary sulfate minerals, commonly found in weathered mine wastes, that release ‘stored acidity’ on subsequent dissolution. To better understand the release of this stored acidity, a kinetic leach column experiment using a synthetic pyritic (5 wt%) mine waste was conducted for a period of 524 weeks. The first 260 weeks watering/flushing was carried out using Milli-Q water during which the leachate pH decreased from 6.0 to 2.0, pyrite passivation layers present initially were removed and secondary sulfate minerals formed. The rate at which acidity was generated from secondary sulfate mineral dissolution was significantly greater than from pyrite oxidation after the calcite-saturated silicate water treatment during the period from 260 to 440 weeks. This suggests that in weathered pyritic wastes, both the amount of acidity and the rate at which it is released may be dominated by acid sulfate minerals rather than residual pyrite. Importantly, it was found that passivation strategies appropriate for reducing pyrite oxidation rates were not effective for reducing the rate of acid release from secondary mineralisation. Significant amounts of lime-saturated water (with high alkalinity) were required to dissolve the secondary sulfate minerals containing the stored acidity before circum-neutral conditions necessary for pyrite passivation could be achieved. It follows therefore that it is necessary to quantify the amount of stored acidity in secondary minerals so that appropriate remediation and acid management strategies can be designed and implemented to achieve long-term sustainable ARD control and mine closure Refereed/Peer-reviewed

Acid and metalliferous release occurring when sulfide (principally pyrite)-containing rock from mining activities and from natural environments is exposed to the elements is acknowledged as a major environmental problem. Acid rock drainage (ARI)) management is both challenging and costly for operating and legacy mine sites. Current technological solutions are expensive and focused on treating ARD on release rather than preventing it at source. We describe here a viable, practical mechanism for reduced ARD through the formation of silicate-stabilized iron oxyhydroxide surface layers. Without silicate, oxidized pyrite particles form an overlayer of crystalline goethite or lepidocrocite with porous structure. With silicate addition, a smooth, continuous, coherent and apparently amorphous iron oxyhydroxide surface layer is observed, with consequent pyrite dissolution rates reduced by more than 90% at neutral pH. Silicate is structurally incorporated within this layer and inhibits the phase transformation from amorphous iron (oxy)hydroxide to goethite, resulting in pyrite surface passivation. This is confirmed by computational simulation, suggesting that silicate-doping of a pseudo amorphous iron oxyhydroxide (ferrihydrite structure) is thermodynamically more stable than the equivalent undoped structure. This mechanism and its controlling factors are described. As a consequence of the greatly reduced acid generation rate, neutralization from on-site available reactive silicate minerals may be used to maintain neutral pH, after initial limestone addition to achieve neutral pH, thus maintaining the integrity of these layers for effective ARD management. Refereed/Peer-reviewed

usc Drinking water treatment sludge (DWTS) can be recycled into low-strength concrete blocks for construction use. The sodium sulfate resistance and leaching behaviours of the DWTS-derived blocks are investigated in this study. The experimental results show that the addition of DWTS degrades the sodium sulfate resistance of the concrete blocks, however CO2 curing compensates for such property, especially in the case of blocks incorporating 30% DWTS. The improvement can be attributed to the formation of crystalline CaCO3 during CO2 curing for microstructure refinement evidenced by X-ray Computed Tomography and Scanning Electron Microscopy. Leaching analyses show that Cu and Al concentrations increased with increasing DWTS content, and CO2 curing adversely increased the leachability of metals due to the decrease of pH, especially at early leaching stage. Nevertheless, the total leaching concentrations of Cu and Al after 60-day test is far below the prescribed limitations, regardless of samples subject to air curing or CO2 curing. In summary, sludge-derived blocks exposed to CO2 curing are safe and behave well in aggressive environments. Therefore, this study showcases a green technology that successfully recycling DWTS into value-added and durable concrete blocks with low environmental impacts. Refereed/Peer-reviewed

