FI100237B - Process and apparatus for producing calcium carbonate - Google Patents

Description

100237

Method and apparatus for preparing calcium carbonate

The present invention relates to a process according to the preamble of claim 1 for the preparation of calcium carbonate, in particular a controlled crystalline calcium carbonate.

According to such a method, calcium carbonate is produced by reacting a calcium oxide-based starting material containing at least some hydrated calcium oxide (i.e., 10 calcium hydroxide) with carbonate ions in an aqueous medium to produce a final suspension of calcium carbonate and then precipitating calcium When the carbonate ions are derived from sodium carbonate, sodium hydroxide can be recovered from the suspension if desired.

15

The invention also relates to an apparatus for producing calcium carbonate according to the preamble of claim 21.

Synthetic or industrial or precipitated calcium carbonate, hereinafter also abbreviated as PCC (Precipitated Calcium Carbonate), has become increasingly common as a filler and blend pigment in the chemical, pharmaceutical, plastics and paper industries and,. as a paper coating pigment. As usage and applications increase, so do the requirements for product properties. Different types of synthetic calcium carbonate. . the most significant product characteristics in the applications are based on the crystallized product <· · ·. · * ;; 25 crystal shape and crystal size. In many applications, the product properties are also significantly advantageously affected by the narrowness of the crystal size distribution, i.e. the uniformity of the crystals.

• · · · • · · * · · *

For the paper industry, calcium carbonate is most commonly produced in the so-called in a satellite mill, i.e. a mill connected to a paper mill, where the following reaction takes place:

Ca (OH) 2 + CO 2 ------> CaCO 3 + H 2 O 100237 2

The aqueous suspension (slaked milk) containing slaked lime is thus carbonated, for example, with carbon dioxide from flue gases or from the flue gases of a lime kiln, whereby precipitated calcium carbonate and water are obtained as the product.

5 Before the generalization of the chlor-alkali process based on electrolysis, sodium hydroxide was prepared by causticizing soda and lime by a known causticization reaction:

Ca (OH) 2 + Na 2 CO 3 ------> CaCO 3 + 2 NaOH

10 in which, in addition to sodium hydroxide, (precipitated) calcium carbonate was obtained.

For ecological reasons, chlorine and lye production is unbalanced worldwide; the use of chlorine is constantly declining and the use of lye is constantly increasing. This has reduced the economic importance of the chlor-alkali process from the preparation of sodium hydroxide and, accordingly, made the causticization reaction increasingly attractive. Thus, in recent years, several causticization processes have been built in areas where, for example, natural soda ash (sodium carbonate) is available. However, in these processes, the lime is constantly circulating through the lime kiln and the product is only lye.

20

In summary, it would be desirable to be able to combine carbonation and causticization to produce both lye and caustic in a single process. of calcium carbonate. However, the combination of processes described above has so far not been practically successful in obtaining high-quality precipitated calcium carbonate, i.e. PCC, suitable as a filler or pigment.

• · • · ·> · · · • · · v · In all processes where a crystallizable product is made, it has been found to be problematic *: **: obtaining the correct crystal size distribution. Thus, for example, in Pigment

Handbook (ISBN 0-471-82833-5) from 1987 states that there is no lime and soda. - * -. 30 precipitation has never resulted in a uniform, controllable crystal size distribution. The same; problems also occur in the production of PCC with flue gas carbonates, however, it has been found that the more intense and continuous the mixing, the better the crystal size distribution.

Particular problems in the causticization process have been the dilution of the product liquor, the economic separation of the resulting PCC crystals from the liquor solution, and the agglomeration of the produced crystals. With regard to the concentration of the lye, it must be noted that in the first stage of the reaction, it is necessary that the reaction medium be sufficiently dilute with respect to the reactants in order for the balance of the causticization reaction to be correct. When the concentration of the soda and the corresponding concentration of the liquor are dilute, the reaction is made to proceed quite completely, though never completely. There is always some non-causticized soda left in the lye solution and always some of the lime remains in the hydroxide form.

No process has been available that advantageously solves all of the above problems.

U.S. Patent No. 3,268,388 discloses a process solution that seeks to produce pure white PCC grade earth by a causticization reaction. According to the method, most of the reaction is carried out when the precipitated carbonate and the as yet unreacted lime hydrate (calcium hydroxide) are in a filter from which the lye always formed can be removed and replaced with new pure soda ash. According to the patent publication, the method can even obtain: · · · 20 0.7 μιη: η particles, but even this method does not obtain a uniform, controllable particle size distribution.

