Nanocomposite solid material based on hexa- and octa-cyanometallates, method for the preparation thereof and method for fixing mineral pollutants using said material

Abstract

A nanocomposite solid material includes nanoparticles of a metal coordination polymer with CN ligands comprising M.sup.n+ cations, in which M is a transition metal and n is 2 or 3; and anions [M′(CN).sub.m].sup.x− in which M′ is a transition metal, x is 3 or 4, and m is 6 or 8. The M.sup.n+ cations of the coordination polymer are bound through an organometallic bond to an organic group of an organic graft chemically attached inside the pores of a support made of porous glass. The material can be used in a method for fixing (binding) a mineral pollutant, such as radioactive cesium, contained in a solution by bringing the solution in contact with the nanocomposite solid material.

Claims

1. A nanocomposite solid material comprising nanoparticles and a support, the nanoparticles comprising a metal coordination polymer with CN ligands comprising cations M.sup.n+, wherein M is a transition metal and n is 2 or 3; and anions [M′(CN).sub.m].sup.x−, wherein M′ is a transition metal, x is 3 or 4 and m is 6 or 8; said M.sup.n+ cations of the coordination polymer being bound through an organometallic bond to an organic group of an organic graft chemically attached inside pores of the support made of porous glass, and the pores of the porous glass being obtained by selective chemical etching of a borate phase of a solid borosilicate glass, the borosilicate glass comprising SiO.sub.2, Na.sub.2O, and B.sub.2O.sub.3, the proportion of each being defined to be within the composition of which is located in a demixing area of a phase diagram of SiO.sub.2—Na.sub.2O—B.sub.2O.sub.3.

2. The material according to claim 1, wherein M.sup.n+ is Fe.sup.2+, Ni.sup.2+, Fe.sup.3+ or Co.sup.2+.

3. The material according to claim 1, wherein M′ is Fe.sup.2+ or Fe.sup.3+ or Co.sup.3+ and m is 6; or else M′ is Mo.sup.5+ and m is 8.

4. The material according to claim 1, wherein [M′(CN).sub.m].sup.x− is [Fe(CN).sub.6].sup.3−, [Fe(CN).sub.6].sup.4−, [Co(CN).sub.6].sup.3− or [Mo(CN).sub.8].sup.3−.

5. The material according to claim 1, wherein the cations M.sup.n+ are Ni.sup.2+, Fe.sup.2+ or Fe.sup.3+ cations and the anions are [Fe(CN).sub.6].sup.3− or [Fe(CN).sub.6].sup.4− anions.

6. The material according to claim 1, wherein the cations are Fe.sup.3+ cations and the anions are [Mo(CN).sub.8].sup.3− anions.

7. The material according to claim 1, wherein the cations are Co.sup.2+ or Ni.sup.2+ cations and the anions are [Co(CN).sub.6].sup.3− anions.

8. The material according to claim 1, wherein the particles have the shape of a sphere or spheroid.

9. The material according to claim 1, wherein the nanoparticles have a size from 3 nm to 30 nm.

10. The material according to claim 1, wherein the organic group is selected from the group consisting of nitrogen-containing groups and oxygen-containing groups.

11. The material according to claim 1, wherein the support appears in the form of particles.

12. The material according to claim 11, wherein the support appears in the form of particles, having a grain size from 10 to 500 μm.

13. The material according to claim 1, wherein the support has a BET specific surface area from 10 to 500 m.sup.2/g and a porosity from 25 to 50% by volume.

14. The material according to claim 1, wherein the support has one or more types of pore sizes selected from the group consisting of microporosity, mesoporosity and macroporosity.

15. The material according to claim 1, wherein the support has an average pore size from 2 to 120 nm.

16. The material according to claim 1, wherein the pores of the support are defined by partitions, or walls, with a thickness from 10 to 60 nm.

17. A method for preparing the material according to claim 1, wherein the following successive steps are carried out: a) preparing a support made of the porous glass of claim 1; b) chemically attaching attachment of the organic graft inside the pores of the support made of porous glass; c) contacting the support made of porous glass inside the pores of which the organic graft is attached with a solution containing the M.sup.n+ ion; d) washing the contacted support one or more times and drying the washed support; e) contacting the dried support made of porous glass with a solution of a complex of [M′(CN).sub.m].sup.x−; f) washing the support contacted with [M′(CN).sub.m].sup.x− one or more times and drying the washed support contacted with [M′(CN).sub.m].sup.x−; g) washing the support contacted with [M′(CN).sub.m].sup.x− one or more times and drying the support; and h) optionally repeating steps c) to g).

18. The method according to claim 17, wherein, prior to chemical etching, the solid sodium borosilicate glass is heat-treated.

19. The method according to claim 17, wherein chemical etching comprises etching with an acid solution.

20. The method according to claim 17, wherein the organic graft is pyridine, and the chemical attachment of the organic graft inside the pores of the support made of porous glass is achieved by bringing the porous support in contact with a solution of (CH.sub.3O).sub.3Si(CH.sub.2).sub.2C.sub.5H.sub.4N.

21. The method according to claim 17, wherein the solution containing the M.sup.n+ ion is a solution of [M(H.sub.2O).sub.6]Cl.sub.2 or [M(H.sub.2O).sub.6]Cl.sub.3.

22. The method according to claim 17, wherein the [M′(CN).sub.m].sup.x− complex fits the following formula: (Cat)x [M′(CN).sub.m], wherein M′, m, and x have the meaning already given in claim 1, and Cat is a cation selected from cations of alkaline metals, quaternary ammomiums, and phosphoniums.

