EP3288915A1 - Method for producing a functionalised geopolymer foam, said functionalised foam, and the uses thereof - Google Patents

Abstract

The invention relates to a method for producing a geopolymer foam comprising nanoparticles of a metal coordination polymer with CN ligands of formula [Alk⁺ _x]Mⁿ⁺[M'(CN)_m]^z- wherein Alk is an alkaline metal, x is 1 or 2, M is a transition metal, n is 2 or 3, M' is a transition metal, m is 6 or 8, and z is 3 or 4. The invention also relates to said geopolymer foam produced in this way and to the uses thereof, especially for trapping caesium or thallium.

Description

 PROCESS FOR PREPARING FUNCTIONALIZED GEOPOLYMER FOAM, FUNCTIONALIZED FOAM AND USES THEREOF

DESCRIPTION

TECHNICAL AREA

The present invention belongs to the field of geopolymers and in particular geopolymer foams useful for the catalysis, filtration and / or decontamination of liquid or gaseous effluents.

 More particularly, the present invention provides a method for functionalizing a geopolymer foam with nanoparticles of a CN-ligated metal coordination polymer comprising metal cations, alkaline cations, and hexa- and octacyanometallate anions, especially hexanedial anions. and octacyanoferrates. The present invention also relates to the geopolymer foam thus functionalized and its uses in particular for the selective extraction of compounds to be recovered or decontaminated such as cesium or thallium.

 Finally, the present invention relates to a particular method for preparing a geopolymer foam for subsequent functionalization and this, using two different adjuvants that are a gas-generating adjuvant and an air-entraining aid.

STATE OF THE PRIOR ART Geopolymers are aluminosilicate materials synthesized from the alkaline activation of an aluminosilicate source such as, for example, metakaolin or fly ash. These are mainly amorphous materials which have an intrinsic porosity of the order of 40-50%, an average pore size of between 4 and 15 nm and a specific surface area of between 40 and 200 m ² / g according to the alkaline activator used ie sodium or potassium [1]. Geopolymers are presented as having good mechanical strength, good fire resistance and acid attacks and can be used in various parts of the industry such as building for thermal insulation, nuclear for waste conditioning [2] or chemistry for the trapping of toxic elements or other heavy metals [3] .

 The geopolymers can be used in the form of foams namely geopolymers with low density, highest possible total porosity i.e. greater than 70% and macroscopic pore size in addition to mesoscopic intrinsic pore size.

 Mineral foams of geopolymers can be synthesized indirectly, namely by using the template method [4] or directly from various porogenic agents [5].

 The so-called "template" method involves making an oil-type emulsion in alkaline activation solution and geopolymerizing the mineral phase around oil drops [4, 6]. The low density final material is obtained either by washing or by heat treatment.

 In the case of a synthesis in a direct way, the macroscopic porosity of the geopolymer can be created by the water vapor generated during the curing of the geopolymer at 150 ° C, which however remains a poorly controllable process. Such a method is notably implemented in the article by Lopez et al, 2014 [7] in which no information on the pore size is given.

 In a variant of the direct method, surfactants can be introduced into the geopolymer solution, still liquid, which during the mechanical stirring step causes air thus creating a macroscopic porosity of the order of one hundred microns. [8, 9]. Another way to make a geopolymer foam is to use chemicals such as aluminum metal [10], silica fume [10, 11] or hydrogen peroxide [8-10]. Indeed, the addition of metal in the geopolymer mixture generates hydrogen by reaction with the alkalis while the addition of peroxide generates oxygen which is less dangerous in terms of gas management in industrial installations than they are nuclear or not.

In addition, the article by Cilla et al, 2014 [12] describes the synthesis of a geopolymer foam by combining hydrogen peroxide used to generate oxygen and an oil comprising triglycerides which causes saponification reactions to generate in situ surfactant molecules. In addition, strong mechanical agitation is used during the process to entrain as much air as possible. The patent application US 2013/055924 [6] describes a similar method generalized to other gas generating compounds.

 Cilla et al compare this foam with foams synthesized from saponification reactions alone or with foams synthesized by the hydrogen peroxide route [12]. They conclude that the combination of the three techniques (hydrogen peroxide + surfactant generated in situ + strong agitation) leads to a total and open porosity much higher than the other two foams and that the density is much lower. However, this work does not describe the size of the samples used for the mechanical strength tests and no explanation is given on the impact of the surfactant on the stabilization of the gas generated by the decomposition of the hydrogen peroxide.

 Last but not least, it is not mentioned in this study whether the synthesized monoliths retain their integrity when washing with hot water to remove glycerol produced during saponification reactions. This essential point before considering the industrial exploitation of such a process had been emphasized by Medpelli et al.

[4].

 The use of geopolymer foam has a certain advantage in the building sector and in particular for thermal insulation [11] but also in the nuclear or chemical field. Indeed, the geopolymer foam can be used on the one hand to trap / adsorb radioactive elements such as cesium but also serves as final containment matrix.

Thus, the adsorption of radioactive elements such as cesium, strontium, cobalt, toxic elements such as arsenic or heavy metals such as cadmium and nickel in a geopolymer has been the subject of scientific studies [13] and a recent article on the use of geopolymer foam to trap cesium [7]. In this article, the foam is contacted with a cesium solution and a sorption capacity is determined according to the formulation parameters. The inventors have therefore set themselves the goal of proposing a process for preparing a geopolymer foam useful in the adsorption of radioactive elements such as cesium, strontium, cobalt, toxic elements such as arsenic or heavy metals such as cadmium and nickel, simple ie low number of steps, easy to implement, reproducible, reliable, economical and advantageously having a reduced environmental footprint, for example by avoiding the use of organic solvents and controlled atmospheres.

STATEMENT OF THE INVENTION

The present invention makes it possible to solve the previously listed technical problems and disadvantages of the materials and methods of the prior art. Indeed, the inventors have developed a protocol for preparing a geopolymer foam adapted for the adsorption of radioactive elements, toxic elements or heavy metals with a number of steps and a reasonable cost.

The present invention consists in the functionalization of the surface of a geopomyler foam with Prussian Blue Analogues (ABP) in the form of nanoparticles of a CN-ligated metal coordination polymer having the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} wherein Alk is an alkali metal, x is 1 or 2, M is a transition metal, n is 2 or 3, M' is a transition metal, m is 6 or 8 and z is 3 or 4.

The functionalization method that is the subject of the present invention makes it possible to obtain, in a reliable, certain and reproducible manner, the stoichiometric compound as defined above: [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} .

The method according to the invention is generally, as a whole, simple, since it uses known and proven processes. Moreover, it is reliable and perfectly reproducible. Indeed, it allows the preparation of a final product whose characteristics, composition - especially with regard to the alkali metal stoichiometry - and properties, are perfectly determined and do not undergo random variations. The The method according to the invention is all the more simple in that it does not require any prior functionalization of the geopolymer foam by organic groups such as grafts.

 The method according to the invention has a low impact on the environment: in particular, it does not generally implement organic solvents but only water and it does not use controlled atmospheres. In addition, it is typically carried out under atmospheric pressure and does not require a reduction of this pressure, especially in the form of a vacuum.

 The functionalized geopolymer foam prepared by the process according to the invention containing an alkali metal in its structure has better extraction capacities, for example cesium. It should be noted that the diversity of the ABP and in particular the various transition metals M 'and alkali metals Alk which can be envisaged makes it possible to obtain analogs that are not only selective with respect to different elements to be eliminated or recovered but also with grafting efficiency on the walls of the improved geopolymer foam.

