CN116119855A - Method and apparatus for treating waste liquid from polarizing plate production - Google Patents

Method and apparatus for treating waste liquid from polarizing plate production Download PDF

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Publication number
CN116119855A
CN116119855A CN202211422968.4A CN202211422968A CN116119855A CN 116119855 A CN116119855 A CN 116119855A CN 202211422968 A CN202211422968 A CN 202211422968A CN 116119855 A CN116119855 A CN 116119855A
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boric acid
waste liquid
polarizing plate
precipitate
liquid
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平野悟
阎峰
藤原义浩
前田泰和
古叶靖尚
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Nitto Denko Corp
Sasakura Engineering Co Ltd
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Nitto Denko Corp
Sasakura Engineering Co Ltd
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    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F9/00—Multistage treatment of water, waste water or sewage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D25/00—Filters formed by clamping together several filtering elements or parts of such elements
    • B01D25/12—Filter presses, i.e. of the plate or plate and frame type
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B35/00—Boron; Compounds thereof
    • C01B35/08—Compounds containing boron and nitrogen, phosphorus, oxygen, sulfur, selenium or tellurium
    • C01B35/10—Compounds containing boron and oxygen
    • C01B35/1027—Oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D3/00—Halides of sodium, potassium or alkali metals in general
    • C01D3/12—Iodides
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/02—Treatment of water, waste water, or sewage by heating
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    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/02—Treatment of water, waste water, or sewage by heating
    • C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
    • C02F1/06—Flash evaporation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/22—Treatment of water, waste water, or sewage by freezing
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    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/38—Treatment of water, waste water, or sewage by centrifugal separation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
    • C02F1/4693—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/58—Treatment of water, waste water, or sewage by removing specified dissolved compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/108—Boron compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/34—Organic compounds containing oxygen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
    • C02F2103/346—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32 from semiconductor processing, e.g. waste water from polishing of wafers
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/06—Controlling or monitoring parameters in water treatment pH
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination

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Abstract

The invention aims to provide a method for treating waste liquid of producing a polarizing plate, which can inhibit waste from generating and effectively recycle boric acid when recycling potassium iodide from the waste liquid of producing the polarizing plate. The solution is a method for treating a waste liquid from the production of a polarizing plate, comprising the steps of: a KI recovery step of separating solid and liquid from a first precipitate produced by evaporating and concentrating a waste liquid from the production of a polarizing plate, and recovering a first filtrate containing potassium iodide; and a boric acid recovery step for recovering boric acid from the first precipitate, the boric acid recovery step comprising: a cooling crystallization step of adding an acid to a solution to be treated in which the first precipitate is dissolved, adjusting the pH of the solution, and cooling the solution to precipitate boric acid crystals; a crystallization separation step for separating the precipitated boric acid crystals; and an electrodialysis step of adding a base to the treated solution from which boric acid crystals are separated, neutralizing the treated solution, and then conducting electrodialysis to recover an acid and a base.

Description

Method and apparatus for treating waste liquid from polarizing plate production
Technical Field
The present invention relates to a method and an apparatus for treating a waste liquid from the production of a polarizing plate, and more particularly to a method and an apparatus for treating a waste liquid from the production of a polarizing plate, in which potassium iodide and boric acid are recovered from the waste liquid.
Background
In the past, a method for treating a waste liquid produced in a process for producing a polarizing plate has been studied, in which the waste liquid contains an inorganic component such as iodine, boron, and potassium and an organic component such as polyvinyl alcohol (PVA).
For example, patent document 1 discloses a method in which a first precipitate containing boric acid and polyvinyl alcohol is produced by evaporating and concentrating a polarizing plate production waste liquid, the first precipitate is separated into solid and liquid to produce a first filtrate, the first filtrate is evaporated and concentrated to produce a second precipitate containing potassium iodide, and the second precipitate is separated into solid and liquid to recover potassium iodide.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open publication No. 2018-89602
Disclosure of Invention
Technical problem to be solved by the invention
The method for treating a waste liquid from polarizing plate production disclosed in patent document 1 can easily and efficiently recover potassium iodide from the waste liquid from polarizing plate production, and recover and discard crystals of boric acid mainly generated during the recovery of potassium iodide, thereby attempting to reduce environmental load.
