PARTICULATE POROUS INORGANIC MATERIAL BASED ON A LEAD VANADATE OR PHOSPHOVANADATE, USEFUL FOR CAPTURING AND CONDITIONING GASEOUS IODINE

Abstract

An inorganic material in a form of open-porosity particles, each of the particles comprising a lead vanadate or phosphovanadate of formula Pb.sub.3-xX.sub.x(VO.sub.4)2.sub.-2y(PO.sub.4)2.sub.y,wherein x = 0 or x > 0 but ≤ 0.33; y = 0 or y > 0 but < 1;X = Ba.sup.2+, Ca.sup.2+, Sr.sup.2+ or Cd.sup.2+; and metallic lead or a lead salt. A method for preparing the material, a method for capturing iodine present in a gaseous effluent as well as a method for conditioning iodine present in a gaseous effluent in a form of an iodoapatite.

Claims

1. An inorganic material in a form of open-porosity particles, wherein each of the particles comprises: a lead vanadate or phosphovanadate of formula (1): ##STR00007## where: x is equal to 0 or x is greater than 0 but no more than 0.33; y is equal to 0 or y is greater than 0 but less than 1; X is Ba.sup.2+, Ca.sup.2+, Sr.sup.2+ or Cd.sup.2+; and metallic lead or a lead salt.

2. The material of claim 1, wherein the metallic lead or the lead salt is intimately mixed with the lead vanadate or phosphovanadate.

3. The material of claim 2, wherein the lead salt is lead(II) sulfide, lead(II) sulfate, lead(II) carbonate, lead(II) bromide, lead(II) chloride, lead(II) fluoride, lead(II) hydroxide, lead(II) selenide, or lead(II) telluride.

4. The material of claim 1, wherein the lead salt is within the pores of the particles.

5. The material of claim 4, wherein the lead salt is lead(II) nitrate, lead(II) chlorate or lead(II) perchlorate trihydrate.

6. The material of claim 1, wherein the lead vanadate or phosphovanadate is of formula (2): ##STR00008## wherein y is equal to 0 or y is greater than 0 but less than 1.

7. The material of claim 6, wherein the particles comprise lead vanadate of formula Pb.sub.3(VO.sub.4).sub.2.

8. The material of claim 1, wherein the particles have dimensions between 300 .Math.m and 3 mm.

9. A method for preparing an inorganic material in a form of open-porosity particles, each of the particles comprising: a lead vanadate or phosphovanadate of formula (1): ##STR00009## where: x is equal to 0 or x is greater than 0 but no more than 0.33; y is equal to 0 or y is greater than 0 but less than 1; X is Ba.sup.2+, Ca.sup.2+, Sr.sup.2+ or Cd.sup.2+; and metallic lead or a lead salt; the method comprising at least the steps of: a) preparing a mixture M comprising at least one precursor of formula (3) or of formula (4): ##STR00010## ##STR00011## where: x is equal to 0 or x is greater than 0 but no more than 0.33; y is equal to 0 or y is greater than 0 but less than 1; X is Ba.sup.2+, Ca.sup.2+, Sr.sup.2+ or Cd.sup.2+; and an alginate of an alkaline metal in water; b) extruding in a divided form the mixture M in an aqueous solution A comprising a lead salt and optionally a barium salt, a calcium salt, a strontium salt or a cadmium salt, whereby beads formed by a hydrogel are obtained; c) drying the beads; and d) calcining the beads, whereby open-porosity particles are obtained; and further comprising: adding metallic lead or a lead salt that is insoluble or only slightly soluble in water to the precursor of formula (3) or (4) and to the alkaline metal alginate in the mixture M; or depositing a lead salt in the pores of the particles obtained at step d).

10. The method of claim 9, which further comprises, between step b) and step c), a replacement of all or part of the water of the hydrogel by an organic solvent having a standard boiling point of less than 100° C.

11. A method for capturing iodine present in a gaseous effluent, comprising putting the gaseous effluent in contact with an inorganic material in a form of open-porosity particles, each of the particles comprising: a lead vanadate or phosphovanadate of formula (1): ##STR00012## where: x is equal to 0 or x is greater than 0 but no more than 0.33; y is equal to 0 or y is greater than 0 but less than 1; X is Ba.sup.2+, Ca.sup.2+, Sr.sup.2+ or Cd.sup.2+; and metallic lead or a lead salt.

12. The method of claim 11, wherein the iodine present in the gaseous effluent is a radioactive iodine.

13. The method of claim 12, wherein the radioactive iodine is iodine-129.

14. A method for conditioning iodine present in a gaseous effluent in a form of an iodoapatite, comprising the steps of: i) capturing the iodine by putting the gaseous effluent in contact with an inorganic material in a form of open-porosity particles, each of the particles comprising: a lead vanadate or phosphovanadate of formula (1): ##STR00013## where: x is equal to 0 or x is greater than 0 but no more than 0.33; y is equal to 0 or y is greater than 0 but less than 1; X is Ba.sup.2+, Ca.sup.2+, Sr.sup.2+ or Cd.sup.2+; and metallic lead or a lead salt; whereby a material comprising lead iodide is obtained; then ii) heat treating the material obtained at step i), whereby the material is transformed into the iodoapatite.

15. The method of claim 14, wherein at step ii), the material is heated at a temperature from 400° C. to 650° C.

16. The method of claim 14, wherein the iodine present in the gaseous effluent is a radioactive iodine.

17. The method of claim 16, wherein the radioactive iodine is iodine-129.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0078] FIG. 1 is an image taken by scanning electron microscopy (or SEM), in backscattered electron mode and at a magnification of x70, of a particle of a material of the invention before filling the pores of this particle with a lead salt.

