# US 6,296,819 B1 · Process for the manufacture of coarse aluminium hydroxide

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- Number: US 6,296,819 B1
- Document ID: US6296819B1
- Status: Granted
- Kind: B1
- Application number: 09/421,538
- Filed: 1999-10-20
- Granted: 2001-10-02
- Earliest claimed: 1998-10-28
- Assignees: Alusuisse Technology & Management Ltd.
- Inventors: Hans Jürg Schenk; Hans-Peter Breu; Arvind Bhasin
- Web page: https://patentgrep.com/patent/US6296819B1

## CPC

- C01F 7/144: from aqueous aluminate solutions by precipitation due to cooling, e.g. as part of the Bayer process
- C01P 2004/50: Agglomerated particles
- C01P 2004/61: Micrometer sized, i.e. from 1-100 micrometer
- C01F: COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts of peroxyacids C01B15/00; sulfides or polysulfides of magnesium, calcium, strontium, or barium C01B17/42; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds other than ammonia or cyanogen containing nitrogen and non-metals and optionally metals C01B21/082; amides or imides of silicon C01B21/087}; metal {imides or} amides C01B21/092, {C01B21/0923}; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanic acid C01C3/14; salts of cyanamide C01C3/16; thiocyanates C01C3/20; {double sulfates of magnesium with sodium or potassium C01D5/12; with other alkali metals C01D15/00, C01D17/00})
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS

## Abstract

A process for the manufacture of coarse aluminum hydroxide via the Bayer Process. The process involves the decomposition of a supersaturated alkaline aluminate liquor in a two stage precipitation process having an agglomeration stage and a growth stage. The agglomeration stage takes place in agglomeration tanks, where the liquor is seeded with fine aluminum hydroxide to induce precipitation and formation of a suspension, followed by a growth stage, where the suspension is seeded with a coarse aluminium hydroxide. Typically, the feed of the supersaturated alkaline aluminate liquor is split over a first agglomeration tank at a higher liquor temperature of 70° to 100° C. and a second agglomeration tank or one or more of a series of second agglomeration tanks at a lower liquor temperature of 50° to 80° C.

## Claims

### Claim 1

A process for manufacturing coarse aluminium hydroxide by decomposition of a supersaturated alkaline aluminate liquor in a two stage precipitation process having an agglomeration stage in agglomeration tanks, connected in series, where the liquor is seeded with fine aluminium hydroxide to induce precipitation and formation of a suspension, the feed of the supersaturated alkaline aluminate liquor to the agglomeration stage is split into a first substream and said first substream is fed to a single first agglomeration tank or to the first and more of a series of first agglomeration tanks, at a higher liquor temperature of 70° to 100° C. and to a second substream and said second substream is fed to a second agglomeration tank or to a series of 2 or more second agglomeration tanks at a lower liquor temperature of 50° to 80° C., the residence time of the suspension in the agglomeration stage tanks is 3 to 12 hours, all of the supersaturated alkaline aluminate liquor being added during the agglomeration stage, followed by a growth stage, where the suspension is seeded with a coarse aluminium hydroxide, yielding at the end of precipitation a strong coarse product hydrate, giving after calcination a sandy alumina with low occluded soda content, compatible with a high liquor productivity.

### Claim 2 (depends on 1)

The process according to claim 1, wherein the amount of liquor split into the first substream represents 30 to 60 percent of the total supersaturated alkaline aluminate liquor flow.

### Claim 3 (depends on 1)

The process according to claim 1, wherein the first substream is fed and distributed to each of a series of 2 or more first agglomeration tanks, at a higher liquor temperature of 70° to 100° C.

### Claim 4 (depends on 3)

The process according to claim 3, wherein the number of series of first agglomeration tanks is two.

### Claim 5 (depends on 1)

The process according to claim 1, wherein the first substream of the supersaturated alkaline aluminate liquor is fed at a temperature of 70° to 90° C.

### Claim 6 (depends on 5)

The process according to claim 5, wherein the temperature of said first substream is 80° to 90° C.

### Claim 7 (depends on 1)

The process according to claim 1, wherein the fine seed is fed into the single first agglomeration tank or is fed in the first agglomeration tank of a series of two or more first agglomeration tanks or is fed and distributed over the first two agglomeration tanks of a series of two or more agglomeration tanks.

