Activation Of Toxic Organic Substance In Soils By Low Molecular Weight Organic Acid

Recently, Organic pollutants entering into soils cause serious problems to ecological risk and to human health. How to remediate the contaminated soils and achieve the sustainable utilization of land resources is of world concerns. Toxic organic substance (TOS) is readily fixed in soil, so understanding the remediation strategies for the contaminated field of fixed TOS is paramount to determine the activation of these TOS by low molecular weight organic acids (LM WOAs).In the research, the sorption, the leaching and desorption of PAHs and PCP, acted as representative TOS, were studied based on present research situation of organic contaminated soil remediation. And the relationships between activation and the nature of LMWOAs, DOM concentrations, metal ion species, soil properties were examined. Main results are shown as follows:1. The impacts of citric acid on sorption of pentachlorophenol (PCP) by three typical zonal soils, including yellow-brown soil, brown-red soil, and red soil in China, were investigated by a batch experiments. The sorption isotherm of PCP by soils can be well described by the Freundlich equation. The sorption capacity of PCP by three test soils was in the order of yellow-brown soil>brown-red soil≥red soil, which was positively correlated to the soil organic matter contents (foc). The presence of citric acid dramatically affected the PCP sorption. The sorption capacity of PCP by brown-red soil and red soil increased firstly and decreased thereafter with the increment of citric acid concentrations from0to100mmol/L. The addition of citric acid significantly enhanced the sorption of PCP in yellow-brown soil. However, the enhancement tended to weaken with the presence of citric acid at higher concentrations. It was observed that the pH values lowered and dissolved organic matter (DOM) concentrations enlarged in the equilibrium solution with the increase of added citric acid concentrations. The sorption of PCP by soil enhanced at the lower pH value and weakened by the higher DOM concentration in solution.2. The impacts of citric acid, tartaric acid and malic acid on leaching of PAHs and dissolution of metal ions by three typical zonal soils in China, including yellow-brown soil, brown-red soil, and red soil, were researched by a dynamic soil column experimental technique. The results showed that PAHs in the contaminated soils can be apparently leached out from the soils by different LMWOAs solutions. Compared with that in CK, using deionized water for leaching, the content of phenanthrene leached out was increased by327.1%、311.6%,316.0%, and contents of pyrene by299.3%、246.3%、277.2%, after the soils were leached with citric acid, tartaric acid and malic acid. The phenanthrene and pyrene in soil columns can be activated and migrated down after leaching by LMWOAs solutions, which were distributed in the order of lower layer>middle layer>upper layer. Experimental data show that concentrations of metal ions increase significantly in leachates in the organic acids treatment, suggesting that the LMWOAs may damage the soil organic-inorganic complexes promoting the dissolution of metal ions, leading to the release of PAHs combined with solid organic matter.3. The effect of LMWOAs on desorption of PAHs in manufactured aromatic hydrocarbons plant-contaminated soils was investigated. Desorption kinetics showed that the desorption was a quick dynamic equilibrium process, which mainly completed within the first24h. PAHs were desorbed in a three stage desorbing process. The results showed that the desorption ratio decreased as the increasing of number of desorption and pyrene desorption rate decreased obviously in the second and third stages compared with phenanthrene. LMWOAs had stronger effects on phenanthrene and pyrene desorption and the desorption capacity was in the order of citric acid> oxalic acid> malic acid. The desorption amounts of phenanthrene and pyrene increased with the increment of LMWOAs concentration, which were281.76and221.77ug/kg respectively with the addition of100mmol/L citric acid, while the desorption amounts were395.25and327.41ug/kg adding1000mmol/L citric acid. Furthermore, the addition of LMWOAs could result in the increment of DOM concentration in solution, and significant correlation between the concentration of DOM and desorption efficiency was found, which may be the main reason that the LMWOAs enhance the phenanthrene, pyrene desorption in soils.