Iron oxide and / or iron hydroxide with reducing agent composition

Abstract

The present invention provides a reducing agent composition for iron oxide and / or iron hydroxide, and a method for reducing iron oxide and / or iron hydroxide by contacting the reducing agent composition with iron oxide and / or iron hydroxide, the reducing agent composition for iron oxide and / or iron hydroxide being a reducing agent composition containing components (A) to (C) and having a pH in the range of 7 to 11, the oxidation-reduction potential when dissolving component (A) in an aqueous solution containing components (B) and (C) becoming -600 mV or less within 20 minutes after the start of dissolving component (A), and the rate of change of the oxidation-reduction potential becoming a value of 0 mV / minute or more within 60 minutes. (A) reducing agent; (B) water-soluble metal chelating agent; (C) amine compound.

Description

TECHNICAL FIELD

[0001] The present application relates to a reducing agent composition for iron oxide and / or iron hydroxide and a method for reducing iron oxide and / or iron hydroxide using the same. BACKGROUND

[0002] Iron oxide is generated in various environments for mechanicals, equipment, and the like in contact with water, and the performance of the mechanicals, equipment, and the like is reduced. For example, in tap water piping, boiler piping for power plants, residential environment equipment, and the like, due to the attachment of iron oxide, a reduction in performance, an unfavorable situation in hygiene or appearance is generated. In addition, in a waste boiler of a nuclear power plant, a decontamination operation for removing radioactive substances is required, and since the radioactive substances exist in a manner of being refined into an oxide film of iron oxide attached to a base material, it is desired to dissolve the oxide film of iron oxide efficiently.

[0003] Thus, various iron oxide removal techniques have been proposed. For example, in Patent Literature 1, a reducing agent composition containing thiourea dioxide, a specific alkali metal anhydrous salt, and an alkali metal bicarbonate is disclosed. In Patent Literature 2, a rust removing composition containing a basic compound, a water-soluble metal chelating agent, and thiourea dioxide is described.

[0004] Patent Literature 1: Japanese Patent Application Laid-Open No. 57-128767

[0005] Patent Literature 2: International Publication No. 2002 / 088427 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] The present application provides a reducing agent composition for iron oxide and / or iron hydroxide, which contains components (A) to (C) below and has a pH in the range of 7 to 11, and when the component (A) is dissolved in an aqueous solution containing the components (B) and (C), the oxidation-reduction potential becomes -600 mV or less within 20 minutes after the start of the dissolution of the component (A), and the rate of change of the oxidation-reduction potential becomes a value of 0 mV / minute or more within 60 minutes.

[0008] (A) Reducing agent

[0009] (B) Water-soluble metal chelating agent

[0010] (C) Amine compound

[0011] Further, the present application provides a method for reducing iron oxide and / or iron hydroxide, in which the reducing agent composition is brought into contact with iron oxide and / or iron hydroxide. DETAILED DESCRIPTION

[0012] In the rust removing composition described in Patent Literature 2, a caustic alkali is mainly used as the basic compound. Further, dithionous acid, which is a reduced species of iron oxide, is generated by mixing dithionous acid and an alkali agent in an aqueous solution, and thus a reduction reaction occurs. However, both the alkali metal bicarbonate used in Patent Literature 1 and the caustic alkali used in Patent Literature 2 have the following problem: the generation rate of dithionous acid is slow, and thus the dithionous acid competes with the inactivation of the reduced species by dissolved oxygen in water, and the dissolution time and the dissolution amount of iron oxide are insufficient.

[0013] Thus, the present application relates to a reducing agent composition for iron oxide and / or iron hydroxide and a reduction method for iron oxide and / or iron hydroxide using the same, which is capable of rapidly generating dithionous acid, which is a reduced active species, from dithionous acid, and of unlimitedly inhibiting the inactivation of the reduced species by dissolved oxygen in water, and thus is capable of sufficiently exhibiting the reduction rate of iron oxide and / or iron hydroxide.

[0014] The present inventors have studied various alkali agents, and as a result, it has been found that by using an amine compound as the alkali agent, dithionous acid, which is a reduced active species, can be rapidly generated from dithionous acid. Thus, the inactivation of the reduced species by dissolved oxygen in water is unlimitedly inhibited, and the reduction rate of iron oxide and / or iron hydroxide can be sufficiently exhibited. As a result, it has been found that iron oxide and / or iron hydroxide can be reduced and dissolved to an amount close to the stoichiometric amount of dithionous acid, and thus the present application has been completed.

