Purification method and apparatus for a treated liquid containing tetraalkylammonium ions

Abstract

This invention provides a method for purifying a treated liquid containing tetraalkylammonium ions, which can suppress resin breakage even when using a strongly acidic cation exchange resin and reduce the content of metal impurities in the treated liquid. The purification method includes an impurity removal step in which the treated liquid containing tetraalkylammonium ions and metal impurities is passed through a container filled with a hydrogen ion-type or tetraalkylammonium ion-type cation exchange resin, thereby reducing the content of the metal impurities in the treated liquid. The degree of crosslinking of the cation exchange resin is 16-24%.

Description

Technical Field

[0001] This invention relates to a purification method and apparatus for reducing the content of metal impurities in a treated liquid containing tetraalkylammonium ions and metal impurities. Furthermore, this invention relates to a method and apparatus for recovering an aqueous solution of tetraalkylammonium salt from a treated liquid to reduce the content of metal impurities in the treated liquid containing tetraalkylammonium ions and metal impurities. Background Technology

[0002] In the manufacture of electronic components such as semiconductor devices, liquid crystal displays, and printed circuit boards, a photoresist film is formed on a substrate such as a wafer. Light is then irradiated through a pattern mask, and the unwanted photoresist is dissolved and developed using a developer. Subsequently, after etching or other processes, the insoluble photoresist film on the substrate is peeled off. Photoresists are classified as positive (soluble in the exposed areas) and negative (insoluble in the exposed areas). For positive photoresists, alkaline developers are primarily used. For negative photoresists, organic solvent-based developers are the mainstream, but alkaline developers are sometimes used as well.

[0003] As an alkaline developer, an aqueous solution of tetraalkylammonium hydroxide (hereinafter also referred to as "TAAH") is typically used. Therefore, the waste liquid discharged in the photoresist developing process (hereinafter also referred to as "photoresist developing waste liquid") contains metal ions (metal impurities) and tetraalkylammonium ions (hereinafter also referred to as "TAA ions") in addition to the photoresist.

[0004] Previously, the mainstream methods for treating photoresist developing wastewater were concentration via evaporation or reverse osmosis, followed by waste disposal (incineration or payment by businesses) or biological decomposition via activated sludge before discharge. However, from the perspective of reducing environmental impact, attempts have been made to recover TAAH from photoresist developing wastewater and reuse it.

[0005] Patent Document 1 discloses a method in which TAA ions are adsorbed onto a cation exchange resin, and then eluted with an acid solution as a tetraalkylammonium salt (hereinafter also referred to as "TAA salt") to recover the TAA ions. In Patent Document 1, during the TAA salt solution recovery process, the pH and / or conductivity of the effluent are measured, and recovery is stopped when these values ​​change by a given amount, thereby obtaining a TAA salt solution with a reduced metal ion concentration. Furthermore, this TAA salt solution is used as a raw material to manufacture TAAH.

[0006] Prior art literature

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2012 / 090699 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, in the method described in Patent Document 1, the recovered TAA salt solution is finally evaporated and concentrated, and then electrolyzed to obtain TAAH. In this concentration process, there is a problem that the metal ions remaining in the TAA salt solution become scale.

[0011] On the other hand, generally speaking, using strongly acidic cation exchange resins to adsorb metallic impurities is an effective method for reducing the amount of metallic impurities. However, if the strongly acidic cation exchange resin is tetraalkylammonium ionic, the resin contains more water and expands compared to the hydrogen ionic form. Therefore, if the conversion between hydrogen ionic and tetraalkylammonium ionic forms is repeated, there is a problem of cracks and resin breakage due to repeated shrinkage and expansion.

[0012] Therefore, an object of the present invention is to provide a purification method and apparatus for a treated liquid containing tetraalkylammonium ions, which can suppress resin breakage even when using a strongly acidic cation exchange resin, thereby reducing the content of metal impurities in the treated liquid. Furthermore, an object of the present invention is to provide a method and apparatus for recovering tetraalkylammonium salt aqueous solutions from a treated liquid containing tetraalkylammonium ions, which can suppress resin breakage even when using a strongly acidic cation exchange resin.

[0013] Technical solutions for solving the problem

[0014] In view of the above problems, the inventors of the present invention have discovered through in-depth research that by using a highly cross-linked, strongly acidic cation exchange resin, resin cracking can be suppressed and the content of metal impurities in the treated liquid containing tetraalkylammonium ions can be reduced, thereby completing the present invention.

[0015] That is, the present invention is a purification method for a liquid to be treated, which includes an impurity removal step. In the impurity removal step, the liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a container filled with a hydrogen ion type or a tetraalkylammonium ion type cation exchange resin, thereby reducing the content of the metal impurities in the liquid to be treated. The degree of crosslinking of the cation exchange resin is 16 to 24%.

[0016] Furthermore, the present invention is a purification apparatus for a treated liquid, which includes an impurity removal unit. In this impurity removal unit, the treated liquid containing tetraalkylammonium ions and metal impurities is passed through a container filled with a hydrogen ion type or a tetraalkylammonium ion type cation exchange resin, thereby reducing the content of the metal impurities in the treated liquid. The degree of crosslinking of the cation exchange resin is 16 to 24%.

[0017] Furthermore, the present invention provides a method for recovering an aqueous solution of tetraalkylammonium salt from a treated liquid. This method includes an impurity removal step in which the treated liquid containing tetraalkylammonium ions and metal impurities is passed through a container filled with a hydrogen ion-type or tetraalkylammonium ion-type cation exchange resin, thereby reducing the content of the metal impurities in the treated liquid. The degree of crosslinking of the cation exchange resin is 16-24%.

[0018] Furthermore, the present invention provides a recovery device for a tetraalkylammonium salt aqueous solution from a treated liquid, the recovery device having an impurity removal unit that passes the treated liquid containing tetraalkylammonium ions and metal impurities into a container filled with a hydrogen ion-type or tetraalkylammonium ion-type cation exchange resin, thereby reducing the content of the metal impurities in the treated liquid, wherein the degree of crosslinking of the cation exchange resin is 16-24%.

