JP7117698B2 - Method for producing inorganic compound-containing aqueous solution - Google Patents

Description

The present invention relates to a method for producing an inorganic compound-containing aqueous solution.

Electrodialysis is known as a technique for separating specific inorganic ions from an aqueous solution containing multiple types of inorganic ions, such as industrial waste liquids and seawater. Such technology is important as a means of treating waste water and recovering rare elements such as iodine.

Examples of such industrial waste liquids include waste liquids containing iodide ions, boric acid, potassium ions, and water-soluble organic substances, such as waste liquids generated in the manufacturing process of polarizing films used in liquid crystal displays and the like. (Patent Documents 1 to 4). Such waste liquid is generally discharged as industrial wastewater after reducing the concentration of specific components such as boron contained in the waste liquid to below the concentration stipulated by wastewater standards by coagulation sedimentation method, coagulation sedimentation filtration method, etc. Or, it is reduced in volume by concentrating and treated as industrial waste.

In recent years, the emission standard value for boron and boron compounds has become stricter at 10 mg/L, and it is difficult to stably reduce the concentration of boron in wastewater to below the emission standard value using conventional treatment methods such as the coagulation sedimentation method. be. In addition, the demand for iodine compounds is increasing more and more in cutting-edge industries, medical applications, etc., and it is preferable to recover and reuse them as much as possible.

A method of concentrating and separating a specific component by subjecting the above-mentioned waste liquid to electrodialysis is also known. For example, in Patent Document 1, a waste liquid discharged in a polarizing plate manufacturing process is subjected to electrodialysis as it is without adjusting the pH to the alkaline side, and inorganic components such as iodide and boric acid, and glycerin, polyvinyl alcohol, etc. There is a method that can efficiently treat and reduce the amount of waste by separating the organic substances into a desalted liquid and a concentrated liquid, and subjecting each liquid to biological treatment, concentration and volume reduction, etc. separately. Proposed. That is, the method of Patent Document 1 is a method of separating inorganic components and organic components by electrodialysis, and does not separate inorganic components such as iodide and boric acid.

Further, in Patent Document 2, a polarizing film manufacturing waste liquid containing iodine, boron, and potassium is adjusted to have a pH of less than 7, and then electrodialyzed to remove iodine and potassium contained in the waste liquid from potassium iodide. A method for separating as In the method of Patent Document 2, boric acid contained in the waste liquid exists in a molecular state (H ₃ BO ₃ state) in a neutral to acidic range of less than pH 7, and even if electrodialysis is performed, boric acid is a concentrated liquid. It is based on the idea that the dissociated iodide ions, which do not move to the water, pass through the anion exchange membrane by electrodialysis and move to the concentrate.

Japanese Patent Application Laid-Open No. 2001-314864 JP-A-2008-13379 JP 2011-157237 A WO2003-014028

"Ultra-high Efficiency Boron Removal Technology from Water", Chemical Equipment, February 2012, p53-58

In Patent Document 2, it is stated that boric acid contained in the waste liquid can be separated from iodide ions by electrodialysis in a molecular state (H ₃ BO ₃ state), that is, in a state that hardly responds to an electric field. . However, according to the studies of the present inventors, when electrodialysis is performed with the pH of an aqueous solution (stock solution) containing boric acid and halogen from neutral to acidic, boric acid in the molecular state also undergoes free diffusion. It has been found that it can pass through an anion exchange membrane and, for example, 20-30 mol % of the boric acid contained in the stock solution may be transferred to the concentrate solution. Therefore, there is room for improvement in obtaining an inorganic compound-containing aqueous solution by reducing the amount of boric acid that moves to the concentration chamber side, separating the separation target from the undiluted solution with higher accuracy.

The present invention has been made in view of the above circumstances, and an inorganic compound is obtained by separating the inorganic anion from the boric acid with high precision from a stock solution containing boric acid and at least one inorganic anion having a halogen. It is an object of the present invention to provide a method for obtaining an aqueous containing solution.

The method for producing an inorganic compound-containing aqueous solution of the present invention comprises an electrodialysis tank comprising a desalting chamber and a concentrating chamber separated from the desalting chamber by an anion exchange membrane. a separation step of subjecting the undiluted solution contained in the desalting chamber to electrodialysis to separate at least one of the halogens from boric acid to obtain an inorganic compound-containing aqueous solution, wherein the pH of the undiluted solution is is 8 or more.

Preferably, the pH of the stock solution is maintained at 8 or higher during the separation step.

Further, the method for producing an aqueous solution containing an inorganic compound of the present invention comprises an electrodialysis tank comprising a desalting chamber and a concentrating chamber separated from the desalting chamber by an anion exchange membrane. a separation step of electrodialyzing the undiluted solution contained in the desalting chamber containing anions and separating at least one of the halogens from boric acid to obtain an inorganic compound-containing aqueous solution, wherein the undiluted solution is It may contain 30 mol % or less of molecular boric acid relative to the total amount of molecular boric acid and ionic boric acid.

Preferably, the boric acid is at least one of B(OH) ₃ , metaboric acid, polyboric acid and their ionic states.

When the halogen contains iodine-containing ions, and in the separation step, the boric acid and iodine-containing ions are separated, and the boron compound aqueous solution on the demineralization compartment side and the iodine compound aqueous solution on the concentration compartment side are respectively separated. preferable.

Preferably, the iodine-containing ions include at least one of iodide ions and iodate ions.

It is preferable to further include a purification step of contacting the iodine compound aqueous solution with a resin that selectively adsorbs boron compounds.

The desalting chamber accommodates the undiluted solution for electrodialysis and is connected to the undiluted solution tank for transferring the undiluted solution to the desalting chamber. It is preferable to further include a step of mixing with the undiluted solution and introducing it into the desalting chamber again for electrodialysis.

A second electrodialysis tank separate from the electrodialysis tank is connected to the electrodialysis tank, and a step of transferring the iodine compound aqueous solution from the concentration chamber to the second electrodialysis tank and performing electrodialysis is provided. and preferred.

The concentration of the aqueous iodine compound solution discharged from the concentration chamber is monitored, and the aqueous iodine compound solution is removed from when the concentration of boric acid in the aqueous iodine compound solution exceeds a predetermined lower limit value before exceeding the predetermined lower limit value. It is preferable to separate it from the recovered iodine compound aqueous solution.

It is preferable to further include a step of bringing the separately separated iodine compound aqueous solution into contact with a strongly basic anion exchange resin for purification.

The anion exchange membrane is preferably a strongly basic anion exchange membrane.

An object of the present invention is to provide a method for obtaining a high-purity inorganic compound-containing aqueous solution containing inorganic anions from a stock solution containing boric acid and at least one halogen-containing inorganic anion.

FIG. 1 is a schematic diagram showing the configuration of an electrodialysis apparatus according to one embodiment of the present invention. FIG. 2 is a diagram for explaining the relationship between pH and the ratio of boric acid in the molecular state. 3 is a graph showing the transfer rate of iodide ions and boric acid to the concentrating chamber side with respect to the energization time in Example 3. FIG. FIG. 4 is a graph showing the transfer rate of iodide ions and boric acid to the concentrating compartment side with respect to the energization time in Comparative Example 2. In FIG.

