Search Images Maps Play YouTube News Gmail Drive More »
Sign in


  1. Advanced Patent Search
Publication numberUS3975496 A
Publication typeGrant
Application numberUS 05/512,579
Publication dateAug 17, 1976
Filing dateOct 7, 1974
Priority dateOct 10, 1973
Also published asDE2448220A1, DE2448220B2, DE2448220C3
Publication number05512579, 512579, US 3975496 A, US 3975496A, US-A-3975496, US3975496 A, US3975496A
InventorsEric Rothwell, Graham Smalley
Original AssigneeAllied Colloids Limited
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Process for settling red mud in the digestion of bauxite
US 3975496 A
The invention provides novel water-soluble copolymers useful as flocculating agents, especially in flocculating the red mud formed during the Bayer process for the production of alumina from bauxite. The copolymers comprise anionic monomer units e.g. acrylic acid units in a mole percentage of less than 50% and acrylamide type units some of which are methylolated.
Previous page
Next page
What is claimed is:
1. In a process for the production of alumina from bauxite comprising the steps of digesting bauxite with aqueous sodium hydroxide to give a suspension of red mud in a solution of sodium aluminate, settling said red mud and processing the resultant supernatant sodium aluminate solution to obtain alumina, the improvement comprising settling said red mud by addition to said suspension of an effective amount of a water-soluble polymer having a molecular weight greater than 0.5 times 10.sup.6 and comprising the recurring monomer units: ##EQU1## in which R.sub.1, R.sub.2 and R.sub.3 are independently selected from the group consisting of hydrogen and methyl; R.sub.4 is selected from the group consisting of OH, OM and NHR.sub.5 SO.sub.3 M where M is a cation such that the polymer is water-soluble and R.sub.5 is --(CH.sub.2).sub.m where m is 1 to 6; and x, y, and z are the mole percentages of the indicated monomer units based on x + y + z = 100, x being 2 to 40 and y+z being 60 to 98.
2. The process of claim 1 wherein x is from 4 to 20.
3. The process of claim 2 wherein z is at least 20% of y + z.

Various synthetic polymers, including acrylamide polymers, are now widely used as flocculating agents. The choice of flocculating agent for any particular system depends inter alia, on the pH of the system. The purpose of the present invention is to provide improved flocculating agents for alkaline systems, for example in red mud flocculation.

During the Bayer process for the production of alumina from bauxite, in which the ore is digested at high temperature and pressure with an aqueous solution of sodium hydroxide, the aluminium content of the bauxite dissolves as sodium aluminate and insoluble impurities remain in suspension. The constitution of these impurities varies with the source of the ore and the conditions of the extraction. A typical bauxite ore analysis would be Al.sub.2 O.sub.3 53.10%, Fe.sub.2 O.sub.3 25.45%, SiO.sub.2 5.75%, TiO.sub.2 2.55% and unaccounted balance 13.15%, which frequently is assumed to be mainly water and some organic material. The impurities include iron oxides, sodium aluminosilicate and titanium oxide. These suspended impurities, which are commonly referred to as red mud because of their characteristic red-brown color and their finely divided state, usually constitute 30% to 50% by weight of the original ore.

For economical operation of the process it is essential that the red mud is settled rapidly, and to produce the required high grade of alumina the separation must be efficient giving overhead liquors of high clarity. Flocculating agents are therefore used to accelerate the settling process and to give good clarities, both factors being of great importance. It is known to use in the process natural products such as starch, synthetic polymers such as homopolymers of acrylic acid and methacrylic acid and their salts for example as described in U.S. Pat. No. 3,390,959, and combinations of starch and polyelectrolyte, as described in French Pat. Nos. 1,470,568 and 1,563,430. Non-ionic polymers such as methylolated polyacrylamide have also been described in USSR Pat. No. 285,912.

Starch based flocculants however are usually required in large quantities and tend to give poor rates of settlement but good clarities. Furthermore the use of starch can lead to persistence of organic matter in the liquors and this can cause problems at later stages in the process such as the hydrolysis stage and liquor concentration stages. On the other hand the clarities obtained with anionic homopolymers are generally inferior to those obtained with starch although superior settling rates have been reported.