However, in the conventional method, it is difficult to recover high-purity boric acid from the crystals of boric acid main body in such a manner that no waste is generated. For example, in a method of dissolving a crystal of a boric acid main body in heated water and then cooling and crystallizing the solution to recover boric acid, a high-purity boric acid can be obtained by adding an acid such as sulfuric acid before cooling and crystallizing the solution, but on the other hand, there is a problem that a salt-containing wastewater mainly containing potassium sulfate or the like is generated as waste.
Accordingly, an object of the present invention is to provide a method and an apparatus for treating a waste liquid from polarizing plate production, which can suppress the generation of waste and efficiently recover boric acid when potassium iodide is recovered from the waste liquid from polarizing plate production.
Technical scheme for solving technical problems
The above object of the present invention can be achieved by a method for treating a waste liquid from the production of a polarizing plate, which is a method for recovering potassium iodide and boric acid from the waste liquid from the production of a polarizing plate, comprising: a KI recovery step of separating solid and liquid from a first precipitate containing boric acid and polyvinyl alcohol, which is produced by evaporating and concentrating a waste liquid from a polarizing plate production process, and recovering a first filtrate containing potassium iodide; and a boric acid recovery step of recovering boric acid from the first precipitate, the boric acid recovery step including: a cooling crystallization step of adding an acid to a solution to be treated in which the first precipitate is dissolved to adjust the pH, and then cooling the solution to precipitate boric acid crystals; a crystallization separation step of separating the boric acid crystals deposited; and an electrodialysis step of adding a base to the treated liquid from which the boric acid crystals are separated, neutralizing the treated liquid, and then conducting electrodialysis to recover an acid and a base.
In the method for treating a waste liquid from production of a polarizing plate, it is preferable that the pH of the liquid to be treated in the cooling crystallization step is adjusted by using an acid recovered in the electrodialysis step.
Further, the neutralization of the treatment solution in the electrodialysis step is preferably performed using the alkali recovered in the electrodialysis step.
Preferably, the electrodialysis step includes a 2-valent cation removal step of removing 2-valent cations contained in the neutralized solution to be treated.
Preferably, the electrodialysis step includes a PVA removal step of removing polyvinyl alcohol contained in the neutralized solution to be treated.
Preferably, the liquid to be treated after desalting in the electrodialysis step is combined with the polarizer manufacturing waste liquid before evaporating and concentrating in the first precipitate recovery step.
The above object of the present invention can be achieved by a device for treating a waste liquid from polarizing plate production, which is a device for recovering potassium iodide and boric acid from a waste liquid from polarizing plate production, comprising: a KI recovery device for separating solid and liquid from a first precipitate containing boric acid and polyvinyl alcohol, which is produced by evaporating and concentrating a waste liquid from a polarizing plate production process, and recovering a first filtrate containing potassium iodide; and a boric acid recovery device for recovering boric acid from the first precipitate, the boric acid recovery device comprising: a cooling crystallization device for adding an acid to the solution to be treated in which the first precipitate is dissolved, adjusting the pH of the solution, and cooling the solution to precipitate boric acid crystals; a crystallization separator for separating the boric acid crystals deposited; and an electrodialysis device for neutralizing the treated liquid from which the boric acid crystals are separated by adding a base thereto, and then conducting electrodialysis to recover the acid and the base.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, it is possible to provide a method and an apparatus for treating a waste liquid from polarizing plate production, which can suppress the generation of waste and efficiently recover boric acid when potassium iodide is recovered from the waste liquid from polarizing plate production.
Drawings
Fig. 1 is a block diagram showing a schematic configuration of a treatment apparatus for a polarizing plate manufacturing waste liquid according to an embodiment of the present invention.