!. * * It has still been known that dry quenching methods produce the finest ··· V: slaked lime crystals. Instead, the crystals 25 of the slaked lime in the wet process tend to grow constantly larger, which is disadvantageous for the causticization process. However, wet quenching is advantageous for PCC processes because it allows> · 4 sand and coarse particles to be separated from dilute lime milk simply by a hydrocyclone.

; The object of the present invention is to obviate the drawbacks associated with the prior art and to provide a completely new solution for the production of calcium carbonate.

100237 4

The invention is based on the idea that it is possible to produce finely divided, fine-grained calcium carbonate by carbonization or causticization, provided that the calcium hydroxide particles are also as uniform as possible and preferably at most about 50 times the particle size of the calcium carbonate particles produced. Most preferably, according to the invention, hydrated calcium oxide is reacted with carbonate ions according to the invention, at least about 80% of the particles of which have a particle size of less than about 3 μηι.

Another essential feature of the invention is that the reaction between the calcium hydroxide and the carbonate ions is allowed to proceed without substantially stirring the reaction mixture until the desired particle size of the calcium carbonate is reached. The reaction is then stopped after a preselected time by applying strong stirring forces to the reaction mixture. The length of time chosen depends on how large and in what shape the particles are to be produced.

More specifically, the method according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

The apparatus according to the invention, in turn, is characterized by what is set forth in the characterizing part of claim 21.

«•«:; Details of the apparatus are set out in the characterizing parts 22 to 26 of the dependent claims.

According to a preferred embodiment of the invention, a PCC suitable for paper coating with a particle or grain size of 0.2 μηι <0 <0 is produced, 4 μιη. It has been found that the above-mentioned grain or particle size gives a CaCO3 crystal element with a cross-sectional to length ratio of about 1. Such a spherical crystal is very well suited for coating paper because of its small size . ··. 30 into the pores on the surface of the paper. The crystals also have a high light scattering ability, so that the calcium carbonate crystals prepared according to the invention can significantly improve the brightness of the paper. As the crystal grows from said value of 0.2 to 0.4 μιη: η, the length of its teaspoon 100237 5 increases faster than its thickness (or diameter), whereby the calcium carbonate crystals become needle-like. Needle-like crystals do not fit as well in the pores of the paper, which is why they do not function as well as fillers as spherical crystals.

5 The desired grain size is achieved by carbonizing calcium hydroxide with a particle size <3 μτη. In order to prevent the crystals of slaked lime from growing too much, it is preferable to carry out the contact between the slaked lime and the soda and / or carbon dioxide as soon as possible after the calcium oxide has been quenched. It is particularly advantageous to make the contact of the slaked lime and soda in which the crystal embryos are formed in a rapidly rotating mixer which produces higher turbulent mixing and shear forces. The impact mixer described below is suitable for this use, for example. The first contact between slaked lime and soda is also referred to in this application as "premix" or "initial mixing".

After premixing, the crystal embryos are allowed to grow undisturbed until they are of the desired size range. By not substantially stirring the reaction mixture (or by not "disturbing" the mixture) is meant that no turbulent stirring forces are applied to the reaction mixture. In practice, the reaction is carried out in a reaction vessel to which the reaction mixture is fed from above and in which the gelled layer containing the formed calcium carbonate falls during the reaction time inside the vessel towards the bottom, with laminar flows in the reaction mixture. However, these do not interfere with the growth of crystal embryos.

After the selected time, the carbonation reaction is stopped by stirring the mixture so efficiently that at least some of the calcium carbonate crystals formed in the reaction mixture are broken. Preferably, the cutting is performed with an efficient mixer using high turbulence, shocks and shear. It is also particularly advantageous for this purpose: to use an impact mixer.

• · · • · • «: **: The preparation of a calcium carbonate product for use as a paper filler takes about 15-35, typically about 20-30 minutes. It has been found that by disturbing the mixture before said time has elapsed and before the crystals have grown to a size of 0.2 to 0.4 .mu.m, a large number of crystals are obtained which are <0.2 and which are not preferred paper pellets. for the production of mimetics.

