OA12036A - Process for the manufacture of a hydralic binder based on anhydrite III or alpha and hydraulic binder thus obtained. - Google Patents

Description

This invention relates to a method of treating a natural calcium sulphate-based pulverulent first raw material. (gypsum) or synthetic (sulfogypsum, phosphogypsum and other by-products of the same type) in order to prepare a new hydraulic binder acting as cement in a very large proportion based on anhydrite III or a (a in the ASTM classification). The invention also relates to the product resulting from said process and which serves as cement.

The gypsums are in various crystalline forms and, at the molecular scale, they have a crimped structure in which alternate a layer of water and two layers of CaSO4.

Gypsums have been used for millennia for the manufacture of plasters, which are one of the oldest known building materials since the sixth millennium BC.

Nowadays, other industries use gypsum 2 12 0 3 6 in particular: the manufacture of cement (as a setting regulateuj '), - agricultural uses, - various industries (chemistry, paper, etc. ..).

The most important uses are the incorporation into the manufacture of cement and gypsum dehydrated plasters.

If in the cement industry, gypsum is incorporated in the baking of clinker and undergoes a high firing of the order of 1400 ° C, in the manufacture of plaster, the essential principle is the total or partial elimination of the water of constitution dugypse, a complex operation that involves decrystallization phenomena difficult to master.

Several types of decalcium sulfate processing methods have been proposed for preparing plaster. In particular, it is known to prepare improved plasters (sometimes referred to as "plasters") which, once cured, have mechanical characteristics significantly higher than those of plasterscurrent. The phenomena which take place during the treatments are poorly known, and the improvement of the mechanical properties is generally attributed to the presence of the anhydrite III or in the products obtained, without knowing exactly the proportion of this variety in these products. nor the conditions which make it possible to obtain it in a stable and reproducible way: it exists only in the state of traces.

Traditionally, these improved plasters are made from gypsum by subjecting it to a wet-cooking phase in an autoclave and then to a hot-drying phase by a stream of hot, dry air. The cooking takes place in the atmosphere of saturating vapor at a pressure of the order of 5 to 10 bar for a period of the order of 10 hours.

To try to overcome the defects of this traditional process of manufacture of improved plaster. (Extremely expensive implementation, unreliable reproducibility), other proposals have been proposed.

These processes, in fact, attempt to reproduce the essential conditions of the traditional process (wet cooking, followed by hot air drying) using different means and technologies (patents FR-2.389.855, FR). -2,445,940, FR-2,572,721, US-2,269,580, US-3,145,980).

The method of the invention has been devised from the following observation, when a calcium sulfate is conventionally treated to obtain "improved plaster", the productobtained is actually a mixture of anhydrous forms (anhydrite γ) or hydrated (semihydrates, bihydrates, ...). The studies of the inventor have shown that this comes mainly from two factors. First of all, anhydridation leading to anhydrite also has other forms, and especially an evolution of the product after baking, with partial transformation of the latter, in particular by rehydration. The essential idea which led to the process of the invention was to produce a stable final product containing a much higher proportion of anhydrite than that contained in the known improved plasters and, for this purpose, to freeze the structure of the compound obtained in the past. after firing by thermal quenching. The subsequent conversion of the formed anhydrite is thus considerably blocked.

According to PCT / FR96 / 00622, the quenching operation is preferably carried out so as to bring the heated material by baking at a temperature below 100 ° C in a time of between 6 and 12 minutes. It can be carried out with cold and dry compressed air, injected at several locations in the moving material, the airflow being adjusted to obtain the appropriate cooling rate.

Nevertheless, this quenching is not effective enough to obtain a proportion of anhydrite XII or has really determined. This latter invention patent application did not allow a very high percentage of anhydrite III to be obtained.

Or 90% and this so as to obtain a hydraulic binder that can serve as cement.

The process according to the invention makes it possible to obtain such a product. The object of the invention is to refine the process in order to obtain a high percentage of stable or soluble anhydrite III.

