Browsing by Author "Xia, F"
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- ItemAnatomy of a complex mineral replacement reaction: Role of aqueous redox, mineral nucleation, and ion transport properties revealed by an in-situ study of the replacement of chalcopyrite by copper sulfides(Elsevier, 2021-10-20) Chaudhari, A; Webster, NAS; Xia, F; Frierdich, AJ; Ram, R; Etschmann, BE; Liu, WH; Wykes, JL; Brand, HEA; Brugger, JThe fluid-driven transformation of chalcopyrite (CuFeS2) into Cu-rich sulfides (e.g., digenite, Cu1.8S; covellite, CuS; and chalcocite, Cu2S) is a complex mineral replacement reaction where the reaction pathway is controlled by the interplay between evolving mineral make-up, texture/porosity, and solution chemistry. This trans-formation was investigated in CuCl2 +H2SO4 solutions under mild hydrothermal conditions (180 to 300 ◦C); the reaction kinetics, nature of minerals formed, and oxidation states of aqueous Fe and Cu were followed in-situ in real-time using synchrotron powder X-ray diffraction (PXRD) and X-ray absorption spectroscopy (XAS). These results are corroborated by an analysis of the textures of reaction products from comparative ex-situ quench experiments. The in-situ and ex-situ experiments revealed that: (i) aqueous Cu2+quickly reduced to Cu+ during chalcopyrite replacement in all experiments, and Fe dissolved as Fe2+; (ii) covellite was the first mineral to form, followed by digenite-high with delayed nucleation; and (iii) a non-quenchable hydrated Fe sulfate mineral (szomolnokite, FeSO4.H2O) formed at 240 ◦C at relatively low concentrations of added CuCl2, which supressed the formation of digenite-high. The quantitative mineral phase evolution retrieved using in-situ PXRD was modelled using a novel dual power law (dual Avrami approach). Avrami exponents revealed that chalcopyrite replacement proceeded initially via a 3-dimensional growth mechanism, followed by diffusion-controlled growth. This is consistent with initial formation of a porous covellite rim around chalcopyrite, confirmed by the observation of the ex-situ reaction products, followed by a second reaction stage where the transport properties of aqueous Fe (released from the chalcopyrite) and aqueous Cu (added from the initial solution) to and from the reaction front become the rate-limiting step; and these two kinetic stages exist even where covellite was the only replacement product. The activation energies calculated for these two kinetic stages were 42.9 ±7.4 kJ mol −1 and 39.3 ± 13.1 kJ mol−1, respectively. We conclude that (i) the replacement of chalcopyrite by covellite and digenite proceeds via an interface coupled dissolution and reprecipitation mechanism; (ii) availabilities of aqueous Cu+ and of Fe2+ play a critical role in covellite nucleation and on the sequence of mineral precipitation during chalcopyrite replacement; the Cu+ to Cu2+ ratio is controlled by the kinetics of Cu2+ to Cu+ reduction, which increases with increasing temperature, and by the transport of Cu2+ through the daughter mineral to the reaction front, while Fe2+ availability is limited at high temperature by the formation of insoluble ferrous sulfate; and (iii) this reaction evolves from a bulk fluid-chemistry controlled reaction (initial formation of covellite) to an interface-controlled reaction (digenite-high or further transformation to covellite). The current findings highlight the complex feedback between Cu2+/Cu+ aqueous redox, mineral nucleation, and ion transport properties during replacement reactions, and the applicability of combined in-situ PXRD and XAS techniques in deciphering complex fluid-driven mineral replacement reactions. © 2021 Elsevier B.V
- ItemCharacterization of porosity in sulfide ore minerals: a USANS/SANS study(GeoScience World, 2014-11-18) Xia, F; Zhao, J; Etschmann, BE; Brugger, J; Garvey, CJ; Rehm, C; Lemmel, H; Ilavsky, J; Han, YS; Pring, APorosity plays a key role in the formation and alteration of sulfide ore minerals, yet our knowledge of the nature and formation of the residual pores is very limited. Herein, we report the application of ultra-small-angle neutron scattering and small-angle neutron scattering (USANS/SANS) to assess the porosity in five natural sulfide minerals (violarite, marcasite, pyrite, chalcopyrite, and bornite) possibly formed by hydrothermal mineral replacement reactions and two synthetic sulfide minerals (violarite and marcasite) prepared experimentally by mimicking natural hydrothermal conditions. USANS/SANS data showed very different pore size distributions for these minerals. Natural violarite and marcasite tend to possess less pores in the small size range (<100 nm) compared with their synthetic counterparts. This phenomenon is consistent with a higher degree of pore healing or diagenetic compaction experienced by the natural violarite and marcasite. Surprisingly, nanometer-sized (<20 nm) pores were revealed for a natural pyrite cube from La Rioga, Spain, and the sample has a pore volume fraction of ~7.7%. Both chalcopyrite and bornite from the massive sulfide assemblage of the Olympic Dam deposit in Roxby Downs, South Australia, were found to be porous with a similar pore volume fraction (~15%), but chalcopyrite tends to have a higher proportion of nanometer-size pores centered at ~4 nm while bornite tends to have a broader pore size distribution. The specific surface area is generally low for these minerals ranging from 0.94 to 6.28 m2/g, and the surfaces are generally rough as surface fractal behavior was observed for all these minerals. This investigation has demonstrated that USANS/SANS is a very useful tool for analyzing porosity in ore minerals. We believe that with this quantified porosity information a deeper understanding of the complex fluid flow behavior within the porous minerals can be expected. © 2014, Mineralogical Society of America.
