Method for separating paper fragments from gypsum waste material

Abstract

This method for separating paper fragments from gypsum waste includes a step for forming a slurry containing gypsum waste and water, a step for separating the slurry into layers while stirring the slurry into a first slurry portion formed by accumulation of the gypsum waste and a second slurry portion containing paper fragments that are piled on top of the first slurry portion and have a lower specific gravity than the gypsum waste, and a step for draining the second slurry portion containing the paper fragments while stirring the slurry.

Description

Method for Separating Paper Pieces from Gypsum Waste

[0001] The present invention relates to a method for separating paper pieces from gypsum waste.

[0002] In recent years, due to the demands for reducing environmental impact and waste volume, the blending ratio of recycled gypsum in gypsum-based building materials such as gypsum boards has been increasing. Recycled gypsum may have paper pieces attached to it. When the content rate of paper pieces increases, there is a problem that the amount of water mixed to give fluidity to the calcined gypsum slurry increases, and the drying energy increases.

[0003] Conventionally, dry separation of hemihydrate gypsum and separation and removal of paper pieces by gypsum modification are known. In the dry separation of hemihydrate gypsum, it is difficult to remove fine paper pieces such as paper powder. In gypsum modification, at least two hemihydration steps are required, so the firing energy increases.

[0004] Patent Document 1 discloses a technique in which waste gypsum boards are crushed, water is added to the crushed material to form a slurry, and the slurry is filtered to separate it into a slurry containing gypsum, and paper and cellulose fibers. Patent Document 2 discloses a method for manufacturing paper materials including a water stirring and crushing step of putting waste gypsum board separated paper pieces into water to subdivide and separate the gypsum attached to the paper pieces, kneading the paper pieces to disperse and suspend plant tissues in water, and eluting water-soluble components and the like to generate a pulp liquid, and a pulp recovery step of recovering pulp from the pulp liquid.

[0005] Japanese Patent Application Laid-Open No. 2009-226309 Japanese Patent Application Laid-Open No. 2020-131067

[0006] In both Patent Documents 1 and 2, a sieving device (screen) is used when separating paper pieces (described as "paper and cellulose fibers" and "pulp" in Patent Documents 1 and 2 respectively) from the slurry. For example, if gypsum adheres to the sieve, it may become impossible to remove paper pieces well.

[0007] An object of the present invention is to provide a method for separating paper pieces from gypsum waste that can satisfactorily remove paper pieces from a slurry containing gypsum waste.

[0008] A method for separating paper fragments from gypsum waste according to one embodiment includes the steps of: forming a slurry containing gypsum waste and water; separating the slurry in layers while stirring the slurry into a first slurry portion formed by the accumulation of the gypsum waste and a second slurry portion containing paper fragments that overlap the first slurry portion and have a lower specific gravity than the gypsum waste; and draining the second slurry portion containing the paper fragments while stirring the slurry.

[0009] According to the present invention's method for separating paper fragments from gypsum waste, paper fragments can be effectively removed from a slurry containing gypsum waste.

[0010] Figure 1 is a flowchart illustrating an example of a method for separating paper fragments from gypsum waste according to the embodiment. Figure 2 is an explanatory diagram illustrating an example of a method for separating paper fragments from gypsum waste according to the embodiment.

[0011] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments will not limit the present disclosure.

[0012] (Embodiment) Figure 1 is a flowchart illustrating an example of a method for separating paper fragments from gypsum waste according to an embodiment. Figure 2 is an explanatory diagram illustrating an example of a method for separating paper fragments from gypsum waste according to an embodiment.

[0013] In this embodiment, a method for separating gypsum and paper fragments from gypsum waste materials such as gypsum boards will be described. As shown in Figure 1, first, gypsum waste materials are prepared (step ST1). The gypsum waste materials used are, for example, gypsum board waste generated at new construction sites or demolition sites of buildings such as houses. Gypsum board waste materials have a structure in which base paper is bonded to a plate-shaped gypsum, and for example, a gypsum board with a product thickness of 12.5 mm is composed of approximately 96 wt% gypsum and approximately 4 wt% base paper.

