Chemical Oxidation Technology For Organic Contaminated Soils At Coking Industrial Sites

PAHs and BTEX are common contaminants in coking industrial sites. Chemical oxidation technique is an effective remediation method which introduces oxidants into contaminated soils to react with pollutants. The types, amounts, and adding methods of the oxidants are key factors to influence the efficiency of chemical oxidation. A series of study were conducted to screen optimum oxidants for remediation of heavy PAHs and BTEX contaminated soils in a coking industrial sites and to evaluate their remediation efficiency. Soil oxidant demand (SOD) at different depths was also investigated. Field tests were employed to verify the efficiency of chemical oxidation for coking polluted soils. The main results were as follows:1.Chemical oxidants could easily remove PAHs such as Any, Ant, Bap, DahA, Bghip and Icdp, but not Fle, Chr and Fla. Permanganate and persulfate removed PAHs with the highest rate of 96.2% and 91.5%,respectively. Modified Fenton reagent could remove PAHs by 79.6%, while hydrogen dioxide and Fenton reagent's efficiency for removing PAHs were lower than 60%.2.Fenton reagent and modified Fenton reagent were the optimum oxidants for removing BTEX, with decreasing percentages of soil BTEX by 82.62% and 73.22%, respectively. Most of the xylene were removed when treated with Fenton reagent and modified Fenton reagent, however, benzene and toluene were resistant to oxidation and Ethylbenzene were the most recalcitrant. The proportions of volatilizing BTEX were 83.35% and 77.42%, respectively, when permanganate and activated persulfate were used as oxidants. That is to say, permanganate and activated persulfate could only stimulate desorption and volatilization of BTEX, but were ineffective for removing BTEX through oxidation. After treated with Fenton reagent and modified Fenton reagent, the soil temperature rised to 35℃and 28℃,respectively,and pH also increased to some extent, suggesting that the changes of temperature and pH were the factors to influence the remediation efficiency of chemical oxidation for BTEX-contaminated soils.3.Soil oxidant demand varied greatly with soil profile depths and related closely with lithology. The typical SOD was about 50 g/kg for clayey silt fill at depth of 0～2m, which was significantly higher than that of soils below. The average SOD was 20～40 g/kg for sandy silt, silt, silty clay and clayey silt. SOD of sand in the bottom of the soil cores was the lowest, which was between 1 and 7 g/kg. Soil TOC was the parameter with the strongest influence on oxidant demand. Contents of clay, silt and PAHs were also positively correlated with soil oxidant demand, while contents of sand were negatively correlated with it.4. Permanganate and persulfate could remove efficiently the PAHs from deep contaminated soil in the field. Concentrations of 16 kinds of PAHs decreased below USEPA preliminary remediation goals using permanganate and persulfate as the oxidant, while concentrations of naphthalene and benzopyrene in certain tested soils exceeded the USEPA preliminary remediation goals after treating with the other oxidants. Cost account result showed that the cost of different oxidants differed a lot, but were all below￥50 per ton of contaminated soils.The results suggested that the chemical oxidation was a cost-effective remediation technique, while the total cost should be calculated by plusing the cost of injection well construction, design, operation and management of oxidant injection equipment.