Experimental Study On Separation And Calcined Whitening Of Kaolin From Coal Gangue

Coal gangue in Inner Mongolia,Anhui,Shanxi,Henan and Shaanxi is rich in kaolin and is mined with coal mining.Coal gangue is often treated as tailings after coal washing,which not only causes serious environmental pollution,but also a great waste of kaolin resources.The chemical composition,phase structure,micropotography,minerals distribution and thermal phase transition of coal gangue in Heidaigou mining of Zhunger,Inner Mongolia provience have been analyzed by means of X-ray fluorescence spectrum(XRF),X-ray diffraction(XRD),energy spectrum analysis(EDS),microscope analysis and thermogravimetric analysis(TG-DSC)in this paper.Results show that the kaolin content of the gangue is as high as 70%,and the main impurities are organic carbon,boehmite,pyrite and anatase.Therefore,mineral processing mainly aims to improve the aluminum content and remove the organic carbon,iron and titanium minerals which will decrease the calcination whiteness of kaolin.And the organic carbon is burned quickly by high temperature calcinations,which can effectively improve the whiteness of kaolin and meet the need of industrial production.Because of the big difference in specific gravity of kaolinite and impurities,gravity separation methods of table separation and centrifugal separation are adopted to separate and purify kaolin from coal gangue.Float-sink experiment was carried out to identify the possibility of gravity separation of kaolin.The results show that the organic carbon is mainly concentrated in the low density grade of-2.0 g/cm3,while the mineral impurities such as boehmite,iron and titanium materials are mainly in the high density grade of +2.6 g/cm3.The natural whiteness of the gangue is very low,only 4.50%,but calcined at 950 ?can improve the whiteness rapidly and make the whiteness reach 74.57%.After removing the low density product of-2.0 g/cm3 and the high density product of +2.6 g/cm3,theoretically,the calcination whiteness of the product can reach more than 85%,and the yield can reach 81.37%.The optimum processing condition of table separation is determined.When the angle is 5°,the stroke is 10 mm and the runs frequency is 350 times/min,the calcination whiteness of the kaolin product reaches the highest value of 85.10%and the yield is 50.19%.The mass rate of Al2O3 is 37.26%,and the recovery of Al2O3 is 53.40%.And the total removal rate of TiO2 and Fe2O3 reaches 69.21%.The results of centrifugal separation test show that when the rotary speed is 800 r/min,the feeding speed is 8.4 L/min,the feeding concentration is 20%and feeding time is 100 s,the calcined whiteness of kaolin product reaches the highest value of 78.80%and the yield is 86.31%.The mass rate and the recovery of Al2O3 are 35.62%and 87.79%,respectively.And the total removal rate of TiO2 and Fe2O3 is 34.16%.The whiteness of kaolin can be improved obviously by high temperature calcination.And the whiteness of the calcined product can reaches 85.93%when the mass rate of particle size less than 8.76 mm reaches 90%,the calcination temperature is 950 ? and the constant temperature time is 3 h.The experimental results show that some iron and titanium impurities can be removed from coal gangue by centrifugal separation and table separation.Further fine grinding and high temperature calcination of kaolin after separation can improve the calcination whiteness of kaolin to a great extent.The research could provide a technological scheme for the preparation of high quality kaolin products from coal gangue which will benefit to the utilization of coal gangue.