 Finally, in functionalized geopolymer foam, the ion exchange during extraction, for example cesium, occurs only with potassium, and there is no release of the transition metal M or M 'which goes into the structure of cyanometalate, which is more advantageous especially from the point of view of compliance with the discharge standards where releasing an alkali metal such as potassium rather than a transition metal is preferable.

Thus, the present invention relates to a process for preparing a geopolymer foam comprising nanoparticles of a CN-ligated metal coordination polymer having the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} in which Alk is an alkali metal, x is 1 or 2, M is a transition metal, n is 2 or 3, M 'is a transition metal, m is 6 or 8 and z is 3 or 4, said process comprising the steps successive stages consisting of: a) contacting a geopolymer foam with a solution containing at least one M ^{n +} ion ^and then washing and optionally drying the geopolymer foam thus obtained;

b) contacting the geopolymer foam obtained after step (a) with a solution containing at least one salt or complex of [M '(CN) _m ] ^{z "} and at least one salt of an alkali metal Alk then wash and eventually dry the geopolymer foam thus obtained, and

 c) optionally repeat steps (a) and (b) at least once. By "geopolymer" or "geopolymer matrix" 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 (ie an aluminosilicate source) ) and a saline solution (ie an activating solution), said mixture being capable of setting and hardening over time. This mixture may also be referred to as "geopolymeric mixture", "geopolymeric composition" or "geopolymeric paste". The hardening of the geopolymer is the result of the dissolution / polycondensation of the finely ground materials of the geopolymeric mixture in a saline solution such as a high pH salt solution (i.e. the activating solution).

More particularly, a geopolymer or geopolymer matrix is an amorphous aluminosilicate inorganic polymer. Said polymer is obtained from a reactive material essentially containing silica and aluminum (ie the aluminosilicate source), activated by a strongly alkaline solution, the solid / solution weight ratio in the formulation being low. The structure of a geopolymer is composed of an Si-O-Al lattice formed of silicate (SiO ₄ ) and aluminate (AlO ₄ ) tetrahedra bound at their vertices by oxygen atom sharing. Within this network, there is (are) one or more charge compensation cation (s) also called compensation cation (s) which make it possible to compensate for the negative charge of the complex AI0 ₄ \ Ledit (s) cation (s) of compensation is (are) advantageously chosen (s) in 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.

By "geopolymer foam" is meant a geopolymer as previously defined, macroporous, mesoporous and optionally microporous, having a density of less than 1.5 g / cm ³ , especially less than 1.2 g / cm ³ , in particular less than at 0.9 g / cm ³ , and more particularly less than 0.6 g / cm ³ .

 By "mesoporous and macroporous geopolymer" is meant a geopolymer having both macropores and mesopores. "Macropores" means 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 a mean diameter of between 2 and 50 nm and especially between 2 and 20 nm.

 Depending on the formulation used, a geopolymer foam may also have micropores. By "micropores" is meant pores or voids having an average diameter of less than 2 nm. When micropores are present, the microporosity is typically less than 15% and especially less than 10% and, in particular, between 5 and 10% by volume relative to the total porosity of the geopolymer.

 In a geopolymer foam, the total porosity corresponding to the macroporosity, the mesoporosity and the possible microporosity is greater than 70%, in particular greater than 75%, and in particular greater than 80% by volume relative to the volume. total of the geopolymer.

The geopolymer foam implemented in the context of the present invention has an open porosity, a penetrating open porosity, a connected (or interconnected) porosity and a closed porosity. Advantageously, the geopolymer foam used in the context of the present invention has percolating pores which connect a first main surface of the geopolymer foam to a second main surface of the geopolymer foam. For the purposes of the present invention, "main surface" means an outer portion of the geopolymer foam, which limits it vis-à-vis its environment. The main surface (s) (s) present (s) typically cavities especially macroscopic, unobstructed. By "nanoparticles of a CN ligand metal coordination polymer having the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^z" "is meant nanoparticles or nanocrystals attached to the surface of the geopolymer foam that is to say fixed not only at one of the main surfaces of the foam but also inside the pores, typically macropores and mesopores, this foam An attachment within the pores corresponds to an attachment at the inner surface of the walls of the channels defining these pores.

 The attachment of these nanoparticles or nanocrystals to the surface of the geopolymer foam corresponds to a physical adsorption typically via electrostatic interactions such as Van der Waals bonds involving the metal cations of the nanoparticles or nanocrystals and reactive non-organic groups on the surface. geopolymer foam such as silanol and aluminol groups. It should be noted that the fixing of these nanoparticles or nanocrystals on the surface of the geopolymer foam does not require any prior preparation of said attachment-type foam of an organic graft at this surface, which, in itself, makes it possible to obtain a simple process.

In the context of the present invention, the nanoparticles correspond to the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} in which Alk is an alkali metal, x is 1 or 2, M is a metal of transition, n is 2 or 3, M 'is a transition metal, m is 6 or 8 and z is 3 or 4.

 In this formula, Alk can be any alkali metal. Advantageously, Alk is chosen from the group consisting of lithium (Li), sodium (Na) and potassium (K). In particular, Alk is potassium (K).

In this formula, M ^{n +} may be any cation of a binding metal having an oxidation state of II or III. Advantageously, M ^{n +} is selected from the group consisting of a ferrous ion (Fe ²⁺ ), a nickel ion (Ni ²⁺ ), a ferric ion (Fe ³⁺ ), a cobalt ion (Co ²⁺ ), a copper ion (Cu ²⁺ ) and a zinc ion (Zn ²⁺ ).

In this formula, M 'can be any cation of a binding metal. Advantageously, when m is 6, M 'is selected from the group consisting of a ferrous ion (Fe ²⁺ ), a ferric ion (Fe ³⁺ ) and a cobalt ion (Co ³⁺ ). Alternatively, when m is 8, M ' is a molybdenum ion (Mo ⁵⁺ ). Thus, [M '(CN) _m ] ^{z "} may be [Fe (CN) ₆ ] ^3" , [Fe (CN) ₆ ] ^{4 -} , [Co (CN) ₆ ] ^{3 -} or [Mo (CN) ₈ ] ^{3 "} .

By way of particular examples, mention may be made of nanoparticles with (i) Fe ²⁺ cations as M ^{n +} cations and [Mo (CN) 8] ^{3 +} anions as [M '(CN) _m ] ^{z -} anions, (ii) Co ²⁺ , Fe ²⁺ , Cu ²⁺ , Zn ²⁺ or Ni ²⁺ cations as M ^{n +} cations and [Co (CN) e] ^{3 -} anions as [M (CN) _m anions] ^{z ~} (iii) Co ²⁺ , Fe ²⁺ , Cu ²⁺ , Zn ²⁺ or Ni ²⁺ cations as M ^{n +} cations and [Fe (CN) e] ^{3 -} anions as [M '(CN) anions ) _m ^"z" or else the cations Co ²⁺ , Cu ²⁺ , Zn ²⁺ or Ni ²⁺ as cations M ^{n +} and the anions [Fe (CN) e] ^{4 "} as anions [M '(CN) _m ] ^{z ~} .

Two more particular examples of formula to which the nanoparticles respond are K [Cu ^M Fe ^m (CN) 6] or K ₂ [Cu ¹¹ Fe ¹¹ (CN) ₆ ].

 In the context of the present invention, the nanoparticles have a sphere or spheroid shape whose diameter is typically between 3 nm and 30 nm. Interestingly, and as a result of the functionalization process described hereinafter, the nanoparticles of the coordinating polymer generally have a uniform size and shape over the entire surface of the geopolymer foam.

