Continuous process for separating strontium cations from liquid medium using material comprising geopolymer and ion exchanger particulates

Abstract

The invention relates to a continuous method for separating strontium cations from a liquid medium containing at least one strontium cation, in particular at least one radioisotope of strontium, for example a cation of 90Sr, in which method the liquid medium is brought into contact with a solid mesoporous material, a solid mesoporous material includes an inorganic matrix made of a mesoporous geopolymer having open mesopores and microparticles of at least one solid inorganic exchanger compound selective for strontium cations and different from the geopolymer, the geopolymer having a single pore size, the particles are distributed in open mesopores of the inorganic matrix and can be in contact with strontium cations contained in the liquid medium; the solid mesoporous material is in the form of non-powdered particles forming a fixed bed, in particular a column filler.

Description

Technical Field

[0001] The present invention relates to a continuous process for separating strontium (Sr) cations from a liquid medium using a material comprising a geopolymer and ion exchanger particles in the form of non-powdered particles forming a fixed bed, for example forming a column packing.

[0002] The term "continuous process" refers to a process that is performed continuously.

[0003] The invention finds particular application in the field of treatment of liquid effluents, and in particular in the field of treatment of radioactive or toxic liquid effluents, to remove strontium cations, in particular such as 90 Sr is a radioactive strontium isotope cation.

[0004] It should be noted that, in this document, the terms "adsorbent", "ion exchanger", "cation exchanger" and "cation exchanger" can be used interchangeably to refer to "cation exchanger". Background Art

[0005] Currently, the materials used in purification columns for purifying liquids containing strontium (Sr) cations, particularly radioactive isotopes including Strontium 90, are based on agglomerated powders in pellet form.

[0006] These pellets usually contain an ion exchanger, such as a zeolite or a crystalline titanate silicate that is most selective for strontium cations, and a binder.

[0007] The binder of the pellets is typically non-porous or slightly porous, which can lead to a loss of effectiveness when using these pellets in column-type fixed-bed processing methods.

[0008] In fact, access to the interior of the pellets is difficult, or even impossible for the effluent to be treated, so the exchange specific surface area is very small.

[0009] As a result, the adsorption kinetics of these materials are slow (due to the low or even non-porous nature of the binder) and the fraction of available active sites is very small, which results in a decreased Sr purification capacity and thus increases the amount of material required to purify a given volume.

[0010] Furthermore, there are numerous publications in the literature on the use of geopolymers for effluent treatment.

[0011] The non-selectivity of geopolymers used for Sr cation purification results in the use of large amounts of material and, therefore, waste.

[0012] Reference [1] describes the synthesis of geopolymers and geopolymer composites containing additives. However, this reference does not mention any specific application of these composites, in particular their use in the treatment of effluents from fixed-bed processes, let alone their use in the selective extraction of strontium in fixed-bed processes.

[0013] In the specific application of the present invention to the selective extraction of strontium in a fixed bed process, the additives must be carefully identified and selected before they are added to the geopolymer so as to impart ion exchange properties that are selective for strontium, depending on the effluent to be treated. This is not discussed at all in the literature [1].

[0014] Reference [1] also does not provide any instructions to ensure the optimal application of the material in the column fixed bed process. In fact, such an application requires a specific shape design of the material filling the column to ensure that the performance of the material (such as its capacity and selectivity, especially the selectivity for strontium) is optimized while minimizing the head loss in the entire device containing the column.

[0015] Reference [2] describes a method for preparing a material consisting of a monolithic geopolymer foam containing nanoparticles of a metal coordination polymer with CN ligands, the molecular formula of which is [Alk + x ]M n+ [M'(CN) m ] z- .

[0016] This document also relates to a foam produced by this process and to the use of this foam for separating metal or metalloid ions from a stream containing said metal or metalloid ions.

[0017] The method for preparing the foam comprises several steps. In a first step a), the geopolymer foam is mixed with a n+ Then, in a second step b), the geopolymer foam obtained at the end of step a) is brought into contact with [M'(CN) m ] z- and contacting with a salt or complex solution of at least one alkali metal salt to obtain a geopolymer foam comprising metal coordination polymer nanoparticles.

[0018] This multi-step approach complicates the overall synthesis of the material, making it difficult to translate to industrial scale. The method further limits the amount of coordination polymer that can be incorporated into the geopolymer.

[0019] In fact, the coordination polymer nanoparticles only coat the surface of the foam's macropores and are not present in its mesopore walls, which limits the contact surface with the effluent and, therefore, the overall capacity of the material.

[0020] In addition, the method described in the literature [2] is only applicable to metal coordination polymer nanoparticles with CN ligands and is not particularly suitable for the selective purification of Sr.

[0021] Document [3] describes a solid material having a plurality of open and at least partially interconnected pores, comprising a matrix made of microporous and mesoporous geopolymers, wherein open macropores that are at least partially interconnected are defined and limited, the macropores being delimited by sides or walls made of microporous and mesoporous geopolymers, and particles of at least one solid compound different from the geopolymer being distributed in the macropores and / or the sides or walls.

[0022] As a result, such materials contain large pores that are interconnected, with sometimes thin pore walls and sharp junctions. Consequently, these pore walls are mechanically weak, especially when effluent passes through them, which can lead to degradation of the pore walls and the formation of fine particles that can easily clog the columns.

[0023] Reference [3] also describes the synthesis method of this material. To form a macroporous network, this synthesis method requires the preparation of a water-in-oil emulsion containing the material precursor and the removal of the oil phase after the material hardens. This greatly increases the complexity of the synthesis method and makes it difficult to achieve industrial production of this material.

[0024] Reference [4] describes the synthesis of a mesoporous material consisting of a geopolymer and zeolite particles, obtained by mixing the two suspensions and then solidifying the geopolymer. This reference does not describe the use of this family of materials in a column method or in the extraction of strontium.

[0025] Therefore, in view of the above, there is a need for a process that can improve the performance of fixed-bed Sr purification processes, that is, it can achieve high Sr binding capacity and high Sr selectivity, as well as fast adsorption kinetics and optimized column dynamics.

[0026] One of the objects of the present invention is to meet the needs of the above-mentioned method.