Fig. 2 is a block diagram showing the configuration of the elements of the apparatus for treating a waste liquid in the production of a polarizing plate shown in fig. 1.
Symbol description
1: a treatment device for waste liquid from polarizing plate production; 2: a KI recovery device; 3: boric acid recovery device; 13: cooling the crystallization device; 14: a crystallization separation device; 18: a PVA removal device; 19: a 2-valent cation removal device; 20: bipolar membrane electrodialysis device.
Detailed Description
An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a block diagram of an apparatus for treating a polarizing plate manufacturing waste liquid according to an embodiment of the present invention. As shown in fig. 1, the treatment apparatus 1 for a polarizing plate production waste liquid includes a KI recovery apparatus 2 and a boric acid recovery apparatus 3. The method of treating the waste liquid for producing a polarizing plate by using the apparatus 1 for treating a waste liquid for producing a polarizing plate will be described below.
First, a KI recovery step of introducing a polarizing plate production waste liquid stored in a stock solution tank into a KI recovery apparatus 2, and separating solid and liquid of a first precipitate formed by evaporation concentration to recover a first filtrate containing potassium iodide is performed. The KI recovery apparatus 2 includes: a first precipitate recovery device 4 for recovering a first precipitate separated from the first filtrate; and a second precipitate recovery device 5 for separating and recovering the solid and liquid of the second precipitate produced by further evaporating and concentrating the first filtrate.
The waste liquid for producing a polarizing plate is a waste liquid generated in a process for producing a polarizing plate used for a liquid crystal display or the like. In the production process of a polarizing plate, a film made of polyvinyl alcohol (PVA) is usually immersed in a potassium iodide (KI) solution, and then boric acid (H) 3 BO 3 ) The resulting film was stretched in an aqueous solution, washed with water, and dried to produce a polarizing plate. Therefore, PVA is mainly contained in the waste liquid from the production of polarizing platesContains KI and H in ionic state 3 BO 3 Etc. The pH of the waste liquid for producing a polarizing plate is in the range of 3.5 to 8.0, and is usually acidic because of the boric acid solution, but may be a waste liquid for producing a polarizing plate in the vicinity of neutrality. In order to suppress corrosion of the production apparatus, a neutralizing agent such as potassium hydroxide may be added to the waste liquid from the production of the polarizing plate.
The first precipitate recovery device 4 into which the polarizer manufacturing waste liquid is introduced has an evaporation concentration device that can concentrate the polarizer manufacturing waste liquid by evaporation. The evaporation and concentration device may be configured by using one or more of known devices such as a heat pump type, a jet drive type, a vapor type, and a flash evaporation type.
When the liquid waste from polarizing plate production is concentrated by an evaporation concentration device, H contained in the liquid waste 3 BO 3 And PVA are mostly formed as sludge, and first precipitates containing these substances are generated in the polarizer manufacturing waste liquid. The first precipitate may also contain H 3 BO 3 And impurities other than PVA.
The first precipitate recovery device 4 further includes a cooling crystallization device that performs cooling crystallization of the polarizer manufacturing waste liquid containing the first precipitate. Examples of the cooling crystallization apparatus include a jacket type and a vacuum type. H in waste liquid from polarizing plate production by means of evaporation concentration device 3 BO 3 When the concentration is sufficiently reduced, the cooling crystallization apparatus may be omitted.
The first precipitate recovery device 4 further includes a solid-liquid separation device for separating the first precipitate in the polarizer manufacturing waste liquid, which is suitably subjected to cooling crystallization after evaporation and concentration, from the first filtrate. Examples of the solid-liquid separation device include various filtration devices such as pressure filtration (filter press), vacuum filtration, and centrifugal filtration, and known structures such as a decanter-type centrifugal separation device. By passing the polarizer manufacturing waste liquid through the solid-liquid separation device, the first precipitate can be separated from the first filtrate in a solid-liquid manner and recovered. By separating the first precipitate, the first filtrate is freed of, for example, about 60 to 90% of H 3 BO 3 Removing e.g. 4About 0 to 60% of PVA. The first precipitate separated is H 3 BO 3 The crystal mainly contains PVA.
