D. Nothaft, K. Issapour
Uplift Geosystems,
United States
Keywords: acid leaching, rare earth elements (REE), acid recycling, bipolar membrane electrodialysis (BPMED), membrane technology, REE refining, phosphate ores, fluoride ores, phosphogypsum
Summary:
Acid leaching is a step common to many rare earth element (REE) extraction processes targeting phosphate, fluoride, clay, and phosphogypsum ores. Leaching rates generally increase with increasing acid concentration, with some REE-bearing mineral leaching reactions being first order with respect to acid concentration up to at least 3 mol H+ / L. Increasing acid concentration can also decrease reactor volumes and make solid/liquid separations more efficient, leading to lower costs. Bipolar membrane electrodialysis (BPMED) is an energy-efficient and safe method for acid recycling, but commercially available BPMED systems are limited to relatively dilute (up to 2 mol H+ / L) acid solutions. To make acid recycling more feasible in REE extraction and purification, we have developed mechanisms for increasing output acid concentration of BPMED systems towards 4 mol H+ / L. Using our novel reactor design platform, we are experimenting with flow rates, saline feed concentrations, and current density, as well as leveraging advances in membrane technology to achieving unprecedented acid concentrations. Modified REE refineries incorporating these developments can benefit from cost savings on reagent procurement, while decreasing solid and liquid wastes.