[0014] The gypsum waste material used in this embodiment is formed into a powder or granular form by crushing gypsum board waste, and includes gypsum waste material of a predetermined particle size or smaller. For example, a four-shaft shredder can be used to crush the gypsum board waste. However, it is not limited to this, and any method or apparatus may be used to crush the gypsum board waste. In the crushing process, the gypsum and base paper of the gypsum board are separated and separated. Since it is difficult to completely separate the base paper from the gypsum in the crushing process, the gypsum waste material formed from the gypsum board waste has some base paper (hereinafter referred to as paper fragments) attached to it. However, the paper fragment content (wt%) in the gypsum waste material is a very small value (for example, about 1 wt% or less) compared to the base paper content (wt%) in the gypsum board described above.

[0015] In this embodiment, "paper piece" may be simply referred to as "paper" or "paper content." Furthermore, in this disclosure, "wt%" can be replaced with "mass%."

[0016] Next, the gypsum waste material formed in step ST1 is mixed with water to form a slurry (step ST2). As shown in Figure 2, the gypsum waste material formed in step ST1 and water are added to the slurry preparation tank 10, and after the entire gypsum waste material formed in step ST1 is circulated in the water, it is stirred with the stirring device 30 to form a slurry 20. As an example of how to form the slurry 20, for example, 300 mL of water is added to 100 g of gypsum waste material formed in step ST1. In this case, the concentration of gypsum waste material in the slurry 20 is 25 wt%.

[0017] The slurry adjustment tank 10 has a drain port 11 that can be opened and closed. The slurry 20 is formed so that its upper surface exceeds the drain port 11. In step ST2 and step ST3, which will be described later, the drain port 11 is closed and the slurry 20 is stored in the slurry adjustment tank 10.

[0018] Next, the slurry 20 is stirred and separated into layers (step ST3). As an example, the stirring blades of the stirring device 30 are rotated to stir the slurry 20 formed in step ST2. At this time, the gypsum waste, which has a relatively high specific gravity, accumulates in the lower layer of the slurry 20, forming a first slurry section 21 mainly containing gypsum waste. Fine particles such as paper scraps, which have a lower specific gravity than the gypsum waste, remain in the water, forming a second slurry section 22 mainly containing fine particles such as paper scraps. The slurry 20 is separated into layers such that the first slurry section 21 and the second slurry section 22 overlap in this order.

[0019] In this embodiment, the slurry 20 is separated into layers while being stirred by the stirring device 30, so that the separation of paper fragments attached to the gypsum waste is further promoted by water convection and contact between the gypsum waste materials. In addition, the paper fragments separated from the gypsum waste are suspended in the water in the second slurry section 22 by the stirring of the stirring device 30. This prevents the paper fragments separated from the gypsum waste from settling and returning to the gypsum waste in the first slurry section 21.

[0020] Next, while stirring the slurry 20, the second slurry section 22 containing the paper fragments is drained (step ST4). The second slurry section 22 is drained from the drain port 11 and stored in the intake tank 40. As a result, the paper fragments separated from the gypsum waste and floating in the second slurry section 22 are discharged into the intake tank 40 along with the water. The first slurry section 21, which mainly contains gypsum waste, remains in the slurry adjustment tank 10.

[0021] In this embodiment, the second slurry portion 22 of the slurry 20 is drained while being stirred by the stirring device 30. In the process of draining the second slurry portion 22, the second slurry portion 22 is drained from the slurry adjustment tank 10 to the external water intake tank 40 without passing through a filtration device such as a screen or sieve. As a result, in this embodiment, regardless of the size of the paper pieces, both fine paper pieces and paper pieces of a predetermined size can be discharged together with the water in the second slurry portion 22.

