JPS6149245B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing calcium silicate or a calcium silicate-gypsum composite having a large bulk specific volume and a large oil absorption amount from gypsum and an alkali silicate. Various methods of producing calcium silicate are known, and various crystal structures are known. However, little is known about the method for producing calcium silicate using gypsum as a calcium raw material. The present inventors have discovered that by mixing alkali silicate and gypsum in an aqueous medium and then performing a hydrothermal reaction, the crystal structure has a gyrolite type, and the bulk specific volume in which amorphous silicon dioxide is incorporated into the crystal. We have already discovered and proposed that calcium silicate with large oil absorption can be obtained. In addition, electron micrographs (5,000 to 10,000 times) of the calcium silicate show that it is composed of an aggregate of flakes with two symmetrical sides, and that the calcium silicate is an aggregate of flakes similar to the petals of a rose flower. I can see that I'm getting used to it. The size of the flakes varies depending on the type of raw materials, raw material ratio, manufacturing conditions, etc., and cannot be absolutely limited, but generally the average diameter in the longitudinal direction is 0.1.
~30U, with a thickness of about 0.005~0.1U, and many have a circular or oval shape. In addition, the calcium silicate obtained by the above reaction has amorphous silicon dioxide incorporated into the diairolite type calcium silicate crystal structure as described above, and the grain boundaries or bonding form of the silicon dioxide can be seen with an electron microscope of about 300,000 times magnification. I can't really tell from the photo. For the above reasons, the calcium silicate has the general formula
It is thought to be expressed as _{2CaO.3SiO.sub.2.nSiO.sub.2.mH.sub.2O} ( _where n and m are positive numbers _, and n is generally 0.1 to 10). In the present invention, calcium silicate having the above properties may be simply abbreviated as petal-like calcium silicate. When the petal-shaped calcium silicate is made from gypsum and alkali silicate, the molar ratio of gypsum/alkali silicate increases depending on the mixing ratio of the raw materials.
If it exceeds 1.1, the composition will be such that gypsum is incorporated into the petal-shaped calcium silicate shown by the above general formula. Similar to the above-mentioned silicon dioxide, grain boundaries or bonding forms of this gypsum cannot be determined in electron micrographs. Therefore, if the above-mentioned calcium silicate into which gypsum is incorporated is expressed according to the above general formula, it becomes 2CaO・3SiO ₂・
It is expressed as _{nSiO2.mH2O.lCaSO4} (where n, m, and l _are positive numbers, n is 0.1 to ₁₀ , and l is 0.01 to 0.9). Hereinafter, in the present invention, the above-mentioned calcium silicate may be abbreviated as a petal calcium silicate gypsum composite. The present inventors have continued research on the production of petal-shaped calcium silicate or petal-shaped calcium silicate plaster composites from gypsum and alkali silicate. The present inventors have discovered that if hydrothermal treatment is performed in the presence of alkali sulfate and unreacted gypsum, which are produced as by-products during hydrothermal treatment, there will be an adverse effect, leading to the completion of the present invention. The present invention comprises a reaction step of mixing and reacting gypsum and an alkali silicate in an aqueous medium, a washing step of washing the solid material obtained in the reaction step, a slurrying step of turning the solid material obtained in the washing step into a slurry solution, A calcium silicate or calcium silicate-gypsum composite comprising a hydrothermal treatment step of hydrothermally reacting the slurry solution obtained in the slurry forming step, and a separation step of separating the calcium silicate or calcium silicate-gypsum composite obtained in the hydrothermal treatment step. This is a manufacturing method. The present invention will be described in detail below, but for the sake of brevity, the description will be made with reference to the accompanying drawings. FIG. 1 of the accompanying drawings is a flow sheet showing typical combinations of steps for carrying out the present invention. The raw materials used in the present invention are gypsum and alkali silicate, such as sodium silicate and potassium silicate, and the necessary amounts of the raw materials are supplied from supply pipes 1 and 2 to the reaction step 4 in which an aqueous medium is present, respectively. Moreover, the gypsum and the alkali silicate can be dissolved or suspended in an aqueous medium in advance and supplied to the reaction step 4, or the raw materials dissolved or suspended in an aqueous medium can be directly supplied to the reaction step 4 through the supply pipe 3. The reaction can also be carried out while being continuously or intermittently supplied. Generally, it is preferable to use the former, that is, gypsum and alkali silicate, dissolved or suspended in an aqueous medium in advance. As described above, the composition of the calcium silicate obtained differs depending on the raw material composition ratio in reaction step 4, that is, the molar ratio of gypsum/alkali silicate. For example, when the molar ratio of gypsum/alkali silicate is generally 1.1 or less, a petal-like calcium silicate is obtained, and when the molar ratio exceeds 1.1, a petal-like calcium silicate gypsum composite is obtained. Further, if the molar ratio is too small, the yield of the target product decreases, not only does the manufacturing cost increase, but also it may become difficult to produce the target petal-shaped calcium silicate, which is not preferable. Moreover, if the molar ratio is too large, it will take a long time to wash and remove unreacted gypsum, which will be described later, and this cannot be said to be industrially advantageous. Therefore, the molar ratio of gypsum/alkali silicate is generally 0.8 to 1.8.
