JPH0450063B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an adsorption and ion exchange material for barium in an aqueous solution and a method for immobilizing barium. High-level radioactive waste liquid contains a relatively large amount of barium, and if left untreated, it can cause pollution and be dangerous. Conventionally, a known method for solidifying barium from high-level radioactive waste liquid is to solidify barium together with other nuclides using borosilicate glass. However, since the borosilicate vitrification method uses nitrates and the like during solidification, it requires a high melting temperature during melting and the crucible material is eroded.
In addition, the solidified material has poor durability as phase separation and crystallization occur due to aging and accumulation of decay heat, and the leaching rate of barium from the solidified material is on the order of 10 ^-7 g/cm ² ·day, which is large. There are drawbacks. The present invention aims to improve the shortcomings of conventional methods, and provides a barium adsorption and ion exchange separation material that has high adsorption or ion exchange properties for barium and has a low leaching rate of barium from the solidified body; To provide an immobilization method. The present inventor first formed a fibrous material from a melt of TiO ₂ and K ₂ O to produce fibrous potassium titanate.
By eluting _the K _{2 O} component from this fibrous potassium titanate with an acid aqueous solution, etc., the fibrous titanium hydrate TiO ₂ succeeded in reducing mH ₂ O (where m=0 to 3)
No. 93460). Furthermore, as a result of continuing research on the properties of the obtained fibrous titania hydrate, it was found that the fibrous titania hydrate adsorbs and ion-exchanges barium in an aqueous solution, forming a barium adsorbent BaO・nTiO ₂・mH ₂ O. (However, it was found that n=2-10, m=2-8). Further, when the barium adsorbent is heated at a temperature around 1000°C, it becomes an immobilized body consisting of a mixture of barium titanate BaO·nTiO ₂ (where n=4 to 5) and titanium dioxide. This type of immobilized body forms a highly durable and stable mineral phase. It has also been found that when this is pressure-molded and sintered, the barium leaching rate is further reduced and the durability is excellent.
Furthermore, it has been found that even if the barium adsorbent is pulverized, pressure-molded, and directly sintered, the same immobilized mineral phase can be obtained. The present invention was completed based on this knowledge. The titania hydrate used in the present invention may be in any form such as an amorphous gel, an amorphous or crystalline powder or granule, or an amorphous or crystalline fibrous material. Although it can be obtained by adsorption or ion exchange, fibrous materials are preferable because they have a large adsorption amount and are easy to handle, and fibrous materials having a crystalline layered structure are particularly preferred. Adsorption and ion exchange of barium in aqueous solution is
The barium aqueous solution may be immersed in an aqueous solution or passed through a column filled with an adsorbent. Barium in aqueous solution is barium adsorbent
BaO·nTiO ₂ ·mH ₂ O (where n and m are the same as above). The adsorption amount and ion exchange amount vary depending on barium concentration, hydrogen ion concentration, reaction time, temperature, etc. In addition, the values of n and m are determined by heating the adsorbent at a temperature of around 1000°C to crystallize it.
The synthetic phase can be identified and determined using X-ray powder diffraction. To immobilize barium, the strontium adsorbent is heat-treated at a temperature of 900 to 1300°C to form a mixture of barium titanate and titanium dioxide (rutile phase). Next, the mixture is pressure-molded at a pressure of 5Kg/cm ² to 500Kg/cm ² and then sintered at a temperature of 1000°C or higher and lower than the melting temperature, which reduces the volume and reduces barium leaching rate, increasing durability. The result will be a large one. Instead of this two-step method of pressure forming and sintering, pressure forming and sintering may be performed simultaneously using a hot press method.