[0015] The reducing agent composition for iron oxide and / or iron hydroxide of the present application is capable of rapidly generating dithionous acid, which is a reduced active species, from dithionous acid, and thus is capable of unlimitedly inhibiting the inactivation of the reduced species by dissolved oxygen in water and sufficiently exhibiting the reduction rate of iron oxide and / or iron hydroxide.

[0016] [Component (A): Reducing agent]

[0017] Dithionous acid can be suitably used as the reducing agent of component (A). The content of component (A) in the reducing agent composition of the present application is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and further preferably 0.03% by mass or more, from the viewpoint of the dissolution amount of iron oxide and / or iron hydroxide, and is preferably 7.8% by mass or less, more preferably 7.0% by mass or less, and further preferably 5.0% by mass or less, from the viewpoint of the solubility of the reducing agent.

[0018] [Component (B): Water-soluble metal chelating agent]

[0019] As the water-soluble metal chelating agent of component (B), aminocarboxylic acid compounds such as nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethyleneglycine, ethyleneglycol ether diamine tetraacetic acid, dicarboxymethylglutamic acid, ethylenediamine-N,N'-disuccinic acid, L-aspartic acid-N,N-diacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, methylglycine diacetic acid, 3-hydroxy-2,2'-iminodisuccinic acid, L-glutamic acid diacetic acid, salts thereof, and the like; phosphonic acid compounds such as hydroxyethane diphosphonic acid, nitrilotris(methylphosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid, ethylenediaminetetramethylene phosphonic acid, salts thereof, and the like; hydroxycarboxylic acid compounds such as gluconic acid, citric acid, salts thereof, and the like are exemplified. Among them, aminocarboxylic acid compounds and phosphonic acid compounds are preferred.

[0020] The content of component (B) in the reducing agent composition of the present application is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and further preferably 0.03% by mass or more, from the viewpoint of increasing the amount of dissolved iron oxide and / or iron hydroxide, and is preferably 40% by mass or less, more preferably 30% by mass or less, and further preferably 20% by mass or less, from the viewpoint of the solubility of the metal chelating agent.

[0021] The total content of component (A) and component (B) in the reducing agent composition of the present application is preferably 0.03% by mass or more, more preferably 0.04% by mass or more, and further preferably 0.05% by mass or more, from the viewpoint of increasing the amount of dissolved iron oxide and / or iron hydroxide, and is preferably 40% by mass or less, more preferably 30% by mass or less, and further preferably 20% by mass or less, from the viewpoint of the solubility of component (A) and component (B).

[0022] On the other hand, when applying the present invention to the decontamination of radioactive materials in nuclear power plant reactor facilities, since iron oxide and / or iron hydroxide dissolve along with the radioactive materials, it is sometimes necessary to suppress the dissolution of iron oxide and / or iron hydroxide in order to reduce the radiation dose to the operator. From this viewpoint, when using the reducing agent composition of the present invention in the decontamination of radioactive materials, the total content of component (A) and component (B) in the reducing agent composition of the present invention is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more. Furthermore, from the viewpoint of not dissolving iron oxide and / or iron hydroxide to a degree necessary to reduce the radiation dose, it is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.08% by mass or less.

[0023] [Component (C): Amine compound]

[0024] Examples of amine compounds that can be used as component (C) include hydrazine, methylamine, monoethanolamine, N,N-dimethylaminoethanol, N,N-diethylaminoethanol, N,N-dibutylaminoethanol, N-(β-aminoethyl)ethanolamine, N-methylethanolamine, 2-ethylaminoethanol, mono-n-butylethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, mono-n-butyldiethanolamine, morpholine, piperazine, aminoethylpiperazine, homopiperazine, piperidine, ethylenediamine, diethylenetriamine, 1,2-propanediamine, dimethylethylenediamine, pentamethyldiethylenetriamine, tetramethylethylenediamine, dimethylaminohexanol, polyethyleneimine, hydrazine, 4-aminomorpholine, 4-aminopiperidine, etc. From the viewpoint of rapid formation of reducing active species, compounds with a 1,2-diamine structure such as N-(β-aminoethyl)ethanolamine, piperazine, homopiperazine, ethylenediamine, diethylenetriamine, and 1,2-propanediamine are preferred.

