Experimental Study On The Migration Law Of Cd(?) In Fly Ash Modified Compacted Clay Cushion

The landfill's cushion is the most critical part of the landfill design.The cushion layer acts as an anti-fouling and anti-leakage effect on the landfill leachate,and is also the last barrier to prevent the landfill leachate from polluting the external environment.Nowadays,the landfill mat is mainly compacted clay.In this paper,fly ash is used to improve the compacted clay cushion,and the feasibility of using compacted fly ash to improve the compacted clay cushion is discussed.Based on the isothermal adsorption experiment,soil column experiment and low temperature nitrogen adsorption experiment,the migration law of Cd(?)in the fly ash modified compacted clay cushion was systematically studied.main tasks as follows:1.The adsorption of Cd(?)in the modified compacted clay cushion was studied under the influence of solid-liquid ratio,reaction time,ion concentration,temperature and pH.It is found that the adsorption process of the modified compacted clay cushion can be described by the Langmuir equation.With the increase of solid-liquid ratio,the maximum adsorption capacity and equilibrium dissociation constant of the two important parameters of the Langmuir equation gradually stabilize.On this basis,The concept of critical soil-water ratio is proposed.The improved compacted clay cushion is a fast process for the adsorption of heavy metals.It is basically stable in 60 minutes.With the increase of ion concentration,temperature and pH,the cushion The adsorption capacity also increases.2.Based on the adsorption experiment,a nonlinear governing equation for contaminant transport considering adsorption is established.The results of soil column experimental data were inverted by Fortran language,and the diffusion coefficient of Cd(II)in compacted clay cushion with ash content of 5%,10%and 15%was obtained.Compared with the clay cushion,the diffusion coefficient decreased by 15.79%,28.21%and 36.84%,respectively,after mixing with 5%,10%and 15%fly ash.3.The single-layer adsorption area and specific surface area of the compacted clay cushion increase with the increase of the amount of fly ash.The integral curve of the adsorption and desorption curves of the clay cushion without the fly ash is“S”type,and the integral curve of the adsorption and desorption curves after the fly ash is "parabolic" It is indicated that after the fly ash is mixed,the pores of the clay cushion are filled,and the width of the pore diameter is also changed from a discontinuous distribution to a continuous distribution.4.The surface morphology of different samples was detected by SEM characterization,which indicated that the fly ash could be filled into the pores of the clay,which reduced the pore width of the clay and reduced the diffusion coefficient of the pollutants in the clay.