JP5988706B2 - Cesium capturing material and method for producing the same - Google Patents

Description

  The present invention relates to a cesium capturing material and a method for producing the same, and more specifically, a cesium capturing material that can be produced by a simple method, has a high cesium capturing ability, and can reduce the problem of waste disposal, and a method for producing the same. About.

The Great East Japan Earthquake that occurred on March 11, 2011 caused a large-scale radioactive material leakage accident at the Tokyo Electric Power Fukushima Daiichi NPS due to the earthquake and the accompanying tsunami, and many radioactive materials were released into the environment. . After the accident, there is an urgent need to remove radioactive cesium with a long half-life from contaminated water that accumulates in the power plant. As a method for removing radioactive cesium in contaminated water, a method of removing it by adsorbing on zeolite, a method of coprecipitation removal with Prussian blue, and the like are employed. The cesium treatment material used here is an inorganic porous material such as natural zeolite and Prussian blue (iron ferrocyanide). These materials have the following problems.
First, it is generally said that the cation exchange capacity of natural zeolite is 80 to 180 meq / 100 g. With 100 g of zeolite, only 11 to 24 g of cesium can be adsorbed at maximum. Although natural zeolite is cheap and abundant in quantity, it has a problem in terms of waste volume reduction because of its low cation exchange capacity and low cesium adsorption. Zeolite adsorbed with radioactive substances is radioactive waste, and cesium adsorbents are required to have a high adsorption capacity that can adsorb more cesium in a smaller amount in order to reduce waste after decontamination.
In addition, Prussian blue decomposes and liberates a cyanide compound in a strong alkaline environment. Since cyanide is very toxic, there is a problem in storage and disposal of waste after cesium adsorption.

Patent Document 1 discloses a cesium adsorbent made of an inorganic ion exchanger supporting ammonium phosphomolybdate. As a method for producing the cesium adsorbent, natural or synthetic porous inorganic material (zeolite, etc.) is brought into contact with a phosphomolybdic acid hydrate solution under reduced pressure, and then impregnated with an ammonium salt solution. A method for converting phosphomolybdate hydrate to ammonium phosphomolybdate is disclosed.
Patent Document 2 discloses a fine particle of Prussian blue-type metal complex as a cesium adsorbent, and an aqueous solution of iron nitrate is mixed and stirred in an aqueous solution of sodium ferrocyanide, and the precipitated blue precipitate (Prussian blue) is centrifuged. Prussian blue-type metal complex nanoparticles are produced by the steps of separation and drying.

Japanese Patent No. 3020158 JP 2011-200856 A

The cesium adsorbent disclosed in Patent Document 1 requires two steps to crystallize ammonium phosphomolybdate in the porous body, which is troublesome and costly to manufacture and is not practical. .
The cesium adsorbent disclosed in Patent Document 2 has a problem in terms of storage and disposal of waste derived from Prussian blue as described above.
The present invention has been made in view of the above, and provides a cesium-capturing material that can be manufactured by a simple method, has a high cesium-capturing ability, and can reduce the problem of waste disposal, and a method for manufacturing the same. For the purpose.

  The present inventors have found that the above problems can be solved by a material containing a magnesium compound and a phosphate compound, and have completed the present invention.

That is, the present invention provides the following [1] to [5].
[1] A cesium capturing material containing a magnesium compound and a phosphate compound, wherein the molar ratio (Mg / P) between the magnesium component and the phosphorus component in the capturing material is 10 or less, and is effective in the cesium capturing material The cesium capture | acquisition material whose content of lime is 1.5 mass% or less.
[2] The cesium trapping material according to [1], wherein the magnesium compound is at least one selected from semi-baked dolomite, magnesium oxide, and magnesium hydroxide.
[3] The above [1] or [2], wherein the magnesium compound is a semi-fired dolomite obtained by firing dolomite at a temperature of 600 to 900 ° C. and having a content of free magnesium oxide of 8% by mass or more. ] The cesium capture | acquisition material of description.
[4] The phosphate compound is composed of potassium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium monohydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate and hydrates thereof. The cesium capturing material according to any one of [1] to [3], which is one or more selected compounds.
[5] The cesium capturing material according to [1] to [4], wherein a molar ratio (Mg / P) of a magnesium component and a phosphorus component in the cesium capturing material is 1.2 to 7.

  According to the present invention, it is possible to provide a cesium capturing material that can be manufactured by a simple method, has a high cesium capturing ability, and can reduce the problem of waste disposal, and a method for manufacturing the same.

The cesium-trapping material according to the present invention is a cesium-trapping material containing a magnesium compound and a phosphate compound, and the molar ratio (Mg / P) between the magnesium component and the phosphorus component in the trapping material is 10 or less, The content of effective lime in the cesium capturing material is 1.5% by mass or less.
Hereinafter, each component will be described in detail.