[0019] Invention Effects

[0020] According to the present invention, a method and apparatus for purifying a treated liquid containing tetraalkylammonium ions can be provided, which can suppress resin breakage by using a highly cross-linked, strongly acidic cation exchange resin and reduce the content of metal impurities in the treated liquid. Furthermore, according to the present invention, a method and apparatus for recovering an aqueous solution of tetraalkylammonium salts from a treated liquid containing tetraalkylammonium ions can be provided, which can suppress resin breakage by using a highly cross-linked, strongly acidic cation exchange resin. Additionally, when using a highly cross-linked and small-particle-size strongly acidic cation exchange resin, in addition to the above, a method and apparatus for purifying a treated liquid with minimal pH fluctuation during the initial flow stage, and a method and apparatus for recovering an aqueous solution of tetraalkylammonium salts from the treated liquid can also be provided. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the structure of a refining apparatus according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram illustrating the structure of a refining apparatus according to an embodiment of the present invention. Detailed Implementation

[0023] <Method for refining the treated liquid>

[0024] The purification method of the present invention includes an impurity removal step, in which a liquid to be treated containing tetraalkylammonium ions and metal impurities is passed through a container filled with a hydrogen ion type (hereinafter also referred to as "H-type") or tetraalkylammonium ion type (hereinafter also referred to as "TAA-type") cation exchange resin, thereby reducing the content of the metal impurities in the liquid to be treated. Furthermore, the purification method of the present invention is characterized by a crosslinking degree of 16-24% for the cation exchange resin. The purification method of the present invention will now be described in detail.

[0025] [Impurity Removal Process]

[0026] The impurity removal process is as follows: the liquid to be treated, containing tetraalkylammonium ions and metal impurities, is passed through a container filled with H-type or TAA-type cation exchange resin, thereby reducing the content of the metal impurities in the liquid to be treated.

[0027] (The liquid being treated)

[0028] In this invention, the treated liquid containing tetraalkylammonium ions and metal impurities is not particularly limited as long as it contains at least tetraalkylammonium ions and metal impurities. However, since these components are present and generated in large quantities in semiconductor manufacturing processes, liquid crystal display manufacturing processes, etc., the treated liquid is preferably a solution derived from photoresist developing waste liquid discharged in such processes. Photoresist developing waste liquid is the waste liquid discharged when developing exposed photoresist with an alkaline developer; it is typically an alkaline aqueous solution with a pH of 10-14. Therefore, in photoresist developing waste liquid, the acidic groups such as carboxyl and phenolic hydroxyl groups of the photoresist dissociate and dissolve as salts in TAA ions derived from TAAH. Therefore, photoresist developing waste liquid is a solution mainly containing photoresist, TAA ions, and metal impurities. The treated liquid involved in this invention, for example, is a solution from which TAA ions from the photoresist developing waste liquid are adsorbed onto a cation exchange resin, and then eluted with an acid such as hydrochloric acid, thereby recovering the TAA salt.

[0029] First, the photoresist developing waste liquid is passed through a container filled with H-type cation exchange resin, causing TAA ions to be adsorbed onto the resin. Since the waste liquid typically contains cations, these metal ions are also adsorbed onto the resin during this process. Furthermore, even if metal ions are present in the waste liquid, due to chemical equilibrium reactions such as complexation, they will not be adsorbed onto the resin if the metal-containing ions themselves become anions, and will instead be discharged from the container. On the other hand, the organic components derived from the photoresist dissolved in the photoresist developing waste liquid are usually in anionic form, making them difficult to adsorb onto the resin, and thus most are removed. Additionally, even in the presence of nonionic components, they will not be adsorbed onto the resin and will be discharged (effervescent) at this stage, thus removing most of them. Alternatively, after passing the photoresist developing waste liquid through the cation exchange resin, the remaining photoresist components and other impurities can be washed away using ultrapure water or a high-purity TAAH aqueous solution.

[0030] Subsequently, by passing an aqueous solution of an inorganic acid such as hydrochloric acid or sulfuric acid through a container filled with a cation exchange resin converted to the TAA type, the hydrogen ions in the aqueous solution are sequentially replaced by the adsorbed TAA ions, and the TAA ions flow out of the container as the acid salt (TAA salt) of the inorganic acid used. Furthermore, by treating the solution containing the obtained TAA salt with a (highly cross-linked) cation exchange resin (preferably with small particle size), the treated liquid according to the present invention can be obtained. The treated liquid thus obtained is a solution containing tetraalkylammonium ions and metal impurities, and the purification method according to the present invention is a purification method for reducing the content of metal impurities in the treated liquid.

[0031] Furthermore, the process of recovering TAAH from photoresist developing waste liquid as a treated liquid containing TAA salt is known, for example, as described in Patent Document 1. Known methods can be appropriately selected for the container, cation exchange resin, type or amount of acid used, and acid flushing method employed in this process. Here, the (highly cross-linked) cation exchange resin used in this process can also be a strongly acidic cation exchange resin with a cross-linking degree of 16% to 24% as described in this invention. In this case, even during this process, resin breakage due to repeated use can be prevented. Moreover, from an operational point of view, it is preferable that the same resin can be used from the process of recovering the treated liquid to the ion exchange process and the impurity removal process described later.

[0032] (Tetraalkylammonium ion)

[0033] As described above, the treated liquid used in this invention is a solution in which TAA ions (TAAH) are dissolved and recovered from the photoresist developer waste liquid as a TAA salt. Specific examples of TAA ions in the treated liquid include ions derived from the photoresist developer liquid that are used as an alkali, such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethyl(2-hydroxyethyl)ammonium hydroxide, triethyl(2-hydroxyethyl)ammonium hydroxide, dimethyldi(2-hydroxyethyl)ammonium hydroxide, diethyldi(2-hydroxyethyl)ammonium hydroxide, hydroxymethyltri(2-hydroxyethyl)ammonium hydroxide, hydroxyethyltri(2-hydroxyethyl)ammonium hydroxide, and tetra(2-hydroxyethyl)ammonium hydroxide. Among these, tetramethylammonium ions and tetrabutylammonium ions derived from tetramethylammonium hydroxide and tetrabutylammonium hydroxide, which are most commonly used, are preferred in this invention, and tetramethylammonium ions derived from tetramethylammonium hydroxide are particularly preferred. The liquid to be treated in this invention is a solution in which the aforementioned tetraalkylammonium ions are recovered, for example, as a chloride salt. Preferably, it is an aqueous solution of tetraalkylammonium chloride such as tetramethylammonium chloride or tetrabutylammonium chloride, and more preferably, an aqueous solution of tetramethylammonium chloride. That is, the tetraalkylammonium ions in the liquid to be treated involved in this invention are preferably tetraalkylammonium ions derived from tetraalkylammonium chloride such as tetramethylammonium chloride or tetrabutylammonium chloride, and more preferably, tetraalkylammonium ions derived from tetramethylammonium chloride.

