JPS61148396A - Method of solidifying and treating radioactive cesium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating cesium and cesium compounds as radioactive waste. The present invention relates to a processing method for fixing cesium (hereinafter simply referred to as cesium).

Current technology and its problems Emissions from reprocessing spent nuclear fuel generated from nuclear power generation, etc., contain fission products that have long half-lives. It is necessary to semi-permanently isolate such high-level radioactive waste from living areas, and various immobilization treatment methods are being considered.

In particular, since cesium, which is a high-level radioactive waste, is an alkali metal with a long half-life, there is a risk that it will leach from the immobilized body during long periods of storage, storage, isolation, etc. There is a demand for an immobilized body that is stable against heat and the like.

Conventionally, the following methods are known as methods for immobilizing high-level radioactive cesium.

(a) A method of immobilization with borosilicate glass or phosphate glass.

(b) A method in which cesium is adsorbed by zeolite and then heated to high temperatures to convert it into a volcite mineral phase and fix it.

(c) A method of sintering and fixing as holerdite-type cesium titanate.

However, in the above method, 10
It is necessary to perform heat treatment at a high temperature of 00° C. or higher, and there is a problem in that part of the cesium evaporates during the heat treatment, corroding containers such as crucibles.

In addition, the immobilized body changes its structure due to the accumulation of decay heat (for example, crystallization of glass), and becomes inferior in heat resistance and durability, and is particularly susceptible to attack by chemicals such as salts, acids, and alkalis, and is resistant to cesium. The leachability is not satisfactory.

Represented by the general formula Zr (HPO4)2 ・nH2O,
Zr0a:P2O5-1 as molar ratio in oxide terms
: Crystalline zirconium phosphate having a two-dimensional layered structure represented by 1 is known as an ion exchanger, and has the property of selectively adsorbing alkali metal ions and separating them by exchange from a mixed liquid in high yield. It has been known. However, since the crystalline zirconium phosphate elutes adsorbed substances such as cesium when it comes into contact with an acidic solution, it is difficult to use it as a fixing agent for semi-permanently fixing cesium.

It is represented by the chemical formula NaZr5+ (POa)a, and the molar ratio in terms of oxide is ZrO2:P2O5-4.
:3 Crystalline zirconium phosphate having an Na-type three-dimensional network structure is also known, and the ion exchange properties of the crystalline zirconium phosphate for cesium ions have been reported (R.

Roy, E.R., Vance and J.
^Iamo, Hat, Res, Bull.

17 585 1982). However, such crystalline zirconium phosphate has a low exchange rate from Na type to C8 type, and the Na compound produced when exchanged causes corrosion of containers, equipment, etc., and furthermore, the solid cesium There is a problem in that Na compounds are mixed into the solidified product and inhibit the stability of the solidified product. In addition, since the exchange from Na type to O8 type occurs in a relatively easy reaction area,
The part replaced by cesium is a highly reactive part, and there is also the problem that cesium is easily leached out.

Means for Solving the Problems In view of the above-mentioned problems of the prior art, the present inventor conducted various experiments and research in order to find a method for stably fixing cesium as radioactive waste for a long period of time. As a result of repeated studies, it was found that cesium can be immobilized by using a specific crystalline zirconium phosphate having a three-dimensional network structure as an immobilizing agent and heating a mixture of the immobilizing agent and cesium. It has been found that fixed crystalline zirconium phosphate is stable for a long period of time and has excellent heat resistance and chemical resistance.

That is, the present invention provides the following: (i) (a) General formula % formula % [However, R represents NH or an amine cation, and O≦n
≦1.0≦m≦2] and (b) crystalline zirconium phosphate, which is represented by formula 4 as an oxide according to analytical calculations and (11)
The present invention relates to a method for immobilizing radioactive cesium, which comprises mixing radioactive cesium and/or a cesium compound so that the temperature becomes -1 or less, and heat-treating the mixture at (iV) 400 to 1250°C.

The crystalline zirconium phosphate used as a cesium immobilizing agent in the present invention was synthesized by the present inventor and has already been patented (Japanese Patent Application No. 59-95275).

The crystalline zirconium phosphate will be explained below.

