AU2018360436B2

AU2018360436B2 - Method and system for recovering pulp fibers from used absorbent articles

Info

Publication number: AU2018360436B2
Application number: AU2018360436A
Authority: AU
Inventors: Toshio HIRAOKA; Takashi Kato; Takayoshi Konishi; Noritomo Kurita
Original assignee: Unicharm Corp
Current assignee: Unicharm Corp
Priority date: 2017-11-01
Filing date: 2018-07-26
Publication date: 2020-12-17
Anticipated expiration: 2038-07-26
Also published as: TWI726234B; JP6762287B2; TW201923195A; CN111278901A; CN111278901B; WO2019087489A1; JP2019085447A; AU2018360436A1; PH12020550534A1; KR102304591B1; KR20200079257A

Abstract

Provided is a method for highly efficiently removing a highly water-absorbent polymer from pulp fibers that have been separated from used absorbent articles and include residual highly water-absorbent polymer. A method for recovering pulp fibers from used absorbent articles that include the pulp fibers and a highly water-absorbent polymer, the method comprising: a solid-liquid separation step (S18) in which a deactivating aqueous solution that includes pulp fibers and highly water-absorbent polymer that have been separated from the used absorbent articles is separated into a solid that includes the pulp fibers and the highly water-absorbent polymer and a liquid that includes the highly water-absorbent polymer and the deactivating aqueous solution and, meanwhile, the highly water-absorbent polymer is smashed; and an oxidizing agent treatment step (S19) in which the pulp fibers and smashed highly water-absorbent polymer included in the separated solid are treated with an aqueous solution that includes an oxidizing agent.

Description

I TITLE METHOD AND SYSTEM FOR RECOVERING PULP FIBERS FROM USED ABSORBENT ARTICLES FIELD

[0001] The present invention relates to a method and system of recovering pulp fibers from used absorbent articles.

BACKGROUND

[0002] Methods are known for recovering recycled pulp fibers from used absorbent articles such as disposable diapers. Patent Literature 1, for example, discloses a method of producing recycled pulp from used sanitary products. The method comprises a process of applying physical force to used sanitary products in an acidic aqueous solution or the like to disintegrate the used sanitary products into pulp fibers and other materials, a process of separating the pulp fibers from the mixture of the pulp fibers and other materials, and a process of treating the separated pulp fibers with an ozone-containing aqueous solution. Treatment of pulp fibers with an ozone-containing aqueous solution can oxidatively decompose, low-molecularize and solubilize superabsorbent polymers remaining in a considerable amount in the separated pulp fibers, and thus remove them from the pulp fibers.

[CITATION LIST] [PATENT LITERATURE]

[0003]

[PTL 1] Japanese Unexamined Patent Publication No. 2016-881

[0004] In order to increase the utility of the pulpfibers recovered from the used absorbent articles, it is important to reduce the concentration of the superabsorbent polymers in the pulp fibers and to increase the treatment efficiency for reducing the superabsorbent polymers concentration. In the method of Patent Literature 1, treating pulp fibers with an ozone-containing aqueous solution oxidatively decomposes the superabsorbent polymers remaining in the pulp fibers, allowing it to be removed from the pulp fibers. However, because a relatively long time is necessary for treatment with an ozone-containing aqueous solution, the method is in need of improvement in terms of improved treatment efficiency. A technique is desired that allows superabsorbent polymers to be removed with high treatment efficiency from pulp fibers with residual superabsorbent polymers, that has been separated from used absorbent articles.

[0005] A potential advantage of the present invention may include providing a method and system that allow superabsorbent polymers to be removed with high treatment efficiency from pulp fibers with residual superabsorbent polymers, that has been separated from used absorbent articles.

[0005A] Any reference to or discussion of any document, act or item of knowledge in this specification is included solely for the purpose of providing a context for the present invention. It is not suggested or represented that any of these matters or any combination thereof formed at the priority date part of the common general knowledge, or was known to be relevant to an attempt to solve any problem with which this specification is concerned.

SUMMARY OF THE INVENTION

[0006] (1) A method of recovering pulp fibers from used absorbent articles that include pulp fibers and superabsorbent polymers, the method comprising: a solid-liquid separation process of, while separating an inactivating aqueous solution that includes pulp fibers and superabsorbent polymers that have been separated from used absorbent articles, into solid containing the pulp fibers and the superabsorbent polymers and liquid containing the superabsorbent polymers and the inactivating aqueous solution, squeezing the superabsorbent polymers in the solid, and an oxidizing agent treatment process of treating the pulp fibers and the squeezed superabsorbent polymers present in the separated solid are treated with an aqueous solution containing an oxidizing agent. In this method, the gel-like (lumpy or approximately spherical) superabsorbent polymers that have absorbed water and remain in the pulp fibers are squeezed (for example, squeezed with a pressure at or above the gel strength) to reduce the thicknesses of the superabsorbent polymers and convert them to a flat or finely divided form. In other words, the method allows the surface areas of the superabsorbent polymers to be greatly increased by squeezing the lumpy or approximately spherical superabsorbent polymers, and can increase the exposed portions by exposing the previously interior portions of the superabsorbent polymers onto the surfaces. In the oxidizing agent treatment process, therefore, it is possible to cause contact between the oxidizing agent and the interior portions of the superabsorbent polymers, which in the case of lumpy or approximately spherical superabsorbent polymers are unlikely to contact with the oxidizing

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agent, thereby allowing the contact areas of the superabsorbent polymers with the oxidizing agent to be increased. This can more efficiently promote oxidative decomposition of the superabsorbent polymers and shorten the oxidizing agent treatment time. As a result, the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased. The oxidizing agent referred to here may be ozone, chlorine dioxide, peracetic acid, sodium hypochlorite or hydrogen peroxide.

[00071 The method may also be (2) the method according to (1) above, wherein the solid-liquid separation process includes a squeezing process of treating the inactivating aqueous solution that includes the pulp fibers and the superabsorbent polymers by a pressurized dewatering method to squeeze the superabsorbent polymers remaining in the pulp fibers. Since the superabsorbent polymers remaining in the pulp fibers are squeezed by a pressurized dewatering method in this method, it is possible to efficiently and reliably carry out solid-liquid separation and squeezing of the superabsorbent polymers on the pulp fibers in a simultaneous manner. In other words, the method can greatly increase the surface areas of the superabsorbent polymers on the pulp fibers, both efficiently and reliably. This allows the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers to be increased. Superabsorbent polymers remaining in pulp fibers are typically superabsorbent polymers adhering onto the surfaces of the pulp fibers.

[0008] The method may also be (3) the method according to (2) above, wherein the pressure during pressurization in the pressurized dewatering method of the squeezing process is 0.02 MPa or more and 0.5 MPa or less. In this method, the pressure during pressurization in the pressurized dewatering method is 0.02 MPa or more and 0.5 MPa or less. Consequently, the method allows superabsorbent polymers remaining in pulp fibers to be sufficiently squeezed without damaging the pulp fibers, allowing the surface areas of the superabsorbent polymers to be increased to a sufficiently high degree. This can increase the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers. If the pressure is below 0.02 MPa, however, the superabsorbent polymers cannot be sufficiently squeezed and consequently the oxidizing agent treatment time cannot be significantly shortened, while if the pressure is higher than 0.5 MPa, it is possible to sufficiently squeeze the superabsorbent polymers, but with the risk of damage to the pulp fibers.

[0009] The method may also be (4) the method according to any one of (1) to (3) above, further comprising, prior to the solid-liquid separation process, a process of separating a portion of the superabsorbent polymers and the inactivating aqueous solution from the inactivating aqueous

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solution containing the pulp fibers and superabsorbent polymers. In this method, prior to the solid-liquid separation process, a fixed amount of superabsorbent polymers and inactivating aqueous solution is separated from an inactivating aqueous solution that includes the pulp fibers and superabsorbent polymers. The method can therefore highly reduce the proportion of superabsorbent polymers in the material (the pulp fibers, superabsorbent polymers and inactivating aqueous solution) supplied to the solid-liquid separation process. This allows the superabsorbent polymers adhering to the pulp fibers to be more efficiently squeezed in the solid-liquid separation process, and can increase the treatment efficiency of removing the superabsorbent polymers from the pulp fibers.

[0010] The method may also be (5) the method according to any one of (1) to (4) above, wherein a proportion of the superabsorbent polymers in the inactivating aqueous solution supplied to the solid-liquid separation process is 50% or lower. In this method, the proportion of the superabsorbent polymers in the inactivating aqueous solution to be separated in the solid-liquid separation process is 50% or lower. This eliminates the need to squeeze an excessive amount of superabsorbent polymers, thus allowing the superabsorbent polymers to be more reliably and efficiently squeezed. This can increase the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers.

[0011] The method may also be (6) the method according to any one of (1) to (5) above, further comprising, prior to the solid-liquid separation process, a process of crushing the used absorbent articles in an inactivating aqueous solution, and a process of separating the inactivating aqueous solution containing the pulp fibers and superabsorbent polymers from the inactivating aqueous solution containing a crushed matter obtained by the process of crushing. This method comprises a process of crushing and a process of separating the inactivating aqueous solution containing pulp fibers and superabsorbent polymers which have been separated from the used absorbent articles, supplied in the solid-liquid separation process. This can inhibit contamination of the inactivating aqueous solution by contaminants (materials other than the pulp fibers and superabsorbent polymers in disposable absorbent articles (for example, films (such as back sheets), nonwoven fabrics (such as top sheets) and elastic solids (such as anti leakage wall rubber)). It is thus possible to more accurately squeeze the superabsorbent polymers without interference by contaminants. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[0012] The method may also be (7) the method according to any one of (1) to (6) above, wherein the inactivating aqueous solution is an acidic aqueous solution.

Since the inactivating aqueous solution in this method is an acidic aqueous solution, the superabsorbent polymers in the used absorbent articles can be reliably dewatered and adjusted to below a predetermined size (for example, particle size). This will allow solid-liquid separation to be easily carried out in the solid-liquid separation process while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[0013] The method may also be (8) the method according to (7) above, wherein the acidic aqueous solution has a pH of 2.5 or lower. Since the acidic aqueous solution in this method has a pH of 2.5 or lower, the superabsorbent polymers in the used absorbent articles can be more reliably dewatered and adjusted to below a predetermined size (for example, particle size). This will allow solid-liquid separation to be more easily carried out in the solid-liquid separation process while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result. Moreover, since the superabsorbent polymers can be adjusted to a predetermined size in a gel state, it becomes easier to squeeze the superabsorbent polymers.

