WO2018007634A1

WO2018007634A1 - Composition in the form of tablets comprising burnt calcium-magnesium compounds, method for obtaining same, and use thereof

Info

Publication number: WO2018007634A1
Application number: PCT/EP2017/067171
Authority: WO
Inventors: Guillaume Criniere; Michael NISPEL
Original assignee: S.A. Lhoist Recherche Et Developpement
Priority date: 2016-07-08
Filing date: 2017-07-07
Publication date: 2018-01-11
Also published as: EP3481776A1; BE1023886B9; FR3053675A1; TW201815676A; BE1023886B1

Abstract

Disclosed is a composition based on burnt calcium-magnesium compounds in the form of tablets, characterized in that said composition comprises quicklime in the form of crushed particles at a concentration of 10 to 100% by weight in relation to the weight of the composition, the composition in the form of tablets having a shatter index of less than 10%. Also disclosed are a method for the preparation of said composition as well as the use thereof.

Description

"TABLET COMPOSITION COMPRISING VOCAL CALCO-MAGNESIVE COMPOUNDS. ITS PROCESS OF OBTAINING AND THEIR

USE "

The present invention relates to a composition in the form of tablets comprising at least one bright calco-magnesium compound, said composition having from 40% to 100% by weight of CaO + MgO equivalent, preferably 60% to 100% by weight of equivalent CaO + MgO, relative to the weight of said composition.

For the purposes of the present invention, the term "bright calco-magnesium compound" is intended to mean a solid mineral material whose chemical composition is mainly calcium oxide and / or magnesium oxide. The living calco-magnesium compounds within the meaning of the present invention therefore comprise quicklime (calcium lime), bright magnesium lime, dolomitic quicklime or bright calcined dolomite, also known as cooked dolomite. The living calcium-magnesium compounds contain impurities, that is, compounds such as silica, SiO _2, or alumina, Al ₂ O ₃ , etc., up to a few percent. It is understood that these impurities are expressed in the aforementioned forms but may actually appear in different phases. It also generally contains a few percent residual CaCO ₃ or MgCO ₃ , called incuits, and some residual Ca (OH) ₂ or Mg (OH) ₂ , due to partial hydration of the live products during cooling, handling and / or storage phases.

Lime means a mineral solid whose chemical composition is mainly calcium oxide, CaO. Quicklime is commonly obtained by calcination of limestone, mainly consisting of CaCO ₃ . Quicklime contains impurities, that is, compounds such as magnesium oxide, MgO, silica, SiO ₂ or alumina, Al ₂ O ₃ , etc., up to a few percent . It is understood that these impurities are expressed in the aforementioned forms but may actually appear in different phases. It also generally contains a few percent of residual CaCO ₃ , called incuits, and a few percent of residual Ca (OH) ₂ , due to the partial hydration of calcium oxide CaO during the cooling phases. handling and / or storage.

According to the present invention, the term "briquette" means a compact having an oblong shape, having a mass of about 5 to 100 g. by briquettes, inscribed in an ellipsoid of flattened or elongated revolution (in English oblate ellipsoid of revolution or prolate ellipsoid of revolution). Typically, the briquettes are in the form of soap or are called briquettes "egg" (in English "egg briquettes")

In contrast, there are tablets that are typically in the form of pellets, as produced by the presses "Titan" of the company "Eurotab". By definition, tablets for industrial use are of regular shape, more particularly in the form of low cylinder height.

Such compositions are well known in the state of the art, see for example WO2015007661. According to this document, compacts (namely briquettes or tablets) are described comprising particles of calco-magnesium compound comprising at least 50% of bright calco-magnesium compound.

According to this document, the mechanical resistance to the fall is measured by means of a test shatter. The compacts described generally have a test Shatter index of less than 10%.

By the terms "Shatter test number" is meant the mass percentage of fines less than 10 mm generated after 4 drops of 2 m from 10 kg of product. These fines are quantified by sieving through a 10 mm square screen at the end of the 4 drops of 2 m.

A detailed analysis of the examples and counterexamples of this document indicates that green tablets having a mechanical resistance to falling were obtained using at least 50% of live products, and that these tablets also have a resistance to aging in a humid atmosphere. On the other hand, when briquettes of living compounds are obtained using living compounds, the shatter test index representing the mechanical strength remains high (between 13 and 15%) and it is necessary to carry out a rather long heat treatment and typically above 1200 ° C if one wants to achieve a test shatter index of less than 10%.

US5186742 discloses lime briquettes containing from 55 to 85% by weight of lime, from 10 to 40% by weight of ash and from 0.1 to 10% by weight of paper fibers as well as optionally a lubricant. The briquettes disclosed in US 5186742 are tested for their resistance to falling, a test which is not comparable to the measurement test. Shatter index test and have a compressive strength between 150 and 300 pounds, which corresponds to a test Shatter index well above 10%.

Calco-Magnesium compounds are used in many industries, such as iron and steel, gas processing, water and sludge treatment, agriculture, building industry, public works and others. They can be used either in the form of pebbles or pieces, or in the form of fines (generally less than 7 mm in size). In some industries, the shape of pebble is nevertheless preferred.

This is the case, for example, in the iron and steel industry, when adding calcium and magnesium compounds to oxygen converters or electric arc furnaces.

During the production of these pebbles and pieces, many fines are generated. These fines typically have limited use potential because they are difficult to transport and handle.

For several years now, the objective in many sectors has been to transform compounds initially in the form of powder into compacts (briquettes or tablets) to facilitate and secure their transport, handling and use.

The heaters always maintain an equilibrium of the materials between the calco-magnésiens compounds in roller and the fines generated before and during the calcination as well as during the manipulations and subsequent operations. Nevertheless, in some cases, an excess of fines is produced. These fines can then be agglomerated to each other in the form of briquettes, tablets or the like, which gives not only the possibility of eliminating excess fines but also artificially increasing the production of calcium and magnesium compounds in pebble adding these briquettes, tablets or the like to the pebbles.

Barnett et al (oll-press briquetting: Compacting fines to reduce waste-handling costs, powder and bulk engineering, vol.24, No. 10, October 2010, 1-6) discloses a method of manufacturing raw briquettes of lime. However, this document is silent as to the production conditions as well as the mechanical properties of briquettes obtained. Briquettes containing excess fines, tablets or the like generally have a lower mechanical strength than calcium and magnesium (calcium magnesium) compounds. roller. They also have aging resistance during storage or handling which is significantly lower than that of calcium and magnesium compounds in a pebble.

This explains the fact that, in practice, the briquetting or tabletting of calcium and magnesium compound fines are not widely used at present. In particular, given the low quality of the briquettes formed by this type of process, it is estimated that the briquetting provides a yield of less than 50%, due to the presence of a very large number of unusable briquettes output of this type of process, which requires a recycling step.

Lubricants and binders are additives often used in agglomeration processes in the form of briquettes, tablets or the like.

Lubricants can be of two types, internal or external. Internal lubricants are intimately mixed with briquetting materials. They favor on the one hand the flowability of the mixture during the feeding of the briqueteuse and on the other hand the rearrangement of the particles within the mixture during the compression. External lubricants are applied to the surfaces of the briquetting rollers and primarily assist in the demolding. In both cases, they reduce the friction on the surface and thus the wear. Lubricants can be liquids such as mineral oils, silicones, etc. or solids such as talc, graphite, paraffins, stearates, etc. In the case of compositions based on living calco-magnesium compounds, stearates are preferred and more particularly calcium stearate or magnesium stearate.

Binders are substances having the property of agglomerating the particles together, either by adhesion forces or by a chemical reaction. They can be of mineral origin (cements, clays, silicates ...), of vegetable or animal origin (celluloses, starches, gums, alginates, pectin, glues, ...), of synthetic origin (polymers, waxes ...). In many cases, they are used and implemented with water that activates their agglomeration properties.

Over the years, many of these additives have been used to increase the strength and durability of briquettes, tablets or the like of calcium and magnesium compounds, for example calcium stearate or paper fibers (see for example US5186742). ), but without this leading to sufficient improvements. Moreover, in many cases, the use of additives currently used for other manufactured industrial products is limited, as is the case in particular for the manufacture of briquettes or tablets of calco-magnesian compounds, either because calco-magnesian compounds react violently with water, or because a potentially negative effect of these additives on the final use of calco-magnesian compounds briquettes.

US Pat. No. 7,105,114 claims a briquetting process for slaked (dolomitic) lime fines using from 0.5 to 5% by weight of binders containing pseudo-plastic carbon chains which significantly improve the mechanical properties of the briquettes and which do not do not have the disadvantages mentioned above. However, this process only leads to obtaining briquettes, half of which already break after falling from a height of between 0.9 and 1.8 m (a fall from a height of between 3 and 6 feet). ), which represents a totally insufficient mechanical resistance.

Briquettes, tablets or the like based on calco-magnesian compounds can also be consolidated by means of a very high temperature heat treatment which leads to the sintering of said briquettes, tablets or the like. For example, in the case of cooked dolomite briquettes, it is known that a heat treatment of one to several hours at a temperature above 1200 ° C., and even ideally above 1300 ° C., leads to an increase in the properties mechanical briquettes. This heat treatment at very high temperature nevertheless leads to a chronological evolution of the texture characteristics of the aforementioned briquettes, it leads in particular to a sharp decrease in both the specific surface area and the pore volume. This is also accompanied by a sharp decrease in water reactivity, as explained in EN 459-2: 2010 E, which has many drawbacks for certain applications.

Therefore, there is a real need to develop tablets of calco-magnesian compound that can be distinguished from products such as tablets that are known today by a marked improvement in their resistance to the fall and also of preferably, by a much better resistance to aging in a humid atmosphere, while preserving the intrinsic properties (structural characteristics) of the calcium and magnesium compound before shaping, in particular its specific surface and / or its pore volume, but especially its reactivity to the water. The object of the invention is to overcome the drawbacks of the state of the art by providing a composition in the form of tablets as mentioned at the beginning, characterized in that said bright calco-magnesium compound comprises quicklime in the form of particles. milled to a concentration of at least 10% by weight and not more than 100% by weight based on the total weight of said composition, said tablet composition having a test Shatter number of less than 10%.

