| Geosynthetic Clay Liner(GCL)is an impervious material widely used in the construction of the bottom liner of the landfill.But GCL is a porous medium after all,it is impossible to completely block the migration of pollutants outward.Therefore,it is of great significance to study the transport law of pollutants in landfill leachate in GCL,so as to predict the possible damage of pollutants to groundwater environment.NH4+ is one of the main pollutants in landfill leachate and the main source of biological toxicity of landfill leachate.Because it does not have an effective degradation pathway,it can maintain a high concentration in landfill leachate for a long time.It will cause serious pollution to the soil and groundwater around the landfill.In order to scientifically assess the environmental risks that NH4+ may cause around landfills,it is necessary to study the law of NH4+ migration in GCL.Based on this,this study focuses on the migration law of NH4+ in domestic sodiumbased modified GCL.The research work mainly focuses on the three main convections of NH4+ in GCL(permeability of GCL),molecular diffusion and adsorption.The process unfolds.In terms of permeability characteristics,the main study is the variation of GCL permeability coefficient under the coupling effect of different concentrations of NH4+solution and effective stress.In terms of diffusion characteristics,a self-made diffusion coefficient tester with heating function was used to study the diffusion behavior of NH4+in GCL at different temperatures,and an attempt was made to establish the correspondence between temperature and diffusion coefficient.In terms of adsorption characteristics,under the premise of determining the adsorption mode of bentonite for NH4+,the initial pH,temperature,and coexisting ions of landfill leachate were studied on the adsorption effect of NH4+ on GCL and the adsorption mode.The main results obtained through research are as follows:1.The permeability coefficient of GCL is obviously increased under the penetration of high concentration NH4+solution.In the concentration range used in the test(500-3000 mg/L),the permeability coefficient of GCL continues to increase as the concentration of NH4+ in the penetration solution increases.2.The effective stress can suppress the negative effect of NH4+ on the permeability coefficient of GCL,but the suppression effect is only effective under the NH4+concentration of 2500 mg/L.When the NH4+concentration reaches 3000 mg/L,the suppression effect disappears.3.Temperature will accelerate the diffusion rate of NH4+in GCL.Diffusion coefficient measurement test results show that when the test temperature increases from 25℃ to 45℃and 65℃,the diffusion coefficient increases from 6.2 × 10-10 m2/s to 7.6 × 10-10 m2/s and 9.4 × 10-10 m2/s.4.The adsorption of bentonite to NH4+can be well in line with Langmuir adsorption and Freundlich adsorption mode.The kinetic and thermodynamic fitting results show that the adsorption kinetics process of bentonite to NH4+conforms to the quasi-second-order reaction kinetic model.5.The pH value of leachate has little effect on the adsorption effect of NH4+on bentonite.When the pH value is 7.0,the adsorption effect of bentonite on NH4+is the best.The effect of temperature on the adsorption of NH4+is more significant.As the temperature increases,the amount of NH4+adsorption decreases,but the temperature will not change the adsorption mode of NH4+on bentonite.Coexisting ion Ca2+ strongly inhibits the adsorption of NH4+ on bentonite,and the higher the Ca2+ concentration,the more severe the inhibition;without Ca2+,the adsorption of NH4+on bentonite complies with the Henry equation,and when Ca2+ is present,the adsorption process on NH4+ bentonite is more suitable Describe with Freundlich equation... |
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