JP7451333B2 - Method for precipitation of gypsum dihydrate particles - Google Patents

Description

The present invention relates to a method for precipitating gypsum particles from gypsum slurry.

Dihydrate gypsum can be recovered by making hemihydrate and/or anhydrous type III gypsum derived from waste gypsum board into a slurry, precipitating dihydrate gypsum particles in the slurry, and performing solid-liquid separation. The recovered gypsum dihydrate can be used as raw material for gypsum board, cement, etc. It is industrially preferable that the precipitated dihydrate gypsum has a large average particle size.

In the precipitation of dihydrate gypsum particles from gypsum slurry, gypsum slurry is obtained by mixing semi-aqueous and/or anhydrous type III gypsum particles with an aqueous medium such as water in a mixing tank. The gypsum slurry is aged in a reaction tank, for example, under stirring, and dihydrate gypsum particles are precipitated in the slurry, and the reaction tank may be one-stage or multi-stage. Note that Patent Document 1 (JP 2020-65965) describes that gypsum granules may be directly supplied to the reaction tank instead of the mixing tank ([0022]).

JP2020-65965

An object of the present invention is to provide a method for precipitating dihydrate gypsum particles that can precipitate dihydrate gypsum having a large average particle size.

The method for precipitating dihydrate gypsum particles of the present invention involves mixing semi-aqueous and/or anhydrous type III gypsum with an aqueous medium and moving the mixture from upstream to downstream through a plurality of reaction vessels arranged in series in multiple stages. In a method of precipitating dihydrate gypsum particles in an aqueous medium,
It is characterized in that semi-aqueous and/or anhydrous type III gypsum is supplied to two or more of the plurality of reaction vessels.

The formation of crystal nuclei in dihydrate gypsum progresses rapidly when the supersaturation level exceeds a certain value, and if the entire amount of gypsum is mixed with an aqueous medium at once, a large amount of crystal nuclei will be generated, and the average size of the precipitated dihydrate particles The diameter becomes smaller.

On the other hand, when hemihydrate and/or anhydrous type III gypsum is distributed and supplied to a plurality of reaction vessels, the total number of dihydrate gypsum crystal nuclei produced is reduced. For example, in the second and third stage reaction vessels, dihydrate gypsum particles have already been precipitated in the upstream reaction vessel, and slurry in which the degree of supersaturation has decreased is supplied. Even if gypsum is supplied to this slurry, an increase in the degree of supersaturation can be suppressed.

Preferably, two or more reaction vessels are fed together with hemihydrate and/or anhydrous type III gypsum as well as an aqueous medium (separation of dihydrate gypsum particles from a gypsum slurry, water, etc.). When the reaction tanks are numbered 1st and 2nd stage from the upstream side, the degree of supersaturation is high in the first stage reaction tank, but the residence time of the gypsum slurry in the tank is longer, and the gypsum dihydrate particles grow. do. In the second and subsequent reaction tanks, an aqueous medium and gypsum are added to the slurry whose degree of supersaturation has decreased on the upstream side. Therefore, the increase in the degree of supersaturation is limited, and the number of crystal nuclei generated is reduced. The dihydrate gypsum particles grown on the upstream side absorb gypsum from the slurry and grow in the downstream reaction tank.

Gypsum is supplied to a plurality of reaction vessels, but in extreme cases, the aqueous medium may be supplied in its entirety to the first stage reaction vessel. In this case, the degree of supersaturation in the first stage reaction tank is low, the number of crystal nuclei generated decreases, and although the residence time in the tank is short, the crystal nuclei grow into dihydrate gypsum particles. In the second and subsequent reaction tanks, gypsum is added to the slurry whose supersaturation level has decreased on the upstream side, so the supersaturation level is lower than when gypsum and the aqueous medium are mixed at once in a mixing tank. Therefore, the number of crystal nuclei generated decreases, and the dihydrate particles that have already grown on the upstream side grow further.

Preferably, semi-aqueous and/or anhydrous type III gypsum granules are fed to two or more reaction vessels without passing through a mixing vessel in which the gypsum is premixed with an aqueous medium.

The number of reaction tanks is preferably three or more stages, and it is preferable that gypsum is not supplied to the lowest stage reaction tank (the tank that supplies the gypsum slurry to the solid-liquid separator). In the lowest reaction tank, the dihydrate particles precipitated in the upstream reaction tank are allowed to grow further without generating crystal nuclei.

Example process diagram

Examples for carrying out the present invention are shown below. The scope of the invention should be determined based on the claims, with reference to the description and well-known techniques in this field, and according to the understanding of those skilled in the art. The scope of this invention is not limited by the examples.

FIG. 1 shows a method for precipitating dihydrate gypsum particles in an example. A gypsum raw material such as waste gypsum board is crushed by a crusher 2 and crushed by a crusher 4 to form gypsum granules. If necessary, metal foreign substances such as metal fittings are removed using a magnetic separator 6, and calcined using a calciner 8 to produce semi-hydrated and/or anhydrous type III gypsum granules. The calcination temperature is, for example, 130°C, and the preferred range is 100°C or more and 140°C or less.

