Removal of cadmium ions from synthetic aqueous solutions with a novel nanosulfonated poly(glycidyl methacrylate) cation exchanger: Kinetic and equilibrium studies

A fundamental investigation of the removal of cadmium ions from aqueous solutions by synthesized sulfonated poly(glycidyl methacrylate) (SPGMA) was conducted under batch conditions. The kinetic and equilibrium results obtained for cadmium sorption with different initial cadmium concentrations onto synthesized SPGMA were analyzed. Kinetic modeling analysis with four different types of kinetic sorption models (pseudo-first-order, pseudo-second-order, simple Elovich, and intraparticle diffusion rate models) was applied to simulate the cadmium-sorption data. The analysis of the kinetic data indicated that the sorption was a second-order process and was pore-diffusion-controlled. An ion-exchange mechanism may have existed in the cadmium-sorption process with the synthesized SPGMA. The cadmium uptake by SPGMA was quantitatively evaluated with equilibrium sorption isotherms. To describe the isotherms mathematically, the experimental data of the removal equilibrium were correlated with the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherm models, and the applicability of these isotherm equations to the sorption systems was compared on the basis of the correlation coefficients. The applicability of the equilibrium isotherm models followed this order: Freundlich > Langmuir > Temkin > D-R. The maximum sorption capacity, determined from the Langmuir isotherm, was 555.55 mg/g at 25°C. Thermodynamic parameters, including changes in the enthalpy, Gibbs free energy, and entropy, were calculated. Positive values for the change in enthalpy and negative values for the change in the Gibbs free energy showed the endothermic and spontaneous nature of sorption, respectively. The relatively small value of the activation energy (32.12 kJ/mol) confirmed that the cadmium-sorption process was diffusion-controlled.