WO2007066167A1

WO2007066167A1 - Process for preparing a stabilized soluble anhydrite iii-based hydraulic binder, hydraulic binder obtained, use of said binder and industrial installation for implementing the process

Info

Publication number: WO2007066167A1
Application number: PCT/IB2005/004006
Authority: WO
Inventors: Crisanto Palacios
Original assignee: Gypsmix (Sarl)
Priority date: 2005-12-07
Filing date: 2005-12-07
Publication date: 2007-06-14
Also published as: ZA200805863B; CN101454256B; CN101454256A; TNSN08241A1; EP2079669A1

Abstract

Process for preparing a stabilized soluble anhydrite III-based hydraulic binder, hydraulic binder obtained, use of said binder and industrial installation for implementing the process. The invention relates to a process for preparing a stabilized soluble anhydrite III-based hydraulic binder. It also relates to the hydraulic binder obtained and to the use of said hydraulic binder in the cement industry. It also relates to an industrial installation for implementing such a process. According to the invention, the preparation of an anhydrite III-based hydraulic binder is carried out a) by heating a calcium sulphate-based pulverulent composition in order to form metastable soluble anhydrite III, and b) by carrying out a mecanosynthesis on the composition obtained in step a) in order to stabilize the soluble anhydrite III. The objective of the invention is to stabilize particles of metastable soluble anhydrite III without having to resort to the cooling of said particles.

Description

Process for preparing a hydraulic binder based on stabilized soluble anhydrite III, hydraulic binder obtained, use of this binder and industrial plant for carrying out the process

Description

The subject of the invention is a process for preparing a hydraulic binder based on stabilized soluble anhydrite III.

It also relates to the hydraulic binder obtained as well as the use of this hydraulic binder in the cement industry.

It also relates to an industrial installation allowing the implementation of such a process.

The invention relates to the technical field of the cement industry and more particularly the cement compositions resulting from the dehydration of calcium sulfate.

Hydraulic binders based on soluble anhydrite III are well known to those skilled in the art. Extensive dehydration - from 220 ^° C. to 360 ^° C. - of natural or synthetic calcium sulphate (gypsum) of formula (CaSO ₄ , 2hbO) or hemihydrate (plaster) of formula (CaSO ₄ , / 4HbO) ₁ leads to the formation of metastable soluble anhydrite III of formula (CaSO ₄ , εhbO) with ε from 0.1 to 0.2. Even further dehydration - from around 400 ^° C. - leads to the formation of anhydrite II (CaSO ₄ , OH2O), which is very slightly hygroscopic. As the metastable anhydrite III solubia is highly hygroscopic, it rehydrates rapidly to hemihydrate, or traditional β plaster, then returns to the state of calcium sulphate depending on the hygrometry of the area.

Those skilled in the art know in particular from patents FR 2733496 (DUSSEL), FR 2767815 (COUTURIER), WO 00/47531 (COUTURIER), WO 2005/000766 (COUTURIER) processes for preparing stabilized solubie anhydrite III which include two successive next steps:

a) baking a powdery composition based on calcium sulphate (natural or synthetic gypsum or plaster) to form the anhydrite III metastable solubia;

b) thermal quenching to stabilize the metastable phase of anhydrite III.

The methods of the prior art therefore teach those skilled in the art to apply thermal stress to the anhydrite III particles so as to make them stable. This sudden cooling is particularly important, because it makes it possible to block and fix the crystal structure of the H1 anhydrite particles in order to stabilize them. This type of known method, however, has a number of drawbacks.

In fact, cooling is generally carried out by injecting cold, dry air into the heart of the material. It appears that the quality of the stabilized anhydrite III particles is not regular, since the cooling is not effective on all of the particles.

In addition, a proportion of moist air present at the time of the cooling step causes rehydration of the metastable anhydrite III to calcium sulphate hemihydrate so that the proportion of stabilized anhydrite III obtained industrially is not very high, unless complex and expensive installation. The object of the present invention is to remedy this state of affairs, in particular because it proposes to effectively stabilize metastable soluble anhydrite III particles, without resorting to cooling said particles.

Another object of the invention is to propose an industrial installation which is simple and inexpensive to carry out for the implementation of this process.

The applicant has now demonstrated that mechanical synthesis makes it possible to effectively stabilize particles of anhydrite II! soluble in metastable phase.

