TWI468346B - Method for recovering iodine from waste liquid from polarized thin film - Google Patents

Description

Method for recovering iodine from waste liquid for manufacturing polarizing film

The present invention relates to a method for recovering iodine from a waste liquid for producing a polarizing film for recovering iodine from a waste liquid produced by a polarizing film; in particular, for a waste liquid for producing a polarizing film which can recover boron after iodine recovery The method of recovering iodine.

In the production process of a polarizing film used for a liquid crystal display or the like, a waste liquid containing iodide ions, boric acid, potassium ions, and water-soluble organic substances is generated. The polarizing film is used to produce a waste liquid, which is usually treated as an industrial wastewater by treating the specific component contained therein by a coagulation method or a filtration method, or by concentration to reduce the volume. After treatment as industrial waste.

However, in recent years, the reference values of boron and compounds in the wastewater discharge standard tend to be as severe as 10 mg/L, and it has been difficult to reduce the boron concentration in the wastewater below the reference value by the conventional agglutination method and filtration method. In addition, in terms of industrial waste, it is also expected to reduce emissions in terms of disposal costs and environmental issues. Therefore, a method which has been proposed in the past is to separate the organic component contained in the waste liquid for manufacturing a polarizing film and the inorganic component such as iodine and boron by electrodialysis, thereby facilitating the concentration treatment thereafter, thereby reducing the amount of waste. Processing method (refer to Patent Document 1). FIG. 6 is a schematic view showing a method of treating a waste liquid for producing a polarizing film described in Patent Document 1. As shown in FIG. 6, in the processing method described in Patent Document 1, the polarizing film production waste liquid 102 stored in the waste liquid tank 101 is sent to the desalination liquid tank 104 by the pump 103, and the pump is reused from the tank. 109 is sent to the electrodialysis unit 105. At the same time, the pure water stored in the concentrate tank 106 is sent to the electrodialysis unit 105 by the pump 110 to start electrodialysis. Then, the desalting liquid 107 containing the organic component separated from the electrodialysis device 105 and the concentrated liquid 108 containing the inorganic component are returned to the desalting liquid tank 104 and the concentrated liquid tank 106, respectively, and then sent to the electrodialysis apparatus 105 again. Electrodialysis was performed in a cycle process by repeating the operation as described above.

Further, in Patent Document 1, it is disclosed that the concentrated liquid 108 is further separated from the boron-containing liquid by ion chromatography or boron selective ion exchange resin treatment, and the solution is prepared as a polarizing film. Reuse. However, the technique described in the patent document 1 is aimed at reducing the amount of waste and reducing the amount of waste, and is a technique for separating the organic component and the inorganic component by facilitating the concentration of the waste film production waste liquid. Therefore, although it is described that the separated inorganic component can be separated into an iodine-containing liquid and a boron-containing liquid by a known method, the specific steps and conditions are not discussed. Generally, the waste liquid for manufacturing a polarizing film is mostly composed of a plurality of waste liquids having different compositions and concentrations. Since the concentration of each component is not constant, the iodine and boron concentrations used in the iodine dyeing step and the boron crosslinking step are adjusted. It is difficult to consider the quality maintenance of the finished product of the polarizing film, and it is not practical to reuse the waste liquid directly as a polarizing plate.

Further, in the case of separating and recovering boron from an aqueous solution containing an inorganic component, a boron-selective ion exchange resin is usually used, and in the past, boron having a boron-selective ion exchange resin adsorbed and removed from wastewater is used in the form of boric acid. A method of regenerating a recovered boron-selective ion exchange resin has been proposed (see Patent Document 2). Further, the cations in the wastewater are adsorbed and removed by the weakly acidic cation exchange resin, and the anions other than boron in the wastewater are removed by the weakly basic anion exchange resin, and then the strong basic anion exchange resin is adjusted to the OH type. Further, a method of adsorbing and removing boron in waste water by mixing an anion exchange resin with a strongly acidic cation exchange resin adjusted to H type has also been proposed (see Patent Documents 3 and 4).

On the other hand, regarding iodine, various methods for recovering iodine from waste liquid have been developed in the past (see, for example, Patent Documents 5 and 6). For example, Patent Document 5 discloses a method of recovering iodine from water containing hydrogen iodide using an ion exchange resin. Further, the inventors of the present invention have found that the waste liquid containing iodine and/or inorganic iodine compound is oxidized or reduced, and the generated free iodine molecule is adsorbed under acidic conditions to a strong alkali which adsorbs iodide ions. In the anion exchange resin, the inorganic salts and the organic substances contained in the waste liquid are separated, and the iodine molecules adsorbed to the strongly basic anion exchange resin are eluted in the form of a hydrogen iodide solution, thereby recovering iodine from the waste liquid. Methods.

