Oxidative Stress Induced by Metal Ions in Bioleaching of LiCoO2 by an Acidophilic Microbial Consortium

Abstract

An acidophilic microbial consortium (AMC) was used to investigate the fundamental mechanism behind the adverse effects of pulp density increase in the bioleaching of waste lithium ion batteries (WLIBs). Results showed that there existed the effect of metal-ion stress on the bio-oxidative activity of AMC. The Li⁺ and Co²⁺ accumulated in the leachate were the direct cause for the decrease in lithium and cobalt recovery yields under a high pulp density. In a simulated bioleaching system with 4.0% (w ⋅v^-1) LiCoO₂, the intracellular reactive oxygen species (ROS) content in AMC increased from 0.82 to 6.02 within 24 h, which was almost three times higher than that of the control (2.04). After the supplementation of 0.30 g⋅L^-1 of exogenous glutathione (GSH), the bacterial intracellular ROS content decreased by 40% within 24 h and the activities of intracellular ROS scavenging enzymes, including glutathione peroxidase (GSH-Px) and catalase (CAT), were 1.4- and 2.0-folds higher in comparison with the control within 24 h. In the biofilms formed on pyrite in the bioleaching of WLIBs, it was found that metal-ion stress had a great influence on the 3-D structure and the amount of biomass of the biofilms. After the exogenous addition of GSH, the structure and the amount of biomass of the biofilms were restored to some extent. Eventually, through ROS regulation by the exogenous addition of GSH, very high metal recovery yields of 98.1% Li and 96.3% Co were obtained at 5.0% pulp density.

Keywords: ROS; acidophilic microbial consortium; biofilm; bioleaching; glutathion; waste lithium ion battery.

FIGURE 1

The structural composition of AMC under the control and test conditions.

FIGURE 2

Time-courses for (A) pH, (B) ORP, (C) Fe³⁺ generation rate, (D) Fe²⁺ concentration, (E) bioleaching efficiency of lithium, and (F) bioleaching efficiency of cobalt during bioleaching process of LiCoO₂ using the two-step method and the exogenous-acid adjustment technique.

FIGURE 3

Time-courses for (A) pH, (B) ORP, (C) Fe³⁺ generation rate, and (D) Fe²⁺concentration under simulated bioleaching system of different Li⁺ concentrations.

FIGURE 4

Time-courses for (A) pH, (B) ORP, (C) Fe³⁺ generation rate, and (D) Fe²⁺concentration in simulated bioleaching system of different Co²⁺ concentrations.

FIGURE 5

Time-courses for (A) pH, (B) ORP, (C) Fe³⁺ generation rate, and (D) Fe²⁺concentration in simulated bioleaching system with varied pulp density of LiCoO₂.

FIGURE 6

Time-courses for FL/OD₆₀₀ for simulated bioleaching system with varied pulp density.

FIGURE 7

Time-courses for (A) pH, (B) ORP, (C) Fe³⁺ generation rate, (D) Fe²⁺concentration, (E) ROS content, and (F) activities of intracellular ROS scavenging enzyme by exogenous GSH for simulated bioleaching system with 4.0% (w⋅v^–1) pulp density of LiCoO₂.

FIGURE 8

CLSM images of biofilms after 7-day incubation on the surfaces of pyrite coupons: (A) no lithium and cobalt ions (control), (B) 2.84 g⋅L^–1 Li⁺, (C) 24.08 g⋅L^–1 Co²⁺, (D) 2.84 g⋅L^–1 Li⁺ + 24.08 g⋅L^–1 Co²⁺, and (E) 2.84 g⋅L^–1 Li⁺ + 24.08 g⋅L^–1 Co²⁺ + 0.30 g⋅L^–1 GSH.

FIGURE 9

Time-courses for (A) pH, (B) ORP, (C) Fe³⁺ generation rate, (D) Fe²⁺concentration, (E) bioleaching efficiency of lithium, and (F) bioleaching efficiency of cobalt under pulp density of 5.0% with and without exogenous GSH.