The crystalline zirconium phosphate used in the present invention has the general formula % (where R represents NHa or an amine cation, and 0≦n
≦1.0≦m≦2], and as an oxide based on analytical calculations, it is expressed by the formula 4 formula %.

The crystalline zirconium phosphate used in the present invention is produced, for example, by the following method. First, a carboxylic acid compound aqueous solution is added to a zirconium compound aqueous solution, or a phosphoric acid compound or its aqueous solution is added to a mixed solution obtained by adding a zirconium compound aqueous solution to a carboxylic acid compound aqueous solution. If a carboxylic acid compound aqueous solution is added after a phosphoric acid compound is added to a zirconium compound aqueous solution, amorphous zirconium phosphate is likely to be produced, resulting in a product with a low degree of crystallinity. The ammonium compound and/or the amine compound may be added at any time during the preparation of the liquid mixture, and no difference in effectiveness is observed depending on the timing of addition. When mixing each raw material, it is desirable to stir the mixture, and especially when adding a phosphoric acid compound, stirring is carried out so that the phosphoric acid concentration does not remain partially high.

In the mixed solution, a zirconium compound (as Zr), a carboxylic acid compound (as 0204), and a phosphoric acid compound (P
In the molar ratio triangular component diagram shown in FIG.
31), C (44, 43, 13) and D (1,97,
2) Each raw material is mixed so that it falls within the area surrounded by the straight line connecting each point, and the amount of ammonium compound and/or amine compound is approximately 0.2 to 100 moles per mole of Zr.

If the composition ratio of each raw material in the reaction mixture is outside the above range, the crystallization rate is slow, the yield is low, amorphous products are mixed, unreacted raw materials remain, or undesired results may occur. Problems such as becoming a crystalline substance containing a crystalline form or two layers occur. The mixed liquid in which each raw material is uniformly dissolved or dispersed may be in the form of a transparent solution or a slurry containing undissolved excess raw materials. The concentration of the reaction mixture is 1,7r from 0.01 to 25%.
The concentration is preferably 0.1 to 10%. A dilute solution with a Zr content of less than 0.01% is economically disadvantageous, while a Zr content of more than 25% precipitates carboxylates, phosphates, etc. It becomes difficult to filter and wash the quality zirconium phosphate with water. The reaction mixture as described above is subjected to the reaction at a pH of 10 or less, preferably at a pH of 0.5 to 7. When the DH of the reaction solution is 7 to 10, crystalline zirconium phosphate with a high water content tends to be produced, and when the pH exceeds 10, crystalline zirconium phosphate with a low degree of crystallinity is produced. The trend becomes larger.

pH adjustment agent 8 for the reaction mixture includes mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid; ammonium hydroxide, ammonium hydrogen carbonate,
Examples include ammonium and alkali metal hydroxides and carbonates such as sodium hydroxide, potassium hydroxide, and sodium carbonate. The reaction temperature (in the present invention, the reaction of raw material components and the crystallization reaction of crystalline zirconium phosphate by aging are collectively referred to as reaction) is preferably 50° C. or higher. If the reaction temperature is less than 50°C, it will take a long time to crystallize the desired product, which is economically disadvantageous. The upper limit of the reaction temperature is not particularly limited, but is approximately 200° C. from the economic point of view. The reaction time can vary widely depending on the type of raw materials (that is, the reactivity of the raw materials), the blending ratio of the raw materials, the concentration of the reaction mixture, the temperature and pH, the desired degree of crystallinity of the reaction product, etc., but is usually 30 It takes about 20 minutes to 20 days.

Examples of zirconium compounds used in the production of crystalline zirconium phosphate include compounds that are water-soluble or become water-soluble due to oxidation; Zirconium, zirconium sulfate, basic zirconium sulfate, zirconium salts of mineral acids such as zirconium nitrate, zirconium salts of organic acids such as zirconyl acetate and zirconyl formate, ammonium zirconium carbonate, sodium zirconium sulfate, ammonium zirconium acetate, sodium zirconium oxalate, Examples include zirconium complex salts such as zirconium ammonium citrate. Among these compounds, zirconium oxychloride, zirconium sulfate, etc. are more preferred.