100237 6 "Impact mixer" for the purposes of this application means a device in which the rotating circumferences have plate-like impact surfaces with excessive shear force (after impact) the liquid and suspension flow in the direction of centrifugal force caused by differences in the speed and / or direction of rotation of successive vanes. The device is used here in such a way that liquid and sludge are always fed into it with a smaller volume flow capacity than is taken out of it. In such a device, the plates are either radial or slightly inclined in the direction of rotation. The ability offered by an impact mixer to perform 10 uniform mixing and shear forces as a result of shocks between a solid and a solid impact surface is, in terms of probabilities, incomparably more uniform than in other types of mixers. Typically, more than 95% of the material flow receives almost 100% of the maximum impact energy and only 5% to 10% of the material receives less than 60% of the maximum impact energy. When this dispersion corresponding to the turbulence intensity of the mixture is many times larger in all, even Dissolver-type so-called “high-shear” mixers, for the reasons mentioned above, the redistribution of the formed aggregates and flocs is almost complete in said shock mixer.

20 The impact mixer is also suitable for use in quenching calcium oxide, as will be apparent from the detailed explanation below. Alternatively, the starting material containing at least partially hydrated calcium oxide is produced by grinding · · the calcium oxide is first up to a grain size of up to 200 times the diameter which 80% of the crystals of slaked lime should fall below, and the calcium oxide is quenched by mixing it with water , in which case strong shear forces are applied to the mixture of calcium oxide and water during mixing.

• * · I f * • · ·

In order to achieve a narrow crystal size distribution of the carbonate product on the surface of each possible • «· 1.,.: Uniformly sized Ca (OH) 2 particle, the crystallization reaction of 30 CaCO 3 is initiated, maintained and stopped as simultaneously as possible by rapid turbulent stirring (e.g. ), the reaction is maintained by leaving the mixture substantially undisturbed for a reaction time in a tank in which crystals il 100237 7 can form under the most homogeneous conditions possible, and after the reaction time an efficient turbulent post-stirring is performed to avoid smaller than desired CaCO3 particles.

According to a preferred embodiment, the process according to the invention is carried out as a causticisation process, in which both PCC-grade paper (rhombic calcite) and a lye solution ready for use in the pulp mill process are produced simultaneously.

In this alternative, the carbonate ions are reacted with calcium hydroxide, e.g. in the form of a sodium carbonate solution. Alternatively, some - even the majority - of the carbonate ions can be introduced with the flue gas or pure carbon dioxide into the process and preferably only the initial nucleation is performed with soda and the resulting liquor is left as a dispersion aid in the mixture, filtration only concentrating the slurry when needed.

The carbon dioxide from the flue gases can also advantageously be introduced by first binding it with NaOH to Na2CO3 and contacting it with Ca (OH) 2 and returning the resulting NaOH or part of it to the gas absorber.

The NaOH prepared by the invention can be used as such in a cellulose mill 20 or concentrated, e.g. by evaporation, it can be sold for other uses.

According to our invention, the process equipment shown can also be used to control the formation of:; the ratio of calcium carbonate to NaOH by feeding carbon dioxide-containing gas or pure carbon dioxide to the process mixer · »» · if the need for lye is less than the equivalent of 25 equivalents of calcium carbonate. Easy gas supply comes; in a so-called collision mixer, because its operation typically: takes place largely with empty operating contents. By changing the proportions of the mixture: · *: The concentration of the NaOH solution can be adjusted between 6 and 15%, making it ready for use in the processes of most pulp mills.

; 30> 1 · '; There are significant advantages to the present invention. Thus, the process is designed to make PCC as simple and simple as possible. The process and apparatus according to the invention are suitable for the formation of calcium carbonate by both causticization reaction and flue gas carbonation, in both cases guaranteeing a very steep crystal size distribution and this controllability. The process according to the invention met the requirements of our experiments excellently, but surprisingly proved to be also suitable for the controlled production of other calcium carbonate crystal forms (arangonite / calcite) and sizes in the causticization process and also when gasification is used in addition to or instead of causticization. The crystal form of the calcium carbonate to be produced is preferably controlled by adjusting the process temperature below +42 to 10 ° C when it is desired to produce calcite crystals, and above +43 ° C when producing arangonite crystals.

The invention will now be examined in more detail with the aid of the accompanying drawings and photographs, in which Figure 1 shows a process diagram of a preferred embodiment of the invention, Figures 2 to 10 show electron micrographs of the reaction mixture at different times (times calculated from premixing).

