EP1419009A1

EP1419009A1 - Method for preparing a composite solid material based on hexacyanoferrates, and method for fixing mineral pollutants using same

Info

Publication number: EP1419009A1
Application number: EP02774878A
Authority: EP
Inventors: Isabelle Bispo; Slobodan Milonjic
Original assignee: Centre National de la Recherche Scientifique CNRS; Commissariat a lEnergie Atomique CEA; Societe Technique pour lEnergie Atomique Technicatome SA; TechnicAtome SA
Current assignee: Centre National de la Recherche Scientifique CNRS; Societe Technique pour lEnergie Atomique Technicatome SA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2001-08-22
Filing date: 2002-08-20
Publication date: 2004-05-19
Also published as: JP2005500158A; EA005634B1; FR2828819B1; FR2828819A1; EA200400327A1; UA76178C2; US20040178385A1; WO2003018193A1

Abstract

The invention concerns a method for making a composite solid material based on metal hexacyanoferrate fixing mineral pollutants, comprising a solid support coated with an anion-exchanging polymer whereto is fixed an insoluble metal hexacyanoferrate forming a thin layer, said method essentially comprising at least a step which consists in contacting said solid support with at least a liquid reagent and at least a washing step with a washing liquid. The invention is characterized in that all the steps of the method are carried out continuously in one and the same vessel, such as a column, wherein the support forms a fluidized bed whereof the fluidization is provided by at least a washing reagent or liquid.

Description

PROCESS FOR THE PREPARATION OF A COMPOSITE SOLID MATERIAL

BASED ON HEXACYANOFERRATES ,.

AND METHOD FOR FIXING MINERAL POLLUTANTS

IMPLEMENTING IT

DESCRIPTION

The present invention relates to a process for the preparation of a solid composite material fixing mineral pollutants based on insoluble hexacyanoferrates.

More specifically, the present invention relates to a process for the preparation of a composite solid material fixing mineral pollutants, based on hexacyanoferrates and cationic polymers, deposited in a film layer on a support. Even more precisely, the present invention relates to a process for the preparation of a composite solid material fixing mineral pollutants formed from a mechanically and chemically stable solid support, coated with a film of an anion exchange polymer, to which a thin layer of insoluble hexacyanoferrate is fixed.

The present invention also relates to a method for fixing at least one mineral pollutant contained in a solution on said composite solid material fixing mineral pollutants.

Numerous mineral fixatives have been used for fixing various mineral pollutants such as metal cations contained in various media and effluents from various industries and in particular from the nuclear industry.

Indeed, the nuclear industry uses for the treatment of effluents of low or medium radioactivity purification techniques with volume reduction consisting in the fixation on mineral solid of the radioisotopes present in the solutions. The volumes currently treated are enormous and reach several tens of thousands of m ³ / year for France. The liquids treated are also varied in nature since it involves treating the cooling water from nuclear power plants as well as the various effluents coming into contact with radioisotopes such as all washing water, resin regeneration solutions etc ...

The hexacyanoferrates, in particular the hexacyanoferrates (II) of Cu, Ni and Co are among the most commonly used mineral fixers, in particular in the nuclear industry because of the high affinity they have for cesium. Inorganic fixing agents of the hexacyanoferrate type have therefore in particular been used to separate, recover and fix the metal ions and in particular the radioactive alkali metal ions such as cesium 137 with long half-life from various industrial and nuclear effluents, for example from strongly acid solutions resulting from the reprocessing of irradiated fuels and from the solutions already mentioned above. Currently, insoluble hexacyanoferrates are used in most processes treatment of liquid radioactive waste by co-precipitation.

The document FR-A-2 765 812 describes the method of preparation and use in column of a material composed of metallic hexacyanoferrate fixed on a solid support chemically and mechanically stable, coated with a thin film of organic polymers exchangers of anions for fixing at least one mineral pollutant, in particular from a liquid or an effluent from the nuclear industry. The product, first prepared, then packaged in the form of a column, allows the total and irreversible fixation of cesium 137.

In this material, the hexacyanoferrate anion is adsorbed on the anion exchange polymer covering a solid support in the form of a film, by interactions of electrostatic type and, therefore, strongly adheres to the support. This bond involves adsorption phenomena in the pores as in the impregnated hexacyanoferrates. The deposit of

1 hexacyanoferrate is carried out uniformly over the entire modified surface of the support. All the possible exchange sites for the polymer are exchanged, the composition and properties of the material are perfectly controlled and reproducible, unlike the materials of the prior art. There is no longer any residual hexacyanoferrates on the surface capable of being released and subsequently disturbing the fixing process. The material has a contact surface of the same order of magnitude as the specific surface of the selected support, thus the reactivity of the copper hexacyanoferrate is increased.

The distribution coefficient of cesium is high (Kd> 100,000) and comparable to those of hexacyanoferrates impregnated with quantities of hexacyanoferrate of 1 to 2% by mass relative to the mass of support. This is in particular the reason why ^" it is possible to easily store the material of this document which is stable and essentially mineral. The method of fixing at least one metal cation (for example Cs ⁺ ) can be implemented separately, either in "column" mode or in "batch" mode, with stirring.

However, in this document, like many documents of the prior art, the process of synthesis, then of fixing, of decontamination, calls for a batch process requiring several stages with transfer of solvents and reagents. It is thus that it is only once the precipitate of metal hexacyanoferrate is synthesized, that it is put in column for the decontamination of the effluents.

Furthermore, in the aforementioned patent publication, in order to obtain good adhesion, good behavior of the polymer on the support and a stable film on this same support, it is in most cases necessary to cross-link the polymer by covalent bond on said support. Crosslinking is in particular essential in order to obtain a stable film, adhering to the support, such as silica, with polymers, such as polyethyleneimines (PEI) and polyvinylimidazoles (PVI). However, these crosslinking and / or fixing steps by covalent bonding or grafting to obtain the immobilization of the polymer, for example PEI on the support are long and difficult. In fact, these stages are carried out in batch mode in an organic medium with reaction times of up to 48 hours and require drying of the support in vacuo beforehand.

In addition, certain documents, such as the document by MT GANZELI VA ENTINI, R. STELLA, L. MAGGI, J. of Radioanalytical and nuclear che istry, 114, n ° 1, 1987, 105-112, mention processes in which the synthesis is carried out in column on mineral supports, such as silica, these processes resting on the principle of percolation of reagents at low flow rates requiring a packing of the solid support.

In these methods, the reactants, such as copper sulphate and sodium ferrocyanide, are previously mixed to form a mixed hexacyanoferrate formed of copper, sodium and potassium. This hexacyanoferrate is then introduced at very low flow rate into a column containing the mineral support. Once the hexacyanoferrate has been fixed on the silica, a certain number of purification steps are carried out in “batch”, thus forcing recourse to a new column setting for decontamination.

