EP3652129A1

EP3652129A1 - Method for obtaining a compacted material and compacted material obtained thereby

Info

Publication number: EP3652129A1
Application number: EP18749043.8A
Authority: EP
Inventors: Claire MICHUD; Antoine Coulon; Aurélien BECK; Jacques Poirier; Emmanuel DE BILBAO
Original assignee: Imertech SAS
Current assignee: Imertech SAS
Priority date: 2017-07-13
Filing date: 2018-07-12
Publication date: 2020-05-20
Also published as: FR3068906B1; JP7190488B2; FR3068906A1; JP2020527494A; KR20200036847A; CA3069615A1; KR102570871B1; WO2019012234A1; US11840488B2; US20200181032A1

Abstract

The invention relates to a method for obtaining a compacted material according to which, a) a set of particles of raw materials is mixed with 1% to 50% by weight of a hydraulic binder to form a dry composition, the percentage being relative to the total weight of the dry composition, the particle size distribution of the raw material particles being characterised by a first reference diameter d90 of 50 millimetres or less and a second reference diameter d10 of 0.08 micrometres or more, b) the dry composition formed in step a) is mixed with 1% to 35% by weight of water so as to form a mixed composition, the percentage being relative to the total weight of the dry composition, c) the mixed composition from step b) is vibrated at a frequency of 20 to 80 Hertz and at an amplitude of at least 0.3 millimetres, while a compressive stress is applied to the mixed composition, the value of the applied compressive stress being at least 2 MegaPascal. The invention also relates to a method for obtaining a multilayer compacted material and to the materials obtained according to said methods.

Description

Process for obtaining a compacted material and compacted material obtained from this process

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates generally to the field of compacted materials.

It relates more particularly to a process for obtaining a compacted material.

It also relates to the compacted material obtained from this process.

BACKGROUND

Many industrial processes use raw materials in the form of natural blocks whose size depends on the industrial process for which they are intended and / or the source or origin of the raw material. In general, the blocks have a characteristic dimension of a few centimeters, for example between 5 centimeters and 20 centimeters.

These blocks are intended to be handled, especially during their extraction, handling, transportation, weighing, conveying, etc., before being used in the industrial process to which they are intended. All of these manipulations generate shocks and friction and leads to the formation of dust, or fine particles of raw material, usually called "fines" that are not desirable in industrial processes using said blocks. It is then known to recycle these fine particles of raw material by manufacturing compacted materials (also called agglomerates or briquettes, unrelated to the actual form of these compacted materials) used in industrial processes usually using natural blocks.

In particular, a method of manufacturing a compacted material used on a roller compression machine is known from a mixture comprising fine particles of raw materials and a hydraulic binder of Portland cement type or molasses. The compacted material obtained from this process, however, generates volatile organic compounds when it is used in industrial processes at high temperature, especially greater than 500 ° C. In addition, this compacted material tends to crumble and then generates so-called "secondary" fine particles. Finally, Rotating machines are worn out prematurely when the fine raw material particles used to form the compacted material are too hard, which is the case of bauxite particles for example.

Also known is a method of manufacturing a "block" type material, implemented on block presses, from a mixture comprising fine particles of raw material and a hydraulic binder type Portiand cement. According to this method, the mixture is placed under a low compressive stress, of the order of 0.01 MegaPascal. The block obtained from this process also generates unwanted "secondary" fine particles. In addition, the block obtained is not suitable for use in high temperature industrial processes.

OBJECT OF THE INVENTION

In order to overcome the above-mentioned drawbacks of the state of the art, the present invention proposes a process for obtaining a compacted material such that the obtained compacted material has improved mechanical compressive strength, generates fewer secondary fine particles, and may be exposed to temperatures between 500 ° C and 1700 ° C.

More particularly, there is provided according to the invention a process for obtaining a compacted material according to which,

a) a dry composition is formed by mixing, on the one hand, a set of particles of raw materials whose particle size distribution is characterized by a first reference diameter d90 of less than or equal to 50 millimeters and a second reference diameter of greater than or equal to equal to 0.08 micrometer with, on the other hand, from 1% to 50% of a hydraulic binder, in mass relative to the total mass of the dry composition,

b) said dry composition formed in step a) is stripped with 1% to 35% water, by weight relative to the total mass of the dry composition, so as to form a batch composition,

c) first vibrating the mixture composition obtained in step b) at a frequency between 20 Hertz and 80 Hertz and at an amplitude greater than or equal to 0.3 millimeter, then, together with the implementation vibration, a compressive stress is applied to said tempered composition,

the value of said applied compressive stress being greater than or equal to 2 MegaPascal. According to the method of the invention, it is thus provided in step c) to couple the vibration of the composition to the application of a high compression stress on this composition to form a compacted material whose mechanical resistance to compression is improved and the rate of erosion is decreased. Decreasing the rate of crumbling amounts to decreasing the generation of fine secondary particles or, which is still equivalent, to increase the abrasion resistance of said compacted material.

According to the method of the invention, it is also possible, in step a), to adjust the size of the particles of raw material of the set of particles as well as the nature of the hydraulic binder used, so that It is possible to adjust the mechanical performance of the compacted material obtained according to the industrial process for which it is intended. The method notably allows, prior to step a), additional sieving and / or crushing operations in order to adjust the size of the particles used and / or to modify the particle size distribution of said particles.

Unexpectedly, the combination of the particle size characteristics of the raw material particles and the nature of the hydraulic binder, in addition to the vibration and the high compression applied to the composition, makes it possible at the same time to improve the mechanical resistance to compression. of the compacted material and to reduce the generation of fine secondary particles, both when handling the compacted material at ambient temperature, and when using the compacted material in industrial processes at high temperature (greater than or equal to 500 ° C) which involve a phase transformation and in particular a melting step of said compacted material.

The method according to the invention also leads to the production of a compacted material which is in the form of a single layer or of several layers of uniform raw materials. This compacted material has a mechanical resistance to early compression, that is to say that it is resistant to compression only a few hours after its formation, especially 24 hours after its formation.

In addition, the process according to the invention generates a compacted material which does not emit volatile organic compounds so that it is possible to use said compacted material in industrial processes at high temperature, by example between 500 ° C and 1700 ° C.

Non-limiting and advantageous features of the process according to the invention, taken individually or in any technically possible combination, are as follows:

a first layer of material is formed with the mixed composition obtained at the end of step b),

in a step p1) prior to step c), at least one other composition is formed by repeating steps a) and b),

in a step p2), placing said other tempered composition obtained in step p1) above said first layer formed at the end of step b), so as to form a stack of at least two layers of wasted compositions, and

in step c), said stack formed in step p2) is then vibrated, at said frequency between 20 Hertz and 80 Hertz, and at said amplitude greater than or equal to 0.3 millimeters, and then, together with said vibrating, applying said compressive stress to said stack;

in a step n1), a core of raw materials is provided, said core having a mechanical strength greater than or equal to 0.1 MegaPascal (MPa),

in a step n2) carried out prior to step c), said nucleus is completely enclosed in at least one of the batched compositions obtained in step b) and / or in step p1), and

in step c), vibration is set at said frequency between

20 Hertz and 80 Hertz and at said amplitude greater than or equal to 0.3 millimeters, said assembly comprising said at least one tempered composition and said enclosed core, then, together with said vibrating, said compressive stress is applied to said assembly;

in a step n2 ') carried out prior to step c), said nucleus is completely enclosed in said batch composition obtained in step b) and / or in at least one of said other batch compositions obtained in step p1), and, in step c), said vibration is set at said frequency between 20 Hertz and 80 Hertz and at said amplitude greater than or equal to 0.3 millimeters, said assembly comprising said at least one tempered composition and said enclosed core, then together with said vibrating, said compressive stress is applied to said set;

said core is a compacted material formed by compaction of another set of particles of raw materials;

said core is obtained according to the process of the invention.

The invention also relates to a method for obtaining a multilayer compacted material according to which,

a first layer is produced according to the following steps:

c) the batch composition obtained in step b) is vibrated at a frequency of between 20 Hertz and 80 Hertz and at an amplitude greater than or equal to 0.3 millimeters, and then, together with the setting into vibration, is applied a compressive stress to said tempered composition,

and, for each subsequent layer, another tempered composition is produced by repeating steps a) and b), placing said other composition on the previous layer, the whole formed by the preceding layer is vibrated, and another composition wasted, and a compressive stress is applied to said set,

the value of the compression stress applied being greater than or equal to 2 MegaPascal, at least for producing the last layer of said multilayer compacted material.

Thus, this other method makes it possible to produce a multilayer compacted material in the form of a stack of layers superimposed on each other. others whose layers of raw materials are agglomerated with each other.

Other nonlimiting and advantageous features of the methods according to the invention, taken individually or in any technically possible combination, are as follows:

- For each layer, it is expected that the vibration implemented in conjunction with the application of the compression stress is de-harmonized;

for each layer, the vibration has an amplitude of between 0.3 millimeters and 5 millimeters, depending on the direction of compression;

- There is further provided a step subsequent to step c) of obtaining the compacted material, during which said compacted material is placed for at least 24 hours in an oven at a predetermined temperature, and at a higher relative humidity. or equal to a threshold value of relative humidity;

for each layer, the particles of raw material of the set or of each set of particles are mineral particles, chosen from: red bauxite, white bauxite, alumina, limestone, lime, carbon, graphite carbon, carbon black, rockwool, glass wool, carbonates, metallurgical effluents, manganese powders or its derivatives, metal ores or mixtures of ores as they may occur during extraction or during manufacturing processes, including metal oxides or iron ores;

for at least one layer or for at least one set of particles of raw materials, the first reference diameter d90 associated with the particle size distribution of the set of particles of raw material is less than 20 millimeters and the second reference diameter d10 associated with said particle size distribution is greater than or equal to 0.1 micrometer;

for each layer, the hydraulic binder is chosen from: Portland cements, calcium aluminate cements, sulfo-aluminous cements, cements mixed with fly ash, cements mixed with blast furnace slags, cements mixed with pozzolans, or a mixture thereof;

for at least one layer or for at least one step a), the hydraulic binder comprises a calcium aluminate cement having a molar ratio C / A of between 0.1 and 3; - For at least one layer or for at least one step a), the hydraulic binder is composed of a set of hydraulic binder particles whose particle size distribution is characterized by a first reference diameter d90 less than or equal to 100 micrometers.

Finally, the invention proposes a compacted material comprising particles of raw material agglomerated with a hydraulic binder, obtained according to one of the methods that are the subject of the invention.

Advantageously, the material according to the invention has a compressive strength greater than or equal to 3 MegaPascal and an erosion rate of less than or equal to 15%.

In the case where the compacted material comprises at least two layers of raw materials agglomerated with each other, said layers of raw materials are inert to each other up to a predetermined threshold temperature.

In particular, in the multilayer compacted material comprising a stack of at least two superimposed layers, the raw material layers are inert to each other up to a predetermined threshold temperature.

In the multilayered compacted material comprising a core enclosed in at least one outer layer, the raw materials of the core are inert with respect to the raw materials of the at least one outer layer in which it is enclosed, up to a threshold temperature predetermined.

