JPH059369B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for synthesizing a silicate having a structure similar to that of a clay naturally occurring as hectorite. <Prior art> As is already known, some natural hectorite clays can form stable gels and exhibit good dispersibility by dispersing a small amount in water, but these Because it contains naturally occurring impurities, it is colored and contains fluorine, making it difficult to obtain a highly pure product. Various studies have been made regarding high-purity hectorite-like synthetic silicates. The following synthesis method is recently known. (a) Kondo et al. added sodium silicate to a slurry in which an ammonia aqueous solution and a magnesium salt aqueous solution were reacted to precipitate magnesium hydroxide to create a composite precipitate of magnesium hydroxide-silica gel, which was filtered and washed with water. A synthesis method is disclosed in which a by-product electrolyte is removed, dispersed in water, and then lithium ions, alkali metal ions, or fluoride ions are added to perform a hydrothermal reaction. (Sanji Kondo, Special Publication No. 51-33080) (b) Torii et al. Free silicic acid obtained by adding concentrated inorganic acid such as hydrochloric acid to a sodium silicate solution,
After reacting magnesium salts and adding aqueous ammonia or an alkaline solution such as caustic alkali, the resulting precipitate is filtered and washed with water to remove by-product electrolytes, and then lithium, sodium ions, etc. are added to perform a hydrothermal reaction. Synthesizes hectorite-type silicates. (Kazuo Torii et al., JP 58-185431) (c) Newman added a solution containing sodium carbonate and water glass to a hot aqueous solution of magnesium sulfate and a lithium compound, and the resulting precipitate, or lithium compound added to magnesium sulfate. Add sodium carbonate to the solution containing the compound to precipitate the insoluble magnesium salt,
Add water glass solution and caustic alkali to this,
The generated precipitate is subjected to a hydrothermal reaction, filtered and washed repeatedly to remove by-product salts, and dried to obtain a hectorite type silicate. (Barbara Susan Newman, Special Publication 1977-813, Special Publication 1973-
48443) Among the above synthetic methods A, B, and C, methods A and B of Kondo and Torii et al. generate a composite precipitate of an insoluble magnesium compound and silica gel, and then filter and wash with water to remove by-product salts. After that, a hydrothermal reaction is carried out. <Problems to be Solved by the Invention> In Kondo's method A, although filtering and washing the magnesium hydroxide-silica composite precipitate with water is relatively easy, it is quite difficult to remove the ammonium salt, and it is difficult to remove the ammonium salt, which is the previous step of the composite precipitate. Both the production process and the subsequent hydrothermal reaction process take a long time. Next, in Torii's method, although the generation time of the composite precipitate is shortened, it is not easy to remove the by-product salts by washing with water, and especially when ammonia is used as the alkaline solution, the remaining ammonia is used in the subsequent process. Makes hydrothermal reactions difficult. Furthermore, in any of the above methods (a) and (b), there is a problem that the contents gel due to the hydrothermal reaction, making it difficult to remove them from the apparatus. Furthermore, the obtained silicate is opaque and has poor dispersibility. On the other hand, although Newman's method C yields a silicate with good dispersibility, the processing steps are complicated and time consuming. Furthermore, it is very difficult to remove the reaction product and the by-product salts by washing with water, and the by-product salt that forms a precipitate based on a sulfate solution (magnesium sulfate) is called sodium sulfate (sodium sulfate).
is the main component, and because it is difficult to recover, the loss of alkali is large. <Means for Solving the Problems> The present invention produces precipitates of magnesium carbonate using carbon dioxide gas, and the entire synthesis process is based on carbonates without using sulfates, thereby improving the conventional synthesis process. A synthesis method has been achieved that solves various problems in the method. In the present invention, the pretreatment step for the hydrothermal reaction is relatively simple, and the reaction product is easily filtered and washed with water, and the liquid and washing liquid are alkali carbonates of high purity.
Most of it can be reused as raw material, and
The product aims to provide a method for producing silicates, which are hectorite-type clays of high purity, have very good gel-forming ability in water, and also exhibit excellent dispersibility. The composition of the present invention that achieves the above object is produced by blowing carbon dioxide gas into a slurry of magnesium hydroxide to produce insoluble magnesium carbonate, and adding a water-soluble silicate solution in the presence of alium carbonate and lithium carbonate. After boiling and maturing the precipitate,
It is characterized by carrying out a hydrothermal reaction at 100 to 250°C, washing the resulting precipitate, and then drying it. The present invention includes reusing the liquid precipitated by the hydrothermal reaction as an alkali carbonate, and adding an alkali carbonate and lithium carbonate to the slurry of magnesium hydroxide in advance, or adding the alkali carbonate and lithium carbonate to the slurry of magnesium hydroxide. Preferred embodiments include adding alkali carbonate and lithium carbonate after blowing carbon dioxide gas to produce insoluble magnesium carbonate. Hereinafter, the present invention will be explained in detail based on Examples and Reference Examples. In the present invention, carbon dioxide gas is blown into a slurry of magnesium hydroxide to generate insoluble magnesium carbonate, and a water-soluble silicate solution (water glass) is produced in the presence of an alkali carbonate and lithium carbonate.