### Claim 8 (depends on 1)

The process according to claim 1, wherein the amount of liquor representing 70 to 40 percent of the total supersaturated alkaline aluminate liquor forming the second substream is fed to the one second agglomeration tank or to one of the second agglomeration tanks or is fed and distributed over two or more or all tanks of the series of second agglomeration tanks.

### Claim 9 (depends on 8)

The process according to claim 8, wherein the amount of liquor representing 70 to 40 percent of the total supersaturated alkaline aluminate liquor forming the second substream is fed to the one second agglomeration tank or to 1, 2, or 3 of the series of second agglomeration tanks.

### Claim 10 (depends on 8)

The process according to claim 8, wherein the amount of liquor representing 70 to 40 percent of the total supersaturated alkaline aluminate liquor forming the second substream is fed to and distributed over 2 of the series of second agglomeration tanks.

### Claim 11 (depends on 8)

The process according to claim 8, wherein the amount of liquor representing 70 to 40 percent of the total supersaturated alkaline aluminate liquor forming the second substream is fed to and distributed over 3 of the series of second agglomeration tanks.

### Claim 12 (depends on 1)

The process according to claim 1, wherein the second substream of the supersaturated alkaline aluminate liquor is fed to the second agglomeration tank or to the series of second agglomeration tanks at a temperature of 60° to 80° C.

### Claim 13 (depends on 12)

The process according to claim 12, wherein the temperature of said second substream is 60° to 70° C.

### Claim 14 (depends on 1)

The process according to claim 1, wherein the temperature of the supersaturated alkaline aluminate liquor sent to the second agglomeration tank or the series of second agglomeration tanks is 5° to 50° C. below the temperature of the supersaturated alkaline aluminate liquor sent to the first agglomeration tank or the series of first agglomeration tanks.

### Claim 15 (depends on 1)

The process according to claim 1, wherein the temperature of the supersaturated alkaline aluminate liquor sent to the second agglomeration tank or the second agglomeration tanks is 15° to 40° C. below the temperature of the supersaturated alkaline aluminate liquor sent to the first agglomeration tank or the series of first agglomeration tanks.

### Claim 16 (depends on 1)

The process according to claim 1, wherein the temperature of the supersaturated alkaline aluminate liquor sent to the second agglomeration tank or the second agglomeration tanks is 20° to 30° C. below the temperature of the supersaturated alkaline aluminate liquor sent to the first agglomeration tank or the series of first agglomeration tanks.

### Claim 17 (depends on 1)

The process according to claim 1, wherein the suspension in the one first agglomeration tank or in the series of agglomeration tanks has a solids content of 100 to 500 g/l.

### Claim 18 (depends on 16)

The process according to claim 16, wherein the solids content of said suspension is 150 to 450 g/l.

### Claim 19 (depends on 16)

The process according to claim 16, wherein the solids content of said suspension is 300 to 400 g/l.

### Claim 20 (depends on 1)

The process according to claim 1, wherein the solids content of the suspension at the end of the growth stage is 300 to 900 g/l.

### Claim 21 (depends on 1)

The process according to claim 1, wherein the solids content of the suspension at the end of the growth stage is 350 to 550 g/l.

### Claim 22 (depends on 1)

The process according to claim 1, wherein the residence time for the precipitation of the suspension in the growth stage is 20 to 50 hours.

### Claim 23 (depends on 1)

The process according to claim 1, wherein the liquor is seeded with fine aluminium hydroxide to induce precipitation and said fine seed is prepared by reslurrying a side stream of the supersaturated alkaline aluminate liquor or of spent liquor prior to being fed to the agglomeration stage.

### Claim 24 (depends on 1)

The process according to claim 1, wherein the coarse aluminium hydroxide is formed by a classification operation of the precipitation suspension leaving at the end of the growth stage, followed by a filtration operation, whereby a coarse seed filter cake is formed and said filter cake is fed to the first precipitation tank of the growth stage.

### Claim 25 (depends on 1)

The process according to claim 1, wherein the coarse aluminium hydroxide is formed by a classification operation of a precipitation suspension leaving at the end of the growth stage, followed by a filtration operation, whereby a coarse seed filter cake is formed and said coarse seed filter cake is reslurried in a side stream of the suspension leaving the agglomeration stage or of cooled supersaturated alkaline aluminate liquor and fed to the first precipitation tank of the growth stage.

### Claim 26 (depends on 1)

The process according to claim 1, wherein the growth stage is made of precipitation tanks in series or precipitation tanks in parallel or a combination of precipitations tanks in series and parallel.