The goals cited above are therefore achieved by a process for the preparation of a hydraulic binder based on anhydrite III, characterized by the fact that:

a) a pulverulent composition based on calcium sulphate is heated to form metastable soluble NI anhydrite,

b) mechanical synthesis is carried out on the composition obtained in step a) to stabilize the soluble H1 anhydrite.

The mechano-synthesis stage makes it possible to stabilize the calcium sulphate particles in the metastable soluble anhydrite III phases by mechanical stress. The hydraulic binder obtained by this process has good resistance to humidity and its rehydration in air is slowed down. In addition, the physical and mechanical performances of the concrete or mortar type products obtained by the use of this binder are at least as good as those of the products obtained by the use of the hydraulic binders known from the prior art.

Preferably, mechanical synthesis consists of micronization between 1,000 rpm and 30,000 rpm by percussion process.

According to an advantageous characteristic of the invention making it possible to vary the physical and mechanical properties of the hydraulic binder, in step a), the temperature and the heating time of the pulverulent composition based of calcium sulphate are regulated so as to form soluble metastable anhydrite III and / or anhydrite II and / or calcium sulphate hemihydrate. The expression “anhydrite Hl and / or anhydrite II and / or calcium sulphate hemihydrate β” should be understood as meaning “soluble anastrite Hl metastable only” or “soluble anhydrite IH metastable and anhydrite II” or “anhydrite Hl metastable soluble and β calcium sulphate hemihydrate "or" anhydrite III metastable soluble and anhydrite II and β calcium sulphate hemihydrate ". In an alternative embodiment, the composition obtained in step a) comprises only metastable soluble anhydrite III and said composition is mixed with anhydrite II and / or β hemihydrate of calcium sulfate, before or after step b). To prevent the metastable soluble anhydrite III particles from rehydrating too quickly before step b), in step a), the temperature and the heating time of the powdered composition based on calcium sulphate are adjusted by so as to form particles having soluble metastable anhydrite III at the core and surface anhydrite II. It is also advantageous to carry out steps a) to b) in a dry atmosphere.

According to a preferred embodiment characteristic, in step a), a pulverulent composition based on natural gypsum or on synthetic gypsum or on calcium sulphate hemihydrate is heated.

To control as precisely as possible the titration in metastable soluble anhydrite III and / or in anhydrite II and / or in calcium sulphate β hemihydrate according to the type of pulverulent composition used, in a first embodiment, heating by direct calcination a powder composition based on natural gypsum having a particle size between 4 mm and 5 mm. In a second embodiment, a pulverulent composition based on synthetic gypsum having a particle size less than 300 μm is heated by flash calcination.

In a third embodiment, a pulverulent composition based on calcium sulphate hemihydrate having a particle size less than 500 μm is heated by flash calcination.

In a fourth embodiment, a pulverulent composition having a particle size between 4 mm and 5 mm is heated by direct calcination, said composition being obtained after the pelletization of synthetic gypsum or calcium sulphate hemihydrate having an initial particle size less than 500 μm.

To improve the stabilization of the metastable soluble anhydrite III particles, the composition obtained in step a) is advantageously mixed with lime or lime hydroxide.

To improve the performance of the hydraulic binder that is the subject of the invention, an adjuvant of the polycarboxylate type is introduced during the mechanical synthesis step.

Given the remarkable properties observed by the applicant, the invention also relates to the hydraulic binder obtained by the process described above. Another object of the invention is a hydraulic binder having particles whose crystal structure comprises soluble anhydrite III phases associated with anhydrite II phases.

According to yet another advantageous characteristic of the invention making it possible to improve the water resistance and the mechanical performance of the material obtained with the binder object of the invention, the latter is combined with cement in a proportion varying from 10% to 30% by weight.

Another object of the invention is an industrial installation allowing the implementation of the process described above and comprising a calcination device and a mechanical synthesis device. Preferably, the mechanical synthesis device is an impact crusher.

To prevent any entry of external humid air, this installation advantageously includes a pressurization device. And preferably, this pressurization device is a dry air compressor disposed at the outlet of the heating device.

To improve the control of the titration of the different particles, the heating device advantageously comprises:

a first active reactor in which part of the pulverulent composition based on calcium sulphate is heated by means of a hot fluid to form anhydrite II,

- A second passive reactor, located downstream of the first active reactor, in which another part of the powdery composition based on calcium sulphate is heated by means of the flow of anhydrite II particles leaving the first active reactor to form a composition titrated in metastable soluble anhydrite III and in anhydrite it and / or in β hemihydrate of calcium sulfate.