Step (a) of the process according to the present invention consists in placing a geopolymer foam in contact with a solution, hereinafter referred to as the Si solution, containing at least one M ^{n +} ion ^and then washing and, if appropriate, drying the foam. geopolymer thus obtained. In other words, this step corresponds to the preparation of a geopolymer foam on the surface of which is adsorbed at least one M ^{n +} ion.

The M ^{n +} ion present in the solution Si may be an ion of any transition metal and in particular a transition metal capable of giving a cyanometalate of this metal which is insoluble. As previously described, the metal M may be chosen from copper, cobalt, zinc, nickel and iron and therefore the M ^{n +} ion present in the Si solution is advantageously chosen from the group consisting of Fe ²⁺ ions. , Ni ²⁺ , Fe ³⁺ , Co ²⁺ , Cu ²⁺ and Zn ²⁺ .

In the Si solution, the M ^{n +} ion is in the form of a metal salt. This salt is advantageously chosen from the group consisting of a nitrate, a sulfate, a chloride, an acetate, a tetrafluoroborate and any of their hydrated forms. By way of example, when the M ^{n +} ion present in the Si solution is Cu ²⁺ , the metal salt used is copper nitrate (CUN O 3).

The metal salt is present in the Si solution in an amount of between 1.10 ³ and 0.5 mol / L and advantageously between 5.10 ³ and 5.10 ² mol / L. Compared with the amount of geopolymer foam, the metal salt is present in the Si solution in an amount of between 0.1 to 20 mmol / g and advantageously between 1 to 5 mmol / g of geopolymer foam to be functionalized.

 The solution Si comprises, in addition to the metal salt as described above, a solvent. This solvent is advantageously water which can be both deionized water, distilled water and ultra-pure water (18.2 ΜΩ). Typically, the solvent in the Si solution is ultra-pure water (18.2 ΜΩ).

 Step (a) of the process according to the invention is carried out at a temperature of between 10 ° C. and 40 ° C., advantageously between 15 ° C. and 30 ° C. and, more particularly, at room temperature (ie 23 ° C. ± 5 ° C), and usually for 4 to 96 hours.

 The contacting during step (a) can be performed in static mode or in dynamic mode. In the "static mode" also called "batch mode", the geopolymer foam is immersed in the solution Si, the latter being optionally subjected to stirring. In the static mode, the duration of the contacting is typically between 12 to 96 hours. In the "dynamic mode" also called "column mode", the Si solution flows on and inside the geopolymer foam. In the dynamic mode, the duration of the contacting is typically between 4 to 24 hours.

At the end of this contact, the geopolymer foam is subjected to washing. Such a washing is intended to remove the excess metal salt as well as the non physically adsorbed M ^{n +} ions, which makes it possible to obtain a stable product with a perfectly defined composition.

If the contacting has been carried out in static mode, the geopolymer foam is removed from the Si solution and then washed by immersing it in a wash solution or by flowing the wash solution on and within the the foam. Yes the contacting was carried out in static mode, replacing the Si solution flowing on and inside the geopolymer foam with the washing solution.

 The washing step and especially when it involves immersing the geopolymer foam in a washing solution may be repeated several times and in particular at least twice, at least three times or at least four times. At each wash, a washing solution, identical or different, can be implemented.

 Advantageously, the washing solution used in step (a) comprises the same solvent as the solvent of the Si solution. Typically, this washing solution is ultra-pure water (18.2 ΜΩ).

 Following this washing, the geopolymer foam may optionally be subjected to drying which is however not mandatory.

Step (b) of the process according to the present invention consists in contacting the geopolymer foam obtained after step (a) ie the geopolymer foam on the surface of which M ^{n +} ions are physically adsorbed with a solution, hereinafter referred to as solution S ₂ , comprising two distinct elements that are, on the one hand, a salt or a complex of [M '(CN) _m ] ^{z ~} and, on the other hand, a salt of Alk alkali metal and then wash and optionally dry the geopolymer foam thus obtained. This solution S ₂ is different from a solution containing only a salt or complex of [M '(CN) _m ] ^z_ , for example a salt of formula [Alk _z / _y ] [M' (CN) _m ]. Of course, the alkali metal salt Alk having an oxidation degree of y, added in addition, is different, distinct from the complex or salt of [M '(CN) _m ] ^{z ~} , for example salt of formula [Alk _z / _y ] [M '(CN) _m ].

In step (b) of the process according to the present invention, the anionic moiety [M '(CN) _m ] ^{z ~} binds to the physically adsorbed M ^{n +} cations at the surface of the geopolymer foam and at the same time alkali insert into the crystal structure. This binding is by formation of relatively strong bonds of the covalent bond type and is generally quantitative, ie all M ^{n +} cations react. The attachment is therefore not random. The insertion of alkalis in all the sites of the crystal structure is possible not only because of the possible presence of alkali in the complex or salt of formula (Cat) _z / y [M '(CN) _m ] as defined below and this, in the case where Cat represents a cation of an alkali metal but also and especially thanks to the presence in addition of an alkali metal salt Alk present in the solution S ₂ . Therefore, it is generally preferable that the same alkali metal is present in the complex or salt of formula (Cat) _z / y [M '(CN) _m ] as well as in the alkali metal salt Alk of the solution S ₂ .

It should be noted that regardless of the nature of the salt or complex of [M '(CN) _m ] ^{z ~} and the amount of alkali which is provided during the dissolution of the salt of [M' (CN) _m ] ^{z ~} (cyanate salt) in solution. Indeed, it is the fact, according to the invention, to add a salt of an alkali metal in addition to the complex or cyanate salt - whether or not the latter is a complex or salt of alkali metal - which makes the desired structure according to the invention as described above is obtained.

In addition, the inventors have shown that, thanks to the addition of an alkali metal salt Alk during step (b) of the process according to the invention, it is possible to obtain, reliably, certain and reproducible, the stoichiometric compound as defined above: [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} , while a non-stoichiometric compound, for example of formula AlkxMi-x [M" M "" ( CN) _6], Alk _x Mi-x [M ^lll M ^"l (CN) _6], Alk ₂ XMI-x [M ^II M" ^l (CN) _6] or AlkxMi [M ^{"M" v} (CN) s ] with x strictly less than 1 is obtained, when this synthesis is carried out without additional addition of an alkali metal salt.

In the solution S ₂ as implemented during step (b), the salt or complex of [M '(CN) _m ] ^{z ~} is in the form of a salt or a complex of formula ( cat) z / y [m '(CN) _m] wherein m, m and z are as previously defined and Cat represents a cation and y represents the oxidation state of the cation Cat. Advantageously, the Cat cation is chosen from the group consisting of the alkali metal cations, the ammonium cation, a quaternary ammonium cation and a phosphonium cation. In particular, the Cat cation is chosen from the group consisting of potassium cation (K ⁺ ), sodium cation (Na ⁺ ), ammonium cation (NH ₄ ⁺ ), tetrabutylammonium (N (C ₄ H 9) ₄ ⁺ ) and tetraphenylphosphonium (P (C6Hs) 4 ⁺ ). More specific examples of formula salt (Cat) z / n [M '(CN) _m ] usable in the context of the present invention are K ₄ Fe (CN) 6, [N (C ₄ H ₉ ) 4] 3 [Fe (CN) 6 ], [N (C ₄ H ₉ ) ₄ ] 3 [Mo (CN) ₈ ] and [N (C ₄ H ₉ ) ₄ ] ₃ [Co (CN) ₆ ].