In the method for producing an inorganic compound-containing aqueous solution of the present embodiment, in an electrodialysis tank comprising a desalting chamber and a concentration chamber separated from the desalting chamber by an anion exchange membrane, the undiluted solution contained in the desalting chamber is It is provided with a separation step (hereinafter also referred to as a first separation step) of performing electrodialysis to fractionate an inorganic compound-containing aqueous solution. The stock solution contains boric acid and an inorganic anion having at least one halogen (hereinafter also referred to as a first anion), and the first inorganic anion is separated from the boric acid by the separation step. It is fractionated as an inorganic compound-containing aqueous solution. The stock solution further satisfies at least one of the following conditions (i) and (ii).
(i) The stock solution has a pH of 8 or higher.
(ii) The stock solution contains 30 mol % or less of molecular boric acid relative to the total amount of molecular boric acid and ionic boric acid.
That is, in the production method of the present embodiment, electrodialysis is performed on the undiluted solution (demineralized liquid) that satisfies the above conditions and is stored in the demineralization chamber, and at least one of the first anions is separated from boric acid. It is provided with a separation step of fractionating as an inorganic compound-containing aqueous solution.

The inorganic compound-containing aqueous solution to be fractionated may be the aqueous solution on the concentration compartment side or the aqueous solution on the desalting compartment side. That is, by electrodialysis, the aqueous solution containing the first inorganic anion that has moved from the desalting compartment to the concentration compartment may be fractionated as an inorganic compound-containing aqueous solution, or ions other than the desired first inorganic anion may be isolated. The aqueous solution containing the first inorganic anion remaining in the desalting chamber after the transfer of the ions to the concentration chamber may be fractionated as an inorganic compound-containing aqueous solution. Moreover, after separating the first inorganic anion from boric acid, an aqueous solution containing boric acid may be recovered as an aqueous solution containing a boron compound.

In this specification, the term "boric acid" in an aqueous solution includes B(OH) ₃ , metaboric acid (O=B-OH) and polyboric acid. It refers to either a molecular state or an ionic state in

The first inorganic anion is not particularly limited as long as it is a halogen-containing inorganic anion, but is preferably an inorganic anion containing at least one of chlorine, bromine and iodine. The first inorganic anion may be an inorganic anion composed only of halogen, or may be an inorganic anion containing an element other than halogen (such as an oxygen atom). Inorganic anions composed only of halogen include single halogen such as fluoride ion (F ⁻ ), chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), iodide ion (I ⁻ ). It may be an inorganic anion containing ions, and may be a polyhalide ion such as I ₂ Cl ⁻ , I ₃ ⁻ , ICl ₂ ⁻ , I ₂ Br ⁻ , IBr ₂ ⁻ . The first inorganic anion preferably contains a single halogen-containing inorganic anion. Inorganic anions containing a single halogen include inorganic anions containing fluorine such as fluoride ions and fluoride ions, inorganic anions containing chlorine such as chloride ions and chlorate ions, bromide ions, and bromate ions. Inorganic anions having bromine such as inorganic anions having bromine, iodide ions, inorganic anions having iodine such as iodate ions, inorganic anions having chlorine, inorganic anions having bromine, and inorganic anions having iodine Any one is preferably included. The halogen-containing inorganic anion may be a complex ion containing a metal element, but is preferably one that does not contain a metal element (that is, an ion other than a metal complex ion).

The stock solution may contain a second inorganic anion that is an inorganic anion other than the first inorganic anion. The second inorganic anion does not include ionic boric acid. The second inorganic anion may be a monovalent inorganic anion or a multivalent inorganic anion. More specifically, sulfate ions, sulfite ions, thiosulfate ions, tetrathionate ions, other sulfur oxoacid ions, nitrate ions, phosphate ions, hydrogen phosphate ions, dihydrogen phosphate ions, carbonate ions, bicarbonate ions, sulfide ions, hydrogen sulfide ions, cyanide ions, and the like.

An inorganic anion can be included in the stock solution by dissolving a salt containing the inorganic anion. Salts containing inorganic anions include alkali metal salts and the like. Further, after dissolving the conjugate acid of the inorganic anion in the stock solution, potassium hydroxide, sodium hydroxide, or the like may be added to adjust the pH.

The method for producing an inorganic compound-containing aqueous solution of the present embodiment utilizes the principle of chromatographic separation using an anion exchange membrane that utilizes electrodialysis for a plurality of inorganic anions contained in a stock solution. Here, in normal chromatographic separation in which the undiluted solution is passed through an anion exchange resin column or the like without using electrodialysis, ions with low selectivity flow out early, and ions with high selectivity flow out last. On the other hand, in the method for producing an inorganic compound-containing aqueous solution of the present embodiment, ions with high selectivity first flow out to the concentration chamber side, and ions with low selectivity flow out later, which is the reverse order of normal chromatographic separation. Inorganic anions tend to pass through the anion exchange membrane. In addition, this tendency may be changed and reversed depending on the affinity with the membrane, the molecular radius, and the liquid conditions on the concentration tank side.
As a result of examination by the present inventors, it has been found that the movement speed of inorganic anions across the anion exchange membrane to the concentration compartment side by electrodialysis is in the following order (ions on the left side have a movement speed of big).
I ₃ ⁻ >I ⁻ >NO ₃ ⁻ >S ₂ O ₃ ²⁻ >Br ⁻ >Cl ⁻ >SO ₄ ²⁻ >IO ₃ ⁻ >HPO ₄ ²⁻ >OH−> boric acid in ionic state

Hereinafter, a case where a stock solution containing boric acid and ions containing iodine is used in the production method of the present embodiment will be described in detail.

Since the production method of the present embodiment can effectively suppress boric acid from passing through the anion exchange membrane, the concentration of boric acid in the aqueous solution containing ions containing iodine that has migrated to the concentration chamber side is further reduced. Thus, the iodine compound aqueous solution in the concentration compartment can be recovered with high purity, and the boron compound aqueous solution remaining in the demineralization compartment can also be recovered.

In the production method of the present embodiment, in the first separation step, ions containing iodine are separated from boric acid by flowing out from the desalting compartment to the concentration compartment through the anion exchange membrane. In addition, separation means that the concentration of ions containing iodine is higher than the concentration of boric acid in the aqueous solution (concentrated liquid) in the concentrating compartment compared to the undiluted solution (that is, the concentration of ions containing iodine is mainly contained an aqueous solution is obtained) and does not only mean that the aqueous solution in the concentrating compartment does not contain any boric acid. In addition, when ions containing iodine flow out into the concentrating compartment, the concentration of ions containing iodine in the aqueous solution (demineralized liquid) in the demineralizing compartment decreases, and compared to the undiluted solution, the concentration of ions containing iodine relative to the concentration of boric acid decreases. An aqueous solution with a low concentration of remains (that is, an aqueous solution mainly containing boric acid is obtained). In the production method of the present embodiment, after iodine-containing ions and boric acid are separated by electrodialysis, the aqueous solutions in the concentration compartment and the demineralization compartment can be recovered as an iodine compound aqueous solution and a boron compound aqueous solution, respectively.

The molar concentration ratio (I/B ratio) of the iodine element derived from the salt containing iodine to the boron element derived from boric acid in the concentrated liquid is preferably 30 or more, and is preferably 40 or more because the higher the better. and more preferably 50 or more. In the production method of the present embodiment, ions containing iodine and boric acid can be efficiently separated, so a high I/B ratio can be easily achieved.

Further, the I/B ratio of the concentrated solution is preferably 5 times or more, more preferably 8 times or more, and even more preferably 10 times or more that of the undiluted solution. In the production method of the present embodiment, the iodine-containing ions and boric acid can be efficiently separated, so a high I/B ratio can be easily achieved compared to the undiluted solution.