According to a preferred embodiment characteristic enabling the mechanical synthesis step to be carried out continuously, a buffer tank is arranged upstream of the mechanical synthesis device. Other characteristics and advantages of the present invention will emerge more clearly on reading the description which follows, given by way of indicative and nonlimiting example, with reference to the appended drawing in which:

FIG. 1 schematically represents a preferred embodiment of the installation which is the subject of the invention,

- Figure 2 is a schematic view of a heating device used in the installation object of the invention.

Referring to FIG. 1, a pulverulent composition based on calcium sulphate is heated in a heating device 1 so as to form only particles of soluble anastrite III metastable or associated with particles of anhydrite II and / or particles of calcium sulphate hemihydrate. The presence of anhydrite II and / or β hemihydrate of calcium sulphate makes it possible to modify the physical and mechanical properties of the hydraulic binder which is the subject of the invention.

The anhydrite ll / HUoiubie anhydrite weight ratio is preferably between 1% and 100% depending on the applications of the hydraulic binder which is the subject of the invention. For example, a binder having an anhydrite ll / HUoiubie anhydrite weight ratio of between 20% and 40% will have good mechanical properties.

The pulverulent composition used is based on natural gypsum, synthetic gypsum (in particular sulfogypsum, phosphogypsum, borogypsum, titanogypsum) or hemihydrate (α or β) of calcium sulfate.

The particle size of the pulverulent composition treated is between 50 μm and 15 mm depending on the nature of the calcium sulphate used.

This pulverulent composition is heated between 180 ^° C. and 600 ^° C. for a time varying from a few seconds to several hours.

The temperature and the heating time depend on several factors including mainly the particle size, the type of composition pulverulent treated and the heating method used. Heating can be carried out directly or indirectly, by flash calcination processes, rotary ovens, cooking pots or any other equivalent calcination device.

The adjustment of the various calcination parameters makes it possible to adjust the proportion of soluble metastable anhydrite III and / or anhydrite II and / or β hemihydrate of calcium sulfate as a function of the final characteristics of the composition sought. Referring to FIG. 2, the heating device advantageously comprises:

a first active reactor 10a in which part 11a of the pulverulent composition based on calcium sulphate is heated by means of a hot fluid generated by a burner 12 to form anhydrite II particles,

- A second passive reactor 10b, arranged downstream of the first active reactor 10a, in which another part 11b of the pulverulent composition based on calcium sulphate is heated by means of the flow of anhydrite particles II 11'b leaving said first active reactor 10a to form a composition titrated in soluble metastable anhydrite IiI and in anhydrite H and / or in calcium sulphate hemihydrate.

This type of heating device makes it possible to control as precisely as possible the proportions between anhydrite II and metastable soluble anhydrite III and optionally calcium sulfate hemihydrate β.

The first reactor 10a and the second reactor 10b can be flash calcination devices. The latter is understood in particular as a device comprising a drying column with a helical ramp in which the pulverulent composition to be treated is transported at high speed (> 2 m / s) by a flow of hot air generated by a burner. According to a first embodiment, the pulverulent composition treated is based on natural gypsum and has a particle size between 1 mm and 15 mm, advantageously between 4 mm and 5 mm.

This pulverulent composition is heated in a rotary oven, advantageously with a triple jacket, between 220 ^° C. and 350 ^° C., preferably at approximately 27 ^° C., for approximately 6 minutes.

According to a second embodiment, the pulverulent composition treated is based on synthetic gypsum and has a particle size of less than 300 μm. This pulverulent composition is heated between 280 ^° C. and 320 ° C. by a flash calcination process in less than 5 seconds.

According to a third embodiment, the pulverulent composition treated is based on hemihydrate (α or β) of calcium sulphate, has a particle size less than 500 μm and, in the same manner as described above, said composition is heated to between 28O ⁰ C and 320 ° C by a flash calcination process in less than 5 seconds.

According to a fourth embodiment, making it possible to effectively use a rotary oven, a composition based on synthetic gypsum or on calcium sulphate hemihydrate having a particle size of less than 500 μm is used. This composition is pelletized to obtain a pulverulent composition having a particle size between 4 mm and 5 mm. The first embodiment applies.

