Comparative study of the effect of structural arrangement of clays in the thermal activation: Evaluation of their adsorption capacity to remove Cd(II)

In this work, comparison of the effect of thermal activation on the physicochemical properties of laminar clays bentonite and vermiculite and sepiolite as fibrous clay and their adsorption capacity of Cd(II) from aqueous solution, were studied. The physicochemical characterization demonstrated that the elimination of superficial, interlaminar and crystalline water resulted in materials with reduced specific surface area, increased negative superficial charges and cation exchange capacity depends of crystalline structure. With an increase in the activation temperatures of 100-300 degrees C, 300-600 degrees C, and 600-900 degrees C, the Cd(II) adsorption capacity of bentonite was reduced by 32, 30, and 55 %, respectively. Increasing the thermal activation temperature of sepiolite from 300 to 800 degrees C, encourage the capacity of sepiolite to adsorb metallic ions by 40 %. Raw vermiculite always presented a better capacity to adsorb Cd(II) than thermally activated vermiculite; sample activated at 300 degrees C adsorbed 50 % less than natural vermiculite. The relation between the chemical and textural properties of the activated clays and their capacity to adsorb Cd(II) demonstrated that the adsorption capacity of the thermally activated clays was strongly dependent on the quantity of negative charge surface and their cation exchange capacity, inferred that the main mechanisms was due to two mechanism, electrostatic interactions of attractive forces between negative superficial charge and cationic specie of Cd(II) and cation exchange between interlaminar cations, OH- in silanols and aluminols groups with Cd(II).