JP2009166045A - Separation tower of mixed ion-exchange resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separation tower for efficiently separating a cation exchange resin from an anion exchange resin used for a mixed bed ion-exchange tower. <P>SOLUTION: The separation tower of a mixed ion-exchange resin comprising a cation exchange resin and an anion exchange resin is intended for separating it via stratification into a cation exchange resin and an anion exchange resin via backwash, wherein an upper resin collector and a lower resin collector are internally provided via a calculated separation boundary between the cation exchange resin and the anion exchange resin after separation by stratification, a resin extracting nozzle is provided between the upper resin collector and the lower resin collector, and the lower resin collector is provided so that switching from the supply of transfer water into the tower to the extraction of resins can be performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a separation column of a mixed ion exchange resin for separating and regenerating a cation exchange resin and an anion exchange resin having a reduced function which are used in a mixed state, and a mixed ion exchange resin using the separation column. It relates to a separation method.

  Supercritical pressure boilers, nuclear power generation and semiconductor manufacturing require extremely pure water. 2. Description of the Related Art Conventionally, a mixed bed type pure water production apparatus that uses a cation exchange resin and an anion exchange resin in a mixed state has been widely adopted as an apparatus for producing high purity pure water. In this apparatus, when the capacity of the ion exchange resin is reduced due to use, it is necessary to regenerate these resins. For regeneration, these resins are first transferred to a separation tower. Therefore, in the separation tower, so-called backwash water flows in from the bottom of the mixed ion exchange resin layer, and the cation exchange resin layer and the anion exchange resin are utilized by utilizing the difference in specific gravity between the cation exchange resin and the anion exchange resin. A backwashing separation process is performed in which the layers are separated into layers.

  Next, after the calming step following backwashing, the cation exchange resin layer and the anion exchange resin layer separated by stratification are separated by taking them out of the system as necessary, and regenerated with a regenerant. Perform the process. Both the regenerated and washed ion exchange resins are returned to the ion exchange device, and again subjected to pure water production through a mixing step. In the calming step after the backwash separation step, most of the cation exchange resin is separated into the lower layer and the anion exchange resin is separated into the upper layer, but it is difficult to completely separate both ion exchange resins. Near the boundary surface of the ion exchange resin layer, a mixed resin layer in which a cation exchange resin and an anion exchange resin are mixed is inevitably generated.

Therefore, in the conventional method, when each ion exchange resin layer is separated and taken out, a part of the mixed resin layer is accompanied by each ion exchange resin layer, so that the regeneration step, that is, regeneration of the anion exchange resin is performed. Then, the accompanying cation exchange resin is brought into Na form upon contact with an anion exchange resin regenerant, for example, an aqueous solution of sodium hydroxide, whereas the accompanying anion exchange resin is regenerated of the cation exchange resin. It is inevitable that a so-called reverse regeneration phenomenon occurs in the SO ₄ form upon contact with an agent such as sulfuric acid. Thus, in order to produce high purity pure water using both regenerated resins, all cation exchange resins must be in the H form and all anion exchange resins must be in the OH form. Entrainment of the mixed resin layer is extremely inconvenient.

  In order to eliminate such inconvenience due to the mixed resin layer, two resin extraction collectors are provided at the upper and lower portions near the boundary surface between the two ion exchange resin layers after the stratification separation, and the anion exchange resin layer is located at the upper part. The resin collector and the mixed resin layer are separated from the system by the lower resin collector, and separated into a cation exchange resin layer, an anion exchange resin layer, and a mixed resin layer. Only the separated cation and anion exchange resin layers are separated. Has been proposed (Japanese Patent Laid-Open No. 56-38136). According to this method, most of the mixed resin layer can be taken out by the lower resin collector, but a small amount of anion exchange resin is still on the surface of the cation exchange resin layer in contact with the mixed resin layer. Therefore, when this cation exchange resin is recycled, there is a problem that high-purity pure water cannot be stably obtained. When extracting the mixed resin layer from the lower resin collector, a part of the cation exchange resin layer in the vicinity of the mixed resin layer can be removed in a larger amount to avoid the problem of anion exchange resin to the cation exchange resin. However, it is not preferable because it is economically disadvantageous, such as an increase in the amount of resin that is subsequently separated and regenerated.

