EP3707098A1

EP3707098A1 - Phosphoric acid preparation

Info

Publication number: EP3707098A1
Application number: EP18827152.2A
Authority: EP
Inventors: Driss Dhiba; Benoît MAGNY; Hamid MAZOUZ; Céline METHIVIER; Jacques Mongoin
Original assignee: Coatex SAS; OCP SA
Current assignee: Coatex SAS; OCP SA
Priority date: 2017-11-09
Filing date: 2018-11-09
Publication date: 2020-09-16
Also published as: FR3073218A1; MA50575A; US20210171349A1; JOP20200111A1; US11702338B2; WO2019092380A1; CN111587219B; RU2020118880A; CN111587219A; FR3073218B1

Abstract

The invention relates to a method for the industrial preparation of phosphoric acid from an aqueous suspension comprising water and particles of at least one phosphate material, dispersed in the presence of at least one anionic polymer-type additive. The phosphoric acid is obtained by treating the suspension with at least one strong acid. The polymer is obtained by means of the polymerisation reaction of at least one acid selected from acrylic acid, methacrylic acid and the salts of same. The invention relates to the use of this anionic polymer and to the method for improving the rheology of the suspension and the hydrodynamics of the reaction medium that is the site of the phosphoric-acid-producing reactions.

Description

Preparation of phosphoric acid

Description

The invention relates to a method for the industrial preparation of phosphoric acid from an aqueous suspension comprising water and particles of at least one phosphated material dispersed in the presence of at least one additive of the anionic polymer type. The phosphoric acid is obtained by treating this suspension with at least one strong acid. The polymer is obtained by polymerization reaction of at least one acid selected from acrylic acid, methacrylic acid and their salts.

The invention relates to the use of this anionic polymer as well as the method for improving the rheology of the suspension and the hydrodynamics of the reaction medium of the phosphoric acid production reactions.

As such, the method for preparing the aqueous suspension comprising water and particles of at least one phosphated material dispersed in the presence of at least one additive of the anionic polymer type is also particularly efficient.

The phosphoric acid thus prepared is a product essential for the manufacture of fertilizers, especially ternary fertilizers, NPK, or binary fertilizers, NP. Phosphoric acid is also used in the manufacture of food products, particularly for the acidification of beverages, or for the treatment of metal surfaces or in the field of microelectronics.

Phosphate rocks are important sources of raw material for the manufacture of phosphoric acid. Phosphoric acid (H3PO4) can be produced mainly by two methods: wet process and thermal process. The wet process is the most used and the phosphoric acid from this route can be used to produce phosphate fertilizers (DAP or diammonium phosphate, MAP or monoammonium phosphate, TSP or triple superphosphate). The heat-treated acid is of higher purity and is generally used for pharmaceuticals or food products. In a wet process unit, phosphoric acid is produced in particular by the action of the strong acid on the natural phosphate ore. Sulfuric acid is the strongest acid used. In this case, insoluble calcium sulfate is formed which is separated by filtration to recover the gypsum. The operating conditions are chosen in order to precipitate the calcium sulphate either in its dihydrate form, producing P 2 O 5 generally at a concentration of 26-32% at 70-80 ° C, or in the hemihydrate form, with P 2 O 5 generally at a concentration of concentration of 40-52% at 90-110 ° C. Evaporation can be used to further concentrate the phosphoric acid subsequently and thus optimize the quality of the acid.

Usually, after extraction, the phosphate rock is treated to be obtained in dry form or in wet form in which it is mixed with water, for example to form phosphate pulp.

In the latter case, a high concentration of phosphate rock makes it possible to reduce the quantity of water used during the treatment of a determined quantity of phosphate rock. Besides a better management of the resource, the reduction of the quantity of water is particularly interesting during the various stages of the preparation of phosphoric acid.

It is also important to be able to impart improved properties to the phosphate rock particles, in particular properties which make it possible to improve the efficiency of the phosphoric acid preparation reaction, for example by improving the hydrodynamics of the preparation reaction. 'Phosphoric acid. Thus, it is important to have improved methods for the production of phosphoric acid, in particular to increase the overall yield of the preparation reaction of phosphoric acid from phosphate rock.

The state of the art presents various evolutions of the phosphoric acid manufacturing process. For example, WO 2017/040795 describes a process for increasing the filtration rate or for improving the clarification of the phosphoric acid produced by a wet process. This process uses in particular a reagent comprising anionic polymer microparticles with a molecular weight greater than 60 million daltons. US 5120519 discloses anti-scale agents used in the digestion of phosphate rock to produce phosphoric acid. These agents are copolymers of acrylamide and acrylic acid, which have a molecular weight of at least 1,000,000 g / mol.

The document WO 2010 080806 relates to the control of the sedimentation of an aqueous synthetic mixture comprising a phosphate, a phosphonate, an anionic polymer, and an anionic polymer-cationic polymer mixture. The flocculating agents used have a molecular weight ranging from 250,000 to 30,000,000 g / mol.

EP 0274177 relates to the production of highly concentrated phosphoric acid by digestion of phosphates with an acid composed essentially of sulfuric acid and phosphoric acid. The process described uses polyacrylamide flocculating agents which have a very high molecular weight.

US 5185135 discloses a suspension from a process for producing wet phosphoric acid. This suspension is dehydrated by filtration using a polymeric filtration aid whose molecular weight ranges from 200,000 to 40,000,000 g / mol.

