Synthesis of magMCM-41 with rice husk silica as cadmium sorbent from aqueous solutions: parameters' optimization by response surface methodology

The magnetic mesoporous silica of magMCM-41 with large surface area (695m(2)g(-1)) and high magnetization (10.79emug(-1)) was synthesized using extracted amorphous silica from rice husk. The synthesized materials were applied for adsorption of Cd(II) ions from aqueous solution in batch operation systems. A highly selective adsorbent was obtained by grafting 3-aminopropyltrimethoxysilane on the pores of the magMCM-41 in which the adsorption capacity of Cd(II) ions increased from 41.8 to 86mgg(-1), under the same conditions. A total of 20 sets of experiments were planned by the central composite design under response surface methodology. The effects of three independent variables pH, initial Cd(II) ion concentration and sorbent dosage were investigated on the adsorption capacity (q(e)) and removal efficiency (R) of cadmium. The best responses for Cd(II) adsorption capacity and removal efficiency were 493.21mgg(-1) and 60.25%, respectively, which was achieved at pH of 5.05, sorbent dosage of 0.1gL(-1) and Cd(II) concentration of 150mgL(-1). Additionally, the obtained value for desirability was equal to 0.807. The theoretical isotherm models were applied to describe the adsorption process that the Langmuir model provides the best correlation of the equilibrium data. The kinetics study revealed that data from the experiments fitted well to the pseudo-second-order equation than the pseudo-first-order equation. The thermodynamic parameters revealed that the adsorption process strongly depended on temperature and indicated the exothermic behavior and spontaneous nature of the adsorption.