PROCESS FOR PREPARING A SOLID MINERAL FOAM

Abstract

The present invention relates to a method for preparing a solid mineral foam comprising the following steps: (a) injecting a gas into a foaming mineral slurry whereby a two-phase mixture is obtained, (b) introducing the two-phase mixture obtained in step (a) into a static mixer whereby a mineral foam is obtained at the outlet of said static mixer, and then (c) allowing the mineral foam obtained in step (b) to harden whereby a solid mineral foam is obtained.

Description

Title of the invention: PROCESS FOR PREPARING A SOLID MINERAL FOAM Technical field

[0001] The present invention relates to the field of mineral materials and in particular mineral materials in the form of solid mineral foams such as cement foam, geopolymer foam or plaster foam.

[0002] Thus, the present invention provides a method for preparing a solid mineral foam from a mineral slurry comprising a hydraulic binder and a surfactant into which gas is injected. The two-phase mixture thus obtained then passes through a continuous static mixer in order to obtain at the output a homogeneous mineral foam of controlled density, the value of which can be controlled by the process parameters over a wide range. STATE OF THE PRIOR ART

[0003] Solid mineral foams, including cement foams, geopolymer foams and gypsum foams, are macroporous materials made from mineral sources.

[0004] These foams are characterized by their lightness, their thermal and acoustic insulation capacity and their fire resistance, which makes them particularly attractive for many applications, particularly in the building and construction sector.

[0005] Thus, cement foams offer good mechanical strength and durability, making this material suitable for lightweight structural elements and insulating panels.

[0006] Geopolymer foams, for their part, are distinguished by good mechanical strength and their excellent resistance to fire and chemical substances, which makes them a suitable choice for specific applications where these properties are crucial, such as (i) construction as a construction or insulation material or (ii) chemistry as a catalyst support or filtration membrane or for trapping toxic elements or other heavy metals.

[0007] Finally, gypsum foams are often used in interior insulation systems due to their permeability to water vapor and their contribution to the regulation of interior humidity.

[0008] There are essentially three methods of manufacturing mineral foams which are used in practice by industrialists.

[0009] A first method consists of adding a pore-forming agent such as silica fume, hydrogen peroxide (H2O2) or aluminum metal powder [1]. This This method presents risks related to the handling of chemicals, as hydrogen peroxide, which generates oxygen, is corrosive and toxic. The aluminum powder, in reaction with the basic medium, generates hydrogen, but induces a heterogeneous nucleation of hydrogen bubbles which can compromise the homogeneity of the final material. In addition, this manufacturing method does not allow for in-line and continuous manufacturing because it involves a chemical reaction.

[0010] A second method involves adding a surfactant to the mineral slurry precursor of the foam which, during the mechanical agitation step, entrains air thereby creating macroscopic porosity. However, this method has limitations in terms of accessible density.

[0011] A third multi-step method consists of preparing, on the one hand, aqueous foam from a foaming aqueous solution and, on the other hand, a mineral grout and then mixing these two products together. International applications WO 2002 / 024595 A1 and WO 2013 / 150148 A1 describe the preparation of lightweight plasterboards, i.e., plaster foam and cement foam, according to such a method [2,3]. The latter is not easy to implement because it involves two separate manufacturing processes, namely that of the aqueous foam and that of the mineral grout.

[0012] To the methods mentioned above, we must add additive manufacturing such as extrusion or 3D printing and the use of sacrificial templates (emulsion, polymer beads, fibers, molds, etc.).

[0013] Given the growing interest in solid mineral foams, the inventors set themselves the goal of proposing a process for preparing them which is simple, easy to implement and which does not have the disadvantages of the methods currently used. Statement of the invention

[0014] The present invention makes it possible to achieve the goal set by the inventors since the latter propose a process which is easy to implement and which makes it possible, in a single step and continuously, to obtain a solid mineral foam whose parameters are controllable.

[0015] Indeed, the present inventors have shown that it is possible to prepare a solid mineral foam with controlled and controllable characteristics, on the basis in particular of:

[0016] - the formulation of the grout and, mainly, its water content and the nature of the foaming surfactant used, which affects viscosity and setting time;

[0017] - process parameters such as the flow rate of the foaming slurry and the gas flow rate, and

[0018] - the geometric parameters of the ball tube such as the diameter of the balls, the length to diameter ratio of the tube.

[0019] These parameters allow perfect control of the porosity rate of the mineral foam produced in terms of material density, mechanical resistance, connected or unconnected porosity, which, in fact, influences its usage properties such as, for example, thermal conductivity and acoustic damping.

[0020] The formulation of the foaming slurry, particularly for reactive pastes, is optimized to have a viscosity and a setting time adapted to the process. The initial composition of these reactive pastes combined with an appropriate surfactant makes it possible to sufficiently delay the drainage of the generated foam. This makes it possible to keep the material homogeneous for the duration of the reaction and therefore the setting time. That is to say to pass from the state of liquid foam at the outlet of the bead tube to the state of solid foam while maintaining the homogeneous gas content throughout the material.

