Equilibrium and thermodynamic studies of Cu(II) removal by iron oxide modified sepiolite

This paper presents the adsorption of Cu(II) from aqueous solution by raw sepiolite (RS) and iron oxide-coated sepiolite (ICS) samples. Adsorption of Cu(II) by sepiolite samples was investigated as a function of the initial Cu(II) concentration, solution pH, ionic strength, temperature and the presence of an inorganic ligand (Cl−, SO42− and HPO42−). Changes in the surface and structure were characterized by means of XRD, IR and XRF techniques. The Langmuir monolayer adsorption capacities of RS and ICS in 0.1 M NaNO3 solution at 298 K were estimated to be 14.96 and 21.56 mg/g, respectively. ΔG, ΔH and ΔS were evaluated for RS and ICS to be −14.14 kJ/mol (at 298 K), 39.03 kJ/mol and 178 J/mol K, and −16.09 kJ/mol (at 298 K), 32.99 kJ/mol and 165 J/mol K, respectively.