【作者】 聂杨；

【导师】 李东；

【作者基本信息】 重庆大学 ， 环境工程， 2011， 硕士

【摘要】 在我国经济飞速发展的同时,土壤重金属污染现象日益严重,已经成为了重要的环境问题之一。电动修复技术作为新兴的土壤原位修复技术,广受关注。虽然在前人的众多研究中认为电动修复技术对于处理重金属污染严重的土壤场地具有高效性及可行性,但是在电动修复实际应用过程中,浓度聚集现象无处不在,这种聚焦现象已经严重的阻碍了电动修复技术在实际工程中的应用。本试验选取铬为目标污染离子,凝胶及土壤为固态介质,探讨了在电动修复过程中引起了目标离子浓度聚集现象的主要机理及原因。本文的主要结论如下:(1)各种离子在凝胶中的迁移速率大小次序与在水中的基本一致。H+离子和OH-离子的迁移速率处于众离子的前列。(2)因为与目标离子共存的离子在某些区域的浓度较高,导致加载在这些区域的电压梯度变低,这将使得目标离子迁移到这些区域时迁移速度显著下降。随着反应的持续进行目标离子将会在这些区域聚集,在修复场地中形成高浓度的污染区域甚至“死区域”,造成电动修复的电耗及修复时间显著增加,把此称为由共存离子诱导电压梯度阱效应导致的聚焦现象。(3)研究发现虽然中和阳极端水解产生的H+离子能提高电动修复过程中的电流效率,但是聚焦现象仍不可避免。若使离子浓度一直维持较低数值,则能有效避免聚焦现象。另外当使离子浓度梯度方向与电流方向一致时亦能有效防止共存离子诱导电压梯度阱效应。(4)土壤中的聚焦现象与凝胶中一致,说明由于共存离子诱导电压梯度阱效应而引起聚焦现象等结论在土壤中也成立。即使是土壤重金属轻污染场地,若要降低电动修复的费用,建议运用组合工艺进行土壤重金属污染修复。本研究从离子的电迁移规律的角度,研究聚焦现象产生的机理和规律,为聚焦现象的消除和利用技术研究提供理论指导。更多还原

【Abstract】 With the rapid development of China’s economy, the growing phenomenon of heavy metal pollution has become an important environmental problem. In recent years, as the in situ remediation, Electrokinetic remediation has been wide concern. Concentration fluctuation and dead zones phenomena (CFDZP) are ubiquitous in the field, pilot and bench tests of electrokinetic remediation (EKR) of soils. CFDZP have severely impeded the application of EKR technology in fields though its effectiveness for many heavy metallic contaminants has been verified by numerous bench tests.In this study a series of deliberately designed experiments with spiked agar and soil were performed to explore the mechanism of CFDZP. To sum up, in the following aspects:(1) The mobilities of ions in agar are measured. It can be found that all ions involved keep their mobility tier in agar as in water. The transfer rates of H+ and OH- are in the front of other ions.(2) The mechanism of CFDZP caused by ion-induce trapping effect (ITE) which is interpreted as that the lower potential gradient caused by co-existing charged ions of high concentration in some zones will cause significant velocity drop for the charged target ions when they migrate into these zones from the zones of higher potential gradient. The accumulation of“trapped”target ions would result in“hot spots”or more severely,“dead zones”in the sites. The EKR duration and electric consumption will vary dramatically.(3) Though neutralizing the H+ ions generated by water electrolysis in anode compartment can improve the current efficiency of electrokinetic remediation process,“dead zone”phenomenon close to anode cannot be mitigated due to the increasing of total ion concentration in anolyte. An effective method was to keep the ion concentration at a low level in the entire electrokinetic remediation process. Modifying the arrangement of electrodes to let current direction normal to concentration gradient of ions can avoid the ion-induced trapping effect to go into effect and hence prevent the occurrence of“hot spots”on the target ion migration way.(4) CFDZP occurs in soil is same as in agar confirm that knowledge about CFDZP obtained from agar experiments is also basically valid in soils. We perhaps should abandon the wish that just resorting to the promising EKR technology a metallic contaminated site could be restored in a reasonable cost and duration, even though the site is just slightly contaminated. Instead, a combined process is more acceptable in field applications.From the perspective of ions’electro-migration mechanism, this study focuses on the mechanism and laws of CFDZP, in order to provide theoretical guidance for eliminating CFDZP and using the technology.更多还原