Preparation Of High-purity And Nanometer Al₂O₃Powder Using Qionglai Kaolin

Kaolin resources are rich in Qionglai. Using Qionglai kaolin as a raw material toprepare alumina powder can improve the kaolin’s additional value and economicefficiency. This is consistent with ‘the production of high add-on product’ idea todevelop Qionglai kaolin. It also can reduce the production cost of alumina.In this paper, synthesis nanometer Al₂O₃powder from Qionglai kaolin wasstudied, which involved four processes of calcined activation, hydrochloric acidleaching, purification by alkali and preparation of nano-alumina.In the step of activation, the chemical composition and physical phase of thekaolinite ore were analyzed by X-Ray Fluorescence （XRF） and X-Ray Diffraction（XRD）, The morphology and thermal and thermogravimetric were characterized byscanning electron microscope （SEM） and DTA-TG respectively. The phase transitionof kaolinite under various calcining temperature were studied with XRD. The resultshowed that significant weight lost at750℃. The crystal kaolin transformed fromcraystalling phase to amorphous metakaolinite. The activity of metakaolinite washigher and was easier to acid leached. But the hyperpyrexia could make the amount ofthe quartz increase, and the activity reduced. Therefore, the optimal activatedtemperature of kaolin is750℃.During hydrochloric acid leaching, some preparing factors on leaching rate wasstudied, such as reaction time, temperature, molar ratio of reactants. The experimentaldatas showed that the higher leaching rate could be achieved at a higher temperaturefor a longer time. Al extraction was83.4%with20wt%HCl and1/3.5molar ratio ofAl/HCl at95℃,2.5h reaction time.Purification of the leaching fluid was investigated with respect to concentration ratio of Al/NaOH and reaction temperature. The concentration of Fe³⁺in the filtratehas be reduced by98.7%as well as Ti⁴⁺by99.1%. The optimum parameters aren（Al）/n（NaOH）=1/5, pH=12¹3, reaction temperature of60℃and reaction30min.Nano-alumina powders were prepared by pyrolysis of the aluminium precursorpowders, ammonium aluminum carbonate hyroxide （AACH）. The precursor wassynthesized by precipitation method under ultrasonic radiation using AlCl3andNH4HCO3as raw materials. The effect of pH value, aging time, ultrasonic energy onthe reaction was researched. After deionized water washing, ethanol washing,centrifugation and vacuum drying, AACH was directly calcined at800℃and1150℃.The changes of the phase structure, particle size and morphology of AACH andaluminum powder were investigated by means of XRD and SEM. The optimumprocess condition was that AlCl3（PEG-6000） solution was added into NH4HCO3solution under ultrasonic radiation80W at pH=9with aging time20h. Particle size of-Al₂O₃is around50nm. Synthesized AACH in ethanol-water solvent, we can accesssmaller nano-powder. Particle size about20nm γ-Al₂O₃was prepared by calciningAACH precursor at800℃. Free-aggregation and high purity-Al₂O₃powders withparticle size about40nm was prepared by calcing AACH precursor at1150℃.