23. The method according to claim 17, wherein steps c) to g) are repeated 1 to 4 times.

24. A method for fixing at least one mineral pollutant contained in a solution, wherein said solution is brought into contact with the nanocomposite solid material according to claim 1, whereby the mineral pollutant is immobilized inside the pores of the solid material.

25. The method according to claim 24, wherein said solution is an aqueous solution.

26. The method according to claim 24, wherein said solution is a process liquid or an industrial effluent.

27. The method according to claim 24, wherein said solution is selected from liquids and effluents from nuclear industry and nuclear installations and from activities applying radionuclides.

28. The method according to claim 24, wherein the method is carried out continuously.

29. The method according to claim 24, wherein the composite solid material fixing mineral pollutants is packed in a column.

30. The method according to claim 24, wherein said pollutant is present at a concentration of 0.1 picogram/L to 100 mg/L.

31. The method according to claim 24, wherein said pollutant stems from a metal or from a radioactive isotope of said metal.

32. The method according to claim 31, wherein said pollutant is selected from anionic complexes, colloids and cations.

33. The method according to claim 24, wherein said pollutant is an element selected from the group consisting of Cs, Co, Ag, Ru, Fe and Tl and isotopes thereof.

34. The method according to claim 24, wherein at the end of the contacting, the nanocomposite solid material is subjected to a treatment for closing its pores.

35. The method according to claim 34, wherein the treatment for closing the pores is a heat treatment carried out at a temperature from 600 to 1,000° C., or a radiative treatment generally of low energy, or a chemical treatment.

36. The method according to claim 35, wherein the chemical treatment is carried out in a basic atmosphere.

37. The material according to claim 9, wherein said size is a diameter.

38. The material according to claim 11, wherein said particles are beads, fibers, tubes or plates.

39. The material according to claim 15, wherein said support has an average pore size from 2 to 20 nm.

40. The method according to claim 19, wherein said etching with an acid solution is followed by etching with a basic solution.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the phase diagram SiO.sub.2Na.sub.2O—B.sub.2O.sub.3 and the demixing areas of this diagram.

(2) FIG. 2 is a graph which illustrates the adsorbed nitrogen volume V.sub.0 (in cm.sup.3/g) versus P/P.sub.0 wherein P is the partial pressure of nitrogen and P.sub.0 is the maximum adsorbed pressure, during the measurement of porosity with a BET apparatus.

(3) The scale of the right ordinates relates to the measurements illustrated by □.

(4) The scale of the left ordinates relates to the measurements illustrated by .square-solid., ◯ and .circle-solid..

(5) The samples are samples of porous glass prepared from the composition of Example 1 which has undergone heat treatments (TT) and chemical etchings (TC) under different conditions.

(6) The measurements illustrated by .square-solid. were conducted on a sample which has not been subjected to any heat treatment and which has undergone chemical etching with 0.5M HCl for 6 hours at 90° C.

(7) The measurements illustrated by ◯ were conducted on a sample which has not been subject to any heat treatment, and which has undergone chemical etching with 0.5M HCl for 24 hours at 90° C.

(8) The measurements illustrated by .circle-solid. were conducted on a sample which has been subjected to heat treatment for 25 hours at 540° C., and which has undergone chemical etching with 0.5M HCl for 6 hours at 90° C.

(9) The measurements illustrated by □ were conducted on a sample which did not undergo any heat treatment and which has undergone chemical etching with 0.5M HCl for 6 hours at 90° C. followed by chemical etching with 1M NaOH for one hour at room temperature.

(10) FIG. 3 is a schematic illustration of the method according to the invention carried out with —(CH.sub.2).sub.2C.sub.5H.sub.4N grafts.

(11) FIG. 4 is a graph which shows the Cs sorption kinetics tests conducted batchwise with the material of Example 2, i.e. a nanocomposite material with a support made of porous glass and nanoparticles of FeNi(CN).sub.6. The concentration of FeNi(CN).sub.6 is 2% based on the mass of the support and 1 g of material/L of solution is used.

(12) The Cs concentration in the solution is plotted in ordinates (in % relatively to the initial concentration) and the time (hours) is plotted in abscissa.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

(13) The invention will now be described in more detail in the following, particularly by referring to the preparation method.

(14) The first step of this method consists in preparing a support made of porous glass.

(15) First of all let us specify that the term of porous as used herein in connection with a support, means that this support contains pores or voids.

(16) Accordingly, the density of this porous support is less than the theoretical density of the non-porous support which is described as a solid material.

(17) The pores may be connected or isolated but in the porous support according to the invention, the majority of the pores are connected and in communication. One then refers to open porosity or interconnected pores.

(18) Generally, in the support made of porous glass of the invention, the pores are percolating pores which connect a first surface of said support to a second main surface of said support.

(19) In the sense of the invention, a support is generally considered as porous when its density is at most about 95% of its theoretical density.

(20) Preferably, this support made of porous glass is a support which is prepared by chemical etching of a starting solid (massive) sodium borosilicate glass, the composition of which is located in the demixing area of the phase diagram SiO.sub.2—Na.sub.2O—B.sub.2O.sub.3.

(21) This composition is given in all the thermodynamic tables of glasses and may therefore be determined by the man skilled in the art, very easily and very rapidly.

(22) Reference may for example be made to the diagram of FIG. 1, an excerpt from Techniques de l'ingénieur, Jul. 10, 2001, part Verres AF3600, written by Jean PHALIPPOU.

(23) On this diagram, the demixing areas are the areas B and D and the area D is preferably adopted according to the invention.

(24) By solid (massive) glass is meant that this starting glass has no or almost no porosity and that this porosity is specifically generated by the chemical etching.

