JPS61191515A - Production of hydrated silicic acid - Google Patents

Abstract

PURPOSE:To produce high-purity porous hydrated silicic acid in large quantities by feeding a raw material of liquid hydrated silicate into a mineral acid phase and by causing a condensation reaction of silanol group to start. CONSTITUTION:The liquid raw material of hydrated silicate (example: water- glass) composed of 50-72wt% moisture content and 21-37wt% Si content is dropped from a nozzle onto the buffer solution phase (example: n-pentane) formed on a mineral acid phase, then is fed into the phase of mineral acid having the concentration of 1-36 normal at a room temp. -100 deg.C through the buffer solution phase, the condensation reaction is caused to take place from the surface of the raw material, and the porous hydrated silicide acid is formed. Thereby, the choking of a raw material-feeding port and the generation of the raw material of dumpling-like hydrated silicic acid can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydrated silicic acid, and more particularly to a method for producing hydrated silicic acid suitable for mass production of high-purity hydrated silicic acid.

[Conventional technology]

Currently, solar energy is attracting attention as a next generation energy resource, and research on solar power generation is progressing.

In particular, silicon batteries are considered the most promising, and there is an urgent need to improve their quality and develop inexpensive manufacturing methods.

Because the silicon used in silicon solar cells must be highly pure, silicon manufactured for semiconductors is currently used. Therefore, the silicon raw material itself is very expensive, which increases the cost of solar cells.

Therefore, attempts have been made to reduce high-purity silicon dioxide using high-purity carbon without contamination to produce silicon that can be used in solar cells. This method has the advantage of greatly reducing energy and cost compared to the method of manufacturing silicon for semiconductors in which metallic silicon is first converted into trichlorosilane and then purified and then reduced.

However, as the natural high-purity silicon dioxide used in this method, there are only some quartz crystals produced as high-quality products, and the amount of resources is limited. For the production of large quantities of solar cells, there is a need for a technology that can purify the abundant silica sand and other low-purity silicate raw materials and convert them into high-purity silicon dioxide.

A method is known in which silica gel is obtained by reacting a partially alkali silicate (commonly known as water glass) with an acid.

[The gap that the invention attempts to solve]

The silica gel is made of highly pure SiO2,
Although it is possible to use such silica gel for the above-mentioned direct reduction, these silica gels usually have a purity of 5i02 of 9.
Even if it is said to have a high purity, it is only about 90% by weight, and it could not be used in the production of silicon for solar cells by the above-mentioned direct reduction in its original state.

This is the amount of 5 contained in silica gel in normal silica gel.
This is due to the fact that impurities other than i02 (such as Na++Cja2+yHg2+) are difficult to escape into the external cleaning solution of silica gel, making it difficult to achieve high purity.

An object of the present invention is to provide a method for producing high-purity hydrated silicic acid that can be used for manufacturing silicon for solar cells, etc. from silicate raw materials with poor purity, and in particular, to provide a method that can be mass-produced.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a liquid hydrated silicate raw material by causing a synthesis reaction of silanol groups from the mineral acid phase and the surface of the raw salt raw material through the raw material supply port. A method for producing hydrated silicic acid is used in which the hydrated silicic acid is changed to porous hydrated silicic acid.

As the buffer liquid provided between the mineral acid phase and the raw material supply port, any liquid that does not easily react with or mix with mineral acids and hydrated silicate can be used, even if it has a specific gravity lower than that of mineral acids. It doesn't matter if it's big. Among them, a buffer liquid with a specific gravity smaller than that of the mineral acid is used. By providing a buffer liquid phase above the mineral acid, liquid hydrated silicate raw material (hereinafter referred to as raw material) is supplied from the buffer liquid phase to the mineral acid phase by its own weight. This is preferable because it can be done.

Examples of buffer liquids having a specific gravity lower than that of mineral acids include organic liquids such as n-pentane and n-hexane.

A method for supplying a liquid hydrated silicate raw material to a mineral acid phase through a buffer liquid phase is as follows: (a) A buffer liquid phase is provided above the mineral acid phase (1) The raw material is dropped into the buffer liquid phase from a nozzle or the like.