[Magnesium compound]
Examples of the magnesium compound used in the present invention include semi-baked dolomite, magnesium oxide, magnesium hydroxide, magnesium chloride, and magnesium sulfate. These magnesium compounds may be used alone or in combination of two or more. Of these, semi-baked dolomite, magnesium oxide, and magnesium hydroxide are preferred.

In the present invention, “semi-baked dolomite” refers to a semi-baked dolomite product mainly composed of magnesium oxide and calcium carbonate. Semi-baked dolomite decalcifies most of the magnesium carbonate in the dolomite component by calcining dolomite at a temperature of 600 to 900 ° C. to make magnesium oxide, while calcium carbonate hardly decarboxylates, It can be obtained by leaving it as it is.
The content of free magnesium oxide in the semi-baked dolomite is preferably 8% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. Free magnesium oxide is measured according to the method described in the examples.
In addition, in order to highly capture cesium in contaminated water, it is desirable that the content of free calcium oxide and calcium hydroxide in the cesium capturing material, that is, the content of effective lime described later, is low. It is desirable to suppress the decarboxylation of calcium carbonate as much as possible. Moreover, it is thought that there is little influence on a human body and the environment by using dolomite derived from nature as a main raw material.

As magnesium oxide, what is generally marketed, or what baked magnesium carbonate or magnesium hydroxide, etc. can be used.
As magnesium hydroxide, commercially available products, natural products obtained by pulverizing natural minerals, synthetic products obtained by synthesis from seawater and quicklime, and the like can be used.

[Phosphate compound]
Examples of the phosphate compound used in the present invention include potassium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium monohydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, and hydration thereof. Thing etc. are mentioned. Phosphoric acid compounds may be used singly or in combination of two or more. Of these, potassium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and hydrates thereof are preferable from the viewpoint of solubility of phosphate compounds and easy availability, and potassium dihydrogen phosphate and This hydrate is more preferred.
The amount of the phosphoric acid compound used is selected in such a range that the molar ratio ([Mg / P] molar ratio) between the magnesium component (Mg) and the phosphorus component (P) of the cesium scavenger described later is 10 or less.

[Cesium capture material]
The cesium capturing material of the present invention preferably contains a magnesium compound and a phosphate compound, and substantially consists of a magnesium compound and a phosphate compound. The cesium trapping material of the present invention may contain other components as long as the effects of the present invention are not hindered. Examples of other components include water for slurrying. Here, “substantially composed of a magnesium compound and a phosphate compound” means that, for example, 95% by mass or more of the constituent components excluding water of the cesium capturing material is a magnesium compound and a phosphate compound.

  The molar ratio (Mg / P) between the magnesium component and the phosphorus component in the cesium trapping material is 10 or less. When the molar ratio is 10 or less, a high cesium capturing effect can be obtained and the treatment can be performed in a short time. The preferable range of the molar ratio of the magnesium component to the phosphorus component is not generally determined by the type of raw material, processing conditions, etc., but is preferably 1.0 to 8.5. If the said molar ratio is 1.0 or more, the usage-amount of a phosphoric acid compound can be reduced and it can process cheaply. From these viewpoints, the molar ratio is more preferably 1.2 to 7, and further preferably 1.3 to 5.5.

  The content of effective lime in the cesium capturing material needs to be 1.5% by mass or less as a solid content conversion amount with respect to the total amount of the cesium capturing material. The content of effective lime is the total content of calcium oxide and calcium hydroxide contained in the cesium capturing material, and is measured according to the method described in the examples. Calcium oxide and calcium hydroxide react with a phosphate compound in water to produce calcium phosphate, which may adversely affect the cesium scavenging effect. If content of the said effective lime is 1.5 mass% or less, the fall of the cesium capture | acquisition effect of this invention can be suppressed.

The cesium capturing material of the present invention can efficiently capture radioactive cesium contained in high-level contaminated water with a smaller amount of use.
In the cesium capturing material of the present invention, cesium is captured by sufficiently contacting the cesium-containing contaminated water, preferably by mixing and stirring the cesium capturing material and the contaminated water.
As the usage-amount with respect to the contaminated water of a cesium capture | acquisition material, the optimal addition amount can be defined according to the cesium density | concentration in contaminated water. For high-concentration contaminated water with a cesium concentration of several thousand mg / L in the contaminated water, for example, the amount of cesium-trapping material used can be reduced by treating it in a multistage manner. From the above viewpoint, the usage amount of the cesium capturing material is preferably 0.05 to 5% by mass with respect to the contaminated water. When the used amount of the cesium capturing material is 0.05% by mass or more, a cesium capturing effect is sufficiently obtained, and when it is 5% by mass or less, a cesium capturing effect according to the addition amount of the cesium capturing material is obtained. In addition, an increase in load and processing cost during stirring can be suppressed. From this viewpoint, the amount of the cesium capturing material used is more preferably 0.1 to 1% by mass, and still more preferably 0.2 to 0.8% by mass with respect to the contaminated water.
The treatment time may be treated until the reaction between the cesium capturing material and cesium reaches equilibrium, and is usually 1 to 24 hours, preferably 2 to 10 hours.

