JPH10236853A - Production of gypsum dihydrate for plasterboard - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce a gypsum dihydrate capable of using as a plasterboard and large in crystal grain size, to reduce the loss of a habit modifier and to produce at low cost. SOLUTION: At the time of producing the gypsum dihydrate by adding a slurry containing a concd. sulfuric acid and more than one kind among calcium carbonate, slaked lime and calcium oxide to a gypsum slurry, the gypsum slurry is circulated through a reaction system while using the habit modifier, and while keeping a slurry concn. in the reaction system in uniform, sodium citrate as the habit modifier is used within a range of 3-5g/L per gypsum slurry, and the slurry concn. is kept in <=50%, and reaction pH is kept in 4-5, and reaction temp. is kept in >=60 deg.C, and a replenishing water is added so that a Mg concn. in the gypsum slurry may be 40-50g/L.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing dihydrate gypsum used as a raw material for gypsum board, and more particularly to a method for producing dihydrate gypsum having a large particle size and thickness and a small loss of a habit modifier which promotes crystal growth. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Generally, gypsum board raw materials include dihydrate gypsum and α-type hemihydrate gypsum.

Gypsum is manufactured using limestone neutralizing agent, sulfuric acid and habit modifier as raw materials, the production equipment is simple, and it is manufactured from various concentrated sulfuric acids.
Suitable as a building material and widely used. However, dihydrate gypsum, which can be used as a raw material for gypsum board, requires large crystal grains in order to increase the strength at the time of curing. However, it is difficult to obtain usable dihydrate gypsum because the control of crystal grains is difficult.

[0004] α-type hemihydrate gypsum (hereinafter abbreviated as α gypsum)
A large crystal grain is produced by a conventionally known α-gypsum production technique. However, α gypsum is not suitable for building materials such as cement and gypsum board, because its production cost is higher than dihydrate gypsum.

[0005] In the production of α-gypsum, the following further problems occur. First, since the temperature of the conversion reaction to α-gypsum is usually as high as 100 ° C., extra external heat energy is required, and equipment such as an autoclave is also required. Further, when manufacturing from waste sulfuric acid generated from smelting waste gas, gypsum production depends on the generation of high-temperature combustion gas containing sulfurous acid, and the required gypsum production cannot be supplied stably. Furthermore, the incorporation of impurities in the gas cannot be prevented.

[0006] Accordingly, if it becomes possible to combine the properties of α-gypsum with dihydrate gypsum at a low cost, the range of use of dihydrate gypsum will be expanded.

[0007]

According to the present invention, dihydrate gypsum having a large crystal grain size, which can be used as a gypsum board, is obtained by using concentrated sulfuric acid recovered in copper smelting as a raw material.
It is an object of the present invention to stably manufacture, reduce loss of a habit modifier, and produce at low cost.

[0008]

DISCLOSURE OF THE INVENTION The gypsum board 2 of the present invention
In the method for producing gypsum, the gypsum slurry is circulated through the reaction system while using the habit modifier, and while maintaining the slurry concentration in the reaction system uniform, concentrated sulfuric acid, calcium carbonate, slaked lime, In obtaining gypsum by adding a slurry containing one or more of quicklime, sodium citrate is used as a habit modifier in a range of 3 to 5 g / l with respect to the gypsum slurry, and the slurry concentration in the reaction system is adjusted to 50 g / l. % Or less,
Make-up water required to set the reaction pH to 4 to 5, the reaction temperature to 60 ° C. or higher, and the impurity concentration to a certain level or less;
Preferably, the Mg concentration in the gypsum slurry is 40 to 50 g.
/ L of make-up water.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The main elements in the manufacturing method of the present invention are as follows.

(1) Reaction pH Concentrated sulfuric acid and a slurry of a neutralizing agent such as calcium carbonate, slaked lime and quick lime are simultaneously added to a gypsum slurry containing gypsum crystals to adjust the pH of the gypsum slurry to 4 to 5. To

[0011] The pH of the gypsum slurry is set mainly by the effect of the habit modifier (eg, sodium citrate). First,
If the pH is 4 or less, the habit modifier will be decomposed, resulting in loss of the habit modifier. If the pH is 5 or more, the effect of the expensive habit modifier will not be obtained, and iron and other impurities in the liquid will be mixed.