(25) The elaboration of this glass is generally carried out first of all by weighing powders of oxides or oxide precursors such as carbonates in the intended proportions with which it will be possible to obtain a glass having the sought composition, in the case of a borosilicate glass located in the demixing area of the phase diagram SiO.sub.2—Na.sub.2O—B.sub.2O.sub.3. The composition of the glass is also generally selected so that the porosity of the substrate made of porous glass may be easily closed without affecting its mechanical and chemical properties and without applying high temperatures.

(26) These powders are then mixed intimately, and the mixture of the powders is placed in a crucible for example made of a rhodium platinum alloy which is positioned in an adequate heating device such as a muffle furnace.

(27) The melting of the mixture of powders in order to obtain the molten glass is generally carried out at a temperature, a so-called glass elaboration temperature which is generally located in the range from 1,300° C. to 1,550° C. This elaboration temperature is generally attained by performing several temperature-raising ramps from room temperature, and by observing temperature plateaus of variable duration between these ramps. The final plateau at the elaboration temperature, for example 1,480° C., may have a duration from 1 to 4 hours, for example 2 hours.

(28) Generally, the molten glass is then cast for example onto a plate, cooled down to its solidification and then crushed. The crushed glass pieces are then again placed in the crucible and then again melted by bringing them to the elaboration temperature as defined above. Generally, the crucible containing the crushed glass pieces is directly introduced into the furnace already brought to the elaboration temperature and this temperature is maintained, for example at 1,480° C., for a sufficient time, generally from 10 to 60 minutes, for example 30 minutes, so that the molten glass is homogeneous.

(29) The molten glass is then again cast, for example on a plate, or cast into a mold if a specific shape is desired, and then cooled down until its solidification.

(30) Optionally, when the glass has been cast on a plate, it is then possible to give it the desired shape, for example, the glass may be again crushed and optionally milled more finely for example by means of a vibratory mill if it is desired to prepare a powder with a finer grain size.

(31) The support made of glass may assume all kinds of shapes.

(32) The support may thus appear in the form of particles such as spheres (beads), fibers, tubes, or plates.

(33) The size of the support may also vary between wide limits.

(34) Advantageously, the support may appear in the form of particles forming a powder and may have a grain size (particle size) from 10 to 500 μm. The size of the particles is defined by their largest dimension which is their diameter in the case of spheres or spheroids.

(35) The method for elaborating the glass, described above may easily be adapted according to the shape and/or the size of the glass support, the preparation of which is desired.

(36) Following the elaboration of the glass and prior to chemical etching, the glass may optionally undergo one or more heat treatments with variable temperatures and durations.

(37) These heat treatment(s) may be carried out before and/or after crushing. Thus, if it is desired to keep the integrity of the shape of the glass, the heat treatment(s) is (are) carried out before crushing otherwise it (they) is (are) carried out after this crushing, the heat treatment time(s) are then different. It is also possible to carry out one or more heat treatment(s) before crushing, and one or more heat treatment(s) after crushing.

(38) This (these) heat treatment(s) has (have) the purpose of enlarging the borate areas and therefore varying the size and morphology of the pores in the final porous glass.

(39) This (these) heat treatment(s) is (are) generally carried out at a temperature which is the growth temperature of the demixed areas and which is generally located between the glass transition temperature (Tg) and the glass transition temperature +350° C. at most. The duration(s) of this (these) heat treatment(s) is (are) very variable and may range up to several days depending on the treatment temperature.

(40) Thus, the heat treatment(s) may be carried out at a temperature between Tg and Tg+350° C. for a duration from 6 to 96 hours.

(41) After this(these) optional heat treatment(s), chemical etching is carried out which is necessary for obtaining porosity inside the glass.

(42) Chemical etching generally comprises etching with an acid solution, such as a solution of hydrochloric acid, for example at a concentration of 0.5 mol/L, optionally followed by etching with a basic solution, such as a soda solution at a concentration of 1 mol/L.

(43) The acid etching generally has a duration from 2 to 48 hours, for example from 6 hours to 24 hours, and is generally carried out at a temperature from 50 to 120° C., for example 90° C.

(44) The optional basic etching generally has a duration from 1 to 3 hours, for example 1 hour, and is generally carried out at room temperature.

(45) Generally, the thereby elaborated porous support is washed, for example with ultra-pure water, once or several times, and then dried for example in an oven at a temperature of 120° C. for 24 hours.

(46) The support may have a specific surface area from 10 to 500 m.sup.2/g, preferably from 50 to 150 m.sup.2/g as measured by BET.

(47) The porosity of the support may also vary within wide limits, generally from 25 to 50%.

(48) The support prepared by the method according to the invention may only have a single type of porosity, for example microporosity, mesoporosity or macroporosity.

(49) Or else, the support prepared by the method according to the invention may simultaneously have several types of porosities selected for example from microporosity (a pore size, for example diameter, generally less than 2 nm), mesoporosity (a pore size, for example diameter, from 2 to 20 nm), and macroporosity (a pore size, for example diameter, of more than 20 nm, for example up to 100 nm).

(50) The average pore size, which is their average diameter in the case of pores with a circular section, generally ranges from 2 to 120 nm.

(51) The porosity and the pore size may be varied and it may be perfectly controlled by modifying the conditions of the optional heat treatments and of the chemical etching(s). Thus, as shown in FIG. 2, the heat treatment and chemical etching conditions may lead to very different porosities.

