The adsorption rates and characteristics of heavy metal ions (Cd, Cr, and Zn) were examined with solutions mixed with red clay, white clay, a mixture of red & white clay and zeolite under various pHs and initial concentrations. As expected, adsorption rates of heavy metal ions generally increased with increasing pH; however, Cr showed a particular behavior. A mixture of red & white clay among the clay minerals tried in this study showed the highest Cr adsorption rate at the low pH conditions (lower than pH 5) and red clay with additions of Cu, Fe and Pb ions at pH 5 showed above an 85% adsorption rate of Cr which was far from expectations. From the result, it is concluded that the adsorption characteristics of heavy metal ions depend not only on the physical properties of the absorbent itself such as the cation exchange capacity (CEC) but also on the concentration and existence of exchangeable cations, pH, ligands, etc..

Keywords: Heavy Metal Adsorption Rate, Cation Exchange Capacity, Red Clay, White Clay, Zeolite