Reducing agent composition for iron oxide and / or iron hydroxide

Abstract

To provide: a reducing agent composition for iron oxide and / or iron hydroxide that can quickly produce dithionous acid as a reduction active species from thiourea dioxide and can minimize the inactivation of reduction species due to dissolved oxygen in water to exhibit a sufficient reduction rate of iron oxide and / or iron hydroxide; and a method for reducing iron oxide and / or iron hydroxide using the same.SOLUTION: Provided are: a reducing agent composition for iron oxide and / or iron hydroxide, comprising components (A)-(C) and having a pH in a range of 7-11, wherein a redox potential when component (A) is dissolved in an aqueous solution containing components (B) and (C) reaches -600 mV or lower within 20 minutes after start of dissolution of component (A), and a rate of change in redox potential reaches a value of 0 mV / min or greater within 60 minutes; and a method for reducing iron oxide and / or iron hydroxide by bringing the reducing agent composition into contact with iron oxide and / or iron hydroxide. (A) Reducing agent, (B) water-soluble metal chelating agent, and (C) amine compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention 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 Art

[0002] Iron oxide occurs in various environments with respect to machines, equipment, etc. that come into contact with water, and degrades the performance of the machines and equipment. For example, in water supply pipes, boiler pipes for power generation, residential environmental facilities, etc., due to the adhesion of iron oxide, performance degradation, and hygienic or aesthetic inconveniences occur. Further, in the decommissioning of nuclear power plants, a decontamination operation of radioactive substances is required, and since the radioactive substances are present so as to be incorporated into the iron oxide film adhering to the base material, it is desired to efficiently dissolve the iron oxide film.

[0003] Therefore, various iron oxide removal technologies have been proposed. For example, Patent Document 1 discloses a reducing agent composition containing thiourea dioxide, a specific alkali metal salt anhydride, and an alkali metal bicarbonate. Patent Document 2 describes a rust removal composition comprising a basic compound, a water-soluble metal chelating agent, and thiourea dioxide.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the rust-removing composition described in Patent Document 2 exclusively uses caustic alkali as the basic compound. Furthermore, a reduction reaction occurs when thiourea dioxide and an alkaline agent are mixed in an aqueous solution to produce dithionic acid, which is a reduced species of iron oxide. However, both the alkali metal bicarbonate used in Patent Document 1 and the caustic alkali used in Patent Document 2 have a slow rate of dithionic acid production, which competes with the rate at which the reduced species is deactivated by dissolved oxygen in the water, resulting in insufficient dissolution time and amount of iron oxide.

[0006] Therefore, the present invention relates to an iron oxide and / or iron hydroxide reducing agent composition that can rapidly generate dithionic acid, a reducing active species, from thiourea dioxide, and can fully exhibit the reduction rate of iron oxide and / or iron hydroxide by suppressing the deactivation of the reducing species by dissolved oxygen in water as much as possible, and to a method for reducing iron oxide and / or iron hydroxide using the same. [Means for solving the problem]

[0007] The inventors, after investigating various alkaline agents, discovered that by using an amine compound as the alkaline agent, dithionic acid, a reducing active species, can be rapidly generated from thiourea dioxide. This minimizes the deactivation of the reducing species by dissolved oxygen in water, allowing the reduction rate of iron oxide and / or iron hydroxide to be fully realized. As a result, the inventors found that iron oxide and / or iron hydroxide can be reduced and dissolved to near the stoichiometric amount of thiourea dioxide, thus completing the present invention.

[0008] The present invention provides a reducing agent composition for iron oxide and / or iron hydroxide, comprising the following components (A) to (C) and having a pH in the range of 7 to 11, wherein when component (A) is dissolved in an aqueous solution containing components (B) and (C), the oxidation-reduction potential becomes -600 mV or less within 20 minutes after the start of dissolution of component (A), and the rate of change of the oxidation-reduction potential becomes 0 mV / min or more within 60 minutes. (A) Reducing agent (B) Water-soluble metal chelating agent (C) Amine compound

[0009] Furthermore, the present invention provides a method for reducing iron oxide and / or iron hydroxide, comprising contacting the aforementioned reducing agent composition with iron oxide and / or iron hydroxide. [Effects of the Invention]

[0010] The reducing agent composition for iron oxide and / or iron hydroxide of the present invention can rapidly generate dithionic acid, which is a reducing active species, from thiourea dioxide, thereby suppressing the deactivation of the reducing species by dissolved oxygen in water and allowing the reduction rate of iron oxide and / or iron hydroxide to be fully exhibited. [Modes for carrying out the invention]

[0011] [Component (A): Reducing agent] Thiourea dioxide is preferably used as the reducing agent for component (A). The content of component (A) 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, from the viewpoint of the high solubility of iron oxide and / or iron hydroxide, 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, from the viewpoint of the solubility of the reducing agent.

