Method for recovering constituting member of used absorbent article

Abstract

To provide a method for recovering constituting members of a used absorbent article, which allows a plurality of constituting members to be collectively recycled in a more simple manner, while an increase in costs is suppressed.SOLUTION: Provided is a method for recovering constituting members of a used absorbent article. The method includes: a dehydration and washing step for dehydrating and washing a mixture being constituting members which include a high water-absorbing polymer with an acid group, and a pulp fiber, by using a solution containing a dehydrator capable of dehydrating the high water-absorbing polymer and the pulp fiber, and containing an oxidizing agent; and a separation and recovery step for separating and recovering at least the high water-absorbing polymer and the pulp fiber together from the matter subjected to dehydration and washing in the dehydration and washing step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering components of used absorbent articles. [Background technology]

[0002] A method for recovering components of used absorbent articles is known. For example, Patent Document 1 discloses a method for recycling absorbent resin derived from used absorbent articles, characterized in that the absorbent resin containing the absorbent liquid is drained from the absorbent resin and the absorbency of the absorbent resin is restored. This method includes (i) an immersion step of immersing a used absorbent article containing a water-absorbing resin that has absorbed the absorbent liquid in an immersion liquid containing a hydrophilic organic solvent; (ii) a crushing step of crushing the used absorbent article into crushed material during or before the immersion step; and (iii) a separation step of separating the absorbent resin from a mixture of the immersion liquid and the crushed material. Patent Document 1 discloses that in step (iii), one or more members selected from pulp, nonwoven fabric, and adhesive may be further separated and recovered, and a sterilization / disinfection step of sterilizing and / or disinfecting the absorbent resin may be performed in parallel with or after the immersion step. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 162082 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, in the separation step, the water-absorbent resin that has been dehydrated and shrunk is taken out from gaps in the pulp, nonwoven fabric, etc. contained in the used absorbent article, dispersed in an immersion liquid, and separated and recovered by a solid-liquid separation means. Furthermore, the pulp, nonwoven fabric, etc. other than the water-absorbent resin are each separated and recovered by a solid-liquid separation means, and reused as recycled pulp and recycled plastic. That is, Patent Document 1 discloses that the water-absorbent resin is separated and recovered from the used absorbent article, and then the pulp and nonwoven fabric are individually separated and recovered.

[0005] However, when reusing components of used absorbent articles, there are cases where a superabsorbent polymer (water-absorbent resin) and pulp fibers (pulp) are used together. In such cases, separating and recovering the superabsorbent polymer and pulp fibers individually may unnecessarily increase the number of steps related to separation and recovery, which may lead to increased costs.

[0006] Therefore, an object of the present invention is to provide a method for recovering components of used absorbent articles, which makes it easy to reuse a plurality of components collectively while suppressing increases in costs. [Means for solving the problem]

[0007] The present invention is a method for recovering components of used absorbent articles, comprising a dehydration and washing step in which a mixture containing the components, a superabsorbent polymer having acid groups and pulp fibers, is dehydrated and washed with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and the pulp fibers, and a separation and recovery step in which at least the superabsorbent polymer and the pulp fibers are separated and recovered together from the product dehydrated and washed in the dehydration and washing step. Effect of the Invention

[0008] According to the present invention, a method for recovering components of used absorbent articles can be provided that makes it easy to reuse a plurality of components collectively while suppressing increases in costs. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a flow chart showing an example of a method for recovering components of used absorbent articles according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present embodiment relates to the following aspects.

[0011] [Embodiment 1] A method for recovering components of used absorbent articles, comprising: a dehydration and washing step in which a mixture containing the components, a superabsorbent polymer having acid groups and pulp fibers, is dehydrated and washed with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and the pulp fibers; and a separation and recovery step in which at least the superabsorbent polymer and the pulp fibers are separated and recovered together from the product dehydrated and washed in the dehydration and washing step.

[0012] In this method, in the dehydration and washing step, the superabsorbent polymer having an acid group and the pulp fiber are combined, and dehydration and washing are performed simultaneously using a dehydrating agent and an oxidizing agent. That is, the moisture absorbed by the superabsorbent polymer and the pulp fiber, which may contain contaminants such as excrement, can be dehydrated from both the superabsorbent polymer and the pulp fiber by the dehydrating agent. At the same time, the contaminants such as bacteria, odorous substances, and coloring substances derived from excrement contained in the superabsorbent polymer and the pulp fiber can be reduced from both the superabsorbent polymer and the pulp fiber by the oxidizing agent. In this way, by dehydrating and washing at least the superabsorbent polymer and the pulp fiber together, the number of steps can be reduced and costs can be reduced compared to the case of performing dehydration and washing separately. In this method, in the separation and recovery step, at least the superabsorbent polymer and the pulp fiber are separated and recovered from the material dehydrated and washed in the dehydration and washing step. This makes it possible to suppress the increase in cost that would occur if the superabsorbent polymer and the pulp fiber were used together when recycling components of used absorbent articles (examples include absorbent sheets, cat litter, sandbag modifiers, and solid fuels) and the superabsorbent polymer and the pulp fiber were used together and then separated and collected. In this way, the synergistic effect of the dehydration and separation process and the separation and collection process makes it possible to easily reuse multiple components collectively in the method for recovering components of used absorbent articles while suppressing an increase in cost.

[0013] [Aspect 2] The method described in Aspect 1, wherein the dehydration and washing step includes a step of dehydrating and washing the mixture further containing the plastic material, which is the constituent component, with the solution, and the separation and recovery step includes a step of separating and recovering the superabsorbent polymer, the pulp fibers and the plastic material together from the material dehydrated and washed in the dehydration and washing step.

[0014] In this method, in the dehydration and washing step, the superabsorbent polymer, pulp fiber, and plastic material are dehydrated and washed simultaneously using a dehydrating agent and an oxidizing agent. That is, the moisture that may contain contaminants contained in each of the superabsorbent polymer, pulp fiber, and plastic material can be dehydrated in all of these materials together by using the dehydrating agent. At the same time, the contaminants contained in each of the superabsorbent polymer, pulp fiber, and plastic material can be reduced in all of these materials together by using the oxidizing agent. As a result, the contaminants can be reduced in all of these materials together. In this way, by dehydrating the superabsorbent polymer, pulp fiber, and plastic material together and washing the superabsorbent polymer, pulp fiber, and plastic material together, the number of steps can be reduced and costs can be reduced compared to the case of dehydrating and washing them individually. In this method, in the separation and recovery step, at least the superabsorbent polymer, pulp fiber, and plastic material are separated and recovered together from the material dehydrated and washed in the dehydration and washing step. This makes it possible to suppress the increase in costs that would occur if the superabsorbent polymers, pulp fibers, and plastic materials used together were to be separated and recovered individually when the constituent parts of used absorbent articles are reused and the materials are used together (for example, cat litter, building materials (including sound-absorbing materials and cement materials), injection molded products, and solid fuels).In this way, the synergistic effect of the above-mentioned dehydration and separation process and separation and recovery process makes it possible to easily reuse multiple constituent parts collectively in the method for recovering constituent parts of used absorbent articles while suppressing an increase in costs.

[0015] [Aspect 3] The method described in Aspect 2, wherein the separation and recovery step includes a step of separating and recovering the plastic material from the superabsorbent polymer, the pulp fibers and the plastic material which have been separated together.

[0016] In this method, the superabsorbent polymer, pulp fibers, and plastic material that are separated together have already been dehydrated and washed. Therefore, by separating the plastic material from the superabsorbent polymer, pulp fibers, and plastic material, a reusable plastic material can be obtained without further washing. This makes it possible to suppress an increase in the number of washing steps and an increase in costs, while also allowing the plastic material of the superabsorbent polymer, pulp fibers, and plastic material that are separated together to be used together to be used individually (e.g., bags made by the inflation method).

[0017] [Aspect 4] The method according to any one of aspects 1 to 3, further comprising a crushing step of crushing the used absorbent articles, the crushing step being carried out before the separation and recovery step, and either before, during or after the dehydration and cleaning step.

[0018] In this method, a crushing step for crushing used absorbent articles is performed before the separation and recovery step and either before, during or after the dehydration and washing step, thereby making it possible to more reliably separate at least the superabsorbent polymer and pulp fibers, or the superabsorbent polymer, the pulp fibers and the plastic material together from the absorbent articles dehydrated and washed in the dehydration and washing step in the separation and recovery step.

[0019] [Aspect 5] The method according to any one of aspects 1 to 4, further comprising a drying step of drying materials separated in the separation and recovery step, the drying step being carried out at least one of after the dehydration and washing step and after the separation and recovery step.

[0020] In this method, the drying step of drying the materials separated together, i.e., the superabsorbent polymer and the pulp fibers, or the superabsorbent polymer, the pulp fibers, and the plastic material, is carried out at least one of after the dehydration washing step and after the separation step. Therefore, since the materials are dehydrated and easily dried in advance in the dehydration washing step, it is possible to reduce the energy required for drying and to make it easier to reuse the materials together. Therefore, the processing burden is reduced compared to the case where the materials are dried separately, and costs can be reduced.

[0021] [Aspect 6] The method described in any one of aspects 1 to 5, wherein the oxidizing agent includes at least one of ozone, hydrogen peroxide, and a chlorine-based substance.

[0022] In this method, the dehydration and washing step contains at least one of ozone, hydrogen peroxide, and a chlorine-based substance, which have strong oxidizing power, as an oxidizing agent, so that contaminants contained in each of the superabsorbent polymer and the pulp fiber, or each of the superabsorbent polymer, the pulp fiber, and the plastic material, can be more reliably reduced together.