The development of amorphous films with a wide transmission window and high refractive index is of growing significance due to the strong demand of integrating functional nanoparticles for the next-generation hybrid optoelectronic films. High-index TeO2-based glass films made via the sol–gel process are particularly suitable as their low temperature preparation process promises high compatibility with a large variety of nanoparticles and substrates that suffer from low thermal stability. However, due to the lack of in-depth understanding of the mechanisms of the formation of undesired metallic-Te (highly absorbing species) in the films, the preparation of high-transmission TeO2-based sol–gel films has been severely hampered. Here, by gaining insight into the mechanistic chemistry of metallic-Te formation at different stages during the non-hydrolytic sol–gel process, we identify the chemical route to prevent the generation of metallic-Te in a TeO2-based film. The as-prepared TeO2-based film exhibits a high transmission that is close to the theoretical limit. This opens up a new avenue for advancing the performance of hybrid optoelectronic films via incorporating a large variety of unique nanoparticles. Refereed/Peer-reviewed

Acid and Metalliferous Drainage (AMD), acid mine drainage or acid rock drainage, is recognised as a critical global environmental issue, resulting predominantly from the oxidation of pyrite..

Acid mine drainage (AMD) from mine wastes is a critical environmental issue worldwide. It is caused principally by the oxidation of pyrite (FeS 2 ) through a combination of complex reactions (physical, chemical, and biological), often associated with toxic metals/metalloids with varying toxicity, such as As, Cd, Pb and Zn. This paper is specifically focused on the role of reactive silicate minerals (including aluminosilicates) in contributing to pyrite surface passivation (at-source control for reduced AMD generation) and neutralisation processes for long-term AMD mitigation. The neutralisation potential of (alumino)silicate minerals (those readily accessible on-site) to buffer acid generation at reduced pH levels in the long-term is also discussed in the review. Overall, the review aims to present cost-effective solutions, using readily available (alumino)silicate minerals, to provide long-term neutralisation and precursors required for pyrite surface passivation (source control) for sustainable at-source geochemical AMD control. Refereed/Peer-reviewed

This study investigates the kinetics of molybdenite (MoS2) flotation in sulfate media (Na+, K+, Ca2+ and Mg2+) with a concentration of 10−4–10−2 M. Results indicate that both monovalent and divalent cations inhibit MoS2 flotation. Three flotation models were used to fit the flotation kinetic data. The Gamma model gives the best goodness of fit in terms of R Adj 2 (adjusted coefficient of determination) and RMSE (root mean square error), however, fails in predicting MoS2 flotation recovery in MgSO4 solution due to the contradictory to the actual flotation trend. In contrast, the rectangular model fits MoS2 flotation in all the sulfate solutions. The flotation rate constant k values decrease with increasing sulfate concentration, indicating that the increased sulfate concentration reduces MoS2 flotation rate. The lowest k was found in the MgSO4 media, suggesting that MgSO4 is most detrimental to MoS2 flotation recovery. In addition, the R∞ was decreased with increasing sulfate concentration in an order of Mg2+ > Ca2+ > K+ > Na+, with the minimum R∞ being obtained in 10−2 M MgSO4, probably due to the formation and adsorption of hydrophilic Mg(OH)2 onto MoS2 surface.

The aim of this study was to test the performance of a novel method for acid rock drainage(ARD) control through the formation of Al(OH)₃₋doped passivating surface layers on pyrite. At pH 2.0 and 4.0, there was no obvious inhibition of the pyrite oxidation rate on addition of 20 mg L⁻¹ Al³⁺ (added as AlCl3·6H2O). In comparison, the pyrite oxidation rate at circumneutral pH (7.4± 0.4) decreased with increasing added Al³⁺ with ≈98%reduction in long-term (282 days) dissolution rates in the presence of 20 mg L−1 Al³⁺. Al3³⁺ was added to the solution and allowed to equilibrate prior to pyrite addition (2 g L⁻¹).Consequently almost all Al³⁺ (>99.9%) was initially present as aluminum hydroxide precipitates at pH 7.4. X-ray photoelectron spectroscopy analysis showed a significant concentration of Al³⁺ (20.3 at. %) on the pyrite surface reacted at pH 7.4 with 20 mg L⁻¹ added Al³⁺, but no Al³⁺ on pyrite surfaces reacted at pH 2.0 and 4.0 with added Al³⁺. Transmission electron microscopy and synchrotron X-ray absorption near edge spectroscopy analyses indicated that compact surface layers containing both goethite and amorphous or nanocrystalline Al(OH)3 formed in the presence of 20 mg L⁻¹ Al³⁺ at circumneutral pH, in contrast to the porous goethite surface layers formed on pyrite dissolved in the absence of Al³⁺ under otherwise identical conditions. This work demonstrates the potential for novel Al-based pyrite passivation of relevance to the mining industry where suitable Al-rich waste materials are available for ARD control interventions. Refereed/Peer-reviewed