[0022] Here, a known method for separating paper fragments from slurry 20 is to use a screen or sieve (see Patent Documents 1 and 2). When a screen or sieve is used, the shape and size of the paper fragments that can be separated may be restricted by the size of the mesh opening, etc. Alternatively, if gypsum waste material adheres to the screen or sieve, the filtration function may decrease, and it may become impossible to separate the paper fragments properly. In this embodiment, since no filtration device such as a screen or sieve is provided, the shape and size of the paper fragments that can be separated are not restricted by the specifications of the screen or sieve, such as the mesh opening. Therefore, the method for separating paper fragments from gypsum waste material in this embodiment can effectively separate the gypsum waste material from the paper fragments.

[0023] Next, the first slurry portion 21 and the second slurry portion 22 separated in step ST4 are dried to recover the gypsum waste and paper scraps (step ST5). The first slurry portion 21 and the second slurry portion 22 are dried, for example, in a dryer at 40°C.

[0024] The gypsum waste collected from the first slurry section 21 is fired at a predetermined temperature to obtain calcined gypsum (hemihydrate gypsum). The obtained calcined gypsum can be used as recycled gypsum. Note that some paper fragments may remain in the gypsum waste collected from the first slurry section 21.

[0025] The paper scraps recovered from the second slurry section 22 can be used as recycled paper. The second slurry section 22 also contains fine-grained gypsum waste that does not accumulate in the first slurry section 21. The gypsum waste contained in the second slurry section 22 can be calcined at a predetermined temperature, similar to the gypsum waste in the first slurry section 21, to obtain calcined gypsum (hemihydrate gypsum). Specific examples of processing methods for the separated first slurry section 21 and second slurry section 22 will be described later in the examples.

[0026] By the method described above, paper fragments can be separated from gypsum waste. Note that the method shown in Figures 1 and 2 is merely an example and can be modified as appropriate. The slurry adjustment tank 10, stirring device 30, water intake tank 40, etc., shown in Figure 2 are schematic representations for clarity and are not limited to these.

[0027] (Example 1) Table 1 shows the amount of gypsum waste material, mass of paper fragments, paper fragment content, paper fragment removal rate, and gypsum waste material recovery rate in each slurry 20 when prepared with different slurry concentrations in the method for separating paper fragments from gypsum waste material according to Example 1. In all cases in Example 1, for example, 100 g of gypsum waste material was used, and water was added to form a slurry 20 to a predetermined slurry concentration.

[0028]

[0029] The "slurry concentration" shown in Table 1 represents the ratio of the mass of gypsum waste (and paper scraps) to the total mass of slurry 20 in step ST2 described above. In Examples 1-1, 1-2, 1-3, 1-4, and 1-5, the concentrations of slurry 20 were 40%, 33%, 25%, 20%, and 10%, respectively.

[0030] Table 1 shows that the "amount of gypsum waste material in the first slurry section" represents the mass of gypsum waste material (excluding the mass of paper fragments) contained in the first slurry section 21 remaining in the slurry adjustment tank 10 after the process of draining the second slurry section 22 (step ST4) described above. Similarly, the "mass of paper fragments in the first slurry section" represents the mass of paper fragments (excluding the mass of gypsum waste material) contained in the first slurry section 21 remaining in the slurry adjustment tank 10 after the process of draining the second slurry section 22 (step ST4) described above.

[0031] Specifically, the remaining first slurry portion 21 is dried in a 40°C dryer, and then calcined in a 155°C dryer for 3 hours to obtain calcined gypsum. The "amount of gypsum waste material in the first slurry portion" is the mass measured after drying at 40°C (excluding the mass of paper fragments). After that, the calcined gypsum obtained by calcining for 3 hours is washed and filtered using a 75 μm sieve. This causes the paper fragments contained in the first slurry portion 21 to adhere to the sieve, separating and recovering the calcined gypsum from the paper fragments.