[0014] The method may also be (9) the method according to (7) or (8) above, wherein the acidic aqueous solution includes citric acid. Since the acidic aqueous solution in this method includes citric acid (at a concentration of 0.5 to 2.0 mass%, for example), the superabsorbent polymers in the used absorbent articles can be more reliably dewatered and adjusted to below a predetermined particle size. This will allow solid-liquid separation to be easily carried out in the solid-liquid separation process while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[0015] (10) A system of recovering pulp fibers from used absorbent articles that include pulp fibers and superabsorbent polymers, the system comprising: a solid-liquid separator which, while separating an inactivating aqueous solution including pulp fibers and superabsorbent polymers that have been separated from the used absorbent articles, into solid containing the pulp fibers and the superabsorbent polymers and liquid containing the superabsorbent polymers and the inactivating aqueous solution, squeeze the superabsorbent polymers in the solid, and an oxidizing agent treatment device which treats the pulp fibers and the squeezed superabsorbent polymers present in the separated solid with an aqueous solution containing an oxidizing agent. In this system, the gel-like (lumpy or approximately spherical) superabsorbent polymers

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that have absorbed water and remain in the pulp fibers are squeezed (for example, squeezed with a pressure at or above the gel strength) to reduce the thicknesses of the superabsorbent polymers and convert them to a flat or finely divided form. In other words, the system allows the surface areas of the lumpy or approximately spherical superabsorbent polymers to be greatly increased by squeezing the superabsorbent polymers, and can increase the exposed portions by exposing the previously interior portions of the superabsorbent polymers onto the surfaces. In the oxidizing agent treatment device, therefore, it is possible to cause contact between the oxidizing agent and the interior portions of the superabsorbent polymers, which in the case of lumpy or approximately spherical superabsorbent polymers are unlikely to contact with the oxidizing agent, thereby allowing the contact areas of the superabsorbent polymers with the oxidizing agent to be increased. This can more efficiently promote oxidative decomposition of the superabsorbent polymers and shorten the oxidizing agent treatment time. As a result, it can increase the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers.

[0016] The system may also be (11) the system according to (10) above, wherein the solid-liquid separator includes a screw press dewaterer which treats the inactivating aqueous solution including the pulp fibers and the superabsorbent polymers, by a pressurized dewatering method to squeeze the superabsorbent polymers remaining in the pulp fibers. Since the superabsorbent polymers remaining in the pulp fibers are squeezed by a pressurized dewatering method using a screw press dewaterer in this system, it is possible to efficiently and reliably carry out solid-liquid separation and squeezing of the superabsorbent polymers on the pulp fibers in a simultaneous manner. In other words, the system can greatly increase the surface areas of the superabsorbent polymers on the pulp fibers, both efficiently and reliably. This can increase the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers. Superabsorbent polymers remaining in pulp fibers are typically superabsorbent polymers adhering onto the surfaces of the pulp fibers.

[00171 The system may also be (12) the system according to (11) above, wherein the pressure during pressurization in the pressurized dewatering method using the screw press dewaterer is 0.02 MPa or more and 0.5 MPa or less. In this system, the pressure during pressurization in the pressurized dewatering method is 0.02 MPa or more and 0.5 MPa or less. Consequently, the system allows superabsorbent polymers remaining in pulp fibers to be sufficiently squeezed without damaging the pulp fibers, allowing the surface areas of the superabsorbent polymers to be increased to a sufficiently high degree. This allows the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers to be increased. If the pressure is below 0.02 MPa, however, the superabsorbent polymers cannot be sufficiently squeezed and consequently the oxidizing agent treatment time cannot be significantly shortened, while if the pressure is higher than 0.5 MPa, it is possible to sufficiently squeeze the superabsorbent polymers, but with the risk of damage to the pulp fibers.

[0018] The system may also be (13) the system according to any one of (10) to (12) above, further comprising, prior to the solid-liquid separator, a drum screen dewaterer which separates a portion of the superabsorbent polymers and the inactivating aqueous solution from the inactivating aqueous solution containing the pulp fibers and superabsorbent polymers. In this system, a fixed amount of superabsorbent polymers and inactivating aqueous solution is separated from an inactivating aqueous solution that includes the pulp fibers and superabsorbent polymers, using a drum screen dewaterer before the solid-liquid separator. The system can therefore highly reduce the proportion of superabsorbent polymers in the material (the pulp fibers, superabsorbent polymers and inactivating aqueous solution) supplied to the solid-liquid separation process. This allows the superabsorbent polymers adhering to the pulp fibers to be more efficiently squeezed by the screw press dewaterer, and can increase the treatment efficiency of removing the superabsorbent polymers from the pulp fibers.

[0019] The system may also be (14) the system according to any one of (10) to (13) above, wherein a proportion of the superabsorbent polymers in the inactivating aqueous solution supplied to the solid-liquid separator is 50% or lower. In this system, the proportion of the superabsorbent polymers in the inactivating aqueous solution to be separated in the solid-liquid separator is 50% or lower. This eliminates the need to squeeze an excessive amount of superabsorbent polymers, thus allowing the superabsorbent polymers to be more reliably and efficiently squeezed. This allows the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers to be increased.

[0020] The system may also be (15) the system according to any one of (10) to (14) above, wherein the inactivating aqueous solution is an acidic aqueous solution. Since the inactivating aqueous solution in this system is an acidic aqueous solution, the superabsorbent polymers in the used absorbent articles can be reliably dewatered and adjusted to below a predetermined particle size. This will allow solid-liquid separation to be easily carried out in the solid-liquid separator while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[0021]

The system may also be (16) the system according to (15) above, wherein the acidic aqueous solution has a pH of 2.5 or lower. Since the acidic aqueous solution in this system has a pH of 2.5 or lower, the superabsorbent polymers in the used absorbent articles can be more reliably dewatered and adjusted to below a predetermined particle size. This will allow solid-liquid separation to be more easily carried out in the screw press dewaterer while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result. Moreover, since the superabsorbent polymers can be adjusted to a predetermined particle size in a gel state, it becomes easier to squeeze the superabsorbent polymers.

[0022] The system may also be (17) the system according to (15) or (16) above, wherein the acidic aqueous solution includes citric acid. Since the acidic aqueous solution in this system includes citric acid (at a concentration of 0.5 to 2.0 mass%, for example), the superabsorbent polymers in the used absorbent articles can be more reliably dewatered and adjusted to below a predetermined particle size. This will allow solid-liquid separation to be easily carried out in the screw press dewaterer while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[ADVANTAGEOUS EFFECTS OF INVENTION]

[0023] According to the method and system of the invention, it is possible to remove superabsorbent polymers with high treatment efficiency from pulp fibers with residual superabsorbent polymers, that has been separated from used absorbent articles.

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 is a block diagram showing an example of a system according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a construction example for the rupturing device and crushing device of FIG. 1. FIG. 3 is a schematic diagram showing a construction example of the third separation device of FIG. 1. FIG. 4 is a schematic diagram showing a construction example of the oxidizing agent treatment device of FIG. 1. FIG. 5 is a partial magnified view showing another construction example of the oxidizing agent treatment device of FIG. 1. FIG. 6 is a flow chart showing an example of a method according to an embodiment of the present invention. FIG. 7 is a graph showing the relationship between pressure level and treatment time in the third separation process.

DESCRIPTION OF EMBODIMENTS

[0025] The method of recovering pulp fibers from used absorbent articles containing pulp fibers and superabsorbent polymers, according to an embodiment of the invention, will now be described. Used absorbent articles are absorbent articles that have been used by a user, and they include absorbent articles that have absorbed and retained liquid excreta of the user, as well as ones that are used but have not absorbed and retained excreta, and ones that are unused but have been discarded. The absorbent article may be a paper diaper, a urine-absorbing pad, a sanitary napkin, a bed sheet or a pet sheet, for example. The method of recovering pulp fibers from used absorbent articles according to this embodiment may be considered to be a method of generating recycled pulp fibers from used absorbent articles, since recycled pulp fibers are generated. The method of recovering pulp fibers from used absorbent articles according to this embodiment may also be considered to be a method of recovering superabsorbent polymers or a method of generating recycled superabsorbent polymers from used absorbent articles, since superabsorbent polymers are recovered with the pulp fibers during the method, and recycled superabsorbent polymers are generated by separation. The method of recovering pulp fibers from used absorbent articles will now be described.

[0026] An example of the construction of an absorbent article will be described first. The absorbent article comprises a top sheet, a back sheet and an absorbent body situated between the top sheet and back sheet. An example of the size of an absorbent article is a length of about 15 to 100 cm and a width of 5 to 100 cm. The absorbent article may also include other members commonly found in absorbent articles, such as a diffusion sheet or anti-leakage wall.

[00271 The structural member of the top sheet may be a liquid-permeable nonwoven fabric, a synthetic resin film having liquid permeation holes, or a composite sheet of the same. The structural member of the back sheet may be a liquid-impermeable nonwoven fabric, a liquid-

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impermeable synthetic resin film, or a composite sheet of the same. The structural member of the diffusion sheet may be a liquid-permeable nonwoven fabric, for example. The structural member of the anti-leakage wall may be a liquid-impermeable nonwoven fabric, for example, and it may include an elastic member such as rubber. The materials of the nonwoven fabric or synthetic resin film are not particularly restricted so long as they can be used as absorbent articles, and examples 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). This embodiment will be described using an absorbent article that has a film as the structural member of the back sheet and a nonwoven fabric as the structural member of the top sheet.

[00281 The structural members of the absorbent body may be the absorbent body materials, i.e. the pulp fibers and the superabsorbent polymers. Pulp fibers are not particularly restricted so long as they can be used as absorbent articles, and cellulosic fibers are an example. Examples of cellulosic fibers include wood pulp, crosslinked pulp, nonwood pulp, regenerated cellulose and semi-synthetic cellulose. The size of the individual pulp fibers may be several tens of pm and preferably 20 to 40 pm, as the average long diameter of the fibers, and several mm and preferably 2 to 5 mm, for example, as the average fiber length. The superabsorbent polymers (SAP) are not particularly restricted so long as they can be used in an absorbent article, and examples are polyacrylic acid salt-based, polysulfonic acid salt-based and maleic anhydride salt based water-absorbent polymers. The (dry) size of the superabsorbent polymer may be several hundred pm and preferably 200 to 500 pm, for example, as the average particle size.

[0029] One side and the other side of the absorbent body are joined to the top sheet and back sheet, respectively, via an adhesive. The portions of the top sheet that extend out from the absorbent body to surround the absorbent body (the perimeter edge portions), as viewed flat, are joined to the portions of the back sheet that extend out from the absorbent body to surround the absorbent body so as to surround the absorbent body (the perimeter edge portions), with an adhesive. The absorbent body is thus wrapped inside a joined structure between the top sheet and the back sheet. The adhesive is not particularly restricted so long as it can be used in absorbent articles and has its bonding force lowered when softened by warm water as described below, and an example is a hot-melt adhesive. Examples of hot-melt adhesives include types based mainly on rubber, such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene and styrene isoprene-styrene, and pressure-sensitive adhesives or heat-sensitive adhesives based mainly on olefins such as polyethylene.

[00301

II

The method of recovering pulp fibers from used absorbent articles containing pulp fibers and superabsorbent polymers, according to an embodiment of the invention, will now be described. For this embodiment, used absorbent articles are recovered or acquired from an external source for reutilization (recycling). The used absorbent articles are encapsulated in a plurality of collecting bags (hereunder also referred to as "collection bags"), so that contaminants (such as excreta) and microbes or odors do not leak out. The individual used absorbent articles in the collection bags are recovered primarily in a rolled-up state or folded state with the excreta discharged top sheet on the inside, so that excreta are not exposed on the front side, and so that odor does not diffuse to the surroundings.