(52) Are thus observed: microporosity for example for a sample without any heat treatment and having been subjected to 6 hour etching in 0.5M HCl at 90° C. (specific surface area of 164 m.sup.2/g). microporosity and mesoporosity for example for a sample without any heat treatment and having been subjected to 24 hour etching in 0.5 M HCl at 90° C. (specific surface area of 146 m.sup.2/g). mesoporosity for example for a sample with a 24 hour heat treatment at 540° C. followed by 6 hour chemical etching in 0.5 M HCl at 90° C. (sample of Example 1, specific surface area of 65 m.sup.2/g). macroporosity for example for a sample without any heat treatment with 6 hour chemical etching in 0.5 M HCl at 90° C. followed by basic etching in 1M NaOH for 1 hour at room temperature (specific surface area of 69 m.sup.2/g).

(53) The support made of porous glass according to the invention has pore walls which may be described as thick, i.e. generally with a thickness from 10 to 60 nm, which is much higher than the partitions, walls of the pores of mesoporous silicas of document (2 to 3 nm) and greatly increases the mechanical strength.

(54) The steps which will now be described for chemical attachment of the organic graft and for preparing nanoparticles of a coordination polymer with CN ligands bound to these grafts inside the pores of the support are substantially similar to those of the method described in the Folch et al. document [16] however with the difference that in that document, the porous support is made of mesoporous silica and not made of glass. Reference may therefore be made to that document as regards notably the reagents and operating conditions applied in these steps but also for the description of the nanoparticles and of their attachment to the surface of the pores via the graft.

(55) Chemical attachment of the organic graft is then achieved inside the pores of the support made of porous glass. This step may also be called functionalization step (see FIG. 3).

(56) The organic graft comprises an organic group which may be designated as a functional group for anchoring nanoparticles.

(57) A functional group for anchoring nanoparticles is a group capable of forming an organometallic bond with the cation M.sup.n+

(58) Examples of such organic groups have already been mentioned above. A preferred organic group is pyridine as this is illustrated in FIG. 3.

(59) The organic group may be directly bound to the support made of porous glass, but it is generally chemically bound, fixed, attached to this support via an arm, linking group and an attachment group chemically attached, fixed, bound, generally through a covalent bond to the support made of porous glass.

(60) The graft thus generally comprises a linking group such as a linear alkylene group with 2 to 6 carbon atoms such as a group —(CH.sub.2).sub.2— (see FIG. 3) which links, connects, said organic group, also called a functional anchoring group, to a group ensuring covalent attachment of the graft to the surface of the pores of the glass support. In the case of a glass, the surface of which is essentially composed of silica, this group ensuring the covalent attachment of the graft is for example an SiO group bound to silanol groups of the surface of the glass.

(61) In order to obtain attachment, fixing, of the graft to the surface of the walls of the pores of the support made of porous glass, this support is therefore brought into contact with a compound comprising said functional anchoring group, an attachment group capable of chemically binding, generally by covalence, to the surface of the glass and optionally a linking group connecting, linking, said functional anchoring group to the attachment group ensuring attachment, generally by covalence, of the graft to the surface of the walls of the pores.

(62) This attachment group may be selected for example from trialkoxysilane groups which react with silanol groups which may be present at the surface of the glass.

(63) Thus, in the case of pyridine, the support in porous glass may be brought into contact with a solution of (CH.sub.3O).sub.3Si(CH.sub.2).sub.2C.sub.5H.sub.4N in a solvent. A preferred solvent is toluene. The solvent is generally refluxed and the duration of the contacting is generally from 12 to 48 hours, for example 24 hours.

(64) At the end of this step, a support made of porous glass functionalized by organic groups such as pyridine groups (see FIG. 3) is therefore obtained.

(65) It is then proceeded with the growth of nanoparticles of a metal coordination polymer with CN ligands inside the pores of the support made of porous glass.

(66) This growth is carried out in two successive steps, optionally repeated.

(67) One begins by bringing into contact the support made of porous glass, inside the pores of which is attached the organic graft, with a solution containing the M.sup.n+ ion, generally in the form of a metal salt.

(68) This solution is a solution in a solvent generally selected from water, alcohols and mixtures of water and of one or several alcohols.

(69) The preferred solvent is methanol.

(70) The metal salt contained in the solution is a salt, the metal of which is generally selected from metals capable of giving a cyanometallate of this metal, such as a hexacyanoferrate of this metal, which is insoluble.

(71) This metal may be selected from all transition metals, for example from copper, cobalt, zinc, cadmium, nickel and iron etc.

(72) Nickel, iron and cobalt are preferred and the M.sup.n+ ion may therefore be selected from Fe.sup.2+, Ni.sup.2+, Fe.sup.3+, and Co.sup.2+.

(73) The metal salt may for example be a nitrate, a sulfate, a chloride, an acetate, optionally hydrated, of one of these metals at a concentration in the solution preferably from 0.01 to 1 mol/L, still preferably from 0.02 to 0.05 mol/L.

(74) Moreover the amount of salt used is preferably about 0.4 mmol/g of treated support.

(75) Advantageously, the solution containing the M.sup.n+ ion may be a solution in water or in an alcohol such as methanol, or a solution in a mixture of water and of one or several alcohol(s).

(76) Advantageously, this solution containing the M.sup.n+ ion may be a solution such as a solution in methanol of [M(H.sub.2O).sub.6]Cl.sub.2 wherein M is preferably Ni, Fe or Co, or of [M(H.sub.2O).sub.6]Cl.sub.3 wherein M is Fe.

(77) The contacting (bringing into contact) which may also be described as impregnation of the support, is generally carried out at room temperature, preferably with stirring, and its duration is generally from 20 to 24 hours.

