| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系 === 90 === Heavy metal contamination is one of soil pollution problems. The major factors of affecting heavy metal adsorption are the colloid components including silicate clays, organic matter (OM) and Fe oxides. Past studies had discussed the adsorption characteristics of heavy metal in soil, but little was related to the interactions of different soil colloids. Cadmium contamination is popularly found in the arable soils of Taiwan. Therefore, Lungchung (Lt, Plinthic Paleaquult) and Santai (St, Typic Hapludert) series with diverse silicate clay, organic matter (OM) and Free Fe oxide (Fed) contents were selected to study Cd adsorption. Clays of the two soils were separated into coarse (0.2-2.0μm) and fine (<0.2μm) fractions after removal of H2O2 and dithionite-citrate-bicarbonate (DCB) extract to remove OM and Fed, respectively.
Results indicate that the determining coefficients (R2) are more than 0.9 in describing the adsorption isotherms of Ca by Langmuir equation. This is related to higher smectite with large specific surface in the St soil. For the two soils, the sequence of adsorption amount of Cd in different clay fractions is fine clay > coarse clay > whole clay, respectively. Higher specific surface and CEC values of finer sized particles cause to increase the adsorption amount of Cd. When OM was removed, the adsorption amount of Cd decreased. But the adsorption amount of Cd increased with the removal of Fed for the H2O2 treated clays, this is resulted from the coating of Fe oxide on the mineral surface to the exposure of adsorption sites. When soil pH increase, the adsorption amount of Cd increased associated with higher variable negative charge on the clay surface.
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