Method for producing an aqueous solution containing iodine using an inorganic flocculant capable of selectively removing fluoride ions and phosphate ions, inorganic flocculant, and recycled aqueous solution

Abstract

To provide a method for producing an iodine component-containing aqueous solution which can maintain iodine ion concentration while reducing fluoride ion concentration and / or phosphate ion concentration in non-treatment water by a coagulation method.SOLUTION: A method for producing an iodine component-containing aqueous solution includes: a coagulation step of bringing non-treatment water containing iodine ions, fluoride ions and / or phosphate ions into contact with an inorganic coagulant which more selectively reacts with the fluoride ions and / or the phosphate ions than the iodine ions, and obtaining an aggregate obtained by reacting the fluoride ions and / or the phosphate ions with the inorganic coagulant; and a separation step of removing the aggregate from the non-treatment water, and causing the iodine ions to remain in the non-treatment water and thereby obtaining treatment water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an iodine-containing aqueous solution using an inorganic flocculant capable of selectively removing fluoride ions and phosphate ions, the inorganic flocculant, and a recycled aqueous solution. [Background technology]

[0002] Various techniques have been developed to selectively recover iodide ions from a non-treatment liquid containing iodide ions and fluoride ions. One such technique is described in Patent Document 1. Patent Document 1 describes a technique for separating iodide ions from a non-treatment liquid containing iodide ions and at least one of fluoride ions and boron ions by electrodialysis (e.g., claim 1 of Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-97182 Summary of the Invention [Problem to be solved by the invention]

[0004] It has been known as a common technique to selectively recover iodide ions from a non-treated solution containing iodide ions and fluoride ions by electrodialysis. However, after investigations by the present inventors, it was found that the electrodialysis method was unable to sufficiently reduce the fluoride ion concentration in untreated water (comparative example in the above-mentioned Patent Document 1), and so the inventors proceeded to investigate methods other than the electrodialysis method. [Means for solving the problem]

[0005] As a result of further investigation, the present inventors have found an inorganic flocculant that selectively reacts with fluoride ions to form flocculants but does not selectively react with iodide ions. Based on this finding, further intensive research has led to the discovery of a flocculation method that can sufficiently reduce the concentration of fluoride ions by using an inorganic flocculant that is not selective for iodide ions, thereby enabling fluoride ions to be selectively separated from untreated water containing iodide ions and fluoride ions, thereby completing the present invention. According to the investigations of the present inventors, it has been found that, similar to fluoride ions, phosphate ions can also be separated selectively from iodide ions by a flocculation method using an inorganic flocculant that is non-selective for iodide ions.

[0006] According to one aspect of the present invention, there are provided the following method for producing an iodine component-containing aqueous solution, an inorganic flocculant, and a recycled aqueous solution. 1. A flocculation step in which untreated water containing iodide ions and fluoride ions and / or phosphate ions is contacted with an inorganic flocculant that reacts selectively with fluoride ions and / or phosphate ions over iodide ions to obtain a flocculate formed by the reaction of the fluoride ions and / or phosphate ions with the inorganic flocculant; a separation step of removing the aggregates from the untreated water and leaving iodide ions in the untreated water, thereby obtaining treated water. 2. A method for producing an iodine component-containing aqueous solution according to 1., A method for producing an iodine-containing aqueous solution, wherein in the flocculation step, the pH of the non-treated water containing the inorganic flocculant is 3.0 or more and 11.5 or less. 3. A method for producing an iodine component-containing aqueous solution according to 1. or 2., The volume frequency particle size distribution is measured using a laser diffraction scattering method, and the particle size at which 50% of the particle size in the volume frequency particle size distribution accumulates from the smallest side is defined as D 50 When the aggregates are 50 The method for producing an aqueous solution containing an iodine component, wherein the particle size is 1 μm or more and 80 μm or less. 4. A method for producing an iodine component-containing aqueous solution according to any one of 1. to 3., A method for producing an iodine-containing aqueous solution, wherein the inorganic flocculant contains one or more selected from the group consisting of a cerium-based flocculant, a zirconium-based flocculant, an aluminum-based flocculant, a calcium-based flocculant, and an iron-based flocculant. 5. A method for producing an iodine component-containing aqueous solution according to any one of 1. to 4., The concentration of iodide ions in the untreated water is C Ia (mg / L), and the concentration of iodide ions in the treated water is C Ib (mg / L), (C Ib / C Ia ) × 100, the recovery rate of iodide ions is 90% or more. 6. A method for producing an iodine component-containing aqueous solution according to 5., The concentration of fluoride ions in the untreated water is C Fa (mg / L), and the concentration of phosphate ions is C Pa (mg / L), and the concentration of fluoride ions in the treated water is C Fb (mg / L), and the concentration of phosphate ions is C Pb (mg / L), Formula [100-[(C Fa -C Fb ) / C Fa 〕×100] is 5% or less, Or, the formula [100-[(C Pa -C Pb ) / C Pa 〕×100], the residual rate of phosphate ions is 5% or less. 7. A method for producing an iodine component-containing aqueous solution according to 6., A method for producing an iodine-containing aqueous solution, wherein the inorganic flocculant has an iodide ion non-selectivity index of 1.5 or more, calculated by [recovery rate of the iodide ion / residual rate of the fluoride ion] or [recovery rate of the iodide ion / residual rate of the phosphate ion]. 8. A method for producing an iodine component-containing aqueous solution according to any one of 1. to 7., The method for producing an aqueous solution containing an iodine component, wherein the concentration of iodide ions in the untreated water is 5 g / L or more. 9. An inorganic flocculant for use in untreated water containing iodide ions and fluoride ions and / or phosphate ions, An inorganic flocculant that is non-selective for iodide ions, but reacts more selectively with fluoride ions and / or phosphate ions than with iodide ions to produce flocculants. 10. A recycled aqueous solution containing iodide ions, the concentration of the iodide ions in the recycled aqueous solution is 5 g / L or more; A recycled aqueous solution in which the concentration of fluoride ions and / or the concentration of phosphate ions contained in the recycled aqueous solution is 8 mg / L or less. 11. A recycled aqueous solution of 10. The recycled aqueous solution contains at least one of cerium ions, zirconium ions, aluminum ions, calcium ions, and iron ions. [Effects of the Invention]

