A process for treating a suspension of solid particles in water using a polymer of a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

Abstract

The present invention relates to a process for treating a suspension of solid particles in water using water-soluble polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid. This process is particularly useful for treating mining industry waste.

Description

Title of the invention: Process for treating a suspension of solid particles in water using a polymer of a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid. Field of the invention

[0001] The present invention relates to a method for treating a suspension of solid particles in water, such as mining residues, using water-soluble polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid. This method comprises the step of contacting said suspension with water-soluble polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid.

[0002] The process according to the invention consists, among other things, of adding said water-soluble polymers to a thickener containing this suspension to be treated and / or of adding said polymers during the transport of said suspension to a deposition area for its dehydration and solidification and / or of adding said polymers to said suspension and then carrying out a mechanical treatment, such as centrifugation, pressing or filtration. Prior state of the art

[0003] Suspensions of solid particles in water include all types of sludge, residues, or waste materials. These suspensions may result from the processing of ores. Examples include industrial sludge or residues and all mining washing and waste products resulting from mining operations, such as coal mines, diamond mines, phosphate mines, and metal mines (aluminum, platinum, iron, gold, copper, silver, etc.). Suspensions may also result from sludge or extraction residues derived from the processing of oil sands. These suspensions of solid particles generally comprise organic and / or mineral particles, such as clays, sediments, sand, metal oxides, petroleum, etc., mixed with water.

[0004] The term "suspension" is used hereafter (including the description of the invention) and refers to suspensions of solid particles as described above.

[0005] The treatment of these residues and other waste materials has become a technical, environmental, and public order problem. The use of synthetic or natural polymers, such as coagulants and flocculants, to separate solids from liquid is a common practice.

[0006] For a long time, and even today, mineral mud produced by physical or chemical ore processing was stored in the open air in basins, ponds, dams, or embankments in semi-liquid form. These large volumes of stored mud therefore create a real danger, especially if the dams fail.

[0007] Since traditional storage solutions are clearly dangerous, an increasing number of national regulations have been published prohibiting the abandonment of these areas. The regulations also call for an obligation to rehabilitate these sites, i.e., the treatment and consolidation of the soil.

[0008] Improving chemical and mechanical treatments of residues or sludge is therefore an important challenge.

[0009] Various attempts have been made over the past few decades to increase the sedimentation rate of tailings in order to efficiently recycle water and reduce tailings volume. The main physical treatments include centrifugation, filtration, electrophoresis, and electrocoagulation.

[0010] On the other hand, chemical processes have emerged. These include a process involving the addition of chemicals, such as sodium silicate, organic flocculants, inorganic coagulants, oxidizing and reducing agents and, more recently, carbon dioxide.

[0011] In 1979-1980, Alsthom Atlantique and SNF (US patent 4,347,140) developed a multi-stage flocculation (super-flocculation) system specifically designed to treat clay tailings ponds from phosphate production in Florida.

[0012] The suspension treatment has been studied continuously: in 1986 according to the process described in document CA 1 273 888, then in 1994 in document WO 96 / 05146, in 2000 in document CA 2 407 869 and in 2004 in document CA 1 515 581.

[0013] In document CA 2 682 542, the process involves the addition of polymers modified by copolymerization and / or branching. Polymers with hydrophobic groups, which were also studied, showed improved treatment of suspensions.

[0014] Despite significant progress in recent years, there remains a need to develop polymers that increase the speed and quantity of water released from suspensions. Improving the physical characteristics of the resulting sludge is also a priority. Description of the invention

[0015] The Applicant has found and developed a process for treating suspensions of solid particles in water using at least one water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid which makes it possible to meet the needs mentioned above.

[0016] Quite surprisingly, the use of at least one water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid allows for the efficient treatment of suspensions of solids.

[0017] More specifically, the present invention relates to a method for treating a suspension of solid particles in water, comprising contacting said suspension with at least one water-soluble polymer of 2-acrylamido-2- methylpropane sulfonic acid, 2-Acrylamido-2-methylpropane sulfonic acid being, before polymerization, a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6°, degrees 2-theta (+ / - 0.1°).

[0018] The presence of the monomer in crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid in the monomeric composition of the water-soluble polymer gives the latter particular properties, allowing it to improve the treatment of solid particles in suspension.

[0019] According to the invention, a water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid improves the performance of suspension treatments such as: - the increase in sludge concentration at the outlet of a thickener, - the dehydration stage and the drying and solidification stages of the suspensions when they are unloaded onto the ground, and - the mechanical treatment of the treated suspensions.

[0020] The best performance of polymers obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid for the treatment of suspensions allows the reduction of the quantity of product required and therefore the reduction of the overall consumption of water and of greenhouse gas emissions such as CO2.

[0021] Another object of the invention relates to a method for flocculating a suspension of solid particles in water, comprising bringing said suspension into contact with at least one water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid, Description of the invention

[0022] The term "polymer" refers to a homopolymer or a copolymer. A copolymer is defined as a polymer obtained from at least two different monomers. It can therefore be a copolymer of at least two monomers chosen from anionic monomers, cationic monomers, nonionic monomers, zwitterionic monomers, hydrophobic monomers, and mixtures thereof.

[0023] By "hydrophilic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, of less than 1, in which the partition coefficient Kow is determined at 25°C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0024] By "hydrophobic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, greater than 1, in which the partition coefficient Kow is determined at 25°C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0025] The octanol / water partition coefficient, Kow, represents the ratio of the concentrations (g / L) of a monomer between the octanol phase and the aqueous phase. It is defined as follows:

[0026] [Math.l] [monomer] ocîa na! ' ï [ m on ome re ] eau

[0027] By definition, a water-soluble polymer is a polymer which gives an aqueous solution without insoluble particles when dissolved under stirring at 25°C and with a concentration of 50 gL 1 in water.

[0028] By "X and / or Y" means "X", or "Y", or "X and Y".

[0029] Also part of the invention are all possible combinations between the The disclosure includes various embodiments, whether preferred or given by way of example. Furthermore, when ranges of values ​​are specified, the bounds are included within those ranges. The disclosure also encompasses all combinations of the bounds within those ranges. For example, the value ranges "1-20, preferably 5-15" imply the disclosure of the ranges "1-5", "1-15", "5-20", and "15-20", as well as the values ​​1, 5, 15, and 20.

[0030] Crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

[0031] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid has a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta. The uncertainty of these peaks is generally on the order of + / - 0.1°.

[0032] X-ray crystallography, radiocrystallography, or X-ray diffractometry is an analytical technique that allows the study of the structure of crystalline matter at the atomic scale. It is based on the physical phenomenon of X-ray diffraction. A diffractometer with a copper source can be used.

[0033] A powder formed from a particular crystalline phase always exhibits diffraction peaks in the same directions. This diffraction pattern thus forms a true signature of the crystalline phase. It is therefore possible to determine the nature of each crystalline phase within a mixture or a pure product.

[0034] This signature is specific to each organic or inorganic crystalline compound, and takes the form of a list of position peaks at an angle of 20 (2-theta).

[0035] This technique is used to characterize matter, in particular the different crystalline forms that can exist for the same chemical molecule.

[0036] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid has a Fourier transform infrared spectrum comprising peaks at 3576 cm⁻¹, 3485 cm⁴, 3310 cm⁴, 3079 cm⁴, 2975 cm⁴, 1658 cm⁴, 1629 cm⁴, 1543 cm⁻¹, 1403 cm⁴, 1321 cm⁴, 1301 cm⁻¹, 1205 cm⁻¹, 1187 cm⁴, 1163 cm⁴, 1046 cm⁻¹, 980 cm⁴, and 629 cm⁴. The uncertainty of these peaks is generally on the order of + / - 8 cm⁴.

[0037] Infrared measurement is carried out by Fourier transform, for example using a Perkin Elmer Spectrum 100 type spectrometer equipped with a single reflection ATR polarization accessory, the accuracy of which is 8 cm4.

[0038] Fourier transform infrared spectroscopy is the analysis of vibrations emitted, absorbed, or scattered by molecules. This technique is sensitive to so-called short interactions (influence of the unit cell on the bonds). In most cases, the Fourier transform infrared spectra of different crystal systems differ significantly. The Fourier transform infrared spectrum therefore reflects the details of the crystal structure of a chemical compound.

[0039] Generally, and unless otherwise indicated, the X-ray diffraction pattern and the infrared spectrum are obtained at 20°C and at a pressure of 1 absolute atmosphere (101,325 Pa).

[0040] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid has a minimum ignition energy greater than 500 mJ, preferably greater than 1000 mJ (1 mJ = 103 joules).

[0041] The minimum ignition energy represents the minimum energy that must be supplied to a product (chemical compound) to cause it to ignite. The energy can be electrical or thermal. The minimum ignition energy is an essential factor for considering the risk of explosion during the handling of the product (transfer, storage, reaction, shaping, etc.).

