JP2020093955A - Method for recycling dihydrate gypsum from waste gypsum boards - Google Patents

Abstract

To provide a recycling method in which a color tone of dihydrate gypsum particles to be recycled from waste gypsum boards is improved.SOLUTION: A method for recycling a dihydrate gypsum from waste gypsum boards includes: calcining a gypsum derived from waste gypsum boards to convert the gypsum into hemihydrate and/or anhydrous type III gypsum granules; mixing the gypsum granules with a slurry including a gypsum or water to prepare a gypsum slurry; and subjecting dihydrate gypsum particles precipitated in the gypsum slurry to solid-liquid separation, wherein the following two steps are performed: a mixing step of mixing a granular or fibrous activated carbon with the gypsum slurry; and a separation step of separating the activated carbon from the gypsum slurry before the solid liquid separation.SELECTED DRAWING: Figure 1

Description

This invention relates to improving the color tone of gypsum dihydrate recovered from waste gypsum board.

Applicants have succeeded in industrializing the recovery of gypsum dihydrate from waste gypsum board. A method for recovering gypsum dihydrate will be described in accordance with the applicant's Patent Document 1 (WO2012/176688A). The waste gypsum board is crushed to separate foreign matters such as paper pieces from the dihydrate gypsum, and the dihydrate gypsum is calcined to be converted into hemihydrate gypsum and the like. Hemihydrate gypsum and the like are mixed with gypsum slurry and the like in a mixing tank and transferred to a precipitation tank to deposit gypsum dihydrate particles in the slurry, and the slurry is refluxed to the mixing tank. The gypsum dihydrate particles precipitated in the slurry are extracted with a solid-liquid separator such as a filter press.

WO2012/176688A

The inventor has noticed that the gypsum dihydrate recovered by this method may be slightly colored such as light brown. Coloring occurs regardless of the gypsum board manufacturer, type of board, etc., and gypsum dihydrate, which is a raw material for the gypsum board, is required to have a white color tone, and coloring is not preferable.

An object of the present invention is to improve the color tone of gypsum dihydrate recovered from waste gypsum board.

This invention is a semi-water and/or anhydrous type III gypsum granules by calcining gypsum derived from waste gypsum board, and the gypsum granules are mixed with a slurry containing gypsum or water to form a gypsum slurry, Solid-liquid separation of dihydrate gypsum particles precipitated in the gypsum slurry, in the method of recovery of dihydrate gypsum from waste gypsum board,
A mixing step of mixing granular or fibrous activated carbon with the gypsum slurry,
Before the solid-liquid separation, a separation step of separating activated carbon from the gypsum slurry is performed.

The inventor initially suspected that the metal ions such as Fe ³⁺ ions in the gypsum slurry were the cause of the coloring, and removed the Fe ³⁺ ions in the slurry with an ion exchange resin or the like. However, coloring did not disappear. Therefore, when activated carbon was added to the gypsum slurry, decolorization was successful. These suggest that colored organic matter that can be adsorbed by activated carbon is present in the gypsum slurry. The origin of such organic substances is considered to be that pastes such as starch widely used for gypsum boards, surfactants, etc., develop color during a long period of time or during calcination of gypsum. The exact mechanism of coloring is unknown, but it is certain that it is due to a substance that can be removed with activated carbon. Further, silica gel is hydrophilic and zeolite is strongly polar, so it is not suitable for removing trace organic substances in an aqueous slurry.

It is considered that the organic matter that causes coloring enters the inside of the gypsum dihydrate particles or exists on the surface of the particles due to adsorption to the gypsum particles. When the recovered gypsum dihydrate particles are washed with water, the color tone can be improved to some extent, that is, the whiteness can be increased, but this is not sufficient. This suggests that a part of the coloring substance penetrates into the gypsum dihydrate particles and cannot be sufficiently removed by washing with water.

When granular or fibrous activated carbon is mixed with the gypsum slurry, the gypsum slurry can be decolorized and the whiteness of the gypsum dihydrate particles can be increased. Hemi-water and/or anhydrous type III gypsum once dissolves upon contact with water and precipitates as gypsum dihydrate. In this process, the presence of activated carbon makes it possible to significantly reduce the amount of the coloring substance (organic substance) as described above, which is adsorbed by the activated carbon and taken into the crystals of gypsum dihydrate during precipitation. It is presumed that this is because In the mixing, activated carbon may be added to the gypsum slurry, gypsum particles and activated carbon may be separately added to water or the like, or gypsum particles and activated carbon may be mixed in advance and added to water or the like. That is, the activated carbon may be mixed with the gypsum slurry, and the mixing process is arbitrary.

When the sheet-shaped activated carbon is brought into contact with the gypsum slurry, gypsum dihydrate is deposited on the surface of the activated carbon, which makes it difficult to remove the coloring substance in the slurry. Therefore, the activated carbon is granular or fibrous, and in the case of granular, it may be granular activated carbon or crushed irregular activated carbon. Then, the activated carbon is mixed with the gypsum slurry, in other words, dispersed in the gypsum slurry, and the separation step separates the activated carbon from the gypsum slurry before solid-liquid separation of the gypsum dihydrate particles. As described above, according to the present invention, the color tone of the recovered gypsum dihydrate particles can be improved.

