JPH0578119A - Production of aqueous solution of sodium silicate - Google Patents

Abstract

PURPOSE:To provide a process for producing an aqueous solution of sodium silicate using cristobalite. CONSTITUTION:Powder of cristobalite is made to react with sodium hydroxide by heating in an autoclave to obtain an aqueous solution of sodium silicate. In the above process, the molar ratio of SiO2 in the cristobalite powder to Na2O in the sodium hydroxide is set to 2-4, the solid/water ratio in the slurry is adjusted to 1.0-0.1, the treating temperature is set to 80-240 deg.C and the reaction is continued for 30min to 2hr after the temperature of the system is raised to the treating temperature.

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 an aqueous sodium silicate solution, and more particularly to a method for producing an aqueous sodium silicate solution using cristobalite as a raw material.

[0002]

BACKGROUND ART It is widely known that a siliceous raw material and an aqueous alkali solution are hydrothermally synthesized in an autoclave to produce sodium silicate, so-called water glass, but the raw material in this case has good reactivity, Moreover, a relatively high-purity siliceous raw material is required, and colloidal silicic acid, precipitated silicic acid, diatomaceous earth, or clay is used for this purpose. Also,
Conventional industrial water glass is specified by JIS standard, and iron and other water-insoluble components are regulated.

However, industrial water glass is a rare substance in which a large amount of a silica component is dissolved, and various use forms such as solidification by casting, spinning, film formation and coating film formation are possible. Considering actual use, it is not always necessary to stick to the conventional idea of uniformly reducing the content of non-alkali metals such as alumina and iron. Although it seems to be sufficient, there have not been many ideas like this for water glass. Therefore, as a raw material for water glass, it has not been performed until now in addition to the above-mentioned raw materials, other siliceous raw materials containing a large amount of silica.

[0004]

This invention contains a considerable amount of impurities such as alumina, and it has been said that it cannot be used as a raw material for water glass in the past, but it is relatively easy to obtain in Japan. It is intended to simply and efficiently produce an aqueous solution of sodium silicate in which the content rate of alumina, iron, magnesium and the like is set to a predetermined value or less by using cristobalite which can be used as a starting material.

[0005]

The present invention is directed to heating cristobalite powder and caustic soda in an autoclave,
In producing the aqueous sodium silicate solution by reacting, the molar ratio of SiO ₂ and Na ₂ O in the cristobalite powder is 2 to 4, the solid matter / water ratio of the slurry is 1.0 to 0.1, and the treatment temperature is 80-240 ° C, reaction time 3 after reaching the treatment temperature
It is a method for producing an aqueous solution of sodium silicate, which is characterized in that the time is within 0 minutes to 2 hours. The present invention will be described below.

The invention of the present application uses, as a siliceous raw material for water glass, cristobalite which has never been neglected. Cristobal rocks are found in large quantities in the Tsugaru district of Shimokita, Aomori prefecture, and their typical chemical composition is shown in Table 1. Cristobal rock is S like this
Despite containing a large amount of iO ₂ , the industrial production method of water glass using this as a raw material has never been attempted by those skilled in the art.

[0007]

[Table 1] The reason is probably that this Cristobal rock has alumina,
It is considered that since a large amount of impurities such as iron are contained, good water glass cannot always be obtained by hydrothermal synthesis in an autoclave as in the conventional case. fact,
Even if hydrothermal synthesis is performed from this cristobalite as a raw material under the same conditions as before to obtain water glass, alumina etc. in the raw material are not removed to below a specified value, and most of them are mixed in water glass. Therefore, it was not possible to efficiently obtain water glass of high purity as defined by JIS standard.

However, according to the results of many experiments conducted by the inventors of the present invention, even in the case where the cristobalite is used as the siliceous raw material, under the condition that the specific conditions are limited, the conventional method is used. It was found that a composition similar to that of water glass can be made. And, it is known that it can be used in the same way as conventional water glass for applications in a certain field. The impurities in the aqueous solution of sodium silicate are alumina (A
l ₂ O ₃ ) 1.5% or less, iron content (Fe ₂ O ₃ ) 0.5%
Below, lime (CaO) 0.3% or less, magnesia (M
gO) is 0.1% or less.

These conditions are set according to the molar ratio (S / N) of SiO _{2 in} the raw material cristobalite and Na ₂ O in caustic soda, and the solid / water ratio in the slurry (hereinafter referred to as "slurry ratio"). ), Reaction treatment temperature, reaction time, etc. Below, including these setting conditions, a method of producing water glass using cristobalite as a siliceous raw material will be described.

