| It was reported that, in the past twenty years, vegetable base of Chongqing has been contaminted by heavy metals such as Cd, Pb, Cu, et al, among which Cd-pollution is most remarkable. Cd is a poisonous heavy metal element, which poses long-term latency, strong mobility, lower concentration and extensive hazardous areas. Therefore, it must be prior to be removed from the environment.At present, the methods of physics, chemistry, and biology have been used to contaminated soil by heavy metals, among which the effect of chemical-remediation and bioremediation is most prominent. However, the environmental risk of chemical-remediation is quite great, which can cause secondary-pollution easily; while bioremediation is a long-term course. Therefore, chemical-enhanced phytoremediation, which is the combination of chemical-remediation and bioremediation, emerges as the times require.The principle of chemical-enhanced phytoremediation is that, on the one hand, utilizing chemicals to elevate the mobility and availability of heavy metals in soil, accelerate the uptake of heavy metals by plant; on the other hand, enhancing the biomass, especially the biomass of shoot, and consequently increasing the total content of heavy metals in plants.Of all chemicals, surfactant and chelator are well received for their properties of solubilization, mobilization and chelation, and so on. Surfactant/chelator-enhanced phytoremediation was developed in the late 1990s, its essence is that using surfactants' solubilization and mobilization, and chelators' chelation to remove the organic pollutants from the contaminated environment, which is difficult to be dissolved and degraded. The effect of surfactant-remediation on contaminated soil, sludge or wastewater is remarkable, which were reported largely at home and abroad. According to the mobilization and solubilization of surfactants, people tried to use surfactants to remove heavy metals, and found that the effect of surfactant-remediation on soil and sediment pollution by heavy metals was evident; the effect was more remarkable when applied by EDTA. Using the lubricating, solubilization, decentralization, and washing of surfactants to change the surface charge of soil and absorbing ability, or exchange the heavy metals from soil surface and then heavy metals will exist in soil solution in the form of chelators, and thus expedite the fluidity of heavy metals in natural environment and the removal of heavy metals.The report was still very few about using surfactant, especially the combination of surfactant and chelator to enhance the phytoremediation on soil or sediment contaminated by heavy metals. Presently, the research on the removal of soil heavy metals by surfactant still remained in laboratory phases, and mostly utilized column washing experiment and batch experiment, which cannot be used in practice. Based on the above principle and assumption, pot-tests, soil cultivation, chemical thermodynamics and kinetic adsorption-desorption experiments were conducted in this study.According to the use of the combination of surfactant and chelator, selecting the optimal combination of surfactant/chelator and their optimal concentration, in order to offer scientific gist of chemical-enhanced phytoremediation and offer new approach on the treatment of soil contaminated by heavy metals.Firstly, the orthogonal design with L18(61 X 36) was used to select the joint application of the six kinds of surfactants (SLS, DBSS, CTAB, CPB, Tween80, TX-100) and EDTA. The results showed that, the types of surfactants were the key factor affecting Cd uptake of plant, and the enhanced remediation of anionic surfactants and nonionic surfactants were more effective than that of cationic surfactants. The joint application of surfactants and EDTA could propel the root Cd transfer to the shoot, and made for the phytoremediation of Cd-contaminated soil.The compared design of pot-tests was used to investigate the effect of two kinds of chelators (EDTA and EGTA) on Cd uptake by juncea var 鈥?mul... |
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