JP 56-38136 A

  In order to solve the above problems, the present inventors made extensive studies on the state of the anion / cation exchange resin layer in the stratified separation of the mixed ion exchange resin, and as a result, mixed after the stratified separation by back washing of the mixed ion exchange resin. Inside the resin layer, the cation exchange resin and the anion exchange resin are unclear, but a boundary surface is formed. The resin layer has a two-layer structure consisting of a layer rich in cation exchange resin and a layer rich in anion exchange resin. When the mixed resin layer is extracted with the lower collector, the anion exchange resin of the layer rich in the anion exchange resin is extracted in the order of the layer rich in the cation exchange resin and then the layer rich in the anion exchange resin. The inventors have found that the surface of the ion exchange resin layer remains in the form of repose angles and have reached the present invention.

The present invention relates to an efficient separation tower for a mixed ion exchange resin for use in desalination treatment and the like for stratified separation of a mixed ion exchange resin having a reduced function by backwashing and subjecting it to a regeneration treatment, and the separation tower. The present invention provides a method for separating the mixed ion exchange resin used. That is, the first gist of the present invention is a separation tower that stratifies and separates a mixed ion exchange resin composed of a cation exchange resin and an anion exchange resin by backwashing, and the anion after stratification separation is placed in the tower. is internally provided upper resin collector and lower resin collector through a calculation separation boundary surface between the exchange resin layer and a cation-exchange resin layer, the resin extraction nozzles are disposed and between the upper resin collector and lower resin collector, also The lower resin collector is a mixed ion-exchange resin separation tower characterized in that it can be switched between supply of the transfer water into the tower and extraction of the resin.

The second gist of the present invention is a separation column in which mixed ion exchange resins composed of a cation exchange resin and an anion exchange resin are stratified and separated from each other by backwashing, and the anion exchange resin after stratified separation in the column The upper resin collector and the lower resin collector are provided through the separation tower wall through the calculated separation interface between the layer and the cation exchange resin layer, and a resin extraction nozzle is installed between the upper resin collector and the lower resin collector. The upper resin collector and the lower resin collector are present in a mixed ion exchange resin separation tower having a plurality of resin extraction holes.

  The third gist of the present invention is a separation tower for stratifying and separating mixed ion exchange resins composed of a cation exchange resin and an anion exchange resin from each other by backwashing. In the tower, an anion exchange resin layer, a cation exchange resin layer, Upper resin collector that is an anion exchange resin extraction tube through the calculated separation interface after stratified separation into an ion exchange resin layer and a mixed resin layer including a calculated separation interface between the anion exchange resin layer and the cation exchange resin layer And a resin extraction nozzle for extracting a part of the mixed resin between the upper resin collector and the lower resin collector. And the upper resin collector and the lower resin collector have a plurality of resin extraction holes and are provided through the separation tower wall. It resides in the fat of the separation column.

  The fourth gist of the present invention is a separation tower that stratifies and separates mixed ion exchange resins composed of a cation exchange resin and an anion exchange resin by backwashing, and the anion exchange resin after stratified separation in the tower An upper resin collector and a lower resin collector are provided in the vicinity of the calculated separation interface between the upper layer and the cation exchange resin layer, and a resin extraction nozzle is provided between the upper resin collector and the lower resin collector. In the method of separating a mixed ion exchange resin using an installed mixed ion exchange resin separation tower, the mixed ion exchange resin of a cation exchange resin and an anion exchange resin to be separated transferred to the tower After introducing backwash water from the lower water collection pipe provided at the bottom of the tower to flow and develop the mixed ion exchange resin, the introduction of the backwash water is stopped and allowed to stand, and the anion exchange resin layer and the mixing A first step of stratifying and separating the ion exchange resin layer and the cation exchange resin layer, introducing transfer water or pressurized air from an upper water collecting pipe provided at the top of the tower, and then removing the anion exchange resin layer from the upper resin collector The second step of extracting, closing the upper resin collector, introducing transfer water from the lower resin collector and flowing the mixed resin layer, introducing transfer water or pressurized air from the upper water collecting pipe, The third step of extracting the upper layer portion of the mixed resin layer from the resin extraction nozzle provided between them, the introduction of the transfer water from the lower resin collector is stopped, and further the resin extraction nozzle is closed and the transfer water or pressurized from the upper water collecting pipe A method for separating a mixed ion exchange resin comprising sequentially performing a fourth step of removing a lower layer portion of the mixed resin from a lower resin collector while introducing air. That.

