Effect Of Nano-Biochar On Transport Of Cd In Heterogeneous Media

As an effective means of carbon sequestration and soil remediation,biochar has been paid more and more attention.However,biochar particles,especially nano biochar particles at the nanoscale,may carry contaminants along the soil profile and pose a potential hazard to groundwater.In this paper,ramie biochar was first prepared from ramie rods and modified with nano-zero valent iron,and then biochar and modified biochar were prepared by mechanical ball milling to produce nano-scale biochar.In this thesis,the cadmium adsorption performance of nano-biochar was investigated,and the mechanism of nano-biochar adsorption of cadmium was analyzed.Secondly,the migration behavior of nano-biochar in heterogeneous media was studied by column experiments under different physical and chemical conditions,and the migration characteristics of nano-biochar in heterogeneous media were explained.Finally,the synergistic migration behavior of nano-biochar and cadmium in heterogeneous media was understood,and the migration law of nano-biochar and heavy metals in heterogeneous media was clarified.This article discussed the effects of nano-biochar and cadmium migration in the environment,which had important guiding significance for the environmental impact of the use and promotion of biochar.（1）The results of adsorption studies on cadmium by biochar indicated that the adsorption capacity of zero-valent iron modified nano-biochar（n ZVI-BC）for Cd²⁺was44.64 mg g^-1,which was greater than the adsorption capacity of nano-biochar（MNBC）for Cd²⁺by 40.82 mg g^-1.The adsorption of biochar to Cd²⁺belonged to a fast adsorption process and conformed to the quasi-second-order dynamic adsorption model.The adsorption of nano-biochar to Cd²⁺was a physical-chemical composite process.The fitting degree of langumir equation of MNBC and n ZVI-BC（R>0.99）was significantly higher than that of freundlich equation,indicating that the adsorption process of MNBC and n ZVI-BC to cadmium was monolayer adsorption.（2）The migration of nano-biochar in heterogeneous media under different physical and chemical conditions was investigated.It was found that increasing flow velocity and low ionic strength could promote the migration of nano-biochar.The outflow rate of MNBC in heterogeneous media was higher than n ZVI-BC.At the same time,because of the different structure of clay minerals,the retention amount in heterogeneous media was from small to large:pure quartz sand<Illite-coated quartz sand<Smectite-coated quartz sand.（3）The research on MNBC and n ZVI-BC’s coordinated migration of cadmium showed that Cd²⁺had a higher migration ability when it migrated alone in the quartz sand column,but the migration ability was weakened in the clay sand coated with clay minerals.Cadmium-contaminated sand columns were washed with different types of biochar which in order to promote the release and further migration of Cd²⁺,while the MNBC promoted more better than n ZVI-BC.According to the experiments of MNBC and n ZVI-BC facilitated Cd²⁺transport on cadmium migration,MNBC promoted Cd²⁺better than n ZVI-BC.This was because of the zeta potential of n ZVI-BC was higher than MNBC,and the adsorption capacity of Cd²⁺was reduced.In addition,for different types of biochar migration methods for Cd²⁺migration,the outflow rate of Cd²⁺in the facilitated migration experiment was higher than the total outflow rate for washing the polluted sand column.This was because of the adsorption sites of the porous media were occupied by biochar nanoparticles during the common migration,which was beneficial to the migration of Cd²⁺.