Changes With The Depth Of Organic Matter Of Soil On Profile And Sorption Behaviors Of Chlorinated Hydrocarbons

On the course of organic contaminants go into groundwater from surface on profile, there are a large mass of organic matter in topsoil/sediment. It plays an important role of sorption of organic contaminants. On the other, as there are so much soil medium in the subsoil on profile. This must do great influence for sorption of organic contaminants. As the result, it will be much usage to begain the researches of sorption of organic contaminants on vedose zone. This research aimed at the organic contaminants of TCE. In the laboratory, with the soil of vidose zone on profile in one area of Beijing, this paper studyed the sorption behaviors of organic contaminants trichloroethylene (TCE) with the changes of compose of soil and organic matter. The results of the research were as follows:(1) The correlation is close among clay content, clay mineral, humification degree and TOC. The clay content of soil compose is the key influence to the content of TOC and the degree of humification of subsoil on profile. Particularly, the clay content influences the content of organic matter, structure and humification degree and organo-mineral complexes. The influence of clay content must be greater than the initial content of organic matter in the era of sedimentation and the deposit years. The differences, such as the content of organic matter, structure, humification degree and the complexes, affect the sorption behaviors of TCE. Consequently, the change of clay content is the key factor to influence the remove and transformation of TCE on vertical profile. The absorbance of alkali liquid can be used to replace HA/FA and HA/TOC to character the degree of humification of soil. (2) The carboxyl functional groups of HAs are mainly COO– and the FAs'are COOH. Thus the acidity of FAs is higher. The structure of HAs is more compact than FAs, and HA has more saturation and more content of carbon than FA extracting from the same soil samples. The humic acids between topsoil and subsoil do not have the same characters. Tophumic acids have much methyl, methylene, hydroxyl group and carbonyl group. Tophumic acids have less humification degree and less stability. Kd and Koc of humic acids extracted from topsoil(tophumic acids) to TCE sorption are bigger than the humic acids exctracted from subsoil(subhumic acids) normally. (3) Organic adsorption behavior of TCE plays a very important role. However, on the course of organic contaminants go into groundwater from surface on profile, there is a large mass of mineral in vadose zone. The sorption of mineral does not be neglected. The TCE adsorption isotherm of soil sample is nonlinearity clearly in subsoil and the contribution ration of mineral adsorption is higher while foc is less. The linear of the adsorption isotherm of soil samples is bigger obviously with a little increasing of content of organic matter on vertical profile. The TCE adsorption isotherm of mineral is Longmuir and there is the biggest adsorption. (4) The adsorption isotherm of sample can be changed by the solute concentration of TCE, foc increases and n values increase gradually. Different concentration of TCE will lead to the much difference in adsorption ratio between organic matter and mineral. The more is concentration of TCE, the higher is sorption rate of organic matter and the less is adsorption rate of mineral. The adsorption rate of mineral changes between 28% and 16% when foc equals 0.16% and TCE changes between 50μg·L-1 and 500μg·L-1. The adsorption rate of mineral changes between 3% and 1% when foc greater than 1% and the influence of the adsorption rate of mineral and organic matter to TCE is less. (5) The mineral is not covered uniformly by organic matter but is distributed irregularly on sorption point after the organo-mineral complex formed in soil. Kaolinite attracts–CH2 easily and montmorillonite aromatic group easily. On the other hand, the complexes can be contracted to form polymerizations with the increasing of organic matter. There is a great deal of interspace in the polymerizations. The higher is the content of organic matter the more compact is the polymerizations. The interspace diameter gets smaller. The results of two aspects affect the TCE sorption of complexes.