Separation method

Abstract

This separation method comprises a supply step (S2) for supplying bubbles, which include at least either nanobubbles or microbubbles, to a mixture that contains a water absorbent polymer and pulp. This separation method comprises a recovery step (S5) for recovering the water absorbent polymer, which has been separated in a mixed liquid that contains the water absorbent polymer and the pulp, since the water absorbent polymer to which bubbles are adhering floats, while pulp settles out in the mixed liquid. This separation method separates a water absorbent polymer and pulp from each other.

Description

[Technical Field]

[0001] The present disclosure relates to a separation method. [Background technology]

[0002] In recent years, attempts have been made to recycle sanitary products such as used disposable diapers. Recycling sanitary products without incineration allows for effective use of resources and reduces the amount of carbon dioxide emitted when incinerated. Typical disposable diapers contain water-absorbent polymers and pulp, and in order to improve recycling efficiency, it is desirable to separate and recover these components.

[0003] As a technology for recycling sanitary products, Patent Document 1 describes a method for producing recycled fibers by removing water-absorbent polymers from fibers containing the water-absorbent polymers. This method includes a step of supplying a mixed liquid containing water-absorbent polymer-containing fibers and water into a treatment tank containing a treatment liquid capable of dissolving the water-absorbent polymer, and discharging the treatment liquid containing the fibers from which the water-absorbent polymer has been dissolved and removed out of the treatment tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 003657 Summary of the Invention [Problem to be solved by the invention]

[0005] According to Patent Document 1, recycled fibers can be efficiently produced by dissolving and removing the water-absorbent polymer from fibers containing the water-absorbent polymer. However, from the viewpoint of recycling, it is preferable to separate and recover not only the fibers but also the water-absorbent polymer.

[0006] Therefore, an object of the present disclosure is to provide a separation method capable of recovering a water-absorbent polymer from a mixture containing the water-absorbent polymer and pulp. [Means for solving the problem]

[0007] A separation method according to the present disclosure includes a supplying step of supplying bubbles including at least one of nanobubbles and microbubbles to a mixture containing a water-absorbent polymer and pulp. The separation method also includes a recovering step of recovering the water-absorbent polymer separated in the mixed liquid containing the water-absorbent polymer and pulp, as the water-absorbent polymer with the attached bubbles floats up and the pulp settles. In the separation method, the water-absorbent polymer and the pulp are separated.

[0008] The water-absorbing polymer may float in the mixed liquid while remaining in a solid state. The water-absorbing polymer may include a polyacrylate-based water-absorbing polymer. The bubbles may have an average bubble diameter of 1 nm to 100 μm. The bubbles may contain at least one gas selected from the group consisting of hydrogen, nitrogen, oxygen, carbon dioxide, air, and noble gases. The separation method may further include a settling step of settling the pulp in the mixed liquid between the supplying step and the recovering step. The separation method may further include a stirring step of stirring the mixed liquid between the supplying step and the settling step.

[0009] A separation method according to the present disclosure includes a supplying step of supplying electrically charged bubbles to a mixture containing a water-absorbent polymer and pulp. The separation method also includes a recovery step of recovering the water-absorbent polymer separated in the mixed liquid containing the water-absorbent polymer and pulp, as the water-absorbent polymer with the attached bubbles rises to the surface and the pulp sinks. In the separation method, the water-absorbent polymer and the pulp are separated. [Effects of the Invention]

[0010] According to the present disclosure, a separation method can be provided that can recover a water-absorbent polymer from a mixture containing the water-absorbent polymer and pulp. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a flowchart showing the flow of the separation method according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, several exemplary embodiments will be described with reference to the drawings. Note that the dimensional proportions of the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0013] The separation method according to the present embodiment is a method for separating a water-absorbent polymer and pulp. For example, the separation method is a method for separating a water-absorbent polymer and pulp from an absorbent article containing the water-absorbent polymer and pulp. Examples of such absorbent articles include disposable diapers, urine absorption pads, sanitary napkins, bed sheets, and pet sheets. The absorbent article includes, for example, a water-permeable top sheet, a waterproof back sheet, and a water-absorbent material disposed between the top sheet and the back sheet. The water-absorbent material contains a water-absorbent polymer and pulp and is capable of absorbing water that has permeated the top sheet.

