| At present, China is facing a serious threat of soil contamination. As the main pollutants in the soil, Heavy metals are easily adsorbed on the surface of colloids and particles of the soil, which can not be biodegradable and can be magnified and accumulated through the food chain. Heavy metals pollution has a long-term potential breakage to animals and plants in soil. The whole ecological environment, human survival and development are seriously threatened. For soil pollution from heavy metals, many remedial techniques are continuously researched and developed. The electrokinetic technology is a very promising technology. This technology is environment-friendly and can be used for in situ remediation, its effect is obvious and has a great large development potential. This paper has studied the remediation of multi-metals (Cd Cu Pb) co-contaminated soils by electrokinetic technology.This paper has conducted a research of the activation to Cd Cu Pb in soils. Experimental has selected EDTA, citric acid, tartaric acid, oxalic acid, acetic acid and deionized water as activator (eluent), soil column leaching experiments were conducted and have compared the activation effect of heavy metals under different concentration and pH of activator. By the percentage of leaching, it can get the best activation effect from the batch experiments. Cd, Cu, Pb’s leaching percentage is 54.43%,55.17%,46.46% respectively with 0.1mol/L pH 6.5 EDTA as eluent. With the increase of the leachate volume, the accumulation of heavy metals increased gradually activation. The cumulative outflow of heavy metals with leachate volume trends were fitted kinetic equation and Analyzed heavy metals desorption mode. Such as, the b of Elovich equations and parabolic equations show that high pH of EDTA can promote desorption of heavy metals.The reaction systems of vertical electrokinetic and horizontal electrokinetic are exploited to remedy multi-metals (Cd Cu Pb) co-contaminated soil and we have investigated electrokinetic remediation of soil. According to the results of activation effect of heavy metals, we have selected EDTA and citric acid as a complexing agent. EDTA and citric acid were introduced cathode chamber in horizontal electrokinetic or were added to the top of the soil in vertical electrokinetic. Our experiments have investigated many conditions, including electrode placement, different types of complexing agent and concentration, reaction time, electrode distance. The conclusions are as follows:The systems of vertical electrokinetic can promote heavy metals migration and aggregation from top to bottom of soil column. Heavy metals can leave soils with the leachate flow from the bottom of the soil column. EDTA is better than citric acid to strengthening complexation of heavy metals. High reaction time and concentrations of solution help to improve remediation effect. Cd, Cu, Pb’s removal rate can reach 56.9%,59.5% and 42.8% respectively in 10d 0.1mol/L EDTA. Comparing with no external voltage, the electrokinetic technology will save 21.8% of the amount of EDTA.The systems of horizontal electrokinetic can promote heavy metals migration toward the anode and cathode at the same time. EDTA-metal complex is stronger than citric acid-metal complex in migration capability; Citric acid is greater than EDTA for pH buffering capacity and has little effect to soil pH. By experimental results, Cd, Cu, Pb’s removal rate can reach 48.3%,46.3% and 40.7% respectively in 10d 0.1mol/L EDTA.Since the increases of electrode distance, the current fluctuations of system have become larger. IH+ and OH- of electrode reaction have little effect to soil pH in central with the increasing electrode distance. It will weaken the migration of heavy metals and makes a lot of heavy metals residues in the middle soil column when electrode distance is widened. So it may affect the remediation results with the increases of electrode distance. By experimental results, we can find that the removal effects of heavy metals can achieve better results when the electrode is held at a distance 10-15cm. Such as Cd, Cu, Pb’s removal rate can reach 64.9%,69.2%,55.7% respectively when the electrode distance is set to 10cm.The horizontal electrokinetic system has a higher current value and need more electric power compared to the vertical electrokinetic system. The horizontal electrokinetic can reduce the amount of activator and improve heavy metals removal rate. The distance between the electrodes is expand, which will reduce the amounts of EDTA per kilogram of soil sample and is bad to pollutants removal effect. |
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