W. Burgess, S. Crawford, N. Siefert
National Energy Technology Laboratory,
United States
Keywords: Rare Earth Elements, Solvent Extraction, Rapid Sensing
Summary:
The development of an economically competitive domestic supply of rare earth elements and yttrium (REY) is necessary for our nation’s economic growth and national security. The achievement of a secure domestic supply of REY requires not only the development of efficient, cost-effective, and environmentally sound processes for recovery of REY from naturally occurring materials and/or recycled products, but also the development of process technology to treat the resulting process streams for the subsequent concentration and precipitation of high-REY content solids. An impediment to the development of such processes is the scarcity of analytical methods that provide rapid determination of the composition of process streams. In this work, a membrane-based extraction process was used to selectively recover REYs from a dilute solution in the presence of much higher concentrations of Ca, Al, and Fe, highlighting an effective method for concentrating REYs in complex streams. In tandem, the use of a portable spectrometer equipped with an immobilized zinc adeninate benzene tricarboxylate metal-organic framework sensing material makes possible the rapid detection of the presence of part-per-million concentrations of Tb and Eu in both weakly acidic and strongly acidic process streams within a few-minute time scale. It was found that a solvent extraction processing time of 15-60 minutes maximized selectivity of REY over the gangue ions while achieving up to 80% REY recovery, < 1% Al recovery and <5% Ca recovery. Taken together, these experiments highlight not only an innovative method for REY purification but also the importance of inexpensive, portable characterization methods for near real-time, semi-quantitative analysis of REY content. This approach thus shows significant promise for the production of REYs from a range of potential feedstocks, a critical step toward developing a robust supply chain of critical metals.