High-Temperature Reaction of Kaolin with Sodium Hydrogen Sulfate

A procedure is described in which kaolin and NaHSO4 are heated in a furnace at temperatures between 200 and 1000 (degree)C. Parameters studied were the reaction temperature and time, proton to alumina molar ratio, calcination temperature and time, and reaction atmosphere. The Al reaction yield grew until reaching a maximum at a reaction temperature of 700 (degree)C and decreasing sharply beyond this temperature. The Ti reaction yield values were lower than the Al reaction yield, showing a maximum at 400 (degree)C and decreasing smoothly as the reaction temperature was increased. The Fe reaction yield showed a maximum in the same range of reaction temperature as Al. Precalcination of kaolin produced only slight increases in reaction yields. BrunauerEmmett-Teller (BET) surface area tests indicated an increase of the BET surface area for short reaction times, reaching values above 100 m^2/g. Products of the reaction were Na3Al(SO4)4)3, NaAl(S04)2, NaAl(SO4)2.xH2O (x = 6 and 12), Na3H(SO4)2, Al2O3, Na2SO4, and mullite.