Assessment of the visible light effect on one-step bacterial leaching of metals from spent lithium-ion batteries cathode pretreated by a bio-chemical lixiviant

Abstract

Over the years, the extensive generation of spent lithium-ion battery cathodes (SLIBCs) and the absence of a practical recycling criterion for these hazardous yet metal-rich urban resources have posed a severe environmental threat. To address this issue, we propose an innovative hybrid strategy based on the characterization of SLIBCs, which includes pretreatment and an evaluation of the effect of visible light on one-step bacterial leaching of SLIBCs. This research presents, for the first time, an evaluation of the impact of visible light on the semiconducting properties of SLIBC and its potential to enhance extracellular electron transfer (EET) between the heterotrophic bacterium Bacillus foraminis and the waste. This increased electron transfer leads to more efficient metal bioleaching. In this strategy, we applied a novel bio-chemical pretreatment to modify the powder structure, considering the high metal content in the waste. This novel approach utilized metabolites from the spent medium of Bacillus foraminis cultures at pH∼5.4 and H2O2 (15% (v/v)). A pulp density of 10 g/L, a duration of 48 h, and a temperature of 60 °C resulted in the extraction of 98% of the manganese content. Subsequently, we assessed the bioleaching of pretreated SLIBC under both visible light and darkness conditions. Results indicate that, under 15,000 lux for 6 days, we achieved acceptable extraction rates: 68% Cu, 41% Li, 25% Co, and 16% Ni. In contrast, in darkness, extraction rates were notably lower, at 23% Cu, 9.9% Li, 3.9% Co, and 2.6% Ni. The increased extraction efficiency under visible light can be attributed to the proposed mechanism of light's effect on enhancing extracellular electron transfer between bacteria and SLIBC with semiconducting properties. FTIR, XRD, and FE-SEM analyses were also instrumental in understanding the effectiveness of the proposed strategy.