[0034] Here, we will describe a representative photoresist developing waste solution discharged from the developing process in semiconductor manufacturing and liquid crystal display manufacturing. In the developing process, single-sheet automated developing equipment is typically used. In this equipment, a process using a developer solution containing TAAH and a subsequent rinsing (substrate cleaning) based on pure water are performed in the same tank. In the rinsing process, 5 to 1000 times the amount of developer solution is used in pure water. Therefore, the developer solution used in the developing process typically becomes waste solution diluted 5 to 10 times. As a result, the composition of the photoresist developing waste solution discharged from this developing process is approximately 0.001 to 2.5% by mass of TAAH, approximately 10 to 100 ppm of resist, and approximately 0 to several tens of ppm of surfactant. Furthermore, waste solution from other processes is sometimes mixed in, and the TAAH concentration may decrease within the above range. The treated solution obtained from photoresist developer waste liquid with a TAAH concentration of, for example, 0.001 to 2.5% by mass has a TAA ion concentration of 0.001 to 2.5% by mass. Alternatively, the treated solution obtained from photoresist developer waste liquid can also be used after adjusting the TAA ion concentration through appropriate concentration or other methods.

[0035] (Metallic impurities)

[0036] Photoresist developing wastewater contains various metal ions as metallic impurities, and therefore the treated solution also contains these metal ions. Examples of metal ions include monovalent ions such as sodium and potassium, divalent ions such as magnesium, calcium, and zinc, and polyvalent ions such as aluminum, nickel, copper, chromium, and iron. Typically, these metal ions are present in the photoresist developing wastewater (treated solution) at a concentration of approximately 0.1 to 1000 ppb. Furthermore, the counterion of tetraalkylammonium ions in photoresist developing wastewater is usually hydroxide ions. However, depending on the plant, in addition to neutralization, at least one of the following is typically selected as a counterion of tetraalkylammonium ions: inorganic anions such as fluoride ions, chloride ions, bromide ions, carbonate ions, bicarbonate ions, sulfate ions, bisulfate ions, nitrate ions, phosphate ions, hydrogen phosphate ions, and dihydrogen phosphate ions, as well as organic anions such as formate ions, acetate ions, and oxalate ions. However, it is believed that since most of these anions are removed during the stage of preparing the treated solution from the photoresist developing waste liquid, they are almost not present in the treated solution.

[0037] (Cation exchange resin)

[0038] In this invention, a strongly acidic cation exchange resin with a crosslinking degree of 16% to 24% is used as the H-type or TAA-type cation exchange resin. Highly crosslinked resins with a crosslinking degree within this range exhibit high strength due to the dense crosslinking structure within the resin. When a cation exchange resin with a crosslinking degree of less than 16% is used, the resin strength becomes insufficient, increasing the likelihood of resin breakage during purification. Furthermore, when a cation exchange resin with a crosslinking degree exceeding 24% is used, the ion exchange rate slows down, and the resin regeneration rate also slows down. Thus, in this invention, it has been found that by using a strongly acidic cation exchange resin with a crosslinking degree as high as 16% to 24%, resin breakage during purification can be suppressed. Furthermore, highly crosslinked cation exchange resins are also preferred because they have a large exchange capacity and can introduce a large number of functional groups.

[0039] As an H-type cation exchange resin, any resin can be used as long as the degree of crosslinking is 16% to 24%. Examples of such H-type cation exchange resins include Amberjet 1060H and 1600H (trade name, manufactured by Organo Corporation), AMBERLITE IRN99H, 200C, and 200CT (trade name, manufactured by DuPont), AMBEREX210 (trade name, manufactured by DuPont), Diaion SK116 (trade name, manufactured by Mitsubishi Chemical Corporation), and Purolite C100X16MBH (trade name, manufactured by PUROLITE Corporation).

[0040] As a TAA-type cation exchange resin, a resin exemplified as the H-type cation exchange resin described above can be pre-ion-exchanged to a TAA-type resin. That is, in the case where the treated liquid is purified using a TAA-type cation exchange resin in the impurity removal process, the purification method according to the present invention can also include the following ion exchange step before the impurity removal process.

[0041] An ion exchange process involves passing a regenerator containing tetraalkylammonium ions into a container filled with hydrogen ion-type cation exchange resin, thereby converting the hydrogen ion-type cation exchange resin into a tetraalkylammonium ion-type cation exchange resin.

[0042] Furthermore, the TAA-type cation exchange resin obtained in this ion exchange process can be used in the impurity removal process. The ion exchange process will be described later.

[0043] The particle size of the cation exchange resin is preferably 200 μm to 720 μm. If the particle size is 720 μm or less, it falls within the typical particle size range for ion exchange resins, making it easy to adapt and utilize existing equipment. Furthermore, if the cation exchange resin has a particle size of 200 μm or more, it has a typical surface area, enabling sufficient removal of metal impurities. Additionally, if the cation exchange resin has a particle size of 200 μm or more, it can suppress the increase in differential pressure between the resin outlet and resin inlet. Moreover, the particle size of the cation exchange resin is more preferably 500 μm to 560 μm in the H-type. Cation exchange resins with small particle sizes within this range have a large resin surface area, making it easier to convert the resin from the H-type to the TAA-type. Therefore, less H-type resin remains when converting the resin to the TAA-type, further suppressing initial pH fluctuations during the flow of the treated liquid. Furthermore, small-particle-size cation exchange resins exhibit excellent metal impurity removal performance due to their large resin surface area. In this invention, particle size refers to the blended average diameter.

[0044] (Using H-type cation exchange resin)

[0045] If a solution containing TAA ions and metal impurities is passed through a container filled with H-type cation exchange resin, hydrogen ions in the resin exchange with TAA ions in the solution, thereby converting the H-type cation exchange resin into a TAA-type cation exchange resin. Furthermore, metal impurities in the solution, which are cations, are also adsorbed by the cation exchange resin, thus reducing the content of metal impurities in the solution. In other words, when using H-type cation exchange resin, to convert the cation exchange resin from H-type to TAA-type, the ion exchange step described later can be omitted; the solution to be purified can be used to convert the cation exchange resin from H-type to TAA-type. The TAA-type cation exchange resin can then be used in the impurity removal process. The ionic form of the cation exchange resin after this process is a mixture of TAA-type and metal ion-type resins. Additionally, hydrogen ion-type cation exchange resin is also present if unreacted exchange groups remain.