[0023] [Aspect 7] The method according to any one of aspects 1 to 6, wherein the dehydrating agent comprises a ketone-based organic solvent.

[0024] In this method, the dehydrating and washing step contains a ketone-based organic solvent that is difficult to oxidize even with a strong oxidizing agent, so that the moisture that may contain contaminants absorbed in the superabsorbent polymer and the pulp fibers, or in the superabsorbent polymer, the pulp fibers, and the plastic material, can be dehydrated together more reliably without being affected by the oxidizing power of the oxidizing agent.

[0025] [Aspect 8] The method described in any one of aspects 1 to 7, further comprising a pretreatment step of reducing the moisture absorbed by the used absorbent article prior to the dehydration and cleaning step.

[0026] This method includes a pretreatment step of reducing the amount of moisture absorbed by the used absorbent article before the dehydration and washing step. Therefore, the amount of moisture in the used absorbent article to be treated in the dehydration and washing step can be reduced in advance in the pretreatment step. This makes it possible to more reliably sterilize, deodorize, and bleach the bacteria, odorous substances, and coloring substances contained in each of the superabsorbent polymer and the pulp fibers, or each of the superabsorbent polymer, the pulp fibers, and the plastic material, together in the dehydration and washing step.

[0027] [Aspect 9] The method described in Aspect 8, wherein the pretreatment step involves subjecting the used absorbent article to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, high-pressure steam treatment, freeze-drying, and an organic solvent treatment.

[0028] In this method, as a pretreatment step before the dehydration and washing step, the used absorbent article is subjected to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, a high-pressure steam treatment, a freeze-drying treatment, and an organic solvent treatment, thereby making it possible to more reliably reduce the moisture in the used absorbent article, which is to be treated in the dehydration and washing step, in advance in the pretreatment step.

[0029] [Aspect 10] The method described in Aspect 9, wherein the pretreatment step includes a step of subjecting the used absorbent article to an acidic aqueous solution treatment in which the superabsorbent polymer is inactivated with an acidic aqueous solution, and the dehydration and cleaning step includes a step of activating the inactivated superabsorbent polymer using alkali metal ions supplied from an alkali metal ion source.

[0030] In this method, by performing an acidic aqueous solution treatment as a pretreatment step, the superabsorbent polymer is inactivated with the acidic aqueous solution, and the moisture absorbed by the superabsorbent polymer can be more appropriately reduced (dehydrated). That is, the amount of moisture to be treated in the dehydration and washing step in the used absorbent article can be more appropriately reduced in advance. In addition, by using an alkali metal ion source in the dehydration and washing step, the superabsorbent polymer can be reactivated by alkali metal ions while remaining in a dehydrated state. Since the reactivated superabsorbent polymer does not absorb moisture, it can be easily handled thereafter, for example, it can be easily dried. As a result, a reactivated superabsorbent polymer can be obtained with reduced contaminants while suppressing an increase in cost.

[0031] Aspect 11 is a method according to aspect 9, wherein the pretreatment step includes a step of performing a polyvalent metal salt treatment on the used absorbent article to inactivate the superabsorbent polymer with polyvalent metal ions supplied from a polyvalent metal salt, and the method further includes a step of substituting the polyvalent metal ions of the inactivated superabsorbent polymer with an acidic substance before the dehydration and cleaning step or during the dehydration and cleaning step, and a step of neutralizing the superabsorbent polymer in which the polyvalent metal ions have been substituted with the acidic substance with an alkaline substance containing sodium during the dehydration and cleaning step.

[0032] In this method, by performing a polyvalent metal salt treatment as a pretreatment step, the superabsorbent polymer is inactivated with polyvalent metal ions, and the moisture absorbed by the superabsorbent polymer can be more appropriately reduced (dehydrated). That is, the amount of moisture to be treated in the dehydration and washing step in the used absorbent article can be more appropriately reduced. In addition, in the superabsorbent polymer, polyvalent metal ions are replaced with an acidic substance (acidic aqueous solution) before or during the dehydration and washing step, and then, during the dehydration and washing step, the superabsorbent polymer in which the polyvalent metal ions have been replaced with the acidic substance is neutralized with an alkaline substance (alkaline aqueous solution) containing sodium, so that the inactivated superabsorbent polymer can be reactivated in addition to the dehydration and washing. As a result, it is possible to obtain a reactivated superabsorbent polymer in which contaminants are suppressed while suppressing an increase in costs.

[0033] [Embodiment 12] A product in which materials recovered together by the method according to any one of embodiments 1 to 11 are used together as materials.

[0034] This product is a product in which the materials collected together by the above method, i.e., superabsorbent polymer and pulp fiber, or superabsorbent polymer, pulp fiber, and plastic material, are used together as materials. Examples of such products include absorbent materials (including absorbent sheets), cat litter, solid fuel, sandbag modifiers, building materials (including sound-absorbing materials and cement materials), injection molded products, etc. In this way, when reusing components of used absorbent articles, by using the materials collected together, it is possible to suppress the increase in costs that would occur if the components were collected separately.

[0035] Hereinafter, a method for recovering components of used absorbent articles according to an embodiment will be described. The recovery method can be considered as a method for producing reusable components, or in other words, a method for producing recycled components (e.g., recycled superabsorbent polymers, recycled pulp fibers).

[0036] However, used absorbent articles include absorbent articles that have been used, for example, those that contain excrement and those that do not contain excrement, as well as unused but discarded absorbent articles, for example, those that have been transferred or the like but not used, and those that have been manufactured or stored but have been disposed of (factory losses, storage losses, etc.). Absorbent articles include those that contain superabsorbent polymers and pulp fibers as absorbent materials, and examples of such articles include disposable diapers, urine pads, sanitary napkins, bed sheets, and pet sheets. Note that recycled superabsorbent polymers refer to superabsorbent polymers derived from used absorbent articles and that have been recovered and regenerated from used absorbent articles. Recycled pulp fibers refer to pulp fibers derived from used absorbent articles and that have been recovered and regenerated from used absorbent articles. Used absorbent articles contain contaminants. Examples of such contaminants include excrement and sebum, bacteria, odorous substances, and coloring substances derived therefrom, machine oils from manufacturing facilities, and various organic substances.

[0037] First, a configuration example of an absorbent article will be described. The absorbent article includes a top sheet, a back sheet, and an absorbent body disposed between the top sheet and the back sheet. An example of the size of the absorbent article is a length of about 15 to 100 cm and a width of 5 to 100 cm. The absorbent article may further include other members that are included in general absorbent articles, such as a diffusion sheet, a leak-proof wall, a side sheet, and an exterior sheet.

[0038] The material of the top sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-permeable nonwoven fabrics, synthetic resin films having liquid-permeable holes, and composite sheets of these. The material of the back sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, and composite sheets of these. The material of the diffusion sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-permeable nonwoven fabrics. The material of the leak-proof wall, side sheet, and exterior sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-impermeable nonwoven fabrics. The material of the nonwoven fabrics and synthetic resin films is not particularly limited as long as it can be used in absorbent articles, and examples thereof include synthetic resins. Examples of synthetic resins include olefin-based resins such as polyethylene and polypropylene, polyamide-based resins such as 6-nylon and 6,6-nylon, and polyester-based resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The nonwoven fabric may be made of natural fibers such as cotton, rayon, etc. In this embodiment, at least the nonwoven fabric and the synthetic resin film are referred to as plastic materials.

[0039] The absorbent material includes absorbent materials, that is, pulp fibers and superabsorbent polymers. Pulp fibers are not particularly limited as long as they can be used in absorbent articles, and examples thereof include cellulosic fibers. Cellulosic fibers include wood pulp, crosslinked pulp, non-wood pulp, regenerated cellulose, semi-synthetic cellulose, and the like. The size of pulp fibers includes an average value of the long diameter of the fibers of, for example, several tens of μm, preferably 20 to 40 μm, and an average value of the fiber length of, for example, several mm, preferably 2 to 5 mm. Superabsorbent polymers (SAPs) are not particularly limited as long as they can be used in absorbent articles and have acid groups, and examples thereof include those containing carboxyl groups, sulfo groups, and the like, and those containing carboxyl groups are preferred. Examples of such superabsorbent polymers include polyacrylates (containing carboxyl groups), polysulfonates (containing sulfo groups, and the like), and polymaleic anhydrides (containing carboxyl groups). The size of the superabsorbent polymer (when dry) can be, for example, an average particle size of several hundred μm, preferably 200 to 500 μm. The absorbent body may include a core wrap sheet formed of a liquid-permeable sheet such as tissue, which encloses the absorbent material.

[0040] One side and the other side of the absorbent are respectively bonded to the top sheet and the back sheet via an adhesive. In plan view, the part (peripheral part) of the top sheet that extends outwardly from the absorbent so as to surround the absorbent is bonded to the part (peripheral part) of the back sheet that extends outwardly from the absorbent so as to surround the absorbent. Therefore, the absorbent is enclosed inside the bonded body of the top sheet and the back sheet. When the absorbent has a core wrap sheet, the absorbent material is bonded to the core wrap sheet via an adhesive. Each of the diffusion sheet, the leak-proof wall, the side sheet, and the exterior sheet is also bonded to other components with an adhesive. There is no particular limit to the adhesive as long as it can be used as an absorbent article, and examples of the adhesive include hot melt adhesives. Examples of hot melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives that are mainly made of rubber such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefin-based adhesives such as polyethylene.

[0041] As described above, an absorbent article having the above-mentioned configuration contains some or all of the above-mentioned contaminants at the stage of a used absorbent article.

