Tolerance of three fungal species to lithium and cobalt: Implications for bioleaching of spent rechargeable Li-ion batteries.

Abstract

This paper aims to quantify the growth and organic acid production of Aspergillus niger, Penicillium chrysogenum and Penicillium simplicissimum when these fungi are exposed to varying levels of lithium (Li) and cobalt (Co). The study also tests whether pre-exposing the fungi to these metals enables the fungi to develop tolerance to Li or Co. When cultures of A. niger, P. chrysogenum or P. simplicissimum were exposed to 250mgl-1 of Li or Co, biomass production and excretion of organic acids were significantly inhibited after 5days of growth compared to cultures grown in the absence of these metals. Pre-exposing cultures of A. niger to 250mgl-1 of Li or Co for 20days significantly increased biomass production when the fungus was subsequently sub-cultured into 250 or 500mgl-1 of Li or Co. However, pre-exposure of P. chrysogenum or P. simplicissimum to 250mgl-1 of Li or Co for 20days did not increase biomass production. Aspergillus niger, but not the Penicillium species, developed tolerance to Li and to Co during the 20-day pre-exposure period. Therefore, processes that utilize fungal bioleaching with A. niger to mobilize and recover valuable metals such as Li or Co should consider a pre-exposure step for fungi to improve their tolerance to metal toxicity. Fungi may have the ability to extract valuable metals such as Li and Co from spent rechargeable batteries. However, the toxicity of the extracted metals can inhibit fungal growth and organic acid production. Pre-exposure to metals may alleviate toxicity for some fungal species. This knowledge can be used to improve the design of bioleaching protocols, increasing the potential for fungal bioleaching to become an economical and environmentally friendly method of recovering Li and Co from spent batteries.