[0021] In summary, the advantages of the process according to the present invention are simplified, in-line and continuous manufacturing, while controlling the final properties of the solid mineral foam according to the desired applications.

[0022] Thus, the present invention relates to a process for preparing a solid mineral foam comprising the following steps:

[0023] (a) injecting a gas into a foaming mineral slurry whereby a mixture biphasic is obtained,

[0024] (b) introducing the two-phase mixture obtained in step (a) into a static mixer, whereby a mineral foam is obtained at the outlet of said static mixer, then

[0025] (c) allowing the mineral foam obtained in step (b) to harden, whereby a solid mineral foam is obtained.

[0026] An example of the elements involved in implementing the method according to the invention is presented in [Fig.l].

[0027] In the context of the present invention, the term "solid mineral foam" means a solid and porous material in the dry state, obtained following the hardening of a plastic mixture containing finely ground materials and water or a saline solution, said plastic mixture being capable of setting and hardening over time. This plastic mixture is also referred to herein as "mineral grout", "mineral mixture" or "geopolymeric paste".

[0028] The solid mineral foam prepared by the process according to the invention has open porosity, penetrating open porosity, connected (or interconnected) porosity and closed porosity. Advantageously, this solid mineral foam has percolating pores which connect a first main surface of the mineral foam to a second main surface of the mineral foam. For the purposes of the present invention, by "main surface" is meant an outer part of mineral foam, which limits it with respect to its environment. The main surface(s) typically present cavities, particularly macroscopic, which are not obstructed.

[0029] In particular, the solid mineral foam prepared by the process according to the invention has macropores and possibly mesopores. By "macropores" is meant pores or voids having an average diameter greater than 50 nm and in particular greater than 70 nm. By "mesopores" is meant pores or voids having an average diameter of between 2 and 50 nm and in particular between 2 and 20 nm. In a solid mineral foam prepared by the process according to the invention, the total porosity corresponding to the macroporosity and the possible mesoporosity is greater than 70%, in particular greater than 75%, and, in particular, greater than 80% by volume relative to the total volume of the solid mineral foam. For example, when the solid mineral foam is a geopolymer foam, the latter has, due to its preparation process iedue to geopolymerization, connected mesopores and unconnected macropores to which are added connected macropores obtained via the preparation method according to the invention.

[0030] In the preparation process according to the invention, the foaming mineral slurry used comprises at least one foaming organic surfactant.

[0031] By "organic surfactant" is meant an organic molecule comprising a lipophilic (apolar) part and a hydrophilic (polar) part. By "foaming organic surfactant" is meant an organic surfactant as previously defined also having a hydrophilic / lipophilic balance (or HLB for "Hydrophilic-Lipophilic Balance") of between 3 and 8. As a reminder, the HLB value of a surfactant can easily be obtained using the Davies formula [4] and the HLB tables for different chemical groups, available to those skilled in the art.

[0032] More particularly, the foaming mineral slurry used in the process of the invention may comprise a single foaming organic surfactant or a mixture of at least two foaming organic surfactants chosen from non-ionic foaming surfactants, anionic foaming surfactants, cationic foaming surfactants, amphoteric surfactants, surfactants with a Bolaforme type structure, surfactants with a Gemini type structure and polymeric surfactants.

[0033] Advantageously, the foaming mineral slurry used in the process of the invention comprises a single foaming organic surfactant or a mixture of at least two foaming organic surfactants chosen from non-ionic foaming surfactants, anionic foaming surfactants and cationic foaming surfactants. In the mixtures of foaming organic surfactants, at least two surfactants are chosen from the same family or from two different families chosen from non-ionic foaming surfactants, anionic foaming surfactants and cationic foaming surfactants.

