Transforming Biotite Waste into a Lithium Resource: Mechanical Activation-Assisted Mild Acid Leaching of Nepheline Syenite By-Products

This study presents an efficient and environmentally friendly approach for lithium recovery from biotite-rich wastes generated during nepheline syenite processing by combining mechanical activation with sulfuric acid leaching. Mechanical activation was applied as a pretreatment to enhance extraction of lithium and minimize acid consumption. After optimizing the process parameters, lithium extraction efficiencies of up to approximately 91% were achieved. The results clearly demonstrated that mechanical activation substantially reduced sulfuric acid demand up to 85.7%, allowing lithium recoveries comparable to those obtained with 1.75 mol L−1 acid in direct leaching to be achieved using only 0.25 mol L−1 acid. Structural and morphological analyses (XRD, SEM, FTIR, and particle size analysis) confirmed progressive amorphization of biotite, accompanied by the weakening of -OH and siloxane (Si-O-Si) bonds. Needle-like and layered biotite particles transformed into rounded and agglomerated morphologies with increasing activation time, leading to an initial decrease in particle size followed by agglomeration-dominated growth. Although crystallinity continuously decreased with activation time, partially reversible behavior was observed beyond 120 min. Overall, mechanical activation enabled a low-acid, and effective process design for lithium recovery from biotite-rich nepheline syenite wastes.