[0046] When using an H-type cation exchange resin, passing the liquid to be treated through it once can reduce the content of metal impurities in the liquid. However, to improve purification efficiency, the liquid can be passed through a TAA-type (and metal ion-type) cation exchange resin again after the first pass. That is, the impurity removal process can be repeated multiple times. If the liquid to be treated is passed through a TAA-type (and metal ion-type) cation exchange resin again, the TAA ions adsorbed on the resin exchange with the metal ions remaining in the liquid, and the metal ions are adsorbed on the resin, thereby further reducing the content of metal impurities in the liquid.

[0047] Furthermore, when using an H-type cation exchange resin to pass the treated liquid through the effluent, the pH of the effluent flowing out of the container becomes strongly acidic due to the influence of hydrogen ions flowing out of the cation exchange resin. Therefore, in this case, the purification method according to the present invention can also include a neutralization step, in which the effluent obtained in the impurity removal step is neutralized. In cases where multiple impurity removal steps are performed repeatedly, for example, a neutralization step of the effluent can be performed after the first impurity removal step, and a second impurity removal step can be performed using the pH-adjusted effluent after the neutralization step. The neutralization step can be performed using known methods. Specifically, for example, it can be performed by storing the effluent in a container such as a storage tank and adjusting the pH using an alkali such as TAAH. Alternatively, only the effluent flowing out at the initial stage of the cyclical flow with drastic pH changes can be stored in another container such as a storage tank for pH adjustment and then mixed with the remaining effluent flowing out later. Furthermore, the effluent flowing out at the initial stage of the cyclical flow with drastic pH changes can be discarded. Examples of bases used in neutralization include tetramethylammonium hydroxide and ammonium hydroxide.

[0048] (Using TAA type cation exchange resin)

[0049] If a liquid containing TAA ions and metal impurities is passed through a container filled with a TAA-type cation exchange resin, the TAA ions in the resin exchange with the metal ions in the liquid, and the metal ions are adsorbed onto the resin. This reduces the content of metal impurities in the liquid. Furthermore, in the ion exchange process, if unreacted exchange groups (hydrogen ions) remain in the cation exchange resin, these hydrogen ions also exchange with the metal ions in the liquid. By using a cation exchange resin that has been pre-converted from the H-type to the TAA-type, when the liquid is passed through, it is not hydrogen ions but TAA ions adsorbed on the resin that exchange with the metal ions in the liquid. Therefore, fluctuations in the TAA ion concentration in the liquid and pH fluctuations at the beginning of the flow can be suppressed. Thus, from the viewpoints of suppressing pH fluctuations at the beginning of the flow and improving the removal efficiency of metal impurities, it is preferable to use a TAA-type cation exchange resin in the impurity removal process.

[0050] (The flow of the treated liquid)

[0051] As a method for passing the liquid to be treated into a container filled with cation exchange resin, conventionally known methods can be appropriately employed depending on the type and shape of the cation exchange resin. Here, in this invention, "container" refers to any container capable of being filled with ion exchange resin, such as an adsorption tower or tank, and capable of purifying the liquid to be treated (either by water or in batches), and is not limited thereto. Specifically, examples include filling a column with cation exchange resin having an inlet at the top and an outlet at the bottom, and continuously passing the liquid to be treated through it using a pump (column method); and passing the liquid to be treated into a container filled with cation exchange resin, allowing it to contact for an appropriate time, and removing the supernatant (batch method). In the column method, the size of the column can be appropriately determined based on the performance of the cation exchange resin, etc. From the viewpoint of efficient purification, it is preferable, for example, that the ratio of column height (L) to diameter (D) (L / D) is 0.5 to 30, and the space velocity (SV) of the liquid to be treated is 1 (1 / hour) or more and 150 (1 / hour) or less.

[0052] (Recovery of effluent)

[0053] In the case of column-feeding, by passing a treated liquid containing tetraalkylammonium ions and metal impurities through the container, an effluent with reduced metal impurity content flows out from one end of the container, and this effluent is then recycled to a storage tank or the like. Furthermore, the resulting purified treated liquid is an aqueous solution of tetraalkylammonium salt. The metal impurity content can be measured, for example, using an Agilent 8900 triple quadrupole ICP-MS (trade name, manufactured by Agilent Technologies, Inc.).

[0054] [Ion exchange process]

[0055] The ion exchange process is a step prior to the aforementioned impurity removal process, in which the H-type cation exchange resin is converted into a TAA-type cation exchange resin; that is, a step to prepare the TAA-type cation exchange resin for use in the impurity removal process. The ion exchange process is performed by passing a regenerant containing TAA ions into a container filled with the H-type cation exchange resin. The H-type cation exchange resin is as described above. When the regenerant containing TAA ions is passed into the H-type cation exchange resin, the hydrogen ions present in the cation exchange resin undergo ion exchange with the TAA ions contained in the regenerant, and the TAA ions are adsorbed onto the cation exchange resin. As a result, the H-type cation exchange resin is converted into a TAA-type cation exchange resin.

[0056] (Regenerant containing tetraalkylammonium ions)

[0057] The regenerant containing TAA ions can be any aqueous solution containing TAA ions, without particular limitation. Specifically, examples of regenerants containing TAA ions include aqueous solutions of methylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, trimethylethylammonium hydroxide, dimethyldiethylammonium hydroxide, trimethyl(2-hydroxyethyl)ammonium hydroxide, triethyl(2-hydroxyethyl)ammonium hydroxide, dimethyldi(2-hydroxyethyl)ammonium hydroxide, diethyldi(2-hydroxyethyl)ammonium hydroxide, hydroxymethyltri(2-hydroxyethyl)ammonium hydroxide, hydroxyethyltri(2-hydroxyethyl)ammonium hydroxide, and tetra(2-hydroxyethyl)ammonium hydroxide. Among these, aqueous solutions of tetramethylammonium hydroxide and tetrabutylammonium hydroxide are most commonly used and are preferred in this invention, with aqueous solutions of tetramethylammonium hydroxide being particularly preferred.

[0058] The content of TAA ions in the regenerator can be set, for example, from 0.1% to 25% by mass.

[0059] (Regenerant flow)

[0060] Regarding the method of passing a regenerant containing TAA ions into a container filled with cation exchange resin, conventionally known methods can be appropriately employed depending on the type and shape of the cation exchange resin. Specifically, examples include filling a column with an inlet orifice at the top and an outlet orifice at the bottom into a column filled with cation exchange resin and continuously passing the solution containing tetraalkylammonium ions through it using a pump (column method), and passing the solution into a container filled with cation exchange resin, allowing it to contact for an appropriate time, and removing the supernatant (batch method). In the column method, the size of the column can be appropriately determined based on the performance of the cation exchange resin. For efficient adsorption of TAA ions, for example, if the TAA ion content is 0.1 to 25% by mass, it is preferable that the ratio of column height (L) to diameter (D) (L / D) is 0.5 to 30, and the space velocity (SV) of the solution is 1 (L / hour) or more and 150 (L / hour) or less.