[0007] According to the present invention, there are provided a method for producing an iodine-containing aqueous solution by a coagulation method, which can reduce the fluoride ion concentration and / or the phosphate ion concentration in untreated water while maintaining the iodide ion concentration, an inorganic coagulant used therein, and a recycled aqueous solution. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram schematically illustrating an example of the configuration of an iodine recovery system according to an embodiment of the present invention. [Figure 2] FIG. 1 is a flow chart showing an example of a method for producing an iodine component-containing aqueous solution according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all drawings, similar components are designated by similar reference numerals, and descriptions thereof will be omitted where appropriate. Furthermore, the drawings are schematic diagrams and do not correspond to actual dimensional proportions.

[0010] An outline of the method for producing an iodine component-containing aqueous solution of this embodiment will be described.

[0011] The method for producing an iodine-containing aqueous solution of this embodiment includes a flocculation step in which untreated water containing iodide ions and fluoride ions and / or phosphate ions is contacted with an inorganic flocculant that reacts selectively with fluoride ions and / or phosphate ions over iodide ions to obtain a flocculate formed by the reaction of the fluoride ions and / or phosphate ions with the inorganic flocculant, and a separation step in which the flocculate is removed from the untreated water, leaving iodide ions in the untreated water, thereby obtaining treated water.

[0012] According to the findings of the present inventors, inorganic flocculants having the flocculation property of iodide ion non-selectivity have been found among organic and inorganic flocculants. Iodide ion non-selective inorganic flocculants selectively react with fluoride ions to form flocculants, but do not selectively react with iodide ions. Such iodide ion non-selectivity has also been confirmed in solutions in which phosphate ions and iodide ions coexist. The resulting aggregates can be easily removed from the system by solid-liquid separation or the like. Therefore, according to the method for producing an iodine-containing aqueous solution using the coagulation method of the present embodiment, it is possible to selectively separate fluoride ions and / or phosphate ions contained in untreated water, thereby reducing the fluoride ion concentration and / or phosphate ion concentration while allowing iodide ions to remain.

[0013] Furthermore, in the coagulation step, by adjusting the pH of the non-treated water containing the inorganic coagulant to fall within a predetermined range, the removal rate of fluoride ions and / or phosphate ions can be increased.

[0014] Furthermore, by setting the amount of inorganic flocculant added in the flocculation step within a predetermined range, the removal rate of fluoride ions and / or phosphate ions can be increased while suppressing the amount of sludge generated from the flocs.

[0015] Furthermore, by appropriately selecting the type of inorganic flocculant in the flocculation step, the size of the flocs (floc size) can be controlled, thereby improving the filterability during solid-liquid separation.

[0016] An example of treated water (recycled aqueous solution) obtained by the method for producing an iodine-containing aqueous solution of this embodiment has an iodide ion concentration of 5 g / L or more, a fluoride ion concentration of 8 mg / L or less and / or a phosphate ion concentration of 8 mg / L or less in terms of phosphorus element, and a pH of 6.8 to 7.8 as needed. Such a recycled aqueous solution is a solution that meets the wastewater standards set forth in the Water Pollution Control Act in terms of the fluoride ion concentration and the phosphate ion concentration.

[0017] In another embodiment, the iodide ion concentration in the recycled aqueous solution is not particularly limited, but may be, for example, 5 g / L or more, or 7 g / L or more, and can be freely selected from an economical viewpoint.

[0018] In another embodiment, the fluoride ion concentration in the recycled aqueous solution can be set in accordance with the emission standards established by Japan or by local municipalities, but is not limited thereto. In the case of recycled aqueous solutions used overseas, the fluoride ion concentration can be set in accordance with the emission standards established by each overseas country. An example of the fluoride ion concentration in the recycled aqueous solution is, for example, 8 mg / L or less, preferably 6 mg / L or less, and more preferably 4 mg / L or less. The phosphate ion concentration in the recycled aqueous solution is, for example, 8 mg / L or less, preferably 6 mg / L or less, and more preferably 4 mg / L or less in terms of elemental phosphorus.