[0025] The reasons for preferring an amine compound having a 1,2-diamine structure as component (C) are as follows. For example, ethylenediamine having a 1,2-diamine structure undergoes an addition reaction with thiourea dioxide, thereby generating aminoethylguanidine (reaction 1). This compound rapidly undergoes an intramolecular cyclization reaction, thereby becoming aminoimidazoline (reaction 2). Further addition of ethylenediamine to this aminoimidazoline yields aminoethylaminoimidazoline (reaction 3). In this reaction, it was found that thiourea dioxide reacts quantitatively with ethylenediamine in a molar ratio of 1:2, proceeding very rapidly. As a result, thiourea dioxide decomposes rapidly to generate dithionite, which is the reducing active species, thereby infinitely suppressing the deactivation of the reducing species caused by dissolved oxygen in water and fully utilizing the reduction rate of iron oxide and / or iron hydroxide. This reaction is considered to be specific to amines having a 1,2-diamine structure.

[0026] [Chemical Formula 1]

[0027]

[0028] Regarding the content of component (C) in the reducing agent composition of the present invention, from the viewpoint of high solubility of iron oxide and / or iron hydroxide, it is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more. In addition, from the viewpoint of pH control, it is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0029] Regarding the molar ratio (C) / (A) of component (C) to component (A) in the reducing agent composition of the present invention, from the viewpoint of high solubility of iron oxide and / or iron hydroxide, it is preferably 1.5 or more, more preferably 1.8 or more, and even more preferably 2 or more. In addition, from the viewpoint of pH control, it is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less.

[0030] [Solvent, any component]

[0031] The reducing agent composition of the present invention preferably uses water as a solvent. In addition, it may contain surfactants, organic acids, inorganic acids, organic salts, inorganic salts, alkalis other than amine compounds, in addition to the components (A) to (C).

[0032] [pH]

[0033] Regarding the pH of the reducing agent composition of the present invention, from the viewpoint of high solubility of iron oxide and / or iron hydroxide, it is 7 or more, preferably 7.5 or more, more preferably 8 or more, and even more preferably 8.5 or more. In addition, it is 11 or less, preferably 10.5 or less, more preferably 10 or less, and even more preferably 9.5 or less.

[0034] [Redox potential]

[0035] The reducing agent composition of the present invention needs to meet the content and pH of components (A) to (C) as described above, and also needs to meet the following conditions. That is, the redox potential when dissolving reducing agent (A) in an aqueous solution containing water-soluble metal chelating agent (B) and amine compound (C) needs to be below -600mV within 20 minutes after the start of dissolving component (A), and the rate of change of redox potential needs to be above 0mV / min within 60 minutes.

[0036] [Iron oxide and / or iron hydroxide as the targets of reduction]

[0037] The iron oxide and iron hydroxide that are the objects of reduction in this invention are compounds commonly known as red rust. Specifically, examples of iron oxide include hematite (denoted as α-Fe₂O₃) and magnetite (denoted as γ-Fe₂O₃). Examples of iron hydroxide include iron(III) hydroxide (denoted as Fe(OH)₃) and iron hydroxide oxyhydroxide, such as goethite (denoted as α-FeOOH), tetragonal lepidocrocite (denoted as β-FeOOH), and lepidocrocite (denoted as γ-FeOOH).

[0038] [Restore Method]

[0039] By contacting the reducing agent composition of the present invention described above with iron oxide and / or iron hydroxide, iron oxide and / or iron hydroxide can be reduced. The temperature at which the reducing agent composition of the present invention is contacted with iron oxide and / or iron hydroxide is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 20°C or higher, and preferably 50°C or lower, more preferably 45°C or lower, even more preferably 40°C or lower. Preferably, the iron oxide and / or iron hydroxide are contacted with a liquid containing components (B) and (C) of the present invention, and then component (A) is dissolved.

[0040] Regarding the embodiments described above, the preferred embodiments of the present invention are further disclosed below.

[0041] <1> A reducing agent composition for iron oxide and / or iron hydroxide is a reducing agent composition containing the following components (A) to (C) and having a pH range of 7 to 11, wherein the redox potential of component (A) when dissolved in an aqueous solution containing components (B) and (C) is -600 mV or less within 20 minutes after the start of dissolution of component (A), and the rate of change of redox potential is 0 mV / min or more within 60 minutes.

[0042] (A) Reducing agent

[0043] (B) Water-soluble metal chelating agents

[0044] (C) Amine compounds

[0045] <2> The reducing agent composition described in <1>, wherein component (A) is thiourea dioxide.