Advantageously, the multilayer compacted material can be used in industrial processes requiring the addition of at least two types of raw materials. Due to its multiple layers, the multilayer compacted material may in particular have a chemical composition close to that desired for the product at the output of the industrial process in which said multilayer compacted material is used. Thus, in addition to the advantages already mentioned for the monolayer compacted material, the multilayer compacted material makes it possible to improve the control of chemical reactions in industrial processes, which limits the production of substandard or off-standard products, while avoiding certain phenomena. classics when two raw materials are used, such as gluing the raw materials together. In addition, the multilayer compacted material optimizes the energy consumption of the industrial processes in which they are used, as well as increase productivity. The compacted multilayer material also allows in certain cases to reduce wear and tear on the facilities in which it is used.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

In the accompanying drawings:

FIG. 1 represents an example of a cumulative particle size distribution of two lots of red bauxite fine particles L1 and L2, the ordinate axis representing the cumulative percentage of fine particles of the batch under consideration having a diameter less than or equal to the size indicated on FIG. the abscissa axis, in mass relative to the total mass of the set of fine particles of this batch, and,

FIG. 2 represents an example of a particle size distribution of a batch of fine red bauxite particles called "ELMIN", of a batch of fine white bauxite particles called "ABP", of a batch of fine Cement cement particles; Fondu® and a batch of Secar® 51 fine cement particles, the y-axis representing the percentage of red bauxite fine particles having a diameter equal to the dimension indicated on the abscissa, in volume relative to the total volume of the set of fine particles in this batch.

The present invention relates to a process for obtaining a compacted material of raw materials for recycling the fine particles of raw materials for use in both industrial processes that require a supply of raw materials in the form of blocks, and in industrial processes which impose high temperatures on said compacted material, especially greater than or equal to 500 ° C.

More specifically, the method according to the invention comprises the following steps:

a) a dry composition is formed by mixing, on the one hand, a set of particles of raw materials whose particle size distribution is characterized by, that is to say defined by, a first reference diameter d90 less than or equal to 50 millimeters and a second reference diameter d10 greater than or equal to 0.08 micrometer with, on the other hand, from 1% to 50% of said hydraulic binder, in mass relative to the total mass of the dry composition, b) stripping said dry composition formed in step a) with 1% to 35% of water, by weight relative to the total mass of the dry composition so as to form a mixture composition,

the value of said applied compressive stress being greater than or equal to 2 MegaPascal (MPa).

The remainder of the description details more precisely each of the steps of the method.

Step a)

In step a), the set of raw material particles comprises particles of raw materials chosen from particles of inorganic or organic raw materials. Preferably, they will be chosen inorganic. They can be inorganic of natural origin, that is to say, raw materials called "mineral", or inorganic raw materials of synthetic origin.

In general, all the raw material particles which are compatible with the hydraulic binder, that is to say which do not react with the hydraulic binder, can be used in step a).

The set of particles of raw materials comprises, for example, the particles of raw materials chosen from the following list of raw materials: red bauxite, white bauxite, alumina, limestone, lime, carbon, especially graphite carbon. and carbon black, rock wool, glass wool, carbonates, or metallurgical effluents, especially slag-type metallurgical effluents.

The set of particles of raw materials may also comprise the particles of raw materials chosen from: powders of manganese or its derivatives, metal ores or mixtures of ores as they may be found during extraction or during manufacturing processes, including metal oxides or iron ores.

Preferably, the raw materials are selected from the following list: red bauxite, white bauxite, alumina, limestone, lime, and carbon black.

More preferably, the raw materials are chosen from the list following: red bauxite, white bauxite, alumina and limestone.

The set of raw material particles comprises one or more types of different raw materials, for example of different physicochemical nature. Thus, the set of raw material particles may as well comprise a single type of raw material as a mixture of several different raw materials.

Preferably, in step a) the set of raw material particles comprises a single type of raw material particles.

In the remainder of the description, the particles of raw materials will be called "fine particles" inasmuch as their diameter is much smaller both to the main dimension of the natural blocks of raw materials and to that of the compacted material obtained by the process. .

Here, the term "diameter" of a particle means the largest dimension of the particle, whatever its shape.

Each particle of the set of particles of raw materials has its own diameter so that the set of particles is characterized by, that is to say defined by, its particle size distribution, also called "particle size", it is that is, by the statistical distribution of the sizes (or diameters) of the particles of the set of particles. The particle size distribution, according to the needs, can be given in volume, in mass, or in number of particles. In the following description, the particle size distribution will always be given in mass, except in Figure 2 where it is given in volume. The particle size distribution given in volume is equivalent to the particle size distribution given in mass to the density factor of the raw material.

More precisely, it is possible to define reference diameters d90, d10 and d50 of the particle size distribution of any set of particles, said reference diameters being quantities representative of the statistical distribution of the particle sizes of this set.

Thus, the first reference diameter d90 representative of the particle size distribution of the set of particles is defined as the diameter below which are located 90% of the fine particles used, in mass relative to the total mass of all of said particles. fine particles.

In other words, for a set of fine particles whose distribution particle size is characterized by, i.e. defined by, a first reference diameter d90 given, 90% of the fine particles of the set have a diameter smaller than this reference diameter d90 given, in mass relative to the total mass of the set of particles, and 10% of the fine particles of the set have a diameter greater than this first reference diameter d90 given, by mass relative to the total mass of the set of particles.

In other words again, the particles of the set of particles having a diameter smaller than the first reference diameter d90 represent 90% of the total mass of the set of particles, when the particle size distribution is in mass.

Here, the first reference diameter d90 representative of the particle size distribution of all the fine particles of raw material mixed in step a) will be chosen less than or equal to 50 millimeters (mm), preferably less than or equal to 20 millimeters ( mm). Preferably, the first reference diameter will be between 15 millimeters (mm) and 100 micrometers (μιτι), preferably between 10 millimeters (mm) and 500 micrometers (μιτι), or even between 5 millimeters (mm) and 1 millimeter (mm). The first reference diameter d90 could still be chosen much lower than those indicated above, for example less than or equal to 1 micrometer. In particular, the first reference diameter d90 may be chosen less than or equal to 20 mm, 15 mm, 10 mm, 5 mm; 1 mm, 900 m, 800 m, 700 m, 600 m, 500 m, 400 μιτι, 300 μιτι, 200 μιτι, 100 μιτι, 50 μιτι, 20 μιτι, 10 μιτι; 5 μιτι, 1 μιτι, 0,5 μιτι, 0,4 μιτι, 0,3 μιτι.

The second reference diameter d10 representative of the particle size distribution of the set of particles is defined as the diameter below which 10% of the fine particles used are present, in mass relative to the total mass of all of said fine particles. .

In other words, for a set of fine particles whose particle size distribution is characterized by, that is to say defined by, a given second reference diameter d10, 10% of the fine particles of the assembly have a diameter less than second reference diameter d10 given, in mass relative to the total mass of all the fine particles, and 90% of the fine particles of the assembly have a diameter greater than this second reference diameter d10 given, in mass relative to to the mass total of all the fine particles.

In other words again, the particles of the set of particles having a diameter smaller than the second reference diameter d10 represent 10% of the total mass of the set of particles, when the particle size distribution is in mass.

The second reference diameter d10 representative of the particle size distribution of all the fine particles of raw material mixed in step a) will itself be greater than or equal to 0.08 micrometer (μιτι), preferably greater than or equal to at 0.1 micrometer (μιτι), said second reference diameter d10 being of course always lower than the first reference diameter d90. Preferably, the second reference diameter d10 will be between 1 micrometer (μιτι) and 5 millimeters (mm), more preferably between 10 micrometers (μιτι) and 1 millimeter (mm), or even between 100 micrometers (μιτι) and 500 micrometers (μιτι). The second reference diameter d10 may in particular be chosen greater than or equal to 0.1 μιτι, 0.2 μιτι, 0.3 μιτι, 0.4 μιτι, 0.5 μιτι, 0.6 μιτι, 0.7 μιτι, 0 , 8 μιτι, 0,9 μιτι, 1 μιτι, 2 μιτι, 3 μιτι, 4 μιτι, 5 μιτι, 6 μιτι, 7 μιτι, 8 μιτι, 9 μιτι, 10 μιτι, 20 μιτι, 50 μιτι, 100 μιτι, 200 μιτι , 500 μιτι, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm.

The median diameter d50 representative of the particle size distribution of a set of particles is the diameter below which 50% of the fine particles used are present, in mass relative to the total mass of all of said fine particles. Thus, for a set of fine particles whose particle size distribution is characterized by, that is to say defined by, a given median diameter d50, 50% by weight of the fine particles of the assembly have a diameter less than this diameter. median d50 given, and 50% by weight of the fine particles of the set have a diameter greater than this median diameter d50 given.

The reference diameters d90, d10 and median d50 characteristic of the particle size distribution, that is to say defining the particle size distribution, of any set of fine particles are obtained from a particle size curve representing the statistical distribution of the size of each of the fine particles in this set.

In practice, the diameters d90, d10 and d50 can be determined by different techniques, such as the sedimentation method (detection by XR absorption) or the laser diffraction method (ISO 13320).

In the context of the present invention, the size of the fine particles is measured according to the ISO 13320 standard by the laser diffraction method with, for example, a Mastersizer 2000 laser-type granulometer marketed by Malvern.

FIG. 1 shows an example of a cumulative particle size distribution of two lots (or sets) L1 and L2 of fine particles of red bauxite. More precisely, in FIG. 1, the ordinate axis represents the cumulative percentage of fine particles of the considered batch having a diameter less than or equal to the dimension indicated on the abscissa axis, in mass relative to the total mass of the set of fine particles of this lot. On this graph, we find for these two batches of fine red bauxite particles, a first reference diameter d90 of about 8 millimeters, a second reference diameter d10 of between about 0.5 millimeters and about 0.315 millimeters, and a median diameter d50. between 2 millimeters and 3.15 millimeters.

The particle size distribution of the fine particles may be monomodal, that is to say that of all the diameters adopted by the particles of the set of particles, a diameter is preponderant compared to the other diameters, or one of the diameters is adopted by a significantly higher percentage of particles compared to other adopted diameters.

Alternatively, the particle size distribution may be multimodal, that is to say that among all the diameters adopted by the particles of the set of particles, several diameters are preponderant compared to the other diameters, or that in ranges of diameters close, some diameters are adopted by a higher percentage of particles.

FIG. 2 shows an example of a bimodal particle size distribution of a batch of fine red bauxite particles called "ELMIN". More precisely, in FIG. 2, the ordinate axis represents the percentage of red bauxite fine particles having a diameter equal to the dimension indicated on the abscissa axis, in volume relative to the total volume of the set of fines. particles of this lot.

On this curve, there are two peaks in the particle size distribution of the particle diameters of the particle set ELMIN, at namely a first peak of particles having a diameter equal to 400 microns (7% by mass of the particles), and a second peak of particles having a diameter equal to about 2.5 microns (0.8% by mass of the particles).

In general, the difference between the first reference diameter d90 and the second reference diameter d10 reflects the extent of the particle size distribution. Thus, the smaller the difference between the first and second reference diameters d90 and d10, the smaller is the "narrow" particle size distribution, that is, the particle diameters of all the particles are included in a restricted range of values, or that the values of the diameters are close to each other. On the other hand, the greater the difference between the first and second reference diameters d90 and d10, the greater the particle size distribution is "wide", that is to say that the particle diameters of all the particles are within a wide range of values, or that the values of the diameters may be distant from each other.

