| Confronted with the problem of Cd contaminated soil, the in-situ immobilization of Cd contaminated soil was done by selecting five curing agents (the diatomite, zeolite, bentonite, vermiculite and hydroxyl-Al pillared modified diatomite) and using pakchoi as indicator plant. Simultaneously, the effects of five curing agents on Cd speciation, the physical and chemical properties of soil, the morphology of pakchoi, and the pakchoi absorption ability of Cd were studied. The main results are as follows.(1) The result of Cd speciation of five curing agents indicates that all five curing agents have some curing agent effect, in which zeolite’s effect is the best. Zeolite make the content of Cd available speciation decline from10.8085mg/kg to8.5529mg/kg, and decrease by20.85%. Selected the content of Cd available speciation in the soil and the Cd available speciation accounting for total speciation as the index, the remediation effect of five curing agents on Cd contaminated soil is as follows:zeolite> hydroxyl-Al pillared modified diatomite> bentonite> vermiculite> diatomite.(2) Firstly the study of five curing agents’effect on physical and chemical properties of Cd contaminated soil shows that all five curing agents can improve CEC(cation exchange capacity), in which when the adding content concentration of bentonite is30g/kg, the biggest CEC is7.65cmoL/kg. And compared with contrast, the CEC has improved25%. Secondly the adding content concentration of bentonite is30g/kg and vermiculite’s is20g/kg, the pH of soil has declined. Except them, others’pH has improved to some extent. Besides the pH of soil has distinct negative correlation with Cd acid extractable Cd of the adding bentonite and hydroxyl-Al pillared modified diatomite soil, has some negative correlation with the adding diatomite soil, and has not distinct correlation with the adding zeolite and vermiculite soil, which concluded that the improvement of pH of soil decreases the acid extractable Cd and promotes the transformation from available Cd to unavailable. Thirdly the acid extractable Cd of soil has some negative correlation with the organic matter of the adding diatomite, zeolite, bentonite and vermiculite in soil. Inthe adding diatomite, zeolite, bentonite and vermiculite of soil, that is to say, the increase of organic matter promotes the decrease of acid extractable Cd of soil, which improves the soil buffering capacity of Cd, and reduces the Cd toxicity in soil. At the same time, adding some concentration five curing agents of soil make the organic matter of soil improvement, in which when adding concentration of hydroxyl-Al pillared modified diatomite in the soil is20g/kg, the organic matter is the most. Compared with contrast, the organic matter in soil improves by27.54%.(3). The result of five curing agents effect on the the morphology of pakchoi indicates that five curing agents can decrease the Cd toxicity effect in the soil, make pakchoi grow and improve its biomass, height and root length. When the adding concentration of zeolite is15g/kg, the pakchoi biomass is biggest, and compared with no curing agents Cd contaminated soil, the biomass has improved by25times.(4). The result of five curing agents effect on the Cd assimilation shows that compared with the contrast(without curing agents Cd contaminated soil), the experiments of adding five curing agents, except the adding concentration of hydroxyl-Al pillared modified diatomite is10g/kg and20g/kg and bentonite is lOg/kg, have decreased the Cd in the pakchoi to some extent. And when the adding concentration of zeolite is30g/kg, the pakchoi have least Cd content; compared with contrast, the Cd content in pakchoi has decreased by74%. And through analyze the Cd enrichment factor, different concentration zeolite, hydroxyl-Al pillared modified diatomite, bentonite and vermiculite(except diatomite) can decrease the Cd enrichment factor to different extent. When the adding concentration of hydroxyl-Al pillared modified diatomite is15g/kg, the pakchoi’s Cd enrichment factor has decreased most, decreased to9.85%. In experiments of five curing agents, only can zeolite decrease Cd enrichment factor in all different adding concentration.To sum up, through comprehensive analyze of the avaliable Cd in the soil, the total content of Cd in the soil, biomass of pakchoi, the pakchoi’s Cd enrichment factor, the Cd content in pakchoi and so on, the conclusion that the five curing agents of in-situ immobilization remedy effect on Cd contaminated soil is zeolite> hydroxyl-Al pillared modified diatomite> bentonite> vermiculite> diatomite can be drawed. |
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