Bioleaching of valuable metals from spent LIBs followed by selective recovery of manganese using the precipitation method: Metabolite maximization and process optimization

Despite the increased demand for resource recovery from spent lithium-ion batteries (LIBs), low Mn leaching efficiencies have hindered the development of this technology. A novel process was devised to enhance the dissolution of metals by producing citric acid using a molasses medium by Penicillium citrinum. This investigation used response surface methodology to investigate the influence of molasses concentration and media components on citric acid production, which demonstrated that molasses (18.5% w/w), KH₂PO₄ (3.8 g/L), MgSO₄.7H₂O (0.11 g/L), and methanol (1.2% (v/v)) were the optimum values leading to the production of 31.50 g/L citric acid. Afterward, optimum inhibitor concentrations (iodoacetic acid: 0.05 mM) were added to accumulate citric acid, resulting in maximum bio-production (40.12 g/L) of citric acid. The pulp density and leaching time effect on metals dissolution was investigated in enriched-citric acid spent medium. The suitable conditions were a pulp density of 70 g/L and a leaching duration of 6 days, which led to the highest dissolution of Mn (79%) and Li (90%). Based on the results of the TCLP tests, the bioleaching residue is non-hazardous, suitable for safe disposal, and does not pose an environmental threat. Moreover, nearly 98% of Mn was extracted from the bioleaching solution with oxalic acid at 1.2 M. XRD, and FE-SEM analyses were utilized for further bioleaching and precipitation mechanism analysis.