Removal of cadmium(II) from aqueous solution by agricultural waste cashew nut shell

Abstract

Cashew nut shell (CNS) is a low cost adsorbent that has been used for the removal of cadmium(II) from an aqueous solution. The effects of various parameters such as solution pH, CNS concentration, contact time, initial cadmium(II) concentration and temperature were examined. The CNS was effective for the quantitative removal of cadmium(II) ions in acidic conditions and equilibrium was achieved in 30 min. The experimental data were analyzed by two-parameter (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich) and three-parameter models (Redlich- Peterson, Koble-Corrigan, Toth and Sips) by nonlinear regression analysis. The characteristic parameters for each isotherms and related correlation coefficients have been determined by using MATLAB 7.1. Thermodynamic parameters such as ΔGo, ΔHo and ΔSo have also been evaluated, and it was found that the sorption process was feasible, spontaneous and exothermic. Pseudo-first-order, pseudo-second-order, Elovich kinetic and intraparticle diffusion models were selected to follow the adsorption process. The results of the kinetic study show that the adsorption of cadmium(II) could be described by the pseudo-second order equation, suggesting that the adsorption process is presumably chemisorption. A single-stage batch adsorber was designed for different adsorbent dose-to-effluent volume ratios using the Freundlich equation. The results indicate that the cashew nut shell could be used to effectively adsorb cadmium(II) from an aqueous solution.