Bioprocessing of spent lithium ion batteries for critical metals recovery - A review

The increasing demand for metals and the concomitant depletion of the primary metallic resources is one of the most important environmental and societal challenges nowadays. Critical metals, rare earth elements, base and precious metals demand is growing day-by-day and driving many metals towards the edge of supply risk. On the other hand, the problems linked to waste generation (especially waste electrical and electronic equipment (WEEE)) are also increasing globally. These end-of-life electronic wastes contain significant concentration of critical raw materials accompanied by harmful substances. Spent Li ion batteries is a kind of WEEE stream, bearing considerable concentrations of valuable metals (like Co, Li, Mn and Ni). If the end-of-life Li ion batteries are not managed properly, there is a high risk that these valuable metals and toxic substances could end into the environment. In order to address the environmental complications, sustainable resource management and boost circular economy, it is important to properly manage and recycle these spent Li ionbatteries. Conventional methods based on high-temperature pyro-metallurgical routes together with hydro-metallurgical processing have been widely studied for the recovery of metals from spent LiBs. However, bio-metallurgical approaches have an edge over their counter parts because of their environmentally friendly nature. Microbe-metal interactions have received special attention both in terms of leaching metals from WEEE and also in recovering metal ions from aqueous streams. Microbial technologies are promising for removing metal ions because of less cost, technical feasibility for large scale applications and no need for addition of toxic chemicals thereby avoiding generation of toxic or hazardous byproducts. In this study, particular emphasis is placed on reviewing the progress made in biohydrometallurgy (i.e. bacterial and fungal leaching practices as one and two-step mode) for the leaching of critical metals from waste lithium ion batteries. Biotechnological methods (e.g. biosorption, bioprecipitation and bioelectrochemical treatment) for the recovery of critical metals from pregnant leachates and aqueous streams are also discussed.