  As a preferred embodiment of the present invention, the resin extraction nozzle of the separation tower is positioned so that the lowest end position of the inner surface of the nozzle is located at or slightly below the calculated separation interface between the anion exchange resin layer and the cation exchange resin layer separated by stratification. The upper resin collector is installed in an anion exchange resin layer approximately 100 to 500 mm above the calculated separation interface between the anion exchange resin layer and the cation exchange resin layer separated by stratification. The resin collector is installed in the cation exchange resin layer about 50 to 300 mm below the calculated separation interface between the anion exchange resin layer and the cation exchange resin layer separated by stratification, the upper resin collector and the lower resin collector. Is provided through the separation tower wall and has a plurality of resin extraction holes, and the mixed ion exchange resin is used for the desalting treatment. It can indicate separation column of the mixed ion exchange resin consisting Rukoto.

  When the separation tower of the present invention is employed, the anion exchange resin does not remain on the surface of the cation exchange resin when the anion / cation exchange resin is separated from the mixed ion exchange resin. It can be separated into an ion exchange resin and an anion exchange resin.

It is the longitudinal cross-sectional schematic for demonstrating the embodiment of the separation column of the mixed ion exchange resin of this invention. It is a longitudinal section schematic diagram showing an example of an embodiment of a resin extraction nozzle of the present invention. It is a longitudinal section schematic diagram showing an example of an embodiment of a resin extraction nozzle of the present invention. It is the longitudinal cross-sectional schematic (FIG. 4A) which shows an example of embodiment of the upper part of this invention, and a lower resin collector (FIG. 4A), and a plane schematic (FIG. 4B). It is the longitudinal cross-sectional schematic diagram (FIG. 5A) which shows an example of embodiment of the upper part of this invention, and a lower resin collector (FIG. 5A), and a plane schematic diagram (FIG. 5B).

  The separation tower of the mixed ion exchange resin of the present invention is used in a mixed bed type pure water production apparatus adopted for supercritical boilers, condensate desalination treatment of nuclear power generation, or production of ultrapure water, etc. This is used for mutual separation of the mixed resins when the mixed ion exchange resin is regenerated. The cation exchange resin of the mixed ion exchange resin applied to the separation tower of the present invention is specifically a strongly acidic cation exchange resin, such as Diaion PK228, PK216, SK1B, SK110, SK112 (trade name: Mitsubishi). The anion exchange resin is a strongly basic anion exchange resin such as Diaion PA312, PA316, SA10A, SA11A, SA12A (trade name: Mitsubishi Chemical Corporation). )) And other commercial products. [Diaion is a registered trademark of Mitsubishi Chemical Corporation. ]

  Next, a method for separating the mixed ion exchange resin by using the mixed ion exchange resin separation tower and the separation tower of the present invention will be described with reference to FIG. FIG. 1 is an example of a schematic vertical cross-sectional view schematically showing a state after the mixed ion exchange resin is stratified and separated by backwashing in the separation tower of the present invention. In the figure, 1 is a separation column, 2 is a mixed ion exchange resin introduction tube, 3 is an anion exchange resin layer, 4 is a cation exchange resin layer, 5 is a mixed resin layer, and 6 is an anion exchange resin layer and a cation. Separation interface with the exchange resin layer, 7 is an upper resin collector, 8 is a lower resin collector, 9 is a mixed resin extraction nozzle, 10 is a cation exchange resin extraction pipe, 11 is an upper water collection pipe, and 12 is a lower water collection pipe .

  In the separation tower of the present invention, the upper resin collector 7 is an anion exchange resin extraction pipe, and the installation position is within the anion exchange resin layer 3 after stratified separation and from the viewpoint of effective use of the anion exchange resin. Is preferably the lower layer of the resin layer. However, in order to prevent contamination of the cation exchange resin, the separation interface between the calculated cation exchange resin layer and the anion exchange resin layer calculated from the amount of anion / cation exchange resin introduced into the separation column It is preferably provided at a position of about 100 to 500 mm above.

