Efficient producing method of iodine concentrated liquid, and recycled aqueous solution produced by producing method of iodine concentrated liquid

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 an efficient method for producing an iodine concentrated solution, and a recycled aqueous solution produced by the method for producing an iodine concentrated solution. [Background technology]

[0002] Various techniques for recovering iodine from waste liquid have been developed. For example, the technique described in Patent Document 1 is known as one such technique. The waste liquid contains iodide ions (I - In addition to iodine components such as sulfate ions (SO4 2- For example, the wastewater usually contains sulfate ions at a concentration of 1 g / L or more, but below the saturation solubility of sulfate, more commonly at around 20 to 50 g / L. Patent Document 1 describes a method of performing electrodialysis on a stock solution that contains iodine-containing inorganic anions and fluorine-containing inorganic anions and is contained in a desalting compartment, 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] Patent Publication No. 2021-079318 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of investigations conducted by the present inventors, it was found that there is room for improvement in 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 problem]

[0005] As a result of further investigation, the present inventors have found that iodine (I2) contained in the waste liquid may adhere to the anion exchange membrane during electrodialysis, which increases the membrane resistance of the anion exchange membrane, thereby reducing the current flow and decreasing the permeation efficiency of iodide ions. In addition, in aqueous solutions, the reversible reaction of triiodide ion (I 3- ←→I - +I2) and the reversible reaction of the pentaiodide ion (I 5- ←→I 3- Such reversible reactions of polyiodide ions can also result in the generation of iodine (I2) in the wastewater. Based on this knowledge, further research was carried out and it was found that iodine (I2) contained in the wastewater can be appropriately reduced to iodide ions (I - The present inventors have found that by maintaining the electrodialysis in this state, it is possible to suppress a decrease in the current flow during electrodialysis and thus a decrease in the permeation efficiency of iodide ions, and have thus completed the present invention.

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

[0007] 1. A reducing agent is added to waste liquid containing iodine components to reduce at least a portion of the iodine (I2) contained in the iodine components to produce iodide ions (I - ) and a reduction step to obtain After the reduction step, an electrodialysis step of separating the waste liquid into an iodine-containing concentrated liquid and a desalted liquid using an electrodialysis device equipped with an anion exchange membrane. 2. A method for producing an iodine concentrated solution according to 1., comprising the steps of: The method for producing an iodine concentrated solution, wherein the reducing agent comprises one or more selected from the group consisting of thiosulfate, sulfite, hydrogen sulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid. 3. A method for producing an iodine concentrated solution according to 1. or 2., comprising the steps of: a concentration of I2 in the waste liquid to which the reducing agent has been added is 20 ppm or less after the reduction step and before the electrodialysis step. 4. A method for producing an iodine concentrated solution according to any one of 1. to 3., The method for producing a concentrated iodine solution includes 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 concentrated solution according to any one of 1. to 4., The method for producing an iodine concentrated solution, wherein the electrodialysis apparatus comprises a continuous circulation type electrodialysis facility. 6. A method for producing an iodine concentrated solution according to any one of 1. to 5., The method for producing a concentrated iodine solution, wherein the circulation pressures of the deionization compartment and the concentration compartment of the electrodialysis apparatus are made the same. 7. A method for producing an iodine concentrated solution according to any one of 1. to 6., A method for producing concentrated iodine solution, wherein the raw material for the waste liquid is waste liquid, waste powder, and waste solids from the manufacturing process or manufacturing equipment of any of the following products containing iodine components: polarizing film, contrast medium, disinfectant, and radiation-related material, or waste liquid or waste solids containing iodine catalysts used in chemical synthesis, such as the synthesis of pharmaceuticals such as antibiotics and antiviral agents. 8. A method for producing an iodine concentrated solution according to any one of 1. to 7., and 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. A method for producing an iodine concentrated solution according to any one of 1. to 8., and recovering iodide salt from the iodine-containing concentrated solution immediately after the electrodialysis step. 10. A method for producing an iodine concentrated solution according to claim 9, comprising the steps of: The method for producing an iodine concentrated solution, wherein the iodide salt comprises an alkali metal iodide salt. 11. A method for producing an iodine concentrated solution according to any one of 1. to 10., a step of passing the obtained desalted liquid through a strong basic anion exchange resin to adsorb iodide ions remaining in the desalted liquid onto the strong basic anion exchange resin, and recovering the iodide ions from the strong basic anion exchange resin. 12. A method for producing an iodine concentrated solution according to any one of 1. to 11., 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 bipolar membrane electrodialysis. 13. A method for producing an iodine concentrated solution according to any one of 1. to 12., comprising the steps of: When the waste liquid contains a boron component, the method includes a boron recovery step of adjusting the pH of the obtained desalted liquid to 11 or more, and then separating and recovering a boron-containing concentrated liquid from the desalted liquid using another electrodialysis device. 14. A recycled aqueous solution containing a metal iodide salt, comprising: The content of iodine (I2) in the recycled aqueous solution is 10 gm / L or more and 370 g / L or less, The recycled aqueous solution has a total organic carbon (TOC) concentration of 1000 ppm or less. 15. The recycled aqueous solution according to claim 14, The recycled aqueous solution has a concentration of the metal iodide salt of 30 g / L or more and 560 g / L or less. Effect of the Invention