Preferably, in the separating step, the activated carbon is sieved from the gypsum slurry by a sieve having an opening which allows the gypsum dihydrate particles to pass through but does not allow the activated carbon to pass through. In other words, activated carbon having a minimum particle size or a large fiber length is used for the particle size distribution (maximum particle size) of the gypsum dihydrate particles, and the activated carbon is separated by sieving.

Particularly preferably, the activated carbon which has been previously sieved and washed on the second sieve having an opening larger than that of the sieve is used in the mixing step. This sieving prevents fine powder and the like from remaining in the gypsum slurry by removing fine powder and the like contained in the activated carbon in advance by, for example, washing (washing) the activated carbon on the screen with water.

The gypsum dihydrate obtained by the manufacturing method adopted in the present invention usually has a substantial maximum particle size of about 300 μm. For this reason, the mesh size of the sieve used in the step of separating from the activated carbon is preferably more than 300 μm, more preferably in the range of 350 to 750 μm, and particularly preferably in the range of 400 to 700 μm. In that case, the opening of the sieve used for the above-mentioned sieving of activated carbon is preferably 800 μm or more, more preferably 1 mm or more. Considering the recovery rate of activated carbon, the mesh size is preferably 5 mm or less, more preferably 3 mm or less.

The figure which shows the collection method of the dihydrate gypsum of an Example

Examples for carrying out the present invention will be shown below. The scope of the present invention should be determined according to the understanding of those skilled in the art, taking into consideration the description of the specification and the well-known technology in this field based on the description of the claims.

Fig. 1 shows a method for recovering gypsum dihydrate. Reference numeral 2 crushes the waste gypsum board with a crusher, removes foreign matters such as paper pieces with a sieve 3, and heats the calcination furnace 4 to, for example, 130°C to 160°C to change into hemihydrate gypsum and/or anhydrous type III gypsum. ..

6 is a mixer, which mixes hemihydrate gypsum and/or anhydrous type III gypsum granules, activated carbon, and the gypsum slurry from the lowermost precipitation tank 11 into a slurry stock solution, and the slurry stock solution is fed to the first-stage precipitation tank 8. Supply. The amount of activated carbon added is preferably 1 kg or more and 10 kg or less per 1 ton of gypsum granules in terms of hemihydrate gypsum. The structure of the mixer 6 is arbitrary, and is a cylindrical tank in the embodiment, but gypsum granules and activated carbon may be charged from the upper part of the gutter as a gutter-shaped flow path. Further, industrial water may be supplied instead of the gypsum slurry, and the gypsum slurry from the middle stage precipitation tanks 9 and 10 may be circulated to the mixer 6. Gypsum dihydrate particles are dispersed in the gypsum slurry, and the slurry stock solution is mixed with the gypsum slurry in the precipitation tank 8 and brought into contact with the seed crystals of gypsum dihydrate.

The activated carbon to be charged is preferably granular shaped activated carbon or crushed activated carbon, which is preferably larger than the particle size of the obtained dihydrate gypsum particles, for example, one which does not pass through a sieve having an opening of 500 μm, preferably an opening of 1 mm. Use one that does not pass through the sieve. Then, in preparation for the case where the activated carbon contains fine powders, it is preferable to use a sieve component that has not passed through the sieve after previously washing with water on a sieve (for example, a vibration sieve) not shown. The sieve used for washing with water (second sieve) has an opening of, for example, 500 μm or more, preferably 1 mm or more, which is equal to or more than the opening of the sieve 20 described later, and the maximum particle size of the dihydrate gypsum particles (about Larger than 300 μm). Then, the fine powder in the activated carbon is removed by washing with water on the sieve so that the fine powder in the activated carbon does not pass through the sieve 20. In the case of gypsum board raw material, there is no reason to ignore the treatment efficiency and to make the maximum particle size of dihydrate gypsum particles exceed 300 μm.

For example, four stages of precipitation tanks 8 to 11 are provided on the downstream side of the mixer 6, and the precipitation tanks 8 to 11 are collectively referred to as a precipitation unit 12. An agitator 14 is provided in each of the precipitation tanks 8 to 11 to stir the slurry, and the gypsum slurry is introduced into the downstream precipitation tank from the upstream precipitation tank due to overflow or the like. A fluid pump may be used to transfer between the precipitation tanks. The number of stages of the precipitation tanks 8 to 11 is arbitrary, and the precipitation section 12 may be configured by only one precipitation tank. The gypsum slurry in the precipitation tanks 8 to 11 is an aqueous slurry containing gypsum dihydrate particles, and the gypsum dihydrate particles act as seed crystals, consuming the hemihydrate gypsum and the like charged into the mixer 6, and the gypsum dihydrate particles are grow up.

