三氯乙烯在不同土壤中的解吸行为

Study on Desorption Behavior of Trichloroethylene on Different Soils

采用w(TOC)(TOC为总有机碳)不同的2种天然土壤以及用H2O2去除大部分软碳和高温灼烧去除全部有机碳后所得到的6种土样为吸附剂,以TCE(三氯乙烯)为研究对象,考察了有机碳含量及组成、矿物质、初始ρ(TCE)等因素对TCE解吸行为的影响,并比较了吸附解吸异质性大小.结果表明,解吸平衡时6种土样的TCE解吸量不到相应吸附量的25%;TCE在6种土样上的解吸等温线表现出更高的非线性特征.所有土样都表现出一定程度的吸附解吸异质性,HI(异质性指数)均大于2.0,其中H2O2氧化土样的异质性更高(HI>4.0).2种原土中有机碳和矿物质对TCE解吸的平均贡献率分别为74%和26%,而H2O2氧化后的2种土样中该值分别为68%和32%;初始ρ(TCE)越高,矿物质的解吸贡献率相对越低.此外,TCE的解吸量与土壤矿物质中孔和微孔的体积也有一定的关系.

Soil is composed of porous solids containing aromatic （hard carbon）, aliphatic carbon （soft carbon） and minerals. In order to investigate influences of different soil compositions on TCE desorption, six types of soil, including two types of natural soil with different organic carbon contents and four types of treated soil were adopted as adsorbents. The treated soils were with most of the low aggregation of soft carbon removed by hydrogen peroxide or with all of organic carbon removed by high temperature ignition from the original soil. The effects of main parameters （organic carbon content and composition, minerals and the initial TCE concentration） on TCE desorption behavior were examined and the heterogeneity indices （HI） were compared. The results showed that TCE desorption quantity was less than 25% in six sorhents after achieving desorption equilibrium. The desorption isotherms of different soils ean be well fitted by the nonlinear Freundlich model, and thermal-treated soils showed the highest nonlinearity among the sorbents. All desorption procedures exhibited hysteresis to some extent with respect to preceding sorption ones, and the average HI of all sorbents were greater than 2.0, in which the tt202-treated soils exhibited the higher hysteresis （HI 〉 4.0）. The organic matters and minerals contributed to TCE desorption rates of 74% and 26% for the two types of natural soli in average. However, in the H2 02 -treated samples, these rates were 68% and 32% , respectively. These results showed that the TCE desorption contributed by minerals decreased with the increase of the organic carbon content. In addition, the higher the initial TCE concentration was, the lower the TCE desorption contribution by minerals was. In summary, desorption quantity of TCE is not only related to the organic carbon content, but also related to organic carbon structure and micropore-mesopore volumes of minerals. These results can give an insight into the desorption mechanisms and promote an accurate model for the transport, fate and risk assessment of TCE in the subsurface environment.