The salt or complex of [M '(CN) _m ] ^{z "} is present in the solution S ₂ in an amount of between 1.10 ³ and 0.5 mol / L and advantageously between 5.10 ³ and 5.10 ^-2 mol / L. . Compared to the amount of geopolymer foam, the salt or complex of [M '(CN) m] ^z is present in the solution S ₂ in an amount of from 0.1 to 20 mmol / g and advantageously from 1 to 5 mmol / g of geopolymer foam to be functionalized.

The solution S ₂ comprises, in addition to the salt or complex of [M '(CN) _m ] ^{z ~} , a salt of an alkali metal Alk with Alk as defined above.

Advantageously, the alkali metal salt Alk is in the form of a nitrate, a sulphate, an iodide, a chloride or a fluoride. A particular example of an alkali metal salt that can be used in solution S ₂ is potassium nitrate.

The alkali metal salt Alk is present in the solution S ₂ in an amount of between 1.10 ³ and 0.5 mol / L and advantageously between 5.10 ³ and 5.10 ² mol / L. Compared with the amount of geopolymer foam, the alkali metal salt Alk is present in the solution S ₂ in an amount of between 0.1 to 20 mmol / g and advantageously between 1 to 5 mmol / g of geopolymer foam. to functionalize. Advantageously, the concentration of salt or complex of [M '(CN) _m ] ^{z ~} and the concentration of alkali metal salt Alk used in the solution S ₂ are identical.

Solution S ₂ comprises, in addition to the salt or complex of [M '(CN) _m ] ^{z ~} and the alkali metal salt Alk as described above, a solvent. This solvent is advantageously water which can be both deionized water, distilled water and ultra-pure water (18.2 ΜΩ). Typically, the solvent in solution S ₂ is ultrapure water (18.2 ΜΩ).

 Step (b) of the process according to the invention is carried out at a temperature of between 10 ° C. and 40 ° C., advantageously between 15 ° C. and 30 ° C. and, more particularly, at room temperature (ie 23 ° C. ± 5 ° C) and this generally for 2 to 96 hours.

The contacting during step (b) can be performed in static mode or in dynamic mode. In the "static mode" also called "fashion batch ", the geopolymer foam is immersed in the solution S ₂ , the latter being optionally subjected to stirring. In the static mode, the duration of the contacting is typically between 12 to 96 hours. In the "dynamic mode" also called "column mode", the solution S ₂ flows on and inside the geopolymer foam. In the dynamic mode, the duration of the contacting is typically between 2 to 24 hours.

At the end of this contact, the geopolymer foam is subjected to washing. Such washing is intended to eliminate the complexes of [M '(CN) _m ] ^{z ~} which have not been fixed on the M ^{n +} cations and makes it possible to obtain a solid support in which there is no longer any [M' (CN) _m ] ^z free, unbound and releasable.

If the contacting has been carried out in static mode, the geopolymer foam is removed from the solution S ₂ and then washed by immersing it in a washing solution or by flowing the washing solution on and inside. foam. If the contacting has been carried out in static mode, the solution S ₂ flowing over and inside the geopolymer foam is replaced by the washing solution.

 The washing step and especially when it involves immersing the geopolymer foam in a washing solution may be repeated several times and in particular at least twice, at least three times or at least four times. At each wash, a washing solution, identical or different, can be implemented.

Advantageously, the washing solution used in step (b) comprises the same solvent as the solvent of the solution S ₂ . Typically, this wash solution is ultra-pure water (18.2 ΜΩ).

 Following this washing, the geopolymer foam may optionally be subjected to drying which is however not mandatory.

Once, step (b) is carried out, a geopolymer foam comprising nanoparticles of a CN-ligated metal coordination polymer having the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} such than previously defined is obtained.

However, the functionalization method according to the invention envisages that the succession of the two contacting steps, namely step (a) of impregnation of the geopolymer foam with an Si solution and the step (b) of impregnating the geopolymer foam obtained following step (a) with a solution S ₂ can be repeated (step (c)).

 In other words, the succession of steps (a) and (b) or impregnation cycle can be carried out only once or be repeated typically from 1 to 10 times ie repeated 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 times, especially in order to perfectly adjust the size of the nanoparticles.

At the end of the process according to the present invention, the nanoparticle weight content of a CN-ligated metal coordination polymer corresponding to the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} as previously Defined is typically 1 to 10% based on the total mass of the functionalized geopolymer foam.

The geopolymer foam used in the context of the present invention may have various sizes and shapes. It can be in the form of beads, particles, microparticles, nanoparticles, monoliths or plates. Those skilled in the art will be able to determine the best size and shape according to the application envisaged for the functionalized geopolymer foam. In a particular embodiment, the geopolymer foam used is in the form of particles of the powder type having a controlled particle size, between 0.1 mm and 10 mm and in particular between 0.5 mm and 1 mm.

 The geopolymer foam used in the context of the present invention may have been prepared by any of the processes for preparing a geopolymer foam known to those skilled in the art and in particular any of the processes described in the present invention. the State Party of the Prior Art above. However, the inventors have developed a method for obtaining a geopolymer foam having fine, homogeneous and stabilized pore sizes and connected porosity.

This process consists in preparing, prior to step (a) as previously defined, a geopolymer foam, by dissolution / polycondensation an alumino-silicate source in an activation solution in the presence of a first gas-generating adjuvant and a second air-entraining admixture.

 In such a process, there is no need to subject the thus prepared geopolymer foam to any treatment to remove, prior to use, chemicals, such as glycerol, generated during the preparation process and to alter geopolymer foam.

In addition, the use of a gas-generating adjuvant and an air-entraining aid in the amounts as described below makes it possible to obtain a geopolymer foam whose macroscopic pores are connected thus allowing any liquid possibly contaminated to progress through the network of macroscopic pores, to fill the mesoscopic porosity which has the highest specific surface area and thus to allow adsorbing on the walls of the geopolymer possible contaminants. This adsorption can be done either by direct exchange with the alkaline compensation cation which serves to compensate for the charge of the aluminum or by exchange with the alkali cation Alk present in the CN ligand metal coordination polymer responding to the [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} as previously defined.

 In the geopolymer foam thus prepared, the macropores are essentially derived from the gas bubbles produced by the gas-generating adjuvant and stabilized by the air-entraining aid, whereas the mesopores result mainly from the process of geopolymerization.

The terms "alumino-silicate source" and "reactive material containing essentially silica and aluminum" are, in the present invention, similar and usable interchangeably.

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

 By "activation solution" is meant the high pH salt solution well known in the field of geopolymerization. The latter is a strongly alkaline aqueous solution which may optionally contain silicate components, especially chosen from the group consisting of silica, colloidal silica and vitreous silica.

 The terms "activating solution", "high pH saline solution" and "high alkaline solution" are, in the present invention, similar and interchangeably usable.

By "strongly alkaline" or "high pH" means a solution whose pH is greater than 9, especially greater than 10, in particular greater than 11 and more particularly greater than 12. In other words, the Activation solution has a concentration of OH ^" 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.

The activation solution comprises the compensation cation or the mixture of compensation cations as previously defined in the form of an ionic solution or a salt. Thus, the activating solution is chosen in particular from an aqueous solution of sodium silicate (Na ₂ SiO 3), potassium silicate (K ₂ SiO ₂ ), sodium hydroxide (NaOH), potassium hydroxide ( KOH), calcium hydroxide (Ca (OH) ₂ ), cesium hydroxide (CsOH) and their derivatives etc. .... Note that preparing a geopolymer foam with potassium compensation cation allows obtain a mesoscopic specific surface 3 times higher than that developed with sodium.

By "gas-generating adjuvant" is meant an adjuvant which, in situ ie in the geopolymeric mixture, is capable of reacting with at least one element present in the latter and / or to decompose so as to produce, by endothermic or exothermic chemical reaction, a gas. Such a gas is chosen in particular from oxygen, hydrogen, nitrogen, carbon monoxide, carbon dioxide, ammonia, methane or a mixture thereof.