[0012] [Component (B): Water-soluble metal chelating agent] The water-soluble metal chelating agents in component (B) include nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol etherdiaminetetraacetic acid, dicarboxymethylglutamic acid, ethylenediamine-N,N'-disuccinic acid, and L-aspartic acid-N,N Examples include aminocarboxylic acid compounds such as -diacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, methylglycinediacetic acid, 3-hydroxy-2,2'-iminodisuccinic acid, L-glutamic acid diacetic acid, and their salts; phosphonic acid compounds such as hydroxyethylidenediphosphonic acid, nitrilotri(methylphosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid, ethylenediaminetetramethylenephosphonic acid, and their salts; and hydroxycarboxylic acid compounds such as gluconic acid, citric acid, and their salts. Among these, aminocarboxylic acid compounds and phosphonic acid compounds are preferred.

[0013] The content of 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, from the viewpoint of the high solubility of iron oxide and / or iron hydroxide, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of the solubility of the metal chelating agent.

[0014] The total content of component (A) and component (B) in the reducing agent composition of the present invention is preferably 0.03% by mass or more, more preferably 0.04% by mass or more, and even more preferably 0.05% by mass or more, from the viewpoint of the high solubility of iron oxide and / or iron hydroxide, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of the solubility of component (A) and component (B).

[0015] On the other hand, when applying the present invention to decontamination work of radioactive materials in the reactor facilities of a nuclear power plant, iron oxide and / or iron hydroxide dissolve together with the radioactive material, so it may be necessary to suppress the amount of iron oxide and / or iron hydroxide dissolved in order to reduce the amount of radiation exposure to workers. From this viewpoint, when using the reducing agent composition of the present invention for decontamination work 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 more iron oxide and / or iron hydroxide than necessary to reduce the amount of radiation exposure, 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.

[0016] [Component (C): Amine compound] The amine compounds in 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, ethyl Examples include rendiamine, diethylenetriamine, 1,2-propanediamine, dimethylethylenediamine, pentamethyldiethylenetriamine, tetramethylethylenediamine, dimethylaminohexanol, polyethyleneimine, hydrazine, 4-aminomorpholine, and 4-aminopiperidine. Among these, those having a 1,2-diamine structure, such as N-(β-aminoethyl)ethanolamine, piperazine, homopiperazine, ethylenediamine, diethylenetriamine, and 1,2-propanediamine, are preferred from the viewpoint of the speed of generation of reducing active species.

[0017] The reason why an amine compound having a 1,2-diamine structure is preferable as the component (C) can be considered as follows. For thiourea dioxide, for example, ethylenediamine having a 1,2-diamine structure undergoes an addition reaction to generate aminoethylguanidine (Reaction 1). This compound rapidly undergoes an intramolecular cyclization reaction to become aminoimidazoline (Reaction 2). Further addition reaction of ethylenediamine to this aminoimidazoline generates aminoethylaminoimidazoline (Reaction 3). It has been found that this reaction proceeds quantitatively with a molar ratio of thiourea dioxide to ethylenediamine of 1:2 and proceeds very rapidly. As a result, thiourea dioxide decomposes to rapidly generate dithionous acid which is a reducing active species, thereby suppressing the inactivation of the reducing species by dissolved oxygen in water to an extreme extent and sufficiently exerting the reduction rate of iron oxide and / or iron hydroxide. This reaction is considered to be a reaction specific to amines having a 1,2-diamine structure.

[0018] [Chemical formula]

[0019] From the viewpoint of the high dissolution amount of iron oxide and / or iron hydroxide, the content of the component (C) 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, still more preferably 0.03% by mass or more. Also, from the viewpoint of pH control, it is preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 15% by mass or less.

[0020] From the viewpoint of the high dissolution amount of iron oxide and / or iron hydroxide, the molar ratio (C) / (A) of the component (C) to the component (A) in the reducing agent composition of the present invention is preferably 1.5 or more, more preferably 1.8 or more, still more preferably 2 or more. Also, from the viewpoint of pH control, it is preferably 10 or less, more preferably 9 or less, still more preferably 8 or less.

