JP7184622B2 - Method for recovering gypsum dihydrate from waste gypsum board - Google Patents

Description

The present invention relates to improving the color tone of gypsum dihydrate recovered from waste gypsum boards.

The applicant has succeeded in industrializing the recovery of gypsum dihydrate from waste gypsum boards. A method for recovering gypsum dihydrate will be described according to Patent Document 1 (WO2012/176688A) of the applicant. The waste gypsum board is pulverized, foreign matters such as paper chips are separated from the gypsum dihydrate, and the gypsum dihydrate is calcined to convert it to gypsum hemihydrate. Gypsum hemihydrate or the like is mixed with gypsum slurry or the like in a mixing tank, transferred to a precipitation tank to precipitate 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 by a solid-liquid separator such as a filter press.

WO2012/176688A

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

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

The present invention calcines gypsum derived from waste gypsum board to form semi-water and/or anhydrous type III gypsum granules, and mixes the gypsum granules with a slurry containing gypsum or water to form a gypsum slurry, In a method for recovering gypsum dihydrate from waste gypsum boards, the gypsum dihydrate particles precipitated in the gypsum slurry are separated into solid and liquid,
a mixing step of mixing 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.

The inventor initially suspected that metal ions such as Fe ³⁺ ions in the gypsum slurry were the cause of the coloration, and removed Fe ³⁺ ions and the like from the slurry using an ion exchange resin or the like. However, the coloring did not disappear. Therefore, when activated carbon was added to the gypsum slurry, decolorization was successful. These facts suggest that colored organic matter that can be adsorbed by activated carbon exists in the gypsum slurry. The origin of such organic matter is thought to be the coloration of pastes such as starch, surfactants, etc., which are widely used in gypsum boards, over a long period of time or during the calcination of gypsum. The exact mechanism of coloration is unknown, but it is certain that it is caused by substances that can be removed with activated charcoal. In addition, silica gel is hydrophilic and zeolite is highly polar, so they are not suitable for removing trace amounts of organic matter in aqueous slurries.

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

Mixing granular or fibrous activated carbon with the gypsum slurry can decolorize the gypsum slurry and increase the whiteness of the gypsum dihydrate particles. Semi-aqueous and/or anhydrous type III gypsum dissolves once in contact with water and precipitates as gypsum dihydrate. In this process, the presence of activated carbon allows the coloring substances (organic substances) as described above to be adsorbed by the activated carbon, and the amount of coloring substances taken into the crystals of gypsum dihydrate during precipitation can be greatly reduced. It is presumed that this is because In mixing, the activated carbon may be added to the gypsum slurry, the gypsum granules and activated carbon may be separately added to water or the like, or the gypsum granules and activated carbon may be mixed in advance and added to the water. That is, any mixing process may be used as long as the gypsum slurry is mixed with activated carbon.

When a sheet of activated carbon is brought into contact with a gypsum slurry, gypsum dihydrate precipitates on the surface of the activated carbon, making it difficult to remove colored substances in the slurry. Therefore, the activated carbon should be granular or fibrous, and in the case of granular activated carbon, it may be granular molded activated carbon or amorphous crushed activated carbon. The activated carbon is then mixed into the gypsum slurry, in other words dispersed in the gypsum slurry, and a separation step separates the activated carbon from the gypsum slurry prior to 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 through a sieve with openings that allow the passage of the gypsum dihydrate particles but not the activated carbon. In other words, an activated carbon having a minimum particle size or a large fiber length is used with respect to the particle size distribution (maximum particle size) of the gypsum dihydrate particles, and the activated carbon is separated by sieving.

Particularly preferably, activated carbon that has been previously sifted and washed on a second sieve with an opening larger than that of the sieve is used in the mixing step. In this sieving, for example, the fine powder contained in the activated carbon is removed in advance by washing (washing) the activated carbon on the sieve with water, thereby preventing the fine powder from remaining in the gypsum slurry.

The gypsum dihydrate obtained by the production method employed in the present invention usually has a substantial maximum particle size of about 300 μm. Therefore, the mesh size of the sieve used in the step of separating the activated carbon preferably exceeds 300 μm, more preferably within the range of 350-750 μm, and particularly preferably within the range of 400-700 μm. At that time, the mesh size of the sieve used for pre-sieving the activated carbon is preferably 800 μm or more, more preferably 1 mm or more. Considering the recovery rate of activated carbon, the opening is preferably 5 mm or less, more preferably 3 mm or less.

A diagram showing a method for recovering gypsum dihydrate according to an embodiment.

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

Fig. 1 shows a method for recovering gypsum dihydrate. In 2, the waste gypsum board is pulverized with a grinder, foreign substances such as paper chips are removed with a sieve 3, and the board is heated to, for example, 130 ° C to 160 ° C in a calciner 4 to change into hemihydrate gypsum and/or anhydrous type III gypsum. .

