A Study Of The Mechanical Characteristic And Pollutants Tranformations Mechanism In Improved Landfill Clay Liners With Sludge Ash And Fly Ash

With the development of city more and more waste is produced. Under the new situation, the capacity of landfill was too large and garbage compositions were too complex. The CCLS put forward new demands for his performance. In this paper, the CCLS was amended with sewage sludge ash and fly ash. Based on triaxial compression test, iso-thermal adsorption test and soil column, the bearing capacity, adsorption property and pollutants transport were researched. Though low temperature nitrogen adsorption test, SEM and XRD, pore size distributions were investigated. The main conclusion is as follows:1. The mechanical behaviors of improved landfill clay liners were reaserched though triaxial compression tests.The amended with sewage sludge ash and fly ash of CCLS has a great effect on stress rupture points, stiffness, the initial tangential modulus, limiting deviatoric stress. Theirs were decreased with the increasing of fly ash contents and were increased with the increasing of sewage sludge ash contents. Under the confining pressure of 50kPa, 100kPa,150 kPa, Mixed with 7% of fly ash, the stress rupture points were lower 36.07%,31.45% and 20%, the stiffness were lower 36.18%,18.83% and 30.22%, the initial tangential modulus were lower 86.26%,102.58% and 10.76%, the limiting deviatoric stress were lower 10.96%,29.97% and 30.91% than CCLS, respectively. Under the confining pressure of 50kPa, 100kPa,150 kPa, Mixed with 7% of sewage sludge ash, the stress rupture points were higher 12.29%,17.82%and 27.11%, the stiffness were higher 86.26%,84.61% and 60%, the initial tangential modulus were lower 19.29%,34.19% and 56.11%, the limiting deviatoric stress were lower 99.01%,66.22% and 63.54%% than CCLS, respectively. The mechanical behaviors of mixed fly ash were greatly improved though mixed sewage sludge ash.2. The results of batch tests show that Pb(?)?Cd(?)?Cu(?)?Ni(?)adsorption to improved landfill clay liners were increased and characterized by a Langmuir isotherm model. Soil-solid ratio has significant effect on the Langmuir isotherm parameters. In order to find adsorption parameters of improved landfill clay liners, the concept of critical solid-liquid ratio was proposed, the Langmuir adsorption parameters were stabilizes at critical solid-liquid ratio.3. Though the experiment data and numerical software, the dispersion coefficient were obtained. The dispersion coefficient of Pb (?) were between 2.1×10-10cm2/s and 5.7×10-10 cm2/s. The dispersion coefficient of Cd (?) were between 2.7×10-10cm2/s and 7.1×10-10 cm2/s. The dispersion coefficient of Cu (?) were between 2.4×10-10cm2/s and 6.9×10-10 cm2/s. The dispersion coefficient of Ni (?) were between 3.1×-10cm2/s and 9.6×10-10 cm2/s. With the increasing of fly ash contents, the dispersion coefficients of heavy metal were decreased. With the increasing of sewage sludge ash contents, the dispersion coefficients of heavy metal were increased. The amended with 3% sewage sludge ash and 7% fly ash of CCLS, the dispersion coefficients of Pb(?), Cd(?)?Cu(?)?Ni(?)were lower 22.85%,21.05%,30.95% and 29.79%. But, The amended with 5% sewage sludge ash and 7% fly ash of CCLS, the dispersion coefficients of Pb(?)?Cd(?)?Cu(?)?Ni(?)were higher 20%,36.84%,16.67% and 19.15%. Therefore, the content of sewage sludge ash should not be more than 5%. If the content of sewage sludge ash should be more than 5%, the CCLS is failure.4. With the increasing of Sewage sludge ash and fly ash contents, the monolayer adsorption area and specific surface area of CCL were increased. The differential curve of pore size distribution was "bimodal", it were consistent with basic differential curve of the clay. The shapes of the integral curve were "S" type and "parabolic" type. The shapes of curve were different, and then slope were not consistent. According to the principle, the curves were divided into the scope of aperture development, the scope of aperture secondary development, the scope of aperture not development. Mixed with fly ash, the integral curve is given priority to "parabola" shape, the aperture width is continuous; Mixed with Sewage sludge ash, integral curve is given priority to "S" type, show that the pore size distribution were discontinuous.5. The surface morphology of samples was obtained. The surface morphology characteristics of clay -fly ash were fly ash particles were filled into the pores of clay. Because the bonding ability between clay and sewage sludge ash were poor, the surface morphology characteristics of clay-sewage sludge ash were sewage sludge ash particles was suspension on the surface of clay. The surface morphology of sewage sludge ash- fly ash-clay was fly ash particles filled a gap of sewage sludge ash.6. Mixed with fly ash, the average aperture width were decreased, and mixed with sewage sludge ash, and the average aperture widths were increased. Aperture width and permeability coefficient, aperture width and the dispersion coefficient of four kinds of heavy metal ions, have certain relevance. With Aperture width is decreasing, permeability coefficient and dispersion coefficient were small fallen. With Aperture width is increasing, permeability coefficient and dispersion coefficient were very substantial increased.