Rare earth elements (REEs) are vital to various emerging technologies, from wind turbines to solid state lighting. REEs are mainly available through mining operations outside the U.S. However, due to import shortages, the prices of these elements have increased drastically in the last decade and the future availability of these elements is at risk. It is now crucial to develop technology to establish domestic sources of REEs. Global phosphate deposits contain 27 million tons of REEs, equal to nearly 200 years of current world demand. More than 38% of REEs end up in phosphogypsum (PG) and sludge during phosphate fertilizer production - the former is a waste from phosphate rock processing and the latter is a secondary waste from PG processing. Therefore, both waste streams are excellent sources for REEs recovery. Here, we developed a liquid phase-based recovery process which could generate 25,000 tons of REEs per year. This is the equivalent of 20% of current world demand. To optimize REEs recovery, we studied NdPO<sub>4</sub> solubility as a model aqueous system through both experimental and computational approaches. Calorimetry of REE-doped gypsum and PG was used to compare the energetics of surface adsorption versus phase stability of REEs in the solid phase, which provides insight into developing an effective recovery process.

Green Technology for REEs Recovery

251st National Meeting (2016)

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