  In addition, the lower resin collector 8 is a part extraction pipe for the mixed resin layer, and at the same time, a supply pipe for transporting water when the upper layer part of the mixed resin layer is extracted. Therefore, in the extraction of the mixed resin layer, the installation position is preferably as close as possible to the inside of the cation exchange resin layer 4 and the upper part of the cation exchange resin layer, but the mixed resin layer is fluidized to extract the mixed resin. Since transfer water for efficiently extracting from the nozzle 9 is introduced, it is preferably provided at a position of about 50 to 300 mm below the calculated separation interface. The shape of each resin collector is not particularly limited, but preferably has a plurality of resin extraction holes, for example, a single extraction pipe having a plurality of resin extraction holes at appropriate intervals, or a single extraction collecting pipe A plurality of branch pipes are provided, and each branch pipe is provided with a plurality of resin extraction holes at appropriate intervals. These resin collectors are installed through the tower wall. 4A, 4B, 5A, and 5B show schematic views of the upper and lower resin collectors.

  Further, in the separation tower of the present invention, it is essential to provide a resin extraction nozzle 9 for extracting the mixed resin between the upper and lower resin collectors. The resin extraction nozzle 9 is installed near the calculated separation boundary surface, preferably at a position slightly below the separation boundary surface or the separation interface. 2 and 3 are schematic sectional views of an example of mounting the resin extraction nozzle 9, but it may be installed in the tower wall as shown in FIG. 2, or as a collector as shown in FIG. Also good. In this case, it is preferable that the lowermost end of the inner surface of the nozzle and the lowermost end of the collector hole be located at a position corresponding to the calculated separation interface between the two resin layers.

  Next, a method for separating the mixed ion exchange resin using the separation tower of the present invention will be described with reference to FIG. First, the mixed ion exchange resin used in the mixed bed pure water production apparatus and the mixed resin separately stored in the intermediate resin storage tank are introduced into the separation tower 1 through the introduction pipe 2 together with the transfer water. Next, the mixed ion exchange resin is fluidly developed while flowing backwash water from the lower water collecting pipe 12 and discharging it from the upper water collecting pipe 11. After developing for a while, the first step of stopping and allowing the backwash water to flow is performed. The flowing ion exchange resin settles due to the difference in specific gravity while the anion exchange resin layer 3 on the upper part, the cation exchange resin layer 4 on the lower part, and the separation boundary surface 6 between the two ion exchange resin layers. A mixed resin layer 5 is formed. FIG. 1 shows the state at this point.

  Next, a second step of extracting the anion exchange resin layer 3 from the upper resin collector 7 by introducing transfer water or pressurized air from the upper water collecting pipe 11 is performed, and the anion exchange resin layer 3 is regenerated. It is transferred to the tower and recycled. Next, the upper resin collector 7 is closed, the transfer water or the pressurized air is introduced from the upper water collecting pipe 11 while introducing the transfer water from the lower resin collector 8 to flow the mixed resin layer 5, and both upper and lower resin collectors are introduced. The 3rd process of extracting the upper layer part of the mixed resin layer 5 from the mixed resin extraction nozzle 9 provided between these is performed. In the present invention, by supplying transport water from the lower resin collector 8, the upper layer portion of the mixed resin layer can be more efficiently removed from the mixed resin extraction nozzle 9. Next, the inflow of the transfer water from the lower resin collector 8 is stopped, the mixed resin extraction nozzle 9 is closed, and the transfer resin or pressurized air is introduced from the upper water collecting pipe 11 while the mixed resin layer 5 is introduced from the lower resin collector 8. The 4th process which takes out a lower layer part is performed.

  In the present invention, by operating in this manner, the upper layer portion of the mixed resin layer 5 which is a portion rich in anion exchange resin is removed by the nozzle 9 and then the lower layer of the mixed resin layer by the lower resin collector 8. Since the portion is taken out, the remaining anion exchange resin in the cation exchange resin layer in contact with the lower layer portion rich in the cation exchange resin can be avoided. The portion rich in anion exchange resin that is the upper layer portion of the mixed resin layer 5 taken out in the third step and the portion rich in cation exchange resin in the lower layer portion of the mixed resin layer 5 taken out in the fourth step are Then, it is transferred to the intermediate resin storage tank and stored. A pure cation exchange resin layer remains in the separation column from which the mixed resin layer has been removed. The cation exchange resin layer may be taken out by the cation exchange resin extraction tube 10 as necessary, transferred to the cation exchange resin regeneration tower and regenerated, or may be regenerated in the separation tower as it is.