[0027] The present invention also aims to provide a method which does not have the drawbacks, limitations and disadvantages of the methods of the prior art, in particular the methods described in the above-mentioned prior art documents, and which overcomes the problems of these methods. Summary of the Invention

[0028] According to the present invention, this and other objects are achieved by a continuous process for producing a strontium ion containing at least one strontium cation, in particular at least one strontium radioisotope, such as 90The invention relates to a method for separating strontium cations from a liquid medium containing strontium cations (Sr cations), wherein the liquid medium is brought into contact with a solid mesoporous material, the solid mesoporous material comprising an inorganic matrix made of a mesoporous geopolymer with open mesopores, and particles of at least one solid inorganic exchanger compound selective for strontium cations and different from the geopolymer, the particles being distributed in the open mesopores of the inorganic matrix and being in contact with the strontium cations contained in the liquid medium; the solid mesoporous material is in the form of non-powdered particles forming a fixed bed, for example forming a column packing.

[0029] By "non-powder-like" it is meant that the particles obtained are of a size large enough not to become suspended in the air or to be carried into the air.

[0030] In the following description, for the sake of simplicity, particles of at least one solid inorganic exchanger compound that is selective for strontium cations and different from the geopolymer are sometimes referred to as active particles.

[0031] Thus, the term "microparticles" applies to solid inorganic exchanger compounds that are selective for strontium cations.

[0032] The inorganic matrix in geopolymers may also be referred to as the "geopolymer binder" or "geopolymer backbone."

[0033] It is important to note that the term "particle" applies to the entire solid mesoporous material, which is a geopolymer / microparticle composite, in the form of a plurality of discrete particles (eg, pellets, extrudates, or beads) forming a fixed bed.

[0034] The method of the present invention differs from the prior art methods in that it utilizes a special material, namely a combination of a geopolymer with a specific porosity and active particles specially selected for selectively binding Sr cations, the active particles being distributed in and accessible through the mesopores, thereby achieving high Sr binding capacity, high Sr selectivity, extremely fast adsorption kinetics, and optimized column kinetics.

[0035] In any case, these capacities, selectivities, and kinetics are higher than those achieved using prior art approaches employing other materials.

[0036] Surprisingly, the method of the present invention has been shown to achieve a higher strontium cation binding capacity, higher strontium cation selectivity and extremely fast strontium cation adsorption kinetics, as shown in the following examples. These strontium cations are specifically radioisotopes of strontium, such as 90 Sr cation.

[0037] The process according to the invention is carried out in particular in a fixed bed, in a column, since the materials used have the necessary robustness and mechanical strength for this purpose and since the particle size of the materials is suitable for such a fixed bed process.

[0038] These excellent adsorption properties (kinetics, capacity, selectivity) are achieved by relatively small amounts of particles of solid inorganic exchanger compounds which are selective for strontium Sr cations, such as zeolites or crystalline titanosilicates.

[0039] As used herein, the terms "geopolymer," "matrix," or "geopolymer backbone" refer to a solid, porous material in the dry state obtained by hardening a mixture comprising a finely ground material (typically an aluminosilicate source) and a saline solution (i.e., an activation solution), which mixture is capable of setting and hardening over time. This mixture may also be referred to as a "geopolymer mixture," "geopolymer composition," or "geopolymer paste." The hardening of the geopolymer occurs due to dissolution / polycondensation of the finely ground material in the geopolymer mixture in the saline solution (e.g., a high pH saline solution, i.e., the activation solution).

[0040] More specifically, the geopolymer, matrix, or geopolymer backbone is an amorphous aluminosilicate inorganic polymer. The geopolymer is derived from a reactive material (i.e., an aluminosilicate source) primarily containing silica and aluminum, activated by a strongly alkaline solution (activating solution), and formulated with a low solid-to-liquid weight ratio. The geopolymer structure consists of a Si-O-Al network formed by silicate (SiO4) and aluminate (AlO4) tetrahedra connected at their vertices by shared oxygen atoms. Within this network, one or more charge-compensating cations (also known as compensating cations) are present, which compensate for the AlO4. - The one or more compensating cations are advantageously selected 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.

[0041] The term "mesoporous geopolymer" is understood to mean a geopolymer having mesopores, exhibiting mesoporosity.

[0042] For the purposes of the present invention, the term "mesopores" is understood to mean pores having an average size (eg diameter) of 2 nm to 50 nm.

[0043] The geopolymer of the solid mesoporous material used in the method according to the invention has a single pore size, ie mesopores, and not a hierarchical porosity like the geopolymer of the material described in document [3].

[0044] Since the solid mesoporous material used in the method according to the invention does not have thin-walled, fragile macroporosity, it is, in particular, more robust and mechanically resistant than the material of document [3].

[0045] Due to their robustness and high mechanical resistance, such solid mesoporous materials can be realized in the form of non-powdered particles, ie particles that cannot be suspended in air and transported therein, forming fixed beds, for example forming column packings.

[0046] The solid mesoporous material used in the method of the present invention is a solid material having open mesopores.

[0047] The term "open mesoporosity" should be understood as meaning that the mesoporosity is accessible to a liquid medium (e.g., an effluent) in contact with the material. The mesopores are at least partially connected (or interconnected), or even fully interconnected, meaning that fluid can pass through the material through these interconnected pores. This mesoporosity also allows fluid to contact the active particles.

[0048] According to the invention, in addition to the mere presence of microparticles of at least one solid inorganic exchanger compound selective for strontium cations, the nature and size of these particles can be selected virtually without any restrictions and independently of the geopolymer matrix.

[0049] Overall, geopolymer frameworks offer many advantages over metal oxide frameworks.

[0050] The synthesis of geopolymers is more easily mastered than the synthesis of metal oxides via the sol-gel process.

[0051] The precursors required for the synthesis of geopolymers are cheaper than the precursors used in the synthesis of metal oxides (mainly alkoxides).

[0052] The geopolymer framework has intrinsically better mechanical strength than the metal oxide framework obtained by the sol-gel process.

[0053] The geopolymer skeleton of the solid mesoporous material implemented according to the method of the present invention contains mesopores, while the metal oxide skeleton does not contain mesopores. In order to generate mesopores in the metal oxide, additional compounds must be added to the formulation, which complicates the system.

[0054] Finally, the solid mesoporous material implemented according to the method of the invention has mesoporosity, high mechanical robustness and incorporates microparticles of at least one solid inorganic exchanger compound selective for strontium cations, suitable for specific fixed bed column applications.

