Rotating Packed Bed Contactors for Rare Earth Element Processing

K. Kent, I. Wang, W. Dean, A. Servis, C. Duval
Case Western Reserve University,
United States

Keywords: rotating packed bed, adsorption, mass transfer


Solvent extraction is the key separation technique used for rare earth element (REE) extraction. Current process equipment used for solvent extraction, such as mixer settlers, are costly, have a large footprint, and generate high volumes of waste. Rotating packed bed (RPB) contactors, which are devices that drive liquid through a continuously rotating bed of packing, are an emerging technology that can decrease the size of process equipment in a REE separation plant. Additionally, the RPB contactors technology can be used for both solvent extraction and solid-liquid separation to recover valuable metals. Adsorption of REE on diglycolamide (DGA) resins have been studied as an alternative to solvent extraction. In this work, a bench-scale RPB contactor packed with DGA resin was developed. RPBs have an applied centrifugal force during the separation process which increases microscale mixing, thereby allowing the same recovery as in traditional packed columns but in a smaller volume. This smaller volume decreases capital expenditures for separation process equipment and opens the potential for building separation process units near mines or REE recycling sites. Prototype RPBs were 3D printed using a Polyjet printer and assembled using commercially available seals, bearings, and motor. Initial testing included investigating REE extraction in packed columns with DGA resin. Neodymium extraction from acidic media was compared for the traditional packed column and the rotating packed bed up to a rotational speed of 2,000 RPM. The figure of merit for comparison is the overall mass transfer coefficient. These experiments are laying the groundwork for process intensification for REE separations using extractive chemistries.