[0042] Next, a method for recovering components of used absorbent articles according to an embodiment will be described. A part or all of the components of used absorbent articles recovered by this recovery method are recycled (reused) as materials for various products.

[0043] FIG. 1 is a flow diagram showing an example of a method for recovering components of used absorbent articles according to an embodiment.

[0044] The method for recovering components of used absorbent articles includes a dehydration and washing step S3 and a separation step (separation and recovery step) S4, and may further include at least one of a crushing step S1, a pretreatment step S2, and a drying step S5. Each step will be specifically described below.

[0045] The crushing step S1 is a step of crushing used absorbent articles. The crushing device is not particularly limited as long as it can expose the superabsorbent polymer and pulp fibers inside, and examples thereof include a biaxial crusher (examples: biaxial rotary crusher, biaxial differential crusher, biaxial shear crusher). As a result, a part or the whole of the used absorbent article is chopped up to generate a plurality of small pieces including one or a plurality of constituent members. The size of the small pieces is not particularly limited as long as it can be handled in each subsequent step, and examples thereof include a square with one to 10 cm sides in a plan view or a size equivalent thereto (approximately the same area). Note that, here, crushing is also defined as a case where the sheets (examples: top sheet, back sheet, exterior sheet) constituting the outer surface of the used absorbent article are torn to release the superabsorbent polymer and pulp fibers inside to the outside. In this case, the multiple small pieces may include one or more pieces of a torn sheet, or one or more lumps containing discharged superabsorbent polymer and pulp fibers.

[0046] The crushing step S1 may be carried out in air or in a liquid. When the crushing step S1 is carried out in a liquid, the liquid may be, for example, water, and the aqueous solution used in the pretreatment step S2, i.e., an acidic aqueous solution (described later) and a polyvalent metal salt aqueous solution (described later). Therefore, when an acidic aqueous solution or a polyvalent metal salt aqueous solution is used as the liquid, the crushing step S1 and the pretreatment step S2 can be said to be carried out simultaneously.

[0047] The crushing step S1 is mainly performed to facilitate separation of one or more components of a used absorbent article from other components in the separation step S4, and therefore may be performed before the separation step S4. Therefore, the crushing step S1 may be performed before the separation step S4, and either before the dehydrating and washing step S3, during the dehydrating and washing step S3, or after the dehydrating and washing step S3. However, before the dehydrating and washing step S3 means either before the pretreatment step S2, during the pretreatment step S2, or after the pretreatment step S2.

[0048] In addition, when the crushing step S1 is not performed and uncrushed used absorbent articles are used as they are in the dehydration and cleaning step S3 (which may or may not have been subjected to the pretreatment step S2), for example, by using an organic solvent (described later) as a dehydrating agent, the adhesive of the used absorbent articles can be dissolved in the organic solvent, and the used absorbent articles can be disassembled into individual component parts.

[0049] The pretreatment step S2 is a step of reducing the moisture absorbed by the used absorbent article (particularly the superabsorbent polymer) of the used absorbent article that has been crushed through the crushing step S1 or has not been crushed, that is, a step of dehydrating the used absorbent article. However, since the pretreatment step S2 is a step performed before the dehydration and washing step S3, it is sufficient that the used absorbent article or its crushed counterpart can be dehydrated to a certain extent, and it is not necessary to dehydrate it completely. The proportion of moisture to be dehydrated can be, for example, 10 to 90% by mass of the moisture absorbed in the used absorbent article.

[0050] Specifically, the pretreatment step S2 is a step of performing at least one of the following pretreatments on the used absorbent article: acidic aqueous solution treatment, polyvalent metal salt treatment, high-pressure steam treatment, freeze-drying treatment, and organic solvent treatment. These treatments are treatments for dehydrating the superabsorbent polymer. The acidic aqueous solution treatment is a treatment for contacting the superabsorbent polymer with an acidic aqueous solution. The polyvalent metal salt treatment is a treatment for contacting the superabsorbent polymer with an aqueous solution containing a polyvalent metal salt. The high-pressure steam treatment is a treatment for contacting the superabsorbent polymer with high-pressure steam. The freeze-drying treatment is a treatment for exposing the superabsorbent polymer to a low-temperature dry atmosphere. The organic solvent treatment is a treatment for contacting the high molecular weight absorbent polymer with a hydrophilic organic solvent. Although known methods can be used for each of these treatments, the acidic aqueous solution treatment and the polyvalent metal salt treatment are particularly as follows.

[0051] The step of performing the acid aqueous solution treatment as the pretreatment step S2 is a step of inactivating the superabsorbent polymer of the used absorbent article with an acid aqueous solution. For example, the used absorbent article (which may or may not have been crushed in the crushing step S1) is immersed in an acid aqueous solution to bring the superabsorbent polymer into contact with the acid and inactivate it. The acid aqueous solution treatment is preferable to the polyvalent metal salt treatment in that it is less likely to leave ash residue.

[0052] The acid (inactivator) in the acidic aqueous solution is not particularly limited, and examples thereof include acidic substances such as inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, and sulfuric acid is preferred from the viewpoint of not containing chlorine and from the viewpoint of cost and the like. Examples of organic acids include carboxylic acids having multiple carboxyl groups (e.g., citric acid), carboxylic acids having one carboxyl group (e.g., acetic acid), and sulfonic acids (e.g., methanesulfonic acid). As organic acids, those having multiple carboxyl groups are preferred, and citric acid is more preferred, from the viewpoint of easily forming a chelate complex with a divalent or higher metal (e.g., calcium) contained in excrement and the like, and of being unlikely to leave ash in the superabsorbent polymer and pulp fibers. The acid concentration of the acidic aqueous solution is not particularly limited as long as it can perform the dehydration function, and examples thereof include 0.1 to 30% by mass. In addition, the acid (inactivator) is preferably selected based on the acid dissociation constant (pK a , in water) a , in water).

[0053] The acidic aqueous solution preferably has a pH in a predetermined range. The upper limit of the pH is preferably 6.0, more preferably 5.0. By having a pH of 6.0 or less, the superabsorbent polymer can be easily dehydrated. The lower limit of the pH is preferably 0.5, more preferably 1.0. By having a pH of 0.5 or more, the pulp fibers, which are another object of recovery, can be less likely to be damaged. However, the pH is a value at 25°C, and is measured, for example, using a twin pH meter AS-711 manufactured by Horiba, Ltd.

[0054] The specific configuration of the device for performing the acidic aqueous solution treatment is not particularly limited as long as it can immerse the superabsorbent polymer in the acidic aqueous solution. The device has, for example, a tank in which used absorbent articles (or crushed ones) containing the superabsorbent polymer can be placed and in which the acidic aqueous solution can be stored, a supplying means for supplying the acidic aqueous solution into the tank, and a stirring means for stirring the acidic aqueous solution in the tank.

[0055] In the acidic aqueous solution treatment, the temperature of the acidic aqueous solution is not particularly limited, and may be, for example, room temperature (25° C.). In order to increase the reaction rate, the acidic aqueous solution may be heated to a temperature range lower than 100° C. The treatment time is not particularly limited, and may be, for example, about 5 to 60 minutes.

[0056] When a step of performing an acidic aqueous solution treatment is performed as the pretreatment step S2, a reactivation step is then performed to activate the superabsorbent polymer inactivated by the acidic aqueous solution treatment using alkali metal ions supplied from an alkali metal ion source. The reactivation step may be performed before the dehydration and cleaning step S3. Alternatively, the reactivation step may be included in the dehydration and cleaning step S3 and therefore may be performed during the dehydration and cleaning step S3. In that case, an aqueous solution containing an alkali metal ion source is added to the solution in the dehydration and cleaning step S3. Alternatively, the reactivation step may be performed after the dehydration and cleaning step S3.

[0057] Specifically, the reactivation process reactivates the inactivated superabsorbent polymer with alkali metal ions in an aqueous alkali solution, which is an aqueous solution containing an alkali metal ion source. At that time, the inactivated superabsorbent polymer is neutralized by replacing the H ions in the superabsorbent polymer with alkali metal ions, and becomes a reactivated superabsorbent polymer. That is, the water absorption ability of the superabsorbent polymer is restored. Note that, when the reactivation process is performed during the dehydration and washing process S3, the reactivated superabsorbent polymer does not absorb water because a dehydrating agent is present around the reactivated superabsorbent polymer.

[0058] Examples of the alkali metal ion include lithium ion, sodium ion, and potassium ion, as well as any combination thereof. The alkali metal ion source is not particularly limited as long as it can supply the alkali metal ion, and examples thereof include hydroxides of alkali metals, and salts of hydroxides of alkali metals and acids having a larger acid dissociation constant than the acid group of the superabsorbent polymer. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide, as well as any combination thereof. Examples of the salt include lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium chloride, sodium chloride, and potassium chloride. The aqueous solution containing the alkali metal ion source is preferably neutral or alkaline, and is preferably alkaline. The concentration of the alkali metal ion source in the alkaline aqueous solution is not particularly limited as long as the superabsorbent polymer is reactivated, and when a hydroxide of an alkali metal is used as the alkali metal ion source, the concentration may be, for example, 0.5 to 50 mass%.

[0059] The specific configuration of the device for carrying out the reactivation process is not particularly limited as long as it can immerse the inactivated superabsorbent polymer in the alkaline aqueous solution. The device has, for example, a tank in which a used absorbent article (or a crushed one thereof) containing a superabsorbent polymer can be placed and in which an alkaline aqueous solution can be stored, a supply means for supplying the alkaline aqueous solution into the tank, and a stirring means for stirring the alkaline aqueous solution in the tank.

