GB1311614A - Method for extracting pure alpha-alumina from clays - Google Patents

Abstract

1311614 Producing Al 2 O 3 from clay ARTHUR D LITTLE Inc 18 March 1971 7240/71 Heading C1A α-Al 2 O 3 is produced by calcining clay, leaching with aqueous HNO 3 , flocculating and removing solids, contacting the leach liquor with an extractant dissolved in a water-immiscible organic solvent to extract Fe, feeding the aqueous Al(NO 3 ) 3 solution into a fluidized bed to form Al 2 O 3 and HNO 3 vapour, and heating the Al 2 O 3 to remove residual NO 3 and form α-Al 2 O 3 . Calcination may be effected at 700- 850‹ C. in a fluidized bed, rotary kiln, or shaft kiln. Leaching may be effected at 100-145‹ C. using 35-55 wt. per cent HNO 3 , at or above atmospheric pressure. The extractant may be di - (2 - ethylhexyl) - hydrogenphosphate with tributul phosphate or a high M. wt. primary amine dissolved in kerosene. The extraction may be effected at 50-60‹ C. in countercurrent using an aqueous/organic volume ratio of 2/1 to 10/1. The fluidized bed may be operated at 150-350‹ C., with gases in the bed containing 25-45 vol. per cent H 2 O vapour to hydrolyse the A1(NO 3 ) 3 . Additional H 2 O may be injected into or below the bed, or may be produced by combustion of the fuel used to heat the bed. Solids may be withdrawn in the gases and/or from an overflow. The final heating may be carried out in a pebble heater in one step at 1000‹ C., or in a first step at 400‹ C. followed by a 2nd step at 1000‹ C. in a rotary kiln. The N oxides evolved may be converted into HNO 3 and recycled together with HNO 3 from the fluidized bed heating. The loaded extractant may be washed with water, stripped with aqueous HC1, washed with water, and recycled.