Method for producing efficient iodine concentrate

Abstract

To provide a producing method of an iodine concentrated liquid excellent in suppressing lowering of a transmission efficiency of iodide ions in an electrodialyzer.SOLUTION: A method for producing an iodine concentrated liquid of the present invention includes a reduction process in which a reducing agent is added to a waste liquid containing iodine components to reduce at least a portion of the iodine (I2) contained in the iodine components to obtain iodide ions (I-), and after the reduction process, an electrodialysis process using an electrodialyzer equipped with an anion exchange membrane to separate the waste liquid into an iodine-containing concentrated liquid and a deionized liquid.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for producing an efficient iodine concentrate. According to the law

Background Art

[0002] Various developments have been made on techniques for recovering iodine from waste liquids. As a technique of this kind, for example, the technique described in Patent Document 1 is known. In addition to iodine components such as iodide ions (I - ), divalent ions such as sulfate ions (SO4 2- ) may also coexist. For example, sulfate ions are usually contained in the waste liquid at a concentration of 1 g / L or more and below the saturation solubility of sulfate, and more generally, may be contained at about 20 to 50 g / L. Patent Document 1 describes a method of performing electrodialysis on a stock solution containing an inorganic anion having iodine and an inorganic anion having fluorine and accommodated in a desalting chamber using a monovalent selective anion exchange membrane or the like (Claim 1, Examples, etc. of Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as a result of the study by the present inventor, it has been found that there is room for improvement in terms of the permeation efficiency of iodide ions in the electrodialysis cell having the anion exchange membrane described in Patent Document 1 above.

Means for Solving the Problems

[0005] ​The present inventors further studied and found that iodine (I2) contained in the waste liquid may adhere to the anion exchange membrane during electrodialysis, thereby increasing the membrane resistance of the anion exchange membrane, reducing the energizing current, and reducing the permeation efficiency of iodide ions. Also, in an aqueous solution, reversible reactions of triiodide ions (I 3- ←→I - +I2) and pentaiodide ions (I 5- ←→I 3- +I2) occur. Due to such reversible reactions of polyiodide ions, iodine (I2) may be generated in the waste liquid. Based on such findings and further intensive research, it was found that by appropriately reducing iodine (I2) contained in the waste liquid to the state of iodide ions (I - ), it is possible to suppress a decrease in the energizing current during electrodialysis and suppress a decrease in the permeation efficiency of iodide ions, and thus the present invention was completed.

[0006] According to one aspect of the present invention, there are provided the following method for producing an iodine concentrate and a recycled aqueous solution.

[0007] 1. A reduction step of adding a reducing agent to a waste liquid containing an iodine component to reduce at least a part of iodine (I2) contained in the iodine component to obtain iodide ions (I - ), and an electrodialysis step of separating the waste liquid into an iodine-containing concentrate and a desalted liquid using an electrodialysis apparatus equipped with an anion exchange membrane after the reduction step, a method for producing an iodine concentrate. 2. The method for producing an iodine concentrate according to 1., wherein the reducing agent contains one or more selected from the group consisting of thiosulfate, sulfite, bisulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid. 3. The method for producing an iodine concentrate according to 1. or 2., wherein A method for producing an iodine concentrate, wherein after the reduction step and before the electrodialysis step, the I2 concentration of the waste liquid to which the reducing agent has been added is 20 ppm or less. 4. A method for producing an iodine concentrate according to any one of 1. to 3., including a pH adjustment step of adjusting the pH of the waste liquid to 9.5 or less before the reduction step. 5. A method for producing an iodine concentrate according to any one of 1. to 4., wherein the electrodialysis device includes continuous circulation type electrodialysis equipment. 6. A method for producing an iodine concentrate according to any one of 1. to 5., wherein the circulation pressures of the desalting chamber and the concentration chamber of the electrodialysis device are the same. 7. A method for producing an iodine concentrate according to any one of 1. to 6., wherein the raw material of the waste liquid is waste liquid, waste powder, and waste solids from the production process or production equipment of a product containing any iodine component of a polarizing film, a contrast agent, a disinfectant, and a radiation-related material, or waste liquid or waste solids containing an iodine catalyst used in chemical synthesis such as pharmaceutical synthesis of antibiotics and antiviral agents. 8. A method for producing an iodine concentrate according to any one of 1. to 7., including a regeneration step of producing one or more selected from the group consisting of iodine, iodide salts, and hydroiodic acid using the obtained iodine-containing concentrate. 9. A method for producing an iodine concentrate according to any one of 1. to 8., wherein an iodide salt is recovered from the iodine-containing concentrate immediately after the electrodialysis step. 10. The method for producing an iodine concentrate according to 9., wherein the iodide salt includes an alkali metal iodide salt. 11. A method for producing an iodine concentrate according to any one of 1. to 10., A method for producing an iodine concentrate, comprising a step of passing the obtained desalted liquid through a strongly basic anion exchange resin to adsorb iodide ions remaining in the desalted liquid onto the strongly basic anion exchange resin, and recovering the iodide ions from the strongly basic anion exchange resin. 12. The method for producing an iodine concentrate according to any one of 1. to 11., A method for producing an iodine concentrate, comprising a step of separating the iodine-containing concentrate into hydroiodic acid and an aqueous hydroxide salt solution by bipolar membrane electrodialysis. 13. The method for producing an iodine concentrate according to any one of 1. to 12., When the waste liquid contains a boron component, after adjusting the obtained desalted liquid to have a pH of 11 or more, a boron recovery step of separating and recovering a boron-containing concentrate from the desalted liquid using another electrodialysis device is included. A method for producing an iodine concentrate. 14. A recycled aqueous solution containing a metal iodide salt, The content of iodine (I2) contained in the recycled aqueous solution is 10 g / L or more and 370 g / L or less, The concentration of total organic carbon (TOC) in the recycled aqueous solution is 1000 ppm or less. Recycled aqueous solution. 15. The recycled aqueous solution according to 14., The concentration of the metal iodide salt is 30 g / L or more and 560 g / L or less. Recycled aqueous solution.