[0032] The collected paper scraps are burned in an electric furnace at 800°C, and the ash is collected. The mass of the ash is measured, and based on the mass of the ash, the mass of the paper scraps is calculated, assuming that the mass of ash produced by the combustion of the paper scraps is 8.4 wt%. The "mass of paper scraps in the first slurry section" is the mass of paper scraps estimated from the mass of ash using the above method (the mass of gypsum waste is not included).

[0033] Table 1 shows that the "amount of gypsum waste material in the second slurry section" represents the mass of gypsum waste material contained in the second slurry section 22 drained in step ST4 (excluding the mass of paper fragments). Similarly, the "mass of paper fragments in the second slurry section" represents the mass of paper fragments contained in the second slurry section 22 drained in step ST4 (excluding the mass of gypsum waste material). In other words, the "mass of paper fragments in the second slurry section" represents the mass of paper fragments removed from the original slurry 20 (excluding the mass of gypsum waste material). The specific measurement methods for the "amount of gypsum waste material in the second slurry section" and the "mass of paper fragments in the second slurry section" are the same as those for the "amount of gypsum waste material in the first slurry section" and the "mass of paper fragments in the first slurry section" described above, and repeated explanations are omitted.

[0034] "Total paper fragment content" indicates the proportion (wt%) of total paper fragments in 100g of gypsum waste material. The total paper fragments correspond to the sum of "mass of paper fragments in the first slurry portion" and "mass of paper fragments in the second slurry portion".

[0035] The "paper fragment removal rate" represents the ratio (%) of the paper fragment mass of the second slurry section 22 to the total paper fragment mass (paper fragment mass of the first slurry section 21 + paper fragment mass of the second slurry section 22). The "paper fragment removal rate" was calculated based on ((paper fragment mass of the second slurry section 22) / (total paper fragment mass)) × 100 (%). A higher "paper fragment removal rate" indicates a higher proportion of the "paper fragment mass of the second slurry section 22" removed from the slurry 20. The "gypsum waste recovery rate" represents the ratio (%) of the gypsum waste material amount of the first slurry section 21 to the total gypsum waste material amount (gypsum waste material amount of the first slurry section 21 + gypsum waste material amount of the second slurry section 22). The "gypsum waste recovery rate" was calculated based on ((gypsum waste material amount of the first slurry section 21) / (total gypsum waste material amount)) × 100 (%). A higher "gypsum waste recovery rate" indicates a higher proportion of "gypsum waste material in the first slurry section 21" recovered from the slurry 20.

[0036] As shown in Table 1, in Example 1-1, the slurry 20 concentration is high at 40%, so the separation of the first slurry section 21 (gypsum waste) and the second slurry section 22 (fine particles including paper fragments) in step ST3 is not successful. As a result, when the second slurry section 22 is drained in step ST4, a large amount of gypsum waste is drained along with the paper fragments, and many of the paper fragments remain attached to the gypsum waste in the first slurry section 21. Therefore, the "paper fragment removal rate" is small. When the slurry concentration increases, the separation of fine particles and gypsum during stirring is not successful, and a large amount of gypsum is washed away during drainage. Also, a large amount of paper is incorporated into the accumulated gypsum, and the mass ratio of paper in the recovered gypsum increases compared to the mass ratio of paper in the gypsum before the operation. By decreasing the slurry concentration, separation during stirring is successful, and the paper ratio in the recovered gypsum decreases. In particular, by performing the operation at a slurry concentration of 25%, a "paper fragment removal rate" of approximately 69.7% was achieved. When the slurry concentration was further diluted, the paper particles were removed, but the amount of water used increased significantly.