[0021] [Solvent, optional component] The reducing agent composition of the present invention preferably uses water as a solvent. In addition to the components (A) to (C), it can contain surfactants, organic acids, inorganic acids, organic salts, inorganic salts, alkali agents other than amine compounds, etc.

[0022] 〔pH〕 From the viewpoint of the high dissolution amount of iron oxide and / or iron hydroxide, the pH of the reducing agent composition of the present invention is 7 or more, preferably 7.5 or more, more preferably 8 or more, still more preferably 8.5 or more, and is 11 or less, preferably 10.5 or less, more preferably 10 or less, still more preferably 9.5 or less.

[0023] 〔Redox potential〕 The reducing agent composition of the present invention needs to satisfy the contents and pH of the above-mentioned components (A) to (C) and also satisfy the following conditions. That is, when the reducing agent (A) is dissolved in an aqueous solution containing the water-soluble metal chelating agent (B) and the amine compound (C), the redox potential becomes -600 mV or less within 20 minutes after the start of dissolution of the component (A), and the change rate of the redox potential becomes a value of 0 mV / min or more within 60 minutes.

[0024] 〔Iron oxide and / or iron hydroxide as the reduction target〕 The iron oxide and iron hydroxide targeted for reduction by the present invention are those generally known as red rust. Specifically, examples of the iron oxide include hematite represented by α-Fe2O3 and maghemite represented by γ-Fe2O3. Examples of the iron hydroxide include iron(III) hydroxide represented by Fe(OH)3 and iron oxyhydroxide, such as goethite represented by α-FeOOH, akaganéite represented by β-FeOOH, and lepidochrome represented by γ-FeOOH. [[ID= nineteen]]

[0025] 〔Reduction method〕 The reducing agent composition of the present invention described above can be used to reduce iron oxide and / or iron hydroxide by contacting it with the iron oxide and / or iron hydroxide. 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 also preferably 50°C or lower, more preferably 45°C or lower, and even more preferably 40°C or lower. It is preferable to contact iron oxide and / or iron hydroxide with a solution containing components (B) and (C) of the present invention, and then dissolve component (A).

[0026] With respect to the embodiments described above, preferred embodiments of the present invention are further disclosed below.

[0027] <1> A reducing agent composition for iron oxide and / or iron hydroxide, comprising the following components (A) to (C), having a pH in the range of 7 to 11, wherein when component (A) is dissolved in an aqueous solution containing components (B) and (C), the oxidation-reduction potential becomes -600 mV or less within 20 minutes after the start of dissolving component (A), and the rate of change of the oxidation-reduction potential becomes 0 mV / min or more within 60 minutes. (A) Reducing agent (B) Water-soluble metal chelating agent (C) Amine compound

[0028] <2> The above, where component (A) is thiourea dioxide. <1> The reducing agent composition described above.

[0029] <3> 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 also 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. <1> or <2> The reducing agent composition described above.

[0030] <4> The component (B) is one or more selected from aminocarboxylic acid compounds, phosphonic acid compounds, and hydroxycarboxylic acid compounds. <1> ~ <3> A reducing agent composition according to any one of the following.

[0031] <5> The above is a description of component (B) being one or more selected from aminocarboxylic acid compounds and phosphonic acid compounds. <1> ~ <4> A reducing agent composition according to any one of the following.

[0032] <6> The above, where component (B) is an aminocarboxylic acid compound. <1> ~ <5> A reducing agent composition according to any one of the following.

[0033] <7> The aminocarboxylic acid compound is one or more selected from nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol etherdiaminetetraacetic acid, dicarboxymethylglutamic acid, ethylenediamine-N,N'-disuccinic acid, L-aspartic acid-N,N-diacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, methylglycinediacetic acid, 3-hydroxy-2,2'-iminodisuccinic acid, L-glutamic acid diacetic acid, and salts thereof. <6> The reducing agent composition described above.

[0034] <8> 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 also preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. <1> ~ <7> A reducing agent composition according to any one of the following.

[0035] <9> 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 also preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. <1> ~ <8> A reducing agent composition according to any one of the following.

[0036] <10> The above is a compound in which component (C) has a 1,2-diamine structure. <1> ~ <9> A reducing agent composition according to any one of the following.

[0037] <11> The compound having a 1,2-diamine structure is one or more selected from N-(β-aminoethyl)ethanolamine, piperazine, homopiperazine, ethylenediamine, diethylenetriamine, and 1,2-propanediamine. <1> ~ <10> A reducing agent composition according to any one of the following.