Examples of the carboxylic acid compound include aliphatic polycarboxylic acids having two or more 1-COOH groups that are water-soluble or become water-soluble with an acid, and salts thereof. Specifically, oxalic acid,
Aliphatic dibasic acids and their salts such as sodium oxalate, sodium hydrogen oxalate, ammonium oxalate, ammonium hydrogen oxalate, lithium oxalate, maleic acid, malonic acid, succinic acid and their salts: citric acid, citric acid Examples include aliphatic oxyacids such as ammonium acid, tartaric acid, and malic acid, and salts thereof. Among these, oxalic acid and its sodium and ammonium salts are more preferred.

Examples of the phosphoric acid compound include compounds that are water-soluble or become water-soluble with an acid. Specifically, at least one of the alkali metal salts and ammonium salts of orthophosphoric acid such as phosphoric acid, monobasic sodium phosphate, dibasic ammonium phosphate, and tribasic sodium phosphate: methaline, pyrophosphoric acid, etc.
Examples include alkali metal salts and ammonium salts of condensed phosphoric acid having P-0-P bonds. Among these, ammonium salts of phosphoric acid and orthophosphoric acid are more preferred.

Examples of ammonium compounds and amine compounds include compounds that are water-soluble or become water-soluble with acid. Examples of ammonium compounds include inorganic ammonium compounds such as ammonium chloride, ammonium sulfate, ammonium nitrate, and ammonium hydrogen carbonate; and organic ammonium compounds such as tetrapropylammonium hydroxide and tetraethylammonium hydroxide. When at least one of the above-mentioned zirconium compound, carboxylic acid compound, and phosphoric acid compound is an ammonium-containing compound, these can be simultaneously used as an ammonium ion source. Amine compounds include monoethanolamine, jetanolamine, triethanolamine, di(
Examples include N-butyl)amine, triethylamine, tripropylamine, pyridine, and N,N-dimethylethanolamine. Among these, ammonium phosphate, aqueous ammonia, ammonium chloride and ammonium oxalate are more preferred.

Produced crystalline zirconium phosphate Hn R1-nZr
2(PO4)3-mH20 (where n1R and m are the same as above) is separated from the liquid phase by known means such as filtration, decantation, centrifugation, etc., and then washed.
Dehydrated and dried according to conventional methods, and further dried at 1080° C. if necessary.
Heat treated at temperatures below 'C. Drying methods include heat drying, air drying, or removal of adsorbed water using a desiccant such as phosphorus pentoxide, calcium chloride, or silica gel. If the heat treatment is carried out at a temperature higher than 1080°C, the desired crystal form will be deformed and zirconium birophosphate (ZrF20y
) etc.

The crystalline zirconium phosphate obtained in this way is
It has a chemically and thermally stable three-dimensional network structure, and contains ammonium ions, hydrogen ions, and H20 with a small molecular diameter.
It is thought to have a zeolite-like tunnel structure that partially contains molecules, etc. in microscopic pores with a network structure.

It is thought that the cesium to be fixed is taken into the pores, and is less directly affected by the external environment.
This makes it difficult for it to leak outside.

In the present invention, the shape of crystalline zirconium phosphate is not limited, and cesium can be adsorbed and immobilized in any shape such as powder or granules. Therefore, a shape suitable for handling may be used depending on the method of use. Further, it may be formed into an arbitrary shape by applying pressure or adding a binder, or it may be used after being fired.

In the present invention, the state of cesium as radioactive waste is not limited, and any form such as powder or solution can be stably immobilized.

To immobilize cesium by the method of the present invention, first,
When cesium is in solid form, crystalline zirconium phosphate and cesium as a fixing agent are mixed to form a homogeneous mixture; when cesium is in solution, the fixing agent and cesium in solution are mixed together. and evaporate to dryness to obtain a homogeneous mixture. When cesium is in the form of a solution and contains an acid, for example, when using a cesium nitrate solution containing a large amount of free nitric acid, zirconium phosphate does not undergo deterioration or change due to the acid. There is no need to neutralize or remove the acid during evaporation to dryness, and a homogeneous solid mixture can be obtained by evaporation to dryness using a known method.

In the present invention, the ratio of the amounts of zirconium phosphate and cesium used is as follows in terms of molar ratio, and preferably:
It shall be 0.9 or less.