[0055] The material implemented according to the method of the invention ensures that the Sr cations contained in the liquid medium (for example the effluent to be treated) have better accessibility to the particles distributed in the material, in particular due to the interconnectivity existing between the mesopores.

[0056] The solid mesoporous material particles are non-powdered particles, such as granules, seeds, pellets, extrudates, beads or spheres, and have a typical average size (e.g., diameter) of 100 μm to 5 mm, preferably 300 μm to 5 mm, more preferably 300 μm to 500 μm. These solid mesoporous material particles form a fixed bed, such as a column packing.

[0057] Generally, particles of the above sizes can actually be classified as non-powdered, as they are not powders, with the strict definition of powder being less than 100 μm. Therefore, these non-powdered particles can avoid the risk of clogging and reduce head loss when used in fixed beds or columns.

[0058] Advantageously, particles having an average size of 300 μm to 5 mm, preferably 300 μm to 500 μm, are particularly suitable for implementation in a fixed bed to fill a column.

[0059] The term "size" generally refers to the largest dimension of a particle of a solid mesoporous material, such as a diameter.

[0060] Advantageously, the particles of at least one solid inorganic exchanger compound selective for strontium cations and different from geopolymers can be selected from the group consisting of nanoparticles (generally defined as having a diameter of 2 nm to 100 nm), submicron particles (generally defined as having a diameter of 100 nm to 1 μm) and micron particles (generally defined as having a diameter of 1 μm to 10 μm), and in particular the average size of the particles of the solid inorganic exchanger compound, for example the diameter, can be 2 nm to 50 μm, preferably 10 nm to 10 μm, more preferably 20 nm to 1 μm.

[0061] The term "size" here also denotes the maximum dimension, for example the diameter, of the particles of the at least one solid inorganic exchanger compound which is selective for strontium cations and which is different from the geopolymer.

[0062] Advantageously, the active particles of at least one solid inorganic exchanger compound selective for strontium cations have the shape of a ball, a bead, a sphere or an ellipsoid, or even of a needle.

[0063] The particles of at least one solid inorganic exchanger compound selective for strontium cations and different from the geopolymer are preferably inorganic mineral particles, ie particles consisting exclusively (100%) of one or more inorganic mineral solid compounds.

[0064] This 100% inorganic mineral microparticle is particularly advantageous in the treatment of radioactive effluents due to its compatibility with nuclear waste disposal channels.

[0065] The material according to the present invention, comprising such active, 100% mineral particles, and the geopolymer itself being 100% mineral, is therefore also 100% mineral, thus making it fully compatible with nuclear waste disposal channels.

[0066] Advantageously, the solid inorganic mineral exchanger compound selective for strontium cations and different from the geopolymer may be selected from the group consisting of: zeolites; alkaline titanosilicates, such as sodium titanate; and mixtures thereof.

[0067] The solid inorganic mineral exchanger compound selective for strontium cations can be selected based on the nature of the liquid (eg, effluent) and the nature of the extracted contaminants to be treated (eg, salinity and pH).

[0068] When the effluent also contains calcium (Ca) cations, the solid inorganic exchanger compound selective for strontium cations can be, for example, an ion exchanger based on sodium titanate to minimize competition between strontium cations and calcium cations; or, when the effluent also contains sodium (Na) cations, it can be an ion exchanger based on LTA zeolite to minimize competition between strontium cations and sodium cations.

[0069] There are no restrictions as to the form of the active particles of the at least one solid compound different from the geopolymer.

[0070] Advantageously, the content of particles of at least one solid inorganic exchanger compound selective for strontium cations and different from the geopolymer is between 0.05% and 70% by weight, preferably between 10% and 40% by weight, relative to the total weight of the solid mesoporous material.

[0071] Advantageously, after contacting the liquid medium with the solid mesoporous material in a fixed bed, the used fixed bed containing the strontium cations fixed to the microparticles is directly converted into a conditioning material. This conditioning material can be obtained by enclosing the solid mesoporous material particles directly in the fixed bed by incorporating a binder (e.g., a geopolymer or cement-based binder) into the fixed bed, forming a dense monolith comprising the mesoporous material particles.

[0072] In summary, the materials implemented according to the method of the present invention are:

[0073] - It has high capacity and selectivity for strontium, as well as fast adsorption kinetics, and is kinetically optimized for column-based adsorption methods. This shortens processing time, ensures a sustained processing rate, and limits the size of the column used, thereby reducing the amount of waste generated during processing.

[0074] -Can be easily formulated for use in packed columns without causing significant head loss throughout the treatment plant.

[0075] - can generally be easily prepared by methods that are simple to implement and readily transferable to industrial scale.

[0076] - High versatility in composition and molding geometry, which allows the material to be adapted to any type of effluent and any type of fixed-bed column process.

[0077] - Generally have chemistry compatible with the waste management sector specific to the nuclear energy sector.

[0078] As described above, the solid mesoporous material implemented according to the method of the present invention can be prepared by the method described below.

[0079] The method for preparing a solid mesoporous material may comprise at least the following consecutive steps:

[0080] a) mixing a first aqueous suspension of microparticles of at least one solid inorganic exchanger compound selective for strontium cations in water or in an aqueous solution containing a surfactant with an aqueous activation solution and a source of aluminosilicate capable of forming a geopolymer by dissolution / polycondensation, thereby obtaining a second aqueous suspension;

[0081] b) allowing the second aqueous suspension to stand and form a geopolymer framework by polycondensation, thereby obtaining an open solid mesoporous material comprising a framework made of a mesoporous geopolymer with open mesopores and microparticles of at least one solid inorganic exchanger compound selective for strontium cations and different from the geopolymer, the microparticles being distributed in the mesopores and accessible through the mesopores.

[0082] Advantageously, step a) comprises the following consecutive steps a1), a2) and a3):

[0083] a1) preparing a first aqueous suspension of microparticles of at least one solid inorganic exchanger compound selective for strontium cations in water or an aqueous solution containing a surfactant;

[0084] a2) adding an aqueous activation solution to the first aqueous suspension of microparticles of at least one solid inorganic exchanger compound selective for strontium cations obtained at the end of step a1), thereby obtaining aqueous suspension a2;

[0085] a3) adding an aluminosilicate source capable of forming a geopolymer by dissolution / polycondensation to the aqueous suspension a2, thereby obtaining the second aqueous suspension.