[0037] In Examples 1-2, 1-3, 1-4, and 1-5, lowering the concentration of the slurry 20 to 33%, 25%, 20%, and 10%, respectively, resulted in good separation of the first slurry section 21 and the second slurry section 22 in step ST3. Specifically, in Examples 1-2, 1-3, 1-4, and 1-5, the "gypsum waste recovery rate" was 75.0% or higher, demonstrating that the outflow of gypsum waste could be suppressed when draining the second slurry section 22 in step ST4. Furthermore, in Examples 1-2, 1-3, 1-4, and 1-5, the second slurry section 22 containing paper fragments could be drained well in step ST4, and the amount of paper fragments adhering to the gypsum waste in the first slurry section 21 could be reduced.

[0038] This demonstrated that a good "paper fragment removal rate" can be achieved in all slurry concentrations (content of gypsum waste material (gypsum particles and paper fragments) in slurry 20) within the range of 10% to 33%. More preferably, it was shown that a "paper fragment removal rate" of 47.5% or more can be achieved in slurry concentrations within the range of 10% to 25% (see Examples 1-3, 1-4, and 1-5). In particular, it was shown that a "paper fragment removal rate" of approximately 69.7% can be achieved when the slurry concentration is 25% (see Example 1-2).

[0039] (Example 2) Table 2 shows the amount of gypsum waste material, the mass of paper fragments, the paper fragment content, and the paper fragment removal efficiency in each slurry 20 when the particle size of the gypsum waste material is varied in the method for separating paper fragments from gypsum waste material according to Example 2. In Example 2, for example, 100 g of gypsum waste material was used, and water was added to form a slurry 20 with a slurry concentration of 25 wt%.

[0040]

[0041] The "amount of gypsum waste material in the first slurry section," "mass of paper fragments in the first slurry section," "amount of gypsum waste material in the second slurry section," "mass of paper fragments in the second slurry section," "total paper fragment content," "paper fragment removal rate," and "gypsum waste material recovery rate" in Table 2 are all the same as in Table 1, so repeated explanations are omitted.

[0042] The "Glyceridity of gypsum waste" shown in Table 2 corresponds to the mesh size (opening) of the sieve used when sieving gypsum waste to separate it into a specified particle size.

[0043] As shown in Table 2, in Example 2-1, slurry 20 was formed using gypsum waste with a particle size m smaller than 150 μm. In Example 2-1, the "paper fragment removal rate" was approximately 79.0%, showing a removal efficiency equivalent to or better than that of Examples 2-2 to 2-5. However, in Example 2-1, because the particle size of the gypsum waste is small, a large amount of gypsum waste exists as fine particles in the second slurry section 22. Therefore, when the second slurry section 22 is drained, the "amount of gypsum waste material in the second slurry section" discharged along with the paper fragments also increases, and the "amount of gypsum waste material in the first slurry section" and the "gypsum waste material recovery rate" decrease.

[0044] In Example 2-3, slurry 20 was formed using gypsum waste material with a particle size m larger than 2000 μm. In Example 2-3 composed only of large-particle gypsum waste material, the size of the paper pieces adhering to the gypsum waste material also becomes larger. Therefore, in step ST3, the paper pieces also accumulate in the lower layer of slurry 20 together with the gypsum waste material. That is, in Example 2-3, the "mass of paper pieces in the first slurry part" is larger than in other examples, and after drainage in step ST4, the paper pieces remaining in the first slurry part 21 increase. For this reason, the "paper piece removal rate" decreases.

[0045] In Example 2-2, slurry 20 was formed using gypsum waste material with a particle size m of 150 μm or more and 2000 μm or less. In other words, Example 2-2 is gypsum waste material having an intermediate particle size m excluding the gypsum waste material of Example 2-1 and Example 2-3. In Example 2-2, it was shown that a "paper piece removal rate" higher than that of Example 2-3 can be achieved, and the "mass of gypsum waste material in the first slurry part" and the "gypsum waste material recovery rate" increase compared to Example 2-1.

[0046] In Example 2-4, slurry 20 was formed using gypsum waste material with a particle size m smaller than 1000 μm. In Example 2-5, slurry 20 was formed using gypsum waste material with a particle size m smaller than 700 μm. Examples 2-4 and Example 2-5 include, for example, small gypsum waste material with a particle size m of 150 μm or less.

