EP0000415A1 - Process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate - Google Patents

Process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate Download PDF

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Publication number
EP0000415A1
EP0000415A1 EP78200085A EP78200085A EP0000415A1 EP 0000415 A1 EP0000415 A1 EP 0000415A1 EP 78200085 A EP78200085 A EP 78200085A EP 78200085 A EP78200085 A EP 78200085A EP 0000415 A1 EP0000415 A1 EP 0000415A1
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EP
European Patent Office
Prior art keywords
calcium carbonate
process according
polyelectrolyte
concentrate
dispersing agent
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EP78200085A
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German (de)
French (fr)
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EP0000415B1 (en
Inventor
Jacques Brahm
Jean-Pierre De Rath
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Solvay SA
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Solvay SA
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D17/00—Pigment pastes, e.g. for mixing in paints
    • C09D17/004—Pigment pastes, e.g. for mixing in paints containing an inorganic pigment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/182—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/182—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds
    • C01F11/183—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds the additive being an organic compound
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/185—After-treatment, e.g. grinding, purification, conversion of crystal morphology
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/02—Compounds of alkaline earth metals or magnesium
    • C09C1/021—Calcium carbonates
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/36—Coatings with pigments
    • D21H19/38—Coatings with pigments characterised by the pigments
    • D21H19/385—Oxides, hydroxides or carbonates
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/36—Coatings with pigments
    • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
    • D21H19/52—Cellulose; Derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer

