Mechanism underlying the bioleaching process of LiCoO₂ by sulfur-oxidizing and iron-oxidizing bacteria

Benefiting from lower operational costs and energy requirements than do hydrometallurgical and pyrometallurgical processes in metal recovery, the bioleaching of LiCoO₂ through the use of sulfur-oxidizing and iron-oxidizing bacteria has drawn increasing attention. However, the bioleaching mechanism of LiCoO₂ has not been clearly elaborated. In the present study, the effects of the energy source of bacteria, such as Fe²⁺, pyrite and S⁰, and the products of bacterial oxidation, such as Fe³⁺ and sulfuric acid, on the chemical leaching of LiCoO₂ were studied. The results indicated that lithium was dissolved by acid, and cobalt was released by the reduction of Fe²⁺ and acid dissolution. The recovery of Li⁺ and Co²⁺ could be significantly improved by pH adjustment. Finally, optimal recoveries of Li⁺ and Co²⁺ were observed in the pyrite group, reaching 91.4% and 94.2%, respectively. By using pyrite as the energy source, the role of bacteria in bioleaching of LiCoO₂ was investigated. The results showed that bacteria could produce sulfuric acid by oxidizing pyrite to promote the mobilization of Li⁺ and Co²⁺. The recovery of lithium and cobalt could be increased to 100.0% and 99.3% by bacteria. Moreover, extracellular polymeric substances secreted by bacteria were found to be a factor for the improvement of Li⁺ and Co²⁺ recovery.