Leaching of brannerite in the ferric sulphate system. Part 3: The influence of reactive gangue minerals

• Published in: Hydrometallurgy Vol. 164; pp. 343 - 354
• Main Authors: Gilligan, Rorie, Nikoloski, Aleksandar N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2016
• Subjects: Apatite; Brannerite; Dissolution; Fluoride; Fluorite; Formations; Hydrometallurgy; Leaching; Phosphate; Phosphates; Uranium; Uranium ores; Apatite; Fluorite; Fluoride; Brannerite; Leaching; Phosphate
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2016.07.008

Brannerite, UTi2O6, is one of the most common refractory uranium minerals and it requires aggressive leaching conditions for efficient uranium extraction. It is often associated with apatite and fluorite, which affect the leaching process by formation of iron-phosphate and iron-fluoride complexes, respectively. While the effects of these gangue minerals on uranium leaching processes are well documented, there is little to no information on these effects specific to brannerite containing ores. At the high acid concentrations required for brannerite dissolution (>25g/L H2SO4), acid soluble gangue will dissolve faster, posing a bigger problem than under milder conditions. The addition of 10g/L fluorapatite reduced the extraction of both uranium and titanium from brannerite over the full range of leaching conditions studied (25–96°C, 25–100g/L H2SO4, 2.8g/L Fe3+). Phosphate caused the formation of secondary titanium oxide on the surface of leached brannerite particles. This was not observed when leaching in the absence of phosphate. The secondary titanium oxide phase was enriched in phosphorus. The negative effects of phosphate on uranium leaching were reduced at higher acid concentrations (>50g/L H2SO4) and increased at higher temperatures (96°C). When leaching high-P refractory uranium ores, higher acid concentrations are needed for effective extraction compared with low-P uranium ores. Elevated temperatures were less effective for increasing uranium extraction, suggesting that the optimum temperature for leaching high-P refractory uranium ores is lower than the optimum temperature for leaching low-P uranium ores. Fluorite (10g/L) had a positive effect on uranium and titanium extraction. This was attributed to the formation of hydrofluoric acid during the dissolution of fluorite. Brannerite particles were heavily pitted and corroded after leaching in the presence of fluorite, with near complete dissolution occurring in 2–3h. •Apatite and fluorite ions formed interfere with reactions between ferric and brannerite.•Hydrofluoric acid formed from fluorite attacks silicates and increases the uranium dissolution.•Phosphates released from apatite complex ferric ions, inhibiting the oxidation of uranium•Phosphate also shown to contribute to the formation of a titanium oxide coating on brannerite.•Higher acid concentration and lower leaching temperature preferred when phosphates present