Definitions

  • the subject of the present invention is the preparation of concentrated aqueous suspensions of calcium carbonate, by crystallization of calcium carbonate in an aqueous medium.
  • concentrated aqueous generally containing from 65 to 80% by weight of crystals.
  • This known method has the disadvantage of requiring an expensive grinding operation. This is in fact imposed by the need to break up the numerous coarse agglomerates of calcium carbonate crystals present in the wet calcium carbonate concentrate. Besides its unfavorable influence on the cost of the process, this grinding operation has the drawback of giving rise to the formation of calcium carbonate fines, which are generally not suitable as a filler.
  • the filter cakes obtained by this known process are in the form of aqueous suspensions of fine crystals, very suitable as a filler in stationery, in plastics and in paints.
  • concentration of calcium carbonate crystals in these aqueous suspensions is generally insufficient to allow them to be stored and handled economically, so that it is necessary to concentrate them by evaporating them.
  • the Applicant has now found that by carrying out the crystallization under specific conditions, it is possible to obtain concentrated aqueous suspensions of fine and regular crystals of calcium carbonate, generally containing more than 65% by weight of dry matter, without requiring grinding or evaporation.
  • the invention therefore relates to a process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate, according to which calcium carbonate is crystallized in dilute aqueous medium, the dilute aqueous suspension of calcium carbonate is separated resulting, a wet calcium carbonate concentrate and said calcium carbonate concentrate is fluidized and homogenized in the presence of a dispersing agent, the crystallization of the calcium carbonate being carried out in the presence of a water-soluble polyelectrolyte and the separation of the wet concentrate from the diluted aqueous suspension being carried out by mechanical means.
  • polyelectrolyte is meant a polymeric substance whose monomeric units have ionizable groups, and which is composed, on the one hand, of a macroion formed of ionic groups of the same sign, linked together by chemical bonds and, on the other hand, a series of counterions of charge opposite to that of the macroion (Encyclopedia of Polymer Science and Technology - John Wiley & Sons - 1969 - Vol.10, p.781).
  • polyacids or their salts, which are polyelectrolytes which, when dissociating, give rise to polymeric anions (polyanions) and to elementary cations such as, for example, protons or monovalent cations derived from alkali metals (Op. cit., p.781 to 784).
  • Polyacids with a weak acid character are preferably used, defined as being polyacids whose pK, measured on a solution of O, OIN in pure water, is greater than 4, preferably 6 (Op. Cit., P .787 to 788).
  • Polyacids with a weak acid character which are very suitable in the context of the invention are those derived from polymers comprising at least one carboxylic group per 10 carbon atoms.
  • polyacids which can be used in the process according to the invention mention may in particular be made of polymers derived from acrylic, methacrylic and alpha-hydroxyacrylic acids, copolymers of maleic acid, carboxylated derivatives of cellulose ethers, and their alkali metal salts.
  • particularly advantageous polyelectrolytes include the alkali metal salts of polyacrylic acids and their derivatives such as poly-alpha-hydroxyacrylic acids, more particularly that known under the name of Polysel CA (BASF) which is based on sodium polyacrylate.
  • BASF Polysel CA
  • the crystallization of calcium carbonate in an aqueous medium can be carried out by any means known per se, for example by reacting a solution of calcium salt and a solution of ammonium carbonate or of alkali metal .
  • the crystallization of calcium carbonate is advantageously carried out by carbonating a milk of lime, preferably by means of a gas containing CO 2 .
  • a lime milk titrating between 25 and 350, preferably between 50 and 250, kg of CaO per m 3 which is prepared in a manner well known per se , by dispersing quicklime in water from the calcination of limestone in a lime kiln.
  • a gas poor in C0 2 for example boiler fumes containing 5 to 15% by volume of C0 2 .
  • a gas rich in CO 2 containing more than 30% of CO 2 ' such as the gas recovered from lime kilns.
  • the respective amounts of lime milk and carbonation gas must be sufficient to ensure as complete carbonation of the lime as possible. These quantities obviously depend on the respective concentrations of the milk of lime and of the gas, as well as on the working conditions, and they can, in each particular case, be easily established by experience.
  • the crystallization is preferably carried out at a temperature of the order of 25 to 60 ° C, for example around 30 to 50 ° C.
  • the amount of polymer incorporated into the aqueous medium depends on various factors, including the working conditions during crystallization and the nature of the polymer used; it can be easily determined by experience, in each case.
  • the calcium carbonate is crystallized by carbonating a lime milk
  • calcium carbonate concentrate is understood to mean a wet cake of calcium carbonate, which has been formed from the abovementioned dilute aqueous suspension of calcium carbonate.
  • essentially mechanical separation means means means by which a suspension of solid material in a liquid is subjected to physical separation into at least one phase highly concentrated in solid matter and one phase very diluted, without additional addition of solid matter in the suspension or change in state of one or the other constituent of the suspension, in particular without evaporation, or solidification of the liquid.
  • a mechanical separation means it is possible, for example, in accordance with the invention, to use filtration, wringing or decantation of the dilute aqueous suspension, which are techniques well known per se. As a variant, it is also possible to combine two or more separate mechanical separation means.
  • filtration which is a technique well known per se, the filter cake collected on the filter then constituting the aforementioned wet concentrate.
  • filtration of the diluted suspension is advantageously carried out under pressure, for example between 0.5 and 15 kg / cm 2 , and it is optionally followed by compression of the filter cake under a pressure between 1 and 20 kg / cm 2 and a sweep by a current of air under a pressure of 0.5 to 6 kg / cm 2 .
  • the temperature at which filtration is carried out and any compression and sweeping has not been found to have a significant influence on the filtration result. In general, it can for example be carried out between 15 and 50 ° C, advantageously at room temperature.
  • the fluidization of the calcium carbonate concentrate consists in subjecting it to mechanical work which transforms it into a fluid, pumpable aqueous suspension. It is generally carried out, in a manner known per se, by mixing the concentrate, for example by means of a paddle, disc or rotary cone mixer.
  • the purpose of homogenization is to ensure an efficient, homogeneous dispersion of the calcium carbonate crystals in the above-mentioned fluid aqueous suspension resulting from the fluidization operation. It is generally obtained by subjecting it to turbulence or intense shearing work by means of a high-speed disperser, for example of the paddle, disc or knife type.
  • the fluidization and the homogenization are preferably carried out separately.
  • the dispersing agent used during fluidization and homogenization has the function of facilitating the dispersion of the calcium carbonate crystals, avoiding the formation of crystal agglomerates. It may for example consist of an inorganic dispersing agent, such as the commercial dispersing agent known under the name of Calgon (Calgon Corp.), which is based on alkali metal polyphosphate. As a variant, the dispersing agent may also consist, at least partially, of an organic dispersing agent, for example a dispersing agent chosen from polyelectrolytes, preferably polyacids.
  • Dispersing agents which have been found to be particularly effective are those known under the names of Polysel CA (BASF) which is a dispersing agent based on sodium polyacrylate and Dispagil (Rhône-Progil) which is a dispersing agent based on ae alkali metal polyphosphate and polyacrylate.
  • BASF Polysel CA
  • Rhône-Progil Dispagil
  • the dispersing agent is preferably added to the calcium carbonate concentrate before carrying out the fluidization and homogenization. It can optionally be added to the dilute aqueous suspension of calcium carbonate, before separation of the calcium carbonate concentrate. However, it has been observed in practice that it is preferable to add the dispersing agent to the calcium carbonate concentrate, after having separated it from the aqueous suspension, since this results, all other things being equal, a decrease in the amount of dispersing agent required.
  • the amount of dispersing agent used to fluidize and homogenize the calcium carbonate concentrate depends on various factors, including the nature of the dispersing agent, the particle size of the calcium carbonate crystals and the calcium carbonate content of the concentrate. It can be easily determined by experience in each case. In general, it is advantageously between 2 and 10 g, preferably 4 and 8 g, per kg of calcium carbonate from the concentrate.
  • the process according to the invention makes it possible to obtain easily, quickly and economically, concentrated, stable aqueous suspensions of regular crystals of calcium carbonate, generally containing at least 65 X, preferably from 68 to 75 X, by weight of crystals, without the need for expensive evaporation treatment or grinding.
  • These concentrated suspensions lend themselves well to long-term storage and handling, without their stability being affected.
  • the calcium carbonate crystals they contain are well formed and regular and are well suited as a filler in stationery, paints and in the manufacture of plastics.
  • a milk of lime was carbonated with a gas containing CO 2.
  • the dilute aqueous suspension of calcium carbonate thus obtained was then filtered under a maximum pressure of 4.5 kg / cm 2 , the filter cake obtained was compressed under a maximum pressure of 17 kg / cm 2 to wring it out, then subjected to an air sweep under pressure equal to 5.3 kg / cm 2 for 10 minutes, thus providing a wet concentrate of calcium carbonate.
  • This calcium carbonate concentrate was then fluidized and then homogenized by successively passing through a kneader then through a disperser, thus providing an aqueous suspension. calcium carbonate.
  • Examples 1 and 2 relate to tests in accordance with the invention.
  • Polysel CA which is a commercial polyelectrolyte based on sodium polyacrylate, was introduced into the milk of lime, which titrated approximately 120 kg of CaO per m 3 .
  • the amount of Polysel CA introduced into the milk of lime was adjusted so that it corresponds approximately to 2.5 g of Polysel CA per kg of crystallized calcium carbonate.
  • the milk of lime was then carbonated with a gas containing between 23 and 27% of CO 2 , at a flow rate of 1350 m 3 / h, for 7 h 15 min. The temperature was maintained at 37 ° C.
  • the calcium carbonate concentrate collected on the filter was fluidized and homogenized in the presence of Calgon which is a commercial dispersing agent based on sodium polyphosphate. 7 g of Calgon were used per kg of calcium carbonate in the concentrate. There was thus obtained a concentrated aqueous suspension containing 68 X of regular crystals of calcium carbonate. This aqueous suspension remained stable for more than 30 days.
  • Example 1 The test of Example 1 was repeated, using a milk of lime titrating about 120 kg of CaO per m 3 and a gas containing between 29 and 32% of CO 2 .
  • the carbonation carried out at 32 ° C, lasted 7h35min., With a gas flow of between 1200 and 1350 m 3 / h.
  • the amount of Polysel CA was adjusted to correspond to 5 g per kg of calcium carbonate.
  • the concentrated aqueous suspension of calcium carbonate obtained contained 71.7% by weight of calcium carbonate crystals; it remained stable for more than 30 days.
  • Example 1 The test of Examples 1 and 2 was repeated, but omitting to add a polyelectrolyte to the milk of lime.
  • Lime milk was used titrating about 122 kg of CaO per m and a gas containing between 24 and 32% CO 2 , at a flow rate set between 1350 and 1500 m 3 / h for 6 h 30 min. The temperature was maintained between 32 and 34 ° C for the duration of the carbonation.
  • the aqueous suspension of calcium carbonate was filtered, and the concentrated calcium carbonate collected on the filter was subjected to a fluidization and homogenization operation as described in Example 1. There was thus obtained an aqueous suspension of calcium carbonate crystals barely containing 63.7% by weight of crystals. This aqueous suspension was also found to be significantly less stable than that of Examples 1 and 2.
  • Example 3 On the other hand, immediately reveals the advantage of the process according to the invention which makes it possible to obtain easily, without evaporation, by simple filtration, stable aqueous suspensions containing more than 68% by weight of calcium carbonate crystals.

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Abstract

L'invention a pour objet un procédé pour la préparation de suspensions aqueuses contenant au moins 65% en poids de carbonate de calcium. Suivant l'invention, on cristallise du carbonate de calcium en milieu aqueux dilué, en présence d'un polyélectrolyte hydrosoluble, on sépare de la suspension aqueuse diluée de carbonate de calcium résultante, un concentré humide de carbonate de calcium, en utilisant un moyen de séparation mécanique, et on fluidifie et homogénéise ledit concentré de carbonate de calcium en présence d'un agent dispersant. L'invention s'applique à la préparation de suspensions concentrées, stables de cristaux de carbonate de calcium, destinées à l'industrie papetière.The invention relates to a process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate. According to the invention, calcium carbonate is crystallized in a dilute aqueous medium, in the presence of a water-soluble polyelectrolyte, a wet concentrate of calcium carbonate is separated from the dilute aqueous suspension of calcium carbonate, using a means of mechanical separation, and said calcium carbonate concentrate is fluidized and homogenized in the presence of a dispersing agent. The invention applies to the preparation of concentrated, stable suspensions of calcium carbonate crystals, intended for the paper industry.