[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. Japanese Laid-Open Patent Publication No. Hei 6-63547 (Patent Document 6)

As described above, in the conventional method, it is difficult to directly use the polarizing film production waste liquid as a polarizing film production solution for reasons of concentration, quality maintenance, economy, and the like. Therefore, in the case where the waste liquid is to be reused by the polarizing film, it is preferable to separately separate, collect, and re-purify the recyclable components such as iodine and boron. However, in order to separate and recover iodine and boron from the waste liquid for manufacturing a polarizing film, the following problems exist.

In other words, as described in Patent Documents 1 and 2, in order to separate and recover boron from waste water or the like, a boron selective chelating resin is usually used, and iodine or the like is also adsorbed in the boron selective chelating resin. In addition to the components other than boron, the amount of boron which can be adsorbed is reduced, and if the component which deteriorates the resin such as iodine is contained in the treatment liquid, the life of the resin is shortened, which is a problem. On the other hand, as in the processing methods described in Patent Documents 3 and 4, by removing the components which deteriorate the resin such as organic substances and iodine from the production liquid of the polarizing film in advance, the life of the resin and the boron can be improved. Recycling efficiency, but the number of equipment and steps in this method is the problem. In addition, the processing methods described in Patent Documents 3 and 4 are a method of performing a large amount of treatment on industrial waste water having a small amount of components to be removed such as boron and iodine, and treating waste liquids of polarized film having high boron and iodine concentrations. It is neither suitable nor costly, and it is very troublesome to replace the resin frequently.

On the other hand, in the conventional methods described in Patent Documents 5 and 6, it is necessary to adjust the pH to the acidic side, and it is preferably less than 3, so that an acid for pH adjustment and an oxidizing agent for oxidizing iodide ions are added. Therefore, the deterioration of the boron selective chelating resin is accelerated, and iodine adsorption is time-consuming, and it is impossible to adsorb all the iodine in the waste liquid to the resin, and the residual iodine in the treated waste liquid is about 0.1 to 0.2 g/L. Therefore, it is difficult to recover boron from the waste liquid after iodine recovery, which is a problem.

The present invention has been made in view of the above problems, and an object of the invention is to provide a method for recovering iodine from a waste liquid for producing a self-polarizing film which is easy and efficient to recover iodine and boron from a waste liquid for producing a polarizing film.

The method for recovering iodine from the waste liquid for producing a polarizing film according to the first invention of the present application is from iodine having a total iodine amount of 2 to 35 g/L, boron of 0.2 to 8 g/L, and potassium of 0.6 to 11 g/L. The method for recovering iodine from a waste liquid for manufacturing a polarizing film; comprising the steps of: adjusting the waste liquid to have a pH of less than 7, and performing electrodialysis, wherein the iodine and potassium contained in the waste liquid are potassium iodide a step of morphological separation; a step of passing the electrodialyzed waste liquid through a strong basic anion exchange resin to adsorb iodine remaining in the waste liquid to the strongly basic anion exchange resin; and from the potassium iodide and the strong base The step of recovering iodine from an anion exchange resin.

The method for recovering iodine from the waste liquid for producing a polarizing film according to the second invention of the present application is a waste of a polarizing film produced by containing iodine having a total iodine amount of 2 to 35 g/L and boron of 0.2 to 8 g/L. A method for recovering iodine from a liquid; characterized in that it comprises the steps of: adjusting the effluent to a pH of less than 2, and adsorbing iodine contained in the waste liquid to a strong basic anion exchange resin adsorbing iodide ions; a step of: adsorbing the waste liquid after the adsorption treatment by the strong basic anion exchange resin, and further adsorbing the iodine remaining in the waste liquid to the other strong alkaline ion exchange resin by using another strong basic ion exchange resin And the step of recovering iodine from the strongly basic anion exchange resin and the other strongly basic ion exchange resin.

The method for recovering iodine from the waste liquid for producing a polarizing film according to the third invention of the present application is a waste of a polarizing film produced by containing iodine having a total iodine amount of 2 to 35 g/L and boron of 0.2 to 8 g/L. A method for recovering iodine from a liquid; comprising the step of adjusting the effluent to a pH of less than 7, and passing the strong basic anion exchange resin to adsorb iodine in the waste liquid to the strongly basic anion exchange resin .

In the iodine recovery method according to the first to third aspects of the present invention, the iodine recovery method may further include the step of adjusting the waste liquid after iodine separation to a pH of 7 or higher and then passing the boron selective chelating resin. a step of adsorbing boron in the waste liquid to the boron selective chelating resin; and a step of recovering boron from the boron selective chelating resin.