[0086] The particle concentration in the second suspension is selected according to the desired final particle concentration of at least one solid inorganic exchanger compound that is selective for strontium cations and that is different from the geopolymer in the prepared material.

[0087] Advantageously, at the end of step a2) and before step a3), the suspension a2 is homogenized, for example by mechanical stirring.

[0088] Advantageously, at the end of step a3) and before step b), the second suspension is homogenized, for example by mechanical stirring.

[0089] The term "mechanical stirring" is generally understood to mean mechanical stirring using a stirring device equipped with an impeller shaft, or preferably using a homogenizing or dispersing device which may be equipped with a dispersing shaft with a rotor / stator system (e.g. Ultra-Turrax, Type) mechanical stirring.

[0090] Advantageously, in step b), the second aqueous solution is left to stand, allowing the geopolymer framework to form by polycondensation in the second aqueous suspension and to be shaped and formed to obtain the selected size and shape.

[0091] The preparation method is very simple and only requires adding active solid particles during the geopolymer synthesis process to prepare solid mesoporous materials.

[0092] Compared to methods requiring the preparation of oil-in-water emulsions, this preparation method is considerably simpler and therefore more reproducible, less time-consuming, and less expensive.

[0093] This preparation method allows the synthesis of materials implemented according to the method of the invention, ie materials with mesopores, which are mechanically robust and integrate active microparticles and improve their accessibility to liquid media, such as effluents to be treated.

[0094] In the present invention, the terms "aluminosilicate source" and "reactive material comprising essentially silica and aluminum" are similar and are used interchangeably.

[0095] Advantageously, the reactive material containing essentially silica and aluminium that can be used to prepare the geopolymer framework of the solid mesoporous material is a solid source containing amorphous aluminosilicates (such as kaolinite or metakaolin), which are known in the art for preparing geopolymers.

[0096] The term "activation solution" is understood to mean a high pH saline solution well known in the field of geopolymerization. The latter is a strongly alkaline aqueous solution that may contain a silicified component, in particular a component selected from the group consisting of silica, colloidal silica and glassy silica.

[0097] The terms "activation solution," "high pH salt solution," and "strong alkaline solution" are similar and are used interchangeably herein.

[0098] The term "strong alkaline" or "high pH" is understood to mean that the pH value of the solution is greater than 9, specifically greater than 10, specifically greater than 11, more specifically greater than 12.

[0099] The activation solution comprises the compensating cation or compensating cation mixture defined above in the form of an ionic solution or salt. Thus, the activation solution is particularly selected from aqueous solutions of sodium silicate (Na2SiO3), potassium silicate (K2SiO2), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), cesium hydroxide (CsOH) and derivatives thereof.

[0100] In summary, the advantages of this method for preparing the solid mesoporous material (i.e., the mesoporous material containing active particles) used in the method of the present invention include at least:

[0101] - The properties of the Sr selective sites directly correspond to the properties of the active particles (nano, submicron or micron particles) integrated into the solid mesoporous material formulation,

[0102] - The preparation process is carried out under mild conditions, at low temperatures, generally at ambient temperature and atmospheric pressure,

[0103] - The preparation method uses commercially available, inexpensive and non-toxic reagents, in particular the activation solution and the aluminosilicate source, and the reaction medium is essentially aqueous.

[0104] In this respect, this preparation method differs from methods involving water-in-oil emulsions in that it does not use organic solvents but only an aqueous phase, making it environmentally friendly and cost-effective.

[0105] The preparation method is simple, reliable, and easy to implement. It requires only simple equipment and apparatus. Specifically, all steps of the preparation method can be performed in a single reactor.

[0106] According to a first embodiment, when the solid material with open mesopores obtained at the end of step b) is in the form of a monolith, then at the end of step b) the following successive steps c), d), e) and f) are carried out:

[0107] c) grinding the monolith to obtain granules;

[0108] d) sieving the granules obtained at the end of step c) to obtain non-powdered particles, such as granules, seeds, pellets, beads or spheres, of a defined average size; preferably, the average size, such as the diameter, is between 100 μm and 5 mm, more preferably between 300 μm and 5 mm;

[0109] e) washing the non-powdery particles obtained at the end of step d);

[0110] f) Dry non-powdered granules.

[0111] Step c) is a coarse grinding step, ie a step which does not seek to control the particle size of the particles obtained, and the particle size of the particles obtained is therefore very large.

[0112] Step d) is performed in order to obtain non-powdery particles having a particle size and a particle size distribution required for the intended use of the material, for example an average particle size of 300 μm to 5 mm, which is the most suitable particle size for column processing methods.

[0113] Step e) is necessary to remove fine particles adhering to the granules after grinding (these fine particles could indeed clog the column) and to remove excess cations generated by geopolymerization.

[0114] One or more rinses may be performed, for example with deionized water.

[0115] Step f) may be performed at a temperature ranging from 30°C to 90°C and for a duration ranging from 1 to 48 hours.

[0116] According to a second embodiment, in step b), the second aqueous suspension is extruded to form extrudates having a defined, controlled shape and size, which may be chosen according to the method of using the solid mesoporous material extrudate.

[0117] According to a third embodiment, the second aqueous suspension can be atomized to form spheres or beads of solid mesoporous material, the size of which is determined according to the application of the method of the invention.

[0118] The method according to the invention can be used in particular for nuclear purification and purification of liquid effluents, wherein the purification is carried out by fixed-bed ion exchange in a column with the material in particulate form.

[0119] Advantageously, the liquid medium may be an aqueous liquid medium, such as an aqueous solution.

[0120] The liquid medium may be a process liquid or an industrial effluent.

[0121] Advantageously, said liquid medium may be chosen from liquids and effluents from the nuclear industry and from installations and activities carrying out radionuclides.

[0122] Typically, the concentration of Sr cations may be in the range of 0.1 pg to 500 mg / L, preferably 0.1 pg to 100 mg / L.

[0123] Zeolites and titanosilicates are particularly suitable for separating strontium.

[0124] After completing the separation process of the invention, in particular when the liquid medium treated is a radioactive effluent, the material in particulate form forming a fixed bed, for example forming a column packing, can be densified by adding a suspension of a geopolymer precursor to the column used.

[0125] The present invention will now be described in more detail, particularly with reference to specific embodiments thereof, and examples are given in particular.

[0126] This description is provided for illustrative and non-limiting purposes and refers to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0127] Figure 1 This is a photograph of the selective geopolymer-adsorbent composite Geopo-Zeo-27 particles (300 μm to 500 μm) obtained in Example 1.