Furthermore, the document WO 2015105464 presents a modification of both the reaction device with a view to optimizing the solubilization rate of the phosphate rock to higher values and to ensuring better crystallization of the gypsum produced, as well as the filtration mode. to improve the filterability of the phosphoric acid slurry. As for the document CN 106395879, it aims to improve the size of the gypsum crystals during the manufacture of phosphoric acid by the wet method, by using a composite additive composed of a sulfonic acid regulator, an organic weak acid, an ammonium salt buffer agent and a high water soluble polymer content dispersant. Similarly US 4501724 proposes a process for the wet manufacture of concentrated phosphoric acid, based on the use of a mixture of sulfur trioxide gas and sulfuric acid instead of concentrated sulfuric acid. This results in a higher heat of reaction allowing the use of a very dilute sulfuric acid or a phosphate resulting from a wet grinding, without affecting the phosphoric acid titer produced.

When preparing phosphoric acid from phosphate rock, it is also important to monitor the overall water balance. Water is needed as a support for the treatment by means of a strong acid of the phosphate rock but its quantity must nevertheless be limited, in particular to avoid diluting the titer of the acid solution produced.

Similarly, in the preparation of phosphoric acid from phosphate rock, it is important to be able to improve the hydrodynamics during the treatment of phosphate rock with the strong acid, in order to reduce loss of phosphorus in an unexpected or co-crystallized form (syncrystallized) in the gypsum crystals formed.

The method for preparing phosphoric acid according to the invention makes it possible to provide a solution to all or part of these problems, in particular by a significant improvement in the phosphoric acid production conditions.

Thus, the invention provides a method of preparing phosphoric acid comprising treating at a temperature of from 40 to 100 ° C, using at least one strong acid, an aqueous suspension (A) comprising water and particles of at least one phosphated material whose size is between 10 and 400 μιη, and dispersed in the presence of at least one anionic polymer with a weight-average molecular weight (M _w ) of between 1,000 and 90,000 g and mol obtained by polymerization reaction of at least one acid selected from acrylic acid, methacrylic acid and their salts.

The use of this anionic polymer for the phosphoric acid preparation method according to the invention makes it possible to obtain a good compromise of the various properties of this preparation process, in particular the chemical yield of the reaction, the fluffability and the phosphoric acid titer. .

In a particularly advantageous manner, the preparation method according to the invention makes it possible to control the viscosity of the aqueous suspension (A).

In a preferred manner for the preparation method according to the invention, the Brookfield viscosity of the aqueous suspension (A), measured 90 seconds after preparation of the suspension, at 25 ° C., at 100 rpm and at a concentration greater than 45 ° C. % by weight of phosphated material is less than 1500 mPa.s or less than 1200 mPa.s, preferably less than 1000 mPa.s, more preferably less than 500 mPa.s or even less than 350 mPa.s or less than 200 mPa.s. More preferably, the Brookfield viscosity of the aqueous suspension (A), measured 90 seconds after preparation of the suspension, at 25 ° C., at 100 rpm and at a concentration greater than 60% by weight of phosphate material, is less at 1500 mPa.s or less than 1200 mPa.s, preferably less than 1000 mPa.s, more preferably less than 500 mPa.s or even less than 350 mPa.s or less than 200 mPa.s.

During the implementation of the method according to the invention, the phosphated material particles are treated in the aqueous suspension (A) comprising water and particles of phosphate material dispersed in the presence of an anionic polymer.

According to the invention, the phosphated material is used in the form of particles whose size is less than 400 μιη. More preferably, the size of these particles is less than 200 μιη or less than 150 μιη. Moreover, the size of these particles is greater than 10 μιη, preferably greater than 30 μιη.

Thus, for the preparation method according to the invention, the particle size of phosphate material can range from 10 to 400 μιη or from 10 to 200 μιη or from 10 to 150 μιη. In a preferred manner, this size can also range from 30 to 400 μιη or from 30 to 200 μιη or from 30 to 150 μιη. For the preparation method according to the invention, the phosphated material particles can be used in dried form. For the preparation method according to the invention, the particles of phosphated material can also be used in the form of an aqueous suspension (B). Preferably, the aqueous suspension (B) has a concentration of phosphate material greater than 45% by weight. More preferably, the aqueous suspension (B) has a concentration of phosphatic material greater than 50%, more preferably greater than 55%, much more preferably greater than 60% or 65%, or greater than 70% or 75% . Most preferably, the aqueous suspension (B) also comprises at least one anionic polymer according to the invention.

Also more preferably, the Brookfield viscosity of the aqueous suspension (B), measured 90 seconds after preparation of the suspension, at 25 ° C, at 100 rpm and at a concentration greater than 45% by weight of phosphated material, preferably greater than 60% by weight of phosphate material, is less than 1500 mPa.s or less than 1200 mPa.s, preferably less than 1000 mPa.s, more preferably less than 500 mPa.s or even less than 350 mPa.s or less than 200 mPa.s.

In a particularly preferred manner, the Brookfield viscosity of the aqueous suspension (B), measured 90 seconds after preparation of the suspension, at 25 ° C., at 100 rpm and at a concentration greater than 60% by weight of phosphate material, is less than 1500 mPa.s or less than 1200 mPa.s, preferably less than 1000 mPa.s, more preferably less than 500 mPa.s or even less than 350 mPa.s or less than 200 mPa.s.

In a preferred manner for the preparation method according to the invention, the dispersion in water of the particles of phosphated material is carried out with stirring by means of a suitable device. More preferably, it is carried out with mechanical stirring. The preparation of the aqueous suspension (A) or of the aqueous suspension (B) according to the invention can be carried out at different temperatures. Preferably, it is carried out at a temperature between 10 and 60 ° C, more preferably between 20 and 50 ° C or between 25 and 50 ° C. Thus, the use of a polymer according to the invention during the phosphoric acid preparation reaction makes it possible to control the properties of the reaction medium and makes it possible, in particular, to control the viscosity of the reaction medium. The polymer used according to the invention is not a flocculating agent.