In the context of the present invention, the particle size distribution can be chosen relatively narrow or wide as needed. In particular, a set of particles of raw materials having a wide particle size distribution will have a better granular stack, so that a lesser amount of hydraulic binder will be necessary to achieve the compacted material. The compacted material made from this set of particles will develop a better mechanical resistance to compression. On the other hand, its erosion rate will be higher than that of a compacted material made from a set of particles having a narrower particle size distribution.

In particular, prior to step a), additional operations of sieving, and / or crushing, and / or grinding, and / or assemblies of different granulometric slices, and / or additions of fillers (fillers in English) are possible in order to adjust the size of the particles used and to change the particle size distribution of said set of particles.

Since the process according to the invention aims to promote the recycling of fine particles of raw materials, it is however important to limit the additional costs and to use as much as possible the fine particles as they are generated during the various steps of handling the blocks. of raw material. Furthermore, advantageously, prior to step a), the fine particles of raw materials are here dried by being placed in an oven at 110 ° C. for 24 hours.

In step a) of the process according to the invention, the fine particles of raw materials, here previously dried, are mixed with the hydraulic binder, and optionally with other dry additives, to form the dry composition.

The preliminary step of drying the raw materials is optional but it is preferred to facilitate the implementation of step b) of mixing the dry composition.

In the remainder of the description, the term "hydraulic binder" denotes a powder, or a mixture of powders, adapted to be mixed with water to form a paste-like material capable of hardening to agglomerate particles together. In other words, in the rest of the description, we will speak of "hydraulic binder" to refer to the materials which, mixed with water, harden cold, without addition of another reactive body and both in the air and in water.

The expression "dry composition" will mean a mixture of dry materials, that is to say with a residual moisture content of less than or equal to 15%, the residual moisture being evaluated by calculating the difference (also called mass loss). ) between the raw mass of a set of raw material particles and its mass after a stay in an oven at 110 ° C for 24 hours, and dividing this difference by said gross mass. In other words, the residual moisture is obtained according to the following formula: [(Gross mass) - (mass after passage in the oven)] / (Gross mass).

Thus, here, the dry composition will designate the mixture of the hydraulic binder with the fine particles of raw materials (said fine particles of raw materials have not necessarily been passed to the oven), and possibly other additives.

A water-tempered composition refers to a dry composition to which water has been added. After a period of contact with the water, a hydraulic binder (or a dry composition comprising a hydraulic binder) cures due to its hydration reaction with water, it is said to "take".

The hydraulic binder is here chosen from: Portland cements, calcium aluminate cements, sulfo-aluminous cements, cements mixed with fly ash, cements mixed with blast furnace slags, cements mixed with pozzolans, or a mixture of these.

Preferably, the hydraulic binder is a set of particles of hydraulic binder, whose particle size distribution is characterized by a first reference diameter d90 less than or equal to 100 microns.

The dry composition comprising the hydraulic binder and all the fine particles of raw materials may have a monomodal or multimodal particle size, that is to say that the assembly formed of the particles of hydraulic binder and raw material may have a unique preponderant diameter or several predominant diameters.

Preferably, the hydraulic binder comprises calcium aluminate cement, i.e., calcium aluminate powder.

Indeed, the use of calcium aluminate cement in the process according to the invention makes it possible to obtain a compacted material generating fewer fine secondary particles, in particular when used in industrial processes at high temperature, it is that is, above 500 ° C.

The use of calcium aluminate cement in the process according to the invention also makes it possible to obtain a compacted material whose disintegration temperature, also known as the melting temperature, is predetermined.

The calcium aluminate cement can be characterized by the molar ratio between the CaO lime (C in the cement manufacturer's notation) and the Al2O3 alumina (A in the cement manufacturer's notation) it contains, more commonly called the ratio C / A (according to the cement manufacturer's notation).

Here, the calcium aluminate cement used has a molar ratio C / A of between 0.1 and 3.

The hydraulic binder may for example be Cement Fondu®, having a C / A ratio equal to 0.95, or SECAR® 51 cement having a C / A ratio equal to 0.71.

Here, the dry composition comprises from 1% to 50% of hydraulic binder, even more preferably from 2.5% to 15% of hydraulic binder, by weight relative to the total mass of the dry composition.

In practice, the amount of hydraulic binder added to the dry composition depends on the nature of the hydraulic binder, the nature of the fine particles raw materials and their granular distribution, and desirable properties for the compacted material, especially in terms of mechanical strength to compression.

In general, an increase in the rate of hydraulic binder in the dry composition leads to an improvement in mechanical performance, but also an increase in cost. So there is a compromise to find.

In addition, the Applicant has found that an increase in the rate of hydraulic binder in the dry composition leads to an increase in mechanical strengths to a certain extent, but an excess of hydraulic binder is not compatible with the operation. compression and is not economically favorable.

It is furthermore possible, in step a), to add additives to the dry composition. In particular, depending on the requirements, it is conceivable to add rheological modifying agents such as surfactants or super plasticizers (also known as shear thinners), as well as retarders or setting accelerators in order to better control the workability of the composition being spoiled. with water, that is to say here the time during which the composition wasted with water has a viscosity allowing its introduction into the compression mold.

The additives also make it possible to better homogenize the mixture between the raw materials and the hydraulic binder, especially in the cases where said raw materials and said binder do not have any particular affinity with each other.

It is in particular possible to add as surfactants the Defoam® sold by Peramin or the Vinapor sold by BASF, as rheofluidifiers Compac500® marketed by Peramin, and as accelerator for setting lithium carbonate.

For example, when rock wool is used as raw material, and Ciment Fondu® cement as a hydraulic binder, it is possible to use lithium carbonate dissolved in concentrated sodium hydroxide as an additive. In practice, it will be possible in particular to generate a composition comprising, by weight relative to the total mass of the dry composition:

- 86.4% rockwool, - 12.9% of Fondu® cement,

0.7% lithium carbonate (L12CO3).

The pH of the mixing water added to this dry composition is adjusted to 13 by adding a few drops of concentrated sodium hydroxide. In practice, in this particular case, for 38 milliliters (ml_) of mixing water, 3.8 milliliters (ml_) of 1 mol / l concentrated sodium hydroxide are added in 34.2 milliliters (ml_) of water.

Since the process according to the invention is intended for the recycling of fine particles of raw materials, it will be sought, for economic reasons, to limit the use of additives as much as possible. However, their use is not prohibited, as long as there is no negative effect, neither on the compression step nor on the final properties of the compacted material at high temperature (greater than or equal to 500 ° C. ).

In practice, in step a), the fine particles of raw materials are weighed, as well as the hydraulic binder, the additives are optionally added and the mixture is mixed manually or not. To facilitate mixing, it is preferred to use a kneader, for example of the Perrier type. Such a kneader may in particular be set to rotate at a speed of 140 rpm for 1 minute in the context of the present invention.

Step b)

The dry composition obtained at the end of step a) is spoiled with

1% to 35% water, by weight relative to the total mass of the dry composition, during step b) of the process according to the invention.

Preferably, the dry composition is mixed with 3% to 15% water, more preferably with 3% to 9% water, by weight relative to the total weight of the dry composition.

In general, sufficient water is added to completely hydrate the hydraulic binder and to wet the surface of the fine raw material particles to obtain a homogeneous water-mixed composition. An excess of water in the composition could make the composition wasted in water too sticky, and cause problems during its demolding after step c) and / or during the cleaning of the mold. In addition, an excess of water could lead to a spinning phenomenon during the compression phase of the composition which would generate fragilities in the final compacted material, said fragilities being created by the evacuation of water according to preferential paths. An insufficient amount of mixing water could, for its part, generate a dusting phenomenon on the surface of the compacted material finally obtained, that is to say, to generate secondary fine particles on the surface of said compacted material.

In practice, in step b), the mixing water is added to the dry composition and mixed. It is particularly possible to mix the composition in the Perrier kneader, for example for 1 minute at a speed of 140 revolutions per minute.

To facilitate the humidification of the composition and the homogenization of the mixture, the water is added, simultaneously or consecutively, in several different zones of the composition.

Step c)

The water-soaked composition thus obtained at the end of step b) is then vibrated.

To do this, the water-mixed composition is introduced into a rigid mold, for example steel, having a shape corresponding to the desired final shape for the compacted material. For example, the mold may have a cylindrical or parallelepiped shape having a characteristic dimension of the order of ten centimeters, in particular equal to 20 centimeters.

Once filled, the mold is vibrated, for example by being placed on a vibrating table, or by any other means of vibration. By "filled" is meant here that the internal volume of the mold is at least partially occupied by the tempered composition.

Due to the vibration, the amount of air trapped within the water-molded composition introduced into the mold is reduced.

In addition, the vibration makes it possible to homogenize the fine particles of raw materials in the mold, in the case where segregation would have occurred during the kneading and / or filling step of the mold. In other words, the vibration makes it possible to homogenize the distribution of the particles in the mold.

The vibration has a frequency between 20 Hertz (Hz) and

80 Hertz (Hz), preferably between 25 Hz and 75 Hz. This frequency range is well adapted to the viscosity of the composition introduced into the mold. For example, the vibration has a frequency equal to 20 Hz, 25 Hz, 30 Hz, 35 Hz 40 Hz, 45 Hz, 50 Hz, 55 Hz, 60 Hz, 65 Hz, 70 Hz, 75 Hz or 80 Hz.

Advantageously, the vibration has an amplitude of between 0.3 millimeters (mm) and 5 millimeters (mm). In particular, the amplitude of vibration may be equal to 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1 , 5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm or 5 mm. The amplitude of vibration here corresponds to the maximum displacement of the mold in a given direction. This range of amplitude is also well adapted to the viscosity of the composition introduced into the mold. In other words, the amplitude represents the difference between the extreme positions of displacement of the mold.

The composition introduced into the mold is vibrated for a time here between 2.5 seconds and 15 seconds.

Then, together with the application of the vibration, a compressive stress is applied to the composition.

Thus, the vibration of the composition is not only implemented prior to the application of the compressive stress, but also during the application of the compressive stress.

Advantageously, during compression of the composition, the vibration is directed in the direction of compression. In other words, the mold is oscillating in the direction of compression.

Thus, for example, if the compression is generally vertical, the mold is displaced upwards and downwards by a few millimeters, namely by a distance equal to the amplitude of vibration, at a predetermined frequency, namely equal to the frequency of vibration.

Advantageously, during the application of the compression stress, the applied vibration is de-harmonized. In other words, the vibration has a non-harmonic profile. Here we mean by "non-harmonic" the fact that the frequency and the amplitude of the vibration are not constant over time, in other words a disharmonic vibration is aperiodic (there is no periodicity of the vibration ). On the contrary, a "harmonic" vibration consists of one or more frequencies and amplitudes that remain constant over time, that is, a harmonic vibration is periodic. In other words, the frequency and amplitude of the de-harmonized vibration applied are not regular over time, that is to say that they adopt values that do not repeat regularly during the implementation of step c).