is added, and the resulting precipitate is boiled and aged. When blowing carbon dioxide gas into the magnesium hydroxide slurry, it is preferable to do so while stirring the slurry. As the carbon dioxide gas, ordinary liquefied carbon dioxide gas or low-sulfur exhaust gas such as lime kiln gas and boiler exhaust gas can be used. It is preferable that carbon dioxide gas be blown in slightly in excess of the theoretical amount of magnesium carbonate to be produced so that no magnesium hydroxide remains. Insoluble magnesium carbonate slurry is produced by blowing carbon dioxide gas into the magnesium hydroxide slurry. Although this magnesium carbonate exists in liquid, it is unstable in air and tends to form basic salts when dried, etc. Products using this basic magnesium carbonate as a raw material have poor dispersibility and become cloudy and precipitate. So I don't like it. In the present invention, since carbon dioxide gas is blown into the slurry, magnesium carbonate is stably produced in the slurry, and ordered columnar magnesium carbonate crystals with a length of 50 to 100 microns are precipitated. An aqueous silicate solution (water glass) is then added in the presence of alkali carbonate and lithium carbonate. In this case, the alkali carbonate and lithium carbonate may be added to the magnesium hydroxide slurry in advance, or they may be added after carbon dioxide gas is blown into the slurry. When adding after blowing carbon dioxide gas, water glass may be added after adding these lithium carbonate and alkali carbonate, or they may be added gradually at the same time. It is preferable to add water glass gradually. In either method, a precipitate with a relatively uniform particle size is obtained. The gel precipitate obtained in this step is boiled for 30 minutes to 1 hour and then subjected to a hydrothermal reaction. The hydrothermal reaction temperature may be between 100°C and 250°C, but if the temperature is low, it will take a long time to obtain the desired product, so the temperature should be set at 200°C.
This autoclaving, which is preferably carried out at ~210° C. for about 3 hours, advances crystallization, resulting in crystals exhibiting a more uniform particle size distribution. Next, this gel-like precipitate is filtered, washed with water to remove adhering by-product salts, and dried to obtain a synthetic silicate. This synthetic silicate has the general formula [Si ₈ (Mg ₆ -a-bLiaHb)O ₂₀ (OH) ₄ ] ^-x xM ⁺ 0≦a<2, x=a+b, 0≦b<2, 0≦a+b< 2M is a hectorite-type clay mineral represented by an alkali metal,
It is a colorless, transparent, and highly pure product with excellent gel-forming ability and dispersibility in water. Therefore, the synthetic silicate obtained in the present invention can be used as a thickener and a binder in paints, water-based inks, abrasives, textile processing agents, cleaners, and because of its high purity, it can be used in cosmetics, pharmaceuticals, toothpaste, fruit juice, beer, etc. It can be suitably used as a fining agent for wine, etc. In the above manufacturing process, the additives of lithium carbonate and alkali carbonate may be appropriately selected so as to correspond to the amounts of each component of the silicate obtained as shown in the above general formula. <Effects of the Invention> As described above, according to the present invention, filtering and washing are extremely easy, and sodium carbonate, which is a by-product salt, can be easily removed compared to conventional methods. Furthermore, since carbonate is used as the lithium compound, the solution and cleaning solution consist of almost pure sodium carbonate solution, and a portion of the solution and cleaning solution can be circulated and reused as an alkali source, making it very economical. Incidentally, when compared with conventional manufacturing methods,
Total filtration and water washing time (in Example 1, filtration with 500 ml of slurry of the produced precipitate, 3 filtration with 120 ml of water each)
Comparing the conventional method: the method of the present invention =
1:0.28, which is about 1/4th of the conventional method when comparing the size of the overflow device with the same processing capacity. Therefore, it has an extremely large advantage when implemented on an industrial scale. <Examples> Next, examples of the present invention will be shown together with reference examples. Example 1 11.04 g of magnesium hydroxide (98%) was added to 250 ml of water in a 500 ml beaker to make a slurry, and 16.7 g of carbon dioxide was blown into this from a liquefied carbon dioxide cylinder over 2 hours. 111 g of water was added to a separate container. Tori, lithium carbonate 0.64
g, soda carbonate 17.3 g, water glass (Na ₂ O: 9.52
%, SiO ₂ 28.64%) and 59.1 g of water are mixed to prepare a solution. Add this to the previously prepared magnesium carbonate slurry (magnesium carbonate precipitated slurry with columnar crystals of 50 to 100μ) for about 30 minutes while stirring.
A gel-like precipitate was obtained. Pour this gel precipitate into a 500 ml flask equipped with a reflux condenser.
The mixture was boiled for an hour, then placed in an autoclave and subjected to a hydrothermal reaction at 200°C for 3 hours at a stirring speed of 150 rpm.
The reaction product was filtered by suction and washed three times with 120 ml of water. In addition, the slurry filtration and water washing speed are as follows:
(Slurry amount 500g, washing water amount each 120ml, over area
269 cm ² suction device) as shown in Table 1. The crystals of this precipitate had a regular shape with a length of 30 to 50 μm. The filtered cake was then dried at 110°C and ground through a 250μ sieve. The analytical values of this hydrous magnesium silicate are shown in Table 2, and the results of X-ray diffraction confirmed that it had a hectorite peak.

