Separation method and reuse method for used non-regenerative mixed bed ion exchange resin, and manufacturing method for single bed ion exchange resin

Abstract

The present invention provides a separation method for a used non-regenerative mixed bed ion exchange resin, with which it is possible to suppress mixing of a counterion exchange resin and the occurrence of cracks in a resin surface, and to obtain an ion exchange resin that is reusable in a wide range of applications. This separation method for a used non-regenerative mixed bed ion exchange resin includes a separation step for separating a strongly acidic cation exchange resin and a strongly basic anion exchange resin which are contained in a used non-regenerative mixed bed ion exchange resin, wherein the separation step includes: a first separation step for bringing a first solution, which is capable of converting the ionic form of at least one of the resins into a salt form, into contact with the non-regenerative mixed bed ion exchange resin; and a second separation step for bringing a second solution, which has an intermediate specific gravity between the true specific gravity of the strongly acidic cation exchange resin and the true specific gravity of the strongly basic anion exchange resin, into contact with the non-regenerative mixed bed ion exchange resin. The first solution is a dilute solution that has a lower concentration than the second solution.

Description

Method for separating and reusing used non-regenerated mixed-bed ion exchange resins and method for producing single-bed ion exchange resins

[0001] The present invention relates to a method for separating and reusing spent non-regenerated mixed bed ion exchange resins, and a method for producing single bed ion exchange resins derived from spent non-regenerated mixed bed ion exchange resins.

[0002] As methods for separating the cation exchange resin and the anion exchange resin contained in used mixed-bed ion exchange resin, the following methods have been investigated: 1. Separation by converting the ionic form of the resin, 2. Separation by performing surface treatment, and 3. Separation by specific gravity using saturated salt water (Patent Document 1).

[0003] Japanese Unexamined Patent Publication No. 51-117179

[0004] However, in the above-mentioned methods 1 and 2, the counter ion exchange resin (hereinafter also referred to as "foreign resin") is mixed into the separated ion exchange resin. In addition, in the above-mentioned method 3, cracks occur on the resin surface due to the simultaneous influence of shrinkage due to the conversion of the ionic form of the resin and shrinkage due to osmotic pressure, which limits the applications of the ion exchange resins (cation exchange resin and anion exchange resin) after separation from the mixed bed ion exchange resin.

[0005] The present invention aims to provide a method for separating used non-regenerated mixed-bed ion exchange resins, which can suppress the incorporation of counter ion exchange resins and the occurrence of cracks on the resin surface, and can produce ion exchange resins that can be reused in a wide range of applications. The present invention also aims to provide a method for recycling ion exchange resins derived from used non-regenerated mixed-bed ion exchange resins separated by the separation method. A further object of the present invention is to provide a method for producing single-bed ion exchange resins using the separation method.

[0006] The present invention provides a method for separating used non-regenerated mixed bed ion exchange resins, comprising a separation step of separating a strongly acidic cation exchange resin and a strongly basic anion exchange resin contained in the used non-regenerated mixed bed ion exchange resin, the separation step comprising: a first separation step of contacting the non-regenerated mixed bed ion exchange resin with a first solution capable of converting the ionic form of at least one of the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the non-regenerated mixed bed ion exchange resin to a salt form; and a second separation step of contacting the non-regenerated mixed bed ion exchange resin that has been subjected to the first separation step with a second solution having a specific gravity intermediate between the true specific gravity of the strongly acidic cation exchange resin and the true specific gravity of the strongly basic anion exchange resin, wherein the first solution is a dilute solution having a lower concentration than the second solution.

[0007] The present invention also relates to a method for recycling used non-regenerated mixed-bed ion exchange resins, in which the strongly acidic cation exchange resin or strongly basic anion exchange resin separated by the above-mentioned method is reused as a non-regenerated mixed-bed ion exchange resin or a single-bed ion exchange resin.

[0008] Furthermore, the present invention is a method for producing a single-bed ion exchange resin, which comprises a step of separating used non-regenerated mixed-bed ion exchange resin using the above method.