[0038] <12> 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 also preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. <1> ~ <11> A reducing agent composition according to any one of the following.

[0039] <13> 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, and from the viewpoint of pH control, it is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. <1> ~ <12> A reducing agent composition according to any one of the following.

[0040] <14> The pH is preferably 7.5 or higher, more preferably 8 or higher, even more preferably 8.5 or higher, and also preferably 10.5 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. <1> ~ <13> A reducing agent composition according to any one of the following.

[0041] <15> The aforementioned <1> ~ <14> A method for reducing iron oxide and / or iron hydroxide, comprising contacting the iron oxide and / or iron hydroxide with a reducing agent composition.

[0042] <16> 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, still more preferably 20 °C or higher, and is preferably 50 °C or lower, more preferably 45 °C or lower, still more preferably 40 °C or lower, in the reduction method described in <15>.

Examples

[0043] Examples 1 to 15, Comparative Examples 1 to 6 Aqueous solutions shown in Tables 1 to 2 were prepared, and the following hematite dissolution test and measurement of oxidation-reduction potential were carried out.

[0044] <pH measurement method> In the compositions shown in Tables 1 to 2, while stirring the components other than thiourea dioxide with a magnetic stirrer, thiourea dioxide was added, and the pH when thiourea dioxide was completely dissolved was measured using a portable pH meter D-72 (manufactured by Horiba, Ltd.) and a pH electrode 9615S-10D (manufactured by Horiba, Ltd.).

[0045] <Hematite dissolution test method> In a glass container with a volume of 50 mL, 40 g of a composition obtained by mixing the components other than thiourea dioxide in the compositions shown in Tables 1 to 2 was prepared, 0.4 g of hematite was added, and stirring was carried out at room temperature using a magnetic stirrer. After stirring for 1 hour after adding thiourea dioxide, sampling was performed, and the sample was filtered using a disposable filter DISMIC 25CS020AN (manufactured by AS ONE Corporation). Then, the iron ion concentration in the aqueous phase was measured using a portable multi-item water quality meter PF-12 (manufactured by MACHEREY-NAGEL) and an iron measurement reagent NANOCOLOR Tube Test Iron 3 (manufactured by MACHEREY-NAGEL), and the iron ion concentration dissolved from hematite was calculated. In Tables 1 and 2, together with the iron ion concentration, the ratio of the iron ion concentration (ppm) to the total content (% by mass) of components (A) and (B) is shown as an index indicating the height of the iron oxide and / or iron hydroxide reduction ability of each composition.

[0046] <Oxidation-reduction potential measurement method> 100 g of a composition was prepared in a 100 mL glass container, containing all components except thiourea dioxide as shown in Tables 1 and 2. The mixture was stirred at room temperature using a magnetic stirrer. While stirring, the oxidation-reduction potential was measured at 10-second intervals, with the time of thiourea dioxide addition being considered 0 seconds, using a portable pH meter D-72 (Horiba, Ltd.) and an ORP electrode 9300-10D (Horiba, Ltd.). The time (in minutes) until the oxidation-reduction potential fell below -600 mV, and the time (in minutes) until the rate of change of the oxidation-reduction potential exceeded 0 mV / min, are shown in Tables 1 and 2.

[0047] [Table 1]

[0048] [Table 2]

Claims

1. A reducing agent composition for iron oxide and / or iron hydroxide, comprising the following components (A) to (C), having a pH in the range of 7 to 11, wherein when component (A) is dissolved in an aqueous solution containing components (B) and (C), the oxidation-reduction potential becomes -600 mV or less within 20 minutes after the start of dissolving component (A), and the rate of change of the oxidation-reduction potential becomes 0 mV / min or more within 60 minutes. (A) Thiourea dioxide (B) Water-soluble metal chelating agent selected from aminocarboxylic acid compounds, phosphonic acid compounds, and hydroxycarboxylic acid compounds (C) Amine compound having an active hydrogen bonded to a nitrogen atom

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 1 or 2, wherein component (C) is a compound having a 1,2-diamine structure.

4. A reducing agent composition according to any one of claims 1 to 3, wherein the molar ratio (C) / (A) of component (A) is 1.5 or more.

5. A reducing agent composition according to any one of claims 1 to 4, wherein the content of component (A) is 0.01% by mass or more and 7.8% by mass or less.

6. A reducing agent composition according to any one of claims 1 to 5, 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, comprising contacting the iron oxide and / or iron hydroxide with a reducing agent composition according to any one of claims 1 to 6.

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

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