Characteristic changes of calcined clay minerals as heavy metal adsorbents

Abstract

Calcined clay minerals were examined as adsorbents for the removal of heavy metals from aqueous solutions. Five clay minerals (kaolinite, dickite, pyrophyllite, hydrobiotite and montmorillonite) were thermally treated at 100–1000°C and were characterized according to cation-exchange capacity (CEC), Brunauer–Emmett–Teller (BET) specific surface area and X-ray diffraction. The CEC and BET specific surface area decreased at high temperature. Kaolinite, dickite and montmorillonite had the lowest crystal order at 800°C. The adsorption capacity of the clay minerals except hydrobiotite decreased with calcination. Hydrobiotite showed a high adsorption capacity of heavy metals regardless of heat treatment. The adsorption capacity of kaolinite and dickite for heavy metals and Cs increased at 1000°C, and that of Cs on hydrobiotite decreased at 800°C. The adsorption sequence of the metals on kaolinite, dickite, pyrophyllite and montmorillonite was Pb > Cs > Co, Ni, Cd for temperatures up to 800°C, and the order for the adsorption on the clay minerals depended on the temperature, according to the adsorption capacity and the distribution coefficient.