[0014] The separation method includes a supplying step S2 and a recovery step S5, as shown in Fig. 1. The separation method may further include a pretreatment step S1, a stirring step S3, and a settling step S4.

[0015] (Pretreatment step S1) The pretreatment step S1 is carried out before the supply step S2. In the pretreatment step S1, the absorbent article is treated so that the absorbent polymer and pulp can be easily separated in a subsequent step. In the pretreatment step S1, the absorbent article is separated into the water-absorbing material and materials other than the water-absorbing material by at least one of mechanical treatment and chemical treatment, and the separated water-absorbing material is recovered. Examples of mechanical treatment include crushing and pressurization. Examples of chemical treatment include chemical treatment in which a chemical is added to dissolve the adhesive. The water-absorbing material containing the water-absorbing polymer and pulp obtained in the pretreatment step S1 may contain residue other than the water-absorbing material that was not completely separated.

[0016] (Supply process S2) In the supplying step S2, bubbles are supplied to the mixture containing the water-absorbent polymer and pulp. The method of supplying the bubbles is not particularly limited, and for example, a bubble liquid in which bubbles are dispersed in a liquid may be prepared, and the bubble liquid may be added to a container containing the mixture containing the water-absorbent polymer and pulp. Alternatively, bubbles may be generated in the mixture containing the water-absorbent polymer, pulp, and liquid.

[0017] The water-absorbing polymer is, for example, a hydrogel having a three-dimensional network structure formed by crosslinking and capable of absorbing water in the mixed liquid. The water-absorbing polymer may be, for example, at least one polymer selected from the group consisting of polyacrylates, polysulfonates, maleic anhydrides, polyaspartates, polyglutamates, and polyalginates.

[0018] The water-absorbing polymer preferably includes a polyacrylate-based water-absorbing polymer. This is because polyacrylate-based water-absorbing polymers are commonly and widely used and can be widely used in recycling technologies. The polyacrylate-based water-absorbing polymer is, for example, a water-absorbing polymer containing at least one polyacrylate structure selected from the group consisting of sodium polyacrylate, potassium polyacrylate, calcium polyacrylate, and magnesium polyacrylate. The shape and size of the water-absorbing polymer are not particularly limited, and any desired shape and size can be used.

[0019] Pulp is, for example, an aggregate of cellulose fibers. Pulp includes at least one pulp selected from the group consisting of wood pulp made from wood, non-wood pulp made from plants other than wood, and recycled pulp made from waste paper or the like. Pulp can be produced by mechanical treatment, chemical treatment, or a combination thereof. The shape and size of the pulp are not particularly limited, and pulp of any desired shape and size can be used.

[0020] The bubbles include at least one of nanobubbles and microbubbles. Such bubbles easily adhere to the water-absorbent polymer and can cause the water-absorbent polymer to float. Furthermore, the smaller the diameter of such bubbles, the smaller the buoyancy, making them easier to retain in water and less likely to disappear by floating to the water surface. However, in this embodiment, the bubbles are not limited to those including at least one of microbubbles and nanobubbles, and electrically charged bubbles may also be used.

[0021] The average bubble diameter of the bubbles is, for example, 1 nm to 100 μm. By setting the average bubble diameter of the bubbles in this range, the bubbles can be attached to the water-absorbent polymer, making it easier for the water-absorbent polymer to float up. The average bubble diameter of the bubbles may be smaller than the diameter of the water-absorbent polymer after swelling. The average bubble diameter of the bubbles is, for example, the average value of the diameters of approximately 100 bubbles measured by image analysis.

