Microbially Assisted Leaching of Uranium—A Review

Due to depletion of high-grade deposits of uranium and generation of large quantities of tailings produced by mining and metallurgical activities, there is a need to find an economical way to recover uranium from low-grade deposits and secondary resources. Bioleaching of uranium from the ores, minerals, and wastes in heap and dumps, besides in-situ biodissolution processes, is rapidly expanding globally, and its economic values may exceed that of the underground mining. The biodissolution of uranium is a consequence of hydrometallurgical treatment of ore with microbial intervention. Uranium bioleaching is mainly driven by the combined action of Fe(III) and the protons that are produced by the activity of chemolithotrophic micro-organisms which use either iron or sulfur as their energy source for their growth. In this review, an attempt has been made to understand the process of bioleaching of uranium while deliberating on mechanism as to whether the reactions are direct or indirect and the role of micro-organisms, besides the types and effectiveness of processes by which uranium is extracted from its ores on bench/industrial/large scale. The processes developed or in vogue for bioleaching of uranium are described in some detail, along with recent initiatives.