Soils Modification For Liners And Service Life Analysis

In recent decades, with the development of industry, soil and water pollution issues frequently occur and have generated great concern. Heavy metals are one main type of the contaminants. Barries are widely used to protect soil and groundwater from contamination, and is a good way to deal with polluted soil, by means of constructing them around the polluted area or a centralized source of pollution, such as a landfill. Thus, this research mainly focused on the mechanism of contaminants transportation in soils, the function of barriers, and how to improve the useness of barriers.In this paper, based on the former research, the mechanism of heavy metals transporting in soil, the mathematics of the transportation procedure, and parameters controlling the transportation are summarized. Both in situ and laboratory experiments were carried out to study this, and some main conclusions are as follows:(1) Based on the mechanism of contaminants transportation through soil, the way to improve the performance of barriers consisting of soils are given, which is by decreasing the hydraulic conductivity and increasing the adsorption redaction. In the circumance of which the hydraulic conductivity meets the requirement, increasing adsorption behavior is a main way to improve the performance of barriers.(2) Equilibrium and kinetic Batch adsorption tests were carried out to investigate the adsorption characteristics of silt, loess, and bentonite towards lead. The effects of initial solute pH value, shaking time, and initial solute on adsorption capability of soil were considered. Using electron spectroscope and X-ray diffraction, it is illustrated that the high adsorption capability of loess is due to the surface precipitation of calcite with lead. The adsorption of lead on silty soil and bentonite is ascribed to cation exchanging process.(3) In situ soil samples were get from the horizontal compact soil layers of landfill built in a loess area of Xi’an city, China, and the concentration of Cl-and Pb(Ⅱ) in soils samples of different depth were tested. Transportation parameters were get from mathematics calculation. The in-situ adsorption behavior of loess towards Pb(Ⅱ) is proved to be excellent, thus, it can be concluded that there is little possibility that the soil near a landfill or polluted area could be polluted by heavy metals especially Pb(II) is a loess area if the barriers are mainly made of loess soil.(4) Laboratory Batch adsorption tests were carried out to investigate the adsorption characteristics of silt-loess, loess-bentonite, silt-bentonite and loess amended silt-bentonite towards lead, to study the adsorption characteristics of mixed soils and to investigate the methods to improve the adsorption capability of soil towards Pb(Ⅱ). This study illustrated that he mix soil combined the merits of individual soils, and the adsorption behavior is directly determined by the proportion of each soil in the mixed soils.(5) Laboratory column tests were carried out to study the transportation of Cl "and Pb(Ⅱ) in silt-bentonite and loess amended silt-bentonite columns. By comparing the hydraulic conductivity, diffusion parameter, dispersion parameter and adsorption parameter of SB and LSB, the role of loess in modifying the silt-bentonite is evaluated. Loess added to silt-bentonite could improve all the four parameters of soils. The breakthrough time of Pb(Ⅱ) transporting through0.6m-thick-LSB cutoff wall is three times of that of a SB cutoff wall. The good porformance of loess in amending SB is induced by its high adsorption ability towards Pb(Ⅱ).