Quicklime in the form of crushed particles is called lime fines from the grinding of quicklime and therefore corresponds to a dimensional reduction of the rock lime. The grinding can be indifferently made from the all-comer at the exit of the oven (out of the oven) and / or at the outlet of the silo (taken out silo) or from the all-coming at the exit of the oven and / or at the output of the silo previously screened. The grinding can be carried out using different types of mills (hammer mill, impact mill ...), either in open circuit (no recirculation loop), or in closed circuit (recirculation loop).

Quicklime in the form of crushed particles is distinguished from lime screen. Screen lime is called lime fines from lime screen. The particle size is defined by the size of the screen. For example, a lime screened at 3 mm results in a 0-3 mm screening lime. Thus the screening on the all-out oven led to a "primary" screening lime. Screening on the all-out storage silo leads to a "secondary" screening lime.

For the purposes of the present invention, the term quicklime in the form of crushed particles, lime fines generally containing more than very fine lime fines screening. Thus, considering, for example, 0-3 mm fines, quicklime fines in the form of crushed particles will typically contain at least 30% by weight, most often at least 40% by weight, or even at least 50% by weight. by weight of very fine less than 100 μιτι, while the screening lime fines often contain at most 25% by weight, or even at most 15% by weight of very fine less than 100 μιτι.

The chemical composition of crushing lime fines is generally more homogeneous than that of lime fines. Thus, if we consider, for example, a lime in rock 10-50 mm cooked with a fuel which generates ashes such as coal (lignite, coal, anthracite ...) or petroleum coke, and that the the 0-3 mm fines resulting from the grinding or screening of this rock lime, it will be noted that the fraction 0-200 μιτι fines 0-3 mm from grinding has a chemistry similar to that of the fraction 200 μιτι-3 mm, while the fraction 0-200 μιτι fines 0-3 mm from the screen contains more impurities than that of the fraction 200 μιτι-3 mm.

Crushing lime fines are generally more reactive than lime fines. Thus, for quick-cooking quick-cooking lime, if the water reactivity (EN459 standard) is measured for 0-3 mm fines, the grinding fines typically have t ₆₀ values of less than 5 min where the Primary screening fines often have t ₆₀ values greater than 5 min.

The term "tablets" designates, as indicated above, within the meaning of the present invention, objects shaped with a technology of industrial compaction or compression of fines through the combined action of two punches (one in the up position). the other in the lower position) on said fines placed in a cavity. The term "tablets" therefore encompasses all the artifacts belonging to the family of tablets and pellets and, more generally, objects with various three-dimensional global shapes, such as, for example, substantially cylindrical, octagonal, cubic or rectangular shapes. with a slight asymmetry between the lower part (the bottom) and the upper part (the top) of said artifacts. Said technology generally uses rotary presses or hydraulic presses.

This type of industrial tabletting process offers a productivity greater than or equal to 0.1 t / h (tons per hour), preferably greater than or equal to 0.5 t / h, advantageously greater than or equal to 1 t / h. h by compacting device (press). Industrial tablets produced in such a process, such as for example by means of a hydraulic press or a rotary press, such as the Eurotab Titan rotary press, have a surface differential between their lower part and their upper part. Consequently, the compact industrial product of the present invention in tablet form will have an asymmetrical shape, which will allow inter alia to obtain a high level of productivity allowing to lead to an industrial application but also to an industrial acceptance of tablets according to the present invention. Indeed, the asymmetrical shape also leads to a decrease in defects in the finished tablets. More particularly, in the case of a tablet having a generally cylindrical three-dimensional shape, this asymmetry will lead to a tablet that can be seen as a truncated cone, if we accentuate the phenomena. Advantageously, the difference between the surface of the upper part (surface of the upper part) and that of the lower part (surface of the lower part) of the tablet is greater than or equal to 0.5%, preferably greater than or equal to 1%, and less than or equal to 10%, preferably less than or equal to 5%, in particular less than or equal to 3%, especially around 2%.

The difference is a relative difference calculated by decreasing the (upper) surface of the upper part by the (lower) surface of the lower part and dividing the result by the median section of the tablet according to [(surface of the upper part - surface of the lower part) / middle section of the tablet]. The upper part (upper part) has been designated herein as being larger than the lower part (lower part) of the tablet. The median diameter corresponds to the diameter measured in the middle of the height of the tablet. The surface of the upper part is the one facing upwards during manufacture, when the tablet is in the die in a representative embodiment, while the surface of the lower part is that facing downwards. Of course, depending on the manufacturing process of tablets and hardware, the opposite is also possible. Similarly, when it rests on a surface such as the floor or a table, the surface of the upper part can also be oriented downwards or in any other orientation.

As can be seen, the tablets according to the present invention exhibit a particularly advantageous Shatter test number of less than 10%, thereby conferring on the tablets sufficient mechanical strength to permit industrial use in most processes using the compounds. calco-magnesiens in the form of pebbles, alone or in mixtures with pebbles.

Surprisingly, it has not yet been possible to explain the reasons for this, that the addition of quicklime in the form of crushed particles at a concentration of at least 10% by weight relative to the weight of the composition made it possible to obtain a strongly improved mechanical resistance to falling. A content as limited as 10% by weight allows to obtain a significant improvement in mechanical strength, although the content of crushed particles can be up to 100% by weight.

For the purposes of the present invention, said bright calco-magnesium compound comprises one or more bright calco-magnesium compound (s). The bright calco-magnesium compound is selected from the group consisting of quicklime (calcium), magnesium lime, bright dolomite lime, calcined dolomite and mixtures thereof, preferably in the form of particles, such as particles from screening, grinding, filter dust and mixing. Said bright calco-magnesium compound can therefore be considered as a calco-magnesian component of the tablet composition, which may contain other compounds. For the purposes of the present invention, the calco-magnesium compound is present in the composition at a concentration of at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight. more particularly at least 80% by weight, or even at least 90% by weight relative to the total weight of said composition.

For the purposes of the present invention, the term "Shatter test number" is used to mean the mass percentage of fines less than 10 mm generated after 4 drops of 2 m from 10 kg of product (tablets). These fines are quantified by sieving through a 10 mm square screen at the end of the 4 drops of 2 m.

The determination of the% by weight of CaO + MgO equivalent is carried out by X-ray fluorescence spectrometry (XRF) as described in the EN 15309 standard. Chemical, semi-quantitative analysis by XRF to determine the relative mass concentration of elements whose atomic mass is between 16 (oxygen) and 228 (uranium), is carried out at the start of the samples milled at 80μιτι and shaped in the form of pellet. The samples are introduced into a PANalytical / MagiX PRO PW2540 apparatus, operating in wavelength dispersion. The measurement is carried out with a power of 50kV and 80 mA, with a Duplex detector.

The results of the analysis give the calcium and cagnesium content and these measurements are reported by weight of equivalent CaO and MgO.

Advantageously, in the composition in the form of tablets according to the present invention, said bright calco-magnesium compound is soft cooking or medium cooking, preferably soft cooking. Live calco-magnesium compounds, such as quicklime, are industrially produced by cooking natural limestones in different types of furnaces such as straight furnaces (regenerative furnaces with double flow, ring furnaces, standard straight furnaces, etc.). rotary kilns. The quality of the calco-magnesium compound, such as for example quicklime, especially its reactivity to water, and the consistency of this quality, are partly related to the type of oven used, the conditions of use of the oven, to the nature of the limestone from which the living calco-magnesium compound originates, or even to the nature and quantity of the fuel used. Thus, it is theoretically possible to produce a whole range of bright calco-magnesian compounds, such as quicklime with reactivities to water ranging from the most explosive to the slowest.

In general, obtaining a quicklime by a gentle firing (900-1000 ° C) makes it possible to obtain a rather reactive lime while obtaining a low reactive lime goes through overcooking to higher temperature (1200-1400 ° C). Overcooking often leads to produce quicklime of less stable quality in terms of reactivity to water because the calcination operation is carried out in a thermal zone where the textural evolution of quicklime is quite sensitive. This over-cooked quicklime is also more expensive to produce than a quicker quicklime because it requires the use of higher temperatures but also because, except to use dedicated ovens, the production of this quicklime sur- Cooking leads to inter-production campaigns to alternate with the production of quick lime which are more commonly used, which is not without problems of stabilization of calcination conditions and therefore problems of stabilization of quality.

The quick lime obtained by gentle firing generally have specific surfaces measured by nitrogen adsorption manometry after degassing under vacuum at 190 ° C for at least 2 hours and calculated according to the multi-point BET method as described in the standard ISO 9277: 2010E greater than 1 m ² / g whereas over-cooked quicklime generally has surfaces well below 1 m ² / g

In the context of this invention, the reactivity of quicklime is measured using the water reactivity test of European Standard EN 459-2: 2010 E. Thus, 150g of quicklime are added with stirring in a Dewar cylindrical of 1.7 dm ³ capacity containing 600 cm ³ of permutated water at 20 ° C. The quick lime is brought in the form of fines of size between 0 and 1 mm. The stirring at 250 rpm is carried out by means of a specific pale. The evolution of the temperature is measured as a function of time, which makes it possible to draw a curve of reactivity. From this curve can be deduced the value t ₆₀ which is the time necessary to reach 60 ° C. The reactivity of cooked dolomite, also called live dolomite, is measured using this same reactivity test. In this case, 120 g of cooked dolomite are added with stirring in a cylindrical Dewar of 1.7 dm ³ capacity containing 400 cm ³ of water permuted at 40 ° C. The cooked dolomite is brought in the form of fines of size between 0 and 1 mm. The stirring at 250 rpm is carried out by means of a specific pale. The evolution of the temperature is measured as a function of time, which makes it possible to draw a curve of reactivity. From this curve can be deduced the value t ₇₀ which is the time necessary to reach 70 ° C.

The composition according to the present invention advantageously comprises a calco-magnesium compound with soft or medium cooking, preferably soft, which is therefore necessarily relatively reactive, thus providing reagent tablets.

According to the present invention, a bright calco-magnesian compound with a soft or medium, preferably soft, cooking is characterized by a value t _{60 of} less than 10 min, preferably 8 min, preferentially 6 min, and still more preferably 4 min when the calco compound -Magnesian alive is a quicklime and a value of t ₇₀ less than 10 min, preferably 8 min, preferably 6 min, and more preferably 4 min when the bright calco-magnésien compound is a cooked dolomite.

