Multi-scale analysis of acidophilic microbial consortium biofilm's tolerance of lithium and cobalt ions in bioleaching

Metal ions stress will inhibit the oxidation capacity of iron and sulfur of an acidophilic microbial consortium (AMC), which leads to reduced bioleaching efficiency. This work explored the impacts of Li+ and Co2+ on the composition and function of AMC biofilms with a multi-scale approach. At the reactor scale, the results indicated that the oxidative activity, the adsorption capacity, and the biofilm formation ability of AMC on pyrite surfaces decreased under 500 mM Li+ and 500 mM Co2+. At the biofilm scale, the electrochemical measurements showed that Li+ and Co2+ inhibited the charge transfer between the pyrite working electrode and the biofilm, and decreased the corrosion current density of the pyrite working electrode. At the cell scale, the content of proteins in extracellular polymers substrate (EPS) increased as the concentrations of metal ions increased. Moreover, the adsorption capacity of EPS for Li+ and Co2+ increased. At the microbial consortium scale, a BugBase phenotype analysis showed that under 500 mM Li+ and 500 mM Co2+, the antioxidant stress capacity and the content of mobile gene elements in AMC increased. The results in this work can provide useful data and theoretical support for the regulation strategy of the bioleaching of spent lithium-ion batteries to recover valuable metals. Nowadays, the amount of wasted lithium-ion batteries increase with the popularity of personal mobile devices and electric vehicles. Improper handling of waste lithium-ion batteries can seriously pollute the ecological environment and is a waste of resources. Bioleaching technology has great potential for the recovery of valuable metals in waste lithium-ion batteries. However, bioleaching efficiency is seriously affected by heavy meatal ions when the biofilm moves forward. This work provides useful experimental evidence and data analysis for a deep understanding of the mechanism of how an acidophilic microbial consortium responds to heavy metal ions with the development of their regulatory strategies.