JP5250742B1 - Method of treating radioactive Cs contaminated water - Google Patents

Abstract

Provided is a method for treating radioactive Cs-contaminated water that can adsorb and remove Cs ions of radioactive Cs-contaminated water quickly and efficiently at low cost.
SOLUTION: A predetermined iron cyano complex and an iron salt compound are reacted in water to form PB (Prussian blue) M (I) _3x Fe (III) _4-x [Fe (II) (CN) ₆ ] ₃ ( M (I) is a monovalent cation, x is 0 or 1), a step (A), a step of adsorbing Cs ions to PB molecules and / or clusters thereof (B), and step (B) Later, Me (II) salt compound (Me (II) is a predetermined divalent transition metal) is added and hydrolyzed so that Me (II) takes a hexagonal crystal structure in the treatment liquid after step (B). II) Including the step (C) containing (OH) ₂ , the ratio (α / β) of the amount α (mol) of the iron cyano complex to the amount β (mol / L) of the Me (II) salt compound is 0. 1-10.
[Selection figure] None

Description

  The present invention relates to a method for treating radioactive Cs-contaminated water, and more particularly to a treatment method for adsorbing and removing Cs ions in contaminated water contaminated with radioactive Cs ions to make them harmless.

  The explosion of the Fukushima Daiichi nuclear power plant on March 11, 2011 released a large amount of radioactive cesium Cs into the environment, causing serious damage over a wide area in eastern Japan. In particular, environmental pollution due to radioactive Cs134 and Cs137 having a long half-life of 2 years and 30 years, respectively, is serious, and various techniques have been used to remove them. For example, adsorbents such as zeolite and Prussian blue pigment are used to remove Cs ions from radioactive Cs contaminated water.

Zeolite has a relatively large specific surface area with a porous adsorbent, silicate groups of the surface Si-O ^- but by it to capture the Cs ions by cation exchange action, Na ions and K ions in contaminated water, When Ca ions, Mg ions, Ca ions, and the like are present at high concentrations, there is a problem that Cs ions cannot be selectively adsorbed, for example, Cs ions captured by an equilibrium action with these cations are desorbed.

  On the other hand, Prussian blue pigments can selectively adsorb Cs ions, and even when treating contaminated water containing cations such as Na ions, K ions and Mg ions like seawater. The influence of the inhibitory action by cations is small compared to zeolite.

However, when Prussian blue pigment is used as an adsorbent, there is a problem that it takes 24 hours or more to obtain a Cs removal rate of 99% or more.
In addition, since the Prussian blue pigment is used in a fine powder state, it is difficult to remove it by filtration even if Cs ions are adsorbed (passes through a sieve mesh). For this reason, in the precipitation / filtration process, it is essential to use a coagulant such as a sulfuric acid band.

  Thus, a porous adsorbent such as zeolite has a large specific surface area and an excellent cation adsorption rate, but has a problem in Cs ion selectivity, while PB has an excellent Cs ion selectivity but has a drawback in a slow adsorption rate. there were.

  In this respect, an adsorbent having a large specific surface area and excellent adsorption characteristics and Cs ion selectivity has been developed. For example, a copper-iron cyanide complex is formed on the surface of mesoporous silica particles via an anchor molecule. Adsorbents that are supported and have excellent Cs ion adsorption performance have been developed (see Non-Patent Document 1).

  However, since an expensive silylating agent is used as an anchor for linking the copper-iron cyanide complex to the silica surface, there is a problem in terms of cost in treating a large amount of Cs-contaminated water.

Thanapon Sangvani et.al J Hazard mater. 2010 October 15; 182 (1-3): 225-231

  Then, an object of this invention is to provide the processing method of radioactive Cs contaminated water which can adsorb and remove Cs ion of radioactive Cs contaminated water quickly and efficiently at low cost.

  In order to solve the above problems, the present inventors have made the following examinations and considerations.

That is, it is considered that the Prussian blue dye pigment conventionally used as an adsorbent is a powder and is adsorbed by trapping Cs ions in the crystal lattice of the Prussian blue dye pigment.
In this case, Cs ions need to diffuse in the crystal lattice. That is, it is considered that the adsorption rate of Cs ions by the Prussian blue pigment is the rate limiting of diffusion of Cs ions into the crystal lattice.
However, since the diffusion coefficient of Cs ions in the crystal lattice is extremely small, it takes 24 hours or more to effectively adsorb and remove Cs ions from Cs-contaminated water, despite excellent adsorption selectivity for Cs ions. It is understood that it took time.

As a result of further diligent investigations based on the above points, it was not used in the form of powder as in the conventional Prussian blue pigment, but it was allowed to act on Cs ions in the state of molecules and / or clusters, and Prussian adsorbed Cs ions in the presence of a hydroxide represented by Me (II) (OH) ₂ having a hexagonal crystal structure (where Me (II) is a divalent transition metal). The inventors have found that coagulating and precipitating blue is important in solving the above-described problems of the present invention, and have completed the present invention.

That is, the method for treating radioactive Cs-contaminated water according to the present invention is represented by M (I) ₄ Fe (II) (CN) ₆ and / or M (I) ₃ Fe (III) (CN) ₆ in water. By reacting an iron cyano complex (where M (I) is a monovalent cation) with a divalent and / or trivalent iron salt compound, M (I) _3x Fe (III) _{4− a} step (A) for obtaining a liquid containing Prussian blue molecules and / or clusters thereof represented by _x [Fe (II) (CN) ₆ ] ₃ (where x is 0 or 1); A) is performed in radioactive Cs-contaminated water and / or the Prussian blue molecules and / or clusters thereof are obtained by mixing with the radioactive Cs-contaminated water after obtaining the Prussian blue-containing liquid in the step (A). A hexagonal crystal structure is formed in the treatment liquid that has undergone the process (B) of adsorbing Cs ions and the process (B). Me (II) (OH) ₂ (where Me (II) is at least one divalent transition metal selected from manganese, cobalt, nickel, copper, zinc and cadmium) In the step (C), the Me (II) salt compound is added after the step (B) and the Me (II) salt compound is hydrolyzed. When a hydroxide is contained in the treatment liquid, the amount of the iron cyano complex is α (mol), and the amount of the Me (II) salt compound is β (mol / L), α and The β ratio (α / β) is 0.1 to 10.
Hereinafter, “Prussian blue” may be abbreviated as “PB”.

