| In China,there are abundant resources of microcrystalline graphite,however,of which the utilization is really low.Therefore,the increase of the additional value of microcrystalline graphite products is badly needed.Under this background,a series of researches on micro-crystalline graphite from different mining areas in Chenzhou,Hunan Province is carried out and some conclusions are drawn in this paper.High-purity expanded microcrystalline graphite is made by purification,oxidation-intercalation and thermal expansion,whose indicators reach the standard of Graphite Anode Material for Lithium Ion Battery(GBT 2453-2009).The change rules of microstructure and electrical conduc-tivity during intercalation and expansion of graphite with different mineralogical characteristics are described systemically in this paper,along with the analysis of the adsorption behavior of Pb2+ onto expanded graphite.According to the different mineralogical characteristics of microcrystalline graphite,those researches also put forward the corresponding development and utilization direction of it,which is beneficial to the rational use of microcrystalline graphite resources and to the increase of the additional value of the products.The research on microcrystalline graphite from different mining areas in Chenzhou,Hunan Province shows that its fixed carbon content ranges from 77.40%to 86.39%,and the mineral components are primarily graphite,chlorite,quartz,calcite and muscovite.The micro-crystalline graphite is mainly of 2H-graphite which contains 3R-graphite of 14.99%?21.63%as well.The graphitization degree of microcrystalline graphite has a certain gap compared with the crystal structure of crystalline graphite.Micro crystalline graphite have good stability in alkaline aqueous solution and its resistivity increases with increase of the disorder structure(the value of ID/IG).The sample of HL5-2T whose resistivity is an order of magnitude higher than other samples has more structure defects and crystallite edges.In order to obtain high purity microcrystalline graphite,the sample of HJC is purified by alkali/acid leaching method and ultrasonic-mixed acid method,respectively.In alkali/acid leaching process,sodium hydroxide can not destroy crystal structure of silicate minerals(such as quartz and mica)completely due to the limitation of water bath temperature,which results in poor purification effect.However,impurities are dissociated and removed quickly in ultrasonic-mixed acid process,and the fixed carbon content of purified microcrystalline graphite is more than 99.9%.Meanwhile,there is no obvious change in the lamellar structure.Finally,the high purity microcrystalline graphite with different structural defects and disorder degree are obtained via an optimized ultrasonic-mixed acid process on HJC and HL5-2.The high purity microcrystalline graphite samples of HJC-C and HL5-2C are used as raw materials to prepare oxidized microcrystalline graphite by modified Hummers method,and the expanded micro-crystalline graphite was prepared via heat treatment at 900?.In the period of oxidation and intercalation,the structural defects and disorder degree of HJC-C-nKP increase with the increase of oxidation degree.Nevertheless,the structural defects of HL5-2C-nKP increases,but the disorder degree of structure reduces greatly at the same time.In the period of thermal treatment,the structural defects and disorder degree of HJC-C-nP reduce,whereas the structural disorder degree of HL5-2C-nKP increases.HL5-2C is more easily oxidized than HJC-C,and the amount of KMnO4 consumes when fully oxidized is also greater.The structural layers of two series of oxidized microcrystalline graphite samples are connected with oxygen-containing functional groups such as hydroxyl,carboxyl and epoxy.The content of oxygen-containing functional groups reduces and the interlamellar space of series of expanded microcrystalline graphite samples increases after the thermal expansion.The structural characteristics of microcrystalline graphite have a significant influence on the conductivity of expanded graphite.The resistivity of the HJC-T and its reaction products are less than that of HL5-2T and its reaction products under the same conditions.And there is no correlation between the resistivity and the ID/IG value when microcrystalline graphite is oxidized.The anion concentration,compac-tion density and trace metal concentration of two series of expanded microcrystalline graphite samples reach the standard of Graphite Anode Material for Lithium Ion Battery(GBT 2453-2009)after purification,oxidation-intercalation and thermal expansion.It is concluded that samples of HJC-C-0.4P and HJC-C-0.8P with low oxidation degree are more suitable to be used as anode materials for lithium ion batteries,considering two aspects of the interlamellar space and the conductivity of samples.The samples of HJC-C-1.6P and HL5-2C-1.6P with high oxidation degree have abundant pore structure and high specific surface area.The research on the absorption behavior of Pb2+ onto the two expanded microcrystalline graphite shows that the absorption behavior is affected by initial concentration,time,pH,adsorbent dosage and temperature.The amount of adsorption is positively correlated with initial concentra-tion,time and pH,and negatively correlated with adsorbent dosage and temperature.The absorption of Pb2+ is attributed to monolayer adsorp-tion,and the adsorption process accords with Langmuir isotherm model and pseudo-first-order kinetic model.The adsorption of Pb2+ is a spontaneous,exothermic,and orderly adsorption process,which belongs to physical adsorption.The amount of adsorption and adsorption rate of HL5-2C-1.6P are greater than that of HJC-C-1.6P under the same conditions,which indicates that the adsorption property of HL5-2C-1.6P is better.The researches of this paper embody the characteristics from mineralogy to mineral materials,which can provide some mineralogical data and application technology reference for exploitation and utiliza-tion of micro crystalline graphite.These researches have significant theoretical meaning and prominent social and economic value. |
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