The principle of separating boric acid and iodine-containing ions in the production method of the present embodiment is as follows. First, B(OH) ₃ exists in a molecular state (that is, B(OH) ₃ itself) in an aqueous solution. More specifically, boric acid in an ionic state includes B(OH) ₄ ⁻ , B ₃ O ₃ (OH) ₄ ⁻ , B ₅ O ₆ (OH) ₄ ⁻ , and B ₃ O ₃ (OH) ₅ ^2- , B ₄ O ₅ (OH) ₄ ^2- and the like, which are in an anionic state, such as polyboric acid-type anions. In addition, boric acid in an ionic state also includes polyborate ions, which are obtained by dehydration condensation of a plurality of boric acids to increase the molecular weight.

A more specific description will be given below with reference to FIG. FIG. 2 is a diagram for explaining the relationship between the pH of an aqueous boric acid solution and the abundance ratio of boric acid in a molecular state. In FIG. 2, the horizontal axis represents the pH of the aqueous solution, and the vertical axis represents the abundance ratio (molar ratio) of boric acid in the molecular state to the total amount of boric acid in the molecular state and the ionic state as the boric acid abundance ratio. . The solid curve in FIG. 2 is a graph created by calculating the abundance ratio of boric acid at each pH from the pKa (9.2) of boric acid assuming the equilibrium reaction of the following chemical formula (1).
B(OH) ₃ +OH−⇔B(OH) ₄ ⁻ (1)
As shown by the solid line in FIG. 2, in the acidic or neutral region of pH 7 or less, boric acid exists in an aqueous solution as boric acid in a molecular state of almost 100%, and as the pH increases, the molecular state rapidly changes. The abundance of boric acid becomes smaller.
In a dilute aqueous solution of boric acid _, the reaction of formula (1) becomes dominant, so the behavior is similar to the solid line curve in Fig. 2, but when the concentration is 0.1 M or higher, B(OH) The proportion of dehydration-condensed polyboric acid begins to increase. For example, the dashed curve in FIG. 2 plots the molar ratio of H ₃ BO ₃ to H ₂ B ₄ O ₇ , a representative polyboric acid, for the equilibrium reaction of (1) as [H ₂ B ₄ 3 is a graph prepared by calculating the abundance ratio of boric acid at each pH, assuming that O ₇ ]/[H ₃ BO ₃ ]=10 ⁻⁴ and considering pKa=4 of H ₂ B ₄ O ₇ . In this case, the abundance ratio of boric acid starts to decrease from around pH 6, which is lower.
Although FIG. 2 merely explains the behavior of the abundance ratio of boric acid with respect to pH for an idealized equilibrium reaction, experimental data of the abundance ratio of boric acid in various ionic states and in the molecular state with respect to actual pH As described in "Ultra-high efficiency boron removal technology from water", Chemical Equipment, February 2012, p53-58 (Non-Patent Document 1), each pH with reference to the data of Non-Patent Document 1 It is possible to estimate the abundance of boric acid in the molecular state. Referring to Non-Patent Document 1, when the pH of the aqueous solution is 8 or higher, the molecular state B(OH) ₃ is 30 mol% or less with respect to the total amount of boric acid in the molecular state and boric acid in the ionic state. tend to become The content of molecular boric acid in the undiluted solution can also be measured in advance by ion chromatography, titration, Raman spectroscopy, NMR, or the like.

Here, in an electrodialysis tank comprising a desalting chamber and a concentrating chamber separated from the desalting chamber by an anion exchange membrane, a stock solution is introduced into the desalting chamber (that is, used as a desalted solution), and the above When electrodialysis is performed on a stock solution having a pH of 8 or more, both ions containing iodine and boric acid in an ionic state can permeate the anion exchange membrane. However, iodine-containing ions have a higher permeation rate across anion exchange membranes than boric acid in the ionic state. The reason for this is that ions containing iodine have high selectivity for anion exchange groups in the anion exchange membrane, so when a voltage is applied to the electrodialysis tank, the desalination compartment side of the anion exchange membrane The iodine-containing ions preferentially adsorbed on the anion exchange groups on the surface move through the anion exchange membrane toward the anode and flow out to the concentrate on the concentration compartment side. On the other hand, boric acid in an ionic state cannot be adsorbed to the anion-exchange groups because the anion-exchange groups on the anion-exchange membrane are occupied by ions containing iodine, and remain in the desalted solution. As electrodialysis progresses and the concentration of ions containing iodine in the desalted solution decreases, ionic boric acid also begins to permeate the anion exchange membrane, and boric acid begins to rapidly flow out to the concentrate side. By monitoring the concentration of boric acid in the concentrate, it is possible to know when boric acid suddenly begins to flow out. can. In addition, since the boric acid in the ionic state can be separated from the organic compounds and the like contained in the undiluted solution by passing the boric acid through an anion exchange membrane, this step can be used to purify the boron compound aqueous solution.

This phenomenon is based on the principle of chromatographic separation that when multiple anions are passed through an anion-exchange resin column, ions with low selectivity flow out first, and ions with high selectivity flow out last. However, in normal chromatographic separation, ionic boron leaks first and then iodine leaks, whereas in the production method of the present embodiment, ions containing iodine leak first and boron is released. It has the opposite effect of leaking out later.

That is, the production method of the present embodiment utilizes not only dialysis of anions by electrodialysis, but also the difference in selectivity between anions with respect to the anion exchange membrane.

In this case, the stock solution is an aqueous solution containing a salt containing iodine and boric acid. However, the stock solution is not particularly limited as long as it is an aqueous solution in which the salt containing iodine and boric acid are dissolved, even if it is not prepared by dissolving the salt containing iodine and boric acid in water. . For example, an alkaline aqueous solution may be added to an aqueous solution containing hydroiodic acid and boric acid to adjust the pH to 8 or higher.

The pH of the undiluted solution is preferably 8.5 or higher, more preferably 9 or higher, even more preferably 10 or higher, and 12 or higher, from the viewpoint of enhancing the ability to separate ions containing iodine from boric acid. is particularly preferred. In addition, since boric acid in the ionic state has a lower selectivity of the anion exchange membrane than hydroxide ions, the ion permeation site of the anion exchange membrane is the hydroxide ion before the boric acid in the ionic state. occupied by Therefore, a higher pH tends to retard the outflow of ionic boric acid into the concentrating compartment, thereby increasing the accuracy of separation from iodide ions. The pH of the undiluted solution may be within the above range when electrodialysis is started. , an initial operation may be performed to set the pH to 8 or higher). Although the upper limit of the pH of the undiluted solution is not particularly limited, it may be 14 from the viewpoint of the durability of the anion exchange membrane against alkali. In addition, the content of molecular boric acid contained in the stock solution is preferably 20 mol% or less, more preferably 10 mol% or less, relative to the total amount of molecular boric acid and ionic boric acid. It is preferably 5 mol % or less, more preferably 5 mol % or less, and particularly preferably substantially 0 mol %. The content of boric acid in a molecular state contained in the stock solution may be within the above range when electrodialysis is started.

Although the salt containing iodine is not particularly limited, it is preferably at least one of an iodide salt and an iodate. The cations contained in the iodide salts and iodates include metal ions such as alkali metal ions, alkaline earth metal ions and rare earth metal ions.

The concentration of the iodine-containing salt in the stock solution is not particularly limited, but the mass of iodine element derived from the iodine-containing salt contained in the stock solution is preferably 1.5 g / L or more, and 2 g / L to 400 g / L. L is more preferred, and 50 g/L to 400 g/L is even more preferred. As explained above, even if the concentration of the salt containing iodine in the undiluted solution is low, the ions containing iodine flow out into the concentrating chamber before the boric acid in the ionic state. can be separated from ions containing .