[0061] The amount of regenerant used for flushing should be appropriately set considering the exchange capacity of the cation exchange resin filled in the container. Furthermore, whether TAA ions are not adsorbed and flow out (breakthrough) when flushing with a solution containing more than the exchange capacity of the cation exchange resin can be confirmed by analyzing the TAA ion concentration in the liquid flowing out of the container using ion chromatography. More simply, the height occupied by the cation exchange resin in the container can be measured. If the counter ion of the cation exchange resin changes from hydrogen ions to TAA ions, the volume expands to approximately twice its original size, depending on the type of cation exchange resin. Therefore, by measuring the volume of the cation exchange resin, the adsorption of TAA ions can be confirmed. Additionally, if the pH of the regenerant used for flushing is alkaline (above 10), and TAA ions are not adsorbed and flow through the container, the pH of the liquid will become alkaline, which can also be confirmed using a pH meter. Furthermore, when the liquid flowing out of the container contains TAA ions, the conductivity of the liquid increases, which can also be confirmed using a conductivity meter.

[0062] (Recovery of effluent)

[0063] In the case of liquid flow in a column manner, by passing a regenerator containing tetraalkylammonium ions through the container, hydrogen ions that have undergone ion exchange with TAA ions flow out from the anions corresponding to the regenerator (salt) used as counter ions from one end of the container, and thus the outflow is recovered into a storage tank or the like.

[0064] [Regeneration process of cation exchange resin]

[0065] The purification method of the present invention may include a regeneration step in which the cation exchange resin that has been in contact with the treated liquid in the impurity removal step is regenerated. The resin regeneration can be performed using known methods, by contacting the resin with an acid to remove impurities such as metal ions and convert the resin from the TAA ionic form to the H-form. The resulting H-form cation exchange resin can be reused in the impurity removal step. The acid used in the regeneration step is not particularly limited as long as it generates hydrogen ions in an aqueous solution; examples include aqueous solutions of inorganic acids such as hydrochloric acid and sulfuric acid. Among these, hydrochloric acid is preferred from the perspectives of industrial inexpensiveness, availability, and ease of concentration adjustment. The concentration and amount of hydrochloric acid used are not particularly limited as long as they are sufficient for the conversion to the H-form and the removal of impurities such as metal ions. Generally, relative to the above-mentioned cation exchange resin, the resin can be converted from the TAA ionic form to the H-form by contacting 1 to 10% by mass of hydrochloric acid with 3 to 20 (L / L - resin). In the regeneration process, in addition to cleaning with the aforementioned inorganic acids, cleaning with ultrapure water or pure water can also be performed as appropriate.

[0066] <Refining apparatus for the treated liquid>

[0067] The purification apparatus of the present invention includes an impurity removal unit that passes a liquid to be treated containing tetraalkylammonium ions and metallic impurities into a container filled with a hydrogen ion-type or tetraalkylammonium ion-type cation exchange resin, thereby reducing the content of the metallic impurities in the liquid to be treated. Furthermore, the purification apparatus of the present invention is characterized by a crosslinking degree of 16-24% for the cation exchange resin. The details of the impurity removal unit are the same as those described for the impurity removal step in the purification method of the present invention.

[0068] When using a TAA-type cation exchange resin, the purification apparatus according to the present invention may also have the following ion exchange units.

[0069] A regenerant containing tetraalkylammonium ions is passed into a container filled with hydrogen ion-type cation exchange resin, thereby converting the hydrogen ion-type cation exchange resin into an ion exchange unit of tetraalkylammonium ion-type cation exchange resin.

[0070] Furthermore, the TAA-type cation exchange resin obtained through this ion exchange unit can be used as the cation exchange resin in the impurity removal unit. Additionally, the details of the ion exchange unit are the same as those described for the ion exchange step in the purification method according to the present invention.

[0071] When using an H-type cation exchange resin, the purification apparatus according to the present invention may also include a neutralization unit that neutralizes the effluent obtained in the impurity removal unit. Details of this neutralization unit are the same as those described for the neutralization step in the purification method according to the present invention described above.

[0072] Furthermore, the purification apparatus according to the present invention may include a regeneration unit that regenerates the cation exchange resin that is in contact with the liquid being treated in the impurity removal unit. Details of this regeneration unit are the same as those described for the regeneration step in the purification method according to the present invention.

[0073] Figure 1 This is a schematic diagram illustrating an example of a purification apparatus that uses a cation exchange resin adjusted to the TAA type by an aqueous TAAH solution to purify the treated liquid. Additionally, in Figure 1The example shown illustrates the use of an adsorption tower as a container for filling cation exchange resin, but the container is not limited to an adsorption tower. First, as an ion exchange unit, a regenerant containing TAA ions (e.g., an aqueous solution of TAAH) is passed from storage tank 3 to adsorption tower 1 filled with H-type cation exchange resin, and the effluent is recovered from waste line 10. Then, as an impurity removal unit, a treated liquid containing TAA ions and metal impurities is passed from storage tank 2 to the adsorption tower 1, and the effluent with reduced metal impurity content in the treated liquid is recovered to storage tank 5. Here, as... Figure 1 As shown, the solutions in storage tanks 2, 3 and 4 can be pumped to adsorption tower 1 by pump 6 according to each solution, or they can be pumped to adsorption tower 1 by switching using a valve.

[0074] The resin in the purified adsorption tower 1 can be reused by cleaning / regenerating it as follows: After flushing the resin in the adsorption tower 1 with ultrapure water (or pure water) through the ultrapure water (or pure water) line 7, an acid such as hydrochloric acid is flushed through the storage tank 4 to remove metal impurities and TAA ions adsorbed on the resin, making the resin H-type. Next, a regenerator containing TAA ions (e.g., a TAAH aqueous solution) (equivalent to an ion exchange unit) is flushed through the storage tank 3, thereby regenerating it as a TAA-type cation exchange resin. The regenerated TAA-type cation exchange resin can be reused as a TAA-type cation exchange resin in the impurity removal unit. Alternatively, after flushing the resin in the purified adsorption tower 1 with ultrapure water (or pure water) through the ultrapure water (or pure water) line 7, it can be directly reused as a TAA-type cation exchange resin in the impurity removal unit. However, as with the latter method, if the resin is directly reused in the impurity removal unit without hydrochloric acid flushing, metallic impurities that cannot be completely washed away by TAAH will remain in the resin. Therefore, the former regeneration method, which involves periodic hydrochloric acid flushing, is preferred. Furthermore, the waste liquid used for cleaning is discharged according to its type based on the values ​​measured by pH meter 8 and conductivity meter 9.