The process according to the invention makes it possible to convert more than 90% of pure calcium sulphate into anhydrite III or a. For this purpose, the present invention relates to a process for the synthesis of a hydraulic binder based on natural calcium sulphate (gypsum) or of synthesis (sulphogypsum, phosphogypsum, titanogypsum, etc.), consisting in heating the calcium sulphate to form: hydraulic binder acting as anhydrite cement III or characterized in that it contains more than 70% of anhydrite III or has stable and soluble and that it consists in carrying out: a baking phase or thermal tempering which carries the temperature of the treated gypsum from room temperature to a temperature between 220 ° C and 350 ° C depending on the characteristics of the treated gypsum, subjecting the product thus obtained to a thermocure quenching reducing its temperature from 220 ° C to 350 ° C to less than 80 ° C C in less than two minutes to stabilize the anhydrite by blocking and crystallographic fixation.According to one embodiment of the method, the heating temperature is 300-310 ° C.

According to a preferred embodiment, the temperature of the heat quench is between 40 ° C and 50 ° C.

According to a preferred embodiment, the rise in temperature takes place between 10 and 40 minutes, depending on the nature and the particle size of the gypsum.

The gypsum treated has before treatment from 0 to 20% of water.

It has a particle size of between 0 and 30 mm.

According to a preferred embodiment, the treated gypsum comprises 5 to 15% water and its particle size is between 0 and 10 mms.

Hydraulic binder acting as an anhydrite-based cement III or obtained by the above process characterized by having greater than 70% anhydrite III or stable and soluble.

Hydraulic binder acting as cement based on anhydriteIII or obtained by the above process characterized by the fact that it contains more than 90% of anhydrite III or has stable or soluble. 1 ° Hydraulic binder acting as cement based on anhydrite III or obtained by the above method characterized by the fact that the mechanical strength is 22 MPA at 24 hours30 MPA at 8 days more than 40 MPA at 14 days.

The present invention also relates to a hydraulic binder acting as cement obtained by carrying out the above process.

The essential inventive concept of the invention was therefore to increase the proportion of anhydrite to the product, the essential means used consisting in limiting, by a rapid cooling, the evolution of the product after cooking. In order to further increase this proportion to anhydrite a, the inventor has also endeavored to optimize the cooking operation so as to obtain the greatest possible quantity of this variety at the end of cooking.

Thus, subjected to heat, the gypsum leads to a series of hydrated or anhydrous products. ,

At around 100 ° C., the α-or β-half-hydrates (depending on whether the reaction is carried out under water vapor pressure or in the open air respectively) are obtained according to the reaction:

CaSO4, 2 H2O "-► CaSO4, 1/2 H2O + 3/2 H2Omonoclinic rhombohedic ..s

6 1 2 0 3 6

At about 300 ° C., anhydrite III or anhydrite is obtained which is very soluble but very unstable and which is rehydrated immediately in half-hydrate on contact with the water in the vapor phase: CaSO 4, 1/2 H 2 O 4 rhombohedral CaSO 4 III (or ) + 1/2 hexagonal H2O At about 300 ° C for the hemihydrate a and 350 ° C for the β, the anhydrite III (or a) is converted to stable anhydrite II (overcooled): CaSO4 III (or a Hexagonal orthorombic CaSO4 II Anhydrite III rehydrates slowly on contact with water.

At 123 0 ° C occurs a new reaction reaction.

CaSO4 II * -> Facet-centered cubic orthorhombic CaSO4 I CaSO4 I anhydrite rehydrates only with great difficulty. Above 125 ° C., the decomposition of anhydrite I is obtained:

CaSO4 I "-> CaO + SO2 + 1/2 O2

The current industrial applications of plaster use only: the hemihydrate a, the hemihydrate β, and -anhydrite II (insoluble or overcooked). Anhydrite III or a, the subject of the present invention, can not be used because of its great instability.