The cesium capturing material used for the treatment of contaminated water containing radioactive cesium is treated as radioactive waste. Examples of radioactive waste processing methods include cement solidification.
Since the amount of the cesium-trapping material of the present invention can be reduced compared to conventional zeolite, the volume of radioactive waste can be reduced.

EXAMPLES Next, although an Example demonstrates this invention in detail, this invention is not restrict | limited by this.
In the examples and comparative examples, the composition analysis of the chemical components of the magnesium compound, the content of effective lime and the content of free magnesium oxide were carried out by the following methods.
(1) Chemical component of magnesium compound The chemical component of the magnesium compound was measured according to the analysis method prescribed in JIS R9011.

(2) Content of effective lime The content of effective lime in the magnesium compound of the present invention is determined in accordance with “11. Method for Quantifying Effective Lime” defined in “Japan Lime Association Standard Test Method (2006)” by the Japan Lime Association. This is the total amount (mass%) of calcium oxide (CaO) and calcium hydroxide [Ca (OH) ₂ ] to be analyzed. From the calculated content of effective lime in the magnesium compound, the content of effective lime in the cesium capturing material was determined.

(3) Content of free magnesium oxide Content of free magnesium oxide is an amount calculated as the amount (mass%) of magnesium oxide (MgO) produced by decarboxylation of magnesium carbonate (MgCO ₃ ) in dolomite Say. The calculation is performed according to the following procedure.
First, CaO, MgO and Ig.loss (loss on ignition) are analyzed by a method defined in “Analyzing Method of Lime” of JIS R9011. Next, one of the following (i) and (ii) is selected depending on whether or not the amount of free calcium oxide obtained by the analysis has reached 1.5% by mass.
(I) When the amount of free calcium oxide is 1.5% by mass or more: The value of MgO obtained by analysis is adopted as the amount of free magnesium oxide as it is.
(Ii) When the amount of free calcium oxide is less than 1.5% by mass: The amount of free magnesium oxide is calculated by [MgO present as MgO—MgCO ₃ obtained by analysis].
The amount of MgO present as MgCO ₃ is determined by the following formula.
MgO present as MgCO ₃ (mass%) = {Ig.loss− (CaO ÷ 56 × 44)} ÷ 44 × 40

(4) Particle size of dolomite The particle size of dolomite was measured using a laser diffraction particle size distribution analyzer, and the particle size when the integrated value in the cumulative particle size curve obtained reached 50% and 90%, respectively, “d50 particle diameter” and “d90 particle diameter”.

(Raw materials)
The raw materials used in Examples and Comparative Examples are as follows.
・ Lightly burned dolomite (through a sieve with 150 μm openings)
・ Hydroxy hydroxide (through a sieve with 150 μm openings)
・ Semi-baked dolomite (through a sieve with 150 μm openings)
・ Calcium carbonate (Kanto Chemical Co., Ltd., special grade, purity 99.5% by mass)
・ Magnesium oxide (manufactured by Kanto Chemical Co., Ltd., special grade, purity 98.0% by mass)
-Potassium dihydrogen phosphate (manufactured by Kanto Chemical Co., Ltd., special grade, purity 99.5% by mass)
Magnesium hydroxide (Kanto Chemical Co., Ltd., first grade, purity 95% by mass)
Table 1 shows chemical components of the dolomite compound.

Examples 1-3
(Preparation of cesium capture material)
A cesium scavenger was prepared by mixing a magnesium compound shown in Table 2 and potassium dihydrogen phosphate (KH ₂ PO ₄ ) as a phosphate compound at a blending ratio shown in Table 2.
(Cesium treatment test)
1 g of a cesium capturing material and 300 ml of an aqueous cesium chloride solution (cesium concentration 1000 mg / l, cesium chloride (manufactured by Kanto Chemical Co., Inc., purity 98.0% by mass)) are placed in a beaker and mixed with stirring with a magnetic stirrer for 6 hours. The mixed solution is collected with a syringe, and the liquid from which the solid matter is removed is extracted using a syringe filter (pore size: 0.45 μm). The cesium concentration of the extracted liquid was measured with an atomic absorption photometer (manufactured by Hitachi, Ltd., “Z-2000”), and the cesium capture rate (%) was determined by the following formula. The results are shown in Table 2.
Cesium capture rate (%) = [(cesium initial concentration−cesium equilibrium concentration) / cesium initial concentration] × 100
(The cesium equilibrium concentration is the concentration of cesium in the solution at the time when the reaction reached equilibrium after stirring for 6 hours.)