The main steps of the process according to our invention are lime quenching, carbonation, carbonation cutting and filtration, which are described below with reference to Figure 1.

• ί 1. Lime quenching • · • · t 25 Lime quenching for the causticisation process (and / or gas carbonation) is carried out • «1 / preferably continuously, depending on the application, for a relatively short time before • · i i carbonation is started. The lime quenching comprises the following steps: t «i · • • · The starting material CaO is fed via a hopper 1 to a pre-milling 2, for example 30 vibratory cone crushers (crushing ratio preferably 2-8, most preferably about 5), where it is ground to a fineness of preferably 5,000- 15,000, preferably <10,000 times the target crystal size of the final product carbonate.

tl 100237 9

Pre-ground CaO is introduced simultaneously with water, for example in the so-called An ATREX-type shock mixer / extinguisher device 3 which, within a short residence time (preferably <1 second), applies to each volume element of the components to be mixed a substantially similar spectrum of shear forces of intense turbulence 5. According to our studies, at least 80% of the calcium hydroxide crystals generated in this way are smaller than 1/200 in diameter from the maximum grain size of the pre-ground CaO 24 hours after the onset of crystallization. Since the solubility of slaked lime in water is only about 2 g / liter, the size of the calcium hydroxide crystal here means the size of the insoluble solid particle in the aqueous suspension, expressed as an approximation of its average diameter.

Calcium oxide-based aqueous slurry (lime milk) from quenching is pumped into 4 intermediate tanks S.

The sodium carbonate solution used in the carbonation can be prepared in the same equipment as the calcium carbonate. The intermediate container of aqueous sodium carbonate solution is marked with reference number 6.

2. Carbonation reaction 20

Since the aim is to make crystals of slaked lime as small and uniform in size as possible as a raw material for the carbonate to be produced, CaO must be pre-ground, quenched ·; as soon as possible and react with soda ash (and / or carbon dioxide) * · * · / as soon as the calcium hydroxide crystals formed do not have time to grow too large or agglomerate.

«*. . CaCO3 crystallization is initiated as simultaneously as possible throughout the batch by «« · * ··· 'the surfaces of the Ca (OH) 2 particles and the Na 2 CO 3 solution (and / or CO 2) being brought into direct contact with each other by efficient initial mixing. Most preferably, this 30 (, is again realized with an ATREX-type impact mixer 9 or the like, which is characterized by the fact that when the device handles a very small amount of mixture at a time and very quickly (residence time <1 100237 10 seconds), the impact mixer the wings of the mixing rings are likely to apply to each particle with sufficient probability the mixing power required to immediately initiate the carbonation reaction.

5 The dosing equipment of the premixer (pumps 7, 8) ensures the correct proportions of the substances required in the reaction, the dosing of the gas to the reaction can also be carried out in connection with the initial mixing. The dosing of the gas is not shown in Figure 1. The strong turbulence in the initial mixing ensures the simultaneous start of the growth of carbonate crystals.

10

The reaction mixture from the initial mixture containing hydrated calcium oxide from the calcium oxide-based starting material and carbonate ions is fed to the PCC reactor 11 from above. The reactor comprises a cylindrical vessel with a vertical longitudinal axis, the lower end of which is conical.

15

The reaction time in reactor 11 depends on the desired crystal size of the final product; with coating PCC from 3 μιη 0 Ca (OH) 2 -> 0.2 μιη <0 <0.4 μιη CaCO3 for about 20-25 minutes.

After the initial mixing, the mixture is not substantially stirred according to the invention, but is allowed to form in the carbonate crystals by continuously reacting the surface layer of Ca (OH) 2 particles with the surrounding soda solution until the entire hydroxide particle reacts to its surface. If the reaction is allowed to proceed long enough, the finished carbonate crystals .11 # separate when the NaOH formed as the second product of the process acts as a dispersant and keeps the formed crystals apart.

• · · • «♦ · $ 2.

i *

Our experiments have clearly shown how, after a reaction time of about 5 minutes: the mixture gels (see example below) when the carbonate crystals formed on the surface of the hydroxide "parent particles" have grown large enough to fill

Ca (OH) 2 particles, thus increasing the viscosity of the mixture (later viscous reaction step 30). As the reaction proceeded sufficiently, the dispersion of carbonate crystals was surprisingly observed after the "parent particles" had run out. 1 shows in our experiments that the mixture becomes liquid again.

