JPH0581524B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a sodium silicate solution. More specifically, the present invention relates to a method for producing a sodium silicate solution purified by a certain method using a specific by-product hydrous amorphous silica as a raw material. When synthesizing fluoride using silicofluoride, hydrated amorphous silica is produced as a by-product (note, formula (1) and
(2)). Currently, industrially, most of such by-product silica is generated as a result of the reuse of fluorine compounds recovered from the phosphoric acid manufacturing process. However, the quality varies widely depending on the method for recovering the raw material fluorine compound or the process for reusing it. The current situation is that the above-mentioned by-product silica
Only the areas with high SiO ₂ purity and good whiteness are
It is only used in the production of finely powdered silica, calcium silicate materials, or water glass. On the other hand, the demand for synthetic zeolite has increased rapidly as it has recently begun to be incorporated into synthetic detergents, and it is important to manufacture and supply zeolite as economically as possible for this purpose. It is important to disseminate it widely and improve the environment of water areas. Type A zeolite suitable for detergent builders is usually produced by a method of hydrothermally synthesizing a composition consisting of silica, alumina and sodium hydroxide, and the following two methods are typical. That is, a method using water glass and sodium aluminate as raw materials, and a method using pretreated solid silica or aluminosilicate as raw materials. In the above case, since all of the raw materials are industrial products, there is little variation in the quality of the raw materials, and although high quality zeolite can be obtained, there is a drawback that the cost of raw materials is high. In the above case, although the raw materials are economically available, the processing costs for refining the raw materials (improving purity) or imparting activity cannot be ignored, and on top of that, it is difficult to dispose of the waste generated by the processing. However, there are also problems such as considerable costs. On the other hand, from the fluoride synthesis step using the aforementioned silicofluoride as a raw material, silica is produced as a by-product, for example, according to the following formula (1) or formula (2). Na ₂ SiF ₆ +NaAlO ₂ +NaOH→ Na ₃ Al ₆ +NaF+SiO ₂ ...(1) H ₂ SiF ₆ +2Al(OH) ₃ → 2AlF ₃・nH ₂ O+SiO ₂ ...(2) Such by-product silica is It is an aggregate of linearly amorphous fine particles with an average particle diameter of 1 μm or less, and is extremely highly chemically active. Its specific chemical composition is
Although it varies depending on the process in which the by-product silica is produced, it generally contains 40 to 60% water by weight.
It contains only small amounts of fluorine, inorganic compounds of alkali metals or alkaline earth metals, and small amounts of organic substances, and contains more than 95% by weight of silica on a scorching basis at 1000°C. However, when the raw material silica fluoride is dissolved, this by-product silica
It is a by-product that is precipitated by the initial reaction.
Therefore, it has the disadvantage that it includes all insoluble impurities in raw materials, impurities resulting from the main process, etc. Therefore, this by-product silica has a variety of hues, ranging from nearly pure white to dark brown. For the above reasons, it is known that only the high-quality silica, which is a by-product when synthesizing fluoride using silicofluoride, can be used in the production of water glass by the wet method. Furthermore, there has been no success in producing high-quality silica solutions or even using them as raw materials for zeolite. In view of the above-mentioned technical circumstances related to the use of by-product silica, the present inventors conducted various studies to enable effective use of this substance. As a result, by dissolving the above-mentioned by-product silica (containing 40 to 60% water by weight) in a sodium hydroxide solution, adding and mixing a small amount of a certain amount of calcium-containing material, and filtering it, colorless I learned that it is possible to produce a transparent silica solution. Furthermore, it was discovered that by using this silica solution and sodium aluminate, high-purity A-type zeolite that is always rich in whiteness regardless of the hue of the by-product silica can be economically produced in a simple process, and the present invention is based on the present invention. I was able to complete it. As is clear from the above description, the first object of the present invention is to provide a method for producing a purified sodium silicate solution using by-product silica. The second purpose is to provide the sodium silicate solution produced by the above method for use in producing A-type zeolite and other uses. Other purposes will become clear from the description below. The present invention has the following main configuration (1) and the following (2) and (3).
It has an embodiment configuration. (1) The following raw materials A, B, and C have a SiO ₂ concentration of 6 to 30% by weight and a [SiO ₂ ]/[Na ₂ O] molar ratio of
1.0 to 3.5, Ca(OH) ₂ concentration is 0.01 to 1.0% by weight, mixed and dissolved, heated and stirred, and filtered to obtain a purified sodium silicate solution. B Sodium hydroxide solution. (b) Hydrous amorphous silica which is produced as a by-product when synthesizing fluoride using silicofluoride (c) One or more compounds selected from calcium hydroxide, xonotrite, and tobermorite. (2) The manufacturing method according to item (1) above, wherein the hydrated amorphous silica is dissolved at 70 to 105°C under normal pressure. (3) Adding one or more CaO-containing compounds, such as calcium hydroxide, xonotlite, tobermorite, as a powder or as an aqueous suspension or solution thereof20
The manufacturing method according to item (1) above, wherein the method is heated and stirred for at least 1 minute. The configuration and effects of the present invention will be explained in detail below. (a) By-product silica used in the present invention: As mentioned above, this silica is an aggregate of amorphous fine particles.
Therefore, it is highly chemically active and can be heated at 60 to 80℃ under normal pressure.