Advantages of the Invention

[0008] According to the present invention, there are provided a method for producing an iodine concentrate excellent in suppressing a decrease in the permeation efficiency of iodide ions in an electrodialysis device, and a recycled aqueous solution produced by the method for producing an iodine concentrate.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description will be omitted as appropriate. Also, the figures are schematic diagrams and do not match the actual dimensional ratios.

[0011] The outline of the method for producing the iodine concentrate of this embodiment will be described.

[0012] The method for producing the iodine concentrate of this embodiment is to add a reducing agent to the waste liquid containing an iodine component, and reduce at least a part of the iodine (I2) contained in the iodine component to obtain iodide ions (I - ) in the reduction step, and after the reduction step, use an electrodialysis device equipped with an anion exchange membrane to separate the waste liquid into an iodine-containing concentrate and a desalted liquid in the electrodialysis step.

[0013] According to the findings of the present inventors, the following malfunction in the electrodialysis device was found. When a waste liquid containing I2 (sometimes referred to as an iodine molecule) is subjected to electrodialysis, iodine molecules present in the desalted liquid adhere to the surface of the anion exchange membrane during the electrodialysis process under constant voltage operation. As a result, the membrane resistance of the anion exchange membrane increases, so the energizing current decreases, and the permeation efficiency of iodide ions decreases. Specifically, it has been found that the processing ability to desalt and concentrate iodide ions from the waste liquid decreases. Based on such findings, further research by the present inventors has found that by appropriately reducing iodine (I2) contained in the waste liquid to the state of iodide ions (I - ), the energization failure during the above electrodialysis can be suppressed, and the operation stability of the electrodialysis device can be improved. Further studies have revealed that by adopting the redox potential as an indicator of the reduced state of iodine (I2), power-on failures can be stably suppressed. Specifically, it is preferable that the redox potential of the waste liquid be 100 mV or less.

[0014] Hereinafter, the configuration of the method for producing the iodine concentrate of the present embodiment will be described in detail.

[0015] FIG. 1 is a cross-sectional view schematically showing an example of the configuration of the electrodialysis apparatus 1. FIG. 2 is a diagram schematically showing an example of the configuration of the iodine recovery system 100. FIG. 3 is a flowchart showing an example of the iodine recovery process.

[0016] An example of the method for producing the iodine concentrate of the present embodiment includes an electrodialysis step of separating the waste liquid 10 containing an iodine component into an iodine-containing concentrate (concentrate 20) and a desalted liquid (desalted liquid 30) using the electrodialysis apparatus 1 of FIG. 1.

[0017] The iodine recovery system 100 of FIG. 2 only needs to include at least equipment for supplying the waste liquid 10 to the electrodialysis apparatus 1, and may further include equipment for treating the concentrate 20 and / or the desalted liquid 30 generated by the electrodialysis apparatus 1.

[0018] The waste liquid 10 (stock solution) is not particularly limited as long as it is a liquid containing an iodine component described later. For example, it includes waste liquid discharged from the manufacturing process of a product containing an iodine component, waste liquid when a product containing an iodine component is discarded, waste liquid discharged from a synthesis process using an iodine component as a reaction catalyst, waste liquid of a cleaning liquid used for cleaning a manufacturing apparatus using an iodine component, and the like.

[0019] As specific raw materials for the waste liquid 10, there are waste liquids, waste powders, and waste solids from the manufacturing process or manufacturing equipment in products containing any iodine component of a polarizing film, contrast agent, disinfectant, and radiation-related material, or waste liquids or waste solids containing an iodine catalyst (organic iodine compound or inorganic iodine compound) used in chemical syntheses such as pharmaceutical syntheses of antibiotics and antiviral agents. These may be used alone or in combination of two or more kinds.

[0020] When the iodine recovery liquid contains organic substances and / or organic solvents in the waste liquid, a known organic substance decomposition treatment may be performed in advance. As one of such organic substance decomposition treatments, for example, an organic component (organic substance or organic solvent) is subjected to a combustion treatment by a combustion method, and the sublimated iodine is adsorbed by an alkaline agent (such as sodium hydroxide and sodium bisulfite) and a reducing agent, and an aqueous solution in which an iodine component is recovered is shown. The iodine component is defined as including, for example, at least one or more selected from the group consisting of iodide ions (I - -), iodine (I2), iodic acid (HIO3), periodic acid (HIO4), and iodides (including inorganic iodine compounds or organic iodine compounds). Also, in an aqueous solution, as described above, iodine (I2) may be generated in the waste liquid due to the reversible reaction of polyiodide ions such as triiodide ions and pentaiodide ions. Here, in the waste liquid derived from the raw materials and the like, iodide ions among the above iodine components are usually contained in an amount of 3% or more, preferably about 3% to 30%. Further, in these waste liquids, sulfate ions are usually contained at a concentration of 1 g / L or more and below the saturation solubility of sulfate, and more generally about 20 to 50 g / L. In addition, the solid matter containing the iodine component usually contains iodine element in an amount of about 30% to 99.8% in terms of mass.