When metal ions, such as cupric ions are complexed by the polymer, problems of subsequent release of these ions, from solid composite material have been observed, requiring long washing steps after contact of the support with the metal salt, such as copper nitrate. Another document by AA KOPYRIN, A. K;

PYARTMAN et al., Radiochemistry, 42, n ° 1, 2000, 83-85, describes that only the fixation of the hexacyanoferrate is done in column, while then, the precipitation, as well as the purification, is done in " batch ”with slow reaction times, since they are of the order of seven days.

The major drawback of these methods is that a single synthesis step is carried out at the same time in the same column, namely the fixing of the ferrocyanide, which is generally the simplest step of the synthesis, while several stages of this same synthesis are implemented in batch, in particular the most tedious stages, such as the purifications. The product obtained then requires, again, a high temperature drying step to remove excess cyanides. Decontamination again requires the product to be re-columned. Another drawback can be cited: in the column - which, we insist on this fact, is in all the processes of the prior art, a column with a fixed, packed bed - there may exist preferential paths, which would be liable to cause a inhomogeneous deposition of meta1 hexacyanoferrate. It appears from the above that there is a need for a process for preparing a material composite solid fixing mineral pollutants based on metal hexacyanoferrate, comprising a solid support coated with a film of an anion exchange polymer, to which is fixed an insoluble metal hexacyanoferrate forming a thin layer, which can be produced fully continuous.

There is, in particular, a need for a process for preparing a composite solid material fixing the pollutants, which can be implemented continuously in a single and same enclosure, which is simple, reliable, and which comprises either a number limited number of stages, all carried out continuously.

This process must, moreover, make it possible to prepare a material whose properties are stable, perfectly controlled and without random variations, and in which the polymer is fixed in an adherent and stable manner to the support, even without resorting to grafting operations and / or complicated and long crosslinking and carried out in "batch" mode. It is obvious that the material prepared by the process must also meet the criteria and requirements which are for the most part already satisfied by the solid composite material of the prior art represented by FR-A-2 765 812. In particular, this material must be chemically and mechanically stable in order to be able to be thus conditioned in a column allowing continuous implementation of the fixing process, of pollutants, of decontamination. The solid composite material fixing mineral pollutants must also have excellent fixing properties, in particular of decontamination, that is to say analogous, or even superior in particular to those of hexacyanoferrates not impregnated on a support. The solid material fixing mineral pollutants must also combine good mechanical stability with a high reaction speed, unlike products in compact form, the low specific surface of which leads to slow reaction rates. In other words, the solid material fixing mineral pollutants, based on metal hexacyanoferrates must present among other things excellent mechanical and chemical stabilities, a high coefficient of affinity or of decontamination, a great reactivity, as well as a good selectivity.

These properties must be obtained with a minimum quantity of mineral fixer of the hexacyanoferrate type of metal.

In addition, in particular in the case of the fixing of radioactive elements, the composite solid material fixing mineral pollutants must be able to be easily stored and / or vitrified without risk by known methods.

Finally, the material prepared by this process must have a composition and properties that are perfectly reproducible and controlled.

The present invention therefore aims to provide a process for the preparation of a composite solid material fixing mineral pollutants based on metal hexacyanoferrates, which does not have the drawbacks, defects, disadvantages, and limitations processes for the preparation of composite solid materials fixing mineral pollutants of the prior art, as represented essentially by the document FR-A-2 765 812, which overcomes the problems of the processes of the prior art and which fulfills, inter alia , the set of needs mentioned above.

The present invention also aims to provide a method for fixing at least one mineral pollutant contained in a solution which uses said composite solid material and which can be carried out continuously, in particular with a reduced duration and a high efficiency. .

This object, and others still, are achieved, in accordance with the invention, by a process for the preparation of a composite solid material fixing mineral pollutants, based on metal hexacyanoferrate, comprising a solid support coated with a film of an anion exchange polymer to which is fixed an insoluble metal hexacyanoferrate forming a thin layer, said method essentially comprising at least one step of bringing said solid support into contact with at least one liquid reagent, and optionally at least one step washing, with an avage liquid, characterized in that all of the process steps are carried out continuously in a single container, such as a column, in which the support forms a fluidized bed, the fluidization of which is provided by said at least one reagent or washing liquid.

The process according to the invention is carried out entirely continuously, in a single container, such as a column, this means that there is no there is no transfer of the material from one container to another during the process, that all the stages of preparation are carried out, successively, continuously, without breaking, without interruption, unlike the processes of the prior art, where certain stages are carried out in “batch” mode, and others are carried out continuously with each time a change of container, and a transfer of the material.

This results in significant time savings, while the yields and production capacities obtained are considerably higher.

The method according to the invention makes it possible to prepare large quantities of material, for example up to hundreds of kilograms, in a relatively short reaction time.

In addition, this process is simple because it only involves a single container, and reliable, the fluidization technique being a known and proven technique.

By “together, process steps”, it is meant that all the process steps are carried out in the same container, for example a column (but this container could also take other forms). The term "preparation" generally covers any operation aimed at obtaining the targeted material, namely synthesis, purification, or the like. Such a method however essentially comprises at least one step of bringing the solid support into contact with at least one liquid reagent and at least one step of washing with a washing liquid. According to the invention, during the process, the solid support forms a fluidized bed, the fluidization of which is ensured by said at least one liquid reagent or washing liquid. Fluidization is generally ensured by a very high flow rate (80 to 280 ml / min) of this reagent or washing liquid sent into the previously fixed bed of solid support, against the current from bottom to top in the bed of solid support. The synthesis of the material, and in particular the deposition of the insoluble metal hexacyanoferrate on the support, is greatly facilitated by the implementation of the fluidized bed, which ensures both the chemical reaction, as well as a perpetual movement of the support. . The method according to the invention allows, in particular, to obtain a homogeneous, uniform deposit of metal hexacyanoferrate on the solid support coated with cationic polymer obtained in the same container, during the previous step of the same continuous process .

The uniformity of the deposit on the support, thanks to the implementation of the fluidized bed, no longer requires compaction thereof and avoids the problems due to the preferential paths encountered in the prior art. The material prepared by the process according to the invention, essentially due to the use of a fluidized bed during its preparation, thus has inherent, improved properties, compared to the prior art, in which the preparation of the material is not made fully continuous in a single column, and in a fluidized bed.

As already indicated above, the material prepared by the process according to the invention is coated with a homogeneous and uniform layer of hexacyanoferrate, which is not the case in analogous materials of the art anterior prepared in "batch" mode and, moreover, without using a fluidized bed. It was also noted that the material prepared by the process of the invention exhibited distribution constants, for example with respect to a solution loaded with radioactive cesium, much higher than those obtained with the products prepared in " batch ”, for example 10 ⁴ mL / g instead of 10 ³ mL / g.