- ItemIsoconversional kinetic modeling and in-situ synchrotron powder diffraction analysis for dehydroxylation of antigorite(American Institute of Chemical Engineers (AIChE), 2018-03-14) Zahid, S; Oskierski, HC; Senanayake, G; Altarawneh, M; Xia, F; Brand, HEA; Oluwoye, I; Dlugogorski, BZMineral carbonation offers permanent and safe disposal of anthropogenic CO2. Well distributed and abundant resources of serpentine minerals and natural weathering of these mineral to stable and environmentally benign carbonates 1, 2 favour the exploitation of these minerals as the most suitable raw material for mineral carbonation. However, slow dissolution kinetics are impeding the large scale implementation of mineral carbonation 3. Heat treatment of serpentine minerals results in enhanced reactivity for subsequent carbonation processes at the expense of an additional energy penalty4. Heat treatment of these minerals results in the removal of structurally bound hydroxyl groups which leads to partial amorphisation of the structure and enhanced reactivity 5. Therefore, understanding the role of the mineralogical changes during dehydroxylation and determination of activation energy (Ea) is crucial for providing an energy efficient solution for commercialisation of mineral carbonation. In-situ synchrotron powder X-ray diffraction (S-PXRD) at the Australian Synchrotron was employed for detailed observation of mineralogical changes and estimation of kinetic parameters during the heat treatment from room temperature to 1000 oC under constant N2 flow. The synchrotron beamline offers high signal to noise ratio necessary for an accurate identification of minor phases and onset temperature for phase transitions. Moreover, the fast data acquisition of S-PXRD enables acquisition of data with temporal resolution, which is crucial for accurate estimation of kinetic parameters. During dehydroxylation via heat treatment, antigorite remained stable up to 520 oC. Above 520 oC, antigorite started to decompose and forsterite formation occurred at around 700 oC. Enstatite formation was observed only after the complete dissociation of antigorite. We performed prograde heating experiments at 2, 4, 6 and 8 oC/min under constant N2 flow for the estimation of Ea via isoconversional kinetic modelling. The change in activation energy with reaction progress showed the multistep nature of dehydroxylation of antigorite. The variation of Ea can be divided into three stages a) nearly constant Ea of 130 kJ/mol (α ≤ 0.25) b) increase in Ea from 130-209 kJ/mol (0.25≤ α ≥0.4) which remained constant at around 204 kJ/mol till α = 0.8. Finally, the reaction ended with an increase in Ea from 204 kJ/mol to 236 kJ/mol. In this study we exploit the potential of in-situ SXRD for determination of isoconversional kinetic parameters in comparison to conventional kinetic analysis based on TGA-DSC methods. While S-XRD based kinetic analysis appears to be sensitive to phase quantification parameters (e.g. peak integration vs. full pattern fitting) it provides valuable structural information that is not available in conventional kinetic methods. S-XRD based kinetic analysis further has the ability to resolve the formation of individual mineral phases, including reaction intermediates (talc-like phases) and products (olivine and enstatite). Consequently, this study will further advance the development of cost and energy-efficient dehydroxylation of serpentine minerals for large scale storage of CO2 by mineral carbonation. © 2018 American Institute of Chemical Engineers
- ItemA large volume cell for in situ neutron diffraction studies of hydrothermal crystallizations(American Institute of Physics, 2010-10-19) Xia, F; Qian, GJ; Brugger, J; Studer, AJ; Olsen, SR; Pring, AA 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 (KAlSi2O6) to analcime (NaAlSi2O6⋅H2O) 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. © 2010, American Institute of Physics
- ItemA thermosyphon-driven hydrothermal flow-through cell for in situ and time-resolved neutron diffraction studies(Wiley-Blackwell, 2010-06-01) Xia, F; O'Neill, B; Ngothai, Y; Peak, J; Tenailleau, C; Etschmann, BE; Qian, G; Brugger, J; Studer, AJ; Olsen, SR; Pring, AA flow-through cell for hydrothermal phase transformation studies by in situ and time-resolved neutron diffraction has been designed and constructed. The cell has a large internal volume of 320 ml and can operate at temperatures up to 573 K under autogenous vapor pressures (ca 8.5 × 106 Pa). The fluid flow is driven by a thermosyphon, which is achieved by the proper design of temperature difference around the closed loop. The main body of the cell is made of stainless steel (316 type), but the sample compartment is constructed from non-scattering Ti-Zr alloy. The cell has been successfully commissioned on Australia's new high-intensity powder diffractometer WOMBAT at the Australian Nuclear Science and Technology Organization, using two simple phase transformation reactions from KAlSi2O6 (leucite) to NaAlSi2O6·H2O (analcime) and then back from NaAlSi2O6·H2O to KAlSi2O6 as examples. The demonstration proved that the cell is an excellent tool for probing hydrothermal crystallization. By collecting diffraction data every 5 min, it was clearly seen that KAlSi2O6 was progressively transformed to NaAlSi2O6·H2O in a sodium chloride solution, and the produced NaAlSi2O6·H2O was progressively transformed back to KAlSi2O6 in a potassium carbonate solution. © 2010, Wiley-Blackwell.
