Phase Analysis of Australian Uranium Ore Concentrates Determined by Variable Temperature Synchrotron Powder X-ray Diffraction.

The chemical speciation of uranium oxides is sensitive to the provenance of the samples and their storage conditions. Here, we use diffraction methods to characterize the phases found in three aged (>10 years) uranium ore concentrates of different origins as well as in situ analysis of the thermally induced structural transitions of these materials. The structures of the crystalline phases found in the three samples have been refined, using high-resolution synchrotron X-ray diffraction data. Rietveld analysis of the samples from the Olympic Dam and Ranger uranium mines has revealed the presence of crystalline α-UO2(OH)2, together with metaschoepite (UO2)4O(OH)6·5H2O, in the aged U3O8 samples, and it is speculated that this forms as a consequence of the corrosion of U3O8 in the presence of metaschoepite. The third sample, from the Beverley uranium mine, contains the peroxide [UO2(η2-O2)(H2O)2] (metastudtite) together with α-UO2(OH)2 and metaschoepite. A core-shell model is proposed to account for the broadening of the diffraction peaks of the U3O8 evident in the samples.

Carbonisation of a polymer made from sulfur and canola oil.

A polymer made from equal masses of sulfur and canola oil was carbonised at 600 °C for 30 minutes. The resulting material exhibited improved uptake of mercury from water compared to the polymer. The carbonisation could also be done after using the polymer to clean up oil spills, which suprisingly improved mercury uptake to levels rivaling commercial carbons.

Radionuclides and stable elements in vegetation in Australian arid environments: Concentration ratios and seasonal variation.

Data on the uptake of elements and radionuclides by flora from soils in arid environments are underrepresented in international databases, especially when comparing across seasons. This study improved the understanding on the uptake of natural uranium-series radionuclides, as well as more than 30 elements, in a range of Australian native flora species that are internationally representative of an arid/semi-arid zone (e.g. Acacia, Astrebla, Atriplex, and Dodonea). Results indicate that the soil-to-plant uptake ratios were generally higher when compared with international data for grasses and shrubs from more temperate environments. The majority of the elemental concentrations in grasses were higher in winter than in summer and the opposite trend was found in shrubs, which suggests that the season of collection potentially introduces variability in the reported concentration ratios. The data also suggest that grasses, being dominant and widespread species in arid zones, may be effective as a reference organism to ensure comparative assessment across sites of interest. The results of this study will improve the confidence of environmental assessments in arid zones.

Oxidative Dissolution of Sulfide Minerals in Single and Mixed Sulfide Systems under Simulated Acid and Metalliferous Drainage Conditions.

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 <5.2 wt % for mixed sulfide experiments), mimicking sulfidic waste rock conditions. Chalcopyrite was found to be most effective in limiting pyrite oxidation and acid generation with 77-95% reduction in pyrite oxidation over 72 weeks, delaying decrease in leachate pH. Sphalerite had the least impact with reduction of pyrite dissolution by 26% over 72 weeks, likely because of the large band gap and poor conductivity of sphalerite. Galena had a smaller impact than chalcopyrite on pyrite oxidation, despite their similar band gaps, possibly because of the greater extent of oxidation and the significantly reduced surface areas of galena (area reductions of >47% for galena vs <1.5% for chalcopyrite) over 72 weeks. The results are directly relevant to mine waste storage and confirm that the galvanic interaction plays a role in controlling acid generation in multisulfide waste even at low sulfide contents (several wt %) with small probabilities (≤0.23%) of direct contact between sulfide minerals in mixed sulfide experiments.

Understanding the mobility and retention of uranium and its daughter products.

Knowledge of the behavior of technologically enhanced naturally occurring radioactive materials derived through the decay of U and its daughter products, and their subsequent fractionation, mobilization and retention, is essential to develop effective mitigation strategies and long-term radiological risk prediction. In the present study, multiple state-of-the-art, spatially resolved micro-analytical characterization techniques were combined to systematically track the liberation and migration of radionuclides (RN) from U-bearing phases in an Olympic Dam Cu flotation concentrate following sulfuric-acid-leach processing. The results highlighted the progressive dissolution of U-bearing minerals (mainly uraninite) leading to the release, disequilibrium and ultimately upgrade of daughter RN from the parent U. This occurred in conjunction with primary Cu-Fe-sulfide minerals undergoing coupled-dissolution reprecipitation to the porous secondary Cu-mineral, covellite. The budget of RN remaining in the leached concentrate was split between RN still hosted in the original U-bearing minerals, and RN that were mobilized and subsequently sorbed/precipitated onto porous covellite and auxiliary gangue mineral phases (e.g. barite). Further grinding of the flotation concentrate prior to sulfuric-acid-leach led to dissolution of U-bearing minerals previously encapsulated within Cu-Fe-sulfide minerals, resulting in increased release and disequilibrium of daughter RN, and causing further RN upgrade. The various processes that affect RN (mobility, sorption, precipitation) and sulfide minerals (coupled-dissolution reprecipitation and associated porosity generation) occur continuously within the hydrometallurgical circuit, and their interplay controls the rapid and highly localized enrichment of RN. The innovative combination of tools developed here reveal the heterogeneous distribution and fractionation of the RN in the ores following hydrometallurgical treatment at nm to cm-scales in exquisite detail. This approach provides an effective blueprint for understanding of the mobility and retention of U and its daughter products in complex anthropogenic and natural processes in the mining and energy industries.

