“Biosorption Isotherms and Thermodynamic Insights into Metal Recovery from Li-Ion Battery Leachates Using Fungal Biomass”

This study investigates the biosorption performance of seven fungal species: Aspergillus niger, Aspergillus fijiensis, Aspergillus flavus, Penicillium ochrochloron, Penicillium simplicissimum, Fusarium solani, and Fusarium proliferatum for the purification of a real leachate generated during the hydrometallurgical processing of NMC-type lithium-ion (Li-ion) batteries, with a focus on the selective removal of Al and Cu impurities. Fungal biomasses were cultivated, washed, lyophilized, and characterized before biosorption experiments. Preliminary screening revealed biosorption capacities for Ni, Co, Mn, and Cu (up to 14 mg/g), whereas Al and Li showed limited uptake (< 2 mg/g). Based on Cu and Al removal efficiencies exceeding 10% and 15%, respectively, A. flavus, A. niger, and P. simplicissimum were selected for further investigation. Parametric studies demonstrated that biosorption was maximized at biomass dosages of 15–20 g/L while increasing temperature enhanced Cu uptake by up to 29% for A. flavus. Isotherm modeling showed that the Freundlich and Koble–Corrigan models best described the experimental data, with correlation coefficients > 0.9, indicating biosorption on heterogeneous surfaces with non-uniform energy distribution. Thermodynamic parameters (ΔG° = [−5 to −50] kJ/mol, ΔH° = [+6] kJ/mol) confirmed that biosorption was spontaneous and endothermic, with increased randomness at the solid–solution interface. Overall, the results demonstrate that fungal biomass, particularly A. flavus, are effective, low-cost biosorbents for selectively removing Cu and Al while retaining Li, Ni, Co, and Mn in solution for downstream recovery.