[0021] Note that the waste liquid 10 uses at least a reduced one, and if necessary, chemical pretreatment or physical pretreatment such as pH adjustment, dilution, and organic substance decomposition / removal treatment may be performed.

[0022] As shown in Fig. 1, the electrodialysis apparatus 1 has a concentration chamber 2, a desalting chamber 3, an ion exchange membrane that separates the concentration chamber 2 and the desalting chamber 3, an anode 4, a cathode 5, and a power source 6. The electrodialysis apparatus 1 is not limited to Fig. 1 and can have a known apparatus configuration.

[0023] An electrode solution is supplied from an electrode solution tank (not shown) to the electrode chamber (anode chamber) containing the anode 4 and the electrode chamber (cathode chamber) containing the cathode 5. The anode chamber and the cathode chamber are respectively arranged on both sides of the electrodialysis cell composed of the concentration chamber 2 and the desalting chamber 3. When a current is applied to the anode 4 and the cathode 5 using the power source 6, electrodialysis starts in the electrodialysis cell. Although known ones can be used as the electrode solution, for example, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous sodium hydrogen sulfate solution, an aqueous potassium sulfate solution, etc. are used. However, when performing bipolar electrodialysis or the like after electrodialysis, the electrode solution used in the electrodialysis apparatus 1 preferably does not contain sulfate.

[0024] In the electrodialysis cell, the concentration chamber 2 and the desalting chamber 3 are each partitioned by an ion exchange membrane (either an anion exchange membrane 7 or a cation exchange membrane 8) and arranged alternately. The electrodialysis apparatus 1 may at least have an arrangement configuration in which the desalting chamber 3, the anion exchange membrane 7, the concentration chamber 2, the cation exchange membrane 8, and the desalting chamber 3 are arranged in this order. From the viewpoint of enhancing the processing capacity, the concentration chamber 2 may have one or more, preferably two or more. Note that an electrolytic solution may be contained in the concentration chamber 2 before electrodialysis. As the electrolytic solution, for example, an aqueous inorganic salt solution having electrical conductivity may be included. For example, when using the electrodialysis apparatus 1 for the first time, ion-exchanged water may be used, and when resuming operation after stopping the operation, the previous concentrated solution may be used. In addition to such an electrolytic solution, an aqueous sodium chloride solution, an aqueous potassium iodide solution, an aqueous sodium iodide solution, etc. may be used. However, the electrolytic solution preferably does not contain sulfate.

[0025] A specific example of the electrodialysis apparatus 1 used for electrodialysis as described above is such that a large number of gasket spacers (also called cell frames) are stacked between a pair of electrodes. An anion exchange membrane 7 or a cation exchange membrane 8 is sandwiched between adjacent cell frames, and as a whole, the anion exchange membrane 7 and the cation exchange membrane 8 are arranged in principle to be positioned alternately. Ion exchange chambers (electrified parts) partitioned by the anion exchange membrane 7 and the cation exchange membrane 8 are formed in each gasket. And in this ion exchange chamber, a chamber where the cation exchange membrane 8 is located on the cathode 5 side and the anion exchange membrane 7 is located on the anode 4 side becomes the desalting chamber 3, and a chamber where the anion exchange membrane 7 is located on the cathode 5 side and the cation exchange membrane 8 is located on the anode 4 side becomes the concentration chamber 2. The desalting chamber 3 and the concentration chamber 2 are arranged alternately. That is, when energization is performed while circulating and supplying a treatment liquid (electrolyte solution) to the desalting chamber 3, the cations in the treatment liquid supplied to the desalting chamber 3 migrate through the cation exchange membrane 8 to the adjacent concentration chamber 2 on the cathode 5 side, and the anions in the treatment liquid migrate through the anion exchange membrane to the adjacent concentration chamber 2 on the anode 4 side. In this way, when the treatment liquid is circulated and supplied to the desalting chamber 3 and at the same time the aqueous salt solution is circulated to the concentration chamber 2, the treatment liquid can be desalted and at the same time, a concentrated liquid 20 with an increased salt concentration can be obtained. As a method for fixing the laminate of these ion exchange chambers between the electrodes, the one using a filter press is preferably used, but it is not limited thereto.

[0026] In this embodiment, at least one or all of the anion exchange membranes 7 included in the electrodialysis apparatus 1 may be composed of monovalent selectivity anion exchange membranes.

[0027] When the anion exchange membrane 7 includes other anion exchange membranes other than the monovalent selectivity anion exchange membrane, known ones may be used as the other anion exchange membranes. For example, a monovalent ion selective permeation anion exchange membrane, a completely permeable anion exchange membrane, or a high-strength alkali-resistant anion exchange membrane may be used, and it is preferable that it is a monovalent ion selective permeation anion exchange membrane.

[0028] The cation exchange membrane 8 is not particularly limited, and a strongly acidic cation exchange membrane, a high-strength alkali-resistant cation exchange membrane, etc. can be used. Further, the cation exchange membrane 8 may be a cation exchange membrane having monovalent ion selectivity.