[0031] A system 1 to be used in the method of recovering pulp fibers from used absorbent articles will be explained first. The system 1 is a system of recovering pulp fibers (and also preferably superabsorbent polymers), and therefore of generating recycled pulp fibers (and also preferably recycled superabsorbent polymers) from used absorbent articles. Fig. 1 is a block diagram showing an example of the system 1 according to this embodiment. The system 1 comprises a third separation device 18 and an oxidizing agent treatment device 19, and preferably it comprises a rupturing device 11, a crushing device 12, a first separation device 13, a first dust removal device 14, a second dust removal device 15, a third dust removal device 16, a second separation device 17 and a fourth separation device 20. This will now be explained in detail.

[0032] The rupturing device 11 and crushing device 12 will be described first. The rupturing device 11 opens holes in collection bags containing used absorbent articles, in the inactivating aqueous solution. The crushing device 12 crushes the used absorbent articles in their collection bags in the inactivating aqueous solution that has sunk below the liquid surface of the inactivating aqueous solution. The inactivating aqueous solution is an aqueous solution that inactivates the superabsorbent polymers, the inactivation resulting in lower water absorption capacity by the superabsorbent polymers. Thus, when the superabsorbent polymer absorbs water in a larger amount than its lowered water absorption capacity, water is discharged until the amount reaches the level permitted by the water absorption capacity, or in other words, dewatering takes place. An example of using an acidic aqueous solution as the inactivating aqueous solution will now be explained.

[0033] Fig. 2 is a schematic diagram showing a construction example for the rupturing device 11 and crushing device 12 of Fig. 1. The rupturing device 11 holds the acidic aqueous solution B supplied through piping that

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is equipped with a valve, for example, and opens holes in the collection bags A that have entered the acidic aqueous solution B. The rupturing device 11 includes a solution tank V and a perforating section 50. The solution tank V holds the acidic aqueous solution B. The perforating section 50 is provided in the solution tank V and opens holes in the surfaces of the collection bags A that have contacted with the acidic aqueous solution B, after the collection bags A have been placed in the solution tank V. The perforating section 50 comprises a feeding section 30 and a bag crusher 40. The feeding section 30 feeds the collection bags A (physically and forcibly) into the acidic aqueous solution B in the solution tank V. The feeding section 30 may be a stirrer, for example, comprising a stirring blade 33, a support shaft (rotating shaft) 32 that supports the stirring blade 33, and a drive unit 31 that rotates the support shaft 32 around the shaft. Rotation of the stirring blade 33 around the rotating shaft (support shaft 32) by the drive unit 31 produces a swirl flow in the acidic aqueous solution B. The feeding section 30 draws the collection bags A toward the bottom section of the acidic aqueous solution B (solution tank V) by the swirl flow. The bag crusher 40 is situated at the lower end (preferably the bottom) of the solution tank V, and it comprises a bag-crushing blade 41, a support shaft (rotating shaft) 42 that supports the bag-crushing blade 41, and a drive unit 43 that rotates the support shaft 42 around the shaft. By rotating the bag-crushing blade 41 around the rotating shaft (support shaft 42) by the drive unit 43, holes are opened in the collection bags A that have moved to the bottom of the acidic aqueous solution B (solution tank V). The "bottom" of the solution tank V is the section below the position at half the height of the solution tank V. The bag-crushing blade 41 in the perforating section 50 of the rupturing device 11 may be vertically adjustable in the solution tank V while it rotates around the rotating shaft (support shaft 42). This will allow the bag-crushing blade 41 to move vertically so that holes can be opened in the collection bags A without having the collection bags A move to the bottom of the acidic aqueous solution B (solution tank V).

[0034] The crushing device 12 crushes the used absorbent articles in the collection bags A, together with their collection bags A, that have sunk below the liquid surface of the acidic aqueous solution B. The crushing device 12 includes a crusher 60 and a pump 63. The crusher 60 is connected with the solution tank V by piping 61, and it crushes the used absorbent articles in the collection bags A that have been fed from the solution tank V together with the acidic aqueous solution B (liquid mixture 91) in the acidic aqueous solution B, together with their collection bags. The crusher 60 may be a twin-screw crusher (for example, a twin-screw rotary crusher, twin-screw differential crusher or twin-screw shearing crusher), an example of which is a SUMICUTTER (product of Sumitomo Heavy Industries Environment Co. Ltd.). The pump 63

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is connected with the crusher 60 by piping 62, and it draws out the crushed matter obtained by the crusher 60 from the crusher 60, together with the acidic aqueous solution B (liquid mixture 92), and feeds it to the following process. The crushed matter contains pulp fibers and superabsorbent polymers, and also other materials (such as the collection bag A material, films, nonwoven fabrics and elastic solids). The rupturing device 11 and crushing device 12 are preferably different apparatuses.

[00351 Referring to Fig. 1, the first separation device 13 agitates the liquid mixture 92 containing the crushed matter obtained from the crushing device 12 and the acidic aqueous solution, washing it to remove the contaminants (excreta, etc.) from the crushed matter while separating the pulp fibers, superabsorbent polymers and acidic aqueous solution (liquid mixture 93) from the liquid mixture 92, and feeds them to the first dust removal device 14. The first separation device 13 may be, for example, a washing machine that comprises a washing tank/dewatering tank and a water tank surrounding it. The washing tank/dewatering tank (rotating drum) is used as a washing tank/sifting tank (separation tank). The sizes of the perforations provided on the peripheral surface of the washing tank are sizes that allow the pulp fibers and superabsorbent polymers in the crushed matter to easily pass through while inhibiting passage of other materials. The washing machine may be, for example, an ECO-22B horizontal washing machine (product of Inax Corp.).

[0036] The used absorbent articles may be crushed together with their collection bags in a gas (for example, air), instead of crushing the used absorbent articles together with their collection bags in the inactivating aqueous solution (for example, the acidic aqueous solution). The rupturing device 11 is not necessary in this case, and the crushing device 12 carries out crushing in air in the absence of the inactivating aqueous solution. The crushed matter and inactivating aqueous solution of the crushing device 12 are then supplied to the first separation device 13.

[00371 When an acidic aqueous solution is not used as an inactivating aqueous solution between the rupturing device 11 and the first separation device 13, the acidic aqueous solution may be added to the inactivating aqueous solution from the first dust removal device 14, and the inactivating aqueous solution containing pulp fibers and superabsorbent polymers supplied from the first dust removal device 14 may essentially be used as the acidic aqueous solution. This allows the specific gravity and size of the superabsorbent polymer to be easily adjusted by the pH.

[0038] While keeping the pH in a predetermined range, the first dust removal device 14

I -r

separates the acidic aqueous solution (liquid mixture 93) containing the pulp fibers and superabsorbent polymers, which has been fed from the first separation device 13, into the pulp fibers and superabsorbent polymers in the acidic aqueous solution (liquid mixture 94) and the other materials (contaminants), using a screen having a plurality of openings. In order to keep the pH in the predetermined range, either a liquid (such as water) that might cause variation in the pH is not added, or if such a liquid is added, it is a liquid having about the same pH (such as an acidic aqueous solution). The predetermined range is a range of pH variation within ±1.0. The first dust removal device 14 may be a screen separator (coarse screen separator), for example. However, the openings of the screen (sieve) are not particularly restricted and may be slits, round holes, rectangular holes or meshes, the screen with round holes being used here. The size of the openings, such as the sizes (diameters) of the round holes, are sizes allowing the pulp fibers and superabsorbent polymers to pass while inhibiting passage of other materials (contaminants) that could not be removed by the first separation device 13, and sizes larger than the widths of the slits of the screen in the second dust removal device 15. The sizes of the round holes may be diameters of 2 to 5 mm, for example, allowing other materials (contaminants) of at least about 10 mm-square sizes or greater to be removed. In the case of slits, the slit sizes (widths) are 2 to 5 mm, for example. From the viewpoint of improved contaminant removal efficiency, the liquid mixture 93 2 fed out from the first separation device 13 may be pressurized (at 0.5 to 1 kgf/cm2, for example) while being supplied to the first dust removal device 14. The first dust removal device 14 may be a pack pulper (by Satomi Seisakusho), for example.

[0039] While keeping the pH in a predetermined range, the second dust removal device 15 separates the acidic aqueous solution (liquid mixture 94) containing the pulp fibers and superabsorbent polymers, which has been fed from the first dust removal device 14, into the pulp fibers and superabsorbent polymers in the acidic aqueous solution (liquid mixture 95) and the other materials (contaminants), using a screen having a plurality of openings. The second dust removal device 15 may be a screen separator, for example. However, the openings of the screen (sieve) are not particularly restricted and may be slits, round holes, rectangular holes or meshes, the screen with slits being used here. The sizes (widths) of the slits are sizes allowing the pulp fibers and superabsorbent polymers to pass while inhibiting passage of other materials (contaminants) that could not be removed by the first dust removal device 14. The sizes of the slits may be widths of 0.2 to 0.5 mm, for example, allowing other materials (contaminants) of at least about 3 mm-square sizes or greater to be removed. In the case of round holes, the sizes (diameters) of the round holes are diameters of 0.2 to 0.5 mm, for example. From the viewpoint of improved contaminant removal efficiency, the liquid mixture 94

2 for fed out from the first dust removal device 14 may be pressurized (at 0.5 to 2 kgf/cm, example) while being supplied to the second dust removal device 15. The pressure is preferably higher than the pressure of the first dust removal device 14 from the viewpoint of removing relatively small contaminants. The second dust removal device 15 may be a Lamo Screen (by Aikawa Iron Works Co.), for example.

[0040] While keeping the pH in a predetermined range, the third dust removal device 16 centrifugally separates the acidic aqueous solution (liquid mixture 95) containing the pulp fibers and superabsorbent polymers, which has been fed out from the second dust removal device 15, into the pulp fibers and superabsorbent polymers in the acidic aqueous solution (liquid mixture 96) and the other materials (large-weight contaminants). The third dust removal device 16 may be a cyclone separator, for example. The acidic aqueous solution (liquid mixture 95) containing the pulp fibers and superabsorbent polymers is supplied into an inverted conical case (not shown) of the third dust removal device 16 at a predetermined flow rate, so that the relatively light specific gravity pulp fibers and superabsorbent polymers in the acidic aqueous solution rise while the heavier specific gravity contaminants (such as metals) fall. The third dust removal device 16 may be an ACT Low Concentration Cleaner (by Aikawa Iron Works Co.), for example.

[0041] The second separation device 17 separates the acidic aqueous solution (liquid mixture 96) containing the pulp fibers and superabsorbent polymers, which has been fed out from the third dust removal device 16, into pulp fibers in the acidic aqueous solution (liquid mixture 97) and superabsorbent polymers in the acidic aqueous solution, using a screen having a plurality of openings. It may therefore be considered to be a dewaterer that removes the acidic aqueous solution from the liquid mixture 96 together with the superabsorbent polymers. The second separation device 17 may be a drum screen separator, for example. However, the openings of the drum screen (sieve) are not particularly restricted and may be slits, round holes, or rectangular or mesh holes, with slits being used here. The sizes (widths) of the slits are sizes allowing the superabsorbent polymers to pass while inhibiting passage of the pulp fibers. In the case of slits, the sizes of the slits are widths of 0.2 to 0.8 mm, for example, allowing most of the superabsorbent polymers to be removed. In the case of round holes, the sizes of the round holes are diameters of 0.2 to 0.8 mmp, for example. The second separation device 17 may be a drum screen dewaterer (by Toyo Screen Kogyo Co., Ltd.), for example.

