High molecular weight polymers containing pendant salicylic acid groups for clarifying Bayer process liquors
View Patent ↗A high molecular weight, water-soluble polymer comprising pendant salicylic acid groups and having a weight average molecular weight of at least about 2,000,000 daltons and use of the polymer for clarifying red mud-containing liquors generated in the Bayer process for the recovery of alumina from bauxite.
1. A method of flocculating suspended solids in a Bayer process liquor comprising adding to the liquor an effective amount of one or more high molecular weight, water-soluble polymers comprising pendant salicylic acid groups incorporated in a polymer chain by a amide linkage and having a weight average molecular weight of at least about 2,000,000 daltons, the polymer prepared by free radical polymerization of one or more salicylic acid containing monomers, one or more acrylate monomers selected from the group consisting of (meth)acrylic acid and salts thereof and alkyl esters of(meth)acrylic acid and one or more polymerizable monomers selected from the group consisting of nonionic, anionic, cationic and zwitterionic monomers.
2. The method of claim 1 wherein the high molecular weight, water-soluble polymers are selected from the group consisting of dispersion polymers, emulsion polymers, inverse emulsion polymers, dry polymers and solution polymers.
3. The method of claim 1 wherein the salicylic acid containing monomers are selected from the group consisting of 4-methacrylamidosalicylic acid or a salt thereof, 4-methacrylamidosalicylic acid phenyl ester or a salt thereof, O-acetyl-4-methacrylamidosalicylic acid or a salt thereof and O-acetyl-4-methacrylamidosalicylic acid phenyl ester.
4. The method of claim 1 wherein the polymerizable nonionic monomers are selected from acrylamide and methacrylamide.
5. The method of claim 1 wherein the polymerizable anionic monomer is 2-acrylamido-2-methyl propanesulfonic acid or a salt thereof.
6. The method of claim 3 wherein the high molecular weight, water-soluble polymers are selected from the group consisting of emulsion polymers and inverse emulsion polymers.
7. The method of claim 6 wherein the high molecular weight, water-soluble polymers comprise about 50 to about 98 mole percent sodium or ammonium acrylate, about 1 to about 20 mole percent 4-methacrylamidosalicylic acid or a salt thereof, 4-methacrylamidosalicylic acid phenyl ester or a salt thereof, O-acetyl-4-methacrylamidosalicylic acid or a salt thereof or O-acetyl-4-methacrylamidosalicylic acid phenyl ester and about 1 to about 30 mole percent acrylamide or methacrylamide.
8. The method of claim 6 wherein the high molecular weight, water-soluble polymers comprise about 50 to about 98 mole percent sodium or ammonium acrylate, about 1 to about 20 mole percent 4-methacrylamidosalicylic acid or a salt thereof, 4-methacrylamidosalicylic acid phenyl ester or a salt thereof, O-acetyl-4-methacrylamidosalicylic acid or a salt thereof or O-acetyl-4-methacrylamidosalicylic acid phenyl ester and about 1 to about 30 mole percent 2-acrylamido-2-methyl propanesulfonic acid or a salt thereof.
9. The method of claim 1 further comprising hydrolyzing the polymer comprising pendant salicylic acid groups prior to addition to the Bayer process liquor.
10. The method of claim 1 further comprising adding one or more anionic or nonionic flocculant(s) to the process stream.
11. The method of claim 10 to wherein the nonionic flocculant is starch, dextran or flour.
12. The method of claim 10 wherein the anionic flocculant comprises poly(meth)acrylic acid.
13. The method of claim 12 wherein the poly(meth)acrylic acid is selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylic acid containing pendant hydroxamic acid groups, poly(alkyl(meth)acrylate), (meth)acrylic acid/alkyl(meth)acrylate copolymers, (meth)acrylic acid/acrylamide copolymers, (meth)acrylic acid/acrylamide copolymers containing pendant hydroxamic acid groups, (meth)acrylic acid/acrylamide/alkyl(meth)acrylate terpolymers, and (meth)acrylic acid/acrylamide/AMPS terpolymers.
14. The method of claim 10 wherein the anionic flocculant is added prior to the polymer comprising pendant salicylic acid groups.
15. The method of claim 10 wherein the anionic flocculant is added after the polymer comprising pendant salicylic acid groups.
16. The method of claim 10 wherein the anionic flocculant is added together with the polymer comprising pendant salicylic acid groups.
17. The method of claim 12 wherein the polymer comprising pendant salicylic acid groups has an RSV of at least about 14 dL/g and the anionic flocculant has an RSV of at least about 21 dL/g.
18. The method of claim 1 wherein the Bayer process liquor is selected from settler feed, settler overflow, digestion blow-off, mud washer in the washer train, feed to the primary polishing filters, feed to a mud settler, feed to the primary alumina crystallization tanks, feed to the secondary and tertiary alumina classifiers or trays, feed to hydrate filters or feed to a centrifuge.