The present invention relates to water solubl copolymers formed from ethylenically unsaturated dibasi carboxylic acids of formula (I) :

where R ¹ = H and R ² = COOH or R = COOH and R = H and the use of the copolymers a flocculating agents, especially in Bayer process liquors. Water soluble anionic polymers formed fro ethylenically unsaturated dibasic acids and ethylenicall unsaturated monobasic acids are known to be useful as meta sequestrants , as builders for detergents, and as scal inhibitors. For instance US-A-4,519,920 describe copolymers of maleic acid and (meth)acrylic acid havin molecular weight up to 8,000, useful as scale inhibitors. The polymers are made by continuously feeding th (meth)acrylic acid during polymerisation to a solution o half-neutralised maleic acid. The aqueous solution of th polymeric product is subsequently neutralised by the use o alkali metal hydroxides or carbonates. EP-A-0106111, EP-A-O106110, EP-A-076992 and

EP-A-075820 all disclose copolymers of a monoethylenicall unsaturated dicarboxylic acid derived compound with monoethylenically unsaturated monocarboxylic acid derive compound. These copolymers are of low molecular weight an are useful as scale inhibitors in detergent compositions.

Higher molecular weight copolymers of ethylenicall unsaturated dibasic carboxylic acids are known for use a coagulants or flocculants. For instance CN-A-103292 describes the use of an acrylamide/maleic anhydrid copolymer as a coagulant to assist the multi-stag flocculation process for washing hydrated titanium dioxide. SU-A-1,411,297 describes the use of a neutralised copolyme

of acrylic acid and maleic anhydride having molecular weight about 1 x 10 as a flocculant for the treatment of aqueous effluent, especially sewage effluent, flocculation. In SU-A-1,028,683 a terpolymer of ammonium aleate, (meth)acrylic acid and ammonium (meth)aerylate is used to flocculate suspended matter from aqueous wastes from galvanic processes. In SU-B-842,041 a copolymer of maleic acid and acrylamide is used to remove suspended matter from impure water. In JP-A-52085287 (1977) a copolymer of acrylamide and up to 5 wt.% ethylenically unsaturated dicarboxylic acid is used as a sedimentation aid and a flocculant. In SU-A-402,530 copolymers of acrylamide with either maleic acid or fumaric acid are used as flocculants. In JP-A-47020078 (1972) acrylic and maleic acid are copolymerised in aqueous solution to form flocculant polymer. There are also several disclosures by Asanov et al and from Dzhalilova et al describing the use of copolymers of maleic acid with either acrylic acid or acrylamide and their use as flocculants for various substrates, including bentonite, sulphur and in water purification. Florea et al in Bui. Univ. Galati, Fasc. 6, 3, 23-32 (1980) and Chem. Abs. 96:102647, describe the use of copolymers of acrylic acid and maleic acid as flocculants for the treatment of sugarbeet juices and for clarifying wines.

US-A-3784526 describes the use of terpolymers of itaconic acid with acrylamide and acrylic acid as a flocculant for various media, including dispersions of red mud from bauxite treatment in the Bayer process. The present inventors have found, however, that the use of itaconic acid can lead to difficulties in polymerisation.

In US-A-4,608,237 the use of anionic polymers or copolymers of acrylic acid are described as crystal modifiers for addition to pregnant Bayer process liquors to minimise interference by sodium oxalate crystals. The polymer which can be provided in the form of a solution, water-in-oil emulsion, dry solid or gel form, may include

comonomers, one less preferred example of which is malei anhydride.

US-A-4,845,192 describes a procedure for extruding an dissolving gel form flocculant polymers and copolymer prior to their use as flocculants. Examples of copolymer for which the process may be used are polyacrylamides an copolymers of acrylamide with, inter alia, malei anhydride. The process is said to be of use for th dissolution of polymers for a variety of thickening an flocculating uses.

According to a first aspect of the present inventio the removal of suspended solids from Bayer process liquor is carried out in the presence of a flocculant polyme which comprises a copolymer of units derived fro ethylenically unsaturated dibasic carboxylic acids o formula (I) :

where R ¹ = H and R ² = COOH or R ¹ = COOH and R ² = H with units derived from ethylenically unsaturate copolymerisable monomer, the polymer having a molecula weight of at least 300,000. In this invention when we say the polymer comprise units "derived from" particular monomers, we intend t cover polymers in which the carboxylic acid moieties unit are in the free acid form, in neutralised form where th counterion is organic or inorganic and is preferably alkal metal or ammonium, or in anhydride form. Likewise monomer used to make the polymer may be in free acid, neutralise or anhydride form.