According to the present invention, the adsorption treatment by electrodialysis and anion exchange resin, the two-stage treatment using a strong basic anion exchange resin adsorbing iodide ions and other ion exchange resins, or the strong basic anion exchange resin alone Since the adsorption treatment, iodine can be easily and efficiently recovered from the waste liquid for manufacturing a polarizing film. Further, since the waste liquid after the iodine separation does not contain iodine, the boron selective chelating resin is not deteriorated, and boron can be easily and efficiently recovered.

Hereinafter, a method of recovering iodine from a waste liquid for producing a polarizing film according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. First, the iodine recovery method according to the first embodiment of the present invention will be described. In the present embodiment, the waste liquid for producing a polarizing film to be treated is pH 3 to 10, and contains iodine having a total iodine amount of 2 to 35 g/L, boron of 0.2 to 8 g/L, and an aqueous solution of potassium of 0.6 to 11 g/L. Further, it may contain a water-soluble organic compound having a zinc content of 1.5 g/L or less and/or a TOC (Total Organic Carbon) conversion of 1 g/L or less. Moreover, the ORP (Oxidation Reduction Potential) of the waste liquid for manufacturing a polarizing film is, for example, 100 to 350 mv.

Figure 1 is a schematic view showing the iodine recovery method of the present embodiment. Further, in Fig. 2, the abscissa is pH, and the ordinate is the concentration of non-dissociated boric acid (H ₃ BO ₃ ), which is a graph showing the relationship between the pH of the solution and the form of boron. As shown in Fig. 1, in the iodine recovery method of the present embodiment, first, a waste liquid for manufacturing a polarizing film to be processed is introduced into the electrodialysis apparatus 1. In the electrodialysis apparatus 1 used in the present embodiment, for example, the cation exchange membrane 4k and the anion exchange membrane 4a are alternately arranged between the anode (+) 2 and the cathode (-) 3, whereby the cation exchange membrane 4k and the anion are exchanged. The film 4a constitutes a plurality of cells. In a state where a direct current is applied between the anode 2 and the cathode 3 of the electrodialysis device 1, the waste liquid is introduced into the central unit 5a, and the iodide ions (I ^- ) and potassium ions (K ⁺ ) in the waste liquid are introduced. Each of them moves to the anode side and the cathode side, and potassium iodide (KI) is formed in the units 5b and 5c on both sides of the central unit 5a. Then, an aqueous solution containing KI of about 50 to 150 g/L is discharged from the electrodialysis device 1.

Here, as shown in Fig. 2, in the case where the pH of the solution is less than 7, most of the boric acid is undissociated and exists as a boric acid molecule. Therefore, in the iodine recovery method of the present embodiment, the pH of the waste liquid placed in the electrodialysis apparatus 1 is set to be less than 7. Thereby, the dissociation of boric acid can be suppressed, so that even if electrodialysis is performed, boric acid does not move, and is discharged in its original state, so that the amount of boron in the waste liquid can be reduced to less than 0.5 g/L without changing the amount of boron in the waste liquid. . On the other hand, in the case where the pH of the waste liquid is greater than 7, since the boric acid dissociates and the amount of boric acid ions increases, boric acid ions are mixed into the iodine concentrate during electrodialysis, so that the waste liquid discharged from the electrodialysis device 1 is The amount of boron is reduced. Further, when the waste liquid is acidic, free iodine is generated to deteriorate the ion exchange membrane, resulting in a decrease in electrodialysis efficiency. Therefore, it is preferred that the pH of the waste liquid be adjusted to be greater than 3. Thereby, the formation of free iodine due to oxidation of air by iodide ions can be suppressed.

Then, the waste liquid discharged from the electrodialysis apparatus 1 is introduced into the strongly basic anion exchange resin 6, and by adsorbing iodine to the strongly basic anion exchange resin 6, the amount of iodine in the waste liquid can be reduced to 1 mg/L or less. . At this time, if the waste liquid is alkaline, boric acid dissociates into boric acid ions and is adsorbed to the strongly basic anion exchange resin 6. Therefore, the pH of the waste liquid when the strong alkali anion exchange resin 6 is introduced is adjusted to be less than 7 in the same manner as described above, and the pH of the waste liquid is deviated from this range by a known method. Further, the pH of the waste liquid is preferably in a range of more than 3 and less than 7.

Then, the waste liquid of the strongly basic anion exchange resin 6 is adjusted to a pH of more than 7 by a known method such as adding sodium hydroxide, and then introduced into the boron selective chelating resin 7. Thereby, boron in the waste liquid can be recovered. At this time, if the pH of the waste liquid is less than 7, the amount of boric acid ions in the waste liquid becomes small, and the recovery efficiency of boron is lowered. Therefore, the pH of the waste liquid fed to the boron selective chelating resin 7 must be adjusted to be greater than 7.

