Remediation of heavy metal contaminated fine grained soils using electrokinetic geosynthetics

Abstract

Among the most promising novel methods for treating heavy metal contamination in fine soils is electrokinetic soil remediation - passing a low-voltage current through the soil that causes the target contaminants to migrate to the electrodes where they can be captured, broken down or immobilized. However, the widespread in-situ application of this process as a creative solution for the problem of metal contamination has been prevented because of a variety of problems, some of which are linked to the available electrodes. The limitations related to the available electrodes include: corrosion of the anodes difficulties in removing contaminated water and gases from the electrodes poor electrical contact of electrodes with the soil, cost of producing functioning electrodes, and limitations related to the physical form of the electrodes. Many of these historical limitations have been eliminated by the introduction of Electrokinetic Geosynthetics (EKGs) which combine electrokinetics with geosynthetics technology to create geosynthetice lectrodes. In this investigation, the use of an EKG system to capture and dispose of zinc ions from kaolin soil is evaluated by conducting extensive labor4tOry tests using specially designed bench scale tanks. A comprehensive test programme was established to include two electrokinetic remediation removal approaches: One Process Approach and Two Process Approach. The former was achieved by electro, migration of metal contaminants towards the cathode electrode without any external enhancement agent while the latter combined soil flushing with the electrokinetic process. The testing technique enabled the study of effects of. water flushing, soil depth, intermittent currents and replenishing draining chambers along the soil profile with deionised water, on the efficiency of cation removal. The respective responses were primarily presented in terms of electrical current/test duration, water content/test duration, zinc concentration/normalised distance from the anode, zinc concentration/ test duration and pW normalised distance from the anode. Results indicated that the EKG system has a lot of potential for cleaning up soil at sites contaminated by heavy metals and other harmful compounds. The in-depth analysis also showed clearly that combining the technique with soil flushing improved the effectiveness of the treatment operation. The study considerably extended the understandinogf the performance of electrokinetic technology particularly in fine grained soil and are as where further research would improve this understanding were highlighted.