四氯乙烯和萘在氧化前后的含水层土壤上的吸附与加标解吸研究

Sorption and Spiked Sample Desorption of Tetrachloroethylene and Naphthalene in Aquifer Soils

采用批量平衡实验法研究了四氯乙烯和萘在过氧化氢氧化前后含水层土壤上的吸附。原土经过氧化氢处理后有机质含量明显降低,但是处理前后的土样对四氯乙烯和萘的吸附差别极小。过氧化氢对原土中极性官能团的破坏使原土中的大分子有机质变为小分子的可溶性有机质离开体系,造成土壤有机质含量降低。这些具有极性官能团的大分子有机质对研究的两种化合物的吸附贡献很小。在调节液固比使各种单一体系中的液相浓度差异达到一至两个数量级的情况下,加标解吸体系下的等温线仍表现为非常规的近似水平线,说明液相浓度的降低不足以使土壤中吸附的化合物发生解吸。这一结果从另一侧面说明两种目标物在研究土壤上的吸附是以在致密有机相上的吸附为主,而这部分有机质不会被过氧化氢所氧化。因此,在评估污染土壤对地下水的危害时,需慎重使用通过吸附实验得到并基于有机质总量的分配系数。

Sorption and desorption of tetrachloroethylene （PCE） and naphthalene （NAP） on the aquifer soils were studied by using bath equilibrium methods. The organic matter contents of the soil samples were decreased obviously after oxidation by hydrogen peroxide （H202） at room temperature, but the sorption isotherms of the two hydrophobic compounds to the aquifer soils before and after oxidation were almost overlapped. Hydrogen peroxide could damage the polar functional groups of organic macromolecular of the original soil into small polar molecules and then left the system by subsequent treatment, which may be the key reason for the decrease of soil organic matter content. These polar functional groups of organic macromolecular had little contribution to sorption of the two non-polar compounds. In the desorption system, the isotherms showed unconventional approximate horizontal while the equilibrium concentration had one to two orders of magnitude differences, which showed that decreasing the equilibrium concentration was not enough to make the compounds desorb from the solid phase, The results showed that sorption of the compounds used in this study to the condensed organic phase dominated the overall sorption on the soil and this part of organic phase was hard to be oxidized by hydrogen peroxide. Thus, it should be careful to make use of the distribution coefficient measured by traditional solid-liquid equilibrium system in soil and groundwater pollution risk assessment.