(11) The raw material is poured into the buffer liquid phase using a toy or nozzle.

1ii1 Immerse the nozzle into the buffer liquid phase and pour the raw material through the nozzle.

(bl A buffer liquid phase is provided below or to the side of the mineral acid phase (
1) Squirt or extrude raw material from a nozzle immersed into a buffered liquid phase.

Among the above methods, the method ((transformation)-(iii)) is preferred because it allows accurate control of the shape of the raw material fed into the mineral acid.

The minimum size for the shape of the raw material supplied into the mineral acid is Oμm.
~/Qtmn (more preferably minimum dimension 100μ)
m to 2 ura) is preferable in order to efficiently obtain high purity silicon dioxide.

Minimum dimensions here! The shape having Qμmy/Qtfa means, for example, if it is a plate-like body or a 7-lake shape, the thickness is jOμm.
The shortest distance from the surface layer of the center of the object, such as ~/Qtmn, the side or diameter of a square or round bar is 50 μm ~/Qtnyn, and the short side of the particle is jo μm ~/Qmm if it is a grain shape. refers to the shape of an object with a diameter of 2jμm-%3mm.

Here, the raw material from which porous hydrated silicic acid is obtained by adding it to mineral acid has a water content of 50 to 72 wt% of the total weight,
and the 5i02 content is 21 to 37'li't of the total weight,
% is preferred.

Moisture content is 7! wt% or more than 5i02
When the content is less than 37 W't%, the hydrated silicate raw material is dissolved in the mineral acid, resulting in porous silicon dioxide, or when the 5i02 content is more than 37 W't%, and alkaline earth metals. Glass using such as (R20-R
O-RnOm-Si02 glass) can be used, and alkaline silicates containing a large amount of water, usually called water glass, are preferably used. These alkali silicates contain less alkaline earth metals, which are relatively difficult to clean.
It is preferable to obtain hydrated silicic acid with a purity of at least 50% by weight, and is also preferable because it is easily available. As the alkali silicate, sodium silicate is preferable from an economical point of view, and a 5i02/Na2O ratio in the range of 2 to 3 J is preferable in terms of ease of melting when preparing the alkali silicate.

The mineral acids used in the present invention include hydrochloric acid, sulfuric acid, nitric acid, and mixed solutions thereof. Here, sulfuric acid and nitric acid are preferred because they are highly effective in extracting and removing the elements Ti and Zr contained in the hydrated silicate raw material. Among these, sulfuric acid is preferable in terms of preventing corrosion of metal instruments and preventing deterioration of the working environment, since the vapor pressure of the gas is lower than that of nitric acid even as a highly concentrated liquid. The concentration of mineral acid is /~ in the case of hydrochloric acid
/2N, nitric acid: /~/Hiroshi, sulfuric acid, 1-3N, mixed acid: /~36N, and sulfuric acid with 6~/rN is preferred. These mineral acids are kept at room temperature ~/00'C
used as the temperature of

As for the ratio of the mineral acid and the raw material added to the mineral acid, it is preferable to use 750 parts by weight or more of the mineral acid per 100 parts by weight of the raw material, taking into consideration the amount of the produced hydrous silicic acid and the mineral acid.

The raw material is preferably supplied to the mineral acid in the form of a minimum dimension of 50 μm-fifi, but plate-like bodies of less than 30 μm,
In granular, rod-shaped, and fibrous bodies, the silicon dioxide produced becomes small particles, resulting in poor filterability/Qmm.For larger plates, granules, and rod-shaped bodies, the silicon dioxide produced becomes large particles, making it difficult to clean. It takes time.

[For production]

According to the present invention, since there is a buffer liquid phase between the mineral acid and the raw material supply port, the raw material can be supplied without bringing the raw material supply port into contact with the mineral acid. For this reason, when raw materials were supplied with the raw material supply port in contact with mineral acid, (a) hydrous silicic acid was generated around the raw material supply port, reducing the effective diameter of the raw material supply port. A phenomenon that blocks the raw material supply port.

(bl) A phenomenon in which hydrated silicic acid grows at the raw material supply port, disrupting the flow of raw materials and generating dumpling-shaped raw material lumps.

Such inconveniences can be avoided.