In an advantageous embodiment of the composition according to the present invention, said quicklime in the form of crushed particles is a quick-cooking quicklime or medium-bake, preferably soft cooking.

Advantageously, said quicklime in the form of crushed particles according to the present invention, has a high water reactivity characterized by a value of t ₆₀ less than 10 min, preferably less than 8 min, preferentially less than 6 min and still preferably lower at 4 min. In a particular embodiment, said tablets have a largest dimension of at most 50 mm, preferably at most 40 mm, more preferably at most 30 mm.

This means that the shelves of the composition in the form of tablets pass through a sieve with square mesh of 50 mm, preferably 40 mm, and in particular 30 mm, respectively.

Preferably, said tablets have a larger dimension of at least 10 mm, preferably at least 15 mm, more preferably at least 20 mm.

By the terms a highest dimension is meant a characteristic dimension of the tablet which is the largest, namely the diameter, the length, the width, the thickness, ...

In one embodiment of the composition in the form of tablets according to the present invention, said tablets are green tablets and have a BET specific surface area greater than or equal to 1 m ² / g, preferably greater than or equal to 1.2 m ² / g, more preferably greater than or equal to 1.4 m ² / g.

In another embodiment of the composition in the form of tablets according to the present invention, said tablets are cooked tablets and have a BET specific surface area greater than or equal to 0.4 m ² / g, preferably greater than or equal to 0, 6 m ² / g, more preferably greater than or equal to 0.8 m ² / g.

For the purposes of the present invention, BET specific surface area is understood to mean the specific surface area measured by nitrogen adsorption manometry after degassing under vacuum at 190 ° C. for at least 2 hours and calculated according to the multi-point BET method such as described in ISO 9277: 2010E and expressed in m ² / g.

In another embodiment of the composition based on bright calco-magnesian compounds in the form of tablets according to the invention, said tablets are raw tablets or cooked tablets, and have a porosity greater than or equal to 30%, preferably greater than or equal to 32%, more preferably greater than or equal to 34%.

By porosity is meant in the sense of the present invention, the total pore volume of mercury determined by porosimetry by mercury intrusion. in accordance with Part 1 of ISO 15901-1: 2005E, which divides the difference between the skeletal density, measured at 30000 psia, and the apparent density, measured at 0.51 psia, by the skeletal density.

Alternatively, the measurement of porosity can also be measured by oil intrusion porosimetry. The density and the porosity of the briquettes are determined by intrusion of kerosene, according to a measuring protocol resulting from the EN ISO 5017 standard. The measurements are carried out on 5 briquettes.

The density of the briquettes is calculated according to the formula ml / (m3 - m2) x Dp and the porosity in percent according to the formula (m3 - ml) / (m3 - m2) x 100.

ml is the mass of these 5 briquettes, m2 is the mass of these 5 briquettes immersed in oil and m3 is the mass of these 5 "wet" briquettes, that is to say impregnated by oil. Dp is the density of oil. In a particular embodiment according to the present invention, the composition is in the form of raw tablets and the tablets have a high water reactivity defined by a value of t ₆₀ less than 10 min, preferentially less than 8 min, preferably lower at 6 min, and still preferably less than 4 min.

In another embodiment according to the present invention, the composition is in the form of cooked tablets and the tablets have a high water reactivity defined by a value of t _{60 of} less than 10 min, preferentially less than 8 min, preferably less than 10 min. at 6 min, and still preferably less than 4 min.

More particularly, according to the present invention, when the composition is in the form of raw tablets and the calco-magnesian compound is mainly quicklime, said composition has a reactivity value t ₆₀ less than 10 min, preferably less than 8. min, preferably less than 6 min and even more preferably less than 4 min. If fluxes are present or for example an iron oxide, to take account of the flux content, such as for example an iron-based compound in the composition, a little more than 150 g of said composition is added in the test. reactivity to have the equivalent of 150g of quicklime added. Advantageously, according to the present invention, when the composition is in the form of raw tablets and the calco-magnesian compound is mainly cooked dolomite, said composition has a reactivity value t ₇₀ less than 10 min, preferably less than 8 min. preferably less than 6 minutes and even more preferably less than 4 minutes. If fluxes are present or for example an iron oxide, to take into account the melting content such as, for example, the iron compound in the composition, a little more than 120 g of said composition is added to the reactivity test for have the equivalent of 120g of cooked dolomite added.

More particularly, according to the present invention, when the composition is in the form of cooked tablets and the calco-magnesian compound is mainly quicklime, said composition has a value t ₆₀ less than 10 min, preferably less than 8 min, preferably less than 6 minutes and even more preferably less than 4 minutes. If fluxes are present or for example an iron oxide, to take account of the flux content, such as, for example, an iron-based compound in the composition, a little more than 150 g of said composition is added in the reactivity test. to have the equivalent of 150g of "free" quicklime added. By quicklime "free" is meant quicklime that has not reacted with iron oxide to lead to calcium ferrites CaFe ₂ 0 ₄ and / or Ca ₂ Fe ₂ 0 ₅ .

In an advantageous embodiment of the composition according to the present invention, said quicklime in the form of crushed particles is present at a concentration of at least 15% by weight, preferably at least 20% and more preferably at least 20% by weight. at least 30%, in particular at least 40% by weight relative to the total weight of said composition.

Advantageously, in the composition according to the present invention, said quicklime in the form of crushed particles is present at a concentration of at most 90% by weight, preferably at most 80%, preferably at most 70%, more preferably at most 50% by weight relative to the total weight of said composition.

In a preferred form of the present invention, the composition based on living calcium-magnesium compounds in tablet form further comprises a binder or a lubricant, preferably in the form of a concentrated aqueous powder or suspension, more particularly chosen from the group consisting of binders of mineral origin such as cements, clays, silicates, binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of synthetic origin such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate, and mixtures thereof, preferably calcium stearate and / or magnesium stearate, at a content of between 0.05 and 0.50% by weight, preferably between 0.05 and 0.30% by weight, such as more preferentially between 0.10 and 0.20% by weight relative to the total weight of said composition.

More particularly, according to the invention, said tablets have an average weight per tablet of at least 5 g, preferably at least 10 g, more preferably at least 12 g, and in particular at least 15 g. boy Wut.

Advantageously, according to the invention, said tablets have an average weight per tablet less than or equal to 100 g, preferably less than or equal to 60 g, more preferably less than or equal to 40 g and in particular less than or equal to 30 g. boy Wut.

In yet another preferred embodiment according to the present invention, said tablets have an apparent density of between 2 g / cm ³ and 3.0 g / cm ³ , preferably between 2.2 g / cm ³ and 2.8 g / cm ³ .

In a particular embodiment according to the present invention, said bright calco-magnesium compound further comprises fine particles of calco-magnesium compound chosen from fine particles rejected in the screening of the cobalt production of said bright calco-magnesium compound, dust calc-magnesian filters and their mixture, at a concentration of at least 10% by weight and at most 90% by weight relative to the total weight of said composition.

Advantageously, in the composition in the form of tablets according to the present invention, said fine particles rejected in the production screen of calco-magnesian compound rollers are fine particles of live dolomite.

In a preferred variant, said fine particles rejected in the calco-magnesian compound pebble production screen are fine particles of quicklime.

Advantageously, in the composition of tablets according to the present invention, said fine particles rejected on screening are fine particles screened at 7 mm during said roll production of said calco-magnesium compound.

More particularly, in the tablet composition according to the present invention, said fine particles rejected on screening are fine particles rejected on screening at 5 mm during said production of rolls of said calco-magnesium compound.

Even more advantageously, said fine particles rejected on screening are fine particles rejected on screening at 3 mm during said production of rolls of said calco-magnesium compound.

In a particular embodiment of the present invention, said fine particles rejected on screening are a mixture of fine particles rejected on screening at 7 mm during said production of rolls of said calco-magnesium compound and / or fine particles rejected on the screen. mm during said production of pebbles of said calco-magnesium compound and / or fine particles rejected at 3 mm screening during the production of pebbles of said calco-magnesium compound.

The fine particles rejected on screening therefore advantageously have a particle size d _{100 of} less than or equal to 7 mm, in particular less than or equal to 5 mm, more particularly less than or equal to 3 mm; a d ₉₀ less than or equal to 3 mm and a d ₅₀ less than or equal to 1 mm.

Within the meaning of the present invention, except if otherwise specified, the notation _x represents a diameter expressed as μιτι, measured by laser granulometry in methanol without sonication, relative to which x% by volume of the particles measured are less than or equal.

In another particular embodiment according to the present invention, said tablet composition further comprises iron-based compound (s) at a concentration of at least 3% by weight and at most 60% by weight. by weight expressed as Fe ₂ O ₃ equivalent relative to the total weight of said composition.

In a preferred embodiment of the present invention, at least one of the iron-based compound (s) is a compound based on iron oxide, preferably active iron, present at a concentration of at least 3% by weight. weight and at most 60% by weight expressed in Fe ₂ 0 ₃ equivalent relative to the total weight of said composition. Advantageously, said composition in tablet form comprises at least 50% by weight of calcium expressed as CaO equivalent, relative to the total weight of said composition.

In particular, said composition in tablet form comprises a Ca / Mg molar ratio greater than or equal to 1, preferably greater than or equal to 2, more preferably greater than or equal to 3.

In a very particular embodiment of the present invention, in which the green tablets contain an iron-based compound which is an iron oxide compound, said green tablets may be advantageously subjected to heat treatment at a temperature between 700 ° C. and 1200 ° C., preferably between 900 ° C. and even 1050 ° C. and 1200 ° C., particularly around 1100 ° C., for a predetermined duration, for example between 5 and 20 minutes, preferably greater than or equal to 7 minutes and less than or equal to 15 minutes, with forming and obtaining cooked tablets in which the compound based on iron oxide is converted, at least partially, into calcium ferrites.

Within the meaning of the present invention, said iron-based compound may be formed from one or more iron-based compounds, together totaling in the composition a content of 3 to 60% by weight relative to the total weight of said composition.

