Adsorption of Hexavalent Chromium using Natural Goethite: Isotherm, Thermodynamic and Kinetic Study

Abstract

This paper examines the potential of natural goethite as an adsorbent for removing Cr(VI) from the aqueous solution through adsorption isotherms, thermodynamics and kinetics study. The study is based on the batch experiments as a function of initial Cr(VI) concentrations, contact time, pH and temperature at fixed solid/solution ratio. The pH has pronounced effect on process of removal and removal is higher in lower pH range, maximum (99.14 %) being at pH 2. The adsorption of Cr(VI) onto goethite is endothermic in nature and therefore, higher temperature favours the uptake. The adsorbent capacity was determined using Langmuir, Freundlich, Dubinin–Radushkevich and Temkin adsorption isotherm models. The results showed that the adsorption fits best to the Langmuir isotherm model with the adsorption capacity 0.727 mg/g. Pseudo-first-order kinetic, pseudo-second-order kinetic and intraparticle diffusion were used to analyze the adsorption kinetic at different initial Cr(VI) concentrations. The kinetic study indicated that the pseudosecond order model explained the adsorption mechanism and intra-particle diffusion was found to be the rate-controlling step. The negative values of Gibb’s free energy explained that the adsorption was feasible and spontaneous.