[0128] Figure 2A Shown are diffraction patterns of the material "Geopo-Zeo" comprising geopolymer and LTA zeolite, and the material "Geopo-0" and LTA zeolite powder prepared in Example 1. The x-axis represents 2θ (in degrees) and the y-axis represents intensity (in arbitrary units).

[0129] Figure 2B Diffraction patterns of a material "Geopo-CST" comprising a geopolymer and sodium crystalline silicotitanate (CST), prepared in Example 1, as well as a material "Geopo-0" and sodium silicotitanate (CST) powder ("CST powder") are shown. The x-axis represents 2θ (in degrees). The y-axis represents intensity (in arbitrary units).

[0130] Figure 3A The pore size distribution of the material "Geopo-0" corresponding to pure geopolymer and the material "Geopo-Zeo" comprising geopolymer and LTA zeolite prepared in Example 1 is shown. The x-axis represents the pore size (in nm) and the y-axis represents dV(r) (in cm 3 / nm / g).

[0131] Figure 3B The pore size distribution of the material "Geopo-CST" containing geopolymer and crystalline sodium silicate titanate (CST) prepared in Example 1 and the pore size distribution of the material "Geopo-0" are shown. The x-axis represents the pore size (in nm) and the y-axis represents dV(r) (in cm 3 / nm / g).

[0132] Figure 4The maximum adsorption capacity of the materials prepared in Example 1 is shown as a function of their weight percentage in zeolite ("-zeo") or titanate ("-CST"), as well as the maximum adsorption capacity of geopolymer ("geopo") alone (see Example 3). The squares ■ represent geopolymer ("geopo") alone, the circles ● represent the material "Geopo-Zeo" containing geopolymer and LTA zeolite, and the triangles ▲ represent the material "Geopo-CST" containing geopolymer and crystalline sodium silicate titanate (CST). The x-axis represents the weight percentage of the adsorbent (zeolite or titanate), and the y-axis represents Q (in mg.g) -1 ).

[0133] Figure 5 The distribution coefficients (KD) of the prepared materials for strontium are shown as a function of the weight percentage of the adsorbent (zeolite or titanate silicate), as well as the distribution coefficients (KD) of geopolymers alone (see Example 3). Squares (■) represent geopolymers alone ("geopo"), circles (●) represent materials containing geopolymers and LTA zeolite ("Geopo-Zeo"), and triangles (▲) represent materials containing geopolymers and crystalline sodium silicate titanate (CST) ("Geopo-CST"). The x-axis represents the weight percentage of the adsorbent (zeolite or titanate silicate), and the y-axis represents the distribution coefficients (KD) relative to Sr (in mL / g).

[0134] Figure 6 The strontium adsorption capacity of the material "Geopo-Zeo-27" prepared in Example 1 and the geopolymer alone (i.e., the material "Geopo-0") is shown as a function of the contact time between the material and the solution. The squares ■ represent the geopolymer, and the triangles ▲ represent the "material Geopo-Zeo-27" containing the geopolymer and LTA zeolite. The x-axis represents the contact time (in minutes), and the y-axis represents the strontium adsorption capacity Q (in mg.g -1 ).

[0135] Figure 7 The trend of the distribution coefficient of materials Geopo-0 and Geopo-Zeo-27 as a function of the Sr concentration in the solution at equilibrium is shown. In other words, Figure 7 The adsorption isotherms of the materials Geopo-0 and Geopo-Zeo-27 in a saline matrix are shown (see Example 3). The squares ■ represent geopolymers, and the triangles ▲ represent the material "Geopo-Zeo-27" containing geopolymers and LTA zeolite. The x-axis represents the Sr concentration in the solution at equilibrium: [Sr]fin (in mg.L) -1 ), the y-axis represents the distribution coefficient KD for Sr (unit: mL.g -1 ).

[0136] Figure 8 Breakthrough curves for the materials "Geopo-Zeo 27," "Geopo-CST-5," and "Geopo-CST-10" prepared in Example 1 are shown. These curves show the relationship between the Sr concentration ([Sr]) (normalized by the initial Sr concentration ([Sr]0)) and the effluent volume flowing through the column (see Example 4). The squares represent the material "Geopo-Zeo-27," the circles represent the material "Geopo-CST-5," and the triangles represent the material "Geopo-CST-10." The x-axis represents the effluent volume (mL) flowing through the column, and the y-axis represents [Sr] / [Sr]0. DETAILED DESCRIPTION

[0137] The following description first describes a specific embodiment of the method for preparing the material implemented in the method according to the present invention.

[0138] A specific embodiment of the method according to the invention is then described, wherein the material is used for separating Sr cations from a liquid medium containing Sr cations.

[0139] In a specific embodiment of the method for preparing the material, the solid particles are particles of at least one solid inorganic exchanger compound that is selective for strontium cations. This specific embodiment of the method for preparing the material implemented in the method of the present invention and a specific embodiment of the separation method of the present invention using the material include the following steps:

[0140] (1) Selecting a selective Sr ion exchanger based on the properties of the effluent to be treated, such as salinity or pH. For example, in the case of competitive adsorption of Sr and Ca, a sodium titanate ion exchanger is preferred; in the case of competitive adsorption of Sr and Na, an LTA zeolite ion exchanger is preferred;

[0141] (2) Synthesize the selected ion exchanger (or use a commercial product) so that it is incorporated into the geopolymer in the desired form while maintaining good extraction kinetics. Therefore, submicron-sized particles are preferred;

[0142] (3) Adjust the composition of geopolymers to make them have high mechanical strength, mesoporous network structure and good compatibility with ion exchangers. For example, the base (K + 、Na + Parameters such as the Si / Al ratio or the amount of water added to the formulation will be particularly important;

[0143] (4) Synthesis of cation exchanger-geopolymer composites by simply adding cation exchangers during geopolymer synthesis;

[0144] (5) Shaping the material in a manner suitable for the constraints of the purification method: coarse grinding of the composite material and sieving to select the particle size most suitable for column methods (usually centered around 300 μm-5 mm), synthetic beads or extrudates, etc.

[0145] (6) washing the material to remove fine particles that could clog the column and to remove excess cations from the geopolymerization process;

[0146] (7) filling the column with the formed material;

[0147] (8) using the effluent containing the radioactive Sr to be extracted to permeate the column;

[0148] (9) drying the column by air flow and then exhausting the column;

[0149] (10) Alternatively, the used cylinders can be densified directly by adding a solution of a geopolymer precursor.