 The person skilled in the art knows various gas-generating additives particularly useful in the field of concretes. Advantageously, the gas-generating adjuvant used in the context of the present invention is chosen from the group consisting of azo compounds, such as azodicarbonamides and their derivatives; hydrazine derivatives, such as p-toluenesulfonylhydrazide, 4,4-oxibis (benzenesulphonylhydrazide) and toluenesulphonylacetonehydrazone; semicarbazides, such as p-toluenesulfonylsemicarbazide; tetrazoles, such as 5-phenyltetrazole, nitroso compounds such as Ν, Ν-dinitrosopentamethylenetetramine; organic peroxides; inorganic peroxides; carbonate compounds or their derivatives such as alkali or alkaline earth metal carbonates or bicarbonates, in particular calcium carbonate and sodium bicarbonate, optionally used in admixture with at least one activating agent, such as the acid citric and one of their mixtures.

 By "one of their mixtures" is meant both a mixture of at least two gas-generating adjuvants belonging to the same chemical family selected from the chemical families mentioned above and a mixture of at least one adjuvant generating gas belonging to a first chemical family selected from the chemical families mentioned and at least one gas-generating adjuvant belonging to a second chemical family chosen from the chemical families mentioned, different from said first chemical family.

 By "organic peroxides" is meant a compound of formula ROOR in which R represents an alkyl group comprising from 1 to 15 carbon atoms, an acyl group -COR 'with R' representing an alkyl group comprising from 1 to 15 carbon atoms. or an aroyl group -COAr with Ar representing an aromatic group comprising from 6 to 15 carbon atoms.

"Alkyl group comprising 1 to 15 carbon atoms" means a linear, branched or cyclic alkyl group, optionally substituted, comprising 1 to 15 carbon atoms, especially 1 to 10 carbon atoms and, in particular, 2 to 6 carbon atoms and optionally a heteroatom such as N, O, F, Cl, P, Si, Br or S .

 By "aromatic group comprising from 6 to 15 carbon atoms" is meant, in the context of the present invention, an optionally substituted aromatic or heteroaromatic group consisting of one or more aromatic or heteroaromatic rings each comprising from 3 to 10 carbon atoms. atoms, the heteroatom (s) which may be N, O, P or S.

 By "substituted" is meant, in the context of the present invention, an alkyl or aromatic group, mono- or poly-substituted, with a linear or branched alkyl group comprising from 1 to 4 carbon atoms, by a group amine, with a carboxylic group and / or with a nitro group.

 By "inorganic peroxides" is meant hydrogen peroxide, inorganic peracids and their salts. Typically, an inorganic peroxide is selected from the group consisting of hydrogen peroxide, perboric, perphosphoric and persulfuric acids and their alkali or alkaline earth metal salts, alkali and alkaline earth metal peroxides such as peroxides of sodium, calcium and magnesium. An inorganic peroxide advantageously used in the context of the present invention is hydrogen peroxide.

 The gas-generating adjuvant is used in a weight content of between 0.01 and 5% and especially between 0.1 and 1% relative to the weight of the geopolymer foam.

 The gas-generating adjuvant may be added to the activation solution or the geopolymeric mixture after addition of the aluminosilicate source.

By "air-entraining aid" is meant an adjuvant capable of forming and / or stabilizing, in the geopolymer, microbubbles of air or gas uniformly distributed in the mass. In the context of the present invention, the microbubbles formed are essentially microbubbles of the gas produced by the gas-generating adjuvant, because of the use of such an adjuvant in addition to a gas-entraining admixture. At these microbubbles, are also added air microbubbles trapped during the mixing of the geopolymer paste.

 The skilled person knows various air entraining additives particularly useful in the field of concrete. Advantageously, the air-entraining adjuvant used in the context of the present invention belongs to the field of surfactants which lower the surface tension of water and facilitate the formation of gas bubbles by reducing the energy required to create gas-water contact surfaces. Such surfactants also allow the formation of an insoluble and hydrophobic film around the gas voids.

 Advantageously, the air-entraining admixture is chosen from anionic surfactants, cationic surfactants, nonionic (or neutral) surfactants and a mixture thereof. One of their mixtures has the same meaning as that previously set forth for gas-generating adjuvants mutatis mutandis.

By "anionic surfactants" is meant a surfactant whose hydrophilic part is negatively charged, in particular chosen from alkyl or aryl sulfonates, sulphates, phosphates, or sulphosuccinates associated with a counter ion such as an ammonium ion (NH ⁴⁺ ), a quaternary ammonium. such as tetrabutylammonium, and alkaline cations such as Na ⁺ , Li ⁺ and K ⁺ . As anionic surfactants, it is possible, for example, to use a sodium alpha olefin sulphonate comprising at least one C 8 -C 20 aliphatic chain and especially C 10 -C 18 and, in particular, C 14 -C 16; tetraethylammonium paratoluenesulphonate, sodium dodecyl sulphate (also known as sodium lauryl sulphate), sodium palmitate, sodium stearate, sodium myristate, sodium di (2-ethylhexyl) sulphosuccinate and alkylbenzene sulfonate such as methylbenzene sulfonate and ethylbenzene sulfonate.

By "cationic surfactants" is meant a surfactant whose hydrophilic part is positively charged, in particular 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 cationic surfactants, it is possible, for example, to use tetrabutylammonium chloride, tetradecylammonium, tetradecyltrimethylammonium bromide (TTAB), alkylpyridinium halides bearing an aliphatic chain and alkylammonium halides.

By "nonionic surfactants" is meant a surfactant whose surface-active properties, in particular hydrophilicity, are provided by unfilled functional groups such as an alcohol, an ether, an ester or an amide, containing heteroatoms such as as nitrogen or oxygen; because of the low hydrophilic contribution of these functions, the nonionic surfactant compounds are most often polyfunctional. As nonionic surfactants, it is possible to use amine oxides, polyethers such as polyethoxylated surfactants such as e.g., polyethylene glycol lauryl ether (Brij ^® 35 or POE23), polyols (sugar-derived surfactants), in particular glucose alkylates such as, for example, glucose hexanate.

Those skilled in the art are aware of various commercially available air-entraining admixtures comprising one or more of the surfactants presented above, natural or synthetic. Such air-entraining admixtures are in particular marketed under the trademark Sika ^® AER, MapeAir and MapePlast by Mapei ^® and Cimpore and Cimprefa by Socli ^® .

 The air-entraining admixture is used in a weight content of between 0.5 and 8% and in particular between 2 and 5% relative to the weight of the geopolymer foam.

 The gas-generating adjuvant may be added to the activation solution or the geopolymeric mixture after addition of the aluminosilicate source. In a particular embodiment, the preparation of the geopolymer foam according to the present invention comprises the following steps:

i) preparing an activation solution, in particular as defined above, comprising an air-entraining admixture, in particular as defined above, ii) adding to the solution obtained in step (i) at least one alumino-silicate source, especially as defined above, and a gas-generating adjuvant in particular as defined above, and then

 iii) subjecting the mixture obtained in step (ii) to conditions permitting hardening of the geopolymer.

Step (i) of the process according to the present invention consists in adding to an activating solution as previously defined, previously prepared, the air-entraining admixture. Prior preparation of the activation solution is a standard step in the field of geopolymers.

 As previously explained, the activation solution may optionally contain one or more silicated component (s), in particular chosen from the group consisting of silica, colloidal silica and vitreous silica. When the activation solution contains one or more silicated component (s), this or these latter (s) is (are) present in an amount of between 100 mM and 10 M, in particular between 500 mM and 8 M and, in particular, between 1 and 6 M in the activation solution.

