有机氯代烃在壤土中的吸附和解吸特性

Sorption and Desorption of Chlorinated Hydrocarbons onto Loam Soil

选取三氯乙烯(TCE)、顺-1,2-二氯乙烯(cis-1,2-DCE)、1,1,1-三氯乙烷(1,1,1-TCA)、1,2-二氯乙烷(1,2-DCA)4种常见的有机氯代烃,通过批次实验研究其在壤土中的吸附和解吸特性。结果表明:4种有机氯代烃在壤土中的吸附平衡时间约为3d;在本文研究的整个浓度范围内,4种有机氯代烃的吸附等温线基本呈线性趋势,但更符合Freundlich模型。对于有机氯乙烯而言,TCE在壤土中的吸附特性较为显著,线性分配系数Kd为0.624L/kg,其次是cis-DCE,Kd为0.238L/kg;对于有机氯乙烷而言,1,1,1-TCA在壤土中的吸附特性较为显著,Kd为0.520L/kg,其次是1,2-DCA,Kd为0.353L/kg。这进一步表明4种有机氯代烃化合物在壤土中的吸附特性与化合物本身的疏水性有关。通过Abdul、Dobbs、Rao和Cong经验公式估算lgKoc值发现,Abdul估算所得lgKoc比实测值偏小,Cong估算lgKoc比实测值偏大,Dobbs和Rao与实测值更为接近;说明Dobbs和Rao经验公式更适用于预测有机氯代烃化合物在壤土的吸附特性。另外,研究发现有机氯代烃的解吸过程具有明显的滞后性,吸附特性较强的物质,其解吸较为缓慢。

The sorption and desorption characteristics of the four organic chlorinated hydrocarbons（trichloroethylene（TCE）,cis-1,2-dichloroethylene（cis-1,2-DCE）,1,1,1-trichloroethane（1,1,1-TCA）,and 1,2-dichloroethane（1,2-DCA））onto loam soil are investigated by a batch of experiments in this study.The results indicate that the sorption equilibrium time of the four chlorinated hydrocarbons onto the loam soil is about three days.The sorption isotherm for all compounds is nearly linear,and fits to Freundlich isotherm slightly over the entire concentration range.As for chloroethylenes,TCE is strongly sorbed to the loam samples（Kd=0.624L/kg）,and followed by cis-DCE（Kd=0.238L/kg）.For chloroethanes,1,1,1-TCA is strongly sorbed（Kd=0.520L/kg）,and followed by 1,2-DCA（Kd=0.353L/kg）.This is consistent with the order of hydrophobicity of the compounds.In addition,the lgKocvalue is estimated by Abdul,Dobbs,Rao and Cong empirical regression formula respectively in this study,and the results show that the estimated lgKocvalue determined by Abdul regression is significantly lower than the calculated value,and the estimated lgKoc value determined by Cong regression is significantly higher than the calculated value,while the estimated lgKocvalues determined by Dobbs and Rao regression are much closer to the calculated values.This demonstrates that the Dobbs and Rao regression is more suitable for lgKocestimation for chlorinated hydrocarbons.Besides,it is found that there is a certain lag in desorption of chlorinated hydrocarbons from the loam soil;and the higher the sorption capacity of chlorinated hydrocarbon,the lower the desorption capacity of chlorinated hydrocarbon.