[0008] According to the present invention, there are provided a method for producing an iodine concentrated solution which is excellent in suppressing a decrease in the permeation efficiency of iodide ions in an electrodialysis apparatus, and a recycled aqueous solution produced by the method for producing an iodine concentrated solution. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of the configuration of an electrodialysis device according to an embodiment of the present invention. [Diagram 2]FIG. 1 is a diagram illustrating an example of the configuration of an iodine recovery system according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a flow diagram showing an example of an iodine recovery process according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In all drawings, similar components are given similar reference numerals and their explanations will be omitted as appropriate. Also, the drawings are schematic diagrams and do not correspond to the actual dimensional ratios.

[0011] An outline of the method for producing a concentrated iodine solution according to this embodiment will be described.

[0012] The method for producing an iodine concentrated solution of this embodiment includes adding a reducing agent to a waste solution containing an iodine component to reduce at least a portion of the iodine (I2) contained in the iodine component to produce iodide ions (I - and, after the reduction step, an electrodialysis step of separating the waste liquid into an iodine-containing concentrated liquid and a desalted liquid using an electrodialysis device equipped with an anion exchange membrane.

[0013] According to the findings of the present inventors, the following operational malfunctions in the electrodialysis apparatus have been found. When wastewater containing I2 (sometimes called iodine molecules) is subjected to electrodialysis, the iodine molecules present in the desalted liquid will adhere to the surface of the anion exchange membrane during the electrodialysis process operated at a constant voltage. As a result, the membrane resistance of the anion exchange membrane increases, the current flow decreases, and the permeation efficiency of iodide ions decreases. Specifically, it was found that the processing capacity for desalting and concentrating iodide ions from wastewater decreases. Based on these findings, the inventors have conducted further research and have found that iodine (I2) contained in wastewater can be appropriately reduced to iodide ions (I - It has been found that by maintaining the electrodialysis in this state, the above-mentioned current failure during electrodialysis can be suppressed and the operational stability of the electrodialysis apparatus can be improved. Further investigation revealed that the electrical conductivity failure can be stably suppressed by using the redox potential as an indicator of the reduction state of iodine (I2). Specifically, it is preferable that the redox potential of the waste liquid is 100 mV or less.

[0014] The configuration of the method for producing a concentrated iodine solution according to this embodiment will be described in detail below.

[0015] Fig. 1 is a cross-sectional view showing a schematic example of the configuration of an electrodialysis device 1. Fig. 2 is a diagram showing a schematic example of the configuration of an iodine recovery system 100. Fig. 3 is a flow diagram showing an example of an iodine recovery process.

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

[0017] The iodine recovery system 100 in FIG. 2 is sufficient if it is equipped with at least a facility for supplying waste liquid 10 to the electrodialysis apparatus 1, and further includes a facility for treating the concentrated liquid 20 and / or desalted liquid 30 produced in the electrodialysis apparatus 1.

[0018] The waste liquid 10 (undiluted liquid) is not particularly limited as long as it is a liquid containing an iodine component described below, but examples thereof include waste liquid discharged from the manufacturing process of a product containing an iodine component, waste liquid discharged during disposal of a product containing an iodine component, waste liquid discharged from a synthesis process using an iodine component as a reaction catalyst, waste liquid of a cleaning solution used for cleaning a manufacturing device using an iodine component, and the like.