[0019] In another embodiment, the pH of the recycled aqueous solution having a fluoride ion concentration of 8 mg / L or less is, for example, 3.0 or more and 8.5 or less, preferably 5.0 or more and 8.0 or less, and more preferably 7.0 or more and 7.5 or less. The pH of the recycled aqueous solution having a phosphate ion concentration of 8 mg / L or less in terms of phosphorus element is, for example, 4.5 to 6.0, preferably 5.0 to 6.0, and more preferably 5.0 to 5.5.

[0020] In another embodiment, the recycled aqueous solution is obtained by a flocculation method, and therefore may contain a portion of an inorganic flocculant as long as the required properties for various applications are not impaired. For example, an example of the recycled aqueous solution may contain at least one of cerium ions, zirconium ions, aluminum ions, calcium ions, and iron ions. Furthermore, an example of the recycled aqueous solution may be configured so that the concentration of at least one of cerium ions, zirconium ions, and calcium ions is, for example, 3 mg / L or more. In another embodiment, an example of the recycled aqueous solution may be configured so that the concentration of aluminum ions is, for example, 1 mg / L or more.

[0021] In this specification, the measurement of pH is performed using the "electrode method," which measures the pH in a solution based on the potential difference generated between a pH electrode and a reference electrode. Iodide ion concentration is measured using ion chromatography, oxidation-reduction titration, ion electrode method, ultraviolet absorption spectrometry, ICP emission spectrometry (high-frequency inductively coupled plasma emission spectrometry), etc. Fluoride ion concentration can be measured using colorimetry, lanthanum-alizarin complexone absorptiometry, ion chromatography, ion electrode method, etc. The phosphate ion concentration can be measured by ICP emission spectroscopy, molybdenum blue absorptiometry, ion chromatography, etc. In the case of ICP emission spectroscopy, the phosphate ion (PO4 -) is set to "94.97" and the atomic weight of the phosphorus element is set to "30.97," and the concentration of phosphate ions converted to phosphorus is calculated from the measured value of the phosphorus element. The concentrations of other elements are measured using ion chromatography, ICP emission spectrometry, etc. The measurement sample may be at a liquid temperature of about 25°C, and if necessary, the pH is adjusted to within a predetermined range using a pH adjuster described below.

[0022] The method for producing an iodine component-containing aqueous solution of this embodiment will be described in detail below.

[0023] FIG. 2 is a flow diagram showing an example of the method for producing an iodine component-containing aqueous solution of this embodiment. As shown in Figure 2, one example of a method for producing an iodine-containing aqueous solution includes a coagulation reaction step in which untreated water 1 is contacted with an inorganic coagulant to obtain a coagulant, and a solid-liquid separation step in which the produced coagulant is removed from untreated water 1 to obtain treated water 5.

[0024] Each step of the method for producing an iodine component-containing aqueous solution shown in FIG. 2 will be described using the iodine recovery system 100 shown in FIG. FIG. 1 is a diagram schematically illustrating an example of the configuration of an iodine recovery system according to this embodiment.

[0025] As shown in FIG. 1, the iodine recovery system 100 includes a reaction vessel 10 and a solid-liquid separation vessel 20. These tanks may be provided as separate tanks and connected by lines for continuous treatment, or may be used in the same tank for batch treatment. Continuous treatment is preferred when the amount of water to be treated is large.

[0026] First, untreated water 1 and inorganic flocculant 2 are introduced into reaction tank 10 in iodine recovery system 100. Then, in reaction tank 10, a mixed liquid containing untreated water 1 and inorganic flocculant 2 is obtained.

[0027] The method for introducing the untreated water 1 and the inorganic flocculant 2 is not particularly limited, but the inorganic flocculant 2 may be introduced after the untreated water 1 is introduced, or the untreated water 1 may be introduced into the reaction tank 10 in which the inorganic flocculant 2 is present. The inorganic flocculant 2 may be introduced in its entirety all at once, or may be introduced in several portions.

[0028] The reaction tank 10 may be equipped with an agitator. The agglomeration reaction can be promoted by agitating the mixture containing the untreated water 1 and the inorganic flocculant 2 at a predetermined agitation speed. The agitation speed is adjusted so that the inorganic flocculant 2 is adequately dispersed.

[0029] The reaction tank 10 may be equipped with a heater. The reaction tank 10 may be used at ambient temperature, but if the ambient temperature is low, the inside of the reaction tank 10 may be heated until the temperature of the mixed liquid reaches a temperature of about 5 to 30°C.

[0030] The untreated water 1 is not particularly limited as long as it is a liquid containing at least iodide ions, fluoride ions and / or phosphate ions, but waste liquid such as industrial wastewater is used. Specific examples of waste liquids include waste liquids from the electronic material manufacturing process and waste liquids from cleaning manufacturing equipment, waste liquids discharged in chemical reactions, waste liquids generated in chemical synthesis such as pharmaceutical synthesis, waste liquids containing industrial plating waste liquids, and solutions in which waste solids are dissolved.