 The air entraining aid is added to the activation solution at once or in several times and even drop by drop for an air entraining aid in liquid form or by dusting for an air entraining aid in solid form. Once the air-entraining aid has been added to the activating solution, the resulting solution is mixed using a kneader, stirrer, magnetic bar, ultrasonic bath or homogenizer. Mixing / kneading during step (a) of the process according to the invention is carried out at a relatively high speed. By "relatively high speed" means, in the context of the present invention, a speed greater than 250 rpm, especially greater than or equal to 350 rpm. Such agitation makes it possible to obtain a uniform solution, in particular a homogeneous solution or a solution of the microemulsion type.

Step (i) of the process according to the invention is carried out at a temperature of between 10 ° C. and 40 ° C., advantageously between 15 ° C. and 30 ° C. and, more particularly, at room temperature (ie 23 ° C. ± 5 ° C) for a period of time between 1 s and 40 s, in particular between 10 s and 30 s and, more particularly, between 15 s and 25 s.

Step (ii) of the process according to the invention consists in bringing into contact the activation solution comprising the air-entraining admixture with the aluminosilicate source as defined above and the gas-generating adjuvant as previously defined.

 The alumino-silicate source may be poured in one or more times on the activating solution containing the air-entraining aid. In a particular embodiment of step (b), the alumino-silicate source may be sprinkled onto the activating solution containing the air-entraining aid.

 Similarly, the gas-generating adjuvant can be poured in one or more times on the activation solution containing the air-entraining aid and even drop-by-drop for a gas-generating adjuvant in liquid form or by dusting for a gas-generating adjuvant in solid form.

 The gas-generating adjuvant may be added to the activating solution containing the air-entraining admixture before, after, or during the addition of the aluminosilicate source.

Advantageously, step (ii) of the process according to the invention is carried out in a kneader in which the activation solution containing the air-entraining admixture has been introduced beforehand. Any kneader known to those skilled in the art can be used in the context of the present invention. By way of non-limiting examples, mention may be made of a NAUTA ^® mixer, a HOBART ^® mixer, a HENSCHEL ^® mixer and a HEIDOLPH ^® mixer.

Step (ii) of the process according to the invention therefore comprises a mixing or kneading of the activation solution containing the air-entraining admixture with the aluminosilicate source and the gas-generating adjuvant. The mixing / kneading during step (ii) of the process according to the invention is initially done at a relatively slow speed. By "relatively slow speed" is meant, in the context of the present invention, a rotational speed of the rotor of the mixer less than or equal to 250 rpm, in particular greater than or equal to 50 rpm and, in particular, between 75 and 200 rpm. By way of non-limiting example, in the case of a standard kneader, the stirring speed is 100 rpm. Once the mixture has been produced and in order to achieve optimum homogenization, the stirring speed can be increased to a value greater than 1000 rpm, in particular greater than 1500 rpm and, in particular, of the order of 2000. rpm (ie 2000 rpm ± 200 rpm).

 Step (ii) of the process according to the invention is carried out at a temperature of between 10 ° C. and 40 ° C., advantageously between 15 ° C. and 30 ° C. and, more particularly, at room temperature (ie 23 ° C. ± 5 ° C) for a period of between 1 min and 15 min, in particular between 2 min and 10 min and, more particularly, between 3 min and 7 min.

 Those skilled in the art will be able to determine the amount of alumino-silicate source to be used in the context of the present invention as a function of their knowledge in the field of geopolymerization.

 Advantageously, in the process according to the present invention, the mass ratio activation / MK solution with activation solution representing the mass of activation solution (expressed in g) and MK representing the mass of alumino-silicate source (expressed in g) used is advantageously between 0.6 and 2 and in particular between 1 and 1.6.

Step (iii) of the process according to the invention consists in subjecting the mixture obtained in step (ii) to conditions allowing the geopolymeric mixture to harden.

 Any technique known to those skilled in the art for curing a geopolymeric mixture can be used during the curing step of the process.

The conditions for curing in step (iii) advantageously comprise a curing step optionally followed by a drying step. The curing step can be done in the open air, under water, in various hermetic molds, by humidifying the atmosphere surrounding the geopolymeric mixture or by applying an impervious coating on said mixture. This cure step can be put implemented at a temperature between 10 ° C and 80 ° C, especially between 20 ° C and 60 ° C and, in particular, between 30 ° C and 40 ° C and can last between 1 and 40 days or longer. It is obvious that the duration of the cure depends on the conditions implemented during the latter and the skilled person will be able to determine the most suitable duration, once the conditions defined and possibly by routine tests.

 When the curing step comprises a drying step, in addition to the curing step, this drying can be carried out at a temperature of between 30 ° C and 90 ° C, in particular between 40 ° C and 80 ° C and, in particular, between 50 ° C and 70 ° C and can last between 6 hours and 10 days, especially between 12 pm and 5 days and, in particular, between 24 hours and 60 hours.

 In addition, prior to the hardening of the geopolymeric mixture, the latter can be placed in molds so as to give it a predetermined shape following this hardening.

It should be noted that during the preparation of the geopolymer foam in accordance with the process according to the invention, metal oxides, and in particular iron oxides or manganese oxides, may be added to the activation solution prior to step (i). ), to a mixture obtained during or following step (i) or to a mixture obtained during or following step (ii), in order to prepare a geopolymer foam in whose walls are incorporated such oxides.

The present invention also relates to a functionalized geopolymer foam capable of being prepared according to a method as defined above. Such a geopolymer foam is characterized by the presence of nanoparticles of a CN-ligated metal coordination polymer corresponding to the formula [Alk ⁺ x] M ^{n +} [M '(CN) _m ] ^{z "} as defined above, fixed at its surface without any organic graft being present to ensure this fixation.

Depending on the formulation parameters used during the preparation of the geopolymer foam, the latter may have a total porosity generally measured by adsorption analysis-nitrogen desorption or mercury porosimeter greater than 70%, especially greater than 75% and, in particular, superior to 80%. It is also possible, by a suitable choice of the gas-entraining admixture, to effectively control the size of the bubbles, in particular to improve the impregnation during the percolation of the fluids to be treated as defined below. The present invention finally relates to the use of such a functionalized geopolymer foam for separating at least one metal or metalloid ion from a stream containing said at least one metal or metalloid ion.

 Thus, the present invention relates to a method for separating at least one metal or metalloid ion from a stream containing said at least one metal or metalloid ion comprising contacting the stream containing said at least one metal or metalloid ion with the foam of functionalized geopolymer according to the invention, whereby a flux depleted in metal or metalloid ions and a geopolymer foam on the surface of which are fixed metal or metalloid ions are obtained.

 In other words, the process according to the invention can be considered as a process for treating a stream containing at least one metal or metalloid ion. By "treatment of a stream containing at least one metal or metalloid ion", it is intended to reduce or reduce the quantity of metal or metalloid ions present in the stream before the implementation of the process according to the invention, ie before the setting in contact with the functionalized geopolymer foam. This reduction or reduction may involve the partial or total elimination of these ions in the stream.

 Alternatively, the method according to the present invention may be of interest in the fixing, at the level of the functionalized geopolymer foam, of metal or metalloid ions for later use in the field of catalysis or chromatography columns. .