In general typical synthetic polymers of the prior art proposed for red mud or other alkaline systems are either nonionic or are anionic. If anionic they are produced from compositions containing at least 80% by weight of anionic monomer.

It is a fact that the very wide range of known polyacrylamide flocculants which find extensive use in other mineral processing operations are rather unsatisfactory in alkaline systems and in particular most fail completely to effect the sedimentation of red mud and hitherto only a few polymers of selected composition have been found to have any effect at all.

We have now found that a new class of polyacrylamide flocculants are useful in alkaline systems, especially in red mud flocculation, both with regard to settlement rate and supernatant clarity. The flocculants are water soluble copolymers comprising the recurring monomer units: ##STR1## and in which R.sub.1, R.sub.2 and R.sub.3 may be the same or different and represent H or CH.sub.3 ; R.sub.4 is OH, OM, or NHR.sub.5 SO.sub.3 M where M is a cation such that the polymer is water soluble, e.g. Na or K, and R.sub.5 is --(CH.sub.2)m.sup.- where m is 1 to 6. x, y and z are the mol % of the indicated monomeric units present in the polymer, x+y+z = 100. x is always less than 50 and this is in marked contrast to the most successful known polymers, since in these the mole % of cationic group has always been above 80.

The polymers of our invention are surprisingly effective and superior to the anionic flocculants of the prior art and the methylolated homopolymers of acrylamide as described in USSR Pat. No. 285,912.

The anionic monomer may be selected from a wide range of anionic monomers including acrylic acid, methacrylic acid and N-sulphohydrocarbon substituted acrylamides ##STR2## where R.sub.1, R.sub.5 and M are as defined above.

For achieving the optimum activity with respect to settlement rate and clarity, especially on red mud, we find that the following relationship should exist between x, y and z, that is the molar percentages of the anionic, amido, and hydroxymethylamido units respectively: x may be 2 to 40, preferably 4 to 20, and most preferably 6 to 15, while y + z = 100 - x, z preferably being at least 20% of y + z, for example 20 to 90%. For example z is often above 20 and is often not above 80.

The copolymer may also include a small amount, e.g. up to 10 mole % based on x+y+z, of other copolymerisable monomers.

The copolymers may be made by any convenient method, for example by methylolation of an acrylamide polymer, for example a copolymer of acrylamide and the required anionic monomer in the desired proportions and of the desired molecular weight for the final polymer.

The requirements of any particular flocculation process, e.g. any particular red mud substrate and plant conditions determines the order of molecular weight of the polymer. If the greater emphasis is upon settlement rate or the substrate is particularly diffiult to settle high molecular weight polymers are preferable, for example 5 to 15 substrate is particularly difficult to clarify lower molecular weight polymers are preferable, for example 0.5 10.sup.6. It is possible to achieve a good overall performance by the use of a blend of terpolymers of high and low average molecular weight. In any case we find that the molecular weight of the polymer should be greater than 0.5

The products of the invention have been found to be particularly effective as flocculating agents in highly alkaline systems where polyacrylamides of the prior art are relatively ineffective. They are particularly effective in the flocculation of red mud, and for assessment of the performance of the various products the following test method was adopted.

Final washed mud from an alumina plant operating the Bayer process was dispersed in water using a high speed mixer. Sodium hydroxide and sodium aluminate were added to adjust the liquor composition to that found under typical plant conditions, and the slurry was digested for 3 hours at 90

The washed mud from the plant had the following characteristics:Suspended solids 26% wt/wt.Specific gravity 1.186Solution pH 12.6

The reconstituted red mud slurry had the following typical composition:

Final washed mud      292 mls/lSodium hydroxide      60 g/lSodium aluminate      281 g/l

The performance of the products was then examined by dosing 250 ml. aliquots of the red mud slurry in 250 ml. measuring cylinders with dilutions of the products at a dosage level of 0.5 ppm product solids on volume of slurry. The settling rate of the flocculated mud suspension at 90 a 50 ml. sample of the supernatant liquor was carefully withdrawn and filtered through a preweighed glass-fibre filter paper. The sediment on the paper was washed with 2 paper with residue was dried at 210 weight of sediment relative to the total liquor. The settlement figures are expressed as percentage mud volume relative to total liquor, and the clarity figures are expressed as g/l.