[0034] As a reminder, non-ionic (or neutral) organic surfactants are compounds whose surfactant properties, in particular hydrophilicity, are provided by uncharged functional groups such as an alcohol, an ether, an ester or even an amide, and may contain heteroatoms such as nitrogen or oxygen. Due to the low hydrophilic contribution of these functions, non-ionic surfactant compounds are most often polyfunctional. In the context of the present invention, the foaming non-ionic surfactants are in particular chosen from alkyl alkoxylates; fatty alcohol alkoxylates; fatty amine alkoxylates; fatty acid alkoxylates; oxoalcohol alkoxylates; alkylphenol alkoxylates; alkyl ethoxylates; fatty alcohol ethoxylates; fatty amine ethoxylates; fatty acid ethoxylates; oxoalcohol ethoxylates;alkylphenol ethoxylates such as, for example, octylphenol and nonylphenol ethoxylates; alcohols, α-diols, polyethoxylated and polypropoxylated alkylphenols having a fatty chain comprising, for example, from 8 to 18 carbon atoms, the number of ethylene oxide or propylene oxide groups possibly being in particular from 2 to 50; complex polymers of polyethylene and polypropylene oxides; copolymers of ethylene and propylene oxides; block copolymers of polyethylene and polypropylene oxides such as, for example, POE-POP-POE triblock copolymers; condensates of ethylene and propylene oxide on fatty alcohols; polyethoxylated fatty amides preferably having from 2 to 30 moles of ethylene oxide; polyethoxylated ethers preferably having from 2 to 30 moles of ethylene oxide; monoesters (monolaurate, monomyristate, monostearate, monopalmitate, monooleate, etc.) and polyesters of fatty acids and glycerol;polyglycerolated fatty amides comprising on average from 1 to 5 and, more specifically, from 1.5 to 4 glycerol groups; oxyethylenated sorbitan fatty acid esters comprising from 2 to 30 moles of ethylene oxide; monoesters (monolaurate, monomyristate, monostearate, monopalmitate, monooleate, etc.) and polyesters of fatty acids and sorbitan, polyoxyethylene sorbitan monoesters; sucrose fatty acid esters; polyethylene glycol fatty acid esters; alkylpolyglucosides; N-alkylglucamine derivatives and amine oxides such as (Ci0-Ci4)alkylamine oxides or N-acylaminopropylmorpholine oxides; polyols (surfactants derived from sugars) in particular glucose alkylates such as, for example, glucose hexanate; surfactants derived from glucoside (sorbitol laurate) or polyols such as glycerol alcohol ethers;alkanolamides and their mixtures. More particularly, as foaming non-ionic surfactants, it is possible to use the foaming non-ionic surfactants described in the; international application WO 2004 / 008463 A2 [5]. Such a surfactant is, for example, chosen from the family of alkylpolyglucosides or alkylpolyetherglucosides, natural derivatives of glucose and biodegradable. These are, for example, “ORAMIX CG-110” from the company SEPPIC, “Glucopon® 215 CS” from the company COGNIS or “Glucopon® 215 UP” from the company BASF.

[0035] Anionic organic surfactants are surfactants whose hydrophilic part is negatively charged. A foaming anionic surfactant usable in the context of the present invention is typically chosen from the group consisting of sulfuric acid esters, phosphoric acid esters, alkyl or aryl sulfonates, alkyl or aryl sulfates, alkyl or aryl phosphates, alkyl or aryl sulfosuccinates or alkyl or aryl sarcosinates associated with a counterion such as an ammonium ion (NH4+), a quaternary ammonium such as tetrabutylammonium, and cations and in particular alkali metal cations, said cations being such as Na+, Li+, Ca2+, Mg2+, Zn2+ and K+.Examples of foaming anionic surfactants that can be used are tetraethylammonium paratoluenesulfonate, sodium dodecyl sulfate (or SDS), sodium lauryl sarcosinate (or sarcosyl), sodium palmitate, sodium stearate, sodium myristate, sodium di(2-ethylhexyl) sulfosuccinate, methylbenzene sulfonate and ethylbenzene sulfonate.

[0036] The cationic organic surfactants have at least one hydrocarbon chain and a polar head, the hydrophilic part of said agent being positively charged. A foaming cationic surfactant that can be used in the context of the present invention is advantageously chosen from quaternary ammoniums comprising at least one C4-C22 aliphatic chain associated with an anionic counterion chosen in particular from boron derivatives such as tetrafluoroborate or halide ions such as F, Br, I or CL. As foaming cationic surfactants that can be used, mention may be made of tetrabutylammonium chloride, tetradecylammonium chloride, tetradecyltrimethylammonium bromide (TTAB), alkylpyridinium halides bearing an aliphatic chain and alkylammonium halides.

[0037] In a particular embodiment, the foaming organic surfactant(s) is / are chosen from the group consisting of carboxylic acid salts, sulfonic acid salts, sulfate salts, sulfuric acid ester salts, phosphoric acid ester salts, alkylpolyglucosides and amine oxides. In an even more particular embodiment, the foaming organic surfactant(s) is / are chosen from the group consisting of alkylpolyglucosides.

[0038] In the foaming mineral slurry used in the process of the invention, the foaming organic surfactant or the mixture of at least two foaming organic surfactants is present in an amount of between 1 g and 100 g, in particular between 10 g and 50 g and, in particular, of the order of 20 g (i.e. 20 g ± 2 g) per liter of foaming mineral slurry.

[0039] There is a threshold, for the liquid fraction contained in the foaming mineral slurry used in the process according to the invention, from which drainage is observed at the level of the mineral foam obtained at the end of step (b) of the process according to the invention. For each formulation of foaming mineral slurry, a person skilled in the art is capable of determining this threshold by routine tests.

[0040] Alternatively, it is possible to prevent this drainage by adding a viscosifying agent or a setting accelerator additive to the foaming mineral grout. In other words, the foaming mineral grout used in the method according to the invention further comprises at least one viscosifying agent and / or at least one setting accelerator.