[0009] According to the present invention, it is possible to suppress the incorporation of counter ion exchange resins and the occurrence of cracks on the resin surface during separation of used non-regenerated mixed-bed ion exchange resins, and it is possible to obtain reusable ion exchange resins for a wide range of applications from used non-regenerated mixed-bed ion exchange resins. The obtained recycled ion exchange resins can be reused as non-regenerated mixed-bed ion exchange resins or single-bed ion exchange resins.

[0010] 1 is a schematic diagram illustrating a part of the technical concept according to the present invention. 2 is a photograph showing the separation state of the mixed bed ion exchange resin after (i) the first separation step and (ii) the second separation step in Example 1. 3 is a photograph showing the separation state of the mixed bed ion exchange resin after the second separation step in Comparative Example 2.

[0011] In the electronics industry, such as liquid crystal and semiconductor manufacturing, where high-purity pure water and ultrapure water are required, non-regenerative ion exchange resin devices are often installed at the end of primary water purification systems or in subsystem water purification systems to remove trace amounts of ions. While single-bed and dual-bed ion exchange resin devices are sometimes used as non-regenerative ion exchange resin devices, mixed-bed ion exchange resin devices are commonly used. In this specification, the ion exchange resins used in mixed-bed non-regenerative ion exchange resin devices, i.e., the ion exchange resins used in mixed-bed non-regenerative ion exchange resin devices, are referred to as "non-regenerative mixed-bed ion exchange resins." When reusing used non-regenerative mixed-bed ion exchange resins after use in a mixed-bed non-regenerative ion exchange resin device, it is first necessary to separate the cation exchange resin (C) from the anion exchange resin (A) contained in the used non-regenerative mixed-bed ion exchange resin. In this process of separating the cation exchange resin and the anion exchange resin, two patterns occur: (a) a pattern in which the cation exchange resin (C) and the anion exchange resin (A) cannot be completely separated, and one resin is partially contaminated with the other resin (a pattern of foreign resin contamination), and (b) a pattern in which the cation exchange resin (C) and the anion exchange resin (A) can be almost completely separated (a pattern of complete separation). The present inventors have intensively investigated methods for reusing used non-regenerated ion exchange resins that have been separated and regenerated in this manner. As a result, they have found that various operations are possible, such as reusing used non-regenerated ion exchange resins assuming the presence of foreign resin contamination (above (a)) or reusing used non-regenerated ion exchange resins assuming only slight resin contamination (a rate of foreign resin contamination less than 0.1%) and almost complete separation (above (b)). Based on these findings, they have completed a series of inventions, including the present invention.

[0012] Among these inventions, the present invention relates to a method for recycling used non-regenerated mixed-bed ion exchange resins, with the premise that the cation exchange resin and the anion exchange resin are almost completely separated. Specifically, this specification describes an invention relating to the recycling of used non-regenerated mixed-bed ion exchange resins, characterized by a method for separating the cation exchange resin and the anion exchange resin contained in the used non-regenerated mixed-bed ion exchange resin. The present invention will be described in detail below.

[0013] <Method for separating used non-regenerated mixed bed ion exchange resin> The method for separating used non-regenerated mixed bed ion exchange resin according to the present invention includes at least a separation step of separating the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the used non-regenerated mixed bed ion exchange resin.

[0014] [Non-regenerated mixed-bed ion exchange resin] As described above, a non-regenerated mixed-bed ion exchange resin is a non-regenerated ion exchange resin used in a mixed-bed state in a mixed-bed non-regenerated ion exchange resin device. Known mixed-bed ion exchange resins can be used as such non-regenerated mixed-bed ion exchange resins. Mixed-bed ion exchange resins are generally mixed-bed ion exchange resins that contain a strongly acidic H-type cation exchange resin and a strongly basic OH-type anion exchange resin. The mixed bed ion exchange resin is not particularly limited, and commercially available products such as ESP-2 (trade name, manufactured by Organo Corporation), AmberTec UP6040 H / OH (trade name, manufactured by DuPont de Nemours), DIAION SMT200L (trade name, manufactured by Mitsubishi Chemical Corporation), UltraClean UCW9966 (trade name, manufactured by Purolite), and LEWATIT UltraPure 1294MD (trade name, manufactured by Lanxess) can be used. The mixing ratio (volume ratio) of the strongly acidic cation exchange resin and the strongly basic anion exchange resin in the mixed bed ion exchange resin is not limited, and the resins can be combined in any mixing ratio. The base material of the mixed bed ion exchange resin may be either a transparent gel type having small pore diameters, a macrolitercular type (MR type) having large pore diameters, or a macroporous type (also called a porous type or a high-porous type).