Although the acid generating properties of pyrite (FeS₂) have been studied extensively, the impact of galvanic interaction on pyrite oxidation, and the implications for acid and metalliferous drainage, remain largely unexplored. The relative galvanic effects on pyrite dissolution were found to be consistent with relative sulfide mineral surface area ratios with sphalerite (ZnS) having greater negative impact in batch leach tests (sulfide minerals only, controlled pH) and galena (PbS) having greater negative impact in kinetic leach column tests (KLCs, uncontrolled pH, >85 wt% silicate minerals). In contrast the presence of pyrite resulted consistently in greater increase in galena than sphalerite leaching suggesting that increased anodic leaching is dependent on the difference in anodic and cathodic sulfide mineral rest potentials. Acidity increases occurred after 44, 20, and 12 weeks in the pyrite-galena, pyrite-sphalerite, and the pyrite containing KLCs. Thereafter acid generation rates were similar with the Eh consistently above the rest potential of pyrite (660 mV, SHE). This suggests that treatment of waste rocks or tailings, to establish and maintain low Eh conditions, may help to sustain protective galvanic interactions and that monitoring of Eh of leachates is potentially a useful indicator for predicting changes in acid generation behavior. Refereed/Peer-reviewed

The dissolution of chalcopyrite in association with pyrite in mine waste results in the severe environmental issue of acid and metalliferous drainage (AMD). To better understand chalcopyrite dissolution, and the impact of chalcopyrite’s galvanic interaction with pyrite, chalcopyrite dissolution has been examined at 75 °C, pH 1.0, in the presence of quartz (as an inert mineral) and pyrite. The presence of pyrite increased the chalcopyrite dissolution rate by more than five times at Eh of 650 mV (SHE) (Cu recovery 2.5 cf. 12% over 132 days) due to galvanic interaction between chalcopyrite and pyrite. Dissolution of Cu and Fe was stoichiometric and no pyrite dissolved. Although the chalcopyrite dissolution rate at 750 mV (SHE) was approximately four-fold greater (Cu recovery of 45% within 132 days) as compared to at 650 mV in the presence of pyrite, the galvanic interaction between chalcopyrite and pyrite was negligible. Approximately all of the sulfur from the leached chalcopyrite was converted to S⁰ at 750 mV, regardless of the presence of pyrite. At this Eh approximately 60% of the sulfur associated with pyrite dissolution was oxidised to S⁰ and the remaining 40% was released in soluble forms, e.g., SO₄²⁻. Refereed/Peer-reviewed

This review covers a wide range of surface analytical techniques: X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), photoemission electron microscopy (PEEM), dynamic and static secondary ion mass spectroscopy (SIMS), electron backscatter diffraction (EBSD), atomic force microscopy (AFM). Others that are relatively less widely used but are also important to the Earth Sciences are also included: Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). All these techniques probe only the very top sample surface layers (sub-nm to several tens of nm). In addition, we also present several other techniques i.e. Raman microspectroscopy, reflection infrared (IR) microspectroscopy and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) that penetrate deeper into the sample, up to several μm, as all of them are fundamental analytical tools for the Earth Sciences. Grazing incidence synchrotron techniques, sensitive to surface measurements, are also briefly introduced at the end of this review. (Scanning) transmission electron microscopy (TEM/STEM) is a special case that can be applied to characterisation of mineralogical and geological sample surfaces. Since TEM/STEM is such an important technique for Earth Scientists, we have also included it to draw attention to the capability of TEM/STEM applied as a surface-equivalent tool.While this review presents most of the important techniques for the Earth Sciences, it is not an all-inclusive bibliography of those analytical techniques. Instead, for each technique that is discussed, we first give a very brief introduction about its principle and background, followed by a short section on approaches to sample preparation that are important for researchers to appreciate prior to the actual sample analysis. We then use examples from publications (and also some of our known unpublished results) within the Earth Sciences to show how each technique is applied and used to obtain specific information and to resolve real problems, which forms the central theme of this review. Although this review focuses on applications of these techniques to study mineralogical and geological samples, we also anticipate that researchers from other research areas such as Material and Environmental Sciences may benefit from this review. Refereed/Peer-reviewed