(78) At the end of this contacting, a solid support is obtained, in which M.sup.n+ cations are bound through an organometallic bond to the functional anchoring groups of the graft. Thus, in the case of pyridine (see FIG. 3) a bond is established between the nitrogen of the ring and the M.sup.n+ cation. The obtained solid product is then separated for example as a powder, for example by filtration.

(79) The separated product is then washed one or several times, for example 1 to 3 times preferably with the same solvent as the solvent of the M.sup.n+ solution, such as methanol.

(80) With this washing operation it is possible to remove the excess metal salt and obtain a stable product with a perfectly defined composition.

(81) A drying step is then carried out generally at room temperature and in vacuo for a duration from 6 to 48 hours, for example 24 hours. Generally, the drying is continued until the mass of the support remains substantially constant.

(82) The support made of porous glass which has reacted with the metal cation M.sup.n+ as described above is then brought into contact with a solution of a complex (which may optionally be called a salt) of [M′(CN).sub.m].sup.x−, for example [M′(CN).sub.m].sup.3−.

(83) This solution is a solution in a solvent selected from water, alcohols and mixtures of water and of one of several alcohol(s).

(84) The preferred solvent is methanol.

(85) The contacting which may also be described as an impregnation of the support, is generally carried out at room temperature, preferably with stirring, and its duration is generally from 20 to 48 hours, for example 24 hours.

(86) This complex generally fits the following formula:

(87) (Cat).sub.x[M′(CN).sub.m], wherein M′, m, and x have the meaning already given above and Cat is a cation generally selected from cations of alkaline metals such as K or Na, quaternary ammoniums such as tetrabutylammonium (TBA), and phosphoniums such as tetraphenylphosphonium (PPh.sub.4). Preferred complexes are the complexes of formula [N(C.sub.4H.sub.9).sub.4].sub.x[M′(CN).sub.m].

(88) Still preferred complexes are the complexes of formula [N(C.sub.4H.sub.9).sub.4].sub.3[M′(CN).sub.m] such as [N(C.sub.4H.sub.9).sub.4].sub.3[Fe(CN).sub.6], [N(C.sub.4H.sub.9).sub.4].sub.3[Mo(CN).sub.8], and [N(C.sub.4H.sub.9).sub.4].sub.3[Co(CN).sub.6].

(89) The solution, for example the methanolic solution of complex or salt is applied at a variable concentration, i.e. the concentration of the salt or complex is generally from 0.01 to 1 mol/L, preferably from 0.02 to 0.05 mol/L.

(90) On the other hand, the solution of the salt or complex of [M′(CN).sub.m].sup.x− applied is prepared so that the mass ratio of the salt or complex to the amount of the impregnation support essentially consisting of the initial support made of porous glass, is preferably from 5 to 20%.

(91) Attachment, fixing, of the anionic portion [M′(CN).sub.m].sup.x−, for example [Fe(CN).sub.6].sup.4−, of the salt or complex is thereby obtained on the M.sup.n+ cations (See FIG. 3), this attachment is accomplished by forming bonds of the covalent type which are relatively strong depending on the medium, and this attachment, fixing, is generally quantitative, i.e. all the M.sup.n+ cations react. The binding therefore does not have any randomness.

(92) At the end of this contacting, the obtained solid product is separated for example as a powder, for example by filtration.

(93) The separated product is then washed one or several times, for example 1 to 3 times preferably with the same solvent as the solvent of the salt or complex solution, such as methanol.

(94) This washing operation has the purpose of removing the salts and complexes of [M′(CN).sub.m].sup.x− which have not been bound to the M.sup.n+ cations and gives the possibility of obtaining a nanocomposite material fixing (binding) mineral pollutants in which there is no longer any free, non-bound [M′(CN).sub.m].sup.x− which may salted out.

(95) The steps for contacting the support in porous glass with the metal cation M.sup.n+ and then of contacting the support made of porous glass with a solution of a salt or a complex of [M′(CN).sub.m].sup.x−, for example [M′(CN).sub.m].sup.3−, may only be carried out once, or else they may be repeated 1 to 4 times (see FIG. 3), in this way it is possible to perfectly adjust the size of the nanoparticles.

(96) The weight content of mineral fixer (binder), i.e. of insoluble metal hexacyanoferrate fixed (bound) on the anion exchanger polymer, is generally from 1 to 10%, for example 3%, based on the mass of the support made of porous glass.

(97) The nanocomposite solid material fixing (binding) mineral pollutants according to the invention may notably be applied but not exclusively in a method for fixing (binding) at least one mineral pollutant for example a metal cation contained in a solution, in which said solution is brought into contact with said composite solid material fixing (binding) mineral pollutants.

(98) The materials according to the invention, because of their excellent properties such as an excellent exchange capacity, excellent selectivity, high reaction rate, are particularly suitable for such a use.

(99) This excellent efficiency is obtained with reduced amounts of mineral fixer (binder) such as insoluble hexacyanoferrate.

(100) Further, the excellent mechanical strength and stability properties of the material according to the invention, resulting from its specific structure allow it to be packed in a column and the fixing (binding) process to be continuously applied, for example in a fluidized bed, which may thus be easily integrated into an existing facility, for example in a processing chain or line comprising several steps.

(101) The solutions which may be treated with the method of the invention and with the composite solid material fixing (binding) mineral pollutants according to the invention are very varied, and may even for example contain corrosive acids, agents, or other agents because of the excellent chemical stability of the material according to the invention.

(102) The material according to the invention may in particular be used over a very wide pH range. For example it is possible to treat nitric aqueous solutions with a concentration ranging for example from 0.1 to 3M, acid or neutral solutions up to a pH of 8, etc. The mineral pollutant which may be fixed (bound) in the method according to the invention may be any mineral pollutant, i.e. for example any pollutant stemming from (based on) a metal or an isotope, preferably a radioactive isotope of this metal, which may be found in the solution.

