Online separation of critical rare earth elements from end-of-life permanent magnets using micro polymer inclusion beads (µPIBs)

Abstract

A column filled with micro polymer inclusion beads (µPIBs) was developed and investigated for the first time. The µPIBs were composed of 60 wt% di-(2-ethyl-hexyl) phosphoric acid (D2EHPA) and 40 wt% poly(vinyl chloride) (PVC) and the column was used for the separation of ions of rare earth elements (REEs) from synthetic solutions and the digest of end-of-life (EOL) rare earth permanent magnets (REPMs). This µPIB packed column was successfully applied to separating La3+ from Gd3+, as representatives of the light and middle REEs, previously achieved by us using a polymer inclusion membrane (PIM) containing the same chemical components as the µPIBs used in this study. The results obtained demonstrated the feasibility of the µPIBs packed in a column for light and middle REE ion separation similarly to their PIM counterpart. The separation potential of the µPIB packed column was further demonstrated by the selective recovery of Nd3+ and Dy3+ from an EOL REPM digest in 2 M sulfuric acid which also contained Fe3+, Co2+, and Ni2+. Nd3+ and Dy3+ could be selectively extracted from the diluted to 0.03 M sulfuric acid digest after the addition of ascorbic acid which reduced Fe3+ to Fe2+. Nd3+ and Dy3+ were separated via selective back-extraction from the µPIB-column using 0.3 and 2 M sulfuric acid receiving solutions, respectively. Thermogravimetric analysis of the µPIBs, before and after application in the µPIB-column, indicated negligible D2EHPA loss after six processing cycles. Thus, these results demonstrated the strong potential of the proposed µPIB-column method for the sustainable recovery of REEs from electronic waste such as REPMs.