[0031] Furthermore, the untreated water 1 includes water whose fluoride ion concentration or phosphate ion concentration exceeds the wastewater standards of each country. The fluoride ion concentration in the untreated water 1 before the inorganic flocculant 2 is added may exceed the discharge standards of each country, for example, more than 8 mg / L. Furthermore, the phosphate ion concentration of the untreated water 1 before the inorganic flocculant 2 is added may be, for example, more than 8 mg / L in terms of elemental phosphorus. In the method for producing an iodine-containing aqueous solution of the present embodiment, in the untreated water 1 containing such a high fluoride ion concentration and / or phosphate ion concentration, the fluoride ion concentration and the phosphate ion concentration can be reduced to below the above-mentioned wastewater standard while suppressing a reduction in the iodide ion concentration.

[0032] The iodide ion concentration in the untreated water 1 is not particularly limited, but may be, for example, 5 g / L or more, 7 g / L or more, and may be suitably selected from the viewpoint of economic efficiency. The higher the concentration of iodide ions contained in the untreated water 1, the more economically advantageous it is.

[0033] The inorganic flocculant 2 used is one that is non-selective to iodide ions, and reacts more selectively with fluoride ions and / or phosphate ions than with iodide ions to generate flocculants. The inorganic flocculant 2 that is non-selective to iodide ions can be suitably used for treating the untreated water 1.

[0034] The inorganic flocculant 2 may include, for example, one or more metal salt flocculants selected from the group consisting of cerium-based flocculants, zirconium-based flocculants, aluminum-based flocculants, calcium-based flocculants, and iron-based flocculants. Among these, cerium-based and aluminum-based flocculants can be used because they can form aggregates (sometimes called flocs) of appropriate size, thereby improving filterability during solid-liquid separation. Furthermore, it is preferable to use a cerium-based flocculant because it has excellent ability to remove fluoride ions and / or phosphate ions and can reduce the amount of flocculant used and the amount of aggregates generated.

[0035] The inorganic flocculant may be in any form, including a powder, a solution (a solution in which the active ingredient is dissolved in a solvent), or a dispersion (a slurry in which the active ingredient is not dissolved in a solvent). Among these, the use of a solution or dispersion of an inorganic flocculant can improve handling. Furthermore, the use of a solution of an inorganic flocculant can enhance the solution flocculation reactivity. When the inorganic flocculant is a solution or dispersion, the lower limit of the concentration of the active ingredient that flocculates the target can be adjusted appropriately depending on the treatment amount, but may be, for example, 5% by mass or more, 10% by mass or more, or 20% by mass or more. The upper limit of the active ingredient concentration is not particularly limited, but from the viewpoint of handleability, it may be 99% by mass or less, 80% by mass or less, or 50% by mass or less. Furthermore, the active ingredient of the inorganic flocculant contained in the solution can be the specific examples of the flocculant described below.

[0036] Examples of cerium-based flocculants include cerium oxide, cerium hydroxide, cerium carbonate, cerium sulfate, and cerium chloride. Among these, cerium carbonate, cerium sulfate, and cerium chloride are preferred from the viewpoint of solvent solubility. As an example of a cerium-based flocculant, a solution of a cerium compound described in Japanese Patent No. 6008455 can be used. An example of a commercially available product of this cerium compound solution is READ-CX(L) manufactured by Nippon Kaisui Co., Ltd. Examples of aluminum-based flocculants that can be used include polyaluminum chloride (PAC), aluminum sulfate (aluminum sulfate), and aluminum chloride. Examples of calcium-based flocculants that can be used include calcium chloride and calcium hydroxide (slaked lime). Examples of iron-based flocculants that can be used include ferric chloride, polyferric sulfate, and ferrous sulfate. The inorganic flocculants exemplified above may be used alone or in combination of two or more. When the inorganic flocculant is added to the reaction vessel 10 multiple times, the same flocculant may be added, or from the second time onwards, a different flocculant may be added in combination or changed to a different flocculant.

[0037] The amount of inorganic flocculant 2 to be added can be determined depending on various treatment conditions (pH during the flocculation reaction, fluoride ion residual rate, phosphate ion residual rate, iodide ion recovery rate, amount of sludge generated, etc.), but as an example, it can also be determined using the adsorption amount below as an indicator.

[0038] The above-mentioned adsorption amount can be calculated in advance based on the relationship between the amount of inorganic flocculant 2 added and the amount of fluoride ions and / or phosphate ions in the untreated water 1 removed thereby. First, calculate the weight (g) of the active ingredient in the added amount (g) of inorganic flocculant 2. Specifically, let M (g) be the added amount of inorganic flocculant 2, and C be the concentration (wt%) of the active ingredient in inorganic flocculant 2 in the powder, solution, or dispersion. CX Then, the weight of the active ingredient is M × C CX For example, if a solution containing 28% by weight of cerium in terms of cesium oxide is used as inorganic coagulant 2 of the solution, the active ingredient is cerium, and C CX is calculated as 28% by weight x [140 / (140+16×2)], where the atomic weight of Ce is 140 and the atomic weight of O is 16. Next, the amount (g) of inorganic flocculant 2 added and the amount of fluoride ions and / or phosphate ions removed from the untreated water 1 when added are measured. The removed fluoride ions and / or phosphate ions react with the active ingredient of inorganic flocculant 2 to form flocculants. The amount of removed fluoride elements C, converted into elemental fluoride (F), is calculated from the amount of removed fluoride ions. F (g) and the amount of removed phosphate (PO4) converted to C P04 Calculate (g). The above F adsorption amount (g / g) is F / (M×C CX ) and the above PO4 adsorption amount (g / g) is calculated from C P04 / (M×C CX ) is calculated. The upper limit of the F adsorption amount is equal to or less than the saturated adsorption amount of fluoride ions by the active ingredient in the inorganic flocculant 2, and is, for example, equal to or less than 400, preferably equal to or less than 390, and more preferably equal to or less than 380. On the other hand, the lower limit of the F adsorption amount is not particularly limited and can be set from an economical viewpoint, but may be equal to or more than 0.1, equal to or more than 1, or equal to or more than 10. The upper limit of the PO4 adsorption amount is equal to or less than the saturated adsorption amount of phosphate ions by the active ingredient in the inorganic flocculant 2, and is, for example, equal to or less than 800, preferably equal to or less than 780, and more preferably equal to or less than 760. On the other hand, the lower limit of the PO4 adsorption amount is not particularly limited and can be set from an economical viewpoint, but may be equal to or more than 0.1, equal to or more than 1, or equal to or more than 10. In this embodiment, the amount of inorganic flocculant 2 added can be adjusted so that it is equal to or less than the above-mentioned F adsorption amount or PO4 adsorption amount.

