Polymer-enhanced ultrafiltration: counterion distribution and its relation with the divalent metal-ion retention properties by sulfonic acid polyelectrolytes

The distribution of divalent counterions and its relation with the retention properties of sulfonic polyelectrolytes were analyzed, and the results were interpreted under the light of the counterion condensation theory using two-zone model and Donnan’s equilibria. In this regard, poly(vinyl sulfonic acid) and sodium poly(styrene sulfonate) solutions at pH 6.0 were diafiltered by the liquid-phase polymer-based retention technique. Metal-ion retention and distribution around polyelectrolyte chains were obtained from the diafiltration experiment as well as the maximum retention capacity (MRC) for each polymer. The MRC values obtained were 0.30, 0.15, 0.21, and 0.26 mmol of metal-ion per mmol of polymer for PVSA–Cu²⁺, PVSA–Cd²⁺, PSS–Cu²⁺ and PSS–Cd²⁺, respectively. The excess of ions added, the volume in the inside cell, and the order of addition of the ions contacted with the polymer were important factors defining the form of the retention profile.