Manufacture of low-soda alumina from clay

The manufacture of low-soda alumina from clay was studied with a major concern in morphological changes during thermal decomposition of the aluminum chloride hexahydrate (AlCl3 . 6H(2)O) derived from clay and calcination of the resultant amorphous alumina. The temperature was varied from 300 to 900 degrees C for decomposition and from 1100 to 1400 degrees C for calcination. Changes in the BET surface area, porosity, and scanning electron microscopic image of the powder surface were observed under the varying conditions of decomposition and calcination. These transitional behaviors then were compared with those of aluminum hydroxide, which has long been used for the commercial production of alumina. A low-soda alumina could be made directly by the thermal decomposition of aluminum chloride hexahydrate derived from clay, whereas an extra step is required to reduce the sodium content with the Bayer process.