The Combined Effects of Galvanic Interaction and Silicate Addition on the Oxidative Dissolution of Pyrite: Implications for Acid and Metalliferous Drainage Control.

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)- and 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 <0.1% of pyrite leached in both bi-sulfide systems. Silicate addition also significantly reduced the dissolution of sphalerite or galena (by 10-44%, except at pH 3 for the pyrite-sphalerite system). These results suggest that silicate addition, for reducing both pyrite dissolution and metalliferous drainage, may be applicable at a broad pH in mixed sulfide systems.

Novel application of X-ray fluorescence microscopy (XFM) for the non-destructive micro-elemental analysis of natural mineral pigments on Aboriginal Australian objects.

This manuscript presents the first non-destructive synchrotron micro-X-ray fluorescence study of natural mineral pigments on Aboriginal Australian objects. Our results demonstrate the advantage of XFM (X-ray fluorescence microscopy) of Aboriginal Australian objects for optimum sensitivity, elemental analysis, micron-resolution mapping of pigment areas and the method also has the advantage of being non-destructive to the cultural heritage objects. Estimates of pigment thickness can be calculated. In addition, based on the elemental maps of the pigments, further conclusions can be drawn on the composition and mixtures and uses of natural mineral pigments and whether the objects were made using traditional or modern methods and materials. This manuscript highlights the results of this first application of XFM to investigate complex mineral pigments used on Aboriginal Australian objects.

Analysis of gold(I/III)-complexes by HPLC-ICP-MS demonstrates gold(III) stability in surface waters.

Understanding the form in which gold is transported in surface- and groundwaters underpins our understanding of gold dispersion and (bio)geochemical cycling. Yet, to date, there are no direct techniques capable of identifying the oxidation state and complexation of gold in natural waters. We present a reversed phase ion-pairing HPLC-ICP-MS method for the separation and determination of aqueous gold(III)-chloro-hydroxyl, gold(III)-bromo-hydroxyl, gold(I)-thiosulfate, and gold(I)-cyanide complexes. Detection limits for the gold species range from 0.05 to 0.30 µg L(-1). The [Au(CN)2](-) gold cyanide complex was detected in five of six waters from tailings and adjacent monitoring bores of working gold mines. Contrary to thermodynamic predictions, evidence was obtained for the existence of Au(III)-complexes in circumneutral, hypersaline waters of a natural lake overlying a gold deposit in Western Australia. This first direct evidence for the existence and stability of Au(III)-complexes in natural surface waters suggests that Au(III)-complexes may be important for the transport and biogeochemical cycling of gold in surface environments. Overall, these results show that near-µg L(-1) enrichments of Au in environmental waters result from metastable ligands (e.g., CN(-)) as well as kinetically controlled redox processes leading to the stability of highly soluble Au(III)-complexes.

A novel route for the synthesis of mesoporous and low-thermal stability materials by coupled dissolution-reprecipitation reactions: mimicking hydrothermal mineral formation.

Replacement reactions ('pseudomorphism') commonly occur in Nature under a large range of conditions (T 25 to >600 degrees C; P 1 to >5 kbar). Whilst mineral replacement reactions are often assumed to proceed by solid-state diffusion of the metal ions through the mineral, many actually proceed via a coupled dissolution and reprecipitation (CDR) mechanism. In such cases, a starting mineral is dissolved into a fluid and this dissolution is coupled with the precipitation of a replacement phase across the reaction front. In cases where there are close relationships between the crystal structures of the parent and newly formed minerals, the replacement can be topotactic (interface-coupled dissolution and reprecipitation). The kinetics and chemistry of the CDR route are fundamentally different from solid-state diffusion and can be exploited i) for the synthesis of materials that are often difficult to synthesise via traditional methods and ii) to obtain materials with unique properties. This review highlights recent research into the use of CDR for such synthetic challenges. Emphasis has been given to i) the use of CDR to synthesise compounds with relatively low thermal stability such as the thiospinel mineral violarite ((Ni,Fe)(3)S(4)), ii) preliminary work into use of CDR for the production of roquesite (CulnS(2)), a potentially important photovoltaic component and, iii) examples where the textures resulting from CDR reactions are controlled by the nature and texture of the parent phase and the reaction conditions; these being the formation of micro-porous gold and three-dimensional ordered arrays of nanozeolite of uniform size and crystallographic orientation.