In practice, one can for example voluntarily disturb the vibration by at least one shock, so as to make the vibration irregular (or aperiodic). Thus, not only is the mold moved regularly, that is to say periodically, in the direction of compression, but it also receives at least a short-term and high intensity perturbation for disharmony vibration. Thus, the de-harmonized vibration has a profile corresponding to the sum of a sinusoidal profile and a disturbance.

For example, the vibration can be created by the rotation of at least one unbalance connected to the vibrating table, and this vibration is de-harmonized by at least one impactor that hits the vibrating table. It is still possible to use movable wedges which are interposed between the unbalances and the plate of the vibrating table so that the rotating unbalances shock the wedges to create an acceleration that de-harmonizes the vibration.

In practice, the specificities that apply preferentially to the vibration that is associated with the application of the compression, in particular the direction of the vibration and the un-harmonization of the vibration, can also be applied to the vibration implemented beforehand. the application of compression.

As has been said, the process according to the invention subjects the composition to a high compression stress, in combination with the vibration.

The compressive stress is defined as a compressive force divided by the surface on which said force applies, said surface being perpendicular to the compressive force, i.e. to the direction of the compressive force.

Here, the compression stress applied to the composition is greater than or equal to 2 MegaPascal (MPa). In particular, the compression stress can be between 2 MegaPascal (MPa) and 5 MegaPascal (MPa). It can still be chosen greater than or equal to 10 MegaPascal (MPa). Thus, it is for example chosen to be equal to 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa. 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa. This high compressive stress makes it possible to keep the fine particles of raw material tight together at the beginning of the setting of the hydraulic binder, which guarantees a great cohesion of the particles. to each other.

In practice, the greater the compressive stress applied to the material, the more the particles of raw materials are packed together and the more the hydraulic binder is forced to fit between said particles to ensure the cohesion of the compacted material. that is, its high compressive strength and low erosion.

In practice, the compressive force is applied homogeneously to one of the faces of the tempered composition introduced into the mold. For example, the compressive force is applied using a piston of equal size to the surface of one of the faces of the mold.

In general, step c) has a sufficiently short duration so that the composition does not have time to take in the mold. In other words, the composition wasted with water, because of the vibration and the application of the compressive stress, is held without the hydraulic binder has really started to react with the water, so that the compacted material obtained at the end of step c) can be demolded without deformation, without having begun to harden. At the end of step c), the composition is sufficiently firm to allow its demolding and its delicate handling.

The compacted material is demolded following step c). After demolding, the compacted material begins to set, i.e. the hydraulic binder is hydrated with water and actually hardens. It develops its mechanical resistance during this hardening.

Advantageously, the demolding of the compacted material is preferably followed by a step during which the compacted material is placed in an oven, at a predetermined temperature, and under an atmosphere whose humidity is controlled. It is during this parboiling step that the hydraulic binder "takes" and therefore that the compacted material cures.

In general, the steaming step amounts to aging the compacted material, that is to say, to harden the material so that it begins to increase in mechanical strength, according to a phenomenon commonly called " structuring ". In the context of the use of an aluminous cement, the setting takes place 2 to 3 hours after the compression step, preferably during the steaming step. This steaming step influences the microscopic structure of the compacted material. In practice, the baking conditions depend on the hydraulic binder used. In particular, the baking is carried out for a predetermined time, at a predetermined temperature and at a relative humidity greater than or equal to a threshold value of relative humidity.

We will choose here to place the compacted material in an oven during

24 hours.

The threshold value of the relative humidity is chosen according to the hydraulic binder used.

For example, when the hydraulic binder used is a calcium aluminate cement, the compacted material is placed in an oven for at least 24 hours, at a relative humidity greater than or equal to 80%.

The relative humidity of the air contained in the oven, also called the hygrometric degree, is defined as the ratio between the partial pressure of the water vapor contained in the air on the saturation vapor pressure (or vapor pressure ) at the same temperature. In other words, the relative humidity indicates the ratio between the water vapor content of the air contained in the oven and the maximum capacity of this air to contain water under predetermined temperature conditions.

The mechanical characteristics of the compacted material surface are crucial to limit the formation of fine secondary particles. To minimize the formation of fine secondary particles, it is necessary that the hydraulic binder is most perfectly hydrated. It happens that the mixing water introduced in step b), prior to the vibration and the application of the compressive stress of step c), is insufficient for the complete hydration of the dry composition, and in particular hydraulic binder. To do this, the relative humidity during the baking must preferably be greater than a first predetermined threshold value of 90%, or even greater than a second predetermined threshold value of 95%.

Moreover, the temperature of the parboiling is also essential to the final microscopic structure of the compacted material, and depends on the hydraulic binder used.

In practice, when the hydraulic binder used is a calcium aluminate cement, the baking is carried out at a temperature between 10 ° C and 28 ° C. Preferably, the parboiling is carried out at a temperature between 15 ° C and 25 ° C, or between 18 ° C and 20 ° C.

In the case of the use of other hydraulic binders such as Portland cement or calcium sulfoaluminates, higher baking temperatures are favorable for the development of mechanical strengths.

When the hydraulic binder used is preferably a calcium aluminate cement comprising calcium mono-aluminate CA as main crystalline phase, with a molar ratio C / A equal to 1, the hydrates formed by the hydration reaction depend on the temperature hydration. However, the higher the hydration temperature, the less the hydrates formed occupy volume, the less the CA phase consumes water molecules to form said hydrates, and the less hydrates formed contribute to the development of mechanical strength of the compacted material . This is the reason why the compacted material should be steamed at a sufficiently high temperature to promote the hydration reaction and thus the hardening of the compacted material, but low enough that the hydrates formed provide the desired properties to the compacted material. and to minimize the phenomenon of conversion of these hydrates (that is to say the chemical transformation of hydrates by a dehydration phenomenon) obtained from calcium aluminate hydraulic binder.

Thus, allowing the compacted material to finish curing in an oven improves the mechanical properties of said compacted material.

Of course, alternatively, it is also possible to allow the material to finish curing in the open air, without stoving.

The compacted material thus obtained forms a uniform layer of raw materials agglomerated by a hydraulic binder.

The compacted material thus obtained is characterized by a compressive strength at 20 ° C greater than or equal to 3 MegaPascal.

In addition, it has a spalling rate of less than 15%, preferably less than 10%. For example the chipping rate may be less than or equal to 15%, 14%, 13%, 12%, 1 1%, 10%, 9%, 8%, 7%, 6%, 5% or less.

This low erosion rate ensures that the material generates few fine secondary particles. That is to say that its resistance to abrasion is high.

The rate of crumbling T, or rate of secondary fine particles generated, returns to the ratio between, on the one hand, the difference between the initial mase of the compacted material and the mass of said compacted material after erosion, and on the other hand, the initial mass of said compacted material. The erosion rate is also expressed according to the following formula:

T = [Initial mass - Final mass] / Initial mass.

The "example" section below specifies in practice how the erosion rate T. is measured.

Advantageously, according to the same principle as what has just been described for obtaining a monolayer compacted material, it is possible to form a multilayer compacted material, that is to say comprising at least two layers of distinct raw materials.

Such a multilayer compacted material may in particular comprise a stack of layers superimposed on each other, or layers enclosed in other layers thus forming a core integrally enclosed in at least one outer layer.

More specifically, the multilayer compacted material comprising a stack of at least two layers superimposed on each other can be obtained according to the process described above, completed as follows:

forming a first layer of material with the batch composition obtained at the end of step b),

in step c), said stack formed in step p2) is then vibrated, at said frequency between 20 Hertz and 80 Hertz, and at said amplitude greater than or equal to 0.3 millimeters, and then, together with said vibrating, applying said compressive stress to said stack.

Step p1) is in all respects similar to steps a) and b) described above.

In other words, in step p1), another dry composition is formed by mixing, on the one hand, another set of particles of raw materials whose particle size distribution is defined by a first reference diameter d90 less than or equal to 50 millimeters and a second reference diameter d10 of greater than or equal to 0.08 micrometer with, on the other hand, from 1% to 50% of a another hydraulic binder, in mass relative to the total mass of the dry composition, then said other dry composition formed is mixed with 1% to 35% water, in mass relative to the total mass of said other dry composition, to form said other tempered composition.

Preferably the two wasted compositions obtained at the end of step b) and after step p1) are different but it is conceivable that they are identical. Their difference may derive in particular from the nature of the particles of raw material, and / or from their particle size distribution, and / or from the nature of the hydraulic binder used, and / or from the quantity of binder used and / or from the quantity of binder used. water used to spoil the dry composition.

It is possible to repeat step p1) as many times as necessary to form as many identical or different tempered compositions as desired superimposed layers in the multilayered compacted material.

The first batch composition obtained after the first step b) is placed in the mold so as to form a first layer of material. The second tempered composition obtained at the end of step p1) is placed on top of this first layer so as to form a stack of two layers. It is thus possible to superpose any number of compositions spoiled in the mold so as to form a corresponding number of layers in the multilayered compacted material.

It is only once all the stacked compositions stacked one above the other in the mold, that the latter is vibrated, under the conditions explained above for the process for obtaining the monolayer material (that is that is, a vibration having at least one frequency between 20Hz and 80Hz and an amplitude greater than or equal to 0.3mm), then, is subjected to the compressive force greater than or equal to 2MegaPascal together with the vibration.

In other words, step c) described above is implemented on the stack of layers formed by the superposition of the wasted compositions. Step c) is, in fact, applied to the first batch composition that is included in said stack. In particular, here neither the first layer formed by the first tempered composition, nor any of the intermediate layers formed by the addition of the other compositions spoiled on top of one another are vibrated or subjected to any compression force before the last wasted composition is placed above all others. It is only after the last set composition has been placed on top of the others that the stack formed is vibrated and then, together with the vibration, subjected to the compressive force, under the conditions described above for the process of obtaining the monolayer material.

This makes it possible to form, in a simple manner, a multilayer compacted material comprising at least two stacked layers.

As an alternative, before the last wound composition is placed on top of the others to form the final stack, it is conceivable to vibrate at least the first layer or an intermediate stack formed of said first layer and any number of intermediate layers deposited over the first layer. It is also conceivable, before the last tempered composition is placed on top of the others to form the final stack, to subject to a compressive force at least the first layer or an intermediate stack formed of said first layer and a number any intermediate layers deposited over the first layer.

Vibration of the intermediate stack allows the particles to optimally match each other. Applying the compression stress, even low, to the intermediate stack makes it possible to obtain, after final demolding, regular layers. The aesthetic appearance of the final multilayer compacted material is thus improved thanks to the intermediate compaction.

The multilayered compacted material comprising a core enclosed in at least one outer layer may be obtained according to one of the processes described above, completed as follows:

in a step n1), a nucleus of raw materials is provided, said core having a mechanical strength greater than or equal to 0.1 MegaPascal (MPa),

in a step n2) or n2 ') prior to step c) processes previously described, said nucleus is completely enclosed in at least one of the batch compositions obtained in step b) and / or in step p1), and

in step c), said vibration is set at said frequency between 20 Hertz and 80 Hertz and at said amplitude greater than or equal to 0.3 millimeters, said assembly comprising said at least one tempered composition and said enclosed core, then together with said vibrating, said compressive stress is applied to said set.

In step n1), the core, intended to form an inner layer of the final multilayer compacted material, has a mechanical strength such that it is possible to manipulate the core to move it.

