Feasibility of reduced iron species for promoting Li and Co recovery from spent LiCoO2 batteries using a mixed-culture bioleaching process

Abstract

The recovery of metals from spent LiCoO₂ batteries (SLBs) is essential to avoid resource wastage and the production of hazardous waste. However, the major challenge in regard to recovering metals from SLBs using traditional bioleaching is the low Co yield. To overcome this issue, a mixed culture of Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans was designed for use in SLBs leaching in this study. With the assistance of Fe²⁺ as a reductant, 99% of Co and 100% of Li were leached using the above mixed-culture bioleaching (MCB) process, thus solving the problem of low metal leaching efficiency from SLBs. Analysis of the underlying mechanism revealed that the effective extraction of metals from SLBs by the Fe²⁺-MCB process relied on Fe²⁺-releasing electrons to reduce refractory Co(III) to Co(II) that can be easily bioleached. Finally, the hazardous SLBs was transformed into a non-toxic material after treatment utilizing the Fe²⁺-MCB process. However, effective SLBs leaching was not achieved by the addition of Fe⁰ to the MCB system. Only 25% Co and 31% Li yields were obtained, as the addition of Fe⁰ caused acid consumption and bacterial apoptosis. Overall, this study revealed that reductants that cause acid consumption and harm bacteria should be ruled out for use in reductant-assisted bioleaching processes for extracting metals from SLBs.

Keywords: Bioleaching; Metal recovery; Reduced iron species; Spent LiCoO(2) batteries; Toxicity reduction.