[0150] The present invention will now be described with reference to the following examples, which are given for illustrative purposes only and are not intended to limit the scope of the invention.

[0151] Examples

[0152] Example 1 : Synthesis of composite materials used in the method according to the invention and reference materials.

[0153] This example describes the synthesis of “selective adsorbent-geopolymer” composite particles implemented in the process according to the invention, which enables efficient and selective purification of Sr from aqueous effluents in batch and continuous processes in columns packed with these particles.

[0154] First, two ion exchange adsorbents selective for Sr were selected:

[0155] -LTA zeolite with high selectivity for Na.

[0156] - Crystalline sodium silicate titanate (CST), an adsorbent with a higher selectivity for Sr than LTA zeolite.

[0157] In addition to their high selectivity for Sr, these two adsorbents were chosen because their microstructural properties are compatible with the intended applications:

[0158] - Their size is small enough to have fast adsorption kinetics (of the order of hundreds of nanometers / micrometers). More specifically, the average particle size of LTA zeolites is between 200 nm and 500 nm, while the average particle size of CST zeolites is less than 100 nm.

[0159] - They are completely mineral and have good radiation resistance;

[0160] - Their resistance to highly alkaline media allows them to be integrated into matrices of the "geopolymer" type.

[0161] The composition of the geopolymer was optimized to produce a mesoporous geopolymer binder, which enables the selective adsorbent to contact the effluent to be treated and is mechanically strong enough not to break during the purification process.

[0162] The synthesis scheme of the "selective adsorbent-geopolymer" composite material implemented in this example is as follows:

[0163] Step 1: Add a predetermined amount of submicron selective adsorbent powder (LTA zeolite or CST) to 1.77 mL of water and allow to stand in an ultrasonic bath for 15 minutes. The adsorbent dosage is calculated to ensure the particles comprise 5% to 27% by weight of the final material. The specific amounts are as follows: 0.420 g for 5% by weight, 0.887 g for 10% by weight, 1.995 g for 20% by weight, and 2.952 g for 27% by weight.

[0164] - Step 2: Add to the suspension obtained at the end of step 1 2.12 mL of a solution consisting of: 81% by weight of a commercial inorganic binder K5020T (purchased from ), the adhesive is based on a modified potassium silicate aqueous solution, specifically comprising: 30 wt% SiO2, 18 wt% K2O and 52 wt% H2O; and 19 wt% KOH (85% concentration, purchased from Sigma- ).

[0165] The suspension was then homogenized manually.

[0166] - Step 3: 2.64 g of clay powder, metakaolin (BASF ) is added to the suspension obtained at the end of step 2.

[0167] The resulting suspension is then homogenized again, either manually or using an Ultra- Homogenizer, under the condition of shear rate of 3000rpm to 5000rpm.

[0168] After standing at room temperature for 48 hours, a solid monolith was obtained.

[0169] - Step 4: Grind the whole material and then sieve the resulting material particles to obtain particles with a size distribution between 300 μm and 500 μm.

[0170] -Step 5: Perform the washing step.

[0171] To do this, 3 g of the material pellets were manually stirred in 100 mL of demineralized water for 30 seconds. This step was repeated 4 times, with the water being changed between each test.

[0172] - Step 6: The material pellets are finally dried at 80°C for about 12 hours.

[0173] Figure 1 This is a photograph of particles (300 μm to 500 μm) of the selective adsorbent-geopolymer composite material Geopo-Zeo-27 obtained at the end of the above synthesis.

[0174] Thus, it can be noted that the process for preparing the material used in the process according to the invention requires only simple steps and is easily transferable to the industrial scale.

[0175] For comparison, a so-called reference material was also prepared in this example. This material consisted solely of geopolymer and contained no adsorbent-active particles, in particular no zeolite or titanosilicate. The preparation method for this material comprised only steps 2, 3, 4, and steps 5 and 6.

[0176] The materials prepared are named according to the percentage of adsorbent in the material. Table 1 summarizes the materials prepared in Example 1 and their names.

[0177] Table 1

[0178] Weight percentage of adsorbent in the material Geopolymer-LTA Zeolite Geopolymer-Titanium Silicate 0 Geopo-0 Geopo-0 5 Geopo-Zeo-5 Geopo-CST-5 10 Geopo-Zeo-10 Geopo-CST-10 20 Geopo-Zeo-20 Geopo-CST-20 27 Geopo-Zeo-27 Geopo-CST-27

[0179] The composite material used according to the method of the present invention and prepared in Example 1 was characterized and used in Examples 2, 3 and 4 below.

[0180] Example 2 : Characterization of the materials prepared in Example 1.

[0181] In this example, the composite material synthesized in Example 1 and the reference material were characterized, on the one hand by X-ray diffraction to verify that the selective mineral exchanger had not been degraded during the synthesis process; on the other hand, by nitrogen adsorption-desorption to verify the presence of mesopores in the geopolymer binder.

[0182] The presence of mesopores in the geopolymer binder allows the mineral exchanger to access the effluent to be treated.

[0183] X-ray diffraction analysis of materials.

[0184] Figure 2A and Figure 2B The diffraction pattern of the material described in Example 1 is shown.

[0185] Figure 2A A diffraction pattern of the material "Geopo-Zeo" comprising geopolymer and zeolite is shown.

[0186] Figure 2B A diffraction pattern of a material "Geopo-CST" comprising geopolymer and titanate is shown.

[0187] These figures show that the LTA zeolite and the CST titanate particles are well incorporated into the composite without any degradation of their crystal structure. Therefore, the crystal structure that determines the material’s affinity for Sr is well preserved.

[0188] The materials were analyzed by nitrogen adsorption-desorption.

[0189] Nitrogen adsorption-desorption analysis was performed on the different materials prepared in Example 1.

[0190] Figure 3A Shown is the pore size distribution of the material "Geopo-Zeo" comprising geopolymer and zeolite, obtained by the "BJH" method (Barrett, Joyner, Halenda model).

[0191] Figure 3B Shown is the pore size distribution of the material "Geopo-CST" comprising geopolymer and titanate, obtained by means of the "BJH" method (Barrett, Joyner, Halenda model).