[0060] In the reactivation treatment, the temperature of the alkaline aqueous solution is not particularly limited, and may be, for example, room temperature (25° C.). In order to increase the reaction rate, the alkaline aqueous solution may be heated to a temperature range lower than 100° C. The treatment time is not particularly limited, and may be, for example, about 5 to 60 minutes.

[0061] The step of performing the polyvalent metal salt treatment as the pretreatment step S2 is a step of inactivating the superabsorbent polymer of the used absorbent article with polyvalent metal ions supplied from the polyvalent metal salt. For example, the step is a step of inactivating the superabsorbent polymer by contacting it with the polyvalent metal ions by immersing the used absorbent article (which may or may not have been crushed in the crushing step S1) in an aqueous solution of the polyvalent metal salt. The polyvalent metal salt treatment is preferable in that dehydration proceeds more easily than the acid aqueous solution treatment.

[0062] The polyvalent metal salt in the polyvalent metal salt aqueous solution is not particularly limited, and examples thereof include alkaline earth metal salts and transition metal salts. Examples of alkaline earth metal salts include salts of beryllium, magnesium, calcium, strontium, and barium, with calcium chloride, calcium nitrate, magnesium chloride, and magnesium nitrate being preferred, and calcium chloride being more preferred. Examples of transition metal salts include salts of iron, cobalt, nickel, copper, and aluminum, with inorganic acid salts or organic acid salts thereof being preferred. Examples of inorganic acid salts include iron chloride, iron sulfate, iron phosphate, iron nitrate, cobalt chloride, cobalt sulfate, cobalt phosphate, cobalt nitrate, nickel chloride, nickel sulfate, copper chloride, copper sulfate, and aluminum sulfate. Examples of organic acid salts include iron lactate, cobalt acetate, cobalt stearate, nickel acetate, and copper acetate. The concentration of the polyvalent metal salt in the aqueous polyvalent metal salt solution is not particularly limited as long as it can perform the dehydrating function, and when an alkaline earth metal salt is used as the polyvalent metal, the concentration is, for example, 0.1 to 10 mass %.

[0063] The specific configuration of the device for performing the polyvalent metal salt treatment is not particularly limited as long as it can immerse a superabsorbent polymer in an aqueous solution of a polyvalent metal salt. The device has, for example, a tank in which a used absorbent article (or a disassembled product thereof) containing a superabsorbent polymer can be placed and in which an aqueous solution of a polyvalent metal salt can be stored, a supply means for supplying the aqueous solution of a polyvalent metal salt into the tank, and a stirring means for stirring the aqueous solution of a polyvalent metal salt in the tank.

[0064] In the polyvalent metal salt treatment, the temperature of the polyvalent metal salt aqueous solution is not particularly limited, and may be, for example, room temperature (25°C). In order to increase the reaction rate, the polyvalent metal salt aqueous solution may be heated at a temperature lower than 100°C. The treatment time is not particularly limited, and may be, for example, about 10 to 120 minutes. The pH of the polyvalent metal salt aqueous solution is not particularly limited, and may be, for example, 11 or less. When an alkaline compound is used, the pH of the aqueous solution is preferably greater than 7 and less than 11.

[0065] When the polyvalent metal salt treatment is performed as the pretreatment step S2, the polyvalent metal ions of the superabsorbent polymer inactivated by the polyvalent metal salt treatment are replaced with an acidic substance (acidic aqueous solution) (acidic substance replacement treatment), and then the superabsorbent polymer in which the polyvalent metal ions have been replaced with the acidic substance is neutralized with an alkaline substance (alkaline aqueous solution) containing sodium (alkaline substance neutralization treatment). The step of replacing the polyvalent metal ions with an acidic substance is performed before the dehydration and cleaning step S3 or during the dehydration and cleaning step S3. When the step is performed during the dehydration and cleaning step S3, an aqueous solution containing an acidic substance is added to the solution in the dehydration and cleaning step S3. On the other hand, the step of neutralizing the superabsorbent polymer with an alkaline substance is performed after the step of replacing the polyvalent metal ions with an acidic substance, during the dehydration and cleaning step or after the dehydration and cleaning step S3. When the step is performed during the dehydration and cleaning step S3, an aqueous solution containing an alkaline substance having sodium is added to the solution in the dehydration and cleaning step S3.

[0066] The step of replacing the polyvalent metal ions with an acidic substance (acidic substance replacement treatment) of the superabsorbent polymer inactivated by the polyvalent metal salt treatment described above is substantially the same as the acidic aqueous solution treatment described above. However, the acid in the acidic aqueous solution is preferably a strong inorganic acid. Examples of such inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, and sulfuric acid is preferred from the viewpoint of not containing chlorine and from the viewpoint of cost, etc.

[0067] The above-mentioned step of neutralizing the superabsorbent polymer in which the polyvalent metal ions have been substituted with an acidic substance using an alkaline substance (alkaline substance neutralization treatment) is substantially the same as the above-mentioned reactivation treatment, except that the alkali metal ion source is an alkaline substance containing sodium, such as sodium hydroxide, and the alkali metal ion in the alkaline aqueous solution, which is the aqueous solution containing the alkali metal ion source, is a sodium ion.

[0068] In the above pretreatment step S2, the ratio of the used absorbent article (or a plurality of small pieces) in the aqueous solution used in the various treatments is not particularly limited, as long as the various treatments can be carried out. The ratio is, for example, 0.1 to 50 mass%, and preferably 1 to 40 mass%. When the ratio is 0.1 mass% or more, the treatments can be carried out efficiently. When the ratio is 50 mass% or less, the various treatments can be carried out easily.

[0069] It is preferable that the pretreatment step S2 includes a step of separating and removing the water generated in the pretreatment step S2 before the dehydration and cleaning step S3. For example, the aqueous solution containing the used absorbent article (or a plurality of small pieces) in the pretreatment step S2 is filtered through a screen or the like to separate and remove the water generated in the pretreatment step S2. In this way, by removing the water once before the dehydration and cleaning step S3, the solution containing the dehydrating agent and the oxidizing agent (described later) in the dehydration and cleaning step S3 is not diluted, and the treatment can be performed at the desired concentration.

[0070] The dehydration and cleaning process S3 is a process in which a mixture containing a superabsorbent polymer having acid groups and pulp fibers, which are components of a used absorbent article, is dehydrated and cleaned with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and pulp fibers.

[0071] The mixture containing the superabsorbent polymer and pulp fibers, which are the components, is not particularly limited as long as it contains the superabsorbent polymer and pulp fibers of a used absorbent article. For example, the mixture may be a used absorbent article that has not been subjected to the crushing step S1 or the pretreatment step S2. When the used absorbent article has been subjected to the crushing step S1, the mixture is a plurality of small pieces formed by crushing the used absorbent article, and contains the superabsorbent polymer and pulp fibers, but the superabsorbent polymer and pulp fibers are not individually separated. When the used absorbent article has been subjected to the pretreatment step S2, the mixture is a used absorbent article that has been subjected to pretreatment, and contains the superabsorbent polymer and pulp fibers that have been dehydrated to a certain extent, but the superabsorbent polymer and pulp fibers are not individually separated. When used absorbent articles have been subjected to both the crushing step S1 and the pretreatment step S2, the mixture is a plurality of small pieces that have been pretreated and contains superabsorbent polymer and pulp fibers that have been dehydrated to a certain extent, but the superabsorbent polymer and pulp fibers are not separated individually. The mixture may also be a mixture containing superabsorbent polymer and pulp fibers that have been prepared separately in advance, regardless of the crushing step S1 or the pretreatment step S2.

[0072] The mixture may further contain a plastic material that is a component of the used absorbent article. In this case, the dehydration and washing step S3 is a step of dehydrating and washing the mixture containing the superabsorbent polymer, pulp fiber, and plastic material that are components of the used absorbent article with a solution containing a dehydrating agent and an oxidizing agent. The mixture containing the superabsorbent polymer, pulp fiber, and plastic material that are components of the used absorbent article is not particularly limited as long as it contains the superabsorbent polymer, pulp fiber, and plastic material of the used absorbent article, and may or may not have been subjected to the crushing step S1 and / or the pretreatment step S2, as in the case of the mixture containing the superabsorbent polymer and pulp fiber described above.

[0073] The solution containing the dehydrating agent and the oxidizing agent may be a solution composed only of the dehydrating agent and the oxidizing agent, or may contain other solvents, such as organic solvents and water, as long as they do not affect the dehydration and oxidation. The total ratio of the dehydrating agent and the oxidizing agent in the solution is, for example, 50% by mass or more, and preferably higher from the viewpoint of the effect of dehydration and oxidation, and therefore is preferably 70% by mass or less, more preferably 80% by mass or less, and even more preferably 90% by mass or less. However, when water is contained as another solvent, the ratio of water is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0074] There are no particular limitations on the dehydrating agent, so long as it is difficult to be oxidized by an oxidizing agent and is capable of dehydrating the superabsorbent polymer and pulp fibers contained in the used absorbent article. The dehydrating agent is, for example, a liquid, and is considered to be capable of dissolving and dehydrating the moisture contained in the components and dissolving and removing contaminants in itself, but is not limited to this mechanism.