In a particular embodiment, the composition according to the present invention is packaged in container types having a content volume greater than 1 m ³ such as large bags, containers, silos and the like, preferably sealed.

More particularly, said shelves have a slightly asymmetrical three-dimensional shape, preferably substantially frustoconical, in which the difference between the surface of the upper part and that of the lower part of the tablet is greater than or equal to 0.5%, preferably greater than or equal to 1%, and less than or equal to 10%, preferably less than or equal to 5%, in particular less than or equal to 3%, especially around 2%.

In an advantageous variant of the present invention, the composition in tablet form consists of raw tablets having a test Shatter number of less than 8%, preferably less than 6%, and more preferably less than 5%, in particular less than 4%. In another advantageous variant of the present invention, the tablet composition consists of cooked tablets having a test Shatter number of less than 6%, preferably less than 4%, and more preferably less than 3%, particular less than 2%, or even less than 1.5%.

Other embodiments of the tablet composition according to the invention are indicated in the appended claims.

The invention also relates to a method of manufacturing a composition in the form of tablets.

The process is characterized in that it comprises the following steps: a) supply of a homogeneous powder mixture comprising at least 40% by weight of CaO + MgO equivalent relative to the weight of said homogeneous powdery mixture, and comprising at least one bright calco-magnesium compound, said at least one bright calco-magnesium compound comprising quicklime in the form of crushed particles at a concentration of at least 10% by weight and at most 100% by weight relative to the total weight of said homogeneous powdery mixture, b) feeding said homogeneous powdery mixture into a confinement space between two punches having a cross section of between 1 and 40 cm ² , advantageously between 1 and 20 cm ² , preferably between 1 and 10 cm ² , in between 2 and 10 cm ² ,

c) compacting said homogeneous mixture to form a product in the form of tablets of three-dimensional shape, by applying a compacting pressure of between 200 MPa and 800 MPa, preferably between 250 MPa and 600 MPa, more preferably between 300 and 500 MPa, and even more preferably between 350 and 500 MPa,

d) releasing the compaction pressure and e) ejecting said product in the form of tablets from said confinement space.

In a particular form of the invention, said powder mixture comprises at most 100% by weight, preferably at most 90% by weight, more preferably at most 88%, in some embodiment at most 80% by weight. more preferably, at most 60% by weight of CaO + MgO equivalent relative to the weight of said composition. Optionally, in the process according to the present invention, step a) is carried out in the presence of a binder or a lubricant, preferably in the form of a concentrated aqueous powder or suspension, more particularly chosen from the group consisting of binders of mineral origin such as cements, clays, silicates, binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of origin synthetic, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate and mixtures thereof, preferably calcium stearate and / or magnesium stearate, at a content of between 0.1 and 1% by weight, preferably between 0.15 and 0.6% by weight, more preferably e 0.2 and 0.5% by weight relative to the total weight of said tablets.

Advantageously, the method according to the present invention further comprises a heat treatment of said collected raw tablets, at a temperature of between 700 ° C. and 1200 ° C., preferably around 900 ° C. for a predetermined duration of between 5 and 20 minutes. , preferably greater than or equal to 7 minutes and less than or equal to 15 minutes, with formation and production of cooked tablets.

Preferably, said homogeneous mixture brought into the process according to the invention comprises a bright calco-magnesium compound with soft or medium cooking, preferably soft cooking.

Advantageously, said quicklime in the form of crushed particles, of said homogeneous mixture brought into the process according to the invention, is a quick-cooking quick-cooking or medium-baking lime, preferably soft-cooking.

Advantageously, said bright calco-magnesium compound is quicklime.

In another advantageous embodiment, said quicklime in the form of crushed particles, of said homogeneous mixture brought into the process according to the invention, has a high water reactivity characterized by a value of t _{60 of} less than 10 min, preferentially less than 8 min, preferably less than 6 min and more preferably less than 4 min.

In yet another advantageous embodiment, said quicklime in the form of crushed particles, of said homogeneous mixture brought into the method according to the invention, is obtained by grinding from quicklime rock whose size is greater than 3 mm, preferably greater than 5 mm, preferably greater than 7 mm, and still preferably greater than 10 mm, and less than 120 mm, preferentially 100 mm, preferably less than 80 mm, and even more preferably less than 60 mm.

In a preferred embodiment, said at least one bright calco-magnesium compound comprises quicklime in the form of crushed particles at a concentration of at least 15% by weight, in particular at least 20% by weight, more preferably preferably at least 30% by weight, particularly preferably at least 40% by weight relative to the total weight of said homogeneous powder mixture.

In another preferred embodiment, said homogeneous mixture based on living calco-magnesium compounds brought into the process according to the invention comprises quicklime in the form of crushed particles at a concentration of at most 90% by weight, in particular of at most 80% by weight, more preferably at most 70% by weight, particularly preferably at most 50% by weight relative to the total weight of said homogeneous powder mixture.

In a particular embodiment of the present invention, said bright calco-magnesium compound further comprises fine particles of calco-magnesium compound chosen from fine particles rejected in the screening of the cobalt production of said bright calco-magnesium compound, dust calc-magnesian filters and their mixture, at a concentration of at least 10% by weight and at most 90% by weight relative to the total weight of said homogeneous powder mixture.

Advantageously, said fine particles rejected in the production screen of calco-magnesian compound rollers are fine particles of live dolomite.

Advantageously, said fine particles rejected on screening are fine particles rejected on screening at 7 mm during said production of rolls of said calco-magnesium compound. More particularly, said fine particles rejected on screening are fine particles rejected on screening at 5 mm during said production of rolls of said calco-magnesium compound.

The fine particles rejected on screening therefore advantageously have a particle size di ₀ o of less than or equal to 7 mm, in particular less than or equal to 5 mm, more particularly less than or equal to 3 mm; a d ₉₀ less than or equal to 3 mm and a d ₅₀ less than or equal to 1 mm.

In another particular embodiment according to the present invention, said homogeneous pulverulent mixture further comprises one or more compounds based on iron, at a concentration of at least 3% by weight and at most 60% by weight. weight expressed as Fe ₂ 0 ₃ equivalent relative to the weight of said mixture.

In a preferred embodiment of the present invention, at least one of the iron-based compound (s) is an iron oxide compound present at a concentration of at least 3% by weight and at most 60% by weight. % by weight expressed as Fe ₂ O ₃ equivalent relative to the weight of said homogeneous mixture, preferably of active iron.

Advantageously, said homogeneous mixture based on living calco-magnesium compounds comprises at least 50% by weight of calcium expressed as CaO equivalent, relative to the total weight of said mixture. In particular, said homogeneous mixture based on living calco-magnesium compounds comprises a Ca / Mg molar ratio greater than or equal to 1, preferably greater than or equal to 2, more preferably greater than or equal to 3.

In a very particular embodiment of the present invention, wherein the green tablets contain an iron-based compound which is an iron oxide compound, the method further comprises a heat treatment of said collected raw tablets, a temperature between 700 ° C and 1200 ° C, preferably between 900 ° C or 1050 ° C and 1200 ° C, more particularly around 1100 ° C, for example for a predetermined period of between 5 and 20 minutes, preferably greater than or equal to 7 minutes and less than or equal to 15 minutes, more particularly greater than or equal to 8 minutes and less than or equal to 13 minutes to obtain cooked tablets in which the iron oxide compound is converted at least partially in calcium ferrites.

In a preferred embodiment of the invention, the method further comprises, before said feeding of a homogeneous powder mixture,

a) feeding a mixer with said at least one bright calco-magnesium compound and

b) a mixture for a predetermined period, sufficient to obtain a homogeneous powder mixture of said at least one bright calco-magnesium compound.

Other embodiments of the process according to the invention are indicated in the appended claims.

The present invention also relates to a method for producing a composite material comprising a plurality of successive layers to form a multilayer structure in which at least one layer is formed with said tablet product of the composition by the method of the present invention. and further comprising a further step of compacting said at least one layer of said compact product into tablets and another compact layer prior to said ejecting step.

The present invention also relates to the use of raw or cooked tablets according to the present invention, in the iron and steel industry, in particular in the manufacture of steel in elementary oxygen converters, in electric arc furnaces, or in the secondary metallurgy, in the treatment of flue gas, in the treatment of water, in the treatment of sludge and wastewater, in agriculture, in the construction industry and in public works, as for example for the stabilization of soils.

The invention also relates to a use of a composition in the form of raw tablets or in the form of tablets cooked according to the present invention in the iron and steel industry, in particular in oxygen converters or in electric arc furnaces.

More particularly, raw or cooked tablets according to the present invention are used in oxygen converters or in electric arc furnaces, mixed with tablets of bright calco-magnesium compounds or with rolls of bright calco-magnesium compounds.

Indeed, during the first minutes of the refining process, there is not enough slag available in the reaction tank to effectively start the dephosphorization reaction in the methods of the state of the art. The use of the composition according to the present invention, thus doped with fluxing agents, is found to melt faster than lime rock, and helps to form a liquid slurry earlier in the process, in comparison with conventional processes, because of homogeneous mixing and shaping of this homogenized mixture which further accelerates the slag forming process and minimizes the formation of high melting slag components such as calcium silicates which usually form during the aforementioned method of the state of the art.

In a preferred embodiment of the process according to the present invention, the process further comprises pretreatment of the modified atmosphere briquettes containing at least 2% by volume of C0 ₂ and at most 30% by volume of C0 ₂ , preferably at most 25% by volume of C0 ₂ , preferably at most 20% by volume of C0 ₂ , more preferably at most 15% by volume of C0 ₂ , more preferably still at most 10% by volume of C0 ₂ with respect to said modified atmosphere.

It has indeed been found according to the present invention that a pretreatment under such a modified atmosphere containing such C0 ₂ % with respect to said modified atmosphere makes it possible to improve the mechanical strength of the briquettes.

The subject of the invention is also the use of a composition in the form of raw tablets or in the form of tablets cooked in a process for refining molten metal, in particular dephosphorizing molten metal and / or desulphurizing molten metal and / or reducing loss of refined metal in the slag.

