Enhancing ultrafiltration with polyelectrolyte to separate heavy metal ions from multicomponent solutions

Polymer-enhanced ultrafiltration (PEUF) is an effective heavy metal separation technique due to coordinate or electrostatic bonds formed between the polymer and the metal ions. In this study, the PEUF technique was used to separate Cr(III), Cu(II), Zn(II), Ni(II), and Cd(II) ions from their equimolar mixture using poly(sodium 4-styrenesulfonate) (PSS) as an ultrafiltration-enhancing polymer. The effects of selected process parameters, i.e. the molar concentration ratio of PSS/total metals (C_PSS/C_Ms), pH, the total metal concentration (C_Ms), and the presence of some accompanying ions on the separation efficiency of individual metal ions were investigated. Then, the PEUF concentration was performed at selected process conditions followed by the decomplexation-ultrafiltration step performed at pH = 1 to separate the polymer and concentrated heavy metals. The process effectiveness was strongly affected by both C_PSS/C_Ms and pH, resulting in high metal rejection coefficients (R_M > 0.9) at C_PSS/C_Ms ≥ 5 and pH ≥ 5. The presence of some coexisting ions, especially SO₄²⁻, PO₄³⁻, EDTA, and Ca²⁺, reduced metal retention. The PEUF concentration process enabled retention of > 96 % of the metal ions and a 6.6-fold increase in their concentration in the retentate. The decomplexation-ultrafiltration step facilitated separation of the polymer and recovery of 85 % of the concentrated metal ions.