[0039] A pH adjuster 3 is introduced into the reaction tank 10 as needed. The pH of the mixed solution in the reaction vessel 10 is adjusted to, for example, about 3 to 12 by the pH adjuster 3. The timing of addition of the pH adjuster 3 is not particularly limited, but it may be added to the untreated water 1 before or after mixing the untreated water 1 with the inorganic flocculant 2. The pH adjuster 3 may be added once or multiple times. For example, after the pH adjuster 3 and the inorganic flocculant 2 are added to the untreated water 1 in that order, additional pH adjuster 3 may be added to readjust the pH.

[0040] The pH of the mixed solution in the reaction vessel 10 is adjusted to an appropriate range depending on the type of inorganic flocculant and the ion species to be adsorbed. The pH of the untreated water 1 containing the inorganic flocculant 2 (e.g., a cerium-based flocculant) and fluoride ions is, for example, 3.0 to 11.5, preferably 3.5 to 10.0, and more preferably 6.0 to 8.0. By setting the pH to the upper limit or less, the removal rate of fluoride ions can be increased. Furthermore, the amount of sludge generated can be suppressed. By setting the pH to the lower limit or more, the settling property of the flocculants can be improved. In another embodiment, the pH of the untreated water 1 containing the inorganic flocculant 2 (e.g., a cerium-based flocculant) and phosphate ions is, for example, 3.0 or more and 11.0 or less, preferably 3.5 or more and 9.0 or less, and more preferably 4.0 or more and 7.0 or less. By setting the pH at or below the upper limit, the removal rate of phosphate ions can be increased. Furthermore, the amount of sludge generated can be suppressed. By setting the pH at or above the lower limit, the settling property of the flocculants can be improved.

[0041] A known acidic or alkaline agent is used as the pH adjuster 3. These may be used alone or in combination of two or more. Examples of the acidic agent that can be used include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and carbonic acid, and organic acids such as methanesulfonic acid, formic acid, acetic acid, citric acid, oxalic acid, and terephthalic acid. Preferably, inorganic mineral acids such as hydrochloric acid and sulfuric acid are used. Examples of the alkaline agent that can be used include sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, ammonia, etc. Preferably, an alkali hydroxide such as sodium hydroxide, potassium hydroxide, calcium hydroxide, or magnesium hydroxide is used.

[0042] A polymer flocculant is introduced into the reaction vessel 10 as required. Polymer flocculants increase the size of fine flocs to an appropriate size, improving separation and allowing the flocs to settle quickly.

[0043] The polymer flocculant may be any known one, such as an anionic, cationic, or nonionic one, and may be used alone or in combination of two or more. Examples of anionic polymer flocculants include sodium alginate, carboxymethyl cellulose, and salts of partial hydrolyzates of polyacrylamide. Examples of cationic polymer flocculants include polyethyleneimine, polythiourea, and polydimethyldiallylammonium chloride. Examples of nonionic polymer flocculants include polyacrylamide. Among these, for example, an anionic polymer flocculant may be used as the polymer flocculant.

[0044] In the mixed liquid in the reaction tank 10, fluoride ions and / or phosphate ions react with the inorganic flocculant 2 to produce flocculants. Then, the untreated water 1 (mixed liquid) containing the flocculants is introduced into a solid-liquid separation tank 20.

[0045] In the solid-liquid separation tank 20, the coagulates are separated as sludge 4 from the untreated water 1 (mixed liquid), and treated water 5 that does not contain the coagulates is collected.

[0046] The solid-liquid separation tank 20 is not particularly limited, and any solid-liquid separation device can be used, such as a settling tank, flotation tank, filter, centrifuge, or membrane separator. When a settling tank or flotation tank is used, a filtration device such as a sand filter may be installed downstream. When all of the flocculants settle (for example, when the pH of the non-treated water 1 containing the flocculants is adjusted to neutral or higher, such as about 7), sufficient solid-liquid separation can be achieved by settling separation. When some of the flocculants do not settle, it is preferable to use liquid filtration separation such as membrane filtration.

