Extraction of Rare Earths from NdFeB Acid Leachate Using Pulsed Disc and Doughnut Column

The production of neodymium-iron-boron (NdFeB) magnet scraps has been increasing, creating an urgent demand for the recovery of rare earths elements from these scraps. Focus on the NdFeB acid leachate – saponified 2-ethylhexyl hydrogen −2-ethylhexylphosphonate (PC-88A) system, this study investigated mass transfer and hydrodynamics in a pulsed disc and doughnut column. Studies on mass transfer of single droplets demonstrated that the mass transfer process from the aqueous phase to the organic phase was enhanced when aqueous droplets serve as dispersed phase. The dispersed phase holdup (xd) and droplet diameter (d32) within the pulsed disc and doughnut column (PDDC) was investigated using NdFeB acid leachate as the dispersed phase. Results indicated that the xd decreased initially and increased subsequently with the increasing pulse intensity, and increased with the increment of flow rate. The evolution of d32 was inversely related to pulse intensity. The xd and d32 of dispersed phase were predicted with average absolute relative errors of 10.76% and 17.37%, respectively. The extraction efficiency of total REEs was 36.15% and mass transfer unit height reached 2 m of PDDC under an optimal condition. Based on estimation, a PDDC with a height of 2 m could realize the complete extraction of total REEs.