II

100237 11 vaccines.

This phenomenon has not been properly taken into account or interpreted in previously known process solutions, as it is known that "gelation" has always been prevented by continuing to stir throughout the reaction, whereby some of the newly formed carbonate crystals are continuously broken, expanding the crystal size distribution to a finer filter. CaC03.

The crystalline form of the calcium carbonate to be produced depends on the temperature at which the crystallization reaction takes place. Calcite crystals are formed at <42.5 ° C and typically longer elongated arangonite crystals at higher temperatures. In order to control the crystal shape, the apparatus 11 is provided with the possibility of thermal control. This is also important because the use of small Ca (OH) 2 particles and efficient initial mixing with an impact mixer increase heat generation in the process.

15 3. Disconnecting carbonation

After the desired reaction time, the reaction mixture is removed from the reactor 11 and passed to the stirred 12 to break the carbonation. This operation, also called post-mixing, is preferably carried out with an impact mixer 1 to 4 times in order to react the unreacted Ca (OH) 2 with respect to the already existing CaCO 3 particles. By selecting the time at which the post-mixing is carried out, the shape and maximum size of the crystals formed can be .11 adjusted. This avoids possible • · • «. *’! formation of undersized carbonate crystals generated by reaction residues. Ice • · «25, ^ competition mixing with an impact mixer helps to keep the crystal size distribution narrow also because it affects our test results and e.g. Kormogorov / Hinze 's law of known turbulence:. even according to the theory of mixing length, it only increases the size of particle agglomerations that it cannot decompose. In the case of post-mixing, the reaction can be intensified by adding carbon dioxide to the mixture if there is no 30. sufficient dissolved soda or the NaOH content of the mixture becomes too concentrated for the causticization reaction to proceed in the desired direction.

<«I I ·« 12 100237 4. Filtration

From the mixer 12, the mixture is pumped 13 to an intermediate tank 15, to which compressed air is pumped from the tank 14. With compressed air, the mixture is conveyed to a filtration 16. The filtration can be carried out even with a very fine cassette-type pressure filter 16, because the CaCO3 crystals , but the NaOH filtrate can always be compressed between them.

The filtration is preferably carried out under pressure of compressed air in order to avoid excessive dilution of the filtrate, usually an aqueous solution of sodium hydroxide.

The sodium hydroxide solution is collected and taken to a tank 20.

The pressure filter is washed with water and the PCC slurry is led to an intermediate tank 21 from which it can be taken to a storage tank 23. At least part of the slurry can also be dried in a dryer 24 to obtain PCC powder.

Spent wash water containing some PCC and sodium hydroxide is recycled to quench 20 calcium oxide.

In the following, the method according to the invention and the process equipment which advantageously implements it will be considered with the help of an application example and the accompanying photographs of the simultaneous production of coating PCC and NaOH by the causticization reaction.

i · * • · • · · • «·

Example • · · "• · · 3Ö., The following experiment demonstrates the performance of the method of the invention under laboratory conditions.

Il 100237 13

Experimental arrangements: 1. Lime quenching: CaO 0 10 mm pre-milled with a vibratory cone crusher <2mm 0. Quenching was performed with an ATREX mixer, temperature 75-80 ° C, solids 12%.

5 Ca (OH) 2 was quenched in the tank for about 20 h.

2. Na 2 CO 3 was dissolved in water> 30 ° C to a ca. 32% saturated solution.

3. The causticization process was performed in the laboratory of the Helsinki University of Technology, where an electron microscope was available to monitor the progress of the process, but the ATREX mixer could not be used for the initial mixing. However, due to the small amount of mixture (50 g of Ca (OH) 2 mixture and 23.5 g of Na 2 CO 3 solution), the process could be started sufficiently simultaneously throughout the mixture by pre-mixing the substances with a laboratory mixer.

4. The temperature was maintained <30 ° C throughout the reaction step. The process material mixture was examined by electron microscopy at 5, 15, 19, 22, 25, 29, 39 and 60 minutes after the start of the causticization reaction. Prior to the reaction, Ca (OH) 2 was also examined by electron microscopy.

20

Test results:

The main steps of the method: • · • · «i '25 / Figure 2 - Ca (OH) 2 particles relatively loose, grain size approx. 2 - 4 μΐη 0.

