Characteristics of oxidative stress and antioxidant defenses by a mixed culture of acidophilic bacteria in response to Co2+ exposure.

During bioleaching of Cobalt from waste lithium-ion batteries, the biooxidation activity of acidophilic bacteria is inhibited by a high concentration of Co ion in the liquid phase. However, the mechanism for Co2+ toxicity to acidophilic bacteria has not been fully elucidated. In this study, the effects of Co2+ concentration on the biooxidation activity for Fe2+, intracellular reactive oxygen species (ROS) level and antioxidant defense systems in a mixed-culture of acidophilic bacteria (MCAB) were investigated. The results showed that the biooxidation activity of the MCAB was inhibited by Co2+. Furthermore, it was indicated that the intracellular ROS contents of the MCAB under conditions of 0.4 M and 0.6 M Co2+ were 2.60 and 3.34 times higher than that under the condition of 0 M Co2+. The increase in intracellular malondialdehyde content indicated that the oxidative damage was induced by Co2+. Moreover, the antioxidant systems in MCAB were affected by Co2+. It was observed that the Co2+ exposure increased the catalase and glutathione peroxidase activities while reducing the superoxide dismutase activity and the intracellular glutathione (GSH) content. It was found that an exogenous GSH supplementation eliminated excess intracellular ROS and improved the biooxidation activity of the MCAB.

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.