Therefore, in order to avoid the above-mentioned inconvenience, the present invention provides a flow direction of the raw material that is conventionally required, a direction approximately the same as the flow rate, and a flow rate of 7.
There is no need to carry out special operations such as a method of extruding the raw material through a nozzle into a mineral acid having a speed of ~20 times (method described in Japanese Patent Application No. 1982-6/7'12).

〔Example〕

2j% sulfuric acid Il in a long and slender cylindrical container with a volume of 1
1 of Kn-pentane was added thereto. Since n-pentane has a lower specific gravity than sulfuric acid and does not react with sulfuric acid, a buffer liquid phase was formed on the sulfuric acid.

After that, a hole of diameter Q, 7ql1m is drilled at j; run pitch /
! A separate shower-like nozzle was inserted into the buffer liquid phase near the interface between the buffer liquid phase and the mineral acid layer so that the raw material flow direction from the nozzle was approximately vertical. Here, making the flow direction of the raw material from the nozzle almost vertical prevents the inconvenience that the flow direction of the raw material flowing out from the nozzle is changed by gravity and the raw materials come into contact with each other and form a larger raw material shape. In addition, even when the jetting speed from the nozzle is reduced, it is difficult to form a dumpling-shaped raw material, so it is preferred.

From the nozzle immersed in the buffer liquid phase, JIS standard No. 3 water glass (moisture content Otsu 0 to 4 Jwt%) was used.

The 5i02 water content 2g-30wt%) was extruded into the buffered liquid phase using pressure from a roller pump for approximately 7 minutes (oog per molecule). At this time, the outflow velocity at the nozzle outlet was estimated to be approximately 90 cm/SeC.

When the water glass was pushed out into the organic layer through the nozzle, it turned into fibers with a diameter of about 7 and sank into the mineral acid layer.

At this time, the nozzle outlet is extremely stable, as phenomena such as clogging of the nozzle outlet and the formation of lump-shaped water glass due to water glass wrapping around the nozzle outlet, which occur when directly submerged into the mineral acid layer at the nozzle outlet, do not occur. Water glasses were being supplied.

The water glass supplied in mineral acid in the form of fibers becomes porous fibrous hydrated silicic acid through the condensation reaction, and the obtained 1R fibrous hydrated silicic acid is taken out and 7 hydrochloric acid/l of firewood is added and treated in the same manner. The heating washing operation was performed twice.

The fibrous hydrated silicic acid thus obtained was transferred to a centrifugal filter, and while being dehydrated, pure water was added and washed until the pH of the filtrate was around d,j.

The solid content was taken out and dried at O''C for 6 hours to obtain silicon dioxide/!09 with a water content of about 3%.

The amount of impurities in this hydrated silicic acid was as shown in Table 1.

Table l (PPM) The hydrated silicic acid obtained in this example was prepared using a conventional method, for example, in a mineral acid having a flow rate approximately the same as the flow direction and flow rate of the liquid hydrated silicate raw material, and a flow rate 7 to 20 times higher. The hydrated silicic acid had a purity approximately equal to or higher than that of the hydrated silicic acid prepared by pouring into the silica.

(Effects of the Invention) According to the present invention, a buffer liquid phase is provided in contact with the alkali acid phase, and the liquid hydrated silicate raw material is supplied through the buffer liquid phase. No hydrous silicate raw material is generated.Hence, the production of hydrous silicic acid can be carried out with the raw material supply port and the mineral acid kept stationary.

Claims (3)

[Claims] (1) A liquid hydrated silicate raw material is supplied into the mineral acid phase from the raw material supply port, and a condensation reaction of silanol groups is caused from the surface of the liquid hydrated silicate raw material to make the liquid hydrated silicate raw material porous. A method for producing hydrated silicic acid, which is characterized in that a buffer liquid phase is provided between a raw material supply port and a mineral acid phase. (2) The method for producing hydrated silicic acid according to claim 1, wherein the liquid hydrated silicate raw material is extruded through a nozzle provided in the buffer liquid phase. (3) the buffer liquid phase is n-pentane and/or n-
The method for producing hydrated silicic acid according to claim 1 or 2, wherein hexane is used.