[0047] In the volume frequency particle size distribution of aggregates measured by the laser diffraction scattering method, the particle sizes at which the particle sizes accumulate from the smallest side to 10%, 50%, and 90% are respectively referred to as D 10 , D 50 , D 90 Let's say. D of aggregates 50 is, for example, 1 μm or more and 80 μm or less, preferably 2 μm or more and 60 μm or less, and more preferably 3 μm or more and 50 μm or less. 50 By making D equal to or greater than the lower limit, the filterability of the aggregates in the solid-liquid separation tank 20 can be improved. 50 By making the amount of the aggregates equal to or less than the upper limit, the settling property of the aggregates in the solid-liquid separation tank 20 can be improved.

[0048] In addition, the aggregates (D 90 -D10 ) / D 50 is, for example, 1.0 or more and 5.0 or less, preferably 1.1 or more and 4.0 or less, and more preferably 1.2 or more and 3.5 or less. By setting it within such a range, the filterability and sedimentation property of the aggregate in solid-liquid separation tank 20 can be balanced.

[0049] The particle size distribution of the aggregates can be measured by the laser diffraction scattering method according to the following procedure. First, a predetermined amount of inorganic flocculant is added to untreated water in a beaker, and the mixture is stirred at 300 rpm using a stirrer, and the pH is adjusted to about 7 using caustic soda or hydrochloric acid. Subsequently, stirring is continued for about 10 minutes after the pH adjustment and then stopped to allow the aggregates (precipitates) to settle. The mixed liquid in the beaker is filtered using filter paper (mesh size: approximately 1 μm, JIS standard 3801: Type 5 C), and the filtration residue (sludge) on the filter paper is dried at 110°C for 2 hours. The obtained filtration residue is dispersed in ion-exchanged water and subjected to ultrasonic treatment under conditions of a frequency of 42 kHz and an irradiation time of 180 seconds, and then the particle size distribution of the aggregates in the dispersion is measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-2300).

[0050] The supernatant of the mixed solution in the reaction vessel 10 may be collected, introduced into another reaction vessel, and an inorganic flocculant may be added to this reaction vessel, thereby carrying out the flocculation reaction treatment two or more times. The separate reaction vessel may be a tank equipped with a stirrer, or a column filled with an inorganic flocculant. The flocculation reaction can be carried out by passing the supernatant through the column. Then, the mixed liquid (untreated water 1) recovered from another reaction tank is introduced into the solid-liquid separation tank 20.

[0051] The separated sediment (sludge 4) is discharged outside the iodine recovery system 100. The discharged sludge 4 is dried and then subjected to sludge treatment. The smaller the amount of sludge 4 generated, the more the equipment costs and treatment costs required for sludge treatment can be reduced.

[0052] The treated water 5 recovered from the solid-liquid separation tank 20 may be subjected to known post-treatments such as pH adjustment, if necessary. The pH of the treatment water 5 is, for example, 3.0 or more and 8.5 or less, preferably 5.0 or more and 8.0 or less, and more preferably 7.0 or more and 7.5 or less.

[0053] In the recovered treated water 5, the iodide ions contained in the untreated water 1 remain, and most of the fluoride ions and / or phosphate ions have been removed. The concentration of iodide ions in the treated water 5 can be set to the same value as that in the recycled aqueous solution. The concentration of fluoride ions and / or the concentration of phosphate ions in the treated water 5 can be set to the same values ​​as those in the recycled aqueous solution.

[0054] In this embodiment, the concentration of iodide ions in the untreated water 1 is C Ia (mg / L), and the concentration of fluoride ions is C Fa (mg / L), and the concentration of phosphate ions is C Pa (mg / L), and the concentration of iodide ions in treated water 5 is C Ib (mg / L), and the concentration of fluoride ions is C Fb (mg / L), and the concentration of phosphate ions is C Pb Defined as (mg / L).

[0055] In the method for producing an iodine component-containing aqueous solution of this embodiment, Ib / C Ia )×100 is, for example, 90% or more, preferably 95% or more, and more preferably 97% or more.

[0056] In another embodiment, in the method for producing an iodine component-containing aqueous solution, a compound of the formula [100-[(C Fa -C Fb ) / C Fa] × 100] is, for example, 15% or less, preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less. In another embodiment, in the method for producing an iodine component-containing aqueous solution, Pa -C Pb ) / C Pa ] × 100] is, for example, 15% or less, preferably 10% or less, more preferably 5% or less, and even more preferably 1% or less.

[0057] In the method for producing an iodine-containing aqueous solution of this embodiment, the iodide ion non-selectivity index of the inorganic flocculant 2, calculated by [recovery rate of iodide ions / residual rate of fluoride ions] or [recovery rate of iodide ions / residual rate of phosphate ions], is, for example, 1.5 or more, preferably 20 or more, and more preferably 30 or more. This increases the efficiency of selective recovery of iodide ions.

[0058] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0059] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0060] (inorganic flocculant) Inorganic flocculant A: Cerium-based flocculant (NIPPON KAISUI CO., LTD., READ-CX(L)) Inorganic flocculant B: Aluminum-based flocculant (polyaluminum chloride (PAC)) Inorganic flocculant C: Calcium-based flocculant (CaCl2)

[0061] (Untreated water (wastewater)) Untreated water A and B having the chemical compositions shown in Tables 1 and 2 below were prepared using wastewater discharged from chemical reactions. Untreated water A: an aqueous solution containing iodide ions and fluoride ions, with the composition shown in Table 1 below Untreated water B: an aqueous solution containing iodide ions and phosphate ions, with the component composition shown in Table 2 below. In Tables 1 and 2, components below the detection limit are not listed.

