JPH0686293B2 - Method for producing α-type hemihydrate gypsum - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing α-type hemihydrate gypsum used as a building substrate, a board material, or a model.

[Conventional technology]

As a method for producing α-type hemihydrate gypsum, a pressurized aqueous solution method, a pressurized steam method, an atmospheric pressure aqueous solution method, etc. are known, but all of them are batch production methods and produce a large amount of α-type hemihydrate gypsum. It was an inappropriate method to do.

As a method for continuously producing an industrially large-capacity α-type hemihydrate gypsum by using the conventional batch system as a continuous production system, the present inventors have added dicitrate containing 0.01% by weight or less of sodium citrate as a habit modifier. We have already proposed a method for continuously producing α-type hemihydrate gypsum by treating gypsum slurry at 140 ° C or higher. (Special public relations
However, it is difficult for the present inventors to continuously produce α-type hemihydrate gypsum with stable quality by using the already proposed production method. We often experienced mixing and formation of type II anhydrous gypsum.

[Problems to be solved by the invention]

Therefore, the present invention intends to provide a continuous production method of stable α-type hemihydrate gypsum that does not contain fine-grained α-hemihydrate gypsum or II-type anhydrite that can eliminate the drawbacks of the conventional method. It is a thing.

[Means for solving problems]

As a result of examining the cause of the quality instability of the α-type hemihydrate gypsum of the proposed method, the present inventors changed the sodium citrate concentration contained in the raw material dihydrate gypsum slurry over time,
It was concluded that the crystal growth rate of α-type hemihydrate gypsum was not stable in the pressurized hydrothermal treatment tank, and by stabilizing the sodium citrate concentration in the pressurized hydrothermal treatment tank constantly. It was found that an α-type hemihydrate gypsum with a continuous and stable quality can be produced.

The present invention has been completed based on this finding,
In transferring the gypsum dihydrate gypsum slurry to α-type hemihydrate gypsum by heat treatment under pressure, dihydrate gypsum slurry containing 0.01% by weight or less of sodium citrate is treated in a pressure hydrothermal treatment tank at a temperature of 140 ° C. or higher for an appropriate time and α In a method for continuously producing mold hemihydrate gypsum, the temperature and electrical conductivity of the dihydrate gypsum slurry is measured, and the addition amount of sodium citrate added to the dihydrate gypsum slurry is adjusted. It is a method for producing α-type hemihydrate gypsum.

The solubility of gypsum dihydrate dissolved in water changes depending on the temperature, and this amount of dissolution can be known from the measured electrical conductivity and temperature by measuring the electrical conductivity of the liquid. Furthermore, when sodium citrate is added to this, the electrical conductivity changes, but the relationship between the change in electrical conductivity and the sodium citrate addition amount that changes depending on the addition amount of sodium citrate in the gypsum dihydrate slurry is If the amount of sodium citrate in the gypsum dihydrate slurry is calibrated beforehand as a function of temperature, the amount of sodium citrate in the dihydrate gypsum slurry can be determined.

These relationships are shown in FIGS. 2 to 4. Figure 2 is a diagram showing the solubility of gypsum dihydrate in water as a function of temperature. Adachi et al. Summarizes the relationship between this solubility and temperature as a cubic equation of equation (1), and shows it as follows. There is. (Gypsum
& Line.No.135,1975, P63~72) S = a + bt + ct 2 + dt 3 ... (1) S: Solubility _{[g-CaSO 4 / kg-H} 2 O ] a, b, c, d: factor [-] t: Temperature (° C) Fig. 3 is a graph showing the relationship between the dissolved gypsum temperature and the electric conductivity at each temperature (40 ° C, 60 ° C, 80 ° C, 100 ° C), and the vertical axis represents the electric conductivity (Λ, unit mS / cm). Logarithmic value, the horizontal axis shows the logarithmic value of dissolved gypsum concentration (CaSO ₄ ). FIG. 4 is a graph showing the relationship between the sodium citrate concentration and the logarithmic value of electrical conductivity.

First, since the solubility of gypsum in dihydrate gypsum slurry can be calculated from the equation (1), the concentration of sodium citrate is obtained from the values of temperature and electric conductivity using the relationships between the graphs of FIGS. 3 and 4. The amount of sodium citrate added can be controlled to an appropriate concentration.

〔Example〕

FIG. 1 is a view showing a flow of an α-type hemihydrate gypsum production method as one embodiment of the present invention.