Easily dissolved in dilute sodium hydroxide solution at temperatures such as . However, this by-product silica generally contains a trace amount such as 0.001% to 1% by weight of effective substances in the reaction process from silicofluoride to fluoride, which causes it to change from white to white. There are various hues that are blackish brown. A sodium hydroxide solution in which such by-product silica is dissolved is colored or cloudy as it is, and has no commercial value. Even if zeolite is synthesized using this sodium silicate solution as a raw material, variously colored zeolites can be obtained. By the way, a typical method for producing the sodium silicate solution, which is one of the raw materials in the above-mentioned method for producing the zeolite used in the product of the present invention, is as follows: (i) quartz is melted together with an alkali metal salt and then cooled; There is a so-called dry method in which the cullet obtained by the process is dissolved in an autoclave, and (2) a so-called wet method in which quartz powder is directly dissolved in a sodium hydroxide solution in an autoclave. In the case of (a) above, the presence of organic substances in the raw materials does not pose a problem. However, in the case of (b) above, its presence causes coloration and turbidity in the product, so
In this case, a method of filtering and purifying by adding activated carbon is adopted. Incidentally, when this activated carbon method was applied to the purification of the sodium silicate solution according to the present invention, some effect in terms of decolorization was observed. However, it was found that the filtration rate for purification was extremely low and ultimately it was not possible to purify economically.
Here, the present inventors, as mentioned above,
By adding and mixing a small amount of a certain calcium-containing substance to a sodium silicate solution in which by-product silica is dissolved in a sodium hydroxide solution, a gel-like amorphous silica compound (hereinafter referred to as gel) is generated in the solution, It has been found that by continuing heating and stirring for a certain period of time and then filtering, not only the colored substances and the above-mentioned turbidity are removed along with the gel, but also the filtration rate becomes unexpectedly high. The calcium-containing substance used in this step of the method of the present invention is one or more compounds selected from calcium hydroxide, xonotlite, or tobermorite, as described in (3) above. Of course, calcium compounds other than these can also be used in the same manner as long as they can be added to the silica solution described above to produce a similar gel. The calcium-containing substance is preferably added to the sodium silicate solution in the form of an aqueous suspension or solution rather than as a powder. In particular, when calcium hydroxide or quicklime is added as a powder, it tends to be insufficiently dispersed in the sodium silicate solution, and the effect is inferior to when it is used as a suspension or an aqueous solution. The timing of adding the calcium-containing substance is not limited to after the by-product silica is dissolved in the sodium hydroxide solution, and may be added before or during the dissolution, but preferably after the sodium silicate solution is prepared. do. The reason for this is not clear. The amount of the calcium-containing substance added is preferably in the range of 0.01 to 1.0% by weight, more preferably 0.05 to 0.3% by weight in terms of Ca(OH) ₂ based on the sodium silicate solution. If the amount of the substance used is insufficient (less than 0.01% by weight), the amount of gel produced will be small and the filtration rate will not improve. On the other hand, if the amount used is large (more than 1.0% by weight), there will be no particular improvement in the effect, and the silica content will be lost (Note).
gel) increases. A sodium silicate solution containing such calcium-containing substances to precipitate a gel is heated for 20 minutes or more (note: at a temperature of 60°C).
~boiling point). If heating or insulating is stopped for less than 20 minutes and the cooled material is attempted to be filtered, the speed of filtration may be significantly reduced. As mentioned above, in the purification process of the sodium silicate solution according to the present invention, the process of adding an appropriate amount of calcium-containing material and heating and aging the gel produced by the addition is an essentially important core of the present invention. By going through this process, colored substances contained in the sodium silicate solution,
Not only substances that cause turbidity but also iron, aluminum, fluorine, etc. are removed at the same time in the subsequent filtration step, and a purified sodium silicate solution, that is, a highly purified sodium silicate solution can be easily produced. As mentioned above, it goes without saying that the method for purifying a sodium silicate solution using by-product silica as a starting material according to the present invention can be similarly applied to purifying an unpurified sodium silicate solution obtained by other manufacturing methods. Nor. A supplementary explanation will be given regarding the by-product silica used in the present invention. In the method of the present invention, the by-product silica is
It must be dissolved in the sodium hydroxide solution while remaining hydrated. Incidentally, JP-A-53-56199 discloses that the solubility is improved when the by-product silica is dried to a water content of about 5% or less. However, according to similar experiments conducted by the present inventors, the dried powder of secondary silica floated on the surface of the sodium hydroxide solution, making it difficult to disperse and dissolve it inside the solution. In addition, it has become clear that such fine powder scatters during handling and deteriorates the working environment, and no effect was observed by drying the water-containing material. The dissolution of secondary silica used in the present invention in a sodium hydroxide solution will be explained using figures. Figures 1 and 2 show dissolution time (hours, minutes) and dissolution rate (%) of by-product silica in sodium hydroxide solution.
shows the relationship curve. The symbols indicating each curve in both figures indicate the dissolution conditions, namely Ma ₂ O% and SiO ₂ /
Na ₂ O molar ratio and temperature and results (pass or fail)
This shows that. These are collectively shown in the table below.