[0015] [Separation Step] The separation step is a step of separating the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in a used non-regenerated mixed bed ion exchange resin after use in the purification treatment of the water to be treated. In the present invention, the separation step includes at least two steps: a first separation step and a second separation step. The first separation step is a step of contacting the used non-regenerated mixed bed ion exchange resin with a first solution capable of converting the ionic form of at least one of the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the used non-regenerated mixed bed ion exchange resin to a salt form. The second separation step is a step of contacting the non-regenerated mixed bed ion exchange resin that has been subjected to the first separation step with a second solution having a specific gravity intermediate between the true specific gravity of the strongly acidic cation exchange resin and the true specific gravity of the strongly basic anion exchange resin. The first solution is a solution having a lower concentration than the second solution (also referred to as a "dilute solution").

[0016] In the method disclosed in Patent Document 1, the cation exchange resin and the anion exchange resin are separated in one step using a separation liquid having an intermediate specific gravity between the resins. However, this conventional method of separating the resins in one step has the problem that, in addition to shrinkage due to the conversion of the ionic form of the resin, the shrinkage due to the osmotic pressure caused by the high concentration of the separation liquid is significantly affected, resulting in the occurrence of cracks (cracking or fractures) on the resin surface. According to the present invention, by providing a first separation step as a pre-step in which separation is performed using a dilute solution having a lower concentration than the separation liquid, the occurrence of cracks due to the concentration of the separation liquid can be suppressed.

[0017] (First Separation Step) In the first separation step, a first solution, which is a dilute solution capable of converting the ionic form of at least one of the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the used non-regenerated mixed bed ion exchange resin into a salt form, is brought into contact with the non-regenerated mixed bed ion exchange resin.

[0018] <First Solution> The first solution is a dilute solution having a lower concentration than the second solution described below. The state of the resin after contacting the first solution with a used non-regenerated mixed-bed ion exchange resin is affected by the flow direction of the first solution. That is, when the first solution is passed through the resin in a downward flow, the two resins do not separate at this stage (see FIG. 2(i)). On the other hand, when the first solution is passed through the resin in an upward flow, the strongly acidic cation exchange resin and the strongly basic anion exchange resin are separated to some extent. The first solution is not particularly limited as long as it is a solution (ionic solution) that can convert the ionic form of at least one of the strongly acidic cation exchange resin and the strongly basic anion exchange resin to a salt form. Examples of such first solutions include aqueous solutions such as saline, hydrochloric acid, sulfuric acid, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonium chloride aqueous solution, calcium chloride aqueous solution, sodium carbonate aqueous solution, sodium sulfate aqueous solution, sodium acetate aqueous solution, and formic acid aqueous solution. However, as mentioned above, the first solution may be any ionic solution, and is not limited thereto. When the first solution is an acid, the ionic form of the strongly basic anion exchange resin is converted to a salt form, and when the first solution is a base, the ionic form of the strongly acidic cation exchange resin is converted to a salt form. Furthermore, when the first solution is a salt, the ionic forms of both the strongly acidic cation exchange resin and the strongly basic anion exchange resin are converted to the salt form.

[0019] The first solution may be a solution of a different type from the second solution described below, or may be a solution of the same type as the second solution but with a different concentration. However, from the viewpoint of operational efficiency in carrying out the separation step, it is preferable that the first solution and the second solution be solutions of the same type. In this case, it is preferable that the first solution is an aqueous solution selected from the group consisting of saline, hydrochloric acid, and an aqueous sodium hydroxide solution.

