PROCESS FOR PRODUCING ALUMINA OF LOW RESIDUAL NITRATE CONTENT FROM BASIC ALUMINIUM NITRATES

1,216,962. Alumina. ALLIED CHEMICAL CORP. 14 July, 1969 [21 Nov., 1968], No. 35423/69. Heading C1A. Alumina is made feeding to a fluidized bed solid particulate basic aluminium nitrate of formula Al 2 O 3 .pN 2 O 5 . 3 H 2 O where p is 1À2-1À65 and z is 3À64-7À21, and maintaining the nitrate in the bed at a temperature of at least 470‹ C. until the resulting alumina contains not more than 0À02 mole of N 2 O 5 per mole of Al 2 O 3 . The basic aluminium nitrate is that which has been obtained by (i) heating aluminium nitrate nonahydrate under superatmospheric pressure at a temperature high enough to cause decomposition but not above 230‹ C., and for a time until 45-60% of the nitric acid values originally in the nitrate have been removed as gaseous decomposition products; (ii) reducing the pressure to atmospheric or below; (iii) cooling the molten residue from (ii) to below its softening point. The fluidizing gas may be N 2 , and the particulate basic aluminium nitrate is preferably of a size that passes through a 40 mesh, but is retained on a 100 mesh screen (U.S. standard). The resulting alumina, whichis partly in the form of hollow spherules, is calcined to alpha-alumina at temperatures of :at least 1000‹ C.