The Characteristic Of Blocking Pollutants And Strength Properties Of Modified Clay Containing SSA As Landfill Liner

The environmental pollution caused by sewage sludge has become one of the most prominent environmental problems in current and future,and the coke material will be produced in the pyrolysis process of sludge,it mainly contains inorganic substances such as silicon,aluminum,and a few organic matters.It also has a certain specific surface area and ion exchange capacity.Landfill liner materials will be eroded on account of the interaction between the migration of liner system in landfill and move of geotechnical medium,leading to the change of the microstructures such as porosity and dielectric properties and affecting the permeability of the material and the pollutant blocking capacity directly.In this research,sewage sludge will be incinerated into ash.The modified clay produced by the ash mix with clay,will become landfill liner material.The adsorption test and microstructure test were performed to determine the modified clay's adsorption characteristics of heavy metal ions and microstructure,phase composition.Permeability test was performed to determine the permeability coefficient of modified clay.A manmade clay cylinder was used to perform the test on pollutant blocking and leaching in modified clay,the change rule of heavy mental ions blocking and pollutant adsorption of modified clay were determined in the test.Mechanical strength test and low temperature N2 adsorption test were performed to indicate the reason of the change happen in mechanical strength and microstructure of modified clay.Based on the above tests,the main research results are as follows:(1)The result of adsorption test shows that the adsorption of Cr(?),Pb(?),Zn(?)and Cu(?)by modified clay containing sewage sludge ash(SSA)followed with Langmuir adsorption curve.The maximum adsorption capacities of ions increased 1.28 times,2.97 times,2.30 times and 2.97 times respectively,under the condition of,compared with pure clay sample,the maximum adsorption capacities.And the adsorption effect of sample containing 5% SSA is similar with that of the sample containing 3% SSA.(2)The result of microstructure test shows that with the increase of the adsorption quantity of heavy metals,the average pore diameter decreased,and the specific surface area increased in modified clay containing SSA.The total pore volume of modified clay containing 3% SSA were 0.154cm3/g and 0.140cm3/g,0.169cm3/g,0.160cm3/g,after the adsorption of Cr(?),Pb(?),Zn(?)and Cu(?)respectively in initial concentration of 250mg/L.After the heavy metals were adsorbed by modified clay,the DTG curves were declined obviously,and accompanied by endothermic phenomenon.(3)The permeability test and test of soil column shows that,the hydraulic conductivity of column mixed with SSA was 19.2~25.3% smaller than the column without SSA,the concentration of heavy metal ion in soil pore water declined with the increase of soil depth.In the modified clay,the concentration of Pb(?)in the pore water at 3~4cm was 44.0~73.8% smaller than the column without SSA.The maximum leaching rate of heavy metal ion in sample was lower in relatively.(4)The result of triaxial shear test shows that compared with pure clay,the shear strength of modified clay was decreased after corroded by landfill leachate.When the content of SSA in modified clay were 0%,1%,3%,5%,the cohesive force were 65.58 kPa,87.27 kPa,112.87 kPa,94.55 kPa respectively,and the internal friction angle were 16.1°,15.5°,14.9°,16.1° respectively.(5)The results of the consolidation test,pore structure test and grain size test shows that after the modified clay was corroded by landfill leachate,the void ratio was increased and the amount of compression was decreased follow with the increase of the content of SSA,and the article composition were different obviously.After corroded by landfill leachate,the compression coefficient of modified clay were between 0.310MPa-1 and 0.391MPa-1,the consolidation coefficient were between 2.446cm2/s and 2.768cm2/s,in grain size test,the percentage of particle size larger than 11.5?m was 35.09~49.42%,the percentage of particle size between 2.3~1.5?m was 2.35~7.28%,and the percentage of particle size smaller than 2.3?m was 46.57~57.63%.