Figure 3 - After about 5 minutes, the mixture begins to arrange into a uniform viscous: mixture in which particles of about 2 μιη 0 are detectable.

• · ·

Figure 4 - about 25 minutes: Particles with a size of 0.2 to 0.4 μιη, after which mixing is started.

• · · 30 .. Electron micrographs of the intermediate stage of the reaction show a rapid change in the composition of the reaction mixture: 100237 14

Figure 5 - about 15 minutes: The particles are still noticeable as roundish, uneven in surface and stuck in each other's gaps; the viscosity of the mixture is high.

Figure 6 - about 19 minutes: A uniform gel-like mass with about 2 μτη 0 bumps. Figure 7 - about 22 minutes: A uniform gel-like mass with little separation of the particles.

Electron micrographs of the situation where the reaction is allowed to continue after 30 minutes: 10 Figure 8 - about 39 minutes: Rod-like crystals 0 1-2 μτη, length 5-10 μm, start to form in the gel (Figure 8).

Figure 9 - about 43 minutes: The crystals shown in the previous figure disintegrate

Figure 10 - about 60 minutes: CaCO3 is mainly in the lye solution in the form of rod-like crystals with a length of about 5-20 μτη and about 0.1 to 1.0 μτη 0 in the form of granular crystals.

15

The experiment showed that when the causticization process is stopped according to the invention, e.g. in the preparation of coating PCC (0.2-0.4 μτη 0) 15-25 minutes after starting the reaction with efficient ATREX mixing, homogenization of the mixture achieves the desired result when the gel-formed the crystals are dispersed with the resulting NaOH and the loose agglomerates in the gel are decomposed.

«· '‘ The experiment further showed that during the high viscous phase of the reaction, within about 5 to 15 minutes of starting, stirring of the mixture is not necessary. It can be concluded that, in addition to the high energy consumption required for mixing,% 5 .: mixing would also be disadvantageous because the mixing of the formed NaCO3 + Ca (0H) 2 »» »• · · * gel with the resulting With NaOH would slow the growth of CaCO 3 crystals. . to the desired size and thus leave too many very small PCC crystals in the product, which make filtration difficult.

• · · • · «30 It was also found that in the gel the crystals grow elongated unless the reaction is interrupted by efficient post-mixing. This confirms that the process according to the invention is: · adjustable by post-mixing to schedule the production of 15 100237 PCC crystals of different shapes and sizes with the desired size distribution.

• 0 • · «• ·» · * · «i tr ·« · («

Im • • · I I * * · l I »·« • · · • t »« · · 4 * i *

Claims (26)