[0042] The third separation device 18, using a screen with a plurality of openings, separates the pulp fibers that has been fed out from the second separation device 17, the inseparable remaining

IV

superabsorbent polymers and the acidic aqueous solution (liquid mixture 97), into solid including the pulp fibers and superabsorbent polymers (mixture 98) and liquid including the superabsorbent polymers and acidic aqueous solution, while applying pressure to the solid portion to squeeze the superabsorbent polymers in the solid. The third separation device 18 may therefore be considered to be a pressure dewatering-type dewaterer that removes the acidic aqueous solution from the liquid mixture 97 together with the superabsorbent polymers. The solid matter (mixture 98) may include slight amounts of acidic water-soluble substances. Fig. 3 is a schematic diagram showing a construction example of the third separation device 18 of Fig. 1. The third separation device 18 may be a screw press dewaterer, for example. The third separation device 18 comprises, for example, a drum screen 81, a screw shaft 82, a screw blade 83, a drive unit 86, a cover 84 and a pressure regulator 85. The drum screen 81 is a cylindrical screen (sieve) provided inside the case 80. The screw shaft 82 extends along the cylindrical shaft of the drum screen 81, its diameter gradually increasing toward the tip section of the drum screen 81. The screw blade 83 is provided in a helical manner on the outer side of the screw shaft 82, and rotates around the inner peripheral surface of the drum screen 81. The pitch of the screw blade 83 may also gradually narrow toward the tip section of the drum screen 81. The drive unit 86 rotates around the screw shaft 82. The cover 84 is provided in a manner closing up the tip section of the drum screen 81. The pressure regulator 85 regulates the pressure being exerted on the cover 84 against the tip section of the drum screen 81. The openings of the drum screen (sieve) 81 are not particularly restricted and may be slits, round holes, or rectangular or mesh holes, with slits being used here. The sizes (widths) of the slits are sizes allowing the superabsorbent polymers to pass while inhibiting passage of the pulp fibers. In the case of slits, the sizes of the slits are widths of 0.1 to 0.5 mm, for example, allowing at least the remaining superabsorbent polymers to be removed. The third separation device 18 feeds out liquid E including the superabsorbent polymers and acidic aqueous solution from the slits on the side walls of the drum screen 81, while feeding out the solid matter including the pulp fibers and superabsorbent polymers (mixture 98) from gaps G between the tip section of the drum screen 81 and the cover 84. The superabsorbent polymers is squeezed when the solid matter (mixture 98) is fed out. The pressure force applied onto the cover may be 0.01 MPa or greater and 1 MPa or less. The third separation device 18 may be a screw press dewaterer (by Kawaguchi Seiki Co., Ltd.).

[00431 The oxidizing agent treatment device 19 treats the pulp fibers including the squeezed superabsorbent polymers in the solid (mixture 98) that has been fed out from the third separation device 18, with an oxidizing agent-containing aqueous solution (treatment solution). The superabsorbent polymers is thus oxidatively decomposed and removed from the pulp fibers, and

I

/ the pulp fibers that no longer contains the superabsorbent polymers is fed out together with the treatment solution (liquid mixture 99).

[0044] Fig. 4 is a schematic diagram showing an example of the construction of the oxidizing agent treatment device 19. When ozone is used as the oxidizing agent, the oxidizing agent treatment device 19 includes a pump 121, a treatment tank 123, a pump 125, an ozone generator 126, an ozone mixer 127 and an ozone decomposer 129. The treatment tank 123 has an acidic aqueous solution as the treatment solution P, and a mixture 98 is supplied from a supply port 122b provided at the top. An acidic aqueous solution is preferred in order to increase the stability of the ozone when ozone is used as the oxidizing agent. The pump 121 draws out the treatment solution P from an outlet 124a at the base of the treatment tank 123 through piping 132, and supplies it into the treatment tank 123 through a supply port 122a at the top of the treatment tank 123. The pump 125 draws out the treatment solution P from an outlet 124b at the base of the treatment tank 123 through piping 136, and supplies it into the treatment tank 123 through a supply port 122c at the bottom of the treatment tank 123. The ozone generator 126 generates ozone-containing gas Z as a gaseous substance, and supplies it to the ozone mixer 127. The ozone mixer 127 mixes ozone-containing gas Z that has been supplied through the piping 135 and is present in the piping 136, with the treatment solution P circulating in the piping 136 toward the supply port 122c at the bottom of the treatment tank 123. The ozone mixer 127 supplies the ozone-containing gas Z into the treatment solution P as numerous fine bubbles. The ozone-containing gas Z may also be another type of gas that contains ozone, such as oxygen gas or ozone-containing air. The ozone generator 126 may be, for example, an ED-OWX-2 ozone water exposure tester by EcoDesign, Inc. or an OS-25V ozone generator by Mitsubishi Electric Corp. The ozone decomposer 129 receives the ozone-containing gas Z that has accumulated at the top of the treatment tank 123 through the piping 134, decomposes and detoxifies the ozone, and discharges it to the outside. The treatment solution P in the treatment tank 123, incidentally, consists of the initial treatment solution P alone, while being converted to a mixture of the treatment solution P and the mixture 98 after starting, and for this embodiment the solution in the treatment tank 123, including the liquid comprising a mixture of the treatment solution P and the mixture 98, is also considered to be the treatment solution P.

[0045] Fig. 5 is a schematic diagram showing an example of another construction of an oxidizing agent treatment device 19. The oxidizing agent treatment device 19 comprises a liquid mixture storage device 110 that stores the pulp fibers-containing mixture 98 together with the treatment solution Pa, and an oxidizing agent treatment device 120 that, using the treatment solution Pa, oxidatively decomposes the squeezed superabsorbent polymers included in the pulp fibers in the treatment solution Pa, removing them from the pulp fibers. The liquid mixture storage device 110 includes a liquid mixture tank 112 and a stirrer 113. The liquid mixture tank 112 stores the mixture 98 that includes the pulp fibers, that has been supplied through piping 131, in the treatment solution Pa. The stirrer 113 agitates the treatment solution Pa in the liquid mixture tank 112 so that the mixture 98 does not settle to the bottom of the treatment solution Pa. The oxidizing agent treatment device 120 includes a pump 121a, a treatment tank 123, an ozone supply apparatus 128, a pump 125a and an ozone decomposer 129. The treatment tank 123 has an acidic aqueous solution as the treatment solution P. The pump 121a continuously supplies the treatment solution Pa that includes the mixture 98 in the liquid mixture tank 112 into the treatment tank 123 at a first flow rate, through piping 132a. The ozone supply apparatus 128 generates ozone-containing gas Z, as a gaseous substance, at the ozone generator 126, and supplies it to the treatment tank 123 through the piping 135. A nozzle 127a that feeds out the ozone-containing gas Z is situated at the bottom (preferably the base) of the treatment tank 123, being in a tubular or flat form, for example. The nozzle 127a continuously supplies the ozone containing gas Z as fine bubbles into the treatment solution P, from the bottom to the top of the treatment tank 123. The pump 125a continuously discharges the treatment solution P in the treatment tank 123 out of the treatment tank 123 through the piping 133, at a second flow rate. The ozone decomposer 129 receives the ozone-containing gas Z that has accumulated at the top of the treatment tank 123 through the piping 134, decomposes and detoxifies the ozone, and discharges it to the outside.

[0046] The oxidizing agent treatment device 19 described above uses ozone as the oxidizing agent, but a different oxidizing agent may be used instead, and it may be a liquid oxidizing agent or a solid oxidizing agent melted in a liquid, instead of a gaseous oxidizing agent. The oxidizing agent may be chlorine dioxide, peracetic acid, sodium hypochlorite or hydrogen peroxide, for example.

[00471 The fourth separation device 20 separates the pulp fibers from the treatment solution (liquid mixture 99) containing the pulp fibers treated by the oxidizing agent treatment device 19 by a screen with a plurality of openings, thus recovering the pulp fibers and generating recycled pulp fibers. The fourth separation device 20 may be a screen separator, for example. However, the openings of the screen (sieve) are not particularly restricted and may be slits, round holes, rectangular holes or meshes, with slits being used here. The sizes (widths) of the slits are sizes that inhibit passage of pulp fibers. The slit sizes are widths of 0.2 to 0.8 mm, for example. In the case of round holes, the sizes (diameters) of the round holes are diameters of 0.2 to 0.8 mmyp, for example.

[0048] The system 1 preferably comprises the ozone treatment device 22, the pH adjustment device 23 and the water storage tank 24. These devices are for regeneration and reutilization of the acidic aqueous solution used in the system 1. Cost for the acidic aqueous solution can be reduced by reutilizing the acidic aqueous solution. The ozone treatment device 22 carries out sterilizing treatment of the acidic aqueous solution 101, with an ozone-containing aqueous solution, after separation of the superabsorbent polymers and acidic aqueous solution by the second separation device 17 and further separation of the superabsorbent polymers. The pH adjustment device 23 adjusts the pH of the acidic aqueous solution 102 subjected to sterilizing treatment in the ozone-containing aqueous solution, and produces regenerated acidic aqueous solution 103. The water storage tank 24 stores the excess portion of the regenerated acidic aqueous solution 103.

[0049] A method of recovering pulp fibers from used absorbent articles will now be explained. The method is a method of recovering pulp fibers (and also preferably superabsorbent polymers), and therefore of generating recycled pulp fibers (and also preferably recycled superabsorbent polymers) from used absorbent articles. Fig. 6 is a flow chart showing an example of a method according to this embodiment. The method comprises a third separation process S18 and an oxidizing agent treatment process S19, and preferably also comprises a hole punching process S11, a crushing process S12, a first separation process S13, a first dust removal process S14, a second dust removal process S15, a third dust removal process S16, a second separation process S17 and a fourth separation process S20. This will now be explained in detail.

[0050] The hole punching process S11 is carried out by the rupturing device 11. Collection bags A encapsulating used absorbent articles are loaded into the solution tank V holding the acidic aqueous solution B, and holes are opened in the surfaces of the collection bags A that contact with the acidic aqueous solution B. When holes have been opened in the collection bags A, the acidic aqueous solution B surrounds and seals the collection bags A so that the contaminants, microbes and odors of the used absorbent articles in the collection bags A are not released to the outside. When the acidic aqueous solution infiltrates into the collection bags A through the holes, gas inside the collection bags A leaks out of the collection bags A, causing the specific gravity of the collection bags A to be heavier than the acidic aqueous solution B, so that the collection bags A settle in the acidic aqueous solution B. The acidic aqueous solution B inactivates the superabsorbent polymers in the used absorbent articles inside the collection bags A.