Boric acid in the stock solution may be formulated by dissolving at least one of B(OH) ₃ , metaboric acid, polyboric acid, and salts thereof in water. The cations in the salts of B(OH) ₃ , metaboric acid, and polyboric acid are not particularly limited, and include metal ions such as alkali metal ions and alkaline earth metal ions. Salts of polyboric acid include, for example, borax.

The concentration of boric acid in the stock solution is not particularly limited, but the mass of boron element derived from boric acid contained in the stock solution is preferably 0.1 g / L to 40 g / L, and 1 g / L to 30 g / L. and more preferably 2 g/L to 10 g/L.

The undiluted solution may contain ions containing iodine and ions other than boric acid in an ionic state. Such an ion may be the second inorganic anion or an organic anion. Organic anions include acetate ions, formate ions, oxalate ions, and the like.

The stock solution may contain non-ionic water-soluble organics. Examples of water-soluble organic substances include glycerin and polyvinyl alcohol.

The stock solution may be a waste liquid containing a salt containing iodine and boric acid, such as a waste liquid discharged in the manufacturing process of the polarizing film.

FIG. 1 is a diagram showing an example of an electrodialysis apparatus 1 of this embodiment. The electrodialysis apparatus 1 of this embodiment is not particularly limited, and a known electrodialysis apparatus can be used. The manufacturing method of this embodiment will be described below with reference to FIG.

The electrodialysis apparatus 1 includes a stock solution tank 2 that contains a stock solution. An alkaline liquid tank 12 may be connected to the undiluted liquid tank 2 as necessary. The alkaline liquid tank 12 contains an alkaline aqueous solution, and the pH of the undiluted liquid tank can be adjusted by adding the alkaline aqueous solution to the undiluted liquid tank. Examples of the alkaline aqueous solution include, but are not particularly limited to, aqueous solutions of sodium hydroxide and potassium hydroxide.

The stock solution may be electrodialyzed after pretreatment to reduce boric acid, boron compounds other than boric acid, and other impurities.

The electrodialysis apparatus 1 includes an electrode chamber (anode chamber) having an anode 8, an electrode chamber (cathode chamber) having a cathode 9, a concentration chamber 11 partitioned from the anode chamber by a cation exchange membrane 6, and a cathode chamber. An electrodialyzer 20 having a desalting chamber 10 partitioned by a cation exchange membrane 6 is provided. The desalting compartment 10 and the concentrating compartment 11 are separated by an anion exchange membrane 7 . The cathode and anode chambers contain polar liquids. Examples of the polar liquid include, but are not particularly limited to, an aqueous sodium hydrogensulfate solution, an aqueous potassium sulfate solution, and the like.

The anion exchange membrane is not particularly limited, and a strongly basic anion exchange membrane or the like can be used. As the anion exchange membrane, a strongly basic anion exchange membrane is preferred. The strongly basic anion exchange membrane may have quaternary ammonium groups as ion exchange groups. In addition, as the anion exchange membrane, a monovalent ion selective permeation anion exchange membrane, a fully permeable anion exchange membrane, or a high-strength alkali-resistant anion exchange membrane may be used. It is preferably an exchange membrane. More specifically, an anion exchange membrane in which quaternary ammonium groups, which are strongly basic anion exchange groups, are introduced into a base film having a styrene-divinylbenzene basic skeleton (styrene-divinylbenzene-based base film). Available. Commercially available anion exchange membranes include Selemion (registered trademark) AMV and Selemion (registered trademark) AMT manufactured by AGC Engineering Co., Ltd., and Selemion (registered trademark) ASV, which is a monovalent anion selective membrane. In addition, Neosepta (registered trademark) ASE (total permeable anion exchange membrane), monovalent anion selective membrane ACS, Neosepta (registered trademark) AXP-D and the like manufactured by Astom Co., Ltd. can also be used.

The cation exchange membrane is not particularly limited, and a strongly acidic cation exchange membrane, a high-strength alkali-resistant cation exchange membrane, and the like can be used. The cation exchange membrane may also be a monovalent ion permselective cation exchange membrane. More specifically, a cation exchange membrane can be used in which sulfonic acid groups, which are strongly acidic cation exchange groups, are introduced into a base membrane having a styrene-divinylbenzene basic skeleton (styrene-divinylbenzene base membrane). . As a commercial product of the cation exchange membrane, Selemion (registered trademark) CMV and Selemion (registered trademark) CMB manufactured by AGC Engineering Co., Ltd. can be used. In addition, Neosepta (registered trademark) CSE and Neosepta (registered trademark) CMB manufactured by Astom Co., Ltd. can also be used.

The undiluted solution contained in the undiluted solution tank 2 is transferred to the desalting chamber 10 through a pipe. As a result, in the desalting chamber 10, a stock solution having a pH of 8 or more, or a stock solution containing 30 mol % or less of boric acid in a molecular state with respect to the total amount of boric acid in a molecular state and boric acid in an ionic state is present. be accommodated. A continuous operation may be performed in which the desalted solution is continuously discharged while the stock solution is continuously supplied to the desalting chamber 10 . During continuous operation, the electrolyte may be supplied by appropriately extracting the concentrated liquid. The aqueous solution contained or circulated in the desalting chamber is called desalted liquid.

Before electrodialysis, the concentration chamber 11 contains an electrolytic solution. The electrolytic solution is not particularly limited, and examples thereof include aqueous solutions of sodium chloride, potassium iodide, and sodium iodide.

Electrodialysis is performed by applying a voltage between the anode and cathode. As shown in FIG. 1, for example, when potassium iodide (KI) is used as an iodine-containing salt, I ⁻ contained in the desalted solution passes through the anion exchange membrane 7 from the desalted solution in the desalting compartment 10. Since it is easily permeable (indicated by long arrows in FIG. 1), it moves to the concentration compartment 11 and K ⁺ permeates the cation exchange membrane 6 to the cathode compartment. On the other hand, boric acid in an ionic state such as B(OH) ₄ ^- contained in the desalted solution is difficult to permeate the anion exchange membrane 7 (represented by short arrows in FIG. 1), stay in

The electrodialysis operating conditions are not particularly limited, but the concentration of ionic boric acid such as iodide ions (I ⁻ ) and borate ions [B(OH) ₄ ⁻ ] in the liquid to be treated is measured in advance and concentrated. If the amount of electricity required for movement to the chamber side is calculated in advance, it can be used as a reference for operating conditions for fractionating each component. While taking into consideration the types and concentrations of coexisting ions and the acceptance conditions on the iodine recovery device side, preliminary experiments are conducted in advance to analyze changes over time in the concentration of ions that move to the concentration chamber side, and determine the operating conditions for the electrodialysis device. more preferably.

During electrodialysis, the pH of the desalted solution is preferably maintained at 8 or higher, preferably 8.5 or higher, from the viewpoint of enhancing the ability to separate ions containing iodine from boric acid. is more preferably maintained at 10 or more, and particularly preferably at 11 or more.

Ions containing iodine flow out into the concentration chamber 11 to generate an iodine compound aqueous solution (referred to as a first concentration liquid). The first concentrated liquid preferably does not contain boric acid, but may contain a small amount of boric acid. For example, the concentration of boron element is preferably 1 g/L or less, such as 0.2 g/L. It is preferable that it is below. Further, the concentration of the boron element derived from boric acid contained in the first concentrated liquid is preferably 10 mol% or less of the concentration of the boric acid-derived boron element contained in the undiluted solution, and is 5 mol% or less. More preferably, it is 3 mol % or less. A first concentrate is transferred from the concentration compartment 11 and stored in the first concentrate tank 3 . The first concentrated liquid may be returned from the first concentrated liquid tank 3 to the concentration chamber 11 and further electrodialyzed to increase the concentration of ions containing iodine.