[0020] The concentration of the first solution is not limited as long as it is lower than the concentration of the second solution. However, from the viewpoint of suppressing the occurrence of cracks on the resin surface, the concentration of the first solution is preferably, for example, less than 3N (less than 3 mol / L in the case of a sodium hydroxide aqueous solution), and more preferably 2N or less (2 mol / L or less in the case of a sodium hydroxide aqueous solution). Furthermore, the concentration of the first solution is preferably 0.1N or more (0.1 mol / L or more in the case of a sodium hydroxide aqueous solution). The concentration of the first solution or the second solution refers to the gram equivalent of the salt, acid, or base contained in each solution.

[0021] (Second Separation Step) In the second separation step, a second solution having a specific gravity intermediate between the true specific gravity of the strongly acidic cation exchange resin and the true specific gravity of the strongly basic anion exchange resin constituting the non-regenerated mixed bed ion exchange resin and having a higher concentration than the first solution is contacted with the non-regenerated mixed bed ion exchange resin that has undergone the first separation step. As shown in Figure 2 (ii), by further contacting the second solution with the non-regenerated mixed bed ion exchange resin that has undergone the first separation step, the strongly acidic cation exchange resin and the strongly basic anion exchange resin are almost completely separated through the second solution. Since the cation exchange resin usually has a higher specific gravity than the anion exchange resin, after the second separation step, the anion exchange resin (A), the second solution (B), and the cation exchange resin (C) are separated from the top in this order. As described below, the first solution passed in the previous step may be removed before the second solution is passed. When this operation is performed, the second solution (B) shown in Fig. 2(ii) contains only the second solution, whereas when this operation is not performed, the second solution (B) shown in Fig. 2(ii) contains not only the second solution but also the first solution that was previously administered.

[0022] <Second Solution> The second solution is not limited as long as it has a higher concentration than the first solution and a specific gravity intermediate between the true gravity of a strongly acidic cation exchange resin and the true gravity of a strongly basic anion exchange resin. Here, the "true specific gravity of a strongly acidic cation exchange resin" in the "intermediate specific gravity between the true gravity of a strongly acidic cation exchange resin and the true gravity of a strongly basic anion exchange resin" refers to the true specific gravity of the H-form or salt-form strongly acidic cation exchange resin after the second solution has been passed through. Furthermore, the "true specific gravity of a strongly basic anion exchange resin" refers to the true specific gravity of the OH-form or salt-form strongly basic anion exchange resin after the second solution has been passed through. In other words, the intermediate specific gravity refers to a specific gravity that is greater than the true specific gravity of the strongly basic anion exchange resin having the corresponding ionic form after the second solution has been passed through, but smaller than the true specific gravity of the strongly acidic cation exchange resin having the corresponding ionic form after the second solution has been passed through. Furthermore, the true specific gravity of the second solution (the intermediate specific gravity) is the true specific gravity of the second solution when the first solution is removed before the second solution is passed through the second solution. If the removal of the first solution is not performed, the true specific gravity is, strictly speaking, the true specific gravity of the mixed solution obtained by mixing the first and second solutions. However, even in the latter case, it is possible to make the true specific gravity of the mixed solution closer to the true specific gravity of the second solution itself by adjusting the amount of the second solution passed through the second solution. Therefore, even in the latter case, the true specific gravity of the second solution (the true specific gravity of the mixed solution) can be considered to be approximately the same as the true specific gravity of the second solution itself by appropriately adjusting the amount of the second solution passed through the second solution.

[0023] Examples of the second solution include aqueous solutions such as saline, hydrochloric acid, and sodium hydroxide solution. As described above, the second solution may be a solution of a different type from the first solution. However, from the viewpoint of operational efficiency in carrying out the separation step, it is preferable that the first solution and the second solution be the same type of solution. Furthermore, from the viewpoint of ease of handling the solvent, the second solution is preferably saline, and may be, for example, saturated saline.