【table】

[Table] The physical properties of the obtained synthetic silicate are as shown in the table below. The magnesium carbonate crystals after carbon dioxide gas injection, the precipitate crystals before the hydrothermal reaction, and the precipitate crystals after the hydrothermal reaction are shown in Figures 1 to 3, respectively, and the formation stage of the magnesium carbonate crystals. It can be seen that a precipitate with a uniform particle size is formed.

[Table] As shown in Table 3, it can be seen that the synthetic silicate of this example has good viscosity characteristics and good dispersibility in both hot water and cold water. Example 2 0.646 g of lithium carbonate (99%) was immediately dissolved in a solution of sodium carbonate (5.68%) after autoclaving, and 11.04 g of magnesium hydroxide (98%) was added thereto. Make slurry. From a liquefied carbon dioxide gas cylinder while stirring these
Blow in 16.7 g of carbon dioxide gas over a period of 2 hours to turn magnesium hydroxide into a slurry liquid containing columnar crystals of magnesium carbonate. This is added with a water glass solution (Na ₂ O:
A solution prepared by diluting 59.1 g of SiO 2 (SiO ₂ 28.49%) with 591.1 g of water (1:1 dilution) was added over 30 minutes to form a gel precipitate. This gel-like precipitate is boiled for 1 hour in a 500 ml flask equipped with a reflux condenser to volatilize carbon dioxide gas. Thereafter, a hydrothermal reaction was carried out in an autoclave at 150 rpm at 210°C for 3 hours. The reaction product was taken out, filtered under suction, and washed three times with 120 ml of water. The resulting cake was dried at 110°C and ground to a particle size of 250μ or less. The composition of the obtained silicate was almost the same as that of Example 1, and its physical properties were also similar to those of Example 1, with good viscosity characteristics and dispersibility, as shown in Table 3. Ta. Example 3 1.29g of lithium carbonate (99%) and sodium carbonate
17.30g and magnesium hydroxide (98%) 11.04
g to 348.5 g in a 500 ml flask, and blow carbon dioxide gas from a liquefied carbon dioxide gas cylinder for 2 hours to obtain a slurry liquid containing magnesium carbonate. Thereafter, the same treatment as in Examples 1 and 2 is carried out to obtain hydrous magnesium silicate. The obtained analytical values are shown in Table 4.