The effective control and treatment of acid mine drainage (AMD) from sulfide-containing mine wastes is of fundamental importance for current and future long-term sustainable and cost-effective mining industry operations, and for sustainable management of legacy AMD sites. Historically, AMD management has focused on the use of expensive neutralising chemicals to treat toxic leachates. Accordingly, there is a need to develop more cost-effective and efficient methods to prevent AMD at source. Laboratory kinetic leach column experiments, designed to mimic a sulfide-containing waste rock dump, were conducted to assess the potential of organic waste carbon supplements to stimulate heterotrophic microbial growth, and supress pyrite oxidation and AMD production. Microbiological results showed that the addition of biosolids was effective at maintaining high microbial heterotroph populations and preventing AMD generation over a period of 80 weeks, as verified by leachate chemistry and electron microscopy analyses. This research contributes to the ongoing development of a cost effective, multi-barrier geochemical-microbial control strategy for reduced mineral sulfide oxidation rates at source. Refereed/Peer-reviewed

Mechanical activation has been applied prior to leaching to improve copper extraction from chalcopyrite. Results showed that 86% copper was extracted within 2 h from chalcopyrite ground with sodium chlorite at 500 rpm, at pH 1.0 (sulfuric acid) and 348 K, greater than from leaching of unground (4.5% copper extraction) and ground chalcopyrite without sodium chlorite (13.5% extraction). Size reduction, structural modification and phase transformation were suggested as three mechanisms for improved copper extraction rate, with the last mechanism found to be dominant. Two leaching steps were proposed, for the first time, for chalcopyrite ground with sodium chlorite, including the first stage primarily determined by the dissolution of copper chlorite formed via a solid state reaction during grinding with chalcopyrite and the second stage dominated by the dissolution of unconverted chalcopyrite. This study suggests that grinding of chalcopyrite with sodium chlorite is beneficial to highly efficient copper extraction from chalcopyrite.

Polycrystalline Ni 3 Pb 2 S 2 (shandite) was synthesised as a non-porous ingot to enable representative surfaces prepared by fracture under UHV to be characterised by X-ray photoelectron spectroscopy (XPS) before and after exposure to air. For an unoxidised surface, the S 2 p 3/2 binding energy was found to be significantly lower than those reported previously for shandite itself and other sulfides having shandite structure, and consistent with the physical and chemical properties of the shandites. The core electron binding energies for the three constituent elements were in agreement with the formal oxidation state representation Ni 0 3 Pb II 2 S −II 2 , analogous to that deduced previously for Ni 3 Sn 2 S 2 . Shandite surfaces were found to oxidise rapidly when initially exposed to air under ambient conditions, and concomitant with the formation of the Ni–O and Pb–O species, to restructure to NiS- and PbS-like surface phases having S core electron binding energies no higher than those for shandite.

Dissolution and oxidation of sulfide minerals play key roles in both acid and metalliferous rock drainage and supergene enrichment. Surface speciation heterogeneity, critical to understanding mechanisms of mineral sulfide dissolution, has to date largely not been considered. To this end synchrotron scanning photoelectron microscopy (SPEM) was employed to examine freshly fractured and partially dissolved chalcopyrite (CuFeS 2 ) surfaces (pH 1.0 HClO 4 solution, redox potential 650 mV relative to a standard hydrogen electrode, 75 °C). S 2− (bulk), S 2 2− and S n 2− were found to be present on all samples at varying concentrations. Oxidation was observed to take place heterogeneously at the sub-micron scale. As compared to chalcopyrite partially dissolved for 5 days, extended dissolution to 10 days did not show appreciably enhanced oxidation of surface species; however surface roughness increased markedly due to the growth/overlap of oxidised sulfur species. On addition of 4 mM iron both S 0 and SO 4 2− were observed but not SO 3 2− , indicating that the greater Fe 3+ activity/concentration promotes heterogeneous sulfur oxidation. On contact of pyrite (FeS 2 ) with chalcopyrite, significantly greater chalcopyrite surface oxidation was observed than for the other systems examined, with S 0 , SO 3 2− and SO 4 2− being identified heterogeneously across the surface. It is proposed that chalcopyrite oxidative dissolution is enhanced by increasing its cathodic area, e.g . contacting with pyrite, while increased Fe 3+ activity/concentration also contributes to increased dissolution rates. The high degree of surface heterogeneity of these surface products indicates that these surfaces are not passivated by their formation. These results suggest that chalcopyrite dissolution will be accelerated when in contact with pyrite at solution redox potential intermediate between the rest potentials of chalcopyrite and pyrite (560 mV and 660 mV, respectively) and/or iron rich acidic waters with resulting enhanced formation of secondary sulfur containing species and release of copper and iron. This in turn suggests accelerated supergene formation and enhanced metalliferous drainage under these conditions.

