A procedure is described in which kaolin and NaHSO 4 are heated in a furnace at temperatures between 200 and 1000 °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 °C and decreasing sharply beyond this temperature. The Ti reaction yield values were lower than the Al reaction yield, showing a maximum at 400 °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. Brunauer−Emmett−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 Na 3 Al(SO 4 ) 3, NaAl(SO 4 ) 2, NaAl(SO 4 ) 2 · x H 2 O ( x = 6 and 12), Na 3 H(SO 4 ) 2, Al 2 O 3, Na 2 SO 4, and mullite.
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Colina et al. (2005) studied this question.
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