If this ratio exceeds 1, cesium will leach out from the immobilized body, which is not preferable.

Next, a mixture of zirconium phosphate and cesium is heated at 400 to 1250°C, preferably 550 to 11oO
Heat treat at ℃. When the heat treatment temperature is lower than 400° C., the amount of cesium immobilized decreases, a sufficiently stable immobilized body cannot be obtained, and especially the chemical resistance becomes insufficient. Also 125
Temperatures higher than 0° C. are not necessary for fixing cesium, and therefore are disadvantageous in terms of energy, and furthermore, the processing vessel is limited to one with high heat resistance, which is not preferable. The heat treatment time is not limited as it depends on the heat treatment temperature, but
Generally, when heat treatment is performed at high temperatures, a short time is sufficient;
Heat treatment at low temperatures requires a long time.

In the present invention, by heating a mixture consisting of cesium and zirconium phosphate, crystalline zirconium cesium phosphate HCs Zr (PO4)3 (0≦n<1)n
1-n 2 is generated. For example, in the case of n-Q in the above formula, it is thought that the immobilization of cesium nitrate follows the reaction formula below.

Hzra (POA)3 +C3NO3-C8Zr
a (POa )3+HNOs Crystalline zirconium cesium phosphate (hereinafter referred to as the immobilized substance), which is the immobilized form of cesium obtained by heat treatment in the present invention, is a stable crystalline substance and has resistance to salts, acids, alkalis, etc. It has excellent chemical resistance, water resistance, heat resistance, etc. Further, in this immobilization reaction, no by-products that would inhibit the stability of the immobilized product are produced. Furthermore, since cesium does not volatilize in this fixation reaction, equipment such as a heating container used for heat treatment is not eroded, and equipment made of special materials is not required.

In the present invention, the immobilized body may be pressure-molded in order to reduce the volume of the immobilized body, and the mixture of crystalline zirconium phosphate and cesium may be heated and molded simultaneously using a hot press. can. mata, theolite, tl
Oxides such as O2, 5I02, and Zr0z, glasses, metals and salts that become stable when heated may be added to the mixture and fixed by heating and sintering.

1 bean standing lid 1 The method of the present invention provides the following excellent effects.

■ There is no volatilization of cesium in the reaction in which crystalline zirconium phosphate fixes cesium, and equipment etc. are not affected.

■ No by-products are generated during the immobilization reaction that would inhibit the stability of the immobilized body.

(2) The immobilized body is stable to heat, and its crystalline phase becomes even more stable by heat treatment.

■ The immobilized body has excellent water resistance and does not leach cesium even when exposed to high temperature water.

■ The crystalline phase of the immobilized product does not change even when it comes into contact with high temperature and high concentration salts.

■ The crystalline phase of the immobilized product does not change even with strong acids, such as aqua regia.

■ The crystalline phase of the immobilized product does not change even when it comes into contact with a high-temperature alkaline aqueous solution.

■ The crystal phase of the immobilized body does not change even when it comes into contact with high-temperature acidic gas, such as sulfuric acid gas.

The immobilized body obtained by the method of the present invention has a strong bond with a three-dimensional structure, and has excellent heat resistance and chemical resistance as described above.
Cesium as radioactive waste can be stably retained for a long period of time without its crystalline state changing due to radiation or the like.

JLI The present invention will be explained in more detail with reference to Examples below. In the examples, instead of the radioactive cesium compound, a natural cesium compound extracted from volcite ore and purified was used. Since radioactive cesium compounds and natural cesium compounds have the same chemical properties, it is thought that the same results as in the examples can be obtained even when radioactive cesium is used.

Example 1 Ammonium chloride 44.60, oxalic acid dihydrate 116
．． Zirconium oxychloride, sodium phosphate dihydrate, equivalent to 55.8 g in terms of lJ, zr02 58. O
A mixed solution (3000G) obtained by sequentially adding J to water was diluted with aqueous ammonia to pl-13,8 and kept in a thermostatic chamber at 90°C for 3 days. Treating the obtained reaction product,
After washing with water, the dehydrated crystalline material was heat treated at 650°C for 3 hours,
After cooling, it was poured into water, dispersed in water, and left in water for 2 days.