When electrodialysis is carried out for a long time, the concentration of ions containing iodine in the demineralization compartment decreases, boric acid in ionic form is easily adsorbed to the ion exchange groups of the anion exchange membrane, and the iodine compound aqueous solution in the concentration compartment 11 The concentration of boric acid increases. Therefore, the concentration of boric acid (boron element) in the iodine compound aqueous solution in the concentration chamber 11 is monitored, and the concentration of boric acid (boron element) in the iodine compound aqueous solution in the concentration chamber 11 is set to a predetermined lower limit value (first Lower limit value), the iodine compound aqueous solution in the concentration compartment 11 may be used as the second concentrated liquid and may be separated into the second concentrated liquid tank 4 separately from the first concentrated liquid. As the predetermined lower limit, for example, the concentration of elemental boron in the concentrate can be 1 g/L. As a method for monitoring the concentration of boric acid (boron element) in the iodine compound aqueous solution in the concentration chamber 11, for example, the concentration of boric acid (boron element) in the iodine compound aqueous solution in the concentration chamber 11 is monitored at regular intervals (for example, one hour). A method of measuring the concentration can be mentioned. The second concentrated liquid may be returned to the raw liquid tank 2, mixed with the raw liquid contained in the raw liquid tank 2, and transferred to the desalting chamber again for electrodialysis.

Further, as the desalination progresses further, the concentration of boric acid in the iodine compound aqueous solution in the concentration chamber 11 further increases. Therefore, the concentration of boric acid (boron element) in the aqueous iodine compound solution in the concentration chamber 11 is monitored, and the concentration of boric acid (boron element) in the aqueous iodine compound solution in the concentration chamber 11 is lower than the predetermined first lower limit. After exceeding a large predetermined lower limit (second lower limit), the iodine compound aqueous solution in the concentration chamber 11 is used as a third concentrated liquid, and a third concentrated liquid tank is added separately from the first and second concentrated liquids. Separate into 5. Whether or not to provide the third concentrated liquid tank in addition to the second concentrated liquid tank can be determined in advance by preliminary experiments or the like, taking into account the composition of the undiluted liquid and whether or not the purity is acceptable for the recovery application.

The first concentrate can be purified to further reduce the concentration of boric acid contained in the first concentrate. The purification method is not particularly limited, but includes a method of contacting boric acid with an adsorbent that selectively adsorbs boric acid. Adsorbents that selectively adsorb boric acid include boron-selective resins or fibers, and resins or fibers having n-methylglucamine as a functional group, for example, are preferred. A resin or fiber having n-methylglucamine as a functional group is preferably a fiber because it is easy to mold and can be used in an adsorption method other than the adsorption tower method. By purifying the first concentrated liquid, the purity of the iodine compound contained in the aqueous iodine compound solution can be increased, and the recovery rate of boric acid can also be increased. The second and third concentrates may be similarly purified.

The desalted solution may be returned to the raw solution tank 2 after electrodialysis. The desalted solution may be mixed with the undiluted solution before electrodialysis and transferred to the desalting chamber 10 to be electrodialyzed again. The desalted solution (boron compound aqueous solution) that has undergone repeated electrodialysis has a sufficiently low concentration of ions containing iodine, and as described above, allows boric acid to permeate the anion exchange membrane and flow out to the concentrated solution side. be able to. Thus, the boron compound aqueous solution can be purified. The iodine compound aqueous solution obtained as the concentrate may be electrodialyzed multiple times. By performing electrodialysis multiple times, an iodine compound aqueous solution with a lower boron element concentration can be obtained.

In the production method of the present embodiment, the first concentrated liquid may be electrodialyzed again to further reduce the concentration of boric acid contained in the first concentrated liquid (second separation step). Specifically, the first concentrated liquid may be returned to the concentration chamber 11 and electrodialyzed again, or returned to the raw liquid tank 2 and transferred to the demineralization chamber 10 again to be electrodialyzed again. good too. Alternatively, the iodine compound aqueous solution is transferred from the concentration chamber 11 to the second electrodialysis chamber via the desalination chamber of another electrodialysis chamber (second electrodialysis chamber) or a second stock solution chamber prepared separately. , electrodialysis may be performed in the separate electrodialysis bath.

The iodine compound contained in the concentrated iodine compound aqueous solution is not particularly limited, but may be an iodine-containing salt, and may be at least one of an iodide salt and an iodate. The iodine-containing ions contained in the iodine-containing salt are the same as the iodine-containing ions contained in the stock solution, and the cations contained in the iodine-containing salt are the polar liquid or the electrolytic solution of the concentration chamber 11 It may be a cation contained in the electrolyte.

Alternatively, the iodine compound may be hydroiodic acid. When producing hydroiodic acid by the production method of the present embodiment, a bipolar membrane may be used. For example, in an electrodialysis chamber, bipolar membranes are arranged on the anode side and the cathode side of the anion exchange membrane, respectively, the region sandwiched between the anode side bipolar membrane and the anion exchange membrane is used as a concentration chamber, and the cathode side bipolar membrane is When electrodialysis is performed using an electrodialyzer with a desalting chamber in the area sandwiched between the anion exchange membrane and the anion exchange membrane, hydrogen ions are generated in the concentrated liquid to produce hydrogen iodide, and water is generated in the desalting chamber side. Since oxide ions are released, there is a tendency to maintain a low pH in the concentration compartment and a high pH in the demineralization compartment even when the hydroxide ions move to the concentrate through the anion exchange membrane.

In FIG. 1, one anion exchange membrane and two cation exchange membranes are used, but two or more cation exchange membranes and two or more anion exchange membranes are alternately used from the anode side. A plurality of desalting chambers and concentrating chambers may be provided. Also, displacement electrodialysis may be performed with three or more liquids and chambers.

Depending on the concentration of the iodine compound and the concentration of the boron compound in the obtained concentrate, the iodine compound contained in the obtained aqueous iodine compound solution may be adsorbed with a strongly basic anion exchange resin. Whether or not to use the strongly basic anion exchange resin may be determined by monitoring the concentration of the aqueous iodine compound solution discharged from the concentration chamber. From the time when the predetermined lower limit is exceeded, the iodine compound aqueous solution is separated from the previously collected iodine compound aqueous solution, and only the separated iodine compound aqueous solution is brought into contact with a strongly basic anion exchange resin. good too.
A commercially available strongly basic anion exchange resin can be used. When the iodine compound aqueous solution contains a boron compound, the boron compound aqueous solution with increased purity of the boron compound may be purified by adsorbing the iodine compound contained in the aqueous solution with a strongly basic anion exchange resin. Thus, by appropriately using an adsorbent according to the concentration of the iodine compound and the concentration of the boron compound in the concentrated liquid, the recovery rate of the iodine compound can be increased and the recovery rate of the boron compound can be increased.

Adsorbents used for purification, such as boron-selective resins or fibers or strongly basic anion exchange resins, need to be regenerated once a predetermined adsorption capacity is reached. When regenerating, acid, alkali, sodium chloride aqueous solution, etc. can be used as a regenerating agent. Regeneration conditions can be confirmed by preliminary experiments in a laboratory or the like. For example, the boron-selective resin or fiber is regenerated in two stages with acid and alkali at a concentration of 1 to 10%, but considering the concentration of boron and iodine contained in the acid and alkali waste liquid, it is returned to the stock solution tank, for example. It is possible to determine the collection destination of the regeneration waste liquid. The same applies to the strongly basic anion exchange resin, and the concentration of sodium chloride used for regeneration and the collection destination of the waste liquid can be determined by preliminary experiments or the like.