A process for the production of calcium carbonate, wherein - a calcium oxide-based precursor containing at least in any male hydrated calcium oxide is reacted with carbonate ions in an aqueous medium for the production of calcium carbonate, - the starting concentration of calcium oxide, hydrated calcium oxide, hydrated level of calcium carbonate precipitates in the medium, forming an aqueous suspension containing calcium carbonate, and 10. the precipitated calcium carbonate is separated from the suspension and subjected to continued treatment to produce the desired end product, characterized in that - at least about 80% of the intended reaction the hydrated calcium oxide particles have a particle size of less than about 3 µm; - the reaction is allowed to proceed without the reaction mixture containing ": hydrated calcium oxide and carbonate ions being substantially stirred, and - the reaction is quenched after one hour. hand selected time by subjecting the reaction mixture to stirring forces. 20 Process according to claim 1, characterized in that the particles of the hydrated calcium oxide subjected to the caustic reaction have a diameter not exceeding 50 times the maximum crystal size of the calcium carbonate produced. • · · • · · «9. f ··; Method according to claim 1 or 2, characterized in that calcium carbonate is prepared having a particle size of substantially 0.2-0.4 µm. • l r Method according to claim 3, characterized in that at least about 80% of the hydrated calcium oxide particles intended for the reaction are less than 10 μτη. 30 Process according to any one of claims 1-4, characterized in that the carbonization reaction is stopped by subjecting the reaction mixture to vigorous stirring, that at least part of the calcium carbonate crystals formed in the reaction mixture can be crushed. 6. Process according to claim 5, characterized in that the mixture is subjected to stirring in a blow mixer. Process according to any one of claims 1-6, characterized in the preparation of calcium carbonate products having a narrow particle size distribution, such as calcium carbonate intended for paper coating, only 15 minutes after the first stirring or when the mixture during the reaction progresses, becomes smooth the stirring reaction mixture which crushes the CaCO 3 crystals. Process according to any of the preceding claims, characterized in that the reaction mixture containing hydrated calcium oxide and carbonate ions is formed: 15: by mixing the aqueous suspension containing the:: ": Process according to any of the preceding claims, characterized in that the carbonate ions are added to the reaction mixture in the form of an aqueous solution of sodium carbonate. «·« • Process according to claim 9, characterized in that carbonate ions are added to the reaction mixture also in the form of carbon dioxide. j; '25 11. Process according to claim 10, characterized in that carbon dioxide is added to the reaction mixture in connection with the first stirring in the form of mixed carbon dioxide gas or a gas mixture containing carbon dioxide, wherein the gas or gas mixture is measured in the mixing zone of the percussion mixer. . 30 Process according to claim 10 or 11, characterized in that carbon dioxide is added to the reaction mixture in connection with the interruption of the carbonation reaction in the form of a mixed carbon dioxide gas or a gas mixture containing carbon dioxide, wherein said gas or gas mixture is fed to the mixing zone in the slag mixer. 5 13. A process according to any one of claims 1-7, characterized in that the carbonate ions are added to the reaction mixture in the form of carbon dioxide. Process according to any of the preceding claims, characterized in that the starting material containing at least partially hydrated calcium oxide is produced by - refining the calcium oxide to a crystal size not exceeding 200 times the diameter of 80% of the crystals of the quenched caustic oxide, and - is quenched by mixing it in water, whereby the mixture formed by the calcium oxide and water is subjected to strong cutting forces in connection with the d5 stirring. 15. A process according to claim 14, characterized in that the calcium oxide is extinguished by mixing it with water in an impact mixer. 20 Process according to claim 14 or 15, characterized in that the calcium oxide is refined to the desired particle size by means of a shaking compress. Method according to any one of claims 14-16, characterized in that calcium oxy- * ;;; it is refined to a maximum particle size of 2 mm. i * 25 • 1 ' The process according to claim 1, characterized in that the calcium carbonate's crystalline crystals in * form are controlled by setting the reaction temperature to a value below +42 ° C in the preparation of calcite crystals and to a value above +43 ° C in the preparation of arangonitkristaller. 30 Process according to claim 9, characterized in that the starting materials have such concentrations that a NaOH solution having a concentration between 6 and 15% is prepared by a caustic reaction. Process according to any of the preceding claims, characterized in that the calcium carbonate is filtered with a pressure filter. A device for producing calcium carbonate, comprising - a reaction vessel (11), wherein a calcium oxide-based precursor containing at least in some men containing hydrated calcium oxide can be reacted with 10 carbonate ions in an aqueous medium to obtain calcium carbonate (10), ) for the calcium oxide-based precursor and aqueous solution containing carbonate ions, and - outlet means (12, 13) coupled to the reaction vessel for removal of the calcium carbonate product from the vessel, characterized in that "": - an impact mixer (9) coupled to said feedstock, in which mixer the calcium oxide-based starting material and the aqueous solution containing carbonate ions can be mixed together before being added to the reaction vessel (11). Apparatus according to claim 21, characterized in that an inlet for carbon dioxide gas or gas containing carbon dioxide is provided in the impact mixer for reacting the carbon dioxide ... with the aqueous suspension of the calcium oxide-based starting material. • · · 1 it • «C Device according to claim 21 or 22, characterized in that a blow mixer (12) is connected to the outlet means and can be used to interrupt the reaction between the hydrated calcium oxide and the carbonate ions. • · · • ♦ Apparatus according to any one of claims 21-23, further comprising a tiling unit (1-4) for the calcium oxide connected to the reactor's feeder for the production of a water suspension containing hydrated calcium oxide, characterized in that said unit comprises a crusher (2). for refining the calcium oxide and an outlet from the crusher coupled mixer (3), where the refined calcium oxide can be reacted with water. 25. Device according to claim 24, characterized in that the crusher is a shaker crusher. 5 Device according to any of claims 21-25, characterized in that the outlet from the impact mixer (12) is coupled to a pressure filter (16), with which the suspended substance can be separated from the water suspension. • · · • · · · · · · • <<· • · · <• · • • • t · • t • · «• · ·