First, the collected Cristobal rock is
It is crushed during use, but its particle size is preferably 1 to 3 mm. If it is 3 mm or more, the reactivity is not good, but further pulverization to 1 mm or less does not affect the reactivity or the like. Put this Cristobal rock powder into a caustic soda solution,
This is stirred and dispersed to form a slurry. in this case,
Silica in Cristobal Rock Powder and Na _{2 in} Caustic Soda
It is an essential requirement to limit the molar ratio (S / N) of O to the range of 2 to 4. If the S / N value is less than 2, devitrification occurs when the solution is concentrated and handling is difficult, which is not preferable. Further, if this exceeds 4, the ability to dissolve the cristobalite powder is insufficient. Slurry ratio is 1.0
~ 0.1. When it exceeds 1, the concentration becomes too high to allow the reaction to proceed sufficiently. Further, if the slurry ratio is less than 0.1, the amount of water will be unnecessarily large and extra energy will be required.

Such a slurry is heated and stirred in an ordinary rotary stirring type autoclave to be reacted. In this case, the treatment temperature can adopt a wide range of 80 to 240 ° C. The lower limit is 80 ° C., and the temperature of the conventional hydrothermal synthesis of water glass is usually 160 to 170 ° C. industrially. Therefore, the lower limit temperature of 80 ° C. in the present invention allows a considerably low temperature reaction. It turns out that By carrying out the low temperature reaction in this manner, it is naturally possible to greatly save energy consumption. Therefore, in the present invention, it is possible to sufficiently manufacture water glass with a heat source such as hot waste water from a factory, boiler waste water, and geothermal water.

The upper limit of the reaction temperature is 240.degree. C., which is much higher than the conventional temperature. The more preferable temperature range in the above temperature range is 120 to 240 ° C.
The reaction temperature in the present invention may be determined within the above range in relation to other conditions such as the above S / N molar ratio, slurry concentration, reaction time and the like.

The reaction time in the autoclave is 30 minutes to 2
Time. This reaction time must be maintained after reaching the above temperature. If this is less than 30 minutes, the reaction is insufficient. Also, the upper limit of the reaction time is 2
If the reaction time is less than this time, the alumina in the raw material Cristobal rock is analsimic (an
This is because it can be easily separated from the filtrate by being fixed as the (alcime).

When the reaction time exceeds 2 hours, the above-mentioned anal sim produced by fixing alumina is
Further goes low molar zeolite _(SiO 2 / _Al 2 _{O 3} molar ratio). When the low-mol zeolite is produced by the hydrothermal reaction, the low-mol zeolite in the form of fine particles is mixed into the filtrate during the subsequent filtration with the reaction product, which makes it impossible to separate good water glass.

Furthermore, in the present invention, by setting the reaction time to 30 minutes to 2 hours as described above, it is found that the alumina contained in the most in Cristobal rock for the first time is efficiently recovered as an anal sim. It has been put out.

In the conventional water glass manufacturing method, the reaction time for hydrothermal synthesis in an autoclave is usually 6 to
Although it was 10 hours, by setting the upper limit to 2 hours as in the present invention, it is possible to fix and separate alumina impurities, but this method also greatly saves energy consumption. .. After the reaction as described above, this is filtered by a conventional method to obtain water glass.

Industrial water glass is JIS K 1408.
There are "silicic acid soda _{Na 2 O · nSiO 2 · xH} 2 O " standards, S / N molar ratio of 1 to 3 items, are each approximately 2.1,2.4,3.1. Further, there is no direct regulation on the trace chemical components to be mixed, but from other literatures etc., Al ₂ O ₃ is 0.2 to 0.7% by weight, CaO and M.
Although it is considered that gO is 0.02% by weight or less and Fe ₂ O ₃ is 0.02% by weight or less, as shown in the following experimental examples and examples, the water glass obtained by the present invention is JIS
Even those containing water glasses Nos. 1 to 3 and out of them can be sufficiently put into practical use. Below, an experimental example is shown and further explained. Experimental example Table 2 shows the main chemical composition of the cristobalite used.

[0018]

[Table 2] The above raw materials, caustic soda, and water were designated as No. 3 in Table 3. The composition was designed as 1 to 4 and stirred. The S / N molar ratio and the slurry ratio of this blended raw material are shown in the right column of the table. The S / N molar ratio of the blended raw material is within the range of 1.25 (No. 1), which is less than 2, and 2 to 4 of the molar ratio, in consideration of the molar ratios of 2 to 4 of the present invention. (No. 2 to 4) was performed. Regarding the slurry concentration, it is possible to stir uniformly,
Moreover, the value is set so that water glass can be obtained efficiently.