[Table] Visual judgment based on five levels of good and bad As is clear from the above, it is clear that if appropriate dissolution conditions are selected, good dissolution results for silica can be obtained within a short time. In addition, the dissolution rate of by-product silica is significantly higher than that of aluminum hydroxide, and in addition, dissolving aluminum hydroxide in a sodium hydroxide solution requires the use of a high-temperature, high-concentration solution. Conditions are favorable. As described above, the rate of dissolution of the by-product silica in the sodium hydroxide solution used in the method of the present invention is highly temperature dependent, and although 60°C is possible, it is preferably 80°C or higher. When dissolving by-product silica in a sodium hydroxide solution, the mixing order,
There are no particular limitations on the timing of stirring or heating. Next, the sodium aluminate solution used in the reaction with the product of the present invention will be described. This product can be prepared from aluminum hydroxide and a sodium hydroxide solution by known methods. However, in many cases, such a liquid exhibits a brown turbidity due to the iron content and organic substances contained in both raw materials (commercially available products), and if this liquid is used as it is in the zeolite synthesis reaction according to the present invention, it will produce zeolite. causes coloration. Research has shown that turbidity can be removed by filtration, but coloration cannot be removed. As a result of further research, it was found that in order to remove this coloring, a silica solution containing about 0.02 to 0.5% by weight of SiO ₂ (as mentioned above) or sodium hydroxide easily soluble silica was thoroughly mixed into the sodium aluminate solution and aged. The colored substances can be easily removed by filtration, and when zeolite is synthesized by reacting the purified sodium aluminate solution with the purified sodium silicate solution, a zeolite with further improved whiteness is obtained. It was found that it was possible to obtain Note that the component composition, reaction, and crystallization conditions in the zeolite synthesis reaction according to the present invention are the same as those in known methods, so descriptions thereof will be omitted. Incidentally, the method for producing A-type zeolite according to the use of the present invention is
A homogeneous composition in which the silica content, sodium hydroxide, and water are within the range for forming type A zeolite is prepared by mixing purified sodium silicate solution, sodium aluminate solution, sodium hydroxide, and water purified by the method described in 1. It is obtained by preparing and crystallizing it. According to the method of the present invention, even if strongly colored by-product silica is used as a starting material, zeolite with excellent whiteness can be synthesized in the end. According to the present invention, a colorless and transparent sodium silicate solution can be produced regardless of the degree of coloration of by-product silica. In other words, colored or contaminated by-product silica (with organic matter, etc.), which could not be used conventionally, can be used 100% effectively. Furthermore, it can be confirmed that by using the sodium silicate solution according to the present invention as a silica source, zeolite with high whiteness can be produced economically. Next, the present invention will be explained in more detail with reference to Examples. Example 1-1 The by-product silica shown in Table 1 was added to a sodium hydroxide solution containing about 6% by weight as NaO ₂ to give a concentration of 16.0% by weight as SiO ₂ , and the mixture was stirred with a stirrer.
A sodium silicate solution was prepared by heating and dissolving at 80°C for 20 minutes. While stirring and maintaining the liquid temperature at 80° C., an aqueous slurry containing 0.1% by weight of calcium hydroxide was added as Ca(OH) ₂ and maintained for 1 hour, resulting in the formation of a small amount of gel. This gel and impurities such as colored substances were filtered using NO-5C filter paper to obtain a sodium silicate solution. Table 1 shows the physical properties of purified sodium silicate and the time required to filter 500 g of sodium silicate. Example 1-2 A purified sodium silicate solution was obtained in the same manner as in Example 1-1, except that by-product silica was added as SiO ₂ at a concentration of 12.0% by weight. Table 1 shows the physical properties and filtration time of the purified sodium silicate solution. Example 1-3 A purified sodium silicate solution was obtained in the same manner as in Example 1-1 except that by-product silica was added as SiO ₂ at a concentration of 18.0% by weight. Table 1 shows the physical properties and filtration time of the purified sodium silicate solution. Application example Aluminum hydroxide is dissolved in sodium hydroxide solution at about 100℃ to form Al ₂ O ₃ : 15.98% by weight, Na ₂ O :
15.49% by weight sodium aluminate solution prepared;
This sodium aluminate solution, the purified sodium silicate solution obtained in Example 1, the sodium hydroxide solution, and water were mixed at the following molar ratio and mol%, and the resulting mixture was heated at 60°C for 1 hour with stirring. The mixture was aged and then kept at 80°C for 4 hours to crystallize type A zeolite. The whiteness of the type A zeolite obtained was 99.
It was hot. [Na ₂ O] / [Al ₂ O ₃ ] = 2.7 (molar ratio) [SiO ₂ ] / [Al ₂ O ₃ ] = 2.0 (molar ratio) [H ₂ O] / [Na ₂ O] + [Al ₂ O ₃ 〕＋〔Si
O ₂ ] + [H ₂ O] = 94.0 (mol%) Comparative example 1-1 Example 1 except that calcium hydroxide was not added
Same as -1. Table 1 shows the physical properties of the sodium silicate solution after filtration and the time required for filtration. Comparative Example 1-2 Example 1 except that calcium hydroxide is not added
I did the same as -2. Table 1 shows the physical properties of the sodium silicate solution after filtration and the time required for filtration. Comparative Example 1-3 Example 1 except that calcium hydroxide is not added
- Same as 3. Table 1 shows the physical properties of the sodium silicate solution after filtration and the time required for filtration.

