Retention of metal ions in ultrafiltration of mixtures of divalent metal ions and water-soluble polymers at constant ionic strength based on Freundlich and Langmuir isotherms

The interactions of water-soluble polymers with metal ions are studied by ultrafiltration using a molecular-weight cut off of 5000 Da polyethersulfone ultrafiltration membrane. The technique allowed analyzing mathematically the distribution of metal ions bound to previously fractionated high molecular-weight water-soluble polymers or free in the solution from variables experimentally measurable. The Langmuir and Freundlich adsorption isotherms for the system poly(sodium 4-styrenesulfonate) (PSS)/Cd2+ and poly(allylamine) (PALA)/Ni2+ are obtained for ultrafiltration experiments performed at constant ionic strength and divalent metal ion concentration two orders of magnitude lower than the polymer concentration. Based on the expressions of these isotherms, the analytical expressions of the retention profiles have been deduced.