Lithium recovery from waste aluminum electrolyte via bioleaching: Comparative insights into acidic and alkaline pathways using Aspergillus niger and Glutamicibacter nicotianae.

With the growing limitations of primary lithium sources, recovering lithium from secondary resources, such as waste aluminum electrolyte (WAE), has gained increasing importance. This study investigates the application of bioleaching as a sustainable and eco-friendly method for lithium recovery from WAE. Two microorganisms with distinct pH preferences were employed: Aspergillus niger (A. niger), known for its production of organic acids and effectiveness in acidic environments, and Glutamicibacter nicotianae (G. nicotianae), a bacterium that thrives in alkaline conditions. Bioleaching experiments were systematically conducted at varying pulp densities (10, 30, and 50 g/L) over 30 days. Under optimal conditions (10 g/L pulp density), A. niger achieved 100 % lithium extraction within 22 days, whereas G. nicotianae achieved 43.75 % lithium recovery after 30 days. Kinetic modelling revealed that lithium dissolution with G. nicotianae was controlled by diffusion through a product layer, while A. niger's bioleaching process was governed by surface chemical reactions. These differences highlight the varying metabolic pathways and interactions of each microorganism with the waste material. The bioleached residues were further characterized using Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) analyses, revealing significant surface and mineralogical changes, particularly with A. niger treatment. The findings demonstrate the distinct mechanisms and efficiencies of acidic versus alkaline bioleaching pathways and provide insights into optimising bioleaching processes for lithium recovery from industrial waste streams.