Sorption Behaviors Of Trichloroethylene On Vadose Medium

Trichloroethylene (TCE) is widespread environmental Chlorinated hydrocarbon(CHs) contaminants in groundwater system. Since it is hard-degradable, soil sorption behaviors play an important role in determining its mobilization, transport and fate during its vertical migration process in vadose zone. Based on batch experiments, this paper studys the soption behaviors of TCE in vadose soil, extracted humic acid and several stimulated samples,the research results are as follows:(1)Comparison study between soil samples and simulated soil mineral samples indicates that: the maximum sorption capacity (MSC) of clay minerals is 200μg·kg-1, MSC of primary minerals is 15μg·kg-1 and the average MSC of soil organic matters (SOM) is about 250 mg·kg-1, which varies greatly. The contribution percentage of SOM to the sorption of TCE in soil is more than 90%.(2)organo-mineral interactions may affcet the structure and composition of SOM molecular, which will influences the sorption behavior in SOM. The value of TOC to clay mineral content(C/M) ratio is a key parameter that reflects the extent of organo-mineral interactions to SOM. The result demonstrates that C/M values decreases with the increase of Koc values.(3)The results of extracted humic acid (HA) batch experiments shows that surface soil of vadose profile contains more linear hydrocarbon and N element than deeper soil layer. Koc values of HA has a negative correlation with C/M value of soil, C/M value is a key parameter reflecting the influence extent of organo-mineral interactions to molecular structure and composition of SOM.(4)The results of organo-minerals mixed sample batch experiment show the existence of threshold intervals between total organic carbon (foc) and Freundlich constant n. Overal, the value of n increases with the increase of foc and a gradual decrease in increase rate until reachs 1 finally. When 0.2%> foc>0.6%, increase rate of n decreases apparently which due to the influences of aggregation of organo-minerals complex to microaggregates and macroaggregates.The appearance of aggregation will protect some sorption sites from TCE.(5) Nuclear magnetic resonance spectroscopy of HA before and after associated with kaolin indicat that kaolin prefer to adsorb aromatic carbon of HA which cause a higher contend of aromaticity for HA-kaolin complex(75%) than source HA (43%). With the increase of HA loading in complex, the aromatic carbon of complex increases which cause lower Koc value because armatic carbon exhibit lower sorption capacity of hydrophobic organic chemicals for its lower hydrophobicity than aliphatic carbon.(6)The vertical variation of C/M in vadose soil profile implys the variation of molecular structure and composition of SOM affected by organo-minerals interactions.The experiment results indicate that upper soil in vadose profile demenstrate lower Koc value(about 250 L·kg-1)with higher TOC and higher C/M value(about 1.5), while lower soil demenstrate higher Koc value(about 500 L·kg-1) with lower TOC and lower C/M value(about 1.5) because soil with higher C/M value contains more aromatic carbon.