Characterisation and leaching studies on the uranium mineral betafite [(U,Ca)(2)(Nb,Ti,Ta)(2)O-7]

Samples of natural betafite from Ambatofotsy Madagascar, Miarinarivo Madagascar and Silver Crater Mine, Canada were characterised using a range of techniques before being leached to extract uranium. The three samples were also heat treated to 1200°C to investigate the effect of recrystallization on uranium extraction. X-ray diffraction analysis showed that anatase was the only crystalline compound present in each of the unheated samples. After being heated to 1200°C all samples exhibited diffraction lines characteristic of betafite and rutile, indicating that the betafite present in the preheated samples was amorphous (metamict). Electron probe microanalysis of the samples showed a high degree of compositional heterogeneity throughout each sample, most likely caused by aqueous fluid interactions forming secondary alteration products. The Ambatofotsy sample was the most altered while the Silver Crater sample was the least altered. All unheated samples were subject to a sulfuric acid leach over 6 h with the extent of uranium dissolution correlated with the degree of alteration. The most highly altered sample had 42% dissolution while the least-altered exhibited only 7%. Dissolution experiments over the temperature range 35-95°C with lower activation energies recorded for the highly-altered samples compared to the less-altered samples. Moreover, increased leaching with increasing metamictisation was observed in studies using variable sulfuric acid concentrations. The compositional and microstructural results presented herein indicates that characterisation prior to leaching is beneficial in determining the feasibility and viability of processing betafite as a potential uranium resource.