[0029] An example of the operation of the electrodialysis apparatus 1 during electrodialysis is as follows. When a direct current is applied between the anode 4 and the cathode 5 using the power source 6, iodide ions (I - ) in the desalting chamber 3 on one side pass through the anion exchange membrane 7 and move to the concentration chamber 2, and cations (including at least one of monovalent cations such as alkali metal ions and divalent cations such as alkaline earth metal ions) in the desalting chamber 3 on the other side pass through the cation exchange membrane 8 and move to the same concentration chamber 2. In this concentration chamber 2, for example, an iodide salt such as potassium iodide (KI) is generated. From the concentration chamber 2, a concentrated solution 20 (iodine-containing concentrated solution) containing the iodide salt is obtained. Note that a desalted solution 30 is obtained from the desalting chamber 3.

[0030] Here, an example of the process flow in the reduction step and the electrodialysis step of the method for producing an iodine concentrated solution will be described with reference to FIGS. 1 and 2.

[0031] First, the waste liquid 10 is stored in the waste liquid tank 11 via the line 12 (pipe).

[0032] The content of iodine (I2) contained in the waste liquid 10 before the reduction treatment is, for example, 10 g / L or more and 370 g / L or less. The content of iodine (I2) in the waste liquid 10 can be quantified by a reducing agent titration method such as sodium thiosulfate using a starch indicator and an absorbance method at a wavelength due to iodine and triiodide ions at 350 nm.

[0033] To the waste liquid 10 in the waste liquid tank 11, a reducing agent is introduced from the reducing agent tank 50 into the waste liquid tank 11 via the line 51. Thereby, at least a part or almost all of the iodine (I2) contained in the waste liquid 10 is reduced to iodide ions (I -) can be achieved. Also, for iodic acid and periodic acid contained in iodine components other than iodine (I2) in the waste liquid 10, it is also possible to change part or all of them into iodide ions. For iodide ions, they can be detected by methods such as instrumental analysis using ion chromatography, analysis of titrating iodide ions, iodine, and iodic acid extracted and separated with an organic solvent, and ultraviolet-visible absorbance analysis.

[0034] The reducing agent contains one or more reducing components selected from the group consisting of, for example, thiosulfate, sulfite, bisulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid. Among these, sulfuric acid-based reducing agents such as thiosulfate, sulfite, and bisulfite are preferred in that they can be used in the neutral region, and bisulfite is more preferred from the viewpoints of handleability, economy, and easy availability.

[0035] The reducing agent is preferably in a liquid state. For example, an aqueous solution containing the above-mentioned reducing components is used. Also, the reducing agent may be used when the liquid temperature of the waste liquid 10 is in the range of, for example, 5°C to 70°C. The reducing agent may be used when the pH of the waste liquid 10 is in the range of, for example, 1 to 9.

[0036] An absorptiometer may be installed in the waste liquid tank 11. The reducing agent can be supplied so that the I2 concentration of the waste liquid 10 in the waste liquid tank 11 measured by the absorptiometry method is maintained below a predetermined value. Here, from the viewpoint of economy, the predetermined value of the I2 concentration is preferably 20 ppm, more preferably 15 ppm, and even more preferably 10 ppm from the viewpoint of efficiency. That is, after the reduction step and before the electrodialysis step, it is preferable that the I2 concentration of the waste liquid 10 added with the reducing agent is maintained at 20 ppm or less. Thereby, a further decrease in the throughput of the electrodialysis device can be suppressed. In the absorptiometry method, the absorbance at 350 nm, which is the absorption wavelength of I2 (iodine molecule), is measured, and the I2 concentration can be quantified using a calibration curve prepared in advance.

[0037] An ORP (Oxidation Reduction Potential) meter may be installed in the waste liquid tank 11. A reducing agent can be supplied so as to maintain the oxidation reduction potential of the waste liquid 10 in the waste liquid tank 11 below a predetermined value. Here, the predetermined value of the oxidation reduction potential is preferably 120 mV. That is, after the reduction step and before the electrodialysis step, it is preferable that the oxidation reduction potential of the waste liquid 10 added with the reducing agent is maintained at 120 mV or less. Thereby, a further reduction in the throughput of the electrodialysis apparatus can be suppressed.

[0038] If necessary, the waste liquid 10 in the waste liquid tank 11 may be subjected to the above chemical pretreatment or physical pretreatment other than the reduction treatment. When the waste liquid 10 contains a boron component, a pH adjustment step of adjusting the pH of the waste liquid 10 to 9.5 or less, preferably 8 or less, more preferably less than 7 may be performed before the electrodialysis step. When the pH of the waste liquid 10 is adjusted to 9.5 or less, most of the boric acid (H3BO3) exists as molecules without dissociation. Therefore, even if electrodialysis is performed, boric acid hardly moves and is discharged into the desalted liquid 30 as it is. Thereby, the boron component and the iodine component in the waste liquid 10 can be efficiently separated.

[0039] When the waste liquid 10 is acidic (pH less than 7) or when an oxidizing agent is present, iodine molecules (I2) are likely to be generated, so the above reducing agent may be added.

[0040] Subsequently, the waste liquid 10 in the waste liquid tank 11 is supplied to the desalting chamber 3 of the electrodialysis apparatus 1 via the line 13. A voltage is applied to the anode 4 and the cathode 5 to perform electrodialysis (electrodialysis step). The desalted liquid 30 generated in the desalting chamber 3 by electrodialysis is recovered via the line 31. On the other hand, the concentrated liquid 20 generated in the concentration chamber 2 by electrodialysis is recovered via the line 22.

