Adsorption of As (III) on Iron Coated Quartz Sand: Influence of Temperature on the Equilibrium Isotherm, Thermodynamics and Isosteric Heat of Adsorption Analysis

Abstract

Abstract The influence of temperature on the sorption of As(III) onto iron oxide coated quartz sand (IOCQS) was studied in the temperature range of 298–318 K. An increase in temperature was found to have positive influence on the adsorption of As(III) ions onto IOCQS surfaces because of increased diffusion of As(III) ions into the pores of IOCQS at higher temperature. The enhanced sorption at higher temperature indicated endothermic adsorption process. Equilibrium isotherms for the adsorption of As(III) on IOCQS were analyzed at different temperatures. Among the conventional isotherms, Freundlich isotherm best predicted specific uptake at different temperatures, followed by Redlich–Peterson, Langmuir and Temkin isotherm models. Various thermodynamic parameters namely heat of adsorption (∆H 0), change in entropy (∆S 0), and Gibbs free energy change (∆G 0) were computed from the equilibrium constant (K D) values. The results indicated positive value for heat of adsorption ∆H 0, a positive ∆S 0 and a negative ∆G 0. Finally, the isosteric heat of adsorption (ΔH st,a) values were calculated and quantitatively correlated with the fractional loading of As(III) onto IOCQS. The surface heterogeneity of adsorbents could be quantitatively described with an isosteric enthalpy function of fractional loading based on Do and Do model. The results show that the IOCQS possesses heterogeneous surface with sorption sites having different activities.