Then, iodine is recovered from the KI aqueous solution discharged from the electrodialysis apparatus 1 and the self-strengthening basic anion exchange resin 6 by a known method, and boron is recovered from the boron selective chelating resin 7. On the other hand, the waste liquid which has passed through the boron-selective chelating resin 7 is removed by a coagulation sedimentation method or the like, and the water-soluble organic substance is removed by an activated sludge method or the like, and the content is such a content. Beyond the wastewater discharge baseline value. Then, adjust the pH to 5.8 ~ 8.6 and then release.

As described above, in the iodine recovery method of the present embodiment, the iodine in the waste film production waste liquid is separated by electrodialysis and a strong basic anion exchange resin, and the iodine in the waste liquid is reduced to 0.01 g/L or less. By separating the boron by the boron selective chelating resin 7, and optimizing the pH of the waste liquid in each step, the waste liquid can be produced from the polarizing film to efficiently recover iodine and boron in a short time. Further, in the iodine recovery method of the present embodiment, the amount of iodine in the waste liquid is reduced to 0.5 g/L by the electrodialysis apparatus 1, so that the amount of the strongly basic ion exchange resin 6 (filling amount) used thereafter is increased. Less than the past. Further, in the iodine recovery method of the present embodiment, iodine and boron are separated from the waste liquid by separation by electrodialysis or adsorption to a resin, so that it can be easily reused without mixing other components.

Next, an iodine recovery method according to a second embodiment of the present invention will be described. The waste liquid for producing a polarizing film to be treated in the present embodiment is an aqueous solution containing 2 to 35 g/L of iodine and 0.2 to 8 g/L of boron in terms of total iodine, and may also contain 0.6 to 11 g/L of potassium. 1.5 g/L of zinc and/or a water-soluble organic compound of 1 g/L or less in terms of TOC (all organic carbon). Further, the pH of the waste film production waste liquid is, for example, 3 to 10, and the ORP (oxidation reduction potential) is, for example, 100 to 350 mv.

Fig. 3 is a schematic view showing the iodine recovery method of the embodiment. As shown in Fig. 3, in the iodine recovery method of the present embodiment, first, a waste liquid for manufacturing a polarizing film is placed in a tank 11 filled with a strong basic anion exchange resin 12 saturated with iodide ions, and placed in a polarizing film. The waste liquid is adjusted to pH less than 2 by adding an acid such as sulfuric acid or hydrochloric acid while stirring the mixture with the mixer 15. Next, an oxidizing agent such as chlorine gas, sodium hypochlorite (NaClO) or hydrogen peroxide is added while stirring, so that the iodide ion in the waste liquid becomes an iodine molecule (I ₂ ), and the I ₂ is a polyiodide molecule (I ₃ ^- , The form of I ₅ ^- ) is adsorbed to the strongly basic anion exchange resin 12. Then, the strongly basic anion exchange resin 12 is separated from the waste liquid.

Then, the waste liquid separated from the strongly basic anion exchange resin 12 is passed through a normal strong alkaline ion exchange resin 13 which is not saturated with iodide ions, and the unadsorbed I ₂ and the pH-adjusting acid contained in the waste liquid are An anion such as a sulfate ion derived from the oxidizing agent is adsorbed to the strongly basic ion exchange resin 13, and the total amount of iodine in the waste liquid is made 0.01 g/L or less.

Then, the waste liquid of the strongly basic ion exchange resin 13 is adjusted to a pH greater than 7 by a known method such as adding sodium hydroxide or the like, and then passed through the boron selective chelating resin 14 to remove the waste liquid. Boron adsorption in. At this time, the reason why the pH of the waste liquid introduced into the boron selective chelating resin 14 is set to be larger than 7 is the same as that of the first embodiment.

Then, iodine (I ₂ , I ₃ ^- , I ₅ ^- ) adsorbed to the strongly basic anion exchange resin 12 and the strongly basic ion exchange resin 13 and boron adsorbed to the boron selective chelating resin 14 are recovered and reused. Specifically, iodine adsorbed to the strongly basic anion exchange resin 12 is recovered as iodide ions by passing an aqueous solution of a reducing agent such as Na ₂ SO ₃ or NaHSO ₃ through the strongly basic anion exchange resin 12. Further, by passing the NaOH aqueous solution through the strongly basic ion exchange resin 13, iodine adsorbed to the strongly basic ion exchange resin 13 is recovered as iodide ions. Boron adsorbed to the boron selective chelating resin 14 is recovered by passing the boron selective chelating resin 14 with an aqueous solution of H ₂ SO ₄ . On the other hand, the waste liquid which has passed through the boron selective chelating resin 14 is subjected to a treatment such as a coagulation sedimentation method or an activated sludge method, and the values of heavy metals such as Zn and water-soluble organic substances are equal to or lower than the wastewater discharge reference value, and the pH is adjusted. After being within the established range, release it again.