【table】

[Table] Example 2 By-product silica was added as SiO ₂ to a concentration of 18.0% by weight, and calcium hydroxide was added as Ca(OH) _2.
The same procedure as Example 1-1 was carried out except that 0.3% by weight was added. Table 2 shows the physical properties of the purified sodium silicate solution and the SiO ₂ concentration in the solution. Example 3 The same procedure as in Example 1-1 was carried out, except that by-product silica was added in an amount of 18.0% by weight as SiO ₂ and tobermorite was added in an amount of 0.3% by weight as Ca(OH) ₂ . Table 2 shows the physical properties of the purified sodium silicate solution and the SiO ₂ concentration in the solution. Example 4 The same procedure as Example 1-1 was carried out, except that by-product silica was added in an amount of 18.0% by weight as SiO ₂ and xonotlite was added in an amount of 0.5% by weight as Ca(OH) ₂ . Table 2 shows the physical properties of the purified sodium silicate solution and the SiO ₂ concentration in the solution. Comparative Example 2 The same procedure as Example 2 was carried out except that calcium hydroxide was Ca(OH) _{2 and} 2.0% by weight, which exceeds the upper limit of 1.0% by weight of the present invention, was added. The sodium silicate solution obtained after filtration was neither colored nor cloudy, but the SiO ₂ concentration in the solution was 16.1%, which was significantly lower than the formulation value of 18.0. Example 5 The same procedure as Example 1-3 was carried out except that white by-product silica having the composition shown in Table-2 was used. Table 2 shows the physical properties of the purified sodium silicate solution and the SiO ₂ concentration in the solution. Comparative Example 3 The same procedure as Example 5 was carried out except that calcium hydroxide was not added. Table 2 shows the sodium silicate solution obtained after filtration.
As shown, it was colored pale brown.

【table】

【table】 [Brief explanation of the drawing]

Figures 1 and 2 show relationship curves between the dissolution time (hours and minutes) of by-product silica in a sodium hydroxide solution and the dissolution rate (%).

Claims (1)

[Scope of Claims] 1. The following raw materials A, B, and C have a SiO ₂ concentration of 6 to 30% by weight and a [SiO ₂ ]/[Na ₂ O] molar ratio of
1.0 to 3.5, Ca(OH) ₂ concentration is 0.01 to 1.0% by weight, mixed and dissolved, heated and stirred, and filtered to obtain a purified sodium silicate solution. (b) Sodium hydroxide solution Hydrous amorphous silica, which is a by-product when synthesizing fluoride using silicofluoride.One or more compounds selected from calcium hydroxide, xonotlite, and tobermorite.