[0022] The gas contained in the bubbles is not particularly limited as long as it can float the water-absorbent polymer in the mixed liquid, and for example, an inert gas that does not decompose the water-absorbent polymer, such as hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, air, noble gases, hydrocarbons such as methane, and nitrogen oxides such as nitric oxide, can be used. Among these, it is preferable that the bubbles contain at least one gas selected from the group consisting of hydrogen, nitrogen, oxygen, carbon dioxide, air, and noble gases. Examples of noble gases include helium and argon. These gases are easily available, have low activity, and are less likely to damage the water-absorbent polymer, making them suitable for recycling water-absorbent polymers.

[0023] The method for generating bubbles is not particularly limited, and known methods can be used, such as a swirling liquid flow method, a static mixer method, an ejector method, a cavitation method, a Venturi method, a pressurized dissolution method, a fine pore method, a rotation method, an ultrasonic method, a steam condensation method, and an electrolysis method. Bubbles may be generated directly in a mixed liquid containing a water-absorbent polymer and pulp, or bubbles may be generated in a liquid not containing a water-absorbent polymer and pulp to prepare a bubbled liquid containing bubbles, and then the bubbled liquid may be added to a mixture containing a water-absorbent polymer and pulp.

[0024] (Recovery process S5) In the recovery step S5, the water-absorbent polymer with attached bubbles rises to the surface in a mixed liquid containing the water-absorbent polymer and pulp, while the pulp sinks, and the water-absorbent polymer separated from the mixed liquid is recovered. While an example in which the mixed liquid contains a water-absorbent polymer, pulp, and water will be described, this embodiment is not limited to this configuration. Since typical water-absorbent polymers and pulp have a higher specific gravity than water and sink in water even after absorbing and swelling in water, it is not easy to separate the water-absorbent polymer and pulp using the difference in their specific gravities. However, bubbles containing at least one of microbubbles and nanobubbles selectively adhere to the water-absorbent polymer rather than to the pulp. The water-absorbent polymer floats in the mixed liquid because its apparent specific gravity becomes lower than that of water due to the attachment of bubbles. On the other hand, bubbles are less likely to adhere to pulp than to the water-absorbent polymer, and pulp, which has a higher specific gravity than water, sinks in the mixed liquid. In this way, the water-absorbent polymer rises in the mixed liquid and the pulp sinks in the mixed liquid, so that the water-absorbent polymer and the pulp are separated.

[0025] As mentioned above, the specific gravity of the polyacrylate-based water-absorbing polymer is larger than that of the liquid in the mixture. For example, the specific gravity of sodium polyacrylate is 1.2 g / cm 3 As mentioned above, the specific gravity of pulp is greater than that of the liquid in the mixed liquid. For example, the specific gravity of cellulose is 1.5 g / cm 3 In this embodiment, the liquid in the mixture is water, so the density is about 1 g / cm 3However, the liquid in the mixture may be a liquid other than water. Examples of liquids other than water are not particularly limited as long as the water-absorbing polymer adheres to the pulp by the bubbles and the pulp settles, but may also be a liquid containing an organic substance such as alcohol.

[0026] The water-absorbent polymer floats up in the mixed liquid while remaining in a solid state. This makes it easy to recover the water-absorbent polymer from the container containing the mixed liquid. The recovered water-absorbent polymer can be recycled through processes such as washing. Note that the term "solid" here also includes gel. Furthermore, "floating up in the mixed liquid while remaining in a solid state" means that the water-absorbent polymer is reduced in molecular weight by an oxidizing agent such as ozone and floats up in the mixed liquid without dissolving. Therefore, it is preferable that the bubbles contain a gas that has a smaller ability to decompose the water-absorbent polymer than ozone.

