| As two important methods for in-situ remediation of heavy metal contaminated soil, stabilization and phytoextraction have attracted more and more attention in the recent years. A survey was conducted to investigate the degree of the heavy metal contamination of a farmland soil in this research. Then, pot experiments were conducted to investigate the effects and persistence of natural sepiolite and lime on soil and crop in acid red soils with different degree of heavy metal contamination. Further, the effects of stabilization on growth and metal extraction by hyperaccumulator-Sedum plumbizincicola were also studied. Field experiments were conducted to study the effects of stabilization. The purpose of this study is to provide theoretical foundation and technical support on "production while repair" that achieve safety corp production on contaminated soil during farming season by applications of sepiolite and lime and high efficient remediation of heavy metal pollution by S. plumbizincicola. The main results were as follow:1) The results of investigation of heavy metal contamination showed that the arable soil layer were mainly slightly to moderately contaminated and the average concentrations of Cd were nearly twice that of the secondary value of Chinese soil environmental quality standards. However the concentration of Pb, Cu and Zn didn’t exceed the secondary value. Element spatial distribution characteristics analysis showed that higher concentration of Cd and Zn were mainly in the eastern, northwestern and southwestern parts of the studied field. Element vertical distribution characteristics analysis showed that the surface soil layer of the profile obviously had accumulated Pb, Cd and Zn. However, heavy metal concentrations of soil below 20 cm did not exceed the secondary value.2) The results of pot experiments showed that when amended with various dosage of sepiolite and lime the concentration of available Cd in severely polluted soil decreased by 85.9% at the largest and the soil pH raise from 4.77 to 7.72, while the concentration of available Cd in slightly polluted soil decreased 97.7% at the largest and the soil pH raised by 3.57 unit. When the dosage of sepiolite was less than 2%, the combined application of 0.1% lime showed more obvious stabilization effects. What’s more, the stabilization with sepiolite and lime could persistently reduce the absorption of Cd and improve the growth of Brassica chinensis for a long time, at least one year according to the duration of this study. When the addition dosage of sepiolite was more than 2%, Cd concentration in the edible parts of B. chinensis met the national food sanitation standard in the slightly contaminated soil and the multiple seasons pot experiment also showed that the passivation effect lasted at least one year.3) The stabilization effect under the condition of field showed that sepiolite and lime have great influence on the quantity of available Cd and pH. The soil pH raised 0.41-0.86 units and the concentration of available Cd decreased 37.5-85.7%. Compared with the control treatment, the Cd concentration of the root, straw and brown rice had decreased but not statistically significant.4) The influence of chemical stabilization on the phytoextraction efficiency by S. plumbizincicola showed that appropriate addition of sepiolite made no significant difference on the uptake of Cd and the growth of S. plumbizincicola. However, high concentration of sepiolite application was not desirable for subsequent phytoextraction. |
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