JPH0724764B2 - Composite adsorbent and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composite adsorbent for removing metals in an aqueous solution, particularly radioactive cesium in a radioactive waste liquid, and a method for producing the same. More specifically, the present invention relates to a composite adsorbent composed of a metal cyanide / titanic acid for adsorbing and removing cesium in an aqueous solution, and a method for producing the same.

(Prior Art) A nuclear facility such as a nuclear power plant or a reprocessing plant produces waste liquid containing various radioactive substances. These radioactive waste liquids are separated into radioactive substances and water by operations such as evaporative concentration, ion exchange, and coagulation sedimentation, water from which the radioactive substances have been sufficiently removed is released, and the concentrated radioactive substances vitrify, It is fixed and stored by a method such as asphalt solidification.

Among these methods, the evaporative concentration method has a very high efficiency of separating water and radioactive substances, that is, decontamination efficiency, but the construction cost and operation cost of the evaporation equipment are high, and the material of the evaporation can is corroded. There are drawbacks such as easy to do. On the other hand, the conventional ion-exchange resin method and coagulation-sedimentation method have a drawback that the decontamination efficiency is low, although the equipment construction cost and the operation cost are small. Usually, radioactive waste liquid is mixed with sodium salt used for washing the extractant of nuclear fuel material, so that sodium nitrate is present and its concentration may reach about 1 mol / l. In this case, the evaporative concentration method has a drawback that the sodium salt is precipitated in the residue of the kettle and the concentration ratio does not increase. Therefore, a special evaporative concentration device is required and solidification is difficult. Further, in the ion exchange resin method, when the concentration of sodium nitrate increases, the adsorption amount of monovalent cations such as cesium decreases due to the selectivity of the ion exchange resin, and the decontamination efficiency tends to decrease.
Furthermore, in the coagulation-sedimentation method, it is known that the decontamination coefficient decreases when sodium nitrate is present. For radioactive substances in waste liquid,
It contains various elements such as ruthenium and zirconium having a low solubility as hydroxides, and alkali metals such as cesium and strontium having a high solubility as hydroxides and alkaline earth metals. Of these, the former ruthenium and the like can be considered as a coagulation-precipitation method in which the ruthenium and the like are precipitated as hydroxides by making the liquid alkaline and coprecipitated with iron hydroxide and removed. The removal of the latter alkali metals and alkaline earth metals is very difficult.

Conventionally, a method using an ion exchanger has been widely studied as a method for removing alkali metals and alkaline earth metals. Titanic acid is known as an adsorbent for alkaline earth metals such as strontium and uranium.
As disclosed in JP-A-57-140644, a composite of titanic acid and an acrylonitrile-based polymer, in which the surface area of titanic acid is made extremely large to improve the adsorption ability and, at the same time, the handling property as an adsorbent is improved. The adsorbent molded product is excellent. Further, in order to adsorb and remove an alkali metal such as cesium, a zeolite, a ferrocyanide metal salt or the like is used, but the ferrocyanide metal salt has a higher adsorption capacity than the zeolite and is high in selectivity. Are better.
The amount of radioactive substances such as cesium in the waste liquid is large as radioactivity but very small in concentration, so an adsorbent with high selectivity is useful in the treatment, and when sodium nitrate coexists. In particular, it is required that cesium has higher selectivity than sodium.

In addition, a high adsorption capacity reduces the amount of used adsorbent that becomes secondary waste, and is particularly suitable for the treatment of radioactive waste liquid.

(Problems to be solved by the invention) However, the metal salts of ferrocyanide produce colloidal substances and slimes (mud substances) at the time of synthesis, or are suspended as fine particles and are extremely difficult to settle. Since the property is also poor, it is not easy to remove water from this colloidal substance or slime and dry it. Further, the metal salt of ferrocyanide obtained by distilling water from this colloidal substance or slime is a glue-like brittle substance,
When it is crushed to be packed in a column, it becomes a very fine powder, and when it is obtained in the form of granules with a large surface area necessary for using it as an adsorbent in the column, it has the disadvantage of a very low yield. .

(Means for Solving Problems) As a result of intensive studies to improve these problems, the present inventors have found that titanic acid having a large surface area is alternately contacted with an alkali ferrocyanide solution and a transition metal salt solution. It was found that an extremely superior composite adsorbent of metal salts of ferrocyanide and titanic acid can be easily obtained by causing the reaction to reach the present invention. That is, the object of the present invention is to
It is an object of the present invention to provide a composite adsorbent which is efficiently adsorbed and removed from an alkali metal, particularly cesium, in an aqueous solution and has improved handleability, and a method for producing the same. The composite adsorbent of the present invention is particularly suitable for the decontamination of cesium, and can be used for treating many solutions containing cesium.