The use of a composition in the form of raw tablets or in the form of cooked tablets according to the present invention in a process for refining molten metal comprises

at least one step of introducing hot metal and possibly iron-based waste into a tank, at least one step of introducing a composition in the form of raw tablets or tablets cooked according to the present invention, preferably in the form of baked tablets according to the present invention, at least one oxygen blowing step in said tank, at least one step of forming a slag with said tablet composition in said tank,

at least one step of obtaining refined metal having a reduced content of phosphorus and / or sulfur compounds and / or an increased content of refined metal from the hot metal by dephosphorization and / or desulfurization, and at least one step of unloading said refined metal having a reduced content of phosphorus and / or sulfur compounds and / or increased to refined metal.

The use according to the present invention further comprises a step of adding quicklime, preferably quicklime rock or compacts of quicklime, in particular tablets or tablets of quicklime.

Other forms of use according to the invention are indicated in the appended claims.

Other features, details and advantages of the invention will emerge from the description given below, without limitation and with reference to examples.

The present invention relates to a method of tabletting a composition comprising at least one bright calco-magnesium compound comprising quicklime in the form of crushed particles at a concentration of at least 10% by weight and at most 100% by weight relative to the total weight of said composition.

The tableting process according to the invention comprises feeding a homogeneous powder mixture comprising at least one bright calco-magnesium compound.

Depending on the intended use of the tablets, it is possible to add additives, for example, in the case of use in the steel industry, fluxes, such as B ₂ 0 ₃ , Na0 ₃ , aluminate calcium, calcium silicate, calcium ferrite such as Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ , Al metal, Mg metal, Fe metal, Mn metal, Mo metal, Zn metal, Cu metal, Si elemental, CaF ₂ C, Cac ₂ , alloys such as CaSi, CaMg, CaFe, FeMn, FeSi, FeSiMn, FeMo; TiO ₂ , a molybdenum oxide, a copper oxide, a zinc oxide, a molybdenum hydroxide, a copper hydroxide, a zinc hydroxide, and mixtures thereof.

Preferably, when iron oxide is present in the green tablets, it is present in the form of an iron-based compound present at a content of at least 3%, preferably at least 12%, more preferably at least 20%, preferably at least 30%, more preferably at least 35% by weight of Fe ₂ O ₃ equivalent relative to the weight of said composition, said iron-based compound having a very fine particle size distribution characterized by a median size d _{50 of} less than 100 μιτι, preferably 50 μιτι and a size of ₉₀ less than 200 μιτι, preferably less than 150 μιτι, preferably less than 130 μιτι, more preferably less than 100 μιτι.

By the terms an iron-based compound is meant for example an iron-based compound, preferably based on iron oxide, characterized by a median size d _{50 of} less than 100 μιτι, preferably 50 μιτι, and a d ₉₀ size less than 200 μιτι, preferably less than 150 μιτι, preferably less than 130 μιτι, more preferably less than 100 μιτι. This iron oxide can be described as active iron, which implies in particular that there is, relative to the total amount of iron oxide present in the iron-based compound, at least 40% of the iron oxide. this iron oxide present in the peripheral layer of the grains of the iron-based compound, this peripheral layer being defined by a thickness of 3 μιτι. In this way, a volume fraction of iron oxide is defined on the surface of the particles of iron oxide, which is likely to react to be converted to ferrite during a heat treatment or directly in situ in the converter.

The particle size distribution of the iron-based compound in the tablet composition is determined by scanning electron microscopy and X-ray mapping, coupled with image analysis.

The measurement is based on the property of iron-based compound particles to emit, when subjected to high energy radiation (eg, a high intensity electron beam), energy X radiation specific (6.398 keV). The detection of this radiation, coupled with the exact knowledge of the position of the electron beam for each observed point, makes it possible to specifically map the particles of the iron-based compound.

Each identified particle is then characterized by its equivalent surface particle diameter (X _ai ), as defined in ISO 13322-1. The particles are then grouped by size fraction particle size fraction.

The active iron fraction in the sense of the invention is in the peripheral layer of each particle of the iron-based compound, in the outer layer with a thickness of 3 μιτι. For each particle size fraction and therefore for each particle size, it is therefore possible to calculate the fraction of iron in the peripheral layer by the formula:

% Fe ' _act ij / particle ⁼ (V ext'V inè / V ext

where V _ext is the volume of the particle of the iron-based compound and V _int the volume at the heart of the particle at more than 3 μιτι of the surface, that is to say the volume corresponding to a spherical particle having a reduced radius of 3 μιτι.

As the particles are considered perfectly spherical, the following formula is obtained for particles whose diameter is greater than 6 μιτι.

⁼ YiPext) ^{3 ~} Wext ^~ 6) ³ ] / (Z) _e¾t ) ³ where D _ext is the diameter of the particle expressed in μιτι, or the size of the particle in the direction of the laser granulometry.

The following formula is obtained for particles whose diameter is less than 6 μιτι:

⁼ 100% The total active iron fraction within the meaning of the invention is therefore the sum over all the particle size fractions of the active iron fraction multiplied by the volume percentage of each particle size fraction obtained by laser granulometry.

% Fe _ac tif = ilumic / particle-° / ° F ^e active / particle

Therefore, in order to have sufficient active iron oxide in the iron-based compound present in the tablets produced by the process according to the present invention, the% active iron must be at least 40%.

As can be seen, according to the present invention, having a fine particle size is not enough, it is actually necessary to achieve the% of active iron oxide within the iron-based compound present in the tablets, which allows to achieve a sufficient ferrite conversion during a pre-heat treatment or in a converter.

Moreover, in the process according to the present invention, it has been found that such an active iron oxide does not penalize the mechanical strength of the tablets formed, even at a high content of 60% by weight relative to the total weight of the tablets. floods. The formation of such green tablets containing a high quantity of active iron oxide also makes it possible to have tablets simultaneously supplying fluxes such as iron oxide (Fe ₂ O ₃ ), but also the ferrites required, provided that if the tablets are raw and they do not directly contain ferrites, the ferrites are formed directly in situ, for example in the converters in which the tablets are used.

The process according to the present invention therefore makes it possible to obtain tablets of calco-magnesian compound whose mechanical strength is not penalized by the addition of fluxing agents, even without heat treatment, whose iron oxide is active, but which Moreover, it is very flexible and powerful, without the aforementioned constraints.

Preferably, according to the present invention, said iron-based compound containing from 3% to 40% Fe ₂ O ₃ equivalent fed as a homogeneous mixture comprises at least 50% active iron oxide, advantageously at least 60% of active iron oxide, particularly preferably at least 70% of active iron oxide, relative to the total weight of Fe ₂ 0 ₃ equivalent.

The powdered homogeneous mixture thus formed is fed into a confinement space between two punches of a Eurotab titan type rotary press. having a section of between 1 and 40 cm ² , advantageously between 1 and 20 cm ² , preferably between 1 and 10 cm ² , in particular between 2 and 10 cm ² .

The homogeneous powdery mixture is then compacted to form a product in the form of tablets of three-dimensional shape, by application of a compacting pressure comprising 200 MPa and 800 MPa, preferably between 250 MPa and 600 MPa, more preferably between 300 and 500 MPa, and still more preferably between 350 and 500 MPa, optionally in the presence of a binder or a lubricant, preferably brought into the form of a concentrated aqueous powder or suspension, more particularly chosen from the group binders of mineral origin such as cements, clays, silicates, binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, adhesives, binders synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate, and mixtures thereof, preferably calcium stearate and / or magnesium stearate, at a content of between 0.05 and 0.50% by weight, preferably between 0.05 and 0.30% by weight, more preferably between 0.10 and 0.20% by weight relative to the total weight of said mixture. The compacting pressure is then released and the product in the form of tablets is ejected to allow its collection.

The Titan rotary press comprises a die having an inner wall defining at least said containment space having a section which tapers downward. The lower section of the confinement space in which the tablet product is housed is smaller than the upper section of the confinement space in which the tablet product is housed, to facilitate the ejection of the product in the form of a tablet. tablet from the containment space, and offers a productivity of at least 100 rpm (tablet per minute). Starting with about thirty kilograms of fines of slaked lime from 0 to 3 mm, 12.7 g of this mixture are successively poured into each of the dies of the tool provided with a substantially cylindrical shape having a section that decreases towards the bottom. for the tablet section and with a diameter of about 21 mm. The compression is carried out under a compression of 500 MPa, with a punch approach speed of 115 mm / s and a holding time of 100 ms. Several kilograms of product are obtained in the form of substantially cylindrical tablets each having a weight of 12.6 g and a median diameter of an average value of 21.4 mm. The upper diameter of the upper (upper) part of the tablets has an average value of 21.51 mm and the lower diameter of the lower (lower) part of the tablets has an average value of 21.29 mm, which respectively leads to a upper surface of the upper part with an average value of 363 mm ² and a lower surface of the lower part with an average value of 356 mm ² . As a result, the difference between the average upper surface and the average lower surface of the shelves relative to the mean median section of the product in tablet form is equal to 2.06% [(average upper surface of the upper-lower surface of the tablet). lower part) / middle section of the product in tablet form]. The height is 15.9 mm and the density is 2.20 g / cm ³ . These tablets are of consistent quality and are free from gross defects.

These compacts in the form of tablets develop a BET specific surface area (measured by manometry with nitrogen adsorption after degassing in vacuo at 190 ° C. for at least two hours and calculated according to the multipoint BET method described in the ISO 9277: 2010E standard). 1.4 m ² / g and have a total mercury pore volume of 34% (determined by mercury introduction porosimetry according to part 1 of ISO 15901-1: 2005E of dividing the difference between skeletal density , measured at 30,000 psia, and apparent density, measured at 0.51 psia, by skeletal density).

An impact test is carried out starting with 0.5 kg of these tablets and successively performing 4 drops of two meters. We weigh the amount of fines less than 10 mm produced at the end of these 4 falls. An impact resistance index of 2.8% is obtained.

In a preferred embodiment of the process according to the present invention, the collected raw tablets are heat-treated at a temperature of between 700 ° C. and 1200 ° C., preferably between 700 ° C. and 1000 ° C., preferably between 800 ° C. and 1000 ° C, for a predetermined period of time.