The first filtrate produced by the first precipitate recovery device 4 is led to the second precipitate recovery device 5. The second precipitate recovery device 5 includes: an evaporation concentration device for evaporating and concentrating the first filtrate to generate a second precipitate containing KI crystals; and a solid-liquid separation device for separating solid and liquid from the second filtrate. The evaporation and concentration device and the solid-liquid separation device included in the second precipitate recovery device 5 may have the same configuration as the evaporation and concentration device and the solid-liquid separation device included in the first precipitate recovery device 4. Due to H contained in the first filtrate 3 BO 3 And the concentration of PVA is sufficiently reduced, so that crystals mainly composed of KI can be recovered as the second precipitate.
Since KI is dissolved in a high concentration in the first filtrate produced by the first precipitate recovery device 4, if the KI can be directly recycled in the production process of the polarizing plate, the second precipitate recovery device 5 may be omitted. That is, the KI recovery process may be performed by the first precipitate recovery apparatus 4 alone.
In the method for treating a waste liquid from polarizing plate production according to the present embodiment, after the first precipitate recovery step, a boric acid recovery step of recovering boric acid from the first precipitate by the boric acid recovery device 3 is performed.
Fig. 2 is a block diagram showing a schematic configuration of the boric acid recovery apparatus 3. As shown in fig. 2, the boric acid recovery apparatus 3 includes a crystallization tank 11, a filter 12, a cooling crystallization apparatus 13, a crystallization separation apparatus 14, a boric acid recovery vessel 15, a liquid tank to be treated 16, a concentration apparatus 17, a PVA removal apparatus 18, a cation removal apparatus 19 having a valence of 2, and a bipolar membrane electrodialysis apparatus 20. The boric acid recovery process by the boric acid recovery apparatus 3 includes a cooling crystallization process S1, a crystallization separation process S2, and an electrodialysis process S3.
In the cooling crystallization step S1, boric acid crystals are precipitated by adding an acid to the solution to be treated in which the first precipitate is dissolved, adjusting the pH of the solution, and then cooling the solution. First, the first precipitate is introduced into the crystallization dissolution tank 11, and dissolved in water to produce a solution to be treated. In the crystallization dissolution tank 11, vapor is preferably introduced together with pure water, and the first precipitate is dissolved in warm water, and the boric acid concentration of the liquid to be treated is preferably in the vicinity of the saturation concentration.
The solution to be treated produced in the crystallization dissolution tank 11 is passed through a filter 12 to remove insoluble matter, and then a pH adjuster is added to adjust the pH to an acidic side (for example, to about pH 4), and the solution is introduced into a cooling crystallization device 13. The pH adjuster is preferably sulfuric acid, but other acids may be used as long as there is no problem in the process.
The cooling crystallization device 13 can use a known device similar to the cooling crystallization device included in the KI recovery device 2, and can cool the treated liquid after the pH adjustment by heat exchange with cooling water, thereby precipitating boric acid crystals having high purity. The cooling temperature of the liquid to be treated, which is achieved by the cooling crystallization device 13, is preferably 20 ℃ or lower, more preferably 10 ℃ or lower. The lower limit of the cooling temperature is not particularly limited, but may be set to, for example, -10 ℃ or higher, and practically 0 ℃ or higher.
In the crystallization separation step S2, the boric acid crystals precipitated in the cooling crystallization step S1 are separated from the liquid to be treated by the crystallization separation device 14. The crystallization separation device 14 preferably performs crystallization separation while maintaining the temperature of the liquid to be treated at the cooling temperature. In the present embodiment, the crystallization separator 14 is a centrifuge, but other devices that can separate solid components from liquid, such as filtration or sedimentation, may be used. The separated boric acid crystals are collected in a boric acid collection container 15 such as a container. The recovered boric acid is suitably dried by a dryer or the like.