[0042] The minimum ignition energy depends on the properties of the powder (composition) as well as its macromolecular structure (particle size, crystalline shape, specific surface area).

[0043] In the case of solids, this energy is the minimum energy of an electrical spark capable of igniting a dust cloud. The higher the value of the minimum ignition energy, the lower the risk posed by the solid during its use, handling, and storage.

[0044] The measurement of the minimum ignition energy is carried out according to the standard NF EN 13821.

[0045] The crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid exhibits four thermal phenomena when observed by differential scanning calorimetry at 49.8°C, 144.8°C, 169.8°C, and 254.3°C. The uncertainty in observing these phenomena is generally on the order of 10°C, advantageously 5°C or less.

[0046] Thermal phenomena are measured by differential scanning calorimetry (DSC). This technique exploits the measurement of the heat variation associated with the thermal denaturation of the compound when it is heated at a constant rate, for example with a heating ramp of 10°C / minute.

[0047] Process for manufacturing the crystalline form of sodium salt

[0048] The process for manufacturing the crystalline form of the sodium salt of 2- acid acrylamido-2-methylpropane sulfonic acid comprises at least the following successive steps: 1) mixing of 2-acrylamido-2-methylpropane sulfonic acid with an aqueous solution SAi and at least one sodium salt, advantageously for at least 1 minute, in order to form an aqueous solution or aqueous suspension SA2; 2) distillation at a pressure lower than atmospheric pressure of the aqueous solution or aqueous suspension SA2 in order to form a suspension Si; 3) solid / liquid separation of the Si suspension and isolation of the Si suspension crystals obtained at the end of step 2) in the form of a Cp composition. The crystals obtained are in crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0049] By sodium salt(s) in step 1), means at least one inorganic salt(s), for example sodium hydroxide, sodium carbonate, sodium bicarbonate or mixtures thereof.

[0050] The temperature and mixing time in step 1) may vary depending, in particular, on the concentration of 2-acrylamido-2-methylpropane sulfonic acid. Those skilled in the art will know how to adjust the temperature and mixing time to optimize crystal formation.

[0051] The process for manufacturing the crystalline form of the sodium salt can be carried out on any form of 2-acrylamido-2-methylpropane sulfonic acid, such as the needle form or the hydrated form.

[0052] The manufacturing process can be carried out on any degree of purity of 2-acrylamido-2-methylpropane sulfonic acid.

[0053] Thus, the process can be carried out downstream of any type of manufacturing process for 2-acrylamido-2-methylpropane sulfonic acid. It can also be carried out on crystals of 2-acrylamido-2-methylpropane sulfonic acid already obtained.

[0054] Step 1) of the process for manufacturing the crystalline form of sodium salt:

[0055] 2-Acrylamido-2-methylpropane sulfonic acid is produced by a manufacturing process as described above (acrylonitrile, fuming sulfuric acid, and isobutylene). 2-Acrylamido-2-methylpropane sulfonic acid may be in the form of a fine powder or shaped in a controlled manner by a process such as compaction, granulation, or extrusion.

[0056] 2-Acrylamido-2-methylpropane sulfonic acid can be added to an aqueous solution S Ai before, after or in parallel with sodium salt, preferably the addition is done in parallel.

[0057] Advantageously, the concentration of the aqueous solution or aqueous suspension SA2 in sodium salt is between 1% by weight and saturation, preferably between 10% by weight and saturation, more preferably between 20% by weight and saturation, more preferably between 30% by weight and saturation, more preferably between 40% by weight and saturation, and even more preferably between 50% by weight and saturation, by weight relative to the weight of the aqueous solution or aqueous suspension SA2.

[0058] 2-Acrylamido-2-methylpropane sulfonic acid and the sodium salt can be added all at once or in several stages. Preferably, they are added in several stages.

[0059] When the addition is made in several stages, the 2-acrylamido-2-methylpropane sulfonic acid and the sodium salt are added in fractions.

[0060] When 2-acrylamido-2-methylpropane sulfonic acid and sodium salt are added in fractions, there is no limit to the number of fractions, advantageously there are at least two fractions, preferably at least three fractions.

[0061] There is no limitation as to the order of addition between 2-acrylamido-2-methylpropane sulfonic acid and the sodium salt. They can be added at the same time (i.e. in parallel), one after the other (2-acrylamido-2-methylpropane sulfonic acid first then the sodium salt, or vice versa), or alternately (a first fraction of 2-acrylamido-2-methylpropane sulfonic acid, then a first fraction of the sodium salt, followed by a second fraction of 2-acrylamido-2-methylpropane sulfonic acid then a second fraction of the sodium salt and so on), preferably they are added at the same time.

[0062] When adding one after the other or alternately, the start of the addition of the second compound (whether it be 2-acrylamido-2-methylpropane sulfonic acid or sodium salt) can start before the end of the addition of the first compound.

[0063] A first fraction Fl of 2-acrylamido-2-methylpropane sulfonic acid advantageously represents at least 1 mol% of the total 2-acrylamido-2-methylpropane sulfonic acid present in the aqueous solution or aqueous suspension SA2, preferably at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol% and even more preferably at least 20 mol%.

[0064] A second fraction F2 of 2-acrylamido-2-methylpropane sulfonic acid advantageously represents at least 1 mol% of the total 2-acrylamido-2-methylpropane sulfonic acid present in the aqueous solution or aqueous suspension SA2, preferably at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol% and even more preferably at least 20 mol%.

[0065] A third fraction F3 of 2-acrylamido-2-methylpropane sulfonic acid advantageously represents at least 1 mol% of the total 2-acrylamido-2-methylpropane sulfonic acid present in the aqueous solution or aqueous suspension SA2, preferably at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol% and even more preferably at least 20 mol%.

[0066] In a particular mode, the process is carried out continuously; in this case, 2-acrylamido-2-methylpropane sulfonic acid and sodium salt are added continuously.

[0067] The amount of 2-acrylamido-2-methylpropane sulfonic acid in the aqueous solution or aqueous suspension SA2 is advantageously between 10 and 90% by weight relative to the total weight of the aqueous solution or aqueous suspension SA2, preferably between 20 and 85% by weight, more preferably between 30 and 80% by weight.

[0068] The mixing in step 1) is advantageously carried out at a temperature between 0 and 90°C, preferably between 5 and 60°C, more preferably between 10 and 40°C, in order to obtain the aqueous solution or aqueous suspension SA2.

[0069] In a particular mode, the aqueous solution or aqueous suspension SA2 may comprise one or more organic solvents.

[0070] The amount of organic solvent can vary depending on the temperature and the amount of 2-acrylamido-2-methylpropanesulfonic acid or sodium salt. This amount is not limited as long as it does not prevent the formation of the crystalline form of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid. A person skilled in the art will be able to determine this limit, which is a routine task. Generally, the aqueous solution or aqueous suspension SA2 contains more water (by volume) than organic solvent.

[0071] The organic solvent(s) are advantageously chosen from the following compounds: - organic acids, advantageously carboxylic acids comprising 1 to 8 carbons; - amides advantageously comprising from 1 to 8 carbon atoms; - alcohols advantageously comprising from 1 to 8 carbon atoms; - ketones advantageously comprising 3 to 8 carbon atoms; - ethers advantageously comprising from 2 to 8 carbon atoms; - esters advantageously comprising from 2 to 8 carbon atoms; - alkanes advantageously comprising 4 to 8 carbon atoms; - halogenated hydrocarbon compounds advantageously comprising from 2 to 8 carbon atoms; - nitriles advantageously comprising from 1 to 8 carbon atoms; or - their mixtures.

[0072] When an organic solvent is used in the context of the invention, the temperature can be adjusted so that the solvent + water mixture remains in liquid form.

[0073] These compounds can be linear or branched. They can be saturated or include unsaturations, an unsaturation corresponding to a double or triple bond (for example C=C or C=C).

[0074] Preferably, the organic solvent is chosen from acrylonitrile, isopropanol, acrylic acid, acetic acid, or mixtures thereof. Preferably, the organic solvent is acrylonitrile.

[0075] The organic solvent is generally in liquid form at the temperature at which steps 2) and 3) are carried out. In addition, it is advantageously partially miscible in water, preferably completely miscible in water.

[0076] The organic solvent may, where appropriate, allow the solubilization of any impurities or by-products present with the 2-acrylamido-2-methylpropane sulfonic acid used to form the aqueous solution or aqueous suspension SA2. However, 2-acrylamido-2-methylpropane sulfonic acid is not necessarily soluble in the solvent.

[0077] In a preferred mode according to the invention, the aqueous solution or aqueous suspension SA2 does not contain any organic solvent.

[0078] The mixing time between the aqueous solution SAb and 2-acrylamido-2-methylpropane sulfonic acid is advantageously at least 1 minute, preferably between 1 minute and 600 minutes, more preferably between 5 minutes and 400 minutes, and even more preferably between 10 minutes and 240 minutes.