Although the combination of boric acid and iodine-containing ions has been described above, the method of the present embodiment can be similarly applied to stock solutions containing any combination of boric acid and the first inorganic anion. and the stock solution may also contain a second inorganic anion. That is, the stock solution may contain boric acid and at least one inorganic anion selected from fluorine-containing ions, chlorine-containing ions, bromine-containing ions, and iodine-containing ions. By using the method of the present embodiment, boric acid and the first inorganic anion can be separated with high accuracy.

Further, in the method of the present embodiment, when the undiluted solution contains a plurality of types of first inorganic anions, two or more types of first inorganic anions may be separated from boric acid and recovered as an inorganic compound-containing aqueous solution. good. In this case, by applying a method such as electrodialysis to the obtained inorganic compound-containing aqueous solution, the first inorganic anions can be further separated from each other. Further, when one or more of the first inorganic anions are separated from boric acid and the aqueous solution containing boric acid still contains the first inorganic anion, the method of the present embodiment is performed. Further applications can separate boric acid and the first inorganic anion.

The method of this embodiment can be similarly applied to a stock solution containing a second inorganic anion instead of the first inorganic anion. That is, another embodiment of the present invention is an electrodialyzer comprising a desalting chamber and a concentrating chamber separated from the desalting chamber by an anion exchange membrane, wherein boric acid and at least one of the second inorganic Anions (sulfate, sulfite, thiosulfate, tetrathionate, other sulfur oxoacids, nitrate, phosphate, hydrogen phosphate, dihydrogen phosphate, carbonate, bicarbonate, sulfide ions, hydrogen sulfide ions, cyanide ions, etc.), and the undiluted solution contained in the demineralization chamber is subjected to electrodialysis to separate at least one of the inorganic anions from boric acid to obtain an inorganic compound-containing aqueous solution. Equipped with a separation step of fractionating as
It may be a method for producing an inorganic compound-containing aqueous solution in which the stock solution satisfies at least one of the following conditions (i) and (ii).
(i) The stock solution has a pH of 8 or higher.
(ii) The stock solution contains 30 mol % or less of molecular boric acid relative to the total amount of molecular boric acid and ionic boric acid.

Since each inorganic anion sequentially flows out to the concentration chamber side according to the above-mentioned moving speed, for example, while monitoring the concentration of each inorganic anion, an aqueous solution containing only one type of inorganic anion is sequentially produced in the concentration chamber side. may be collected.

According to the method of the present embodiment, the first inorganic anion and boric acid contained in the stock solution can be separated with high accuracy. For example, the following indices can be used as criteria for separation accuracy. First, the molar concentration X ^S of the separation target (inorganic anions separated from boric acid) and the molar concentration B ^S of boric acid (in terms of boron element) in the stock solution before electrodialysis are obtained, and their ratio (X ^S /B ^S ) is calculated. Then, X ^R is the molar concentration of the separation target in the aqueous solution in the chamber (concentration chamber or desalting chamber) on the fractionation side, and BR is the molar concentration of boric acid, and their ratio (X ^R / ^BR ) is ^calculated . calculate. According to the method of the present embodiment, for example, ^XR / ^BR is ^preferably 5 times or more of ^XS / ^{BS, and more preferably XR/BR is 10} times or more of ^XS /BS.

[Example 1]
(1) Electrodialysis Apparatus As an electrodialysis apparatus, Microacylizer EX3B manufactured by Astom Co., Ltd. was used. As the ion exchange membrane, a strongly acidic cation exchange membrane (trade name: Neosepta CSE) and a monovalent anion selective membrane (trade name: Neosepta AXP-D) manufactured by Astom Co., Ltd. are used as one unit, and 10 units are used. A two-chamber method electrodialysis apparatus was used. The effective membrane area is 550 cm ² .
(2) Stock solution composition In pure water, 5.9 g/L of boron element mass of boric acid (B(OH) ₃ ) and 269 g/L of iodine element mass of potassium iodide are dissolved. Potassium oxide was added to adjust the pH to 13, and a synthetic stock solution 1 was prepared. From Non-Patent Document 1, it was estimated that the synthetic stock solution 1 contained 1 mol % or less of molecular state boric acid with respect to the total amount of molecular state boric acid and ionic state boric acid.
(3) Electrodialysis Experiment The raw synthetic solution 1 was introduced into the desalting chamber of the electrodialysis apparatus and electrodialysis was performed under the operating conditions of an average current of 1.1A and a voltage of 10V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
After 3 hours of operation, the concentrations of iodide ions and boric acid in the concentrating compartment were measured to be 219 g/L of elemental iodine and 125 mg/L of elemental boron, respectively. As for the concentration of elemental iodine, 96.8% of the elemental iodine in the demineralized liquid was transferred to the concentrated liquid. Moreover, since the boric acid transferred to the concentrated liquid was 2.5% in terms of boron element, 97.5% of the boric acid was separated from the iodide ions. When the molar concentration ratio (I/B ratio) of elemental iodine to elemental boron was calculated, it was 3.8 for the synthetic undiluted solution 1, whereas it was 149 for the concentrated solution. The desalted solution had a pH of 13 after electrodialysis for 3 hours. Moreover, the pH of the concentrate was 12.4.

[Example 2]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. The same ion exchange membrane as in Example 1 was used.
(2) Stock solution composition In pure water, 5.2 g/L of boron element mass of boric acid (B(OH) ₃ ) and 365 g/L of iodine element mass of potassium iodide are dissolved, A synthetic stock solution 2 was prepared by adding potassium hydroxide to adjust the pH to 8.5. From Non-Patent Document 1, it was estimated that the synthetic stock solution 2 contained 20 mol % of boric acid in molecular state with respect to the total amount of boric acid in molecular state and boric acid in ionic state.
(3) Electrodialysis Experiment The raw synthetic solution 2 was introduced into the desalting chamber of the electrodialysis apparatus and electrodialysis was performed under the operating conditions of an average current of 1.1A and a voltage of 10V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
After 3 hours of operation, 77.2% of the iodide ions in the demineralized liquid were transferred to the concentrated liquid and separated from 92.8% of boric acid. The I/B ratio was calculated to be 6.0 for Synthetic Stock Solution 2 versus 63 for Concentrate. The pH of the desalted solution after electrodialysis was 8.8. Moreover, the pH of the concentrate was 7.8.

[Example 3]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. As the ion exchange membrane, one unit of a strongly acidic cation exchange membrane (trade name: Neosepta CSE) and a strongly basic anion exchange membrane (trade name: Neosepta ASE, total permeable anion exchange membrane) manufactured by Astom Co., Ltd. It was used as a 10-unit two-chamber electrodialysis apparatus. The effective membrane area is 550 cm ² .
(2) Stock solution composition In pure water, 6.1 g/L of boron element mass of boric acid (B(OH) ₃ ) and 242 g/L of iodine element mass of potassium iodide are dissolved, Potassium hydroxide was added to adjust the pH to 13.1, and a synthetic stock solution 3 was prepared. From Non-Patent Document 1, it was estimated that the synthetic stock solution 3 contained 1 mol % or less of molecular state boric acid with respect to the total amount of molecular state boric acid and ionic state boric acid.
(3) Electrodialysis Experiment The synthetic stock solution 3 was introduced into the desalting chamber of the electrodialysis apparatus and electrodialysis was performed under the operating conditions of an average current of 1.2A and a voltage of 10V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
After 3.25 hours (195 minutes) of operation, 95.6% of the iodide ions in the demineralized liquid were transferred to the concentrated liquid and separated from 95.8% of boric acid. After operation, the concentrations of iodide ions and boric acid in the demineralization compartment and concentrating compartment were measured. In the demineralization compartment, the concentrations of iodide ions and boric acid were 1.3 g/L by mass of elemental iodine and 7.84 g/L by mass of elemental boron, respectively. In the enrichment compartment, the concentrations of iodide ions and boric acid were 200.8 g/L by mass of elemental iodine and 0.22 g/L by mass of elemental boron, respectively. The I/B ratio was calculated to be 3.4 for Synthetic Stock Solution 3 and 93.3 for the Concentrate Solution. The pH of the desalted solution after electrodialysis was 12.9. Moreover, the pH of the concentrate was 12.0.

