| Most layered silicates are important nonmetallic minerals, and they are endowed with many process properties such as plasticity, fire resistance, and chemical stability etc. for their special crystal structure. They are widely used in fields of ceramic, rubber, coating, fire resistance materials etc. Nanometer porous material, high quality ceramics and fire resistance materials with layered silicates had been made in both domestic and overseas with quick development of functional materials.In the text, three representative layered silicates are chosen as research objects, structural transformation and acid dissociation behaviors of aluminum of kaolinite, pyrophyllite and illite, were studied by Thermogravimetry-Differential scanning calorimetry (TG-DSC), Aluminum-27 Magic angle spinning nuclear magnetic resonance (Al MAS NMR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) etc.. The results provide a theoretical base for preparation nanometer porous materials, high quality ceramics and fire resistance materials etc. by using layered silicates. It can be concluded as follows:1) Thermal behaviors of aluminum of layered silicatesKaolinite: Al-O octahedral sheets remain AlⅥunder 450℃in kaolinite; hydroxyl groups are removed from 450℃to 550℃, kaolinite transforms to metakaolin, and AlⅥchanges into AlⅣ, AlⅤbecause of dehydroxylation; from 550℃to 991℃, there exsits coordination of AlⅣ, AlⅤ, AlⅥin metakaolin; accompanied by formation ofγ-Al2O3 and mullite above 991℃, the aluminum's structure changes to AlⅥand AlⅣPyrophyllite: Phase composition is pyrophyllite with AlⅥunder 500℃; between 500℃to 932℃, hydroxyl groups are removed, and pyrophyllite transforms into dehydrated pyrophyllite, whose coordinations of aluminum are AlⅣAlⅤand AlⅥ; from 932℃to 1141℃, aluminum's phase changes into dehydrated pyrophyllite and primary mullite; above 1141℃, the formation of mullite causes the change of aluminum structure to AlⅣand AlⅥ. Illite: aluminum structures are AlⅣand AlⅥas a result of substitution of Al3+ for Si4+ in tetrahedra of illite below 543℃; from 543℃to 1001℃, OH groups are removed, and illite transforms into dehydrated illite with three aluminum structure of AlⅣ, AlⅤ, AlⅥ, but few quantity of AlⅤ, between 1001℃and 1181℃, and the main phases are dehydrated illite; above 1181℃, aluminum phases change into mullite with AlⅣand AlⅥ.2) Acid dissociation behaviors of aluminum of thermally activated layered silicatesIt was shown that the acid dissociation of aluminum of thermally activated kaolinte is better than those on activated pyrophyllite and activated illite.Kaolinite: The acid dissociation of AlⅥof kaolinite raw ore is bad, after thermal treatment, the acid dissociation properties of different coordination aluminum of metakaolin are different, AlⅤof metokaolin is well, while AlⅣand AlⅥof metakaolin is bad; however, AlⅣand AlⅥofγ-Al2O3 and mullite are unable to dissolve in acid. Results obtained by acid dissociation shows a maximum Al2O3 leaching ratio of 97% can be obtained under the conditions of activating at 900℃for 15min, and acid leaching at 120℃for 120min with mass fraction 20% of HCl solution, and liquid/solid of 10. Specific surface area increases from 22.42 m /g of kaolinite to 304.84 m /g of leached kaolinite.Pyrophyllite: When activation temperature goes up to 750℃, the acid dissociation of aluminum in pyrophyllite is improved; but the acid dissociation properties of aluminum in dehydrated pyrophyllite are very bad, AlⅣand AlⅥof mullite are unable to dissolve in acid. Results of acid dissociation show that Al2O3 leaching ratio reaches a maximum of 20.38% under the conditions of activating at 750℃for 15min, and acid leaching at 150℃for 120min with mass fraction 20% of H2SO4 solution, and leaching liquid/solid of 5.Iillite: Compared to kaolinite and pyrophyllite, the acid dissociation properties of aluminum of thermally activated illite are the worst. The acid dissociation of illite is the best at the activating temperature of 650℃, few aluminum of dehydrated illite dissolves in acid, but AlⅣand AlⅥof mullite are unable to dissolve in acid. Results of acid dissociation show that Al2O3 leaching ratio reaches a maximum of 16.13% under the conditions of activating at 650℃for 15min, and acid leaching at 150℃for 120min with mass fraction 20% of H2SO4 solution, and leaching liquid/solid of 5.
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