[0079] The mixing of the compounds in step 1) can be carried out by various technologies. By way of example and without limitation, we can mention reactors with agitators, loop reactors, static mixers, microreactors, plug flow reactors, agitated filter-dryer reactors, for example Nutsche, paddle mixers, twin-cone mixers, plowshare mixers, and disc mixers.

[0080] The pH of step 1) is advantageously controlled between 6 and 14, preferably between 8 and 14, more preferably between 10 and 14, even more preferably between 12 and 14, even more preferably between 13 and 14.

[0081] Step 2) of the process for manufacturing the crystalline form of sodium salt:

[0082] The distillation of the aqueous solution or aqueous suspension SA2 is carried out at a pressure lower than atmospheric pressure. It is generally carried out in a vacuum distillation device, which is typically an evaporator. It is therefore also referred to here as "vacuum distillation".

[0083] When the aqueous solution or aqueous suspension SA2 is distilled, typically by passing through an evaporator, crystals of the sodium salt of acrylamido-2-methyl-2-propanesulfonic acid begin to form. There is then coexistence of the aqueous solution or aqueous suspension SA2 comprising acrylamido-2-methyl-2-propanesulfonic acid, at least one sodium salt, and crystalline solid particles of the sodium salt of acrylamido-2-methyl-2-propanesulfonic acid.

[0084] The distillation of the aqueous solution or aqueous suspension SA2 can be carried out using an evaporator. This can be a falling film evaporator, a rising film evaporator, a scraped thin-film evaporator, a short-path evaporator, a forced-circulation evaporator, a spiral-tube evaporator, or a flash-cooling evaporator. It can also be a continuously stirred reactor. Preferably, the distillation takes place in a scraped thin-film evaporator, a short-path evaporator, or a forced-circulation evaporator. Even more preferably, the distillation takes place in a scraped thin-film evaporator.

[0085] Generally, an evaporator is a device comprising an inlet for the solution to be treated (aqueous solution or aqueous suspension SA2), an outlet for removing the distilled solvent (water and any organic solvents), and an outlet for removing the Sp suspension

[0086] The residence time of the aqueous solution or aqueous suspension SA2 in the distillation device (advantageously under vacuum), which is advantageously an evaporator, in other words, the distillation time at a pressure below atmospheric pressure, is advantageously between 1 second and 600 seconds, preferably between 3 seconds and 300 seconds, and more preferably between 30 seconds and 100 seconds. The residence time corresponds to the time required to carry out step 2), that is, the time required to prepare the suspension Si by distilling the aqueous solution or aqueous suspension SA2. In other words, in the case of an evaporator, it is the residence time of the acrylamido-2-methyl-2-propanesulfonic acid (and / or its crystalline form of sodium salt) between the inlet and outlet of the device.This residence time depends on the amount of water (and any organic solvents), 2-acrylamido-2-propanesulfonic acid, and sodium salt present in the aqueous solution or aqueous suspension SA2. A person skilled in the art will be able to adjust this residence time to obtain 2-acrylamido-2-propanesulfonic acid in the crystalline form of sodium salt, depending on the quantity of the constituents of the aqueous solution or aqueous suspension SA2.

[0087] Distillation can be carried out in a vertical or horizontal evaporator. Preferably, it is carried out in a vertical evaporator.

[0088] The aqueous solution or aqueous suspension SA2 can flow co-currently or counter-currently with the vapors generated by evaporation. Preferably, it flows counter-currently with the vapors in the distillation apparatus. In other words, the aqueous solution or aqueous suspension SA2 is preferably introduced into the distillation apparatus, advantageously an evaporator, co-currently or counter-currently with respect to the distilled solvent.

[0089] The aqueous solution or aqueous suspension SA2 can circulate through one or more evaporators in series before obtaining the suspension Si. Preferably, it circulates in a single evaporator.

[0090] The pressure during distillation is advantageously between 1 and less than 1000 mbar absolute (1 mbar = 100 Pa). It is preferably less than 900 mbar absolute, more preferably less than 800 mbar absolute, more preferably less than 700 mbar absolute, more preferably less than 600 mbar absolute, more preferably less than 500 mbar absolute, more preferably less than 400 mbar absolute, more preferably less than 300 mbar absolute, more preferably less than 200 mbar absolute, more preferably less than 100 mbar absolute, and even more preferably less than 50 mbar absolute, and advantageously greater than 1 mbar absolute. The absolute pressure corresponds to the pressure relative to zero pressure (vacuum).

[0091] In a particular embodiment, step 2) includes an optional step 2') to facilitate solvent evaporation. Step 2') then consists of increasing the temperature of the aqueous solution or aqueous suspension SA2; in other words, the distillation according to step 2') is carried out at high temperature.

[0092] Heating during distillation can be achieved using various technologies. By way of example, and without limitation, we can mention heating with steam, hot water, electricity, vapor compression, or a heat pump. Thus, the distillation apparatus can be of the double-walled type, with a hot heat transfer fluid circulating between the two walls.

[0093] The aqueous solution or aqueous suspension SA2 is advantageously heated to a temperature between more than 5°C and 95°C, preferably between more than 10°C and 60°C, more preferably between more than 20°C and 40°C.

[0094] When the aqueous solution or aqueous suspension SA2 is heated, the temperature is advantageously higher than the temperature of step 1).

[0095] The temperature rise of the solution or aqueous suspension SA2 is advantageously carried out at a rate of between 0.1 and 10°C / hour, preferably between 0.2 and 9°C / hour, more preferably between 0.3 and 8°C / hour, and even more preferably between 0.5 and 5°C / hour.

[0096] The temperature rise may not be constant throughout the process. For example, the aqueous solution or aqueous suspension SA2 may be heated by 5°C per hour for the first three hours, and then heated at a rate of 10°C per hour until the final temperature is reached.

[0097] According to another particular embodiment of the invention, step 2) may include an optional step 2"), following or instead of step 2'), allowing to increase the productivity and profitability of the process of the invention by accelerating the crystallization of acrylamido-2-methyl-2-propane sulfonic acid in crystalline form as a sodium salt. Step 2") then consists of lowering the temperature of the aqueous solution or aqueous suspension SA2.

[0098] The aqueous solution or aqueous suspension SA2 is advantageously cooled to a temperature between 5 and less than 95°C, preferably between 10 and less than 60°C, more preferably between 20 and less than 40°C.

[0099] When the aqueous solution or aqueous suspension SA2 is cooled, the temperature is advantageously lower than the temperature of steps 1), 2) and optionally 2').

[0100] The temperature decrease of the aqueous solution or aqueous suspension SA2 is advantageously carried out at a rate of between 0.1 and 10°C / hour, preferably between 0.2 and 9°C / hour, more preferably between 0.3 and 8°C / hour, and even more preferably between 0.5 and 5°C / hour.

[0101] The temperature decrease may not be constant throughout the process. For example, the aqueous solution or aqueous suspension SA2 may be cooled by 5°C per hour for the first three hours, and then cooled at a rate of 10°C per hour until the final temperature is reached.

[0102] During the cooling of the aqueous solution or aqueous suspension SA2, crystals of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid are formed and a suspension Si is obtained.

[0103] In a particular mode, previously obtained sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid can be added during this step to modify the formation of the Sp II suspension. This is a crystallization seeding that allows for better control of the crystallization temperature, crystal particle size, particle size distribution, purity of the final product, and, potentially, yield. The sodium salt crystals of the acid

[0104] 2-acrylamido-2-methylpropane sulfonic thus added advantageously have a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta (+ / - 0.1°). According to a particular embodiment of the invention, the solvent distilled in step 2) can be partially or totally recycled to form the aqueous solution SAi of step 1). In other words, the distilled solvent is advantageously recycled at least partially into the aqueous SAp solution

[0105] According to another particular embodiment of the invention, the distilled solvent can be recycled partially or totally, generally to wash the sodium salt crystals of acrylamido-2-methyl-2-propane sulfonic acid obtained after liquid / solid separation step 3), in an optional step 4), with or without a pretreatment step.

[0106] The suspension Sb obtained advantageously comprises between 30 and 80% by weight of 2-acrylamido-2-methylpropane sulfonic acid in crystalline form of sodium salt, relative to the total weight of the suspension Si, preferably between 50 and 60% by weight.

[0107] During step 2), the pH is advantageously greater than 10, preferably greater than 11, more preferably greater than 12, even more preferably the pH is between 13 and 14.

[0108] Step 3 of the process for manufacturing the crystalline form of sodium salt:

[0109] Sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid contents in the suspension Si obtained at the end of step 2) are isolated by a liquid / solid separation step and are in the form of a composition Ci.

[0110] The liquid / solid separation step can be carried out using various technologies. By way of example, and without limitation, we can mention the use of a centrifuge, a decanter, a filter press, a stirred smoother filter, a belt filter, a disc filter, or a rotary drum filter. Preferably, the liquid / solid separation is carried out using a centrifuge. The liquid / solid separation can also be carried out by gravity settling.

