A Study On Remedying The Soil Contaminated With Cadmium And Lead By Applying Four Mineral Materials

Effects of in situ immobilization by applying 4 mineral materials were deeply studiedto remedy Cd-Pb contaminated soil. Experiment of the in situ immobilization was carriedout by means of pot experiment with rape as indicator plant. Na-modified bentonite,bentonite, zeolite and diatomite were used in the experiment as studied mineral materials.Cd-Pb contaminated soil was stimulated by adding water-soluble Cd and Pb compoundreagent. Results of the experiment were summarized as follows:1. Na-modified bentonite, bentonite, zeolite and diatomite can be used to remedyCd-Pb contaminated soil as amendments of the in situ immobilization. Suitable contents ofadded these mineral materials are 30—40g·kg^-1 and able respectively to decrease over 15%and 25% of Cd and Pb contents absorbed by rape, in which zeolite is one of the mostpotential to decrease Cd contents absorbed by rape. Diatomite is one of the most effectivein situ immobilization in the mineral materials to remedy the soil contaminated with Pb.2. Na-modified bentonite, bentonite and zeolite mainly depend on increasing CEC tofix Cd and Pb in the soil, but diatomite does not. Because Cd and Pb fixed by increasingCEC may be released to solution of the soil again and become available Cd and Pb,potentiality of their resulting in contamination again is much more than diatomite.Diatomite has priority to in situ immobilization of remedying Cd-Pb contarninated soil.3. It is an important form of in situ immobilization that bentonite, zeolite and diatomitedecrease bioavailability of Cd and Pb to inhibit rape absorbing these metals by increasingpH in the Cd-Pb contaminated soil. Na-modified bentonite is just able to inhibit rapeabsorbing Cd but Pb by means of increasing pH in the soil.4. Bioavailability of Cd and Pb can be decreased by decreasing contents of rapidlyavailable N and P in the soil for the mineral materials to remedy Cd-Pb contaminated soil.It is an important factor that diatomite is able to decrease contents of rapidly available Nand P in the soil, which results in inhibiting rape to uptake Cd and Pb to remedy the soiltogether. Meanwhile, inhibiting rape to uptake Cd and Pb results from Na-modifiedbentonite's decreasing contents of rapidly available N and zeolite's decreasing contents ofrapidly available P in the soil. The effect of bentonite does not come into being in this way.5. Applying the 4 mineral materials to remedy the Cd-Pb contaminated soil, thesemineral materials respectively result in Cd-Pb interaction which Cd promote Pb to beabsorbed in the soil, and Na-modified bentonite else result in Cd-Pb interaction which Pbpromote Cd to be absorbed in the soil. Therefore, It is difficulty to indicate the effectiveness of remedying the Cd-Pb contaminated soil that single content of available Cdor Pb in the soil are used as an indicator to assess effects of in situ immobilization byapplying the mineral materials.