[Example 4]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. As the ion exchange membrane, a standard bipolar membrane (trade name: Neosepta BPX-4) and a high-strength anion exchange membrane (trade name: Neosepta ASE) manufactured by Astom Co., Ltd. are used as one unit, and a two-chamber method of 10 units is used. An electrodialysis device was used. The effective membrane area is 550 cm ² .
(2) Stock solution composition In pure water, 5.3 g/L of boron element mass of boric acid (B(OH) ₃ ) and 235 g/L of iodine element mass of potassium iodide are dissolved, A synthetic stock solution 4 was prepared by adding potassium hydroxide to adjust the pH to 12.8. From Non-Patent Document 1, it was estimated that the synthetic stock solution 4 contained 1 mol % or less of molecular boric acid with respect to the total amount of molecular boric acid and ionic boric acid.
(3) Electrodialysis Experiment The raw synthetic solution 4 was introduced into the desalting chamber of the electrodialysis apparatus and electrodialysis was performed under the operating conditions of an average current of 2.0A and a voltage of 20V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
After 5 hours of operation, 81.6% of the iodide ions in the demineralized liquid were transferred to the concentrated liquid, and 98.6% of boric acid was separated. After operation, the concentrations of iodide ions and boric acid in the demineralization compartment and concentrating compartment were measured. In the demineralization compartment, the concentrations of iodide ions and boric acid were 2.4 g/L by mass of elemental iodine and 5.78 g/L by mass of elemental boron, respectively. In the enrichment compartment, the concentrations of iodide ions and boric acid were 222.5 g/L by mass of elemental iodine and 0.08 g/L by mass of elemental boron, respectively. The I/B ratio was calculated to be 3.8 for Synthetic Stock Solution 4 versus 224 for the Concentrate Solution. The pH of the desalted solution after electrodialysis was 14. Also, the pH of the concentrate was -0.23.

[Example 5]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. As the ion exchange membrane, the same membrane as in Example 1 was used.
(2) Stock solution composition In pure water, 25.4 g/L of boron element mass of boric acid (B(OH) ₃ ) and 245 g/L of iodine element mass of potassium iodide are dissolved, A synthetic stock solution 5 was prepared by adding potassium hydroxide to adjust the pH to 13.2. From Non-Patent Document 1, it was estimated that the synthetic stock solution 5 contained 1 mol % or less of molecular boric acid with respect to the total amount of molecular boric acid and ionic boric acid.
(3) Electrodialysis experiment The raw synthetic solution 5 was introduced into the desalting chamber of the electrodialysis apparatus, and electrodialysis was performed under operating conditions of an average current of 1.1A and a voltage of 10V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
After 3 hours of operation, 93.5% of the iodide ions in the demineralized liquid were transferred to the concentrated liquid and separated from 98.4% of boric acid. After operation, the concentrations of iodide ions and boric acid in the demineralization compartment and concentrating compartment were measured. In the demineralization chamber, the concentrations of iodide ions and boric acid were 13.8 g/L by mass of elemental iodine and 28.1 g/L by mass of elemental boron, respectively. In the enrichment compartment, the concentrations of iodide ions and boric acid were 213.6 g/L by mass of elemental iodine and 0.39 g/L by mass of elemental boron, respectively. The I/B ratio was calculated to be 0.82 for Synthetic Stock Solution 5 versus 46.6 for the Concentrate Solution. The pH of the desalted solution after electrodialysis was 13.1. Moreover, the pH of the concentrate was 12.1.

[Example 6]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. As the ion exchange membrane, the same membrane as in Example 3 was used.
(2) Stock solution composition To pure water, boric acid (B(OH) ₃ ) for a boron element mass of 5.35 g/L, potassium bromide for a bromine element mass of 37.1 g/L, and chlorine 16.4 g/L of potassium chloride in terms of mass of elements, 18.0 g/L of potassium sulfate in terms of mass of sulfate ions, and 45.6 g/L of potassium hydrogen phosphate in terms of mass of hydrogen phosphate ions was dissolved, and sodium hydroxide was added to adjust the pH to 9.9 to prepare a synthetic stock solution 6. From Non-Patent Document 1, it was estimated that the synthetic stock solution 6 contained 5 mol % of boric acid in molecular state with respect to the total amount of boric acid in molecular state and boric acid in ionic state.
(3) Electrodialysis experiment The raw synthetic solution 6 was introduced into the desalting chamber of the electrodialysis apparatus, and electrodialysis was performed under operating conditions of an average current of 1.1A and a voltage of 10V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
When the operation was carried out for 1.5 hours, 97.8% of bromide ions, 97.0% of chloride ions, 43.2% of sulfate ions, and 6.0% of hydrogen phosphate ions in the desalted solution were obtained. 1% was transferred to the concentrate and separated with 96.2% boric acid. After operation, the concentrations of bromide ions, chloride ions and boric acid in the desalting and concentrating compartments were measured. In the demineralization compartment, the concentrations of bromide ions, chloride ions and boric acid are respectively 0.32 g/L by mass of elemental bromine, 0.64 g/L by mass of elemental chlorine and 6.02 g/L by mass of elemental boron. /L. In the enrichment compartment, the concentrations of bromide ions, chloride ions and boric acid are respectively 32.1 g/L by mass of elemental bromine, 17.1 g/L by mass of elemental chlorine and 0.18 g/L by mass of elemental boron. was L. The Br/B ratio was calculated to be 0.94 for Synthetic Stock Solution 6 versus 23.8 for the concentrate. Further, when the Cl/B ratio was calculated, it was 0.94 for the synthetic undiluted solution 6, while it was 28.5 for the concentrated solution. The pH of the desalted solution after electrodialysis was 10.1. Moreover, the pH of the concentrate was 9.1.

[Comparative Example 1]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. As the ion exchange membrane, the same membrane as in Example 1 was used.
(2) Stock solution composition To pure water, 5.2 g/L of boron element mass of boric acid and 310 g/L of iodine element mass of potassium iodide are added, and sulfuric acid is added to adjust the pH to 3. .3 and a synthetic stock solution 7 was prepared. From Non-Patent Document 1, it was estimated that the synthetic stock solution 7 contained 99 mol % or more of molecular boric acid with respect to the total amount of molecular boric acid and ionic boric acid.
(3) Electrodialysis experiment The raw synthetic solution 7 was introduced into the desalting chamber of the electrodialysis apparatus and electrodialysis was performed under the operating conditions of an average current of 1.1A and a voltage of 10V. In the concentration compartment, 700 ml of 0.1 M NaCl was used as electrolyte.
After 3 hours of operation, 72% of the iodide ions in the desalted solution were transferred to the concentrate, whereas during electrodialysis, boric acid was also transferred to the concentrate in proportion to time and concentrated. The concentration of elemental boron in the liquid increased, and as much as 18% of boric acid moved to the concentration chamber. The I/B ratio was calculated to be 4.3 for Synthetic Stock Solution 7 vs. 15 for Concentrate Solution.

