| Electrokinetic remediation technology becomes one of the important methods for remediation of contaminated soils, because it can help to remove many pollutants and to treat the low permeability soil, which also has the advantage of low cost and high efficiency. However, electrolytic leading to "polarization phenomenon"——pH was lower near the anode and pH increased near the cathode——limits its widespread application in the treatment of contaminated soils, by the electrokinetic remediation. From the perspective of changing the electrode structure and selection of permeable reactive active material, we developed a permeable reactive composite electrode with depolarization in this thesis. The permeable reactive materials can neutralise/adsorb H+and OH-produced by water electrolysis, to achieve effective control of the soil pH value, while pouring heavy metal pollutants migrating from soil, and greatly improved the removal efficiency of heavy metals. After remediation, electrode was removed to realize the purpose of removing thoroughly heavy metals from soil.This technology can be applied conveniently. It has great significance for promoting electrokinetic remediation technology and its applications.This thesis'main contents and findings include the following:Selection and performance of Permeable Reactive Materials(PMM). The PRM selection of activated carbon, synthetic zeolite, natural zeolite, is included as well as; comparison of the natural zeolite with different particle size (20,40,100mesh). The results showed that:adding the alkaline synthetic zeolite can reduce the decline rate of pH at the anode; adding the cathode acidification activated carbon/zeolite can reduce the increase rate of the pH value, and the zeolite is superior to activated carbon; the results obtained with phosphoric acid acidification of permeable reactive materials are better than that with acetic acid acidification; the smaller the particle size of zeolite, the stronger the pH buffering effect; the buffering effect of soil pH increases as the acidity of phosphoric acid increases.Structure and preparation of permeable reactive composite electrodePRCE). For anionic heavy metal pollution, e.g. the chromium(VI), exploring the zeolite+ graphite, Fe0+graphite, zeolite, Fe0+graphite as the anode electrode, respectively, the acidification zeolite+graphite electrode as the cathode electrode; for cationic heavy metal pollution, e.g. cadmium (Ⅱ), nickel (Ⅱ), lead (Ⅱ), copper (Ⅱ), exploring the synthetic zeolite+graphite as the anode electrode, the zeolite+graphite, Fe0+graphite, the acidification zeolite+Fe0+graphite electrode for the cathode electrode, respectively. The results showed that:zeolite can effectively and neutralize/adsorpte OH-and H+produced by water electrolysis, reduce fluctuations of soil pH to the maximum extent, avoid the formation of acid-base migration zone; Fe0can fix/stable heavy metal ion according oxidation reduction reaction. Therefore, the PRCE with Fe0and zeolite is the best composite electrode.The removal of anionic heavy metal. Different test conditions, including permeable reactive material, different voltage gradient, soil water content, were analyzed. The results showed that:in the laboratory test(pole spacing is10cm,), Cr(Ⅵ) migrate toward the anode from cathode; after5days, Cr(VI) removal rate reaches more than95%, under the conditions of using acidified zeolite+graphite composite electrode as cathode, using synthetic zeolite+Fe0+graphite composite electrode as anode,2V/cm; when the voltage gradient from1Ⅴ/cm to2V/cm, the removal rate increased to17.8%; from2V/cm to3V/cm, the removal rate was not changed significantly; the increase of water content is helpful for Cr(Ⅵ) removal, when the moisture content is49%, after5days, Cr(Ⅵ) removal rate reached over97%.The removal of cationic heavy metal. Different test conditions, including permeable reactive material, voltage gradient, test run time, etc. were analyzed. The results showed that:no matter what the electrodes, whether the electrode replace or not, Cd(Ⅱ), Ni(Ⅱ), Pb(Ⅱ) and Cu(Ⅱ) migrate toward the cathode from anode under the action of the electric field. Test results of Cd(Ⅱ) and Ni (Ⅱ)are similar, Pb(Ⅱ) and Cu(Ⅱ) are similar; under the conditions of1.5V/cm Cd, Ni, Pb and Cu occurrence enrichment in the anode, and the mean removal rate in the cathode and the middle part is that:Cd is91.1%, Ni is77.9%, Pb is53.1%, Cu is51.8%; test run time is prolonged from5days to10days, the removal rate of Cd, Ni, Pb and Cu in the anode of from75.6%,77.6%,30%,39.8%to98.5%,99.9%,61.4%,71.2%etc.The remediation of real Cr-contaminated soils. The real Cr-contaminated soils come from contaminated site, remediated under the hexagon electrode matrix.The results showed that:under the conditions of hexagonal matrix, using acidification zeolite+graphite composite electrode at the cathode and zeolite+iron+graphite composite electrode at the anode can effectively control soil pH values. After5,10,15,20,25,30days, the soil pH around8.5(initial soil pH of8.37). Hexavalent chromium converse to trivalent chromium with low toxicity, or completely remove from the soil into the permeable reactive composite electrode in the test. |
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