The Study On Effect Of Nano-biochar On Transport Of Cd And Pb In Saturated Porous Media

Biochar is widely used as an effective heavy metal adsorbent material.However,nanobiochar can carry pollutants and migrate,which poses a potential threat to the groundwater environment.In this paper,ginkgo biloba leaves were used as raw materials to prepared ginkgo biloba biochar and magnetic ginkgo biloba biochar.Ball-milling modification was performed to prepare nano-biochar.Scanning electron microscope(SEM),energy spectrometer(EDS),X-ray diffractometer(XRD),BET,fourier transform infrared spectrometer(FTIR)were used to characterize biochar.And hysteresis loop test(VSM)was used to test the magnetic properties of materials.By carrying out indoor static adsorption experiments and column elution experiments,the adsorption of Ginkgo biloba biochar(BC)and its nano-biochar(MBC),magnetic biochar(HBC),and nano-magnetic biochar(MHBC)on Cd and Pb were studied.The removal performance and the migration of Cd and Pb in the quartz sand column were affected by biochar and other physical and chemical factors during the process.The adsorption characteristics of Cd and Pb and the competitive adsorption characteristics of Cd and Pb on biochar were revealed by the four kinds of biochars made of ginkgo biloba as raw materials,and the migration law of nano-biochar in cooperation with Cd,Pb and Cd,Pb systems was clarified.The results of this study can play a certain theoretical guidance and theoretical basis for the process of using modified nano-biochar to remediate soil and risk assessment.(1)The adsorption isotherm experiment results of Cd and Pb on BC,HBC,MBC and MHBC showed that Langmuir was the best fitting model.This result indicated that the adsorption behavior was monolayer adsorption.And the adsorption performance was MHBC>MBC>HBC>BC.The effect of ball milling to improve the adsorption performance was more obvious than the effect of adding magnetism.The adsorption kinetics experiment showed that the adsorption of Cd and Pb by the four kinds of biochar conformed to the quasitwo-stage dynamic adsorption model.The result indicated that the adsorption of heavy metals by biochar was a physical-chemical compound behavior.(2)There were competitive adsorption of Cd and Pb on biochar,and Pb had a more competitive advantage for the adsorption site.In the competitive adsorption of Cd and Pb,for MBC and MHBC,the adsorption capacity of Cd was more easily affected by the competitive relationship.(3)With the increased of ionic strength,the adsorption amount of Cd and Pb by BC,HBC,MBC and MHBC were all decreased.With the increased of p H,the adsorption amount of Cd by biochar increased,and the adsorption amount of Pb showed increased first and then decreased.Compared with BC and HBC,the adsorption of Cd and Pb by MBC and MHBC was less affected by ionic strength and p H.Ball-milling can increased the stability of biochar adsorption of heavy metals.(4)The recovery rate of nano-biochar migration in saturated porous media decreased significantly with the increased of ionic strength and decreased of flow rate.Compared with MHBC,the migration of MBC was more susceptibled by IS changed.(5)When biochar entered the sand column,it would carry part of the Cd and Pb that were previously retained in the sand column,and MBC was easier to carry Cd and Pb to migrate than MHBC.Cd and Pb could affected the mobility of each other when they migrated at the same time.(6)The outflow of MBC was greater than MHBC.And the promotion effect of MBC on Cd and Pb was stronger than MHBC.