A comparative bio-oxidative leaching study of synthetic U-bearing minerals: Implications for mobility and retention

In this study, the effects of bio-oxidative leaching on several synthetic uranium minerals - Uraninite [UO₂], Pitchblende [U₃O₈], Coffinite [USiO₄], Brannerite [UTi₂O₆] and Betafite [(U,Ca)₂(Ti,Nb,Ta)₂O₇]) compared to chemical leaching in the presence of pyrite was investigated. In all cases, bio-oxidative leaching was faster and increased overall %U extraction compared to chemical leaching. The results indicated that the bio-oxidative leachability of the uranium minerals was in the order: pitchblende≈ uraninite > coffinite>> brannerite > betafite. The leaching of pitchblende and uraninite was fast and complete; U extraction from coffinite was slower over 28 days' during the bioleaching. The use of thermophiles doubled the recovery of U from refractory brannerite. The results highlight the significant capability of bio-leaching in the recovery of U from brannerite; both mesophilic and thermophilic bacteria was found to enhance U recovery likely through enhanced breakdown of the titanate structure. Brannerite is often found in significant quantities within ore tailings due to its refractory nature, which can lead to subsequent release of U into the environment. Conversely, betafite is highly stable in the presence of mesophile and moderate thermophiles, which suggested that betafite materials can be a viable future host for long term storage for spent nuclear fuels.