The raw tablets are therefore brought into a high temperature oven where they undergo a heat treatment of these tablets to a temperature of less than or equal to 1200 ° C, preferably less than or equal to 1000 ° C. They are then cooled and collected in the form of cooked tablets to among other things improve their resistance to aging and their resistance to falling.

The heat treatment time is related to the temperature of the heat treatment (the time is shorter as the temperature is high) and the thickness of the bed of tablets (the time increases with the thickness of the bed to leave the time to heat to diffuse inside the bed). Thus under "monolayer" conditions, the heat treatment is preferably carried out at about 900 ° C. for a predetermined duration of between 3 and 20 minutes, preferably greater than or equal to 5 minutes and less than or equal to 15 minutes, more particularly greater than or equal to 7 minutes and less than or equal to 13 minutes, with obtaining cooked tablets. In "monolayer" condition, each reduction in the heat treatment temperature of 50 ° C leads to double the heat treatment time.

When the heat treatment is carried out in "multilayer" condition, that is to say that the tablets are in the form of a static bed of shelves of a certain thickness, it is understood that the heat treatment time must be increased to allow time for the heat to penetrate the heart of the tablet bed. As an indication, for a bed thickness of 100 mm, the heat treatment is preferably carried out at about 900 ° C. for a predetermined period of between 6 and 40 minutes, preferably greater than or equal to 10 minutes and less than or equal to 30 minutes, more particularly greater than or equal to 14 minutes and less than or equal to 26 minutes.

For example, a heat treatment for a period of time of 10 to 20 minutes at 900 ° C is sufficient for a layer of tablets up to 100 to 150 mm thick in the oven. Typically it is necessary to double the heat treatment time for a 50 ° C drop in temperature.

The bright calco-magnesium compound is advantageously a calco-magnesian compound with soft or medium cooking, preferably soft cooking.

In a very particular embodiment of the present invention, wherein the green tablets contain an iron-based compound which is an iron oxide compound, the method further comprises a heat treatment of said collected raw tablets, a temperature between 900 ° C and 1200 ° C, preferably between 1050 ° C and 1200 ° C, in particular around 1100 ° C, for a predetermined time with formation and obtaining cooked tablets in which the compound based on iron is converted, at least partially, to calcium ferrites.

The raw tablets are therefore brought into a high temperature oven where they undergo a heat treatment of these tablets at a temperature of less than or equal to 1200 ° C. They are then cooled and collected in the form of baked tablets to, among other things, promote the formation of calcium ferrites, which are sought after in iron and steel applications, and improve their resistance to aging and their resistance to falling.

The heat treatment time is related to the temperature of the heat treatment (the time is shorter as the temperature is high) and the thickness of the bed of tablets (the time increases with the thickness of the bed to leave the time to heat to diffuse inside the bed). Thus under "monolayer" conditions, the heat treatment is preferably carried out at about 1100 ° C. for a predetermined duration of between 3 and 20 minutes, preferably greater than or equal to 5 minutes and less than or equal to 15 minutes, more particularly greater than or equal to 7 minutes and less than or equal to 13 minutes, to obtain cooked tablets, in which said active iron oxide is converted into calcium ferrite. In "monolayer" condition, each reduction in the heat treatment temperature of 50 ° C leads to double the heat treatment time.

When the heat treatment is carried out in "multilayer" condition, that is to say that the tablets are in the form of a static bed of shelves of a certain thickness, it is understood that the heat treatment time must be increased to allow time for the heat to penetrate the heart of the tablet bed. As an indication, for a bed thickness of 100 mm, the heat treatment is preferably carried out at around 1100 ° C. for a predetermined period of between 6 and 40 minutes, preferably greater than or equal to 10 minutes and less than or equal to 30 minutes, more particularly greater than or equal to 14 minutes and less than or equal to 26 minutes.

To carry out these heat treatments, a horizontal oven such as for example a tunnel oven, a passage oven, a trolley furnace, a roller kiln or even a mesh belt furnace can be used. Alternatively, any other conventional furnace type, but not leading to the alteration of the integrity of compacts, for example due to too much attrition, can be used. Cooling can either be carried out conventionally in the downstream part of the furnace or outside the furnace, for example in a countercurrent vertical cooler for the cooling air or in a fluidized bed cooler. cooling air in case of quenching.

In a particular embodiment, the cooling after the heat treatment is carried out rapidly in less than 15 min, preferably in less than 10 min, in a fluidized bed by cooling air.

In a preferred form according to the present invention, the process comprises, before said feeding of a homogeneous powdery mixture,

a) feeding a mixer with said at least one bright calco-magnesium compound and

In a variant of the invention, the homogeneous mixture based on calco-magnesium compound comprises at least 10% by weight of crushed quicklime particles, preferably at least 20% by weight, more particularly at least 30% by weight and at most 100% by weight relative to the total weight of said mixture.

The "raw" tablets are advantageously based on quick lime (possibly dolomitic) in the form of particles rejected on screening during the production of pebbles and quicklime in the form of crushed particles.

They are also characterized by a calcium and magnesium mass content of at least 40%, preferably at least 60%, preferably at least 70% and at most 100%, preferentially 95% expressed as CaO equivalents. and MgO. Chemical analysis is done by FX.

The determination of the% by weight of CaO + MgO and Fe ₂ O ₃ equivalents is carried out by X-ray fluorescence spectrometry (RFX) as described in the EN 15309 standard. Chemical, semi-quantitative, RFX analysis for to determine the relative mass concentration of the elements whose atomic mass is between 16 (oxygen) and 228 (uranium) is carried out at the beginning of the samples milled at 80μιτι and shaped in the form of pellet. The samples are introduced into a PANalytical / MagiX PRO PW2540 apparatus, operating in wavelength dispersion. The measurement is carried out with a power of 50kV and 80 mA, with a Duplex detector.

The results of the analysis give the content of calcium, magnesium and iron and these measurements are reported respectively by weight of equivalent CaO and MgO, and by weight of equivalent Fe ₂ 0 ₃

They preferentially contain 0.05 to 0.50% of lubricant, for example stearate such as calcium or magnesium stearate, preferably 0.10 to 0.20% by weight.

They are in the form of tablets (typical soap, balls, platelets ... known to those skilled in the art and issued from tangential roller presses) and have a size of at least 10 mm, preferably from minus 15mm and at most 50mm, preferably at most 40mm, preferably at most 30mm, an sense of their passage through a square mesh screen.

The green tablets of the composition have a good mechanical resistance characterized by a Shatter Test Index ("STI", ie mass percentage of fines less than 10 mm after 4 drops of 2 m) of less than 8%, preferably less than 6%, 5% , 4%.

They are also characterized by a BET specific surface area greater than or equal to 1 m ² / g, preferably 1.2 m ² / g, preferably 1.4 m ² / g.

The porosity of the green tablets is greater than or equal to 30%, preferably greater than or equal to 32%, more preferably greater than or equal to 34%.

Raw tablets have an apparent density of between

2.0 and 3.0, preferably between 2.2 and 2.8.

Raw tablets have good resistance to aging. Thus, when they are exposed to a humic atmosphere containing, for example, 5 to 15 g / m ³ of absolute humidity, the degradation of their mechanical properties (STI) only occurs above 1.5% mass, preferably 2% of weight gain, and even more preferably 2.5% of weight gain, following the hydration reaction of CaO quicklime Ca (OH) ₂ . The fired tablets of the present invention have a Shatter Test Index ("STI", ie mass percentage of fines less than 10mm after 4 falls of 2m) of less than 6%, preferably less than 4%, 3%, 2%. Indeed, in certain embodiments of the process according to the present invention, the cooked briquettes have a test Shatter index of less than 8%, sometimes less than 6%, less than 4%, less than 3%, or even around 2%. %.

They are also characterized by a BET specific surface area greater than or equal to 0.4 m ² / g, preferably greater than or equal to 0.6 m ² / g, more preferably greater than or equal to 0.8 m ² / g

The porosity is greater than or equal to 30%, preferably greater than or equal to 32%, more preferably greater than or equal to 34%.

Cooked tablets have a bulk density of 2.0 to 3.0, preferably 2.2 to 2.8.

Cooked tablets have good resistance to aging. Thus, when they are exposed to a humic atmosphere containing, for example, 5 to 15 g / m ³ of absolute humidity, the degradation of their mechanical properties (STI) occurs only above 4% of mass preferably 4.5% of weight gain, and more preferably 5% of weight gain, following the hydration reaction of CaO quicklime Ca (OH) ₂ .

Examples. -

Example 1.- Tablets of quicklime, derived from fines of quicklime grinding

Crushed quick lime fines were prepared from a soft-baked rock lime produced in a parallel-flow regenerative furnace. The grinding is carried out in a hammer mill equipped with a 2 mm screen and a recirculation loop for sizes greater than 2 mm. These grinding quicklime fines contain 71% of particles greater than 90 μιτι, 37% of particles greater than 500 μιτι, 21% of particles greater than 1 mm and 1% of particles between 2 and 3 mm. The t ₆₀ value of the water reactivity test is 0.9 min. The BET specific surface area (measured by nitrogen adsorption manometry after degassing under vacuum at 190 ° C. for at least two hours and calculated according to the BET mutlipoints method as described in the ISO 9277: 2010E standard) is 1.7. m ² / g- These crushed quicklime fines contain 95.7% CaO and 0.8% MgO by weight.

A Gericke GCM450 powder mixer with a capacity of 10 dm ^{3 is used} , equipped with standard 7 cm radius blades used in rotation at 350 rpm (ie 2.6 m / s). This mixer is used in continuous mode to prepare a mixture of:

99.9% by weight of these crisp lime fines,

0.1% by weight of calcium stearate powder.

The total flow rate of the powder is 300 kg / h and the residence time is 3.5 s. The mixture obtained is very homogeneous.

A rotary press equipped with a turret with a diameter of 1700 mm is used. On the peripheral part of the turret are distributed 67 frustoconical cavities with a diameter of 26 mm with, on either side, 67 lower punches and 67 upper punches. This press is equipped with a feed system for the mixture to be compacted (feed zone), lower and upper compression rollers (compression zone) and extraction rollers (extraction and collection zone).