[0062] [Table 1]

[0063] [Table 2]

[0064] In Tables 1 and 2, component symbols such as I, F, and PO4 represent ions. Fluoride ion (F - ) was measured by the ion electrode method using a water quality analyzer (Horiba, Ltd., F-73). The ion electrode method measures free fluoride ions in the measurement solution. The measurement mode of the water quality analyzer (Horiba, Ltd., F-73) was switched, and the pH of the solution was measured using the pH electrode attached to the device at a liquid temperature of approximately 20 to 25°C. In addition, iodide ions (I - ), phosphate ions (PO4 3- ), and other ions were measured by ICP emission spectrometry using an ICP emission spectrometer (Rigaku, CIROS CCD). However, the phosphate ion concentration is a value converted from the measured phosphorus element concentration. The same method was used for the composition analysis of the treated water described below.

[0065] <Test 1: pH during the flocculation process> Examples 1 to 5 In Test 1, a predetermined amount of untreated water A in Table 1 was placed in a beaker, and 0.6 mass% of inorganic flocculant A was added to the untreated water A. Then, sodium hydroxide was used as a pH adjuster to adjust the pH of the untreated water A to the value shown in Table 3, and the mixture was stirred using a jar tester according to the stirring conditions below (flocculation process). The amount of inorganic flocculant added (% by mass) refers to the mass ratio of a given volume of untreated water contained in a beaker, where the given mass of untreated water calculated from the liquid specific gravity is taken as 100% by mass. For example, an amount of inorganic flocculant added of 0.6% by mass means that 6d (g) is added to 1000 mL of untreated water, calculated from the formula: 1000 mL × liquid specific gravity d of untreated water × 0.6 (% by mass). [Stirring conditions] ·Speed: 100rpm~300rpm Time: 10-15 minutes ·Temperature (liquid temperature): 20℃~25℃ After stirring, the aggregates formed in the beaker were allowed to settle, and the supernatant solution in the beaker was collected to obtain the treated water of Examples 1 to 5. The composition of the obtained treated water was analyzed using the method described above. The results are shown in Table 3.

[0066] Examples 6 to 10 The treated waters of Examples 6 to 10 were obtained in the same manner as in Example 1, except that untreated water B in Table 2 was used instead of untreated water A, the amount of inorganic flocculant A added was changed to 1.0 mass%, and sodium hydroxide or sulfuric acid was used as the pH adjuster. The results of the composition analysis of this treated water are shown in Table 4.

[0067] In Table 3, the F removal rate is calculated by multiplying the concentration of fluoride ions in untreated water by C Fa (mg / L), the concentration of fluoride ions in the treated water is C Fb (mg / L), [(C Fa -C Fb ) / C Fa ]×100. In Table 4, the PO4 removal rate is calculated by dividing the concentration of phosphate ions in untreated water by C Pb (mg / L), the concentration of phosphate ions in the treated water is CPa (mg / L), [(C Pa -C Pb ) / C Pa ]×100. The recovery rate of iodide ions (I recovery rate) is calculated by multiplying the concentration of iodide ions in untreated water by C Ia (mg / L), and the concentration of iodide ions in the treated water is C Ib (mg / L), (C Ib / C Ia ) × 100. In all of the Examples in Tables 3 and 4, the recovery rate of iodide ions was 90% or more.

[0068] As can be seen from Tables 3 and 4, in Examples 1 to 10, the results were such that fluoride ions and phosphate ions could be reduced while iodide ions remained.

[0069] [Table 3]

[0070] [Table 4]

[0071] <Test 2: Amount of flocculant added> (Examples 11 to 17) In Test 2, a predetermined amount of untreated water A from Table 1 was placed in a beaker, and one of inorganic flocculants A to C was added in the amount (mass %) shown in Table 5.The pH of the untreated water A was then adjusted to approximately 7.0 to 7.5 using sodium hydroxide as a pH adjuster, and the water was stirred using a jar tester under the same stirring conditions as in Test 1 above (flocculation process). After stirring, the aggregates formed in the beaker were allowed to settle, and the supernatant solution in the beaker was collected to obtain the treated water of Examples 11 to 17. The composition of the obtained treated water was analyzed by the method described above. The results are shown in Table 5.

[0072] (Examples 18 to 21) The treated waters of Examples 18 to 21 were obtained in the same manner as in Example 11 above, except that untreated water B in Table 2 was used instead of untreated water A, one of inorganic flocculants A to C was added in the amount (mass %) shown in Table 5, and the pH of untreated water B was adjusted to approximately 6.0 to 6.5. The results of the composition analysis of this treated water are shown in Table 6.

[0073] As can be seen from Tables 5 and 6, in Examples 11 to 21, the results were such that fluoride ions and phosphate ions could be reduced while iodide ions remained.