A further advantage of the products of the invention is that unlike products of the prior art they may be prepared on site, and by minor variation of the reaction conditions the product performance can be controlled to compensate for the day to day variations which occur in the red mud characteristics, which normally cannot be adequately dealt with by the application of any single flocculating agent of the prior art.


A copolymer of acrylamide and sodium acrylate containing 60% by weight acrylamide and 40% by weight sodium acrylate and having a 1% solution viscosity in 3 molar sodium chloride solution of 88 cs. (Polymer A) was dissolved in water to give a 1% solution. Sodium hydroxide was added to adjust the pH of the solution to 10.0 and then formalin was added in an amount equimolar with the amide content of the solution. The reaction was allowed to continue for 24 hours at 40 referred to in Table 1 as Polymer B.

Reactions were similarly carried out on a copolymer containing 80% by weight acrylamide and 20% by weight sodium acrylate (Polymer C) with a 1% solution viscosity in 3 molar sodium chloride solution of 80 cs., to give Polymer D, and on a copolymer containing 90%, acrylamide and 10% sodium acrylate (Polymer E) with a 1% solution viscosity in 3 molar sodium chloride solution of 99 cs. to give Polymer F, and on polyacrylamide (Polymer G) with a 1% solution viscosity in 3 molar sodium chloride solution of 77 cs. to give Polymer H, a product of the prior art. The performance of these polymers was compared with Polymer I a sodium polyacrylate polymer of the prior art.

                                  TABLE 1__________________________________________________________________________          Settling Rates    SupernatantMole %         Percentage mud volume vs.                            Clarity          time(mins)PolymerMethylolated amide          10 mins.                20 mins.                      30 mins.                             g/l__________________________________________________________________________A    0         93.6  81.6  68     0.278B    20        86.4  71.2  60     0.134C    0         94.4  80.8  72     0.238D    21        83.2  67.2  56     0.112E    0         NDML* 78    73     0.280F    26        88.8  64.8  55.2   0.038G    0         NDML  NDML  72     0.334H    46        NDML  80.3  58.2   0.140I    --        86.4  69.6  62.4   0.088Noaddition--        96.2  88.2  76     0.726__________________________________________________________________________ *NDML indicates no definite mud line had been formed at this time.

These results clearly show the improvement in both settlement rate and clarity obtained on methylolation of anionic copolymers. Also is demonstrated the superiority of product in the preferred range of compositions, Polymer F, over products of the prior art, Polymers H and I.


A 1% solution of polyacrylamide with a 1% solution viscosity in 3 molar brine of 77 cs. was caused to react with formaldehyde and various mole proportions of sodium bisulphite to give a range of products of different methylol and sulpho methylene content ( -- CH.sub.2 SO.sub.3 Na).

              TABLE 2______________________________________Molar ratio of reactants                 Product analysisPolymer  Amide   Formal-  Bisulphate                           Mole % Mole %          dehyde           Methylol                                  Sulphome-                                  thylene______________________________________J      1       1        1.5     6.5    29.0K      1       1        0.75    40.5   14.5L      1       1        0.25    80.0   5.0______________________________________

The products were tested in comparison with Polymers H and I of the prior art at the same dosage level of 0.5 ppm solids product on slurry and the results are given in Table 3.

              TABLE 3______________________________________Settling RatesPercentage mud volume vs. time(mins)                       ClarityPolymer 10 mins.   20 mins.  30 mins. g/l______________________________________H       78.4       65.2      60.4     0.194I       77.6       58.8      55.4     0.164J       76.6       58.4      52.8     0.134K       79.2       60.0      54.6     0.108L       79.6       60.0      54.0     0.106Noaddition   94.0       88.8      80.0     0.698______________________________________

Thus it is clearly seen the compositions of the invention Polymers J and especially K and L are significantly better then compositions Polymers H and I of the prior art.