[0027] The pH of the mixed liquid is not particularly limited as long as it can separate the water-absorbent polymer from the pulp. From the viewpoint of increasing the recovery rate of the water-absorbent polymer, the pH of the mixed liquid is preferably 2.5 to 11. The pH of the mixed liquid may be 6 or higher. The pH of the mixed liquid may also be 8 or lower. The pH of the mixed liquid can be adjusted by adding citric acid, sodium hydroxide, or the like to the liquid.

[0028] As described above, in this embodiment, the water-absorbent polymer floats up in the mixed liquid, and therefore the water-absorbent polymer can be easily recovered from the container containing the mixed liquid. The method for recovering the water-absorbent polymer is not particularly limited, and for example, the container containing the mixed liquid may be tilted and the water-absorbent polymer that has floated to the surface of the mixed liquid may be removed and recovered from the container. Alternatively, the water-absorbent polymer that has floated to the surface of the mixed liquid may be recovered from the container by scooping it out.

[0029] In the recovery step S5, not only the water-absorbent polymer but also the precipitated pulp may be recovered. The method for recovering the pulp is not particularly limited, and for example, the pulp may be recovered by sucking it out from the bottom of the container containing the mixed liquid. Alternatively, the pulp and liquid above the precipitated pulp may be removed from the container, and then the pulp remaining at the bottom of the container may be recovered. An oxidizing agent such as ozone may be added to the recovered pulp to decompose and remove traces of the water-absorbent polymer adhering to the pulp.

[0030] (Sedimentation step S4) In the settling step S4, the pulp in the mixed liquor is allowed to settle between the supply step S2 and the recovery step S5. Pulp has a higher specific gravity than water, and bubbles large enough to cause the pulp to float are unlikely to adhere to the surface of the pulp. Therefore, the pulp tends to settle in the mixed liquor. The method for settling the pulp is not particularly limited, and the pulp can be settled by a known method. As described above, since the specific gravity of pulp is higher than that of water, the pulp can be settled by, for example, stopping the generation of bubbles and allowing the mixture to stand still.

[0031] (Mixing process S3) In the stirring step S3, the mixed liquid is stirred between the supply step S2 and the settling step S4. By stirring the mixed liquid in the presence of bubbles, the entanglement between the water-absorbent polymer and the pulp is loosened and the bubbles adhere to the water-absorbent polymer. In addition, it is possible to move the pulp that is present in the floating path of the water-absorbent polymer and inhibits the floating of the water-absorbent polymer. This causes the water-absorbent polymer to float and the pulp to easily settle, thereby promoting separation of the water-absorbent polymer and the pulp. The method for stirring the mixed liquid is not particularly limited, and it can be stirred by a known method. The mixed liquid may be stirred using, for example, a stirrer, a glass rod, or the like. In addition, the mixed liquid may be stirred, for example, by shaking the container containing the mixed liquid.

[0032] As described above, the separation method according to this embodiment includes a supplying step S2 of supplying bubbles containing at least one of nanobubbles and microbubbles to a mixture containing a water-absorbent polymer and pulp. The separation method also includes a recovering step S5 of recovering the water-absorbent polymer separated in the mixed liquid containing the water-absorbent polymer and pulp, as the water-absorbent polymer with the attached bubbles floats up and the pulp settles. In the separation method, the water-absorbent polymer and the pulp are separated.

[0033] The separation method according to this embodiment also includes a supplying step S2 of supplying electrically charged bubbles to a mixture containing a water-absorbent polymer and pulp. The separation method also includes a recovering step S5 of recovering the water-absorbent polymer separated in the mixed liquid containing the water-absorbent polymer and pulp, as the water-absorbent polymer with the attached bubbles floats up and the pulp sinks. In the separation method, the water-absorbent polymer and the pulp are separated.

[0034] Therefore, according to the separation method of this embodiment, it is possible to recover the water-absorbent polymer from a mixture containing the water-absorbent polymer and pulp. [Example]

[0035] Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[0036] [Example 1] (Preparation of bubble water) First, bubble water was prepared. Specifically, 1 L of ion-exchanged water was placed in a pressure vessel (Unicontrols, TA90N). Next, nitrogen was pumped into the pressure vessel from a gas cylinder at 0.2 MPa, and the vessel was manually shaken. The nitrogen inlet pipe was closed, and the bubble water containing at least one of nanobubbles and microbubbles was poured from the pressure vessel into an empty beaker.

