Separation of light rare earth ions from aqueous solution by shear-induced orderly dissociation coupling with ultrafiltration and phosphorylated chitosan as complexant

Light rare earth ions (La(III), Ce(IV), and Nd(III)) were separated from an aqueous solution using a novel water-soluble polymer phosphorylated chitosan (PCS) as complexant by shear-induced orderly dissociation coupling with ultrafiltration (SIOD-UF). The optimized pH and P/RE (mass ratio of PCS to rare earth ions) for the rejection of rare earth ions by coupling with ultrafiltration (C-UF) were investigated, and the shear stabilities of PCS-RE complexes were also studied for the selective separation of mixed rare earths. The critical shear rate (γ_c) at which PCS-RE complexes begin to dissociate at pH 7.0 were 1.31 × 10⁵, 1.63 × 10⁵, and 1.81 × 10⁵ s⁻¹ for La, Ce, and Nd complexes, respectively. It showed the sequence of shear stability was PCS-Nd > PCS-Ce > PCS-La, which is consistent with the analysis by the frontier molecular orbital theory. Highly selective separation of Ca(II), La(III), Ce(IV), and Nd(III) and the regeneration of PCS were successfully realized at one time by SIOD-UF. The results showed that the maximum separation coefficient β_Ca/La, β_La/Ce, and β_Ce/Nd reached 57.1 37.1 and 20.4, respectively, and the complexation property of regenerated PCS only a little loss compared with the original after 10 times cycles.