Description

La présente invention a pour objet la préparation de suspensions aqueuses concentrées de carbonate de calcium, par cristallisation de carbonate de calcium en milieu aqueux.The subject of the present invention is the preparation of concentrated aqueous suspensions of calcium carbonate, by crystallization of calcium carbonate in an aqueous medium.

Afin de réduire l'encombrement au stockage des cristaux de carbonate de calcium destinés notamment aux industries du papier, des matières plastiques et des peintures, et pour faciliter par ailleurs leur manutention, il est avantageux de les stocker et de les transporter sous forme de suspensions aqueuses concentrées, contenant généralement de 65 à 80 X en poids de cristaux.In order to reduce the space requirement during storage of the calcium carbonate crystals intended in particular for the paper, plastic and paint industries, and to further facilitate their handling, it is advantageous to store and transport them in the form of suspensions. concentrated aqueous, generally containing from 65 to 80% by weight of crystals.

A cet effet, dans le brevet belge 819 747 de Gewerkschaft Victor Chemische Werke, déposé le 10 septembre 1974, on propose un procédé suivant lequel on cristallise du carbonate de calcium en milieu aqueux, on filtre la suspension aqueuse de carbonate de calcium résultante pour en séparer un concentré humide de carbonate de calcium, on fluidifie et homogénéise le concentré de carbonate de calcium en présence d'un agent dispersant, et on soumet la suspension concentrée de carbonate de calcium ainsi obtenue à un broyage humide.To this end, in Belgian patent 819,747 to Gewerkschaft Victor Chemische Werke, filed on September 10, 1974, a process is proposed according to which calcium carbonate is crystallized in an aqueous medium, the resulting aqueous suspension of calcium carbonate is filtered to separating a wet calcium carbonate concentrate, the calcium carbonate concentrate is fluidized and homogenized in the presence of a dispersing agent, and the concentrated suspension of calcium carbonate thus obtained is subjected to wet grinding.

Ce procédé connu présente le désavantage de nécessiter une opération coûteuse de broyage. Celle-ci est en effet imposée par la nécessité de briser les nombreux agglomérats grossiers de cristaux de carbonate de calcium présents dans le concentré humide de carbonate de calcium. Outre son influence défavorable sur le coût du procédé, cette opération de broyage présente l'inconvénient de donner lieu à la formation de fines de carbonate de calcium, qui ne conviennent généralement pas comme matière de charge.This known method has the disadvantage of requiring an expensive grinding operation. This is in fact imposed by the need to break up the numerous coarse agglomerates of calcium carbonate crystals present in the wet calcium carbonate concentrate. Besides its unfavorable influence on the cost of the process, this grinding operation has the drawback of giving rise to the formation of calcium carbonate fines, which are generally not suitable as a filler.

On a essayé d'éviter l'opération de broyage, en exécutant la cristallisation du carbonate de calcium dans un milieu aqueux contenant un sel.de métal alcalin ou alcalino-terreux de l'acide nitrilotriacétique, à titre d'agent dispersant, et en filtrant ensuite la suspension diluée de carbonate de calcium résultante, comme décrit dans la demande de brevet allemand 1 116 203, déposée le 13 octobre 1959, au nom de Farbenfabriken Bayer AG.An attempt has been made to avoid the grinding operation, by carrying out the crystallization of calcium carbonate in an aqueous medium containing an alkali or alkaline earth metal salt of nitrilotriacetic acid, as a dispersing agent, and by then filtering the resulting dilute calcium carbonate suspension, as described in German patent application 1,116,203, filed October 13, 1959, in the name of Farbenfabriken Bayer AG.

Les gâteaux de filtration obtenus par ce procédé connu se présentent sous la forme de suspensions aqueuses de cristaux fins, convenant bien comme matière de charge en papeterie, dans les matières plastiques et dans les peintures. Toutefois, la concentration en cristaux de carbonate de calcium de ces suspensions aqueuses est généralement insuffisante pour permettre leur stockage et leur manutention de manière économique, de sorte qu'il est nécessaire de les concentrer en les évaporant.The filter cakes obtained by this known process are in the form of aqueous suspensions of fine crystals, very suitable as a filler in stationery, in plastics and in paints. However, the concentration of calcium carbonate crystals in these aqueous suspensions is generally insufficient to allow them to be stored and handled economically, so that it is necessary to concentrate them by evaporating them.

La Demanderesse a maintenant trouvé qu'en exécutant la cristallisation dans des conditions particulières, il est possible d'obtenir des suspensions aqueuses concentrées de cristaux fins et réguliers de carbonate de calcium, contenant généralement plus de 65 % en poids de matière sèche, sans nécessiter un broyage ni une évaporation.The Applicant has now found that by carrying out the crystallization under specific conditions, it is possible to obtain concentrated aqueous suspensions of fine and regular crystals of calcium carbonate, generally containing more than 65% by weight of dry matter, without requiring grinding or evaporation.

L'invention concerne donc un procédé pour la préparation de suspensions aqueuses contenant au moins 65 % en poids de carbonate de calcium, suivant lequel on cristallise du carbonate de calcium en milieu aqueux dilué, on sépare, de la suspension aqueuse diluée de carbonate de calcium résultante, un concentré humide de carbonate de calcium et on fluidifie et homogénéise ledit concentré de carbonate de calcium en présence d'un agent dispersant, la cristallisation du carbonate de calcium étant opérée en présence d'un polyélectrolyte hydrosoluble et la séparation du concentré humide de la suspension aqueuse diluée étant effectuée par un moyen mécanique.The invention therefore relates to a process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate, according to which calcium carbonate is crystallized in dilute aqueous medium, the dilute aqueous suspension of calcium carbonate is separated resulting, a wet calcium carbonate concentrate and said calcium carbonate concentrate is fluidized and homogenized in the presence of a dispersing agent, the crystallization of the calcium carbonate being carried out in the presence of a water-soluble polyelectrolyte and the separation of the wet concentrate from the diluted aqueous suspension being carried out by mechanical means.

On entend par polyélectrolyte, une substance polymérique dont les unités monomériques possèdent des groupes ionisables, et qui est composée, d'une part, d'un macroion formé de groupes ioniques de même signe, reliés entre eux par des liaisons chimiques et, d'autre part, d'une série de contre-ions de charge opposée à celle du macroion (Encyclopedia of Polymer Science and Technology - John Wiley & Sons - 1969 - Vol.10, p.781).By polyelectrolyte is meant a polymeric substance whose monomeric units have ionizable groups, and which is composed, on the one hand, of a macroion formed of ionic groups of the same sign, linked together by chemical bonds and, on the other hand, a series of counterions of charge opposite to that of the macroion (Encyclopedia of Polymer Science and Technology - John Wiley & Sons - 1969 - Vol.10, p.781).

