Response surface methodology approach for optimization of Cu2+ and Pb2+ removal using nanoadsorbent developed from rice husk

Abstract

In this study, central composite design (CCD) a subset of response surface methodology (RSM) was employed for the evaluation of mathematical model equation and optimization of prime parameters for the removal of Cu2+ and Pb2+ from aqueous solution using rice husk nanoadsorbent (RHN). The interactive effect of three independent variables viz. pH, adsorbent dose and initial metal ion concentration on Cu2+ and Pb2+ adsorption were investigated. Relative significance of variables in removal action was depicted by analysis of variance (ANOVA). pH 6.7, adsorbent dose 0.7 g/L and initial concentration 21 mg/L for Cu2+ and pH 4, adsorbent dose 0.4 g/L and initial concentration 50 mg/L for Pb2+ were found to be influential for 82% and 76% respectively. The removal efficiency was determined by constructing second-order regression equation model using Design Expert Software. Kinetic, Isotherm and thermodynamic studies were executed to enumerate the adsorption capacity of Cu2+ and Pb2+. Langmuir adsorption capacity was found to be 13.003 mg/g and 6.101 mg/g respectively for Cu2+ and Pb2+ indicating physico-chemical adsorption. Pseudo second-order kinetic model described the adsorption process very well. Intraparticle diffusion systemically interpreted the adsorpion of Cu2+ and Pb2+ on the nanoadsorbent surface. Free energy, Enthalpy and Entropy change revealed spontaneous and endothermic nature of the adsorption process. The recyclability of nanoadsorbent RHN was also investigated upto three cycles.