The process chemistry and mineralogy of brannerite leaching

Brannerite (UTi2O6) is the most important uranium mineral after uraninite and coffinite, and the most common refractory uranium mineral. As the more easily leachable uranium ores are becoming exhausted, it is necessary to process the complex and refractory ores in order to meet the growing demand for uranium as an energy source. This typically requires either more intense leaching conditions or a better-designed process based on sound understanding of feed mineralogy and reaction chemistry. The present study was carried out to provide information that will enable the development of a more effective processing strategy for the extraction of uranium from ores containing brannerite. The leaching behaviour of brannerite in sulphate media under moderate temperature conditions was investigated and compared with its relative leachability in alternative acid and alkaline systems. The feed and the leached residues were characterized by XRD and SEM-EDX techniques. Brannerite dissolutions of up to 95% after 5 hours of leaching in ferric sulphate media, up to 89% in ferric chloride media under similar conditions, and up to 82% in 24 hours in sodium carbonate media were obtained. Since alkaline leaching was considered promising for acid-consuming ores, leaching was repeated with a high-carbonate brannerite-bearing ore, with comparable extractions. Mineralogical characterization showed that altered and amorphous regions are a regular feature of brannerite, and that pitting is typically observed on the surface of the leached grains. The leaching results, coupled with mineralogical data, showed that the uranium and titanium in brannerite generally dissolve congruently, with faster dissolution of the altered and amorphous regions in the brannerite grains than of the crystalline regions. We conclude that the extent of brannerite alteration is a key factor in process selection, along with the grade, liberation size, and gangue mineralogy