Hydrometallurgy is a second core research thrust of the Laboratory for Strategic Materials, focused on the selective and efficient recovery of critical metals using aqueous-phase chemical processes. Our research spans leaching, solution purification, and metal separation strategies tailored to complex feedstocks, including primary ores, ionic clays, and diverse secondary resources such as electronic and battery wastes. We have developed and optimized hydrometallurgical routes for the extraction and separation of a wide range of elements, including rare earth elements (REEs), Li, Ni, Co, Mn, Ti, Nb, and Sc. Emphasis is placed on improving selectivity, reducing reagent consumption, and minimizing environmental impact through process intensification and innovative chemistry. This work underpins scalable and sustainable pathways for critical materials recovery and complements our efforts in advanced separation and recycling technologies.