[0037] (Separation test) Next, a separation test was carried out. Specifically, 10 mL of ion-exchanged water was added to 30 mg (0.3 mass%) of a water-absorbent polymer made of sodium polyacrylate and 70 mg (0.7 mass%) of cellulose pulp, and the mixture was stirred for 1 minute to swell the water-absorbent polymer and pulp. Next, 200 mL of the bubble water obtained as described above was added to the swollen water-absorbent polymer and pulp.

[0038] The mixture containing the absorbent polymer, pulp, and bubble water was stirred 10 times with a spoon and allowed to stand for approximately 3 minutes. Next, the beaker was gently shaken manually, and then tilted to collect the upper and lower layers. The collected liquid from each layer was suction filtered, and the collected samples were air-dried and weighed. The recovery rate of each layer was calculated by dividing the mass of the upper layer after drying by the mass of the absorbent polymer (30 mg) initially added, and the mass of the lower layer after drying by the mass of the pulp initially added (70 mg). The results are shown in Table 1.

[0039] [Example 2] In the separation test, the water-absorbent polymer and pulp were swollen with ion-exchanged water, and then 100 mg of citric acid was added to the mixture so that the citric acid concentration was approximately 1% by mass, followed by stirring for 30 seconds. The recovery rate of each layer was calculated in the same manner as in Example 1.

[0040] [Example 3] (Preparation of bubble water) First, bubble water was prepared. Specifically, 300 mL of a pH 13.5 NaOH aqueous solution was placed in a pressure vessel (Unicontrols, TA90N). Next, nitrogen was pumped into the pressure vessel from a gas cylinder at 0.2 MPa, and the vessel was manually shaken. The nitrogen inlet pipe was closed, and bubble water containing at least one of nanobubbles and microbubbles was poured from the pressure vessel into an empty beaker.

[0041] (Separation test) Next, a separation test was carried out. Specifically, 10 mL of ion-exchanged water was added to 30 mg (0.3% by mass) of water-absorbent polymer and 70 mg (0.7% by mass) of pulp, and the mixture was stirred for 1 minute to swell the water-absorbent polymer and pulp. Next, 300 mL of the bubble water obtained as described above was added to the mixture. Except for this, the recovery rate of each layer was calculated in the same manner as in Example 1.

[0042] [Example 4] (Preparation of bubble water) First, 1.5 L of ion-exchanged water was placed in a beaker. Next, air was bubbled using a microbubble generator (AURA TEC: OM4-MDG-045) until the water in the beaker turned white and bubbles appeared on the surface, producing bubble water containing at least one of nanobubbles and microbubbles. The average bubble diameter of bubbles measured by laser diffraction and scattering when the cumulative value of the particle size distribution on a number basis was 50% was approximately 1 μm.

[0043] (Separation test) Next, a separation test was carried out. Specifically, 20 mL of ion-exchanged water was added to 60 mg (0.3% by mass) of water-absorbent polymer and 140 mg (0.7% by mass) of pulp, and the mixture was stirred for 1 minute to swell the water-absorbent polymer and pulp. Next, 150 mL of the bubble water obtained as described above was added to the swollen water-absorbent polymer and pulp. Except for this, the recovery rate of each layer was calculated in the same manner as in Example 1.

[0044] [Example 5] In the separation test, the water-absorbent polymer and pulp were swollen with ion-exchanged water, and then 200 mg of citric acid was added to the mixture so that the citric acid concentration was approximately 1% by mass, followed by stirring for 30 seconds. The recovery rate of each layer was calculated in the same manner as in Example 4.

