Polymers enhancing ultrafiltration separation of Cd(II) ions

Polymer-enhanced ultrafiltration (PEUF) was applied to separate Cd(II) ions from an aqueous solution. The PEUF method involves metal ions binding with polymeric ligands and the separation of macromolecular compounds in the ultrafiltration process. Three different polymers, that is, polyethyleneimine (PEI), poly(sodium acrylate) (PSA), and poly(sodium 4-styrenesulfonate) (PSS), were used as metal-binding agents and a direct comparison of their efficiency for Cd(II) ions separation was conducted. Apart from the type of the polymer used, some other process parameters, that is, Cd(II) ions concentration, polymer-to-metal concentration ratio, pH, and the presence of additional salts, were investigated and their impact on Cd(II) rejection coefficient was determined. At selected process conditions, an ultrafiltration concentration of model Cd(II) solutions was conducted for each examined polymer, followed by a decomplexation process and a recovery of the concentrated metal from the solution. All three polymers enhanced the effectiveness of the ultrafiltration separation of Cd(II) ions. High Cd rejection coefficients R_Cd > 0.9 were observed at process conditions: polymer/ Cd molar ratio of 5 (for PSA and PSS) or 7.5 (PEI) and pH ≥ 4 (for PSS), pH ≥ 5 (for PSA), and pH ≥ 6 (for PEI). After the concentration process, the decomposition of polymer-Cd bonds and the recovery of concentrated Cd(II) ions were effective at pH = 2 in the PEUF assisted with PEI or PSA.