Study On Purification And Processing Of Aphanitic Graphite And Adsorption Of Heavy Metals Using The Products

Amorphous graphite is featured by the plentiful reservation,low graphitization,small size and easy oxidation,leading to be a low-cost raw material for the preparation of graphene.Currently,graphene is synthesized with the ultrapure amorphous graphite of 99% purity,which obtained from the deep purification of flotation concentrates through the leaching of acidic-basic method and hydrofluoric acid method.On the other hand,the purification could be simultaneously realized in the preparation of graphene oxide.Therefore,it might be efficient way to synthesize graphene oxide by using a low-purity amorphous graphite as the raw material.In addition,in the multi-stage of grinding/flotation,long time of strong collision between steel balls and graphite sheets would result in the strong contamination of iron on graphite surfaces.This iron contamination has to be removed before the graphite products could be accepted by the markets.This study worked on the preparation of graphene oxide adsorbent for Zn(II)and Cd(II)removal from water with low-purity amorphous graphite concentrates as the raw material.The concentrates were obtained multi-stage of grinding/flotation process,containing various grades of graphite with different recovery.The objectives are to verify the possibility of synthesizing graphene oxide adsorbent with low-purity graphite concentrate.Also,based on that iron-beard particles might strongly adsorb arsenic in water,the iron-contaminated graphite concentrate was tested as the adsorbent for eliminating As(V)from water.The main conclusions have been achieved as follows:(1)The graphene oxide sheets synthesized with low-purity amorphous graphite contained a large amount of oxygenous groups with the thickness of about 2 nm,leading to be a good adsorbent for Zn(II)in water.The adsorption obeyed to pseudo-second-order kinetics model and Langmuir isotherm.The adsorption mechanism was attributed to the complexation of Zn(II)with the hydroxyl and carboxyl ions on graphite oxide surfaces,while the electrostatic attraction between cation Zn(II)and the negative surfaces helped the approaching of Zn(II)to the surfaces.(2)The graphene oxide synthesized from low-purity amorphous graphite is a good adsorbent for Cd(II)in water with the adsorption capacity of 1792.6 mg/g.The adsorption obeyed to Langmuir isotherm and pseudo-second-order kinetics model.The adsorption mechanism was attributed to the chemical adsorption and the functional group on the surface of the graphene oxide helped the adsorption.(3)Iron-contaminated graphite concentrate is a good adsorbent of arsenic in water,which might be a potential way to be used for arsenic removal from water because of the low costs.The mechanisms were due to the large surface area and numerous adsorption sites for arsenic on the graphite surfaces.In summary,this work presented a novel concept,systemic and integrative researches for the purification of amorphous graphite,synthesis of graphene oxide and application as adsorbent.This research might be greatly significant for the application of amorphous graphite in water treatments.