[0111] Step 3) is advantageously carried out at a temperature between -20 and 40°C, preferably between -5 and 30°C.

[0112] Preferably after step 3) of liquid / solid separation, the sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid are not dried.

[0113] The isolated composition Ci has a sodium salt crystal content of 2-acrylamido-2-methylpropanesulfonic acid advantageously between 40 and 99%, preferably between 60 and 99% by weight, more preferably between 60 and 98%, by weight relative to the weight of composition Ci. The remainder of composition Ci may be water and / or solubilized sodium salt of 2-acrylamido-2-methylpropanesulfonic acid, and / or sodium salt introduced in step 1).

[0114] At the end of this step 3), the crystals are characterized as being crystals of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0115] In a particular mode, the liquid phase obtained as a result of the liquid / solid separation is used totally or partially in the aqueous solution S Ai of step 1).

[0116] During step 4) the pH is advantageously controlled between 6 and 14, preferably between 8 and 14, more preferably between 10 and 14, even more preferably between 12 and 14, even more preferably between 13 and 14.

[0117] Step 4) of the process for manufacturing the crystalline form of sodium salt:

[0118] In an optional step 4), the composition Ci containing the crystals obtained at the end of step 3) is washed using a washing solution.

[0119] The washing solution may be water, an aqueous solution of sodium salt (saturated or unsaturated), or a solution (saturated or unsaturated) of sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (advantageously in the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid), preferably it is a saturated solution of a sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0120] Examples of sodium salt solutions include a solution of sodium hydroxide, sodium carbonate, sodium bicarbonate, or mixtures thereof.

[0121] The washing solution may comprise one or more organic solvents.

[0122] The amount of organic solvent may vary depending on the temperature, the amount of sodium salt of 2-acrylamido-2-methylpropane sulfonic acid or the amount of sodium salt.

[0123] Advantageously, the washing solution does not include any organic solvent.

[0124] As already indicated in relation to step 1), the organic solvent is advantageously chosen from organic acids, amides, alcohols, ketones, ethers, esters, alkanes, halogenated hydrocarbon compounds, nitriles, or mixtures thereof. Preferably, the organic solvent is chosen from acrylonitrile, isopropanol, acetic acid, or mixtures thereof. More preferably, the organic solvent is acrylonitrile.

[0125] In a particular mode, the washing of the composition Ci obtained at the end of step 3) is carried out by spraying the washing solution onto said composition Ci.

[0126] In a particular mode, the washing of the composition Ci obtained at the end of step 3) is carried out by suspending the composition Ci in the washing solution.

[0127] The weight ratio between the aqueous washing solution and the composition Ci obtained at the end of step 3) is advantageously between 0.05:1 and 10:1 and more preferably between 0.1:1 and 5:1.

[0128] This washing step is advantageously carried out at a temperature between -5 and 40°C, preferably between 0 and 30°C. A person skilled in the art will know how to adjust the temperature so as not to solubilize the crystals of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0129] The sodium salt crystals of 2-acrylamido-2-methylpropane sulfonic acid obtained at the end of this optional step 4) can be isolated from the washing solution by a liquid / solid separation step, in the form of a C2 composition.

[0130] The liquid / solid separation step can be carried out using various technologies. By way of example, and without limitation, we can mention the use of a vertical or horizontal centrifuge, a decanter, a filter press, a belt filter, a disc filter, a pusher filter, or a rotary drum filter. Liquid / solid separation can also be carried out by gravity settling.

[0131] In a particular mode, the recovered washing solution can be used, totally or partially, again in step 4), with or without a prior treatment step.

[0132] In a particular mode, the recovered washing solution can be used, totally or partially, in the aqueous solution SAi in step 1), with or without a prior treatment step.

[0133] The pH of the washing solution in step 5 is advantageously controlled between 6 and 14, preferably between 8 and 14.

[0134] Step 5) of the process for manufacturing the crystalline form of sodium salt:

[0135] In an optional step 5), the composition Ci obtained at the end of step 3) or the composition C2 obtained at the end of step 4) is dried.

[0136] The drying stage can be carried out by various technologies. By way of example and without limitation, we can cite the use of all drying technologies by convection, conduction or radiation (fluidized bed dryer, flow bed dryer, conveyor belt drying, microwave drying, heated agitated smoothing filter drying, high frequency radiation drying, infrared, spray drying).

[0137] The drying operation can be carried out at atmospheric pressure or under vacuum.

[0138] The drying step can be carried out discontinuously (batch) or continuously.

[0139] Other steps in the process of manufacturing the crystalline form of the salt of sodium:

[0140] During the manufacturing process, i.e., during steps 1) to 5), and regardless of the step, it is possible to introduce at least one polymerization inhibitor to prevent the possible polymerization of 2-acrylamido-2-methylpropane sulfonic acid or its salt. This inhibitor may be chosen, without limitation, from hydroquinone, paramethoxyphenol, phenothiazine, 2,2,6,6-tetramethyl(piperidin-l-yl)oxyl, 4-hydroxy-2,2,6,6-tetramethyl(piperidin-l-yl)oxyl, phenylenediamine derivatives, or mixtures thereof.

[0141] Preferably, the inhibitor is paramethoxyphenol or 4-hydroxy-2,2,6,6-tetramethyl(piperidin-1-yl)oxyl.

[0142] The amount of inhibitor introduced relative to the amount of 2-acrylamido-2-methylpropane sulfonic acid introduced in step 1) is advantageously between 0.001% and 5% by weight, more preferably between 0.01% and 1% by weight.

[0143] The inhibitor can be introduced during any one or more steps of the process. Preferably, it is introduced in additional quantity during step 1). More preferably, the inhibitor is part of the aqueous solution SAi introduced in step 1).

[0144] The manufacturing process (steps 1) to 5)) can be carried out continuously or discontinuously (in batch). Composition of the water-soluble polymer

[0145] The water-soluble polymer is obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid, and advantageously from at least one other monomer which may be selected from hydrophilic nonionic monomers and / or hydrophilic anionic monomers and / or hydrophilic cationic monomers and / or hydrophilic zwitterionic monomers and / or hydrophobic monomers and mixtures thereof. It may be a polymer of several distinct monomers or a homopolymer.

[0146] Advantageously, the nonionic hydrophilic monomer(s) that may be used in the context of the invention are chosen, in particular, from the following group: acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkylacrylamides, N,N-dialkylmethacrylamides, N-vinylpyrrolidone, hydroxyalkyl acrylates, hydroxyalkyl methacrylates, and mixtures thereof. Among these nonionic monomers, the alkyl groups are advantageously C1-C5, more advantageously C1-C3. They are preferably linear alkyls. Preferably, the nonionic hydrophilic monomer is acrylamide.

[0147] The water-soluble polymer advantageously comprises between 1 and 99 mol% of non-ionic hydrophilic monomer(s), preferably between 40 and 95 mol%, more preferably between 45 and 90 mol%.

[0148] Advantageously, the hydrophilic anionic monomer(s) that may be used in the context of the invention may be selected from a wide range of sources. These monomers may have vinyl functional groups (advantageously acrylic, maleic, fumaric, malonic, itaconic, or allylic), and contain a carboxylate, phosphonate, phosphate, sulfate, sulfonate, or other anionically charged group. The anionic monomer may be in acidic form or as an alkaline earth metal salt, an alkali metal salt, or an ammonium salt. Examples of suitable monomers include acrylic acid; methacrylic acid; dimethylacrylic acid; itaconic acid; crotonic acid; maleic acid; fumaric acid; acrylamidoundecanoic acid; 3-acrylamido-3-methylbutanoic acid; maleic anhydride; 2-acrylamido-2-methylpropanesulfonic acid (ATBS); strong acid monomers having, for example, a sulfonic acid or phosphonic acid function such as vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropylacrylate, allylphosphonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane disulfonic acid; water-soluble salts of these monomers such as their alkali metal, alkaline earth metal, or ammonium salts; and mixtures thereof.In this list, the monomers mentioned as strong acid type exhibiting a sulfonic acid type function do not include the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0149] The water-soluble polymer advantageously comprises between 0.1 and 100 mol% of hydrophilic anionic monomer(s), preferably between 1 and 99 mol%, more preferably between 5 and 70 mol%, and even more preferably between 10 and 50 mol%. In this case, these percentages also include the crystalline form monomer of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid.

[0150] In a particular embodiment of the invention, the hydrophilic anionic monomer(s), other than 2-acrylamido-2-methylpropane sulfonic acid in crystalline form of the sodium salt, can be salified.

[0151] By "salified," it is understood that at least one acid function of the anionic monomer is replaced by a salt that neutralizes the negative charge of the acid function. In other words, the unneutralized (unsalified) form corresponds to the acidic form of the monomer, for example RC(=O)-OH in the case of the carboxylic acid function, while the neutralized form of the monomer corresponds to the form RC(=O)-O X+, where X+ is a positively charged counterion (for example, a metal salt or an ammonium compound). The neutralization of the acid functions of the water-soluble polymer may be partial or total.