[Table] The synthetic silicate of this example is also shown in Tables 3 and 4.
As shown in the table, it had a hectorite type composition and suitable viscosity characteristics and dispersibility. Reference example: 45.7 g of magnesium sulfate (MgSO ₄ 7H ₂ O) and 0.12 g of lithium sulfate (Li ₂ SO ₄・H ₂ O) in 174.2 g of water
Dissolve in g. To this is added 152.2 g of sodium carbonate solution (Na ₂ CO ₃ 11.37%) over 15 minutes with stirring. Furthermore, a diluted solution prepared by adding 53.5 g of water to 59.1 g of water glass (SiO ₂ 28.49%, Na ₂ O 9.15%) was added to this solution over a period of 30 minutes. This slurry is boiled at 100°C for 1 hour, and then subjected to a hydrothermal reaction at 207°C for 3 hours in an autoclave. The reaction product is filtered and washed three times with 120 ml of water. The cake is dried at 110℃ and ground to 250μ or less. By the above production method, a synthetic silicate having the composition shown in the following table can be obtained.

[Table] The processing time and physical properties of this reference example are shown in Tables 1 and 3 in comparison. As is clear from Table 3, the production method of this reference example has the same viscosity characteristics and dispersibility as the present invention, but as is clear from Table 1, the elapsed time is significantly longer than that of the present invention. It turns out that over-cleaning is difficult. Incidentally, as shown in FIGS. 4 to 6, the gel product is non-uniform compared to that of the present invention.

[Brief explanation of drawings]

1 to 3 are micrographs showing the crystalline state of the product in Example 1 of the present invention, and FIG. 1 shows the magnesium carbonate precipitate after carbon dioxide treatment,
Figure 2 shows the precipitate after addition of water glass, and Figure 3 shows the precipitate after hydrothermal synthesis. Figures 4 to 6 are micrographs showing the crystalline state of the product in the conventional method shown in the reference example. Figure 4 shows the magnesium carbonate precipitate produced from magnesium sulfate, and Figure 5 shows the precipitate before the hydrothermal reaction. , FIG. 6 shows the precipitate after the hydrothermal reaction.

Claims (1)

[Claims] 1 Blow carbon dioxide gas into a slurry of magnesium hydroxide to produce insoluble magnesium carbonate, and add a water-soluble silicate solution in the presence of an alkali carbonate and lithium carbonate to boil and ripen the resulting precipitate. A method for producing a silicate having a hectorite-like structure, which comprises carrying out a hydrothermal reaction at 100 to 250°C, washing the resulting precipitate, and then drying it. 2. A method for producing a silicate according to claim 1, characterized in that the precipitated liquid from the hydrothermal reaction is reused as the alkali carbonate. 3. The method for producing a silicate according to claim 1, characterized in that an alkali carbonate and/or a caustic alkali, and lithium carbonate are added in advance to the slurry of magnesium hydroxide. 4. The method for producing a silicate according to claim 1, which comprises blowing carbon dioxide gas into a slurry of magnesium hydroxide to produce insoluble magnesium carbonate, and then adding alkali carbonate and lithium carbonate.