[0041] Any viscosifying agent and any setting accelerator agent known and used in the field of geopolymers, cements and / or plasters can be used in the context of the present invention.

[0042] Typically, the viscosity agent(s) usable in the present invention is / are chosen from the group consisting of water-soluble polymers, hydrocolloids, heteropolysaccharides such as, for example, polyglucosidic polymers with branched trisaccharide chains, cellulose derivatives and polysaccharides such as polysaccharides containing glucose as the sole monomer. As particular examples, the viscosity agent(s) usable in the context of the present invention is / are chosen from the group consisting of xanthan gum, guar gum, ragar-agar, carrageenan, sodium alginate, caseinate, gelatin, pectin, starch, cellulose, 2-hydroxyethylcellulose (HEC) and chitosan.

[0043] When implemented, the viscosifying agent(s) is / are present in an amount of between 0.1 g and 10 g per liter of foaming mineral grout.

[0044] Typically, the setting accelerator(s) usable in the present invention is / are chosen from the group consisting of inorganic sodium or calcium salts such as sodium nitrate (NaNO3), calcium nitrate (Ca(NO3)2), and calcium chloride (CaCl2).

[0045] When implemented, the setting accelerator(s) is / are present in an amount of between 0.01% and 1% by mass relative to the mass of foaming mineral grout.

[0046] In a first embodiment of the invention, the solid mineral foam prepared by the method according to the invention is a geopolymer foam. In this first form of implementation, the method comprises a preliminary step of preparing a geopolymeric grout obtained by mixing at least one alumino-silicate source with an activation solution.

[0047] By "geopolymer", is meant, in the context of the present invention, a solid and porous material in the dry state, obtained following the hardening of a mixture containing finely ground materials (i.e. the aluminosilicate source) and a saline solution (i.e. the activation solution), said mixture being capable of setting and hardening over time. The hardening of the geopolymer is the result of the dissolution / polycondensation of the finely ground materials of the geopolymeric mixture in the saline solution such as a saline solution of high pH (i.e. the activation solution).

[0048] More particularly, a geopolymer is an amorphous alumino-silicate inorganic polymer. Said polymer is obtained from a reactive material containing essentially silica and aluminum (i.e. the alumino-silicate source), activated by a strongly alkaline solution. The structure of a geopolymer is composed of a Si-O-Al network formed of silicate (SiO4) and aluminate (A1O4) tetrahedra linked at their vertices by sharing oxygen atoms. Within this network, there are one or more charge compensating cation(s), also called compensation cation(s), which make it possible to compensate for the negative charge of the A1O4 complex.Said compensation cation(s) is (are) advantageously chosen from the group consisting of alkali metals such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs); alkaline earth metals such as magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba); and mixtures thereof.

[0049] The expressions “reactive material containing essentially silica and aluminum” and “alumino-silicate source” are, in the present invention, similar and can be used interchangeably.

[0050] The reactive material containing essentially silica and aluminum that can be used to prepare the geopolymer foam used in the context of the invention is advantageously a solid source containing amorphous aluminosilicates. These amorphous aluminosilicates are in particular chosen from natural aluminosilicate minerals such as illite, stilbite, kaolinite, pyrophyllite, andalusite, bentonite, kyanite, milanite, grovenite, amesite, cordierite, feldspar, allophane, etc.; calcined natural aluminosilicate minerals such as metakaolin; synthetic glasses based on pure aluminosilicates; aluminous cement; pumice; calcined by-products or residues of industrial exploitation such as fly ash and blast furnace slag respectively obtained from the combustion of coal and during the transformation of iron ore into cast iron in a blast furnace; and mixtures thereof. In a particular embodiment, the aluminosilicate source is metakaolin.

[0051] The high pH saline solution also known, in the field of geopolymerization, as "activation solution" is a strongly alkaline aqueous solution which may optionally contain silicate components chosen in particular from the group consisting of silica, colloidal silica and vitreous silica.

[0052] The expressions "activation solution", "high pH saline solution" and "strongly alkaline solution" are, in the present invention, similar and can be used interchangeably.

[0053] By "strongly alkaline" or "high pH" is meant a solution whose pH is greater than 9, in particular greater than 10, in particular greater than 11 and, more particularly, greater than 12. In other words, the activation solution has an OH concentration greater than 0.01 M, in particular greater than 0.1 M, in particular greater than 1 M and, more particularly, between 5 and 20 M.

[0054] In addition, the activation solution comprises the compensating cation or the mixture of compensating cations in the form of an ionic solution or a salt. Thus, the activation solution is in particular chosen from an aqueous solution of sodium silicate (Na2SiO3), potassium silicate (K2SiO2), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), cesium hydroxide (CsOH) and their derivatives, etc. In particular, the activation solution used in the invention is a strongly alkaline aqueous solution of potassium silicate (K2SiO3). More particularly, the activation solution used in the invention is an aqueous solution prepared from K5020T marketed by the company Woellner and made alkaline by adding KOH.