The liquid to be treated from which boric acid crystals are separated by the crystallization separator 14 is stored in a liquid tank 16 to be treated. Since the liquid to be treated supplied to the liquid to be treated tank 16 contains some boric acid which has not been precipitated, the liquid to be treated in the liquid to be treated tank 16 is concentrated by the concentrating device 17, and then cooled and crystallized again by the cooling and crystallizing device 13, whereby the recovery rate of boric acid can be improved. The concentration device 17 may have the same configuration as the evaporation concentration device of the first precipitate recovery device 4, for example. The concentration and cooling crystallization of the treated liquid after the crystallization separation are repeated by batch processing, whereby the recovery rate and purity of boric acid gradually decrease, and thus the number of repetitions is preferably, for example, about 3 to 4 times. The pure water may be appropriately supplied to the liquid to be treated 16 in association with the concentration of the liquid to be treated. The boric acid recovered in the boric acid recovery vessel 15 may be supplied to the liquid to be treated 16 according to purity, and dissolved in the liquid to be treated to be recrystallized.
In the electrodialysis step S3, the acid and the base are recovered from the solution to be treated from which boric acid crystals are separated in the crystallization separation step S2. The solution to be treated in the solution tank 16 is neutralized by adding a neutralizing agent, and then supplied to the bipolar membrane electrodialysis device 20 through the PVA removing device 18 and the 2-valent cation removing device 19. The neutralizing agent is preferably potassium hydroxide (KOH), but when the recovered alkali is used outside the system, it may be other alkaline aqueous solution such as sodium hydroxide (NaOH).
The PVA removing device 18 is a device that selectively removes PVA contained in the liquid to be treated, and for example, activated carbon in the form of particles, honeycomb, or the like that adsorbs and removes PVA by contact with the liquid to be treated can be suitably used. The material of the activated carbon is not particularly limited, and for example, activated carbon obtained by firing natural materials such as wood, synthetic resins, and the like can be used.
The 2-valent cation removing device 19 is a device for selectively removing 2-valent cations such as magnesium ions and calcium ions contained in the liquid to be treated, and for example, a known device such as a resin column packed with a chelate resin can be used. By passing the solution to be treated through the 2-valent cation removing device 19, the degradation of the membrane performance due to precipitation of magnesium ions, calcium ions, or the like can be suppressed in the bipolar membrane electrodialysis device 20, and the recovery efficiency of the acid and the base can be maintained satisfactorily. Further, as in the present embodiment, by providing the PVA removing device 18 in the front stage of the 2-valent cation removing device 19, the performance of the chelate resin or the like of the 2-valent cation removing device 19 can be well maintained.
The bipolar membrane electrodialysis device 20 is a well-known 3-chamber type structure in which, for example, an anion exchange membrane and a cation exchange membrane are disposed between 2 bipolar membranes, and an acid chamber, a salt chamber, and a base chamber are formed between the two bipolar membranes, and by supplying a solution to be treated to the salt chamber and supplying pure water to the acid chamber and the base chamber, acid (sulfuric acid in the present embodiment) can be discharged from the acid chamber, base (KOH in the present embodiment) can be discharged from the base chamber, and the acid tank and the base tank can be recovered, respectively.
The treated liquid desalted by the salt chamber of the bipolar membrane electrodialysis device 20 is returned to the raw liquid tank shown in fig. 1 and is joined to the polarizer manufacturing waste liquid, whereby KI contained in a small amount is recovered by the KI recovery device 2. A part of the neutralized liquid to be treated discharged from the liquid tank 16 may be returned to the raw liquid tank. For the impurities accumulated by returning the liquid to be treated to the raw liquid tank, a part of the liquid to be treated returned from the liquid tank 16 to the raw liquid tank may be branched and discarded.