[0024] The concentration of the second solution is not limited as long as it allows the intermediate specific gravity to be achieved. However, from the viewpoint of completely separating the strongly acidic cation exchange resin and the strongly basic anion exchange resin, the concentration of the second solution is preferably such that the true specific gravity is at least 0.02 g / mL higher than that of the strongly basic anion exchange resin having the corresponding ionic form and at least 0.02 g / mL lower than that of the strongly acidic cation exchange resin having the corresponding ionic form. That is, the difference between the true specific gravity of the strongly basic anion exchange resin having the corresponding ionic form and that of the second solution is preferably 0.02 g / mL or more, and the difference between the true specific gravity of the strongly acidic cation exchange resin having the corresponding ionic form and that of the second solution is preferably 0.02 g / mL or more. Furthermore, the difference between the true specific gravity of the strongly basic anion exchange resin having the corresponding ionic form and that of the second solution is preferably 0.5 g / mL or less, and more preferably 0.2 g / mL or less. Similarly, the difference between the true specific gravity of the strongly acidic cation exchange resin having the corresponding ionic form and the true specific gravity of the second solution is preferably 0.5 g / mL or less, more preferably 0.2 g / mL or less.

[0025] A method for contacting the first and second solutions with a non-regenerative mixed-bed ion exchange resin includes, for example, sequentially passing the first and second solutions through a non-regenerative mixed-bed ion exchange resin packed in an appropriate container such as an ion exchange resin tower. The method for passing each solution can be appropriately determined. The flow direction of each solution may be either upflow or downflow. However, especially when passing the second solution, passing the solution in an upflow manner is preferred from the viewpoint of efficiently separating the cation exchange resin and the anion exchange resin. The amount of the first solution passed can be, for example, an amount equal to or greater than the amount required to satisfy the exchange capacity of the strongly acidic cation exchange resin and the strongly basic anion exchange resin. After passing the first solution, the second solution may be passed subsequently. Alternatively, after passing the first solution, the first solution may be pressure-fed with a gas (such as nitrogen or air) and extracted, and then the second solution may be passed. The amount of the second solution passed through the second pipette may be, for example, an amount sufficient to separate the strongly acidic cation exchange resin from the strongly basic anion exchange resin. The second solution may be circulated as long as the concentration is maintained at a level sufficient to maintain the desired intermediate specific gravity. If the second solution is passed through the second pipette while the first solution remains, the true specific gravity of the second solution will change significantly. However, by increasing the amount of the second solution, the second solution (including the first solution) can be adjusted to the desired intermediate specific gravity. Therefore, the amount of the second solution passed through the second pipette may be appropriately adjusted to achieve the desired intermediate specific gravity.

[0026] After the second separation step, the strongly acidic cation exchange resin and the strongly basic anion exchange resin separated by the second solution (optionally containing the first solution) can be recovered as follows. First, the anion exchange resin is discharged from the upper discharge pipe by backwashing (upward flow) using the second solution. Then, the cation exchange resin is discharged from the lower discharge pipe by downward flow using the second solution. In this way, the separated resins can be recovered, but the method for recovering the resins is not limited to the above method as long as both resins can be separated and recovered.

[0027] The foreign resin contamination rate of the ion exchange resins (strongly acidic cation exchange resin and strongly basic anion exchange resin) obtained by the separation method of the present invention is preferably less than 0.1%. The foreign resin contamination rate refers to the proportion (volume basis) of foreign resins (anion exchange resins) contained in the cation exchange resin obtained after separation, or the proportion (volume basis) of foreign resins (cation exchange resins) contained in the anion exchange resin obtained after separation. The foreign resin contamination rate can be calculated using the following formula (I): Foreign resin contamination rate (%) = (volume of foreign resins contained / total volume of ion exchange resins) × 100 (I)

[0028] In the separation method according to the present invention, the occurrence of cracks on the resin surface is suppressed, and therefore the ion exchange resin obtained by separation has a high PBC (percentage of perfect sphericity). In the present invention, the reduction rate (X-Y(%)) of the PBC (Y(%)) of each ion exchange resin separated through the second separation step from the PBC (X(%)) of each ion exchange resin before separation is preferably less than 5%. Furthermore, the reduction rate of the PBC is more preferably less than 4%. The PBC of an ion exchange resin can be calculated using the following formula (II): PBC (%) = (1 - number of resins that are not spherical or have scratches / total number of resins observed) × 100 (II). It is preferable that the total number of resins observed for PBC measurement be 100 or more before evaluation.