Dans le cadre de l'invention, il s'est avéré intéressant d'utiliser, des polyacides, ou leurs sels, qui sont des polyélectrolytes qui, en se dissociant, donnent naissance à des anions polymériques (polyanions) et à des cations élémentaires tels que, par exemple, des protons ou des cations monovalents dérivés de métaux alcalins (Op. cit., p.781 à 784). On utilise de préférence des polyacides à caractère acide faible, définis comme étant des polyacides dont le pK, mesuré sur une solution à O,OIN dans l'eau pure, est supérieur à 4, de préférence à 6 (Op. cit., p.787 à 788).In the context of the invention, it has been found advantageous to use polyacids, or their salts, which are polyelectrolytes which, when dissociating, give rise to polymeric anions (polyanions) and to elementary cations such as, for example, protons or monovalent cations derived from alkali metals (Op. cit., p.781 to 784). Polyacids with a weak acid character are preferably used, defined as being polyacids whose pK, measured on a solution of O, OIN in pure water, is greater than 4, preferably 6 (Op. Cit., P .787 to 788).

Des polyacides à caractère acide faible convenant bien dans le cadre de l'invention sont ceux dérivant de polymères comprenant au moins un groupe carboxylique pour 10 atomes de carbone. A titre d'exemples de polyacides utilisables dans le procédé suivant l'invention, on peut notamment citer les polymères dérivés des acides acrylique, méthacrylique et alpha-hydroxyacrylique,les copolymères de l'acide maléique, les dérivés carboxylés des éthers cellulosiques, et leurs sels de métaux alcalins.Polyacids with a weak acid character which are very suitable in the context of the invention are those derived from polymers comprising at least one carboxylic group per 10 carbon atoms. As examples of polyacids which can be used in the process according to the invention, mention may in particular be made of polymers derived from acrylic, methacrylic and alpha-hydroxyacrylic acids, copolymers of maleic acid, carboxylated derivatives of cellulose ethers, and their alkali metal salts.

Suivant l'invention, des polyélectrolytes particulièrement avantageux comprennent les sels de métaux alcalins des acides polyacryliques et de leurs dérivés tels que les acides poly-alpha-hydroxyacryliques, plus particulièrement celui connu sous le nom de Polysel CA (BASF) qui est à base de polyacrylate de sodium.According to the invention, particularly advantageous polyelectrolytes include the alkali metal salts of polyacrylic acids and their derivatives such as poly-alpha-hydroxyacrylic acids, more particularly that known under the name of Polysel CA (BASF) which is based on sodium polyacrylate.

Dans le procédé suivant l'invention, la cristallisation du carbonate de calcium en milieu aqueux peut être exécutée par tout moyen connu en soi, par exemple en faisant réagir une solution de sel de calcium et une solution de carbonate d'ammonium ou de métal alcalin.In the process according to the invention, the crystallization of calcium carbonate in an aqueous medium can be carried out by any means known per se, for example by reacting a solution of calcium salt and a solution of ammonium carbonate or of alkali metal .

Suivant l'invention, la cristallisation du carbonate de calcium est avantageusement exécutée en carbonatant un lait de chaux, de préférence au moyen d'un gaz contenant du C02. Dans cette forme de réalisation de l'invention, on peut par exemple utiliser un lait de chaux titrant entre 25 et 350, de préférence entre 50 et 250, kg de CaO par m3, que l'on prépare de manière bien connue en soi, en dispersant dans de l'eau, de la chaux vive provenant de la calcination du calcaire dans un four à chaux. Pour carbonater le lait de chaux on peut faire usage d'un gaz pauvre en C02, par exemple des fumées de chaudière contenant de 5 à 15 % en volume de C02. En variante, on peut évidemment aussi utiliser un gaz riche en CO2, contenant plus de 30 % de C02' tel que le gaz récupéré des fours à chaux.According to the invention, the crystallization of calcium carbonate is advantageously carried out by carbonating a milk of lime, preferably by means of a gas containing CO 2 . In this embodiment of the invention, it is possible for example to use a lime milk titrating between 25 and 350, preferably between 50 and 250, kg of CaO per m 3 , which is prepared in a manner well known per se , by dispersing quicklime in water from the calcination of limestone in a lime kiln. To carbonate the milk of lime, it is possible to use a gas poor in C0 2 , for example boiler fumes containing 5 to 15% by volume of C0 2 . As a variant, it is obviously also possible to use a gas rich in CO 2 , containing more than 30% of CO 2 ' such as the gas recovered from lime kilns.

Les quantités respectives de lait de chaux et de gaz de carbonatation doivent être suffisantes pour assurer une carbonatation aussi complète que possible de la chaux. Ces quantités dépendent évidemment des concentrations respectives du lait de chaux et du gaz, ainsi que des conditions de travail, et elles peuvent, dans chaque cas particulier, être établies facilement par l'expérience. On exécute de préférence la cristallisation à une température de l'ordre de 25 à 60° C, par exemple voisine de 30 à 50°C.The respective amounts of lime milk and carbonation gas must be sufficient to ensure as complete carbonation of the lime as possible. These quantities obviously depend on the respective concentrations of the milk of lime and of the gas, as well as on the working conditions, and they can, in each particular case, be easily established by experience. The crystallization is preferably carried out at a temperature of the order of 25 to 60 ° C, for example around 30 to 50 ° C.

Dans le procédé suivant l'invention, la quantité de polymère incorporée au milieu aqueux dépend de divers facteurs, parmi lesquels les conditions de travail pendant la cristallisation et la nature du polymère utilisé; elle peut être déterminée aisément par l'expérience, dans chaque cas. A titre d'exemple, dans le cas particulier où on cristallise le carbonate de calcium en carbonatant un lait de chaux, on peut avantageusement utiliser, à titre de polyélectrolyte, entre 1 et 10 g, de préférence entre 2 et 6 g, de polyacrylate de métal alcalin par kg de matière sèche de la suspension aqueuse diluée de carbonate de calcium.In the process according to the invention, the amount of polymer incorporated into the aqueous medium depends on various factors, including the working conditions during crystallization and the nature of the polymer used; it can be easily determined by experience, in each case. By way of example, in the particular case where the calcium carbonate is crystallized by carbonating a lime milk, it is advantageous to use, as polyelectrolyte, between 1 and 10 g, preferably between 2 and 6 g, polyacrylate of alkali metal per kg of dry matter in the dilute aqueous suspension of calcium carbonate.

On entend par concentré de carbonate de calcium, un gâteau humide de carbonate de calcium, qui a été formé à partir de la suspension aqueuse diluée précitée de carbonate de calcium.The term “calcium carbonate concentrate” is understood to mean a wet cake of calcium carbonate, which has been formed from the abovementioned dilute aqueous suspension of calcium carbonate.

