JPH10287421A - Production of synthetic gypsum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a synthetic gypsum having a crystal shape with thickness, and a large lightly put bulk density by reacting a calcium carbonate comprising crystals having specific particle sizes with sulfuric acid at a specified pH. SOLUTION: Sulfuric acid of a suitable amount is charged to a reaction vessel 1 by opening a sulfuric acid-charging line 2. Calcium carbonate including >=90 wt.% crystals having <=60 μm particle size is charged to the reaction vessel by opening the calcium carbonate-charging line 3 while stirring the interior of the reaction vessel 1 with a mixer 5, and reacted while maintaining the pH so as to be 4-6. Further, the formed gypsum is discharged from the reaction vessel 1 in a slurry state by operating a slurry-discharging pump 6, and separated by a solid-liquid separation 7. The separated gypsum is discharged to outside of the system through a gypsum-discharging line 8. The liquid phase remaining after separating the gypsum is returned through a thickener 10 to the reaction vessel 1. A pH value of the gypsum slurry in a returning line 9 is measured by a pH controller 4, and the pH value in the reaction vessel 1 is regulated based on the measured result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing synthetic gypsum by reacting sulfuric acid and calcium carbonate, and more particularly to a method for producing synthetic gypsum having an improved crystal shape.

[0002]

2. Description of the Related Art One of the methods for producing gypsum is a method in which sulfuric acid and calcium carbonate are directly reacted. Gypsum produced by this method is called synthetic gypsum. The outline of a conventional synthetic gypsum manufacturing method is as follows. That is,
Water is added to the calcium carbonate powder to form a slurry, and the slurry is reacted with sulfuric acid to obtain synthetic gypsum. At this time, the reaction between sulfuric acid and calcium carbonate is carried out at pH 2
It was performed under the following conditions. This is because if the pH is increased above 2, the reaction rate decreases, and a large amount of unreacted calcium carbonate remains in the gypsum.

Most of synthetic gypsum is a raw material for gypsum board. This gypsum board is manufactured through the following steps. First, gypsum as a raw material is heated to obtain hemihydrate gypsum. After crushing this, water is added to make a slurry, and further additives are added and sandwiched between board base papers,
Gypsum board is obtained by natural drying, cutting, and heat drying.
During this time, the hemihydrate gypsum changes to dihydrate gypsum, but at this time it becomes fine fibrous gypsum, and the crystals or the crystal and the base paper are entangled, so that a gypsum board with high strength can be obtained.

[0004] Incidentally, gypsum produced as a by-product from other processes such as flue gas desulfurization is used besides synthetic gypsum in the production of gypsum board. Among these, synthetic gypsum is used as a raw material for gypsum board. Has been evaluated as difficult to use. This is because the hemihydrate gypsum obtained by heating the synthetic gypsum is too finely broken when crushed, it is difficult to increase the fluidity when adding water to make it into a slurry, and it was by-produced from other processes This is because it is necessary to add more water than gypsum, so that the drying speed in the gypsum board drying step is adversely affected, and productivity cannot be increased.

[0005] The light bulk specific gravity is used as an index for evaluating the ease of use of raw material gypsum. Light weight bulk specific gravity is 3 pieces of dry gypsum passed through a 16 mesh sieve.
Sprinkle gently into a 00ml measuring cylinder and 300m
This is the specific gravity measured before filling gypsum and setting the gypsum by applying vibration or the like, and it is said that gypsum with a higher specific gravity has higher gypsum board productivity. The light-weight bulk specific gravity of gypsum by-produced from the flue gas desulfurization process, which is evaluated as easy to use as a raw material for gypsum board, was 0.9 to 0.95, whereas synthetic gypsum was 0. From 0.5 to 0.6, there was a large difference.

Further, according to microscopic observation, gypsum crystals which are evaluated to be easy to use as a raw material for gypsum board are often thick, have a nearly columnar shape, and have a large crystal size. There are many. On the other hand, synthetic gypsum has many plate-like crystals and needle-like crystals having no thickness, and the crystal size is relatively small.

[0007] Summarizing these findings, it can be said that gypsum, which is easy to use as a raw material for gypsum board, has a thick crystal form and a large bulk specific gravity.
One of the methods for increasing the thickness of a crystal is to introduce a seed crystal serving as a nucleus into a reaction tank, thereby suppressing the generation of excessive gypsum crystal nuclei. There is a limit to the increase in thickness. It is also known that a rapid reaction can be suppressed by lowering the temperature of the raw material. However, there is a limit to increasing the amount of surplus water generated, lowering the temperature of the reaction tank, and increasing the crystal thickness. Therefore, it is not a preferable method.