Indeed, the functionalized geopolymer foam prepared by the process according to the invention, because of its excellent properties such as excellent exchange capacity, excellent selectivity and a high reaction rate, is particularly suitable for such uses. This excellent efficiency is achieved with reduced amounts of inorganic fixer such as cyanometallate of the insoluble metal M. In addition, the excellent properties of strength and mechanical stability of the functionalized geopolymer foam prepared by the process according to the invention, resulting from its specific structure allow its conditioning in column and the continuous implementation of the separation / fixing process for example in a fluidized bed, which can thus be easily integrated into an existing installation, for example in a chain or processing line comprising several steps.

 At the end of the process according to the invention, the elements in the stream to be treated, such as cations, are immobilized in the geopolymer foam functionalized according to the invention by sorption, that is to say by exchange. ionic or adsorption within nanoparticles, within the structure of nanoparticles, themselves physically linked to the surface of the foam.

Also, by "flux containing at least one metal ion or metalloid" is meant a liquid or gaseous flow in which the present invention aims to separate, recover or eliminate unwanted metal ions or metalloids or, conversely, metal ions or metalloids of interest. Thus, the flow implemented in the context of the present invention may be any liquid or gaseous flow may contain at least one metal ion or metalloid.

 The liquid flow implemented in the context of the present invention may be in the form of a monophasic solution, a microemulsion, a suspension and / or a dispersion. The liquid stream used may be an aqueous solution which may optionally contain acids, bases or organic compounds. Alternatively, this solution may also be a solution in a pure organic solvent such as ethanol (absolute alcohol), acetone or the like, in a mixture of these organic solvents, or in a mixture of water and a or more of these organic solvents miscible with water.

By way of example, the liquid or gaseous flow implemented in the context of the present invention may be chosen from an external air sample, an air sample from industries in the chemical, food, pharmaceutical, cosmetic or nuclear field. , city water, river water, water from seawater, lake water, effluent from a wastewater treatment plant, wastewater, household liquid effluent, medical or hospital liquid effluent or industrial liquid effluent such as effluent from the nuclear industry or any other nuclear-related activity or effluent from the non-nuclear industry or a mixture thereof.

 Among the various liquids and effluents of the nuclear industry, nuclear installations and activities using radionuclides that can be treated with the functionalized geopolymer foam prepared by the process according to the invention, mention may be made, for example, of cooling water from power plants, and all other effluents coming into contact with radioisotopes such as all wash water or resin regeneration solutions.

 Among the various liquids and effluents of the non-nuclear industry, mention may be made of cement plant effluents containing thallium, which is a violent poison.

 Thus, the streams and solutions that can be treated with the functionalized geopolymer foam fixing metal or metalloid ions, prepared by the process according to the invention are very varied, and may even contain, for example, corrosive, acidic or other agents, because of the excellent chemical stability of the foam according to the invention. The functionalized geopolymer foam prepared by the process according to the invention can be used in particular over a very broad pH range. For example, it will be possible to treat nitric aqueous solutions of concentration ranging for example from 0.1 to 3 M, acidic or neutral solutions up to a pH of 10.

For the purposes of the present invention, the term "metal or metalloid ion" means an undesired metal or metalloid ion such as an impurity or a contaminant or, on the contrary, a metal or metalloid ion of interest, capable of to be present or present in a stream as previously defined. This metal ion or metalloid may, in addition, be toxic, harmful and / or radioactive.

The present invention can be implemented with any metal ion or metalloid known to those skilled in the art. Advantageously, the metal ion is an ion of a poor metal, an ion of an alkaline earth metal, an ion of a transition metal, an ion of an actinide or an ion of a lanthanide. Among the metal ions or metalloids concerned by the present invention, there are also the ions of a heavy metal or a heavy metalloid. As a reminder, a heavy metal or metalloid is a metallic or metalloid element whose density exceeds 5 g / cm ³ such as mercury, lead, cadmium, copper, arsenic, nickel, zinc, cobalt and manganese.

 It should be noted that the use of a functionalized geopolymer foam in the walls of which metal oxides have been introduced, and in particular iron oxides or manganese oxides, makes it possible to increase the absorption or scavenging efficiency of the metals. heavy or other toxic elements such as arsenic or mercury and this, because of the intrinsic properties of such oxides.

 Advantageously, the metal or metalloid ion, in the context of the present invention, is an ion of a metal or a metalloid as defined above having a degree of oxidation greater than or equal to 1, in particular greater than or equal to 2. The metal ion or metalloid may in particular be an ion of a radionuclide. By way of illustrative examples, the metal or metalloid ion may be, in the context of the present invention, an ion of an element chosen from mercury, gold, silver, platinum, lead, iron, indium, gallium, aluminum, bismuth, tin, cadmium, copper, arsenic, nickel, zinc, titanium, cobalt, manganese, palladium, radium , ruthenium, thorium, uranium, plutonium, actinium, ytterbium, erbium, terbium, gadolinium, europium, neodymium, praseodymium, cerium, cesium, thallium , strontium and lanthanum.

 In the context of the present invention, the metal or metalloid ion may be in free form in the form of colloids or in complexed form. The metal ion or metalloid can come from a stable metal or metalloid or one of its radioactive isotopes.

 The metal ion or metalloid may be present in the stream to be treated in very dilute form or much more concentrated. Thus, the amount of said ion in a liquid stream to be treated may be between 1 μg and 100 mg / l of liquid flow, in particular between 1 μg and 10 mg / l of liquid flow and, in particular, between 10 μg and 1 mg / l of liquid flow.

By way of examples of use of the functionalized geopolymer foam which is the subject of the present invention, mention may be made of the fixing of cesium which contributes a large part of the gamma activity of the liquids of the nuclear industry and is selectively fixed by hexacyanoferrates or the fixation of thallium present in cement plant effluents and also selectively fixed by hexacyanoferrates.

 The fixing method which implements the functionalized geopolymer foam which is the subject of the present invention is preferably implemented continuously, in particular by using this foam in the form of particles, packaged for example in the form of a column, the foam preferably forming a fluidized bed whose fluidization is provided by the flow to be treated, but the fixing method can also be implemented batchwise, in "batch" mode, the contacting of the foam and the flow to be treated being then carried out preferably with stirring. Column conditioning allows continuous processing of large quantities of flows, with a high flow thereof.

 The contact time of the flow to be treated with the functionalized geopolymer foam object of the present invention is variable and can range, for example, from 1 min to 1 h for continuous operation and, for example from 10 min to 36 h and for example, 24 hours for "batch" operation.

 Since the functionalized geopolymer foam may be in the form of monoliths, the latter may be used as a conditioning material trapping the elements contained in this packaging and likely to flow out of it.

Other features and advantages of the present invention will become apparent to those skilled in the art on reading the examples below given for illustrative and non-limiting, with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a photograph of a geopolymer foam prepared according to the process of the invention and of cylindrical shape with a diameter of 50 mm. Figure 2 shows the experimental results of the specific surface of a geopolymer foam prepared according to the method of the invention, measured by adsorption / desorption of nitrogen.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

I. Synthesis of a Fieopolymer Foam

An alkaline solution ie an activating solution is prepared to which are added the air entrainer AER5 then the metakaolin and the foaming agent which is hydrogen peroxide (H2O2). The products used are metakaolin from Pieri Premix MK (Grade Construction Products), NaOH (Prolabo, 98%), sodium silicate (Betol 39T from Woellner), H ₂ 0 ₂ (Prolabo, 50% v) and of AER5 (SIKA).

 The composition of the foam is given in Table 1 below:

 Table 1: Composition of the geopolymer foam

Upon introduction of H2O2, the foam begins to form by release of oxygen bubbles. The foam is stabilized 4-5 hours later. The introduction of 3% by weight of the AER5 makes it possible to stabilize relatively fine and homogeneous pore sizes and especially a connected porosity (FIG. 1).