(2) Reaction temperature In the pH range of 4 to 5, the gypsum solubility becomes higher at a reaction temperature of about 60 ° C. than normal temperature. If the reaction temperature becomes higher than this, the local temperature rise due to the heat of dilution for using concentrated sulfuric acid becomes severe. In practice, a reaction temperature of 6
When the temperature is 5 ° C., crystal growth is optimal, and when concentrated sulfuric acid is used, it is possible to eliminate the need for external heat supply due to heat of dilution.

(3) Slurry concentration By keeping the total amount of slurry in the reaction system constant and filtering and recovering the amount of gypsum produced from the amount of sulfuric acid used, gypsum with a concentration of 50% or less is maintained. The slurry is circulated to constantly circulate the gypsum seed crystals.

The slurry concentration of the gypsum slurry is preferably higher for the purpose of repeating seed crystals, but was set to 50% from the upper limit of the performance of the solid-liquid separator. Actually, in a batch-type solid-liquid separation device or the like, the slurry concentration fluctuates at the time of crystal recovery and at the time of suspension.

(4) Concentration of habit modifier A gypsum dihydrate with large crystal grains is produced by adding a habit modifier required for the growth of gypsum seed crystals so as to have a concentration of 3 to 5 g / l. The habit crystal material is preferably sodium citrate.

As a result of a study on various habit modifiers, it was found that sodium citrate had the greatest habit modifier effect. Furthermore, an average particle size of 5 that can be used as a gypsum board
Crystals having a large thickness of 0 μ or more were obtained at a sodium citrate concentration of 3 to 5 g / l. However, if the concentration is 5 g / l or more, no more habit crystal effect can be obtained.
/ L.

(5) Mg Concentration Make-up water is added which is the minimum necessary to bring the concentration of impurities, particularly Mg, brought into the limestone below a certain level, specifically 40 to 50 g / l. This minimizes the amount of effluent to reduce the loss of habit modifier and produces gypsum at low production cost.

[0018]

【Example】

Example 1 Table 1 shows the results of beaker tests using various habit modifiers.

[0019]

[Table 1]

[Embodiment 2] FIG. 1 shows a specific flowchart of this embodiment. The physical quantity in square brackets ([]) is controlled as described above.

Therefore, in a reaction tank for producing gypsum, a gypsum slurry containing gypsum crystals that can be gypsum seed crystals is constantly circulated at a slurry concentration of 40 to 50%. Here, a slurry of 95-98% concentrated sulfuric acid recovered from sulfurous acid-containing high-temperature combustion gas generated in copper smelting and limestone as a neutralizing agent is simultaneously added to the gypsum slurry to adjust the pH to 4-5.
And

The pH can be controlled by keeping the amount of sulfuric acid constant and changing the slurry addition amount of the neutralizing agent, or by keeping the slurry addition amount of the neutralizing agent constant and changing the sulfuric acid amount. . However, in general limestone crushing equipment, the slurry concentration of lime milk (charcoal milk) to be produced fluctuates.
30%), pH control with sulfuric acid was employed. This method allows gypsum production at a stable pH.

The reaction system constituting the reaction system is divided into two stages, and concentrated sulfuric acid is separately added to the primary reaction tank and the secondary reaction tank to control the reaction temperature and protect the equipment at the same time. An abnormal reaction was prevented, specifically, a local temperature rise was prevented.

As a habit modifier, sodium citrate is used, and its addition amount is 3 to 5 g / l. The analysis of citric acid itself takes time, and if it is used as a control item, the concentration of citric acid will not be stable.However, if the concentration of sodium in the reaction system is used as an alternative value to control the concentration of citric acid, it will be easier. It was found that the concentration of citric acid could be controlled.

The liquid balance in the process is shown in Table 2 together with other experimental conditions. The loss of the habit modifier was minimized and the magnesium concentration of the impurities accompanying the limestone was 50 g / l.
It is operated with the minimum supply water so as not to exceed.