Comparative Examples 1-2
A cesium capturing material was prepared in the same manner as in Example 1 except that the magnesium compound shown in Table 2 was used and no phosphate compound was used, and a cesium treatment test was conducted in the same manner as in Example 1.
Comparative Example 3
A cesium capturing material was prepared in the same manner as in Example 1 except that the magnesium compound shown in Table 2 was used, and a cesium treatment test was performed in the same manner as in Example 1.
Comparative Example 4
A cesium capturing material was prepared in the same manner as in Example 1 except that calcium carbonate was used in place of the magnesium compound, and a cesium treatment test was conducted in the same manner as in Example 1.
Comparative Example 5
A cesium capturing material was prepared in the same manner as in Example 1 except that only the phosphate compound was used without using the magnesium compound, and a cesium treatment test was conducted in the same manner as in Example 1.

Comparing Examples 1 to 3 with Comparative Examples 4 and 5, it can be seen that cesium in water can be captured by a combination of a magnesium compound and a phosphate compound. This is presumably because magnesium, phosphorus contained in the cesium scavenger and cesium contained in the water make some water-insoluble compounds. From Comparative Examples 1 and 2, it is understood that the cesium capturing ability is low in the dolomite fired substance alone containing no phosphate compound. Moreover, when Examples 1 and 3 are compared with Comparative Example 3, it can be seen that cesium is not captured when a large amount of calcium component (effective lime) having high solubility in water is present. This is presumably because phosphorus in the phosphoric acid compound makes a compound with eluted calcium in preference to magnesium and cesium.
From the above, it has been found that a composite material in which a phosphoric acid compound is combined with a magnesium compound having an effective lime content of a specific amount or less is useful as a cesium scavenger.

Examples 4-10
A cesium-trapping material was prepared in the same manner as in Example 1 except that the amount of potassium dihydrogen phosphate added to 1.2 g of the half-baked dolomite used in Example 1 was changed to the ratio shown in Table 3. A cesium treatment test was conducted in the same manner as in Example 1. The results are shown in Table 3.
Example 11
From the results of Examples 4 to 10, the [Mg / P] molar ratio was set to 2.1 of Example 5 with the highest cesium trapping effect, and the total mass of the cesium trapping material was set to 3.0 g, as in Example 1. The cesium treatment test was conducted by the method. The results are shown in Tables 3 and 4.

Comparative Examples 6-8
A cesium treatment test was conducted in the same manner as in Example 1 except that 3 g of natural zeolite or synthetic zeolite shown in Table 4 was used as the cesium scavenger. The results are shown in Table 4.

In Examples 4 to 11, when the [Mg / P] molar ratio is 2.1, the cesium capturing ability of the cesium capturing material is maximized, and the range of the [Mg / P] molar ratio is preferably 1.2 to 7, It turns out that 1.3-5.5 is more preferable.
From the results of Example 11 and Comparative Examples 6 to 8, it can be seen that the cesium-capturing material of the present invention has a higher cesium-capturing ability than the conventional zeolite.

  Since the cesium capture | acquisition capacity | capacitance of the cesium capture | acquisition material which concerns on this invention is higher than the conventional zeolite, it turns out that the high cesium capture | acquisition effect is exhibited by a small amount of use, and the contaminated water containing a lot of radioactive cesium can be processed efficiently. It is also expected that the problem of waste storage and disposal will be reduced.

Claims (4)

A cesium capturing material containing magnesium compound and a phosphoric acid compound, the molar ratio of magnesium component and the phosphorus component of the cesium in capturing material (Mg / P) is 10 or less, the effective lime of the cesium in the capturing material Ri der content 1.5 mass% or less,
The magnesium compound is at least one selected from semi-baked dolomite, magnesium oxide, and magnesium hydroxide;
The phosphoric acid compound is selected from potassium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, potassium monohydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate and hydrates thereof 1 A cesium scavenger that is a compound of more than species . It said magnesium compound, the content of Yu away magnesium oxide is semi-sintered dolomite is 8 mass% or more, cesium trapping agent according to claim 1. The cesium capture | acquisition material of Claim 1 or 2 whose molar ratio (Mg / P) of the magnesium component in the said cesium capture | acquisition material and a phosphorus component is 1.2-7. It is a method of manufacturing the cesium capture | acquisition material of Claim 2, Comprising: Semi-baking dolomite obtained by baking a dolomite at the temperature of 600-900 degreeC, and manufacture of a cesium capture | acquisition material Method.