In addition to these improved properties and advantages fundamentally linked to its specific method of preparation, the material according to the invention has a structure substantially similar to that described in document FR-A-2 765 812, namely, the material prepared by the process according to the invention has a specific structure in which the mineral fixer as such, ie the metal hexacyanoferrate, is in the form of a thin layer which is immobilized on a polymer phase fixed on a support, said support being solid and advantageously, chemically and mechanically stable, and being protected and isolated from the action of the medium by the underlying polymer layer. Therefore, the material prepared according to the invention is also chemically and mechanically stable and combines these stabilities with a high reaction rate, and is perfectly suited for column packaging • for fixing and decontamination. It will be seen later that, in fact, this column is preferably advantageously according to the invention the same as that in which the material is prepared.

For example, ^'the mechanical stability of the material prepared according to the invention has proved perfect column, after washing with pure water for several days, corresponding to more than 10,000 column volumes.

In the material prepared according to the invention, the hexacyanoferrate anion is adsorbed on the polymer, by interactions of electrostatic type, and therefore strongly adheres to the support.

The bond which exists between the anionic part of the metal hexacyanoferrate, and the support coated with the anion exchange polymer, is an electrostatic type bond, which is not a weak bond of a mechanical nature essentially involving phenomena adsorption in the pores as is the case in impregnated hexacyanoferrates, for example on silica gel. The deposition of the hexacyanoferrate is, as already indicated, carried out uniformly over the entire modified surface of the support.

All the possible exchange sites of the anion exchange polymer are exchanged, the composition and the properties of the material according to the invention are therefore perfectly controlled and reproducible. There is no longer any excess hexacyanoferrate material on the surface, capable of being released and disturbing the fixing process thereafter. The material prepared according to the invention also has a contact surface which is of the same order of magnitude as the specific surface of the chosen support. Consequently, the reactivity of hexacyanoferrate is increased. The distribution coefficient of the material prepared according to the invention, which is preferably 10,000 to 100,000 (mg / L) for one gram of material, is high and is comparable to that of massive hexacyanoferrates, but the amounts of exacyanoferrates used are advantageously much lower than those of hexacyanoferrates impregnated on silica.

Thus the material prepared according to the invention generally comprises an amount of metal hexacyanoferrate fixed from 1 to 10% by weight, preferably from 2 to 3% by weight relative to the mass of the support, this value is to be compared to the 30% value for the hexacyanoferrates impregnated on silica mentioned above.

The quantity of ferrocyanide which is fixed and rejected after its use is limited, and the same efficiency is obtained for a quantity, for example ten times less, of hexacyanoferrate, since all the fixed product is effective.

This is in particular the reason why, it is possible to easily store the material prepared according to the invention, which is stable and essentially mineral, and / or to vitrify it which was previously impossible with the materials of the prior art.

More specifically, the solid support can be chosen from the supports known to those skilled in the art and suitable for the use described; these solid supports can be organic or mineral and are generally chosen from chemically and mechanically stable solid supports.

The support will thus preferably be chosen from mineral oxides such as silica, alumina, titanium oxide, zirconium oxide, diatomaceous earth, glasses, and zeolites; a preferred support is silica, readily available at a reasonable cost. The support may be in any form, but because it must be fluidized, it will preferably be in the form of particles such as grains, beads or spheres; or fiber. The particle size of the support, in the form of particles, defined by the size of the particles, that is to say the diameter in the case of spherical particles, can vary within wide limits and will generally be from 1 to 500 μm, preferably greater than or equal to 10 μm, more preferably still greater than or equal to 30 μm, for example.

The specific surface of the support can also be variable, for example from 10 to 500 m ² / g, preferably 30 to 500 m ² / g. The support is preferably a porous support to allow better fixation of the polymer.

The average pore size of the support is variable, and is preferably 100 to 1000 Å.

The anion exchange polymer of the composite solid material fixing mineral pollutants according to the invention is derived from an organic polymer which has been optionally provided with cationic groups by any process known to those skilled in the art.

This organic polymer is preferably chosen from polyvinylimidazoles, copolymers of vinylimidazole with at least one other monomer, for example a vinyl monomer, polyethyleneimines, polyamines and any polymer carrying a cationic group or the like or capable of being provided with it. .

Examples of these polymers are given for example in document EP-A-0 225 829 and document DE-A-30 07 869.

Any polymer is suitable on the condition that it forms a film, or film very adherent to the surface of the support, for example by adsorption in the pores or by covalent bond using a suitable grafting, and that it is or that it can be a carrier of cationic groups.

Furthermore, and for better resistance of the polymer adsorbed on the support, it is generally preferable to crosslink the polymer. For the grafted polymer, crosslinking is generally not necessary. According to a particularly preferred embodiment of the invention, the polymer is a non-crosslinked polymer, which comprises as anion exchanger groups only quaternary ammonium groups, and which does not contain primary, secondary and tertiary amino groups.

More preferably, said cationic polymer, the anion exchanger is a Polybrene ^® or bromide hexadimethrine or poly (dibromide N, N, N ', N' -tétraméthyltriméthylènehexamêthylènediammonium) (Cι ₃ H ₃₀ Br ₂ N ₂₎ _x . CAS No [2 8728-55-4], which is a water-soluble polymer, widely used in biochemical applications and which contains only quaternary ammonium groups.

The polybrene formula is as follows:

These preferred specific polymers greatly improve the properties of the composite materials of the prior art, in particular of the materials described in document FR-A-2 765 812. These specific preferred polymers exhibit excellent adhesion to the support, such as silica, without requiring any crosslinking.

The preferred polymers adhere to the support, in an excellent manner, without crosslinking or fixing by covalent bond. Since the preferred polymer does not have primary and secondary and tertiary groups, the formation of unstable metal complexes is avoided, as well as the subsequent release of metal ions, such as copper, from the material.

Therefore with the preferred polymers, the properties of the composite material are perfectly controlled, stable and do not undergo random variations. The film is strongly adherent to the support and this film is extremely stable. It may be thought that the excellent adhesion of the preferred polymers, such as polybrene, to the support, comes from the interaction between the NR ₄ ⁺ of the polymer and the silanol groups of the support.

The metal hexacyanoferrate which is attached to the anion exchange polymer can be any hexacyanoferrate known to those skilled in the art, it can be chosen, for example, from copper, cobalt, zinc, cadmium, nickel, iron hexacyanoferrates and the like. mixed hexacyanoferrates relating to these salts.

It should be noted that the process for the preparation of the invention of a solid composite material fixing mineral pollutants, based on metal exacyanoferrate, comprising a solid support coated with a film of an exchange polymer anions, to which is fixed an insoluble metal hexacyanoferrate forming a thin layer is absolutely not limited to steps, operating parameters of these steps, reagents, and possible particular washing liquids.