Suivant l'invention, pour séparer le concentré de carbonate de calcium de ladite suspension aqueuse diluée, on utilise des moyens de séparation essentiellement mécaniques. Dans le cadre de l'invention, on entend, par moyens de séparation essentiellement mécaniques, des moyens par lesquels on soumet une suspension de matière solide dans un liquide, à une séparation physique en au moins une phase très concentrée en matière solide et une phase très diluée, sans apport supplémentaire de matière solide dans la suspension ni changement d'état de l'un ou l'autre constituant de la suspension, en particulier sans évaporation, ni solidification du liquide.According to the invention, to separate the calcium carbonate concentrate from said dilute aqueous suspension, essentially mechanical separation means are used. In the context of the invention, the term “essentially mechanical separation means” means means by which a suspension of solid material in a liquid is subjected to physical separation into at least one phase highly concentrated in solid matter and one phase very diluted, without additional addition of solid matter in the suspension or change in state of one or the other constituent of the suspension, in particular without evaporation, or solidification of the liquid.

A titre de moyen de séparation mécanique, on peut par exemple utiliser, conformément à l'invention, une filtration, un essorage ou une décantation de la suspension aqueuse diluée, qui sont des techniques bien connues en soi. En variante, on peut aussi combiner deux ou plusieurs moyens de séparation mécanique distincts.As a mechanical separation means, it is possible, for example, in accordance with the invention, to use filtration, wringing or decantation of the dilute aqueous suspension, which are techniques well known per se. As a variant, it is also possible to combine two or more separate mechanical separation means.

Suivant l'invention, on préfère utiliser, à titre de moyen de séparation mécanique, une filtration, qui est une technique bien connue en soi, le gâteau de filtration recueilli sur le filtre constituant alors le concentré humide précité. De manière connue en soi, on exécute avantageusement une filtration de la suspension diluée sous pression, par exemple entre 0,5 et 15 kg/cm2, et on la fait éventuellement suivre d'une compression du gâteau de filtration sous une pression comprise entre 1 et 20 kg/cm2 et d'un balayage par un courant d'air sous une pression de 0,5 à 6 kg/cm2. La température à laquelle on exécute la filtration ainsi que la compression et le balayage éventuels ne s'est pas avérée avoir une influence notable sur le résultat de la filtration. D'une manière générale, on peut par exemple exécuter celle-ci entre 15 et 50°C, avantageusement à température ambiante.According to the invention, it is preferred to use, as a mechanical separation means, filtration, which is a technique well known per se, the filter cake collected on the filter then constituting the aforementioned wet concentrate. In a manner known per se, filtration of the diluted suspension is advantageously carried out under pressure, for example between 0.5 and 15 kg / cm 2 , and it is optionally followed by compression of the filter cake under a pressure between 1 and 20 kg / cm 2 and a sweep by a current of air under a pressure of 0.5 to 6 kg / cm 2 . The temperature at which filtration is carried out and any compression and sweeping has not been found to have a significant influence on the filtration result. In general, it can for example be carried out between 15 and 50 ° C, advantageously at room temperature.

La fluidification du concentré de carbonate de calcium consiste à soumettre celui-ci à un travail mécanique qui le transforme en une suspension aqueuse fluide, pompable. Elle est généralement réalisée, de manière connue en soi, par un malaxage du concentré, par exemple au moyen d'un mélangeur à palettes, à disques ou à cônes rotatifs.The fluidization of the calcium carbonate concentrate consists in subjecting it to mechanical work which transforms it into a fluid, pumpable aqueous suspension. It is generally carried out, in a manner known per se, by mixing the concentrate, for example by means of a paddle, disc or rotary cone mixer.

L'homogénéisation a pour fonction d'assurer une dispersion efficace, homogène des cristaux de carbonate de calcium dans la suspension aqueuse fluide précitée résultant de l'opération de fluidification. Elle est généralement obtenue en soumettant celle-ci à une turbulence ou un travail de cisaillement intense au moyen d'un disperseur à grande vitesse, par exemple du type à palettes, à disques ou à couteaux.The purpose of homogenization is to ensure an efficient, homogeneous dispersion of the calcium carbonate crystals in the above-mentioned fluid aqueous suspension resulting from the fluidization operation. It is generally obtained by subjecting it to turbulence or intense shearing work by means of a high-speed disperser, for example of the paddle, disc or knife type.

Dans le procédé suivant l'invention, la fluidification et l'homogénéisation sont de préférence exécutées séparément.In the process according to the invention, the fluidization and the homogenization are preferably carried out separately.

L'agent dispersant utilisé pendant la fluidification et l'homogénéisation a pour fonction de faciliter la dispersion des cristaux de carbonate de calcium, en évitant la formation d'agglomérats de cristaux. Il peut par exemple consister en un agent dispersant minéral, tel que l'agent dispersant du commerce connu sous le nom de Calgon (Calgon Corp.), qui est à base de polyphosphate de métal alcalin. En variante, l'agent dispersant peut aussi consister, au moins partiellement, en un agent dispersant organique, par exemple un agent dispersant choisi parmi les polyélectrolytes, de préférence les polyacides.The dispersing agent used during fluidization and homogenization has the function of facilitating the dispersion of the calcium carbonate crystals, avoiding the formation of crystal agglomerates. It may for example consist of an inorganic dispersing agent, such as the commercial dispersing agent known under the name of Calgon (Calgon Corp.), which is based on alkali metal polyphosphate. As a variant, the dispersing agent may also consist, at least partially, of an organic dispersing agent, for example a dispersing agent chosen from polyelectrolytes, preferably polyacids.

Des agents dispersants du commerce qui se sont avérés particulièrement efficaces sont ceux connus sous les noms de Polysel CA (BASF) qui est un agent dispersant à base de polyacrylate de sodium et de Dispagil (Rhône-Progil) qui est un agent dispersant à base ae polyphosphate et de polyacrylate de métal alcalin.Commercial dispersing agents which have been found to be particularly effective are those known under the names of Polysel CA (BASF) which is a dispersing agent based on sodium polyacrylate and Dispagil (Rhône-Progil) which is a dispersing agent based on ae alkali metal polyphosphate and polyacrylate.

L'agent dispersant est de préférence ajouté au concentré de carbonate de calcium avant d'opérer la fluidification et l'homogénéisation. Il peut éventuellement être ajouté à la suspension aqueuse diluée de carbonate de calcium, avant séparation du concentré de carbonate de calcium. On a toutefois observé, en pratique, qu'il est préférable d'ajouter, l'agent dispersant au concentré de carbonate de calcium, après avoir séparé celui-ci de la suspension aqueuse, car il en résulte, toutes autres choses étant égales, une diminution de la quantité d'agent dispersant nécessaire.The dispersing agent is preferably added to the calcium carbonate concentrate before carrying out the fluidization and homogenization. It can optionally be added to the dilute aqueous suspension of calcium carbonate, before separation of the calcium carbonate concentrate. However, it has been observed in practice that it is preferable to add the dispersing agent to the calcium carbonate concentrate, after having separated it from the aqueous suspension, since this results, all other things being equal, a decrease in the amount of dispersing agent required.