- ItemUnderstanding solvothermal crystallization of mesoporous anatase beads by in situ synchrotron PXRD and SAXS(American Chemical Society, 2014-07-07) Xia, F; Chen, DH; Scarlett, NVY; Madsen, IC; Lau, D; Leoni, M; Ilavsky, J; Brand, HEA; Caruso, RASubmicrometer-sized mesoporous anatase (TiO2) beads have shown high efficiency as electrodes for dye-sensitized solar cells and are recoverable photocatalysts for the degradation of organic pollutants. The detailed mechanism for crystallization of the amorphous TiO2/hexadecylamine (HDA) hybrid beads occurring during the solvothermal process needs to be understood so that reaction parameters can be rationally refined for optimizing the synthesis. In this work, the solvothermal crystallization was monitored by in situ synchrotron powder X-ray diffraction (PXRD) and synchrotron small-angle X-ray scattering (SAXS) techniques. In situ PXRD provided crystallization curves, as well as the time evolution of anatase crystallite mean size and size distribution, and in situ SAXS provided complementary information regarding the evolution of the internal bead structure and the formation of pores during the course of the solvothermal process. By exploring the effects of temperature (140-180 °C), bead diameter (300 and 1150 nm), bead internal structure, and solvent composition (ethanol and ammonia concentrations) on this process, the crystallization was observed to progress 3-dimensionally throughout the entire bead due to solvent entrance after an initial fast partial dissolution of HDA from the nonporous precursor bead. On the basis of the kinetic and size evolution results, a 4-step crystallization process was proposed: (1) an induction period for precursor partial dissolution and anatase nucleation; (2) continued precursor dissolution accompanied by anatase nucleation and crystal growth; (3) continued precursor dissolution accompanied by only anatase crystal growth; and (4) complete crystallization with no significant Ostwald ripening. © 2014 American Chemical Society.
- ItemUnderstanding the generation and evolution of reaction-induced porosity in the replacement of calcite by gypsum: a combined microscopy, X-ray micro-tomography, and USANS/SANS study(Australian Nuclear Science and Technology Organisation, 2021-11-25) Kartal, M; Xia, F; Mata, JP; Sokolova, AV; Adegoke, A; Putnis, AFluid-mediated mineral replacement reactions are common in natural systems and are essential for geological and engineering processes. In these reactions, a primary mineral is replaced by a product mineral via a mechanism called coupled dissolution-reprecipitation. This mechanism leads to the preservation of the shape of the primary mineral into the product mineral. The product mineral includes reaction-induced porosity contributing to enhanced permeability, which is crucial for the replacement reaction to progress from the surface to the core of the primary mineral grain. These reaction-induced pores are complex in size, shape and connectivity, and can evolve with time. However, the mechanisms of the creation and evolution of such pores are still poorly understood. Therefore, we investigated the replacement of calcite (CaCO3) by gypsum (CaSO4.2H2O) to understand porosity creation in the replacement stage and the evolution of such porosity after complete replacement. This replacement reaction is important for the applications such as groundwater reservoir evaluation, CO2 sequestration, cultural heritage preservation, and acid mine drainage remediation. Samples collected at various reaction stages over 18 months were characterised by ultra-small-angle neutron scattering and small-angle neutron scattering (USANS/SANS), ultra-high-resolution electron microscopy (UHR-SEM), and X-ray micro-computed tomography (X-μCT). Results show the formation of micro-voids in the core of the gypsum grain and the generation of nanometre-sized elongated pores in the newly formed gypsum crystals. Micrometre-sized pores were mostly open, while pores smaller than 30 nm were mainly closed. After complete replacement, continued porosity coarsening occurred in the 18 months’ time, driven by Ostwald ripening.