The Column Model Test And Numerical Simulation Of Leaching Characteristics Of Solidified/Stabilized Heavy Metal Contaminated Soil Under Acid Rain

The solidification/stabilization (S/S) technology has been widely used to remediate soils contaminated with heavy metals. Meanwhile, the impact of acid rain on contaminated soil can not be ignored. So it is necessary to research the leaching properties of S/S soil contaminated with heavy metals under acid rain conditions. And evaluate the long-term environmental security characteristics of contaminated soils.With the financial support of National High Technology Research and Development Program (2013AA06A206), National Natural Science Foundation (41330641), and Outstanding Youth Foundation of Jiangsu Province (BK2012022), the physical/chemical characteristics, leaching behaviors of heavy metals, seepage and leaching characteristics using soil column test were studied in this thesis, also included the numerical simulation of the soil column test. Conclusions obtained are as followed:(1) The heavy metal leaching behaviors and environmental security characteristics of S/S soil were invesgated through the sulfuric acid& nitric acid method, the desorption curve test and the 1-D semi-dynamic leching test. Results indicate that leached mass of Pb, Zn and Cd of remediated soil decreased by 66%,27% and 50% compared to contaminated soil without S/S under sulfuric acid& nitric acid method. And the desortion curves of the three heavy matals fitted Freundlich model well. Also, the leaching mechanism of Pb, Zn and Cd are diffusion controlled. Their apparent diffusion coefficient is 1.05×10-16 m2/s、7.84×10-13 m2/s、 2.11 × 10-12 m2/s respectively according to US EPA Method 1315. Their diffusion coefficient is 1.33×10-16 m2/s、1.01×10-12 m2/s、2.89×10-12 m2/s respectively according to ASTM C1308-08.(2) The percolation and soil-water characteristics were invesgated through penetration test and SWCC tests. Results showed that the saturated hydraulic conductivity of S/S soil is 3.46×10-6 m/s. The fitted parameters a, n m of soil water characteristic curve using Fredlund-Xing model is equal to 26.6 kPa,3.68,0.51, respectively.(3) The seepage and leaching properties of S/S soil under rainfall conditions were studied through soil column model test. The results showed that the Pb, Zn, Cd concentration of exudate at the bottom of the soil column has the same change rule versus time, for the initial stage with higher value, followed by a rapid decline, and keep stable at last. The concentration of Pb (or Zn, or Cd) of exudate has a good negative linear correlation with its pH, and has a good positive linear correlation with its EC.(4) This thesis used Geostudio to simulate the soil column test. The results indicate that when the time of rainfall is long enough, the soil volumetric water content and the exudation rate at the bottom of column eventually reaches a steady state. And the result of concentration of each heavy metal in exudate at bottom of model is similar to soil column test, indicating that GeoStudio can simulate the transfer and leaching of heavy meatals in soil column model well. And the prediction equation of the cumulative leaching mass at the bottom of column changed with W/S (ratio of infiltration and volume of soil column) are obtained.