[0051]

By inactivation of the superabsorbent polymer in the used absorbent articles, whereby its water-absorbing capacity decreases, the superabsorbent polymer becomes dewatered and its particle size is reduced, making it more manageable in each of the subsequent processes and improving the treatment efficiency. An acidic aqueous solution, i.e. an aqueous solution of an inorganic acid or organic acid, is used as the inactivating aqueous solution because it avoids residue of ash content in the pulp fiber compared to an aqueous solution of lime or calcium chloride, and because it allows the degree of inactivation (the particle size and the size of the specific gravity) to be easily adjusted by the pH. The pH of the acidic aqueous solution is preferably 1.0 to 4.0 and more preferably 1.2 to 2.5. If the pH is too high, it may not be possible to sufficiently lower the water-absorbing capacity of the superabsorbent polymer. The sterilizing power can also be potentially lowered. If the pH is too low there will be a risk of corrosion of the equipment, and large amounts of alkaline chemicals will be necessary for neutralizing treatment during waste water treatment. In order to separate the pulpfibers and superabsorbent polymers from the other materials, it is particularly preferred for the pulp fiber size and specific gravity and the superabsorbent polymer size and specific gravity to be relatively similar. By therefore adjusting the pH of the acidic aqueous solution to between 1.0 and 4.0, the superabsorbent polymer can be reduced even further by inactivation, so that the pulp fiber size and specific gravity and the superabsorbent polymer size and specific gravity can be made relatively similar. Examples of organic acids include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid and ascorbic acid, with hydroxycarbonate-based organic acids such as citric acid, tartaric acid and gluconic acid being particularly preferred. The chelating effect of citric acid traps metal ions and the like present in excreta, allowing their removal, and the washing effect of citric acid can potentially provide a high fouling component-removal effect. Examples of inorganic acids include sulfuric acid, hydrochloric acid and nitric acid, with sulfuric acid being preferred from the viewpoint of cost and the absence of chlorine. The pH will vary depending on the water temperature, where the pH for the purpose of the invention is the pH measured at an aqueous solution temperature of 20°C. The organic acid concentration of the organic acid aqueous solution is not particularly restricted, but when the organic acid is citric acid it is preferably 0.5 mass% to 4 mass%. The inorganic acid concentration of an inorganic acid aqueous solution is also not particularly restricted, but when the inorganic acid is sulfuric acid it is preferably 0.1 mass% to 0.5 mass%.

[0052] In the rupturing device 11 shown in Fig. 2, for example, first rotation of the stirring blade 33 around its rotating shaft (support shaft 32) produces a swirl flow in the acidic aqueous solution B, whereby the collection bags A are physically and forcibly drawn toward the base of the acidic aqueous solution B (solution tank V). The collection bags A that have moved to the

/_ I

base have holes opened in them by contact with the bag-crushing blade 41, due to rotation of the bag-crushing blade 41 around its rotating shaft (support shaft 42). When the bag-crushing blade 41 is vertically adjustable in the solution tank V, the bag-crushing blade 41 can be moved vertically to open holes in the collection bags A without having the collection bags A drawn toward the base of the acidic aqueous solution B (solution tank V) by a swirl flow.

[0053] The crushing process S12 is carried out by the crushing device 12. The acidic aqueous solution B that includes collection bags A that have had holes opened and have sunk below the liquid surface of the acidic aqueous solution B, i.e. the liquid mixture 91, is discharged from the solution tank V while the used absorbent articles in the collection bags A are crushed in the acidic aqueous solution B, together with their collection bags A. In the crushing device 12 shown in Fig. 2, for example, first the used absorbent articles in the collection bags A that have been fed out from the solution tank V together with the acidic aqueous solution B are crushed by the crusher 60 in the acidic aqueous solution B, together with their collection bags A (submerged crushing process). In the crusher 60, the liquid mixture 91 is supplied to a rotating rotary blade and spacer that are facing inward and mutually engaged in the twin-screw crusher, thus crushing each whole collection bag A. The acidic aqueous solution B (liquid mixture 92) containing the crushed matter obtained by the crusher 60 (submerged crushing process) is then drawn out from the crusher 60 by the pump 63 (drawing-out process), and fed out to the next process.

[0054] The crushing process S12 preferably has a process of crushing the used absorbent articles together with their collection bags A so that the average crushed matter size is 50 mm to 100 mm. Absorbent articles are assumed to have lengths of about 150 to 1000 mm and widths of 100 mm to 1000 mm. By crushing so that the average crushed matter size is 50 mm to 100 mm, it is possible to reliably form cuts in the back sheets and/or top sheets of each of the used absorbent articles. This will allow the pulp fibers to be essentially removed without remnants, through the cuts in each of the used absorbent articles, so that the pulp fibers recovery rate (total amount of regenerated pulp fibers/total amount of pulp fibers in supplied used absorbent articles) can be increased. If the average size is less than 50 mm, materials other than the pulp fibers (such as films (such as the materials of the collection bags A or back sheets), nonwoven fabrics (such as top sheets) or elastic solids (such as anti-leakage wall rubber)) will be cut too small, and it will be difficult to separate those materials from the pulp fibers in the subsequent processes. As a result, the contaminants (other materials) contaminating the regenerated pulp fibers will increase, lowering the pulp fibers recovery rate. If the average size is larger than 100 mm, on the other hand, it will be difficult to form cuts in the used absorbent articles. This will result in used absorbent articles from which the pulp fibers cannot be removed, thus lowering the pulp fibers recovery rate.

[0055] The first separation process S13 is carried out by thefirst separation device 13. Washing is carried out, wherein the liquid mixture 92 that includes the crushed matter and acidic aqueous solution obtained by the crushing device 12 is agitated and the contamination is removed from the crushed matter, while separating the liquid mixture 92 into the pulpfibers, superabsorbent polymers and acidic aqueous solution, and the other materials. During this time, an acidic aqueous solution may be separately added to increase the washing effect and/or to adjust the pH. As a result, the pulp fibers, superabsorbent polymers and acidic aqueous solution in the liquid mixture 92 (also partially including other materials) are separated through the perforations and fed out from the first separation device 13 (liquid mixture 93). The other materials in the liquid mixture 92, without the pulp fibers, superabsorbent polymers and acidic aqueous solution, cannot pass through the perforations and remain in the first separation device 13, or are fed out by a different route. Some of the other materials, however, cannot be separated and are fed out together with the liquid mixture 93. When a washing machine is used as the first separation device 13, the sizes of the perforations in the washing tank that functions as a sieve may be 5 mm to 20 mmp, when they are round holes, or when the holes have other shapes they may be of sizes with approximately equal areas as round holes.

[00561 For the crushing process of crushing the used absorbent articles as described above (from the hole punching process S1I(rupturing device 11) to the first separation process S13 (first separation device 13)), this method (system) comprises at least a hole punching process SI1 (rupturing device 11) and a crushing process S12 (crushing device 12). Since the used absorbent articles held in the collection bags are thus crushed in the inactivating aqueous solution together with their collection bags, there is virtually no mixture of contaminants or microbes with the inactivating aqueous solution and no generation of odors, at least until crushing is started. Moreover, even if there is mixture of contaminants or microbes in the inactivating aqueous solution or generation of odors when the used absorbent articles are crushed, since the inactivating aqueous solution containing the contaminants or microbes is fed out from the solution tank together with the crushed matter almost simultaneously with the crushing, the contaminants or microbes can be flushed out with virtually none remaining in the solution tank. Furthermore, since odors can be sealed off by the inactivating aqueous solution, odor generation can also be greatly reduced. This can inhibit fly-off of contaminants and microbes or release of odors during crushing of the used absorbent articles.

[00571

The used absorbent articles may be crushed together with their collection bags in a gas (for example, air), instead of crushing the used absorbent articles together with their collection bags in the inactivating aqueous solution (for example, the acidic aqueous solution). The hole punching process S1 is not necessary in this case, and the crushing process S12 carries out crushing in air in the absence of the inactivating aqueous solution. The inactivating aqueous solution is then supplied to the first separation process S13, together with the crushed matter from the crushing process S12.

[00581 When an acidic aqueous solution is not used as an inactivating aqueous solution between the hole punching process S11 and the first separation process S13, the acidic aqueous solution from the first dust removal process S14 is preferably added so that the inactivating aqueous solution containing pulp fibers and superabsorbent polymers supplied from the first dust removal process S14 is essentially used as the acidic aqueous solution. This allows the specific gravity and size of the superabsorbent polymers to be easily adjusted by the pH.

[0059] The first dust removal process S14 is carried out by the first dust removal device 14. The acidic aqueous solution containing the pulp fibers and superabsorbent polymers that have been fed out from the first separation device 13, i.e. the liquid mixture 93, has its pH maintained in a predetermined range while the screen separates it into the acidic aqueous solution containing the pulp fibers and superabsorbent polymers, and the other materials (contaminants). As a result, the pulp fibers, superabsorbent polymers and acidic aqueous solution in the liquid mixture 93 (also partially including other materials) are separated through the screen and fed out from the first dust removal device 14 (liquid mixture 94). The other materials in the liquid mixture 93, without the pulp fibers, superabsorbent polymers and acidic aqueous solution, cannot pass through the screen and remain in the first dust removal device 14, or are fed out by a different route. Some of the other materials, however, cannot be separated and are fed out together with the liquid mixture 94.

[0060] The acidic aqueous solution preferably has the pH adjusted so that the differences between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber are each within predetermined ranges, at least until the first dust removal process S14. The "predetermined range" may be, for example, one being within a range of 0.2 to times compared to the other. In this case, the processes before the first dust removal process S14 may be considered to be an inactivating process of mixing the pulp fibers and the superabsorbent polymers with an acidic aqueous solution with the pH adjusted so that the differences between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber are each within predetermined ranges, for inactivation of the superabsorbent polymers.

[0061] The combined concentration of the pulp fibers and superabsorbent polymers in the acidic solution during the first dust removal process Si4 may be 0.1 mass% or greater and 10 mass% or lower, for example, and is preferably 0.1 mass% or greater and 5 mass% or lower. The ratio between the pulp fibers and the superabsorbent polymers in the acidic solution may be 50 to 90 mass%:50 to 10 mass%, for example.

[0062] The second dust removal process S15 is carried out by the second dust removal device 15. The acidic aqueous solution containing the pulp fibers and superabsorbent polymers that has been fed out from the first dust removal device 14, i.e. the liquid mixture 94, has its pH maintained in a predetermined range while the screen separates it into the acidic aqueous solution containing the pulp fibers and superabsorbent polymers, and the other materials (contaminants). As a result, the pulp fibers, superabsorbent polymers and acidic aqueous solution in the liquid mixture 94 (also partially including other materials) are separated through the screen and fed out from the second dust removal device 15 (liquid mixture 95). The other materials in the liquid mixture 94, without the pulp fibers, superabsorbent polymers and acidic aqueous solution, cannot pass through the screen and remain in the second dust removal device 15, or are fed out by a different route. Some of the other materials, however, cannot be separated and are fed out together with the liquid mixture 95. The acidic aqueous solution has the pH adjusted so that the differences between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber are each within predetermined ranges.

[0063] The third dust removal process S16 is carried out by the third dust removal device 16. The acidic aqueous solution containing the pulp fibers and superabsorbent polymers, i.e. the liquid mixture 95, which has been fed out from the second dust removal device 15, has its pH maintained within a predetermined range while being centrifugally separated in the inverted conical case into the pulp fibers and superabsorbent polymers in the acidic aqueous solution and the other materials (large-weight contaminants). As a result, the pulp fibers, superabsorbent polymers and acidic aqueous solution in the liquid mixture 95 are fed out from the top of the third dust removal device 16 (cyclone separator) (liquid mixture 96). At the same time, the other heavy materials such as metals in the liquid mixture 95, without the pulp fibers, superabsorbent polymers and acidic aqueous solution, are fed out from the bottom of the third dust removal device 16 (cyclone separator). The acidic aqueous solution has the pH adjusted so that the differences between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber are each within predetermined ranges.