On the contrary, the process according to the invention can be implemented successfully, whatever the steps involved in this process, the conditions of these steps and whatever the reagents and washing liquids used, provided , of course, that all steps of the method are performed, in accordance with ^~ 1 the invention continuously in a single container, wherein the support forms a fluidized bed, the fluidization is provided by said at least one reagent liquid or any washing liquid.

In particular, the process according to the invention can be, for example, any process for the preparation of a composite solid material defined above, in which while retaining substantially the same steps, the same reagents, and the same washing liquids, the adaptation is carried out consisting in carrying out all of said steps continuously in a single container, such as a column, in which the support forms a fluidized bed, the fluidization of which is ensured by the liquid reagents or washing liquids, if any.

A preparation process which can be adapted to be carried out in accordance with the process of the invention, continuously, and in a fluidized bed is, for example, the process described in the document. FR-A-2 765 812 to the description of which reference may be made.

Such a process may include a crosslinking step which is difficult and time-consuming to carry out with heating to approximately 60 ° C. This is the reason why, in a preferred embodiment of the invention, the preparation process is carried out without crosslinking, preferably using particular cationic polymers. Such a method comprises the following successive steps:

- impregnation of a solid support with an aqueous solution of an anion exchange polymer to form a film of said polymer on said solid support;

- washing with demineralized water; impregnation of the solid support thus coated with a film of anion exchange polymer, with an aqueous solution of alkali metal hexacyanoferrate; washing with demineralized water said solid support coated with a film of anion exchange polymer to which an alkali metal hexacyanoferrate is attached; - Adding an aqueous solution of a metal salt to said coated solid support, to form a composite solid material fixing mineral pollutants, comprising the solid support coated with a film of anion exchange polymer to which is fixed a hexacyanoferrate insoluble metal forming a thin layer. - washing with demineralized water.

In this embodiment of the process of the invention, the anion exchange polymer is preferably chosen from anion exchange polymers, non-crosslinked, comprising as anion exchange groups only quaternary ammonium groups and not comprising no primary, secondary and tertiary amino groups. Polyethyleneimines (PEI) can also be chosen, but this involves tedious intermediate and final rinsing steps.

In addition to the advantages already mentioned above, linked to the continuous and fluidized implementation of the process, the process according to the invention in this preferred embodiment, essentially thanks to the use of the specific polymers described above and of preference of polybrene has many advantages, among others:

the adsorption of the polymer, which is soluble in water, takes place in an aqueous medium, from an aqueous solution and not in an organic medium, without prior drying, under vacuum, of the support, and this contact time is reduced, for example to 1 hour;

the adhesion of the polymer to the support, such as silica, is stable, which eliminates the steps of crosslinking, carried out at 60 ° C., (very long) and of fixing by covalent bonding, in addition, the step of creation of cationic groups does not exist either, since the polymer advantageously comprises from the outset the necessary cationic groups. For PEI, however, an acid pH step must be used to protonate it.

In other words, in this embodiment of the process of the invention, a strongly adherent polymer film is obtained in a single adsorption step by simple contact, without placing under vacuum, of a duration, for example, close to 1 hour, without prior drying and crosslinking, instead of having to resort to at least three long and difficult stages the duration of which can go up to 48 hours, which are energy consuming and require vacuum, drying and a heater. In addition :

- Fixation of the hexacyanoferrate anion by impregnation using a solution of exacyanoferrate. of alkali metal can be done in a simplified manner, preferably from pure water; when insoluble metal 1'hexacyanoferrate precipitation step, the copper chelate formation is avoided, because the polymer used in this, preferred form of the process according to the invention, which is advantageously a polybrene ^®, does not generally contain primary, secondary or tertiary amino groups to prevent the formation of complexes with copper.

In other words, during this precipitation step of the metal hexacyanoferrate, such as copper, there is no formation of complexes between the polymer, such as polybrene "and the metal ions of the solution, such as copper, since the nitrogen atoms are in the form of quaternary ammoniums devoid of free doublets, which is not the case with the supports, such as silica, treated with other polymers, such as PEI and PVI, or with amino silicas, for which formation has been observed unstable complexes between nitrogen atoms and metal, such as copper.

Consequently, in this preferred form of the process according to the invention, and the fact that there is no salting out of metal ions from the material, the long washing operations following the contacting of the support with a metal salt are greatly reduced.

The invention finally relates to a method for fixing at least one mineral pollutant such as a metal cation contained in a solution, in which a composite solid material fixing the mineral pollutants is first prepared, based on hexacyanoferrate from metal, comprising a solid support coated with a film of an anion exchange polymer to which an insoluble metal hexacyanoferrate is fixed by the process described above without a final drying step, then said solution is continuously contacted with said composite solid material fixing mineral pollutants, in the same container, such as a column, where said material was prepared.

This fixing process has the advantage of being able to be carried out continuously following, preferably, immediately, immediately after, the process for preparing the composite solid material; the latter remains in the same container, which eliminates a long, difficult transfer operation, as well as column packaging of the material also long and difficult.

In addition, the composition of the product obtained is such that there is no need at the end of the preparation to have recourse to a final stage of drying the material before decontamination, fixing the pollutants, since there is no There are no excess ferrocyanides.

Indeed, in the final synthesized product, the composition of the product is such that M / Fe (M. = metal), for example Cu / Fe ≈ 1, while for a product synthesized in “batch” mode Cu / Fe = 2 .

Decontamination, fixing can therefore be carried out according to the invention immediately after preparation, without drying, in the same device. The contacting of the material and the solution to be depolluted can be carried out in the column for example by percolation of the solution through the material, or else in a particularly advantageous manner by means of a (in a) similar fluidized bed. to that used for the synthesis of the material, said fluidized bed being formed by the composite solid material, the fluidization of which is ensured by the solution containing the mineral pollutant; that is to say, in this case, it is the entire fixing process, including the synthesis, which is carried out in the same fluidized bed and in the same container, such as a column.

We can say that it is thanks to the specific characteristics inherent in the preparation process, which affect the prepared material, that the fixing process can be carried out, preferably, immediately after this in the same container, preferably also in a fluidized bed, without loss of time, transfer and other conditioning step.

The fixing method according to the invention is very simple, because it only implements one device, namely a single container such as a column, which is extremely advantageous, in particular, in the case of the treatment of radioactive fluids. In addition, the overall duration of the process is greatly reduced.

In addition, the method for fixing pollutants according to the invention has all the other advantages inherent in the material prepared. These advantages being essentially linked to the preparation in a fluidized bed, which have already been indicated above, namely in particular clearly higher partitioning constants and the absence of preferential paths. The invention will now be described in more detail in the following, with particular reference to the preparation process in its preferred embodiment.

The first step of this process consists in impregnating a solid support with an organic polymer solution on said solid support.