A large volume cell for in situ neutron diffraction studies of hydrothermal crystallizations.

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.

A simple colorimetric FIA method for the determination of pyrite oxidation rates.

A method for the rapid determination of the oxidation rate of naturally occurring pyrite (FeS(2)) samples is presented. The progress of the oxidation reaction was followed by measurement of the concentration of total dissolved iron using flow injection analysis. Iron was determined using UV-vis detection after reaction with the colorimetric reagent 5-sulfosalicylic acid in the presence of ammonia. The calibration function was linear between 5 and 150 mg L(-1), and the detection limit was 0.46 mg L(-1). The relative standard deviation was typically less than 1% (n=10) and the measurement frequency was 60/h. The method was used to quantify the oxidation rate of 10 ground and cleaned pyrite samples (53 µm

Towards the identification of plant and animal binders on Australian stone knives.

There is limited information regarding the nature of plant and animal residues used as adhesives, fixatives and pigments found on Australian Aboriginal artefacts. This paper reports the use of FTIR in combination with the chemometric tools principal component analysis (PCA) and hierarchical clustering (HC) for the analysis and identification of Australian plant and animal fixatives on Australian stone artefacts. Ten different plant and animal residues were able to be discriminated from each other at a species level by combining FTIR spectroscopy with the chemometric data analysis methods, principal component analysis (PCA) and hierarchical clustering (HC). Application of this method to residues from three broken stone knives from the collections of the South Australian Museum indicated that two of the handles of knives were likely to have contained beeswax as the fixative whilst Spinifex resin was the probable binder on the third.

Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans.

While the role of microorganisms as main drivers of metal mobility and mineral formation under Earth surface conditions is now widely accepted, the formation of secondary gold (Au) is commonly attributed to abiotic processes. Here we report that the biomineralization of Au nanoparticles in the metallophillic bacterium Cupriavidus metallidurans CH34 is the result of Au-regulated gene expression leading to the energy-dependent reductive precipitation of toxic Au(III)-complexes. C. metallidurans, which forms biofilms on Au grains, rapidly accumulates Au(III)-complexes from solution. Bulk and microbeam synchrotron X-ray analyses revealed that cellular Au accumulation is coupled to the formation of Au(I)-S complexes. This process promotes Au toxicity and C. metallidurans reacts by inducing oxidative stress and metal resistances gene clusters (including a Au-specific operon) to promote cellular defense. As a result, Au detoxification is mediated by a combination of efflux, reduction, and possibly methylation of Au-complexes, leading to the formation of Au(I)-C-compounds and nanoparticulate Au(0). Similar particles were observed in bacterial biofilms on Au grains, suggesting that bacteria actively contribute to the formation of Au grains in surface environments. The recognition of specific genetic responses to Au opens the way for the development of bioexploration and bioprocessing tools.

Crystal chemistry of mimetite, Pb10(AsO4)6Cl1.48O0.26, and finnemanite, Pb10(AsO3)6Cl2.

The crystal chemistries of synthetic mimetite, Pb(10)(As(5+)O(4))(6)(Cl(2 - x)O(x/2)), a neutral apatite, and finnemanite, Pb(10)(As(3+)O(3))(6)Cl(2), a reduced apatite, were characterized using a combination of X-ray powder diffraction, neutron diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Both phases conform to hexagonal P6(3)/m symmetry; however, the temperature-driven transformation of clinomimetite to mimetite described earlier was not confirmed. The average mimetite structure is best described through the introduction of partially occupied oxygen sites. A better understanding of the mixed arsenic speciation in apatites can guide the formulation of waste form ceramics and improve models of long-term durability after landfill disposal.

Autocorrelation infrared analysis of mineralogical samples: the influence of user controllable experimental parameters.

Autocorrelation infrared (ACIR) analysis is based upon the application of the autocorrelation function corr(alpha,omega') = integral(-infinity)(infinity) alpha(omega + omega') alpha(omega) d omega to standard Fourier transform infrared (FTIR) transmission spectra. We present a rigorous examination of the effect of experimental parameters such as dilution ratio, spectral resolution, grinding time and pressing conditions upon the ACIR analysis of haematite. Results were found to vary by less than 4.5% irrespective of sample preparation, instrumental and data collection parameters. For a series of perovskite samples, the relationship between the measured effective linewidth and material composition appears to be reproducible, even though the absolute magnitudes of delta corr values do not. Our results further indicate that the ACIR technique is indeed valid for comparative analysis of synthetic sample sequences that vary slightly in composition or structural state, provided that primary spectra are all recorded by the same instrument.