(103) This pollutant is preferably selected from anionic complexes, colloids, cations and mixtures thereof.

(104) Preferably this is a pollutant, such as a cation from an element selected from Tl, Fe, Cs, Co, Ru, Ag, . . . and isotopes, in particular radioactive isotopes thereof, among which mention may be made of .sup.58Co, .sup.60Co, .sup.55-59Fe, .sup.134Cs, .sup.137Cs, .sup.103,105,106,107Ru. The metal cation is in particular the cesium cation Cs.sup.+ or the thallium cation Tl.sup.2+.

(105) The anionic complex is for example RuO.sub.4.sup.2−.

(106) A preferred use of the material according to the invention is the fixing (binding) of the cesium which contributes for a large part to the gamma activity of liquids of the nuclear industry and which is selectively fixed (bound) by hexacyanoferrates.

(107) The concentration of the pollutant(s) such as cation(s) may vary between wide limits: for example, it may be for each of the latter from 0.1 picogram to 100 mg/L, preferably from 0.01 mg/L to 10 μg/L.

(108) The solution to be treated by the method of the invention is preferably an aqueous solution, which, in addition to the pollutant(s) such as cation(s) to be fixed (bound), may contain other salts in solution such as NaNO.sub.3 or LiNO.sub.3 or further Al(NO.sub.3).sub.3 or any other soluble salt of an alkaline or earth alkaline metal at a concentration which may attain 2 mol/L. The solution may also contain, as indicated above, acids, bases and even organic compounds.

(109) The solution to be treated may also be a solution in a pure organic solvent such as ethanol (absolute alcohol) acetone or other solvent, in a mixture of these organic solvents, or in a mixture of water and of one or more of these organic solvents which are miscible with water.

(110) The material according to the invention thus has the advantage of being able of treating solutions which cannot be treated with organic resins.

(111) This solution may consist in a process liquid or in an industrial effluent or in any other solution which may in particular stem from nuclear installations and industry or from any other activity related to the nuclear industry.

(112) Among the various liquids and effluents of the nuclear industry, nuclear installations and activities applying radionuclides which may be treated by the method of the invention, for example mention may be made of the waters for cooling power stations, and of all the various effluents coming into contact with radio-isotopes such as all the washing waters, solutions for regenerating resins, etc.

(113) It is however obvious that the method according to the invention may also be applied in other non nuclear fields of activities, such as industrial fields or other fields.

(114) Thus, hexacyanoferrates selectively fix (bind) thallium and this property may be exploited in the purification of cementwork effluents in order to reduce or suppress discharges and emissions of this element which is a violent poison.

(115) It was seen that the fixing (binding) method according to the invention is preferably applied continuously, the nanocomposite material according to the invention, preferably in the form of particles, then being packed for example in the form of a column, the material preferably forming a fluidized bed, the fluidization of which is ensured by the solution to be treated, but the fixing (binding) method may also be applied batchwise, in a batch mode, the contacting of the exchange material and of the solution to be treated then being preferably achieved with stirring. The packing of the material in a column allows continuous treatment of significant amounts of solution, with a high flow rate of the latter.

(116) The contacting time of the solution to be treated with the material according to the invention, is variable and may for example range from 1 minute to 1 hour for continuous operation and, for example from 10 minutes to 25 hours preferably from 10 minutes to 24 hours for batch operation.

(117) At the end of the fixing (binding) process, the pollutants found in the solution, such as cations, are immobilized in the fixing (binding) nanocomposite solid material (exchanger) according to the invention by sorption i.e. by ion exchange or adsorption inside the nanoparticles, inside the structure of the nanoparticles, themselves chemically bound to the surface of the walls of the pores of the glass support.

(118) The porosity of the material according to the invention, because it consists essentially of glass may be easily closed with a treatment carried out under mild conditions, i.e. which do not cause any modification of its mechanical and chemical properties and especially no release, no salting-out of the immobilized pollutant such as cesium, by volatilization of the latter.

(119) This treatment which allows the pores of the material according to the invention to be closed, in which the pollutants are trapped, may be carried out by applying an external stress to the material which may be a thermal, radiative, chemical or other stress.

(120) In the case when a heat treatment is carried out, the latter is carried out at a low temperature, i.e. generally at a temperature below 1,000° C., for example from 600 to 850° C., notably 800° C., for a duration for example from 5 to 30 minutes, for example 6 minutes. Such a treatment is carried out at a temperature which is well below the temperatures applied for vitrification of the porous supports notably made of silica of the prior art which causes volatilization of the pollutants such as cesium. According to the invention, this heat treatment does not cause vitrification of the support but simply closure of the pores of the latter which is demonstrated by the decrease in the specific surface area.

(121) In the case when a treatment is carried out by irradiation of the substrate, the latter is generally a low energy treatment for example achieved by bombardment with Ar, Kr or Xe ions, for example under the following conditions: 70 MeV Ar or 250 MeV Kr, with a fluence from 2×10.sup.10 to 10×10.sup.10 ions/cm.sup.2.s.

(122) In the case when the closure of the porosity is accomplished with a chemical treatment, a basic atmosphere is generally used such as for example an ammonia containing atmosphere, generally at room temperature for a duration for example from 1 to several hours, preferably from 1 to 12 hours.

(123) The nanocomposite solid material according to the invention, the porosity of which has been closed, may be directly stored, since its very great mechanical and chemical stabilities and its essentially mineral nature allow such storage without there occurring any degradation of the product leading to emanations of hydrogen.