The solid support is one of those which have already been mentioned above, a preferred carrier is silica Lichrospher ^® 100 from Merck ^®, the polymer is also one of the preferred polymers which have been mentioned above, still preferred polymers being a polybrene ^® (PB), preferably a polybrene ^® of molecular mass 4,000 to 6,000 g / mol supplied by the company Sigma Aldrich ^® or else a polyethyleneimine of molecular mass (10,000 g / mol) supplied by the same company .

According to the invention, this solid support is placed in a container, such as a column, and forms at the start of the process a fixed bed. The fluidization of this bed is created by circulating in this fixed bed a current (against the current) of liquid reagent or possibly a washing liquid. The techniques for creating a fluidized bed are well known to those skilled in the art. Generally, the reagent or liquid enters the container or the column by an inlet orifice and crosses the fixed bed at a rate sufficient to cause its fluidization, without entraining, however, the particles from which the bed is formed and leaves by an outlet. The container, such as a column, is generally vertical and is, for example, in the form of a straight vertical cylinder, into which the liquid or liquid reagent enters through an inlet orifice provided at the base of the cylinder and crosses, in ascending, vertical flow, the bed which is thus fluidized, and the liquid is discharged at the top of the column, through an outlet orifice provided in the other base of the cylinder.

According to an advantageous aspect of the invention, the polymer solution is a solution in water, for example in demineralized water. The solution generally has a concentration of 20 to 100 g / l. The impregnation is carried out by bringing the solid support into contact with the polymer solution at a flow rate, for example, from 80 to 280 ml / min, sufficient to cause fluidization, for a sufficient time, which is surprisingly according to the invention short, for example 1 hour (instead of 24 to 48 hours in "batch" mode), whereby a uniform coating of polymer is obtained on the solid which isolates and protects the solid support, which follows its forms "and porosities, and which retains its specific surface.

The fixing of the polymer on the solid support is essentially governed by an adsorption phenomenon with interactions of electrostatic type, this fixing is according to the invention relatively strong without the need for grafting by covalent bonds.

At the end of this step, a solid support is thus obtained directly, coated with a film of anion exchange polymer.

By film is meant as already indicated above, a uniform coating over the entire surface of the solid support and which substantially retains the specific surface of the latter. This film generally has a thickness of 2 to 3 nm.

Then, continuously carried out, preferably immediately after the first step, rinsing with demineralized water of the solid support coated with a polymer film, it suffices for this simply to replace the stream of polymer solution by a stream of demineralized water at a flow rate, for example from 80 to 280 ml / min sufficient to maintain fluidization.

Then carried out in the next step, the impregnation of the support coated with a film of anion exchange polymer with an aqueous solution of hexacyanoferrate (II) or (III) of alkali metal.

This step is carried out again continuously, preferably immediately after the previous step, it suffices for this to simply replace the stream of demineralized water with an alkali metal hexacyanoferrate solution.

The starting alkali metal hexacyanoferrate is preferably chosen from sodium or potassium hexacyanoferrates (II) and (III).

The aqueous solution of alkali metal hexacyanoferrate used at a variable concentration, that is to say that the concentration of the salt of hexacyanoferrate (II) or (III) of alkali metal in particular potassium or sodium is preferably from 1 to 100 g / 1, for example from 50 g / 1.

On the other hand, the aqueous solution of hexacyanoferrate used is prepared in such a way that the mass ratio of the salt of hexacyanoferrate (II) or (III) of alkali metal, in particular potassium or sodium, to the quantity of the impregnation support essentially consisting of the initial solid support such as silica, is preferably 5 to 10%. The impregnation does not have to be carried out at a defined, adjusted pH, controlled for example by a buffer. It is a solution in water, preferably pure, demineralized water. The flow rate of the solution is, for example, from 80 to 280 ml / min, so as to ensure or maintain the fluidization.

This gives the fixation of the anionic part [Fe (CN) ₆ ] ^{4 "} on the cationic groups of the polymer, this fixation is done by formation of electrostatic type bonds which are relatively strong depending on the medium, and this fixation is generally quantitative , that is to say that all the cationic sites of the polymer react, the fixing therefore has no randomness.

The solid support thus coated with a film of anion exchange polymer to which an alkali metal hexacyanoferrate is attached is then subjected to a washing operation. Washing is carried out continuously, preferably immediately after the previous step.

The purpose of the washing operation is to remove the alkali metal hexacyanoferrate salts which have not been fixed on the polymer and makes it possible to obtain a composite material fixing mineral pollutants in which there is no longer any free, unbound hexacyanoferrate which can be released.

Washing is carried out with demineralized water. The amount of rinse solution used is variable and can range from 100 to 1000 ml per gram of product treated.

The flow rate of the rinsing solution is such that the fluidization is adequately ensured.

The next step is the addition of an aqueous solution of metal salt to the solid support coated with a film of an anion exchange polymer, to which the hexacyanoferrate anion is attached. This step is also according to the invention carried out continuously, preferably immediately after the previous step, replacing the rinsing solution with a solution of metal salt.

The metal salt contained in this aqueous solution is a salt whose metal corresponds to the insoluble hexacyanoferrate which it is desired to obtain as has already been indicated above.

This metal is chosen, for example, from copper, cobalt, zinc, cadmium, nickel and iron, etc.

The metal salt will therefore be for example a nitrate, a sulphate, a chloride, an acetate of one of these metals at a concentration in the aqueous solution preferably from 0.01 to 1 mol / 1, more preferably from 0, 02 to 0.05 mol / 1.

The amount of salt used is moreover preferably about 0.4 mmol / g of treated support.

The addition of the aqueous solution of the metal salt does not have to be done at a defined pH, using of a buffer solution. The aqueous solution is a solution in pure water, demineralized.

The flow rate of the aqueous solution of the metal salt is such that the bed remains fluidized. Finally, in a final step, the final material is washed, which thus comprises the solid support coated with a film of an anion exchange polymer to which an insoluble metal hexacyanoferrate is attached, forming a thin layer. This last washing step is carried out in the same manner and under the same conditions as the washing step already described above, using pure demineralized water.

This step is carried out continuously, and preferably immediately after the previous step.

It is generally compulsory to introduce into demineralized water an alkali metal salt, for example sodium, the anion of which is preferably the same as that of the metal salt used in the previous step, and optionally , in addition, the corresponding acid: it is possible to use, for example, sodium nitrate and nitric acid.

This washing operation makes it possible to remove the excess metal salt and to obtain a stable final product with a perfectly defined composition. It must be followed by a final step of rinsing with demineralized water.

Finally, a drying step is carried out.

In general, drying is continued until the mass of the support remains substantially constant. However, this drying step is preferably generally omitted if one proceeds to it, and continuously fixing the pollutants contained in a solution. The content by weight of mineral fixer, that is to say of insoluble metal hexacyanoferrate fixed on the anion exchange polymer is generally from 1 to 10%, for example 3% relative to the mass of the mineral support such as silica . It has been observed by analysis by neutron activation that the atomic ratio of M ₂ / Fe can vary from 1 to 5 without the fixing properties, in particular of decontamination being affected.