  According to the present invention, Cs ions of radioactive Cs-contaminated water can be adsorbed and removed quickly and efficiently at a low cost.

In Example 18, it is a graph which shows the pH dependence of Cs ion concentration. 14 is a graph showing changes with time in Cs ion concentration in Example 19.

  Hereinafter, although the processing method of radioactive Cs contaminated water concerning this invention is demonstrated in detail, the range of this invention is not restrained by these description, The range which does not impair the meaning of this invention except the following illustrations. And can be changed as appropriate.

The method for treating radioactive Cs-contaminated water of the present invention essentially comprises the following steps (A) to (C). As will be understood from the following description, the steps (A) to (C) do not have to be performed sequentially, and may be performed simultaneously.
In addition, in this invention, the addition method of various chemical | medical agents may be used with any form, such as a granule, a powder, aqueous solution, a dispersion liquid, and is not specifically limited.

[Process (A)]
In step (A), an iron cyano complex represented by M (I) ₄ Fe (II) (CN) ₆ and / or M (I) ₃ Fe (III) (CN) ₆ , divalent and By reacting with a trivalent iron salt compound, the PB molecule represented by M (I) _3x Fe (III) _4-x [Fe (II) (CN) ₆ ] ₃ and / or its cluster This is a step of obtaining a containing liquid.

Here, M (I) is a monovalent cation, and examples thereof include Li ⁺ , Na ⁺ , K ⁺ , NH ₄ ^{+ and the} like, preferably Na ⁺ and / or K ⁺ .
The divalent and / or trivalent iron salt compound is not particularly limited, but (divalent or trivalent) iron chloride, nitrate, sulfate, organic acid salt, and the like are preferable.
X is 0 or 1.

The synthesis reaction of PB in the step (A) is carried out by using an iron cyano complex (ferrocyan compound) represented by M (I) ₄ Fe (II) (CN) ₆ and / or M (I) ₃ Fe (III) (CN ) The reaction is carried out by a reaction of an iron cyano complex (ferricyan compound) represented by ₆ and a divalent and / or trivalent iron salt compound, as specifically described below.

  That is, first, synthesis from a ferrocyan compound is as shown in the following reaction formula (1).

  The synthesis from the ferricyan compound is as shown in the following reaction formulas (2) to (4).

  Although the ideal form of PB is considered to be insoluble (PB2), in the actual reaction, the main product is water-soluble (PB1), and the adsorption of Cs ions is more than water-insoluble (PB2). It is thought that water-soluble (PB1) plays an important role.

[Process (B)]
In the step (B), the step (A) is performed in radioactive Cs-contaminated water, and / or the PB-containing liquid is obtained in the step (A) and then mixed with the radioactive Cs-contaminated water, whereby PB molecules and / or This is a step of adsorbing Cs ions to the cluster.
That is, the step (B) may be performed simultaneously with the step (A) by performing the step (A) in the radioactive Cs-contaminated water, or may be performed after mixing with the radioactive Cs-contaminated water after the step (A). Both are good.
Thus, in the present invention, the (PB1) and / or (PB2) produced in the reactions (1) to (4) is allowed to act on Cs ions without being separated from the aqueous solution. Unlike the conventional method to add, adsorption | suction of Cs ion reaches an equilibrium in a short time (for example, about 1 hour).

  The reaction in which the PB molecule captures Cs ions is shown in Formula (5).

  In the above formula (5), when m = n = 1, a PB molecule is represented, and when n ≧ m> 1, a cluster of PB molecules is represented.

  Here, the mechanism by which PB molecules bind preferentially to Cs ions over other alkali metal ions such as Na ions and K ions, and alkaline earth metal ions such as Mg ions and Ca ions is described in R.A. G. It can be explained by the HSAB rules proposed by Pearson (see Pearson, Ralph G. (1963). "Hard and Soft Acids and Bases". J. Am. Chem. Soc. 85 (22): 3533-3539. ).

That is, according to the HSAB rule, Cs is an alkali metal having a main quantum number of 6, and the lowest vacant atomic orbital LUAO of the Cs ion is 6s orbital. In comparison, it is classified as a soft acid that is easily polarized. That is, the order of the hardness and softness of the alkali ions as acid is as follows.
Soft Cs ⁺ >> K ⁺ > Na ^{+ to} Mg ^{2+ to} Ca ²⁺ hard

On the other hand, PB ions Fe (III) [Fe (II) (CN) ₆ ] ⁻ are classified as soft bases. According to the HSAB rule, hard acids bind strongly to hard bases and soft acids bind strongly to soft bases, but the bonds formed between hard and soft bases or between soft and hard bases are weak. Therefore, Cs ions are more strongly bound to PB ions than other alkali metal ions or alkaline earth metal ions.
HSAB rules are described in quantum chemistry (G. Klopman (1968). “Chemical Reactivity and Concept of Charge- and Frontier-Controlled Reactions” J. Am. Chem. Soc. 90 (2): 223-234. reference).
According to this, the stabilization energy (−ΔE) due to the bond formation between the acid and the base is expressed by the formula (6).