[0192] It can be seen that the synthesized materials are all mesoporous materials, and the pore size distribution is concentrated between 4 and 40 nm. Since zeolite and titanite selective adsorbents do not have mesopores, the mesopores of the geopolymer binder are detected.

[0193] Thus, after the shaping step, the selective adsorbent dispersed in the geopolymer binder can come into contact with the ions to be immobilized (Sr in these examples) through the mesopores of the geopolymer.

[0194] It should be noted that the presence of selective adsorbent particles in the material formulation can modify the mesopore size to some extent. However, this is not a problem, as the measured mesopore sizes are systematically large enough to allow rapid ion diffusion.

[0195] Therefore, the synthesized material has crystalline sites composed of zeolite and titanosilicate selective adsorbents, crystalline regions, which will make the material more selective for Sr, and a mesoporous network that allows ion access to these crystalline sites as well as fast adsorption kinetics.

[0196] Example 3 : Adsorption performance of the material prepared in Example 1 in batch mode.

[0197] In this example, testing was performed in batch mode to evaluate the adsorption performance of the material prepared in Example 1.

[0198] In the first step, the adsorption capacity and selectivity of the material were studied. The purpose of these tests was to observe the effect of the presence of selective adsorbents (zeolites and titanates) in the material formulation on its adsorption capacity Q (mg.g -1 ) and selectivity for strontium (using the selectivity coefficient K D (mL.g -1 ) indicates the influence of).

[0199] In order to evaluate the maximum adsorption capacity of the materials, adsorption tests were carried out in a high concentration Sr solution.

[0200] To estimate the maximum adsorption capacity of a material, the protocol for these adsorption tests was as follows:

[0201] - 50 mg of the material in the form of 300-500 μm particles was placed in 50 mL of a high-salinity aqueous matrix (deionized water) containing 0.25 mol / L of NaNO3, 50 ppm of Ca (Ca(NO3)2 salt) and 200 ppm of Sr (Sr(NO3)2 salt).

[0202] - Stir with a rotary stirrer for 24 hours.

[0203] -After stirring, 15 mL of the supernatant was taken with a syringe, filtered with a 0.22 μm needle filter, and the residual Sr concentration of the sampled filtered solution was analyzed.

[0204] The extraction or adsorption capacity Q for Sr (the amount of Sr captured per gram of material) is then determined as follows:

[0205]

[0206] Among them, [Sr] init and [Sr] fin represent the initial Sr concentration and final Sr concentration in the solution (mg.L -1 ), V is the volume of the solution (mL), and m is the weight of the material (g).

[0207] Figure 4 The maximum adsorption capacity of the materials is shown as a function of the weight percentage of adsorbent.

[0208] It can be seen that, regardless of the adsorbent used, the adsorption capacity of the material increases with the adsorbent concentration, thus demonstrating the significance of the presence of this adsorbent in the material and its accessibility to the treatment solution due to the mesoporosity of the geopolymer.

[0209] In order to estimate the value of the material's partition coefficient (the ratio between the amount of Sr captured by the material and the amount of Sr remaining in the solution), adsorption tests were performed in solutions with low Sr concentrations.

[0210] To estimate the values of the material partition coefficients, the protocol for these adsorption tests was as follows:

[0211] - 50 mg of the material in the form of 300-500 μm particles was placed in 50 mL of a high-salinity aqueous matrix (deionized water) containing 0.25 mol / L of NaNO3, 50 ppm of Ca (Ca(NO3)2 salt) and 200 ppm of Sr (Sr(NO3)2 salt).

[0212] - Stir with a rotary stirrer for 24 hours.

[0213] -After stirring, 15 mL of the supernatant was taken with a syringe, filtered with a 0.22 μm needle filter, and the residual Sr concentration of the sampled filtered solution was analyzed.

[0214] Then, the distribution coefficient K for Sr is D Determine as follows:

[0215]

[0216] Among them, [Sr] init and [Sr] fin represent the initial and final Sr concentrations in the solution (mg / L), V is the volume of the solution (mL), and m is the weight of the material (g).

[0217] Figure 5 shows the material partition coefficient K D Variation with adsorbent weight percentage.

[0218] It can be seen that no matter what adsorbent is used, the distribution coefficient of the composite material to Sr increases with the increase of adsorbent concentration, which proves the importance of the presence of adsorbent in the material.

[0219] However, the effects of the two adsorbents were different, with the K of pure geopolymer being D 667mL.g -1 When 27 wt% of LTA zeolite is added to the material, K D Increased to 1120mL.g -1 , while at the same concentration of CST, KD It increases to 5648mL.g -1 .

[0220] It should be noted that these values were obtained under the condition of an initial Sr concentration of 2 ppm. It will be shown below that when the initial Sr concentration decreases, its distribution coefficient K D The value will increase.

[0221] This difference can be explained by the composition of the solutions used for the tests, in particular the concentrations of Na and Ca, and by the nature of the adsorbents used. In fact, CST showed a higher selectivity for Sr relative to Ca and Na than LTA zeolite.

[0222] Furthermore, two materials were investigated in batch mode: Geopo-0 and Geopo-Zeo-27.

[0223] These studies were kinetic studies and full isothermal studies.

[0224] Kinetic studies

[0225] The adsorption kinetics of a material can be characterized by analyzing its adsorption as a function of the contact time between the material and the effluent to be treated.

[0226] The test protocol for studying the adsorption kinetics of the material is as follows:

[0227] - 50 mg of the material in the form of 300-500 μm particles was placed in 50 mL of a high-salinity aqueous matrix containing 0.25 mol / L NaNO3, 50 ppm of Ca (Ca(NO3)2 salt) and 50 ppm of Sr (Sr(NO3)2 salt).

[0228] - Prepare multiple sample batches and subject them to rotary stirring conditions for stirring times ranging from 5 minutes to 48 hours.

[0229] -After stirring, 15 mL of the supernatant was taken with a syringe, filtered with a 0.22 μm needle filter, and the residual Sr concentration of the sampled filtered solution was analyzed.

[0230] Figure 6 The adsorption capacity of Sr for the two materials studied (Geopo-27 and Geopo-0) is shown as a function of the contact time between the materials and the solution.

[0231] Thus, this example shows that the method according to the invention uses pelletized material and can therefore be used in an adsorption column, ensuring rapid adsorption kinetics (reaching equilibrium within 24 hours) due to the mesoporosity of the geopolymer binder, which allows easy access of the ions to the selective adsorbent particles.