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

The transformation of pyrrhotite to Fe disulfide (pyrite and/or marcasite) under hydrothermal conditions was studied experimentally by probing the effects of temperature (up to 220 degrees C, vapor-saturated pressures), ΣS(-II) concentrations, pH, and availability of oxygen on reaction progress and on the resulting textures. The pyrrhotite to Fe disulfide reaction proceeded by a dissolution-reprecipitation mechanism under all conditions. Marcasite and pyrite formed under both oxic and anaerobic conditions, which is inconsistent with the traditionally assumed polysulfide route for FeS₂ formation (oxidants required for polysulfide formation). The nature of the products was controlled by the level of supersaturation of the solution with respect to Fe disulfide minerals. Marcasite formed preferentially at low pH or S(-II)-deficient solutions (saturation index << 1000), while pyrite was the main product at saturation indices >1000. Different textures were obtained for the replacement of pyrrhotite by either pyrite or marcasite. Pyrite formation proceeded by direct replacement of pyrrhotite and, simultaneously, by overgrowth from solution. The pyrite crystals were 10 um in size and randomly oriented. In comparison, marcasite crystals were 1 um in size, and no significant overgrowth was observed. At pH₂₁ degrees C

We present the results of an experimental study into the sulfidation of magnetite to form pyrite/marcasite under hydrothermal conditions (90–300 C, vapor saturated pressures), a process associated with gold deposition in a number of oredeposits. The formation of pyrite/marcasite was studied as a function of reaction time, temperature, pH, sulfide concentration, solid-weight-to-fluid-volume ratio, and geometric surface area of magnetite in polytetrafluoroethylene-lined autoclaves(PTFE) and a titanium and stainless steel flow-through cell. Marcasite was formed only at pH21C 2 and formed even under basic conditions (up topH21C 12–13). Marcasite formation was favored at higher temperatures. Fine-grained pyrrhotite formed in the initial stageof the reaction together with pyrite in some experiments with large surface area of magnetite (grain size

Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses.

Irradiation resistance of as-studied scintillating glass samples were tested under the 60Co γ-ray radiation at doses between 60 and 700 Gy. Photoluminescence properties of glasses with and without cerium ions were investigated to show the effect of cerium (III) on the luminescence of ZnO. Ultraviolet and visible optical transmittance spectra were compared before and after irradiation treatment. The so-called radiation-induced absorption coefficient (RIAC) was introduced to compare more effectively the radiation damage on glass samples. The much reduced transmittance change and decreased RIAC value in UV–Vis region indicate that the density of electron centers and hole centers caused by radiation decreased, which helps to confirm that the reduction and oxidation reaction of cerium ions took place in radiation process. From RIAC curves, it can be seen that TiO2 enhances the irradiation resistance of sample in UV region. However, high TiO2 content has negative effect on visible transmittance of glasses after the higher dose irradiation (700 Gy).

ZnO–SiO2–BaO(BaF2) glasses are studied in the search for a novel scintillating material. Photoluminescence of such glasses was measured within 8–300 K including the decay kinetics and also the XPS spectra were obtained on selected samples to have information about Zn–O–Si bonding in the glass. Glass emission occurs in the violet-blue spectral range and decay kinetics is governed by the decay times of hundreds ns – units μs. XPS measurements reveal the higher binding energy of the Zn 2P electron and the lower kinetic energy of the Auger Zn L 3 M 4 , 5 M 4 , 5 electron, as well as the lower binding energy of the Si 2P electron, which implies the participation of Zn 2 + cations in the glass network to form the Zn–O–Si bond.