[0029] As described above, the separation method of the present invention performs a two-stage separation process on used non-regenerated mixed-bed ion exchange resin, thereby preventing the incorporation of other resins and the occurrence of cracks on the resin surface. As a result, the ion exchange resin can be reused over a long period of time. Furthermore, because the generation of fine particles and TOC elution caused by cracks in the resin are suppressed, when the ion exchange resin is reused, the deterioration of the quality of the ultrapure water to be purified is suppressed, and stable operation is possible by preventing an increase in differential pressure.

[0030] <Method for Reusing Used Non-Regenerated Mixed-Bed Ion Exchange Resins> The separated strongly acidic cation exchange resins and strongly basic anion exchange resins obtained using the separation method of the present invention can be reused as non-regenerated mixed-bed ion exchange resins or single-bed ion exchange resins after undergoing a regeneration step. That is, the method for reusing used non-regenerated mixed-bed ion exchange resins of the present invention is a method for reusing the recycled strongly acidic cation exchange resins and / or strongly basic anion exchange resins obtained through the separation method of used non-regenerated mixed-bed ion exchange resins of the present invention as non-regenerated mixed-bed ion exchange resins or single-bed ion exchange resins, respectively. The regeneration step can be carried out by a known method.

[0031] <Method for producing single-bed ion exchange resin> As described above, the separation method according to the present invention makes it possible to obtain an ion exchange resin derived from a used non-regenerated mixed-bed ion exchange resin that can be reused as a single-bed ion exchange resin. That is, the present invention can also be said to be a method for producing a single-bed ion exchange resin, which includes a step of separating a used non-regenerated mixed-bed ion exchange resin using the separation method according to the present invention. Note that the respective descriptions of the separation method according to the present invention can also be applied to the method for producing a single-bed ion exchange resin according to the present invention.

[0032] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0033] The following tests were carried out using ESP-2 (trade name, manufactured by Organo Corporation) as a used non-regenerated mixed-bed ion exchange resin.

[0034] Example 1: 3 L of 1N (1 mol / L) saline solution as a first solution was passed downward through an acrylic column packed with 1000 mL of the mixed bed ion exchange resin (first separation step). During this process, the strongly acidic cation exchange resin in the mixed bed ion exchange resin was converted to the Na form, and the strongly basic anion exchange resin was converted to the Cl form. At this stage, as shown in FIG. 2(i), the two resins were not separated and remained in the same state as before the first solution was passed through (before separation). Subsequently, the first solution was removed by pressure pumping with air, and then 20 L of saturated saline solution (true specific gravity: 1.19) as a second solution was passed through the mixed bed ion exchange resin in an upward flow (second separation step). As a result, as shown in FIG. 2(ii), the cation exchange resin (C) and the anion exchange resin (A) were separated through the second solution (B).

[0035] First, the anion exchange resin was extracted from the upper extraction pipe by backwashing (upward flow) using the second solution. Subsequently, the cation exchange resin was extracted from the lower extraction pipe by downward flow using the second solution. The foreign resin contamination rate and PBC (perfect sphericity) of the obtained cation exchange resin and anion exchange resin were measured by the methods described below. The PBC was also measured for the cation exchange resin and anion exchange resin before separation. The results are shown in Table 1.

[0036] (Foreign Resin Contamination Rate) First, 20 mL of each of the recovered cation exchange resins or anion exchange resins was placed in a container containing 100 mL of saturated saline. The number of anion exchange resins that had risen from the cation exchange resin layer or that had settled in the anion exchange resin layer was visually confirmed, and then the resins were recovered. The volume of each recovered (contaminated) resin was measured, and the foreign resin contamination rate was calculated from the resulting resin volume using the following formula: Foreign Resin Contamination Rate (Cation) = (Volume of Contaminated Anion Exchange Resin / 20 mL) × 100 (%) Foreign Resin Contamination Rate (Anion) = (Volume of Contaminated Cation Exchange Resin / 20 mL) × 100 (%). The foreign resin contamination rate (cation) indicates the rate of anion exchange resins mixed into cation exchange resins, and the foreign resin contamination rate (anion) indicates the rate of cation exchange resins mixed into anion exchange resins.

