Application of a thermally modified agrowaste material for an economically viable removal of Cr(VI) from aqueous solutions

Abstract

Removal of Cr(VI) from aqueous solutions has been investigated by adsorption on a low-cost adsorbent, calcined rice husk (CRH). Rice husk is an agrowaste material. It was thermally treated in a muffle furnace at 650®C for 2 h to obtain CRH. The adsorbent, CRH, was characterized with X-ray diffraction and scanning electron microscopy for phase determination and its surface characteristics, respectively. The pHzpc of the adsorbent was 8.82. The effect of important parameters, i.e., initial concentration, adsorbent dose, temperature, and pH, on the removal of Cr(VI) was studied. The removal decreased by increasing the temperature from 25 to 45®C. The pH of the aqueous solutions affected the removal of Cr(VI) significantly, and the removal decreased from 69 to 47% by varying the pH of the solutions from 2.0 to 10.0. The writers achieved 89% removal of Cr(VI) at an initial Cr(VI) concentration of 1.69 × 10-6 M, at 25®C and pH 2.0. Equilibrium adsorption data for the removal of Cr(VI) were analyzed by using Langmuir, Freundlich, and Tempkin isotherm models. The values of thermodynamic parameters, i.e., G®, H®, and S®, were determined. The negative value of H® confirmed the exothermic nature of removal of Cr(VI) through adsorption on CRH. The present study revealed that CRH can be an economically viable alternative for the removal of Cr(VI) from aqueous solutions © 2013 American Society of Civil Engineers.