The flocculant polymer preferably has a molecula weight of at least 500,000, more preferably at leas 1,000,000 or more. The intrinsic viscosity(at 25°C in 1 NaCl buffered to pH 7.0 with 0.1M sodium phosphate) i

preferably at least 1 dl/g, more preferably at least 5 dl/g, for instance more than 10 dl/g.

The flocculant polymer used in this aspect of the invention is a copolymer of a dibasic acid of formula (I) with a copolymerisable monomer.

Maleic acid is the preferred monoethylenically unsaturated dibasic carboxylic acid monomer. At low levels of incorporation of dibasic acid monomer(eg 8%) flocculant polymers formed using fumaric acid monomer have molecular weight comparable with those formed using maleic acid monomer. At high levels of incorporation of dibasic acid monomer, however, the use of maleic acid monomer results in polymers with a higher molecular weight than the molecular weights of polymers based on fumaric acid monomer. It is possible to use a mixture of acids according to formula

(I).

The copolymerisable monomer may be non-ionic, anionic or cationic, most preferably non-ionic or anionic. A mixture of copolymerisable monomers may be used. The monomer is preferably selected from sulphonic and carboxylic acid monomers, especiallyAMPS and (meth)acrylic acid, and nonionic monomers, for instance selected from (meth)acrylamide, vinyl acetate, lower alkylene, aromatic vinylic compounds, lower alkyl (meth)aerylates, lower alkyl (meth)acrylamides. Preferably the comonomer comprises (meth)acrylic acid and/or (meth)acrylamide.

The flocculant polymer preferably comprises at least 5 mol% units derived from maleic and/or fumaric acid, more preferably at least 10 mol%, for instance 20 mol% or more, for instance up to 50 mol%.

In this invention the polymer is preferably provided in a form such that the carboxylic acid groups are wholly or partially neutralised, for instance by being present in the form of alkali metal, ammonium or amine salts. Usually at least 50%, preferably at least 80%, more preferably substantially 100% of the carboxylic acid groups present in the polymer are neutralised.

The flocculant polymer is preferably formed fr monomer components such that the anionic content i preferably at least 0.50 meq/g. The anionic content i calculated from the starting monomer mixture and assumi 100% conversiom, the weight of polymer including the weig of any counterions, which may be added in a pos neutralisation step.

The Bayer process liquors which are treated accordi to the second aspect of the invention are preferably thos which have as the main dispersed solid phase red mud. T liquors may thus be that settled in the primary settle and/or the various red mud washing stages. Alternativel or additionally the liquor may be the pregnant liqu treated before passing through the Kelly filter to clarif before precipitation of alumina trihydrate. T flocculants may also be used in the separation precipitated alumina trihydrate.

The invention is of particular benefit in t settlement and washing of red mud. In such processes t flocculant polymers used down the washing train may diff from one another, for instance by having graduall decreasing ionicity.

The polymer may be used in conjunction with oth natural or synthetic flocculant polymers known to be usef for the treatment of red mud-containing liquors. F instance the flocculant polymers may be used in conjuncti with dextran as described in our copending application E A-0367437 or with starch based flocculants. The floccula polymer may be used in conjunction with other chemic additives, for instance, with lime as described in o copending application EP-A-0352030.

According to a second aspect of the present inventio a new water soluble polymer flocculant comprises units a) , b) and c) derived from at least three ethylenical unsaturated monomers, in which the units are derived fr the following compounds:

a) ethylenically unsaturated dibasic carboxylic acids of formula (I) :

where R ¹ = H and R ² = COOH or R ¹ = COOH and R ² = H b) ethylenically unsaturated monobasic carboxylic acids c) copolymerisable termonomer selected from non-ionic, cationic and anionic ethylenically unsaturated compounds and the polymer has a molecular weight of at least 300,000.

In this aspect of the invention also the polymer is preferably provided in a form such that the carboxylic acid groups are wholly or partially neutralised, for instance by being present in the form of alkali metal, ammonium or a ine salts. Usually at least 50%, preferably at least 80%, more preferably substantially 100% of the carboxylic acid group present in the polymer are neutralised.