MMP

Mb *

IkaAMMeiNbffi 7 1 2 0 3 6

We also know the diversity of the plaster in the building and its many weaknesses in resistant, held moisture, hanging on some supports, etc.

The present invention relates to a hydraulic binder obtained by a specific and novel heat treatment of gypsecomportant two essential phases. The first so-called dehydration to obtain a high percentage of anhydride SO4Ca III (or a). The second phase of brutal cooling results in "blocked" crystallography and renders SO4Ca III anhydrite stable or stable and its use possible.

This sudden cooling called thermal tempering in dry atmospheres has never been practiced in the plaster industry.

Industrial plasters are obtained solely by dehydration and baking gypsum without undergoing any thermal cooling, which is the main object of 1'invention.

The technical conditions of this new hydraulic binder object of the invention comprise: 1) a dehydration phase comprising a temperature rise of the gypsum to be treated at low humidity (from 3 to 15% water).

The rise in temperature is carried out in a time of 10 to 40 minutes to reach a temperature of 220 to 350 ° C according to the gypsum substrate, or more precisely between 300 ° C and 310 ° C. 2 °) The brutal cooling or quenching thermal in atmospheres.

This thermal quenching or sudden cooling never contemplated or used in the gypsum industry, allows to destabilize the anhydrite SO4Ca III or a very soluble and blocking crystallization obtained by this thermal shock which must lower, in less than two minutes, the temperature of 220-350 ° C to less than 80 ° C. 8 1 2 0 3 6

Thanks to a high percentage of CaSO4 III anhydrite or exstable and soluble (over 70 or even 90%), we obtain a remarkable hydraulic binder that competes advantageously with most current binders.

The characteristics of this new binder are: - its fire resistance: flammability classified in the category Mosuivant the standard NF P 92-507, - an excellent catch with sea water, - a remarkable catch on all supports, and - its taken at very low or high temperature, etc.

The industrial applications of this binder should be of interest to the cement, concrete and plaster industries, inert waste or industrial by-products, the manufacture of mixtures with materials that combine well with calcium sulphate, and the creation of habitat. developing countries, and so on.

The manufacture of this hydraulic binder must make use of known techniques: cooking at low temperature (220 to 350 ° C) to be cool. It can be performed by very simple installations.

This hydraulic binder has, apart from its technical qualities, an interest: - economic, - energy saving, - ecological: no pollution.

After complete dehydration, a percentage of more than 50% of SO4Ca III anhydrite or even 70 to 80%, while the sudden cooling leads to crystallization of the anhydrite SO4Ca III or made it stable and soluble and allowing its industrial use.

The following conditions of implementation appear to provide the best results. The rate of humidity of the parent material is checked beforehand and this level is adjusted, if necessary, to a value substantially between 12% and 20%; The cooking operation is then carried out by feeding the pulverulent material to temperature, by heating the assembly under conditions suitable for raising the temperature of the gases above the bed of material to a value between 350 and 550.degree. ° C, and to increase the average temperature in the core of the material to a value higher than 220 ° C and lower than 350 ° C. The heating may for example be effected by means of infrared radiants disposed above the bed of material, the emission power of said radiants being regulated in correlation with the exposure time of the material.

A possible explanation of the best results obtained with these operating conditions is as follows,

The temperature of 220-350 ° C in the heart of the bed of estideal material to produce anhydrite has in the absence of other varieties.The value of extracted water escapes above the bed of material in a warmer atmosphere whose temperature is above its critical point (365 ° C). It quickly reaches the supercritical state, which avoids or limits rehydration and surface evolution of the material, so that at the end of cooking, the proportion of anhydrite a is very high (without it being possible to give precise proportions since samplings before cooling evolve immediately).

The exothermic transformation reaction of the anhydrite in bassanite is very quickly blocked by cooling quistabilize the anhydrite a. Moreover, it seems that cooling completely blocks the evolution of anhydrite a towards plasterbassanite, which is found only in trace amounts in the final product (unlike known binders which have a high proportion of this variety).