q _a : charge of M (I) ion q _b : charge of PB ion b ε: dielectric constant of reaction field r _ab : bond distance between M (I) and PB Γ _ab : Coulomb repulsion term E _m ^* : PB ion b the highest occupied molecular orbital (HOMO) energy E _n ^*: cation a minimum unoccupied atomic orbital (LUAO) energy c _m: maximum value of the coefficient of atomic orbitals that constitute the HOMO of PB ion c _n: M (I ) Coefficient of the LUAO function of ions β: Resonance integral term of LUAO of M (I) and HOMO of PB ions

The larger the value of -ΔE on the left side of Equation (6), the more stable the acid-base bond is. The first and second terms on the right-hand side mean the energy stabilization by the Coulomb interaction and solvation of the positive charge of the M (I) ion and the negative charge of the PB ion, respectively. The first and second terms contribute.
In the case of Cs ions and PB ions having a small charge density, the contribution of the first and second terms to the -ΔE value is small. On the other hand, the third term means a interaction soft acid and a soft base, the LUAO and soft base soft acids Cs ions PB ions Fe (III) Fe (II) (CN) 6 - the highest occupied molecular orbital The strong interaction between (LUMO) greatly contributes to the increase in -ΔE value. That is, in this case, | E _m ^* −E _n ^* | in the third term is small and β ² is large, so the third term contributes to an increase in the −ΔE value.
In the interaction between Na ions, K ions, Mg ions, and Ca ions that are hard acids and PB ions that are soft bases, the contribution to the increase in −ΔE by the first to third terms of Equation (6) is small. That is, these cations and PB ions do not form a strong bond.

Therefore, in the following formula (7), the equilibrium reaction is inclined to the right in the following order.
M (I) ⁺ : Cs ⁺ >> K ⁺ > Na ⁺

Next, the mechanism unique to the present invention of rapid adsorption of Cs ions by PB will be described as follows.
That is, the PB generated in the step (A) is in a molecular state immediately after the generation and / or in a minute aggregate (cluster) in which several molecules are aggregated.
As a result, the contact surface between the generated PB molecule and Cs ion is constantly updated in the aqueous solution. As a result, the contact between the Cs ion and the PB molecule and / or its cluster is efficiently performed, and the adsorption equilibrium is achieved in a short time. It is considered to be done. Under stirring conditions, particularly rapid adsorption is possible.
On the other hand, when adding fine PB having a grown crystal structure as in the prior art, the adsorption rate of Cs ions reaches the adsorption equilibrium because the diffusion rate of Cs ions in the crystal lattice is rate-limiting. It is thought that it took more than one day before.

[Process (C)]
Step (C) is represented by Me (II) (OH) ₂ (where Me (II) is a divalent transition metal) having a hexagonal crystal structure in the treatment liquid that has undergone step (B). This is a step of containing a hydroxide (hereinafter, sometimes simply referred to as “Me (II) hydroxide”).

  Me (II) is not particularly limited as long as the hydroxide is a divalent transition metal having a hexagonal crystal structure. Examples thereof include manganese, iron, cobalt, nickel, copper, zinc, and cadmium. .

  Examples of the method for adding Me (II) hydroxide to the treatment liquid that has undergone the step (B) include a Me (II) salt compound in advance and / or after the step (B). The method of hydrolyzing this Me (II) salt compound is mentioned.

Preferred examples of the Me (II) salt compound include the Me (II) chloride, nitrate, sulfate, carbonate, phosphate, and organic acid salt.
The Me (II) salt compound may be preliminarily contained in the treatment liquid, or may be added separately after the step (B), or both.
In addition, a trivalent transition metal salt such as iron (III) chloride is contained in the treatment liquid, and this is reduced to iron (II) chloride with a reducing agent, or a monovalent transition metal salt such as chloride. A method of adding a Me (II) salt compound by adding copper (I) to a treatment liquid and oxidizing it to copper (II) chloride also falls within the scope of the present invention.

  Conversion to Me (II) hydroxide by hydrolysis of the Me (II) salt compound is represented by the following reaction formula (8).

  Such hydrolysis can easily proceed by adjusting the pH of the aqueous solution.

Here, the substance of the PB molecule and / or its cluster which adsorbs Cs ions is mainly (PB1) or (PB2) in the above formulas (1) to (4), and in step (A) Since the PB is rapidly formed by the reaction between the iron cyanide complex and the Me (II) salt compound, the number of PB molecules adsorbing Cs ions is related to the number of iron cyano complexes.
Therefore, when the amount of iron cyano complex is α (mol) and the amount of Me (II) salt compound is β (mol / L), the ratio of α and β (α / β) is the number of PB molecules and Me ( II) A parameter that correlates with the ratio of the number of hydroxides.

In the present invention, the range of the parameter α / β is preferably from 0.1 to 10, and more preferably from 0.2 to 6.
In order to obtain the effect of insolubilization and aggregation of PB molecules adsorbed with Cs ions, even if α / β is made smaller than 0.1, no further improvement effect can be expected. Rather, excessive Me (II) salt compound May impair the water quality of the treatment liquid. On the other hand, when α / β exceeds 10, the effect of insolubilization and aggregation of PB molecules adsorbed by Cs ions by Me (II) hydroxide becomes insufficient, and in the filtration step, PB molecules adsorbed Cs ions and / or There is a possibility that the cluster may pass through the filter mesh.
In particular, when considering the drainage standard value of the total cyan concentration of the treatment liquid, α / β is preferably 0.1 to 1.0.

