| Since the 20 th century,economic develops rapidly,it improves people’s living standard, but also brings some environmental problems,especially heavy metal pollution. Chromium salt is one of the main series of products of inorganic chemical industry, during the production of Chromium salt and metallic chromium, will produce large amounts of chromium slag. Chromium slag pile up for a long time, resulting in the severely pollution of soil and groundwater. In some areas, the content of total chromium in soil is more than 10000 mg/kg, hexavalent chromium content in the soil is more than 1322 mg/kg.Electrokinetic remediationas one of the in situ remediation technologies,has the characteristics of high efficiency, energy saving, wide applicable scope, is the research focus at home and abroad. According to the early stage of the research study,removal efficiency of chromium contaminated soil by general electrokinetic remediation is low, the main factors are:the pollution soil by chromium slag with high concentration of chromium, strong alkaline,complex coexisting pollutants, Cr mainly in the precipitation state and residual state. In the process of electric precipitation state Cr and residual state Cr are difficult to dissolve, not been moved by electric field.The preacidificationelectrokinetic remediation technology was put forward to solve the problem of low total chromium removalefficiencyusingconventional electrokinetic method for chromium contaminated soil.The experiments were conducted on chromium residue contaminated soils collected from a chemical factory in China. In present study, the effects of acidification time, concentrations of acetic acid, citric acid and hydrochloric acidon removal of chromium from soils were studied by changing the acidification pretreatment conditions, and then speciation analysis of chromium was also conducted to study the regularity of Cr in different speciation. On this basis, combined with PRB technology to repair the chromium contaminated soil.Through experimental analysis, draw the following conclusions:(1)electrokinetic remediation removal efficiency of chromium from chromium contaminated soil was significant enhanced with acidizing pretreatment. The total chromium(Cr(T)) and hexavalent chromium(Cr(Ⅵ)) removal rate of the group acidized by citric acid(0.9mol/L) for 5 days was up to 26.97% and 77.66%; while the Cr(T) and Cr(Ⅵ) removal rate of the group without acidification was 6.23% and 19.01% respectively.(2) The removal ratio of chromium depended on acid-concentration and acid type. In addition, part of chromium with the state of carbonate-combined will be converted into water-soluble state through to acidification to improve the removal rate. Within the appropriate concentration range, the higher concentration of acid is, the more chromium releases.(3) The chromium removal ratios of the citric acid acidification groups was higher than the acetic acid mainly due to the citric acid is a complexing agent, which has the complexation ability tothe carbonate-combined chromium released by acidification and then enhance the chromium removal efficiency.(4)The major speciation of chromium removed from soils by acidification-electrokinetics remediation was acid-soluble speciation, revivification speciation and oxidation speciation, and the residual chromiumbiological availability was reduced.(5)EK/PRB combined remediation technology can significantly improve the removal efficiency of total chromium, total chromium removal rate reached 33.87%, compared with EK-08 group, which use the ordinary electric repair technology, the removal rate of EK-11 increased more than two times. |
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