A 25% solution of sodium 2-acrylamide-2 methylpropanesulphonate was polymerised using 1 ppm Fe.sup.2.sup.+ and 50 ppm potassium persulphate as initiator to give Polymer M having a 1% solution viscosity of 12 cs. in 3 molar sodium chloride solution.

Similarly prepared was a copolymer Polymer N containing 90% acrylamide and 10% sodium 2-acrylamide-2-methyl propane sulphonate showing a 1% solution viscosity of 78 cs. in 3 molar sodium chloride solution.

A 1% solution of Polymer N in deionised water was reacted at pH 10 and 40 amide content of the solution to give Polymer O.

Polymers M, N, and O were tested in comparison with polymers I and J by the standard test procedure using a batch of slurry which was difficult to settle at a dosage level of 0.5 ppm solids product on slurry.

              TABLE 4______________________________________Settling RatesPercentage mud volume vs.time (mins)                       ClarityPolymer 10 mins.   20 mins.  30 mins. g/l______________________________________M       96         85        75       0.40N       96         86        75       0.22O       95         83        73       0.14I       95         84        75       0.38J       94         82        71       0.12Noaddition   97         87        83       0.88______________________________________

Thus again it is seen that products of the invention Polymers O and J give significantly better results than products of the prior art Polymer I and other related products whose compositions fall outside the scope of the invention Polymers M and N.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3575868 *Jun 6, 1968Apr 20, 1971Atlas Chem IndFlocculating agent comprising starch and polyacrylic acid
US3716617 *Apr 13, 1970Feb 13, 1973Sumitomo Chemical CoProcess for producing alumina
US3755531 *Aug 19, 1971Aug 28, 1973Kao CorpProcess for refining alumina
Non-Patent Citations
1 *Central Patents Index, Basic Abstracts Journal, Derwent Pub. Ltd., London, Nov. 19, 1971, Abstract 61030S (U.S.S.R. Pat. No. 285,912).
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4075125 *Jul 9, 1976Feb 21, 1978Chiyoda Chemical Engineering & Construction Co., Ltd.Catalysts for hydrodemetallization of hydrocarbons containing metallic compounds as impurities
US4090955 *May 5, 1976May 23, 1978American Cyanamid CompanySelective flocculation of minerals from a mixture or an ore
US4274945 *Nov 7, 1979Jun 23, 1981American Cyanamid CompanyIron ore beneficiation by selective flocculation
US4282087 *May 21, 1979Aug 4, 1981American Cyanamid CompanySelective flocculation for iron values
US4289613 *Nov 19, 1979Sep 15, 1981American Cyanamid CompanyLow molecular weight hydrolyzed polymers or copolymers as depressants in mineral ore flotation
US4289752 *Nov 13, 1978Sep 15, 1981Societe Anonyme Dite: L'orealCosmetic compositions containing N-alkylacrylamide or N-alkylmethacrylamide based copolymers
US4478795 *Oct 18, 1982Oct 23, 1984Diamond Shamrock Chemicals CompanyAluminum trihydroxide deliquoring with anionic polymers
US4545902 *Sep 17, 1984Oct 8, 1985Nalco Chemical CompanyFlocculants for bauxite (red mud)
US4599390 *Sep 18, 1985Jul 8, 1986Union Carbide CorporationHigh molecular weight water-soluble polymers and flocculation method using same
US4767540 *Feb 11, 1987Aug 30, 1988American Cyanamid CompanyPolymers containing hydroxamic acid groups for reduction of suspended solids in bayer process streams
US4839060 *Oct 21, 1987Jun 13, 1989Suncor, Inc.Methylated starch compositions and their use as flocculating agents for mineral wastes, such as bauxite residues
