Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/11/2005
Publication Date: 10/7/2005
Citation: Popov, K.I., Yachmenev, V., Barinov, A. 2005. Enhancement of the Electrokinetic Remediation of Soil Containment with U(VI) by Chelating Agents. In Nowack, B. and VanBriesen, J.M. (Eds) ACS Symposium Series No. 910 "Biogeochemistry of Chelating Agents," p. 398-420.
Interpretive Summary: Electrokinetic (EK) soil decontamination is rapidly becoming a very attractive alternative technique to traditional “pump and treat” methods for remediation of soils contaminated with a variety of contaminants, including radionuclides and heavy metals. This in-situ extraction technique utilizes a direct current (DC) electric field to transport charged contaminant species throughout the soil pore solution to a collection zone. Likewise, non-charged, organic contaminants could be flushed and extracted from the contaminated soil by exploiting electroosmosis phenomena, which is a flow of pore liquid in soil, induced by an electric field gradient. Our research established that the specific EK technique based on combination of the DC electric field (0.7~1.8 V/cm) and citric acid (an inexpensive and environmentally benign complexant) afforded an effective decontamination of heavy clay soil from Oak Ridge K-25 well below the targeted release level of 52 ppm (35 pCi/g). The ability of citric acid to act as a highly efficient complexing agent for such hazardous heavy metals as Uranium, Lead and Mercury could be effectively utilized for remediation of the contaminated soils thus opening new uses for this byproduct of the US citrus industry. In addition to significant advancement of the electrokinetic remediation technique, introduction of citric acid as chelating agent to the treated soil also revealed totally new phenomena, dramatic increase of the electroosmotic flow in the soil pores. This effect opens interesting possibilities for development of new techniques for controlled delivery of nutrients and/or pesticides/fungicides to the plant roots. If enacted, this could decrease the chemical load on fertile soil and also increase crop production as the result of more precise delivery of the nutrients to the plant roots. Groups benefiting from this development include the agricultural, industrial, environmental and academic scientists and the consumer.
Technical Abstract: The various effects of introduction of chelating agents during electrokinetic remediation of clay soil contaminated with uranium (VI) in pilot scale electrokinetic tests are reported. The combination of the DC electric field (0.7~1.8 V/cm) and citric acid (an inexpensive and environmentally benign complexant) afforded an effective decontamination of heavy clay soil from Oak Ridge K-25 well below the targeted release level of 52 ppm (35 pCi/g). Uranium (VI) content in the remediated soil sample (19.4 kg) was reduced from 566 ppm to 41.3 ppm within 477 hours with estimated total power consumption of 1058 kWh/(ton of soil). In addition to significant advancement of the electrokinetic remediation technique, an introduction of the chelating agents to treated soil also revealed a variety of new phenomena such as significant change of zeta-potential of clay particles, change in mobility of background cations and, unexpectedly, dramatic increase of the electroosmotic flow in the soil pores. The electrokinetic remediation tests also confirmed that knowledge of the precise chemical speciation of the metal/complexant species under various pH conditions was crucial in the prediction of the solubilization efficiency of the chelating agents.