[0079] FIG. 2 is an image similar to the one in FIG. 1 but taken at a magnification of x1 100.

[0080] FIG. 3 illustrates the microstructure, obtained by SEM, at a magnification of x1 000, of a particle of a material of the invention after exposing this material to diiodine vapours.

[0081] FIG. 4 illustrates the elementary mapping of iodine, as obtained by energy-dispersive X-ray spectroscopy (or EDS) at a magnification of x1 000, for a particle of a material of the invention after exposing this material to diiodine vapours.

EXAMPLE OF AN EMBODIMENT OF THE INVENTION

I - Preparation of a Material of the Invention

[0082] A material of the invention, consisting of porous particles of lead vanadate, Pb.sub.3(VO.sub.4).sub.2, the pores of which comprise lead(II) nitrate, Pb(NO.sub.3).sub.2, is prepared in accordance with the following operating protocol: [0083] an aqueous solution of sodium alginate (Sigma-Aldrich) is added, under magnetic stirring, to an aqueous suspension of lead pyrovanadate, Pb.sub.2V.sub.2O.sub.7, to obtain an aqueous mixture comprising 2% by mass sodium alginate and 3% by mass Pb.sub.2V.sub.2O.sub.7 (i.e. 2 g of sodium alginate and 3 g of Pb.sub.2V.sub.2O.sub.7 for 100 g of water), which is maintained under weak magnetic stirring for 4 hours; [0084] 2) the mixture obtained at step a) is extruded in the form of drops in an aqueous solution comprising 0.27 mol/L of lead(II) nitrate; this extrusion consists in circulating the mixture in a pipe that comprises a needle at one of the ends thereof and the other end of which is connected to a peristaltic pump, and causing the mixture obtained at step a) to fall drop by drop, via the opening in the tip of the needle, in an aqueous solution of lead(II) nitrate, by means of which gelatinous beads are obtained, with dimensions typically between 0.5 mm and 10 mm; these beads are formed by a mixture of Pb.sub.2V.sub.2O.sub.7 and lead alginate, the divalent lead ions having in fact replaced the monovalent sodium ions of the alginate during the extrusion; [0085] 3) the gelatinous beads obtained at the end of step 2) are subjected to a water/ethanol exchange, which enables the hydrogel that constitutes them to be transformed into an alcohol gel; to do this, the beads are drained, rinsed with water and placed in immersion in a bath of ethanol for 10 minutes; this immersion is repeated three times; [0086] 4) the alcohol gel beads obtained at step 3) are subjected to drying at 60° C. for one night; [0087] 5) the dried alcohol-gel beads are subjected to a calcination at 500° C. for 1 hour and 30 minutes under air (with a temperature rise ramp of 5° C./min); then [0088] 6) the particles obtained at step 5) are immersed in an aqueous solution comprising 0.1 mol/L of lead(II) nitrate for one hour, and they are then dried at 90° C. for 24 hours.

[0089] In the course of step 5), the alginate present in the alcohol-gel beads is decomposed and these beads are transformed into particles, with dimensions typically between 300 .Math.m and 3 mm, and which comprise an inorganic skeleton composed of lead vanadate. The initial presence of organic matter, represented by the alginate, in the beads makes it possible to generate porosity. In parallel, Pb.sub.2V.sub.2O.sub.7 is converted into Pb.sub.3(VO.sub.4).sub.2 because of its reaction with the lead included in the lead alginate that formed at step 2). This reaction can be written schematically as follows:

##STR00006##

[0090] As for step 6), this makes it possible to fill the pores of the particles of lead(II) nitrate able to form lead iodide, Pbl.sub.2, by reaction with the gaseous iodine.

[0091] FIGS. 1 and 2 correspond to images taken under SEM, in backscattered electron mode, of a particle of the material as obtained at step 5 above. FIG. 1 corresponds to a magnification of x70 while FIG. 2 corresponds to a magnification of x1 100.

[0092] FIG. 1 shows an overall view of the particle while FIG. 2 shows the porous nature of this particle, the porosity corresponding to the small black dots of pseudospherical shape.

II - Exposure of the Material of the Invention to Gaseous Iodine

[0093] The material as obtained at point I above is exposed to vapours of diiodine I.sub.2, at 60° C. for 16 hours.

[0094] FIGS. 3 and 4 illustrate, in the first case, the microstructure of a particle of the material as observed at the end of this exposure by SEM, and, in the second case, the mapping X of the iodine as observed for this particle by EDS. FIGS. 3 and 4 correspond to a magnification of x1 000.

[0095] On FIGS. 3 and 4, the darkest zones in grey level, one of which is shown by the arrow numbered 1, correspond to zones rich in lead iodide, Pbl.sub.2, while the lightest zones in grey level, one of which is shown by the arrow numbered 2, correspond to zones rich in lead vanadate, Pb.sub.3(VO.sub.4).sub.2.

III - Consolidation of the Material of the Invention in an Iodoapatite

[0096] The material loaded with iodine, as obtained at point II above, is subjected to heat treatment corresponding to a reactive sintering by SPS at 400° C. for 30 minutes, with a temperature rise ramp of 50° C./min and under uniaxial pressure of 40 MPa.

REFERENCES CITED

[0097] WO-A-96/18196 [0098] WO-A-2009/047246 [0099] R. Yousefi et al., Current Applied Physics 2014, 14(8), 1031-1035