The raw material dihydrate gypsum slurry is supplied from the dihydrate gypsum slurry supply tank 4 to the pressurized hydrothermal treatment tank 11 via the pipe 5, and the pressurized hydrothermal treatment tank 11 continuously agitates the dihydrate gypsum with the stirrer 19 to obtain the hemihydrate gypsum dihydrate. The level detector 21 detects the level so that the amount of the retained slurry 18 in the pressurized water heat treatment tank 11 becomes constant, and the control valve 23 is operated by the level controller 22 to operate the double water through the pipe 20. The amount equivalent to the supply amount of the gypsum slurry is extracted, the coarse particle-containing slurry 25 is classified into the fine particle slurry 26 via the liquid cyclone 24, the coarse particle side 25 is sent to the product α-hemihydrate gypsum recovery step, and the fine particle side 26 is the above-mentioned. It is circulated to the dihydrate gypsum slurry supply tank 4. The dihydrate gypsum slurry supply tank 4 is also supplied with sodium citrate from the dihydrate gypsum slurry 1 and the sodium citrate storage tank 2. The amount of sodium citrate supplied to the dihydrate gypsum slurry supply tank 4 is The electric conductivity and temperature of the raw material dihydrate gypsum slurry supplied to the pressurized hydrothermal treatment tank 11 are detected by the electric conductivity detector 6 and the thermometer 8, and the detection signals are processed by the amplifiers 7 and 9, respectively. The signal is processed by the operation controller 10, and the cutting device 3 is operated to adjust the signal. Arithmetic controller
At 10, the following calculation is performed.

(Calculation controller calculation items) (1) Calculate the saturated dissolved gypsum concentration C ^* in the raw material dihydrate gypsum slurry (b) Substitute a, b, and c of dihydrate gypsum in Table-1 into equation (1). ) The measured value is used for t in the equation (1). (2) Calculation of habit modifier concentration (a) If the saturated dissolved gypsum concentration at t ° C is known from the above, the following (2) obtained from the relationship in Fig. 3 From the formula, the electric conductivity due to CaSO ₄ is known.

Λ ^* = α (t) ^t (C ^* ) ^m … (2) Λ ^* : electric conductivity [mS / cm] t: temperature [° C] C ^* : saturated dissolved gypsum concentration obtained in item (1) above [ g / kg-H ₂ O) (B) The sodium citrate concentration can be calculated from the difference between the calculated values of the measured electrical conductivity Λ and Λ ^* .

Cadd = β (Λ−Λ ^* ) Cadd: Sodium citrate concentration [wt%] Λ: Electric conductivity of the supplied gypsum dihydrate slurry [mS / c
m] β: Coefficient [−] (β is measured and determined in advance in the same manner as α, n, m above.) The operating conditions and device specifications in this example are as follows.

(Operating conditions) (1) Raw material dihydrate gypsum slurry concentration: 15 wt% (2) Sodium citrate concentration: 0.01 wt% (3) Pressurized water heat treatment concentration: 140 ° C (4) Pressurized water heat treatment tank hold liquid amount: 200 l (Main equipment Conditions) (1) Gypsum raw material supply tank volume: 2000 l (2) Pressurized water heat treatment tank volume: 250 l (3) Pressurized water heat treatment tank Stirrer: turbine type (4) Same as above Stirrer stirring power: 1 kW / m ³ Next of the present invention In order to show the effect, FIG. 5 shows a 100 times enlarged photograph of the product α hemihydrate gypsum.

〔The invention's effect〕

As described above, by controlling and maintaining the sodium citrate concentration in the dihydrate gypsum raw material slurry at a desired concentration, it has become possible to continuously produce α-type hemihydrate gypsum of stable quality.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the method of the present invention, FIG. 2 is a graph showing the relationship between the solubility of dihydrate gypsum in water and temperature, and FIG.
FIG. 4 is a graph showing the relationship between the dissolved gypsum concentration and the electrical conductivity at each temperature, FIG. 4 is a graph showing the relationship between the sodium citrate concentration and the electrical conductivity, and FIG. 5 is the α obtained in the examples of the present invention. It is a micrograph (100 times) of the crystal structure of hemihydrate gypsum.

Front page continuation (72) Inventor Jun Taya 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Laboratory (56) Reference JP 62-27326 (JP, A) Japanese Patent Publication Sho 53-15835 (JP, B2)

Claims (1)

[Claims] 1. Sodium citrate is added to a dihydrate gypsum slurry under pressure hydrothermal treatment to transform it into α-type hemihydrate gypsum.
In a method for continuously producing α-type hemihydrate gypsum by treating a dihydrate gypsum slurry containing 0.01% by weight or less at a temperature of 140 ° C or higher in a pressurized hydrothermal treatment tank for a suitable time, the temperature and electrical conductivity of the dihydrate gypsum slurry The method for producing α-type hemihydrate gypsum, characterized in that the addition amount of sodium citrate added to the dihydrate gypsum slurry is adjusted by measuring the degree.