[0152] The salt form advantageously corresponds to the salts of alkali metals (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium (for example the ammonium ion or a tertiary ammonium). The preferred salt is the sodium salt.

[0153] Salification can take place before, during or after polymerization.

[0154] In a particular embodiment according to the invention, the water-soluble polymer advantageously comprises between 1 and 100 mol% of anionic monomer(s) in salified form, preferentially between 20 and 100 mol%, more preferably between 50 and 100 mol% and even more preferably between 80 and 100 mol%.

[0155] Advantageously, the cationic hydrophilic monomer(s) that can be used in the context of the invention are chosen, in particular, from monomers derived from vinyl-type motifs (advantageously acrylamide, acrylic, allylic, or maleic), these monomers having a quaternary phosphonium or ammonium function. Examples include, in particular and without limitation, quaternized dimethylaminoethyl acrylate (ADAME), quaternized dimethylaminoethyl methacrylate (MADAME), dimethyldiallylammonium chloride (DADMAC), acrylamido propyltrimethyl ammonium chloride (APTAC), and methacrylamido propyltrimethyl ammonium chloride (MAPTAC). The quaternizing agent can be chosen from alkyl chlorides, dialkyl sulfates, or alkyl halides. The alkyl groups are advantageously C1-C3 and linear. Preferably, the quaternizing agent is chosen from methyl chloride or diethyl sulfate.

[0156] A person skilled in the art will know how to prepare the quaternized monomers, in particular by protonation, for example using an alkyl halide of the type RX, where R is a CrC3 alkyl group and X is a halogen (in particular methyl chloride). Furthermore, the present invention also covers DADMAC, APTAC, and MAPTAC type monomers in which the halide counterion is fluoride, bromide, or iodide instead of chloride.

[0157] In a preferred embodiment according to the invention, the cationic hydrophilic monomer is selected from diallyldialkyl ammonium salts such as diallyl dimethyl ammonium chloride (DADMAC); acidified or quaternized dialkyl-aminoalkylacrylamides; acidified or quaternized dialkyl-aminoalkylmethacrylamides, such as methacrylamido-propyl trimethyl ammonium chloride (MAPTAC), acrylamido-propyl trimethyl ammonium chloride (APTAC), and mixtures thereof. Advantageously, the alkyl groups are CrC3.

[0158] The water-soluble polymer advantageously comprises between 0 and 20 mol% of cationic monomer(s), preferably between 0 and 6 mol%.

[0159] Advantageously, the hydrophilic zwitterionic monomer(s) may be a derivative of a vinyl-type motif (advantageously acrylamide, acrylic, allyl, or maleic), this monomer having a quaternary amine or ammonium function and an acid function of the carboxylic (or carboxylate), sulfonic (or sulfonate), or phosphoric (or phosphate) type. Examples include, in particular and without limitation, derivatives of dimethylaminoethyl acrylate, such as 2-((2-(acryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, the 3-((2-(acryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate, 4-((2-(acryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(acryloyloxy)ethyl](dimethylammonio)acetate, dimethylaminoethyl methacrylate derivatives such as 2-((2-(methacryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate, 4-((2-(methacryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(methacryloyloxy)ethyl](dimethylammonio)acetate, dimethylamino propylacrylamide derivatives such as 2-((3-acrylamidopropyl) dimethylammonio) ethane-1-sulfonate, 3-((3-acrylamidopropyl) dimethylammonio) propane-1-sulfonate, 4-((3-acrylamidopropyl) dimethylammonio) butane-1-sulfonate, [3-(acryloyloxy) propyl] (dimethylammonio) acetate, derivatives of dimethylamino propyl methylacrylamide such as 2-((3-methacrylamidopropyl) dimethylammonio) ethane-1-sulfonate,3-((3-methacrylamidopropyl)dimethylammonio)propane-1-sulfonate, 4-((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate and [3-(methacryloyloxy)propyl](dimethylammonio)acetate and mixtures thereof.

[0160] The water-soluble polymer advantageously comprises 0 and 20 mol% of zwitterionic monomer(s), more preferably between 0 and 10 mol%.

[0161] Hydrophobic monomers, having a partition coefficient Kow greater than 1, may also be used in the preparation of the water-soluble polymer used in the process of the invention. They are preferably selected from the following list: alkyl, arylalkyl, and / or ethoxylated and / or propoxylated (meth)acrylamide esters; alkyl, arylalkyl, or dialkyl and / or ethoxylated and / or propoxylated (meth)acrylamide derivatives; cationic allyl derivatives having an alkyl, arylalkyl, or dialkyl chain and / or an ethoxylated and / or propoxylated chain; hydrophobic anionic or cationic (meth)acryloyl derivatives; and anionic or cationic monomeric (meth)acrylamide derivatives bearing a hydrophobic chain. The hydrophobic monomers may include halogen atoms, for example, chloride.

[0162] Among these hydrophobic monomers: - Alkyl groups are preferably at C3-C20. Alkyls at C6-C20 are preferably linear alkyls, while alkyls at C3-C5 are preferably branched. - the arylalkyl groups are preferably at C7-C25, more preferably at C7-C15, - the ethoxylated chains preferably comprise 6 to 100 -CH2-CH2-O- groups, more preferably 10 to 40, - the propoxylated chains preferably comprise 0 to 50 -CH2-CH2-CH2-O- groups, more preferably 0 to 20.

[0163] The water-soluble polymer advantageously comprises less than 5 mol% of hydrophobic monomers.

[0164] When the water-soluble polymer includes hydrophobic monomers, they are present in such quantity that the polymer remains soluble in water.

[0165] Monomers exhibiting a fluorescent function can also be used within the scope of the invention. A monomer exhibiting a fluorescent function can be detected by any suitable method, for example, by fluorometry with a fixed-wavelength fluorometer. Generally, detection of the monomer exhibiting a fluorescent function occurs at the excitation and emission maxima, which can be determined using a scanning fluorometer.

[0166] Monomers having a fluorescent function are chosen, for example, from monomers comprising sodium styrene sulfonate and styrene sulfonic acid, vinylimidazole and its derivatives, 9-vinyl anthracene and its derivatives, pyranine and its derivatives, coumarin and its derivatives, quinolaxin and its derivatives, pinacyanol and its derivatives, xanthydrol and its derivatives, luminol and its derivatives, dabsyl and its derivatives, 3-hydroxy-2-methylene-3-(l-naphthyl)propionic acid and its derivatives, rhodamine and its derivatives, N-dibenzosuberenylacrylamide and its derivatives, N-9-xanthenyllacrylamide and its derivatives, naphthalic derivatives, fluorescein and its derivatives, pyrene and its derivatives, carbostyril and its derivatives, pyrazoline and its derivatives, allyl dibenzosuberenol and its derivatives, chinconicine and its derivatives, quininone and its derivatives, luminol and its derivatives, and cinchoninone and its derivatives.

[0167] In a particular embodiment according to the invention, the water-soluble polymer may comprise at least one cyclic monomer having a hydrolyzable function. Advantageously, the cyclic monomer(s) having a hydrolyzable function are chosen from cyclic ketene acetals, thionolactones, and mixtures thereof.

[0168] The cyclic ketene acetal is advantageously chosen from: 2-methylene-1,3-dioxepane (MDO), 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), 2-methylene-4-phenyl-1,3-dioxolane (MPDL), 2-methylene-1,3,6-trioxocane (MTC), and mixtures thereof. Preferably, it is 2-methylene-1,3-dioxepane (MDO).

[0169] The thionolactone is advantageously chosen from: Dibenzo[c,e]oxepine(7H)-5-thione (DOT), e-thionocaprolactone, 3,3-dimethyl-2,3-dihydro-5Hbenzo[e] [1,4]dioxepine-5-thione (DBT) and mixtures thereof. Preferably, it is 3,3-dimethyl-2,3-dihydro-5Hbenzo[e] [1,4]dioxepine-5-thione.

[0170] In a particular mode according to the invention, the water-soluble polymer may comprise at least one LCST group.

[0171] According to the general knowledge of a person skilled in the art, a group at LCST corresponds to a group whose solubility in water for a concentration The specific heat transfer coefficient (HTC) of a polymer is determined by its temperature and changes depending on salinity. This coefficient is defined as a heating transition temperature that indicates a lack of affinity for the solvent. This lack of affinity results in opacification or loss of transparency, which can be caused by precipitation, aggregation, gelation, or viscosification of the solvent. The minimum HTC is called the LCST (Lower Critical Solubility Temperature). For each concentration of the polymer at the LCST, a heating transition temperature is observed. This temperature is higher than the LCST, which represents the minimum point on the HTC curve. Below this temperature, the polymer is soluble in water; above this temperature, the polymer loses its solubility in water.