La quantité d'agent dispersant utilisée pour fluidifier et homogénéiser le concentré de carbonate de calcium dépend de divers facteurs, parmi lesquels la nature de l'agent dispersant, la granulométrie des cristaux de carbonate de calcium et la teneur en carbonate de calcium du concentré. Elle peut être déterminée aisément par l'expérience dans chaque cas. D'une manière générale, elle est avantageusement comprise entre 2 et 10 g, de préférence 4 et 8 g, par kg de carbonate de calcium du concentré.The amount of dispersing agent used to fluidize and homogenize the calcium carbonate concentrate depends on various factors, including the nature of the dispersing agent, the particle size of the calcium carbonate crystals and the calcium carbonate content of the concentrate. It can be easily determined by experience in each case. In general, it is advantageously between 2 and 10 g, preferably 4 and 8 g, per kg of calcium carbonate from the concentrate.

Le procédé suivant l'invention permet d'obtenir facilement, rapidement et de manière économique, des suspensions aqueuses concentrées, stables de cristaux réguliers de carbonate de calcium, contenant généralement au moins 65 X, de préférence de 68 à 75 X, en poids de cristaux, sans nécessiter de traitement coûteux d'évaporation, ni de broyage. Ces suspensions concentrées se prêtent bien à un stockage de longue durée et à des manutentions, sans que leur stabilité en soit affectée. Les cristaux de carbonate de calcium qu'elles contiennent sont bien formés et réguliers et conviennent bien comme matière de charge en papeterie, dans les peintures et dans la fabrication des matières plastiques.The process according to the invention makes it possible to obtain easily, quickly and economically, concentrated, stable aqueous suspensions of regular crystals of calcium carbonate, generally containing at least 65 X, preferably from 68 to 75 X, by weight of crystals, without the need for expensive evaporation treatment or grinding. These concentrated suspensions lend themselves well to long-term storage and handling, without their stability being affected. The calcium carbonate crystals they contain are well formed and regular and are well suited as a filler in stationery, paints and in the manufacture of plastics.

Les exemples d'application suivants vont illustrer l'invention sans toutefois en limiter la portée.The following application examples will illustrate the invention without, however, limiting its scope.

Dans ces exemples, on a carbonaté un lait de chaux avec un gaz contenant du C02. La suspension aqueuse diluée de carbonate de calcium ainsi obtenue a ensuite été filtrée sous une pression maximum de 4,5 kg/cm2, le gâteau de filtration obtenu a été comprimé sous une pression maximum de 17 kg/cm2 pour l'essorer, puis soumis à un balayage d'air sous pression égale à 5,3 kg/cm2 pendant 10 minutes, fournissant ainsi un concentré humide de carbonate de calcium. Ce concentré de carbonate de calcium a ensuite été fluidifié puis homogénéisé par passage successivement dans un malaxeur puis dans un disperseur, fournissant ainsi une suspension aqueuse de carbonate de calcium.In these examples, a milk of lime was carbonated with a gas containing CO 2. The dilute aqueous suspension of calcium carbonate thus obtained was then filtered under a maximum pressure of 4.5 kg / cm 2 , the filter cake obtained was compressed under a maximum pressure of 17 kg / cm 2 to wring it out, then subjected to an air sweep under pressure equal to 5.3 kg / cm 2 for 10 minutes, thus providing a wet concentrate of calcium carbonate. This calcium carbonate concentrate was then fluidized and then homogenized by successively passing through a kneader then through a disperser, thus providing an aqueous suspension. calcium carbonate.

Les exemples 1 et 2 concernent des essais conformes à l'invention.Examples 1 and 2 relate to tests in accordance with the invention.

Exemple 1Example 1

Avant la carbonatation, on a introduit dans le lait de chaux, qui titrait environ 120 kg de CaO par m3, du Polysel CA qui est un polyélectrolyte du commerce à base de polyacrylate de sodium. La quantité de Polysel CA introduite dans le lait de chaux a été réglée de manière qu'elle corresponde approximativement à 2,5 g de Polysel CA par kg de carbonate de calcium cristallisé. On a ensuite carbonaté le lait de chaux avec un gaz contenant entre 23 et 27 % de C02, sous un débit de 1350 m3/h, pendant 7h15min.. La température a été maintenue à 37°C.Before carbonation, Polysel CA, which is a commercial polyelectrolyte based on sodium polyacrylate, was introduced into the milk of lime, which titrated approximately 120 kg of CaO per m 3 . The amount of Polysel CA introduced into the milk of lime was adjusted so that it corresponds approximately to 2.5 g of Polysel CA per kg of crystallized calcium carbonate. The milk of lime was then carbonated with a gas containing between 23 and 27% of CO 2 , at a flow rate of 1350 m 3 / h, for 7 h 15 min. The temperature was maintained at 37 ° C.

Le concentré de carbonate de calcium recueilli sur le filtre a été fluidifié et homogénéisé en présence de Calgon qui est un agent dispersant du commerce à base de polyphosphate de sodium. On a utilisé 7 g de Calgon par kg de carbonate de calcium du concentré. On a ainsi obtenu une suspension aqueuse concentrée contenant 68 X de cristaux réguliers de carbonate de calcium. Cette suspension aqueuse est restée stable pendant plus de 30 jours.The calcium carbonate concentrate collected on the filter was fluidized and homogenized in the presence of Calgon which is a commercial dispersing agent based on sodium polyphosphate. 7 g of Calgon were used per kg of calcium carbonate in the concentrate. There was thus obtained a concentrated aqueous suspension containing 68 X of regular crystals of calcium carbonate. This aqueous suspension remained stable for more than 30 days.

Exemple 2Example 2

On a répété l'essai de l'exemple 1, en utilisant un lait de chaux titrant environ 120 kg de CaO par m3 et un gaz contenant entre 29 et 32 % de C02. La carbonatation, effectuée à 32°C, a duré 7h35min., avec un débit de gaz compris entre 1200 et 1350 m3/h. On a réglé la quantité de Polysel CA pour qu'elle corresponde à 5 g par kg de carbonate de calcium.The test of Example 1 was repeated, using a milk of lime titrating about 120 kg of CaO per m 3 and a gas containing between 29 and 32% of CO 2 . The carbonation, carried out at 32 ° C, lasted 7h35min., With a gas flow of between 1200 and 1350 m 3 / h. The amount of Polysel CA was adjusted to correspond to 5 g per kg of calcium carbonate.

Pour la fluidification et l'homogénéisation du concentré de carbonate de calcium recueilli sur le filtre, on a fait usage, à titre d'agent dispersant, de 4 g de Polysel CA par kg de carbonate de calcium.For the fluidization and homogenization of the calcium carbonate concentrate collected on the filter, use was made, as dispersing agent, of 4 g of Polysel CA per kg of calcium carbonate.

La suspension aqueuse concentrée de carbonate de calcium obtenue contenait 71,7 % en poids de cristaux de carbonate de calcium; elle est restée stable pendant plus de 30 jours.The concentrated aqueous suspension of calcium carbonate obtained contained 71.7% by weight of calcium carbonate crystals; it remained stable for more than 30 days.

