Preparation of alumina of improved purity by iron removal

Claim 2

The process of claim 1 wherein a temperature for the contacting is from about 150* F. to about 225* F.

Claim 3

The process of claim 1 wherein a temperature for contacting is from about 160* F. to about 200* F.

Claim 4

The process of claim 1 wherein the surface area of the seed is from about 3 square meters per liter to about 9 square meters per liter of said moving stream.

Claim 5

The process of claim 1 wherein the surface area of the seed is from about 1 square meter per liter to about 20 square meters per liter of said moving stream, the alumina content of the stream is such that the Al2O3 to total caustic ratio of the stream is from about 0.3:1 to about 0.8:1 and the liquor holding time is from about 5 minutes to about 30 minutes.

Claim 6

In a process for reducing the iron content of sodium aluminate liquor by seeding with alumina hydrate, the improvement which comprises contacting a moving stream of sodium aluminate liquor having an Al2O3:total caustic ratio of from about 0.3:1 to about 0.8:1 with sufficient alumina hydrate seed to provide a seed surface area of from about 1 square meter per liter to about 20 square meters per liter of said moving stream of sodium aluminate liquor for a liquor-holding time of from about 5 minutes to about 30 minutes, with substantially no longitudinal mixing of said sodium aluminate liquor with said alumina hydrate, thereby precipitating not more than about 10 grams of iron-containing alumina hydrate per liter of said stream of sodium aluminate, and separating a resulting stream of sodium aluminate of reduced iron content from the precipitated iron-containing alumina hydrate.

Claim 7

The improvement of claim 7 wherein the process is continuous, said contacting and separating being done continuously.

Claim 8

The improvement of claim 7 wherein the surface area of the alumina hydrate seed contacted with the moving stream of sodium aluminate liquor is from about 3 square meters per liter to about 10 square meters per liter of said moving stream of sodium aluminate liquor and the temperature of the moving stream of sodium aluminate liquor is from about 150* F. to about 225* F.

Claim 9

The improvement of claim 7 wherein the separating of the resulting stream of sodium aluminate liquor of reduced iron content from the precipitated iron-containing alumina hydrate is by liquid cyclone, centrifuge or filter.

Claim 10

The improvement of claim 7 wherein, after separating the stream of sodium aluminate of reduced iron content from the precipitated iron-containing alumina hydrate, alumina hydrate of improved purity is subsequently precipitated and separated from said resulting stream of sodium aluminate.

Claim 11

The improvement of claim 7 wherein the precipitated iron-containing alumina hydrate is recycled to form part of the alumina hydrate seed with which the stream of sodium aluminate liquor is contacted and a portion of the precipitated iron-containing alumina hydrate is separated from said iron-containing alumina hydrate being recycled and is replaced with fresh alumina hydrate seed.

Claim 12

In a process for production of alumina by precipitation of alumina hydrate from a sodium aluminate liquor derived from an alumina-bearing source, the improvement which comprises contacting a stream of iron-containing sodium aluminate liquor having an Al2O3 to total caustic ratio of from about 0.3:1 to about 0.8:1 for a holding time of from about 5 minutes to about 30 minutes and at a temperature of from about 150* F. to about 225* F. with sufficient alumina hydrate seed to provide a seed surface area of from about 1 square meter per liteR to about 20 square meters per liter of said stream, said contacting being accomplished with substantially no longitudinal mixing of said sodium aluminate with said alumina hydrate, thereby precipitating iron-containing alumina hydrate from said stream of sodium aluminate liquor in an amount of not more than about 10 g./l. of said stream, separating said iron-containing alumina hydrate from said stream of sodium aluminate, recycling said iron-containing alumina hydrate to serve as additional seed for a further contacting and, in a separate step, precipitating alumina hydrate of improved purity and reduced iron content from said stream from which said iron-containing alumina hydrate has been separated.

Claim 13

The improvement of claim 13 wherein said surface area is from about 3 square meters per liter to about 9 square meters per liter of said stream and said temperature is from about 160* F. to about 200* F.

Claim 14

A process for reducing the iron content of sodium aluminate liquor which comprises conducting a stream of sodium aluminate liquor substantially unidirectionally, introducing alumina hydrate seed to said stream and moving same concurrently therewith at a rate of movement which is substantially the same as the rate of movement of said stream and with substantially no longitudinal mixing and substantially no backflow of the alumina hydrate against the sodium aluminate liquor, and separating resulting precipitated iron-containing alumina hydrate from said stream of sodium aluminate liquor, said stream of sodium aluminate liquor remaining after separation of said precipitated iron-containing alumina hydrate therefrom containing less iron than the original stream of sodium aluminate liquor to which the alumina hydrate seed is introduced.