The Study Of Remediation On Chromium-polluted Clay With Electrokinetics

Electrokinetic remediation was the soil remediation technology rose in 1980s. More than 10 countries and districts such as America,Canada,Germany,Holland,England and so on had carried out this work and gained lots of research achievements in succession. However, this technology researches were still in start-up period in the continent of our country and the relevant researches were less.China yields a great quantity of chromium salts for the world, which the annual output exceeds 1.6×10~5 tons for a good deal of waste residues contained chromium were emerged in the production of chromium salts, according to statistics, 6.0×10~6 tons of chromium residues were accumulated at present and 4×10~6 tons were not managed effectively in these years. For history reasons chromium residues were piled up simply, dissolved chromium caused by rainfall and so on can be permeated into surrounding soils and ground waters which generated serious pollution to the environment. The piled-up area of chromium residues was regarded as key managing object and the key chromium remediation technology was badly in need in our country. Consequently this article take the clay contaminated by chromium residues of Qingdao Red Star Chemical Plant as research object, using electrokinetic remediation technology for removing chromium experiment. The major research contents consist of optimum voltage for remediation, experimental study of EK-PRB(Fe~0), effect of adding reinforcing agent, effect of interval energy supply for electrokinetic remediation of clay contaminated by chromium. The study results showed as follows:First, electrokinetic remediation could remove chromium of soil samples as highest removing rate as 58.26%. 50V was proved to be the effective and economic removing voltage while the corresponding voltage gradient was 1.25V/cm. Cr(Ⅵ) moved toward anode in the form of oxygenated anion, the moving of Cr(Ⅲ) was complicated for transforming between deposit state and dissociate state, the concentration of Cr(Ⅵ) in electrolyte of anode could reach saturation easily which caused inhibitory action for removing Cr(Ⅵ).Second, EK-PRB(Fe~0) could remove chromium effectively, the highest remove rate of total chromium and Cr(Ⅵ) achieved 80.53% and 70.47% respectively, it is not only beneficial to removing of Cr(Ⅵ), but also reduced remediation energy consumption to renew electrolytes of the two poles at regular intervals.Third, citric and EDTA would contribute to dissolving out the chromium of soils, this measure not only improved chromium removing rate, but also reduce energy consumption. The reducing action of sodium sulfite for Cr(Ⅲ) made Cr(Ⅵ) translate Cr(Ⅲ), hence, the content of Cr(Ⅲ) in soils rised obviously.Fourth, Changed energy supply patterns could reduce energy consumption effectively on condition that ensuring remediation efficiency. Power on continuously under condition that power on time unchanged and interrupt time changed, there was not much difference for the removing rate of total chromium between interrupted for one day with power on for one day(A), interrupted for two days with power on for one day(B) and voltage increased gradually interrupting for two days with powering on for one day(C), the rank for energy consumption was demonstrated as C<A<B<power on continually.