[0046] <3> According to the reducing agent composition described in <1> or <2>, the content of component (A) is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.03% by mass or more, and preferably 7.8% by mass or less, more preferably 7.0% by mass or less, and even more preferably 5.0% by mass or less.

[0047] <4> The reducing agent composition according to any one of <1> to <3>, wherein component (B) is one or more selected from aminocarboxylic acid compounds, phosphonic acid compounds and hydroxycarboxylic acid compounds.

[0048] <5> The reducing agent composition according to any one of <1> to <4>, wherein component (B) is selected from one or more aminocarboxylic acid compounds and phosphonic acid compounds.

[0049] <6> The reducing agent composition according to any one of <1> to <5>, wherein component (B) is an aminocarboxylic acid compound.

[0050] <7> The reducing agent composition according to <6>, wherein the aminocarboxylic acid compound is selected from one or more of the following: hypozonotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraaminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, ethylene glycol ether diaminetetraacetic acid, dicarboxymethylglutamic acid, ethylenediamine-N,N'-disuccinic acid, L-aspartic-N,N-diacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, methylglycine diacetic acid, 3-hydroxy-2,2'-iminodisuccinic acid, L-glutamic acid diacetic acid, and their salts.

[0051] <8> The reducing agent composition according to any one of <1> to <7>, wherein the content of component (B) is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.03% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0052] <9> The reducing agent composition according to any one of <1> to <8>, wherein the total content of component (A) and component (B) is preferably 0.03% by mass or more, more preferably 0.04% by mass or more, even more preferably 0.05% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0053] <10> A reducing agent composition according to any one of <1> to <9>, wherein component (C) is a compound having a 1,2-diamine structure.

[0054] <11> The reducing agent composition according to any one of <1> to <10>, wherein the compound having a 1,2-diamine structure is selected from one or more of N-(β-aminoethyl)ethanolamine, piperazine, homopiperazine, ethylenediamine, diethylenetriamine and 1,2-propanediamine.

[0055] <12> The reducing agent composition according to any one of <1> to <11>, wherein the content of component (C) is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.03% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0056] <13> The reducing agent composition according to any one of <1> to <12>, wherein the molar ratio (C) / (A) of component (C) to component (A) is preferably 1.5 or more, more preferably 1.8 or more, and even more preferably 2 or more. Furthermore, from the viewpoint of pH control, it is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less.

[0057] <14> The reducing agent composition according to any one of <1> to <13>, wherein the pH is preferably 7.5 or higher, more preferably 8 or higher, even more preferably 8.5 or higher, and preferably 10.5 or lower, more preferably 10 or lower, even more preferably 9.5 or lower.

[0058] <15> A method for reducing iron oxide and / or iron hydroxide, wherein the reducing agent composition of <1> to <14> is contacted with iron oxide and / or iron hydroxide.

[0059] <16> According to the reduction method described in <15>, the temperature at which the reducing agent composition is brought into contact with iron oxide and / or iron hydroxide is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 20°C or higher, and preferably 50°C or lower, more preferably 45°C or lower, even more preferably 40°C or lower.

[0060] Example

[0061] Examples 1-15, Comparative Examples 1-6

[0062] Prepare the aqueous solutions shown in Tables 1 and 2, and perform the following hematite dissolution test and redox potential determination.

[0063] <pH Measurement Method>

[0064] While stirring the components other than thiourea dioxide in the composition shown in Tables 1-2 with a magnetic stirrer, thiourea dioxide was added, and the pH at which thiourea dioxide was completely dissolved was measured using a portable pH meter D-72 (manufactured by Horiba Corporation) and a pH electrode 9615S-10D (manufactured by Horiba Corporation).

[0065] <Test Method for Hematite Dissolution>

[0066] In a 50 mL glass container, 40 g of a composition containing all components except thiourea dioxide (as shown in Tables 1-2) was prepared. 0.4 g of hematite was added, and the mixture was stirred at room temperature using a magnetic stirrer. After stirring for 1 hour following the addition of thiourea dioxide, a sample was taken. The sample was filtered using a disposable DISMIC 25CS020AN filter (ASONE). The iron ion concentration in the aqueous phase was measured using a portable multi-parameter water quality analyzer PF-12 (MACHEREY-NAGEL) and the NANOCOLOR Tube Test Iron 3 reagent (MACHEREY-NAGEL). The concentration of iron ions dissolved from the hematite was calculated.

