US5008089A — Recovery of alumina from bauxite

Claim 1

Independent Claim 223 words

In a process in which bauxite is digested in an aqueous alkaline liquor and the resultant red mud is flocculated with a flocculating agent and separated from the digestion liquor in a primary separation stage, the overflow liquor of the primary separation stage is optionally subjected to a secondary clarification stage in which suspended red mud particles are flocculated and separated from the liquor, and the red mud from the said primary separation stage and optional secondary clarification stage is then washed in a plurality of sequential wash stages in each of which the mud is washed with a wash liquor, flocculated with a flocculating agent and separated from the wash liquor, and the flocculating agent in at least one stage selected from the said primary separation stage, secondary clarification stage and the wash stages comprises a synthetic anionic polymeric flocculant, the improvement wherein the flocculating agent further comprises at least about 0.02 mg/l of a dextran having a molecular weight of at least about 500,000, wherein said synthetic anionic polymeric flocculant has a molecular weight of at least about 0.5 million, and is a water soluble polymer formed from 40-100% anionic monomer and 60-0% non-ionic monomer, and wherein the anionic monomer is selected from the group consisting of (meth) acrylic acid, (meth) allylsulfonic acid, vinyl sulfonic acid and 2-acrylamido-2-methyl propane sulfonic acid.

Claim 2

Dependent Claim 223 words

In a process in which bauxite is digested in an aqueous alkaline liquor and the resultant red mud is flocculated with a flocculating agent and separated from the digestion liquor in a primary separation stage, the overflow liquor of the primary separation stage is optionally subjected to a secondary clarification stage in which suspended red mud particles are flocculated and separated from the liquor, and the red mud from the said primary separation stage and optional secondary clarification stage is then washed in a plurality of sequential wash stages in each of which the mud is washed with a wash liquor, flocculated with a flocculating agent and separated from the wash liquor, and the flocculating agent in at least one stage selected from the said primary separation stage, secondary clarification stage and the wash stages comprises a synthetic anionic polymeric flocculant, the improvement wherein the flocculating agent further comprises at least about 0.02 mg/l of a dextran having a molecular weight of at least about 500,000, wherein said synthetic anionic polymeric flocculant has a molecular weight of at least about 0.5 million, and is a water soluble polymer formed from 40-100% anionic monomer and 60-0% non-ionic monomer, and wherein the anionic monomer is selected from the group consisting of (meth) acrylic acid, (meth) allylsulfonic acid, vinyl sulfonic acid and 2-acrylamido-2-methyl propane sulfonic acid.

Claim 3

Dependent Claim 24 words

The improvement according to claim 1 in which the dextran is added to the liquor prior to addition of the synthetic anionic polymeric flocculant.

Claim 4

Dependent Claim 19 words

The improvement according to claim 1 in which the said at least one stage is the primary settlement stage.

Claim 5

Dependent Claim 21 words

The improvement according to claim 1 in which the dextran has a molecular weight in the range 500,000 to 10 million.

Claim 6

Dependent Claim 21 words

The improvement according to claim 1 in which dextran is added in an amount in the range 0.2 to 10 mg/l.

Claim 7

Dependent Claim 21 words

The improvement according to claim 1 in which dextran is added in an amount in the range 0.5 to 5 mg/l.

Claim 8

Dependent Claim 24 words

The improvement according to claim 1 in which the anionic polymeric flocculant is added in an amount in the range 0.5 to 20 mg/l.

Claim 9

Dependent Claim 24 words

The improvement according to claim 1 in which the anionic polymeric flocculant is added in an amount in the range 1 to 10 mg/l.

Claim 10

Dependent Claim 23 words

The improvement according to claim 1 in which the liquor in said stage has a sodium carbonate content of at least 10 g/l.

Claim 11

Dependent Claim 23 words

The improvement according to claim 1 in which the liquor in said stage has a sodium carbonate content of at least 20 g/l.

Claim 12

Dependent Claim 23 words

The improvement according to claim 1 in which the liquor in said stage has a sodium carbonate content of at least 50 g/l.

Claim 13

Dependent Claim 22 words

The improvement according to claim 1 in which the amount of synthetic anionic polymeric flocculant is greater than the amount of dextran.

Claim 14

Dependent Claim 42 words

The improvement according to claim 1 in which the anionic flocculant is 1-10 mg/l of a polymer formed from 40-100% acrylic acid and 60-0% acrylamide, and wherein 0.5-5 mg/l dextran is added to the aqueous liquor before the said addition of polymer.

Claim 15

Dependent Claim 16 words

The improvement according to claim 13 in which the treated liquor is the primary settlement liquor.

Claim 16

Dependent Claim 189 words

In a process in which bauxite is digested in an aqueous alkaline liquor and the resultant red mud is flocculated with a flocculating agent and separated from the digestion liquor in a primary separation stage, the overflow liquor of which is optionally subjected to a secondary clarification stage in which ,further suspended red mud particles are flocculated and separated from the liquor, and the red mud from the primary separation stage and, if present, optionally also the secondary clarification stage is then washed in a plurality of sequential wash stages in each of which the mud is washed with a wash liquor, flocculated with a flocculating agent, and separated from the wash liquor, the improvement wherein the flocculating agent in at least one stage selected from the primary separation stage, secondary clarification stage and the wash stages comprises a first addition of 0.5 to 5 mg/l dextran having a molecular weight of at least about 500,000, and a second addition of 0.1 to 10 mg/l of a polymer formed from 40 to 100% acrylic acid and 60to 0% acrylamide having a molecular weight of at least about 0.5 million.

Claim 17

Dependent Claim 189 words

In a process in which bauxite is digested in an aqueous alkaline liquor and the resultant red mud is flocculated with a flocculating agent and separated from the digestion liquor in a primary separation stage, the overflow liquor of which is optionally subjected to a secondary clarification stage in which ,further suspended red mud particles are flocculated and separated from the liquor, and the red mud from the primary separation stage and, if present, optionally also the secondary clarification stage is then washed in a plurality of sequential wash stages in each of which the mud is washed with a wash liquor, flocculated with a flocculating agent, and separated from the wash liquor, the improvement wherein the flocculating agent in at least one stage selected from the primary separation stage, secondary clarification stage and the wash stages comprises a first addition of 0.5 to 5 mg/l dextran having a molecular weight of at least about 500,000, and a second addition of 0.1 to 10 mg/l of a polymer formed from 40 to 100% acrylic acid and 60to 0% acrylamide having a molecular weight of at least about 0.5 million.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1994-04-15	1994-10-15	1995-04-16	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1998-04-15	1998-10-15	1999-04-16	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2002-04-15	2002-10-15	2003-04-16	$7700.00	Window Closed / Lapsed

Recovery of alumina from bauxite

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