The solid composite material. fixing mineral pollutants prepared by the process according to the invention, is preferably immediately after its preparation - the possible final drying step being omitted - used in fixing at least one mineral pollutant, for example of a cation metallic contained in a solution, wherein said solution is brought into contact with said composite solid material fixing mineral pollutants.

According to the invention, this fixing is carried out continuously in the same container, such as a column where the solid material has been prepared. Therefore, no conditioning, transfer is necessary.

The materials prepared according to the invention, because of their excellent properties such as excellent exchange capacity, excellent selectivity, a reaction speed _. high are particularly suitable for such use.

This excellent efficiency is obtained with reduced amounts of mineral fixative such as insoluble hexacyanoferrate.

Column packaging makes it possible to continuously process large quantities of solutions, with a high flow rate thereof, for example from 1.5 to 80 ml / min. Due to its continuous implementation, the fixing method can thus be easily integrated into an existing installation, for example in a chain or treatment line comprising several stages. The solutions which can be treated by the process of the invention and with the composite solid material fixing mineral pollutants prepared according to the invention, are very varied, and may even contain, for example, corrosive agents, acids, bases or others, made of the excellent chemical stability of the material prepared according to the invention.

The material prepared according to the invention can be used in particular over a very wide range of PH. For example, it is possible to treat aqueous nitric solutions with a concentration ranging, for example, from 0.1 to 3M, acidic or neutral solutions up to a pH 8, basic solutions, etc. It is however necessary to adapt the nature of the solid support to the nature of the solution treated. It is for example known that silica does not generally resist at a basic pH, and it is then preferable to use a solid support, for example made of Ti0 ₂ , the use of the composite material can then be extended, for example, to pH 10. The mineral pollutant capable of being fixed in the fixing method according to the invention can be any mineral pollutant, that is to say for example any pollutant derived (based) from a metal or an isotope, preferably from a radioactive isotope, of this metal, likely to be in solution.

This pollutant is preferably chosen from anionic complexes, colloids, cations and their mixtures.

It is preferably a pollutant, such as a cation derived from an element chosen from Tl, Fe, Cs, Co, Ru, Ag, ... and the isotopes, in particular the radioactive isotopes of these- Ci, among which we can cite ⁵⁸ _C o, ⁶⁰ _C o, ⁵⁵ " ⁵⁹ Fe, ¹³⁴ _C s, ¹³⁷ _C s," ^{3, ι} os ^, ιo ₅ ^, ιo ⁷ _{Ru> The} metal cation is in particular Cesium Cs ⁺ or Thallium Tl ²⁺ .

The anionic complex is for example

RuO ^.

A preferred use of the material prepared according to the invention is the fixation of cesium which contributes to a large part of the gamma activity of liquids from the nuclear industry and which is selectively fixed by the hexacyanoferrates.

The concentration of pollutant (s) such as cation (s) can vary between wide limits: for example it can be for each of thereof of 0.1 picogram to 100 mg / 1 of ^'preferably

0.01 mg / 1 to 10 μg / 1.

The solution to be treated by the fixing process of the invention is preferably an aqueous solution which, in addition to the pollutant (s) such as one or more cation (s) to be fixed, may contain other salts in solution such than NaNo ₃ or LiN0 ₃ or alternatively A1 (N0 ₃ ) ₃ or any other soluble salt of alkali or alkaline earth metal at a concentration of up to 2 moles / l. The solution may also contain, as indicated above, acids, bases, and even organic compounds.

The solution to be treated can 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 one or more several of these water-miscible organic solvents.

The material prepared according to the invention thus has the advantage of being able to treat solutions which cannot be treated with organic resins.

This solution can consist of a process liquid or an industrial or other effluent which can originate in particular from industry and nuclear installations or from any other activity linked to nuclear power.

Among the various liquids and effluents from the nuclear industry, nuclear installations and activities using radionuclides which can be treated by the process of fixing the invention, for example, may be cited the cooling water from power stations, and all the various effluents coming into contact with radioisotopes such as all washing water, solutions for regenerating resins, etc.

It is however obvious that the fixing method according to the invention can also be implemented in other fields of activity, industrial or other, non-nuclear. Thus, hexacyanoferrates selectively fix thallium and this property could be exploited in the purification of cement effluents to reduce or eliminate the releases and emissions of this element which is a violent poison. The contact time of the solution to be treated with the exchanger material is variable and can range from 1 minutes to 1 hour with continuous operation according to the invention.

It should be noted that this duration is notably shorter than in the analogous processes carried out in batch or partly in batch, partly continuously, in different containers.

At the end of the fixing process, the solid composite fixing material (exchanger) prepared according to the invention in which, for example, the metal cations of the exacyanoferrate have been exchanged by the cations in the solution can be directly stored, because its very high mechanical and chemical stabilities and its essentially mineral nature allow such storage without degradation of the product leading to hydrogen fumes, or it can be treated by a process allowing conditioning for long-term storage, for example by vitrification. Vitrification is particularly suitable in the case where the fixed cations are radioisotopes and the support is silica.

The material prepared according to the invention, thanks to its specific structure, and unlike the exchanger materials of the prior art based on hexacyanoferrate, can be vitrified without danger because the quantities of mineral fixative are limited and decontamination in air safe.

The following examples, given by way of nonlimiting illustration, firstly illustrate the process for the preparation of the invention, in which the preparation of composite exchanger materials is carried out, in accordance with the invention in a column in a fluidized bed, then the results obtained by using these composite exchanger materials in the context of the fixing of cations, in accordance with the fixing method of the invention, that is to say in the same column as that used for the synthesis materials according to the first step of the fixing process of the invention, the process being applied to the fixing of cesium from radioactive effluents.

The examples illustrate the process of synthesis, then of fixing. EXAMPLE 1

In this example was carried out the synthesis of hexacyanoferrate thin layer immobilized on silicas coated with a polymer phase anion exchange, said phase being prepared from a ^® polybrene or polyethyleneimine (PEI), in accordance to the process of preparation, of synthesis, of the invention: namely, in a fluidized bed column (Examples 1A and 1B).

Furthermore, for comparison, the synthesis of hexacyanoferrates in a thin layer was also carried out, by a preparation process not in accordance with the invention: namely, in “batch” mode: Example 1C or in mixed mode: Example 1D.

EXAMPLE 1A

In this example, in accordance with the process according to the invention, the anion exchange polymer is a polybrene (PB) having the following structure and characteristics: Molar mass 4,000 to

6000 g / moles.