(124) However it may possibly be necessary in certain cases to conduct lixiviation tests.

(125) In the solid material according to the invention, the porosity of which has been closed, it may be stated that one has an encapsulation of the pollutant such as Cs in a glass.

(126) The material according to the invention may therefore be used directly, with a simple treatment for closing the pores, as a confinement matrix, in a safe and reliable way, without any risk of salting out, release of the immobilized pollutant, such as cesium, which was impossible with the materials of the prior art which require for confinement, treatments, for example vitrification, carried out at a high temperature, causing release of the pollutants, in particular cesium by volatilization.

(127) The material according to the invention, and the fixing (binding) method applying it provides a solution to one of the essential unsolved problems which all the materials and methods of the prior art have, whether they are notably solid or composite.

(128) The invention will now be described with reference to the following examples, given as an illustration and not as a limitation.

(129) In the Examples 1 to 4 which follow, powders of porous glasses were first synthesized by controlled demixing (Example 1) and then by chemical etching; and then grafting and growth of nickel ferrocyanide particles were carried out in these porous glasses (Example 2).

(130) Tests for extracting cesium from a solution rich in sodium nitrate were then conducted by using the thereby obtained powders (Example 3).

(131) Finally, tests for closing the porosity of these powders in order to convert them into a solid material used as a matrix for the packaging of the thereby trapped Cs were carried out (Example 4).

(132) The operating mode for these 4 steps is the following:

Example 1: Synthesis of Porous Glasses

(133) The composition of the initial glass is SiO.sub.2 75 mol %; Na.sub.2O 5 mol %; B.sub.2O.sub.3 20 mol %. The precursors used are commercial powders of SiO.sub.2 (Sifraco®), Na.sub.2CO.sub.3 (Prolabo®) and H.sub.3BO.sub.3 (Prolabo®), respectively.

(134) In order to obtain a batch of 100 g of glass, it is proceeded with weighing 72.58 g of SiO.sub.2 powder, 8.53 g of Na.sub.2CO.sub.3 powder and 39.86 g of H.sub.3BO.sub.3 powder. The silica and the sodium carbonate are heated beforehand to a temperature of 250° C., in order to remove any residual trace of water.

(135) After this weighing, these powders are mixed intimately and then placed in a rhodium platinum crucible and placed in a muffle furnace.

(136) In order to achieve the synthesis of the glass, first of all a first heat treatment is carried out according to the following cycle: a rise in temperature at a rate of 100° C./h is carried out from room temperature up to 150° C., and then a plateau of 2 hours at this temperature is observed; a temperature ramp at a rate of 50° C./h is carried out up to 300° C., and then a plateau of 2 hours at this temperature is observed; a temperature ramp at a rate of 150° C./h is carried out up to 1,200° C., and then another temperature ramp of 400° C./h is carried out up to 1,480° C., and a one hour plateau is observed at this temperature.

(137) At the end of this first heat treatment, the molten glass is cast on a plate and then crushed with a hammer.

(138) The crushed glass pieces are then put back into the crucible and directly introduced into the furnace brought to 1,480° C., this temperature is maintained for 30 minutes for good homogenization.

(139) Finally, the molten glass is again cast onto a plate, crushed with a hammer and finely milled by means of a vibratory mill.

(140) The obtained powder has grains with a size of less than 125 μm.

(141) For glass heat-treated for 24 hours at 540° C., the following chemical etching was carried out:

(142) 3 g of the obtained powder are placed in a Savillex® (this is a sealed Teflon container) with 30 mL of an HCl solution, at a concentration of 0.5 mol/L.

(143) This Savillex® is then placed for 6 hours in an oven at 90° C. After this chemical etching, the powder is then filtered and washed with ultra pure water several times, and then dried in the oven at 120° C. for 24 hours.

(144) A specific surface area and porosity measurement is then conducted with a BET apparatus.

(145) A microporous (with about 7 m.sup.2/g of microporosity) and mesoporous sample with a specific surface area of 65 m.sup.2/g and a pore size of 8 nm is obtained.

Example 2: Grafting and Synthesis of Nickel Hexacyanoferrate Nanoparticles in the Porous Glass

(146) The grafting of —(CH.sub.2).sub.2C.sub.5H.sub.4N within the pores of the glass, prepared in Example 1 is accomplished by refluxing the porous glass powder in toluene in the presence of the organic compound (CH.sub.3O).sub.3Si(CH.sub.2).sub.2C.sub.5H.sub.4N for one night.

(147) Then, 2 g of the thereby grafted glass powder are placed in a 3.65.10.sup.−2M[Ni(H.sub.2O).sub.6]Cl.sub.2 solution in methanol.

(148) This mixture is stirred for one night at room temperature.

(149) After filtration, the powder is washed several times with methanol and then dried in vacuo at room temperature for 24 hours.

(150) In a second phase, the thereby obtained powder is put into a 2.5 10.sup.−2M solution of the complex [N(C.sub.4H.sub.9).sub.3][Fe(CN).sub.6] in methanol. The mixture is stirred for 48 hours at room temperature. The powder is then filtered, washed several times with methanol and dried in vacuo. These treatments first with the metal salts and then with the cyanometallate precursors are repeated a second time.

(151) The chemical analyses of the thereby obtained powder show an Fe content of the order of 2% by mass.

Example 3: Fixing Cesium

(152) The grafted glass powders elaborated in Example 2 are then tested as to the fixing of Cs (see FIG. 4).

(153) The solution used for these tests contains 0.1 mol/L of NaNO.sub.3 and the pH is comprised between 7 and 8. The large sodium nitrate content is required for correctly simulating the ionic force of actual industrial solutions.

