Acid treatment of south Tunisian palygorskite: Removal of Cd(II) from aqueous and phosphoric acid solutions

Natural palygorskite and the activated samples were applied as adsorbents for the removal of Cd(II) from aqueous solutions. The effects of various experimental parameters were investigated. The adsorption isotherms of activated palygorskites for Cd(II) could be described by the Freundlich model. The acid activated sample showed a higher adsorption capacity for Cd(II) than the natural palygorskite. The retention of Cd(II) ions by palygorskite occurs dominantly by specific adsorption. A different behaviour was observed in the phosphoric acid medium. Despite increases in the surface areas upon acid activation, improvements in the adsorption were not observed, as a result of the decreasing number of negative surface sites, as main centers for specific adsorption.