Equilibrium, Kinetic, and Thermodynamic Analysis of Cd(II) Sorption from Aqueous Solutions using Polymeric Microcapsules containing an Acidic Organophosphonic Extractant

Abstract

The equilibrium, kinetics, and thermodynamics of Cd(II) sorption from aqueous solutions onto polymeric microcapsules has been studied. Microcapsules were prepared by immobilizing an acidic organophosphonic extractant in a polymeric matrix prepared from styrene and ethylene glycol dimethacrylate following in situ free-radical suspension polymerization. Scanning electronic microscopy showed that the microcapsules were spherical and exhibited a rough surface with an average BET surface area of 12–20 m² g⁻¹ and an approximate pore size of 7.0 nm. The microcapsules were contacted with aqueous solutions containing Cd(II) approximately 100 mg L⁻¹ at an initial pH = 4.0 to study their sorptive behaviour over a temperature range of 293–323 K. The results of equilibrium experiments showed that the results filled the Langmuir isotherm model. The experimental kinetics followed a pseudo-second order model with an activation energy of 47.1±2.2 kJ mol⁻¹. Thermodynamics measurements showed that sorption is spontaneous and exothermic and that entropy had a negative value.

Keywords:

• Cadmium(II)
• microcapsules
• sorption
• equilibrium
• kinetics
• thermodynamics

ACKNOWLEDGMENTS

The authors gratefully acknowledge the support of The National Fund of Science and Technology of Chile (CONICYT) through project FONDECYT Nº 1100151. C. Araneda acknowledges a Doctoral Fellowship from CONICYT.