[0019] Specific examples of raw materials for the waste liquid 10 include waste liquid, waste powder, and waste solids from the manufacturing process or manufacturing equipment of products containing iodine components such as polarizing films, contrast media, disinfectants, and radiation-related materials, or waste liquid or waste solids containing iodine catalysts (organic iodine compounds or inorganic iodine compounds) used in chemical synthesis such as the synthesis of pharmaceuticals such as antibiotics and antiviral agents. These may be used alone or in combination of two or more.

[0020] When organic matter and / or an organic solvent is contained in the waste liquid, the iodine recovery liquid may be subjected to a known organic matter decomposition treatment in advance. As one of such organic matter decomposition treatments, for example, an aqueous solution in which organic components (organic matter and organic solvent) are burned by a combustion method, and the sublimated iodine is adsorbed with an alkali agent (e.g., sodium hydroxide and sodium hydrogen sulfite) and a reducing agent, and the iodine component is recovered is shown. The iodine component is, for example, iodide ion (I - ), iodine (I2), iodic acid (HIO3), periodic acid (HIO4), and iodides (including inorganic iodine compounds or organic iodine compounds). In addition, as mentioned above, in aqueous solutions, iodine (I2) can be generated in the wastewater due to reversible reactions of polyiodide ions such as triiodide and pentaiodide ions. Here, the waste liquid derived from the raw materials contains iodine ions among the above iodine components, usually at 3% or more, preferably about 3% to 30%. Furthermore, these waste liquids contain sulfate ions at a concentration of 1 g / L or more and below the saturated solubility of sulfate, more generally about 20 to 50 g / L. Furthermore, solids containing iodine components usually contain about 30% to 99.8% iodine element by mass.

[0021] The waste liquid 10 used is at least subjected to reduction treatment, but if necessary, it may be subjected to chemical or physical pretreatment such as pH adjustment, dilution, organic matter decomposition / removal treatment, etc.

[0022] As shown in Fig. 1, electrodialysis device 1 has a concentration compartment 2, a deionization compartment 3, an ion exchange membrane separating the concentration compartment 2 and the deionization compartment 3, an anode 4, a cathode 5, and a power source 6. Electrodialysis device 1 is not limited to the configuration shown in Fig. 1 and may have a known device 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 disposed on either side of an electrodialysis cell composed of a concentration chamber 2 and a deionization chamber 3. When a current is applied to the anode 4 and the cathode 5 using a power source 6, electrodialysis begins in the electrodialysis cell. As the electrode solution, a known solution can be used, for example, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of sodium hydrogen sulfate, an aqueous solution of potassium sulfate, etc. However, when performing bipolar electrodialysis after electrodialysis, the electrode solution used in the electrodialysis device 1 is preferably one that does not contain sulfate.

[0024] In the electrodialysis cell, the concentrating compartments 2 and the deionizing compartments 3 are partitioned by ion exchange membranes (either anion exchange membrane 7 or a cation exchange membrane 8) and arranged alternately. The electrodialysis device 1 may have at least a configuration in which a deionization compartment 3, an anion exchange membrane 7, a concentration compartment 2, a cation exchange membrane 8, and a deionization compartment 3 are arranged in this order, and from the viewpoint of increasing the processing capacity, may have one or more concentration compartments 2, preferably two or more concentration compartments 2. The concentrating chamber 2 may contain an electrolyte before electrodialysis. The electrolyte may contain, for example, an aqueous solution of an inorganic salt having electrical conductivity. For example, ion-exchanged water may be used when the electrodialysis device 1 is used for the first time, and the previous concentrated solution may be used when the device is continuously used after being stopped and then restarted. In addition to such electrolytes, an aqueous solution of sodium chloride, an aqueous solution of potassium iodide, an aqueous solution of sodium iodide, or the like may be used. However, it is preferable that the electrolyte does not contain sulfate.