[0172] In a particular mode according to the invention, the water-soluble polymer may comprise at least one UCST group.

[0173] According to the general knowledge of those skilled in the art, a UCST group corresponds to a group whose solubility in water, for a given concentration, changes below a certain temperature and as a function of salinity. It is a group exhibiting a cooling transition temperature that defines its lack of affinity for the solvent medium. This lack of affinity for the solvent results in opacification or a loss of transparency, which may be due to precipitation, aggregation, gelation, or viscosification of the medium. The maximum transition temperature is called the "UCST" (Upper Critical Solution Temperature). For each concentration of a UCST group, a cooling transition temperature is observed. This temperature is lower than the UCST, which is the maximum point on the curve.Above this temperature, the polymer is soluble in water; below this temperature, the polymer loses its solubility in water.

[0174] The quantities of the different monomer(s) will be adjusted by a person skilled in the art so as not to exceed 100% molar during the preparation of the water-soluble polymer. Water-soluble polymer

[0175] The 2-acrylamido-2-methylpropane used to obtain the water-soluble polymer is advantageously at least 50 mol% in the crystalline form of the sodium salt before polymerization, preferably between 70 and 100 mol%. More preferably, 100 mol% of the 2-acrylamido-2-methylpropane sulfonic acid used is in the crystalline form of the sodium salt.

[0176] In a preferred embodiment according to the invention, the water-soluble polymer contains only anionic hydrophilic monomers and nonionic hydrophilic monomers. In other words, it is preferably obtained from at least an anionic hydrophilic monomer and at least one non-ionic hydrophilic monomer.

[0177] In a particular embodiment according to the invention, the water-soluble polymer comprises between 0.1 and 100 mol% of 2-acrylamido-2-methylpropanesulfonic acid, preferably between 2 and 60 mol%, more preferably between 3 and 50 mol%, advantageously with at least 50 mol% of the 2-acrylamido-2-methylpropanesulfonic acid used in the crystalline form of the sodium salt, preferably between 70 and 100 mol%. More preferably, 100 mol% of the 2-acrylamido-2-methylpropanesulfonic acid used is in the crystalline form of the sodium salt.

[0178] In a particular embodiment according to the invention, the water-soluble polymer comprises between 1 and 99 mol% of non-ionic hydrophilic monomers, preferably between 40 and 95 mol%, more preferably between 45 and 90 mol%; and between 1 and 99 mol% of 2-acrylamido-2-methylpropanesulfonic acid, preferably between 5 and 70 mol%, more preferably between 3 and 50 mol%, advantageously with at least 50 mol% of the 2-acrylamido-2-methylpropanesulfonic acid used being, before polymerization, in the crystalline form of the sodium salt, preferably between 70 and 100 mol%. More preferably, 100 mol% of the 2-acrylamido-2-methylpropanesulfonic acid used is in the crystalline form of the sodium salt.

[0179] In a preferred embodiment according to the invention, the water-soluble polymer is a polymer based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid, with at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid used in the crystalline form of the sodium salt.

[0180] Preferably, the water-soluble polymer is a polymer consisting of acrylamide, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid with at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid used in the crystalline form of the sodium salt.

[0181] The water-soluble polymer can be partially or totally post-hydrolyzed.

[0182] According to the invention, the water-soluble polymer can have a linear, branched, cross-linked, star-shaped or comb-shaped structure. This structure can be obtained, according to the general knowledge of a person skilled in the art, for example by selection of the initiator, the transfer agent, the polymerization technique such as RAFT (Reversible-Addition Fragmentation chain transfer), NMP (Nitroxide-Mediated Polymerization) or ATRP (Atom Transfer Radical Polymerization), the incorporation of structural monomers, or the concentration.

[0183] The water-soluble polymer can further be structured by a branching agent. A structured polymer is defined as a non-linear polymer that has side chains such that, when this polymer is dissolved in water, it exhibits a high state of entanglement leading to very high low-gradient viscosities.

[0184] The branching agent is advantageously chosen from: - structural agents, which may be chosen from the group comprising polyethylene unsaturation monomers (having at least two unsaturated functions), such as vinyl, allylic, acrylic and epoxy functions, and examples include methylene bisacrylamide (MBA), triallyamine, or tetraallylammonium chloride or 1,2-dihydroxyethylene bis-(N-acrylamide), and / or - monomers having at least two epoxy functional groups, - monomers having at least one unsaturated function and one epoxy function, - macroinitiators such as polyperoxides, polyazo and polytransfer agents such as polymer-capturing polymers, and polyols, and / or - functionalized polysaccharides.

[0185] The amount of branching agent in the water-soluble polymer is advantageously less than 40,000 ppm, relative to the total weight of monomers in the water-soluble polymer, preferably less than 10,000 ppm, more preferably less than 5,000 ppm.

[0186] In a particular mode, the amount of branching agent is at least equal to 0.1 ppm, relative to the total weight of monomers of the water-soluble polymer, preferably at least 1 ppm.

[0187] When the water-soluble polymer includes a branching agent, the polymer remains soluble in water. A person skilled in the art will know how to adjust the amount of branching agent, and possibly the amount of transfer agent, to achieve this result.

[0188] In a preferred mode according to the invention, the water-soluble polymer does not comprise a branching agent.

[0189] In a particular mode according to the invention, the water-soluble polymer comprises a transfer agent.

[0190] The transfer agent is advantageously chosen from methanol, isopropyl alcohol, sodium, calcium, magnesium, or potassium hypophosphite; 2-mercaptoethanol; 3-mercaptopropanol; dithiopropylene glycol; thioglycerol; thioglycolic acid; thiohydracrylic acid; thiolactic acid; thiomalic acid; cysteine; aminoethanethiol; sodium, calcium, magnesium, or potassium methallysulfonate; and mixtures thereof. Preferably, it is sodium hypophosphite.

[0191] The amount of transfer agent in the water-soluble polymer is advantageously between 0 and 100,000 ppm, relative to the total weight of the monomers in the polymer, preferably between 0 and 10,000 ppm, more preferably between 0 and 1,000 ppm, and even more preferably between 0 and 100 ppm. When present, the transfer agent represents at least 0.1 ppm, relative to the total weight of the monomers in the water-soluble polymer, preferably at least 1 ppm.

[0192] In a particular mode according to the invention, the water-soluble polymer does not comprise a transfer agent.

[0193] In general, the water-soluble polymer does not require the development of a specific polymerization process. Indeed, it can be obtained using all polymerization techniques well known to those skilled in the art. These may include, in particular, solution polymerization; gel polymerization; precipitation polymerization; emulsion polymerization (aqueous or inverse); suspension polymerization; reactive extrusion polymerization; water-in-water polymerization; or micellar polymerization.

[0194] Polymerization is generally a radical polymerization, preferably by inverse emulsion polymerization or gel polymerization. By radical polymerization, we include free radical polymerization using UV, azo, redox, or thermal initiators, as well as controlled radical polymerization (CRP) techniques or matrix polymerization techniques.

[0195] Examples of controlled radical polymerization techniques include, but are not limited to, iodine transfer polymerization (ITP), nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer polymerization (RAFT), which includes MADIX technology (macromolecular design by interchange of xanthates), various organometallic-mediated radical polymerization (OMRP), and organoheteroatom-mediated radical polymerization (OHRP).

[0196] As already indicated, the water-soluble polymer can be post-hydrolyzed. Post-hydrolysis is the hydrolysis reaction of the polymer after its formation by polymerization of monomer(s). This step consists of the reaction of hydrolyzable functional groups of advantageously non-ionic monomers, more advantageously amide or ester functions, with a hydrolyzing agent. This hydrolyzing agent can be an enzyme, an ion-exchange resin, or an acid. Br0nsted (for example, a hydrohalic acid) or a Brpnsted base (for example, an alkali hydroxide or an alkaline earth hydroxide). Preferably, the hydrolyzing agent is a Brpnsted base. During this post-hydrolysis step of the water-soluble polymer, the number of carboxylic acid groups increases. This is because the reaction between the base and the amide or ester groups present in the water-soluble polymer produces carboxylate groups.

[0197] The water-soluble polymer can be in liquid, gel or solid form when its preparation includes a drying step such as spray drying, drum drying, radiation drying such as microwave drying, or fluidized bed drying.

[0198] The water-soluble polymer advantageously has a molecular weight of at least 0.5 million g / mol, preferably between 0.5 and 40 million g / mol, more preferably between 5 and 30 million g / mol. The molecular weight is understood to be the average molecular weight by weight. According to a particular embodiment, the water-soluble polymer may have a molecular weight between 5,000 and 100,000 g / mol or between 100,000 and 500,000 g / mol.