[0075] Examples of the dehydrating agent include organic solvents. Examples of the organic solvent include hydrophilic organic solvents and polar organic solvents. Examples of organic solvents that belong to at least one of these groups include ketone-based organic solvents and alcohol-based organic solvents. Examples of other organic solvents include fluorine-based organic solvents. Examples of the ketone-based organic solvent include acetone. Acetone dissolves water well, is not easily oxidized by an oxidizing agent, and has the property of protecting functional groups. Therefore, acetone can dehydrate the superabsorbent polymer and pulp fibers while suppressing the decomposition (dissolution) of the constituent members, particularly the easily decomposed superabsorbent polymer, and can remove part or all of the contaminants contained in these constituent members. In addition, when the dehydrating agent is an organic solvent, it can dissolve the adhesive that bonds the constituent members of the used absorbent article, making it easier to separate the constituent members from each other. Examples of the alcohol-based organic solvent include ethanol and methanol. Examples of the fluorine-based organic solvent include 1-chloro-2,3,3-trifluoropropene and 1,1,1,3,3-pentafluorobutane.

[0076] The proportion of the dehydrating agent in the solution is, for example, 50% by mass or more. In terms of the effect of dehydration and removing contaminants, the proportion of the dehydrating agent in the solution is preferably higher, and when the oxidizing agent is a gas, the proportion is preferably 70% by mass or more, and more preferably 90% by mass or more.

[0077] There are no particular limitations on the oxidizing agent, so long as it can remove contaminants contained in used absorbent articles while suppressing their effects on the constituent members (e.g., oxidative decomposition of superabsorbent polymers, damage to pulp fibers). The oxidizing agent is, for example, a liquid or a gas mixed into a liquid, and is thought to reduce contaminants by oxidatively decomposing the contaminants, lowering their molecular weight, and making them more soluble in the solution, but is not limited to this mechanism.

[0078] Examples of the oxidizing agent include ozone, hydrogen peroxide, and chlorine-based substances (e.g., chlorine), or a combination of two or more of them. These oxidizing agents have a relatively high oxidizing power, and therefore tend to reduce contaminants contained in components of used absorbent articles, such as superabsorbent polymers and pulp fibers, plastic materials, etc. This makes it possible to remove bacteria and reduce odorous and colored substances, and to sterilize, deodorize, and decolorize (bleach) the components. Note that when acetone is used as a dehydrating agent, hydrogen peroxide is not used as an oxidizing agent.

[0079] The oxidizing agent may be mixed into the liquid dehydrating agent, or may be mixed into another solvent (eg, organic solvent, water) and then mixed into the dehydrating agent.

[0080] When gaseous ozone is used as an oxidizing agent and gaseous ozone is supplied to a dehydrating agent to form a solution containing a dehydrating agent and an oxidizing agent, the ozone concentration in the solution is not particularly limited as long as it can reduce contaminants contained in the components. The ozone concentration is, for example, 0.2 to 2 mass ppm, preferably 0.4 to 1.5 mass ppm. A concentration of 0.2 mass ppm or more makes it easy to reduce contaminants, and a concentration of 2 mass ppm or less can suppress oxidative decomposition of the superabsorbent polymer and damage to pulp fibers. The contact time between the ozone-containing solution and the components is not particularly limited as long as it can reduce contaminants contained in the components. The contact time is generally shorter when the ozone concentration is high and longer when the ozone concentration is low. The contact time is, for example, 1 to 200 minutes, preferably 2 to 60 minutes. The product of ozone concentration (ppm by mass) and contact time (min) (hereinafter also referred to as "CT value") is preferably 0.2 to 40 ppm by mass·min, more preferably 0.5 to 20 ppm by mass·min. A CT value of 0.2 ppm by mass·min or more can easily reduce contaminants, and a CT value of 40 ppm by mass·min or less can suppress oxidative decomposition of components, particularly highly water-absorbent polymers that are easily decomposed. Treatment with ozone can reduce contaminants contained in components, for example, remove bacteria, and reduce odorous and colored substances, and can sterilize, deodorize, and decolorize (bleach) the components. Examples of ozone generators that supply gaseous ozone to a dehydrating agent include the ED-OWX-2 ozone water exposure tester manufactured by Ecodesign Co., Ltd., the OS-25V ozone generator manufactured by Mitsubishi Electric Corporation, and the REX MC ozonizer MC-985S manufactured by a subsidiary of Rex Industrial Co., Ltd.

[0081] When a gas (e.g., ozone) is used as the oxidizing agent, the oxidizing agent may be supplied to the dehydrating agent, for example, by the following method. In this method, an oxidizing agent is generated in a predetermined amount by an oxidizing agent generator, and the oxidizing agent is continuously supplied to the dehydrating agent in the treatment tank at a predetermined air volume, while the same air volume of waste oxidizing agent (used oxidizing agent) is continuously discarded (discharged) outside the treatment tank. In this case, a flow of the oxidizing agent is easily generated, new oxidizing agent is easily continuously supplied to the surface of the component, and reactants are easily continuously discharged from the surface. Therefore, the oxidation reaction on the surface of the component can proceed more reliably.

[0082] Alternatively, the oxidizing agent may include either an active species generated by irradiating another oxidizing agent contained in the solution with ultraviolet light, or an active species generated by irradiating water and / or another oxidizing agent contained in the solution with ultraviolet light when the solution contains water. For example, when the wavelength of ultraviolet light is 253.7 nm, the active species generated by the reaction between ultraviolet light and an oxidizing agent (ozone + water, hydrogen peroxide), i.e., hydroxyl radicals, can decompose at least a part of the pollutant (organic matter). When the wavelength of ultraviolet light is 184.9 nm, the active species generated by the reaction between ultraviolet light and water, i.e., hydroxyl radicals, can decompose at least a part of the pollutant (organic matter).

[0083] The proportion of used absorbent articles (or a plurality of small pieces) in the above solution is not particularly limited as long as the above dehydration and washing step S3 can be carried out. The proportion may be, for example, 0.1 to 20% by mass, and preferably 1 to 10% by mass. When the proportion is 0.1% by mass or more, the treatment can proceed efficiently. When the proportion is 20% by mass or less, the dehydration and washing can proceed easily.

[0084] Contaminants such as excrement, sebum, bacteria, odorous substances, and coloring substances derived from them, machine oils in manufacturing equipment, and various organic substances are believed to be reduced as follows. That is, by dehydration, mainly contaminants absorbed inside the components are discharged to the outside together with moisture. At that time, the contaminants attached to the components are discharged to the outside along with the released moisture. At the same time, by oxidation, mainly contaminants attached to the components (including those discharged from the inside and attached) are oxidatively decomposed, reduced in molecular weight, solubilized, and removed. This also makes it possible to sterilize, deodorize, and bleach the components. However, the reduction of contaminants in the above-mentioned components is not limited to this mechanism.

[0085] In the dehydration washing step S3, the temperature of the dehydration washing is not particularly limited as long as the dehydration washing treatment can be performed, but is at least performed at a temperature lower than the boiling point of the dehydrating agent. The temperature of the dehydration washing can be, for example, room temperature (e.g., 25°C) to 50°C, and preferably 30 to 40°C. When the temperature is room temperature or higher, the time required for dehydration and washing can be easily shortened. When the temperature is 50°C or lower, evaporation (boiling) of the organic solvent can be easily suppressed, dehydration condensation of the acid group of the highly absorbent polymer can be suppressed, and the decrease in the water absorbency can be easily suppressed. The time of the dehydration washing is not particularly limited as long as the dehydration washing treatment can be performed, but can be, for example, 1 to 200 minutes.

[0086] The specific configuration of the device for performing the dehydration and washing step S3 is not particularly limited as long as it can bring into contact (or immerse) a mixture containing components of used absorbent articles (e.g., superabsorbent polymer, pulp fiber, plastic material) with a solution containing a dehydrating agent and an oxidizing agent. The device has, for example, a tank in which used absorbent articles (or crushed ones) can be placed and in which a solution containing a dehydrating agent and an oxidizing agent can be stored, a supplying means capable of supplying the dehydrating agent and the oxidizing agent into the tank, and a stirring means capable of stirring the solution in the tank.

[0087] However, in the present method, when an acidic aqueous solution treatment is performed as the pretreatment step S2 and the reactivation treatment is performed during the dehydration and washing step S3, it is preferable that the solution containing the oxidizing agent and the dehydrating agent in the dehydration and washing step S3 contains as little unnecessary moisture as possible (except for the moisture discharged from the used absorbent article). An aqueous solution containing an alkali metal ion source is supplied to the solution in addition to the oxidizing agent and the dehydrating agent. In this way, the reactivation treatment is performed while the dehydration and washing step S3 is being performed. In this case, the used absorbent article (or its crushed product) may be supplied after the aqueous solution containing the alkali metal ion source is supplied to the solution containing the oxidizing agent and the dehydrating agent, or the used absorbent article may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and after a predetermined time has elapsed, the aqueous solution containing the alkali metal ion source may be supplied.

[0088] However, in this method, when a polyvalent metal salt treatment is performed as the pretreatment step S2 and the acidic substance replacement treatment is performed during the dehydration and washing step S3, it is preferable that the solution containing the oxidizing agent and the dehydrating agent in the dehydration and washing step S3 contains as little moisture as possible (except for the moisture discharged from the used absorbent article). An aqueous solution containing an acidic substance is supplied to the solution in addition to the oxidizing agent and the dehydrating agent. In this way, the acidic substance replacement treatment is performed while the dehydration and washing step S3 is being performed. In this case, the aqueous solution containing the acidic substance may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and then the used absorbent article (or crushed product thereof) may be supplied, or the used absorbent article may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and the aqueous solution containing the acidic substance may be supplied after a predetermined time.