Starting from 10 tons of the mixture, the rotary press is fed so that the filling time of the cavities is 0.6 s and it is compacted at a speed of 13 revolutions per minute (ie a linear velocity of 1.14 m / s) at a surface pressure of 410 MPa (220 kN) with a punch approach speed of 100 mm / s and a holding time of 100 ms.

9.7 tons of tablets are obtained with an average weight of 27.7 g and an average density of 2.05. These tablets have a diameter of 26.6 mm and a height of 24.3. These tablets develop a BET surface area of 1.6 m ² / g and have a total pore volume of mercury (determined by mercury intrusion porosimetry according to Part 1 of ISO 15901-1: 2005E which consists of dividing the difference between skeletal density, measured at 30000 psia, and apparent density, measured at 0.51 psia, by skeletal density) of 37%.

The water reactivity of the tablets is determined by adding 150 g of these tablets, previously crushed in the form of fines of size between 0 and 1 mm, to 600 cm ³ of water at 20 ° C. The value t ₆₀ is 1.1 min. We made a Shatter Test starting from 10 kg of these tablets by successively realizing 4 falls of 2 m. We weigh the amount of fines less than 10 mm generated at the end of these 4 falls. A Shatter Test Index of 2.7% is obtained.

Example 2.- Quicklime tablets, derived from a mixture of fines of quick-grinding quick-grinding lime and fines of quicklime of screening

The grinding quicklime fines are those of Example 1. The quick lime screen fines were recovered at the end of the screening through a screen at 3 mm of the all-comer at the outlet of a furnace. rotary equipped with a preheater. These slices of quicklime contain in aggregate 74% of particles greater than 90 μιτι, 60% of particles greater than 500 μιτι, 47% of particles greater than 1 mm and 18% of particles between 2 and 3 mm. The value t ₆₀ of the water reactivity test is 4 min. The BET surface area is 1.2 m ² / g These fine bright screening lime contained 97.1% CaO and 0.7% MgO by weight.

The mixture, produced according to the method of Example 1, consists of:

0.1% by weight of calcium stearate powder,

99.9% by weight of a 50:50 mixture by weight of these quick-grinding lime fines and these quick-lime slicing fines.

The tablets are produced starting from this mixture according to the method of Example 1. 9.5 tons of tablets having an average weight of 27.4 g and an average density of 2.05 are obtained. These tablets have a diameter of 26.6 mm and a height of 24.1. These tablets develop a BET specific surface area of 1.4 m ² / g and have a total pore volume of mercury of 36%.

The water reactivity of the tablets is determined by adding 150 g of these tablets, previously crushed in the form of fines of size between 0 and 1 mm, to 600 cm ³ of water at 20 ° C. The value t ₆₀ is 1.8 min.

We made a Shatter Test starting from 10 kg of these tablets by successively realizing 4 falls of 2 m. We weigh the amount of fines less than 10 mm generated at the end of these 4 falls. A Shatter Test Index of 3.2% is obtained. Example 3.- Dolomitic quicklime tablets, derived from a mixture of quick-grinding quick-cooking fines and cooked dolomite fines

The grinding quicklime fines are those of Example 1. The cooked grinding dolomite fines were prepared from a cooked rock dolomite produced in a parallel flow regenerative furnace. The grinding was carried out in a hammer mill. These fired dolomite grinding fines contain in total 91% of particles greater than 90 μιτι, 44% of particles greater than 500 μιτι, 31% of particles greater than 1 mm and 17% of particles greater than 2 mm and 8% of particles. between 3 and 5 mm. The value t ₇₀ of the water reactivity test is 3.1 min. The BET specific surface area is 2.8 m ² / g. These burnt dolomite fines contain 58.5% CaO and 38.4% MgO by weight.

The mixture, produced according to the method of Example 1, consists of: 0.1% by weight of calcium stearate powder,

- 99.9% by weight of a mixture 70:30 by weight of these quick lime grinding fines and fired dolomite fines.

The tablets are produced starting from this mixture according to the method of Example 1. 9.6 tons of tablets having an average weight of 27.8 g and an average density of 2.04 are obtained. These tablets have a diameter of 26.6 mm and a height of 24.5. These tablets develop a BET specific surface area of 2.2 m ² / g and have a total pore volume of mercury of 36%.

We made a Shatter Test starting from 10 kg of these tablets by successively realizing 4 falls of 2 m. We weigh the amount of fines less than 10 mm generated at the end of these 4 falls. A Shatter Test Index of 3.9% is obtained.

Example 4.- Quicklime tablets, derived from a mixture of quick-grinding quicklime fines and iron oxide fines

The grinding quicklime fines are those of Example 1. The iron oxide fines originate from the grinding of an Fe ₂ O ₃ type iron ore passing through a sieve at 150 μιτι and characterized in particle size. Coulter laser (based on the diffraction of light and according to the theories of Fraunhofer and Mie) by a d ₁₀ of 0.5 μιτι, a d ₅₀ of 12.3 μιτι and a d ₉₀ of 35.7 μιτι. These iron oxide fines contain 64.6% Fe.

99.9% by weight of a 90:10 mixture by weight of these grinding quicklime fines and these iron oxide fines.

Tablets are produced from this mixture according to the method of Example 1. 9.7 tons of tablets are obtained with an average weight of 29.3 g and an average density of 2.15. These tablets have a diameter of 26.6 mm and a height of 24.5. These tablets develop a BET surface area of 1.7 m ² / g and have a total pore volume of mercury of 36%.

The water reactivity of the tablets is determined by adding 166.7 g of these tablets, previously crushed in the form of fines of size between 0 and 1 mm, to 600 cm ³ of water at 20 ° C. The 166.7 g of tablets correspond to 150 g of quicklime. The value t ₆₀ is 1.2 min.

We made a Shatter Test starting from 10 kg of these tablets by successively realizing 4 falls of 2 m. We weigh the amount of fines less than 10 mm generated at the end of these 4 falls. A Shatter Test Index of 3.6% is obtained.

The volume fraction of the iron oxide at the surface of the iron oxide particles in the tablet composition is 85%. Iron oxide therefore contains 85% of active iron.

The tablets are also characterized by performing a heat treatment of 10 min at 1100 ° C (charging / hot turning) on 3 of these tablets after which a powder of particle size less than 80 μιτι is prepared. This is characterized by X-ray diffraction and phase quantization is performed by ietveld analysis. 83% of the total iron is in the form of CaFe ₂ 0 ₄ or Ca ₂ Fe ₂ 0 ₅ calcium ferrites, and 17% is still in the Fe ₂ 0 _{3 form} .

Example 5.- Quicklime tablets, derived from crushed quick lime fines, heat-treated

Starting from 1 ton of tablets of Example 1, arranged in boxes so that the thickness of the tablet bed is 100 mm, a heat treatment of 20 minutes at 900 ° C. is carried out, with ramps of rise and fall in temperature of 40 ° C per minute.

Tablets having an average weight of 27.5 g and an average density of 2.04 are obtained. These tablets have a diameter of 26.6 mm and a height of 24.3. These tablets develop a BET surface area of 1.3 m ² / g and have a total pore volume of mercury of 38%.

The water reactivity of the tablets is determined by adding 150 g of these tablets, previously crushed in the form of fines of size between 0 and 1 mm, to 600 cm ³ of water at 20 ° C. The value t ₆₀ is 1.0 min.

We made a Shatter Test starting from 10 kg of these tablets by successively realizing 4 falls of 2 m. We weigh the amount of fines less than 10 mm generated at the end of these 4 falls. A Shatter Test Index of 1.8% is obtained.

Example 6.- Quicklime tablets, derived from a mixture of quick-grinding quick-grinding fines and iron oxide fines, heat-treated

Starting from 1 ton of tablets of Example 4, arranged in boxes so that the bed thickness of tablets is 100 mm, a heat treatment of 20 min at 1100 ° C. is carried out, with ramps of rise and fall in temperature of 50 ° C per minute.

Tablets having an average weight of 29.0 g and an average density of 2.13 are obtained. These tablets have a diameter of 26.6 mm and a height of 24.5. These tablets develop a BET specific surface area of 1.1 m ² / g and have a total pore volume of mercury of 38%.

We made a Shatter Test starting from 10 kg of these tablets by successively realizing 4 falls of 2 m. We weigh the amount of fines less than 10 mm generated at the end of these 4 falls. We obtain a Shatter Test Index of 1.1%.

The volume fraction of the iron oxide at the surface of the iron oxide particles in the tablet composition is 87%. The iron compound thus contains 87% of active iron.

Starting from 30 of these heat-treated tablets, a powder having a particle size of less than 80 μιτι is prepared. This is characterized by X-ray diffraction and phase quantization is performed by ietveld analysis. 82% of the total iron is in the form of CaFe ₂ 0 ₄ calcium ferrites or

Ca ₂ Fe ₂ O ₅ , and 18% is still in the form Fe ₂ O ₃ .

The water reactivity of the tablets is determined by adding 178.2 g of these tablets, previously crushed in the form of fines of size included between 0 and 1 mm, at 600 cm ³ of water at 20 ° C. The 178.2 g of tablets correspond to 150 g of quicklime (that is to say not in the form of calcium ferrites). The value t ₆₀ is 1.5 min.

It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made without departing from the scope of the appended claims.

Claims

"CLAIMS"

1. Composition in tablet form comprising at least one bright calco-magnesium compound, said composition having at least 40% by weight of CaO + MgO relative to the weight of said composition, characterized in that said calco-magnesium compound comprises quicklime in the form of crushed particles at a concentration of at least 10% by weight and at most 100% by weight relative to the total weight of said composition, said tablet composition having a Shatter index test less than 10%.

2. Composition in tablet form according to claim 1, wherein said quicklime in the form of crushed particles is quicklime soft cooking or medium cooking, preferably soft cooking.

3. A composition according to claim 1 or claim 2, wherein said tablets have an uppermost dimension of at least 10 mm, preferably at least 15 mm, more preferably at least 20 mm.

A tablet composition according to any one of the preceding claims, wherein said tablets have a maximum dimension of at most 50 mm, preferably at most 40 mm, more preferably at most 30 mm.

Tablet composition according to any one of claims 1 to 4, wherein said tablets are green tablets and have a BET specific surface area greater than or equal to 1 m ² / g, preferably greater than or equal to 1, 2 m ² / g, more preferably greater than or equal to 1.4 m ² / g.

