JPS593404B2 - Method for producing alkali silicate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an alkali silicate, particularly a method for increasing the silica ratio (Si02/Na20) when producing an alkali silicate by reacting silica stone with a caustic alkali more than the wet method. This is related to.

The production methods for alkali silicates such as sodium silicate are roughly divided into dry methods and wet methods.

In both cases, silica stone and caustic alkali are used as raw materials, but in the dry method, a flame is directly blown onto these raw materials to cause them to melt and react, and this method is superior to the wet method. Although this method has the advantage of having high reactivity and making it easy to increase the silica ratio, it requires a large amount of heat and is not a desirable method from the viewpoint of energy conservation, which has become a major concern in various fields in recent years.

On the other hand, the wet method can obtain alkali silicate with less energy than the dry method;
In stage reactions, the silica ratio tends to be somewhat lower.

In view of this, the present inventor conducted various studies and examinations with the aim of improving the reaction rate between silica stone and caustic alkali, thereby increasing the silica ratio. It has been found that the above object can be achieved by pulverizing silica stone to a predetermined particle size in order to improve reactivity, by performing the pulverization in the presence of caustic alkali.

Thus, in the present invention, when obtaining an alkali silicate by digesting silica stone and a caustic alkali in an autoclave, the silica stone serving as a raw material is ground in advance to a particle size of 1 to 500 μ in the presence of an aqueous caustic alkali solution without heating. An object of the present invention is to provide a method for producing an alkali silicate.

In the present invention, there are no particular restrictions on the silica stone used, but
For example, crystalline silica stone that is inherently difficult to react, such as α-cristobalite crystal in α-quartz, is particularly suitable.

Also, the amount of caustic alkali used to crush silica stone can be used in the amount required for the reaction in the autoclave later, or can it be used in a smaller amount?
In order to improve milling efficiency and reactivity, it is more effective to use the entire amount required for the reaction.

The particle size of the silica stone to be crushed is approximately 1 to 5 in order to effectively improve the reaction rate and silica ratio in the autoclave.
It is appropriate to crush the powder to about 00μ, preferably about 1 to 80μ.

To carry out such pulverization, a pulverizer such as a ball mill, a vibration mill, or a colloid mill can be used.

Furthermore, if the concentration of the caustic alkali used for pulverization is too high or if it is in a solid state, the caustic alkali will not be distributed throughout the silica stone, making it impossible to achieve the intended purpose of the present invention.

For this reason, it is appropriate to use an aqueous solution whose concentration is usually about 5 to 50% by weight.

The reason why the reaction rate improves when the method of the present invention is adopted is not necessarily clear, but the reaction rate of the method of the present invention is higher than that of a method in which pre-pulverized silica stone is sprinkled with caustic alkali. From the areas where improvement is seen, the silica fine powder and caustic alkali present in the pulverized product are mixed during the pulverization process, and this mixture sufficiently adheres to the surface of the granular silica stone, which causes the silica to react during the cooking reaction in the autoclave.
It seems to promote the reaction between silica stone and caustic alkali.

Thus, in the present invention, the silica stone crushed to a predetermined particle size is
The mixture is introduced into an autoclave together with caustic alkali, and additional caustic alkali is added as required, and then digested.

Cooking is carried out at a pressure of 3 to 30 kFi/cr/l and a temperature of 130 to
Appropriately, the heating time is 1 to 10 hours at 240°C.

If these conditions are deviated from, it is not preferable because a sufficient reaction rate may not be obtained, a greater effect may no longer be expected, or energy will simply be wasted.

Among these ranges, it is particularly preferable to use a reaction time of 1 to 5 hours at a pressure of 8 to 20 kg/cm and a temperature of 170 to 220° C., since the highest reaction rate can be expected most efficiently.

When the method of the present invention is adopted, the ratio of silica stone and caustic alkali (calculated as Na20) used as raw materials is
O2 minutes 10 minutes car 00 parts by weight Na2010 to maximum 33.
2 parts by weight is employed, and the silicate ratio of the alkali silicate thus obtained can be as high as 2.8, and the reaction rate can also be as high as 93 factors.

Of course, if it is desired to obtain an alkali silicate having a higher silicate ratio than the above, a predetermined amount of a reactive silicic acid raw material such as by-product silica, amorphous silicic acid such as silica gel, cristobalite, opalite, etc. may be used. , the reaction may be carried out according to a conventional method.

The caustic alkali used in the present invention is usually caustic soda, but also alkali metal hydroxides such as caustic potash.

Next, the present invention will be explained by examples.

488 parts by weight of 2.07 kg of caustic soda were added to 2.4 kg of crystalline silica having α-quartz crystals with an average particle size of 80 to 100 mm.
It was introduced into a ball mill with a capacity of 14.6A, and the number of revolutions was 5.
Grinding was carried out at Or-p, m and a temperature of 30 to 50°C for 5 hours to obtain silica stone with an average particle size of 40 to 100 μm.

This was placed in an autoclave together with the above caustic soda and digested at a pressure of 18 kg/cnt and a temperature of 206° C. for 3 hours.

When the reaction product was analyzed according to the analysis method of JISK-1408, sodium silicate with S i02 / Na 20-2.8 was obtained, and the reaction rate was 93% with respect to the raw material silica stone.
Met.

For comparison, the same silica stone was dry crushed, only the same particle size as above was taken out, and the same amount of caustic soda was used to react in the same manner as above, and the silica ratio was as low as 2.4. Moreover, the reaction rate was as low as 80%.

Claims (1)

[Scope of Claims] 1. In obtaining an alkali silicate by digesting silica stone and a caustic alkali in an autoclave, the silica stone serving as a raw material is ground in advance to a particle size of 1 to 500 μ in the presence of an aqueous caustic alkali solution without heating. A method for producing an alkali silicate, which comprises: 2 The amount of caustic alkali used for crushing is 5i of silica stone.
2. The method according to claim 1, wherein the amount of Na is 2010 to 33.2 parts by weight per 100 parts by weight.