US5008089 *Oct 13, 1989Apr 16, 1991Allied Colloids LimitedRecovery of alumina from bauxite
US5286391 *Feb 4, 1993Feb 15, 1994Nalco Chemical CompanyRed mud flocculation
US5346628 *Oct 29, 1993Sep 13, 1994Nalco Chemical CompanyPolymers for flocculating red mud from bayer process liquors
US5368745 *Sep 2, 1993Nov 29, 1994Cytec Technology Corp.Method of flocculating low metal oxide content solids in a liquid
US5653946 *Jul 14, 1994Aug 5, 1997S.N.F.Process for fluidifying aqueous suspensions of red muds in the production of alumina by the bayer process
US5716530 *Dec 13, 1996Feb 10, 1998Nalco Chemical CompanyBiopolymer use as a sand filter aid
US5837215 *Jul 18, 1997Nov 17, 1998Nalco Chemical CompanyMethod of removing insoluble materials from bayer process with fatty acid and fatty acid free polymer flocculants
US5853677 *Apr 18, 1997Dec 29, 1998Cytec Technology Corp.Concentration of solids by flocculating in the Bayer process
US5951955 *Nov 6, 1996Sep 14, 1999Cytec Technology Corp.Concentration of solids in the Bayer process
US6036869 *Dec 12, 1997Mar 14, 2000Nalco Chemical CompanyWater continuous methyl acrylate emulsion polymers for improved flocculation of red mud in the Bayer process
US6048463 *May 8, 1998Apr 11, 2000Nalco Chemical CompanyWater continuous methyl acrylate emulsion polymer combinations and methyl acrylate emulsion homopolymers for improved flocculation of red mud in the bayer process
US6086771 *Nov 30, 1998Jul 11, 2000Nalco Chemical CompanyWater continuous emulsion polymers for improving scale control in the bayer process
US6210585Mar 30, 2000Apr 3, 2001Nalco Chemical CompanyFatty acid free latex polymer flocculants
US8097167Jan 4, 2007Jan 17, 2012Basf SeConcentration of suspensions
US8350254 *Feb 12, 2008Jan 8, 2013Kyungsung University Industry Cooperation FoundationMultilayer polymer electroluminescent device comprising water-soluble polymer layer containing cations and method for fabricating the same
US8506822Dec 8, 2011Aug 13, 2013Basf SeConcentration of suspensions
US20100252821 *Feb 12, 2008Oct 7, 2010Dong Kyu ParkMultilayer polymer electroluminescent device comprising water-soluble polymer layer containing cations and method for fabricating the same
USRE31900 *Mar 16, 1983May 28, 1985American Cyanamid CompanyProcess for the flocculation of suspended solids
EP0314855A2Jan 14, 1988May 10, 1989American Cyanamid CompanyPolymers containing hydroxamic acid groups for reduction of suspended solids in bayer process streams
EP0352030A1 *Jul 14, 1989Jan 24, 1990Allied Colloids LimitedProcess for separating red mud in the recovery of alumina from bauxite
EP1368390A1 *Dec 19, 2001Dec 10, 2003Ondeo Nalco CompanyHigh molecular weight polymers containing pendant salicylic acid groups
WO2013060700A1Oct 24, 2012May 2, 2013Basf SeConcentration of suspensions
WO2014019993A1Jul 29, 2013Feb 6, 2014Basf SeConcentration of suspensions
U.S. Classification423/122, 526/287, 526/304, 210/734, 525/385, 526/240, 423/131, 525/329.4, 209/5, 525/154, 423/121
International ClassificationC02F1/54, C01F7/06, B03D1/016, C08F220/58, C08F220/56, C08F220/04
Cooperative ClassificationC08F220/58, B03D1/016, C08F220/56, C08F220/04, C01F7/0653, C02F1/54
European ClassificationC08F220/58, C02F1/54, C01F7/06G2, C08F220/56, B03D1/016, C08F220/04
Legal Events
Jul 22, 1994ASAssignment
Effective date: 19940421
Jun 9, 1994ASAssignment
Effective date: 19940421
Jun 8, 1994ASAssignment
Effective date: 19940421