[0037] (PBC) The cation exchange resin and anion exchange resin before separation, and the cation exchange resin and anion exchange resin obtained by separation were each observed using an optical microscope. Specifically, the resins were arranged so that 100 resins could be observed in the field of view, and the number of spherical resins, cracked resins, crushed resins, and non-spherical irregularly shaped resins was counted, and the PBC was calculated using the above formula (II). In the above formula (II), "non-spherical resins or resins with scratches" includes cracked resins, crushed resins, and non-spherical irregularly shaped resins.

[0038] Comparative Example 1: 20 L of saturated saline solution was passed upward through an acrylic column packed with 1,000 mL of the mixed-bed ion exchange resin used in Example 1, thereby separating the strongly acidic cation exchange resin and the strongly basic anion exchange resin in a single stage. The cation exchange resin and anion exchange resin recovered by the same method as in Example 1 were subjected to measurement of the foreign resin contamination rate and PBC in the same manner as in Example 1. The results are shown in Table 1.

[0039] Example 2 The strongly acidic cation exchange resin and the strongly basic anion exchange resin in a mixed-bed ion exchange resin were separated in two stages by the same procedure as in Example 1, except that a 1 N (1 mol / L) aqueous sodium hydroxide solution was used as the first solution and a 3.55 N (12.5 mass%) aqueous sodium hydroxide solution (true specific gravity: 1.13) was used as the second solution. The cation exchange resin and anion exchange resin recovered by the same method as in Example 1 were measured for the foreign resin contamination rate and PBC in the same manner as in Example 1. The results are shown in Table 2.

[0040] Comparative Example 2: The strongly acidic cation exchange resin and the strongly basic anion exchange resin in a mixed-bed ion exchange resin were separated in two stages using the same procedure as in Example 2, except that the first solution and the second solution were used interchangeably. Figure 3 shows the state of separation of the cation exchange resin and the anion exchange resin. The cation exchange resin and the anion exchange resin recovered by the same method as in Example 1 were measured for the foreign resin contamination rate and PBC in the same manner as in Example 1. The results are shown in Table 2.

[0041]

[0042]

[0043] As shown in Table 1, the method of Example 1, in which the first separation step is performed using a dilute solution with a lower concentration than the solution used in the second separation step, and then the second separation step is performed using saturated saline solution, was found to be able to suppress the occurrence of cracks on the resin surface while maintaining a low rate of foreign resin contamination, compared to the method of Comparative Example 1, in which separation is performed in one step.

[0044] Furthermore, as shown in Table 2, in Comparative Example 2, in which a solution with a higher concentration than the second solution was used as the first solution, the foreign resin contamination rate (cation) increased and the PBC also decreased. Note that this example shows an example in which saline or sodium hydroxide solution was used as the first and second solutions. However, a person skilled in the art would expect that similar results to those of Examples 1 and 2 would be obtained even when other ionic solutions were used.