For a constant concentration of particles of phosphated material and for constant stirring conditions, the reaction medium has in particular a reduced viscosity in the presence of the polymer according to the invention relative to the reaction medium comprising no polymer. The hydrodynamics of the reaction medium is then better controlled; it is improved.

In a particularly advantageous manner, the preparation method according to the invention thus makes it possible to control the hydrodynamics of the reaction medium for preparing phosphoric acid. Thus, and preferably for the preparation method according to the invention, the hydrodynamics of the reaction medium for preparing phosphoric acid is improved by means of the anionic polymer used. The use of anionic polymer lowers the viscosity of the suspension resulting from the preparation reaction, making it possible to increase the Reynolds number, and consequently to improve the hydrodynamics of the reaction for preparing phosphoric acid, according to the formula:

η for which

Re represents the Reynolds number,

p represents the density of the fluid [kg / m ³ ],

- V _moy represents the characteristic speed of the fluid [m / s],

D represents the characteristic dimension [m],

- η represents the dynamic viscosity of the fluid [Pa-s].

Preferably, the method according to the invention is carried out in a turbulent regime or in a very turbulent regime. Preferably, the Reynolds number during the implementation of the method according to the invention is greater than or equal to 2100, preferably greater than 2500 or 3000, or even greater than these values. Preferably, the method according to the invention makes it possible to increase the Reynolds number relative to a medium that does not comprise a polymer according to the invention. Preferably, this increase in Reynolds number is greater than 10% or greater than 20%. Also advantageously with respect to methods of preparing phosphoric acid of the state of the art, the method of preparation according to the invention makes it possible to maintain or increase the chemical yield of the reaction. Thus, preferably, the method for preparing phosphoric acid according to the invention makes it possible to achieve a chemical yield of the phosphoric acid preparation reaction greater than 90% by weight of phosphorus equivalent within the initial phosphate material. More preferably according to the invention, the chemical yield of the phosphoric acid preparation reaction is greater than 92%, more preferably greater than 94% or even 95% or even greater than 96% or 98%, by weight. of phosphorus equivalent within the initial phosphate material. Also particularly advantageously with respect to methods of preparing phosphoric acid of the state of the art, the method of preparation according to the invention makes it possible to reduce the amount of residual sulphate ions in the aqueous solution of phosphoric acid. prepare. Preferably, the aqueous phosphoric acid solution comprises residual sulphate ions in a concentration by weight ranging from 20 to 35 g / l. More preferably, the aqueous phosphoric acid solution comprises residual sulfate ions in a concentration by weight ranging from 22 to 26 g / l.

Also advantageously with respect to methods for the preparation of phosphoric acid of the state of the art, the preparation method according to the invention makes it possible to obtain an aqueous solution of phosphoric acid whose phosphoric acid titer is particularly interesting. Preferably, the phosphoric acid prepared has a P ₂ 0 ₅ titre greater than 25%, more preferably greater than 28% or 30%.

Also advantageously with respect to methods for the preparation of phosphoric acid of the state of the art, the preparation method according to the invention makes it possible to obtain an aqueous solution of phosphoric acid whose concentration by weight of acid phosphoric acid is particularly interesting. Preferably, the aqueous solution of phosphoric acid prepared at a concentration by weight of phosphoric acid prepared between 20 and 45%, more preferably between 25 and 40%, more preferably between 30 and 35%.

The method of preparing phosphoric acid according to the invention comprises treating an aqueous suspension (A) comprising water and particles of at least one phosphated material by means of at least one strong acid.

In a preferred manner according to the invention, the aqueous suspension (A) can be prepared beforehand. Thus, the method for preparing phosphoric acid according to the invention may comprise

(a) the preparation, optionally with stirring, of a mixture of water, particles of phosphate material and at least one anionic polymer obtained by reaction of polymerizing at least one acid selected from acrylic acid, methacrylic acid and their salts to form the aqueous suspension (A);

(b) treating the aqueous suspension (A) with at least one strong acid to form an aqueous solution of phosphoric acid.

During the implementation of the phosphoric acid preparation method according to the invention, the phosphated material particles undergo an acid attack during the treatment of the aqueous suspension (A) with the aid of the strong acid. During this acid attack, phosphogypsum particles are formed.

Phosphogypsum is a gypsum of phosphate origin. It is calcium sulphate. Various forms of calcium sulfate may be present, including calcium sulfate hydrate, calcium sulfate dihydrate or anhydrous calcium sulfate.

In a preferred manner according to the invention, the strong acid used during the treatment of the aqueous suspension (A) is a strong mineral acid. More preferably according to the invention, the strong acid has a pKa of less than 4 or less than 3, or even less than 2.5. Even more preferentially, the strong acid is chosen from sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and mixtures thereof. Even more preferably, the strong acid is sulfuric acid, phosphoric acid or mixtures thereof.

The phosphogypsum crystals formed during the implementation of the preparation method according to the invention may be of different shapes or of different sizes.