Alternatively, the barium adsorbent may be directly pressure-molded and sintered, or may be directly hot-pressed. The barium adsorption and ion exchange material of the present invention includes:
The material is titanate, which immobilizes the barium in a TiO ₆ octahedral linkage pattern, which provides superior immobilization compared to traditional immobilization in borosilicate glass. Stable even at high temperatures. In addition, in the present invention, K ₂ O・nTiO ₂ (n=2
In the production of items 4) to 4), in the flux method, Na ₂ O may be mixed into the starting fiber composition, and in the melting method, Na ₂ O may be mixed in at the same level as an impurity. However, when the amount of Na ₂ O increases, it coexists with potassium hexatitanate, rutile, etc. in the flux method, and fiber separation becomes difficult in the melt method. Example 1 (1) Production of fibrous potassium titanate (i) Melting method TiO ₂ and K ₂ CO ₃ powders were mixed at a molar ratio of 2:1. Approximately 45 g of the mixture was filled into a 100 ml platinum crucible and melted by heating at 1000 to 1100° C. for 30 minutes. The melt was discharged into another metal container (the bottom of which was water-cooled from the outside), where it was rapidly cooled and crystallized into fibers. This crystallized product was a single phase fiber of K ₂ Ti ₂ O ₅ . The resulting fibrous crystalline mass was
It was defibrated by immersing it in water for about 2 hours. The defibrated fibers were bundles with a diameter of 0.1 to 0.5 mm and an average length of 5 mm. This fiber has poor crystallinity, so
Heated at 900°C for 30 minutes. This is K ₂ Ti ₄ O ₉ and
The fiber was a mixed phase of K ₂ Ti ₂ O ₅ . K ₂ Ti ₄ O ₉
The formation of the phase was due to some potassium in the K ₂ Ti ₂ O ₅ phase being eluted with water. (ii) Flux method TiO ₂ and K ₂ CO ₃ powders in a molar ratio of 1:0.33
The composition {(K ₂ O) _1/3 ·TiO ₂ ) was mixed with K ₂ MoO ₄ powder in a ratio of 30:70 (mol%). Approximately 80 g of the mixture was filled into a platinum crucible of approximately 100 ml, heated and melted at 1150°C for 4 hours, and then slowly cooled to 950°C at a rate of 4°C/h to grow fibers. The obtained fibrous crystalline material was taken out from the crucible by dissolving the flux with water. The fibers were aggregates of bundle-like single crystals with an average length of 2 mm and a diameter of 0.05 to 0.1 mm, and were composed of a single K ₂ Ti ₄ O ₉ phase. In addition, by using Na ₂ CO ₃ instead of the fiber composition {(K ₂ O) _1/3・TiO ₂ }, the fiber composition {(Na ₂ O) _1/3・TiO ₂ }
However, the actual product was K ₂ Ti ₄ O ₉ fibers, and relatively long fibers were obtained without any particular adverse effects. Furthermore, when a large amount of Na ₂ CO ₃ component is added, a mixed phase of potassium hexatitanate (K ₂ Ti ₆ O ₁₃ ), rutile (TiO ₂ ), etc. is formed. (2) Production of fibrous titania hydrate (i) Melt-processed fiber The fiber obtained by the method (1)-(i) above is
Approximately 10 at a ratio of 10g to 1000ml of HCl aqueous solution
immersed in the aqueous solution for an hour to extract the _K2O component;
The titanium hydrate was obtained by washing with water and air drying. The X-ray powder diffraction pattern of the titanium hydrate using a copper anticathode showed that it was a crystalline fiber showing broad peaks around 2θ=10°, 25.6°, and 48.6°. (ii) Flux method fiber The fiber obtained by the method (1)-(ii) above is
Approximately 10 at a ratio of 10g to 1000ml of HCl aqueous solution
immersed in the aqueous solution for an hour to extract the _K2O component;
The titanium hydrate was obtained by washing with water and air drying. The X-ray powder diffraction diagram of the titania hydrate shows the strongest peak at 2θ = 9.8°, 17.8°, 24.3°, 27.3°,
