Bayer Cake as a Secondary Resource for Lithium Recovery: Leaching, Purification, and Residue Reusability

Bayer cake generated during the Bayer process represents a promising secondary resource for lithium recovery. Following lithium extraction, the residual Bayer cake may be partially recycled back into the Bayer process. Lithium was successfully leached from the Bayer cake using sulfuric acid, and the effects of temperature, acid concentration, and solid-to-liquid ratio on leaching performance were investigated. The highest lithium recovery yield (99.55%) was achieved at a solid-to-liquid ratio of 160 g/L, a temperature of 80 °C, and a sulfuric acid concentration of 0.5 M. Under these conditions, the aluminum leaching efficiency was 59.58%. The resulting leachate contained 0.90 g/L lithium and 7.20 g/L aluminum, while only 35.7% of the treated Bayer cake could be recycled to the Bayer process. Increasing the solid-to-liquid ratio to 200 g/L reduced lithium and aluminum leaching efficiencies to 81.36% and 42.58%, respectively. The corresponding lithium and aluminum concentrations in the leachate were 0.88 g/L and 6.95 g/L. Under these conditions, the proportion of Bayer cake recyclable to the process increased to 49.7%. As sulfuric acid leaching lacks selectivity toward lithium, further purification of the leachate was required. Purification experiments were conducted using various combinations and dosages of 220 g/L NaOH solution, H3PO4, Al-cake, Li3PO4, Li2CO3, MgO, and Ca(OH)2. Among the tested reagents Li3PO4, Li2CO3, MgO, and Ca(OH)2, proved to be the most effective, reducing the aluminum concentration in solution to below 1 mg/L. However, purification with MgO, and Ca(OH)2 resulted in the introduction of Mg and Ca impurities into the solution, respectively.