Electrokinetic Remediation of Mercury-contaminated Soils

A series of batch tests were conducted to investigate the relative desorption potential of mercury from kaolin and glacial till soils under the effect of three extractant agents, namely, KI, NaEDTA and NaCl (all of them with a concentration of 0.1 M). These tests were conducted under different pH conditions (within a pH range between 2 and 12). Also batch tests using deionized water were performed for comparison purposes. The extractant agents were selected from the solutions that form strong soluble complexes with mercury. The results of the batch tests revealed that the extractant agent KI was the most effective agent for removing mercury from both soils. Na-EDTA also, but in lesser extend, exhibited mercury removal. Electrokinetic tests were conducted to evaluate the effect of the extractant agents Na-EDTA and KI. For comparison purposes, electrokinetic baseline tests using deionized water were also carried out. All of these electrokinetic tests were conducted under the same conditions of voltage gradient (1 V/cm) and extractant ion concentration (0.1 M). The results of these electrokinetic tests revealed that KI was efficient in removing mercury from soils, while Na-EDTA did not show any significant removal of mercury. Overall, 95% removal was achieved from kaolin; however, only 77 % removal was achieved from glacial till mainly as a result of existence of insoluble mercury complexes in this soil. INTRODUCTION Throughout the country there are numerous contaminated sites that have been polluted with mercury as a result of accidental spills and improper disposal practice. These mercurycontaminated soils have adverse effects on the ecology and human health. According to the United Stated Environment Protection Agency (USEPA), mercury-contaminated soils must now be treated with the Best Demonstrated Available Technology (BDAT), which is retorting or roasting (i.e., thermal treatment technology). The high cost of this technology and the insufficient national capacity to treat mercury-contaminated soils by the BDTA, as pointed out by the gas industry, make it necessary to study other technologies in order to treat the numerous already polluted soils. Research performed to date shows that electrokinetic remediation is a viable method to remove different heavy metals from various soil types (Reddy and Shirani, 1997; Reddy et al., 1997; Reddy and Parupudi, 1997; Reddy et al., 1999; Reddy and Chinthamreddy, 199; Chinthamreddy and Reddy, 1999). In this research the enhancement of the electrokinetic remediation of mercury-contaminated clayey soils was investigated under laboratory conditions. The 1 Proceedings of the International Containment & Remediation Technology Conference, Orlando, Florida, USA, June 2001. 2 Associate Professor & Director of Geotechnical & Geoenvironmental Engineering Laboratory, Tel: (312)996-4755; Fax: (312)996-2426, e-mail: [email protected] (corresponding author) 3 Graduate Research Assistant