[0075] Figure 2 This is a schematic diagram illustrating an example of a purification apparatus that uses an H-type cation exchange resin to purify the treated liquid. Additionally, in Figure 2An example of using an adsorption tower as a container for filling cation exchange resin is shown, but the container is not limited to an adsorption tower. First, as an impurity removal unit, the liquid to be treated, containing TAA ions and metal impurities, is passed from storage tank 12 to adsorption tower 11 filled with H-type cation exchange resin, and the effluent is recovered into storage tank 14. The resulting effluent is strongly acidic, and can therefore be neutralized as needed. Specifically, an aqueous solution containing an alkaline substance (e.g., TAAH) is passed from storage tank 13 to storage tank 14 for neutralization. Here, in the initial stage of the liquid being treated in the impurity removal process, hydrogen ions in the H-type cation exchange resin undergo ion exchange with TAA ions and metal ions, causing a sharp drop in the pH of the effluent. Therefore, if the strongly acidic solution flowing out in the initial stage of the flow is mixed with the subsequent effluent in storage tank 14, the amount of alkalinity required for neutralization increases, which is therefore undesirable. Therefore, it is preferable to check the pH of the effluent at the initial stage of the flow by installing a pH meter 17 in front of the waste liquid line 19, and discharge the strongly acidic effluent from the waste liquid line 19 in front of the storage tank 14. Furthermore, a pH meter 17 is also installed in the storage tank 14 to adjust the pH of the final effluent. After repeated impurity removal processes, the effluent (neutralized as needed) is then passed from the storage tank 14 to the adsorption tower 11, and the effluent is returned to the storage tank 14.

[0076] The resin in the purified adsorption tower 11 can be reused by cleaning / regenerating it as follows: After cleaning the resin in the adsorption tower 11 with ultrapure water (or pure water) through the ultrapure water (or pure water) line 16, the effluent recovered in the storage tank 14 is passed back to the adsorption tower 11, thereby regenerating it as a TAA-type cation exchange resin. Alternatively, after cleaning the resin in the adsorption tower 11 with ultrapure water (or pure water) through the ultrapure water (or pure water) line 16, a TAAH aqueous solution is passed through the storage tank 13, thereby regenerating it as a TAA-type cation exchange resin. The regenerated TAA-type cation exchange resin can then be reused as a TAA-type cation exchange resin in the impurity removal unit. Furthermore, while the former method reduces the amount of reagent used, it is inefficient in converting the resin to the TAA form, considering the pH of the effluent. Therefore, from the viewpoint of conversion efficiency to the TAA form of the resin, the latter method is preferred. Furthermore, since metallic impurities that cannot be completely removed using TAAH remain in the resin, therefore, as per [the relevant regulations]... Figure 1 As described in the purification apparatus, it is preferable to periodically combine the regeneration methods for hydrochloric acid (not shown) circulating solution.

[0077] The purification apparatus according to the present invention can also use anion exchange resin and a particulate removal filter in combination. When combining them, the container filled with anion exchange resin can be placed before or after the container filled with cation exchange resin, or the ion exchange resins of both can be mixed and filled into the same container. Furthermore, the container filled with anion exchange resin is preferably placed before the storage tank 5 or storage tank 14. In addition, the particulate removal filter is preferably provided between the container filled with cation exchange resin and / or anion exchange resin and the storage tank 5 or storage tank 14. Moreover, known filters can be appropriately selected as the anion exchange resin and the particulate removal filter, but the anion exchange resin is preferably converted to the C1 type.

[0078] <Recovery Method of Tetraalkylammonium Salt Aqueous Solution>

[0079] As described above, the purification method of the present invention is a method for reducing the content of metal impurities in a treated liquid containing tetraalkylammonium ions and metal impurities. However, the present invention can also be described as a method for recovering purified tetraalkylammonium salt aqueous solution from a treated liquid by reducing the content of metal impurities in the treated liquid containing tetraalkylammonium ions and metal impurities. That is, the treated liquid purified by the purification method of the present invention is a recovered tetraalkylammonium salt aqueous solution. Moreover, by contacting the tetraalkylammonium salt aqueous solution, for example, with an anion exchange resin or by electrolysis, a high-purity TAAH solution can be obtained.

[0080] The method for recovering tetraalkylammonium salt aqueous solution according to this invention is a method for recovering tetraalkylammonium salt aqueous solution from a treated liquid. It includes an impurity removal step in which the treated liquid containing tetraalkylammonium ions and metal impurities is passed through a container filled with a hydrogen ion-type or tetraalkylammonium ion-type cation exchange resin, thereby reducing the content of the metal impurities in the treated liquid. The method for recovering tetraalkylammonium salt aqueous solution is characterized by a crosslinking degree of 16-24% for the cation exchange resin. The detailed description of the method for recovering tetraalkylammonium salt aqueous solution according to this invention is the same as that of the purification method according to this invention, and therefore, the description is omitted.

[0081] <Recovery device for tetraalkylammonium salt aqueous solution>

[0082] As described above, the purification apparatus of the present invention is an apparatus for reducing the content of metal impurities in a treated liquid containing tetraalkylammonium ions and metal impurities. However, the present invention can also be described as an apparatus for recovering purified tetraalkylammonium salt aqueous solution from a treated liquid by reducing the content of metal impurities in the treated liquid containing tetraalkylammonium ions and metal impurities. That is, the treated liquid purified by the purification apparatus of the present invention is a recovered tetraalkylammonium salt aqueous solution. Moreover, by contacting or electrolyzing the tetraalkylammonium salt aqueous solution with an anion exchange resin as described above, a high-purity TAAH solution can be obtained.

[0083] The tetraalkylammonium salt aqueous solution recovery device involved in this invention is a device for recovering tetraalkylammonium salt aqueous solution from the treated liquid. It includes an impurity removal unit that passes the treated liquid containing tetraalkylammonium ions and metal impurities through a container filled with a hydrogen ion-type or tetraalkylammonium ion-type cation exchange resin, thereby reducing the content of the metal impurities in the treated liquid. The tetraalkylammonium salt aqueous solution recovery device is characterized by a crosslinking degree of 16-24% for the cation exchange resin. The detailed description of the tetraalkylammonium salt aqueous solution recovery device involved in this invention is the same as that described above for the purification device involved in this invention, and therefore, the description is omitted.

