A Comparative Study On Remediation Of Real Lead-contaminated Soils And Simulated Soil Samples By Electrokinetic Remediation Process

Soil contamination with heavy metals has become a serious environmental problem in China recently. Electrokinetic remediation(EKR) is one of the most effective remediation processes for low permeability soil. Many research proved EKR a good method for contaminated kaolin, but the optimum condition for kaolin cannot be repricated for actual contaminated soil. In this paper, EKR experiments were carried out with both the simulated lead-contaminated kaolin and actual lead-contaminated soil specimens. The main conclusions are as follows:1、 A comparative study on the extracting behaviors of kaolin and real leadcontaminated soils with different extractantsExtracting experiments were conducted on kaolin and real lead-contaminated soils by acetic acid, citric acid and EDTA-2Na. The results showed that both acetic acid and EDTA-2Na were good extractants of Pb for kaolin, while only 44.4 % of Pb could be extracted out by citric acid with a concentration of 0.20 mol/L. For the real lead-contaminated soils, the effects of the extractants were in the order of EDTA-2Na > citric acid > acetic acid. When the concentration of EDTA-2Na was 0.10 mol/L, more than 92.0 % of Pb was extracted out, while negligible Fe was extracted out.2、Comparative study of the EKR processes on kaolin and real lead-contaminated soilsEKR processes were conducted on kaolin and real lead-contaminated soils, and both KNO3 and EDTA-2Na were used as catholyte to make a comparison. As catholyte, EDTA-2Na could effectively adjust the pH of electrolytes and soils, and as a result, promote the remediation effects of Pb. For kaolin, a concentration rate(C/C0) of 2.11 and 4.45 at S3 was achieved when the catholyte was KNO3 and EDTA-2Na, respectively. While for real leadcontaminated soils, no enrichments were achieved with both catholytes. The remediation effect on kaolin was much better than on the real lead-contaminated soil owing to that the main existing form of Pb in actual lead-contaminated soils was reducible, while in kaolin it was soluble. Furthermore, the properties(mineral component, CEC, buffering capacity for acid or alkali, et al.) of the real lead-contaminated soil was more complicated than that of the kaolin, which will also affect the migration of Pb.3 、 Influence of enhanced EKR on the remediation process of real leadcontaminated soilsThe experiment conditions were enhanced to examine the influence on the EKR processes of real contaminated soils. The results showed that, the increase of potential gradient(from 2 V/cm to 4 V/cm) could enlarge the current, and lower the pH of soil to acid range. As a result, the remediation effect was promoted and 2.44 times of Pb was concentrated at the third slice of soil from anode to cathode with a energy consumption of 748.8 kWh/m3. When the EKR process was combined with chemical leaching, the current in the preliminary stage was increased, and a concentration rate of 1.70 was achieved at S3 with a energy consumption of 140.3 kWh/m3. The extend of treatment time from 240 h to 480 h would lead to the expanding of alkali soil region towards the anode, which will prevent the migration of contaminates. As a result, the concentration rate at S3 was only 1.69 with a energy consumption of 187.8 kWh/m3.The behavior of kaolin and actual lead-contaminated soils during the EKR processes were compared in this paper. These works provide a theory foundation to the practical application of EKR.