A series of Ce3+-doped phosphate, borate, silicate and germanate glasses were prepared and their optical properties were investigated. Experimental observations on transmission and photoluminescence spectra show obvious Nephelauxetic effect depending on the optical basicity of glasses. Especially, addition of alkaline earth oxides as a substitution of glass network former contributes to the further red shifts of excitation and emission bands due to increases in the number of less polarized non-bridging oxygen ions which increase the optical basicity of the system.

This study combined physical data from synchrotron SAXS, FTIR and microscopy with in-silico molecular structure predictions and mathematical modeling to examine inulin adjuvant particle formation and structure. The results show that inulin polymer chains adopt swollen random coil in solution. As precipitation occurs from solution, interactions between the glucose end group of one chain and a fructose group of an adjacent chain help drive organized assembly, initially forming inulin ribbons with helical organization of the chains orthogonal to the long-axis of the ribbon. Subsequent aggregation of the ribbons results in the layered semicrystalline particles previously shown to act as potent vaccine adjuvants. γ-Inulin adjuvant particles consist of crystalline layers 8.5 nm thick comprising helically organized inulin chains orthogonal to the plane of the layer. These crystalline layers alternate with amorphous layers 2.4 nm thick, to give overall particle crystallinity of 78%. Refereed/Peer-reviewed

To better understand chalcopyrite dissolution in hydrogeochemical processes and the related environmental issue of acid and metalliferous drainage (AMD), the kinetics as well as the influence of solution composition and the nature of surface species formed during chalcopyrite dissolution have been examined under the controlled conditions of Eh 650 mV (SHE), pH 1.0–2.0 and 75 °C, with/without 4 mM Fe2+ addition. SEM and XPS analyses indicate that the surface products, both at micro- and nano-scales, did not passivate dissolution under the conditions examined. Extensive S0 was formed mostly as discrete particles rather than coatings on the chalcopyrite surface. Jarosite was only observed for dissolution at pH 2.0 with 4 mM added Fe2+. Without Fe2+ addition, the initial dissolution rate was observed to be only correlated to H+ activity as a H + 0.12 ( ± 0.01 ) , indicating chalcopyrite dissolution was controlled via chemical oxidation of chalcopyrite by H+/O2. When reaction between chalcopyrite and Fe3+ predominated chalcopyrite dissolution (i.e. later stage of dissolution without Fe2+ addition), the dissolution rate was found to be positively correlated to the activities of Fe3+, as a Fe 3 + 1.54 ( ± 0.07 ) , and H+, as a H + 0.13 ( ± 0.05 ) . When 4 mM Fe2+ was added, no clear correlation was observed between the dissolution rate and the activities of either Fe3+or H+. It is proposed that the relative reactive surface area may not be proportional to that predicted by a shrinking sphere model as was assumed for derivation of the rate laws for the systems without added Fe2+, with the predicted rate being greater than the measured rate. Irrespective, it is clear that the addition of a relatively low Fe2+ concentration plays an important role in accelerating the copper dissolution rate at this Eh.

Licensee MDPI, Basel, Switzerland.Laboratory kinetic leach column (KLC) tests were carried out to define the conditions required to control acid generation from a highly reactive, potentially acid-forming (PAF) iron ore waste rock. It was found that lime addition (0.1 wt % blended) plus either blending of silicates (25 wt % K-feldspar and 25 wt % chlorite), or addition of a non-acid forming (NAF) top cover containing about 10% dolomite (PAF:NAF = 5:1 wt %), when watered/flushed with lime-saturated water, greatly reduced acid generation as compared to the control KLC (PAF alone, watered/flushed with Milli-Q water), but did not result in circum-neutral pH as required for pyrite surface passivation and effective acid and metalliferous drainage (AMD) mitigation. In contrast, the combined use of these treatments—blended lime and silicates with an NAF cover and watering/flushing with limesaturated water—resulted in leachate pH of ≈12 (up to 24 weeks). Mass balance calculations for Ca2+ and scanning electron microscopy (SEM) analyses suggest that calcite or gypsum may have formed in the NAF-amended KLCs and lime with added silicate KLC. Although the combined approach in the form trialled here may not be practical or cost-effective, control of a highly reactive natural PAF waste by pyrite surface passivation appears to be possible, and an improved treatment methodology (e.g., slightly increased lime blending without the need for further lime watering/flushing) could usefully be examined in the future. Refereed/Peer-reviewed