The mechanical strength in question here is the compressive strength, expressed in MegaPascal (MPa), evaluated according to the protocol described in the EN196 standard.

In step n1, the core may be a natural solid material, such as a bauxite or limestone block.

It may also be a synthetic solid material obtained by any compaction process, for example by compaction or by granulation of fines of natural or synthetic origin.

In particular, the core can be obtained by a compaction process already known.

Alternatively, the core may be a compacted material obtained according to one of the methods of the invention described above. In other words, the core may be a "monolayer" compacted material obtained according to steps a), b) and c) previously described, or a multilayer material comprising a stack of at least two layers obtained according to steps a), b ), p1), p2) and c) previously described.

When the core is a compacted material obtained by any compaction process, the core preferably comprises a set of raw material particles which exhibit characteristics similar to those of the set of particles used in step a) to obtain the composition for enclosing said core. In particular, the particle size distribution and the nature of the raw materials of the other set of particles used to form the core are those described above with reference to step a). However, the nature of the particles of raw materials, respectively the particle size distribution, of the other set of particles used to form the core is not necessarily identical to the nature of the particles of raw materials, respectively to the particle size distribution, of the set of particles used to form the composition intended to enclose the core.

Preferably, in the final multilayer compacted material, the core and the outer layer (s) compacted around it are different. This difference may, for example, stem from the nature of the raw materials they comprise, and / or from the particle size distribution of their respective set of particles.

When the core is obtained according to one of the processes of the invention described above, it is possible that the quantity, the particle size distribution and the nature of the hydraulic binder used to form the core are similar to those of the binder used in the composition intended for to enclose said core, that is to say that the hydraulic binder of the core has the characteristics described above. Conversely, the nature, particle size distribution and / or amount of the hydraulic binder used to form the core may not be identical to that of the hydraulic binder used to form the tempered composition (s) surrounding the core.

Whatever the method adopted for supplying the nucleus in step n1), in step n2) or n2 '), the nucleus is completely enclosed in at least one batch composition obtained in step b) and / or in step p1). In other words, said tempered composition is placed both under, around and on the core so as to completely enclose said core in said tempered composition.

According to a first possibility, the nucleus can thus be entirely enclosed in a single, interfered composition, for example that obtained in step b) (step n2).

For this purpose, for example, said tempered composition obtained in step b) is placed at the bottom of a mold of dimensions (height and width) greater than those of the core, the core is deposited therein which will then form the "heart" of the multilayer compacted material, then filling the lateral space between the core and the mold and completely covering said core with said tempered composition.

The nucleus can also be enclosed in the mixture obtained at the outcome of step p1) of the method described above. In this case, the final multilayer compacted material obtained has a first layer and then a second layer in which is completely enclosed said core (step n2 ')).

According to a second possibility, the core can be enclosed in two distinct and different mixed compositions, so that it is partially surrounded by a first tempered composition and partially surrounded by a second tempered composition. This amounts to trapping the kernel at the interface between two superimposed layers of a stack of layers (variant of step n2 ').

For this purpose, for example, said tempered composition obtained in step b) is placed at the bottom of a mold of dimensions (height and width) greater than those of the core, the core is deposited therein which will then form the "heart" of the multilayer compacted material, filling the lateral space between the core and the mold with the same mixture wasted up to half the height of the core, and then fills the lateral space between the core and the mold with a second tempered composition obtained for example at the end of step p1), and completely covers said core with said second composition wasted.

Step c) is similar to that previously described except that in the case of the multilayer material with a core enclosed in at least one outer layer, the vibration, then the compressive stress and the vibration, are applied together. the set comprising the tempered composition (s) and the enclosed core.

The application of the compression constraint to the set comprising the tempered composition (s) and the enclosed nucleus in fact causes the application of this compressive stress on the core as well as the application of this compressive stress on the or the spoiled compositions. Thus step c) is implemented, in fact, at least on the first composition wasted.

A multilayer compacted material comprising a core completely enclosed in at least one outer layer is thus obtained.

In a variant, it is easily understood that the core used in step n1) can itself be a multilayer compacted material comprising another core enclosed in a layer, that is to say a multilayer compacted material obtained according to the process which just described.

The rest of what has been described in the process of obtaining the monolayer compacted material is also applicable to the multilayer compacted material obtained according to one of the methods of the invention (multilayer compacted material comprising a stack of layers superimposed on each other or multilayer compacted material comprising a layer encapsulated in at least one outer layer) .

The multilayer compacted material comprising a stack of layers superimposed on each other may also be obtained according to a process for obtaining a multilayer compacted material according to which, a first layer is produced according to the steps of:

b) said dry composition formed in step a) is stripped with 1% to 35% water, by mass relative to the total mass of the dry composition so as to form a batch composition,

c ') the batch composition obtained in step b) is vibrated at a frequency of between 20 Hertz and 80 Hertz and at an amplitude greater than or equal to 0.3 millimeters, and then, together with the setting in vibration, one applies compression stress to said tempered composition.

Steps a) and b) of this method of obtaining a multilayer compacted material comprising a stack of layers are in all respects similar to steps a) and b) described above for the process for obtaining the monolayer compacted material.

Step c ') is in all respects similar to that described above for step c) of the process for obtaining the monolayer compacted material, with the difference that it is not imperative that the value of the compression stress applied in step c ') is greater than or equal to 2 MPa. It may for example be of the order of 0.1 MPa.

This first layer forms the lower layer of the stack of layers.

Then, for the formation of the next layer, another composition tempered by repeating steps a) and b) described above and placing said other composition spoiled on the previous layer.

In practice, at the end of step c ') of forming the first layer, and it is intended to add directly into the mold the other water-mixed composition obtained according to said steps a) and b) repeated (and similar).

Thus, placing said other composition wasted over the first layer already formed, in the same mold.

Preferably, the other composition mixed with water is different from the first water-mixed composition used to form the first layer of material, in particular in that it comprises a set of fine particles of raw materials whose nature is different from that of the set of raw material particles of the first layer, and / or whose particle size distribution is different. The hydraulic binder used in this other water-mixed composition may be the same or different, as are the proportions of binder and raw materials.

For example, it is conceivable for the first layer to be formed from a first dry composition comprising, by weight relative to the total mass of said first dry composition, 85% of red bauxite whose particle size distribution has a first diameter of reference d90 less than or equal to 20 millimeters and a second reference diameter d10 greater than or equal to 0.08 micrometers and 15% cement Cement Fondu®, and that the second layer is formed from a dry composition comprising, by mass relative to the total mass of said second dry composition, 95% CaCO3 limestone whose particle size distribution has a first reference diameter d90 less than or equal to 20 millimeters and a second reference diameter d10 greater than or equal to 0.08 micrometers and 5% cement Cement Fondu®.

It is then planned to mix this second composition with water and to introduce the second composition thus mixed into the mold already containing the first layer of material. The second composition may be mixed with water in the same proportions as the first composition or not.

For example, in the example given above, the first dry composition is mixed with 7% water, by weight relative to the total mass of the first dry composition, while the second composition dry is tempered with 5% water, by mass relative to the total mass of said second dry composition.

The assembly formed by the previous layer (here the first layer) and the other tempered composition which covers it is then vibrated, and a compressive stress is applied to the assembly.

As for the formation of the first layer, it first vibrates the assembly formed of the first layer and the tempered composition which covers it, then, while maintaining the vibration, the compressive stress is applied to the whole .

The vibration and the application of the compressive stress are in all respects similar to what has been described for the formation of the first layer. In particular, as for the formation of the first layer, the vibration is carried out at a frequency between 20 Hertz and 80 Hertz and at an amplitude greater than or equal to 0.3 millimeter, while the compressive stress is not necessarily greater or equal to 2 MPa.

Thus, step c ') is carried out on the assembly formed by the first and second layers.

Vibration of the assembly formed by the first and second layers allows the particles to optimally match each other.

Applying the compression stress, even low, to this set provides, after final demolding, regular layers. The appearance of the final multilayered compacted material is thus improved thanks to the intermediate compaction.

The same goes for the formation of each subsequent layer.

In other words, for the formation of each subsequent layer, a new spoiled composition is obtained by repeating steps a) and b) and this new spoiled composition is introduced into the mold, over the previous layer, and therefore necessarily over all previously formed layers. The assembly comprising the previously formed layers and the new tempered composition is vibrated, and then together with the vibration, a compressive stress is applied to this set. More specifically, for each subsequent layer, step c ') is carried out on the new assembly comprising the previously formed layers and the new composition wasted.

It is essential for obtaining the multilayer compacted material that the value of the compression stress applied is greater than or equal to 2 MegaPascal, for example greater than or equal to 10 MegaPascal, at least for producing the last layer of said multilayer compacted material. that is to say for the upper layer of the stack. Thus, for the last layer, or upper layer of the stack, step c) described above is carried out. It should be noted that the application of a compressive stress greater than or equal to 2 MPa on the last layer causes, in fact, the application of this compressive stress on all the layers of the stack.

Thus, if the compacted material comprises only two layers, it is not necessary, although it is possible, that the value of the compression stress is greater than or equal to 2 MPa for the formation of the first layer, but It is imperative that the value of the compressive stress applied for the formation of the second layer is greater than or equal to 2 MPa. Preferably, the value of the compressive stress applied to form the second layer will be greater than or equal to 5 MPa, or even greater than or equal to 10 MPa.

Preferably, during the manufacture of the multilayer compacted materials according to this method, the intermediate compression stress received by the water-mixed composition forming either the first layer of the compacted material or an intermediate layer of said compacted material, is lower than the final compressive stress directly preceding the demolding of the multilayer compacted material. In particular, the intermediate compression stress may be less than 2 MegaPascal. For example, it can be of the order of 0.1 MegaPascal.

In other words, it is not necessary that all of the compressive stresses received by the multilayer compacted material during the multiple steps c) of the method of obtaining the multilayer compacted material is greater than or equal to 2 MPa to implement the process of the invention. On the contrary, it suffices that one of the compression stresses implemented during one of the steps c) of the method according to the invention is greater than or equal to 2 MPa for the method to be implemented according to the invention. Preferably, the last compressive stress, directly preceding the demolding of the multilayer compacted material, is greater than or equal to 2 MPa, better still greater than or equal to 5 MPa, and still more preferably greater than or equal to 10 MPa.

The application of at least one very large compressive stress for the final layer of the multilayer material ensures that all the layers will be integral with each other, and that the fine particles will be agglomerated properly. However, it will be possible to apply a compression stress greater than or equal to 2 MPa during the formation of each layer if necessary, to further strengthen the compressive strength of the multilayer compacted material.

Preferably, all the compressive stresses applied during the different steps of the process are applied in the same direction of compression.

In a variant, the compressive stresses applied during the various process steps are applied in different compression directions.

The multilayer compacted material (bilayer or more) obtained can then be demolded, and optionally steamed according to the steaming step described above.

It is also possible to combine the method of obtaining the multilayer compacted material comprising a core enclosed in an outer layer and one of the processes for obtaining the multilayer compacted material comprising a stack of layers. This makes it possible to form a hybrid multilayer compacted material having both a core enclosed in a first layer, and at least a second layer superimposed on the assembly comprising said core enclosed in said first layer.