Exemple 3 (essai comparatif)Example 3 (comparative test)

On a répété l'essai des exemples 1 et 2, mais en omettant d'ajouter un polyélectrolyte au lait de chaux. On a utilisé un lait de chaux titrant environ 122 kg de CaO par m et un gaz contenant entre 24 et 32% de CO2, sous un débit réglé entre 1350 et 1500 m3/h pendant 6h30min. La température a été maintenue entre 32 et 34°C pendant toute la durée de la carbonatation. On a filtré la suspension aqueuse de carbonate de calcium, et on a soumis le concentré de carbonate de calcium recueilli sur le filtre, à une opération de fluidification et d'homogénéisation de la manière décrite à l'exemple 1. On a ainsi obtenu une suspension aqueuse de cristaux de carbonate de calcium contenant à peine 63,7 % en poids de cristaux. Cette suspension aqueuse s'est en outre avérée nettement moins stable que celle des exemples 1 et 2.The test of Examples 1 and 2 was repeated, but omitting to add a polyelectrolyte to the milk of lime. Lime milk was used titrating about 122 kg of CaO per m and a gas containing between 24 and 32% CO 2 , at a flow rate set between 1350 and 1500 m 3 / h for 6 h 30 min. The temperature was maintained between 32 and 34 ° C for the duration of the carbonation. The aqueous suspension of calcium carbonate was filtered, and the concentrated calcium carbonate collected on the filter was subjected to a fluidization and homogenization operation as described in Example 1. There was thus obtained an aqueous suspension of calcium carbonate crystals barely containing 63.7% by weight of crystals. This aqueous suspension was also found to be significantly less stable than that of Examples 1 and 2.

Une comparaison des exemples 1 et 2, d'une part, avec l'exemple 3, d'autre part, fait apparaître immédiatement l'intérêt du procédé suivant l'invention qui permet d'obtenir facilement, sans évaporation, par simple filtration, des suspensions aqueuses stables contenant plus de 68 % en poids de cristaux de carbonate de calcium.A comparison of Examples 1 and 2, on the one hand, with Example 3, on the other hand, immediately reveals the advantage of the process according to the invention which makes it possible to obtain easily, without evaporation, by simple filtration, stable aqueous suspensions containing more than 68% by weight of calcium carbonate crystals.

L'invention n'est pas limitée aux exemples qui précèdent, de nombreuses modifications pouvant y être apportées.The invention is not limited to the above examples, many modifications can be made to it.

Claims (18)

1 - Procédé pour la préparation de suspensions aqueuses contenant au moins 65 % en poids de carbonate de calcium, suivant lequel on cristallise du carbonate de calcium en milieu aqueux dilué, on sépare, de la suspension aqueuse diluée de carbonate de calcium résultante, un concentré humide de carbonate de calcium et on fluidifie et homogénéise ledit concentré de carbonate de calcium en présence d'un agent dispersant, caractérisé en ce qu'on cristallise le carbonate de calcium en présence d'un polyélectrolyte hydrosoluble et en ce qu'on sépare le concentré de carbonate de calcium de la suspension diluée de carbonate de calcium par un moyen de séparation mécanique.1 - Process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate, according to which calcium carbonate is crystallized in a dilute aqueous medium, a concentrate is separated from the dilute aqueous suspension of calcium carbonate wet with calcium carbonate and said calcium carbonate concentrate is fluidized and homogenized in the presence of a dispersing agent, characterized in that the calcium carbonate is crystallized in the presence of a water-soluble polyelectrolyte and in that the calcium carbonate concentrate from the dilute calcium carbonate suspension by mechanical separation. 2 - Procédé suivant la revendication 1, caractérisé en ce qu'on choisit le polyélectrolyte parmi les polyacides et leurs sels de métaux alcalins.2 - Process according to claim 1, characterized in that the polyelectrolyte is chosen from polyacids and their alkali metal salts. 3 - Procédé suivant la revendication 2, caractérisé en ce qu'on choisit le polyélectrolyte parmi les polyacides à caractère acide faible et leurs sels de métaux alcalins.3 - Process according to claim 2, characterized in that the polyelectrolyte is chosen from polyacids of weak acid character and their alkali metal salts. 4 - Procédé suivant la revendication 3, caractérisé en ce qu'on choisit le polyélectrolyte parmi les polyacides dérivés des polymères comprenant au moins un groupe carboxylique pour 10 atomes de carbone et leurs sels de métaux alcalins.4 - Process according to claim 3, characterized in that the polyelectrolyte is chosen from polyacids derived from polymers comprising at least one carboxylic group for 10 carbon atoms and their alkali metal salts. 5 - Procédé suivant la revendication 4, caractérisé en ce qu'on choisit le polyélectrolyte parmi les polymères dérivés des acides acrylique, méthacrylique et alpha-hydroxyacrylique, les copolymères de l'acide maléique, les dérivés carboxylés des éthers cellulosiques, et leurs sels de métaux alcalins.5 - Process according to claim 4, characterized in that the polyelectrolyte is chosen from polymers derived from acrylic, methacrylic and alpha-hydroxyacrylic acids, copolymers of maleic acid, carboxylated derivatives of cellulose ethers, and their salts. alkali metals. 6 - Procédé suivant la revendication 5, caractérisé en ce que le polyélectrolyte est un polyacrylate de sodium.6 - Process according to claim 5, characterized in that the polyelectrolyte is a sodium polyacrylate. 7 - Procédé suivant la revendication 5, caractérisé en ce que le polyélectrolyte est un poly-alpha-hydroxyacrylate de sodium.7 - Process according to claim 5, characterized in that the polyelectrolyte is a sodium poly-alpha-hydroxyacrylate. 8 - Procédé suivant l'une quelconque des revendications I â 7, caractérisé en ce qu'on règle la quantité de polyélectrolyte dans le milieu aqueux dilué de la cristallisation, de manière que la suspension diluée contienne entre 1 et 10 g de polyélectrolyte par kg de matière sèche.8 - Process according to any one of claims I to 7, characterized in that the quantity of polyelectrolyte in the dilute aqueous medium of the crystallization is adjusted, so that the dilute suspension contains between 1 and 10 g of polyelectrolyte per kg dry matter. 9 - Procédé suivant la revendication 8, caractérisé en ce que la suspension diluée contient entre 2 et 6 g de polyélectrolyte par kg de matière sèche.9 - Process according to claim 8, characterized in that the diluted suspension contains between 2 and 6 g of polyelectrolyte per kg of dry matter. 10 - Procédé suivant l'une quelconque des revendications 1 à 9, caractérisé en ce que, pour cristalliser le carbonate de calcium, on carbonate un lait de chaux.10 - Process according to any one of claims 1 to 9, characterized in that, to crystallize the calcium carbonate, carbonate a milk of lime. II - Procédé suivant la revendication 10, caractérisé en ce qu'on carbonate le lait de chaux avec un gaz contenant du C02.II - Method according to claim 10, characterized in that carbonate the milk of lime with a gas containing C0 2 . 12 - Procédé suivant la revendication 10 ou 11, caractérisé en ce qu'on carbonate le lait de chaux à une température comprise entre 25 et 60°C.12 - Process according to claim 10 or 11, characterized in that carbonate the milk of lime at a temperature between 25 and 60 ° C. 13 - Procédé suivant l'une quelconque des revendications 1 à 12, caractérisé en ce que le moyen de séparation mécanique comprend une filtration de la suspension diluée de carbonate de calcium.13 - Process according to any one of claims 1 to 12, characterized in that the mechanical separation means comprises filtration of the dilute suspension of calcium carbonate. 14 - Procédé suivant l'une quelconque des revendications 1 à 13, caractérisé en ce que le moyen de séparation mécanique comprend un essorage.14 - Method according to any one of claims 1 to 13, characterized in that the mechanical separation means comprises a spin. 15 - Procédé suivant la revendication 14, caractérisé en ce qu'on filtre la suspension aqueuse diluée de carbonate de calcium et on essore le gâteau de filtration résultant en le comprimant et en le soumettant à un balayage par un courant d'air.15 - Process according to claim 14, characterized in that the dilute aqueous suspension of calcium carbonate is filtered and the resulting filter cake is wrung out by compressing it and subjecting it to sweeping by a stream of air. 16 - Procédé suivant l'une quelconque des revendications 1 à 15, caractérisé en ce que, pour fluidifier et homogénéiser le concentré de carbonate de calcium, on utilise entre 2 et 10 g d'agent dispersant par kg de carbonate de calcium.16 - Process according to any one of claims 1 to 15, characterized in that, to fluidify and homogenize the calcium carbonate concentrate, between 2 and 10 g of dispersing agent are used per kg of calcium carbonate. 17 - Procédé suivant la revendication 16, caractérisé en ce qu'on utilise entre 4 et 8 g d'agent dispersant.17 - Process according to claim 16, characterized in that between 4 and 8 g of dispersing agent are used. 18 - Procédé suivant l'une quelconque des revendications 1 à 17, caractérisé en ce qu'on introduit l'agent dispersant directement dans le concentré de carbonate de calcium.18 - Process according to any one of claims 1 to 17, characterized in that the dispersing agent is introduced directly into the calcium carbonate concentrate.
EP78200085A 1977-07-11 1978-07-07 Process for the preparation of aqueous suspensions containing at least 65% by weight of calcium carbonate Expired EP0000415B1 (en)