[0045] [Example 6] First, 1 L of ion-exchanged water was placed in a beaker. Next, using a microbubble generator (AURA TEC: OM4-MDG-045), the water in the beaker was bubbled until it turned white and bubbles appeared on the surface, producing bubbled water containing at least one of nanobubbles and microbubbles. The average bubble diameter of bubbles measured by laser diffraction and scattering at a cumulative value of 50% in the particle size distribution on a number basis was approximately 1 μm. Next, 200 mL of the above bubbled water was added to a beaker containing 100 mL of 1.78 g / L NaOH aqueous solution, producing bubbled water consisting of a pH 12.3 NaOH aqueous solution.

[0046] Next, a separation test was carried out. Specifically, 20 mL of ion-exchanged water was added to 60 mg (0.3% by mass) of water-absorbent polymer and 140 mg (0.7% by mass) of pulp, and the mixture was stirred for 1 minute to swell the water-absorbent polymer and pulp. Next, 300 mL of the bubble water with a pH of 12.3 obtained as described above was added to the swollen water-absorbent polymer and pulp. Except for this, the recovery rate of each layer was calculated in the same manner as in Example 4.

[0047] [Example 7] (Preparation of bubble water) First, 1 L of ion-exchanged water was placed in a beaker. Next, nitrogen gas from a gas cylinder was bubbled into the beaker using a microbubble generator (Fresh by Design, PY101CF-E) to prepare bubbled water containing at least one of nanobubbles and microbubbles.

[0048] Next, a separation test was carried out. Specifically, 20 mL of ion-exchanged water was added to 60 mg (0.3% by mass) of water-absorbent polymer and 140 mg (0.7% by mass) of pulp, and the mixture was stirred for 1 minute to swell the water-absorbent polymer and pulp. Next, 150 mL of the bubble water obtained as described above was added to the swollen water-absorbent polymer and pulp. Except for this, the recovery rate of each layer was calculated in the same manner as in Example 1.

[0049] [Example 8] In the separation test, the water-absorbent polymer and pulp were swollen with ion-exchanged water, and then 200 mg of citric acid was added to the mixture so that the citric acid concentration was approximately 1% by mass, followed by stirring for 30 seconds. The recovery rate of each layer was calculated in the same manner as in Example 7.

[0050] [Comparative Example 1] First, 20 mL of ion-exchanged water was added to 60 mg (0.3% by mass) of water-absorbent polymer and 140 mg (0.7% by mass) of pulp, and the mixture was stirred for 1 minute to swell the water-absorbent polymer and pulp. Next, 200 mL of ion-exchanged water was further added to the swollen water-absorbent polymer and pulp, and bubbles with an average bubble diameter of more than 1 mm were generated in this mixture by bubbling. Except for this, the recovery rate of each layer was calculated in the same manner as in Example 1.

[0051] Comparative Example 2 In the separation test, the water-absorbent polymer and pulp were swollen with ion-exchanged water, and then 200 mg of citric acid was added to the mixture so that the citric acid concentration was approximately 1% by mass, followed by stirring for 30 seconds. The recovery rate of each layer was calculated in the same manner as in Comparative Example 1.

[0052] Comparative Example 3 In the separation test, the water-absorbent polymer and pulp were swollen with ion-exchanged water, and then 200 mL of bubble water with a pH of 12.3 obtained in Example 6 was added to the swollen water-absorbent polymer and pulp, and bubbles with an average bubble diameter of more than 1 mm were generated in this mixed liquid by bubbling. Except for this, the recovery rate of each layer was calculated in the same manner as in Comparative Example 1.

