Enhanced bioleaching of granite-type uranium ore pretreated by microwave: process optimisation and kinetics

Microwave pretreatment based on selective heating effectively improved the bioleaching properties of encapsulated granite-type uranium deposits. A mixed bacterial strain containing Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was used to leach uranium from granite-type uranium ore pretreated by microwave. Effect of three important variables (i.e. pH, pulp concentration, Fe2+ concentration) on uranium leaching was investigated with response surface methodology based on central composite design. The most influential factor is the Fe2+ concentration, followed by the pulp concentration and the initial pH of the leaching system. The interaction between Fe2+ concentration and pulp concentration has the most significant impact on uranium leaching. The optimized conditions are as follows: pH of 1.58, pulp density of 10.11%, Fe2+ concentration of 3.67 g/L and the predicted maximum uranium extraction is 93.91%, which is consistent with the experimental result (93.71%). Kinetics studies shows the biological leaching of the uranium ore pretreated by microwave is jointly controlled by chemical reaction and diffusion, but mainly controlled by chemical reaction with apparent activation energy of 71.17 kJ/mol. This may be ascribed to the increase in cracks and porosity of the ore after microwave pretreatment, which strengthened the diffusion effect of the bioleaching process.