Transport Of Ball-milled Biochar In Saturated Porous Media And Its Interactionwith Cd (Ⅱ)

Biochar is a promising and important multifunctional material,and plays an increasingly important role in the field of carbon sequestration,soil fertilization and remediation,and contaminant immobilization.In recent years,there developed many methods to modify biochar,but those methods would produce a series of environmental problems.Ball milling technology,commonly used in the field of mechanochemistry,is the very method which is very friendly to the environment and wouldn’t produce any pollutants.In this study,ball-milled biochar（BMBC）was prepared via an optimized ball milling method.BET,FT-IR,SEM.EDS etc.were used to characterize BMBC.Those results reveal the changes of properties of biochar before and after ball milling.Column experiments and batch adsorption experiments were used to evaluate the transport behavior of BMBC in saturated porous media.This study focused on the effect of particle sizes of granular porous media,flow velocity,pH and ionic strength,the coupling effect of humic acid and different cation types,and the interactions between Cd and BMBC.These researched are of great significance for the scientific and objective evaluation of the environmental effects and potential threats of BMBC.This study yielded the following conclusions:（1）After ball milling,the average particle size of biochar was 267 nm.The specific surface area was increased from 84.39 m² g^-1 to 179.31 m² g^-1.The surface elements,including carbon（C,73.37%）,oxygen（O,18.47%）,phosphorus（P,0.77%）,calcium（Ca,5.10%）,magnesium（Mg,1.27%）,aluminum（Al,0.35%）and potassium（K,0.31%）were merely changed,and with it the types of surface oxygen functional groups,such as hydroxyl group（-OH）,carboxyl group（-COOH）,carbonyl group（-CO）,ketone group（-OR）or others.Functional groups changed in quantities,not types.（2）High flow rate and pH,large medium size and low ionic strength promoted transport of BMBC.Flow velocity and medium size mainly affected the properties of quartz sand column.Reduction of the dispersion coefficient of quartz sand column raised transportability of BMBC.The stability of BMBC was mainly influenced by pH and ionic strength.Low pH and high ionic strength made BMBC become unstable and aggregate,thus increased the particle size and subjected to greater blocking effect.（3）The presence of humic acid strongly facilitated transport of BMBC,and the higher the concentration of humic acid,the stronger facilitated effect.The cations of different valence states had different effects on the transport of BMBC.High valence cations had a greater retardation effect on BMBC transport,and this retardation further increases as their ionic strength increased.When humic acid and different valence cations were present at the same time,the roles of the two exhibited certain antagonistic effects.（4）The results of the batch adsorption experiments showed the theoretical maximum adsorption capacity of BMBC for Cd was 26.95 mg g^-1,and adsorption achieved an equilibrium in the first 60 min.Due to the strong adsorption of Cd by BMBC,existence of BMBC in the medium led to the decrease of effluent Cd and releasing Cd at a slow rate.The presence of a small amount of Cd in the solution environment slightly inhibited the transport of BMBC.Contrarily,BMBC facilitated Cd transport in porous media after adsorption.