THE EFFECT OF HYDRATION ON ADSORPTION AND DESORPTION OF HEAVY METALS IN SOILS

Abstract

Cr, Ni, and Cd adsorption–desorption on five characterized Taiwan soils was studied. The potential for toxicity and the fate of metals in the soils is dependent upon the ability of the metals to desorb into the aqueous phase. To simulate field conditions, the soils were subjected to wet–dry cycles. The amount and rate of desorption was found to decrease with increasing number of cycles. The wet–dry cycle effect in the desorption of metals from soils is related to the soil composition, with desorption being easiest from sandy soil with low organic content. The desorption process is much slower than adsorption process. More than 95% of each metal adsorption takes place within one hour, and the amount of metal adsorbed from solution reached equilibrium in one day. In contrast, less than 20% metal desorption could be attained after 3 days each of four wet–dry cycles for Cr, Ni, and Cd.

Keywords:

• Soil
• Hexavalent chromium
• Cadmium
• Organic matter
• Desorption
• Wet–dry cycle

ACKNOWLEDGMENTS

We would like to acknowledge the National Science Council, Taiwan, for the support of this project (NSC 88-2211-E-041-003). We also thank Dr. Robert Ehrlich for his instruction, suggestions, and encouragement.