The units a are preferably derived from maleic acid, in which R ¹ = H and R ² = COOH.

In this aspect of the invention the units b are preferably derived from acrylic, methacrylic, crotonic or pentenoic acid, most preferably acrylic acid. Mixtures of b units may be used. The units c are preferably derived from copolymerisable nonionic or anionic compounds. Anionic compounds are for instance 2-acrylamido 2-methylpropane sulphonic acid (AMPS) or vinylsulphonic acid. Copolymerisable nonionic compounds are for instance lower alkyl esters of (meth) acrylic acid, lower alkyl amide derivatives of (meth)acrylamide, lower alkalene, aromatic vinyl compounds, or, most preferably (meth)acrylamide, most preferably acrylamide. Mixtures of two or more termonomer may be used. With respect to the first aspect of the invention, the flocculant polymer used therefore is most conveniently the flocculant terpolymer of this second aspect of the invention.

The flocculant polymer has a molecula weight of a least 300,000, preferably at least 500,000, more preferabl at least 1,000,000 or more. The intrinsic viscosity (a 25°C in IM NaCl buffered to pH 7.0 with 0.1M sodiu phosphate) is preferably at least 1 dl/g, more preferabl at least 5 dl/g, for instance more than 10. dl/g.

The flocculant polymer according to the second aspec of the invention preferably comprises at least 5 mol. units derived from the dibasic carboxylic acid of formul (I), more preferably at least 10 mol.%, for instance 2 mol.% or more for instance up to 50 mol%. Units b ar generally present in an amount of at least 5 mol.%, mor preferably at least 10 mol.%, most preferably 20 mol.% o more. Units derived from c are present in an aiaount of a least 1 mol.%, preferably at least 5 mol.%, for instanc more than 10 mol.%.

The polymer is preferably formed from monome components such that the anionic content of the polymer i at least 0.055 meq/g, more preferably at least 0.1 meq/g. The anionic content is calculated from the starting monome mixture and assuming 100% conversion, the weight of polyme including the weight of any counterions, which may be adde in a post-neutralisation step. For some applications, especially in the Bayer process, the anionic content i preferably at least 0.50 meq/g.

The new flocculant polymer may be used for th separation of suspended matter from aqueous liquors, wher anionic polymers are generally useful. Anionic polymer are generally used to remove inorganic suspended material from aqueous liquors. The suspended solids may thus b minerals such as clays or mineral ores. The polymers ar found to be particularly useful in various mining industr applications. Polymers which have a very high anioni content are found to be of particular use in the treatmen of Bayer process liquors.

The flocculant polymers of both aspects of thi invention may be produced in the form of a lo

concentration aqueous solution, by inverse phase emulsion or suspension polymerisation or by bulk aqueous (gel) polymerisation. In each of these processes the starting monomers are dissolved in aqueous solution. It is possible for one or more of the monomers to be added after polymerisation has started, for instance, by continuous gradual addition of one monomer which is more reactive than the others which may help to maintain a relatively constant polymer composition throughout the polymerisation. It is generally, however, unnecessary to use that technique and preferably all of the monomers are dissolved in the solution before polymerisation starts.

Where the total concentration of monomers in aqueous solution is relatively low, the polymer product may remain a pourable liquid, in which case it may be subsequently sold as such. Where the aqueous solution has a relatively high concentration of monomer, for instance more than 10%, for instance more than 25%, up to 50% or more, the product is generally a gel. The gel is preferably subsequently dewatered, by known techniques such as solvent extraction or direct drying, and comminuted to form a dry powder.

Where the polymerisation is an inverse phase polymerisation, the aqueous monomer phase is dispersed into water-immiscible solvent. An inverse emulsion polymerisation is conducted in the presence of emulsifier and the droplets formed are small, for instance less than 5 μm in diameter, especially around 1 or less than 1 μm in diameter. Where the polymerisation is an inverse suspension polymerisation, the aqueous phase is dispersed into the organic phase in the presence of an amphipathic polymeric stabiliser (known per se) , and the droplets formed are relatively large, for instance more than 50 μm in diameter, usually at least 100 μm in diameter, up to 500 μm. The product of an emulsion polymerisation may be subsequently sold and used as such. Alternatively it may be recovered as a solid, by known procedures in which the

dispersed phase is coagulated before or after dewatering Alternatively the liquid, emulsion product may be dewatere and then sold as a liquid product. The product of suspension polymerisation is recovered in dry form, b dewatering, usually by azeotropic distillation and the separation of the dry beads from the organic solvent.