Of course, it is possible by combining the steps of the various methods described, to obtain hybrid multilayer compacted materials comprising both several nuclei enclosed in several outer layers and several superimposed layers. It is essential that during the formation of the last layer, the compression stress applied is greater than or equal to 2 MPa, but for the intermediate layers, this is not imperative.

Advantageously, whatever the number of layers of the multilayer compacted material formed, said layers of raw materials are inert between them up to a predetermined threshold temperature. In other words, the layers do not react with each other until the temperature reaches a predetermined threshold temperature substantially higher than the ambient temperature. In other words again, the raw materials of a layer do not react with the raw materials of a neighboring layer, before reaching the predetermined threshold temperature. In particular, they do not react with each other before reaching a temperature greater than or equal to 500 ° C. Alternatively, they do not react with each other before reaching a temperature greater than or equal to 400 ° C, or greater than or equal to 300 ° C, or greater than or equal to 200 ° C, or greater than or equal to 1 10 ° C. This is true both for the multilayer compacted material with stack of layers, and for the multilayer compacted material with a core enclosed in an outer layer and for the hybrid multilayer compacted material.

In particular, in the multilayer compacted material comprising at least one core enclosed in at least one outer layer, the raw materials of the core are inert with respect to the raw materials of the outer layer or layers, up to the predetermined threshold temperature. .

Whatever the number of layers of the multilayer compacted material formed, said multilayered compacted material has, like the monolayer compacted material, a compressive strength greater than or equal to 3 MegaPascal. Thus, the multilayered compacted material can be handled without decomposing.

In addition, in the multilayered compacted material, all the layers in contact with the outside generate few secondary fine particles, at least up to the melting temperature of said multilayered compacted material.

Thus, in the case of the multilayer compacted material with stack of layers, each layer of the multilayer compacted material generates few fine secondary particles, at least up to the melting temperature of said multilayered compacted material. In the case of the multilayer compacted material comprising a core enclosed in an outer layer, the outer layer generates few fine secondary particles, at least up to the melting temperature of said multilayered compacted material.

The melting temperature of the multilayered compacted material may be predetermined by suitably selecting the hydraulic binder of the composition of each layer of said multilayer compacted material.

Preferably, in the case of the multilayer compacted material with a core enclosed in at least one outer layer, the melting temperature of said multilayer compacted material may be predetermined by suitably selecting the hydraulic binder of the composition of the outer layer.

With the method according to the invention it is possible to manufacture multilayer compacted materials, including a stack of layers, a core enclosed in an outer layer, or a combination of these configurations. These multilayered compacted materials can be used in industrial processes requiring the addition of at least two types of raw materials, especially in fusion processes that may require the use of alumina-rich (partially or completely hydrated) raw material blocks and lime (pure or partially carbonated).

In practice, the multilayer compacted material may be designed to have a chemical composition close to that desired for the product obtained at the output of said industrial process. Controlling the composition of the multilayer material makes it possible to improve the control of chemical reactions in industrial processes, especially in the melting furnaces by homogenizing the chemical composition within said furnaces. This limits the production of substandard or substandard products, while avoiding certain classic phenomena when two raw materials are used in an industrial process, such as the bonding of raw materials between them or the advance of an embankment (especially in ovens fusion).

Examples

In the following description are presented various examples of compacted materials manufactured according to the method of the invention and according to other methods not in accordance with the invention for comparison. The compacted materials formed are then characterized by mechanical tests.

I. Manufacturing devices

The compacted materials manufactured according to the method of the invention can be obtained on a device called "miniature", also called "laboratory".

The miniature device comprises a press marketed under the name Styl'One Evolution by the company MEDELPHARM, assistant to a device generating vibrations. The Styl'One press includes two opposite punches, namely a lower punch and an upper punch. Here, the upper punch makes it possible to apply the compressive stress by exerting a force at most equal to 50 kiloNewton (kN). The lower punch is held in abutment and connected to the vibration generating device.

The vibration generating device comprises an axis of rotation, one end of which is in contact with the lower punch and the other end of which carries an unbalance, that is to say a mass whose shape is asymmetrical with respect to the axis of rotation. rotation. The unbalance can weigh between 3 grams and 16 grams and be rotated at a speed of between 40 revolutions per second (40 Hz) and 60 revolutions per second (60 Hz). With this system, the vibration amplitudes are between 0.35 millimeter and 1.05 millimeter.

The water-mixed composition is introduced into a mold of rectangular steel section, measuring 23 millimeters wide by 31 millimeters long, and placed centrally with respect to the axis of the two punches. The compressive stress experienced by the composition contained in the mold is then at most 70 MPa. In practice, it will be chosen here equal to 1 1 MPa.

The conditions of manufacture of the compacted materials in the miniature device are summarized in Table I-A below:

Table l-A

The compacted product obtained is demolded manually and then placed in an oven for 24 hours at 20 ° C. and at a relative humidity of 90%.

The compacted materials manufactured according to the method of the invention can be obtained on a so-called "pilot" device.

The pilot device comprises a vibrating press as described in the patent application EP1875996 of the company QUADRA.

The plant includes a raw material mixing station which overcomes the casting / molding station of the formulated material.

The water-tempered composition is prepared by means of a kneader conical. It is then introduced into a mold containing 30 briquette impressions, 4 cm thick steel, in order to withstand pounding pressures of 25 MPa maximum. The mold is placed under the pestles. The compressive stress experienced by the composition contained in the mold will here be between 1, 5 and 25 MPa.

The manufacturing conditions of the compacted materials in the pilot device are summarized in Table I-B below:

Table l-B

The compacted product obtained is demolded manually and then placed in an oven for 24 hours at 18 ° C., and at a relative humidity of 95%.

II. Resistance and crumbling tests

Once obtained, the compacted materials are mechanically tested in order to evaluate their mechanical compressive strength and their rate of crumbling, the latter testifying to the greater or lesser generation of fine secondary particles.

A mechanical compressive strength greater than or equal to 3 MPa ensures that the compacted material can be handled and transported without breaking. It is therefore considered satisfactory in the context of the present invention.

A low erosion rate, that is to say less than or equal to 15%, is synonymous with a high resistance to abrasion, and therefore a low generation of fine secondary particles during the various manipulations of the material. compacted and / or when used in an industrial process. Such a level of crumbling is considered satisfactory in the context of the present invention.

Whether to evaluate their resistance to mechanical compression or their rate of crumbling, the compacted materials can be tested after step d) of steaming of said compacted materials directly following their release from the mold, or after cooking simulating their introduction into a industrial process at high temperature, said cooking being itself carried out after step d) of parboiling said compacted materials.

When the compacted materials are tested directly after step d) of baking, at room temperature and without further heat treatment, it will be called "cold" tests.

On the contrary, when they are tested after cooking, we will talk about "hot" tests. In practice, the baking of the compacted materials is divided into three phases: a first phase of temperature rise of 50 ° C per hour, a second so-called "stage" phase of a duration of 1 hour 45 to a set temperature here chosen equal at 700 ° C or 900 ° C, and a third cooling phase at 50 ° C per hour. The compacted materials are tested after their return to room temperature.

11.1 Mechanical resistance to compression

The mechanical resistance to compression, expressed in MegaPascal (MPa) is evaluated according to the protocol described in the EN196 standard, on a so-called 3R press typical of the evaluation of cementitious materials. The press is marketed under the name Ibertest®.

In practice, the compacted materials are placed on a fixed platen, and centered under a movable upper punch adapted to apply a predetermined compressive force to the compacted material.

The punch is first brought into contact with the material and a compressive force is then applied to the compacted material in the same direction as that applied during the manufacture of the compacted material. The compressive force is applied until the material breaks. The compressive strength (Rc) of the compacted material corresponds in practice to the stress applied at the time of breaking of the material. The rise in compression is of the order of 2400 Newton per second, and the maximum force that can be applied is 200 kiloNewton. The test is performed on at least three samples. The average is then carried out and considered as the mechanical resistance to compression of the studied material.

II .2 Chipping rate

Two tests for measuring chipping rate are possible, depending on the size of the compacted materials obtained: the test of the mixer for compacted materials of large size (greater than 10 centimeters); and the Jar test for smaller materials. The concrete mixer test is based on the ASTM "Los Angeles" test for evaluating aggregate attrition.

In practice, five large compacted materials are weighed and placed in a 174-liter mixer (model RS180 LESCHA) in steel, 60cm in diameter, rotating at 24 revolutions per minute. The compacted materials are left for 30 minutes in the rotating concrete mixer.

The contents of the concrete mixer are sieved to 40 mm, and the fine particles passing through the sieve are considered to be secondary fine particles. The larger pieces that have not passed through the sieve are weighed for comparison with the initial mass introduced into the mixer.

More precisely, it is possible to calculate the rate of crumbling T, or rate of secondary fine particles generated, such as the difference between the initial mass and the final mass of compacted materials, relative to the initial mass, also expressed according to the following formula :

T = [Initial mass - Final mass] / Initial mass.

The jar test makes it possible in particular to evaluate the generation of fine secondary particles of the compacted materials obtained with the miniature device.

Similarly, several blocks of compacted material, for example 5, are weighed and placed in a 6-liter cylindrical jar, 15 centimeters in diameter and 15 centimeters in height, the interior of which is covered with Linatex. that is, a very smooth rubber material. The jar is rotated at 45 revolutions per minute for 30 minutes (ie 1350 revolutions in total) and the mass loss of the compacted materials is evaluated.

As for the test of the mixer, it is then possible to calculate the rate of crumbling T, or rate of generation of the fine secondary particles, according to the following formula:

T = [Initial mass - Final mass] / Initial mass.

III. Compacted materials manufactured

Various examples of compacted materials have been made from various raw materials and various hydraulic binders.

III.1 Raw materials

The raw materials used in the different examples are red bauxite and white bauxite. It is also possible to use limestone, carbon black and rock wool.

The carbon black that could be used is for example marketed under the name Thermax®N990. It is composed of 99.1% by mass of amorphous carbon black.

The rock wool that could be used is the one sold, for example, under the name Le Flocon 2® - Rockwool.

It is also possible to use 99.5% pure alumina by weight, hereinafter referred to as "Alumina test".

Table II shows the chemical composition of the other raw materials used or which could be, namely that of red bauxite, white bauxite and limestone, in percentage by mass (ie in mass relative to to the total mass of the raw material considered).

Table II

Table III below shows the particle size and the density of some of the dry raw materials, that is to say after their passage in the oven at 110 ° C. for 24 hours.

Table III

III.2 Hydraulic binder

The hydraulic binders used in the various examples are Ciment Fondu®, Secar® 51 cement. It is also possible to use Portland cement.

The Portland cement that could be used is for example marketed under the name CEM I 52,5R MILKE PREMIUM.

Tables IV and V below show respectively the chemical composition and the mineralogical composition of Cement Fondu® cement and Secar® 51 cement, in percentage by weight (in mass relative to the total mass of the cement considered).

Table IV

FIG. 2 represents the particle size distribution of two of the lots of fine particles of raw materials used, namely fine particles of white bauxite called "ABP" and fine particles of red bauxite called "ELMIN", as well as those of two batches of fine cement particles used, namely cement Cement Fondu® and cement Secar® 51. In this FIG. 2, the ordinate axis represents the percentage of fine particles having a diameter equal to the dimension indicated on the abscissa axis, in volume relative to the total volume of the set of fine particles of each batch considered.

