SELECTIVE AND SEQUENTIAL PRECIPITATION FOR CRITICAL MINERAL EXTRACTION FROM SECONDARY SOURCES

Utilizing secondary sources such as electronic waste and mine tailings for critical material extraction presents significant potential for addressing their supply risk. However, conventional methods for separating mixed metals are often chemical- and energy-intensive, relying heavily on organic ligands, ionic liquids, and ion-selective membranes or electrodes. Achieving sustainable production of valuable critical elements from secondary sources necessitates a paradigm shift away from these resource-intensive processes. We present two novel approaches based on the coupling of ion diffusion and precipitation kinetics. Simply by placing a mixed salt solution on top of a hydrogel loaded with a precipitating agent, we obtained spatially separated precipitates along the reactor. Another approach involves a constant pumping of reactant solutions under laminar flow that drives reactions far from the thermodynamic equilibrium and results in selective precipitation at the fluid interface. Our proof-of-concept studies have been demonstrated for separating transition metals with modeled feedstocks representative of lithium-ion battery cathodes and rare earth elements from NdFeB permanent magnets and mine tailings. We expect these approaches to be broadly relevant to chemical separations from complex feed streams and diverse chemistries—enabling more sustainable materials extraction and processing.