[0053] [Table 1]

[0054] In Examples 1 to 8, three types of microbubble generators were used to generate bubbles containing at least one of microbubbles and nanobubbles. As a result, in all cases, the bubbles selectively adhered to the water-absorbent polymer, causing the water-absorbent polymer to float up in the mixed solution, while the pulp settled to the bottom of the beaker due to its own weight, resulting in separation into an upper layer primarily composed of the water-absorbent polymer and a lower layer primarily composed of pulp. Because the water-absorbent polymer floated up after being separated from the pulp, the water-absorbent polymer could be easily recovered. The density of bubbles generated by visual observation varied depending on the microbubble generator, and the higher the bubble density, the higher the recovery rate of the water-absorbent polymer. Furthermore, separation into upper and lower layers occurred under acidic, neutral, and basic conditions, but the recovery rate of the water-absorbent polymer was higher under acidic and neutral conditions than under basic conditions.

[0055] On the other hand, in Comparative Examples 1 to 3, bubbles with an average bubble diameter of more than 1 mm were generated, but neither the water-absorbent polymer nor the pulp rose to the surface in the mixed liquid, and instead sank to the bottom of the beaker due to their own weight, so the water-absorbent polymer could not be recovered. In Comparative Examples 1 to 3, it is believed that the bubbles with an average bubble diameter of more than 1 mm did not easily adhere to either the water-absorbent polymer or the pulp.

[0056] The reason why bubbles adhere more to the absorbent polymer than to the pulp is presumed to be as follows. That is, absorbent polymers such as the polyacrylate-based absorbent polymers mentioned above have a high degree of ionization, and the carboxylate ions (R-COO) formed in the liquid -) and positively charged counter ions, forming an electric double layer. On the other hand, pulp has a lower degree of ionization than the water-absorbent polymer. Bubbles containing at least one of microbubbles and nanobubbles have a negative zeta potential, and therefore are thought to adhere to the water-absorbent polymer, which forms more counter ions than pulp, causing the water-absorbent polymer to float. On the other hand, pulp has a low positive charge, and bubbles are less likely to adhere to it, so it is thought that it sinks due to its own weight. Note that this embodiment is not limited to the above mechanism, but based on the above mechanism, it is estimated that the same effect can be achieved with charged bubbles, not limited to bubbles containing at least one of microbubbles and nanobubbles.

[0057] The entire contents of Patent Application No. 2020-184207 (filing date: November 4, 2020) are incorporated herein by reference.

[0058] Although several embodiments have been described, the embodiments can be modified or varied based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined, unless they are mutually inconsistent. [Explanation of symbols]

[0059] S1 Pretreatment process S2 supply process S3 Mixing process S4 Sedimentation process S5 Recovery process

Claims

1. a supplying step of supplying bubbles containing at least one of nanobubbles and microbubbles to a mixture containing a water-absorbing polymer and pulp; a recovery step of recovering the water-absorbent polymer separated in the mixed liquid containing the water-absorbent polymer and the pulp, as the water-absorbent polymer with the bubbles attached thereto rises and the pulp settles; Including, A separation method for separating the water-absorbent polymer from the pulp.

2. The separation method according to claim 1 , wherein the water-absorbing polymer floats in the mixed liquid while remaining in a solid state.

3. The separation method according to claim 1 or 2, wherein the water-absorbing polymer comprises a polyacrylate-based water-absorbing polymer.

4. The separation method according to any one of claims 1 to 3, wherein the bubbles have an average bubble diameter of 1 nm to 100 µm.

5. 5. The separation method according to claim 1, wherein the bubbles contain at least one gas selected from the group consisting of hydrogen, nitrogen, oxygen, carbon dioxide, air and noble gases.

6. The separation method according to any one of claims 1 to 5, further comprising a settling step of settling the pulp in the mixed liquid between the supplying step and the recovering step.

7. The separation method according to claim 6, further comprising a stirring step of stirring the mixed liquid between the supplying step and the settling step.

8. a supplying step of supplying electrically charged bubbles to a mixture containing a water-absorbing polymer and pulp; a recovery step of recovering the water-absorbent polymer separated in the mixed liquid containing the water-absorbent polymer and the pulp, as the water-absorbent polymer with the bubbles attached thereto rises and the pulp settles; Including, A separation method for separating the water-absorbent polymer from the pulp.

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