JPS621293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to adsorption and exchange materials for strontium ions in aqueous solutions.

High-level radioactive waste liquid contains strontium, which is dangerous and can cause pollution if left untreated.

For this purpose, it is important to selectively adsorb and separate it, fix it, and confine it within a crystal to ensure safety.

Conventionally, the only known method for separating strontium from high-level radioactive waste liquid is to exchange strontium ions with sodium ions using zeolite. However, the exchange capacity and selectivity are small, and there are also safety problems in post-adsorption processing (immobilization).

The present invention aims to improve the drawbacks of conventional methods, and provides a strontium ion adsorption and ion exchange separation material that has high selectivity and adsorption or ion exchange properties for strontium ions, and has excellent immobilization. There is something to do.

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 the fibrous potassium titanate with an acid aqueous solution, etc., the fibrous titanium hydrate TiO ₂ We succeeded in producing mH ₂ O (m=0 to 3). (Special Application No. 53-676856,
54-93460) Further, as a result of continuing research on the properties of the obtained fibrous titanium hydrate, it was found that the fibrous titania hydrate adsorbs and ion-exchanges strontium in an aqueous solution and becomes a strontium adsorbent Sr _x O.・_nTiO2・
mH ₂ O (where x is 0.5 to 1, n = 2 to 8, m
= 2 to 8).

The present invention was completed based on this knowledge.

The titanium 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 containing strontium. 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 strontium in an aqueous solution may be carried out by immersion in the aqueous solution or by passing the strontium aqueous solution through a column filled with an adsorbent.

Strontium in an aqueous solution is absorbed by the strontium adsorbent Sr _x O・nTiO ₂・mH ₂ O (where x, n,
m is the same as above). The amount of adsorption and the amount of ion exchange vary depending on the concentration of strontium, hydrogen ion concentration, reaction time, temperature, etc. Further, the values of x, n, and m can be determined by heat-treating the adsorbent at a temperature of around 1000° C. to crystallize it, and identifying the synthesized phase using X-ray powder diffraction.

The strontium adsorption and ion exchange material of the present invention is a titanate, and strontium is immobilized in the TiO ₆ octahedral connection mode.
The immobilization is superior compared to that of traditional silicate zeolites, which are immobilized in the SiO ₄ tetrahedral linkage mode. In addition, although the radiation decay process generates considerably high temperatures, it is stable even at high temperatures, and is particularly stable under hydrothermal conditions (700℃, 1000 atm hot water), making it an excellent material for stably fixing strontium. have an effect.

In addition, in the present invention, when producing K ₂ O・nTiO ₂ , the flux method uses a method similar to that of the starting fiber composition.
Na ₂ O may be mixed in, and there is no problem even if Na ₂ O is mixed in as an impurity even in the melting method. but,
When the amount of Na ₂ O increases, it coexists with potassium hexatitanate, rutile, etc. in the flux method, and defibration 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° 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. The resulting fibrous crystalline mass was defibrated by immersing it in water for about 2 hours. The diameter of the defibrated fiber is 0.1
They were in the form of bundles of ~0.5 mm, with an average length of 5 mm.
Since this fiber has poor crystallinity, it was heated at 900°C for 30 minutes. This was a mixed phase fiber of K ₂ Ti ₄ O ₉ and K ₂ Ti ₂ O ₅ .

(ii) Flux method TiO ₂ and K ₂ CO ₃ powders in a molar ratio of 1:0.33
A composition with a proportion of {(K ₂ O) 1/3・TiO ₂ },
Furthermore, K ₂ MoO ₄ powder was mixed in a mol% ratio of 30:70. Approximately 80 g of the mixture was filled into a approximately 100 ml platinum crucible, heated and melted at 1130°C for 4 hours, slowly cooled to 950°C at a rate of 8°C/h, heated and melted again at 1130°C for 4 hours, and then melted at 1130°C for 4 hours.
Fibers were grown by slow cooling to 950°C at a rate of °C/h and repeated growth reactions.

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 }, {(Na ₂ O) 1/3・
TiO ₂ } was used, but the actual product is
K ₂ Ti ₄ O ₉ fibers were produced, and relatively long fibers were obtained without any particular adverse effects observed. moreover
When a large amount of the Na ₂ O 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) The fibers obtained by the method (1)-(i) above were
Approximately 1 at a ratio of 10g to 100ml 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 10g at a ratio of 10g to 100ml 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 titania hydrate is 2θ=
The most intense peak is at 9.8°, 17.8°, 24.3
It shows comparatively weak but sharp diffraction peaks at angles such as ゜, 27.3゜, 30.0゜, 33.7゜, and 37.5゜.

(3) Adsorption and ion exchange of strontium in aqueous solution (i) 2 g per 1 saturated aqueous solution of 0.04MSrOH
The titania hydrate fibers produced by the method (2)-(i) above were soaked for 6 days without stirring, and then filtered and air-dried.

As a result of chemical analysis of this adsorbent,
_{The composition of Sr0.9Ti4.0O8.9}・_{6.7H2O is} shown _. The exchange capacity for strontium of this composition is
It is 4.5meq/g.

This powder X-ray diffraction diagram shows that 2θ=25.2°,
Broad peaks were observed around 25.6°, 36.4°, and 44.0°. The product that was heat-treated at 1000℃ for 30 minutes was identified from the powder X-ray diffraction pattern as strontium titanate SrTiO ₃ and rutile.
It became a mixed phase of TiO ₂ . This follows the reaction:

SrTi ₄ O ₉ →SrTiO ₃ +3TiO ₂ (ii) The titanium hydrate fiber produced by the method (2)-(ii) above is soaked in the same manner as in (3)-(i) above,
Air-dried.

Results of chemical analysis of this adsorbent
_{The composition is Sr 1.0 Ti 6.0 O 13.0 ・}6.7H ₂ O. The exchange capacity for strontium of this composition is
It is 3.8meq/g. This powder X-ray diffraction diagram shows a sharp strongest line peak at 2θ = 8.1°, as well as 15°, 16.1°, 23.9°, 26.6°,
Broad peaks were observed around 30°, 34°, and 41°.

When the adsorbent was heat-treated at 1000° C. for 30 minutes, a mixed phase of strontium titanate SrTiO ₃ and rutile TiO ₂ was identified from powder X-ray diffraction. This follows the reaction:

SrTi ₆ O ₁₃ →SrTiO ₃ +5TiO ₂

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)
A material for adsorbing and exchanging strontium ions in aqueous solutions. 2. The adsorption and exchange material for strontium ions 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.