Abstract
Ion-adsorption clays represent one of the world’s most strategically important sources of rare earth elements (REEs), essential for electric vehicles, wind turbines, defense technologies, and advanced manufacturing. Yet current processing practices rely heavily on ammonium-based lixiviants, which generate environmentally burdensome effluents, increase impurity co-leaching, and pose challenges for regulatory compliance, especially as governments strengthen oversight of critical mineral extraction. This work introduces a sustainable, ammonia-free hydrometallurgical approach that leverages sodium citrate as an environmentally benign lixiviant for selective REE recovery. Experimental results demonstrate that citrate-based leaching substantially reduces impurity dissolution while maintaining strong REE extraction performance. Mechanistic analysis indicates that the process operates through ligand-assisted desorption, preserving clay structure and enabling application in both heap and agitated leaching operations. Two downstream recovery strategies were evaluated to assess industrial readiness. Oxalic acid precipitation from citrate leachates yielded high-purity mixed REE oxalates meeting typical refinery feed specifications, while carbonate-based precipitation produced significantly lower REO grades, increasing refining complexity. These findings highlight clear pathways for integrating citrate leaching into existing or emerging REE supply chains. For government and industry stakeholders, this citrate-based flowsheet offers a practical means to reduce environmental liabilities, improve permitting viability, and enhance the long-term sustainability of rare earth production. By improving selectivity, lowering chemical burdens, and generating high-quality products, the process supports policy goals around responsible critical-mineral development while providing industry with a scalable and regulation-friendly alternative to conventional ammonium systems.