Chelating water-soluble polymers associated with ultrafiltration membranes for metal ion removal

Abstract

This article describes the retention properties of commercial chelating water-soluble polymers, for different metal ions in aqueous solution using a liquid-phase polymer-based retention (LPR) technique. The polymers studied were poly(ethyleneimine) or P(EI) (water-free and a 50 % aqueous solution) and poly(ethyleneimine epichlorohydrin) or P(EIE) (a 17 % aqueous solution). These commercial polymers were fractionated by ultrafiltration membranes and then characterized by Fourier-transformed infrared spectroscopy. The extraction process was performed using the following metal ions: Cu²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cr³⁺. In the washing studies, we varied the pH (3, 5 and 7) and retention time. The results showed that P(EI) showed high retention for all the metal ions at pH 7 and for selective retention of Cu²⁺ at pH 5, while P(EIE) showed selective retention of Cu²⁺ ions at pH 7. Using the enrichment method, the maximum retention capacity of Cu²⁺ and Cd²⁺ was achieved using a 50 % aqueous solution of P(EI) at pH 5 and 7, respectively. Finally, charge–discharge experiments for Cu²⁺ were analysed by changing the pH from basic to acidic over three cycles. These results showed that it is possible to remove metal ions and regenerate the removal capacity of the polychelatogens using the LPR technique.