[0199] The molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to those skilled in the art and can be calculated from the reduced viscosity values ​​for different polymer concentrations by a graphical method consisting of plotting the reduced viscosity values ​​(ordinate axis) against the concentration (abscissa axis) and extrapolating the curve down to zero concentration. The intrinsic viscosity value is plotted on the ordinate axis or using the least squares method. The molecular weight can then be determined by the Mark-Houwink equation: [q] = KM [q] represents the intrinsic viscosity of the polymer determined by the solution viscosity measurement method. K represents an empirical constant. M represents the molecular weight of the polymer, a represents the Mark-Houwink coefficient. K and a depend on the particular polymer-solvent system.

[0200] Process for treating a suspension of solid particles in water

[0201] The Applicant has surprisingly discovered that the use of a water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid improves the performance of suspension treatments such as: - the increase in sludge concentration at the outlet of a thickener, - the dehydration stage and the drying and solidification stages of the suspensions when they are unloaded onto the ground, and - the mechanical treatment of the treated suspensions.

[0202] The invention therefore relates to a method for treating a suspension of solid particles in water, comprising contacting said suspension with at least one water-soluble polymer, said polymer being obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid. This method therefore involves mixing said suspension with the water-soluble polymer.

[0203] Such treatment can be carried out in a thickener, which is a retention zone, generally in the form of a tube section several meters in diameter with a conical bottom in which the particles can settle. According to a specific embodiment, the aqueous suspension is conveyed by means of a pipe (pipeline) to a thickener, and the water-soluble polymer is added to said pipe.

[0204] In a particular embodiment, the water-soluble polymer is added to a thickener that already contains the suspension to be treated. In a typical mineral processing operation, suspensions are often concentrated in a thickener. This results in a higher-density slurry exiting the bottom of the thickener, and an aqueous fluid released from the treated suspension (called liquor) exiting by overflow from the top of the thickener. The addition of the water-soluble polymer increases the concentration of the slurry and increases the clarity of the liquor.

[0205] In a particular embodiment, the water-soluble polymer is added to the particle suspension during its transport, via a pipe, to a deposition zone. Preferably, the water-soluble polymer is added in the pipe that transports the suspension to the deposition zone. The treated suspension is then spread over this deposition zone for dehydration and solidification. The deposition zones may be open, such as an undefined area of ​​soil, or closed, such as a basin or a cell.

[0206] An example of these treatments during the transport of the suspension is the spreading of the suspension treated with the water-soluble polymer on the ground for dehydration and solidification, and then the spreading of a second layer of the treated suspension on the first solidified layer.

[0207] Another example is the continuous spreading of the suspension treated with the water-soluble polymer such that the treated suspension falls continuously onto the suspension previously discharged in the deposition zone, thus forming a mass of treated material from which the water is extracted.

[0208] In a particular mode, the water-soluble polymer is added to the suspension, and then a mechanical treatment is carried out, such as centrifugation, pressing, or filtration.

[0209] The water-soluble polymer can be added simultaneously in different stages of the suspension treatment, i.e. for example in the pipe (pipeline) transporting the suspension to a thickener and in the slurry exiting the thickener which will be conveyed either to a settling area or to a mechanical treatment device.

[0210] The water-soluble polymer can be added to the aqueous suspension to be treated in liquid or solid form. It can be added as an emulsion (advantageously water-in-oil), an aqueous or oily polyphasic particulate suspension, or a powder. Preferably, the polymer is added as an aqueous solution obtained from a concentrated form of the polymer, such as a powder, a water-in-oil emulsion, or an aqueous or oily polyphasic particulate suspension.

[0211] In a particular mode, the aqueous polyphasic particulate suspension preferably comprises: - 15 to 60% by mass of at least one water-soluble polymer in the form of a solid particle with an average size between 5 and 500 pm; - 15 to 45% by mass of at least one salt of an alkali metal and / or at least one salt of an alkaline earth metal; - at least one thickening agent other than the water-soluble polymer; - at least 10% water by mass; and said suspension having a Brookfield viscosity between 500 and 20,000 cps at a temperature of 20°C, and said suspension having a density between 1.1 and 2 kg.L *.

[0212] In a particular embodiment, the oily particulate polyphasic suspension preferably comprises: - 15 to 60% by mass of at least one water-soluble polymer in the form of a solid particle with an average size between 5 and 500 pm; - at least one viscosifying agent other than the water-soluble polymer; - at least 10% oil by mass; and said suspension having a Brookfield viscosity between 500 and 20,000 cps at a temperature of 20°C, and said suspension having a density between 0.6 and 1.4 kg.L *.

[0213] Brookfield viscosity is measured with a Brookfield apparatus, fitted with an LV module, the module being able to rotate at a speed of 30 revolutions per minute, for example, the The measurement is advantageously carried out at 20°C. The density is measured at 20°C, at a pressure of 1 atm, i.e. 101,325 Pa.

[0214] When the water-soluble polymer is in solid form, it can be partially or totally dissolved in water using a polymer preparation unit such as the Polymer Slicing Unit (PSU) disclosed in document EP 2 203 245.

[0215] In a particular embodiment, the water-soluble polymer is added to the suspension in combination with at least one other polymer, synthetic or natural. These polymers may be added simultaneously or separately (before or after the addition of the water-soluble polymer). The other polymer may be water-soluble or swellable in water. It may be a dispersant, a coagulant, or a flocculant.

[0216] In a particular embodiment, the water-soluble polymer is added to the suspension in combination with a salt such as a calcium and / or magnesium salt. The water-soluble polymer and the salt may be added simultaneously or separately. The salts may be inorganic or organic. Suitable salts include calcium chloride, calcium acetate, calcium sulfate, calcium nitrate, calcium hydroxide, calcium carbonate, magnesium chloride, magnesium acetate, magnesium sulfate, magnesium nitrate, magnesium hydroxide, magnesium carbonate, calcium formate, calcium gluconate, calcium propionate, tricalcium phosphate, and calcium succinate.

[0217] The quantity of water-soluble polymer added to the aqueous suspension is advantageously between 50 and 5000 g per tonne of solid particles, by dry weight, of the suspension, preferably between 250 and 2000 g / t, more preferably between 500 and 1500 g / t. The quantity depends on the nature and composition of the suspensions to be treated; those skilled in the art will know how to adjust this quantity, which remains a routine adjustment for them.

[0218] According to the invention, the process makes it possible to efficiently treat a suspension of solid particles and more particularly of mineral particles.

[0219] Suspensions of solid particles in water include all types of sludge, residues, or waste materials. These suspensions originate particularly from mineral extraction and take the form of suspensions of mineral particles. They may, for example, consist of industrial sludge or residues and all mine washing and waste products from mining operations, such as coal mines, diamond mines, phosphate mines, and metal mines (aluminum, platinum, iron, gold, copper, silver, etc.). Suspensions may also originate from oil sands extraction, for example, sludge or extraction residues derived from oil sands processing. These suspensions generally include organic and / or mineral particles, such as, for example, clays, sediments, sand, metal oxides, petroleum, etc... mixed with water.

[0220] Generally, suspensions of solid particles are concentrated and contain between 5% and 60% by weight of solid particles, preferably between 20% and 50% by weight of solid particles, relative to the total weight of said suspensions.

[0221] The process according to the invention can also be useful for treating residues from oil sands extraction: so-called "fine tailings," that is, those containing a large quantity of clay, and for treating so-called "mature" fine tailings, or Mature Fine Tailings (MFT), that is, these same fine tailings after several years of sedimentation, and containing an even greater quantity of clay. The process according to the invention can also be used to treat so-called "fresh" tailings, that is, those coming directly from the operation of separating the bitumen from the soil from which it (the bitumen) is extracted.

[0222] Method for flocculating a suspension of solid particles in water

[0223]

[0224]

[0225] The present invention also relates to a method for flocculating a suspension of solid particles in water, comprising bringing said suspension into contact with at least one water-soluble polymer obtained from the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta. All the embodiments previously described concerning the process of treating a suspension of solid particles in water are also applicable to the process for flocculating a suspension of solid particles in water. The following examples are given only as an illustration of the object of the invention, without limiting it in any way. Examples

[0226] Example 1: Synthesis of 2-acrylamido-2-methylpropane sulfonic acid

[0227] In a 2000 ml double-jacketed stirred reactor, 1522 grams of acrylonitrile containing 0.4% water by weight and 180 grams of fuming sulfuric acid containing 104% H2SO4 (18% oleum) are added. The mixture is stirred for 1 hour and cooled by the reactor's double jacket, which maintains the temperature of the sulfonant mixture at -20°C.

[0228] 97 grams of isobutylene are added to the previous sulfonant mixture, at a flow rate of 1.6 grams / minute.

[0229] The temperature of the mixture is controlled at 45°C during the introduction of isobutylene. The particles of 2-acrylamido-2-methylpropanesulfonic acid precipitate in the mixture, and the solids content is approximately 20% by weight. The reaction mixture is filtered through a Buchner filter and dried under vacuum at 50°C. The resulting solid is 2-acrylamido-2-methylpropanesulfonic acid and is in the form of a very fine white powder.