[0064] This method (system) comprises the dust removal process of removing the contaminants (other materials) as described above (at least the second dust removal process S15 (second dust removal device 15) and third dust removal process S16 (third dust removal device 16) in the first dust removal process S14 (first dust removal device 14) to third dust removal process S16 (third dust removal device 16)). Therefore, based on size, the pulp fibers and superabsorbent polymers can be easily separated from mainly the resin materials among the other materials of the used absorbent articles without the pulp fibers and superabsorbent polymers (the second dust removal process S15 (second dust removal device 15)), allowing them to be easily separated by specific gravity from the materials with high specific gravity among the other materials, such as metal materials (third dust removal process S16 (third dust removal device 16)). Next, the pulp fibers and superabsorbent polymers are separated from each other (second and third separation processes S17, S18 (second and third separation devices 17, 18), allowing recovery of the pulp fibers and superabsorbent polymers from the used absorbent articles. The number of treatments carried out for separation of the pulp fibers and superabsorbent polymers from the other materials can thus be reduced. In other words, the treatment efficiency for separation of the superabsorbent polymers and pulp fibers can be increased.

[0065] The second separation process S17 is carried out by the second separation device 17. The acidic aqueous solution containing the pulp fibers and superabsorbent polymers, i.e. the liquid mixture 96, which has been fed out from the third dust removal device 16, is separated into pulp fibers in the acidic aqueous solution and superabsorbent polymers in the acidic aqueous solution, using a drum screen. As a result, the acidic aqueous solution containing the superabsorbent polymers is separated from the liquid mixture 96 through the drum screen, and is fed out from the second separation device 17. At the same time, the acidic aqueous solution containing the pulp fibers in the liquid mixture 96 is unable to pass through the drum screen, and is fed out from the second separation device 17 by a separate route (liquid mixture 97). The superabsorbent polymers can later be separated from the separated superabsorbent polymers and acidic aqueous solution by the screen separator. This process, therefore, can be considered to be a process of separating and recovering the superabsorbent polymers, and therefore a process of generating recycled superabsorbent polymers.

[0066] The third separation process S18 is carried out by the third separation device 18. The pulp fibers, inseparable remaining superabsorbent polymers and acidic aqueous solution, i.e. the liquid mixture 97, which has been fed out from the second separation device 17, is separated by

/- V

the drum screen into a solid including the pulp fibers and superabsorbent polymers, i.e. the mixture 98, and a liquid E including the superabsorbent polymers and acidic aqueous solution. The superabsorbent polymers in the solid is squeezed by pressurization during the separation. As a result, the acidic aqueous solution containing the superabsorbent polymers is separated from the liquid mixture 97 through the drum screen, and is fed out from the third separation device 18. At the same time, the pulp fibers in the liquid mixture 97 wherein the superabsorbent polymers has been squeezed is unable to pass through the drum screen, and is fed out of the third separation device 18 through the gap of the cover at the tip section of the drum screen (mixture 98).

[00671 For example, in the third separation device 18 shown in Fig. 3, first the liquid mixture 97 containing the pulp fibers, superabsorbent polymers and acidic aqueous solution, which has been fed out from the second separation device 17, is loaded into the drum screen 81 and reaches the periphery of the screw shaft 82. Rotation of the screw shaft 82 by the drive unit 86 causes the liquid mixture 97 surrounding the screw shaft 82 to be pressed against the side walls of the drum screen 81 by the screw shaft 82 and screw blade 83, while being conveyed toward the tip section of the drum screen 81. During this time, the superabsorbent polymers and acidic aqueous solution pass through the screen on the side walls of the drum screen 81 and are thus separated from the liquid mixture 97, while the pulp fibers and a portion of the superabsorbent polymers remain in the drum screen 81. That is, the mixture 98, which is the solid containing the pulp fibers and superabsorbent polymers, and the liquid E containing the superabsorbent polymers and acidic aqueous solution, are separated from the liquid mixture 97. The mixture 98 is also pressurized while being forcibly fed out through the gap G between the tip section of the drum screen 81 and the cover 84 that has been pressed in the opposite direction from the direction in which the mixture 98 is conveyed. The superabsorbent polymers in the mixture 98 are squeezed by the process of being conveyed and fed out under pressurization. The liquid E, on the other hand, is fed out from the case 80. The pressure force applied onto the cover 84 may be 0.01 MPa to 1 MPa, for example, and is preferably 0.02 MPa or more and 0.5 MPa or less. If the pressure is below 0.02 MPa, the superabsorbent polymers will become difficult to squeeze and the oxidizing agent treatment time will not be significantly shortened, while if the pressure is higher than 0.5 MPa, the superabsorbent polymers will be sufficiently squeezed, but with the risk of damage to the pulp fibers.

[00681 The oxidizing agent treatment process S19 is carried out by the oxidizing agent treatment device 19. The pulp fibers in the solid and the squeezed superabsorbent polymers that have been fed out from the third separation device 18 are treated with an aqueous solution comprising an z I oxidizing agent. This causes the superabsorbent polymers to be oxidatively decomposed and removed from the pulp fibers. As a result, the superabsorbent polymers that was adhering on the pulp fibers of the mixture 98 (for example, remaining on the surfaces of the pulp fibers) is oxidatively decomposed by the aqueous solution (treatment solution) containing the oxidizing agent (for example, ozone), being converted to low-molecular-weight organic material that is soluble in the aqueous solution, and being removed from the pulp fibers. The state of the superabsorbent polymers which is oxidatively decomposed and converted to low-molecular weight organic materials that are soluble in the aqueous solution is a state in which the superabsorbent polymers pass through a 2 mm screen. This allows removal of the impurities such as superabsorbent polymers in the pulp fibers, to produce pulp fibers with a high level of purity, and to allow sterilization, bleaching and deodorization of the pulp fibers by the oxidizing agent treatment.

[0069] In the oxidizing agent treatment device 19 shown in Fig. 4, for example, the mixture 98 that includes the pulp fibers separated in the third separation process S18 (with residual superabsorbent polymers) is supplied into the treatment solution P through the supply port 122b provided at the top of the treatment tank 123. The treatment solution P is an acidic aqueous solution (to inhibit inactivation of the ozone and to inactivate the superabsorbent polymers), and it usually has a specific gravity of 1. Therefore, the pulp fibers gradually settle from the top toward the bottom of the treatment solution P. The ozone-containing gas Z generated by the ozone generator 126, on the other hand, is mixed with the treatment solution P at the ozone mixer 127 and is supplied from the supply port 122c to the treatment tank 123 through piping 136. The ozone-containing gas Z is continuously released from a region near the supply port 122c at the bottom of the treatment tank 123 in a state offine bubbles (for example, microbubbles or nanobubbles) in the treatment solution P. In other words, the ozone-containing gas Z gradually rises from the bottom toward the top of the treatment solution P. Inside the treatment solution P, the pulp fibers that settle from top to bottom and the ozone-containing gas Z that rises from bottom to top proceed in opposite directions and impact each other. The ozone containing gas Z also adheres to the surfaces of the pulpfibers, enveloping the pulp fibers. During this time, the ozone in the ozone-containing gas Z reacts with the superabsorbent polymers in the pulp fibers, whereby the superabsorbent polymers are oxidatively decomposed and dissolved in the treatment solution P. This causes the superabsorbent polymers on the pulp fibers to be removed from the pulp fibers. The countercurrent flow can increase the likelihood of contact between the superabsorbent polymers in the pulp fibers and the ozone-containing gas Z. The pulp fibers also settle at the base of the treatment tank 123, while the ozone containing gas Z escapes to the space at the top of the treatment tank 123. The ozone in the ozone-containing gas Z that has accumulated at the top of the treatment tank 123 is decomposed and detoxified by the ozone decomposer 129, and is released to the outside. Next, the treatment solution P (which includes pulp fibers) at the base of the treatment tank 123 is supplied through piping 132 into the treatment tank 123 from the supply port 122a provided at the top of the treatment tank 123, using the pump 121. This allows the pulp fibers in the treatment solution P to resettle from the top of the treatment solution P toward the bottom, so that it can react with the ozone-containing gas Z that rises back from the bottom toward the top. The treatment solution P that includes pulp fibers treated by the ozone-containing gas Z is thus supplied from the bottom (base) of the treatment tank 123 back to the top of the treatment tank 123, making it possible to forcibly generate a continuous and stable flow of fluid (containing pulp fibers) from the top to the bottom in the treatment tank 123. This can further increase the likelihood of contact between the superabsorbent polymers in the pulp fibers and the ozone-containing gas Z. In addition, since the pulp fibers are repeatedly treated by the ozone-containing gas Z, virtually all of the superabsorbent polymers in the pulp fibers can be removed and the purity of the pulp fibers can be drastically increased. When using the oxidizing agent treatment device 19 of Fig. 4, the oxidizing agent treatment process S19 is preferably carried out in a batch process.

[00701 When the ozone-containing gas Z is supplied to the treatment solution P, the ozone concentration in the treatment solution P may be 1 to 50 ppm by mass, for example. The ozone 3 concentration in the ozone-containing gas Z may be 40 to 200 g/m3, for example. The concentration of pulp fibers (including superabsorbent polymers) in the treatment solution P may be 0.1 to 20 mass%, for example. The residence time of the pulp fibers in the treatment tank 123 may be 2 minutes to 60 minutes, for example. The ozone-containing gas Z is fed out in the form of microbubbles (bubbles with diameters of about 1 to 1000 pm) or nanobubbles (bubbles with diameters of about 100 to 1000 nm). Specifically, since microbubbles or nanobubbles are fine bubbles with large surface areas per unit volume and a slow rising rate in liquid, the likelihood of contact of the bubbles with the pulp fibers is increased. Fine bubbles can also contact the surfaces of more pulp fibers. The individual pulp fibers can thus be enveloped in an evenly distributed manner by the fine bubbles, and the contact area between the pulp fibers and the ozone-containing gas Z can be further increased. In addition, contact of more bubbles with the pulp surfaces slows the settling rate of the superabsorbent polymers-containing pulp fibers due to the buoyancy of the fine bubbles, and can further increase the contact time between the pulp fibers and the ozone-containing gas Z. This allows the superabsorbent polymers in the pulp fibers to be oxidatively decomposed more reliably and removed from the pulp fibers.

