The Transport And Transmission Characteristics Of Cd(?)?Cu(?) In Clay Liner Modified By Sludge-based Activated Carbon

The landfill lining anti-seepage system is a key barrier to curb the release of pollutants from landfill.Many pollutants,especially heavy metals,can still penetrate the liner to pollute the surrounding soil and water environment under the action of diffusion.Mixed the clay and SAC with adsorption properties,not only the migration of pollutants can be inhibited effectively,but also the thickness of the liner doesn't need to be increased.In this way,the efficiency of the liner is improved while the construction cost is saved.This is a technological innovation for selection and improvement of landfill lining materials.In this paper,SAC was prepared with 4 factors and 4 levels.The SAC prepared under different conditions were characterized by iodine adsorption test,low-temperature nitrogen adsorption test and scanning electron microscope,and the best SAC preparation conditions were selected.According to the modified clay with different SAC content,the adsorption kinetics test and isothermal adsorption test were carried out,and the pseudo two order equation,Elovich equation,Weber-Morris equation,Langmuir equation and Freundlich equation were combined to explore the kinetic model and isothermal adsorption characteristics of SAC modified clay.With different concentration of heavy metal ion,permeation and reverse pressure and SAC content,the permeability tests of modified clay were carried out.Through the experiments,the following conclusions are drawn.?1?When ZnCl₂ was selected as the activator,the iodine adsorption value was significantly higher than that of other activators,and micropores greater than 1 nm in SAC were highly developed.?2?The adsorption and desorption isotherms of SAC belonged to type IV isotherm.The distribution of pore size was mainly concentrated in 2¹0 nm.The optimal scheme for the preparation of SAC was as follows:the activation agent was ZnCl₂,the activation temperature was 400?,the impregnation ratio was 1:1,and the concentration of activator was 50%.?3?The adsorption equilibrium of SAC modified clay on heavy metal ions increased with time and then tended to be stable.With the increase of the solid particle concentration S/L,the adsorption capacity of the soil samples showed a downward trend,and the adsorption equilibrium qt decreased when the adsorption equilibrium was reached.?4?Adsorption of Cd?II?and Cu?II?by SAC modified clay conformed to pseudo two order kinetics,and the adsorption was mainly on the adsorption of single molecular layer.And SAC had a good effect on the improvement of clay adsorption.?5?Under the action of Cd?II?and Cu?II?solution,the permeability coefficient of SAC modified clay increased first and then decreased and tended to be stable.The permeability coefficient was distributed in the range of 1.10×10^-9 cm/s¹.03×10^-8 cm/s and1.12×10^-9 cm/s⁹.27×10^-9 cm/s,respectively,and the basic requirements of the landfill lining material were met.?6?The response surface model was established by the response of ion concentration,SAC content and permeation reverse pressure.With the increase of the concentration of Cd?II?and Cu?II?,the permeability coefficient of SAC modified clay activated carbon was increased slightly.With the increase of reverse pressure,the permeability coefficient of SAC modified clay was increased.And the content of SAC had no obvious effect on the permeability coefficient of SAC modified clay.