It is most preferable to choose from a range of degrees. The gypsum used in the present invention is not particularly limited, and natural gypsum and synthetic gypsum can be used, and there is an advantage that gypsum, which is a by-product of flue gas desulfurization, can be used as it is. Further, as long as the gypsum is soluble, any type of gypsum, such as hemihydrate gypsum or dihydrate gypsum, can be used. The term soluble means that it is sufficient that it is dissolved in the reaction step, and it may be in a suspended state in preparing the raw materials. Generally, it is most preferable to use gypsum in a state in which it has been dissolved or suspended in an aqueous medium in an amount of 10% (by weight) or less. In addition, considering economic efficiency, it is generally advisable to adjust the concentration to 1 to 10% (by weight). Furthermore, it is most preferred that the concentration of the gypsum in the reaction step is generally between 0.5 and 5% (by weight). As the alkali silicate used in the present invention, sodium silicate, potassium silicate, etc. are generally preferably used as described above. Furthermore, since alkali silicates are usually classified according to standards No. 1 to No. 4 and are commercially available, it is preferable to use these commercially available products as they are in the present invention. Of course, even those having a large molar ratio of SiO ₂ /R ₂ O (where R is alkali), for example 4 to 6.5, can be used without particular restriction as long as they are soluble. The reaction process of the present invention may be carried out either continuously or in patches. In the case of a continuous method, the raw material may be fed continuously or intermittently into the aqueous medium, but in the case of a batch method, it is preferable to add an alkali silicate to the aqueous medium containing gypsum. In addition, in the reaction step, it is generally preferable to carry out the reaction under stirring. The reaction conditions in this reaction step in the present invention are not particularly limited, and generally normal pressure and room temperature are sufficient. Since the solubility of gypsum in water is greatest in the temperature range of 10 to 70°C, it is most suitable to carry out the reaction within this temperature range. The reaction time varies depending on the reaction temperature, stirring method, etc., and cannot be absolutely limited, but generally a range of 30 to 2 hours is most widely used. Since the reaction time can be easily determined in a laboratory, it may be determined in advance according to various conditions. Further, the water ratio in the reaction step may be selected from the range of 10 to 100 to the reactant obtained in the reaction step. Although calcium silicate is produced in the solid obtained in the reaction step, unreacted raw materials and by-produced alkali sulfate are mixed therein. As described above, the gypsum in the unreacted raw material and the alkali sulfate produced as a by-product have a large influence on the properties of the bulk specific volume of calcium silicate in the hydrothermal reaction described later. Therefore, in the present invention, it is necessary to separate unreacted gypsum and by-produced alkali sulfate from the reaction system obtained in reaction step 4. For this purpose, a washing step 5 is required to wash the solid matter obtained in the reaction step 4. The cleaning means is not particularly limited, and any known method may be used. For example, a method of supplying water to the reaction system obtained in reaction step 4 to wash it, or a method of separating solid matter from the reaction system by filtration and washing the separated solid matter, etc. are employed. Generally, it is most suitable to separate the solid matter from the reaction system by filtration and wash it with water. The degree of washing varies depending on the raw material ratio in the reaction process and cannot be absolutely limited. In general, the number of times of washing, the amount of washing water, etc. may be determined in advance according to various conditions. Although the temperature of the washing water is not particularly limited, when separating unreacted gypsum, a temperature of 10 to 70°C, which generally has the highest solubility of gypsum, is suitable. The solids obtained in the washing step are then turned into a slurry solution by supplying an aqueous medium through a supply pipe 8 in a slurrying step 7. The concentration of the slurry solution is not particularly limited and may be selected as appropriate, but generally the water ratio may be selected from a range of 10 to 100 times, preferably 30 to 80 times. Since the slurry solution is subjected to a hydrothermal reaction as described below, the higher the temperature, the better in terms of energy saving. Therefore, as shown in FIG. 1, calcium silicate or calcium silicate obtained in the hydrothermal treatment step
Most preferably, part or all of the hot water from which the gypsum composite is separated is recycled. The slurry solution obtained in the slurry forming step 7 is subjected to hydrothermal treatment in a hydrothermal treatment step 9.