[00711 In the oxidizing agent treatment device 19 shown in Fig. 5, the pulp fibers separated by the third separation process S18 (with residual superabsorbent polymers) are mixed with the acidic aqueous solution as the treatment solution Pa. The treatment solution Pa is supplied to the liquid mixture tank 112 through the piping 131, and stored. The treatment solution Pa in the liquid mixture tank 112 is also continuously supplied at a first flow rate to the treatment tank 123 through the piping 132a, by control of the flow rate of the pump 121a. The pulp fibers are thus supplied into the treatment solution P from the supply port 122 provided at the top of the treatment tank 123. The treatment solution P is an acidic aqueous solution, and its specific gravity is approximately 1. Therefore, the pulp fibers gradually settle from the top toward the bottom of the treatment solution P. The ozone-containing gas Z produced at the ozone generator 126, on the other hand, is supplied to the treatment tank 123 through piping 135, and is continuously released as fine bubbles (for example, microbubbles or nanobubbles) into the treatment solution P through the nozzle 127a of the treatment tank 123. In other words, the ozone-containing gas Z gradually rises from the bottom toward the top of the treatment solution P. Inside the treatment solution P, the pulp fibers that settle from top to bottom and the ozone containing gas Z that rises from bottom to top proceed in opposite directions and impact each other. The ozone-containing gas Z also adheres to the surfaces of the individual pulp fibers, enveloping the pulp fibers. During this time, the ozone in the ozone-containing gas Z reacts with the superabsorbent polymers in the pulp fibers, whereby the superabsorbent polymers are oxidatively decomposed and dissolved in the treatment solution P. This causes the superabsorbent polymers on the pulp fibers to be removed from the pulp fibers. The countercurrent flow can increase the likelihood of contact between the superabsorbent polymers in the pulp fibers and the ozone-containing gas Z. The pulp fibers also settle at the base of the treatment tank 123, while the ozone-containing gas Z escapes to the space at the top of the treatment tank 123. Next, the treatment solution P (including pulp fibers) at the base of the treatment tank 123 is continuously discharged at a second flow rate out of the treatment tank 123 from a discharge port 124 of the treatment tank 123, through piping 133, by control of the flow rate at the delivery pump 125a. The ozone in the ozone-containing gas Z that has accumulated at the top of the treatment tank 123 is decomposed and detoxified by the ozone decomposer 129, and is released to the outside. Thus, the treatment solution Pa is continuously supplied at the first flow rate into the treatment tank 123 from the top of the treatment tank 123, while the treatment solution P is continuously discharged at the second flow rate out of the treatment tank 123 from the bottom (base) of the treatment tank 123. It is thus possible to forcibly generate a continuous and stable flow of fluid (including pulp fibers) from top to bottom in the treatment tank 123. This can increase the likelihood of contact between the superabsorbent polymers in the pulp fibers and the ozone-containing gas Z. When using the oxidizing agent treatment device 19 of Fig. 5, the oxidizing agent treatment process S19 is preferably carried out as a continuous process.

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[00721 When the oxidizing agent is ozone, however, inactivation of the ozone can be inhibited if the treatment solution is an acidic aqueous solution, and the effect of the ozone (oxidative decomposition, sterilization, bleaching and deodorization of the superabsorbent polymers) can thus be increased. In addition to inactivating the superabsorbent polymers, using an acidic aqueous solution for the crushing process or dust removal process allows continuity between each of the treatment processes, without any inconveniences due to differences in the aqueous solution used in different treatment processes, allowing the treatment to be carried out in a stable and reliable manner. From the viewpoint of reducing the effect of acid on operating personnel and equipment, an organic acid is preferred for the acidic aqueous solution, with citric acid being preferred from the viewpoint of metal removal.

[0073] The first flow rate and second flow rate are preferably identical. If the first flow rate and second flow rate are identical, then the amount of treatment solution P in the treatment tank 123 can be kept constant, allowing stable and continuous treatment to be carried out. However, the first flow rate and second flow rate do not need to be completely identical at all times, and they may be only essentially identical when averaged over time (within 5% error).

[0074] The fourth separation process S20 is carried out by the fourth separation device 20, whereby the treatment solution containing the pulp fibers that has been treated in the oxidizing agent treatment device 19, i.e. the liquid mixture 99, passes through a screen with a plurality of openings and is separated into pulp fibers and treatment solution from the liquid mixture 99. As a result, the treatment solution 104 passes through the screen from the liquid mixture 99, and is separated and fed out from the fourth separation device 20. The separated treatment solution 104, i.e. the oxidizing agent treatment solution, may be returned to the oxidizing agent treatment device 19 and reutilized. This can reduce cost for the oxidizing agent treatment solution. The pulp fibers in the liquid mixture 99 cannot pass through the screen and remains in the fourth separation device 20, or is fed out by a different route. This process may be considered to be a process of separating and recovering pulp fibers, and therefore a process of generating recycled pulp fibers.

[00751 The specific gravity of the superabsorbent polymer was measured by the specific gravity bottle method described in "Tests for density and relative density of chemical products" of JIS K 0061. The specific gravity of the water-absorbent polymer before water absorption was 1.32 g/ml. The specific gravity during inactivation in a citric acid aqueous solution at pH 2 was 1.04 g/ml, and the specific gravity during inactivation in a citric acid aqueous solution at pH 4 was

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1.01 g/ml. The size of the superabsorbent polymer (after water absorption), on the other hand, is difficult to measure, and therefore the size (diameter) was calculated as follows, assuming the superabsorbent polymer to be spherical. Specifically, the size (diameter) of the superabsorbent polymer after water absorption was estimated by calculating the volume expansion from the amount of water in the aqueous solution after absorption of water by the superabsorbent polymer, with the mean diameter of the superabsorbent polymer before water absorption as 200

pm. Calculation of the volume expansion was carried out in the following manner. First, the amount of water absorbed by the superabsorbent polymer (per particle) was calculated. A volume of water corresponding to that amount of water was assumed to be the volume V of the superabsorbent polymer after water absorption, and the radius r of the superabsorbent polymer after water absorption was determined based on the formula V = 4/3r 3 . The diameter, as twice the radius r, was recorded as the size of the superabsorbent polymer (after water absorption). As a result, the gel diameter upon inactivation with a citric acid aqueous solution at pH 2 was approximately 420 pm, and the gel diameter upon inactivation with a citric acid aqueous solution at pH 4 was approximately 540 pm.

[0076] The proportion of the pulp fibers and superabsorbent polymers in the acidic aqueous solution were measured in the following manner. First, a portion of the acidic aqueous solution was taken as a sample and placed on a 200 mesh filter, to measure the sample weight WO. The sample on the filter was then suspended for 5 minutes to drain the water, and then absolutely dried by a predetermined absolute drying method (heating and drying at 120°C for 10 minutes), and the absolute dry weight WI of the dried sample was measured. The dried sample was then immersed in an aqueous solution containing ozone, and the resulting substance was absolutely dried by the same absolute drying method and the absolute dry weight W2 was measured for the pulp fibers. The weight obtained by subtracting the absolute dry weight W2 from the absolute dry weight WI was used as the weight of the superabsorbent polymers, and the proportions of the pulp fibers and superabsorbent polymers in the acidic aqueous solution were calculated by the following formulas. (Proportion of pulp fibers)= (absolute dry weight W2)/(sample weight WO) (Proportion of superabsorbent polymers)= (absolute dry weight W I- absolute dry weight W2)/(sample weight WO) In terms of weight proportion, the solid weight of contaminants is extremely low and can be ignored.

[00771 The concentration of ozone in the aqueous solution was measured in the following manner. First, in a 100 mL graduated cylinder containing approximately 0.15 g of potassium iodide and 5 mL of a 10% citric acid solution there was placed 85 mL of an ozone-dissolved aqueous solution. The reaction product was transferred to a 200 mL Erlenmeyer flask. A starch solution was added to cause coloration to violet, titration was performed with 0.01 mol/L sodium thiosulfate while stirring until the mixture became colorless. The following formula was used based on the titration value, to calculate the concentration of ozone in the aqueous solution. Concentration of ozone in aqueous solution (ppm by mass)= 0.01 mol/L sodium thiosulfate (mL) required for titration x 0.24 x 0.85 (mL)

[0078] This method preferably includes an ozone treatment process S22 and a pH adjustment process S23. These processes are for regeneration and reutilization of the acidic aqueous solution used in the method described above. Cost for the acidic aqueous solution can be reduced by reutilizing the acidic aqueous solution. The ozone treatment process S22 carries out sterilizing treatment of the acidic aqueous solution 101 with an ozone-containing aqueous solution, after separation of the superabsorbent polymers and acidic aqueous solution by the second separation process S17 and further separation of the superabsorbent polymers. The pH adjustment process S23 adjusts the pH of the acidic aqueous solution subjected to sterilizing treatment in the ozone containing aqueous solution, and produces regenerated acidic aqueous solution 103. The acidic aqueous solution 103 is supplied to the crushing device 11, for example. Alternatively, it is supplied to the first separation process S13 when there is no hole punching process S11, and crushing is carried out in the crushing process S12 without using an inactivating aqueous solution. Alternatively, as necessary, it may be supplied to another process (apparatus) that requires an acidic aqueous solution. The excess portion of the acidic aqueous solution 103 is stored in the water storage tank 24.

[00791 The method of recovering pulp fibers from used absorbent articles containing pulp fibers and superabsorbent polymers comprises at least a solid-liquid separation process (solid-liquid separator), or in other words a third separation process S18 (third separation device 18) and an oxidizing agent treatment process S19 (oxidizing agent treatment device 19), for a recovery process of recovering pulp fibers (second separation process S17 (second separation device 17) to fourth separation process S20 (fourth separation device 20)). In the third separation process S18 (third separation device 18), the gel-like (lumpy or approximately spherical) superabsorbent polymers that have absorbed water and remain in the pulp fibers are squeezed to reduce the thicknesses of the superabsorbent polymers and converted to a flat or finely divided form. The squeezing is typically squeezing of the gel-like superabsorbent polymers under pressure at or greater than the gel strength. That is, the method or system allows the surface areas of the superabsorbent polymers to be greatly increased by squeezing the lumpy or approximately spherical superabsorbent polymers, and can increase the exposed portions by exposing the interior portions of the superabsorbent polymers onto the surfaces. In the oxidizing agent treatment process S19 (oxidizing agent treatment device 19), therefore, it is possible to cause contact between the oxidizing agent and the interior portions of the superabsorbent polymers, which in the case of a lumpy or approximately spherical superabsorbent polymers are unlikely to contact with the oxidizing agent, thereby allowing the contact area of the superabsorbent polymers with the oxidizing agent to be increased. This can more efficiently promote oxidative decomposition of the superabsorbent polymers and shorten the oxidizing agent treatment time. As a result, the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased.

[0080] As a preferred mode of this embodiment, the third separation process S18 (third separation device 18) may include a squeezing process (screw press dewaterer) in which an inactivating aqueous solution (such as an acidic aqueous solution) containing pulp fibers and superabsorbent polymers is treated by a pressurized dewatering method, to squeeze the superabsorbent polymers remaining in the pulp fibers. Since the superabsorbent polymers remaining in the pulp fibers are squeezed by a pressurized dewatering method in this method or system, it is possible to efficiently and reliably carry out solid-liquid separation and squeezing of the superabsorbent polymers on the pulp fibers in a simultaneous manner. In other words, it is possible to greatly increase the surface areas of the superabsorbent polymers on the pulp fibers, both efficiently and reliably. This allows the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers to be increased.