[0025] A specific example of the electrodialysis device 1 used for the above-mentioned electrodialysis has a number of gasket spacers (also called chamber frames) stacked between a pair of electrodes, with anion exchange membranes 7 or cation exchange membranes 8 sandwiched between adjacent chamber frames, such that the anion exchange membranes 7 and cation exchange membranes 8 are, in principle, arranged alternately as a whole, and an ion exchange chamber (current-carrying section) partitioned by the anion exchange membranes 7 and cation exchange membranes 8 is formed in each gasket. The ion exchange compartments are arranged such that the deionization compartments 3 and the concentration compartments 2 are arranged alternately, with the deionization compartments 3 being the compartments in which the cation exchange membrane 8 is located on the cathode 5 side and the anion exchange membrane 7 on the anode 4 side, and the concentration compartments 2 being the compartments in which the anion exchange membrane 7 is located on the cathode 5 side and the cation exchange membrane 8 on the anode 4 side. That is, when a current is applied while a treatment liquid (electrolyte liquid) is circulated and supplied to the deionization compartments 3, the cations in the treatment liquid supplied to the deionization compartments 3 pass through the cation exchange membrane 8 and migrate to the concentration compartment 2 on the adjacent cathode 5 side, and the anions in the treatment liquid pass through the anion exchange membrane and migrate to the concentration compartment 2 on the adjacent anode 4 side. In this way, when the treatment liquid is circulated and supplied to the deionization compartments 3, and at the same time a salt water solution is circulated to the concentration compartments 2, the treatment liquid is desalted and a concentrated liquid 20 with an increased salt concentration can be obtained. The method for fixing the laminate of these ion exchange chambers between the electrodes is preferably, but not limited to, a filter press.

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

[0027] When anion exchange membrane 7 includes an anion exchange membrane other than a monovalent ion selective anion exchange membrane, the other anion exchange membrane may be a known one, for example, a monovalent ion selective permeable anion exchange membrane, a fully permeable anion exchange membrane, or a high-strength alkali-resistant anion exchange membrane, and a monovalent ion selective permeable anion exchange membrane is preferable.

[0028] There is no particular limitation on the cation exchange membrane 8, and a strongly acidic cation exchange membrane, a high-strength alkali-resistant cation exchange membrane, etc. may be used. The cation exchange membrane 8 may also be a cation exchange membrane selective for monovalent ions.

[0029] An example of the operation of the electrodialysis device 1 during electrodialysis is as follows. When a direct current is applied between the anode 4 and the cathode 5 using a power source 6, iodide ions (I - ) passes through anion exchange membrane 7 and moves to concentration compartment 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 deionization compartment 3 on the other side pass through cation exchange membrane 8 and move to the same concentration compartment 2. In this concentration compartment 2, iodide salts such as potassium iodide (KI) are produced. A concentrated solution 20 containing iodide salts (iodine-containing concentrated solution) is obtained from concentration compartment 2. A deionized solution 30 is obtained from deionization compartment 3.

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

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

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

[0033] A reducing agent is introduced from a reducing agent tank 50 to the waste liquid 10 in the waste liquid tank 11 through a line 51. This reduces at least a part or almost all of the iodine (I2) contained in the waste liquid 10 to produce iodide ions (I -It is also possible to convert a part or all of the iodic acid and periodic acid contained in the iodine components other than iodine (I2) contained in the waste liquid 10 into ions, i.e., iodide ions. Iodide ions can be detected using a variety of methods, including instrumental analysis using ion chromatography, titration of 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 thiosulfate, sulfite, hydrogen sulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid. Among these, sulfuric acid-based reducing agents such as thiosulfate, sulfite, and hydrogen sulfite are preferred because they can be used in the neutral range, and hydrogen sulfite is more preferred from the viewpoints of handling, economy, and availability.

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

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

[0037] An ORP (Oxidation Reduction Potential) meter may be installed in the waste liquid tank 11. A reducing agent can be supplied so that the oxidation-reduction potential of the waste liquid 10 in the waste liquid tank 11 is maintained at or below a predetermined value. Here, the predetermined value of the redox potential is preferably 120 mV. In other words, after the reduction step and before the electrodialysis step, the redox potential of the waste liquid 10 to which the reducing agent has been added is preferably maintained at 120 mV or less. This can further suppress a decrease in the throughput of the electrodialysis device.

[0038] If necessary, the waste liquid 10 in the waste liquid tank 11 may be subjected to the above-mentioned chemical or physical pretreatment other than the reduction treatment. When the waste liquid 10 contains a boron component, a pH adjustment step may be performed before the electrodialysis step, in which the pH of the waste liquid 10 is adjusted to 9.5 or less, preferably 8 or less, and more preferably less than 7. When the pH of the waste liquid 10 is adjusted to 9.5 or less, most of the boric acid (H3BO3) is not dissociated and exists as molecules, so that even when electrodialysis is performed, the boric acid hardly moves and is discharged as it is into the desalted liquid 30. This allows the boron component and the iodine component in the waste liquid 10 to be separated efficiently.

