Synthesis, characterisation and dissolution of brannerite. a uranium titanate mineral
Creators: name: Charalambous, Fiona
Publisher: name: RMIT University
Year: 2024

description: The uranium titanate mineral brannerite (UTi2O6), which is found in numerous uranium ore bodies around the world, is a mineral that may be a potential future source for increased uranium production. In this thesis the characteristics and dissolution chemistry of both natural and synthetic brannerites have been investigated in detail. Natural samples were investigated to identify the major minerals that are in close association with naturally occurring brannerite. Leaching chemistry of all natural and synthetic brannerites have been studied under conditions that are used in uranium minerals processing. An electrochemical leaching study of synthetic brannerite was undertaken to examine the surface behaviour of synthetic brannerite suspended in tank based leaching conditions similar to those used in uranium mineral processing. Characterisation studies conducted on two naturally occurring brannerites ore bodies from South Australia, focussed on their chemistry and mineralogy, and involved the use of use of multiple characterisation techniques (X-ray Diffraction Analysis, Raman Spectroscopy, Scanning Electron Microscopy and Electron Probe Micro Analysis). Recrystallization of the natural brannerite samples (via heat treatment) were also investigated. From the results obtained, the natural brannerite samples contained brannerite that was rich in thorium and also uranothorite and thorianite-uraninite phases. Gangue mineralogy phases found in both mineral samples were rutile quartz, aluminosilicates, unidentified REE-containing phosphates, zircon, titanates and apatite. After heat treatment the natural brannerite samples contained a high-Th brannerite and the thorianite-uraninite phase in the unheated samples was decomposed into separate ThO2 and UO2 phases. One of the research aims of this thesis was to synthesise and characterise a brannerite that has little impurities (rutile and uraninite) and use this synthetic product to investigate the maximum extraction of uranium. <br><br>This investigation was undertaken to gain detailed knowledge into the rate of dissolution of the synthesised brannerite over a range of conditions (temperature, [H2SO4] and [Fe] / ORP). One for the major findings from this research indicated that [Fe(III)] (over the range 3 – 12 g/L) did not have a significant influence on dissolution at a reaction temperature of 50 °C (in 15 g/L H2SO4). Yet at 95 °C in 15 g/L H2SO4, increasing [Fe(III)] (over the range 3 – 12 g/L) leads to significant increases in the dissolution rate. These aforementioned dissolution tests were conducted to probe the mechanism of synthetic brannerite dissolution and were compared with respect to the electrochemical behaviour of this synthetic mineral. An investigation was undertaken to determine the reason why this uranium mineral is not readily leachable under mild conditions and to determine if passivation was occurring on the surface of synthetic brannerite. When dissolution tests for the two natural brannerite samples were conducted under identical conditions investigated for synthetic brannerite, the results showed that the effect of increasing [Fe(III)], [H2SO4], and temperature was to increase the solubility of uranium from brannerite. Uranium recovery processes from brannerite is not straightforward process and influenced by the mineralogical characteristics of the ore. Synthetic and natural brannerites can achieve high uranium extraction rates providing that acid strength, oxidant strength and temperatures are maintained at high levels. <br>