[0084] The present invention will be specifically described below through examples.

[0085] Example

[0086] Na, Mg, K, and Ca were added as metallic impurities to 1000 ml of a 10% (w / w) tetramethylammonium chloride (TMAC) aqueous solution, followed by the addition of an appropriate amount of a 25% (w / w) tetramethylammonium hydroxide (TMAH) aqueous solution, to prepare a treatment solution with a pH of 8–10. Furthermore, the amount of each metallic impurity added was approximately the same as the amount of metallic impurities contained in actual photoresist developing waste liquid.

[0087] [Example 1]

[0088] (Ion exchange process)

[0089] This embodiment was tested using a batch method. 10 ml of AMBERJET 1060H (trade name, manufactured by Organo Corporation, degree of crosslinking: 16%) was added to a 200 ml beaker made of PFA as a strong acidic cation exchange resin of type H. 100 ml of a 2.4% by mass TMAH aqueous solution was added as a regenerant containing tetraalkylammonium ions. The beaker was rotated and stirred every 15 minutes, and the resin was impregnated for a total of 1 hour. The supernatant was removed until no more resin flowed out. After repeating this operation twice, the process of adding 100 ml of ultrapure water (UPW), gently stirring, and removing the supernatant was repeated three times to remove residual TMAH through washing.

[0090] (Impurity removal process)

[0091] After removing the ultrapure water used for cleaning in the ion exchange process to the limit of the resin surface, add 100 ml of the above-prepared treatment solution, rotate the beaker and stir every 15 minutes, and immerse the resin for a total of 30 minutes.

[0092] (Measuring metal concentration and pH)

[0093] The supernatant after impregnation was collected, and the pH and metal concentration were measured. pH was measured using a portable multi-functional water quality meter (trade name: MM42-DP, manufactured by Toa DKK Corporation). Metal concentration was measured using an Agilent 8900 triple quadrupole ICP-MS (trade name, manufactured by Agilent Technologies Corporation). Table 1 shows the percentage reduction (%) of each metal impurity concentration in the purified treated liquid relative to the unpurified treated liquid, as well as the pH value of the purified treated liquid. Additionally, the characteristic values ​​of the cation exchange resin in Table 1 are the manufacturer's catalog values.

[0094] [Example 2]

[0095] As the H-type strongly acidic cation exchange resin, AMBERLITE (registered trademark) IRN99H (trade name, manufactured by DuPont, degree of crosslinking: 16%) was used. Except for this, the ion exchange process and impurity removal process were performed in the same manner as in Example 1, and the pH and metal concentration were measured in the same manner as in Example 1. The results are shown in Table 1.

[0096] [Table 1]

[0097]

[0098] In Examples 1 and 2, experiments were conducted using the same volume of cation exchange resin with the same degree of crosslinking and the same regeneration dosage. As shown in Table 1, the pH of the purified treated solution was strongly acidic (1) in Example 1 and weakly acidic (4) in Example 2. This is because the AMBERLITE IRN99H used in Example 2 has a smaller particle size and larger surface area compared to the AMBERJET 1060H used in Example 1. Specifically, it is believed that the former is more easily converted to the TMA type during the ion exchange process, resulting in less residual H-type resin. Consequently, the initial pH fluctuation caused by hydrogen ion efflux is suppressed during the impurity removal process. Furthermore, it is also observed that Example 2, using resin with a smaller particle size, exhibits higher performance in removing metal impurities compared to Example 1.

[0099] [Example 3]

[0100] This embodiment was tested using the column method (see reference). Figure 1 As a strongly acidic cation exchange resin of type H, 36 ml of AMBERLITE (registered trademark) IRN99H (trade name, manufactured by DuPont, degree of crosslinking: 16%) was added to an adsorption tower (φ19 mm, length 300 mm PFA column), and the resin was converted to TMA type by passing a 2.5% by mass TMAH aqueous solution (ion exchange step). Next, 30 BV of the treated liquid used in Example 1 was passed through the TMA-type resin at a rate of 5 times the resin volume per hour (impurity removal step). BV (Bed volume) represents the flow rate multiple relative to the resin volume. The pH and metal concentration of the resulting effluent were measured in the same manner as in Example 1. The results are shown in Table 2.

[0101] [Example 4]

[0102] This embodiment was tested using the column method (see reference). Figure 2 As the H-type strongly acidic cation exchange resin, AMBERLITE (registered trademark) IRN99H (trade name, manufactured by DuPont, degree of crosslinking: 16%) was used, as in Example 3. 36 ml of the H-type resin (not converted to TMA type) was added to the same adsorption tower as in Example 3, and 30 BV of the liquid to be treated used in Example 1 was passed through at a rate of 5 times the resin volume per hour (impurity removal step). The pH and metal concentration of the resulting effluent were measured, as in Example 1. The results are shown in Table 2.

[0103] [Table 2]

[0104]

[0105] As shown in Table 2, in the impurity removal process, in Example 3, which used a TMA-type cation exchange resin, and in Example 4, which used an H-type cation exchange resin, the content of metal impurities was significantly reduced. In particular, in Example 3, where the resin was pre-converted to TMA type before the treated liquid was passed through in the ion exchange process, the pH fluctuation was less during the impurity removal process because the metal impurities underwent ion exchange with the TMA. Furthermore, Example 3 also showed better results than Example 4 regarding Na removal performance.

[0106] Furthermore, if the results of Examples 1 and 2 are compared with those of Examples 3 and 4, the latter shows higher performance in removing metal impurities and less pH variation. However, this is because column purification is generally more efficient than batch purification.

[0107] [Examples 5-6, Comparative Examples 1-2]

[0108] (Measurement of perfect sphericity)

[0109] In a 200ml beaker prepared with PFA, 5ml of the H-type cation exchange resin shown in Table 3 was added. 50ml of a 25% (w / w) TMAH aqueous solution was added as a regenerator containing tetraalkylammonium ions, and the mixture was stirred and soaked for two hours. Afterward, the supernatant was removed, and the resin in the beaker was washed three times (totaling 150ml) with ultrapure water. This step is equivalent to the ion exchange step of the present invention, and is performed to confirm the presence or absence of resin breakage under conditions where the TMAH concentration is higher than usual. The perfect sphericity of the obtained resin was measured using the following method.

[0110] Using a microscope (trade name: digital microscope, manufactured by KEYENCE Co., Ltd.), observe 500 resin samples and calculate the ratio of perfectly spherical solids to all observed solids using the following formula (percentage of perfect sphericity).