The outline of the present invention will be described below.

According to the present invention, an extremely excellent adsorbent can be obtained when a small amount of cesium is removed by utilizing the large surface area of titanic acid. That is, titanic acid is usually
Since it acts as an anion exchanger in acidic or neutral conditions, the ferrocyan ion is first ion-exchanged and adsorbed. Then, the ferrocyan ion and the transition metal ion forming a sparingly soluble salt are brought into contact with each other and reacted. further,
A ferrocyan ion is subjected to a catalytic reaction, and then a transition metal ion is subjected to a catalytic reaction to increase the surface area of the ferrocyanide metal salt and pile up in layers to produce a stable adsorbent having a strong bond. be able to. Moreover, since radioactive cesium can be fixed stably, it is extremely excellent as an adsorbent. In addition, it is considered that titanium ferrocyanide is sufficiently generated in part, and that the coexistence of titanium ferrocyanide shows good results for the adsorption of cesium.

In the production of the metal cyanide / titanic acid composite adsorbent of the present invention, as titanic acid, urea or ammonia water and urea or caustic alkali or ammonia water are added to an aqueous solution of titanium sulfate or titanium tetrachloride for hydrolysis. It is possible to use those produced by a method such as a method in which an aqueous solution of titanium sulfate or titanium tetrachloride is simply heated and hydrolyzed.

The titanic acid may be in the form of powder, granules, spheres, or the like, but in order to support a large amount of metal cyanide salt, a powder having a very large surface area or a composite adsorbent can be used as a column. Considering that it is used after being filled in, the spherical titanate / acrylonitrile copolymer composite adsorbent disclosed in JP-A-57-140644 can also be used.

In the production of the composite adsorbent of the present invention, potassium ferrocyanide, sodium ferrocyanide, ammonium ferrocyanide and the like can be used as the alkali ferrocyanide. In addition, transition metal salts include nitrates of metal ions such as cobalt, zinc, iron, manganese, nickel, chromium, molybdenum, cadmium, tungsten, and copper,
Any sulfate, chloride or other water-soluble salt can be used.

In producing the composite adsorbent of the present invention, the concentration of the alkali ferrocyanide solution and the transition metal salt solution can be used in the range of 1% by weight to the concentration of each saturated solubility, but usually 5 to 30% by weight is used. It is considered easy. further,
The temperature of the solution during the production is in the range from room temperature to the boiling point of each solution, but the production at a temperature close to the boiling point can provide a more excellent composite adsorbent.

In the present invention, for example, after titanic acid / acrylonitrile copolymer composite adsorbent is decomposed into an alkali ferrocyanide solution and reacted by heating and contacting, titanic acid is taken out,
After washing with water, it is transferred into a transition metal salt solution and dispersed therein, and again brought into contact with heat to react. After performing this operation one or more times, it is possible to provide an extremely excellent composite adsorbent by washing with water and storing in water, or by drying. Further, the alkali ferrocyanide solution and the transition metal salt solution used here can be used again after adjusting the concentration by various methods. According to this method, the ferrocyanide metal salt not only causes no colloidation phenomenon, but also has an extremely large surface area, and an adsorbent that does not need to be adjusted in particle size by an operation such as pulverization is obtained. The utilization efficiency of alkali halides and transition metal salts is extremely high.

(Examples) Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1 Titanium sulfate (reagent grade 1, Ti82g / l) was added to a beaker (300 ml).
Add 100 ml and gradually add 73 ml of ammonia water (28%) with stirring. After adding aqueous ammonia, heat on a sand bath, bring to a boiling state for 1 hour, and keep boiling for 30 minutes. Rinse the cooled product thoroughly with water. The titanic acid produced is about 250 ml in the wet state. 3 in this titanic acid suspension
Add 20 ml of 0 wt% potassium ferrocyanide aqueous solution,
Heat on a hot plate at 80 ° C for about 1 hour. The supernatant liquid containing potassium ferrocyanide is transferred to another container, and washed with deionized water about 2-3 times with pure water at 100 ml / time. Then 60
Add 10 ml of a wt% cobalt nitrate aqueous solution and heat on a hot plate at 80 ° C. for about 1 hour. The cobalt nitrate aqueous solution supernatant is transferred to another container and washed with pure water at a rate of about 100 ml / time for 2-3 times. Add the potassium ferrocyanide supernatant again.
Heat on a hot plate at 80 ° C for about 1 hour. The potassium ferrocyanide aqueous solution is transferred to another container and washed with pure water at about 50 ml / time for 2-3 times. Next, the cobalt nitrate supernatant is added and heated on a hot plate at 80 ° C. for about 1 hour.
The cobalt nitrate aqueous solution is transferred to another container and washed with pure water 7 to 8 times by decantation. This composite adsorbent becomes, for example, a fine powder that is dry when air-dried.