The purpose of the hydrothermal treatment is to grow the calcium silicate or calcium silicate-gypsum composite obtained in the reaction step 4. By the hydrothermal treatment, the calcium silicate or calcium silicate-gypsum composite grows into the petal-like shape. The hydrothermal treatment may generally be carried out at a temperature of 150 to 250°C. Generally, it is preferable to carry out the hydrothermal treatment in an autoclave. Further, the hydrothermal treatment time is not particularly limited, and may be any time that allows sufficient growth into the petal shape. The hydrothermal treatment time may be determined in advance according to various conditions, but generally a range of 3 to 24 hours is most suitable. The calcium silicate or calcium silicate-gypsum composite obtained in the hydrothermal treatment step 9 is an aggregate in which petal-shaped flakes have grown. The calcium silicate or calcium silicate-gypsum composite is separated in step 1.
Separate at 0. The separated calcium silicate or calcium silicate-gypsum composite 12 is washed and dried as necessary to become a product. Further, since the solution obtained by separating the calcium silicate or the calcium silicate-gypsum composite is generally a high-temperature aqueous medium, it is preferably used as the aqueous medium in the slurry forming step 7 via the circulation pipe 11. The separation of calcium silicate or calcium silicate-gypsum complex in the separation step is not particularly limited, and any known separation means can be employed. For example, filtration using a heat-resistant filter cloth, separation using a centrifuge, etc. may be used. As is clear from the above description, the present invention is a manufacturing method that can produce an excellent petal-shaped calcium silicate or petal-shaped calcium silicate gypsum composite by industrially simple means. EXAMPLES In order to explain the present invention more specifically, the present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. In addition, various measured values in the following Examples and Comparative Examples were obtained as follows. (b) Bulk specific volume Calcium silicate in a mortar with 200 mesh sieve 80%
It was ground to the point where it passed through the grains. The pulverized calcium silicate was used to measure bulk specific gravity according to JIS K6220 Sections 6 and 8. (B) Oil absorption amount Calcium silicate in a mortar and sieved with 200 mesh 80%
Milled to passing particle size. The pulverized calcium silicate was used to measure oil absorption according to JISK6220, item 19. Example 1 The following implementation was carried out according to the flow sheet shown in FIG. 1 of the attached drawings. That is, in the reaction process, 880g of 2
Water gypsum and 20ml of water were added to a mixing reaction tank and stirred well. Then, while stirring the slurry, 0.243 mol/sodium silicate (SiO ₂ /Na ₂ O molar ratio 2.5) 20 was added at a rate of 0.5/min over 40 minutes at 25° C. under atmospheric pressure. In this case, the preparation CaSO ₄ /
The Na ₂ O.nSiO ₂ molar ratio was 1.05. In the washing step, the slurry obtained in the reaction step was taken out into a nuttie fitted with a filter cloth and filtered under reduced pressure (400 mHg), and then 30 g of water was added to wash the product. The cake obtained in the above washing step was transferred to a slurrying step, that is, a stirring tank, and high temperature water (80 to 90° C.) was added thereto and stirred uniformly to form a slurry. The slurry obtained in the slurry process is autoclaved (inner volume
50), sealed, and hydrothermally treated at 200°C for 5 hours. After the reaction was completed, the product slurry was taken out into a filter fitted with a heat-resistant filter cloth and vacuumed (400
mHg) filtered. The product after separation in the above separation process is 120
Dry at ℃ for 16 hours. The yield of this dry matter is 1084g
It was hot. Bulk specific volume is 25.7cc/g, oil absorption is 6.9
It was cc/g. In addition, the result of X-ray diffraction showed a pattern of diailolite type calcium silicate. The results of chemical analysis showed that CaO2 was 4.9%, _SiO2 was 65.8%, and the loss on ignition was 9.3%. From this result, the calcium silicate obtained in the above procedure is 2CaO・3SiO ₂・
It was confirmed that it was 1.93SiO ₂ .2.32H ₂ O. Figure 2 shows a 10,000x magnification photo taken using an electron microscope.
From this, the average diameter in the longitudinal direction is approximately 2U and the thickness is
It was confirmed that the flower is composed of an aggregate of petals smaller than 0.1U. Example 2 1170g of flue gas desulfurization byproduct gypsum (purity 99.8%),
20 of water was added to the mixing reaction tank and stirred well. This slurry was heated at 25°C under atmospheric pressure while stirring.
