Simultaneous leaching of Li, Ga, and REEs from coal fly ash and a novel method for selective leaching of Li and Ga

Lithium (Li), gallium (Ga), and rare earth elements (REEs) are essential in various industries due to their wide range of applications, and extraction of rare metals from coal fly ash (CFA) has become a hot topic in recent years. This study investigates the simultaneous leaching of Li, Ga, and REEs from CFA using both inorganic and organic acids. High leaching efficiencies, exceeding 90%, were achieved for Li (90.4%), Ga (90.5%), and REEs (92.7%) with 3 M HCl leaching. The leaching efficiency of citric acid is lower, but it can achieve a leaching rate of 70–80% at low concentration (0.5 M). A novel two-stage acid leaching approach is proposed for the selective leaching of Li and Ga from CFA. In the first step, 1 M HCl leaching results in the leaching of most Li (71.12%) and a small amount of Ga (2.63%). Subsequently, 2 M HCl leaching led to the leaching of a small amount of Li (18.14%) and most of Ga (83.93%). The silicic acid gel produced during low HCl concentration leaching exhibited a stronger affinity for Ga3+ than for Li+, with significantly higher adsorption energy for Ga (−211.554 kcal/mol) compared to that for Li (−3.481 kcal/mol). This two-stage acid leaching process ingeniously utilized H2SiO3 to achieve the selective separation and leaching of Li and Ga.