Flocculant polymers according to the invention may b provided by a process in which acids of formula (I) ar copolymerised with an ethylenically unsaturated anioni comonomer, in which the monomers are polymerised i substantially wholly neutralised form and dissolved i aqueous solution, and the product polymer is subsequentl recovered as a solid.

The process of polymerisation is, for instance conducted as an aqueous gel polymerisation or an invers phase suspension polymerisation. The monomers may all b dissolved in the aqueous solution before polymerisation o a portion of one of the monomers may be added afte polymerisation has started for instance continuously.* It is usually preferred for the flocculant polymer t be provided for use in a partially or wholly neutralise form. It is most convenient for the neutralisation to b carried out on the monomers rather than on the produc polymer. The monomer starting materials to be used in th process for producing the polymer are therefore usuall provided in partially or, preferably, wholly neutralise form, for instance in the form of the alkali metal salt o ammonium or amine salt. Where the raw materials ar provided in the acid or anhydride form neutralisation i conducted by dissolution of the starting materials int aqueous solutions of, for instance, alkali metal hydroxid or ammonia, as the case may be.

It is necessary for the acid of formula (I) , or it anhydride if applicable, used to form the flocculan polymer material to be in its wholly neutralised form, whe the product is required to be supplied in its neutralise

form, since the half neutralised form of the acid has low solubility in water.

In the process the polymerisation may be initiated using conventional systems. The initiation may be by irradiation, optionally in the presence of photosensitiser components, - or, preferably, may be initiated by free radicals formed chemically, for instance by the use of a redox couple or by thermal initiators, which decompose to form free radicals above a certain temperature. In many instances it may be convenient to use a combination of redox and thermal initiation.

The amount of initiator and the polymerisation conditions (including the concentration of monomer, temperature of initiation and polymerisation, rate of reaction, control of retarders, inhibitors, chain transfer agents, crosslinking agents and other compounds which may interfere with the polymerisation, and the recovery procedures) are controlled by techniques known to those skilled in the art, to achieve the desired molecular weight whilst retaining adequate water solubility.

The flocculant polymer product may be mixed with diluents or with other flocculant ingredients, or admixed with additives which can assist in the storage stabilisation of the polymer or its subsequent use as a flocculant, to form a composition.

By the use of the present invention it has been found that very cost efficient flocculation of Bayer process liquors can be achieved. The use of the flocculant polymers gives low under flow solids volume (i.e. the separated solid contains low amounts of liquid) , as well as high degrees of clarity for the supernatant liquor, i.e. achieves good overall solids removal. It is believed that these results are due in part to the use of very high anionic content polymers, and in part to the achievement of very high molecular weight for maleic acid containing polymers, which hitherto have not been achieved. The

flocculants may be produced from monomers which are cheap, readily available and easy to polymerise.

The following examples illustrate the invention:

Examples

In all of the following examples slurries of Baye process liquors are made up from the individual components so as to simulate the liquor at various stages of the re mud circuit. The slurry, once made up, is treated with the flocculant polymer under test at the stated dose level, b a process in which the rate of settlement of solids from the liquor is determined by following the rate at which the level of the solids drops in a measuring cylinder, the volume of the underflow solids settled out after the process is recorded, and the clarity of the supernatant is determined in a "wedge" test. In this last test, the supernatant liquor is placed into a vessel which has a wedge shape, with the point of the wedge facing downwards. The rear face of the transparent container is marked with a series of graduations from 0 to 46, the highest of which is at the top of the wedge. The number recorded for the wedge test is the highest number which can be seen clearly through the solution in the container.

In these tests therefore a product which has suitable properties gives a high settlement rate, a low underflow volume and a high reading for the supernatant clarity wedge reading. In general in the tests the comparative product against which the products of the invention are compared is of the optimum sodium acrylate/acrylamide copolymer ratio on our range previously used on the liquor and of a similar molecular weight to the products of the invention. In each instance the polymer products of the invention were made by a process in which maleic anhydride was dissolved.