[0055] Furthermore, the activation solution / aluminosilicate source mass ratio in the geopolymeric grout type mineral grout is advantageously between 1.2 and 2.1 and in particular between 1.4 and 2. As a particular example, the activation solution / MK ratio is of the order of 1.55 (i.e. 1.55 ± 0.10) or of the order of 1.88 (i.e. 1.88 ± 0.10).

[0056] In a second embodiment of the invention, the solid mineral foam prepared by the method according to the invention is a hydraulic cement foam. The hardening of this foam is the result of the hydration of finely ground materials of the cement slurry.

[0057] In this second form of implementation, the method comprises a preliminary step of preparing a cement grout obtained by mixing at least one cement or clinker with water.

[0058] Indeed, the finely ground materials of the cement grout consist, in whole or in part, of a finely ground clinker. By "clinker" is meant a mixture comprising one or more elements chosen from the group consisting of:

[0059] - a limestone,

[0060] - a limestone having a CaO content varying between 50 and 60%,

[0061] - a source of alumina such as ordinary bauxite or red bauxite,

[0062] - a clay, and

[0063] - a sulfate source such as gypsum, calcium sulfate hemihydrate, plaster, natural anhydrite or sulfocalcium ash,

[0064] said element(s) being crushed, homogenized and brought to a high temperature above 1200°C, in particular above 1300°C, in particular of the order of 1450°C (i.e. 1450°C ± 100°C, advantageously 1450°C ± 50°C). The high temperature cooking step is called "clinkerization". After the preparation of the clinker and before or during its grinding, at least one other additive such as a source of sulfate as previously defined can be added to it.

[0065] In addition, the W / C ratio in the mineral grout of the hydraulic cement grout type is advantageously between 0.3 and 1.5 and in particular between 0.4 and 1. By "W / C ratio" is meant the mass ratio of the quantity of water to the quantity of cement (i.e. dry cement mix which corresponds to the cement mix without water or saline solution). These quantities are those used at the time of formulation of the mineral grout of the hydraulic cement grout type.

[0066] In this second embodiment of the invention, the hydraulic cement foam can be obtained from a Portland cement or a composite Portland cement. A Portland cement advantageously comprises between 50 and 70% of tricalcium silicate [(CaO)3SiO2], between 10 and 25% of dicalcium silicate [(CaO)2SiO2], between 5 and 15% of tricalcium aluminate [(CaO)3Al2O3], between 5 and 10% of tetracalcium aluminoferrite [(CaO)4Al2O3Fe2O3]. Such a Portland cement can be mixed with secondary compounds to give a “composite Portland cement” in which the quantity of secondary compounds such as limestone or blast furnace slag is greater than 3%, in particular between 5 and 80%, in particular, between 10 and 60% by weight relative to the total weight of said composite Portland cement. Advantageously, the Portland cement or composite Portland cement used has an E / C ratio of between 0.3 and 1.5 and in particular between 0.4 and 1.

[0067] In this second embodiment of the invention, the hydraulic cement foam can also be obtained from an aluminous cement, i.e. the clinker of which mainly comprises calcium aluminates.

[0068] Furthermore, in this second embodiment of the invention, the hydraulic cement foam can be obtained from a sulfo-aluminous and / or ferro-cement. aluminous. These clinkers are cementitious binders with rapid hardening properties and obtained by clinkering at a temperature varying between 1200°C and 1350°C of mixtures containing at least one source of lime such as limestones having a CaO content varying between 50 and 60%, at least one source of alumina and at least one source of sulfate as previously defined. Advantageously, a sulfo-aluminous clinker comprises between 28 and 40% of A12O3, between 3 and 10% of SiO2, between 36 and 43% of CaO, between 1 and 3% of Fe2O3, and between 8 and 15% of SO3. A ferro-aluminous clinker comprises between 25 and 30% of A12O3, between 6 and 12% of SiO2, between 36 and 43% of CaO, between 5 and 12% of Fe2O3, and between 5 and 10% of SO3.

[0069] In a third embodiment of the invention, the solid mineral foam prepared by the method according to the invention is a plaster foam. The hardening of this foam is the result of the hydration of finely ground materials present in a plaster grout or paste.

[0070] In this third form of implementation, the method therefore comprises a preliminary step of preparing a plaster grout obtained by mixing plaster with water.

[0071] In the present invention, the term "plaster" means a hydratable calcium sulfate. In the present invention, the term "hydratable calcium sulfate" means anhydrous calcium sulfate (anhydrite II or III) or hemihydrated calcium sulfate (CaSO4 ^2^0) in its crystalline form a or [3. Such compounds are well known to those skilled in the art and are generally obtained by firing a gypsum.