The cobalt ferrocyanide / titanate composite adsorbent thus produced was packed in a column having an inner diameter of 8 mm, and a cesium nitrate solution (cesium concentration 100 mg / l, sodium nitrate concentration 4
(0 g / l, neutral) was passed through the column at a flow rate of 1 ml per minute, and a breakthrough curve was created from the effluent amount and the cesium concentration in the effluent. The cesium concentration up to was less than the detection limit (0.06 mg / l) by an atomic absorption spectrometer, and a decontamination coefficient of at least 1000 or more was obtained.

The equilibrium adsorption amount obtained from this breakthrough curve is 0.18 meq / g.
(Dried body).

Example 2 30 ml of a titanic acid / acrylonitrile copolymer composite adsorbent (spherical, 28 to 35 mesh) was placed in a beaker (200 ml), and 10
Add 60 ml of a wt% potassium ferrocyanide aqueous solution and leave it for about 1 hour. The potassium ferrocyanide aqueous solution is transferred to another container, and washed with deionized water at a rate of about 50 ml / time for 2-3 times. Next, 60 ml of a 10 wt% cobalt nitrate aqueous solution is added, and the mixture is left for about 1 hour. The cobalt nitrate aqueous solution is transferred to another container and washed with deionized water about 7 times 8 times with pure water at about 50 ml / time.

The adsorbent thus produced was packed in a column having an inner diameter of 8 mm, and a cesium nitrate solution (cesium concentration 100 mg / l, sodium nitrate concentration 40 g / l, neutral) was passed through the column at a flow rate of 1 ml / min, and When a breakthrough curve was created from the amount of effluent and the concentration of cesium in the effluent, cesium was extremely selectively adsorbed, and the concentration of cesium before breakthrough was below the detection limit (0.06 mg / l) by an atomic absorption spectrometer. And a decontamination factor of at least 1000 or more was obtained. The equilibrium adsorption amount obtained from this breakthrough curve was 0.0077 meq / g (dry matter). Furthermore, the cesium concentration of the cesium nitrate solution is 10 mg.
The equilibrium adsorption amount was 0.0046 meq / g, assuming / l.

Example 3 30 ml of a titanic acid / acrylonitrile copolymer composite adsorbent (spherical, 28 to 35 mesh) was placed in a beaker (200 ml), and 10
60% by weight aqueous potassium ferrocyanide solution is added, and the mixture is heated on a hot plate at 80 ° C. for about 1 hour. Transfer the potassium ferrocyanide aqueous solution to another container, and by the decantation method,
Wash with pure water about 50 ml / time 2-3 times. Then 10% by weight
Add 60 ml of cobalt nitrate solution on the hot plate.
Heat at 80 ° C for about 1 hour. The cobalt nitrate aqueous solution is transferred to another container and washed with deionized water about 7 times 8 times with pure water at about 50 ml / time.

The adsorbent thus produced was packed in a column having an inner diameter of 8 mm, and a cesium nitrate solution (cesium concentration 100 mg / l, sodium nitrate concentration 40 g / l, neutral) was passed through the column at a flow rate of 1 ml per minute, When a breakthrough curve was created from the effluent volume and the cesium concentration in the effluent, cesium was extremely selectively adsorbed, and the cesium concentration before breakthrough was the detection limit (0.06 mg / l) by an atomic absorption spectrometer. The decontamination coefficient was at least 1000 or more. The equilibrium adsorption amount obtained from this breakthrough curve was 0.102 meq / g (dry matter). Furthermore, the cesium concentration of the cesium nitrate solution is 10 mg.
The equilibrium adsorption amount was 0.056 meq / g, assuming / l.

Example 4 A beaker (200 ml) was charged with 30 ml of titanic acid / acrylonitrile copolymer composite adsorbent (spherical, 28 to 35 mesh),
60% by weight aqueous potassium ferrocyanide solution is added, and the mixture is heated on a hot plate at 80 ° C. for about 1 hour. Transfer the potassium ferrocyanide aqueous solution to another container, and by the decantation method,
Wash with pure water about 50 ml / time 2-3 times. Then 10% by weight
Add 60 ml of cobalt nitrate solution on the hot plate.
Heat at 80 ° C for about 1 hour. The cobalt nitrate aqueous solution is transferred to another container, and washed by decantation with pure water at about 50 ml / time for 2-3 times. Again 10 wt% potassium ferrocyanide aqueous solution 60
Add ml and heat on a hot plate at 80 ° C for about 1 hour. Transfer the potassium ferrocyanide aqueous solution to another container,
By decantation, wash with water about 50 ml / time 2-3 times. Next, 60 ml of a 10 wt% cobalt nitrate aqueous solution is added, and the mixture is heated on a hot plate at 80 ° C. for about 1 hour. The cobalt nitrate aqueous solution is transferred to another container and washed with deionized water about 7 times 8 times with pure water at about 50 ml / time.