Table V

ΙΙΙ.3 Compacted materials

Example 1

In Example 1, the mechanical resistance to compression and crumbling of a compacted material of red bauxite particles obtained according to the process of the invention (Example 1a) were compared to those of a natural red bauxite block (Example 1 ref), and to those of a compacted material of red bauxite particles obtained according to a process not in accordance with the invention (Example 1b). Here, the method not according to the invention differs from the method according to the invention in that it does not implement vibration.

Step a): the dry composition used to manufacture the compacted materials of Examples 1a and 1b comprises, by weight relative to the total mass of the dry composition, 85% of red bauxite of "ELMIN" type and 15% of cement Ciment Fondu®, whose respective properties have been described in Parts III.1 and III.2.

In practice, all the red bauxite particles were sieved with a 560 micron sieve so that its particle size distribution has a first reference diameter d90 equal to 520 micrometers, a second reference diameter d10 equal to 5.6 micrometers, and a median diameter d50 equal to 255 micrometers.

Step b): this dry composition is mixed with 10% water, by weight relative to the total mass of the dry composition. To do this, the water-mixed composition is kneaded by hand for 1 minute.

Step c): for Example 1a, the water-mixed composition is then introduced into the mold described in point I (Manufacturing device), in order to be processed by the miniature device which implements the vibration.

For example 1b, the water-tempered composition is treated by the miniature device which does not implement any vibration.

Table VII below summarizes the conditions for obtaining the compacted materials of Examples 1a and 1b.

Table VII

Example 1a Example 1b

Red bauxite 15.5 g 15.5 g

Granulometry (bauxite) d90 = 520 μηη d90 = 520 μηη

d10 = 5.6 μηη d10 = 5.6 μηη

Ciment® Melted 2.7 g 2.7 g

Mixing water 1, 8 g 1, 8 g

Mixing time 1 minute 1 minute Example 1a Example 1b

Miniature miniature manufacturing device

Compression time 1 minute 1 minute

Constraint of

1 1 MPa 1 1 MPa

compression

Vibration frequency 60 Hz 0 Hz

Vibration amplitude 1.05 mm 0 mm

Table VIII below summarizes the results obtained for the compacted materials of Examples 1a and 1b and for the natural block of red bauxite (Example 1 ref).

The rate of crumbling was measured according to the Jar test for the compacted materials of Examples 1a and 1b and according to the test of the mixer for the natural bauxite block.

Table VIII

According to the results obtained, the process according to the invention makes it possible to obtain compacted materials (Example 1a) having a compressive strength, colder, greater than that of compacted materials obtained by the non-compliant process. invention (Example 1b). Thus, the fact of subjecting the composition to vibration, both prior to the application of the compressive stress and during said application, makes it possible to improve the mechanical resistance to cold compression (in this case, a 23% improvement in said mechanical resistance to cold compression). In addition, the compacted material obtained according to the process of the invention (Example 1a) has a much lower rate of spalling than the natural red bauxite block (Example 1 ref), both hot and cold. Indeed, thanks to the process according to the invention, the compacted material generates, cold, about 2.5 times less fine secondary particles than the natural block, and, hot, about 6 times less fine secondary particles than said block natural.

Example 2

Example 2 follows the principle of Example 1, but with compacted white bauxite particles and a natural white bauxite block.

Thus, in Example 2, the mechanical compressive strength and the erosion rate of a compacted material of white bauxite particles obtained according to the process of the invention (Examples 2a, 2c) were compared with those of a natural block of white bauxite (Example 2ref), and to those of a compacted material of white bauxite particles obtained according to a process not in accordance with the invention (Examples 2b, 2d). Here, as in Example 1, the process not according to the invention differs from the method according to the invention in that it does not implement vibration.

Step a): the dry composition used to manufacture the compacted materials of Examples 2a and 2b comprises, by weight relative to the total weight of the dry composition, 85% white bauxite and 15% Secar® 51 cement, the properties of which are as follows: respective components have been described in Parts III.1 and III.2.

The dry composition used to manufacture the compacted materials of Examples 2c and 2d comprises, by weight relative to the total mass of the dry composition, 50% of white bauxite, 35% of pure 99.5% by weight test alumina and 15% Secar® 51 cement, the respective properties of which have been described in Parts III.1 and III.2.

Step b): the dry compositions of Examples 2a, 2b, 2c and 2d are mixed with 10% water, by weight relative to the total mass of the corresponding dry composition. They are kneaded by hand for 1 minute.

Step c): for Examples 2a and 2c the water-tempered compositions are processed by the miniature device which implements vibration at a frequency of 60Hz and 0.35 millimeters amplitude, and a compression stress of 1 1 MPa. For examples 2b and 2d, the water-tempered compositions are processed by the miniature device which implements a compression stress of 11 MPa but no vibration.

Table IX below summarizes the conditions for obtaining the compacted materials of Examples 2a and 2b.

Table IX

Table X below summarizes the results obtained for the compacted materials of Examples 2a, 2b, 2c and 2d and for the natural block of white bauxite (Example 2ref). The rate of crumbling was measured according to the Jar test for the compacted materials of Examples 2a and 2b and according to the test of the mixer for the natural bauxite block.

Paintings

Thus, as was shown with Example 1, the mechanical resistance to cold compression is improved for the compacted materials obtained according to the process of the invention (Example 2a) compared to those obtained according to the process which does not comply with the invention (Example 2b) which does not implement vibration.

As for Example 1, the erosion rate of the compacted materials obtained according to the process of the invention (Example 2a) is also much lower than that of the natural white bauxite block (Example 2ref), both hot and cold. 'Cold.

Finally, by comparing the results of Examples 1a and 2a, it appears that the process according to the invention makes it possible to obtain compacted materials with different raw materials, namely here as well with particles of white bauxite as with particles of red bauxite. In both cases, both hot and cold, the mechanical resistance to compression is largely greater than 10 MPa and the erosion rate below 10%.

Example 3

In Example 3, the mechanical compressive strength and the erosion rate were compared for materials compacted according to the process of the invention (Examples 1a and 2a), and for materials compacted under a very high stress. compression, but without vibration (Examples 3a, 3b and 3d).

The dry composition used to manufacture the compacted materials of Examples 3a and 3b comprises, by weight relative to the total mass of the dry composition, 85% of red bauxite and 15% of Cement Fondu® cement or Secar® 51 cement, of which the respective properties have been described in parts III.1 and III.2. In practice, the set of red bauxite particles has been sieved with a sieve 4 millimeters so that its particle size distribution has a first reference diameter d90 equal to 3.5 millimeters, a second reference diameter d10 equal to 315 microns, and a median diameter d50 equal to 2 millimeters.

The dry composition of Examples 3a and 3b is mixed with 7% water, by weight relative to the total mass of the dry composition.

The dry composition used to make the compacted material of Example 3d comprises 85% white bauxite and 15% Cement Fondu® cement, the respective properties of which have been described in parts III.1 and III.2. In this case, the dry composition is mixed with 12% water, by weight relative to the total mass of the dry composition.

In Examples 3a, 3b and 3d, irrespective of the composition mixed with the water formed, the said composition is then introduced into a cylindrical mold 39 millimeters in diameter and 80 millimeters high, in order to receive a compressive stress of the water. 40 MPa, by a hydraulic press marketed under the name Zwick®.

In Example 3c, the compressive strength of a material not comprising a hydraulic binder, compacted under a very high compressive stress, without vibration was also evaluated.

Table XI below summarizes the conditions for obtaining the compacted materials of Examples 3a, 3b, 3c and 3d. Table XI

Table XII below summarizes the results obtained for the compacted materials of Examples 3a, 3b, 3c and 1a which can be directly compared. The rate of crumbling was measured according to the Jar test for the compacted materials of Examples 3a, 3b and 3d. Table XII

Table XIII below summarizes the results obtained for the compacted materials of Examples 3d and 2a that can be directly compared.

Table XIII

The results of Tables XII and XIII show that when in the course of its manufacturing, the material is subjected to a very high compressive stress but to no vibration (Examples 3a, 3b and 3d), its compressive strength is lower than when subjected to both a high compressive stress and vibration (Examples 1a and 2a). Thus, subjecting the material to a very high compressive stress during its manufacture is not sufficient to improve its mechanical compressive strength. It is the combination of the application of a high compressive stress and of a vibration, said vibration being implemented both during and before said compression, which makes it possible to generate compacted materials having a mechanical strength. satisfactory compression.

In addition, the results of Tables XII and XIII demonstrate that the fact of subjecting the material to a vibration, in combination with a high compressive stress (Examples 1a and 2a) makes it possible to significantly reduce the rate of erosion, when hot and cold, compared to subjecting the material only to a high compressive stress (Examples 3a, 3b and 3d), without vibration. Subjecting the material to a very high compression stress during its manufacture does not reduce its rate of erosion below that of a natural block. It is the combination of the application of a high compressive stress and of a vibration, said vibration being implemented both during and before said compression, which makes it possible to generate compacted materials having a crumbling satisfactory.

Finally, Example 3c shows that the hydraulic binder plays an essential role in the holding of the compacted material. In other words, the fine particles of raw materials, even when subjected to a very high compressive stress, do not develop sufficient cohesion to stand mechanically. Thus, it is necessary to use a hydraulic binder to agglomerate said fine particles of raw materials together.

Example 4

In Example 4, the compressive strength and the erosion rate were compared for compacted materials according to the method of the invention (Examples 1a and 2a) and for compacted materials according to a method implementing low compressive stress and vibration (Examples 4a and 4b).

Dry composition used to make compacted materials examples 4a and 4b comprise, by weight relative to the total mass of the dry composition, 85% red bauxite (Example 4a) or white bauxite (Example 4b), and 15% Cement Fused cement (Example 4a) or Secar®51 cement (Example 4b), the respective properties of which have been described in Parts III.1 and III.2.

In these two examples 4a and 4b, the dry composition is mixed with 4% water, by weight relative to the total mass of the dry composition. The composition thus mixed is introduced into an oil mold, made of steel of large size. The mold here has a square section of 100 millimeters side. The mold is placed under a large press attached to a vibrating table. In practice, the water-mixed composition introduced into the mold is vibrated beforehand and during the application of the compressive stress.

The conditions of manufacture of the compacted materials in the laboratory device are summarized in Table XIV below:

Table XIV

The compacted materials of Examples 4a and 4b thus obtained are demolded manually and then placed for 24 hours in an oven at 20 ° C., at a humidity of relative of 90%.

Table XV below summarizes the results obtained for the compacted materials of Examples 4a and 1a, on the one hand, and 4b and 2a on the other hand. The rate of crumbling was measured according to the concrete mixer test for the compacted materials of Examples 4a and 4b.

Table XV

The comparison of the results obtained with the compacted materials of Examples 4a and 1a, on the one hand, and 4b and 2a, on the other hand, shows that the compressive strength, both cold and hot, is improved. in the case where the material is obtained according to the method of the invention with respect to the case where the material is obtained according to an existing method implementing a low compressive stress and a vibration. In particular, the compressive strength is multiplied by 3 between Examples 4a and 1a.