[0081] As a preferred mode of this embodiment, the pressure during pressurization in the pressurized dewatering method in the squeezing process (screw press dewaterer) of the third separation process S18 is 0.02 MPa or more and 0.5 MPa or less. In this method or system, the pressure during pressurization in the pressurized dewatering method is 0.02 MPa or more and 0.5 MPa or less It therefore allows superabsorbent polymers remaining in pulp fibers to be sufficiently squeezed without damaging the pulp fibers, allowing the surface areas of the superabsorbent polymers to be increased to a sufficiently high degree. This allows the treatment efficiency for removal of the superabsorbent polymers from the pulp fibers to be increased. If the pressure is below 0.02 MPa, however, the superabsorbent polymers cannot be sufficiently squeezed and the oxidizing agent treatment time cannot be significantly shortened, while if the pressure is higher than 0.5 MPa, it is possible to sufficiently squeeze the superabsorbent polymers, but with the risk of damage to the pulp fibers.

[0082] As a preferred mode of this embodiment, the method may comprise, before the third separation process S18 (third separation device 18), a process of separating a portion of the superabsorbent polymers and inactivating aqueous solution from the inactivating aqueous solution containing the pulp fibers and superabsorbent polymers, or in other words, a second separation process S17 (drum screen dewaterer of the second separation device 17). This method or system comprises the drum screen dewaterer of the second separation process S17 (second separation device 17) before the third separation process S18 (third separation device 18). The method or system can therefore highly reduce the proportion of superabsorbent polymers in the material (the pulp fibers, superabsorbent polymers and inactivating aqueous solution) supplied to the third separation process S18 (third separation device 18). This allows the superabsorbent polymers adhering to the pulp fibers to be more efficiently squeezed in the third separation process S18 (third separation device 18), and can increase the treatment efficiency of removing the superabsorbent polymers from the pulp fibers.

[0083] As a preferred mode of this embodiment, the proportion of the superabsorbent polymers in the inactivating aqueous solution supplied to the third separation process S18 (third separation device 18) may be 50% or lower. In this method or system, the proportion of the superabsorbent polymers in the inactivating aqueous solution to be separated in the third separation process S18 (third separation device 18) is 50% or lower. This eliminates the need to squeeze an excessive amount of superabsorbent polymers, thus allowing the superabsorbent polymers to be more reliably and efficiently squeezed. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can thus be increased.

[0084] As a preferred mode of this embodiment, the method may further comprise, before the third separation process S18 (third separation device 18), a process (including S12) in which used absorbent articles are crushed in an inactivating aqueous solution, and a process (including S13, and preferably S14 to S16) in which an inactivating aqueous solution containing pulp fibers and superabsorbent polymers is separated from an inactivating aqueous solution containing crushed matter obtained from the crushing process (including S12). This method or system comprises a process of crushing an inactivating aqueous solution containing pulp fibers and superabsorbent polymers separated from the used absorbent articles, which is supplied in the third separation process S18 (third separation device 18), and a separating process of washing it. Using a crushing process and a separating process can inhibit contamination of the inactivating aqueous solution by contaminants (materials other than the pulp fibers and superabsorbent polymers in disposable absorbent articles (for example, films and nonwoven fabrics) and elastic solids). It is thus possible to more accurately squeeze the superabsorbent polymers without interference by contaminants. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[0085] As a preferred mode of this embodiment, the inactivating aqueous solution may be an acidic aqueous solution. Since the inactivating aqueous solution in this method or system is an acidic aqueous solution, the superabsorbent polymers in the used absorbent articles can be reliably dewatered and adjusted to below a predetermined size (particle size, for example). This will allow solid liquid separation to be easily carried out in the third separation process S18 (third separation device 18) while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

[0086] As a preferred mode of this embodiment, the acidic aqueous solution may have a pH of 2.5 or lower. Since the acidic aqueous solution in this method or system has a pH of 2.5 or lower, the superabsorbent polymers in the used absorbent articles can be more reliably dewatered and adjusted to below a predetermined size (particle size, for example). This will allow solid-liquid separation to be more easily carried out in the third separation process S18 (third separation device 18) while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result. Moreover, since the superabsorbent polymers can be adjusted to a predetermined size in a gel state, it becomes easier to squeeze the superabsorbent polymers.

[00871 As a preferred mode of this embodiment, the acidic aqueous solution may include citric acid. Since the acidic aqueous solution in this method or system includes citric acid (at a concentration of 0.5 to 2.0 mass%, for example), the superabsorbent polymers in the used absorbent articles can be more reliably dewatered and adjusted to below a predetermined particle size. This will allow solid-liquid separation to be easily carried out in the third separation process S18 (third separation device 18) while squeezing the superabsorbent polymers. The treatment efficiency for removal of the superabsorbent polymers from the pulp fibers can be increased as a result.

EXAMPLES

[00881 An Example of the method of recovering pulp fibers from used absorbent articles will now be described.

[0089] In this Example, the third separation process S18 and oxidizing agent treatment process S19 of the method were carried out on crushed absorbent articles from which the materials other than pulp fibers and superabsorbent polymers had been removed. The relationship between the pressure applied during pressurization in the third separation process S18 and the treatment time for oxidizing agent treatment in the oxidizing agent treatment process S19 was examined. Specifically, the absorbent articles used were adult disposable diapers (unused) that had been treated from the crushing process S12 to the second separation process S17, as a liquid mixture 97. In the third separation process S18, the pressure applied during pressurization in the pressure dewatering method (the pressure applied to the cover) was changed 0 to 3.3 kgf/cm2 (0 to 0.32 MPa). The time at which the superabsorbent polymers was no longer detected in the pulp fibers during the oxidizing agent treatment process S19 was measured as the treatment time. The treatment time was the time at which superabsorbent polymers were no longer detected in the oxidizing agent treatment process S19, during extraction of a predetermined amount of pulp fibers at fixed time intervals and detection of whether or not superabsorbent polymers were adhering to the pulp fibers.

[0090] The following procedure was used to determine whether or not superabsorbent polymers were adhering to the pulp fibers. After extracting and draining 10 g of pulp fibers, the fibers were untwisted under light and observed under a magnifying glass at 20x magnification, and it was visually confirmed whether or not any polymer residue was present. Polymer residue, when present, is easily visible because it reflects light and shines.

[0091] Fig. 7 shows the results of examining the relationship between the pressure applied during pressurization and the treatment time for oxidizing agent treatment. Fig. 7 is a graph showing the relationship between pressure applied during pressurization and treatment time for oxidizing agent treatment. The abscissa is applied pressure (kgf/cm2), and the ordinate is treatment time (min). As shown here, based on a treatment time of 40 minutes for an applied pressure of 0 kgf/cm2,,it was shown that the treatment time reducing effect was low with alow applied

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/ pressure, with the treatment time reducing effect increasing as the applied pressure increased. It was also shown that the treatment time reducing effect became saturated at above a certain pressure. From the viewpoint of reducing the treatment time, therefore, the pressure is preferably 0.2 kgf/cm2 (0.02 MPa) or higher. From the viewpoint of saturation of the reducing effect or reliability of the reducing effect, the pressure is preferably 5 kgf/cm2 (0.5 MPa) or lower. The pressure is also preferably 0.5 kgf/cm2 (0.05 MPa) or higher, or 3 kgf/cm2 (0.3 MPa).

[0092] This embodiment has been described assuming a film as the structural member of the back sheet and a nonwoven fabric as the structural member of the top sheet. However, embodiments wherein a nonwoven fabric is the structural member of the back sheet and a film is the structural member of the top sheet, or wherein films are the structural members of both the back sheet and the top sheet, may also be carried out by the same method as the embodiment described above, and can exhibit the same function and effect.

[00931 The absorbent article of the present invention is not restricted to the embodiments described above and can incorporate appropriate combinations and modifications without departing from a scope of the object and gist of the invention.

REFERENCE SIGNS LIST

[0094] S18 Third separation process S19 Oxidizing agent treatment process

[0095] In this specification, the terms 'comprises', 'comprising', 'includes', 'including', or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.

Claims

The claims defining the invention are as follows:

1. A method of recovering pulp fibers from used absorbent articles that include pulp fibers and superabsorbent polymers, the method comprising: a solid-liquid separation process of, while separating an inactivating aqueous solution that includes pulp fibers and superabsorbent polymers that have been separated from used absorbent articles, into solid containing the pulp fibers and the superabsorbent polymers and liquid containing the superabsorbent polymers and the inactivating aqueous solution, squeezing the superabsorbent polymers in the solid; and an oxidizing agent treatment process of treating the pulp fibers and the squeezed superabsorbent polymers present in the separated solid with an aqueous solution containing an oxidizing agent, wherein: the solid-liquid separation process includes a squeezing process of treating the inactivating aqueous solution that includes the pulp fibers and the superabsorbent polymers by a pressurized dewatering method to squeeze the superabsorbent polymers remaining in the pulp fibers; and the pressure during pressurization in the pressurized dewatering method of the squeezing process is 0.02 MPa or more and 0.5 MPa or less.

2. The method according to claim 1, further comprising, prior to the solid-liquid separation process, a process of separating a portion of the superabsorbent polymers and the inactivating aqueous solution from the inactivating aqueous solution containing the pulp fibers and superabsorbent polymers.

3. The method according to claim 1 or 2, wherein: a proportion of the superabsorbent polymers in the inactivating aqueous solution supplied to the solid-liquid separation process is 50% or lower.

4. The method according to any one of claims I to 3, further comprising, prior to the solid-liquid separation process, a process of crushing the used absorbent articles in an inactivating aqueous solution, and a process of separating the inactivating aqueous solution containing the pulp fibers and superabsorbent polymers from the inactivating aqueous solution containing a crushed matter obtained by the process of crushing.

5. The method according to any one of claims 1 to 4, wherein: the inactivating aqueous solution is an acidic aqueous solution.

6. The method according to claim 5, wherein: the acidic aqueous solution has a pH of 2.5 or lower.

7. The method according to claim 5 or 6, wherein: the acidic aqueous solution includes citric acid.

8. A system of recovering pulp fibers from used absorbent articles that include pulp fibers and superabsorbent polymers, the system comprising: a solid-liquid separator which, while separating an inactivating aqueous solution including pulp fibers and superabsorbent polymers that have been separated from used absorbent articles, into solid containing the pulp fibers and the superabsorbent polymers and liquid containing the superabsorbent polymers and the inactivating aqueous solution, squeezes the superabsorbent polymers in the solid; and an oxidizing agent treatment device which treats the pulp fibers and the squeezed superabsorbent polymers present in the separated solid with an aqueous solution containing an oxidizing agent, wherein: the solid-liquid separator includes a screw press dewaterer which treats the inactivating aqueous solution including the pulp fibers and the superabsorbent polymers by a pressurized dewatering method to squeeze the superabsorbent polymers remaining in the pulp fibers; and the pressure during pressurization in the pressurized dewatering method using the screw press dewaterer is 0.02 MPa or more and 0.5 MPa or less.

9. The system according to claim 8, further comprising, prior to the solid-liquid separator, a drum screen dewaterer which separates a portion of the superabsorbent polymers and the inactivating aqueous solution from the inactivating aqueous solution containing the pulp fibers and superabsorbent polymers.

10. The system according to claim 8 or 9, wherein: a proportion of the superabsorbent polymers in the inactivating aqueous solution supplied to the solid-liquid separator is 50% or lower.

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11. The system according to any one of claims 8 to 10, wherein: the inactivating aqueous solution is an acidic aqueous solution.

12. The system according to claim 11, wherein: the acidic aqueous solution has a pH of 2.5 or lower.

13. The system according to claim 11 or 12, wherein: the acidic aqueous solution includes citric acid.