Advantageously, the preparation method according to the invention makes it possible to obtain, during the treatment with sulfuric acid, particular phosphogypsum particles. Particularly advantageously, the preparation method according to the invention makes it possible to obtain crystalline forms of particular phosphogypsum particles which can be separated, in particular by filtration, very effectively. And very advantageously, these phosphogypsum particles have acicular (A), tabular (B) and compact crystal or polycrystalline (C) forms. In addition to their specific morphologies, these different crystalline forms can be characterized by their dimensions, generally according to the sizes presented in Table 1. length (μιη) width (μιη) thickness (μιη) needle crystals 80-500 20-100 5-10 tabular crystals 40-200 30-150 5-10 compact crystals 40-200 30-150 several tens polycrystalline aggregates sphere 50 to 50 100 μιη in diameter

Table 1

In a preferred manner, the preparation method according to the invention makes it possible to obtain gypsum crystals whose folability is improved. Advantageously, these gypsum crystals have a compact morphology. In particular, the three dimensions - length, width and thickness - of these crystals are relatively close. Preferably, thanks to these relatively close dimensions, the gypsum crystals resulting from the implementation of the preparation method according to the invention have a general morphology close to a spherical shape or of a shape that can be inscribed in a spherical or quasi-spherical volume. Thus, preferably, the method of preparation according to the invention makes it possible to obtain gypsum crystals whose sphericity (ratio between the radius of the inscribed circle of the particle and the radius of the circumscribed circle of the particle) which measures the difference between the shape of the particles with respect to a spherical particle is close to 1.

The preparation method according to the invention therefore allows efficient filtration of the phosphogypsum particles. Thus, the overall chemical yield of the phosphoric acid preparation is particularly advantageous. According to the invention, the evaluation of the overall chemical yield of the phosphoric acid preparation expressed in P2O5 equivalent is carried out by comparing the titre of the P ₂ O ₅ losses in the phosphogypsum during the preparation of the acid solution. strong product, with the title in P ₂ 0 ₅ of the phosphate rock of departure. Loss titration is performed for the gypsum wash solutions from which the impregnated P ₂ 0 ₅ is recovered, and for the gypsum crystals in which P2O5 is present in unreacted or syncrystallized form. The overall return is then evaluated according to the equation for which

Rd represents the chemical yield (%),

Pt represents the total losses in P ₂ 0 ₅ in the gypsum,

CaOpp represents the CaO title in phosphate,

- CaOgy represents the CaO title in gypsum,

P ₂ 0 ₅ pp represents the P ₂ 0 ₅ titre in phosphate.

Advantageously, the implementation of the preparation method according to the invention makes it possible to improve the chemical yield of the phosphoric acid preparation. The improvement may result in particular from a limitation of the losses of unreacted P ₂ 0 ₅ during the preparation of phosphoric acid, a reduction in the losses of the syncrystallized P ₂ 0 ₅ in the gypsum or even a better separation of the gypsum to reduce losses of P ₂ 0 ₅ remaining impregnated in the solid filtration residue. In a preferred manner according to the invention, the separated phosphogypsum crystals are of oblong shape of size approximately 250 μιη or of size 220-350 μιη (Ql). Also preferably according to the invention, the separated phosphogypsum crystals are of semi-oblong shape of size about 150 μιη or of size 125-160 μιη (Q2). Also preferably according to the invention, the separated phosphogypsum crystals are of more compact shape or star size of about 50 μιη or size about 40-85 μιη (Q3).

Preferably, the preparation method according to the invention comprises the separation (c) of the aqueous solution of phosphoric acid and phosphogypsum crystals formed during treatment (b). More preferably, these phosphogypsum crystals are separated by filtration.

Preferably, the preparation method of the invention improves the separation of gypsum crystals from phosphoric acid by filtration. More preferably, the filtration or filtration coefficient is improved by more than 0.5 tP ₂ 05 / m ² / d or 1 tP ₂ 0 ₅ / m ² / day or even 2 tP ₂ 0 ₅ / m ² / d, compared to a separation method that does not implement polymer. An essential characteristic of the aqueous suspension (A) used according to the invention is to comprise at least one anionic polymer combined with water and with particles of at least one phosphate material. The anionic polymer according to the invention is obtained by polymerization reaction of at least one acid selected from acrylic acid, methacrylic acid and their salts.

During the preparation of the anionic polymer used according to the invention, the polymerization reaction uses at least one anionic monomer comprising at least one polymerizable olefinic unsaturation and at least one carboxylic acid function, in particular an anionic monomer comprising at least one polymerizable ethylenic unsaturation and at least one carboxylic acid function. Preferably the anionic monomer is selected from acrylic acid, methacrylic acid, an acrylic acid salt, a methacrylic acid salt. This polymerization reaction can also implement these two acrylic and methacrylic acids and their salts. The polymer used according to the invention may also be a copolymer obtained by a polymerization reaction employing at least one other acid chosen from acrylic acid, methacrylic acid, maleic acid, itaconic acid and their salts, and at least one another comonomer which may be an ester of an acid selected from acrylic acid and methacrylic acid. As other comonomers which can be used in the preparation of the copolymer according to the invention, mention may be made of a nonionic monomer chosen from esters of an acid comprising at least one monocarboxylic acid function, in particular an ester of an acid selected from acrylic acid, methacrylic acid, an acrylic acid salt, a methacrylic acid salt and mixtures thereof. Examples of such comonomers include a compound selected from styrene; vinylcaprolactam; alkyl acrylate, in particular C 1 -C 10 alkyl acrylate, preferentially C 1 -C 4 alkyl acrylate, more preferably methyl acrylate, ethyl acrylate, propyl acrylate, isobutyl acrylate, n-butyl acrylate; alkyl methacrylate, in particular C 1 -C 10 alkyl methacrylate, preferentially C 1 -C 4 alkyl methacrylate, more preferably methyl methacrylate, ethyl methacrylate, propyl methacrylate, isobutyl methacrylate, n-butyl methacrylate; aryl acrylate, preferably phenoxyethyl acrylate; aryl methacrylate, preferably phénoxyethylmethacrylate. Methyl acrylate, ethyl acrylate, propyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isobutyl methacrylate and n-butyl methacrylate are particularly preferred. . As other comonomers which can be used during the preparation of the copolymer according to the invention, mention may also be made of a compound chosen from 2-acrylamido-2-methylpropanesulphonic acid, 2-acrylamido-2-methylpropane sulpho acid salt. ethoxymethacrylate sulfonic acid, ethoxymethacrylate sulfonic acid salt, sodium methallyl sulfonate, styrene sulfonic acid and their salts.

