Ultrafiltration enhanced with poly(sodium acrylate) as an effective method for separation of heavy metals from multicomponent solutions

Polymer-enhanced ultrafiltration was used to separate heavy metal ions from their multicomponent mixtures. Model solutions containing an equimolar mixture of Cu(II), Zn(II), Cd(II), Ni(II), Cr(III) were supplemented with poly(sodium acrylate) PSA (a metal-binding polymer) and the ultrafiltration process was carried out. The separation effectiveness of individual metal ions was studied under various process conditions (amount of PSA, pH, total metal concentration, presence of coexisting ions), and the possibility of simultaneous or selective (competitive) separation of individual ions from a multicomponent mixture was evaluated. Effective simultaneous separation of metal ions occurred in solutions containing a sufficient polymer dosage (polymer/metal molar ratio C_PSA/C_M ≥ 7) and at a sufficiently high pH (pH ≥ 6). Since the polymer showed differential affinity for the metals tested (Cr(III) ≈ Cu(II) > Cd(II) >> Zn(II) > Ni(II)), partially selective separation of ions from the mixture at a decreased pH or lowered C_PSA/C_M was possible. In addition, certain co-occurring ions (especially versenate, EDTA) decreased the separation effectiveness of Cu(II), Zn(II), Cd(II) and Ni(II). These preliminary observations were confirmed by the ultrafiltration concentration of the metal mixture, carried out at different values of the process parameters, and the subsequent decomplexation–ultrafiltration process (pH = 2), enabling the recovery of concentrated metal solutions of varying composition, depending on the process conditions.