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

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

[0041] At this time, at least a part of the desalted liquid 30 may be supplied to the waste liquid tank 11 via a line 32 branched off from the line 31, and a mixed desalted liquid obtained by mixing the desalted liquid 30 and the waste liquid 10 may be supplied again to the desalting chamber 3. In other words, the waste liquid 10 supplied to the desalting chamber 3 may contain the desalted liquid 30. By repeating the electrodialysis in this manner, the iodide ion concentration in the desalted solution 30 can be reduced to a desired value.

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

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

[0044] In addition, when two or more electrodialysis devices are provided, a first concentrated solution produced from a first electrodialysis device may be supplied to a desalting compartment of a second electrodialysis device. Furthermore, a second desalted solution produced in the desalting compartment of the second electrodialysis device may be mixed with the first concentrated solution and supplied again to the desalting compartment of the second electrodialysis device.

[0045] Alternatively, an electrodialysis device 1 equipped with a continuous circulation type electrodialysis facility may be used. Such an electrodialysis apparatus 1 can be continuously operated by continuously supplying the waste liquid 10 or a mixed desalted liquid to the desalted liquid 30 while continuously discharging the desalted liquid 30.

[0046] In addition, the circulation pressures of the deionization compartment 3 and the concentration compartment 2 of the electrodialysis apparatus 1 may be controlled to be the same. This makes it possible to prevent internal leakage (permeation) from the higher pressure compartment to the lower pressure compartment due to a pressure difference between the circulation pressures of the deionization compartment 3 and the concentration compartment 1. Specifically, it is possible to prevent impurities in the deionization compartment 3 from entering the concentration compartment 2, or to prevent iodine components in the concentration compartment 2 from returning to the deionization compartment 3, thereby reducing the efficiency of iodine permeation.

[0047] The iodine-containing concentrate (concentrated solution 20) obtained by the electrodialysis step of the method for producing an iodine concentrate of the present embodiment can be used as a recycled aqueous solution containing a metal iodide salt. The iodine concentration in the recycled aqueous solution may be, for example, equal to or lower than the saturation concentration of the alkali metal iodide salt, and is 30 to 560 g / L, and preferably 80 to 350 g / L. The iodine concentration in the recycled aqueous solution can be measured as the total iodine concentration by instrumental analysis using an ICP (inductively coupled optical emission spectrometry) and an ion chromatography device.

[0048] The metal iodide salt in the recycled aqueous solution contains, for example, at least one or more of alkali metal iodide salts and alkaline earth metal iodide salts.

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

[0050] The recycled aqueous solution such as the above-mentioned concentrated solution may be stored in a plastic container. The resin container may contain 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. This can prevent iodide ions from being oxidized to iodine molecules in the recycled aqueous solution stored in the resin container, thereby improving the stability of the solution. In order to further improve the stability of the solution, the above-mentioned reducing agent may be added to the recycled aqueous solution.

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

[0052] The method for producing an iodine concentrated solution may include a regeneration step of producing one or more selected from the group consisting of iodine (I2), iodide salts, and hydroiodic acid, using the iodine-containing concentrated solution (concentrated solution 20) obtained after the electrodialysis step as a recycled aqueous solution, as shown in Fig. 3. Such a regeneration step may be performed using an apparatus other than the electrodialysis apparatus 1 described above. The iodine, iodide salt, and hydroiodic acid regenerated (recycled) in the above-mentioned method for producing an iodine concentrated solution may each be in the form of an aqueous solution, and the iodine and iodide salt may be in the form of a powder (including granules).

[0053] The method for producing an iodine concentrated solution can recover hydroiodic acid using the obtained concentrated solution 20. For example, as shown in Fig. 3, the method for producing an iodine concentrated solution may include a step of separating an iodine-containing concentrated solution (concentrated solution 20) into hydroiodic acid and an aqueous hydroxide salt solution by bipolar membrane electrodialysis (bipolar electrodialysis step). Here, bipolar membrane electrodialysis is a method in which bipolar membranes that generate hydrogen ions and hydroxide ions, in addition to cation exchange membranes and / or anion exchange membranes, are arranged in sequence between an anode and a cathode, and a treatment liquid is supplied to each chamber separated by the membranes and an electric current is passed through to obtain an acid and an alkali from a neutral salt.

