Focusing Phenomena In Electrokinetic Remediation Of Chromium- Contaminated Soil

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.