| Soil contaminated by heavy metals is one of the environmental problems thatshould be resolved. Soil pollution is accumulative, lagging, dormant, andirretrievable and so on, which causes its treatment to be more difficult. Therefore,remeditiation technology used in heavy-metal contaminated soil is an importantlink to guaranteeing continual farm. These topic, which adopted the simulatedheay metal contaminated soil and the acutal heavy soil respectively, studied theelectrokinetic processes in condition of both the fixed voltage and the fixedelectric'current, the enchanced measure applied to remediation of the strong pHbuffering capacity soil and the the processing effictiveness of the actualheavy-metal contaminated soil by using electrokinetic technology as the researchmethod. The tests drew the conclusions below:(1) Conditoioned on the fixed voltage, the electrokinetic test indicated that improvement of pH in the soil near the cathode without controlling the pH of catholyte, caused heavy metal Cd and Pb to precipitate in the area and didn't favor removal of Cd and Pb; the soil near the anode was acidified excessively without controlling the pH of anolyte,which caused the soil's pH to be lower than its PZC leading to counter-electroosmosis that didn't favor the removal of Cd and Pb. The enchanced measure to control the pH of eltrolyte effectively prevented above phenomenon from occuring, then improved the removal efficiencies of heavy metal Cd and Pb in entire soil. Conditioned on the enchanced condition, average removal efficiencies of Cadmium and Lead in soils improve from 68% and 37% to 87% and 51% in the total digestion, respectively; correspondingly from 81% and 50% to 97% and 73% in theexchangeable fraction, respectively.(2) Conditioned on the fixed current density, the electrokinetic test indicated that size of current density directly influenced the change extent to pH in soil, but didn't correlate with the jumping point of pH in soil: the temperature in soil increases along with the improvement of current density, which enchanced the rate of electroosmosis flow due to reducing the hole fluid viscosity, but the excessive temperature caused moisture evaporation lead to reducing the moisture content in soil which affected electroosmosis flow 3causing the removal efficiency to reduce; moreover, the total voltage rose with the current density, and it was possbile that the total voltage surpassed the rated voltage in power source; therefore, it was important to determine the appropriate current density. In terms of the change of pH of soil, total voltage and temperture in soil by three kind of current density experience, 1.06mA/cm2 was the more appropriate current density. Under this current density condition, the enchanced measure to control the pH of eltrolyte effectively prevented above phenomenon from occuring, but the total voltage reduced with running time, which could reduce the velocity of migration of the heavy metal Cd2+ and Pb2+ ions to cathode. Under the enchanced condition, average removal efficiencies of Cadmium and Lead in soils was 95.6% and 48% in the exchangeable fraction, respectively.(3) The test, which adopted the simulated Cd-contaminated soil having strong pH buffering capacity, studied the processing effictiveness of the Cd pollutant by contasting to two experiments by not adding EDTA to the catholyte and adding EDTA to the catholyte. The test indicated that keeping neutrality in anolyte and weak basicity in catholyte suppressed the hydrogen ions to move into the soil, which made the conditon for forming Cd complex compoud. It was difficult to remove heavy metal Cd without EDTA in catholyte; however, EDTA complexing anions moved toward the anode and soak the soil under the electric field by adding EDTA to the catholyte, and formed the che... |
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