Fe(III)-Sn(IV) mixed binary oxide-coated sand preparation and its use for the removal of As(III) and As(V) from water: Application of isotherm, kinetic and thermodynamics

Adsorptive removal of As(III) and As(V) by a binary Fe(III)-Sn(IV) mixed oxide-coated sand (ITOCS) has shown 89.33 and 93.59% efficiencies from their 500 μg/L solutions, respectively. Batch experiments were performed to optimize contact time, initial concentration, dosage, pH of solutions and temperature. The adsorption data was modeled by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms at 293, 303 and 313 K. Langmuir adsorption capacities were found to be 82.64 and 227 μg/g, for As(III) and As(V), respectively, at 8.0 g/L dosage, 60 min contact time at solution pH 7. The adsorption process followed pseudo-second order kinetics with film diffusion step controlling the mechanism. Gibbs free energy of adsorption of As(III) and As(V) was found to be −12.5 and −13.42 kJ/mol at 313 K, respectively. Negative values in both cases indicated spontaneous nature of the adsorption process. The values of enthalpy of adsorption were 4.763 and 33.82 kJ/mol for As(III) and As(V), respectively, suggesting endothermic nature of the adsorption process for both ions. The results indicated that ITOCS would find a good place as an adsorbent for the removal of arsenic from water.