Selective separation of Dy(III), Yb(III) and Y(III) by complexation and orderly decomplexation coupling with ultrafiltration based on rotating disk membrane and a DFT study

Heavy rare earth elements have emerged as pivotal metals for industrial advancements. Nevertheless, their separation and purification pose considerable challenges. This work investigated the utilization of shear-induced dissociation coupled with ultrafiltration (SID-UF) as a separation process, employing phosphonic chitosan (PCS) as complexing agent for the separation and recovery of Dy(III), Yb(III), and Y(III). The results demonstrated that the rejection rates of rare earth ions surpassed 90.0 % at pH 6.0 with a PCS/RE mass ratio of 6. The order of shear stability of the PCS-RE complexes was determined to be PCS-Yb > PCS-Dy > PCS-Y. Leveraging this difference in stability, the high separation coefficients βY/Dy, βY/Yb and βDy/Yb among rare earth ions reached 12.38, 13.37 and 10.92, respectively. By controlling the shear rate on the rotating disk membrane, the complexes could be orderly decomplexed to achieve the selective separation of ternary heavy rare earth ions. Furthermore, the DFT calculations of the interaction energy (Eint) corroborated these experimental findings by confirming the PCS-Yb complex as the most stable (Eint = −38.80 kcal·mol−1) and PCS-Y as the least stable (Eint = –23.79 kcal·mol−1). Charge transfer played an important role in the origin of the stability differences of PCS-RE complexes. Collectively, the experimental and theoretical results underscore that SID-UF is an efficient, eco-friendly and promising technique for the selective separation and recovery of heavy rare earth ions.