Preparation And Characterization Of Magnetic Biochar And Its Adsorption Properties Of Inorganic Ions

Magnetic modification,as one of biochars modification methods,was a new idea for soil remediation.As a composite absorption material,magnetic biochars can strengthen the effect of passivation of heavy metals in soil and magnetic properties of iron oxide minerals can separate biochars from soil after application.These unique features can reduce the risk of heavy metal transportation in the soil environment.In this dissertation,the material properties of magnetic biochars produced at different pyrolysis temperatures（200℃,400℃,600℃）and their adsorption behavior of Cd（II）and NO₃^-were carefully investigated.In order to achieve this goal,pine chip and corn straw were chosed as raw biomass and the magnetic biochars were made as follow:the biomass were magnetized through chemical co-precipitation method and followed by hydrothermal activation and pyrolysis under N₂atmosphere for carbonization（where choosing pyrolysis temperature as 200°C,400°C and600°C）;then the produced magnetic biochars materials were washed by water and ethanol constantly.The final results and conclusions we obtained were as follow:（1）surface area and alkaline functional groups of magnetic biochars made from pine chip（MBP）was improved as pyrolysis temperature increases;while surface area of corn straw magnetic biochars（MBC）showed no change.The ash content and atom ratio containing O/C and（O+N）/C of MBC is higher than MBP and increased gradually as pyrolysis temperature increases.After washing by water-ethanol,the ferrite particles on the surface and in the pore channel of magnetic biochars were exfoliated for both MPB and MPC,and the specific surface area and the amount of surface negative charge was increased.（2）MBs at 400℃ showed the best adsorption capacity for Cd（II）;but after washed by water-ethanol,the adsorption capacity of Cd（II）for both magnetic biochars decreased,especially for MBP.（3）The fitting results of Langmuir model and Freundlich model showed that Freundlich model was suitable for describing the adsorption of Cd（II）on pine wood,magnetic pine,MPB and MPC pyrolytic above 200°C.As pyrolysis temperature increasing,the heterogeneous adsorption of MBP is enhanced,but the MBC showed the opposite results.For the samples washed with water-ethanol,the Langmuir model is suitable to describe their adsorption of Cd（II）and the results showed,after washing,the heterogeneous adsorption for all samples decreased.（4）Magnetic biomass showed the highest adsorption capacity for NO₃^-.As pyrolysis temperature increasing,the adsorption capacity for NO₃^-by MBP and MBC（including water-ethanol washed samples）showed no obvious change.This result indicated that the magnetization enhanced the NO₃^-adsorption capability,and washing process helped to exposure active NO₃^-adsorption sites.（5）Fitting result shows that Freundlich model are suitable for describing the process of isothermal adsorption of NO₃^-by MBs.After water-ethanol washing,MBs’heterogeneity adsorption effect for NO₃^-was enhanced.