As another method, it is known that when ions such as aluminum and iron are present in a reaction tank, crystal growth in a direction other than the thickness direction is inhibited, and crystals having a relatively large thickness are obtained. Compared with the size of the crystal in the plane direction, it takes time to obtain a crystal of the same size as the conventional one, it is necessary to enlarge the reaction tank, and it is necessary to collect and recycle used aluminum, iron, etc. However, it has not been realized yet for the purpose of producing simple synthetic gypsum because the process becomes too complicated.

[0009]

In view of the above, the present invention provides a synthetic gypsum suitable for the production of gypsum board,
It is an object of the present invention to establish a method for producing a synthetic gypsum having a thick crystal form and a large bulk specific gravity of light weight.

[0010]

The object of the present invention is to prepare a synthetic gypsum by using calcium carbonate containing 90% by weight or more of crystals having a particle size of 60 μm or less, and adjusting the pH of the reaction between sulfuric acid and calcium carbonate to 4%. The problem can be solved by setting the number to 6 or less.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of an apparatus capable of suitably implementing the present invention. Is a pH controller, 5 is a mixer, 6 is a slurry discharge pump, 7 is
Denotes a solid-liquid separator, 8 denotes a gypsum lead-out line, 9 denotes a return line, and 10 denotes a thickener.

Into the reaction tank 1, sulfuric acid is introduced from a sulfuric acid introduction line 2, and a slurry of calcium carbonate is introduced from a calcium carbonate introduction line 3, and reacted. The reaction tank 1 is provided with a mixer 5 so that the contents can be stirred. The generated gypsum is discharged from the reaction tank 1 by the slurry discharge pump 6 in a slurry state. Gypsum is separated from the gypsum slurry using the solid-liquid separation device 7. The separated gypsum is led out of the system from the gypsum lead-out line 8. The remaining liquid phase from which the gypsum is separated is returned to the reaction tank 1 by removing excess water by the thickener 10. In addition, a part of the gypsum slurry derived from the reaction tank 1 is always returned to the reaction tank 1 by the return line 9. During this process, the pH is adjusted to p.
The pH is measured in the reaction tank 1 by opening and closing the sulfuric acid introduction line 2 and the calcium carbonate introduction line 3 based on the measurement result.

The reaction tank 1 preferably has corrosion resistance to sulfuric acid and calcium carbonate used in the reaction.
The size and shape are not particularly limited. Each of the sulfuric acid introduction line 2 and the calcium carbonate introduction line 3 is provided with an opening / closing means such as an electromagnetic valve, and the opening / closing means is connected to the pH controller 4 and is controlled under the control. The pH controller 4 constantly monitors the pH value of the gypsum slurry in the return line 9 and plays a role in maintaining the pH set value of the reaction tank 1.

The shape and number of the mixer 5 and the position of the mixer 5 are not limited as long as the mixer 5 can uniformly stir the inside of the reaction tank 1 so that the pH value in the tank is not biased. For example, a propeller in the reaction tank 1 may be rotated from a driving unit provided on the upper outside of the reaction tank 1 through a transmission means such as a shaft, or a small-sized propeller may be provided on a side surface of the reaction tank 1. May be attached in plurality.

In the solid-liquid separation device 7, most of the transported gypsum slurry is processed. However, a part of the gypsum slurry is not processed and the
Will be sent back to you. This is to prevent clogging of the pipes, and to return the precipitated gypsum to the reaction tank 1 again for reaction, and to obtain the gypsum efficiently by using the gypsum as a crystal nucleus. For example, as the solid-liquid separation device 7, a centrifuge or the like can be suitably used.

Next, an example of the manufacturing method of the present invention using the present apparatus will be described. First, the sulfuric acid introduction line 2 is opened, and an appropriate amount of sulfuric acid is introduced into the reaction tank 1. Further, the calcium carbonate introduction line 3 is opened while stirring the inside of the reaction tank 1 with the mixer 5 to continuously introduce calcium carbonate. Next, the slurry discharge pump 6 is operated to discharge the generated gypsum from the reaction tank 1 in a slurry state. The gypsum is separated by applying the gypsum slurry to the solid-liquid separation device 7. The separated gypsum is led out of the system through the gypsum lead-out line 8. The remaining liquid phase from which the gypsum has been separated is returned to the reaction tank 1 through the thickener 10. Further, the pH of the gypsum slurry in the return line 9 is measured by the pH controller 4, and the pH in the reaction tank 1 is adjusted based on the result. In this example of the production method, sulfuric acid is introduced into the reaction tank 1 in advance, and calcium carbonate is introduced therein. Conversely, calcium carbonate slurry is introduced first, and Sulfuric acid may be introduced.

