Zn(II) Sorption From Aqueous Solutions Using Polymeric MicrocapsulesContaining 2-Ethylhexylphosphonic Acid Mono-2-Ethylhexyl Ester

Abstract

Zn(II) sorption from aqueous solutions was studied on polymeric hydrophobic microcapsules (MCs) containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester as the extractant (PC-88A). The microcapsules were synthesised by adding this extractant during in situ radical polymerisation using styrene and ethylene glycol dimethacrylate (EGDMA) as starting monomers and benzoyl peroxide as the polymerisation initiator. SEM analysis of the microcapsules indicated that they had a spherical shape and a rough surface. A set of experiments was designed to study Zn(II) sorption behaviour onto MCs using aqueous solutions containing 100 mg/L of Zn(II) with an initial pH of 4.0. A Langmuir isotherm model fitted the experimentally observed equilibrium sorption data well. Results of kinetics experiments conducted between 293 and 323 K were well explained by a pseudo-second order kinetic model with an activation energy of 43.27 kJ mol -1 .Calculated thermodynamic parameters revealed that the chemisorption process was spontaneous and exothermic. The observed negative entropy change indicated that the metal bound to the extractant on the surface of MCs would generate a moderately ordered structure.