[0072] Furthermore, the W / P ratio in the mineral grout of the plaster grout type is advantageously between 0.3 and 1.5 and in particular between 0.4 and 1. By "W / P ratio" is meant the mass ratio of the quantity of water to the quantity of plaster (i.e. dry plaster, without water or saline solution). These quantities are those used at the time of formulation of the mineral grout of the plaster paste type.

[0073] Whatever the nature of the mineral grout used in the preparation process, its prior preparation is a technique known in the field of geopolymers, cements and plasters.

[0074] Step (a) of the method according to the invention consists of injecting a gas into the foaming mineral slurry. More particularly, the foaming mineral slurry kept under agitation in a container or tank is conveyed from this container or tank to a static mixer and gas is injected into the foaming mineral slurry during this conveying.

[0075] A mixer, a magnetic bar, an agitator, an ultrasonic system, a homogenizer or a recirculating pump can be used to maintain while stirring the foaming mineral grout, in order to maintain its composition homogeneous.

[0076] The conveyance of the foaming mineral slurry from the container in which it was prepared and / or placed to the static mixer is typically carried out by pumping. A person skilled in the art will be able to determine, without inventive effort, the type and characteristics of the pump to be used for this purpose.

[0077] The gas injected into the foaming mineral slurry during the process according to the invention may be any gas. It may in particular be chosen from the group consisting of air, oxygen, carbon dioxide, helium, argon and nitrogen and a mixture thereof. Advantageously, the gas used in the context of the invention is air.

[0078] A person skilled in the art will be able to determine, without inventive effort, the flow rate at which the foaming mineral slurry or the two-phase mixture comprising this slurry and the injected gas is conveyed to the static mixer as well as the flow rate and pressure at which the gas is introduced into the foaming mineral slurry as a function of the desired properties of the solid mineral foam, in particular in terms of density and mechanical resistance, and this, as a function of the applications targeted for this solid mineral foam.

[0079] Thus, the flow rate at which the foaming mineral slurry or the two-phase mixture comprising this slurry and the injected gas is typically conveyed to the static mixer is between 10 L / h and 1000 L / h and in particular between 20 L / h and 500 L / h. This flow rate is ensured by the pump used to collect the foaming mineral slurry from the container / tank.

[0080] The flow rate at which the gas is injected into the foaming mineral grout is between 10 L / h and 1000 L / h and in particular between 20 L / h and 500 L / h. This flow rate is typically ensured by an electronic flow meter.

[0081] The pressure at which the gas is injected into the foaming mineral grout is between 1.105 Pa (1 bar) and 5.104 Pa (50 bar) and in particular between 1.5.105 Pa (1.5 bar) and 1.10 4 Pa ​​(10 bar).

[0082] Any type of static mixer can be used in the context of the method of the invention. The piling up of the objects filling the latter creates a porous medium which promotes the mixing of the two phases (foaming mineral slurry and gas) which comprise the two-phase mixture introduced into the static mixer.

[0083] Typically, the static mixer can be made of different types of materials and in particular its packing can be made of objects of different shapes, different sizes and different materials.

[0084] In a particular embodiment, the static mixer implemented in the invention is a helical static mixer.

[0085] In another embodiment, the mixer implemented in the invention is a static bead mixer, in particular a static glass bead mixer and, in particular, a static bead mixer such as that described in the experimental part below.

[0086] The hardening step (c) during the process according to the invention advantageously comprises a curing step and / or a drying step. A person skilled in the art will be able to determine, without inventive effort, the conditions to be implemented depending on whether the mineral foam to be hardened is a geopolymer foam, a cement foam or a plaster foam.

[0087] When step (c) of the method according to the invention comprises a curing step, the latter can be carried out by humidifying the atmosphere surrounding the mineral foam obtained at the end of step (b) or by applying an impermeable coating to said foam. This curing step can be carried out at a temperature between 10°C and 60°C, in particular between 15°C and 50°C and, in particular, at room temperature (i.e. 20°C ± 3°C) and can last between 1 and 40 days, in particular between 5 and 30 days and, in particular, between 10 and 20 days.

[0088] When step (c) comprises a drying step, the latter can be carried out at a temperature between 30°C and 110°C, in particular between 40°C and 80°C and, in particular, of the order of 50°C (50°C ± 5°C) and can last between 6 h and 10 days, in particular between 12 h and 5 days and, in particular, of the order of 24 h (i.e. 24 h ± 3°h). Advantageously, step (c) comprises a curing step followed by a drying step, as previously defined.

[0089] Furthermore, prior to the hardening of the mineral foam obtained at the end of step (b), the latter may be placed in molds so as to give it a predetermined shape following this hardening. On the contrary, the shape of the mineral foam may be obtained after step (c) of the process, in particular by subjecting the solid mineral foam obtained to one or more of the following treatments: cutting, grinding, crushing, planing, etc.

[0090] The present invention also relates to the use of a static mixer as previously defined and in particular a static ball mixer for preparing a solid mineral foam.