In the present invention, the active material that captures Cs ions is considered to be αPB · βMe (II) (OH) ₂ .
Therefore, the amount (mol) of PB and the amount (mol) of Me (II) hydroxide are represented by the amount (mol) of iron cyano complex and the amount (mol) of Me (II) salt compound, respectively.
According to the present invention, for example, when Cs ions are effectively removed from 1000 mL of Cs-contaminated water having a Cs ion concentration of 10 mg / L, the object of the present invention can be sufficiently achieved if α + β is 2.5 mmol or more. it can.

The pH of the aqueous solution when the Me (II) salt compound is hydrolyzed is preferably in the range of 3 to 11, more preferably pH 6 to 10.
If the pH is less than 3, the intended effect may not be obtained without hydrolysis of the Me (II) salt compound. In addition, if the hydrolysis pH is too high, the PB molecules are decomposed, and the cyan concentration of the treatment liquid may exceed the environmental standard value or the wastewater standard value, and the aggregated structure is broken and the insolubilized Cs adsorbed PB is regenerated. There is a risk of dissolving or regenerating clusters of PB molecules.

As another method for incorporating the Me (II) hydroxide into the treatment liquid that has undergone the step (B), the Me (II) hydroxide and / or Me (II) is added after the step (B). By adding this oxide, Me (II) hydroxide may be contained in the treatment liquid.
In addition, by containing iron powder or zinc powder in the treatment liquid and oxidizing it with air or corrosion, Me (II) hydroxide such as Fe (OH) ₂ or Zn (OH) ₂ The method of making it contain also falls under the category of the present invention.

  Regarding the mechanism by which PB molecules and / or their clusters are insolubilized and agglomerated by the coexistence of Me (II) hydroxide in the treatment liquid by the above-described method, resulting in coarse particles (usually 1 μm or more in particle size) Although the details are not clear, the present inventors considered as follows.

That is, when a Me (II) salt compound is used for the aggregation and precipitation of PB molecules and / or clusters thereof, the aggregation / insolubilization of PB molecules or PB molecule clusters adsorbing Cs ions is caused by Me (II) salt compound molecules. The Me (II) salt compound is insolubilized by forming a cross-linking bond with the PB molecule by the interaction between the d orbital of Me (II) and the π electron of the cyano group of the PB molecule and / or its cluster. Further, when the Me (II) salt compound is hydrolyzed by adjusting the pH of the treatment liquid to a weak acid to a weak alkali, a Me (II) hydroxide is generated to form a crystal structure. The solubility product of this Me (II) hydroxide is as small as 10 ⁻¹² or less.
Since the Me (II) hydroxide of the present invention has a hexagonal crystal structure, a layered structure is formed in the c-axis direction of the crystal while forming a crosslinked structure via the cyano group of the PB molecule and / or its cluster. The crystal grows to form coarse particles of 1 μm or more.
As a result, the coarse particles are considered to have a structure in which PB molecules bonded to Cs and / or clusters thereof are intercalated between layers of the layered structure of Me (II) hydroxide.

On the other hand, when adding Me (II) hydroxide, Me (II) oxide, Me (II) metal powder, etc. for aggregation and precipitation of PB molecules and / or their clusters, Due to the action, PB molecules and / or clusters thereof are cross-linked on the crystal surface of the poorly water-soluble Me (II) hydroxide. Since the Me (II) hydroxide has a hexagonal crystal and a layered structure, the crystal plane of the Me (II) hydroxide cross-linked with the PB molecule and / or its cluster is peeled off by stirring in the treatment process.
Then, it is considered that the exfoliated crystal plane grows in a layered manner by intercalating PB molecules and / or clusters thereof between layers, and coarse particles having a particle diameter of 1 μm or more are formed.

  Many Me (II) hydroxides are unstable and are easily dehydrated and condensed in the dry state to be converted to the oxide Me (II) O. Since Me (II) O is converted into Me (II) hydroxide by hydration reaction in an aqueous solution, Me (II) O and Me (II) hydroxide can be considered equivalent in the present invention.

In general, in the water treatment process, a method of adding a sulfate band Al ₂ (SO ₄ ) ₃ or iron salt Fe (III) to aggregate fine particles is widely used. Further, a method of adding magnesium salt MgSO ₄ or the like to insolubilize heavy metals in the waste liquid is employed. However, in the present invention, the effect is not obtained even if the above-mentioned flocculant or insolubilizing agent is applied instead of the Me (II) salt compound. This is presumably because Al (III), Fe (III), and Mg (II) belong to a hard acid and cannot form a bond due to the interaction of the soft base with the cyano group of the PB molecule.

  However, in the present invention, it is not excluded to use an inorganic and / or organic flocculant to accelerate the sedimentation rate and filtration rate of the aggregate. For example, by adding a small amount of an anionic polymer flocculant, it is possible to significantly increase the precipitation rate of the Cs ion-trapping aggregate.

  A part of the host Me (II) hydroxide intercalated with PB molecules and / or clusters thereof as a guest is dehydrated to form the oxide Me (II) O. It can be shown by equation (9).

  In the above equation (9), x + y = 1, and m and n are positive numbers.

[Other processes]
After the PB molecules and / or clusters thereof are aggregated and precipitated with Me (II) hydroxide in the step (C), the precipitate is usually removed by filtration.
In this case, it is preferable to adjust the pH of the treatment liquid during filtration. The range is preferably pH 3-11, more preferably pH 5-10, and particularly preferably pH 6-8.

