MXPA00004395A - Method for making calcium carbonate - Google Patents

Abstract

The invention concerns a method for making calcium carbonate and/or calcium and magnesium carbonate particles, which consists in treating a basic pH aqueous medium containing Ca(OH)2 and/or Ca(OH)2-Mg(OH)2 by injecting therein gaseous CO2 to form calcium carbonate and/or calcium and magnesium carbonate, and recuperating the formed carbonate particles. The invention is characterised in that the treatment of the aqueous medium is carried out in the presence of at least an additive selected among the group consisting of hydrazine, hydroxylamine, hydroxylamine soluble salts, and their mixtures.

Description

PROCEDURE FOR THE MANUFACTURE OF CALCIUM CARBONATE The subject of the present invention is a process for the manufacture of calcium carbonate and calcium carbonate and magnesium, in which an aqueous medium of basic pH and containing Ca (OH) 2 and / or Ca (OH) is treated. 2- Mg (OH) 2 by injection of the gaseous CO2 to form calcium carbonate and / or calcium carbonate and magnesium, and in which the carbonate particles formed are recovered. A method of this type has been described, for example, in U.S. Patent No. 4900533. A method for the manufacture of vaterite is known from WO 92/01629. In this procedure, CO2 is injected in a controlled manner into a medium containing calcium hydroxide and an acid salt of an organic amine. The amine salt reacts with Ca (OH) 2 to provide an amine that maintains the medium at a basic pH and a calcium salt soluble in the acid of the amine salt. The salt thus formed is then carbonated to give the vaterite. Likewise, document FR 2405903 discloses a process in which calcium is solubilized in an aqueous medium thanks to ethanolammonium nitrate to convert calcium into soluble calcium nitrate, and the calcium-rich filtrate is recovered to CO2 carbonation. The particles thus obtained are of high purity and have a whiteness index of approximately 99.5 and a zero yellowing index. The procedure according to this document needs two stages of filtration which makes them expensive. In CN 85103821 a process of carbonation of lime slurry by addition of sodium acid carbonate in the presence of ethanolamine and hydrazine or Na dithionite is described. This procedure has the disadvantage that it uses a mode of carbonation which involves the production of NaOH which is eliminated after washing. The degree of whiteness obtained by this method is also insufficient for numerous applications. The present invention is directed to a simple process that allows, by using particular additive (s), to reduce the harmful influence of the impurities on the whiteness of the carbonate particles, while avoiding excessively excessive whiteness. In the process according to the invention, the treatment of the aqueous medium is carried out in the presence of at least one additive selected from the group consisting of hydrazine, hydroxylamine, soluble salts of hydroxylamine, and mixtures thereof. This group has the advantage of introducing in the reaction medium a powerful reducing agent that will reduce in a basic medium, among others Mn4 + to M2 + and Fe3 + to Fe2 +, without the need for any other additive. Advantageously, said aqueous medium contains an amount of said additive corresponding to 0.035 to 5% by weight of Ca (OH2 and / or Ca (OH) 2 - Mg (OH) 2.

