Synergistic enhancement of metal extraction from spent Li-ion batteries by mixed culture bioleaching process mediated by ascorbic acid: Performance and mechanism

Pure and mixed cultures of microorganisms are used to leach spent Li-ion batteries (LIBs) to extract high-value metals. However, a low metal leaching efficiency is a general problem, hindering the commercialization of spent LIBs bioleaching. Therefore, a mixed culture bioleaching (MCB) process, mediated by ascorbic acid (AA), is proposed to promote the leaching of spent LIBs. Results show that the AA-MCB process leaches 94% Co and 95% Li at a pulp density of 20 g L-1, realizing 54% Co and 31% Li enhancement. Mass spectrometry analysis showed that a reduced bioleaching system is constructed by the mixed culture, AA, and AA products. In this system, bacteria promote LiCoO2 exposure on spent LIB surface by producing bioacid. Therefore, the refractory Co(III) easily reduces to soluble Co(II) by AA and its products, leading to the destruction of the crystalline structure of LiCoO2. Furthermore, bioacid facilitates easy leaching of Co and Li from structurally damaged LiCoO2. Ulti-mately, the AA-MCB process transforms spent LIBs from hazardous to general solid waste, exhibiting no bio-toxicity to Escherichia coli growth. Therefore, bioleaching process intensification by adding a green organic reducing agent is a promising alternative for effective metal extraction from spent LIBs, enriching the current recycling technologies of spent LIBs.