The activated carbon mixed in the mixer 6 adsorbs a coloring substance considered to be a water-soluble organic substance in the slurry stock solution and prevents the coloring substance from penetrating into the gypsum dihydrate particles. Therefore, the activated carbon may be charged into the precipitation tanks 9 to 11, but is preferably mixed with the slurry in the mixer 6, the first-stage precipitation tank 8 or the pipes 18 and 19 described later.

For example, the gypsum slurry is introduced from the lowermost precipitation tank 11 into the mixer 6 by the fluid pump P1 via the pipe 18, and the mixer 6 to the precipitation part 12 are circulated. Note that the gypsum slurry may be circulated to the mixer 6 from the precipitation tanks 8 to 10 other than the lowermost precipitation tank 11.

The gypsum slurry is extracted from the lowermost precipitation tank 11, and activated carbon is removed by a sieve 20 such as a vibration sieve. When the slurry contains foreign matter such as paper pieces, the foreign matter is also removed at the same time. The gypsum slurry that has passed through the sieve 20 is treated with a solid-liquid separator such as a filter press 16 to separate into a filtrate and gypsum dihydrate particles. The separated filtrate is supplemented with water lost by the filter press 16 or the like, and is refluxed to, for example, the first stage precipitation tank 8 through the fluid pump P2 and the pipe 19.

The opening of the sieve 20 is equal to or smaller than the opening of the sieve for cleaning the activated carbon (second sieve). In the embodiment, the opening of the sieve 20 is, for example, 500 μm, and the opening for cleaning the activated carbon is 1 mm. Further, the maximum particle size of the gypsum dihydrate particle is about 300 μm, most of the gypsum dihydrate particle passes through the sieve 20, and only a part of the gypsum dihydrate particle such as particles adhering to the activated carbon is captured by the sieve 20. To be done. The sieving of the activated carbon may be carried out, for example, between the precipitation tanks 10 and 11, but if it is carried out between the precipitation tank 11 and the filter press 16, the amount of treated slurry can be reduced.

Experimental Example A dihydrate gypsum granule was prepared in the following manner, and the color tone of the obtained dihydrate gypsum granule was evaluated by Hunter whiteness W (Lab). That is, the gypsum dihydrate granules were dried to remove adhering water, then molded at 10 MPa, and the surface thereof was brought into direct contact with an NF333 simplified spectrophotometer manufactured by Nippon Denshoku Industries Co., Ltd. to measure Hunter whiteness.

Experimental example 1
The waste gypsum board was crushed and crushed to obtain waste dihydrate gypsum with an average particle size of 2 mm, and the waste gypsum board was heated to 130°C with a hot air dryer to obtain hemihydrate gypsum. Hemihydrate gypsum at 100 g/hr, crushed activated carbon with a particle size distribution range of 1 to 3 mm (washed on a vibrating sieve with 1 mm opening) at 0.8 g/hr, water at 60°C at 200 mL/hr, concentration The mixture was fed into 3000 mL of 40 mass% gypsum slurry for 40 hours, during which the slurry was constantly stirred and the slurry temperature was kept at 60°C.

The slurry after aging for 40 hours was collected, the activated carbon and the gypsum slurry were separated with a sieve having an opening of 0.5 mm, and the separated gypsum slurry was filtered to extract gypsum dihydrate granules. When the whiteness was measured as described above after drying the gypsum dihydrate granules, the Hunter whiteness was 89.7.

Comparative Example 1
Gypsum dihydrate gypsum was obtained in the same manner as in Experimental Example 1 except that activated carbon was not added, and the whiteness of Hunter was measured. The Hunter whiteness was 78.5, which was lower than that of Experimental Example 1.

Comparative example 2
50 g of gypsum dihydrate gypsum extracted in Comparative Example 1 was washed with 100 mL of ion-exchanged water, filtered and dried, and then the whiteness of Hunter was measured. The Hunter whiteness was 78.8, and the whiteness improvement by washing with water was slight.

2 Crusher 3,20 Sieve 4 Calcination furnace 6 Mixer 8-11 Precipitator 12 Precipitator 14 Stirrer 16 Filter press 18, 19 Piping
P1,P2 fluid pump

Claims (3)

The gypsum derived from the waste gypsum board is calcined to form semi-water and/or anhydrous type III gypsum granules, and the gypsum granules are mixed with a slurry containing gypsum or water to form a gypsum slurry. Solid-liquid separation of the precipitated dihydrate gypsum particles, in the method of recovering dihydrate gypsum from waste gypsum board,
A mixing step of mixing granular or fibrous activated carbon with the gypsum slurry,
A method for recovering gypsum dihydrate from waste gypsum board, characterized in that a separation step of separating activated carbon from the gypsum slurry is performed before the solid-liquid separation. In the separation step, the activated carbon is sieved from the gypsum slurry by a sieve having an opening that allows the gypsum particles to pass through but does not pass the activated carbon. The gypsum dihydrate gypsum from the waste gypsum board according to claim 1, wherein Recovery method. The method for recovering gypsum dihydrate from waste gypsum board according to claim 2, characterized in that activated carbon previously washed on the second sieve having an opening larger than that of the sieve is used in the mixing step.

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