Application Of Organic Materials And Clay Minerals To The Remediation Of Heavy Metal Contaminated Soils

Through the adsorption-desorption experiment in laboratory and the pot experiment in greenhouse conditions, the deactivated behavior and mechanisms of heavy metals in soil by the organic material and clay mineral were studied in this paper. The main results showed that:1. The adsorption-desorption characteristics and mechanisms of Pb²⁺ by the complex of palygorskite and humic acid were studied in this experiment.(1) The capacity of Pb²⁺ adsorbed on the complex of palygorskite and humic acid was significantly higher than on the single palygorskite and humic acid respectively.(2) The capacity of Pb²⁺ adsorbed on the complex of palygorskite and humic acid was increased significantly at pH>4.(3) The coexistence of Pb²⁺and Cu²⁺ significantly reduced the adsorption of Pb²⁺ and Cu²⁺ on the complex of palygorskite and humic acid in the condition of higher Pb²⁺ concentration.(4) The desorption rate of Pb²⁺ from the complex of palygorskite and humic acid was lower than that from palygorskite and decreased with the increase of Pb²⁺ concentration in the solution.(5) The content of soluble humic acid was significant greater in the solution of the complex of palygorskite and humic acid than that in the solution of the single humic acid.(6) The analysis of infrared spectrum indicated that many absorption peaks were broadened or disappeared when Pb²⁺ was adsorbed by the complex of palygorskite and humic acid, while some absorption peaks were still observed when Pb²⁺ was adsorbed by the single humic acid.2. The deactivated behavior of heavy metals by the organic material and clay mineral and its impact on the growth of plants were studied in the pot experiment.(1) The organic material and clay mineral had slight impact on the change of soil pH, but significantly decreased the electrical conductivity in soil solution at the seedling period. The organic material and clay mineral also significantly decreased the concentration of Zn²⁺,Cu²⁺ in the soil solutions, but unsignificantly to Pb²⁺ and Cd²⁺.(2) The organic mineral added in the soils effectively increased the biomass of the soybean and cowpea's seedlings, plants and seeds. While the impronement of two plants by the clay mineral added in the soils was inferior to the organic material although the growth of plants was also improved to some extent when the clay mineral added in the soils. (3) The organic material and the clay mineral added in the soils had significantly greater effects on the content of chlorophyll, MDA and praline in the leaves of two plants and the activity of SOD and POD were also affected, compared with the control.(4) The organic material significantly decreased the concentration of Zn²⁺, Cu²⁺, Pb²⁺ and Cd²⁺ in Cowpea's seedlings, plants and seeds while the clay mineral's effect was inferior to the organic material, and comparatively the deactivated effects by the organic material and the clay mineral to cowpea was better than to young soybean.