  When the mixed ion exchange resin is separated by the above method, a pure anion exchange resin is usually separated in the anion exchange resin regeneration tower, and a pure cation exchange resin is separated and stored in the separation tower 1. Each of the separated ion exchange resins is regenerated using an acid or alkali regenerant, and both the regenerated resins are mixed to be supplied to a pure water production apparatus. On the other hand, the mixed resin separated by the mixed resin extraction nozzle 9 and the lower resin collector 8 and transferred to the intermediate resin storage tank is stored until the next separation of the mixed ion exchange resin in the pure water production apparatus. In this case, it is transported to the separation tower and subjected to the separation operation together. By such an operation, the mixed ion exchange resin can be separated into a pure cation exchange resin and an anion exchange resin, and the loss of the resin can be reduced.

As described above, when the separation tower of the present invention is used to separate and regenerate a mixed ion exchange resin that has been used in the production of pure water and has a reduced function, not only an anion exchange resin but also a cation exchange resin layer can be used. It is separated in a pure state without leaving an anion exchange resin on the surface layer. Accordingly, the anion exchange resin and the cation exchange resin thus obtained have high purity, and each resin is a Na-type cation exchange resin and an SO ₄ -type anion exchange resin by a regenerant during regeneration. Since it is not accompanied by generation | occurrence | production, highly purified pure water can be stably manufactured using both resin after reproduction | regeneration.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.
[Example]
In the separation tower having an inner diameter of 2100 mm and a straight barrel part height of 5800 mm shown in FIG. 1, a lower resin collector is installed horizontally at a position 1480 mm above the lower resin support plate, and an upper resin collector is installed horizontally at 500 mm above the lower resin collector. A resin extraction nozzle was opened on the side wall at a position 150 mm above the collector. The inner diameter of each resin collector and nozzle is 100 mm, and the installation position is the distance from the center of the tube. The upper and lower resin collectors were provided with five branch pipes in one extraction collecting pipe, and a plurality of resin extraction holes having an inner diameter of 7 mm were formed in each branch pipe at equal intervals.

  In this separation tower, strongly acidic cation exchange resin Diaion (registered trademark) PK228, 5350 liters (volume in H form) and a strongly basic anion exchange resin diamond whose functions are reduced by the ammonia-type operation of condensate demineralization treatment. After transferring the mixed resin with ion PA 312,3150 liter (volume in OH form), the mixed resin stored in the intermediate resin storage tank [Diaion (registered trademark) PK228,550 liter (volume in H form) ), Diaion PA312, 1200 liters (volume in OH form)]. Next, backwash water was introduced from the lower water collection pipe of this separation tower at LV8 m / h, and the ion exchange resin was backwashed and separated and then settled and separated into a cation exchange resin layer, a mixed resin layer, and an anion exchange resin layer.

  Next, transfer water was introduced from the upper water collecting pipe of the separation tower at LV 9 m / h, and the anion exchange resin was extracted from the upper resin collector and transferred to the anion exchange resin regeneration tower. Next, the upper resin collector is closed, and the transfer water (LV 9 m / h) flows in from the upper water collecting pipe and the transfer water also flows in from the lower resin collector at LV 2 m / h, and the upper part of the mixed resin layer is extracted from the resin extraction nozzle. It was. After that, the nozzle was closed and the inflow of the transfer water from the lower resin collector was stopped, and the lower layer portion of the mixed resin layer was extracted from the lower resin collector while the transfer water was flowing in from the upper water collecting pipe, and was extracted from the nozzle and the lower resin collector. The mixed resin layer was transferred to an intermediate resin storage tank and stored.

  After sufficiently mixing the cation exchange resin remaining in the separation tower by the above operation, about 8 liters of this cation exchange resin was collected and packed into an acrylic column having an inner diameter of 100 mm and a height of 2000 mm. Back washing water was introduced from the bottom of the column at LV 10 m / h for 30 minutes for back washing, and the anion exchange resin laminated on the surface of the cation exchange resin layer after settling was collected and its volume was measured. Next, the volume was calculated from the layer height of the cation exchange resin remaining in the column, and the mixing ratio of the anion exchange resin to the cation exchange resin was determined. The results are shown in Table 1.