Acid and metalliferous drainage (AMD) is broadly accepted to be a major global environmental problem facing the mining industry, requiring expensive management and mitigation. A series of laboratory-scale kinetic leach column (KLC) experiments, using both synthetic and natural mine wastes, were carried out to test the efficacy of our pyrite passivation strategy (developed from previous research) for robust and sustainable AMD management. For the synthetic waste KLC tests, initial treatment with lime-saturated water was found to be of paramount importance for maintaining long-term circum-neutral pH, favourable for the formation and preservation of the pyrite surface passivating layer and reduced acid generation rate. Following the initial lime-saturated water treatment, minimal additional alkalinity (calcite-saturated water) was required to maintain circum-neutral pH for the maintenance of pyrite surface passivation. KLC tests examining natural potentially acid forming (PAF) waste, with much greater peak acidity than that of the synthetic waste, blended with lime (≈2 wt %) with and without natural non-acid-forming (NAF) waste covers, were carried out. The addition of lime and use of NAF covers maintained circum-neutral leachate pH up to 24 weeks. During this time, the net acidity generated was found to be significantly reduced by the overlying NAF cover. If the reduced rate of acidity production from the natural PAF waste is sustained, the addition of smaller (more economically-feasible) amounts of lime, together with application of NAF wastes as covers, could be trialled as a potential cost-effective AMD mitigation strategy. Refereed/Peer-reviewed

Zinc oxide (ZnO) was embedded in barium and fluorine silicate glass matrices, and luminescence properties of as-prepared glass samples were studied. For the fluorine-free glasses, a blue emission was observed. With partial substitution of BaF2 for BaO in glass compositions, emission spectra of glasses show an obvious blue shift to the near-UV region. For the BaO-free glasses, the dominant UV emission shifts to the near-band-edge exciton emission position of ZnO and also shows a red shift with increasing BaF2. At the same time, a visible emission shoulder appears in the blue to green region and becomes weak with introduction of increasing BaF2.

Chalcopyrite-containing deposits frequently comprise other sulfide and various silicate and carbonate minerals. Under acidic leaching conditions, as encountered in acid mine drainage or during industrial hydrometallurgical processing, these minerals can dissolve and release various impurities that may subsequently impact the leach behaviour of chalcopyrite. To gain further insight into these effects, batch leaching of chalcopyrite under controlled conditions of 75 °C, pH 1 and Eh 750 mV SHE in the presence of selected cationic impurities, that are common components of these associated minerals, has been examined. The addition of pre-equilibrated Fe2 + in the range of 20–50 mM gave rise to a negative reaction order using the initial rate method (IRM). In contrast, the IRM analysis indicated a positive reaction order for added Fe2 + over the range 5–20 mM; however, the overall leach processes generally slowed compared to leaching in the absence of added cations. This may be due to increasing iron concentrations, due to chalcopyrite dissolution, as leaching progressed. Results from the IRM analysis also indicated that Al3 + (5–50 mM) and K+ (5–150 mM) both resulted in positive reaction orders and accelerated chalcopyrite leaching, while Ca2 + (5–20 mM), Si oxyanions (5–50 mM), Na+ (5–50 mM) and Mg2 + (5–50 mM) all slowed the leach process. Porous sulfur layers, observed by scanning electron microscopy, do not appear responsible for these trends as their morphologies appear almost the same for leaching with and without added impurities. Time-of-flight secondary ion mass spectroscopic analyses showed no significant differences between samples collected from leaching in the absence and presence of impurities indicating that surface species within the top one to two monolayers do not contribute to the reduced leach efficiency. X-ray photoelectron spectroscopic analyses suggested that Fe(III)–O/–OH surface speciation may be associated with the reduced leach efficiency observed in the presence of some of the impurities.

