Browsing by Author "Senanayake, G"

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    Beneficial effect of iron oxide/hydroxide minerals on sulfuric acid baking and leaching of monazite
    (Elsevier B. V., 2022-05) Demol, J; Ho, E; Soldenhoff, KH; Karatchevtseva, I; Senanayake, G
    The sulfuric acid bake/leach process is an established industrial process for the extraction of rare earths from hard-rock monazite ores/concentrates. The chemical reactions in the monazite acid bake can be strongly influenced by the gangue mineralogy of the ore/concentrate. In this work, the beneficial effect of three iron oxide/hydroxide minerals, namely hematite, goethite and magnetite, added to high grade monazite concentrate in the acid bake (temperature range of 200–800°) and leach process was investigated to understand the role of iron gangue. Baked solids and leach residues were characterised by elemental analyses, XRD, SEM-EDS and FT-IR. It was found that the addition of iron minerals to the monazite acid bake had a significant impact on bake chemistry, acting to significantly increase the leaching of both the rare earth elements and thorium, compared to monazite alone, mainly for temperatures above 300 °C. The increased dissolution of rare earth elements and thorium was attributed to the formation of an amorphous and insoluble iron sulfate-polyphosphate type phase in preference to insoluble rare earth and thorium containing polyphosphates identified during acid baking of monazite alone. After baking at 650 °C, the iron sulfate-polyphosphate type phase was altered to a more soluble form, leading to an increase in dissolution of iron, phosphorus and thorium. Acid baking at 800 °C led to the formation of FePO4, Fe2O3, CePO4 (monazite) and in some cases CeO2, causing a decrease in leaching of rare earths and thorium, and either an increase or a decrease in leaching of iron and phosphorus depending on the formation of FePO4 versus Fe2O3. Crown Copyright © 2022 Published by 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