[0054] Specifically, the concentrated solution 20 (e.g., KI concentrated solution) discharged from the electrodialysis device 1 is introduced into the bipolar membrane electrodialysis device. If necessary, the concentrated solution 20 may be acidified by adjusting the pH to less than 7. When a direct current is applied to the bipolar membrane electrodialysis device, the iodide salt in the concentrated solution 20 is electrolyzed, and an aqueous solution of hydroiodic acid (HI solution) and an aqueous solution of hydroxide (e.g., KOH) are discharged. Thereafter, the HI solution is purified by distillation to obtain hydroiodic acid.

[0055] Moreover, the method for producing an iodine concentrated solution can recover iodine (I2) using the obtained concentrated solution 20. As shown in FIG. 3, when a concentrated solution 20 containing iodide ions is oxidized, iodine (I2) is obtained.

[0056] The method for producing an iodine concentrate can use the resulting concentrate 20 to recover iodide salts. As shown in Figure 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 a concentrated iodine solution, the above-mentioned oxidation, neutralization, and reduction methods are not particularly limited, and known means can be used. The iodide salt includes, for example, metal iodide salts such as alkali metal iodide salts and alkaline earth metal iodide salts. Specific examples of iodide metal salts include potassium iodide, sodium iodide, calcium iodide, magnesium iodide, cesium iodide, etc. These may be used alone or in combination of two or more. In addition, alkaline earth metals may cause damage to the ion exchange membrane. Therefore, in the method for producing iodine concentrate of this embodiment, when the waste liquid 10 contains alkaline earth metals, it is preferable to include a step of removing the alkaline earth metals before the above-mentioned 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, a poorly soluble salt formed by a hydroxide or carbonate may be separated. If necessary, a pH adjustment may be performed as a pretreatment for forming a poorly soluble salt.

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

[0058] Specifically, the desalted liquid 30 discharged from the electrodialysis device 1 is passed through a strongly basic ion exchange resin, and iodide ions are adsorbed on the 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 adjusted to less than 7, preferably 3 or more and less than 7, as in the above-mentioned electrodialysis. This makes it possible to selectively separate iodide ions by suppressing the adsorption of borate ions formed by dissociating boric acid onto the strongly basic anion exchange resin. Thereafter, iodine (I2) can be recovered from the strongly basic anion exchange resin by a known means.

[0059] Furthermore, 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 the iodine concentrate may include a boron recovery step in which the pH of the desalted liquid 30 containing a boron component is adjusted to, for example, 7 or more, preferably 8 or more, more preferably 11 or more, and then a boron-containing concentrate (boric acid concentrate) is separated and recovered from the desalted liquid 30 using another electrodialysis device. 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 obtained when passing through the strongly basic anion exchange resin described above, is passed through a boron-selective chelating resin to adsorb boric acid ions. Thereafter, boric acid can be recovered from the boron-selective chelating resin by a known means.

[0062] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of the present invention are included in the present invention. EXAMPLES

[0063] 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.

[0064] <Manufacture of electrodialysis equipment> The monovalent selective anion exchange membrane was placed in a tabletop test device (Micro Acilyzer (registered trademark) S3, manufactured by Astom Corporation) to assemble an electrodialysis device. Using the obtained electrodialysis device, electrodialysis tests were performed on each of the monovalent selective anion exchange membranes of each Example and Comparative Example. The procedure for assembling the electrodialysis device of Example 1 will now be specifically described. First, a monovalent selective anion exchange membrane (ACS-8T, manufactured by ASTOM CORPORATION) was punched out using a punching die made for a tabletop test device (hereinafter referred to as S3). Similarly, a cation exchange membrane (CMX-SB, manufactured by ASTOM CORPORATION) was punched out. We prepared 12 punched cation exchange membranes (hereinafter referred to as CMX) ([1]~

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

[10] ). Using these, the following stacking order was used: anode frame, end packing, CMX[1], concentration compartment gasket, ACS[1], deionization compartment gasket, CMX[2], ····, CMX

[10] , concentration compartment gasket, ACS

[10] , deionization compartment gasket, CMX

[11] , concentration compartment gasket, CMX

[12] , end packing, and cathode frame. Spacer meshes were fitted into the conductive parts of the concentration compartment gasket and cathode compartment gasket. The ACS was installed so that its monovalent selective surface faced the deionization compartment. Bolts were passed through the four corners of the frame and tightened to the specified torque to obtain the stack. The stack was inserted between the anode chamber and the cathode chamber and fixed to the main body by tightening the bolts at the four corners. S3 has three magnetic pumps built in, which connect the desalted liquid tank to the desalting chamber connection hole, and the concentrated chamber tank to the concentrated chamber connection hole, and then return to the original tank after passing through the stack. The third pump passes from the electrode solution tank to the cathode chamber and anode chamber in series and returns to the tank. If necessary, connect the pipes to a heat exchanger or place a cooler or heater in the tank to adjust the temperature. The anode and cathode plates used were platinum-coated titanium plates. These plates are connected to a rectifier capable of supplying direct current.