For example, four reaction vessels 11 to 14 in series (reaction vessel 11 on the most upstream side, reaction vessel 14 on the most downstream side) are provided, and the number of reaction vessels is, for example, three or more, preferably four or five. The semi-aqueous and/or anhydrous type III gypsum granules obtained by calcination and the solid-liquid separator 18 are placed in the three upstream reaction vessels 11 to 13 or the two upstream reaction vessels 11 and 12. Supply the filtrate in equal amounts. Particularly preferably, the gypsum granules and the filtrate are supplied to all reaction tanks 11 to 13 on the upstream side, excluding the reaction tank 14 on the most downstream side.

For example, the gypsum granules are supplied in equal amounts to a plurality of upstream reaction tanks, but the supply is not limited to equal amounts, and the filtrate does not need to be supplied in equal amounts to these reaction tanks. In an extreme case, the filtrate may be supplied only to the reaction tank 11 on the most upstream side, and the gypsum particles may be supplied to a plurality of reaction tanks 11 to 13 or 11 and 12.

The temperature of the gypsum slurry in the reaction vessels 11 to 14 is, for example, 60° C.±20° C. In the reaction vessels 11 to 14, the gypsum slurry is stirred by stirring blades (not shown). The concentration of the gypsum slurry in the lowermost reaction tank 14 is, for example, 40 wt%, preferably 20 wt% or more and 50 wt% or less. If the total internal volume of reaction vessels 11 to 14 is divided by the total volume of filtrate and gypsum (true specific gravity is approximately 2.3) supplied per hour, the amount of gypsum slurry in four reaction vessels 11 to 14 is calculated as follows: The total residence time is determined. This time is, for example, 5 hours or more and 20 hours or less, preferably 10 hours or more and 15 hours or less.

The gypsum slurry in the lowest reaction tank 14 is passed through a sieve 16 to separate paper powder and solid foreign matter. The gypsum slurry is then treated with a solid-liquid separator 18 such as a filter press to separate it into dihydrate gypsum powder and filtrate. Industrial water or the like is replenished to compensate for the water lost in the sieve 16 and the solid-liquid separator 18, and the water is refluxed to the reaction vessels 11 to 13 or the reaction vessels 11 and 12.

Laboratory equipment reagent grade gypsum dihydrate was calcined at 130°C to form gypsum hemihydrate. Tap water was used as the aqueous medium, reaction tanks each having a volume of 400 mL and equipped with a stirrer were arranged in four stages in series, water and gypsum hemihydrate were continuously supplied, and overflowing gypsum slurry was allowed to flow into the reaction tank on the downstream side. Furthermore, the gypsum slurry that overflowed from the reaction tank at the lowest stage was discharged from the reaction system, and the particle size of the gypsum dihydrate particles was measured. In order to reflect the difference in reaction conditions in the average particle size of gypsum dihydrate particles, the gypsum slurry concentration was lowered, and the supply amount of gypsum hemihydrate was 12 g/h in total, and the amount of clean water was 720 mL/h in total. h, and the gypsum slurry temperature was maintained at 50°C.

Experimental example 1
Gypsum hemihydrate was continuously supplied at a rate of 6 g/h each, and clean water was continuously supplied at a rate of 360 mL/h to the top and second stage of the four-stage reaction tanks. For 48 hours from 24 hours after the start of supply, the average particle size of dihydrate gypsum particles in the gypsum slurry overflowing from the lowest reaction tank was measured by a laser light scattering method. The average value measured over 48 hours was 92 μm.

Experimental example 2
Gypsum hemihydrate was continuously supplied at a rate of 4 g/h and clean water was continuously supplied at a rate of 240 mL/h to the third-stage reaction tank from the top of the four-stage reaction tank. The average particle size of the water gypsum particles was measured. The average value measured over 48 hours was 104 μm.

Comparative Example Gypsum hemihydrate was continuously supplied at a rate of 12 g/h and clean water at 720 mL/h only to the uppermost reaction tank, and the other conditions were the same as in Experimental Example 1, and the average particle size of gypsum dihydrate particles was measured. . The average value measured over 48 hours was 79 μm.

Comparing the experimental example and the comparative example, it was found that the average particle size of gypsum dihydrate could be increased by dispersing and supplying gypsum to a plurality of reaction vessels. Next, when comparing Experimental Example 1 and Experimental Example 2, it was found that dihydrate gypsum having a larger average particle size could be obtained by supplying gypsum to each reaction tank except the bottom stage.

2 crusher 4 crusher 6 magnetic separator 8 calciner 11 to 14 reaction tank 16 sieve 18 solid-liquid separator

Claims (3)

A method of mixing semi-aqueous and/or anhydrous type III gypsum with an aqueous medium and precipitating dihydrate gypsum particles in the aqueous medium while moving the mixture from upstream to downstream through multiple reaction vessels arranged in series in multiple stages. In,
A method for precipitating gypsum dihydrate particles, the method comprising supplying the gypsum to two or more of the plurality of reaction tanks. The method for precipitating dihydrate gypsum particles according to claim 1, characterized in that the gypsum and an aqueous medium are supplied to the two or more reaction vessels. The dihydrate gypsum particles according to claim 1 or 2, characterized in that the gypsum is supplied in the form of granules to the two or more reaction tanks without passing through a mixing tank in which the gypsum is mixed in advance with an aqueous medium. precipitation method.

Images