Aluminum Company of America

Lawrence Keith Hudson

Thomas G Swansiger

Kenneth I Savage

John M Stinson, Jr

Back reactions of dissolved alumina from a high caustic-lime digest of anorthosite and other alumina-containing siliceous materials can be eliminated or mitigated by control of particle size of digestible material; and time and temperature of separation of the alumina-bearing liquid from the solid residues. In one embodiment the back reaction is further controlled by adjustment of the caustic concentration of the digest effluent.

Process for recovery of alumina from high-silica ore

An improved process is provided for the recovery of sodium aluminate crystallized from a digest of caustic and lime with high-silica aluminous materials. The digest solution is concentrated by evaporation and then seeded with Na.sub.2 Al.sub.2 O.sub.4.2.5H.sub.2 O crystals to crystallize alumina from the solution as Na.sub.2 Al.sub.2 O.sub.4.2.5H.sub.2 O. The crystals are then separated from the mother liquor solution by filtration or centrifugation. The crystals are then washed with a solution having a lower caustic content than the mother liquor and an alumina concentration of about 50 grams per liter to remove any mother liquor remaining on the crystals. The sodium aluminate crystals are used as a feed for a subsequent Bayer processing step.

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Oakmont, PA, United States of America

Lawrence Keith Hudson