A mixer 6 mixes granules of hemihydrate gypsum and/or anhydrous type III gypsum, activated carbon, and gypsum slurry from the lowest precipitation tank 11 to obtain a slurry stock solution, and the slurry stock solution is fed to the first precipitation tank 8. supply. The amount of activated carbon charged is preferably 1 kg or more and 10 kg or less per 1 ton of gypsum granules in terms of gypsum hemihydrate. The structure of the mixer 6 is arbitrary, and although it is a cylindrical tank in the embodiment, it may be a gutter-shaped channel into which the gypsum granules and activated carbon are introduced from the upper part of the gutter. Furthermore, instead of the gypsum slurry, industrial water may be supplied, and the gypsum slurry from the intermediate deposition tanks 9 and 10 may be circulated to the mixer 6 . Gypsum particles are dispersed in the gypsum slurry, and the slurry undiluted 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 molded activated carbon or crushed activated carbon, and preferably has a particle diameter larger than that of the gypsum dihydrate particles to be obtained. Use those that do not pass through the sieve of In preparation for the case where the activated carbon contains fine powder, it is preferable to use the sieved components that have not passed through the sieve (for example, a vibrating sieve) by washing with water in advance. The mesh size of the sieve (second sieve) used for washing with water is, for example, 500 μm or more, preferably 1 mm or more, and is greater than or equal to the mesh size of the sieve 20 described later. 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 . Also, in the case of gypsum board raw materials, there is no reason to ignore the treatment efficiency and set the maximum particle size of the gypsum dihydrate particles to more than 300 μm.

For example, 4 stages of precipitation tanks 8 to 11 are provided downstream of the mixer 6, and the precipitation tanks 8 to 11 are collectively referred to as a precipitation section 12. The precipitation tanks 8 to 11 are provided with stirrers 14 to stir the slurry, and the gypsum slurry is introduced from the upstream precipitation tank into the downstream precipitation tank due to overflow of the gypsum slurry. In addition, you may transfer between deposition tanks with a fluid pump. The number of stages of the deposition tanks 8 to 11 is arbitrary, and the deposition section 12 may be composed of only one stage of the deposition tank. The gypsum slurry in precipitation tanks 8 to 11 is an aqueous slurry containing gypsum dihydrate particles. grow up.

The activated carbon mixed in the mixer 6 adsorbs coloring substances considered to be water-soluble organic substances in the undiluted slurry and prevents the coloring substances from penetrating into the gypsum dihydrate particles. For this reason, the activated carbon may be put into the precipitation tanks 9 to 11, but is preferably mixed with the slurry in either the mixer 6, the first precipitation tank 8, or pipes 18 and 19, which will be described later.

For example, the gypsum slurry is introduced from the lowermost deposition tank 11 to the mixer 6 through the pipe 18 by the fluid pump P1 and circulated from the mixer 6 to the deposition section 12 . The gypsum slurry may be circulated to the mixer 6 from the precipitation tanks 8 to 10 other than the precipitation tank 11 at the bottom.

A gypsum slurry is extracted from the lowermost deposition tank 11, and activated carbon is removed by a sieve 20 such as a vibrating sieve. If the slurry contains foreign matter such as paper chips, the foreign matter is also removed at the same time. The gypsum slurry that has passed through the sieve 20 is treated by a solid-liquid separation device such as a filter press 16 to separate into a filtrate and gypsum dihydrate particles. The separated filtrate is replenished with the water lost in the filter press 16 and the like, and is returned to, for example, the first-stage precipitation tank 8 by means of the fluid pump P2 and the pipe 19.

The mesh size of the sieve 20 is less than that of the sieve (second sieve) for cleaning activated carbon, and in the embodiment, the mesh size of the sieve 20 is, for example, 500 μm, and the mesh size of the sieve for cleaning activated carbon is 1 mm. The maximum particle size of the gypsum dihydrate particles is about 300 μm. 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 slurry to be treated can be reduced.

EXPERIMENTAL EXAMPLE Gypsum dihydrate granules were prepared as follows, and the color tone of the obtained gypsum dihydrate granules was evaluated by Hunter whiteness W (Lab). That is, after drying the gypsum dihydrate granules to remove adhering water, the granules were molded at 10 MPa, and the surfaces of the gypsum granules were brought into direct contact with a simple spectrophotometer NF333 manufactured by Nippon Denshoku Industries Co., Ltd. to measure the Hunter whiteness.

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

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

Comparative example 1
Gypsum dihydrate granules were obtained in the same manner as in Experimental Example 1 except that no activated carbon was added, and the Hunter whiteness was measured. The Hunter whiteness index was 78.5, which was lower than Experimental Example 1.

Comparative example 2
After washing 50 g of the gypsum dihydrate granules extracted in Comparative Example 1 with 100 mL of ion-exchanged water, filtering and drying, the Hunter whiteness was measured. The Hunter whiteness index was 78.8, and the whiteness index was slightly improved by washing with water.

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

Claims (3)

Gypsum derived from waste gypsum board is calcined to form semi-aqueous and/or anhydrous type III gypsum granules, the gypsum granules are mixed with a slurry containing gypsum or water to form a gypsum slurry, and the gypsum slurry is In a method for recovering gypsum dihydrate from a waste gypsum board, the gypsum dihydrate particles are solid-liquid separated,
a mixing step of mixing granular or fibrous activated carbon with the gypsum slurry;
A method for recovering gypsum dihydrate from waste gypsum boards, characterized by performing a separation step of separating activated carbon from the gypsum slurry before the solid-liquid separation. In the separation step, the activated carbon is sieved from the gypsum slurry through a sieve having a mesh size that allows the gypsum dihydrate particles to pass through but not the activated carbon to pass through the gypsum dihydrate from the waste gypsum board according to claim 1. collection method. 3. The method of recovering gypsum dihydrate from waste gypsum board according to claim 2, wherein activated carbon preliminarily washed on a second sieve having a mesh size larger than that of said sieve is used in said mixing step.

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