Thus, the product obtained by receiving the binder according to the invention referred to above (without load) was subjected to flammability tests according to standard NF P 92-507 (0.30 m / 0.40 m test pieces subjected to radiation from a heat source _______ ..Il * · * 10 1 2 0 3 6 constant). The determination of the four indices provided for in this standard (ignition index, development index, maximum flame length index, combustibility index) made it possible to classify the product as one of the best-performing categories in the categories prescribed by the standard.

In addition, strength tests according to the standard gave the following results: compressive strength: 40 MPa, and flexural strength: 10 MPa.

In addition, qualitative tests in immersed conditions have shown that the product has good resistance qualities in this situation. The study described below of the dehydration of decalcium sulphate has made it possible to improve the process according to the invention to obtain a true hydraulic binder acting as cement.

The attached drawings are given as illustrative and non-limiting examples. They represent a preferred embodiment of the invention. They will easily understand the invention.

Figure 1 is a thermal dehydration curve of the gypsum.

Figure 2 shows a Doehlert network with two dimensions.

Figure 3 shows a tiling of the uniform space.

Figure 4 shows a uniform Doehlert network with three dimensions.

FIG. 5 is a view showing the superposition of XA-ray spectra. ~ Dehydration of calcium sulphate: The study concerns the treatment of a pulverulent material based on calcium sulphate with a view to the manufacture of a new hydraulic fluid, having interesting characteristics of any setting speed, and certain physical properties (thermal conductivity, mechanical strength, acoustical isolation, etc.).

This process consists in combining two successive types of treatment: heating the pulverulent material to a temperature of between 220.degree. And 350.degree. C., in order to form anhydrite (or anhydrite III) (see FIG. 1). subjecting the material thus heated to thermal quenching in order to stabilize this metastable phase.

Thus its evolution towards other crystallographic varieties will be blocked and the rehydration in bassanite, major phase of plaster, avoided. f. ,! t,. '. . · *** 15 B-Methodology of the plans of experiments:

K - Many experiments have been carried out empirically on natural gypsum but also phosphogypsum, titanogypsum, borogypsum and desulphurphy.

However, the inventor has used the planning of experience to determine: the influence of the factors likely to intervene on the formation of phaseanhydrite has and to limit the number of manipulations. We have therefore varied the temperature from 280 to 320 ° C., the duration of the stage from 10 minutes to 70 minutes, and we have operated with 3 granulometric slices: <80, -80 -100, -100-200 pm.

The methodology of the experimental plans, based on a mathematical and statistical approach, involves modeling the phenomenon from a polymer written in adimensional coded variables. To each of these variables denoted Xi corresponds, '-,,' \> a natural variable Uj. following the equation:: K = Ù? x'xaU,

12 12 0 3 6 Where i = the value factor of the natural variable i for the experiment a - value of the natural variable i at the center of the experimental domain ur = Lr / '^ ur °] X "= value of the variable coded i for the experiment at AU = no varation of the natural variable i: 5 ';

au-Lt-ut U

In the framework of the development of this new hydraulic binder, the strategy is the use of the Doehlert uniform network, a strategy which makes it possible to estimate (by the least squares law) the coefficients of a polynomial model.

Indeed, in a coded space [(-1) (+1)] for the variables studied, the general equation is given below: y = + Σ *. χι + Σ b "+ Σ b, x <x," "* i = l icj 15

With y = measured response (output parameter) bo = mean value of the response 13 1 2 0 3 6 bi = main effect of the variable ibit = square effect of the variable i bjj = interaction effect between variables i and j5

In the case of two variables are represented in FIG. 3, the seven experiments carried out according to a centered hexagon centered in a circle of radius 1.

The two variables being the temperature (280 to 320 ° C) and the time (10 to 70 min), the experiment matrix (in coded variables) and the experimental design (in natural variables) are given in Table 1 .