Preferably, the anionic polymer according to the invention is prepared in the absence of acrylamide or in the absence of Ν, Ν'-methylenebisacrylamide; the polymer according to the invention is not crosslinked.

Preferably, the polymer used according to the invention is partially or completely neutralized. More preferably, it is partially or completely neutralized by means of at least one derivative selected from an alkali metal, an alkaline earth metal and mixtures thereof, in particular a derivative comprising at least one element chosen from lithium, sodium, calcium and magnesium. and mixtures thereof, for example NaOH, KOH, Ca (OH) ₂ . Sodium, calcium and mixtures thereof are particularly preferred. The neutralization by means of sodium and calcium can be carried out using at least one compound selected from NaOH, Ca (OH) ₂ and mixtures thereof. The respective proportions of sodium and calcium can vary quite widely. For example, the Na / Ca molar ratio can range from 98/2 to 30/70, preferably from 95/5 to 40/60, more preferably from 90/10 to 30/70 or from 90/10 to 40/60. more preferably from 70/30 to 40/60, in particular 50/50.

Preferably, the anionic polymer used according to the invention has a molecular weight (M _w) between 2000 and 90 000 g / mol, preferably between 1 000 and 2 000 to 50 000 g / mol, even more preferably between 1,000 or 2,000 to 10,000 g / mol, and more preferably between 1,500 and 2,000 to 8,000 g / mol. According to the invention, the molecular weight (Mw) is measured by size exclusion chromatography (CES). The preferred polymers used according to the invention are homopolymers of acrylic acid or copolymers of acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid, in particular neutralized homopolymers of acrylic acid or neutralized copolymers. of acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid. The more particularly preferred polymers used according to the invention are neutralized homopolymers of acrylic acid or neutralized copolymers of acrylic acid and of 2-acrylamido-2-methylpropanesulphonic acid, whose molecular weight (Mw) is between 1,000 and 10,000 g / mol, preferably between 1,500 and 8,000 g / mol. Examples of particularly preferred copolymers used according to the invention are chosen from

Polymer (PI): homopolymer of molecular weight 5000 g / mol obtained by polymerization of acrylic acid in the presence of copper sulfate, iron sulfate, hydrogen peroxide and 2- (1-carboxyethylsulfanylcarbothioylsulfanyl acid ) propanoic (DPTTC - CAS number 6332-91-8), neutralized with sodium and calcium (70/30 molar relative to the amount of acrylic acid);

Polymer (P2): homopolymer with a molecular weight of 4,200 g / mol and obtained by polymerization of acrylic acid in the presence of copper sulphate, iron sulphate, sodium hydrogen peroxide and sodium hypophosphite, neutralized with sodium and calcium (90/10 molar to the amount of acrylic acid);

Polymer (P3): polymer with a molecular mass of 4,800 g / mol and obtained by polymerization of acrylic acid in the presence of sodium persulfate and sodium hypophosphite, neutralized with sodium and calcium (50/50 molar with respect to the amount of acrylic acid);

Polymer (P4): copolymer with a molecular mass of 3,800 g / mol and obtained by polymerization of acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid (77.5 / 12.5 by weight) in the presence of persulfate of sodium and sodium hypophosphite, neutralized with sodium and calcium (50/50 molar relative to the amount of acrylic acid)

Polymer (P5): homopolymer with a molecular mass of 4,200 g / mol and obtained by polymerization of acrylic acid in the presence of copper sulphate, iron sulphate, hydrogen peroxide and sodium hypophosphite, neutralized with sodium and calcium (30/70 molar relative to the amount of acrylic acid).

For the method according to the invention, the amount of anionic polymer used can vary quite widely. Preferably, the amount by weight (dry / dry) of anionic polymer used is between 0.05 and 5%, more preferably between 0.1 and 2%, relative to the amount of phosphate material. Also preferably for the preparation method according to the invention, the amount by weight (dry / dry) of anionic polymer used is between 0.1 and 5% by weight relative to the amount of phosphate material. More preferably for the method of preparation according to the invention, the amount by weight (dry / dry) of anionic polymer used is between 0.15 and 2% by weight relative to the amount of phosphate material.

Due to the particular properties conferred on the particles of phosphate material combined with the anionic polymer used according to the invention, the acidic treatment of the aqueous suspension (A) is improved. Thus, the aqueous suspension (A) comprises a foam phase whose volume is limited or even zero during the acid treatment. Preferably, during this treatment using a strong acid of the aqueous suspension (A) according to the invention, this suspension comprises a foam phase whose volume is reduced to 40% or even reduced to 20% of the total volume of suspension.

Advantageously, the aqueous suspension (A) according to the invention has an apparent density, measured by means of a pycnometer and for a solids content greater than 60% by weight, of between 1.5 and 2, of preferably between 1.7 to 2.

During the acid treatment of the aqueous suspension (A) according to the invention, conditions of the phosphoric acid preparation reaction are modified. The implementation of an anionic polymer according to the invention therefore makes it possible to modify parameters of the phosphoric acid preparation reaction.