As described above, in the iodine recovery method of the present embodiment, the iodide ions in the waste liquid of the polarizing film production are separated into the form of polyiodide molecules by the strong basic anion exchange resin 12 saturated with iodide ions, and then The unadsorbed I ₂ in the waste liquid is separated by the usual strong basic ion exchange resin 13 which is not saturated with iodide ions, so that only the iodide ion is adsorbed by the strong basic anion exchange resin 12 saturated with iodide ions. The amount of the ion exchange resin used can be reduced by 1/5 to 1/3, and the recovery efficiency of iodine can be improved at the same time. Further, in the iodine recovery method of the present embodiment, the amount of iodine in the waste liquid can be reduced to 0.01 g/L or less by passing the waste liquid through the strongly basic anion exchange resin 12 and the strongly basic ion exchange resin 13. Thereafter, boron is separated by the boron selective chelating resin 14, so that boron can be efficiently recovered without deteriorating the boron selective chelating resin 14. Further, in the iodine recovery method of the present embodiment, since iodine and boron are separated from the waste liquid by adsorption to the resin, the recovered product can be easily reused without mixing other components.

Next, an iodine recovery method according to a third embodiment of the present invention will be described. In the same manner as in the second embodiment, the waste liquid containing the iodine in an amount of 2 to 35 g/L and the boron in an amount of 0.2 to 8 g/L of the total amount of iodine is used in the same manner as in the second embodiment. Further, there are cases in which water-soluble organic compounds containing 0.6 to 11 g/L of potassium, zinc of 1.5 g/L or less, and/or TOC of 1 g/L or less are contained. Moreover, the pH of the waste liquid for manufacturing such a polarizing film is, for example, 3 to 10, and the ORP (oxidation reduction potential) is, for example, 100 to 350 mv.

Fig. 4 is a schematic view showing the iodine recovery method of the embodiment. As shown in Fig. 4, in the iodine recovery method of the present embodiment, first, a waste liquid for producing a polarizing film having a pH of less than 7 by a known method is introduced into the strongly basic anion exchange resin 21 to adsorb iodide ions. Here, the basic anion exchange resin 21 is strongly. At this time, since the pH of the waste liquid is adjusted to be less than 7, the dissociation of boric acid in the waste liquid can be suppressed, and the decrease in the amount of boron before and after the passage of the strongly basic anion exchange resin 21 can be prevented.

Then, the waste liquid which has passed through the strongly basic anion exchange resin 21 is adjusted to have a pH of more than 7 by a known method such as addition of sodium hydroxide, and then introduced into the boron selective chelating resin 22. Thereby, boron in the waste liquid can be recovered. Here, the reason why the pH of the waste liquid introduced into the boron selective chelating resin 22 is adjusted to be larger than 7 is the same as that of the first and second embodiments.

Then, iodine adsorbed to the strongly basic anion exchange resin 21 and boron adsorbed to the boron selective chelating resin 22 are separately recovered and reused. On the other hand, the waste liquid which has passed through the boron selective chelating resin 22 is subjected to a treatment such as a coagulation sedimentation method or an activated sludge method, and the values of heavy metals such as Zn and water-soluble organic substances are equal to or lower than the wastewater discharge reference value, and the pH is adjusted. After being within the established range, release it again.

As described above, in the iodine recovery method of the present embodiment, since the waste liquid for manufacturing a polarizing film is introduced into the strongly basic anion exchange resin 21, only the iodide ions contained therein are adsorbed to the resin, so that the waste liquid can be discharged in a short time. The iodine in the separation. Further, in the present embodiment, since iodine and boron are separated from the waste liquid by adsorption to the resin, it is possible to easily reuse the recovered iodine and boron without mixing other components. Further, in the iodine recovery method of the present embodiment, since an acid such as an acid or an oxidizing agent for pH adjustment which is conventionally used is not required, anion treatment such as sulfate ions from such chemicals can be omitted.

Next, an iodine recovery method according to a fourth embodiment of the present invention will be described. In the same manner as in the second embodiment, the waste liquid for producing a polarizing film of the present embodiment is an aqueous solution containing 2 to 35 g/L of iodine and 0.2 to 8 g/L of boron in terms of total iodine, and also contains 0.6. ~11 g/L of potassium, 1.5 g/L of zinc, and/or a water-soluble organic compound of 1 g/L or less in terms of TOC (all organic carbon). Further, the pH of the waste film production waste liquid is, for example, 3 to 10, and the ORP (oxidation reduction potential) is, for example, 100 to 350 mv.