6. A composition based on bright calco-magnesium compounds in the form of tablets according to any one of claims 1 to 4, wherein said tablets are cooked tablets and have a BET specific surface area greater than or equal to 0.4 m ² / g, preferably greater than or equal to 0.6 m ² / g, more preferably greater than or equal to 0.8 m ² / g.

7. tablet composition according to any one of claims 1 to 6, wherein said tablets have a porosity greater than or equal to 30%, preferably greater than or equal to 32%, more preferably greater than or equal to 34%.

A composition based on bright calco-magnesium compounds in tablet form according to any one of claims 1 to 7, wherein said quicklime in the form of crushed particles is present at a concentration of at least 15%, preferably at least 20%, and more preferably at least 30%, in particular at least 40% by weight relative to the total weight of said composition.

9. Composition in tablet form according to any one of claims 1 to 8, wherein said quicklime in the form of crushed particles is present at a concentration of at most 90% by weight, preferably at most 80%, preferably at most 70%, more preferably at most 50% by weight, relative to the total weight of said composition.

10. Composition in tablet form according to any one of claims 1 to 9, further comprising a binder or a lubricant, more particularly selected from the group consisting of binders of mineral origin such as cements, clays, silicates binders of vegetable or animal origin, such as celluloses, starches, gums, alginates, pectin, glues, binders of synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate, and mixtures thereof, preferably calcium stearate and / or magnesium stearate, at a content of between 0.05 and 0.50% by weight, preferably between 0.05 and 0.30% by weight, more preferably between 0.10 and 0.20% by weight per ratio to the total weight of ladi composition.

The tablet composition according to any one of claims 1 to 10, wherein said tablets have an average tablet weight of at least 5 g, preferably at least 10 g, more preferably at least 10 g. minus 12 g, and in particular at least 15 g.

12. Composition in tablet form according to any one of claims 1 to 11, wherein said tablets have an average weight per tablet less than or equal to 100 g, preferably less than or equal to 60 g, more preferably less than or equal to at 40 g and in particular less than or equal to 30 g.

Tablet composition according to any one of claims 1 to 12, wherein said tablets have an apparent density of between 2 g / cm ³ and 3.0 g / cm ³ , preferably between 2.2 g / cm 3. ³ and 2.8 g / cm ³ .

14. Composition in tablet form according to any one of the preceding claims, characterized in that said bright calco-magnesium compound further comprises fine particles of calco-magnesian compound selected from fine particles rejected in the screening of the production of pebbles of said bright calco-magnesium compound, calco-magnesian filter dust and their mixture, at a concentration of at least 10% by weight and at most 90% by weight relative to the total weight of said composition.

Tablet composition according to any one of the preceding claims, characterized in that said composition further comprises iron-based compound (s) at a concentration of at least 3% by weight and of at most 60%, for example not more than 40% by weight expressed as Fe ₂ 0 ₃ equivalent relative to the total weight of said composition.

16. Composition in tablet form according to any one of claims 1 to 15, packaged in types of containers having a volume of content greater than 1 m ³ such as large bags, containers, silos and the like, preferably sealed.

Tablet composition according to any one of claims 1 to 16, wherein said tablets have a slightly asymmetrical three-dimensional shape, preferably substantially frustoconical, in which the difference between the surface of the upper part and that of the part of the tablet is greater than or equal to 0.5%, preferably greater than or equal to 1%, and less than or equal to 10%, preferably less than or equal to 5%, in particular less than or equal to 3%, in particular around 2%.

The tablet composition according to any of claims 1 to 5 and 7 to 17, wherein the tablets are green tablets having a test Shatter number of less than 8%, preferably less than 6%, and still more preferably less than 5%, in particular less than 4%.

Tablet composition according to any one of claims 1 to 4 and 6 to 17, wherein the tablets are cooked tablets having a test Shatter number of less than 6%, preferably less than 4%, and still more preferably less than 3%, in particular less than 2%.

20. A method of manufacturing a composition in the form of tablets, comprising the following steps:

a) supplying a homogeneous powdery mixture comprising at least 40% by weight of CaO + MgO equivalent relative to the weight of the said homogeneous powdery mixture, and comprising at least one bright calco-magnesium compound, the said at least one calco-magnesium compound vivid mixture comprising quicklime in the form of crushed particles at a concentration of at least 10% by weight and at most 100% by weight relative to the weight of the said homogeneous powdery mixture, b) feeding the homogeneous powdery mixture into a space of confinement between two punches having a section between 1 and

40 cm ² , advantageously between 1 and 20 cm ² , preferably between 1 and 10 cm ² , in particular between 2 and 10 cm ² ,

The method of manufacturing a tablet composition according to claim 20, wherein said compressing step is carried out in the presence of a binder or a lubricant, preferably in the form of an aqueous powder or suspension. concentrated, more particularly selected from the group of binders of mineral origin such as cements, clays, silicates, binders of plant or animal origin, such as celluloses, starches, gums, alginates, pectin glues, binders of synthetic origin, such as polymers, waxes, liquid lubricants such as mineral oils or silicones, solid lubricants such as talc, graphite, paraffins, stearates, in particular calcium stearate, magnesium stearate, and mixtures thereof, preferably calcium stearate and / or magnesium stearate, at a content of between 0.1 and 1% by weight, preferably between 0.15 and 0.6% by weight, more preferably between 0.2 and 0.5% by weight relative to the total weight of said mixture.

22. A method of manufacturing a tablet composition according to claim 20 or claim 21 further comprising a heat treatment of said collected raw tablets at a temperature between 700 ° C and 1200 ° C, preferably in the vicinity. 900 ° C.

23. A method of manufacturing a composition in tablet form according to any one of claims 20 to 22, comprising a step of heat treatment of said tablets for a predetermined period of between 5 and 20 minutes, preferably greater than or equal to 7. minutes and less than or equal to 15 minutes, with training and obtaining cooked tablets.

24. A method of manufacturing a tablet composition according to claim 20 or claim 21, wherein said quicklime in the form of crushed particles is quicklime cooking soft or medium, preferably soft cooking.

25. A method of manufacturing a composition in tablet form according to any one of claims 20 to 24, wherein said quicklime in the form of ground particles having a high water-reactivity characterized by a lower value t ₆₀ at 10 min, preferably less than 8 min, preferentially less than 6 min and more preferably less than 4 min.

26. A method of manufacturing a composition in tablet form according to any one of claims 20 to 25, wherein said quicklime in the form of crushed particles is obtained by grinding from rock lime whose size is greater. at 3 mm, preferably greater than 5 mm, preferably greater than 7 mm, and even more preferably greater than 10 mm, and less than 120 mm, preferably less than 100 mm, preferably less than 80 mm, and still more preferably less than 60 mm.

A method of manufacturing a tablet composition according to any one of claims 20 to 26, wherein said at least one bright calco-magnesium compound comprises quicklime in the form of crushed particles at a concentration of at least 15% by weight, in particular at least 20% by weight, more preferably at least 30% by weight, particularly preferably at least 40% by weight relative to the total weight of said mixture homogeneous powder.

A method of making a tablet composition according to any one of claims 20 to 27, wherein said at least one bright calco-magnesium compound comprises quicklime in the form of crushed particles at a concentration of at most 90% by weight, in particular at most 80% by weight, more preferably at most 70% by weight, more preferably at most 50% by weight, relative to the total weight of said homogeneous powdery mixture.

29. A method of manufacturing a tablet composition according to any one of claims 20 to 28, wherein said bright calco-magnesium compound further comprises fine particles of calco-magnesium compound selected from fine particles rejected at screening the production of rollers of said bright calco-magnesium compound, calco-magnesium filter dust and mixing thereof at a concentration of at least 10% by weight and at most 90% by weight relative to the total weight of said composition .

A method of making a tablet composition according to any one of claims 20 to 29, wherein said homogeneous powdery mixture further comprises one or more iron-based compounds, at a concentration of at least 3% by weight and at most 60% by weight expressed as Fe ₂ 0 ₃ equivalent relative to the weight of said mixture.

A method of manufacturing a tablet composition according to claim 30, wherein said tablets are green tablets and wherein at least one of the one or more iron-based compounds is an iron oxide, preferably a active iron oxide present at a concentration of at least 3% by weight and at most 60% by weight expressed as Fe ₂ O ₃ equivalent relative to the weight of said mixture.

A method of manufacturing a tablet composition according to claim 30 and claim 31, further comprising a heat treatment of said collected raw tablets, at a temperature between 700 ° C and 1200 ° C, preferably in the vicinity. of 1100 ° C.

33. A method of manufacturing a composition in tablet form according to any one of claims 30 to 32, for a predetermined period of between 5 and 20 minutes, preferably greater than or equal to 7 minutes and less than or equal to 15 minutes. , more particularly greater than or equal to 8 minutes and less than or equal to 13 minutes with access to tablets in which the iron oxide compound is converted to calcium ferrites.

34. The method according to any one of claims 20 to 30, further comprising, before said feeding of a homogeneous powdery mixture, a) feeding a mixer with said at least one bright calco-magnesium compound and

A process for producing a composite material comprising a plurality of successive layers to form a multilayered structure wherein at least one layer is formed with said tablet product of the composition by the method of any one of claims 20 to 20. And further comprising a further step of compacting said at least one layer of said compact product and another compact layer prior to said ejecting step.

36. The process according to any one of claims 20 to 35, further comprising pretreating the modified atmosphere briquettes containing at least 2% by volume of CO ₂ and at most 30% by volume of CO ₂ , preferably at most 25% by weight. % by volume of C0 ₂ , preferably at most 20% by volume of C0 ₂ , more preferably at most 15% by volume of C0 ₂ , more preferably still at most 10% by volume of C0 ₂ with respect to said modified atmosphere.

37. Use of the composition according to claims 1 to 19 or from the process according to claims 20 to 36, in the iron and steel industry, in particular in the manufacture of steel in elementary oxygen converters, in electric arc furnaces, or in secondary metallurgy, in flue gas treatment, in water treatment, in sludge and wastewater treatment, in agriculture, in the building industry and in public works, as example for soil stabilization.