It shows relatively weak but sharp diffraction peaks at 30.0°, 33.7°, 37.5°, etc. (3) Adsorption and ion exchange of barium in aqueous solution (i) 0.1MBa(OH) _2g per 100ml of aqueous solution
The titania hydrate fibers produced by the method (2)-(i) above were soaked for 10 days while stirring at 200 rpm, and then filtered and air-dried. As a result of chemical analysis of this adsorbent, BaTi _4.2
The composition of O _9.4・5.5H ₂ O was shown. The exchange capacity for barium of this composition is 4.9 meq/g. The barium content is 23.4wt%. (ii) Soaking the titania hydrate fiber produced by the method in (2)-(ii) above in the same manner as in (3)-(i) above,
Air-dried. Results of chemical analysis of this adsorbent
The composition of BaTi ₈ O ₁₇・5.7H ₂ O is shown. The exchange capacity for barium with this composition is 2.6meq/
It is g. The barium content is 15.3wt%. (4) Molding/immobilization The two types of barium adsorbents obtained in (3) above were crushed, and about 0.2 g was made into pellets with a diameter of 1.3 cm and a thickness of 0.1 cm under a pressure of 500 Kg/cm ² . After molding, 1000
It was baked at 1200°C for 1 hour. The obtained immobilized mineral phase was as shown in Table 1 below.

[Table] The mineral phase of both adsorbents after firing at 1200°C for 20 hours was the same as when firing for 1 hour. Barium pentatitanate BaTi ₅ O ₁₁ was found to decompose into barium tetratitanate (BaTi ₄ O ₉ ) and rutile at temperatures between 1100 and 1200 °C. The specific surface area of the obtained sintered body was 1×10 ⁵ cm ² /g as measured by nitrogen gas adsorption method. (5) Leaching of barium in pure water 0.3 to 0.4 g of the solidified material obtained by the method (4) above was immersed in 10 ml of distilled water, and changes in the amount of barium leached over time were examined at room temperature. Regarding the amount of barium leached at each time repeated 7 times at 24 hour intervals
It was analyzed and determined using the EDTA adaptation method. The results are shown in Table 2. The leaching rate was calculated using the following formula. L=A/C・S・T L: Leaching rate (g/cm ² ·day), A = Leaching amount of barium (g) C: Barium content, S: Surface area of sample (cm ² ), t: Leaching time (day).

[Table] The above results indicate that barium leaching is extremely small. Effects of the Invention The titanium hydrate of the present invention has barium adsorption and ion exchange properties, and when it is used to adsorb and fix barium in an aqueous solution, the leaching rate can be extremely reduced. The results are as follows. We believe that this method can be particularly effectively used as a treatment method for high-level radioactive waste liquid.

Claims (1)

[Claims] 1 Potassium titanate K ₂ O・nTiO ₂ (however, n
Titanium hydrate TiO ₂ mH ₂ O obtained by extracting the K ₂ O component from = 2 to 4) (where m = 0 to 3)
Adsorption and ion exchange material for barium in aqueous solution. 2. The adsorption and ion exchange material for barium in an aqueous solution according to claim 1, wherein potassium titanate is obtained by forming a fibrous material of a melt of TiO ₂ and K ₂ O and crystallizing it. 3 Potassium titanate K ₂ O・nTiO ₂ (however, n
Titanium hydrate TiO ₂ mH ₂ O obtained by extracting the K ₂ O component from = 2 to 4) (where m = 0 to 3)
By adsorbing and ion-exchanging barium in aqueous solution, barium adsorbent BaO・nTiO ₂・mH ₂ O
(However, n = 2 to 10, m = 2 to 8), and the barium adsorbent was heated to 900 to 1300°C to form barium titanate BaO・nTiO ₂ (however, n = 4 to 5).
and titanium dioxide. 4. The method for immobilizing barium according to claim 3, wherein the barium adsorbent or the mixture of barium titanate and titanium dioxide is pressure-molded and sintered.