 From the volumes and masses measured after the setting of the foam, the main characteristics of the foam can be obtained and are given in Table 2 below.

The macroscopic porosity is due to the oxygen released during the decomposition of the H2O2 and the total porosity is the macroscopic porosity + the porosity mesoscopic. Mesoscopic porosity is determined on a solid geopolymer sample by water porosimetry. It is around 40%.

 Table 2: Composition of the geopolymer foam

Specific surface area was also measured by nitrogen adsorption / desorption. The results are shown in FIG. 2. The specific surface area measured by BET is equal to 44.8 m ² / g and a mean pore diameter (measured by the BJH method on the desorption branch) equal to 9.7 nm is got. These values of specific surface area and mean diameter correspond, of course, to the mesoporous network of the solid geopolymer.

II. Functionalization of the fideopolymer foam as synthesized in point I.

 This functionalization was carried out via an impregnation mode

"Batch", i.e. by contacting 7.3 g of support to be grafted, i.e. of geopolymer foam, with 1 L of the different impregnation solutions.

Two impregnation solutions are needed: one containing a copper salt (CuNO 3 at 10 ^-2 mol / L), the second SOI 2 containing a mixture of potassium ferrocyanide salt (K ₄ Fe (CN) 6 to 10 ^{~ 2} mol / L) and potassium salt (KNO3 to

10 ^"2 mol / L).

An impregnation cycle corresponds to contacting the geopolymer foam first with the Soli solution for 24 h, then after washing with water, with the SO 2 solution for 24 h. Functionalization was continued up to 3 impregnation cycles. III. Use of the fieopolymer foam as functionalized in point II.

An extraction test was carried out with a sample of the functionalized geopolymer foam prepared in point II, brought into contact with a synthetic solution of sodium nitrate doped with ¹³⁷ Cs, representative of an industrial effluent, for 24 hours with stirring. .

 The chemical composition of this solution is given in Table 3 below.

 Table 3: Composition of the solution

The results of the test on Cs analysis before and after contact are given in Table 4 below. The test carried out verifies the decontamination efficiency of the functionalized geopolymer foam.

Table 4: Extraction Result of ¹³⁷ Cs

with functionalized geopolymer foam

REFERENCES

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Claims

1) Process for preparing a geopolymer foam comprising nanoparticles of a CN-ligated metal coordination polymer having the formula [Alk ⁺ _x ] M ^{n +} [M '(CN) _m ] ^{z "} in which Alk is an alkali metal , x is 1 or 2, M is a transition metal, n is 2 or 3, M 'is a transition metal, m is 6 or 8 and z is 3 or 4, said process comprising the successive steps of:

a) contacting a geopolymer foam with a solution containing at least one M ^{n +} ion ^and then washing and optionally drying the geopolymer foam thus obtained;

b) contacting the geopolymer foam obtained after step (a) with a solution containing at least one salt or complex of [M '(CN) _m ] ^{z ~} and at least one salt of an alkali metal Alk then wash and optionally dry the geopolymer foam thus obtained; and

 c) optionally repeat steps (a) and (b) at least once.

2) Process according to claim 1, characterized in that said alkali metal is selected from the group consisting of lithium (Li), sodium (Na) and potassium (K).

3) Process according to claim 1 or 2, characterized in that said cation of a transition metal M ^{n +} is chosen from the group consisting of a ferrous ion (Fe ²⁺ ), a nickel ion (Ni ²⁺ ), a ferric ion (Fe ³⁺ ), a cobalt ion (Co ²⁺ ), a copper ion (Cu ²⁺ ) and a zinc ion (Zn ²⁺ ).

4) Process according to any one of claims 1 to 3, characterized in that said anion [M '(CN) _m ] ^z - is [Fe (CN) ₆ ] ^{3 "} , [Fe (CN) ₆ ] ^4" , [Co (CN) ₆ ] ^{3 "} or [Mo (CN) ₈ ] ^3" . 5) Process according to any one of claims 1 to 4, characterized in that said nanoparticles of a metal coordination polymer with CN ligands correspond to the formula K [Cu ^M Fe ^IM (CN) 6] or K ₂ [Cu ^{ll ll} Fe (CN) _6]. 6) Process according to any one of claims 1 to 5, characterized in that, in the solution of step (a), the ion M ^{n +} is in the form of a metal salt, advantageously chosen from the group consisting of a nitrate, a sulfate, a chloride, an acetate, a tetrafluoroborate and any of their hydrated forms. 7) Process according to any one of claims 1 to 6, characterized in that, the alkali metal salt Alk is in the solution of said step (b), in the form of a nitrate, a sulphate, an iodide, chloride or fluoride.

8) Process according to any one of claims 1 to 7, characterized in that said geopolymer foam is prepared, prior to said step (a), by dissolution / polycondensation of an alumino-silicate source in an activation solution in the presence of a first gas generating adjuvant and a second air entraining aid. 9) The method of claim 8, characterized in that said gas generating adjuvant is selected from the group consisting of azo compounds, such as azodicarbonamides and their derivatives; hydrazine derivatives, such as p-toluenesulfonylhydrazide, 4,4-oxibis (benzenesulfonylhydrazide) and toluenesulfonylacetonehydrazone; semicarbazides, such as p-toluenesulfonylsemicarbazide; tetrazoles, such as 5-phenyltetrazole, nitroso compounds such as Ν, Ν-dinitrosopentamethylenetetramine; organic peroxides; inorganic peroxides; carbonate compounds or their derivatives such as alkali or alkaline earth metal carbonates or bicarbonates, in particular calcium carbonate and sodium bicarbonate, optionally used in admixture with at least one activating agent, such as the acid citric and one of their mixtures. 10) Process according to claim 8 or 9, characterized in that said air-entraining admixture is chosen from anionic surfactants, cationic surfactants, nonionic surfactants and a mixture thereof.

11) Method according to any one of claims 8 to 10, characterized in that said preparation of the geopolymer foam comprises the following steps:

 i) preparing an activating solution, comprising an air-entraining aid,

 ii) adding to the solution obtained in step (i) at least one aluminosilicate source and a gas-generating adjuvant, and then

 iii) subjecting the mixture obtained in step (ii) to conditions permitting hardening of the geopolymer. 12) Process according to claim 11, characterized in that metal oxides are added to the activation solution prior to said step (i), to a mixture obtained during or following said step (i) or to a mixture obtained during or following said step (ii). 13) Geopolymer foam capable of being prepared according to a process as defined in any one of claims 1 to 12.

14) Use of a geopolymer foam according to claim 13 for separating at least one metal ion or metalloid from a stream containing said at least one metal ion or metalloid.

15) Use according to claim 14, characterized in that said stream containing at least one metal ion or metalloid is selected from an external air sample, an air sample from industries of the chemical, food, pharmaceutical, cosmetic or nuclear , city water, water from river, seawater, lake water, effluent from a treatment plant, wastewater, household liquid effluent, medical or hospital liquid effluent or industrial liquid effluent such as effluent from the nuclear industry or any other activity related to nuclear power or an effluent from the non-nuclear industry or a mixture thereof.

16) Use according to claim 14 or 15, characterized in that said metal ion or metalloid is an ion of a member selected from mercury, gold, silver, platinum, lead, iron, indium, gallium, aluminum, bismuth, tin, cadmium, copper, arsenic, nickel, zinc, titanium, cobalt, manganese, palladium, radium, ruthenium, thorium, uranium, plutonium, actinium, ytterbium, erbium, terbium, gadolinium, europium, neodymium, praseodymium, cerium, cesium, thallium, strontium and lanthanum.