Mechanism underlying the bioleaching process of LiCoO 2 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 LiCoO ₂ through the use of sulfur-oxidizing and iron-oxidizing bacteria has drawn increasing attention. However, the bioleaching mechanism of LiCoO ₂ has not been clearly elaborated. In the present study, the effects of the energy source of bacteria, such as Fe ²⁺ , pyrite and S ⁰ , and the products of bacterial oxidation, such as Fe ³⁺ and sulfuric acid, on the chemical leaching of LiCoO ₂ were studied. The results indicated that lithium was dissolved by acid, and cobalt was released by the reduction of Fe ²⁺ and acid dissolution. The recovery of Li ⁺ and Co ²⁺ could be significantly improved by pH adjustment. Finally, optimal recoveries of Li ⁺ and Co ²⁺ 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 LiCoO ₂ was investigated. The results showed that bacteria could produce sulfuric acid by oxidizing pyrite to promote the mobilization of Li ⁺ and Co ²⁺ . 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 Co ²⁺ recovery.
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