As described above, the method for treating a waste liquid from polarizing plate production according to the present embodiment is configured such that in the boric acid recovery step, alkali is added to the liquid to be treated after separation of boric acid crystals for neutralization, and then acid and alkali are recovered by electrodialysis, so that it is possible to suppress new waste generated by recovery of boric acid and reduce environmental load.
The acid and the base recovered by electrodialysis may be used outside the system, but are preferably used in the treatment apparatus 1 for the waste liquid from polarizing plate production. That is, the acid recovered by electrodialysis can be used as a pH adjuster for the liquid to be treated in the cooling crystallization step S1, and the base recovered by electrodialysis can be used as a neutralizing agent for the liquid to be treated in the electrodialysis step S3. Thus, the product from the waste liquid from the polarizing plate production can be effectively utilized without being discharged to the outside, whereby zero liquid discharge (ZLD: zero Liquid Discharge) for waste liquid treatment and recycling of waste can be realized.

Claims (7)

1. A method for treating waste liquid from manufacturing a polarizing plate is characterized in that:
the method for recovering potassium iodide and boric acid from the waste liquid of manufacturing the polaroid comprises the following steps:
a KI recovery step of separating solid and liquid from a first precipitate containing boric acid and polyvinyl alcohol, which is produced by evaporating and concentrating a waste liquid from a polarizing plate production process, and recovering a first filtrate containing potassium iodide; and
a boric acid recovery step of recovering boric acid from the first precipitate,
the boric acid recovery process comprises the following steps of;
a cooling crystallization step of adding an acid to a solution to be treated in which the first precipitate is dissolved, adjusting the pH of the solution, and then cooling the solution to precipitate boric acid crystals;
a crystallization separation step of separating the precipitated boric acid crystals; and
and an electrodialysis step of adding a base to the treated liquid from which the boric acid crystals are separated, neutralizing the treated liquid, and then conducting electrodialysis to recover an acid and a base.
2. The method for treating a waste liquid from polarizing plate production according to claim 1, wherein:
the pH of the solution to be treated in the cooling crystallization step is adjusted using the acid recovered in the electrodialysis step.
3. The method for treating a waste liquid from polarizing plate production according to claim 1 or 2, wherein:
neutralization of the treatment solution in the electrodialysis step is performed using the alkali recovered in the electrodialysis step.
4. The method for treating a waste liquid from polarizing plate production according to any one of claims 1 to 3, wherein:
the electrodialysis step includes a 2-valent cation removal step of removing 2-valent cations contained in the neutralized solution to be treated.
5. The method for treating a waste liquid from polarizing plate production according to any one of claims 1 to 4, wherein:
the electrodialysis step includes a PVA removal step of removing polyvinyl alcohol contained in the neutralized solution to be treated.
6. The method for treating a waste liquid from polarizing plate production according to any one of claims 1 to 5, wherein:
and merging the treated liquid after desalting in the electrodialysis step with the polarizer manufacturing waste liquid before evaporating and concentrating in the first precipitate recovery step.
7. A treatment device for a waste liquid in the manufacture of a polaroid is characterized in that:
which is a device for recovering potassium iodide and boric acid from a waste liquid of polarizing plate production, comprising:
a KI recovery device for separating solid and liquid from a first precipitate containing boric acid and polyvinyl alcohol, which is produced by evaporating and concentrating a waste liquid from a polarizing plate production process, and recovering a first filtrate containing potassium iodide; and
boric acid recovery means for recovering boric acid from the first precipitate,
the boric acid recovery apparatus includes:
a cooling crystallization device for adding an acid to the solution to be treated in which the first precipitate is dissolved, adjusting the pH of the solution, and cooling the solution to precipitate boric acid crystals;
a crystallization separation device for separating the precipitated boric acid crystals; and
and an electrodialysis device for neutralizing the treated liquid from which the boric acid crystals are separated by adding a base thereto, and then conducting electrodialysis to recover the acid and the base.
CN202211422968.4A 2021-11-15 2022-11-15 Method and apparatus for treating waste liquid from polarizing plate production Pending CN116119855A (en)

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