Adsorption of Cd²⁺, Ni²⁺ and Zn²⁺ in aqueous solutions using anhydrite and red mud

ABSTRACT

Various minerals and industrial waste have been studied for use as an adsorbent, in particular the anhydrite and the red mud. The red mud is an insoluble residue that is generated in large quantities during the processing of bauxite. The anhydrite is a calcium sulfate (CaSO₄), crystallized as a rhombic way, and used as raw material in the industry. In this study, the Cd²⁺, Ni²⁺ and Zn²⁺adsorption capacity by anhydrite and by red mud was evaluated using adsorption isotherms obtained by the Langmuir and Freundlich models. The materials used showed adsorption ≥75±1% for all metals in aqueous solutions with a concentration of 0.5 mmol.25 mL^-1. The Langmuir isotherm was more appropriate to describe the phenomenon of Cd²⁺, Ni²⁺ and Zn²⁺ removal, with highest adsorption capacity at 0.47 and 0.51 mmol.g^-1 for Cd²⁺, 1.18 and 1.56 mmol.g^-1 for Ni²⁺, and 0.84 and 1.47 mmol.g^-1 for Zn²⁺, respectively. These values were higher than those ones obtained for other materials described in previous studies.

Keywords:
red mud; anhydrite; metals; wastewater treatment