[Comparative Example 2]
(1) Electrodialysis apparatus The same electrodialysis apparatus as in Example 1 was used. As the ion exchange membrane, the same membrane as in Example 3 was used.
(2) Stock solution composition In pure water, 6.5 g/L of boron element mass of boric acid and 250 g/L of iodine element mass of potassium iodide are dissolved, and potassium hydroxide is added. The pH was adjusted to 3.1 and a synthetic stock solution 8 was prepared. From Non-Patent Document 1, it was estimated that the synthetic stock solution 8 contained 99 mol % or more of boric acid in molecular state with respect to the total amount of boric acid in molecular state and boric acid in ionic state.
(3) Electrodialysis Experiment The raw synthetic solution 8 was introduced into the desalting chamber of the electrodialysis apparatus and electrodialysis was performed under the operating conditions of an average current of 0.8A and a voltage of 10V. Note that 700 ml of 0.1 M NaCl was used as an electrolytic solution in the concentration chamber.
After 5 hours of operation, 85.8% of the iodide ions in the demineralized solution were transferred to the concentrate, whereas during electrodialysis boric acid also transferred to the concentrate in proportion to time. As the concentration of the boron element in the concentrated liquid increased, 30.9% of boric acid moved to the concentrated compartment. After operation, the concentrations of iodide ions and boric acid in the demineralization compartment and concentrating compartment were measured. In the demineralization compartment, the concentrations of iodide ions and boric acid were 34.3 g/L by mass of elemental iodine and 5.61 g/L by mass of elemental boron, respectively. In the enrichment compartment, the concentrations of iodide ions and boric acid were 168.8 g/L by mass of elemental iodine and 1.35 g/L by mass of elemental boron, respectively. The I/B ratio was calculated to be 3.3 for synthetic stock solution 8 versus 9.2 for concentrate. The pH of the desalted solution after electrodialysis was 3.6. Moreover, the pH of the concentrate was 3.9.

FIG. 3 is a graph in which the vertical axis represents the movement ratio and the horizontal axis represents the energization time for Example 3. In FIG. The migration ratio is the molar ratio (%) of elemental iodine and elemental boron in the concentrate to the stock solution. FIG. 4 is a graph in which the vertical axis represents the moving ratio and the horizontal axis represents the energization time for Comparative Example 2. As shown in FIG. In FIG. 3, until around 200 minutes, iodide ions are the main ions that migrate to the concentrating compartment side, and boric acid hardly migrates. After 200 minutes, when the concentration of iodide ions in the desalting compartment decreases, ionic boric acid begins to pass through the anion exchange membrane and flows out to the concentrating compartment. On the other hand, in FIG. 4, both the iodide ions and the boric acid migrate to the concentrating chamber side substantially in proportion to the energization time, so it can be seen that the separation accuracy is low. Note that, in FIG. 3, the molar ratio (%) of elemental iodine in the concentrated solution to the undiluted solution slightly exceeds 100% at around 200 minutes due to fluctuations in the moisture content on the concentration chamber side and measurement errors. Variation within the error range.

Polarizing films are used in cameras and liquid crystal displays, and are an indispensable material for our future lives, so the demand for them is increasing more and more. Elements such as iodine and boron used in the production process are valuable resources, so it is preferable to recover as much of the elements contained in the mixed waste liquid containing iodine, boron, etc. from the process as possible. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to highly purify and recover elements such as iodine and boron using an electrodialyzer, thereby significantly reducing the load on the next step.

DESCRIPTION OF SYMBOLS 1... Electrodialysis apparatus, 2... Stock solution tank, 3... 1st concentrate tank, 4... 2nd concentrate tank, 5... 3rd concentrate tank, 6... Cation exchange membrane, 7... Anion exchange Membrane 8 Anode 9 Cathode 10 Demineralization compartment 11 Concentration compartment 12 Alkaline tank 20 Electrodialysis tank.

Claims (11)

boric acid,Iodineand at least one inorganic anion havingIodine compoundEquipped with a separation step of fractionating as an aqueous solution,
The stock solution has a pH of 8 or higher the law of nature,
The concentration of the inorganic anion having iodine in the stock solution is 1.5 g/L or more in terms of mass of iodine element,
The concentration of boric acid in the aqueous iodine compound solution discharged from the concentration chamber is monitored, and when the concentration of boric acid exceeds a predetermined lower limit value, the aqueous iodine compound solution exceeds the predetermined lower limit value. Separately from the previously collected iodine compound aqueous solution, A method for producing an inorganic compound-containing aqueous solution. 2. The method for producing an inorganic compound-containing aqueous solution according to claim 1, wherein the pH of the stock solution is maintained at 8 or higher during the separation step. boric acid,Iodineand at least one inorganic anion havingiodine compoundsEquipped with a separation step of fractionating as an aqueous solution,
The undiluted solution contains 30 mol % or less of molecular boric acid relative to the total amount of molecular boric acid and ionic boric acid. death,
The concentration of the inorganic anion having iodine in the stock solution is 1.5 g/L or more in terms of mass of iodine element,
The concentration of boric acid in the aqueous iodine compound solution discharged from the concentration chamber is monitored, and when the concentration of boric acid exceeds a predetermined lower limit value, the aqueous iodine compound solution exceeds the predetermined lower limit value. Separately from the previously collected iodine compound aqueous solution, A method for producing an inorganic compound-containing aqueous solution. The method for producing an inorganic compound-containing aqueous solution according to any one of claims 1 to 3, wherein the boric acid is at least one of B(OH) ₃ , metaboric acid, polyboric acid, and their ionic states. . 3. In the separation step, the boric acid and the iodine-containing inorganic anion are separated, and the boron compound aqueous solution on the demineralization chamber side and the iodine compound aqueous solution on the concentration chamber side are separated, respectively. 5. A method for producing an inorganic compound-containing aqueous solution according to any one of 1 to 4. The method for producing an inorganic compound-containing aqueous solution according to any one of claims 1 to 5, wherein the iodine-containing ions include at least one of iodide ions and iodate ions. The method for producing an inorganic compound-containing aqueous solution according to any one of claims 1 to 6 , further comprising a purification step of contacting the aqueous iodine compound solution with a resin that selectively adsorbs boron compounds. wherein the desalting chamber contains a stock solution for electrodialysis and is connected to a stock solution tank for transferring the stock solution to the desalting chamber;
8. The method according to any one of claims 1 to 7 , further comprising a step of returning said iodine compound aqueous solution to said raw solution tank, mixing it with a raw solution for electrodialysis, and introducing it into said desalting chamber again for electrodialysis. 10. A method for producing an inorganic compound-containing aqueous solution according to the above item . A second electrodialysis tank separate from the electrodialysis tank is connected to the electrodialysis tank,
The method for producing an inorganic compound-containing aqueous solution according to any one of claims 1 to 8 , comprising a step of transferring the iodine compound aqueous solution from the concentration chamber to the second electrodialysis tank and performing electrodialysis. 10. The method for producing an inorganic compound-containing aqueous solution according to claim 9 , further comprising the step of contacting the separately separated aqueous iodine compound solution with a strongly basic anion exchange resin to purify it. The method for producing an inorganic compound-containing aqueous solution according to any one of claims 1 to 10 , wherein the anion exchange membrane is a strongly basic anion exchange membrane.

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