[0041] At this time, at least a part of the desalting liquid 30 may be supplied to the waste liquid tank 11 via the line 32 branched from the line 31, and the mixed desalting liquid in which the desalting liquid 30 and the waste liquid 10 are mixed may be supplied to the desalting chamber 3 again. That is, the waste liquid 10 supplied to the desalting chamber 3 may contain the desalting liquid 30. By repeating the electrodialysis in this way, the iodide ion concentration in the desalting liquid 30 can be reduced to a desired value.

[0042] On the other hand, at least a part of the concentrated liquid 20 may be supplied to the concentrated liquid tank 21 via the line 23 branched from the line 22, and the concentrated liquid 20 in the concentrated liquid tank 21 may be supplied to the concentration chamber 2 again via the line 24. By repeating the electrodialysis in this way, the iodide ion concentration in the concentrated liquid 20 can be concentrated to a desired value.

[0043] Also, if necessary, a reducing agent may be introduced from the reducing agent tank 50 into the concentrated liquid 20 in the concentrated liquid tank 21 via the line 52. The I2 concentration and / or the redox potential of the concentrated liquid 20 in the concentrated liquid tank 21 may also be managed so as to be maintained below the above-mentioned predetermined value using various measuring instruments.

[0044] When two or more electrodialysis devices are provided, the first concentrated liquid generated by the first electrodialysis device may be supplied to the desalting chamber of the second electrodialysis device. Further, the second desalting liquid generated in the desalting chamber of the second electrodialysis device may be mixed with the first concentrated liquid and supplied to the desalting chamber of the second electrodialysis device again.

[0045] Also, the electrodialysis device 1 provided with a continuous circulation type electrodialysis facility may be used. Such an electrodialysis device 1 enables continuous operation in which the desalting liquid 30 is continuously discharged while continuously supplying the waste liquid 10 or the mixed desalting liquid to the desalting liquid 30.

[0046] Further, the circulation pressures of the desalting chamber 3 and the concentration chamber 2 included in the electrodialysis device 1 may be controlled to be the same. This can suppress the occurrence of internal leakage (water permeation) from the higher-pressure side to the lower-pressure side due to a differential pressure being generated between the circulation pressures of the desalting chamber 3 and the concentration chamber 1. Specifically, it is possible to suppress a decrease in the efficiency of permeating iodine due to impurities in the desalting chamber 3 entering the concentration chamber 2, or the iodine component in the concentration chamber 2 returning to the desalting chamber 3.

[0047] The iodine-containing concentrated liquid (concentrated liquid 20) obtained by the electrodialysis step of the method for producing an iodine concentrated liquid of the present embodiment can be utilized as a recycled aqueous solution containing a metal iodide salt. The iodine concentration in the recycled aqueous solution may be, for example, not more than the saturation concentration of the alkali metal iodide salt, and is 30 to 560 g / L, preferably 80 to 350 g / L. The iodine concentration in the recycled aqueous solution can be measured as the total iodine concentration by an instrumental analysis method using an ICP (inductively coupled plasma optical emission spectrometer) and an ion chromatograph.

[0048] The metal iodide salt of the recycled aqueous solution contains, for example, at least one or two or more kinds such as an alkali metal iodide salt and an alkaline earth metal iodide salt.

[0049] The concentration of total organic carbon (TOC) contained in the recycled aqueous solution is, for example, 1000 ppm or less. The concentration of TOC in the recycled aqueous solution can be measured by an instrumental analysis method using a TOC meter.

[0050] The recycled aqueous solution such as the above concentrated liquid may be stored in a resin container. The resin container may include a liquid phase (recycled aqueous solution) and a gas phase (upper space) inside, and the gas phase may be replaced with an inert gas such as nitrogen gas. Thereby, in the recycled aqueous solution stored in the resin container, it is possible to suppress the oxidation of iodide ions into iodine molecules. Thereby, the liquid stability can be enhanced. Further, from the viewpoint of further enhancing the liquid stability, the above reducing agent may be added to the recycled aqueous solution.

[0051] Next, an example of the process flow of the regeneration step of the method for producing the iodine concentrate will be described with reference to FIG. 3.

[0052] Subsequently, the method for producing the iodine concentrate can include a regeneration step of producing one or more selected from the group consisting of iodine (I2), iodide salts, and hydroiodic acid, as shown in FIG. 3, using the obtained iodine-containing concentrate (concentrate 20) as a recycled aqueous solution after the electrodialysis step. Such a regeneration step may be carried out using a device different from the above-described electrodialysis device 1. The iodine, iodide salts, and hydroiodic acid regenerated (recycled) by the above method for producing the iodine concentrate may each be in an aqueous solution, and the iodine and iodide salts may be in powder form (including granules).

[0053] The method for producing the iodine concentrate can recover hydroiodic acid using the obtained concentrate 20. For example, the method for producing the iodine concentrate may include a step (bipolar electrodialysis step) of separating the iodine-containing concentrate (concentrate 20) into hydroiodic acid and an aqueous solution of a hydroxide salt by bipolar membrane electrodialysis, as shown in FIG. 3. Here, the bipolar membrane electrodialysis method is a method of sequentially arranging bipolar membranes that generate hydrogen ions and hydroxide ions in addition to cation exchange membranes and / or anion exchange membranes between an anode and a cathode, supplying a treatment liquid to each chamber partitioned by the membranes, applying an electric current, and obtaining an acid and an alkali from a neutral salt.