A ‘new’ type of arsenian pyrite was formed during experimental replacement of magnetite under hydrothermal conditions (T = 125 and 220 °C; Psat) and in the presence of S(-II) and various As-containing species. The amount of As in pyrite depended on the As-source, with sources containing cationic As (As(II), As(III) and As(V)) resulting in considerably higher amounts of As in the product arsenian pyrite than anionic sources. The highest As content was 23.83 ± 0.20 wt%, corresponding to a S:Fe:As molar ratio of 2:0.58:0.42. Electron probe micro-analyses revealed an inverse correlation between the Fe and As contents in the arsenian pyrite, indicating that As is substituting for Fe. Arsenic concentrations were highly inhomogeneous within the pyrite rim; in general, higher As contents were found within solid pyrite growing on the outer rim, compared to the highly porous and texturally complex pyrite found close to the reaction boundary. This likely reflects different uptake mechanisms for As during the pyrite nucleation and growth stages. X-ray Absorption Near Edge Structure (XANES) analyses showed that the As in the arsenian pyrite was predominantly in the form of As(II). Cross-sectional X-ray photoelectron spectroscopy (XPS) analysis of the arsenian pyrite confirmed the presence of As(II), but also showed evidence for more oxidized species (As(III) and As(V) oxides), as well as small amounts of polymeric As–As bonding. This indicates a large difference between As in the bulk (XANES measurements) and at the pyrite surface (XPS). Ab initio XANES calculations are consistent with As replacing Fe in pyrite in the form of As(II). Our experimental study suggests that the formal oxidation state of As in this type of arsenian pyrite is close to +2, and that in addition to fluid composition and oxidation state, the reaction path leading to pyrite formation plays a significant role in controlling the chemistry of arsenian pyrite. Refereed/Peer-reviewed

A large-volume single-pass flow-through cell forin situneutron diffraction investigation of hydrothermal crystallization processes is reported. The cell is much more versatile than previous designs owing to the ability to control independently and precisely temperature (up to 673 K), pressure (up to 46 MPa), flow rate (0.01–10 ml min−1) and reaction-fluid volume (≥65 ml). Such versatility is realized by an innovative design consisting of a room-temperature and ambient-pressure external fluid supply module, a high-pressure reaction module which includes a high-temperature sample compartment enclosed in a vacuum furnace, and a room-temperature and high-pressure backpressure regulation module for pressure control. The cell provides a new avenue for studying various parameters of hydrothermal crystallizations independently,in situand in real time at extreme hydrothermal conditions (e.g.supercritical). The cell was successfully commissioned on the high-intensity powder diffractometer beamline, Wombat, at the Australian Nuclear Science and Technology Organisation by investigating the effect of pressure on the hydrothermal pseudomorphic conversion from SrSO4(celestine) to SrCO3(strontianite) at a constant temperature of 473 K and flow rate of 5 ml min−1. The results show that the increase of pressure exerts a nonlinear effect on the conversion rate, which first increases with increasing pressure from 14 to 20 MPa, and then decreases when pressure further increases to 24 MPa.

A hydrothermal cell with 320 ml internal volume has been designed and constructed for in situ neutron diffraction studies of hydrothermal crystallizations. The cell design adopts a dumbbell configuration assembled with standard commercial stainless steel components and a zero-scattering Ti-Zr alloy sample compartment. The fluid movement and heat transfer are simply driven by natural convection due to the natural temperature gradient along the fluid path, so that the temperature at the sample compartment can be stably sustained by heating the fluid in the bottom fluid reservoir. The cell can operate at temperatures up to 300 °C and pressures up to 90 bars and is suitable for studying reactions requiring a large volume of hydrothermal fluid to damp out the negative effect from the change of fluid composition during the course of the reactions. The capability of the cell was demonstrated by a hydrothermal phase transformation investigation from leucite (KAlSi(2)O(6)) to analcime (NaAlSi(2)O(6)⋅H(2)O) at 210 °C on the high intensity powder diffractometer Wombat in ANSTO. The kinetics of the transformation has been resolved by collecting diffraction patterns every 10 min followed by Rietveld quantitative phase analysis. The classical Avrami/Arrhenius analysis gives an activation energy of 82.3±1.1 kJ mol(-1). Estimations of the reaction rate under natural environments by extrapolations agree well with petrological observations.