This dispersion was then suctioned and air-dried indoors for 2 days to obtain 63.3G of white powder. This product was analyzed to contain 49.7% ZrO2, 3.0% P205, and 8207.3%, giving a product composition of 4ZrOa.3P205.4H20 expressed in molar ratio of oxides.

Furthermore, the peak position and intensity of this product measured by X-ray diffraction are shown in FIG. Further, the results of thermobalance-differential thermal analysis are as shown in FIG. This white powder can be analyzed by X-ray diffraction,
From the results of thermobalance-differential thermal analysis and chemical analysis, crystalline zirconium phosphate H2r2 (POa) s ・1, 58
It was confirmed that 20 tealcos.

H2r2 (POa)3 ・1 obtained in this way
．． Add 238.C1 of sNO3 aqueous solution to 5H2055, OQ [crystalline zirconium phosphate:cesium nitrate - 1:0.55 (molar ratio)], and after thorough dispersion, evaporate in an evaporating dish. It was dried and solidified.

This dried product was placed in a porcelain crucible and heat-treated for 4 hours in an electric furnace adjusted to 700°C to obtain 60 g of white powder. The obtained white powder had no change in appearance from the powder state before heat treatment, and no change was observed in the crucible container. A cesium leaching test was conducted on the white powder after heat treatment using the following method.

(a) Cesium leaching test sample in pure water 5. OQ was immersed in IOO* distilled water, heated and stirred for 7 hours while refluxing using a magnetic hotspot stirrer, then stopped heating and left to stand for 17 hours, and this was repeated 7 times. The amount of leaching was measured by atomic absorption spectrometry.

(b) Cesium leaching test in various chemical solutions Instead of the pure water used in the leaching test in (a), N/10 NaO
H,N/10 HCl3.5%NaCQ and saturated C
Using each aqueous solution of (OH)2, the amount of cesium leached was measured in the same manner as in (a).

(c) Leaching test sample of cesium in aqua regia
:1), stirred for 7 hours at an exchange temperature, and allowed to stand for 17 hours, which was repeated 7 times, and the amount of cesium leached was measured by atomic absorption spectrophotometry.

(d) Reactivity with powdered drugs Each powdered drug of NHt H80t, Na2COs, and H3803 was separately added to 5.0 g of the sample for 3. After adding OQ and uniformly mixing in a mortar, heat treatment was performed in an electric furnace at 550°C for those to which NHa +soL had been added, and at 450°C for the others for 6 hours. After cooling, each heat-treated product was heated to 100%
- and heated under reflux for 18 hours, and the amount of cesium leached and released was measured by atomic absorption spectrophotometry.

As a result of conducting the cesium leaching tests described in (a) to (d) above, no cesium leaching was observed in all cases.

Therefore, it is clear that crystalline zirconium phosphate with immobilized cesium has excellent water resistance and chemical resistance.

Example 2 Crystalline zirconium phosphate H obtained in the same manner as Example 1
2r2 (Pot)3 ・1.5H205, 5.0% C5NO3 aqueous solution is added to Oa, and cesium nitrate is 0.3.0.6.0.8 per mole of zirconium phosphate.
and 160 mol of each mixed solution was prepared. After each liquid mixture was evaporated to dryness at 110°C, it was pulverized to obtain a homogeneous mixture, and the mixture was heat-treated at 700°C for 3 hours in an electric furnace. For each sample, N/
A cesium leaching test was conducted using 108C12. The results are shown in Figure 4. In addition, in Fig. 4, the vertical axis is 1
Shows the amount of cesium leached per day.

From FIG. 4, it is clear that when the amount of cesium is less than 0.6 mole per mole of zirconium phosphate, there is almost no leaching of cesium. Further, even when cesium was 1 mole, the amount of leaching was as low as 1.2×10'g/C■''-day.

