Study Of The Greening Revegetation And Environmental Safety Of The SS-B Stabilized Soil With Heavy Metal Contaminants

This dessertation presents a systematic study that through optimizing the ingredient proportion and the dosage of the self-developed SS-B, with the combination of theoretical and laboratory research, evaluates the leaching toxicity, soil fertility, phytotoxity, transportation of water and contaminats in the soil, soil leaching properties under the exposure of acid rain, human health risks and potential ecological risks of the soils with muliple heavy-metal contaminats (Pb, Zn and Cd) after the stabilization process. The following results are aquired from the study:(1) SS-B planting soil that is suitable for revegetation in the contaminanted site is obtained by mixing SS-B stabilized soil and the loam soil. The results from sulphuric acid & nitric acid leaching tests show that when the immobilization ratio of the Pb, Zn and Cd in the SS-B stabilized soil can reach to 69.8%, 94.2% and 99.3% after the ingredients and dose of the binder is optimized. The pH and EC value, soil fertility, germination index of the SS-B planting soil meet the standard requirement. The pot trial shows that the contaminants in the SS-B planting soils has no suppression effect of the cabbage growth. The phytoavailablities of Pb and Zn in the SS-B planting soil decrease by 46% and 77% respectively when compared with untreated soils.(2) The parameters for seepage and pollutant transportation in SS-B planting soil are obtained. Saturated permeability coefficient of the SS-B planting soil is 5.02×10-6 m/s, which is much higher than the tranditonal cement-based stabilized soil. The Fredlund-Xing model is used to describe the SWCC curves of the SS-B planting soil. Frendlich equation is used to fit the SPLP desorption test results and the effective diffusion coefficient (D*) is calculated in the semi-dynamic leaching tests. D* of Pb, Zn, Cd in SS-B planting soil are 1.11×10-10 m2/s、4.90×10-11 m2/s、4.57×10-12 m2/s respectively.(3) The unsaturated pollutant transportation characteristics in SS-B planting soil are studied. Results from the colum model test show that the concentrations of Pb, Zn and Cd in the leachate from the SS-B planting soil remain stable after 10 d raining, which are 0.10 mg/L,1.50 mg/L and 0.05 mg/L respectively and meet the standard requirement. Numerical modelling is included to evaluate the unsaturated pollutant transportation in SS-B planting soil when exposed to acid rain.(4) Results from risk assessment indicates that the SS-B planting soil possess good environmental safety characteristics. The results from US EPA human exposure risk assessment shows that the SS-B planting soil has no carcinogenic risk and non-carcinogenic risk to the human (RI=8.32×10-7<10-6, ∑HQ=7.69×10-3<1).The Hakanson method shows that the potential ecological risk index RI=269.86, which is classified as medium ecological risk, Cd contribute the most (269.41) while Pb and Zn contributes littel (0.22 and 0.23 respectively). The site modeling used to evaluate the potential groundwater pollution when the SS-B planting soil is exposed to 100-year acid rain indicates that the heavy metals that transfer into the groundwater do not pose carcinogenic risk and non-carcinogenic risk to the human (∑HQ=5.07×10-6<1,RI=3.81×10-9<10-6).