ALUMINA PRODUCTION BY NITRIC ACID EXTRACTION OF CLAY

摘要

There is provided an economically feasible and attractive process for the extraction of alumina values from clay using nitric acid comprising the steps of: 1. pelletizing the clay into generally spherical particles having a diameter of between about 5-8 and about 1 mm and a free moisture content of between about 17 and 22%; 2. calcining the pellets formed in step 1 at a temperature of between about 1100 and 1550.degree.F in a fluidized bed reactor; 3. extracting the calcined clay pellets obtained in step 2 in about 30 to about 40% nitric acid for a period of between about 1 and about 4 hours at atmospheric pressure and a temperature of between about 220 and about 270.degree.F to produce an aluminum nitrate product solution comprising between about 8 and 13 weight percent: alumina and between about 5 and about 20% less nitric acid than required by stoichiometry to form normal aluminum nitrate(i.e., a "basic" solution of aluminum nitrate); 4. purifying the "basic" aluminum nitrate product of step 3 by (a) precipitation of iron oxide by holding the product of step 3 for a period of at least about 2 hours and at a temperature of between about 80 and about 120.degree.C in the presence of a small amount (about 1 to about 3%) of iron oxide seed material; and (b) filtering the liquor derived from step 4(a) through a bed of the solids remaining from step 2 in the presence of a suitable flocculant to remove siliceous impurities, 5. crystalizing aluminum nitrate nonahydrate from the product of step 4(b); 6. decomposing the crystalized aluminum nonahydrate produced from step 5(a) in at least a three-step process involving: (a) evaporation of nitric acid from the molten crystals to provide a solution of basic Aluminum Nitrate containing at least about 16.5 and preferably at least about 20% by weight alumina and recovery of the heat of condensation of the vapors thus produced; (b) low temperature decomposition of the basic aluminum nitrate liquor to infusible basic aluminum nitrate solids at a temperature of between about 150 and 200.degree.C; for a period of at least about 1/2 hour; and (c) further decomposition of infusible basic aluminum nitrate solids in one or two stages at a temperature of between about 600 and 1300.degree.F for a period of from about 2 to about 7 hours; 7. calcining the residual metallurgical grade alumina at a temperature of between about 1900 and 2200.degree.F, and 8. reconstituting to nitric acid the NOX gases from step 6(c).