[0089] Furthermore, in the case of performing a polyvalent metal salt treatment as the pretreatment step S2, and performing an alkaline substance neutralization treatment in the middle of the dehydration and washing step S3 after the acidic substance replacement treatment, it is preferable that the solution containing an oxidizing agent and a dehydrating agent in the dehydration and washing step S3 contains as little unnecessary moisture as possible (except for the moisture discharged from the used absorbent article). An aqueous solution containing an alkaline substance containing sodium is supplied to the solution in addition to the oxidizing agent and the dehydrating agent. Thereby, the alkaline substance neutralization treatment is performed while the dehydration and washing step S3 is being performed. In that case, the used absorbent article (or its crushed product) may be supplied after the aqueous solution containing an alkaline substance containing sodium is supplied to the solution containing the oxidizing agent and the dehydrating agent, or the used absorbent article may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and after a predetermined time has elapsed, the aqueous solution containing an alkaline substance containing sodium may be supplied.

[0090] When both the acidic substance replacement treatment and the alkaline substance neutralization treatment are performed in the dehydration and washing step S3, first, used absorbent articles (or crushed products thereof) are supplied to a solution containing an oxidizing agent and a dehydrating agent, and a dehydration and washing treatment is performed for a predetermined time (e.g., 1 to 30 minutes). Next, an aqueous solution containing an acidic substance is supplied to the solution, and an acidic substance replacement treatment is performed for a predetermined time (e.g., 1 to 30 minutes). Next, an aqueous solution containing an alkaline substance including sodium is supplied to the solution, and an alkaline substance neutralization treatment is performed for a predetermined time (e.g., 1 to 30 minutes).

[0091] The separation step S4 is a step of separating at least the superabsorbent polymer and the pulp fibers together from the solution containing the mixture containing the superabsorbent polymer and the pulp fibers. In this separation step S4, the solution containing the mixture containing the superabsorbent polymer and the pulp fibers is separated into the pulp fibers and the superabsorbent polymer, and a solution containing contaminants and other materials. As a result, the pulp fibers and the superabsorbent polymer that have been dehydrated and washed and have reduced contaminants and other materials are separated together and recovered. Here, the separation step S4 can also be called a separation and recovery step, since components such as the pulp fibers and the superabsorbent polymer are separated and recovered.

[0092] The specific configuration of the device for carrying out the separation step S4 is not particularly limited as long as it can separate the solution containing the mixture containing the superabsorbent polymer and pulp fiber into the pulp fiber and superabsorbent polymer and the solution containing the contaminants and other materials. For example, the device may have a screen that does not allow the superabsorbent polymer and pulp fiber to pass through, but allows the solution (including the contaminants and other materials (small foreign matter)) to pass through. If the mixture contains other materials (large foreign matter) larger than the superabsorbent polymer and pulp fiber, the device may further have a screen that allows the superabsorbent polymer and pulp fiber to pass through, but does not allow the other materials (large foreign matter) to pass through.

[0093] Since the pulp fibers and the superabsorbent polymer are separated and collected together, the pulp fibers and the superabsorbent polymer can be easily reused together as materials for a single product. Such products include absorbent sheets, absorbents, cat litter, sandbag modifiers, and solid fuels. The superabsorbent polymer and the pulp fibers that have been separated together may be further separated from each other using a screen or the like.

[0094] However, the absorbent sheet is an absorbent article, and is formed, for example, by arranging the pulp fibers and the superabsorbent polymer, which are separated and recovered together, as they are, or by mixing them with unused absorbent material, between the top sheet and the back sheet as an absorbent material. The absorbent body is formed, for example, by wrapping the pulp fibers and the superabsorbent polymer, which are separated and recovered together, as they are, or by mixing them with unused absorbent material, as an absorbent material in a core wrap sheet. Cat litter is a water-absorbent granular material, and is formed, for example, by molding the pulp fibers and the superabsorbent polymer, which are separated and recovered together, into granular form together with molten resin. The sandbag modifier is a material that imparts water retention to the soil, and is, for example, by scattering the pulp fibers and the superabsorbent polymer, which are separated and recovered together, on the soil as they are, or by forming them into an absorbent sheet and placing them on the soil. The solid fuel is solid fuel itself, and is formed by melting and molding the pulp fibers and the superabsorbent polymer, which are separated and recovered together, with flammable resin.

[0095] The above-mentioned solution may further contain a plastic material that is a component of the used absorbent article. In this case, the separation step S4 is a step of separating the superabsorbent polymer, pulp fiber, and plastic material together from the solution containing a mixture of the superabsorbent polymer, pulp fiber, and plastic material that are components of the used absorbent article. As a result, the pulp fiber, superabsorbent polymer, and plastic material that have been dehydrated and washed and have reduced contaminants and other materials are separated and recovered together. An example of an apparatus that achieves this is an apparatus having one or more screens as described above.

[0096] Since the pulp fiber, the superabsorbent polymer, and the plastic material are separated and collected together, the pulp fiber, the superabsorbent polymer, and the plastic material can be easily reused together as materials for a single product. Such products include cat litter, building materials (including sound-absorbing materials and cement materials), injection molded products, and solid fuels. The plastic material may be further separated from the pulp fiber, the superabsorbent polymer, and the plastic material that have been separated together using a screen or the like. This allows the plastic material to be used in an individual manner (e.g., bags by the inflation method).

[0097] However, cat litter is formed, for example, by melting the plastic material from among the pulp fiber, super absorbent polymer, and plastic material that are separated and collected together, and molding the pulp fiber, super absorbent polymer, and plastic material together into granular form. Sound-absorbing material is a bag or plate-shaped product in which sound-absorbing granular material (such as plastic material) is packed to a certain thickness, and is formed, for example, by melting the plastic material from among the pulp fiber, super absorbent polymer, and plastic material (which may further include resin) that are separated and collected together, and molding the pulp fiber, super absorbent polymer, and plastic material together into granular or plate form. Cement material is a material for concrete or mortar, and is formed, for example, by mixing all or part of the pulp fiber, super absorbent polymer, and plastic material that are separated and collected together into cement. Injection-molded products are injection-molded products, and are formed, for example, by melting the pulp fiber, super absorbent polymer, and plastic material (which may further include resin) that are separated and collected together, and molding them into injection form. The solid fuel is formed, for example, by melting and molding pulp fibers, superabsorbent polymers, and plastic materials (with the addition of flammable resins) that have been separated and recovered together.

[0098] The drying step S5 is a step of drying at least the superabsorbent polymer and the pulp fibers separated in the separation step S4.

[0099] The drying step S5 is carried out by placing the components in a dry atmosphere at a temperature higher than room temperature, or by blowing dry air at a temperature higher than room temperature onto the components. The drying temperature is, for example, 40 to 110°C, and preferably 50 to 100°C. A drying temperature of 40°C or higher can shorten the drying time. A drying temperature of 110°C or lower can suppress adhesion between components and deterioration of the components due to heat. The drying time is, for example, 30 to 300 minutes. The drying step S5 may be carried out under reduced pressure, for example, 0.1 to 100 kPa, in order to accelerate drying.

[0100] The drying step S5 is performed at least one of after the dehydrating and cleaning step S3 and before the separating step S4, and after the separating step S4. However, in cases where the components are easily dried by using a dehydrating agent in the dehydrating and cleaning step S3, the drying step S5 can be omitted.

[0101] This method may include a re-supply step of recovering the dehydrating agent (e.g., organic solvent) from the solution after the separation step S4 and supplying it to the dehydration and washing step S3. In this re-supply step, the dehydrating agent in the solution from which at least the superabsorbent polymer and pulp fibers have been separated in the separation step S4 is recovered, and after reducing contaminants as necessary, it is supplied to the dehydration and washing step S3.

[0102] For example, the solution from which at least the superabsorbent polymer and pulp fibers have been separated contains contaminants such as excrement in addition to the dehydrating agent. Therefore, the solution is heated and / or depressurized to boil and evaporate the dehydrating agent contained in the solution. The dehydrating agent is then recovered by cooling the vapor. In other words, the dehydrating agent is distilled. As a result, the recovered dehydrating agent has reduced contaminants. The dehydrating agent is then supplied again to the dehydration and washing step S3.

[0103] In this way, in the method for recovering components of used absorbent articles, in the dehydration and washing step S3, the superabsorbent polymer having an acid group and the pulp fiber are combined, and dehydrated and washed simultaneously using a dehydrating agent and an oxidizing agent. That is, the moisture absorbed by the superabsorbent polymer and the pulp fiber, which may contain contaminants such as excrement, can be dehydrated from both the superabsorbent polymer and the pulp fiber by the dehydrating agent. At the same time, the contaminants contained in the superabsorbent polymer and the pulp fiber, such as bacteria, odorous substances, and coloring substances derived from excrement, can be reduced from both the superabsorbent polymer and the pulp fiber by the oxidizing agent. In this way, by dehydrating and washing at least the superabsorbent polymer and the pulp fiber together, the number of steps can be reduced and costs can be reduced compared to the case of performing dehydration and washing separately. In this method, in the separation step (separation and recovery step) S4, at least the superabsorbent polymer and the pulp fiber are separated and recovered from the material dehydrated and washed in the dehydration and washing step S3. This makes it possible to suppress the increase in cost that would occur if the superabsorbent polymer and the pulp fiber were used together when recycling components of used absorbent articles (examples include absorbent sheets, cat litter, soil conditioners, and solid fuels) and the superabsorbent polymer and the pulp fiber were used together and then separated and collected. In this way, the synergistic effect of the dehydration and separation step S3 and the separation step (separation and collection step) S4 makes it possible to easily reuse multiple components collectively while suppressing the increase in cost in the method for collecting components of used absorbent articles.