(154) In a 50 mL volume of this solution, 4.4 g of CsNO.sub.3 are introduced (which gives a concentration of 60.2 mg/L) and also 50 mg of the grafted porous glass obtained in Example 2 (i.e. 1 g of grafted porous glass per L of solution).

(155) The initial measured concentration (Ci) of Cs is 60.2 mg/L.

(156) The whole is stirred for 25 hours at room temperature. After filtration, the solution is analyzed by ion chromatography.

(157) After this filtration step, the residual solution is analyzed.

(158) The final measured concentration (Cf) of Cesium is 44.3 mg/L.

(159) The decontamination factor (Kd) is calculated in this way:
Kd=(Ci−Cf)/Cf*Vsol/msupport
This factor is therefore equal to 372 mL/g in this example.

(160) In this example, 20 mg of Fe were grafted per gram of glass, and 16.5 mg of Cs were fixed (bound) per g of glass.

Example 4: Closing the Porosity

(161) Closing the porosity in order to confine the thereby trapped cesium is accomplished by a heat treatment from 5 to 10 minutes at 800° C.

(162) For example, a heat treatment of the porous sample for 6 minutes at 800° C. reduces the specific surface area of a sample heat-treated for 24 hours at 540° C., and then chemically treated with 0.5 M HCl for 24 hours from a 73 m.sup.2/g specific surface area to a specific surface area of 19 m.sup.2/g, which demonstrates closing of the pores.

REFERENCES

(163) [1] J. Lehto, L Szirtes, “Effects of gamma irradiation on cobalt hexacyanoferrate (II) ion exchangers”, Radiat. Phys. Chem. 43, (1994), 261-264. [2] H. Loewenschuss, “Metal ferrocyanide complexes for the decontamination of caesium from aqueous radioactive waste”, Radioactive waste management 2, (1982), 327-341. [3] Mimura et al. J., Nucl. Sci Technol., 34, (1997), 484, and 34, (1997), 607. [4] E. H. Tusa, A. Paavola, R. Harjula, J. Lehto, “Industrial scale removal of cesium with hexacyanoferrate exchanger—Process realization and test run”, Nuclear Technology, 107, (1994), 279. [5] R. Harjula, J. Lehto, A. Paajanen, L. Brodkin, E. Tusa, “Removal of radioactive cesium from nuclear waste solutions with the transition metal hexacyanoferrate ion exchanger CsTreat”, Nuclear Science and Engineering, 137, (2001), 206-214. [6] R. Harjula, J. Lehto, A. Paajanen, E. Tusa, P. Yarnell, “Use inorganic ion exchange materials as precoat filters for nuclear waste effluent treatment”, Reactive and Functional Polymers, 60, (2004), 85-95. [7] H. Mimura, M Kimura, K. Akiba, Y. Onodera, “Selective removal of cesium from highly concentrated sodium nitrate neutral solutions by potassium nickel hexacyanoferrate (II)-loaded silica gels”, Solvent extraction and ion exchange, 17(2), 403-417, (1999). [8] R. D. Ambashta, P. K. Wattal, S. Singh, D. Bahadur, “Nano-aggregates of hexacyanoferrate (II)-loaded magnetite for removal of cesium from radioactive wastes”, Journal of Magnetism and Magnetic Materials, 267, (2003), 335-340. [9] A. Mardan, R. Ajaz, “A new method for preparation of silica potassium cobalt hexacyanoferrate composite ion exchanger from silica sol”, J. Radioanalytical and Nuclear Chemistry, Vol. 251, No. 3, (2002), 359-361. [10] L. Sharygin, A. Muromskiy, M. Kalyagina, S. Borovkov, “A granular inorganic cation-exchanger selective to cesium”, J. Nuclear Science and Technology, 44 (5), 767-773, (2007). [10 bis] L. M. Sharygin; V. E. Moiseev; A. Yu Muromski, et al., Inorganic spherical granual composite sorbent based on zirconium hydroxide and its production process, RU-A-2113024. [11] C. Loos-Neskovic, C. Vidal-Madjar, J. Dulieu, A. Pantazaki, Application FR-A1-2 765 812 (Jul. 9, 1997), Application WO-A1-99/02255. [12] C. Loos-Neskovic, C. Vidal-Madjar, B. Jimenez, A. Pantazaki, V. Federici, A. Tamburini, M. Fedoroff, E. Persidou, “A copper hexacyanoferrate/polymer/silica composite as selective sorbent for the decontamination of radioactive caesium”, Radiochim. Acta., 85, (1999), 143-148. [13] S. Milonjic, I. Bispo, M. Fedoroff, C. Loos-Neskovic, C. Vidal-Madjar, “Sorption of cesium on copper hexecyaniferrate/polymer/silica composites in batch and dynamic conditions”, Journal of Radioanalytical and Nuclear Chermistry, Vol. 252, (2002), 497-501. [14] Chin-Yuang Chang, L. K. Chau, W. P. Hu, C. Y. Wang, J. H. Liao, “Nickel hexacyanoferrate multilayers on functionalized mesoporous silica supports for selective sorption and sensing of cesium”, Microporous and mesoporous materials, 109, (2008), 505-512. [15] Y. Lin, X. Cui, “Electrosynthesis, characterization and application of novel hybrid materials based on carbon nanotube-polyaniline-nickel hexacyanoferrate nanocomposites”, Journal of Materials Chemistry, 16, (2006), 585-592. [16] Folch, B., Guari et al., “Synthesis and behaviour of size controlled cyano-bridged coordination polymer nanoparticles within hybrid mesoporous silica”, (2008), New Journal of Chemistry, Vol. 32, Number 2, 273-282.