Preferably, the Mn content of Ca (OH) 2 and / or the Ca (OH) 2- Mg (OH) 2, because the treatment of the aqueous medium in the presence of a previously mentioned additive is carried out so that said aqueous medium contains from 1 to 8 moles, preferably 2 to 6 moles of additive per mole of Mn. According to a particular feature, said treatment is carried out at atmospheric pressure, advantageously under a pressure higher than atmospheric pressure, preferably under a real pressure comprised between 1.2.105 Pa and 10.105 Pa, this treatment being carried out at a temperature comprised between 10 and 100. ° C, advantageously between 20 and 95 ° C, preferably between 30 and 60 ° C, for example about 40 ° C. According to an advantageous form of a process according to the invention, the formed carbonate particles or a suspension containing these particles are subjected to a treatment for decomposing the additive. For example, a suspension of formed carbonate particles is recovered and then subjected to a treatment to decompose the additive that is still present in the particles. Said treatments consist for example of a treatment with hypochlorite (for example sodium) and / or with water having a temperature higher than 20 ° C., for example a temperature between 20 and 100 ° C, in particular a temperature of 70 ° C or more and / or with steam. According to an implementation of the process, after treatment of the aqueous medium by injection of CO2, the carbonate particles formed are separated from the medium, and the medium is at least partially reused to form an aqueous medium containing Ca (OH) 2 and or Ca (OH) 2-Mg (OH) 2 and at least one of said additives. For example, in the process according to the invention, the aqueous medium containing Ca (OH) 2 and / or Ca (OH) 2-Mg (OH) 2 is formed by extinction of CaO and / or CaO-MgO by a aqueous medium, said additive being added to said aqueous medium before, during and / or after the extinction. Finally, the invention also relates to calcium carbonate particles having an Mn content expressed in MnO, which comprises between 80 ppm and 500 ppm, in particular between 90 and 250 ppm, and more precisely between 100 and 200 ppm, a content Fe expressed in Fe2O3 comprising between 500 and 2000 ppm, in particular less than 1000 ppm, a diameter by weight less than 5 μm, a whiteness index measured at 457 nm greater than or equal to 95, but less than 99 and an index yellowing less than or equal to 1.5, but greater than 0.5. These particles have a sufficient whiteness but not excessive. The invention also relates to calcium carbonate and magnesium particles having an Mn content expressed in MnO ranging from 50 ppm to 500 ppm, in particular between 90 and 250 ppm, and more precisely between 100 and 200 ppm, a Fe content expressed as Fe2 O3 less than 2000 ppm, in particular less than 1000 ppm, a mean diameter by weight less than 5 μm, a whiteness index measured at 457 nm greater than or equal to 95, but less than 99, and a Yellowness index less than or equal to 1.5, but greater than 0.5. The features and details of the invention will be highlighted in the following detailed description in which reference is made to the accompanying drawings. In these drawings figures 1 to 3 schematically show the methods of the invention. In the process according to Figure 1, an aqueous medium containing, for example, 0.05 to 2.5% additive is prepared in 1. In 2, CaO particles are added to the aqueous medium so as to form a suspension or slurry of Ca (OH) 2. In 3, CO2 is injected into the suspension, for example at a rate of 10 to 200 g of CO2 / hour / liter. Advantageously, the temperature of the suspension is regulated in 3 for example between 20 and 60 ° C, preferably at approximately 40 ° C. The CO2 injection is advantageously carried out in a tank maintained at a real pressure of 1.2.105 to 10105 Pa, preferably 1.5 to 3.105 Pa. In 4, calcium carbonate particles are recovered, for example, by filtration. The filtrate or liquid phase is then reused for the preparation in 1 of the aqueous medium destined for the extinction of CaO. The process represented by Figure 2 is similar to that shown in Figure 1 except that it is used as a hydrazine additive and that a suspension of calcium carbonate particles is subjected to a treatment by means of an aqueous solution containing hypochlorite. of sodium, in order to eliminate any vestige of hydrazine. By drying in 6, dry particles are obtained. The process according to Figure 3 is similar to that of Figure 2, except that a soluble salt of hydroxylamine (for example a strong acid salt) is used as an additive, this additive being added in 2 during, but preferably after the extinction of the lime, and because in 5 the suspension of carbonate particles recovered in 4 is subjected to a treatment with hot water for example by steam (more than 120 ° C), this treatment being able to decompose any traces of hydroxylamine. Next, embodiments will be described.

EXAMPLE 1 A lime slurry was prepared by reaction of quicklime and water. The lime used contains 510 ppm of Fe expressed in the form of Fe2? 3 and 125 ppm of Mn expressed in the form of MnO. The solid content of the slurry was, for example, 10% by weight. Other calcium oxide oxides are possible. The pH of the lime slurry thus formed was about 12. After having brought the temperature back to 40 ° C, the additives according to the invention were added in an amount corresponding to 0.2% by weight of quicklime used. The CO2 is then bubbled into the slurry at the rate of 20 g CO2 / hour / liter. After CO2 bubbling, the pH decreased to reach a value of about 8-8.5 at the end of the bubbling operation. The following table provides the characteristics of the carbonates obtained in this way This table shows that using the additives according to the invention (HZ hydrazine hydrate N2H4H2O, CHA hydroxylamine hydrochloride NH2OH.HCl, SHA, hydroxylamine sulfate (NH2OH) 2.H2SO4), it was possible to increase in relation to the reference particles (without additive) the whiteness of the particles approximately in two points, reducing at the same time the index of yellowing of the same in at least one point. Using other additives such as sodium tetrahydroboride (THB), it was not possible to obtain said increase in whiteness, combined with said decrease in yellowing. The whiteness index measured at 457 nm (R 457) and the yellowness index (l: J :) were measured on an Elrepho 2000 device from DATACOLOR. The average diameter in weight (dso) is expressed in μm.

EXAMPLE 2 Example 1 was repeated but using quicklime having different Fe and Mn levels (expressed in Fe2? 3 and MnO), and using hydrazine as an additive, a ratio of 0.2% by weight of quicklime. The following table provides the whiteness index of the calcium carbonate particles prepared without hydrazine (R 457 hydrazine).

EXAMPLE 3 Example 2 is repeated, except that 0.1% hydrazine is used. The following table gives the whiteness index of the calcium carbonate particles prepared without additive (reference R 457) and with hydrazine (R457 HZ).

In order to remove any traces of hydrazine in the carbonate particles, the particles can be subjected to treatment by means of an aqueous solution containing sodium hypochlorite.