[0091] Other characteristics and advantages of the present invention will become apparent to those skilled in the art upon reading the examples below given for illustrative and non-limiting purposes, with reference to the appended figures. Brief description of the drawings

[0092] [Fig. 1] already presented is a diagram of the method according to the invention and of the various devices implemented during the latter.

[0093] [Fig.2] shows a photograph of a ball tube.

[0094] [Fig.3] shows a photograph of foam A prepared in accordance with method according to the invention in example 1.

[0095] [Fig.4] shows a photograph of foam B prepared in accordance with the process according to the invention in Example 1.

[0096] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0097] Example 1: Production of two “geopolymer” reactive paste foams.

[0098] To manufacture two geopolymer foams according to the method of the invention, an activation solution is prepared using a commercial potassium silicate solution (Woellner K5020T) to which potassium hydroxide (KOH) and water (H2O) are added. Table 1 below shows the composition of the commercial potassium silicate solution.

[0099] [Tables 1 % by mass Si o2 % by mass k2o % by mass H2O K5020T 29.8 18.3 51.9

[0100] Table 1: Composition of Woellner K5020T solution

[0101] Table 2 below shows the concentrations of the two activation solutions used.

[0102] [Tables2] Activation solution % by mass H 2o % by mass KOH % by mass K50 20T A(13H2O) 26.63 14.44 58.93 B (18H2O) 39.81 11.85 48.34

[0103] Table 2: composition of the activation solution

[0104] These solutions are mixed with an alumino-silicate source: metakaolin (Argical M1000).

[0105] A foaming surfactant, Glucopon 215 UP BASF, is then added to these formulations. The ratio [metakaolin mass / activation solution mass] is optimized in order to have a rheological behavior adapted to the generation of foam in this process, as indicated in Table 3 below.

[0106] [Tables3] Solutions % mass metakaolin % mass solutio n activati ​​on Surfactant concentration [g / L] Density (g.cm3) Zero shear viscosity (Pa.s) Infinite shear viscosity (Pa.s) A(13H2 O) 39.28 60.73 20 1.67 0 minute—0.70 tlminute—0.09 1195minutes 0.37 1195minutes 0.24 B (18H2 O) 34.67 65.33 20 1.55 0 minute 0.14 Ominute 0.03 1195 minutes 0.26 1195 minutes 0.03

[0107] Table 3: composition and properties of the foaming grout

[0108] Zero and infinite shear viscosities are extracted using the cross model from experimental data measured on glucopon-free geopolymers. These are acquired with a TAinstrument DHR2 imposed stress rheometer and a duvet geometry over a shear range of 5 s 1 to 200 s

[0109] The foaming mineral slurry thus formed is pumped with a Prominent Beta 5T5B0232 diaphragm pump (adjustable in volume and stroke frequency). During this pumping step, the slurry is kept stirring with a magnetic bar and a magnetic stirrer. The air injection is controlled using a Brooks gas mass flow regulator (0 to 300 mL / min).

[0110] This foaming slurry / gas mixture then passes into a static bead mixer, made with a 20 cm long PVC tube with an internal diameter of 2 cm, containing packed glass beads with a diameter of 2 to 2.4 mm ([Fig.2]). The foam created at the outlet is transported by a simple flexible tube.

[0111] The foam thus generated is weighed in a beaker to obtain its wet density (mass of foam / volume of foam). This value being corrected with the density of the initial foaming slurry, the liquid fraction of the foam is obtained (% of liquid in the foam).

[0112] The liquid fraction of the foam generated can be controlled by modifying the liquid flow rate and / or the gas flow rate for the same formulation. Table 4 below shows the results of the two foams formulated in this example:

[0113] [T ables 4] Foams Air pressure (bar) Qair (L / h) Qliquid (L / h) Density of wet foam (g. cm3) Liquid fraction (%) Gas fraction (%) A(13H2 O) 2 80 36 0.805 48.19 51.81 B (18H2 O) 2 150 36 0.388 26.65 73.35

[0114] Table 4: Process settings and wet foam properties

[0115] The foams obtained are poured into Teflon molds measuring 4*4*16 cm3 and left to stand at 20°C and 100% RH (Relative Humidity) until a solid material is obtained.

[0116] These test pieces are then demolded to observe the homogeneity and stability of the solid foam. The setting of the material freezes and traps the gas bubbles and the metakaolin particles, avoiding intensive drainage.

[0117] The foam is placed in an oven at 50°C for 24 hours to dry the formed material, then weighed to deduce the dry density of the foam (mass of material / volume of material). The mechanical resistances are also measured, the results are presented in Table 5 below:

[0118] [Tables5] Foams Dry density (g.cm3) Compressive strength (MPa) A(13H2O) 0.315 1.64 B (18H2O) 0.194 < 1

[0119] Table 5: results of dry foams

[0120] This innovative process allows, depending on the formulations and process settings, the manufacture of solid mineral foams with different properties and therefore uses. Indeed, a foam for construction will have to meet a certain mechanical resistance while a foam for insulation can be lighter.