Referring to FIG. 1, at the outlet of the heating device 1, the calcium sulphate particles associated in phases with soluble metastable anhydrite IiI and / or anhydrite II and / or calcium sulphate hemihydrate, are conveyed via a conduit. transport 2, via an Archimedes screw, to a buffer tank 3. This buffer zone makes it possible to control the quantity of calcined pulverulent composition introduced into the mechanical synthesis device 4, the treatment flow rate of the latter being lower than the flow rate of calcined product leaving the oven. The buffer zone is made up of a dry ambient air silo. At the outlet of the heating device 1, the soluble anhydrite III particles being in the metastable phase, it is advantageous to keep a dry atmosphere throughout the installation (air humidity less than 10%, preferably included between 0 and 5%) from the outlet of the heating device 1 to the mechanical synthesis device 4.

To control this humidity, an overpressure device is used to prevent any introduction of humid outdoor air.

As shown in FIG. 1, this overpressure device consists of a dry air compressor 5 arranged at the outlet of the heating device 1 and arranged with humidity sensors so as to pressurize the transport conduits and the whole installation, in particular the buffer tank 3 and the mechanical synthesis device 4. Any other equivalent overpressure device is suitable.

In order to maintain a dry atmosphere throughout the installation which is the subject of the invention, it is possible. also use humidity extractors arranged with humidity monitors.

To prevent the anhydrite III particles soluble in the metastable phase from rehydrating in the event of the introduction of humid outside air, the various calcination parameters can also be adjusted to form particles having anhydrite! heart and anhydrite II on the surface. For example, a pulverulent composition based on natural gypsum having a particle size of 15 mm is used which is heated using a rotary oven with three envelopes, for 6 minutes at 400 ^° C. Since the anhydrite It is slightly hygroscopic, the metastable soluble anhydrite III remains protected by the anhydrite II envelope. The particles of metastable soluble anhydrite III and / or anhydrite II and / or β hemihydrate of calcium sulfate are advantageously mixed between 1% and 15% by weight with lime or lime hydroxide.

A device for introducing lime or lime hydroxide 6 is arranged for this purpose with the transport pipe, between the outlet of the heating device 1 and the buffer tank 3. This post-calcination mixture aims to improve the physico- chemical which takes place in the rest of the process at the mechanical synthesis stage. If at the level of the heating device 1, the calcination parameters are adjusted to form only particles of anhydrite II! soluble metastable (possibly wrap with a layer of anhydrite II), a device for introducing anhydrite II and / or β hemihydrate of calcium sulfate (not shown) can be arranged after, or advantageously before, the device of mechanical synthesis 4.

The mechanical synthesis operation consists in modifying the crystal structure of the anhydrite particles Hi by mechanical stress on said particles in order to stabilize the metastable phase of soluble anhydrite III. This operation can be carried out at temperatures varying between 15 ^° C. and 250 ^° C.

This mechanical synthesis also makes it possible to associate the anhydrite III phase with the anhydrite it and / or hemihydrate β phases of calcium sulphate to form a new type of hydraulic binder.

We can also plan to perform a mechanical synthesis directly on a mixture containing stabilized soluble anhydrite III (for example Gypcement®) of anhydrite II and / or β hemihydrate of calcium sulfate to obtain a hydraulic binder comprising particles whose crystal structure comprises soluble anhydrite III phases associated with anhydrite II phases. In the process which is the subject of the invention, mechanical synthesis preferably consists of a centrifugal micronization between 1,000 rpm and 30,000 rpm (rapid kinetic action) making it possible to induce a topochemical reaction on the calcined material. The mechanical synthesis device 4 is advantageously a grinder, preferably "percussion process causing the particles to burst".

The micronization step also makes it possible to obtain a homogeneous granular composition and stable and dense particles of between 1 μm and 300 μm, preferably between 6 μm and 10 μm.

An adjuvant, preferably a polycarboxylate is optionally associated with the composition during the mechanical synthesis step in order to improve certain physico-mechanical performances of the hydraulic binder thus obtained.

On leaving the mechanical synthesis device 4, the hydraulic binder can be stored in a storage area 7 before being conditioned.

The hydraulic binder obtained has quite remarkable characteristics:

- stability to humidity and water absorption (less than 2%),

- high particle density,

- high solubility,

- high mechanical strengths in association with any form of aggregate: Rc varying from 40 MPa to 80 Mpa and Rf varying from 10 Mpa to 20 Mpa.

- very low porosity linked to the fineness of the binder allowing the production of over-densified materials,

- increased adhesion performance on any type of support, compatibility with water-reducing additives inducing very high performance composite technologies, - exceptional aesthetic qualities resulting from the fineness and density of the materials obtained by combining the aggregates studied,

- Improvement in the fire behavior of the compositions produced from said hydraulic binder.