Fig. 5 is a schematic view showing the iodine recovery method of the embodiment. As shown in Fig. 5, in the iodine recovery method of the present embodiment, first, the polarizing film production waste liquid 32 is placed in the tank 31, and sulfuric acid or hydrochloric acid is added while stirring with a stirrer 35 to adjust the pH to less than 2. Then, stirring is continued, and a predetermined concentration of sodium hypochlorite aqueous solution is added to the polarizing film production waste liquid 32. Thereby, iodine in the polarizing film production waste liquid 32 crystallizes and precipitates, and settles on the bottom of the tank 31. Then, the iodine crystal 33 is separated from the upper clear liquid by a filter 34. Then, the iodine crystal 33 is washed with water, dissolved in a reducing agent aqueous solution such as sodium sulfite, and then purified by a known method and reused. On the other hand, the cleaning liquid of the upper clear liquid and the iodine crystal 33 is introduced into the strong alkaline anion exchange resin 36 to adsorb residual iodine, and the total iodine amount in the waste liquid (upper clear liquid and washing liquid) is made. It is 0.01 g/L or less.

Then, the waste liquid (the upper clear liquid and the washing liquid) of the strongly basic anion exchange resin 36 is adjusted to have a pH of more than 7 by a known method such as adding sodium hydroxide, and boron selective chelation is carried out. Resin 37. Thereby, boron in the waste liquid can be recovered. Here, the reason why the pH of the waste liquid introduced into the boron selective chelating resin 37 is adjusted to be larger than 7 is the same as that of the above-described first to third embodiments.

Then, iodine adsorbed to the strongly basic anion exchange resin 36 and boron adsorbed to the boron selective chelating resin 37 are separately recovered and reused. On the other hand, the waste liquid which has passed through the boron selective chelating resin 37 is subjected to a treatment such as a coagulation sedimentation method or an activated sludge method, and the values of heavy metals such as Zn and water-soluble organic substances are equal to or lower than the wastewater discharge reference value, and the pH is adjusted. After being within the established range, release it again.

As described above, in the iodine recovery method of the present invention, iodine in the waste liquid for manufacturing a polarizing film is precipitated and recovered, and the upper clear liquid and the cleaning liquid are passed through a strong basic anion exchange resin to remain therein. The adsorption of iodine on the resin greatly reduces the amount of strong alkaline ion exchange resin used, and at the same time increases the recovery efficiency of iodine. Further, in the iodine recovery method of the present embodiment, since the amount of iodine in the waste liquid is reduced to 0.01 g/L, the boron selective chelating resin 37 is further introduced, so that the boron selective chelating resin can be prevented. Under the deterioration of 37, boron is efficiently recovered.

(Example 1)

Hereinafter, the effects of the present invention will be specifically described by way of examples and comparative examples. Further, the form of the present invention is not limited to this. First, an embodiment of the present invention will be described. In the present embodiment, first, a polarizing film having a total iodine amount of 16 g/L, a boron amount of 5.4 g/L, a potassium amount of 4.9 g/L and a pH of 5.2 was used to produce a waste liquid of 5 L, and an electrodialysis apparatus was used. Storm (shares), Azure Leza S3 type), using 1 L of water as a dialysate, and dialysis was carried out at a constant voltage of 10 V for 1.5 hours. Further, the membrane area of this electrodialysis apparatus was 0.055 m ² . The anion exchange membrane used A-192 and the cation exchange membrane used K-501-SB. As a result, the amount of iodine in the waste liquid after electrodialysis was 0.4 g/L, and the amount of boron was 5.2 g/L. Further, the amount of iodine in the K1 aqueous solution discharged from the electrodialysis apparatus was 74 g/L, and the amount of boron was 0.7 g/L.

Then, 20 ml of a strongly basic anion exchange resin was placed in a chromatography tube having an inner diameter of 20 mm and a length of 300 mm, and the waste liquid after electrodialysis was introduced at a flow rate of 0.15 L/min. In this case, as a strongly basic anion exchange resin (bonded to a quaternary ammonium salt of a styrene-divinyldiphenyl copolymer), Nippon Nylon NSA100 manufactured by Mitsubishi Chemical Corporation was used. As a result, the liquid was introduced in 33 minutes, and the iodide ion concentration after the liquid was introduced was 0.01 g/L or less. Then, the pH of the waste liquid after passing through the strongly basic anion exchange resin was adjusted to 8 with a 0.1 mol/L aqueous sodium hydroxide solution, and then a boron selective chelating resin was introduced. By the above treatment, the iodine recovery rate was 99.5%, and the boron recovery rate was 99.8%.