[0121] For liquid effluent decontamination or filtration applications, reactive paste foams are interesting given their macroscopic porosities which must be connected.

[0122] The foams A and B obtained are presented respectively in Figures 3 and 4. These photographs allow the difference in lightening of the foams obtained to be observed, despite this difference in density all the foams manufactured with this process are homogeneous and their porosity is connected.

[0123] Example 2: Production of two “geopolymer” foams from a single formulation.

[0124] In this example, the manufacture of different foams from the same geopolymer formulation by changing the process parameters is described. The formulation is described in Table 6:

[0125] [Tables: Solution % mass m etakaolin % mass sol ution activation Surfactant concentration [ g / L] Density (g. cm3) CetD(2:20 p.m.) 38.26 61.74 20 1.643

[0126] Table 6: composition and properties of the foaming grout

[0127] This foaming slurry is pumped into the process and then the parameters (air flow rate, pump flow rate) are modified in situ in order to obtain different characteristics of the foam at the outlet. These are presented in Table 7 below:

[0128] [Tables7] Foams Air pressure (bar) Qair (L / h) Qliquid (L / h) Density of wet foam (g. cm3) Liquid fraction (%) Gas fraction (%) C 2 150 36 0.430 26.17 73.87 D 2 80 25 0.545 33.20 66.80

[0129] Table 7: Process settings and wet foam properties

[0130] The foams obtained are cast, stored and dried under the same conditions as those detailed in Example 1. The values ​​of the dry densities and mechanical resistances are presented in Table 8 below:

[0131] [Tables8] Foams Dry density (g.cm3) Compressive strength (MPa) C 0.337 0.865 D 0.396 2.15

[0132] Table 8: results of dry foams

[0133] This process allows, for the same formulation, the manufacture of solid foams with different properties and therefore uses. These process parameters can be modified continuously during the operation. References

[0134] [1] Patent application FR 2512808 A1 published on March 18, 1983.

[0135] [2] International application WO 2002 / 024595 A1 published on March 28, 2002.

[0136] [3] International application WO 2013 / 150148 A1 published on October 10, 2013.

[0137] [4] Davies, 1957, “A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent” Gas / Liquid and Liquid / Liquid Interface. Proceedings of the International Congress of Surface Activity (1957): 426-438.

[0138] [5] International application WO 2004 / 008463 A2 published on January 22, 2004.

Claims

Claims

1. A method for preparing a solid mineral foam comprising the following steps: (a) injecting a gas into a foaming mineral slurry whereby a two-phase mixture is obtained, (b) introducing the two-phase mixture obtained in step (a) into a static mixer whereby a mineral foam is obtained at the outlet of said static mixer, and then (c) allowing the mineral foam obtained in step (b) to harden whereby a solid mineral foam is obtained.

2. Preparation process according to claim 1, characterized in that said foaming mineral slurry comprises at least one foaming surfactant.

3. Preparation process according to claim 2, characterized in that said at least one foaming surfactant is chosen from the group consisting of carboxylic acid salts, sulfonic acid salts, sulfate salts, sulfuric acid ester salts, phosphoric acid ester salts, alkylpolyglucosides and amine oxides.

4. Preparation process according to claim 2 or 3, characterized in that said at least one foaming surfactant is present in an amount of between 1 g and 100 g, in particular between 10 g and 50 g and, in particular, of the order of 20 g (i.e. 20 g ± 2 g) per liter of foaming mineral slurry.

5. Preparation process according to any one of claims 1 to 4, characterized in that said foaming mineral slurry further comprises at least one viscosifying agent and / or at least one setting accelerator agent.

6. Preparation process according to any one of claims 1 to 5, characterized in that said mineral foam is a geopolymeric foam and that said process comprises a prior step of preparing a geopolymeric grout obtained by mixing at least one aluminosilicate source with an activation solution.

7. Preparation process according to claim 6, characterized in that the mass ratio of activation solution / aluminosilicate source used in the geopolymeric grout type mineral grout is between 1.2 and 2.1 and in particular between 1.4 and 2.

8. Preparation process according to any one of claims 1 to 5, characterized in that said mineral foam is a hydraulic cementitious foam.

9. Preparation process according to any one of claims 1 to 5, characterized in that said mineral foam is a plaster foam.

10. Preparation process according to any one of claims 1 to 9, characterized in that said gas is chosen from the group consisting of air, oxygen, carbon dioxide, helium, argon, nitrogen and a mixture thereof.

11. Preparation process according to any one of claims 1 to 10, characterized in that said static mixer is a static bead mixer.

12. Preparation process according to any one of claims 1 to 11, characterized in that said hardening step (c) comprises a curing step and / or a drying step.

13. Use of a static mixer and in particular a static bead mix for preparing a solid mineral foam.

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