Removal of Mercury from Clayey Soils Using Electrokinetics

Abstract

Numerous sites have been polluted with mercury as a result of accidental spills and improper disposal practices, and these mercury-contaminated sites may have adverse effects on human health and the environment. Innovative and cost-effective remediation techniques are urgently needed, and this study was performed to investigate the use of electrokinetics for mercury-contaminated soils. Initially, batch tests were performed on two soils, kaolin and glacial till, spiked with mercury(II) to investigate mercury desorption and complexation under different pH environments (pH range 2–12). The complexing agents included disodium ethylenediaminetetraacetate (Na-EDTA), potassium iodide (KI), and sodium chloride (NaCl), and these solutions were used at a concentration of 0.1 M. In addition, deionized water was used for comparison purposes. Based on the batch tests, Na-EDTA and KI were identified as the complexing agents with the greatest potential. The removal efficiency of these complexing agents was then examined by conducting electrokinetic experiments that employed the same solution concentration (0.1 M) and voltage gradient (1.0 VDC/cm) conditions. These tests indicated that for both soils, KI was a more effective complexing agent than Na-EDTA under electrokinetics. For the kaolin soil, the electrokinetic treatment using KI removed approximately 97% of the initial contaminant present (500 mg/kg of Hg(II)), leaving a residual concentration of 16 mg/kg of Hg in the soil, whereas on the glacial till soil, KI removed only 56% of the initial contaminant present (500 mg/kg of Hg(II)), leaving a residual concentration of 220 mg/kg of Hg in the soil. The lower Hg removal from glacial till is attributed to the presence of organic matter, which increased mercury adsorption or the formation of insoluble mercury surface complexes.

Keywords:

• Electrokinetic remediation
• Electrokinetics
• Soils
• Remediation
• Metals
• Mercury

Acknowledgments

The financial support provided by the Gas Research Institute, the Institute of Gas Technology, and the University of Illinois at Chicago for this research is gratefully acknowledged.