Adsorption of uranium from aqueous solution on heat and acid treated sepiolites

In this work adsorption of uranium on natural, heat and acid treated sepiolite was studied. For acid treatment HCl and H2SO4 were used separately. Heat and acid treatment caused some changes in sepiolite such as surface area, micropore volume (cm3/g) and average pore diameter (A). Different amounts of Mg ions were extracted from the lattice depending on the type of acid. After acid treatment with HCl, the amount of Mg left in the sepiolite changed a little. During H2SO4 treatment the sepiolite structure was progressively transformed into amorphous silica. These heat and acid treatments changed adsorption capacity and mechanism of uranium on sepiolite. Data obtained from the adsorption experiments were applied to Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. Using these isotherms different adsorption capacities were found for natural and treated sepiolite samples. The capacity values were 3.58x10-3, 3.14x10-3, 2.78x10-3 and 1.55x10-3 mol/g for HCl treated, heat treated, natural and H2SO4 treated sepiolite samples, respectively. In order to evaluate the adsorption mechanism adsorption energies were calculated by the D-R isotherm. According to the adsorption energy values uranium fixed to the natural and heat treated sepiolite surface with ion exchange (12.75 and 12.12 kJ/mol, respectively). Simple physical attractions were the driving force for adsorption on HCl and H2SO4 treated ones (6.62 and 6.87 kJ/mol, respectively).