EXAMPLE 1

A red mud slurry was formed having a composition such as to simulate that of a primary thickener feed. Such a

slurry is formed of 30 g/1 red mud solids in a liquor containing 200 g/1 NaOH and 50 g/1 Na ₂ C0 ₃ and maintained at 90°C. High molecular weight water soluble anionic flocculants, as listed below, were added at 1, 2 & 3 mg/1. The settlement rate of solids was recorded in centimetres per minute. The volume of the settled underflow was recorded after 10 minutes settlement and the clarity of the supernatant was recorded after 10 minutes settlement.

In aqueous hydroxide of a concentration sufficient to neutralise the maleic anhydric fully to form disodium maleate, any comonomer was then added to the solution, such that other acids were fully neutralised. The total monomer concentration in the aqueous solution was 20-50%, typically 30%. To the aqueous solution was then added a free radical initiator system consisting of a redox initiator pair in combination with a thermal initiator and polymerisation allowed to free rise to completion. The polymer was recovered as a powder by chopping the wet gel and drying it in a fluid bed drier at about 60°C then grinding the dried particles to a particle size of about 500μm.

The inclusion of sodium maleate provides benefit in term of increased settlement rate, lower underflow volume an better supernatant clarity.

EXAMPLE 2

A red mud slurry was formed having a composition suc as to simulate that of a typical 1st Washer. Such a slurr is formed of 30 g/1 red mud solids in a liquor containin 96 g/1 NaOH and 24 g/1 Na ₂ C0 ₃ and maintained at 80°C. Hig molecular weight water soluble anionic flocculants, as i Example 1, were added at 1, 2 & 3 mg/1.

The remaining procedures was as in Example l.

The inclusion of sodium maleate provides benefits in terms of increased settlement rate and lower underflow volumes. Supernatant clarities are slightly worse than when no maleate is present, but acceptable.

EXAMPLE 3

A slurry as in example 2 was used, and products as listed below were added at 1, 2 & 3 mg/1. The remaining test procedure is as in Example 1.

Inclusion of sodium maleate increases the settlement rate obtained and provides a decrease in underflow volume. Supernatant clarities are all similar, but improve as sodium maleate content increases.

EXAMPLE 4

A red mud slurry was formed having a composition suc as to simulate that of a typical 2nd Washer. Such slurr is formed of 40 g/1 red mud solids in a liquor containin 56 g/1 NaOH and 14 g/1 Na ₂ C0 ₃ . High molecular weight wate soluble anionic flocculants, as in Example 3 were added a 3, 4 & 5 mg/1.

The remaining procedure was as in Example 3.

On this slurry an optimum sodium maleate content i observed with product Bl.

EXAMPLE 5

A slurry as in Example 4 was used. High molecula weight water soluble anionic flocculants, as listed below, were added at 2, 3 & 4 mg/1. The settlement rate of solid was recorded in centimetres per minute. The volume of th settled underflow was recorded after 10 minutes settlemen and the clarity of the supernatant was recorded after 1 minutes settlement.

Results tend to improve as maleate content increases, although optimum results are obtained with Product C2.

EXAMPLE 6

A red mud slurry was formed having a composition such as to simulate that of a 5th =» Final Washer Feed. Such a slurry is formed of 50 g/1 red mud solids in a liquor containing 25 g/1 NaOH. High molecular weight, water soluble anionic flocculants as listed below were added at 1, 2 & 3 mg/1. The remaining procedure was as in Example 1.

All samples containing sodium maleate provide benefit ove that without sodium maleate. Optimum results are provide by product D2. Example 7

A slurry made to stimulate the red mud washers of Bayer plant was prepared using the following ratios o ingredients taken from an operational plant: Thickener underflow 1 part First washer overflow 2 parts Second washer overflow 1 part The slurry was mixed and stored in a hot box at 95°c This slurry has the following characteristics. Solids 160 g/1

Total Alkali 171. 9 g/1

Total Caustic 144. 1 g/1

A1 ₂ 0 ₃ 93 .8 g/1

500ml of the slurry were taken in 500ml measuring cylinders and mixed using 5 strokes of a plunger. The same products as in Example 1 were used. Dose levels ranging from 4 to 8 mg/1 were added to individual cylinders and mixing was achieved by a total of 4 strokes of a plunger. The settlement rate of the solids was recorded, the underflow volume was measured after allowing 30 minutes settlement and the underflow solids calculated.

The solids remaining in the overflow after 30 minutes were determined by removing a 50ml aliquot and filtering through a pre-weighed filter paper. The residue was washed with deionised water. The filter paper and residue was oven-dried and then reweighed to allow the solids to be calculated.