Thus, in addition to a method for preparing phosphoric acid from an aqueous suspension (A), the invention also relates to a method for improving the hydrodynamics of the phosphoric acid preparation reaction. The method for improving the hydrodynamics of the phosphoric acid preparation reaction by treatment at a temperature ranging from 40 to 100 ° C using at least one strong acid, an aqueous suspension (A) of particles of at least one phosphated material whose size is between 10 and 400 μιη, comprises the use of at least one anionic polymer with a weight-average molecular mass (M _w ) of between 1,000 and 90,000 g / mol and obtained by polymerization reaction of at least one acid selected from acrylic acid, methacrylic acid and their salts.

Preferably, the method for improving the hydrodynamics according to the invention makes it possible to reduce the phosphoric acid losses, expressed in P2O5 equivalent. Particularly preferably, the method of the hydrodynamic improvement according to the invention reduces the loss of phosphoric acid, expressed as P2O5 equivalent, by reducing losses of P ₂ 0 ₅ present in the phosphate rock which n is not attacked during the acid treatment or by reducing the P ₂ 0 ₅ equivalent losses which are bound to the phosphorus present in syncrystallized form within the phosphogypsum crystals.

Also preferably, the method for improving the hydrodynamics according to the invention makes it possible to increase the overall yield of the phosphoric acid production reaction.

For the hydrodynamic improvement method according to the invention, the characteristics of the reaction for preparing phosphoric acid are those of the reaction for preparing phosphoric acid defined according to the invention.

For the hydrodynamic improvement method according to the invention, the polymer is the anionic polymer used during the phosphoric acid preparation reaction defined according to the invention. For the hydrodynamic improvement method according to the invention, the phosphated material is the phosphated material used during the phosphoric acid preparation reaction defined according to the invention. The particular, advantageous or preferred characteristics of the preparation method according to the invention make it possible to define, in a similar manner, hydrodynamic improvement methods according to the invention which are particular, advantageous or preferred.

In a particularly effective manner, the various aspects of the invention make it possible to improve the efficiency of the various stages using the phosphated material. In particular, the invention allows a significant improvement in the overall chemical yield of the phosphated rock treatment used for the preparation of phosphoric acid.

The following examples illustrate the various aspects of the invention.

Example 1 Preparation of Phosphate Rock Pulp

From a phosphate rock pulp which is an aqueous suspension comprising water and particles of phosphated material, the characteristics of this suspension are determined. The phosphate material comes from the Khouribga deposits (Morocco). The pulp is prepared by mixing water and crushed and crushed phosphate rock, and optionally the anionic polymer according to the invention.

Granulometry of particles of phosphate material:

The particle size distribution of the phosphate rock pulp was measured using a Malvern Mastersizer 2000 laser diffraction granulometer. The results obtained are shown in Table 2.

Table 2 Density of the pulp:

The density is determined at 25 ° C by means of a pycnometer of size 1501/100 (Sheen S230729) whose volume is 100 cm ³ . The clean pyknometer is weighed empty. The homogenized phosphated rock pulp is introduced into the pyknometer; the air present is purged and the pyknometer is closed. The solid pycnometer is weighed. The mass of the empty pycnometer is subtracted from the mass of the solid pycnometer, the value of this difference is multiplied by 10 and the density of the phosphate rock pulp is obtained. The results are shown in Table 3.

Table 3

The use of a polymer according to the invention makes it possible to significantly increase the phosphate rock dry extract as well as the density of the pulp while allowing easy handling of this concentrated pulp.

Viscosity of the pulp:

In a 250 ml beaker at 25 ° C., 300 g of phosphate rock pulp are introduced with stirring by means of a mechanical stirrer (600 rpm - for 2 min). If necessary, the polymer according to the invention is added in the dry / dry polymer quantities relative to the amount of dry phosphate rock presented in Table 3. Stirring is stopped and then, after 90 seconds, the 23 ° C the viscosity by means of a Brookfield viscometer equipped with a mobile type S63 at a rotation speed of 100 rev / min. The results are shown in Table 4. dry extract viscosity

(% by weight) (mPa.s) pulp without polymer 70 non-measurable (pulp) pulp with polymer (PI) 0.2% in> 70 230

weight

pulp with polymer (P3) 0.3% in> 70,260

weight

pulp with polymer (P4) 0.4% in> 70 229

weight

Table 4

While the pulp without polymer does not allow measurement of the viscosity, the pulp comprising the polymer according to the invention has a controlled viscosity which makes it easy to handle and transportable especially by gravity.

Example 2 Preparation of Phosphoric Acid and Characterization of its Quality

The phosphated material particles of an aqueous suspension according to Example 1 are brought into contact with sulfuric acid according to the phosphoric acid dihydrate manufacturing process. A slurry is obtained which is filtered to separate the phosphogypsum and obtain an aqueous solution of phosphoric acid. A strong phosphoric acid solution is obtained. If necessary, it can be concentrated by evaporation of water under vacuum. Washing the phosphogypsum with a dilute solution of phosphoric acid or with water or with water rich in sulphate can make it possible to obtain solutions of medium or low phosphoric acid.

The procedure is analogous to different suspensions prepared according to Example 1.

The preparation reaction of phosphoric acid is characterized by different parameters. The filtration time provides information on the shape of the phosphogypsum crystals present in the phosphate material. The filtration time also provides information on the quality of the phosphoric acid produced. Density gives information on the acid's titer phosphoric acid produced and must be greater than 1.266 at 25 ° C to achieve a generally acceptable quality.