Thus, the application of a high compressive stress, combined with the application of the vibration, both before and during the application of the compression stress, makes it possible to generate compacted materials whose mechanical resistance to compression is improved compared to compacted materials obtained according to existing methods. The erosion rate of the compacted materials obtained according to the process of the invention is also lowered compared to that of the natural blocks, and to that of compacted materials obtained according to the existing method using a low compressive stress and a vibration.

Thus, it is clear from the description as a whole and from the examples that the combination of the application of a vibration and a high compressive stress makes it possible to obtain compacted materials whose mechanical compressive strength and crumbling are satisfactory.

It also appears that the combination of the application of a compression stress and a vibration according to the invention increases the density of the compacted materials, which shows the decrease in porosity and a homogeneous distribution of the constituents of the composition in the compacted material (no segregation, sedimentation or inhomogeneous distribution of constituents).

Example 5

In Example 5, a compacted bilayer material of red bauxite particles and limestone is obtained according to a process according to the invention (Example 5a).

The dry compositions used to manufacture the compacted material of Example 5a respectively comprise, by weight relative to the total mass of said dry composition, for the first layer 85% of "EB" type red bauxite and 15% of cement Cement Fondu®, and for the second layer 95% limestone CaCO3 and 5% cement Cement Fondu® whose respective properties have been described in parts III.1 and III.2.

In this example 5a, the dry composition for the first layer is mixed with 7% water, by weight relative to the total weight of said dry composition. The dry composition for the second layer is mixed with 5% water, by weight relative to the total weight of said dry composition. The composition for the first layer thus tempered is introduced into an oil mold, made of large steel. The mold here has a square section of 100 millimeters side. The composition for the second layer thus tempered is then introduced onto the composition for the first layer in said mold. The mold is placed under a large press attached to a vibrating table. In practice, the two compositions spoiled with water introduced into the mold are vibrated beforehand and during the application of the compressive stress.

The manufacturing conditions of the compacted material in the laboratory device are summarized in Table XVI below:

Table XVI

Table XVII below summarizes the results obtained for the compacted bilayer material of Example 5a.

The rate of crumbling was measured according to the Jar test for the compacted materials of Example 5a. Table XVII

Thus, it appears that the process according to the invention makes it possible to obtain compacted two-layer materials whose mechanical resistance to compression is quite satisfactory.

Example 6

In Example 6, the compressive strength and the density of a compacted material of red bauxite particles obtained according to the process of the invention at different compression values (Examples 6a to 6f) were compared.

The manufacturing conditions of the compacted material in the pilot device are summarized in Table XVIII below:

Table XVIII

Example Example Example Example Example Example

6a 6b 6c 6d 6th 6f

Particles 185 kg 185 kg 185 kg 185 kg 185 kg 185 kg raw materials from bauxite bauxite bauxite bauxite bauxite bauxite red red red red red

Granulometry d90 <8 d90 <8 d90 <8 d90 <8 d90 <8 d90 <8

(bauxite) mm mm mm mm mm mm d10 <315 d10 <315 d10 <315 d10 <315 d10 <315 d10 <315 μιτι μιτι μιτι μιτι μιτι μιτι μιτι

Binder 35 kg 35 kg 35 kg 35 kg 35 kg 35 kg Hydraulic Cement Cement Cement Cement Cement Cement

Fondu® Fondu® Fondu® Fondu® Fondu® Fondu®

Water of

16,5 kg 16,5 kg 16,5 kg 16,5 kg 16,5 kg 16,5 kg tempering

Time of 10 10 10 10 10 10 compression seconds seconds seconds seconds seconds seconds Example Example Example Example Example Example 6a 6b 6c 6d 6th 6f

Constraint of

4 MPa 8 MPa 12 MPa 16MPa 20MPa 25MPa compression

Frequency

68 Hz 68 Hz 68 Hz 68 Hz 68 Hz 68 Hz vibration

Amplitude About Approximately About Approximately Environ Approximately about 1 -2 mm -1 -2 mm 1-2 mm -1 -2 mm 1-2 mm -1 -2 mm vibrations

Table XIX below summarizes the results obtained for the compacted materials of Examples 6a to 6f.

Table XIX

Thus, it emerges that whatever the compression stress value, greater than 2 MPa, the process according to the invention makes it possible to obtain compacted materials whose mechanical compressive strength is extremely satisfactory, cold as well as hot.

Example 7

In Example 7, the mechanical resistance to compression and the density of a compacted material of red bauxite particles obtained according to the process of the invention at different levels of binders (Examples 7a, 7b) were compared to Example 6b.

The manufacturing conditions of the compacted material in the pilot device are summarized in Table XX below:

Table XX

Table XXI below summarizes the results obtained for the compacted materials of Examples 7a and 7b, compared with Example 6b.

Table XXI

Example 8 (core)

In Example 8, the compressive strength and erosion rate of a "core" material, also called "core-shell" material compacted red bauxite particles whose core (also called heart) is of a different composition are obtained according to a process according to the invention (Examples 8a and 8b).

The dry compositions used to manufacture the compacted material of Example 8a respectively comprise, in mass relative to the total mass of said dry composition, for the tempered composition, referred to as the outer layer, 85% of red bauxite EB and 15% of cement Ciment Fondu®, and for the core 100% red bauxite EB whose respective properties have been described in parts III.1 and III.2.

In this example 8a, the dry composition for the outer layer is mixed with 7% water, by weight relative to the total mass of said dry composition. The dry composition for the core is tempered with 5% water, by weight relative to the total mass of said dry composition.

The dry compositions used to manufacture the compacted material of Example 8b respectively comprise, in mass relative to the total mass of said dry composition, for the outer layer 85% of red bauxite EB and 15% of cement Cement Fondu®, and for the 95% EB red bauxite core and 5% Cement Fondu® cement whose respective properties have been described in Parts III.1 and III.2.

In this example 8b, the dry composition for the outer layer is mixed with 7% water, by weight relative to the total weight of said dry composition. The dry composition for the core is mixed with 7% water, by weight relative to the total weight of said dry composition.

The composition for the core layer thus tempered is introduced into an oil-molded, cylindrical, steel mold 30 mm in diameter. The mold is placed under a large press attached to a vibrating table. The core is thus pressed and jointly vibrated according to the method according to the invention.

Then, 16g of the tempered outer layer is introduced to the bottom of a second cylindrical steel mold with a diameter of 40mm, and then the "core" cylinder previously formed is placed in the middle and covered with the remainder of the outer layer composition.

The manufacturing conditions of the compacted material in the "miniature" laboratory device are summarized in Table XXII below: Table XXII

Table XXIII below summarizes the results obtained for the compacted materials of Examples 8a and 8b.

Table XXIII

Thus, it appears that the process according to the invention makes it possible to obtain compacted "core-shell" type materials whose mechanical resistance to compression is satisfactory.

Claims

1. Process for obtaining a compacted material according to which,

the value of said applied compressive stress being greater than or equal to 2 MegaPascal.

2. Method according to claim 1, wherein

3. The process according to claim 1, wherein

in a step n2) carried out prior to step c), said nucleus is completely enclosed in said molded composition obtained in step b), and in step c) is vibrated at said frequency between 20 Hertz and 80 Hertz and at said amplitude greater than or equal to 0.3 millimeters, said assembly comprising said at least one tempered composition and said enclosed core, then, together with said vibrating, said compressive stress is applied to said assembly.

4. The process according to claim 2, wherein

in a step n1), a core of raw materials is provided, said core having a mechanical strength greater than or equal to 0.1

MegaPascal (MPa),

in a step n2 ') carried out prior to step c), said nucleus is completely enclosed in said batch composition obtained in step b) and / or in at least one of said other batch compositions obtained in step p1), and,

5. Method according to one of claims 3 and 4, wherein said core provides in step n1) is a compacted material formed by compaction of another set of particles of raw materials.

6. Method according to one of claims 3 to 5, wherein said core is obtained according to the method of one of claims 1 and 2.

7. Process for obtaining a multilayer compacted material according to which, a first layer is produced according to the following steps:

a) a dry composition is formed by mixing, on the one hand, a set of particles of raw materials whose particle size distribution is characterized by a first reference diameter d90 of less than or equal to 50 millimeters and a second reference diameter of greater than or equal to equal to 0.08 micrometer with, on the other hand, from 1% to 50% of a hydraulic binder, in mass relative to the total mass of the dry composition, b) said dry composition formed in step a) is stripped with 1% to 35% water, by weight relative to the total mass of the dry composition, so as to form a batch composition,

c ') vibrating the batch composition of step b) at a frequency between 20 Hertz and 80 Hertz and at an amplitude greater than or equal to 0.3 millimeter, then, together with the vibration, is applied a compressive stress to said tempered composition,

8. Method according to one of claims 1 to 7, wherein it is expected that the vibration implemented in conjunction with the application of the compression stress is de-harmonized.

9. Method according to one of claims 1 to 8, wherein the vibration has an amplitude of between 0.3 millimeters and 5 millimeters, depending on the direction of compression.

10. Method according to one of claims 1 to 9, wherein it is further provided a step subsequent to step c) of obtaining the compacted material, during which said compacted material is placed for at least 24 hours in an oven at a predetermined temperature, and at a relative humidity greater than or equal to a threshold value of relative humidity.

1 1. Process according to one of Claims 1 to 10, according to which the particles of raw material of each set of particles are mineral particles, chosen from: red bauxite, white bauxite, alumina, limestone, lime, carbon, graphite carbon, carbon black, rock wool, glass wool, carbonates, metallurgical effluents, powders of manganese or its derivatives, metal ores or mixtures of ores as they can occur during extraction or during manufacturing processes, including metal oxides or iron ores.

12. Method according to one of claims 1 to 1 1, wherein for at least one set of particles of raw materials, the first reference diameter d90 associated with the particle size distribution of said set of particles of raw material is less than 20 millimeters and the second reference diameter d10 associated with said particle size distribution is greater than or equal to 0.1 micrometer.

13. Method according to one of claims 1 to 12, wherein the hydraulic binder is selected from: Portland cements, calcium aluminate cements, sulfo-aluminous cements, cements mixed with fly ash, cements mixed with blast furnace slags, cements mixed with pozzolans, or a mixture of these.

14. Method according to one of claims 1 to 13, wherein in step a), the hydraulic binder comprises a calcium aluminate cement having a molar ratio C / A of between 0.1 and 3.

15. Method according to one of claims 1 to 14, wherein in step a), the hydraulic binder is composed of a set of particles of hydraulic binder whose particle size distribution is characterized by a first reference diameter d90 lower or equal to 100 micrometers.

16. Compacted material comprising particles of raw material agglomerated with a hydraulic binder, obtained according to the method of one of claims 1 to 15.

17. Compacted material according to claim 16 having a compressive strength greater than or equal to 3 MegaPascal and an erosion rate of less than or equal to 15%.

18. A multilayer compacted material obtained according to the process of one of claims 2 or 4 to 15 comprising a stack of at least two superposed layers of inert raw materials to each other up to a predetermined threshold temperature.

19. Multilayer compacted material obtained according to the process of one of claims 3 to 6, comprising a core enclosed in at least one outer layer, wherein the core raw materials are inert with respect to the raw materials of said minus an outer layer in which it is enclosed, up to a predetermined threshold temperature.