Browsing by Author "Dlugogorski, BZ"

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    Chemical and isotopic signatures of waters associated with the carbonation of ultramafic mine tailings, Woodsreef Asbestos Mine, Australia
    (Elsevier, 2016-10-15) Oskierski, HC; Dlugogorski, BZ; Oliver, TK; Jacobsen, GE
    Extensive carbonate crusts have formed on the tailings of the Woodsreef Asbestos Mine, sequestering significant amounts of CO2 directly from the atmosphere. The physico-chemical (pH, T, conductivity), chemical (cations, dissolved inorganic carbon (DIC)) and isotopic (δ2H, δ18O, δ13CDIC, F14C) signatures of waters interacting with the tailings and associated carbonate precipitates provide insight into the processes controlling carbonation. We observe two distinct evolutionary pathways for a set of stream and meteoric-derived water samples, respectively, with both groups generally being characterised as moderately alkaline, bicarbonate-dominated and Mg-rich waters. Stream water samples are supersaturated with CO2 and therefore prone to degassing, which, in combination with evaporation, drives carbonate supersaturation and precipitation. Isotopic signatures indicate soil CO2 as the main carbon source in the stream waters entering the tailings pile, whereas water emerging downstream of the tailings pile may also contain carbon from the dissolution of isotopically light bedrock magnesite in an open system with respect to soil CO2. The evolution of meteoric-derived waters on the other hand, partly occurs under CO2-limited conditions, which results from reduced CO2 ingress at depth and/or a temporal lag between fluid alkalisation and kinetically hindered uptake of CO2 into alkaline solution. A high pH, Mg-rich meteoric water absorbs atmospheric CO2 after discharging into a tunnel within the tailings pile, resulting in high DIC concentrations with atmospheric carbon isotope signature. Evaporation of the water at the discharge point in the tunnel drives precipitation of hydromagnesite (Mg5(CO3)4(OH)2·4H2O), displaying a clear atmospheric isotope signature, broadly consistent with previous estimates of carbon and oxygen isotope fractionation during precipitation of hydrated Mg-carbonate. © 2016, Elsevier B.V.
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    Isoconversional 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, BZ
    Mineral 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
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    Sequestration of atmospheric CO2 in a weathering-derived, serpentinite-hosted magnesite deposit: 14C tracing of carbon sources and age constraints for a refined genetic model
    (Elsevier, 2013-12-01) Oskierski, HC; Dlugogorski, BZ; Jacobsen, GE
    The Attunga magnesite deposit is texturally and geochemically distinct from other spatially associated, serpentinite-hosted magnesite deposits in the Great Serpentinite Belt, New South Wales, Australia, such as the hydrothermal Piedmont magnesite deposit or widespread silica–carbonate alteration zones. Cryptocrystalline magnesite at Attunga predominantly occurs in nodular masses and irregular, desiccated veins that occupy pre-existing cracks and pore spaces resulting from fracturing and weathering of the host rock. Incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of MgO and CaO from the serpentinite. Pore spaces and permeability created during weathering and fracturing of the host rock provide access for CO2-, MgO- and CaO-bearing meteoric waters which led to an increase of volume during carbonation. SiO2 is only mobilised during more advanced stages of weathering and late stage infiltration of SiO2-bearing waters and precipitation of opal-A lead to local silicification of the serpentinite. Stable carbon and oxygen isotope signatures show that nodular magnesite at Attunga has formed under near-surface conditions incorporating carbon from C3-photosynthetic plants and oxygen from meteoric waters. Radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and, together with distinct stable carbon and oxygen isotope signatures, indicate that magnesite at Attunga precipitated from low temperature, supergene fluids. Even though there is no direct geochemical and isotopic evidence, some textural observations and field relationships for weathering-derived magnesite deposits suggest the prior existence of a possibly Early Triassic, hydrothermal magnesite deposit at Attunga. The presence of a pre-existing magnesite deposit may entail the localised formation of the weathering-derived magnesite at Attunga, but the predominance of weathering-related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at Attunga. Conventional radiocarbon ages of about 50 ka represent a maximum age constraint for the formation of the magnesite deposit during Quaternary weathering. A significant amount of atmospheric CO2 has been sequestered via the biosphere and carbonation of serpentinite at Attunga. © 2013, Elsevier Ltd.
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    Sequestration of atmospheric CO2 in chrysotile mine tailings of the Woodsreef Asbestos Mine, Australia: quantitative mineralogy, isotopic fingerprinting and carbonation rates
    (Elsevier B.V., 2013-11-04) Oskierski, HC; Dlugogorski, BZ; Jacobsen, GE
    Since closure of the Woodsreef Asbestos Mine, located in the Great Serpentinite Belt (GSB), New South Wales, Australia, extensive carbonate-rich crusts have formed by recessive weathering of fine-grained material on the surface of the tailings pile. A relationship exists between the mode of carbonate occurrence, the mineralogy and the isotopic fingerprint of carbonates from the tailings pile. Vertical carbonate crusts, covering most of the tailings, predominantly consist of the hydrated Mg-carbonate hydromagnesite (Mg5(CO3)4(OH)2·4H2O), which has precipitated from evaporating meteoric waters incorporating atmospheric CO2, as reflected in high δ18O, δ13C and F14C signatures, respectively. Low and variable concentrations of magnesite, dolomite and calcite represent bedrock carbonate, which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high δ18O, low δ13C and F14C, a signature typical for ‘weathering-derived’ magnesite deposits in the GSB. The carbonate fraction of deep cement samples, collected from 70 to 120 cm below the surface, representing the bulk tailings material at depth, predominantly consists of pyroaurite (Mg6Fe2(CO3)(OH)16·4H2O) and, despite stable isotope signatures similar to bedrock, contains significant radiocarbon. This indicates that pyroaurite, forming under different conditions as hydromagnesite, may represent an additional trap for atmospheric CO2 in the Woodsreef mine tailings. The distribution of carbonates and quartz, together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric-derived carbonate, strongly indicates that dissolution and re-precipitation of bedrock carbonate is not a dominant process in the Woodsreef tailings. The cations for carbonate formation are instead derived from the dissolution of serpentine minerals (lizardite and chrysotile) and brucite. The internal standard method and the reference intensity method have been used with X-ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite, respectively. Considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that, between 1400 and 70,000 t of atmospheric CO2 have been sequestered in the mine tailings since closure of the mine 29 a ago. Carbonation rates of 27 g C m− 2 y− 1 and 1330 g C m− 2 y− 1 are significantly higher than background rates of CO2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of CO2 in carbonate minerals. © 2013 Elsevier B.V.