Characterization of hydroxybenzoic acid chelating resins: Equilibrium, kinetics, and isotherm profiles for Cd(II) and Pb(II) uptake

Abstract

Chelating ion-exchange resins were synthesized by polycondensation of ortho/para hydroxybenzoic acid with resorcinol/catechol employing formaldehyde as cross-linking agent at 80±5 °C in DMF. The resins were characterized by FTIR and XRD. The uptake behaviour of synthesized resins for Cd(II) and Pb(II) ions have been studied depending on contact time, pH, metal ion concentration and temperature. The sorption data obtained at optimized conditions were analyzed by the Langmuir and Freundlich isotherms. Experimental data of all metal-resin system were best represented by the Freundlich isotherm. The maximum obtained sorption capacity for cadmium was 69.53 mg g-1 and 169.32 mg g-1 for lead. The adsorption process follows first order kinetics and the specific rate constant Kr was obtained by the application of the Lagergan equation. Thermodynamic parameters ΔG ads, ΔSads and ΔHads were calculated for the metal-resin systems. The external diffusion rate constant (Ks) and the intra-particle diffusion rate constant (Kid) were calculated by the Spahn-Schlunder and Weber-Morris models, respectively. The sorption process was found to follow an intra-particle diffusion phenomenon.