[Embodiment 2]

Next, a description will be given of Embodiment 2 of the present invention. In the present embodiment, first, 10 L of a waste liquid having a total iodine content of 16 g/L, a boron amount of 5.4 g/L, and a pH of 5.2 is placed in a beaker, and then a strong alkali saturated with iodide ions is added. Anion exchange resin 250ml. Then, sulfuric acid was added while stirring with a stirrer to adjust the pH to 2. Then, 330 ml of a 12% by mass aqueous sodium hypochlorite solution was added over 4 hours to convert the iodide ions into iodine molecules and adsorbed to the ion exchange resin. In this case, as a strong basic anion exchange resin, Nylon NSA100 manufactured by Mitsubishi Chemical Corporation was used. As a result, the amount of iodine in the waste liquid after the completion of the adsorption was 0.1 g/L, the amount of boron was 5.4 g/L, and the iodine adsorption rate was 99.4%. Then, 40 ml of a strong basic anion exchange resin (manufactured by Mitsubishi Chemical Corporation, Namigen NSA100) which was not saturated with iodide ions was placed in a column having a column inner diameter of 20 mm and a length of 300 mm at a flow rate of 0.15 L/min. Pass the waste liquid after electrodialysis. As a result, the liquid was introduced in 70 minutes, and the iodide ion concentration after the liquid was introduced was 0.01 g/L or less.

Then, the resin from which the iodine was adsorbed was separated from the waste liquid, transferred into a 2 L beaker, and 200 ml of a 35 mass% NaHSO ₃ solution and 1600 ml of water were added, and the mixture was stirred for 3 hours. As a result, the amount of iodine in the solution after stirring for 3 hours was 88 g/L, the amount of boron was 0.01 g/L or less, and the desorption ratio was 99.6%. On the other hand, after the pH of the waste liquid passed through the strongly basic anion exchange resin was adjusted to 8 with a 0.1 mol/L aqueous sodium hydroxide solution, a boron selective chelating resin was introduced. By the above treatment, the iodine recovery rate was 99.9%, and the boron recovery rate was 99.8%.

[Example 3]

Next, a description will be given of Embodiment 3 of the present invention. First, a strong alkaline anion exchange resin 1L was packed into a column having a column inner diameter of 50 mm and a length of 700 mm, and was produced by a polarizing film having a total iodine amount of 16 g/L, a boron amount of 5.4 g/L, and a pH of 5.2. The waste liquid was passed through the waste liquid after electrodialysis at a flow rate of 0.15 L/min. In this case, as a strong basic anion exchange resin, Nylon NSA100 manufactured by Mitsubishi Chemical Corporation was used. As a result, the amount of iodine in the liquid taken at the outlet of the column after 60 minutes from the start of the liquid introduction was 0.01 g/L or less, and the amount of boron was 5.4 g/L. Further, the amount of iodine in the liquid taken at the outlet of the column after 90 minutes from the start of the liquid introduction was 16 g/L or less, and the amount of boron was 5.4 g/L.

Then, an ion exchange resin for adsorbing iodide ions was introduced at a flow rate of 1 ml/min in a 1 mol/L NaCl solution to desorb the iodide ions from the resin. As a result, the iodide ion desorption rate after 24 hours from the start of the liquid introduction was 94%. On the other hand, after adjusting the pH of the waste liquid adsorbed by the strongly basic anion exchange resin to a pH of 8 with a 0.1 mol/L aqueous sodium hydroxide solution, a boron selective chelating resin was introduced. By the above treatment, the iodine recovery rate was 99.9%, and the boron recovery rate was 99.8%.

(Example 4)

Next, a description will be given of Embodiment 4 of the present invention. In the present embodiment, first, 10 L of a waste liquid having a total iodine amount of 16 g/L, a boron amount of 5.4 g/L, and a pH of 5.2 is placed in a beaker, and then sulfuric acid is added while stirring with a stirrer. Adjust the pH to 2. Then, 442 ml of a 12% by mass aqueous sodium hypochlorite solution was added to precipitate iodine in the waste liquid in the form of iodine crystals. Then, the iodine crystals were allowed to settle, and the iodine crystals were separated from the upper clear liquid by a filter. Then, the separated iodine crystals were washed with 2 L of tap water, and the washing liquid and the upper clear liquid were passed through a chromatography tube having an inner diameter of 20 mm and a length of 300 mm at a flow rate of 0.15 L/min to fill 20 ml of strong alkali. Anion exchange resin (manufactured by Mitsubishi Chemical Corporation).