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

[0066] As a result of the above electrodialysis, the maximum current value was 0.31 A in Example 1, 0.27 A in Example 2, and 0.22 A in Comparative Example 1, and the dialysis time was 40 min in Example 1, 66 min in Example 2, and 97 min in Comparative Example 1. The end point of dialysis was based on the electrical conductivity of the desalted liquid. The above results show that the electrodialysis methods of Examples 1 and 2 have a higher maximum current value and a shorter dialysis time than Comparative Example 1, and therefore can suppress a decrease in the permeation efficiency of iodide ions in the electrodialysis device. [Explanation of symbols]

[0067] 1 Electrodialysis equipment 2 Concentration chamber 3 Desalination room 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 Concentrate 21 Concentrate tank 22, 23, 24 lines 30 Desalination solution 31, 32 lines 50 Reductant tank Lines 51 and 52 100 Iodine Recovery System

Claims

1. A reducing agent is added to the waste liquid containing the iodine component to reduce the iodine (I ２ iodide ions (I － a reduction step to obtain After the reduction step, an electrodialysis step of separating the waste liquid into an iodine-containing concentrated liquid and a desalted liquid using an electrodialysis device equipped with an anion exchange membrane.

2. A method for producing an iodine concentrated solution according to claim 1, comprising the steps of: The method for producing an iodine concentrated solution, wherein the reducing agent comprises one or more selected from the group consisting of thiosulfate, sulfite, hydrogen sulfite, oxalic acid, formic acid, hydrazine, and hypophosphorous acid.

3. A method for producing an iodine concentrated solution according to claim 1 or 2, After the reduction step and before the electrodialysis step, the I of the waste liquid to which the reducing agent has been added is ２ A method for producing an iodine concentrated solution having an iodine concentration of 20 ppm or less.

4. A method for producing an iodine concentrated solution according to claim 1 or 2, The method for producing an iodine concentrated solution includes 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 concentrated solution according to claim 1 or 2, The method for producing an iodine concentrated solution, wherein the electrodialysis apparatus comprises a continuous circulation type electrodialysis facility.

6. A method for producing an iodine concentrated solution according to claim 1 or 2, The method for producing a concentrated iodine solution, wherein the circulation pressures of the deionization compartment and the concentration compartment of the electrodialysis apparatus are made the same.

7. A method for producing an iodine concentrated solution according to claim 1 or 2, The method for producing a concentrated iodine solution, wherein the raw material for the waste liquid is a waste liquid, waste powder, and waste solid from a manufacturing process or manufacturing equipment for a product containing an iodine component, such as any 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 the synthesis of pharmaceuticals such as antibiotics and antiviral agents.

8. A method for producing an iodine concentrated solution according to claim 1 or 2, and 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. A method for producing an iodine concentrated solution according to claim 1 or 2, and recovering iodide salt from the iodine-containing concentrated solution immediately after the electrodialysis step.

10. A method for producing an iodine concentrated solution according to claim 9, comprising the steps of: The method for producing an iodine concentrated solution, wherein the iodide salt comprises an alkali metal iodide salt.

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

12. A method for producing an iodine concentrated solution according to claim 1 or 2, 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 bipolar membrane electrodialysis.

13. A method for producing an iodine concentrated solution according to claim 1 or 2, When the waste liquid contains a boron component, the method includes a boron recovery step of adjusting the pH of the obtained desalted liquid to 11 or more, and then separating and recovering a boron-containing concentrated liquid from the desalted liquid using another electrodialysis apparatus.

14. 1. A recycled aqueous solution containing a metal iodide salt, The iodine (I ２ The content of is 10 gm / L or more and 370 g / L or less, The recycled aqueous solution has a total organic carbon (TOC) concentration of 1000 ppm or less.

15. The recycled aqueous solution according to claim 14, The concentration of the metal iodide salt is 30 g / L or more and 560 g / L or less.

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