In this embodiment, since the filtrate is used for pulverizing limestone, most of the added water is discharged as gypsum crystallization water and adhesion water, and only 16% of makeup water needs to be discharged to the outside of the system. Thus, gypsum production with a minimum amount of habit modifier of 0.45 kg per ton of gypsum is possible.

[0027]

[Gypsum production conditions] Balance (at the time of 1000 WET-t / month production) Inlet: 98% sulfuric acid 18.6t / day Limestone 18.6t / day (MgO: 0.6%) Cake washing water 17.4t / Day Medium crystal agent solution 1 t / day Moisture in sulfuric acid 0.4 t / day Makeup water 8.3 t / day Source: gypsum 33.6 t / day (moisture: 5%) Gypsum adhering water 1.7 t / day gypsum crystals Water 6.7 t / day Cake washing liquid 17.4 t / day Filtrate 1.3 t / day (Mg in the system: 50 g / l) Concentration and addition amount of habit modifier Citric acid 5 g / l 15.2 kg / day Reaction time 24 hours continuous reaction pH Primary reaction tank: 5.2 Secondary reaction tank: 4.9 Seed crystal circulation amount Seed crystal / formed gypsum = 10 times weight ratio Reaction temperature 60-75 ° C Slurry concentration 50% target

In the present embodiment, a crystal having a rice grain-like shape and a thick average particle size of 45 which can be used as a raw material for a gypsum board is used.
Gypsum dihydrate of ５１51 μm was obtained stably. An example of this microstructure photograph (FIG. 2b) is shown in comparison with the microstructure photograph of the conventional waste acid gypsum (FIG. 2a).

Further, the habit modifier which required 7.7 kg per gypsum t by a method without repeating the filtrate can be reduced to 0.45 kg by recycling the liquid in the process.

According to this method, the equipment can be significantly reduced. That is, since the slurry concentration is high, a thickener is unnecessary. Since the heat of dilution of concentrated sulfuric acid can be used as it is for the reaction temperature, no sulfuric acid dilution equipment is required. Since the dissolution of limestone is promoted by the habit modifier, the capacity of the limestone crushing equipment can be reduced.

[0031]

Since the present invention is configured as described above, it is very easy to control the slurry concentration and temperature in the reaction system, and to supply gypsum board gypsum in a stable operation with little fluctuation. It is possible.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of a method for producing dihydrate gypsum of the present invention.

FIG. 2A is a diagram showing an example of a microstructure photograph (400 times) of waste gypsum which is a representative of conventional dihydrate gypsum, and FIG. 2B is a microstructure photograph of dihydrate gypsum produced by the present method. It is a figure showing an example of (400 times).

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[Procedure amendment]

[Submission date] February 27, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0003

[Correction method] Change

[Correction contents]

[0003] Gypsum is produced using a neutralizing agent such as limestone, sulfuric acid and a habit modifier as raw materials, the production equipment is simple, and it is produced from sulfuric acid of various concentrations, which is very advantageous in terms of cost. Suitable as a building material and widely used. However, dihydrate gypsum, which can be used as a raw material for gypsum board, requires large crystal grains in order to increase the strength at the time of curing. However, it is difficult to obtain usable dihydrate gypsum because the control of crystal grains is difficult.

Claims (2)

[Claims] 1. A gypsum slurry is circulated through a reaction system using a habit modifier, and concentrated sulfuric acid, calcium carbonate, slaked lime and quick lime are added to the gypsum slurry while maintaining a uniform slurry concentration in the reaction system. When obtaining gypsum by adding a slurry containing at least one kind, sodium citrate is used as a habit modifier in a range of 3 to 5 g / l with respect to the gypsum slurry, and the slurry concentration in the reaction system is 50% or less. And the reaction p
A method for producing gypsum dihydrate for a gypsum board, characterized in that H is set to 4 to 5, the reaction temperature is set to 60 ° C. or higher, and make-up water necessary for maintaining the impurity concentration at a certain level or lower is added. 2. The Mg concentration in a gypsum slurry is 40 to 50.
The method for producing gypsum dihydrate for a gypsum board according to claim 1, wherein makeup water is added so as to be g / l.