EXAMPLE 4 Example 2 is repeated except that a quicklime containing 910 ppm of Fe expressed in the form of Fe2 ?3 and 175 ppm of MnO is used. The additives used consisted of hydrazine (HZ) at the rate of 0.1 and 0.2% by weight of quick lime, hiroxylamine hydrochloride (CHA) at the rate of 0.1 and 0.2% by weight of quick lime, hydroxylamine sulfate (SHA) at of 0.2% by weight of quick lime, and mixtures of these additives. The following table gives the whiteness index and the yellowing index of calcium carbonate particles with an average diameter between 2 and 2.5 μm.

Tests were also carried out, using cooked dolomite (CaO-MgO) as the starting material instead of CaO. A more significant whiteness of the carbonate particles and an attenuation of the yellow appearance were similarly observed.

The calcium carbonate particles produced by the process according to the invention, in particular the particles having: * a content of Mn expressed in MnO comprising between 80 ppm and 500 ppm, preferably comprises between 90 and 250 ppm, more precisely between 100 and 200 ppm, * a Fe content expressed as Fe2O3 comprising between 500 ppm and 2000 ppm, preferably below 1000 ppm, * a mean diameter by weight less than 5 μm, preferably less than 3 μm, * an index of whiteness measured at 457 nm greater than or equal to 95, but less than 99, and * a yellowness index less than or equal to 1.5 but greater than 0.5 which has numerous applications as additives for paints, plastics, rubber, adhesive, papers, etc. The same applies to the calcium carbonate and magnesium particles produced by the process according to the invention, in particular those having: * a content of Mn expressed in MnO comprising between 50 ppm and 500 ppm, preferably between 90 and 250 ppm, more precisely between 100 and 200 ppm, * a Fe content expressed as Fe2O3 below 2000 ppm, preferably below 1000 ppm, * and values of a mean diameter by weight, a whiteness index and a yellowness index as indicated above, for the calcium carbonate particles according to the invention.

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. Process for the manufacture of particles of calcium carbonate and / or calcium and magnesium carbonate, in which an aqueous medium of basic pH is treated and which contains Ca (OH) 2 and / or Ca (OH) 2-Mg (OH) 2 by injection of the gaseous CO2 to form calcium carbonate and / or calcium carbonate and magnesium, and in which the formed carbonate particles are recovered, characterized in that the aqueous medium is treated in the presence of less an additive selected from the group consisting of hydrazine, hydroxylamine, soluble salts of hydroxylamine and mixtures thereof.

2. Process according to claim 1, characterized in that said aqueous medium contains an amount of said additive corresponding to 0.035 to 5% by weight of Ca (OH) 2 and / or Ca (OH) 2-Mg (OH) 2.

3. Method according to claim 1 or 2, characterized in that the Mn content of Ca (OH) 2 and / or Ca (OH) 2-Mg (OH) 2 is determined, and that the treatment of the aqueous medium in presence of at least one additive mentioned, so that said aqueous medium contains from 1 to 8 moles, preferably from 2 to 6 moles, of said at least one additive for each mole of Mn.

4. Method according to any of claims 1 to 3, characterized in that said treatment is carried out under a pressure higher than atmospheric pressure, preferably under a pressure comprised between 1, 2,105 Pa and 10,105 Pa. 5.- Procedure according to the claim 4, characterized in that the treatment is carried out at a temperature comprised between 10 and 100 ° C. 6. Method according to any of the preceding claims, characterized in that the formed carbonate particles are subjected to a treatment to decompose said at least one additive. 7. Process according to claim 6, characterized in that the carbonate particles formed are recovered and that they are subjected to a treatment to decompose said at least one additive still present in the particles. 8. Process according to claim 6 or 7, characterized in that the carbonate particles formed or recovered, preferably in the form of a suspension, are subjected to a treatment with hypochlorite and / or with water having a temperature above 70 ° C. 9. Process according to any of the preceding claims, characterized in that after the treatment of the aqueous medium by injection of CO2, the carbonate particles formed are separated from the medium, and the medium is at least partially reused to form an aqueous medium containing Ca (OH) 2 and / or Ca (OH) 2-Mg (OH) 2, and at least one of said additives. 10. Process according to any of the preceding claims, characterized in that the aqueous medium containing Ca (OH) 2 and / or Ca (OH) 2-Mg (OH) 2 is formed by extinction of CaO and / or Ca-MgO in an aqueous medium, the additive being added to said aqueous medium before, during and / or after the extinction. 11. Calcium carbonate particles having a content of Mn expressed in MnO comprising between 80 ppm and 500 ppm, a content of Fe expressed in Fe2O3 comprised between 500 ppm and 2000 ppm, a mean diameter in weight less than 5 μm , an average whiteness index at 450 nm, greater than or equal to 95, but less than 99, and a yellowness index less than or equal to 1.5 but greater than 0

5. 12.- Calcium carbonate and magnesium particles that have a Mn content expressed as MnO between 50 ppm and 500 ppm, Fe content expressed as Fe2O3 below 2000 ppm, average diameter by weight less than 5 μm, a whiteness index measured at 450 nm, greater than or equal to 95, but less than 99, and a yellowness index less than or equal to 1.5 but greater than 05.