[0074] In Tables 5 and 6, the iodide ion non-selective index (I non-selective index) was calculated by the ratio of I recovery rate / F residual rate or I recovery rate / PO4 residual rate. The I recovery rate is explained in Tables 3 and 4. The F residual rate was calculated as (100% - F removal rate), and the PO4 residual rate was calculated as (100% - PO4 removal rate). When compared at the same addition amount of 1.0 mass%, inorganic flocculant A had a higher I non-selectivity index than other inorganic flocculants B and C, and was found to be able to efficiently and selectively recover iodide ions.

[0075] [Table 5]

[0076] [Table 6]

[0077] <Test 3: I concentration in untreated water> Sodium iodide was dissolved in untreated water A in Table 1 to prepare untreated water A' in which the iodide ion concentration was increased from about 37 g / L to about 100 g / L. In Test 3, 0.2 to 0.6 mass% of inorganic flocculant A was added to the obtained untreated water A', the pH of the untreated water A' was adjusted to approximately 7.0 to 7.5 with sodium hydroxide, and the water was stirred using a jar tester under the same stirring conditions as in Test 1 above (flocculation process). After stirring, the aggregates formed in the beaker were allowed to settle, and the supernatant solution in the beaker was collected to obtain the treated water of Examples 22 to 24. The composition of the obtained treated water was analyzed using the method described above. The results are shown in Table 7.

[0078] As can be seen from Table 7, in Examples 22 to 24, even in untreated water A' containing a high iodide ion concentration, the results showed that fluoride ions and phosphate ions could be reduced while leaving iodide ions.

[0079] [Table 7]

[0080] The volume frequency particle size distribution of the aggregates was measured by laser diffraction scattering method according to the following procedure. <Measurement of particle size distribution by laser diffraction scattering method> First, 0.6% by mass of the inorganic flocculant in Table 8 was added to the untreated water in Table 8 in a beaker, and the mixture was stirred at 300 rpm using a stirrer, and the pH was adjusted to approximately 7 using caustic soda or hydrochloric acid. Subsequently, after the pH adjustment, stirring was continued for about 10 minutes and then stopped to allow the aggregates (precipitates) to settle. The mixed liquid in the beaker was filtered using filter paper (mesh size: approximately 1 μm, JIS standard 3801: type 5 C), and the filtration residue (sludge) on the filter paper was dried at 110° C. for 2 hours. The obtained filtration residue was dispersed in ion-exchanged water and subjected to ultrasonic treatment under conditions of a frequency of 42 kHz and an irradiation time of 180 seconds, and then the particle size distribution of the aggregates in the dispersion was measured using a laser diffraction particle size distribution analyzer (SALD-2300, manufactured by Shimadzu Corporation). In the volume frequency particle size distribution of the aggregates, the particle sizes at which the particle sizes accumulate from the smallest side to 10%, 50%, and 90% are respectively called D 10 , D 50 , D 90 The particle size results are shown in Table 8. The flocculant produced using inorganic flocculant A showed no filter clogging and exhibited superior filterability compared to the flocculant produced using inorganic flocculant C.

[0081] [Table 8] [Explanation of symbols]

[0082] 1 Untreated water 2. Inorganic flocculants 3 pH adjuster 4. Sludge 5 Treated water 10 Reaction vessel 20 Solid-liquid separation tank 100 Iodine Recovery System

Claims

1. An inorganic flocculant used for untreated water containing iodide ions and fluoride ions and / or phosphate ions, The concentration of the fluoride ions in the untreated water before adding the inorganic flocculant is more than 8 mg / L, and / or the concentration of the phosphate ions in the untreated water is more than 8 mg / L in terms of phosphorus element; the inorganic flocculant includes a calcium-based flocculant, An inorganic flocculant that is non-selective for iodide ions and reacts selectively with fluoride ions and / or phosphate ions rather than iodide ions to produce flocculants.

2. An inorganic flocculant for use in untreated water containing iodide ions and fluoride ions and / or phosphate ions, The concentration of the iodide ions in the untreated water before adding the inorganic flocculant is 5 g / L or more; the inorganic flocculant includes a calcium-based flocculant, An inorganic flocculant that is non-selective for iodide ions and reacts selectively with fluoride ions and / or phosphate ions rather than iodide ions to produce flocculants.

3. An inorganic flocculant for use in untreated water containing iodide ions and fluoride ions and / or phosphate ions, comprising: The inorganic flocculant is added in such an amount that the F adsorption amount, as defined below, is 0.1 or more and 400 or less, or the PO 4 adsorption amount is 0.1 or more and 800 or less, the inorganic flocculant includes a calcium-based flocculant, An inorganic flocculant that is non-selective for iodide ions and reacts selectively with fluoride ions and / or phosphate ions rather than iodide ions to produce flocculants. (Definition of F adsorption amount and PO 4 adsorption amount) The F adsorption amount (g / g) is calculated from C F / (M×C CX ). The PO 4 adsorption amount (g / g) is calculated from C P04 / (M×C CX ). where: M is the amount (g) of the inorganic flocculant added. C CX is the concentration (wt %) of the active ingredient in the inorganic flocculant. C F is the amount of removed fluorine element (g) calculated from the amount of removed fluorine ions in terms of elemental fluorine (F). C P04 is the amount of removed phosphate (g) calculated as phosphate (PO 4 ) from the amount of removed phosphate ions.

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