Complexation of a Ligand with a Surfactant Micelle for Soil Heavy Metal Desorption

The ligands iodide (I⁻) and thiocyanate (SCN⁻), alone or in admixture, in combination with a non-ionic surfactant, Triton X-100, were evaluated as washing agents for heavy metal desorption from a contaminated soil. After seven successive washings, selective sequential extraction (SSE) was performed to determine the heavy metal content that remained associated with each geo-chemical fraction of the soil. The surfactant with 0.336 mol L⁻¹ of ligand I⁻ removed 75% Cd and 23% Cu, whereas the mobilization of Zn and Pb were not significant after 7 washings. At a concentration of 0.286 mol L⁻¹, the ligand SCN⁻ in the presence of surfactant removed 36% Cd, 44% Cu and 77% Zn. Among the washing agents, the combination of I⁻ and SCN⁻ produced the highest desorption efficiencies 95% Cd, 48% Cu, and 3.1% Pb, but not for Zn. The SCN⁻ ligand extracted the most Zn (77%). The SSE procedure indicated that the I⁻ removed metals from the exchangeable, carbonate and oxide fractions whereas SCN⁻ removed metals only from the exchangeable fraction. Both ligands, in the presence of surfactant, removed Cu from all fractions except the exchangeable sites, whereas only SCN⁻ plus surfactant removed Zn from all fractions. The ligand mixture plus surfactant mobilized only limited quantities of Pb from the oxide and residual fractions.

Keywords:

• Nonionic surfactant
• ligand
• heavy metal
• sequential extraction
• soil.

This project was financially supported by the Natural Science and Engineering Research Council of Canada.