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LU77723 1977-07-11

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EP0035640A2 (en) * 1980-02-08 1981-09-16 Hoechst Aktiengesellschaft Highly concentrated filler slurries
EP0108842A1 (en) * 1982-11-10 1984-05-23 Ciba Specialty Chemicals Water Treatments Limited Calcium carbonate dispersions
EP0120808A2 (en) * 1983-02-25 1984-10-03 Ciba-Geigy Ag Finely divided calcium carbonate and method of preparing it
EP0296610A2 (en) * 1987-06-24 1988-12-28 Maruo Calcium Company Limited Glycol dispersion of calcium carbonate
EP0850685A2 (en) * 1996-12-27 1998-07-01 Ecc International Limited Dispersed aqueous suspensions
US10040694B2 (en) 2011-10-05 2018-08-07 Imerys Sa Precipitated calcium carbonate particles and use thereof

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US4756897A (en) * 1986-06-23 1988-07-12 Kerr-Mcgee Corporation Process for preparing concentrated byproduct nitrate solutions
US4732748A (en) * 1986-12-10 1988-03-22 Cyprus Mines Corporation Finely divided calcium carbonate compositions
US4888308A (en) * 1987-02-10 1989-12-19 Chemical Products Corporation Glass manufacture using dense, unsintered, granular alkaline earth metal carbonates
US5275650A (en) * 1987-10-23 1994-01-04 Coatex S.A. Agent for grinding lime to augment its reactivity
US5181662A (en) * 1989-01-27 1993-01-26 Coatex S.A. Process for grinding calcium carbonate in aqueous media
US5593488A (en) * 1995-08-24 1997-01-14 Ecc International Inc. Acid resistant calcium carbonate composition and uses therefor
US5531821A (en) * 1995-08-24 1996-07-02 Ecc International Inc. Surface modified calcium carbonate composition and uses therefor
US5593489A (en) * 1995-10-20 1997-01-14 Ecc International Inc. Acid resistant carbonate composition containing an aluminum or magnesium hydroxide methods of preparation and uses therefor
US5711799A (en) * 1996-03-13 1998-01-27 Ecc International Inc. Acid tolerant calcium carbonate composition and uses therefor
US5653797A (en) * 1996-04-26 1997-08-05 National Gypsum Company Ready mixed setting-type joint compound and method of making same
KR100190596B1 (en) * 1996-05-03 1999-06-01 규 재 유 METHOD OF MANUFACTURING 0.1-1.0º¡ CALCIUM CARBONATE
US6083317A (en) * 1996-11-05 2000-07-04 Imerys Pigments, Inc. Stabilized calcium carbonate composition using sodium silicate and one or more weak acids or alum and uses therefor
GB9624085D0 (en) * 1996-11-20 1997-01-08 Ecc Int Ltd Precipitates and their production
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0035640A2 (en) * 1980-02-08 1981-09-16 Hoechst Aktiengesellschaft Highly concentrated filler slurries
EP0035640B1 (en) * 1980-02-08 1985-01-16 Hoechst Aktiengesellschaft Highly concentrated filler slurries
EP0108842A1 (en) * 1982-11-10 1984-05-23 Ciba Specialty Chemicals Water Treatments Limited Calcium carbonate dispersions
EP0120808A2 (en) * 1983-02-25 1984-10-03 Ciba-Geigy Ag Finely divided calcium carbonate and method of preparing it
EP0120808A3 (en) * 1983-02-25 1987-06-16 Ciba-Geigy Ag Finely divided calcium carbonate and method of preparing it
EP0296610A2 (en) * 1987-06-24 1988-12-28 Maruo Calcium Company Limited Glycol dispersion of calcium carbonate
EP0296610A3 (en) * 1987-06-24 1990-12-12 Maruo Calcium Company Limited Glycol dispersion of calcium carbonate
EP0850685A2 (en) * 1996-12-27 1998-07-01 Ecc International Limited Dispersed aqueous suspensions
EP0850685A3 (en) * 1996-12-27 1999-01-07 Ecc International Limited Dispersed aqueous suspensions
US6140376A (en) * 1996-12-27 2000-10-31 Imerys Minerals, Ltd. Dispersed aqueous suspensions
US10040694B2 (en) 2011-10-05 2018-08-07 Imerys Sa Precipitated calcium carbonate particles and use thereof

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IT1099568B (en) 1985-09-18
LU77723A1 (en) 1979-03-26
US4242318A (en) 1980-12-30
FI62272C (en) 1982-12-10
JPS6317771B2 (en) 1988-04-15
BG49609A3 (en) 1991-12-16
ES471586A1 (en) 1979-01-16
IN147648B (en) 1980-05-17
IT7825558A0 (en) 1978-07-11
FI62272B (en) 1982-08-31
JPS5418498A (en) 1979-02-10
EP0000415B1 (en) 1981-04-29
ATA496878A (en) 1983-03-15
DK308478A (en) 1979-01-12
DE2860643D1 (en) 1981-08-06
FI781991A (en) 1979-01-12

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