Leaching behaviour of natural and heat-treated brannerite-containing uranium ores in sulphate solutions with iron(III)

• Influence of temperature, [H2SO4] and [Fe(III)] on natural brannerite dissolution.
• Crystallisation of natural brannerite significantly hinders dissolution.
• Evidence indicating formation of TiO2 passivation layer during dissolution.

Uranium leaching tests were conducted on two naturally occurring, highly metamict brannerite ores from the Crockers Well and Roxby Downs deposits, South Australia. The ores were leached over a range of temperatures and Fe(III) and H2SO4 concentrations. As well, samples of the ores were calcined at 1200 °C in air to investigate the effect of thermally induced recrystallisation on uranium dissolution. For the unheated samples, a maximum of ∼80% U dissolution was obtained using an Fe(III) concentration of 12 g/L, an acid concentration of 150 g/L H2SO4 and a temperature of 95 °C. The heat treated samples performed poorly under identical conditions, with maximum uranium dissolution of <10% recorded. High uranium dissolution from natural brannerite can be achieved providing; (i) acid strength, oxidant strength and temperatures are maintained at elevated levels (compared to those traditionally used for uraninite leaching), and, (ii) the brannerite has not undergone any significant recrystallisation (e.g. through metamorphism).