Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/106292
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Type: Theses
Title: Scavenging of uranium in experimental and natural samples
Author: Li, Kan
Issue Date: 2016
School/Discipline: School of Chemical Engineering
Abstract: The hypothesis that interface coupled dissolution-reprecipitation reactions (ICDR) can play a key role in scavenging minor elements has been investigated via exploring the fate of U during the experimental sulfidation of hematite to chalcopyrite and the exsolution of chalcopyrite from bornite digenite solid solution (bdss) under hydrothermal conditions. The results of experiments with two kinds of Uranium (U) sources; either as solid UO₂₊ₓ(s) or as a soluble uranyl complex, differed from the U-free experiments. In the reactions from hematite to chalcopyrite under 220-300°C hydrothermal conditions, pyrite precipitated initially, before the onset of chalcopyrite precipitation. In addition, when UO₂₊ₓ(s) was included in the experiments, enhanced hematite dissolution led to increased porosity and precipitation of pyrite+magnetite within the hematite core. However, in uranyl nitrate bearing experiments, abundant pyrite formed initially, before being replaced by chalcopyrite. Uranium scavenging was mainly associated with the pyrite precipitation, as a result that a thin U-rich layer along the original hematite grain surface precipitated out. In the reactions of chalcopyrite exsolution from bdss during annealing under hydrothermal conditions in a solutions nominally containing Cu(I) and hydrosulfide in a pH₂₅°C [°C subscript] ~6 acetate buffer, a similar U-rich rim was observed along the original grain when uranyl nitrate as U-source was included in the reactions. The precipitation of uranium was related to the presences of HS- in buffer. Chemical mapping and X-ray absorption near edge structure (XANES) spectroscopy showed the UO₂₊ₓ(s) was the mainly restricted to the U-rich layer. The two sets of experiments demonstrate that the presence of minor components can affect the pathway of ICDR reactions. Reactions between U- and Cu-bearing fluids and hematite or chalcopyrite can explain the Cu-U association prominent in some iron oxide-copper-gold (IOCG) deposits. In this study, synchrotron-based X-ray fluorescence (SXRF) mapping was used to trace the distribution of uranium in natural samples from different geological contexts (sandstone-hosted U-deposit; IOCG) for investigating the deportment of uranium and its paragenesis in the context of thin-section scale textural complexity. It has been confirmed that the enrichment of U occurs via late dissolution-reprecipitation reactions in the bornite ores of the Moonta and Wallaroo IOCG deposits (South Australia), and that the U distribution in the ores of sandstone-hosted U-deposit is complex. Image analysis also revealed a number of new results for other minor elements, e.g. (i) the distribution of μm-sized Pt-rich grains and evidence for Ti-mobility during the formation of schistosity at the Fifield Pt prospect (New South Wales, Australia); (ii) the presence of Ge contained in organic matter and of Hg minerals associated within quartzite clasts in the Lake Frome U ores (South Australia); and (iii) confirmation of the two-stage Ge-enrichment in the Barrigão deposit, with demonstration of the presence of Ge in solid solution in the early chalcopyrite (Portuguese Iberian Pyrite Belt).
Advisor: Brugger, Joel
Pring, Allan
Ngothai, Yung My
Hooker, Antony
O'Neill, Brian Kevin
Dissertation Note: Thesis (Ph.D.) (Research by Publication) -- University of Adelaide,School of Chemical Engineering, 2016.
Keywords: scavenging
uranium
mineral replacement
IOCG deposits
sulfidation reaction
interface coupled dissolution-reprecipitation reactions
Research by Publication
Provenance: Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.
This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
DOI: 10.4225/55/59532ea22d2d6
Appears in Collections:Research Theses

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