[0067] Tables 1 and 2 show the iron ion concentrations and, as an indicator of the reducing power of iron oxide and / or iron hydroxide in each composition, show the ratio of iron ion concentration (ppm) relative to the total content (mass%) of components (A) and (B).

[0068] <Methods for Determining Oxidation-Reduction Potential>

[0069] In a 100 mL glass container, 100 g of a composition containing all components except thiourea dioxide as shown in Tables 1 and 2 was prepared and stirred at room temperature using a magnetic stirrer. While stirring, a portable pH meter D-72 (manufactured by Horiba Corporation) and an ORP electrode 9300-10D (manufactured by Horiba Corporation) were used to record the redox potential at 10-second intervals, with the moment of thiourea dioxide addition set to 0 seconds. The time (in minutes) until the redox potential reached -600 mV or below and the time (in minutes) until the rate of change of redox potential reached 0 mV / min or above are shown in Tables 1 and 2.

[0070] [Table 1]

[0071]

[0072] [Table 2]

[0073]

Claims

1. A reducing agent composition for iron oxide and / or iron hydroxide, comprising components A to C and having a pH range of 7 to 11. The content of component A is ≥0.01% by mass and ≤7.8% by mass. The content of component C is 0.01% by mass or more and 25% by mass or less. The molar ratio of component C to component A, C / A, is greater than 2 and less than 7.

42. The redox potential of component A during dissolution in an aqueous solution containing components B and C is below -600 mV within 20 minutes after the dissolution of component A begins, and the rate of change of redox potential is above 0 mV / min within 60 minutes. A: Thiourea dioxide; B: Water-soluble metal chelating agent; C: Amine compounds.

2. The reducing agent composition according to claim 1, wherein, Component B is an aminocarboxylic acid compound.

3. The reducing agent composition according to claim 2, wherein, The aminocarboxylic acid compounds are selected from one or more of the following: α-triacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraaminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, ethylene glycol ether diaminetetraacetic acid, dicarboxymethylglutamic acid, ethylenediamine-N,N'-disuccinic acid, L-aspartic-N,N-diacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, methylglycine diacetic acid, 3-hydroxy-2,2'-iminodisuccinic acid, L-glutamic acid diacetic acid, and their salts.

4. The reducing agent composition according to any one of claims 1 to 3, wherein, Component C is a compound with a 1,2-diamine structure.

5. The reducing agent composition according to claim 4, wherein, The compound having a 1,2-diamine structure is selected from one or more of N-(β-aminoethyl)ethanolamine, piperazine, homopiperazine, ethylenediamine, diethylenetriamine, and 1,2-propanediamine.

6. The reducing agent composition according to any one of claims 1 to 3, wherein, The content of component B is 0.01% by mass or more and 40% by mass or less.

7. A method for reducing iron oxide and / or iron hydroxide, wherein the reducing agent composition of any one of claims 1 to 6 is contacted with iron oxide and / or iron hydroxide.

8. The method for reducing iron oxide and / or iron hydroxide according to claim 7, wherein the method is carried out in a temperature range of 5°C or higher and 40°C or lower.

9. A reducing agent composition for iron oxide and / or iron hydroxide, comprising components A to C and having a pH range of 7 to 11. The redox potential of component A during dissolution in an aqueous solution containing components B and C is below -600 mV within 20 minutes after the dissolution of component A begins, and the rate of change of redox potential is above 0 mV / min within 60 minutes. The content of component A is ≥0.01% by mass and ≤7.8% by mass. The content of component C is 0.01% by mass or more and 25% by mass or less. The molar ratio of component C to component A, C / A, is greater than 2 and less than 7.42, and The combined content of component A and component B is 0.03% by mass or more and 40% by mass or less. A: Thiourea dioxide; B: Aminocarboxylic acid compounds; C: Amine compounds.

10. The reducing agent composition according to claim 9, wherein, Component C is a compound with a 1,2-diamine structure.

11. The reducing agent composition according to claim 10, wherein, The compound having a 1,2-diamine structure is selected from one or more of N-(β-aminoethyl)ethanolamine, piperazine, homopiperazine, ethylenediamine, diethylenetriamine, and 1,2-propanediamine.

12. A method for reducing iron oxide and / or iron hydroxide, wherein the reducing agent composition of any one of claims 9 to 11 is contacted with iron oxide and / or iron hydroxide.

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