Coded variables (Xi) "Natural variables (υΑ) n ° XI X2 Temperature (° C) Time (min) 1 1 0 320 40 2 -1 0 280 40 3 0,5 0,866 310 70 4 -0,5 -0,866 290 0.5 -0.866 310 10 6 -0.5 0.866 290 70 7 0 0 300 40 Table 1 Experimental matrix and experimental plan for a uniform two-dimensional Doehlert network

This model is therefore characterized by five temperature values and three time levels.

For example, for the temperature we have:

(320 + 280) / 2 = 300 ° C with Q'0 = 280 ° C = 320 ° C

AlJ ~ (320 + 280) / 2 = 20 ° C and Xf = 0.5

14 1 2 0 3 6

This strategy has two advantages: indeed, if, after carrying out the seven experiments of the centered hexagon represented in FIG. 4, only four results (percentage of anhydrite u, represented in bold in FIG. 4) are interesting, only three manipulations are necessary to construct the second regular hex centered. One approach would build a third hex.

Thus the tiling of the space in a uniform manner is achieved and the optimum conditions for obtaining anhydrite have been defined. - Moreover, to study the influence of a third factor, (for example particle size) only six additional experiments will be necessary (three of granularities superior to that used for the realization of the first seven trials and three of lower granularities, this of manymmetric).

Thus the three-dimensional representation of the Doehlert uniform network is done by a sphere centered with the hexagon in the equatorial plane. It is then characterized by several values of the temperature, seven time levels and three size gradients (see figure 5).

The planning of experiments will therefore allow us to delimit considerably the number of manipulations. The experimental matrix, the experimentation plan and the results are given in Table 2. C - The results: From a natural gypsum, the inventor made the thirteen manipulations determined by the experimental plan to be shown in FIG. The thermal weight analysis (ATP) and the differential sensitivity test (DSC) made it possible to determine the percentage of anhydrite a. X-ray diffractometry has made it possible to highlight the phases present, and to distinguish two varieties of iHbOi ui-awMUtbi _IJI. 15 12 0 3 6 of CaSO4a we will call ar and u2 (see Figure 6).

The results are shown in Table 2 below:

Experimental matrix Experimentation plan Answer N ° XI X2 X3 T ° ('C) Time (min.) - Granulometry (gm)% of anh at end reaction * Qty of anh «2® 1 1 0 0 320 40 80-100 86.1 127.5 • 2 -1 0 0 280 40 80-100 89.7 120.7 o 3 0.5 0.866 0 310 70 80-100 90.3 119.8 • 4 -0.5 -0.866 0 290 10 80- 100 87.3 118.6 O 5 0.5 -0.866 0 310 10 80-100 84.2 130.5 • 6 -0.5 0.866 0 290 70 80-100 86.8 120.2 • 7 0.5 0.829 0.816 310 50 100-200 89.4 122.0 • 8 - 0.5 -0.829 -0.816 290 30 <80 74.7 135.5 o 9 0.5 -0.829 -0.816 310 30 <80 89.9 118.2 • 10 0 0.577 -0.816 300 60 <80 83.3 130.8 • 11 -0.5 0.829 0.816 290 50 100-200 81.5 132.9 • 12 0 -0.577 0.816 300 2 0 100-200 86.5 120.9 • 13 0 0 0 300 '40 80-100 90.9: 110.1 •

Table 2 Experiment matrix, experimental design and analysis result of the products treated from a gypsaturel. 15 · much 16 12 0 3 6 little or very little heating temperature or high temperature heating and / or low temperature * endothermic reaction Bassanite -> Anhydrite ® proportion of anhydrite a2 in a mixture of bassanite and anhydrite

As shown in manipulations No. 13, No. 3 and No. 9, the best anhydrite and (790%) propellants are obtained for a heating temperature of 300 to 30 ° C. We also noted that these good results correspond to the temperatures of the endothermic reaction of the minimum bassanite (110 ° C in the case of Experiment 13).