The Applicant has found experimentally that by combining the hydraulic binder obtained in accordance with the invention, with cement, for example of the Portland type or a calcium hydroxide (Lime), the material obtained had a water resistance and performance improved mechanical, especially when mixing from 70% to 90% w / w _m éiange hydraulic binder object of the invention with 10% to 30% w / pméiange cement. Mechanical performance is increased from 10% to 15%.

Claims

1. Process for the preparation of an anhydrite-based hydraulic binder

III, characterized by the fact that:

a) a pulverulent composition based on calcium sulphate is heated to form metastable soluble anhydrite III,

b) mechanical synthesis is carried out on the composition obtained in step a) to stabilize the soluble anhydrite III.

2. Method according to claim 1, characterized in that the mechanical synthesis consists of a micronization between 1,000 rpm and 30,000 rpm by percussion process.

3. Method according to one of the preceding claims, characterized in that in step a), the temperature and the heating time of the pulverulent composition based on calcium sulphate are adjusted so as to form l metastable soluble anhydrite III and / or anhydrite 11 and / or β hemihydrate of calcium sulphate.

4. Method according to one of claims 1 or 2, characterized in that before step b), the composition obtained in step a) is mixed with anhydrite I! and / or β hemihydrate of calcium sulphate.

5. Method according to one of the preceding claims, characterized in that in step a), the temperature and the heating time of the pulverulent composition based on calcium sulphate are adjusted so as to form particles having soluble metastable anhydrite III at the core and surface anhydrite II.

6. Method according to one of the preceding claims, characterized in that steps a) to b) are carried out in a dry atmosphere.

7. Method according to one of the preceding claims, characterized in that in step a), heating a pulverulent composition based on natural gypsum or synthetic gypsum or calcium sulphate hemihydrate.

8. Method according to one of the preceding claims, characterized in that in step a), a direct pulverulent composition based on natural gypsum having a particle size between 4 mm and 5 mm is heated by direct calcination.

9. Method according to one of claims 1 to 7, characterized in that in step a), is heated by flash calcination a pulverulent composition based on synthetic gypsum having a particle size less than 300 microns.

10. Method according to one of claims 1 to 7, characterized in that in step a), is heated by flash calcination a powder composition based on calcium sulphate hemihydrate having a particle size less than 500 μm.

11. Method according to one of claims 1 to 7, characterized in that in step a), a pulverulent composition having a particle size between 4 mm and 5 mm is heated by direct calcination, said composition being obtained after the pelletization of synthetic gypsum or calcium sulphate hemihydrate having an initial particle size less than 500 μm.

12. Method according to one of the preceding claims, characterized in that the composition obtained in step a) is mixed with lime or lime hydroxide.

13. Method according to one of the preceding claims, characterized in that during step b), polycarboxylate is introduced.

14. Hydraulic binder comprising stabilized soluble anhydrite III, characterized in that it is obtained by the process according to one of claims 1 to 13.

15. Hydraulic binder characterized by the fact that it comprises particles whose crystal structure comprises soluble anhydrite III phases associated with anhydrite II phases.

16. Use of a hydraulic binder according to one of claims 14 to 15, for the preparation of a material of the concrete or mortar type.

17. Use according to claim 16, characterized in that the hydraulic binder is combined with cement in a proportion varying from 10% to 30% by weight.

18. Industrial installation for implementing the method according to one of claims 1 to 13, comprising a calcination device (1) and a mechanical synthesis device (4).

19. Installation according to claim 18, characterized in that the mechanical synthesis device (4) is a centrifugal mill.

20. Installation according to one of claims 18 to 19, characterized in that it comprises a pressurization device (5).

21. Installation according to claim 20, characterized in that the pressurization device (5) is a dry air compressor disposed at the outlet of the heating device (1).

22. Installation according to one of claims 18 to 21, characterized in that the heating device (1) comprises:

a first active reactor (10a) in which a part (11a) of the pulverulent composition based on calcium sulphate is heated by means of a hot fluid to form particles of anhydrite II,

- a second passive reactor (10b), arranged downstream of the first active reactor (10a), in which another part (11b) of the pulverulent composition based on calcium sulphate is heated via the flow of anhydrite II particles (11 ′ a) leaving the first active reactor (10a) to form a composition titrated in metastable soluble anhydrite III and in anhydrite II and / or in calcium sulphate hemihydrate β.

23. Installation according to one of claims 18 to 22, characterized in that a buffer tank (3) is arranged upstream of the mechanical synthesis device (4).