[0054] Specifically, the concentrate 20 (for example, KI concentrate) discharged from the electrodialysis device 1 is introduced into a bipolar membrane electrodialysis device. If necessary, the pH of the concentrate 20 may be adjusted to less than 7 to acidify it. When a direct current is applied to the bipolar membrane electrodialysis device, the iodide salt in the concentrate 20 is electrolyzed, and an aqueous solution of hydroiodic acid (HI solution) and an aqueous solution of a hydroxide (for example, KOH) are discharged. Thereafter, the HI solution is distilled and purified to obtain hydroiodic acid.

[0055] In addition, iodine (I2) can be recovered using the obtained concentrated solution 20 in the method for producing the iodine concentrate. As shown in FIG. 3, when the concentrated solution 20 containing iodide ions is oxidized, iodine (I2) is obtained.

[0056] The method for producing the iodine concentrate can recover iodide salts using the obtained concentrated solution 20. As shown in FIG. 3, when the hydroiodic acid obtained above is neutralized, an iodide salt is obtained. Also, when the iodine (I2) obtained above is reduced and neutralized, an iodide salt is obtained. In the method for producing the iodine concentrate, the above oxidation, neutralization, and reduction methods are not particularly limited, and known means can be used. Note that the iodide salt includes, for example, iodide metal salts such as alkali metal iodide salts and alkaline earth metal iodide salts. Specific examples of the iodide metal salt include, for example, potassium iodide, sodium iodide, calcium iodide, magnesium iodide, cesium iodide, etc. These may be used alone or in combination of two or more. Note that alkaline earth metals may cause damage to the ion exchange membrane. For this reason, in the method for producing the iodine concentrate of the present embodiment, when the waste liquid 10 contains alkaline earth metals, it is preferable to include a step of removing alkaline earth metals before the above electrodialysis step. For example, the alkaline earth metals can be separated by a method using a cation exchange resin or a precipitation method. In the precipitation method, poorly soluble salts formed by hydroxides or carbonates, etc. may be separated. If necessary, pH adjustment may be performed as a pretreatment for forming the poorly soluble salt.

[0057] On the other hand, iodine (I2) can be recovered using the obtained desalted solution 30 in the method for producing the iodine concentrate. As shown in FIG. 3, the method for producing an iodine concentrate may include a step of passing the obtained desalted liquid 30 through a strongly basic anion exchange resin to adsorb iodide ions remaining in the desalted liquid 30 onto the strongly basic anion exchange resin, and recovering iodine from the strongly basic anion exchange resin.

[0058] Specifically, the desalted liquid 30 discharged from the electrodialysis apparatus 1 is passed through a strongly basic ion exchange resin, and iodide ions are adsorbed onto this strongly basic anion exchange resin. At this time, the pH of the desalted liquid 30 when passing through the strongly basic anion exchange resin is less than 7, preferably adjusted to 3 or more and less than 7, in the same manner as the above-described electrodialysis. Thereby, it is possible to suppress the adsorption of borate ions formed by the dissociation of boric acid onto the strongly basic anion exchange resin, and selectively separate iodide salt ions. Thereafter, iodine (I2) can be recovered from the strongly basic anion exchange resin by known means.

[0059] When the waste liquid 10 contains a boron component, boron (B2) can be recovered from the obtained desalted liquid 30 containing the boron component.

[0060] The method for producing an iodine concentrate may include a boron recovery step of adjusting the desalted liquid 30 containing a boron component so that the pH is, for example, 7 or more, preferably 8 or more, more preferably 11 or more, and then separating and recovering a boron-containing concentrate (boric acid concentrate) from the desalted liquid 30 using another electrodialysis apparatus. When the boron-containing concentrate is acidified and crystallized, boric acid (H3BO3) can be recovered.

[0061] In addition, the desalted liquid 30 containing a boron component having a pH of 7 or more, or the desalted liquid 30 when passing through the above-described strongly basic anion exchange resin, is passed through a boron-selective chelating resin to adsorb borate ions. Thereafter, boric acid can be recovered from the boron-selective chelating resin by known means.