The procedure is as follows: - a silica support (Silica Gel 100 ^® ) supplied by the company Merck®, having a particle size of 0.063 to 0.200 mm, and a porosity of 100 μm, is impregnated with polybrene (PB) supplied by the SIGMA Company

(S)

ALDRICH, by contacting in a column under a fluidized bed for a period of 1 h or 24 h in a solution at 15% by mass of polymer in water demineralized, at flow rates ranging from 1.5 mL / min. at 280 mL / min. depending on the amount of product synthesized;

- The support thus coated is rinsed with demineralized water, it should be noted that no drying under vacuum is to be carried out;

- the anion exchange film support is brought into contact with, impregnated with, a concentrated solution of sodium hexacyanoferrate II (50 g / 1) in water (no buffer); - the support is then rinsed with demineralized water; a copper hexacyanoferrate (II) is formed on the film surface by adding an aqueous solution of 2.10 ^"2 M copper (II) nitrate in demineralized water;

- the excess of hexacyanoferrate (II) ^' is removed by washing with a sodium nitrate solution and then with demineralized water.

The elementary analysis of the final product obtained is given in Table I below.

EXAMPLE 1B

In this example, in accordance with the process according to the invention, the ion-exchange polymer is a polyethyleneimine (PEI) supplied by the company Sigma Aldrich.

The procedure is the same as in Example 1A, except that the polymer produced is different and crosslinked in a fluidized bed. The elementary analysis of the final product obtained is also given in Table I below.

TABLE I

Elemental composition of the materials prepared according to the invention based on copper hexacyanoferrate (the percentages are percentages by mass per g of silica)

Comparative Example 1C

In this example, the material was prepared in “batch” as follows:

- a silica support (Silica Gel 100 ^®) supplied by the company Merck® having a particle size of 0.063 to 0.200 mm, and a porosity of 100 .mu.m, is impregnated with polyethylimine (PEI) supplied by SIGMA ALDRICH ^® Company, contacting in “batch” for a period of 10 h in a solution at 15% by mass of polymer in demineralized water, and then crosslinked for 2 h at reflux at 60 ° C. with an agent crosslinking the diglycidyl ether of the 1-4 butane diol (BUDGE) sold by the company Aldrich - The support thus coated is rinsed with demineralized water, and dried under vacuum;

- the anion exchange film support is brought into contact in “batch” with, impregnated with, a concentrated solution of sodium hexacyanoferrate II (50 g / 1) in water for 4 h; the support is then rinsed with demineralized water; a copper hexacyanoferrate (II) is formed on the film surface by addition of an aqueous solution of 2.10 ^"2 M copper (II) nitrate in demineralized water for 4 h; the excess of hexacyanoferrate (II) is eliminated by washing with a 2 M sodium nitrate solution, then a 0.1 M nitric acid solution and then with demineralized water.

Example 1D: comparison

In this example, the procedure for preparing the material is mixed: it was prepared in "batch" and in column with packing of the phase (which is different from the fluidized bed according to the invention), as follows: - a silica support (Silica Gel 100 ^® ) supplied by the company Merck®, having a particle size of 0.063 to 0.200 mm, and a porosity of 100 μm, is impregnated with polyethylimine (PEI) supplied by the company SIGMA ALDRICH ^® , by placing in “batch” contact for a period of 10 h in a solution at 15% by mass of polymer in demineralized water, and then crosslinked for 2 h at reflux at 60 ° C. with an agent crosslinking the diglycidyl ether of 1-4 butane diol (BUDGE) sold by the company Aldrich

- The support thus coated is rinsed with demineralized water, and dried under vacuum;

- • the anion exchanger film support is packed in a column and brought into contact and impregnated by percolation at a low flow rate ranging from

1.5 to 5 mL / min with a concentrated solution of sodium hexacyanoferrate II (50 g / 1) in water; the support is then rinsed with demineralized water; a copper hexacyanoferrate (II) is formed on the film surface by adding an aqueous solution of 2.10 ^"2 M copper (II) nitrate in demineralized water; the excess of exacyanoferrate (II) is removed by washing with a 2M sodium nitrate solution, then a 0.1 M nitric acid solution and then with demineralized water.

EXAMPLE 2: Cesium fixation tests

In this example, we studied the fixation of radioactive cesium ¹³ Cs and ¹³⁷ Cs contained in various effluents, on various products based on hexacyanoferrate, namely:

- The composite exchanger materials according to the invention prepared according to the first step of the process of the invention in Examples 1A and 1B above.

- comparative materials 1C and 1D. - The selectivity of cesium for the phases, products, composites is defined thanks to the distribution constant Kd (1) between a solid phase and a liquid phase charged with ¹³ Cs and ¹³⁷ Cs.

Amount of Cs * fixed per gram of solid phase Amount of Cs * remaining per ml of solution

The higher the value of Kd, the more the Cs * is retained in the solid phase. A Kd value greater than 10,000 for contact times of 24 h represents an excellent affinity of cesium for the solid phase.

The radioactive effluents treated are real effluents from the OSIRIS cell of the SACLAY nuclear studies center, the characteristics of which relating to radioactivity are mentioned in Table II. On the one hand, it is the water for cooling the cell which is designated by “OSI” in the table and whose pH is neutral, and on the other hand the rinsing, regeneration, resins solution. which is designated by “BF6” in the table and which is constituted by a 0.1 M nitric acid solution. In order to increase the accuracy of the counts, a ¹³⁴ Cs tracer was added to the OSI solution.

TABLE II Radioactivity of solutions treated in curia by m ³

* Plotter adds

*, * Very variable depending on the solutions The test procedure is as follows:

10 to 20 mg of product are added to 50 mL (cm ³ ) of radioactive solution to be treated and stirred for a period of 10 minutes or a day depending on the tests.

At the end of the chosen duration, the solution is filtered, its radioactivity is measured by gamma spectrometry and is compared with that of the starting solution.

The values thus obtained make it possible to calculate the coefficient _. distribution ¹³⁷ Cs representative of the affinity of the product by this element. In the present case, it can be expressed as being the ratio of the fixed radioactivity per gram of product to the residual radioactivity in solution per cm ³ of solution. In other words the distribution coefficient Kd of cesium is established according to equation (2):

„, Activity of the blank - Activity of the solution * Volume of filtered solution (ml).„.

Kd = - - (2)

Mass of sample (g) * Activity of the solution

The higher the value of Kd, the more the Cs ⁺ is retained in the solid phase. A Kd value greater than 10,000 for contact times of 24 for solutions at pH = 7 represents an excellent affinity of cesium for the solid phase.

The results of tests carried out during different contact durations (10 minutes and 1 day) with different solutions (water of “OSI” cooling to a pH close to 7, and resin washing water “BF ₆ ”, that is to say 0.1 M nitric solution pH ≈ 1) and with different samples of prepared hexacyanoferrate products by the method according to the invention (Ex. 1A and 1B) and (Ex. 1C and 1D) are grouped in Table III below:

TABLE III

Distribution constants for distribution coefficients Kd (cesium) on various hexacyanoferrate products (per g of product)

The results indicated above show that the distribution constants obtained with the products synthesized in a fluidized bed according to the first step of the process of the invention are much greater than those obtained with the products synthesized in “batch” mode or in mixed mode.

