The Research On Immobilization Remediation Of Lead And Cadmium Contaminated Soil

With the development of industry and agriculture, soil heavy metals pollution becomes increasingly serious. Among available remediation techniques, in situ stabilization has become a research focus of the remediation of soil heavy metal pollution. Soil incubation experiment and pot experiment were conducted to compare the effects of various organic and inorganic amendments on the chemical fractions of Pb and Cd in soil. The major research results are as follows:(1) The results showed that among organic passivation agents, silkworm excrement achieved the optimal immobilizing efficiency by decreasing the concentration of Pb and Cd in TCLP leachates by34.8%and34.8%, respectively. Furthermore, among inorganic passivation agents, red mud had the highest immobilizing efficiency by decreasing the concentration of Pb and Cd in TCLP leachates by23.6%and23.6%, respectively.(2) The results of soil incubation experiment showed that the addition of silkworm excrement significantly increased the organic matter content, and slightly decreased the soil acidity. The application of red mud dramatically increased the soil pH, and has no effect on the organic matter content. The combined treatment of silkworm excrement and red mud significantly increased the soil pH and organic matter content, with the organic matter content increased by more than18%and the soil pH increased from4to about6, which was suitable for crop growth. In addition, The combined treatments of silkworm excrement and red mud achieved the greatest immobilizing efficiency by decreasing concentration of Pb and Cd in TCLP leachates by44.5%and47.5%, respectively, and effectively promoted the transformation of acid-extractable Pb and Cd into residual fraction. The remediation efficiency descended in the order: combined treatments of silkworm excrement and red mud>silkworm excrement>red mud.(3) The results of the pot experiment indicated that the combined treatments of silkworm excrement and red mud was the most effective in promoting the growth of Brassia chinensis L. and reducing the accumulation of heavy metals in Brassia chinensis L.. The combined treatments of silkworm excrement and red mud dramatically increased the average plant height and dry biomass of Brassia chinensis L., and the maximal increasing rates were194.0%and735.0%, respectively. In addition, the combined treatments of silkworm excrement and red mud effectively decreased the concentration of Pb and Cd in Brassia chinensis L, and the maximal decreasing rates were82.7%and76.3%, respectively. The application of silkworm excrement and red mud was proved to be effective in alleviating the toxicity of Pb and Cd to Brassia chinensis L. and promoting the growth of Brassia chinensis L.. According to the results of soil incubation experiment and pot experiment, the optimal treatment was3%silkworm excrement+1%red mud.(4) Correlation analysis results indicated that heavy metals in acid extractable and reduction fractions were more readily absorbed by Brassia chinensis L., while oxidation and residual fractions were difficult to be accumulated. The increase of soil pH and organic matter content effectively promoted the transformation of heavy metals in acid extractable and reduction fractions into oxidation and residual fractions. The combined treatment of silkworm excrement and red mud significantly increased soil pH and organic matter content, and it consequently achieved the optimal immobilizing effects.