Hereinafter, although the processing method of the radioactive Cs contaminated water concerning this invention is demonstrated in detail using an Example, this invention is not limited to these Examples.
Since there are restrictions on the availability of radioactive Cs-contaminated water, many of the examples were substituted with available stable isotope ¹³³ Cs.
However, the chemical and physical events observed below are in complete agreement with those of ¹³⁷ Cs and ¹³⁴ Cs, which are radioisotopes of ¹³³ Cs.
Accordingly, the following examples in which Cs was removed from simulated contaminated water containing ¹³³ Cs, simulated seawater, and radioactive Cs contaminated water also demonstrate the effects on ¹³⁷ Cs and ¹³⁴ Cs, which are radioisotopes.
Of the chemicals used in the following Examples and Comparative Examples, all chemicals other than sodium ferrocyanide decahydrate were manufactured by Kishida Chemical Co., Ltd.

[Example 1]
1.5 g (3.55 mmol) of potassium ferrocyanide trihydrate was added to 1 L of simulated Cs-contaminated water having a Cs ion concentration of 100 mg / L, followed by 1.0 g of iron (III) chloride hexahydrate (3 .7 mmol) was added to form PB.
Next, 1.0 g (5.9 mmol) of manganese (II) sulfate monohydrate was added.
Stirring was continued while adjusting the pH to 7.0 by adding 5 mol / L sodium hydroxide aqueous solution. One hour after the start of the treatment, the stirring was stopped and the mixture was allowed to stand. The treatment liquid was filtered using a filter paper having a mesh size of 1 μm and 5C to obtain a filtrate.
The Cs ion concentration of the filtrate was measured with an inductively coupled plasma mass spectrometer (ICP-MS) 7000x manufactured by Agilent. Moreover, the total cyan density | concentration of the filtrate was implemented based on JISK0102 38.1.2 and 38.2.
The Cs ion concentration of the filtrate was 0.001 mg / L (lower limit of quantification 0.001 mg / L), and the removal rate was 99.999%. Further, the total cyan density was not detected (lower limit of quantification 0.01 mg / L).

[Example 2]
The same procedure as in Example 1 was carried out except that 0.06 g (0.355 mmol) of manganese (II) sulfate monohydrate was added in Example 1.
The Cs ion concentration of the filtrate was 0.1 mg / L, and the removal rate was 99.9%.

Example 3
PB was synthesized by adding 1.5 g (3.55 mmol) of potassium ferrocyanide trihydrate and 1.0 g (3.7 mmol) of iron (III) chloride hexahydrate to 10 mL of distilled water, and the aqueous solution was directly used as Cs. The same procedure as in Example 1 was performed except that 1 L of simulated Cs-contaminated water having an ion concentration of 100 mg / L was added.
The Cs ion concentration of the filtrate was 0.004 mg / L, and the removal rate was 99.996%. Further, the total cyan density was not detected (lower limit of quantification 0.01 mg / L).

Example 4
Example 1 PB was synthesized in the same manner as in Example 1 except that 1.2 g (3.6 mmol) of potassium ferricyanide anhydride and 0.72 g (3.6 mmol) of iron (II) chloride tetrahydrate were mixed. It carried out like.
The Cs ion concentration of the filtrate was 0.002 mg / L, and the removal rate was 99.998%. Further, the total cyan concentration was 0.02 mg / L (lower limit of determination 0.01 mg / L).

Example 5
After adding 0.5 g of sodium sulfite anhydride as a reducing agent to 0.6 g (1.8 mmol) of potassium ferricyanide anhydride and 0.76 g (1.8 mmol) of potassium ferrocyanide trihydrate in Example 1, iron chloride was added. (II) Tetrahydrate was added in the same manner as in Example 1 except that 0.72 g (3.6 mmol) was added to synthesize PB.
The Cs ion concentration of the filtrate was 0.001 mg / L, and the removal rate was 99.999%. The total cyan density was 0.8 mg / L.

Example 6
1.45 g (3 mmol) of sodium ferrocyanide decahydrate (manufactured by Alfa Aesar) was added to 1 L of simulated Cs-contaminated water having a Cs ion concentration of 100 mg / L, followed by iron (III) chloride hexahydrate under stirring. 0.87 g (3.2 mmol) of the product was added to produce PB.
Next, 10 mL of an aqueous solution of 0.39 g (3.0 mmol) of nickel (II) chloride was added.
Stirring was continued for 1 hour while adjusting the pH to 8.0 with a 5 mol / L aqueous sodium hydroxide solution. The pH adjustment was stopped and the mixture was further stirred for 1 hour and then allowed to stand. The pH of the treatment liquid was 7.2.
The treatment liquid was filtered through 5C filter paper having a sieve mesh of 1 μm to obtain a filtrate. The Cs ion concentration and total cyanide concentration of the filtrate were measured in the same manner as in Example 1.
The Cs ion concentration of the filtrate was 0.001 mg / L (lower limit of quantification 0.001 mg / L), and the removal rate was 99.999%. Further, the total cyan density was 0.9 mg / L.

Example 7
Example 6 is the same as Example 6 except that 10 mL of an aqueous solution containing 0.2 g (1.5 mmol) of cobalt (II) chloride and 0.2 g (1.5 mmol) of nickel (II) chloride was added to the simulated Cs-contaminated water. It carried out like.
The Cs ion concentration of the filtrate was 0.004 mg / L, and the removal rate was 99.996%. Further, the total cyan density was not detected (lower limit of quantification 0.01 mg / L).