[0230] Example 2: Synthesis of the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid

[0231] In a 1000 mL double-jacketed stirred reactor, 439 grams of a 22% sodium hydroxide solution (by weight in water) are added. To the preceding mixture are added 452 grams of 2-acrylamido-2-methylpropanesulfonic acid (white powder obtained from Example 1).

[0232] The mixture is stirred for 30 minutes, at 10°C, to form an aqueous solution SA2.

[0233] The aqueous solution SA2 is heated to a temperature of 40°C under a vacuum of 50 mbar for 20 minutes, then the temperature is maintained at atmospheric pressure for 30 minutes, and then cooled to a temperature of 10°C. The cooling time between 40°C and 10°C is 6 hours. A suspension Si of sodium salt crystals of 2-acrylamido-2-methylpropanesulfonic acid is obtained. The suspension Si is filtered using a Robatel vertical centrifuge. A solid of composition Ci is obtained, containing 80% by weight of sodium salt crystals of 2-acrylamido-2-methylpropanesulfonic acid.

[0234] The solid obtained is ground to form a powder which is then analyzed by X-ray diffraction over an angular range of 10 to 90°. The equipment used is a Rigaku miniflex II diffractometer equipped with a copper source.

[0235] The resulting solid has an X-ray diffraction pattern having the peaks The following characteristics: 11.7°; 12.2°; 13.2°; 13.5°; 25.1°; 25.8°; 26.9°; 29.1° 38.4°; 39.6°; 41.1°; 42.9° ; 15.6° ; 16.8° ; 17.8° ; 18.5° ; 19.1° ; 20.6° ; 21.4° ; 23.3° ; ; 29.5° ; 31.0° ; 33.0° ; 33.6° ; 34.4° ; 35.2° ; 35.9° ; 37.1° ; ; 45.1° ; 46.0° ; 47.2° ; 47.6° degrees 2- theta (+ / - 0.1°).

[0236] Example 3: Synthesis of 2-acrylamido-2-methylpropane polymers sulfonic

[0237] Water-soluble polymers of different monomeric compositions are obtained by reaction in a 1.5 L reactor equipped with a mechanical stirrer, a thermometer, and a nitrogen inlet. The monomers are introduced into the reactor in the presence of distilled water. An appropriate amount of sodium hydroxide is added in order to neutralize exactly 100% of the acid monomers (ATBS). The total concentration of monomers in the reaction mixture is 25% by weight.

[0238] Two types of ATBS (2-acrylamido-2-methylpropane sulfonic acid) powder are used, one in crystalline form of the sodium salt (polymer B); the other is not in crystalline form of the sodium salt, but in needle and acid form (polymer A).

[0239] The resulting mixture is homogenized, then cooled and degassed under a stream of nitrogen. Polymerization is then initiated using a sodium hypophosphite and tert-butyl hydroperoxide redox system. The resulting gel, obtained after polymerization, is then ground and dried in a drying oven to obtain a powder.

[0240] The different polymers obtained are all water-soluble polymers with high molecular weights between 10 and 12 million g / mol.

[0241] Polymer A (counterexample) is a polymer of acrylamide (70 mol%) and 2-acrylamido-2-methylpropane sulfonic acid in non-crystalline and acidic form (30 mol%).

[0242] Polymer B (example according to the invention) is a polymer of acrylamide (70 mol%) and 2-acrylamido-2-methylpropane sulfonic acid in crystalline form of the sodium salt (30 mol%).

[0243] Polymers A and B are dissolved in tap water to obtain aqueous solutions having a polymer concentration of 0.4% by weight relative to the total weight of the solution. Both solutions are mechanically stirred at 500 rpm until the polymers are completely dissolved and clear, homogeneous solutions are obtained. Example 4: Treatment of a mining effluent

[0244] A series of flocculation tests is carried out on a mining effluent from a coal mine, and having a solids content of 18.2% by weight.

[0245] A quantity of each solution, corresponding to a polymer dosage of 280 g of polymer per tonne of dry matter of the mine effluent, is added to 200 g of mine effluent and then a complete mixing is carried out manually until optimal flocculation and water release is observed.

[0246] The result is expressed using the LNE (Net Water Release), which corresponds to the total amount of water recovered 1 hour after the flocculation test, less the amount of water unduly added during the incorporation of the aqueous polymeric solution into the suspension. The same LNE is calculated after 24 hours, providing a good indication of the maximum water release.

[0247] The LNE with polymer A is 59 mL versus 83 mL with polymer B. The LNE after 24 hours with polymer A is 70 mL versus 90 mL with polymer B. The water released during flocculation with polymer B is clearer than that released during flocculation with polymer A.

[0248] The results of this experiment clearly demonstrate that the use of 2-acrylamido-2-methylpropane sulfonic acid in crystalline sodium salt form makes it possible to obtain a more effective polymer for flocculating a mining effluent from a coal mine.

[0249] Example 5: Treatment of red sludge from a Bayer process

[0250] Another series of tests is carried out on a red mud from a Bayer process, and having a solids content of 22.8% by weight.

[0251] Polymer C (counterexample) is a polymer of acrylamide (35 mol%) and 2-acrylamido-2-methylpropane sulfonic acid in non-crystalline and acidic form (65 mol%).

[0252] Polymer D (example according to the invention) is a polymer of acrylamide (35 mol%) and 2-acrylamido-2-methylpropane sulfonic acid in crystalline form of the sodium salt (65 mol%).

[0253] The same test protocol as that used on mining effluent from a coal mine is applied, with the difference that the quantity of polymer added is here 740 g of polymer per tonne of dry red mud.

[0254] The LNE (1 hour) with polymer C is 39 mL versus 51 mL with polymer D. The LNE after 24 hours with polymer C is 43 mL versus 60 mL with polymer D. The water released during flocculation with polymer D is clearer than that released during flocculation with polymer C.

[0255] The results of this experiment clearly demonstrate that the use of 2-acrylamido-2-methylpropane sulfonic acid in crystalline sodium form makes it possible to obtain a more effective polymer for flocculating red mud from a Bayer process.

Claims

Demands

1. A process for treating a suspension of solid particles in water, comprising contacting said suspension with at least one water-soluble polymer of 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid being, before polymerization, a crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid having a powder X-ray diffraction pattern comprising peaks at 11.7°; 12.2°; 13.2°; 13.5°; 15.6°; 16.8°; 17.8°; 18.5°; 19.1°; 20.6°; 21.4°; 23.3°; 25.1°; 25.8°; 26.9°; 29.1°; 29.5°; 31.0°; 33.0°; 33.6°; 34.4°; 35.2°; 35.9°; 37.1°; 38.4°; 39.6°; 41.1°; 42.9°; 45.1°; 46.0°; 47.2°; 47.6° degrees 2-theta.

2. A process according to claim 1, characterized in that at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid of the water-soluble polymer is, prior to polymerization, in the crystalline form of the sodium salt.

3. A process according to any one of claims 1 or 2, characterized in that the water-soluble polymer is a polymer of the crystalline form of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid, and of at least one hydrophilic monomer selected from nonionic monomers, anionic monomers, cationic monomers, zwitterionic monomers and mixtures thereof.

4. The process according to claim 3, characterized in that the non-ionic hydrophilic monomer is selected from acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides, N,N-dialkylmethacrylamides, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyridine, N-vinylpyrrolidone, hydroxyalkylacrylates, hydroxyalkyl methacrylates.

5. A process according to any one of claims 1 to 4, characterized in that the water-soluble polymer comprises between 1 and 99 mol% of non-ionic monomers, and between 1 and 99 mol% of 2-acrylamido-2-methylpropane sulfonic acid, at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid being, prior to polymerization, in the crystalline form of the sodium salt.

6. A process according to any one of claims 1 to 5, characterized in that the water-soluble polymer is a polymer based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid, at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid being, before polymerization, in the crystalline form of the sodium salt, or a polymer consisting of acrylamide, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid, at least 50 mol% of the 2-acrylamido-2-methylpropane sulfonic acid being, before polymerization, in the crystalline form of the sodium salt.

7. A process according to any one of claims 1 to 6, characterized in that the water-soluble polymer has a weight-average molecular weight of between 0.5 and 40 million g / mol.

8. A process according to any one of claims 1 to 7, characterized in that the amount of water-soluble polymer added to the aqueous suspension is between 50 and 5000 g per tonne of solid particles, in dry weight, of the suspension.

9. A process according to any one of claims 1 to 8, characterized in that the aqueous suspension of solid particles is derived from ore extraction and consists of a suspension of mineral particles.

10. A method according to any one of claims 1 to 9, characterized in that the suspension of solid particles contains between 5% and 60% by weight of solid particles.

11. A method according to any one of claims 1 to 10, characterized in that the aqueous suspension is transported by means of a pipe to a deposition zone and in that the water-soluble polymer is added to said pipe.