[0045] The present invention includes the following configurations: [Configuration 1] A method for separating used non-regenerated mixed bed ion exchange resins, comprising a separation step of separating a strongly acidic cation exchange resin and a strongly basic anion exchange resin contained in the used non-regenerated mixed bed ion exchange resin, the separation step comprising: a first separation step of contacting the non-regenerated mixed bed ion exchange resin with a first solution capable of converting the ionic form of at least one of the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the non-regenerated mixed bed ion exchange resin to a salt form, and a second separation step of contacting the non-regenerated mixed bed ion exchange resin that has been subjected to the first separation step with a second solution having a specific gravity intermediate between the true specific gravity of the strongly acidic cation exchange resin and the true specific gravity of the strongly basic anion exchange resin, wherein the first solution is a dilute solution having a lower concentration than the second solution. [Configuration 2] The method for separating used non-regenerated mixed bed ion exchange resins according to Configuration 1, wherein the first solution is an aqueous solution selected from the group consisting of saline, hydrochloric acid, sulfuric acid, aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous ammonium chloride, aqueous calcium chloride, aqueous sodium carbonate, aqueous sodium sulfate, aqueous sodium acetate, and aqueous formic acid. [Configuration 3] The method for separating used non-regenerated mixed bed ion exchange resins according to Configuration 1 or 2, wherein the second solution is an aqueous solution selected from the group consisting of saline, hydrochloric acid, and aqueous sodium hydroxide. [Configuration 4] The method for separating used non-regenerated mixed bed ion exchange resins according to any of Configurations 1 to 3, wherein the first solution is the same type of solution as the second solution. [Configuration 5] The method for separating used non-regenerated mixed bed ion exchange resins according to any of Configurations 1 to 4, wherein the reduction in PBC (percent sphericity, %) of each ion exchange resin separated through the second separation step from the PBC (%) of each ion exchange resin before separation is less than 5%. [Configuration 6] A method for reusing a used non-regenerated mixed-bed ion exchange resin, comprising reusing a strongly acidic cation exchange resin or a strongly basic anion exchange resin separated by the method described in any one of Configurations 1 to 5 as a non-regenerated mixed-bed ion exchange resin or a single-bed ion exchange resin.[Configuration 7] A method for producing a single-bed ion exchange resin, comprising the step of separating a used non-regenerated mixed-bed ion exchange resin using the method according to any one of Configurations 1 to 5.

[0046] While certain preferred embodiments of the present invention have been shown and described in detail above, it should be understood that the present invention is not limited to the above-described embodiments, but that various changes and modifications are possible without departing from the spirit or scope of the appended claims.

[0047] This application claims priority based on Japanese Patent Application No. 2024-018308, filed February 9, 2024, the entire contents of which are incorporated herein by reference.

[0048] A: Anion exchange resin B: Second solution C: Cation exchange resin

Claims

1. A method for separating used non-regenerated mixed bed ion exchange resins, comprising a separation step of separating the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the used non-regenerated mixed bed ion exchange resin, the separation step comprising: a first separation step of contacting the non-regenerated mixed bed ion exchange resin with a first solution capable of converting the ionic form of at least one of the strongly acidic cation exchange resin and the strongly basic anion exchange resin contained in the non-regenerated mixed bed ion exchange resin to a salt form; and a second separation step of contacting the non-regenerated mixed bed ion exchange resin that has been subjected to the first separation step with a second solution having a specific gravity intermediate between the true specific gravity of the strongly acidic cation exchange resin and the true specific gravity of the strongly basic anion exchange resin, wherein the first solution is a dilute solution having a lower concentration than the second solution.

2. The method for separating spent non-regenerated mixed bed ion exchange resin according to claim 1, wherein the first solution is an aqueous solution selected from the group consisting of saline, hydrochloric acid, sulfuric acid, aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous ammonium chloride, aqueous calcium chloride, aqueous sodium carbonate, aqueous sodium sulfate, aqueous sodium acetate, and aqueous formic acid.

3. The method for separating spent non-regenerated mixed bed ion exchange resin according to claim 1, wherein the second solution is an aqueous solution selected from the group consisting of saline, hydrochloric acid, and aqueous sodium hydroxide.

4. The method for separating spent non-regenerated mixed bed ion exchange resin according to claim 1, wherein said first solution is the same type of solution as said second solution.

5. The method for separating used non-regenerated mixed-bed ion exchange resins according to claim 1, wherein the PBC (percentage of complete sphericity, %) of each ion exchange resin separated through the second separation step is reduced by less than 5% from the PBC (%) of each ion exchange resin before separation.

6. A method for reusing used non-regenerated mixed-bed ion exchange resins, characterized in that the strongly acidic cation exchange resin or strongly basic anion exchange resin separated by the method of any one of claims 1 to 5 is reused as a non-regenerated mixed-bed ion exchange resin or a single-bed ion exchange resin.

7. A method for producing a single-bed ion exchange resin, comprising the step of separating used non-regenerated mixed-bed ion exchange resin using the method according to any one of claims 1 to 5.

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