EXAMPLE 3 Column decontamination tests

Percolation of a radioactive solution, which is an “OSI” solution, or a “BF6” solution as defined above, on the synthesized phases, whether or not according to the invention, conditioned in the synthesis column, makes it possible to determine the affinity of cesium for this, by calculating the decontamination coefficient.

The decontamination factor is the activity of the solution before passing over the phase over the activity of the solution after passing over the phase (3).

Solution activity (e.g. OSI) rd = (3)

Activity of the fraction recovered

In practice to collect the solution, a tube with a double filter is immersed in 3 L of OSI solution, as described in Table III.

The first filter is a frit which retains particles larger than 20 μm, the next is a filter with lower porosity. A peristaltic pump placed in series draws at a flow rate of 1.5 to 5 mL / min. the solution to a stainless steel column (30 * 5 mm) containing 1 g of composite. This column is closed at each end by a frit and shielded over its entire height by a leaden castle with a thickness of 5 cm. At the outlet of the column, 50 ml of eluate are collected in a bottle of eluate every 250 ml of treated solution. The entire assembly is placed in a retention tank with a volume of 10 mL. The radioactivity of the eluates, as well as of the control, is then measured by gamma spectrometry.

The results are reported in Table IV.

TABLE IV

Decontamination coefficient as a function of the column volume and the nature of the composite product

The values reported in this table are only limit values because we are within the acceptance limits of the equipment, with the exception of those obtained in "batch".

The product prepared in "batch" has a decontamination coefficient much lower than that of the products synthesized in a fluidized bed, in accordance with the invention.

Claims

1. Process for the preparation of a composite solid material fixing mineral pollutants, based on metal exacyanoferrate, comprising a solid support coated with a film of an anion exchange polymer to which is fixed an insoluble metal hexacyanoferrate forming a thin layer, said method essentially comprising at least one step of bringing said solid support into contact with at least one liquid reagent and at least one step of washing with a washing liquid, characterized in that all of the steps of the method are produced continuously in a single container, such as a column, in which the support forms a fluidized bed, the fluidization of which is ensured by said at least one reagent or optional washing liquid.

2. Method according to claim 1, characterized in that the amount of fixed metal hexacyanoferrate is from 1 to 10% by weight relative to the mass of the solid support.

3. Method according to claim 1, characterized in that the support is chosen from silica, alumina, titanium oxide, zirconium oxide, diatomaceous earth, zeolites, and glasses.

4. Method according to any one of the preceding claims, characterized in that the support is in the form of particles such as grains, balls or spheres; or fiber.

5. Method according to claim 4 characterized in that the support is in the form of particles, and has a particle size of 1 to 500 microns.

6. Method according to any one of claims 4 to 5 characterized in that the support has a specific surface of 10 to 500 m ² / g.

7. Method according to any one of claims 4 to 6 characterized in that the support has an average pore size of 100 to 1000 Å.

8. Method according to claim 1 characterized in that said anion exchange polymer is derived from an organic polymer, said organic polymer having optionally been provided with cationic groups.

9. Method according to claim 8 characterized in that said organic polymer is chosen from polyvinylimidazoles, copolymers of vinylimidazole with at least one other monomer, polyethyleneimines (PEI), and non-crosslinked polymers comprising as exchange groups anions only of quaternary ammonium groups and not comprising primary and secondary, and tertiary amino groups, such as a polybrene.

10. Method according to any one of claims 1 to 9 characterized in that said metal hexacyanoferrate is chosen from copper, cobalt, zinc, cadmium hexacyanoferrates, nickel hexacyanoferrate, iron hexacyanoferrate, and mixed hexacyanoferrates relating to these salts.

11. Method according to any one of claims 1 to 10, comprising the following successive steps:

- washing with demineralized water; impregnation of the solid support thus coated with a film of anion exchange polymer, with an aqueous solution of alkali metal hexacyanoferrate; washing with demineralized water said solid support coated with a film of anion exchange polymer to which an alkali metal hexacyanoferrate is attached;

- Adding an aqueous solution of a metal salt to said coated solid support, to form a composite solid material fixing mineral pollutants, comprising the solid support coated with a film of anion exchange polymer to which is fixed a hexacyanoferrate insoluble metal forming a thin layer. washing with demineralized water.

12. The method as claimed in claim 11, in which the anion exchange polymer is chosen from non-crosslinked anion exchange polymers comprising as anion exchange groups only quaternary ammonium groups and not comprising primary amine groups and secondary, and tertiary and possibly polyethyleneimines (PEI).

13. Method according to claim 11 characterized in that the organic polymer solution is a solution in water, for example in demineralized water.

14. The method of claim 11 characterized in that said alkali metal hexacyanoferrate is chosen from hexacyanoferrates (II) and (III) of sodium or potassium.

15. The method of claim ^'11 characterized in that the aqueous solution of alkali metal exacyanoferrate is a solution in pure water, demineralized.

16. The method of claim 11 characterized in that said metal salt is chosen from copper, cobalt, nickel, cadmium, zinc, iron salts.

17. The method of claim 11 characterized in that the anion of said metal salt is chosen from nitrates, sulfates, chlorides, and acetates.

18. Method for fixing at least one mineral pollutant such as a metal cation contained in a solution, in which a composite solid material fixing the mineral pollutants is first prepared, based on metal hexacyanoferrate, comprising a solid support coated with a film of an anion exchange polymer to which an insoluble metal hexacyanoferrate is attached by the process according to any one of claims 1 to 17 without final drying step, then continuously contacting said solution with said solid composite material fixing mineral pollutants, in the same container, such as a column, where said material was prepared.

19. The method of claim 18, wherein said contacting is carried out by percolation of the solution through the composite solid material fixing the mineral pollutants.

20. The method of claim 18, wherein the contacting is carried out in a fluidized bed formed by the composite solid material whose fluidization is ensured by the solution containing the mineral pollutant.

21. The method of claim 18 characterized in that said solution is an aqueous solution.

22. The method of claim 18 characterized in that said solution is a process liquid or an industrial effluent.

23. The method of claim 18 characterized in that said solution is chosen from liquids and effluents from industry and nuclear installations and from activities using radionuclides.

24. Method according to any one of claims 18 to 23, characterized in that said pollutant is present at a concentration of 0.1 picogram at 100 mg / 1.

25. Method according to any one of claims 18 to 24, characterized in that said pollutant comes from a metal or a radioactive isotope of said metal.

26. The method of claim 25, characterized in that said pollutant is chosen from anionic complexes, colloids and cations.

27. A method according to any one of claims 18 to 26, ^• characterized in that said pollutant is an element chosen from Cs, Co, Ag, Ru, Fe and Tl and the isotopes thereof.