0.243 mol/sodium silicate (SiO ₂ /Na ₂ O molar ratio 2.5) 20 was added at a rate of 0.4/min over 50 minutes. In this case, the charged CaSO ₄ /Na ₂ O·nSlO ₂ molar ratio was 1.40. The subsequent operations were performed in the same manner as in Example 1, but
The high temperature solution obtained in the separation process was used as the high temperature water in the slurry process. As a result, the yield of the dried product was 1208 g. The bulk specific volume of the dried product was 21.4 cc/g, and the oil absorption amount was 6.3 cc/g. Moreover, the X-ray diffraction diagram of this dried product contained peaks of type anhydrite and gyrolite type calcium silicate. As a result of chemical analysis of the dried product,
2CaO・3SiO ₂・2.03SiO ₂・2.55H ₂ O・0.11CaSO ₄
It was confirmed that the compound was Fig. 3 shows an electron microscope photograph of the dried product at a magnification of 10,000 times, and it was confirmed that it was composed of petals with a longitudinal diameter of 2U and a thickness of 0.1U or less. The crystals that appeared to be Sho-type anhydrite could not be visually identified from the electron micrograph in Figure 3, and it was determined that this dried material was a calcium silicate-gypsum complex in which gypsum was incorporated into petal-shaped calcium silicate. . Example 3 The amount of dihydrate gypsum and sodium silicate in Example 1
The treatment was carried out in the same manner as in Example 1, except that the SiO ₂ /Na ₂ O molar ratio and concentration, autoclave treatment temperature, and treatment time were changed as shown in Table 1. In this case, the charged CaSO ₄ /Na ₂ O・nSiO ₂ molar ratio is both 1.05.
It was hot. Further, the high temperature water obtained in the separation step of Example 2 was used in the slurry forming step in No. 1 of Table 1. Similarly, No.2 has No.1, No.3 has No.2, No.4 has No.4.
For No. 3 and No. 5, the high temperature water obtained in the separation process of No. 4 was used. It was confirmed by X-ray diffraction, electron microscopic observation, and chemical analysis that the obtained dried product was petal-shaped calcium silicate in each case. The results are shown in Table 1.

[Table] Example 4 The same procedure as in Example 2 was carried out except that the amount of gypsum by-product of flue gas desulfurization in Example 2 was changed as shown in Table 2, and potassium silicate was used instead of sodium silicate. The results were as shown in Table 2. In this case, the high temperature solution obtained in the separation step of Example 3 (Table 1, No. 5) was used in the slurrying step of Table 2, No. 1. Similarly, the high temperature water obtained in the separation process of No.1 was used for No.2, No.2 for No.3, No.3 for No.4, and No.4 for No.5. . According to X-ray diffraction, chemical analysis, and electron microscopy observation of the dried product obtained, Table 2 No. 1 is petal-shaped calcium silicate, and Table 2 No. 2 and No. 3 are petal-shaped calcium silicate.
Gypsum composites No. 4 and No. 5 were confirmed to be a mixture of petal-shaped calcium silicate gypsum composite and molded anhydrite.

[Table] Comparative Example 1 The same procedure as in Example 1 was carried out except that the washing step and slurrying step of Example 1 were carried out, and the slurry obtained in the reaction step was directly transferred to an autoclave. The yield of dry matter in this case was 1152 g. The bulk specific volume of the dried product was 18.8 cc/g and the oil absorption amount was 5.9 cc/g, both of which were lower than in Example 1. Further, an electron micrograph of the dried product confirmed that the external shape of the dried product was an aggregate of flakes almost similar to that of Example 1.

[Brief explanation of the drawing]

Figure 1 shows one of the typical flow sheets of the present invention.
It is an explanatory diagram showing an example. In addition, FIG. 2 shows Example 1
Electron micrograph of calcium silicate obtained in (1)
FIG. 3 shows an electron micrograph (10,000 times magnification) of the calcium silicate gypsum composite obtained in Example 2. In FIG. 1, each number indicates the following. 1, 2 and 3 are supply pipes for raw materials or aqueous medium, 4 is a reaction process, 5 is a washing process,
6 is a cleaning water supply pipe, 7 is a slurry process, 8
1 is a supply pipe, 9 is a hydrothermal treatment process, 10 is a separation process, 11 is a circulation pipe, and 12 is a calcium silicate or calcium silicate gypsum composite obtained in the process of FIG. 1, respectively.

Claims (1)

[Claims] 1. A reaction step of mixing and reacting gypsum and an alkali silicate in an aqueous medium, a washing step of washing the solid material obtained in the reaction step, and a slurry solution of the solid material obtained in the washing step. Silicic acid characterized by comprising a slurry forming step, a hydrothermal treatment step of hydrothermally treating the slurry solution obtained in the slurry forming step, and a separation step of separating calcium silicate or calcium silicate-gypsum composite obtained in the hydrothermal treatment step. A method for producing a calcium or calcium silicate-gypsum composite. 2 High temperature water obtained in the separation step of separating the calcium silicate or calcium silicate-gypsum composite
The method according to claim 1, wherein part or all of the method is recycled to the slurry forming step.