Example 3 Same as Example 2 and TH7r2 (Pot)s ・1
, 5H201, Omo) For It 1: CS N
A mixed solution containing large amounts of O5O13, 0, 6, 0, 9, 1, 2, and 1.5 moles was prepared, evaporated to dryness, and then heat treated at 680°C for 5 hours in an electric furnace. The material was subjected to X-ray diffraction analysis. Figure 5 shows the X-ray diffraction pattern. In FIG. 5, the 0 mark is the diffraction peak of zirconium cesium phosphate, the Δ mark is the zirconium phosphate diffraction peak, and the X mark is the diffraction peak of soluble cesium.

From Figure 5, the amount of CsNOs added is HZ r 2 (POi
)3 ・1.5H It can be seen that if the amount is less than 0.9 mole per mole of 20H, only crystals of cesium zirconium phosphate will be produced, but if it is more than 1.2 mole, soluble cesium will be produced.

Example 4 In the same manner as in Example 1, a mixture obtained by crystallization, washing with water, and dehydration was heat-treated at 650° C. for 5 hours in an electric furnace. The obtained substance was confirmed to be crystalline zirconium phosphate H2r2(POA)3 from the results of X-ray diffraction and compositional analysis. This crystalline zirconium phosphate 59.8a was added with a 5% by weight CsN0a aqueous solution 298. (crystalline zirconium phosphate:cesium nitrate - 1:0.6 (molar ratio)), evaporated to dryness, and separated the dried product into approximately 10g portions in an electric furnace at 600°C and 700°C. , 800°C, 1000°C and 1200°C for 5 hours.

The X-ray diffraction pattern of the heat-treated product is shown in FIG. In Figure 6, C is the diffraction peak of CsNOs, Δ is H2r2 (Po
t)a f) Diffraction peaks, O is the diffraction peak of cesium zirconium phosphate, P is the diffraction peak of pyrophosphate, a high temperature product of H2r2(Pot)a.

This heat-treated product was subjected to a cesium leaching test using N/10 HCQ in the same manner as the leaching test in Example 1 (b). The results are shown in FIG.

It is clear from FIG. 7 that no cesium leaches out when the heating temperature is 700° C. or higher. Also, the heating temperature is 60
The cesium leaching layer at 0°C is also 9,5X 10-'o
/cm2-day was very small.

Also, from Figure 6, at 1200°C, the excess HZ r
It can be seen that 2 (P Ot ) 3 has changed to pyrophosphate, which is a high temperature product, but the leaching test results in Figure 7 show that there is no cesium leaching even when the heating temperature is 1200°C. It is clear that the stability of zirconium cesium phosphate is not inhibited.

Example 5 Zirconium phosphate was prepared by various methods shown below.

(a) Zirconium oxychloride crystal Zr0Ca, 8H
Add water to 20114, 5Q to dissolve it and make the liquid volume 7009
After that, add oxalic acid crystal H2C No. 20/2820 to this.
1000 g of an aqueous solution containing 62.7 g was added with stirring. Next, 350 g of an aqueous solution containing ammonium hydrogen phosphate NH 443.8Q was added to this mixture with stirring, and then 3N aqueous ammonia was added to adjust the pH of the mixture to 4.5. The mixture was dehydrated by keeping it in a thermostatic chamber at 96°C under atmospheric pressure for 5 days, and then the cake-like product was treated in a dry mold at 105°C for 20 hours to obtain a white powder of 58.40. . This white powder was found to be crystalline zirconium phosphate NHa Zr2 (Pot)s from the results of compositional analysis, X-ray diffraction, and thermobalance-differential thermal analysis.

(b) NH4Zrt (POa) obtained in (a)
)s was heat treated in an electric furnace at 580°C for 24 hours. The obtained substance was analyzed in the same manner as in (a) and was confirmed to be crystalline zirconium phosphate H2r2 (Pom)3.

(C) (a) NHa Zrt (PO
A) 3 was heat treated in an electric furnace at 730°C for 10 hours.

The obtained substance was analyzed in the same manner as in (a), and as a result, (
The material b) was found to be crystalline zirconium phosphate H2r2 (Pot)a with a slightly different xsi+ diffraction peak intensity.

(d) NH42r2 (Pot) obtained by (a)
3 was heat-treated at 770° C. for 1 hour in an electric furnace. The obtained substance was analyzed in the same manner as in (a), and the results (b) and (C) showed that the fJ substance was crystalline zirconium phosphate H2r2 (Pot)a with a slightly different X-ray diffraction peak intensity.
It turned out to be.