[0062] As described above, the embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can be adopted. Further, the present invention is not limited to the above-described embodiments, and modifications, improvements, etc. within the scope capable of achieving the object of the present invention are included in the present invention. Examples of reference embodiments are appended below. 1. A reduction step of adding a reducing agent to a waste liquid containing an iodine component to reduce at least a part of iodine (I 2 ) contained in the iodine component to obtain iodide ions (I - ), and a method for producing an iodine concentrate, comprising an electrodialysis step of separating the waste liquid into an iodine-containing concentrated liquid and a desalted liquid using an electrodialysis apparatus equipped with an anion exchange membrane after the reduction step. 2. The method for producing an iodine concentrate according to 1., wherein the reducing agent contains one or more selected from the group consisting of thiosulfate, sulfite, bisulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid, and the method for producing an iodine concentrate. 3. The method for producing an iodine concentrate according to 1. or 2., wherein after the reduction step and before the electrodialysis step, the I 2 concentration of the waste liquid to which the reducing agent has been added is 20 ppm or less, and the method for producing an iodine concentrate. 4. The method for producing an iodine concentrate according to 1. or 2., wherein before the reduction step, the method for producing an iodine concentrate includes a pH adjustment step of adjusting the pH of the waste liquid to 9.5 or less. 5. The method for producing an iodine concentrate according to 1. or 2., wherein the electrodialysis apparatus is equipped with continuous circulation type electrodialysis equipment, and the method for producing an iodine concentrate. 6. The method for producing an iodine concentrate according to 1. or 2., wherein the circulation pressures of the desalting chamber and the concentration chamber of the electrodialysis apparatus are the same, and the method for producing an iodine concentrate. 7. The method for producing an iodine concentrate according to 1. or 2., wherein the raw material of the waste liquid is a waste liquid or waste powder and waste solid from the manufacturing process or manufacturing apparatus of a product containing an iodine component of any one of a polarizing film, a contrast agent, a disinfectant, and a radiation-related material, or a waste liquid or waste solid containing an iodine catalyst used in chemical synthesis such as pharmaceutical synthesis of antibiotics and antiviral agents, and the method for producing an iodine concentrate. 8. The method for producing an iodine concentrate according to 1. or 2., wherein the method for producing an iodine concentrate includes a regeneration step of producing one or more selected from the group consisting of iodine, iodide salts, and hydroiodic acid using the obtained iodine-containing concentrated liquid. 9. The method for producing an iodine concentrate according to 1. or 2., wherein iodide salts are recovered from the iodine-containing concentrated liquid immediately after the electrodialysis step, and the method for producing an iodine concentrate. 10. A method for producing an iodine-concentrated solution according to 9., wherein the iodide salt contains an alkali metal iodide salt, and the method for producing an iodine-concentrated solution. 11. A method for producing an iodine-concentrated solution according to 1. or 2., wherein the obtained desalted solution is passed through a strongly basic anion exchange resin to adsorb iodide ions remaining in the desalted solution onto the strongly basic anion exchange resin, and the method for producing an iodine-concentrated solution includes a step of recovering the iodide ions from the strongly basic anion exchange resin. 12. A method for producing an iodine-concentrated solution according to 1. or 2., wherein the method for producing an iodine-concentrated solution includes a step of separating the iodine-containing concentrated solution into hydroiodic acid and an aqueous hydroxide salt solution by a bipolar membrane electrodialysis method. 13. A method for producing an iodine-concentrated solution according to 1. or 2., wherein when the waste liquid contains a boron component, after adjusting the obtained desalted solution to have a pH of 11 or higher, a boron recovery step of separating and recovering a boron-containing concentrated solution from the desalted solution using another electrodialysis device is included, and the method for producing an iodine-concentrated solution. 14. A recycled aqueous solution containing a metal iodide salt, wherein the content of iodine (I 2 ) contained in the recycled aqueous solution is 10 g / L or more and 370 g / L or less, and the concentration of total organic carbon (TOC) in the recycled aqueous solution is 1000 ppm or less. The recycled aqueous solution. 15. A recycled aqueous solution according to 14., wherein the concentration of the metal iodide salt is 30 g / L or more and 560 g / L or less. The recycled aqueous solution.

Example

[0063] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the descriptions of these examples at all.

[0064] <Manufacture of Electrodialysis Device> A monovalent selective anion exchange membrane was installed in a bench-top test device (manufactured by Astom Co., Ltd., Micro Analyzer (registered trademark) S3) to assemble an electrodialysis device. Using the obtained electrodialysis device, an electrodialysis test was conducted on each of the monovalent selective anion exchange membranes of each example and each comparative example. Hereinafter, the procedure for assembling the electrodialysis device of Example 1 will be specifically described. First, a monovalent selective anion exchange membrane (manufactured by Astom Co., Ltd., ACS-8T) was punched out using a die made for a bench-top test device (hereinafter referred to as S3). Similarly, a cation exchange membrane (manufactured by Astom Co., Ltd., CMX-SB) was punched out. Twelve (12) punched cation exchange membranes (hereinafter referred to as CMX) ([1] to

[12] ) and ten (10) monovalent selective anion exchange membranes (hereinafter referred to as ACS) ([1] to

[10] ) were prepared. Using these, an anode frame, end packing, CMX [1], concentration chamber gasket, ACS [1], desalination chamber gasket, CMX [2], ······, CMX

[10] , concentration chamber gasket, ACS

[10] , desalination chamber gasket, CMX

[11] , concentration chamber gasket, CMX

[12] , end packing, and cathode frame were stacked in this order. Note that spacer meshes were inserted into the current-carrying parts of the concentration chamber gasket and the cathode chamber gasket. Also, the ACS was mounted such that the monovalent selective surface faced the desalination chamber. Bolts were passed through the four corners of the frame and tightened to a predetermined torque to obtain a stack. This stack was inserted between the anode chamber and the cathode chamber and tightened with bolts at the four corners to be fixed to the main body. Three magnetic pumps are built into S3. Each of them connects the desalted liquid tank and the desalination chamber communication hole, and the concentrated liquid tank and the concentrated chamber communication hole, passes through the stack, and then returns to the original tank. Also, the third pump passes through the cathode chamber and the anode chamber in series from the electrode liquid tank and returns to the tank. Connect the piping to the heat exchanger as needed, or put a cooler or a heater in the tank to adjust the temperature. Platinum-coated titanium plates were used for the anode plate and the cathode plate. These electrode plates are connected to a rectifier that can supply direct current.

