Bioleaching of Uranium from Ores and Rocks with Filamentous Fungi

Tariq Bhatti ¹ Olli H. Tuovinen ^2*

• ¹ Pakistan Institute of Engineering and Applied Sciences, Nilore, Islamabad, Islamabad, Pakistan
• ² Department of Microbiology, The Ohio State University, Columbus, Ohio, United States

The purpose of this article is to review the role of filamentous fungi in the leaching of uranium from ores and rocks. Fungi produce short chain fatty acids by fermentation and partial oxidation of organic compounds. Biomass can be separated from the culture and organic acids in spent media dissolve and sequester uranium from minerals in ores and rocks. Oxide, carbonate, and silicate ores of uranium containing hexavalent uranium are amenable for this treatment. The production of short chain fatty acids by fungi can be maximized for the process. Uranium dissolution and sequestration is attributed mostly to the formation of soluble U(VI)-carboxylate complexes with citric and oxalic acids, but other carboxylic acids can also sequester uranium. The leach solutions are in the range of pH 1.5-3.5 as the low pH facilitates proton attack on the minerals and minimizes the precipitation of metals in the leach solution. Two types of uranium leaching processes by fungi have been tested; a one-step leaching, whereby biomass is not separated before contact with uranium mineral, and a two-step leaching, which employs spent medium after fungal biomass has been removed. Process optimization to pilot stage has not been reported in the literature. To date, this article is the first to review the role of filamentous fungi in uranium bioleaching from ores and rocks.