Take 10 ml each of titanic acid / acrylonitrile copolymer composite adsorbent and titanic acid / acrylonitrile copolymer composite adsorbent loaded with ferrocyanide metal salt,
It was thoroughly washed, air-dried, and each volume and weight were measured. The results are shown in Table 1.

Therefore, it is understood that cobalt ferrocyanide is supported at a ratio of 0.05 (g / ml) on the titanate / acrylonitrile copolymer composite adsorbent.

The adsorbent thus produced was packed in a column having an inner diameter of 8 mm, and a cesium nitrate solution (cesium concentration 100 mg / l, sodium nitrate concentration 40 g / l, neutral) was passed through the column at a flow rate of 1 ml per minute, When a breakthrough curve was created from the amount of effluent and the concentration of cesium in the effluent, cesium was extremely selectively adsorbed, and the concentration of cesium before breakthrough was below the detection limit (0.06 mg / l) by an atomic absorption spectrometer. And a decontamination factor of at least 1000 or more was obtained. The equilibrium adsorption amount obtained from this breakthrough curve was 0.166 meq / g (dry matter).

Comparative Example 1 In order to compare the performance of the adsorbent of the present invention with the performance of zeolite conventionally used for removing cesium in radioactive waste liquid, natural zeolite was packed in a column having an inner diameter of 8 mm, and cesium nitrate (cesium concentration was measured). 100 mg / l, sodium nitrate concentration 40 g / l, neutral) is passed through the column at a flow rate of 1 ml per minute,
A breakthrough curve was created from the effluent volume and the cesium concentration in the effluent. The cesium concentration until the breakthrough was below the detection limit (0.06 mg / l) by an atomic absorption spectrometer, and the equilibrium adsorption amount obtained from this breakthrough curve was 0.29 meq / g (dry form). Furthermore, the cesium concentration of the cesium nitrate solution was set to 10
The equilibrium adsorption amount was 0.046 meq / g in mg / l.

The relationship between the cesium concentration of the adsorbent and the equilibrium adsorption amount in Examples 2 to 4 and Comparative Example 1 is shown in the drawings.

Examples 5 to 13 In producing a composite adsorbent by the same method as in Example 4, various transition metal nitrate aqueous solutions were used instead of the 10 wt% cobalt nitrate aqueous solution. However, molybdenum was an aqueous solution of potassium molybdate, and tungsten was an aqueous solution of potassium tungstate.

The adsorbent thus produced was packed in a column having an inner diameter of 8 mm, and a cesium nitrate solution (cesium concentration 100 mg / l, sodium nitrate concentration 40 g / l, neutral) was passed through the column at a flow rate of 1 ml / min, and When a breakthrough curve was created from the effluent amount and the cesium concentration in the effluent, cesium was extremely selectively adsorbed, and the cesium concentration before breakthrough was below the detection limit (0.06 mg / l) by an atomic absorption spectrometer. And a decontamination factor of at least 1000 or more was obtained. Table 2 shows the relationship between the equilibrium adsorption amount of cesium obtained from the breakthrough curve and the transition metal used.

(Effect of the invention) According to the present invention, a composite adsorbent that efficiently adsorbs and removes an alkali metal in an aqueous solution and has improved handleability is obtained, which is particularly suitable for decontamination of cesium.
4 to Comparative Example 1 and Comparative Example 1, in the low cesium concentration region (cesium concentration of 0.1 mg / l or less), the adsorbents of the present invention each show a higher equilibrium adsorption amount than zeolite.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing is a graph showing the relationship between the cesium concentration of the adsorbent and the equilibrium adsorption amount in Example 2, Example 3, Example 4, and Comparative Example 1.

Claims (2)

[Claims] 1. A ferrocyanide metal salt / titanic acid composite adsorbent obtained by supporting a ferrocyanide metal salt on titanic acid. 2. Adsorbing alkali ferrocyanide on titanic acid, and further reacting with a transition metal salt,
1. A method for producing a composite adsorbent of a metal cyanide / titanic acid complex, which comprises depositing a metal cyanide on a titanic acid, which comprises depositing a metal cyanide on the titanic acid.