Enhanced Electrokinetic Remediation Of Matals-Oganics Mixture Contaminated Soils

Thousands of sites are contaminated with both heavy metals and organic compounds, which brought the difficulties and challenges for soil remediation. Electrokinetic remediation has potential to remove heavy metals and organic compounds from soil by electromigration and electroosmotic flow. In this paper, copper and pyrene were selected as the representative pollutants, the impact of controlling pH and adding hydroxypropyl-β-cyclodextrin (HPCD) on the pollutants migration was studied. The removal effects and the pollutants migration by combining different oxidants with EK under various conditions were also compared, and then the influences of different types of soil on the migration of pollutants during the process of the EK were illustrated.The results showed that soil acidity plays an important role in the removal efficiency of pollutant. Low pH was not only beneficial to the desorption and migration of heavy metals in soils, but also useful for the transportation and degradation of organic pollutants. Alkaline soil conditions cause heavy metals precipitation, which is not effective for the migration of heavy metals and the desorption of organic compounds from soil.Addtion of Na2S2O8in catholyte gave the highest removal efficiency of copper and pyrene, reaching93.6%and49.5%, respectively, which could be ascribed to the decomposition of Na2S2O8and H+production. Acidic conditions are conducive to the migration of copper and degradation of pyrene. When6%H2O2was added in the anolyte and the catholyte pH was controlled at3.5, the removal of pollutants was not very high, and they were66.3%and42.6%, respectively. Increasing the doses of H2O2could enhance the oxidation efficiency. The oxidation of pyrene by NaClO is not obvious, and the alkaline condition also inhibited the migration of heavy metals. For pyrene, KMnO4is the best oxidant, the removal rate reached51.7%. The removal of pyrene reached87%and95%in S4and S5sections near the cathde. In addition, as MnO2increased adsorption potential of heavy metals, copper absorption occurs near the cathode.When cathode chamber was filled witn H2O2(12%) for different types of soils in EK-Fenton remediation, the pH of catholyte was maintained at an acid value around3.5 whithout pH control. Not only did the oxidation of organics but also the migtation of heavy metals increase. In the three different types of soils, the removal rate of pyrene followed this order:black soil>brown soil>red soil,while the order of copper was just opponent.Black soil with the high pH is conducive to the generation of electroosmotic flow, with which H2O2and organic pollutants is more contacted and oxidation efficiency of pyrene is higher. The fractionations of heavy metals were the main factor restricting the migration of heavy metals which was related to the soil pH, OM and Fe/Mn oxides content. Red soil with high acid-soluble content favored the migration of metals, and high pH and OM concent of brown soil and black soil inhibited the removal of heavy metals.