(e) NHA Zr2 (Pot
)s was heat-treated at 540° C. for 1 hour in an electric furnace. The obtained substance was analyzed in the same manner as in (a), and as a result, NHa
It was found to be a mixture of Zr2(POa)3 and H7r2(Pot)3.

(f) Zirconium oxychloride crystal Zr0cI22 ・
Add water to 8H2019, 6Q to dissolve it, and reduce the liquid volume to 200
g, and then add oxalate crystal HaCzOt ・2
300 g of an aqueous solution containing H2012,6Q was added with stirring. This mixture was then added with ammonium hydrogen phosphate (9
Aqueous solution 1 containing 12.6 g of 8% NHA H2Pot
After adding 00 g with stirring, 3M constant ammonia water was added to adjust the pH of the mixture to 3.5. This mixture was kept in a thermostatic chamber at 96% atmospheric pressure for 3 days, filtered and washed with water, and the cake-like product obtained was dried in a constant temperature and humidity atmosphere at 32°C and 40% humidity to produce a white powder of 15.2 oz. I got it. This white powder was found to be NHt Zr2 (Pot)a from the results of compositional analysis, thermobalance-differential thermal analysis, and X-ray diffraction, and was γ-type zirconium phosphate (general formula, 7 8 NHa Zr (Pot)a) containing ammonium as an impurity. PO4)2n
2-n·mH2O, O≦n≦2).

(0) Zirconium oxychloride crystal 22.6Q1 oxalic acid crystal 8.1g and ammonium hydrogen phosphate (85,4
Using %NH482PO direct) 7.4a as a raw material, a cake-like product was obtained in the same manner as in (r). This cake-like product was heat-treated in a dry mold at 105° C. for 24 hours to obtain 144 g of a white lump. Composition analysis, thermobalance - differential thermal analysis, X
According to the results of line diffraction, this white lump is NHA Zr2
(POz)3, and it was found that it contained a zirconium compound with high water content and poor crystallinity as an impurity.

Each of various crystalline zirconium phosphates obtained by the methods of (a) to (g) or crystalline zirconium phosphate containing impurities 5.0 to 1 (however, the one obtained by (L) is 50Q), Add 21.60% of a 5.0% by weight C8NO3 aqueous solution (all cesium/crystalline zirconium phosphates are 0.0%).
After being well dispersed, the mixture was evaporated to dryness, and the dried product was heat-treated in an electric furnace at 750° C. for 3 hours to fix cesium.

Next, the heat-treated product was immersed in 100-g distilled water, and a cesium leaching test was conducted in the same manner as in Example 1 (a), and the amount of cesium leached was measured by atomic absorption spectrophotometry. , no leaching of cesium was observed.

[Brief explanation of drawings]

Figure 1 shows a zirconium compound (as Zr), a carboxylic acid compound (as C20), and a phosphoric acid compound (as P) for producing crystalline zirconium phosphate used in the present invention.
FIG. Fig. 2 is a graph showing the peak position and intensity of the crystalline zirconium phosphate synthesized in Example 1 by X-ray diffraction, and Fig. 3 is a thermobalance-differential thermal analysis of the crystalline zirconium phosphate synthesized in Example 1. 4 is a graph showing the cesium leaching test results of Example 2, FIG. 5 is an X-ray diffraction diagram of Example 3, FIG. 6 is an X-ray diffraction diagram of Example 4, and FIG. is a graph showing the cesium leaching test results of Example 4. (That's all) Figure 1 Zr (tiL%) Figure 4

Claims (1)

[Claims] [1] (i) (a) General formula H_nR_1_-_nZr_2(PO_4)_3·mH
_2O (wherein R represents NH_4 or an amine cation, 0≦n≦1, 0≦m≦2); (b) a crystal represented by the formula 4ZrO_2.3P_2O_5 as an oxide according to analytical calculations; Mix crystalline zirconium phosphate and (ii) radioactive cesium and/or cesium compound so that (iii) cesium/crystalline zirconium phosphate (molar ratio) = 1 or less, (iv) at 400 to 1250°C. A method for immobilizing radioactive cesium, which is characterized by heat treatment.