Example 8
0.87 g (1.8 mmol) of sodium ferrocyanide decahydrate containing 1 mg of Cs-contaminated simulated seawater containing 3.0% sodium chloride, 0.5% magnesium chloride, and 0.05% potassium chloride, containing 10 mg / L of Cs ions Then, under stirring, iron (III) hexahydrate 0.54 g (2.0 mmol / L) was added to synthesize PB, and then cobalt (II) chloride 0.4 g (3.1 mmol) was added. ) Was added.
The mixture was stirred for 30 minutes while maintaining the pH of the treatment solution between 8 and 9 with a 5 mol / L sodium hydroxide aqueous solution. When stirring was further continued, the pH of the treatment solution became 7.0 after 1 hour. Stirring was stopped and the treatment liquid was suction filtered through a glass filter having a sieve mesh of 1 μm to obtain a filtrate.
As a result of measuring the Cs ion concentration and the total cyanide concentration of the filtrate in the same manner as in Example 1, the Cs ion concentration was 0.001 mg / L and the removal rate was 99.99%. No total cyan concentration was detected (lower limit of quantification 0.01 mg / L).

Example 9
In Example 8, 0.7 g (3.5 mmol) of iron (II) chloride tetrahydrate was added instead of cobalt (II) chloride, and 1.0 g of sodium sulfite anhydrous ( 8 mmol) was carried out in the same manner as in Example 8.
The Cs ion concentration of the filtrate was 0.008 mg / L, and the removal rate was 99.92%. The total cyan density was 0.02 mg / L.

Example 10
The same procedure as in Example 8 was performed except that 0.7 g (3.5 mmol) of zinc sulfate (II) was added instead of cobalt chloride (II) in Example 8.
The Cs ion concentration of the filtrate was 0.012 mg / L, and the removal rate was 99.88%. The total cyan density was 0.02 mg / L.

Example 11
In Example 8, 0.52 g (3.2 mmol) of anhydrous iron (III) chloride was added instead of cobalt (II) chloride, and then 6.3 g (5 mmol) of anhydrous sodium sulfite was added. The same procedure as in No. 8 was performed.
The Cs ion concentration of the filtrate was 0.008 mg / L, and the removal rate was 99.92%. The total cyan density was 0.03 mg / L.

Example 12
Except that 1 L of Cs-contaminated simulated seawater of Example 8 was replaced with 1 L of Cs-contaminated simulated seawater containing 3.0 mg of sodium chloride, 0.5% magnesium chloride and 0.05% potassium chloride containing 1 mg / L of Cs ions. All were carried out in the same manner as in Example 8.
Manganese (II) sulfate, iron (II) chloride tetrahydrate, nickel (II) chloride, copper (II) sulfate, zinc (II) sulfate, and cadmium (II) nitrate are also equivalent to cobalt (II) chloride. Equivalent amounts were added and each was carried out in the same manner.
No Cs ion was detected in any of the filtrates (lower limit of quantification 0.001 mg / L). All the cyan densities were also less than the environmental standard value (0.05 mg / L).

Example 13
Sodium ferrocyanide decahydrate 0.8 g (1.65 mmol) in 1 L of Cs-contaminated simulated seawater containing 3.0% sodium chloride, 0.5% magnesium chloride and 0.05% potassium chloride containing 10 mg / L Cs ion Then, 0.45 g (1.66 mmol / L) of iron (III) chloride hexahydrate was added with stirring to synthesize PB, and then 0.3 g of cobalt hydroxide (II) (3. 3 mmol) was added to adjust the pH to 7-8 and stirring was continued.
After 3 hours, stirring was stopped and the mixture was allowed to stand. The treatment liquid was filtered with 5C filter paper, and the Cs ion concentration and the total cyan density were measured for the filtrate by the same method as in Example 1.
Further, copper (II) hydroxide, nickel (II) hydroxide, manganese (II) oxide, zinc (II) oxide, and iron (II) oxide were similarly used instead of cobalt hydroxide (II). However, the addition of iron (II) oxide was carried out while maintaining the dissolved oxygen concentration of the treatment liquid at 0 ppm with sodium hydrogen sulfite.
Table 1 shows the measurement results.

Example 14
Sodium ferrocyanide decahydrate (1.05 g, 2.17 mmol) was added to 1 L of Cs-contaminated simulated seawater containing 3.0% sodium chloride, 0.5% magnesium chloride, and 0.05% potassium chloride. Then, 0.6 g (2.2 mmol / L) of iron (III) chloride hexahydrate was added with stirring to synthesize PB, and then copper (II) sulfate and cobalt (II) chloride were synthesized. After each addition under the condition that the α / β value was changed, the pH of the treatment liquid was adjusted to 7 to 8 and stirring was continued. After 1 hour, stirring was stopped and the mixture was allowed to stand. The treatment liquid was filtered with 5C filter paper, and the Cs ion concentration and the total cyan density were measured for the filtrate by the same method as in Example 1.
Table 2 shows α / β, α + β, and measurement results.

Example 15
The incinerated ash contaminated with radioactive Cs was washed with water to prepare radioactive Cs-contaminated water with a radioactive concentration of 490 Bq / kg.
The breakdown of the radioactive concentration of Cs is as follows: Cs137: 290Bq / kg, Cs134: 200Bq / kg
Cation: Ca ²⁺ : 2400 mg / L K ⁺ : 2.0% Na ⁺ : 8700 mg / L
Anion: SO ₄ ²⁻ : 1800 mg / L Cl ⁻ : 2.6%
The pH of the contaminated water was 11.5.
After adjusting the pH to 7 by adding 4 mol / L sulfuric acid to 1 kg of the contaminated water, 0.5 g (1 mmol) of sodium ferrocyanide decahydrate was added. Subsequently, 0.4 g (1.2 mmol) of iron (III) chloride tetrahydrate was added with stirring.
Next, 0.3 g (1.8 mmol) of manganese (II) sulfate monohydrate was added.
Stirring was continued for 0.5 hours while adjusting the pH to 8 with 5 mol / L sodium hydroxide.
After 0.5 hour, the stirring was stopped, and the treatment liquid was suction filtered with a 1 μm sieve Teflon (registered trademark) filter to obtain a filtrate.
The radioactivity concentration was measured for the filtrate. The measurement of the radioactivity concentration was performed for a predetermined time with a radioactivity measurement apparatus CAN-OSP-NAI manufactured by Hitachi Aloka.