As the particle size of the calcium carbonate used in the production method of the present invention increases, unreacted calcium carbonate remaining in the gypsum after the reaction with sulfuric acid increases. Conversely, the finer the calcium carbonate, the more likely it is to react with sulfuric acid and less likely to remain in the gypsum. However, when trying to reduce the particle size of calcium carbonate, the time required for pulverization becomes longer, and there is a limit in terms of the performance of a mill used for pulverization, and it is difficult to make calcium carbonate finer without limitation. Therefore, in the present invention, calcium carbonate having a particle size of 90% by weight or more containing 60 μm or less of particle size is used.

In the present invention, the pH of the reaction between sulfuric acid and calcium carbonate is set to 4 or more and less than 6. When the pH is less than 4, the shape of the synthetic gypsum is not so much improved, and when the pH is 6 or more, the amount of unreacted calcium carbonate remaining in the synthetic gypsum sharply increases, and the recovery rate of the synthetic gypsum deteriorates. Would.

[0019]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

Water is added to calcium carbonate having a particle size of about 3 mm, and crystals having a particle size of 60 μm or less are formed using a wet pulverizer.
The mixture was finely pulverized so as to contain at least 50% by weight, and adjusted to be a 50% by weight slurry. Using this and 50% sulfuric acid as raw materials, synthetic gypsum was produced four times in total using the apparatus shown in FIG. 1 while changing the pH. As a comparative example, 90% by weight of a conventionally used crystal having a particle size of 80 to 100 μm or less was used.
A synthetic gypsum was produced using the calcium carbonate contained above at a pH of 2. Table 1 shows the pH of the liquid phase, the light specific bulk specific gravity of the obtained gypsum, and the residual amount of calcium carbonate.

[0021]

[Table 1]

In the three examples, the synthetic gypsum obtained had a light bulk specific gravity of 0.8 to 0.9 as shown in Table 1.
And the specific bulk density of conventional synthetic gypsum, 0.5 to 0.
6 was greatly exceeded. In particular, the light weight bulk specific gravity of 0.90 in Example 1 is comparable to the data of gypsum manufactured by the flue gas desulfurization method, which is said to be easy to use as a raw material for gypsum board. The remaining amount of calcium carbonate is 2 for every 3 times
%, And good results have been obtained despite the fact that the reaction was carried out by raising the pH. Further, when the synthetic gypsum obtained in the examples was observed with a microscope, all the gypsums were thicker than the conventional gypsum and the corners of the crystals were rounded.

In Comparative Example 1, the pH was set to 2 using calcium carbonate containing 90% by weight or more of crystals having a particle size of 80 to 100 μm or less as in the conventional operating conditions. The light bulk specific gravity was 0.60, and the remaining amount of calcium carbonate was 2.83%. In Comparative Example 2, the pH in the reaction tank was set to 6. Light weight bulk specific gravity is 0.75, which is improved as compared with the data of the conventional gypsum, but the residual amount of calcium carbonate is 15.50%.
And it is very bad.

[0024]

As described above, the synthetic gypsum production method of the present invention uses calcium carbonate containing 90% by weight or more of crystals having a particle size of 60 μm or less, and adjusts the pH at the time of the reaction to 4 to 6%.
It is possible to produce a synthetic gypsum having a thick crystal form and a high bulk specific gravity of light weight. p
By increasing the H and causing the reaction, the metal corrosiveness of the reaction solution can be suppressed, the service life of the apparatus can be expected to be long, and the maintenance cost of the equipment can be reduced.

The water used in the reaction is recovered and reused for calcium carbonate slurry. However, since the reaction rate between sulfuric acid and calcium carbonate has been improved, the concentration of sulfate groups in the water has been reduced. Lower, which allows
The gypsum generated by the reaction between the sulfate group and calcium carbonate in the water can be prevented from depositing on the inner wall of the pipe. Even if the reaction conditions are changed from the conventional one, the existing equipment can be used as it is, so that it is not necessary to make new capital investment.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an apparatus for implementing the present invention.

[Explanation of symbols]

 1 reaction tank 4 pH controller

Claims (1)

[Claims] 1. A method for producing synthetic gypsum, wherein gypsum is obtained by a reaction between sulfuric acid and calcium carbonate, comprising using calcium carbonate containing 90% by weight or more of crystals having a particle size of 60 μm or less, A method for producing synthetic gypsum, wherein the pH is 4 or more and less than 6.