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Remediation of a soil contaminated with cadmium or lead was performed by a soil washing process using aescin as a biosurfactant. The removal of cadmium and lead from the soil was evaluated as a function of aescin concentration and pH in a batch process. A 30-mM aescin solution was most effective in the removal of cadmium and lead at pH 6.8. Cadmium and lead migrated from the soil to the aescin-containing aqueous phase, depending on the pH value. We found that 41% of cadmium (pH 7.8) and 25% of lead (pH 2.8) in the soil matrix migrated into a 30-mM aescin solution. Also, the complexation of aescin with cadmium and lead ions was confirmed by Fourier transform infrared spectroscopy and electrical conductivity measurements. As a result, the maximal complexation capacity of aescin with metal ions was approximately aescin/cadmium = 2:1 and aescin/lead = 3:1 on a molar basis. It was suggested that aescin may sequester cadmium and lead ions by the carboxylic and saccharide moieties. Then, the complex of aescin with cadmium or lead may migrate to the aqueous phase as the result of dispersion. JSD 1, 247-250 (1998). FIG. 3. Shift of carboxylate bands in Fourier transform-infrared spectra of aescin and metal aescinates as evidence for the complexation of aescin with cadmium and lead. FIG. 4. Addition effect of lead ion (3 mM) on electrical conductivity of the aescin solution. FIG. 5. Addition effect of cadmium ion (3 mM) on electrical conductivity of the aescin solution.

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