[0065] [Evaluation of Electrodialysis] Using the electrodialysis device manufactured above, electrodialysis was carried out under the following dialysis conditions, and the dialysis time (min) and the current value (A) were measured over time. (Dialysis Conditions) · Desalted liquid: 20 g / l KI aqueous solution, 1000 mL · Concentrated liquid: Ion-exchanged water, 100 mL · Electrode liquid: 9 g / l KOH aqueous solution, 500 mL · Applied voltage: 10 V constant voltage However, for the desalted liquid of Comparative Example 1, a KI aqueous solution with an I2 concentration of 45 ppm, which was prepared by adding a predetermined amount of iodine (I2) to a 20 g / l KI aqueous solution, was used. For the desalted liquid of Example 1, a predetermined amount of potassium sulfite (reducing agent) was added to the KI aqueous solution prepared in Comparative Example 1, and a KI aqueous solution with an I2 concentration of 0 ppm (below the measurement limit) was used. For the desalted liquid of Example 2, a predetermined amount of potassium sulfite (reducing agent) was added to the KI aqueous solution prepared in Comparative Example 1, and a KI aqueous solution with an I2 concentration of 20 ppm was used. The I2 concentration in the desalted liquid was measured at 25 °C and 350 nm using an absorptiometer, and quantified using a calibration curve prepared in advance. Also, as a result of measuring the oxidation-reduction potential in the desalted liquid using an ORP meter, it was 120 mV for Example 1, 280 mV for Example 2, and 290 mV for Comparative Example 1.

[0066] As a result of the above electrodialysis, the maximum current value was 0.31 A for Example 1, 0.27 A for Example 2, and 0.22 A for Comparative Example 1, and the dialysis time was 40 min for Example 1, 66 min for Example 2, and 97 min for Comparative Example 1. The dialysis end point was based on the electric conductivity of the desalted liquid. From the above results, in the electrodialysis methods of Examples 1 to 2, compared with Comparative Example 1, the maximum current value was high and the dialysis time was short, indicating that the decrease in the permeation efficiency of iodide ions in the electrodialysis apparatus could be suppressed.

Explanation of Signs

[0067] 1 Electrodialysis apparatus 2 Concentrating chamber 3 Desalting chamber 4 Anode 5 Cathode 6 Power supply 7 Anion exchange membrane 8 Cation exchange membrane 10 Waste liquid 11 Waste liquid tank 12, 13 Lines 20 Concentrated liquid 21 Concentrated liquid tank 22, 23, 24 Lines 30 Desalted liquid 31, 32 Lines 50 Reducing agent tank 51, 52 Lines 100 Iodine recovery system

Claims

1. Adding a reducing agent to the waste liquid containing an iodine component to reduce at least a part of the iodine (I ２ ) contained in the iodine component to obtain iodide ions (I － ); a reduction step, After the reduction step, using an electrodialysis device equipped with an anion exchange membrane, separating the waste liquid with a pH of 3 or more and 9 or less into an iodine-containing concentrated liquid and a desalinated liquid; an electrodialysis step, After the reduction step, measuring the I ２ concentration of the waste liquid by spectrophotometry, and by adding the reducing agent, maintaining the I ２ concentration of the waste liquid measured by spectrophotometry at 20 ppm or less, A method for producing an iodine concentrated liquid.

2. The method for producing an iodine concentrated liquid according to claim 1, wherein The reducing agent contains one or more selected from the group consisting of thiosulfate, sulfite, bisulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid. A method for producing an iodine concentrated liquid.

3. The method for producing an iodine concentrated liquid according to claim 1 or 2, wherein When the waste liquid contains a boron component, a pH adjustment step of adjusting the pH of the waste liquid to 9.5 or less before the reduction step is included. A method for producing an iodine concentrated liquid.

4. The method for producing an iodine concentrated liquid according to claim 1 or 2, wherein The electrodialysis device is equipped with continuous circulation type electrodialysis equipment. A method for producing an iodine concentrated liquid.

5. The method for producing an iodine concentrated liquid according to claim 1 or 2, wherein The circulation pressures of the desalting chamber and the concentration chamber of the electrodialysis device are the same. A method for producing an iodine concentrated liquid.

6. The method for producing an iodine concentrated liquid according to claim 1 or 2, wherein A method for producing an iodine concentrate, wherein the raw material of the waste liquid is waste liquid, waste powder, and waste solids from a manufacturing process or manufacturing apparatus in a product containing an iodine component of any one of a polarizing film, a contrast agent, a disinfectant, and a radiation-related material, or waste liquid or waste solids containing an iodine catalyst used in chemical synthesis such as pharmaceutical synthesis of antibiotics and antiviral agents.

7. A method for producing an iodine concentrate according to claim 1 or 2, comprising a regeneration step of producing one or more selected from the group consisting of iodine, iodide salts, and hydroiodic acid using the obtained iodine-containing concentrate.

8. A method for producing an iodine concentrate according to claim 1 or 2, wherein an iodide salt is recovered from the iodine-containing concentrate immediately after the electrodialysis step.

9. A method for producing an iodine concentrate according to claim 8, wherein the iodide salt contains an alkali metal iodide salt.

10. A method for producing an iodine concentrate according to claim 1 or 2, comprising a step of passing the obtained desalted liquid through a strongly basic anion exchange resin to adsorb iodide ions remaining in the desalted liquid onto the strongly basic anion exchange resin, and recovering the iodide ions from the strongly basic anion exchange resin.

11. A method for producing an iodine concentrate according to claim 1 or 2, comprising a step of separating the iodine-containing concentrate into hydroiodic acid and an aqueous hydroxide salt solution by bipolar membrane electrodialysis.

12. A method for producing an iodine concentrate according to claim 1 or 2, When the waste liquid contains a boron component, after adjusting the obtained desalted liquid so that the pH becomes 11 or more, a boron recovery step of separating and recovering a boron-containing concentrated liquid from the desalted liquid using another electrodialysis device is included, and a method for producing an iodine concentrated liquid.

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