At this time, the total iodine amount of the upper clarified liquid was 0.3 g/L, the amount of boron was 5.4 g/L, the sulfate ion concentration was 7.8 g/L, the chloride ion concentration was 3.0 g/L, and the sodium concentration was 1.9 g/L. Further, the washing liquid had a total iodine content of 0.3 g/L, a boron amount of 0.09 g/L, a sulfate ion concentration of 0.1 g/L, a chloride ion concentration of 0.05 g/L, and a sodium concentration of 0.04 g/L. The liquid of the washing liquid of the upper clear liquid was passed in for 80 minutes, and the concentration of iodide ions after the liquid was introduced was 0.01 g/L or less.

Then, the separated iodine crystals were dissolved in 1600 ml of a 3 mass% NaHSO ₃ solution, and purified by a known method to obtain 153 g of iodine. Further, the resin to which iodine was adsorbed was separated from the waste liquid, transferred to a 200 ml beaker, and ₃ ml of a 35 mass% NaHSO ₃ solution and 40 ml of water were added thereto, followed by stirring for 3 hours. As a result, the amount of iodine in the solution after stirring for 3 hours was 90 g/L, the amount of boron was 0.01 g/L or less, and the desorption ratio was 99.0%. Further, the waste liquid after the adsorption treatment of the strongly basic anion exchange resin was adjusted to pH 8 with a 0.1 mol/L aqueous sodium hydroxide solution, and then a boron selective chelating resin was introduced. By the above treatment, the iodine recovery rate was 97.5%, and the boron recovery rate was 99.8%.

1, 105. . . Electrodialysis unit

2. . . anode

3. . . cathode

4k. . . Cation exchange resin

4a. . . Anion exchange resin

5a, 5b, 5c. . . Cell

6, 21, 36. . . Strong alkaline anion exchange resin

7, 14, 22, 37. . . Boron selective ion exchange resin

11, 31. . . groove

12. . . Strong alkaline anion exchange resin

13. . . Ion exchange resin

15, 35. . . Mixer

32, 102. . . Polarized film manufacturing waste liquid

33. . . Iodine crystal

34. . . Filter

101. . . Waste tank

103, 109, 110. . . Pump

104. . . Desalting tank

106. . . Concentrate tank

107. . . Desalting solution

108. . . Concentrate

Fig. 1 is a schematic view showing a method of recovering iodine according to a first embodiment of the present invention.

Fig. 2 is a graph showing the relationship between the pH of a solution in which the concentration of undissociated boric acid (H ₃ BO ₃ ) is an ordinate and the presence form of boron, with pH as an abscissa.

Fig. 3 is a schematic view showing a method of recovering iodine according to a second embodiment of the present invention.

Fig. 4 is a schematic view showing a method of recovering iodine according to a third embodiment of the present invention.

Fig. 5 is a schematic view showing a method of recovering iodine according to a fourth embodiment of the present invention.

Fig. 6 is a schematic view showing a treatment method of a waste liquid for producing a polarizing film described in Patent Document 1.

1. . . Electrodialysis unit

2. . . anode

3. . . cathode

4k. . . Cation exchange resin

4a. . . Anion exchange resin

5a, 5b, 5c. . . Cell

6. . . Strong alkaline anion exchange resin

7. . . Boron selective ion exchange resin

Claims (3)

A method for recovering iodine from a waste liquid for producing a polarizing film is a polarizing film comprising iodine having a total iodine content of 2 to 35 g/L, boron of 0.2 to 8 g/L, and potassium of 0.6 to 11 g/L. The method for recovering iodine from waste liquid; characterized in that it comprises the steps of: adjusting the waste liquid to pH less than 7, and performing electrodialysis, separating iodine and potassium contained in the waste liquid in the form of potassium iodide; The step of reducing the amount of boron in the waste liquid to reduce the amount of iodine to less than 0.5 g/L; and passing the electrodialyzed waste liquid through a strong basic anion exchange resin to adsorb iodine remaining in the waste liquid The strongly basic anion exchange resin, the step of reducing the amount of iodine in the waste liquid to less than 1 mg/L; and the step of recovering iodine from the potassium iodide and the strongly basic anion exchange resin. A method for recovering iodine from a waste liquid for producing a polarizing film is a method for recovering iodine from a waste liquid containing a iodine having a total iodine amount of 2 to 35 g/L and a boron polarizing film of 0.2 to 8 g/L. The method comprises the steps of: adjusting the waste liquid to have a pH of less than 7, and passing the iodine in the waste liquid to the strong basic anion exchange resin through a strong basic anion exchange resin. A method for recovering iodine from a waste liquid for producing a polarizing film according to the first or second aspect of the invention, comprising the steps of: adjusting a waste liquid after iodine separation to a pH of 7 or more, and passing the iodine a boron selective chelating resin to adsorb boron in the waste liquid to the boron selective chelating resin; The step of recovering boron from the boron selective chelating resin.