1) Before treatment with Cs-contaminated water Measurement time: 30 minutes Radioactivity concentration: 490 Bq / kg (detection limit 20 Bq / kg)

2) Filtrate after treatment Measurement time: 1 hour Radioactivity concentration: ND (detection limit: 10 Bq / kg)
Further, the total cyan density was not detected (lower limit of quantification 0.01 mg / L).

Example 16
Example 15 Example 15 except that manganese sulfate (II) monohydrate was replaced with iron sulfate (II) sulfate heptahydrate 0.5 g (1.8 mmol) instead of sodium sulfate anhydride 0.5 g in Example 15. It carried out like.
The radioactivity concentration due to radioactivity Cs in the treated filtrate was not detected (detection limit: 10 Bq / kg for both ¹³⁷ Cs and ¹³⁴ Cs). Further, the total cyan density was not detected.

Example 17
The same operation as in Example 15 was conducted except that manganese (II) sulfate monohydrate was replaced by 0.29 g (1.8 mmol) of copper (II) sulfate in Example 15.
The radioactivity concentration due to radioactivity Cs in the treated filtrate was not detected (detection limit: 10 Bq / kg for both ¹³⁷ Cs and ¹³⁴ Cs). Further, the total cyan density was not detected.

[Comparative Example 1]
₄ g of PB (manufactured by Dainichi Seika Kogyo Co., Ltd .: NH ₄ Fe (III) Fe (II) (CN) ₆ ) was added to 1 L of simulated Cs-contaminated water having a Cs ion concentration of 100 mg / L used in Example 1 and stirred for 2 hours. went. 1 g of sulfuric acid band Al ₂ (SO ₄ ) ₃ was added, and the pH of the treatment liquid was adjusted to 9.0 with a 5 mol / L aqueous sodium hydroxide solution while stirring. Subsequently, 1 mL of a 0.1% aqueous solution of an anionic polymer flocculant (Acoflock A115 manufactured by MT Aquapolymer Co., Ltd.) was added to form flocs, and then the treatment liquid was filtered through 5C filter paper.
The Cs ion concentration of the filtrate was measured in the same manner as in Example 1.
The Cs ion concentration of the filtrate was 55.6 mg / L, and the removal rate was 44.4%.

[Comparative Example 2]
For 1 L of simulated seawater having a Cs ion concentration of 10 mg / L, as in Comparative Example 1, 1 g of PB manufactured by Dainichi Seika Kogyo was added, the pH was adjusted to 8, and stirring was performed for 24 hours. 100 mL of a treatment solution was collected after 1 hour, 6 hours, and 8 hours from the addition of PB. The same anionic polymer flocculant as in Comparative Example 1 was added to each of the collected treatment liquids, followed by filtration with 5C filter paper. The Cs ion concentration of the filtrate was measured in the same manner as in Comparative Example 1. Regarding the passage of 24 hours, the remaining treatment liquid was added with a flocculant to form a precipitate, followed by filtration in the same manner to measure the Cs ion concentration. Table 3 shows the Cs ion concentration in the filtrate of each elapsed time sample.

[Comparative Example 3]
₄ g of PB (manufactured by Dainichi Seika Kogyo Co., Ltd .: NH ₄ Fe (III) Fe (II) (CN) ₆ ) was added to 1 L of simulated Cs-contaminated water having a Cs ion concentration of 100 mg / L used in Example 1 and stirred for 1 hour. went.
After the stirring, when the treatment liquid was filtered with 5C filter paper, PB also passed through the filter paper, and a bitumen filtrate was obtained.

[Comparative Example 4]
1 g of PB (manufactured by Dainichi Seika Kogyo Co., Ltd .: NH ₄ Fe (III) Fe (II) (CN) ₆ ) was added to 1 L of simulated Cs contaminated water having a Cs ion concentration of 100 mg / L used in Example 1, followed by manganese sulfate. (II) 1.0 g was added and stirred for 2 hours. Meanwhile, the pH of the treatment liquid was adjusted to 9.0 with a 5 mol / L sodium hydroxide aqueous solution. After the stirring, the treatment liquid was filtered with 5C filter paper.
The Cs ion concentration of the filtrate was measured in the same manner as in Example 1.
The Cs ion concentration of the filtrate was 64.5 mg / L, and the removal rate was 35.5%.

[Comparative Example 5]
To 1 L of simulated sea water of Example 8, 1 g (2.1 mmol) of sodium ferrocyanide decahydrate was added with stirring, and then 0.57 g (2.1 mmol) of iron (III) chloride tetrahydrate was added. PB was synthesized. After stirring for 15 minutes, 1.14 g (4.2 mmol) of iron (III) chloride tetrahydrate was added as a flocculant. Iron (III) chloride was hydrolyzed while adjusting the pH to 8.5 with a 5 mol / L aqueous sodium hydroxide solution. One hour after PB synthesis, stirring was stopped and the mixture was allowed to stand, and the treatment liquid was filtered with 5C filter paper, and the Cs ion concentration and total cyan concentration were measured for the filtrate.

[Comparative Example 6]
The same procedure as in Comparative Example 5 was carried out except that the flocculant was changed to 1.0 g (8.3 mmol) in Comparative Example 5 and the hydrolysis was adjusted to pH 9.5.

[Comparative Example 7]
Comparative Example 5 was carried out in the same manner as Comparative Example 5 except that the flocculant was replaced by 0.75 g (5.0 mmol) of aluminum (III) sulfate and the hydrolysis was adjusted to pH 8.5.

