Remediation Of Soils Polluted By Heavy Metal Chrome Using Organic Acids

Industrial civilization has brought about a rapid development for society. However,“three wastes”produced by industry also caused severe damage to the environment which will further affect the flora, fauna and human health while in the development. Soil is the survival resources of human. Chromium contaminated in soil is also subject to considerable concern. Soil washing metheod is a development potential of the soil heavy metals pollution removal techniques, especially for soils for a high sand content. Leaching of soil remediation technologies, especially in situ remediation technology applications has advantages of simple, efficient and cost less. Therefore, leachting of soil remediation technologies for the research is very promising.The organic acid is chose as soil eluent, including citric acid, tartaric acid, oxalic acid. Through the oscillation leaching test, we can investigate the effect of leaching and analyze the cause of the effect by pH, leaching concentration and leaching time. At the same time, artificial chelator EDTA is used to compare the effect of leaching. The fractionation test is used to investigate morphological changes of chromium in the soil before and after the leaching tests. In addition, multi-stage leaching and soil column leaching are further carried out to investigate the mechanism of chromium leaching by organic acid. Meanwhile, through fractionation tests, morphological changes of multi-stage leaching and soil column leaching are investigated and the advantages of organic acid leaching technology are further explained.Through the pH test, we can get suitable pH 4 for citric acid, tartaric acid and oxalic acid leaching. The suitable pH value for EDTA is broadly from 3 to 7. Through the concentration test, we can get the best leaching concentration of citric acid and tartaric acid is 0.4 mol·L^-1, the best leaching concentration of oxalic acid is 0.8 mol·L^-1, the best leaching concentration of EDTA is 0.1 mol·L^-1. Meanwhile the regression analysis is used in concentration tests data. Through dynamic test, the suitable leaching time for three organic acids and EDTA are all 24 hours, and the mass transfer equation would be used for fitting the experimental data. The experiments show that citric acid is a little better than the other two organic acid in the leaching effect. The fractionation tests are used in leaching test, multi-stage leaching to obtain tests data. These data show that the chromium form of soil sample in this study is main residual fraction, followed by exchangeable and carbonate. The citric acid has good leaching effect on residual fraction, followed by the exchangeable and carbonate which have biological availability.In soil column leaching experiment, the pore volume in the column environment of the soil sample is measured and it’s 200ml. One pore volume is a unit of leaching volume. Citric acid is selected as organic acid, EDTA and distilled water are as contrasts. The pH, leaching concentration and leaching time which are obtained from oscillation tests are as leaching conditions. Through intermittent and continuous leaching, the leaching effect of three eluent is investigated. Fractionation is used next to the soil sample which is leached by citric acid. This fractionation data is compared with the data from oscillation test so that we can investigate advantages and disadvantages of the two tests. Meanwhile, we can investigate the removal effect of the form that has biological availability for column leaching. The experiment data show that the removal effect of residual is similar to oscillation leaching. Exchangeable and carbonate in the intermittent and continuous column leaching are better than oscillation leaching. And continuous leaching is better than intermittent leaching.