[Comparative example]
The mixed ion exchange resin was separated by a conventional method using a separation tower having the same specifications except that no nozzle was provided in the separation tower of the example. The specification conditions of the ion exchange resin and the stratification separation conditions of the mixed ion exchange resin by backwashing were the same as in the examples. The anion exchange resin was extracted from the upper resin collector in the same manner as in the example. Next, the mixed resin layer was extracted from the lower resin collector while flowing water from the upper water collecting pipe at LV9 m / h. After sufficiently mixing the cation exchange resin remaining in the separation column after the above operation, about 8 liters of this cation exchange resin was collected, and the anion exchange resin with respect to the cation exchange resin was collected by the same operation procedure as in the example. The mixing rate was determined. The results are shown in Table 1.

[Table 1]
Volume of anion exchange resin Volume of cation exchange resin Mixing rate Example 5 ml 7760 ml 0.06%
Comparative Example 68ml 7690ml 0.88%

DESCRIPTION OF SYMBOLS 1 Separation tower 2 Mixed ion exchange resin introduction pipe 3 Anion exchange resin layer 4 Cation exchange resin layer 5 Mixed resin layer 6 Separation interface 7 Upper resin collector 8 Lower resin collector 9 Mixed resin extraction nozzle 10 Cation exchange resin extraction pipe 11 Upper water collecting pipe 12 Lower water collecting pipe 13 Resin support plate 14 Resin extraction hole 15 Branch pipe

Claims (8)

A separation tower that stratifies and separates mixed ion exchange resins composed of a cation exchange resin and an anion exchange resin by backwashing, and in the tower, an anion exchange resin layer and a cation exchange resin layer after stratification separation is internally provided upper resin collector and lower resin collector through a calculation separation boundary surface, and the resin extracted nozzles are installed between the upper resin collector and lower resin collector, also transfer water to said lower resin collector in the tower The mixed ion exchange resin separation tower is provided so that the supply and the resin extraction can be switched. The mixed ion-exchange resin separation tower according to claim 1, wherein the upper resin collector and the lower resin collector of the separation tower are provided through the separation tower wall and have a plurality of resin extraction holes. A separation tower that stratifies and separates mixed ion exchange resins composed of a cation exchange resin and an anion exchange resin by backwashing, and in the tower, an anion exchange resin layer and a cation exchange resin layer after stratification separation through the calculation separation boundary plane upper resin collector and lower resin collector provided through separation column wall, resin extraction nozzles are disposed and between the upper resin collector and lower resin collector, upper resin collector and lower A separation tower for mixed ion exchange resin, wherein the resin collector has a plurality of resin extraction holes . A separation tower for stratifying and separating mixed ion exchange resins comprising a cation exchange resin and an anion exchange resin by backwashing, and an anion exchange resin layer, a cation exchange resin layer, and an anion exchange resin in the tower The upper resin collector, which is an anion exchange resin extraction pipe, and a partial extraction pipe of the mixed resin through the calculated separation interface after stratified separation into a mixed resin layer including a calculated separation interface between the layer and the cation exchange resin layer A lower resin collector that is also a supply pipe for the transfer water is installed in the tower , and a resin extraction nozzle for extracting a part of the mixed resin is installed between the upper resin collector and the lower resin collector, and the upper resin collector The mixed ion-exchange resin separation tower , wherein the lower resin collector has a plurality of resin extraction holes and is provided through the separation tower wall .   The resin extraction nozzle of the separation tower is installed such that the lowermost position of the inner surface of the nozzle is located at or slightly below the calculated separation interface between the anion exchange resin layer and the cation exchange resin layer separated by stratification. The mixed ion exchange resin separation tower according to any one of claims 1 to 4.   The upper resin collector of the separation tower is installed in an anion exchange resin layer about 100 to 500 mm above the calculated separation interface between the anion exchange resin layer and the cation exchange resin layer separated by stratification. Item 6. A separation column of a mixed ion exchange resin according to any one of Items 1 to 5.   The lower resin collector of the separation tower is installed in a cation exchange resin layer lower by about 50 to 300 mm from a calculated separation interface between the anion exchange resin layer and the cation exchange resin layer separated by stratification. Item 7. A mixed ion exchange resin separation tower according to any one of Items 1 to 6.   The mixed ion exchange resin separation tower according to any one of claims 1 to 7, wherein the mixed ion exchange resin of the separation tower is used for a desalting treatment.

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