[0047] In Examples 2-4 and Example 2-5, the "mass of paper pieces in the first slurry part" shows small values of about 0.17 wt% and 0.16 wt%. That is, in Examples 2-4 and Example 2-5, the mass of the paper pieces adhering to the gypsum waste material in the first slurry part 21 is small. Therefore, it was shown that in Examples 2-4 and Example 2-5, the gypsum waste material and the paper pieces can be satisfactorily separated in step ST3. As a result, in Examples 2-4 and Example 2-5, a high "paper piece removal rate" of 69% or more can be achieved, and the "mass of gypsum waste material in the first slurry part" is 80.3 g and 77.6 g respectively, and it was shown that a high value of about 80% can be secured for the "gypsum waste material recovery rate".

[0048] From the above results, it is preferable that the particle size of the gypsum waste material is between 150 μm and 2000 μm. More preferably, the particle size of the gypsum waste material is smaller than 1000 μm or smaller than 700 μm. By forming the slurry 20 using gypsum waste material within this particle size range, the first slurry portion 21 and the second slurry portion 22 can be separated well. As a result, paper fragments can be effectively removed by draining the second slurry portion 22 from the slurry 20, and the amount of gypsum waste material that can be recovered can also be increased.

[0049] The numerical values ​​in Examples 1 and 2 described above are merely examples and are not limited thereto. For example, the mass of gypsum waste (and paper scraps) used to form the slurry 20 was set to 100 g, but it may be 100 g or more, or 100 g or less.

[0050] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0051] Furthermore, this disclosure may also take the following form.

[0052] (1) A method for separating paper fragments from gypsum waste, comprising the steps of: forming a slurry containing gypsum waste and water; separating the slurry in layers, while stirring the slurry, into a first slurry portion formed by the accumulation of the gypsum waste and a second slurry portion overlapping the first slurry portion and containing paper fragments having a lower specific gravity than the gypsum waste; and draining the second slurry portion containing the paper fragments while stirring the slurry. (2) The method for separating paper fragments from gypsum waste according to (1), wherein the content of the gypsum waste in the slurry is 10 wt% or more and 33 wt% or less. (3) The method for separating paper fragments from gypsum waste according to (1) or (2), wherein the particle size of the gypsum waste is 150 μm or more and 2000 μm or less. (4) The particle size of the gypsum waste is smaller than 1000 μm. The method for separating paper fragments from gypsum waste according to (1) or (2). (5) In the step of draining the second slurry portion, the second slurry portion is drained without passing through a filtration device. The method for separating paper fragments from gypsum waste according to any one of (1) to (4).

[0053] 10 Slurry adjustment tank 11 Drain outlet 20 Slurry 21 First slurry section 22 Second slurry section 30 Agitator 40 Water intake tank

Claims

1. A method for separating paper fragments from gypsum waste, comprising: a step of forming a slurry containing gypsum waste and water; a step of separating the slurry into layers, while stirring the slurry, into a first slurry portion formed by the accumulation of the gypsum waste and a second slurry portion overlapping the first slurry portion and containing paper fragments having a lower specific gravity than the gypsum waste; and a step of draining the second slurry portion containing the paper fragments while stirring the slurry.

2. The method for separating paper fragments from gypsum waste according to claim 1, wherein the content of gypsum waste in the slurry is 10 wt% or more and 33 wt% or less.

3. The method for separating paper fragments from gypsum waste according to claim 1 or claim 2, wherein the particle size of the gypsum waste is 150 μm or more and 2000 μm or less.

4. The method for separating paper fragments from gypsum waste according to claim 1 or claim 2, wherein the particle size of the gypsum waste is smaller than 1000 μm.

5. The method for separating paper fragments from gypsum waste material according to claim 1, wherein in the step of draining the second slurry portion, the second slurry portion is drained without passing through a filtration device.

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