[0104] In a preferred embodiment of the present method, in the dehydration and washing step S3, the superabsorbent polymer, pulp fiber, and plastic material are dehydrated and washed simultaneously using a dehydrating agent and an oxidizing agent. That is, the moisture contained in each of the superabsorbent polymer, pulp fiber, and plastic material, which may contain contaminants, can be dehydrated in all of these materials by using the dehydrating agent. At the same time, the contaminants contained in each of the superabsorbent polymer, pulp fiber, and plastic material can be reduced in all of these materials by using the oxidizing agent. This allows the contaminants to be reduced in all of these materials. In this way, by dehydrating the superabsorbent polymer, pulp fiber, and plastic material together and washing the superabsorbent polymer, pulp fiber, and plastic material together, the number of steps can be reduced and costs can be reduced compared to the case of dehydrating and washing them separately. In the present method, in the separation step (separation and recovery step) S4, at least the superabsorbent polymer, pulp fiber, and plastic material are separated and recovered together from the material dehydrated and washed in the dehydration and washing step S3. This makes it possible to suppress the increase in costs that would occur if the superabsorbent polymers, pulp fibers, and plastic materials used together were to be separated and recovered individually when the constituent parts of used absorbent articles are reused and the materials are used together (for example, cat litter, building materials (including sound-absorbing materials and cement materials), injection molded products, and solid fuels).In this way, the synergistic effect of the above-mentioned dehydration and separation step S3 and separation step (separation and recovery step) S4 makes it possible to easily reuse multiple constituent parts collectively while suppressing the increase in costs in the method for recovering constituent parts of used absorbent articles.

[0105] In a preferred embodiment of this method, the superabsorbent polymer, pulp fibers, and plastic materials separated together in the separation step (separation and recovery step) S4 have already been dehydrated and washed in the dehydration and washing step S3. Therefore, by separating the plastic materials from the superabsorbent polymer, pulp fibers, and plastic materials, a reusable plastic material can be obtained without further washing. This makes it possible to suppress an increase in the number of washing steps and thus an increase in costs, while also allowing the plastic materials of the superabsorbent polymer, pulp fibers, and plastic materials separated together to be used together to be used individually (e.g., bags made by the inflation method).

[0106] In a preferred embodiment of this method, a crushing step S1 for crushing used absorbent articles is performed before the separation step (separation and recovery step) S4 and either before, during or after the dehydration and washing step S3. This makes it possible to more reliably separate at least the superabsorbent polymer and pulp fibers, or the superabsorbent polymer, pulp fibers and plastic material together from the material dehydrated and washed in the dehydration and washing step S3 in the separation step (separation and recovery step) S4.

[0107] In a preferred embodiment of the present method, the materials separated together, i.e., the superabsorbent polymer and pulp fibers, or the superabsorbent polymer, pulp fibers, and plastic material, are dried in a drying step S5 at least one of the steps after the dehydration and washing step S3 and the separation step (separation and recovery step) S4. Therefore, since the materials are dehydrated and easily dried in advance in the dehydration and washing step S3, the energy required for drying can be reduced and the materials can be easily reused together. Therefore, the processing burden is reduced compared to the case where the materials are dried separately, and costs can be reduced.

[0108] In a preferred embodiment of the present method, the dehydration and washing step S3 contains at least one of ozone, hydrogen peroxide, and a chlorine-based substance, which have strong oxidizing power, as an oxidizing agent, so that contaminants contained in the superabsorbent polymer and the pulp fiber, or the superabsorbent polymer, the pulp fiber, and the plastic material, can be more reliably reduced together.

[0109] In a preferred embodiment of the present method, the dehydrating and washing step S3 contains a ketone-based organic solvent that is difficult to oxidize even with a strong oxidizing agent, so that the moisture that may contain contaminants absorbed in the superabsorbent polymer and the pulp fiber, or in the superabsorbent polymer, the pulp fiber, and the plastic material, can be dehydrated together more reliably without being affected by the oxidizing power of the oxidizing agent.

[0110] In a preferred embodiment, the method includes a pretreatment step S2 for reducing the amount of moisture absorbed by the used absorbent article before the dehydration and washing step S3. Therefore, the amount of moisture in the used absorbent article to be treated in the dehydration and washing step S3 can be reduced in advance in the pretreatment step S2. This makes it possible to more reliably sterilize, deodorize, and bleach the bacteria, odorous substances, and coloring substances contained in each of the superabsorbent polymer and the pulp fiber, or each of the superabsorbent polymer, the pulp fiber, and the plastic material, all together in the dehydration and washing step S3.

[0111] In a preferred embodiment of the present method, the used absorbent article is subjected to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, a high-pressure steam treatment, a freeze-drying treatment, and an organic solvent treatment as a pretreatment step S2 prior to the dehydration and washing step S3, thereby more reliably reducing the moisture in the used absorbent article in advance, which is to be treated in the dehydration and washing step S3, in the pretreatment step S2.

[0112] In a preferred embodiment of the present method, the pretreatment step S2 is performed with an acidic aqueous solution to inactivate the superabsorbent polymer, thereby more appropriately reducing (dehydrating) the moisture absorbed by the superabsorbent polymer. That is, the amount of moisture to be treated in the dehydration and washing step S3 in the used absorbent article can be more appropriately reduced in advance. In addition, by using an alkali metal ion source in the dehydration and washing step S3, the superabsorbent polymer can be reactivated by alkali metal ions while remaining in a dehydrated state. Since the reactivated superabsorbent polymer does not absorb moisture, it can be easily handled thereafter, and for example, it can be easily dried. As a result, a reactivated superabsorbent polymer can be obtained with reduced contaminants while suppressing an increase in cost.

[0113] In another preferred embodiment of the present method, the polyvalent metal salt treatment is performed as the pretreatment step S2, whereby the superabsorbent polymer is inactivated with the polyvalent metal ion, and the moisture absorbed by the superabsorbent polymer can be more appropriately reduced (dehydrated). That is, the amount of moisture to be treated in the dehydration and washing step S3 in the used absorbent article can be more appropriately reduced. In addition to that, in the superabsorbent polymer, the polyvalent metal ion is replaced with an acidic substance (acidic aqueous solution) before or during the dehydration and washing step S3, and then, during the dehydration and washing step S3, the superabsorbent polymer in which the polyvalent metal ion has been replaced with the acidic substance is neutralized with an alkaline substance (alkaline aqueous solution) containing sodium, so that the inactivated superabsorbent polymer can be reactivated in addition to the dehydration and washing. As a result, it is possible to obtain a reactivated superabsorbent polymer in which contaminants are suppressed while suppressing an increase in cost.

[0114] This product is a product in which the materials collected together by the above method, i.e., superabsorbent polymer and pulp fiber, or superabsorbent polymer, pulp fiber, and plastic material, are used together as materials. Examples of such products include absorbent materials (including absorbent sheets), cat litter, solid fuel, sandbag modifiers, building materials (including sound-absorbing materials and cement materials), injection molded products, etc. In this way, when reusing components of used absorbent articles, by using the materials collected together, it is possible to suppress the increase in costs that would occur if the components were collected separately. EXAMPLES

[0115] Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these examples. In the following examples, the dehydration and washing step S3, which may affect the separation step (separation and recovery step) S4, was examined.

[0116] (1) Sample (a) For stability testing of dehydrating agents 0.1 g of a commercially available highly water-absorbent polymer (polyacrylate-based) was prepared, and the highly water-absorbent polymer was allowed to absorb 50 ml of distilled water to prepare sample A. A plurality of similar samples A were prepared. (b) For testing the removability of pollutants 10 g of a superabsorbent polymer (having an odor and coloration) removed from a used absorbent article containing excrement was prepared as sample B. A plurality of similar samples B were prepared.

[0117] (2) Evaluation method (a) Stability test of dehydrating agents (a-1) Dehydration test Acetone was prepared as a dehydrating agent. Example 1: One of the samples A was immersed in 200 ml of acetone in a container (Deschem three-neck flat-bottom flask reactor with a capacity of 500 ml, the same applies below) for 3 hours, and then the wet weight and dry weight were measured. Comparative Example 1: One of the samples A was immersed in 200 ml of distilled water in a container for 3 hours, and then the wet weight and dry weight were recorded. (a-2) Oxidation test Ozone was prepared as the oxidizing agent. Example 2: One of the specimens A was immersed in 200 ml of acetone in a container, and ozone was supplied to the container so that the generation rate was 60 mg / h and the air volume was 13 L / min. The same volume of waste ozone was continuously discharged outside the container. The wet weight and dry weight of specimen A were measured one hour after the start of the ozone supply. Example 3: One of the specimens A was immersed in 200 ml of acetone in a container, and ozone was supplied to the container so that the generated amount was 60 mg / h and the air volume was 13 L / min. The same amount of waste ozone was continuously discharged outside the container. The wet weight and dry weight of specimen A were measured 3 hours after the start of the ozone supply. Comparative Example 2: One of the specimens A was immersed in 200 ml of distilled water in a container, and ozone was supplied to the container so that the generated amount was 60 mg / h and the air volume was 13 L / min. The same amount of waste ozone was continuously discharged outside the container. The wet weight and dry weight of specimen A were recorded 3 hours after the start of the ozone supply. The ozone was supplied using an ozone generator: REX MC Ozonizer MC-985S manufactured by Rex Industrial Co., Ltd. (hereinafter the same applies.) Although the concentration of ozone dissolved in acetone could not be measured, it was thought to be in the range of approximately 0.2 to 2 ppm by mass.

