Abstract

The removal of Cd(II) and Cu(II) ions from aqueous solutions was studied by sorption onto microcapsules prepared by copolymerizing ethylene glycol dimethacrylate (EGDMA) and styrene (ST). The microcapsules were prepared by an in situ radical polymerization method by adding the extractant compound, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, and the monomers to the continuous aqueous phase. The extractant was immobilized within the microcapsules (MCs) which presented a spherical shape with rough surface. High productions of MCs with an important retention of extractant were achieved. Microcapsules constituted by a copolymer of 65% EGDMA and 35% ST presented best capacity of sorption of both metals. These MCs presented sufficient degree of cross-linking and a suitable balance of hydrophilic-hydrophobic character. The experimental data from chemisorption of metals onto the microcapsules fitted well the applied pseudo-second-order kinetics model. The alkylphosphonic extractant presented a higher rate constant and a higher equilibrium sorption capacity for Cd(II) than for Cu(II) at the pH used in this study. © 2008 Elsevier B.V. All rights reserved.