Electrokinetic Remediation of Mercury-Contaminated Soils Using Iodine/Iodide Lixiviant

In-situ remediation of mercury-contaminated soils, by electrokinetic or other means, is difficult because of the low solubility of mercury and its compounds. In this research, enhanced electrokinetic remediation of HgS-contaminated soils using I2/I- lixiviant was investigated using bench-scale electrokinetic cells. The thermodynamic conditions under which the lixiviant could be effective were determined by constructing a pE−pH diagram for the Hg−S−I system. Introduced near the cathode, the lixiviant migrated through the soil to the anode by electromigration. Mercury, released by the oxidation of HgS compounds by I2, was complexed as HgI42-. The negative complex continued to electromigrate toward the anode. Up to 99% of the Hg present in laboratory-contaminated soils could be removed. Electrokinetic treatment of a field-contaminated soil, containing more organic matter than the laboratory-contaminated soil, occurred much slower. The critical issues in determining the efficacy of the process are the oxidation of reduced Hg by I2 and I3- and the transport of the resultant HgI42- complex.