In the experiment, the raw material slurry was put in a rotary stirring type autoclave (φ17 mm × length 100 mm) for 80
℃, 120 ℃, 140 ℃, 160 ℃, 200 ℃, 24
In carrying out the reaction at each temperature of 0 ° C., heating, stirring were carried out for 30, 60 and 120 minutes in each case. The reaction solution obtained here was filtered with an aspirator using 5C filter paper to be separated into a filtrate and a residue. The SiO ₂ / Na ₂ O molar ratio of the filtrate (water glass) obtained here was as shown in Table 4. Further, in the same table, the ratio SiO ₂ / Na ₂ O molar ratio in the filtrate calculated from the residue when the caustic soda used was completely reacted and Al ₂ O ₃ was fixed as an analsim was shown. ..

[0020]

[Table 3]

[0021]

[Table 4] Furthermore, in Table 5, among those shown in Table 4, 200 ° C, 6
The chemical composition of the residue, the molar ratio of the components of the residue, and the reaction rate of the raw cristobalite were shown when the reaction was performed for 0 minutes.

[0022]

[Table 5] In order to produce sodium silicate efficiently and reproducibly from the raw materials, it is necessary to obtain the filtrate component as close as possible to the set S / N molar ratio. From the Cristobal rock shown in Table 2,
When the residual component is calculated assuming that all the alumina components are fixed as analcime and that Fe ₂ O ₃ , CaO and MgO are fixed by solid solution etc., it becomes 22.5% by weight based on the unit weight of the cristobalite. 87.9% by weight of the silica component will be eluted. The SiO ₂ / Na ₂ O molar ratio of the filtrate component in that case is 1.16, S / N = when the set molar ratio is S / N = 1.0.
It is calculated to be 1.97 for 2 and 2.93 for S / N = 3 and 4.14 for S / N = 4. However, the results of the experiment are shown in Table 4 above, and it can be seen that the higher the reaction temperature, the closer to the set molar ratio. As is apparent from this table, a more preferable processing temperature is in the range of 140 to 240 ° C. The fact that the molar ratio of the actual filtrate is lower than the set molar ratio is understood to be because the above-mentioned residue composition contains not only the anarsime mineral but also the unreacted cristobalite.

This is considered to be clear from the residual components shown in Table 5. That is, in terms of the molar ratio of the residual components, if only the original analcime is used, Na ₂ O: Al ₂ O ₃ : Si
It should be clear from the fact that although the molar ratio of O ₂ should be 1: 1: 4, the ratio of SiO 2 gradually increases over the set molar ratios of 1 to 4.

In Table 4, the compounding molar ratio is 4.0,
When the temperature is 200 ° C. or higher, the solid phase of the slurry may adhere to the wall of the tube, and the S / N molar ratio of the filtrate is low.

Tables 6 to 11 show the above experiments in more detail. That is, when the treatment temperature and the treatment time (holding time) are determined in correspondence with the set molar ratio of S / N, alumina, iron, lime and magnesia contained in the filtrate (water glass) have good reproducibility. It shows that it can be within the range.

That is, Tables 6 to 11, as described above,
Setting the molar ratio to 1.0, 2.0, 3.0, 4.0,
80 ℃, 120 ℃, 140 ℃, 160 ℃, 200 ℃, 2
In carrying out the reaction at each temperature of 40 ° C., the reaction was carried out for each of the above temperatures at the time of 30 minutes, 60 minutes, and 120 minutes, respectively. In this case, the filtrate molar ratio, the residue (w
t%), the chemical composition (wt%) of the filtrate, and the presence or absence of devitrification when the filtrate is heated and concentrated to a viscosity of about 1000 poise.

[0027] Incidentally, the chemical composition of the filtrate (wt%) is, ^Si ++++ dissolved in the ^filtrate, Na ^{+, Al} +++, Fe
^+++, respectively ^Ca ++, the ^{Mg ++} as the oxide S
iO _{2, Na 2 O,} and displayed as _{Al 2 O 3, Fe 2 O} 3, CaO and MgO, it is intended as a% by weight relative to the total weight of these oxides.