The amount of free sulfate present in the acid (g / L) is estimated from the level of unreacted residual sulfuric acid when treating the phosphate material particles of the slurry. It makes it possible to provide information on the evolution of the phosphoric acid preparation reaction. Preferably, the aqueous phosphoric acid solution comprises residual sulphate ions in a concentration by weight ranging from 20 to 35 g / l. More preferably, the aqueous phosphoric acid solution comprises residual sulfate ions in a concentration by weight ranging from 22 to 26 g / l.

The filterability of the suspension of phosphate material (ton of P205 / m ² / day) makes it possible to evaluate the capacity of production of strong phosphoric acid. The filterability of phosphogypsum is related to its crystallinity. Particular forms of phosphogypsum crystals can lead to stacks that degrade filtration efficiency or filter clogging. On a scale of 1 to 7, the filterability should be from 5 to 7, preferably from 6 to 7. The filterability F is calculated according to the formula: for which

A represents the specific constant of the measurement technique,

B represents the moisture content of the phosphogypsum (% by weight),

tl represents the filtration time of the strong phosphoric acid (s),

t2 represents the filtration time of the average phosphoric acid (s),

t3 represents the filtration time of the weak phosphoric acid (s).

The filterability results obtained are shown in Table 5.

Table 5 The presence of polymer according to the invention in the aqueous suspension of particles of phosphated material makes it possible to obtain maintained or even improved filterability while making it possible to increase the dry extract. The yield of the strong phosphoric acid production method is improved.

Performance of the phosphoric acid preparation reaction and quality of the phosphoric acid produced: density and strength of the acid

After acid treatment and filtration of the suspension of phosphate material, the density of the strong phosphoric acid is measured by means of a graduated gravimeter of 1200 to 1300 or 1300 to 1400, and at a temperature of 25.degree. C. The titration of the phosphoric acid solution is carried out in a known manner as such. The results obtained are shown in Table 6.

Table 6

The presence of the polymer according to the invention in the aqueous suspension of particles of phosphated material makes it possible to prepare a very concentrated pulp with very improved properties. The title in P ₂ 0 ₅ is improved. Likewise, the acid density is improved.

In preparing the phosphoric acid by treating the aqueous suspension of phosphatic material particles with sulfuric acid, the phosphogypsum (calcium sulfate) crystals must be of controlled size in order to improve their separation by filtration. The sizes and dimensions of the crystals of different filtration retents are determined by means of an optical microscope (Olympus SZX-ILLD200, DF PLFL lens 1.6 * PF) producing images processed using Imagej software. Different crystal forms are present: acicular (A), tabular (B), or compact crystal or polycrystalline (C) forms. For these crystals of different forms, several size ranges are present. Among these crystals, there are oblong-shaped crystals of size about 250 μιη or 220-350 μιη (Ql), semi-oblong shaped crystals of size about 150 μιη or 125-160 μιη (Q2) and crystals of form more compact or star-sized about 50 μιη or 40-85 μιη (Q3). Crystals of type (Q3) allow the best results of filtration. The results are shown in Table 6.

The relative amounts of (Q3) type crystals are increased and the phospholysis crystal yield is improved.

Evaluation of losses of phosphoric acid produced:

When preparing the phosphoric acid expressed as P2O5 equivalent, the overall chemical yield of the phosphoric acid preparation can be reduced due to acid losses. Generally, the method of preparing the acid leads to acid losses in different forms. These losses can be identified and measured. Part (A) of the product losses corresponds to the phosphoric acid present in the phosphate rock which is not attacked during the acid treatment. Part (B) of the phosphoric acid product losses is bound to the entrapped acid in syncrystallized form within the phosphogypsum crystals. Part (C) of phosphoric acid product losses results from the presence of acid in solution in the wash water. The results are shown in Table 7. pulp (dry extract -% in

losses in P ₂ 0 ₅ (% by weight) yield in P ₂ 0 ₅ wt.

(% in weight)

A B C pulp without polymer (60) 0.12 0.81 0.82 92.0 pulp without polymer (> 70) 0.12 0.67 0.67 94.3 pulp with polymer (P4)

0.03 0.2 0.1 98.6

0.4% by weight (> 70)

Water Tab 7 In addition to a strong improvement in the overall yield of the phosphoric acid preparation reaction, the use of a polymer according to the invention during the phosphoric acid preparation reaction from the aqueous suspension of phosphatic material particles allows to reduce the different losses of phosphoric acid. In particular, the acid losses resulting from the phosphate material not attacked during the acid treatment, are greatly reduced.

Claims

claims

A method of preparing phosphoric acid comprising treating at a temperature of from 40 to 100 ° C by means of at least one strong acid, an aqueous suspension (A) comprising water and particles of from less a phosphate material whose size is between 10 and 400 μιη, and dispersed in the presence of at least one anionic polymer of molecular weight in weight (M _w ) of between 1000 and 90 000 g / mol and obtained by reaction of polymerization of at least one acid selected from acrylic acid, methacrylic acid and their salts.

A method of preparation according to claim 1 wherein the Brookfield viscosity of the aqueous suspension (A), measured 90 seconds after preparation of the suspension, at 25 ° C, at 100 rpm and at a concentration greater than 45% by weight of phosphated material, preferably greater than 60% by weight of phosphated material, is less than 1500 mPa.s or less than 1200 mPa.s, preferably less than 1000 mPa.s, more preferably less than 500 mPa.s. or even less than 350 mPa.s or less than 200 mPa.s.

Method of preparation according to one of claims 1 or 2 wherein the strong acid used is selected from sulfuric acid, nitric acid, hydrochloric acid, and a mixture of these acids.

Preparation method according to one of claims 1 to 3 for which the strong acid used is sulfuric acid.

