1,2-二氯乙烷和1,2-二氯丙烷在某污染场地包气带的吸附-解吸特性

1,2-二氯乙烷(1,2-DCA)和1,2-二氯丙烷(1,2-DCP)是某污染场地地下水中检出最高的挥发性有机污染物。文中采用批试验方法,研究污染场地包气带中三种不同深度土壤样品对1,2-DCA和1,2-DCP的吸附-解吸特性。结果表明:土壤中有机质决定其吸附行为,三种土壤对1,2-DCA和1,2-DCP的吸附符合Henry线性等温方程,分配系数在20.49～22.43L.kg-1,1,2-DCA和1,2-DCP在三种土壤中分别具有相似的吸附能力;同一土壤中两种目标污染物的吸附能力为Kd(1,2-DCA)>Kd(1,2-DCP),但差别不大。1,2-DCA和1,2-DCP在三种土壤中的解吸可用Freundlich等温方程拟合,解吸的难易程度与土壤中黏粒含量相关,黏粒含量越高,目标污染物的解吸越困难,第三层(地下4.9～5.1m)土壤的防污能力较强;两种污染物在三种土壤中的解吸都存在明显的滞后效应,1,2-DCP的滞后指数比1,2-DCA的大。

Adsorption and desorption of1,2-dichloroethane and1,2-dichloropropane by soils in an unsaturated zone

1,2-Dichloroethane(1,2-DCA)and 1,2-dichloropropane(1,2-DCP)are two kinds of volatile organic compounds(VOCs)which are among the most frequently detected pollutants in groundwater at one contaminated site.In this paper the adsorption and desorption of 1,2-DCA and 1,2-DCP on three soil samples collected from the vadose zone are studied by batch experiments.The results showed that the adsorption isotherms of 1,2-DCA and 1,2-DCP fit linear Henry isotherm equations well,and the partition coefficient(Kd)ranges from 20.49 to 22.43 L·kg-1.The adsorption capacity of 1,2-DCA and 1,2-DCP on the three soils are very similar,suggesting that the contents of natural organic matter are responsible for adsorption.For the same soil,the adsorption capacity of 1,2-DCA is slightly higher than that of 1,2-DCP.Meanwhile,the desorption isotherms of the two pollutants can be described with nonlinear Freundlich isotherm equations.Differences in desorption capacities among the soils are related to the clay contents;the higher clay contents,the lower desorption capacity.The soil within the deepest layer,which is about 4.9-5.1 m below surface,has the lowest vulnerability to 1,2-DCA and 1,2-DCP.Desorption of both chemicals has significantly retarded and the hysteresis indices of 1,2-DCP are higher than those of 1,2-DCA.