[0232] Complete isothermal study

[0233] The purpose of these tests was to determine the values of the partition coefficient at very low Sr concentrations that would best represent the Sr concentrations found in radioactive effluents.

[0234] The protocol for these tests, aimed at establishing adsorption isotherms, was as follows:

[0235] - 50 mg of the material in the form of 300-500 μm particles were placed in different batches containing 50 mL of a high-salinity aqueous matrix (deionized water) containing 0.25 mol / L -1 NaNO3, 50ppm Ca (Ca(NO3)2 salt), Sr concentration (Sr(NO3)2 salt) between 0.1 and 200mg.L -1 between.

[0236] - Each batch of material was placed under rotary stirring conditions for 24 hours.

[0237] -After stirring, 15 mL of the supernatant was taken with a syringe, filtered with a 0.22 μm needle filter, and the residual Sr concentration of the sampled filtered solution was analyzed.

[0238] Figure 7 The trend of the material distribution coefficient as a function of the Sr concentration in the solution at equilibrium is shown.

[0239] in other words, Figure 7 Shown are the adsorption isotherms produced for Geopo-0 and Geopo-Zeo-27 materials in saline matrices.

[0240] The most representative distribution coefficient of radioactive effluents is located at the plateau level at the lowest strontium concentration. Therefore, it can be seen that the presence of a selective adsorbent in the material has a significant effect on the selectivity of the material for strontium. In the considered matrix (0.25 mol / L NaNO3 and 50 ppm Ca (Ca(NO3)2 salt)), the K of Geopo-0 material is D About 1030mL.g -1 , while the K of Geopo-Zeo-27 material D Reach 2044mL.g -1 .

[0241] In summary, the mesoporous and multiphase microstructure of the materials used in the process of the present invention allows:

[0242] - First, the material can be made into a pelletized form that can be used in cartridges while maintaining fast adsorption kinetics

[0243] -Secondly, improve the material's selectivity for Sr.

[0244] Example 4 : Material performance in fixed bed purification processes

[0245] In this example, in order to demonstrate the importance of the microstructure of the composite particulate material used in the purification method according to the present invention for its performance in a fixed bed, the composite particulate material implemented in accordance with the method of the present invention and described in Example 1 was tested in a column.

[0246] The test was conducted according to the following scheme:

[0247] -Put the sieved 300μm to 500μm particles into a glass column with a height of H = 3cm and a diameter of D = 1cm.

[0248] -The column is placed in an assembly consisting of an effluent reservoir, a peristaltic pump and a pressure gauge at the head of the column to measure the head loss.

[0249] Using this component, a penetration curve (defined below) can be generated.

[0250] Contains 0.25mol.L -1 The aqueous effluent (deionized water) of 50 ppm of NaNO3, 50 ppm of Ca (Ca(NO3)2 salt) and 100 ppm of Sr (Sr(NO3)2 salt) was heated at 20 mL.h. -1 The flow rate of 200 μg / ml flowed through the packed column, and the Sr concentration in the sample collected at the outlet was measured as a function of time by ICP-OES to obtain a breakthrough curve.

[0251] Figure 8 Breakthrough curves, ie the Sr concentration (normalized by the initial Sr concentration) as a function of the effluent volume passing through the column, are shown for the materials Geopo-Zeo27, Geopo-CST-5 and Geopo-CST-10.

[0252] The figure shows that the breakthrough curve is S-shaped with a steep slope, which is exactly as expected and shows ideal performance in the column method.

[0253] The higher the amount of adsorbent, the greater the volume that can be processed by the same amount of material, and the slope of the curve is vertical.

[0254] refer to

[0255] [1]WO-A1-2018 / 015490.

[0256] [2]WO-A1-2016 / 173950.

[0257] [3]WO-A1-2021 / 152248.

[0258] [4]PAPA et al., "Zeolite-geopolymer composite material: Production and characterization", Journal of Cleaner Production, 17 (2018) 76-84.

Claims

1. A method of producing a radioactive isotope of strontium containing at least one strontium cation, in particular at least one strontium cation, such as 90 A continuous process for separating said strontium cations from a liquid medium containing Sr cations, wherein: The liquid medium is brought into contact with a solid mesoporous material comprising an inorganic matrix made of a mesoporous geopolymer with open mesopores and particles of at least one solid inorganic exchanger compound, the geopolymer having a single pore size, the inorganic exchanger compound being selective for the strontium cations and different from the geopolymer, the particles being distributed in the open mesopores of the inorganic matrix and being in contact with the strontium cations contained in the liquid medium; the solid mesoporous material forming a fixed bed in the form of non-powdered particles, for example forming a column packing.

2. The method according to claim 1, wherein the particles of the solid mesoporous material, such as granules, seeds, pellets, beads, extrudates or spheres, have an average size, such as a diameter, of 100 μm to 5 mm, preferably 300 μm to 5 mm, more preferably 300 μm to 500 μm.

3. The method according to claim 1 or 2, wherein the particles of at least one solid inorganic exchanger compound selective for strontium cations and different from the geopolymer are selected from the group consisting of nanoparticles, submicron particles and micron particles, in particular having an average size, such as diameter, of 2 nm to 50 μm, preferably 10 nm to 10 μm, more preferably 20 nm to 1 μm.

4. The method according to any one of the preceding claims, wherein the solid inorganic exchanger compound selective for the strontium cations and different from the geopolymer is chosen from the group consisting of: zeolites; alkaline titanosilicates, such as sodium titanate; and mixtures thereof.

5. The method according to any one of the preceding claims, wherein the content of particles of at least one solid inorganic exchanger compound selective for the strontium cations and different from the geopolymer is from 0.05% to 70% by weight, preferably from 10% to 40% by weight, relative to the total weight of the solid mesoporous material.

6. The method according to any one of the preceding claims, wherein the liquid medium is an aqueous liquid medium, such as an aqueous solution.

7. The method according to any one of the preceding claims, wherein the liquid medium is selected from liquids and effluents of the nuclear industry and facilities and activities in which radionuclides are used.

8. A method according to any one of the preceding claims, wherein After contacting the liquid medium with the solid mesoporous material in a fixed bed, the spent fixed bed is converted directly into conditioning material, in particular by enclosing the particles of the solid mesoporous material directly within the fixed bed by incorporating a binder into the fixed bed.

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