[0118] (b) Pollutant removal test Acetone was prepared as a dehydrating agent, and ozone was prepared as an oxidizing agent. Example 4: One of the samples B was immersed in 250 ml of acetone in a container, and ozone was supplied to the container so that the generation rate was 60 mg / h and the air volume was 13 L / min. The same volume of waste ozone was continuously discharged outside the container. One hour after the start of the ozone supply, the sample B was measured to see if odorous substances had been removed (presence or absence of odor) and if colored substances had been removed (presence or absence of decolorization). Comparative Example 3: One of the samples B was immersed in 250 ml of acetone in a container, and ozone was not supplied. After 1 hour, the sample B was measured to see if the odorous substances had been removed (presence or absence of odor) and if the colored substances had been removed (presence or absence of decolorization). Comparative Example 4: One of the samples B was immersed in 250 ml of distilled water in a container, and ozone was not supplied. After 1 hour, the sample B was measured to see if the odorous substances had been removed (whether or not there was an odor), if the colored substances had been removed (whether or not there was a decolorization), and if the colored substances had been removed (whether or not there was a decolorization). Comparative Example 5: One of the samples B was immersed in 250 ml of distilled water in a container, and ozone was supplied to the container so that the generation rate was 60 mg / h and the air volume was 13 L / min. The same volume of waste ozone was continuously discharged outside the container. One hour after the start of the ozone supply, the sample B was measured to see if odorous substances had been removed (presence or absence of odor) and if colored substances had been removed (presence or absence of decolorization).

[0119] However, in the case of the sample (superabsorbent polymer), whether the odorous substances of the sample had been removed (presence or absence of odor) was confirmed by the examiner by smelling and comparing the odor of sample B before and after the pollutant removal test. In addition, whether the colored substances of the sample had been removed (presence or absence of decolorization) was confirmed by the examiner by visually comparing the color of sample B before and after the pollutant removal test.

[0120] (3) Evaluation results (a) Stability test of dehydrating agents The evaluation results are summarized in Table 1 below. (a-1) Dehydration test The wet weight of the superabsorbent polymer was initially 50.1 g, and decreased to 48 g in Comparative Example 1, showing almost no change, but decreased significantly to 0.47 g in Example 1. From such a comparison of the wet weights of Example 1 and Comparative Example 1, it was confirmed that the superabsorbent polymer was dehydrated by using acetone as a dehydrating agent. (a-2) Oxidation test The dry weight of the superabsorbent polymer was initially 0.10g, and in Comparative Example 1, it was 0.073g, with almost no change, and in Examples 1 to 3, it was 0.070g, 0.070g, and 0.067g, with almost no change. From such a comparison of the dry weights of Examples 1 to 3 and Comparative Example 1, it was confirmed that the superabsorbent polymer was not oxidatively decomposed even when acetone was used as a dehydrating agent and ozone was used as an oxidizing agent. On the other hand, the wet weight and dry weight of Comparative Example 2 were 11g and 0.034g, which were significantly reduced compared to the wet weight and dry weight of Comparative Example 1, which were 48g and 0.073g. From such a comparison of the wet weight and dry weight of Comparative Examples 1 and 2, it was confirmed that the superabsorbent polymer was oxidatively decomposed in distilled water at the ozone concentration of this example. Therefore, when ozone was used in distilled water, a part of the superabsorbent polymer was oxidatively decomposed, but when the same concentration of ozone was used in acetone, it was confirmed that the superabsorbent polymer was not oxidatively decomposed. In addition, the wet weight of the superabsorbent polymer was initially 50.1 g, and in Comparative Example 1 it was 48 g, showing little change, but in Examples 1 to 3 it was 0.47 g, 0.58 g, and 0.41 g, showing a marked decrease. From such a comparison of the wet weights of Examples 1 to 3 and Comparative Example 1, it was confirmed that when acetone was used as a dehydrating agent, dehydration was achieved to the same extent as when ozone was not used, even when ozone was used as an oxidizing agent.

[0121] [Table 1]

[0122] (b) Pollutant removal test The evaluation results are summarized in Table 2 below. In Table 2, "◯" indicates that deodorization or decolorization was achieved, and "×" indicates that deodorization or decolorization was not achieved. Regarding the deodorization and decolorization of the superabsorbent polymer, in Example 4, both deodorization and decolorization were good (◯), but in Comparative Example 3, deodorization was achieved (◯) but decolorization was not achieved (×). In Comparative Example 4, neither deodorization nor decolorization was achieved (×). In Comparative Example 5, the superabsorbent polymer was decomposed, and evaluation was not possible. From the comparison of Example 4 and Comparative Examples 3 to 5, it was confirmed that when acetone was used as a dehydrating agent and ozone was used as an oxidizing agent, the odor of the superabsorbent polymer disappeared (deodorized) and coloring disappeared (decolorized). However, when acetone was used as a dehydrating agent and an oxidizing agent was not used, the superabsorbent polymer was deodorized but not decolorized.

[0123] [Table 2]

[0124] Good results were obtained in deodorization and decolorization, that is, reduction of odorous and colored pollutants. Since these odorous and colored pollutants are difficult to remove, it is believed that other pollutants, such as excrement, sebum, bacteria derived from them, machine oils in manufacturing facilities, and various organic substances, can also be similarly removed or reduced. Although details are omitted, the same results were obtained with pulp fibers as with superabsorbent polymers in terms of dehydration. Furthermore, the same results were obtained with pulp fibers and plastic materials as with superabsorbent polymers in terms of deodorization and decolorization.

[0125] <Wet weight measurement method> The method for measuring the wet weight is as follows. (1) Prepare a bag made of a PE mesh sheet (PE200, Sanplatec, opening 102 μm) and measure the mass A of the bag. (2) The absorbed superabsorbent polymer to be measured is placed in a PE mesh sheet bag, the bag is removed, and the bag is left on a draining net for 15 minutes to drain the water. (3) Measure the mass B of the PE mesh sheet bag (containing the superabsorbent polymer) after draining the water in (2) above. (4) (Mass B - Mass A) is the wet weight of the absorbed superabsorbent polymer to be measured.

[0126] <Method of measuring dry weight> The method for measuring the dry weight is as follows. (1) The superabsorbent polymer in the PE mesh sheet bag obtained by the above wet weight measurement method is transferred to a heat-resistant container. (2) The container (containing the superabsorbent polymer) is left in an atmosphere at 105° C. for 3 hours to completely dry the superabsorbent polymer. (3) The mass of the dried superabsorbent polymer is measured and used as the dry weight.

[0127] The abduction method of the present invention is not limited to the above-described embodiments, and suitable combinations and modifications can be made without departing from the scope and spirit of the present invention. [Explanation of symbols]

[0128] S3 Dehydration and washing process S4 Separation process

Claims

1. A method for recovering components of used absorbent articles, comprising the steps of: a dehydration and washing step in which the mixture containing the superabsorbent polymer having an acid group and the pulp fibers, which are the constituent members, is dehydrated and washed with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and the pulp fibers; a separation and recovery step of separating and recovering at least the superabsorbent polymer and the pulp fibers from the material dehydrated and washed in the dehydration and washing step; A method comprising:

2. The dehydrating and cleaning step includes a step of dehydrating and cleaning the mixture further containing the plastic material that is the component member with the solution, The separation and recovery step includes a step of separating and recovering the superabsorbent polymer, the pulp fibers, and the plastic material together from the material dehydrated and washed in the dehydration and washing step. The method of claim 1.

3. The separation and recovery step includes a step of separating and recovering the plastic material from the superabsorbent polymer, the pulp fibers, and the plastic material that are separated together. The method of claim 2.

4. The method further includes a crushing step of crushing the used absorbent article, The crushing step is carried out before the separation and recovery step, and before, during, or after the dehydration and washing step. The method according to claim 1 or 2.

5. Further comprising a drying step of drying the material separated in the separation and recovery step; The drying step is carried out at least one of after the dehydration and washing step and after the separation and recovery step. The method according to claim 1 or 2.

6. The oxidizing agent includes at least one of ozone, hydrogen peroxide, and a chlorine-based substance. The method according to claim 1 or 2.

7. The dehydrating agent includes a ketone-based organic solvent. The method according to claim 6.

8. The method further includes a pretreatment step of reducing moisture absorbed by the used absorbent article before the dehydration and cleaning step. The method according to claim 1 or 2.

9. The pretreatment step includes subjecting the used absorbent article to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, a high-pressure steam treatment, a freeze-drying treatment, and an organic solvent treatment. The method according to claim 8.

10. The pretreatment step includes a step of subjecting the used absorbent article to an acidic aqueous solution treatment in which the superabsorbent polymer is inactivated with an acidic aqueous solution, The dehydration and washing step includes a step of activating the inactivated superabsorbent polymer with alkali metal ions supplied from an alkali metal ion source.

10. The method of claim 9.

11. The pretreatment step includes a step of subjecting the used absorbent article to a polyvalent metal salt treatment in which the superabsorbent polymer is inactivated with polyvalent metal ions supplied from a polyvalent metal salt, The method comprises: a step of substituting the polyvalent metal ions of the inactivated superabsorbent polymer with an acidic substance before or during the dehydration and washing step; neutralizing the superabsorbent polymer in which the polyvalent metal ions have been substituted with the acidic substance using an alkaline substance containing sodium during the dehydration and washing process; Further comprising:

10. The method of claim 9.

12. A product in which the materials collected together by the method according to claim 1 or 2 are utilized together as materials.

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