  Table 4 shows the Cs ion concentration and the total cyan concentration of the filtrates of Comparative Examples 5 to 7.

[Comparative Example 8]
10 g of natural zeolite was added to 1 L of Cs-contaminated simulated seawater having a Cs ion concentration of 10 mg / L, and the mixture was stirred for 1 hour and filtered through 5C filter paper.
As a result of measuring the Cs ion concentration of the filtrate by the same method as in Example 1, the Cs ion concentration was 8.0 mg / L and the removal rate was 20%.

[Example 18: Effect of pH of treatment liquid]
Cesium carbonate Cs ₂ CO ₃ composed of stable element ¹³³ Cs was dissolved in 1 L of distilled water to prepare simulated Cs-contaminated water having a Cs ion concentration of 100 mg / L.
1.5 g (3.5 mmol) of potassium ferrocyanide trihydrate was added to the simulated Cs-contaminated water, followed by 1.0 g (3.7 mmol) of iron (III) chloride hexahydrate with stirring. . Simultaneously with the addition, the simulated aqueous solution turned dark blue and PB was produced. Next, 0.68 g (4 mmol) of manganese sulfate (II) monohydrate was added, and the mixture was stirred for 3 hours while adjusting the pH with a 5 mol / L sodium hydroxide aqueous solution. Filtered through.
The Cs ion concentration of the filtrate was quantified with an inductively coupled plasma mass spectrometer (ICP-MS) 7000 × manufactured by Agilent. The Cs ion concentration of the treatment liquid with respect to the pH of the treatment liquid is shown in FIG.
It was found that the technique of the present invention has a high Cs removal efficiency in a wide range of pH 4-11.
In addition, according to the present invention, it was confirmed that the influence of alkali ions and alkaline earth metal ions in Cs-contaminated water is small and Cs ions can be removed quickly and efficiently with simulated seawater having a Cs ion concentration of 10 mg / L.

[Example 19: Verification of rapidity of Cs ion removal effect]
1) Preparation of simulated seawater 3% sodium chloride and 0.5% potassium chloride were dissolved in distilled water, and cesium carbonate was added to prepare simulated seawater having a Cs ion concentration of 10 mg / L.

2) PB treatment To 1 L of simulated seawater, 0.87 g (1.8 mmol) of sodium ferrocyanide decahydrate was added and stirred. Subsequently, 540 mg (2.0 mmol / L) of iron (III) chloride hexahydrate was added with stirring.
Simultaneously with the addition, the simulated seawater turned dark blue.

3) PB insolubilization treatment After stirring for 15 minutes, 0.5 g (3 mmol) of manganese (II) sulfate monohydrate as a Me (II) salt compound was added to the treatment liquid. Then, 5 mol / L sodium hydroxide aqueous solution was added, and the Me (II) salt compound was hydrolyzed in the range of pH 6-9 of a process liquid.
Further, stirring was continued while adjusting the pH to 8. After 1 hour, 3 hours, 6 hours, and 24 hours from the start of the treatment, 100 mL of the treatment solution was collected.

4) Filtration The treatment liquid collected at each treatment time was filtered through 5C filter paper. The filtrate was applied to a sample for measuring Cs ion concentration by ICP-MS.
In addition to manganese (II) sulfate monohydrate, 3 mmol each of cobalt (II) chloride, iron (II) chloride, nickel (II) chloride, copper (II) chloride, and zinc (II) acetate was added to the above. Processing was carried out. The result is shown in FIG. In FIG. 2, the result of the comparative example 2 is also shown for comparison (“PB” in FIG. 2).

  In the present invention, it has been found that a treatment time of 1 to 3 hours is sufficient, and the effect of the invention is lost over a long treatment. This is because the oxidation reaction of the transition metal Me (II) and the dehydration condensation reaction of the formed Me (II) hydroxide occur in a long time treatment, and the Me (II) intercalated with PB molecules and clusters thereof. This is probably because the layered structure of hydroxide is wrinkled.

  The method for treating radioactive Cs-contaminated water of the present invention can be suitably used as a treatment method for quickly and efficiently adsorbing and removing Cs ions from water contaminated with Cs ions.

Claims (2)

In water, an iron cyano complex represented by M (I) ₄ Fe (II) (CN) ₆ and / or M (I) ₃ Fe (III) (CN) ₆ (where M (I) is monovalent) M (I) _3x Fe (III) _4-x [Fe (II) (CN) ₆ ] ₃ (provided that cation) is reacted with a divalent and / or trivalent iron salt compound. a step (A) for obtaining a liquid containing Prussian blue molecules and / or clusters thereof represented by x being 0 or 1;
The step (A) is carried out in radioactive Cs-contaminated water, and / or the Prussian blue molecules and / or by mixing with the radioactive Cs-contaminated water after obtaining the Prussian blue-containing liquid in the step (A). A step (B) of adsorbing Cs ions to the cluster;
Me (II) (OH) ₂ having a hexagonal crystal structure in the treatment liquid having undergone the step (B) (where Me (II) is at least selected from manganese, cobalt, nickel, copper, zinc and cadmium) A step (C) of containing a hydroxide represented by (a kind of divalent transition metal);
Including
In the step (C), the Me (II) salt compound is added after the step (B), and the Me (II) salt compound is hydrolyzed so that the hydroxide is contained in the treatment liquid. When the amount of the iron cyano complex is α (mol) and the amount of the Me (II) salt compound is β (mol / L), the ratio of α to β (α / β) is 0. The processing method of radioactive Cs contamination water which is 1-10.   The method for treating radioactive Cs-contaminated water according to claim 1, wherein the ratio of α and β (α / β) is 0.1-1.

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