FIG. 6 allows qualitative and semi-quantitative detection of the phases present in theprocessed products. Indeed, if the treated product is a mixture of anhydriteax and bassanite, it is the line at 2.80 Å which has 100% intensity.

On the other hand, the significant presence of anhydrite <x2 in the product leads to the increase of the line at 3.49A which then passes to 100% of intensity, and the appearance more and more clear of larry to 2.85A of the anhydrite ot2. At the same time the intensity of the lines at 6.02, 3.01 and 2.80 Å decreases. Thus, the observation of the superposition of the X-ray spectra shows an increase in the proportion of the anhydrite phase a 2 with the temperature in an anhydrite and bassanite mixture.

Thus, the invention described makes it possible to obtain a product, a true hydraulic binder, containing more than 70% of stable and soluble anhydrite (even 80 to 90%) and whose characteristics are astonishing: - rapid setting: in three minutes | ΙμΜ * ΜΜΙμΜΙΙ | 17 12 0 3 6 setting accelerator high mechanical resistance (35 MPA at 7 days) thermal and sound insulation treatment of industrial residues: inerting or 5 resistances coated with façadeschap of buildings - prefabrication of individual houses, etc.

This hydraulic binder has, apart from its technical qualities, an interest: economic, energy saving, ecological: no pollution.

The process according to the invention thus makes it possible to convert more than 90% of pure calcium sulphate into anhydrite III or tx.

In any gypsum, there is pure calcium sulphate plus impurities.

Depending on the purity of the calcium sulphate, different types of cement are obtained. Whatever the finished products, the new binder has less than 10% "plasters". , k ·> * ·· «-» 5 * · '* * »· -> ..i

Claims (9)

18 1 2 0 3 6 Claims 1. Process for the synthesis of a hydraulic binder based on natural calcium sulphate (gypsum) or of synthesis (sulphogypsum, phosphogypsum, titanogypsum), consisting in heating the calcium sulphate to form: a hydraulic binder acting as a cement based on anhydrite III or characterized by the fact that it contains more than 70% of anhydrite III or has stable and soluble and that it consists in producing: - a baking phase or thermal tempering which carries the temperature of the treated gypsum from room temperature to a temperature of between 220 ° C and 350 ° C depending on the characteristics of the gypsum treated, - subjecting the product thus obtained to a thermic quenching tempering lowering its temperature of 220oC-350 ° C to less than 80 ° C in less than two minutes with the aim of stabilize anhydrite by blocking and crystallographic fixation. 2. Method according to claim 1 characterized by the fact that the heating temperature is 300-310 ° C. 3. Method according to claim 1 characterized in that the temperature of the thermal quenching is between 40 ° C and 50 ° C. 4. Method according to claim 1 characterized by the fact that the rise in temperature takes place between 10 and 40 minutes, depending on the nature and grain size of the gypsum. 5. Process according to claim 4, characterized by the fact that the treated gypsum comprises before treatment from 0 to 20% of water, its particle size is between 0 and 30 mm. 6. Method according to. claim 5 characterized in that the treated gypsum comprises 5 to 15% water and its particle size is between 0 and 10 mms. 7. hydraulic binder acting as anhydrite cement III or obtained by the above process according to any one of claims 1 to 6 characterized in that 19 12 0 3 6 it contains more than 70% of anhydrite III or has stable and soluble. 8. hydraulic binder acting as anhydrite cement III or obtained by 1 (2 above method according to any one of claims 3 to 6 characterized in that it contains more than 90% of anhydrite III or has stable or soluble. 9. Hydraulic binder acting as anhydrite cement III or obtained by the above process according to any one of Claims 1 to 6, characterized in that the mechanical strength is 22 MPa at 24 hours 30 MPa at 8 days over 40 MPA to 14 days.