[0028]

[Table 6]

[0029]

[Table 7]

[0030]

[Table 8]

[0031]

[Table 9]

[0032]

[Table 10]

[0033]

[Table 11] As shown in Tables 6 to 11, regardless of the S / N molar ratio,
Within the treatment time of 60 minutes, within the treatment temperature range of 80 to 140 ° C., the alumina component keeps its elution amount in the filtrate as it is or gradually increases. This means that the precipitation and growth of zeolite minerals such as analcime are in progress, indicating that there is a tendency for the alumina component to be mixed in the filtrate. It can be seen that when the treatment time reaches 60 to 120 minutes, the alumina component in the filtrate decreases, especially when the set molar ratio is 2 to 3.
Even in this case, it can be seen that the effect is particularly large in the holding temperature range of 120 to 140 ° C.

When the treatment temperature is 80 to 120 ° C., the amount of alumina eluted is small and it seems that there is a good effect, but the reaction rate is not sufficient and the formation of sodium silicate solution is efficient in terms of productivity. Absent. As for the elution of the iron component into the sodium silicate solution, the elution amount increases as the treatment temperature rises in the range of 200 to 240 ° C, but at a temperature of 200 ° C or less, it should be approximately 0.2 to 0.3% or less. Can be done. The elution of calcium and magnesia into sodium silicate can be reduced to such a level that practically no problem occurs.
It is effective at processing temperatures above ℃.

The present invention will be further described below with reference to examples.

Example 1 Cristobalite having the chemical composition shown in Table 12 was used, and Table 13 was used.
The raw materials shown below were blended.

[0037]

[Table 12]

[0038]

[Table 13] The reaction temperature was 200 ° C. and the reaction time was 60 minutes. Table 14 shows the S / N molar ratio of the filtrate, the residue, and the chemical composition of the filtrate in this case. Table 14 also shows the presence or absence of devitrification when the filtrate was heated and concentrated to increase its viscosity to about 1000 poise.

[0039]

[Table 14] As shown in Table 14, even when using cristobalite which is a low siliceous raw material, it is possible to set alumina in the filtrate to 0.09 to 0.56% at a set molar ratio of 2.0 to 3.4. I can. Even when the filtrate was heated and concentrated to increase its viscosity to about 1000 poise, there was no devitrification. Example 2 Using cristobalite of good quality chemical composition shown in Table 15,
The raw materials shown in Table 16 were blended.

[0040]

[Table 15]

[0041]

[Table 16] The reaction temperature was 200 ° C. and the reaction time was 60 minutes. Table 17 shows the S / N molar ratio of the filtrate, the residue, and the chemical composition of the filtrate in this case. In addition, in Table 17, the filtrate was heated and concentrated to about 1
The presence / absence of devitrification when the viscosity is increased to 000 poise is also shown.

[0042]

[Table 17] As shown in Table 17, when high-quality cristobalite is used, the set molar ratio is 2.2 to 3.7, and the alumina in the filtrate can be 0.05 to 0.20%. Further, even if the filtrate was concentrated by heating to increase the viscosity to about 1000 poise, neither devitrification occurred. Example 3 Cristobalite having the chemical composition shown in Table 18 was used, and Table 19 was used.
The raw materials shown below were blended. The reaction has an internal volume of 1 liter,
It was carried out in an autoclave equipped with a magnetic stirrer. Table 2
0 shows the filtrate component.

[0043]

[Table 18]

[0044]

[Table 19]

[0045]

[Table 20] Temperature rise is 90 minutes from room temperature to 200 ° C, holding time is 60
And the temperature was lowered for 240 minutes. The rotation speed of the stirring blade in the autoclave was 100 r. p. m. And Set molar ratio 2.
The filtrate molar ratio was 3 to 2.4, and the filtrate molar ratio was 1.86 to 2.18. Residue is about 50%, elution of alumina and iron is 0.0
It was 5 to 0.6 and 0.00 to 0.98.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takehiko Moriya 2-12-12 Fukuda-cho, Miyagino-ku, Sendai-shi, Miyagi Prefecture (72) Inventor Koichi Sakiyama 3-85-6, Mutsukawa, Minami-ku, Yokohama-shi, Kanagawa Yokohama Park Town g-908 (72) Inventor Shuji Yuda 2-35-1 Kitanakagusuku, Izumi-ku, Sendai City, Miyagi Prefecture

Claims (1)

[Claims] 1. SiO ₂ in the cristobalite powder when producing an aqueous sodium silicate solution by heating and reacting the cristobalite powder with caustic soda in an autoclave.
And the caustic soda Na ₂ O molar ratio of 2 to 4, the slurry solids / water ratio of 1.0 to 0.1, and the treatment temperature of 80 to 24.
A method for producing an aqueous solution of sodium silicate, which is characterized in that the reaction time is 0 ° C. and the reaction time is 30 minutes to 2 hours after reaching the treatment temperature.