[0111] Perfect sphericity (%) = ((500 - number of solids with cracks or gaps) / 500) × 100

[0112] The results and degree of crosslinking are shown in Table 3. In addition, in Table 3, AMBERLYST (registered trademark) 16WET (trade name) used in Comparative Example 1 and AMBERLITE (registered trademark) IRN97H (trade name) used in Comparative Example 2 were both manufactured by DuPont.

[0113] [Table 3]

[0114]

[0115] As shown in Table 3, Examples 5 and 6, which use highly cross-linked, strongly acidic cation exchange resins, exhibit a high complete sphericity. That is, it can be seen that these resins are difficult to crack or fissure even in TMAH aqueous solutions with high TMA ion concentrations, and the resins are difficult to break even when repeatedly used in ion exchange processes, impurity removal processes, etc.

[0116] On the other hand, Comparative Examples 1 and 2, which used resins with a crosslinking degree lower than that specified in this invention, had a complete sphericity of 91-98%. It is evident that these resins, compared to the resins used in the examples, are more prone to cracking due to repeated use, and the damage to the ion exchange resin matrix is ​​more easily exacerbated.

[0117] Explanation of reference numerals in the attached figures

[0118] 1: Adsorption tower

[0119] 2: Storage tank (for the liquid being treated)

[0120] 3: Storage tank (TAAH)

[0121] 4: Storage tank (acid)

[0122] 5: Storage tank (outflow liquid)

[0123] 6: Pump

[0124] 7: Ultrapure water pipeline

[0125] 8: pH meter

[0126] 9: Conductivity meter

[0127] 10: Waste liquid pipeline

[0128] 11: Adsorption Tower

[0129] 12: Storage tank (for the liquid being treated)

[0130] 13: Storage Tank (TAAH)

[0131] 14: Storage tank (outflow liquid)

[0132] 15: Pump

[0133] 16: Ultrapure water pipeline

[0134] 17: pH meter

[0135] 18: Conductivity meter

[0136] 19: Waste liquid pipeline.

Claims

1. A method for purifying a liquid to be treated, characterized in that, The purification method for the treated liquid includes an impurity removal step, in which the treated liquid containing tetraalkylammonium ions and metal impurities is passed through a container filled with a strong acidic cation exchange resin of hydrogen ion type or tetraalkylammonium ion type, thereby reducing the content of the metal impurities in the treated liquid. The degree of crosslinking of the strong acid cation exchange resin is 16-24%, and the exchange capacity of the strong acid cation exchange resin in the hydrogen ion form is 2.4 eq / LR or higher.

2. The purification method for the treated liquid according to claim 1, wherein, The strongly acidic cation exchange resin is a tetraalkylammonium ionic resin. The refining method further includes an ion exchange step before the impurity removal step. In this ion exchange step, a regenerant containing tetraalkylammonium ions is passed into a container filled with a hydrogen ion-type strong acid cation exchange resin, thereby converting the hydrogen ion-type strong acid cation exchange resin into a tetraalkylammonium ion-type strong acid cation exchange resin. In the purification method of the liquid being treated, the tetraalkylammonium ion-type strong acid cation exchange resin obtained in the ion exchange step is used in the impurity removal step.

3. The method for purifying the liquid to be treated according to claim 1 or 2, wherein, The particle size, i.e. the adjusted average diameter, of the strongly acidic cation exchange resin is 500–560 μm in the hydrogen ion form.

4. The method for purifying the liquid to be treated according to claim 1 or 2, wherein, The purification method for the treated liquid further includes a regeneration step, in which the strongly acidic cation exchange resin that came into contact with the treated liquid in the impurity removal step is regenerated.

5. The method for purifying the liquid to be treated according to claim 1 or 2, wherein, The liquid being treated is a solution derived from waste liquid discharged during the photoresist developing process.

6. A purification apparatus for a liquid being processed, characterized in that, The purification apparatus for the treated liquid includes an impurity removal unit. This unit passes the treated liquid, containing tetraalkylammonium ions and metallic impurities, through a container filled with a strong acidic cation exchange resin of hydrogen ion type or tetraalkylammonium ion type, thereby reducing the content of the metallic impurities in the treated liquid. The degree of crosslinking of the strong acid cation exchange resin is 16-24%, and the exchange capacity of the strong acid cation exchange resin in the hydrogen ion form is 2.4 eq / LR or higher.

7. The purification apparatus for the liquid to be treated according to claim 6, wherein, The strongly acidic cation exchange resin is a tetraalkylammonium ionic resin. The refining apparatus also includes an ion exchange unit that passes a regenerant containing tetraalkylammonium ions into a container filled with a hydrogen ion-type strong acid cation exchange resin, thereby converting the hydrogen ion-type strong acid cation exchange resin into a tetraalkylammonium ion-type strong acid cation exchange resin. The purification apparatus for the treated liquid uses a tetraalkylammonium ion-type strong acid cation exchange resin obtained from the ion exchange unit for the impurity removal unit.

8. The purification apparatus for the liquid to be treated according to claim 6 or 7, wherein, The particle size, i.e. the adjusted average diameter, of the strongly acidic cation exchange resin is 500–560 μm in the hydrogen ion form.

9. A method for recovering an aqueous solution of a tetraalkylammonium salt from a treated liquid, characterized in that, The method for recovering the tetraalkylammonium salt aqueous solution from the treated liquid includes an impurity removal step. In this step, the treated liquid containing tetraalkylammonium ions and metal impurities is passed through a container filled with a strong acidic cation exchange resin of hydrogen ion type or tetraalkylammonium ion type, thereby reducing the content of the metal impurities in the treated liquid. The degree of crosslinking of the strong acid cation exchange resin is 16-24%, and the exchange capacity of the strong acid cation exchange resin in the hydrogen ion form is 2.4 eq / LR or higher.

10. A recovery device for an aqueous solution of a tetraalkylammonium salt from a treated liquid, characterized in that, The recovery device for the tetraalkylammonium salt aqueous solution from the treated liquid includes an impurity removal unit. This unit passes the treated liquid containing tetraalkylammonium ions and metal impurities through a container filled with a strong acidic cation exchange resin of hydrogen ion type or tetraalkylammonium ion type, thereby reducing the content of the metal impurities in the treated liquid. The degree of crosslinking of the strong acid cation exchange resin is 16-24%, and the exchange capacity of the strong acid cation exchange resin in the hydrogen ion form is 2.4 eq / LR or higher.

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