Empirical modeling and CCD-based RSM optimization of Cd(II) adsorption from aqueous solution on clinoptilolite and bentonite

Abstract

In the present study, adsorption of Cd(II) ion from an aqueous solution on natural clinoptilolite (NC), natural bentonite (NB), modified clinoptilolite (MC) and modified bentonite (MB) were investigated. Response surface methodology (RSM) and central composite design (CCD) were used for NC and NB in order to investigate the effect of pH and contact time on adsorption efficiency and process optimization. Based on statistical analysis, the Cd(II) adsorption model was highly significant, with very low p-values. pH’s 5.35 and 3.89, and contact times 20.49 and 16.27 h, with adsorption efficiency 94.86% and 87.42%, were found to be optimum for Cd(II) ion adsorption on NC and NB, respectively. The experimental data was fitted to adsorption isotherm models, indicating the monolayer sorption of Cd(II). The Jossesns, Unilan, Baudu, and Freundlich models were selected as the best models, with correlation coefficients of 0.8973, 0.9930, 0.9267, and 0.9723, and with lowest error for NC, NB, MC, and MB, respectively, with negligible differences compared to the experimental values. The results showed that the NC adsorption efficiency is higher than NB in both cases.