Utilization of response surface methodology, kinetic and thermodynamic studies on cadmium adsorption from aqueous solution by steel slag

Abstract

The study aims to separate a heavy metal of cadmium ions from an aqueous solution using steel slag as an adsorbent. The process was modeled using the response surface methodology based on the central compound design (RSM-CCD). Four variables of temperature, contact time, initial Cd(II) concentration, and rotation rate were considered in the ranges of 20–80 °C, 15-300 s, 20–100 mg L−1, and 100–900 rpm, respectively. The influences of studied parameters on the Cd(II) adsorption capacity and percentage were investigated. A quadratic regression model was proposed by the analysis of variance to predict the equilibrium Cd(II) adsorption capacity. The Redlich–Peterson isotherm model depicted the better fitting with experimental data than other models, and the results of kinetic modeling indicated that the pseudo-second-order model was well suited for the Cd(II) adsorption process using steel slag. Furthermore, the thermodynamic parameters demonstrated an exothermic and non-spontaneous adsorption process under studied temperatures.