Preparation method according to one of claims 1 to 4 wherein the phosphoric acid prepared has a P ₂ 0 ₅ titre greater than 25%, more preferably greater than 28% or 30%.

Preparation method according to one of claims 1 to 5 comprising

(a) the preparation, optionally with stirring, of a mixture of water, particles of phosphate material and at least one anionic polymer obtained by polymerization reaction of at least one acid selected from acrylic acid, methacrylic acid and their salts, to form the aqueous suspension (A);

(b) treating the aqueous suspension (A) with at least one strong acid, preferably with sulfuric acid, to form an aqueous phosphoric acid solution.

7. Preparation method according to claim 6 comprising (c) the separation of the aqueous phosphoric acid solution and the phosphogypsum particles formed during the treatment (b).

8. Preparation method according to claim 7 for which the separated phosphogypsum crystals

• are oblong in size about 250 μιη or 220-350 μιη (Ql), semi-oblong shape of size about 150 μιη or 125-160 μιη (Q2) and more compact or star shape size about 50 μιη or 40-85 μιη (Q3), preferably predominantly more compact or star-shaped in size about 50 μιη or 40-85 μιη (Q3); or

• have a sphericity (ratio between the radius of the inscribed circle of the particle and the radius of the circumscribed circle of the particle) close to 1.

9. Method of preparation according to one of claims 7 and 8 for which the phosphogypsum particles are separated by filtration. 10. Method of preparation according to one of claims 1 to 9 wherein the aqueous solution of phosphoric acid prepared has a weight concentration of phosphoric acid prepared between 20 and 45%, preferably between 25 and 40%, and more preferably between 30 and 35%. 11. Method of preparation according to one of claims 1 to 10 for which the particles of phosphate material are used in dried form.

12. Method of preparation according to one of claims 1 to 10 for which the phosphate material particles are implemented in the form of an aqueous suspension (B), preferably in the form of an aqueous suspension (B). whose concentration of phosphate material is greater than 45% by weight.

13. Method of preparation according to claim 12 wherein the aqueous suspension (B) also comprises at least one anionic polymer defined according to claim 1. 14. Preparation method according to claim 13 for which the aqueous suspension (B) has a concentration in phosphatic material greater than 50%, preferably greater than 55%, more preferably greater than 60% or 65% or even greater than 70% or 75%. 15. Method of preparation according to one of claims 13 and 14 for which the Brookfield viscosity of the aqueous suspension (B), measured 90 s after preparation of the suspension, at 25 ° C, at 100 rpm and at a concentration of greater than 45% by weight of phosphated material, preferably greater than 60% by weight of phosphate material, is less than 1500 mPa.s or less than 1200 mPa.s, preferably less than 1000 mPa.s, plus preferentially less than

500 mPa.s or even less than 350 mPa.s or less than 200 mPa.s.

16. Method of preparation according to one of claims 1 to 15 for which the polymer is partially or completely neutralized, preferably partially or completely neutralized with a derivative comprising at least one element selected from lithium, sodium, calcium, magnesium and mixtures thereof, more preferably selected from sodium, calcium and mixtures thereof.

17. Method of preparation according to one of claims 1 to 16 wherein the anionic polymer is obtained by a polymerization reaction also implementing at least one ester of an acid selected from acrylic acid and methacrylic acid.

18. Method of preparation according to one of claims 1 to 17 wherein the anionic polymer has a weight-average molecular weight (Mw) of from 2,000 to 90,000 g / mol, preferably from 2,000 to 50,000 g / mol. more preferably from 2,000 to 10,000 g / mol, and more preferably from 2,000 to 8,000 g / mol.

19. Method of preparation according to one of claims 1 to 18 for which the amount by weight (dry / dry) of anionic polymer used is between 0.1 and 5%, preferably between 0.15 and 2%. , relative to the amount of phosphate material.

20. Preparation method according to one of claims 1 to 19 for which the phosphated material particles have a size less than 400 μιη, preferably less than 200 μιη or less than 150 μιη or whose size is greater than 10 μιη, preferably greater than 30 μιη.

21. Method of preparation according to one of claims 1 to 20 for which the strong acid has a pKa of less than 4 or less than 3 or 2.5, or for which the strong acid is selected from sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and mixtures thereof.

22. Method of preparation according to one of claims 1 to 21 for which the aqueous suspension comprises a foamy phase whose volume is reduced to 40% or even reduced to 20% of the total volume of the suspension or for which the aqueous suspension has a apparent density, measured by means of a pycnometer and for a solids content greater than 60% by weight, ranging from 1.5 to

2, preferably ranging from 1.7 to 2.

23. Method for improving the hydrodynamics of the phosphoric acid preparation reaction by treatment at a temperature ranging from 40 to 100 ° C., using at least one strong acid, an aqueous suspension (A) of particles of at least one phosphated material whose size is between 10 and 400 μιη, comprising the use of at least one anionic polymer with a weight-average molecular weight (Mw) of between 1,000 and 90,000 g / mol and obtained by polymerization reaction of at least one acid selected from acrylic acid, methacrylic acid and their salts.

24. A hydrodynamic improvement method according to claim 23, in which the phosphoric acid losses, expressed in P2O5 equivalent, are reduced, preferably by reducing the losses of P ₂ 0 ₅ present in the phosphate rock which is not attacked during the acid treatment or reduction of losses of P ₂ 0 ₅ which are linked to phosphorus present as syncristallisée within crystals phosphogypsum.

25. hydrodynamic improvement method according to one of claims 23 and 24 for which the preparation reaction of phosphoric acid, the polymer and the phosphated material are defined according to one of claims 1 to 22.