JPH0454618B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing hydrated silicic acid, and particularly to a method for producing hydrated silicic acid suitable for mass production of highly purified hydrated silicic acid. [Prior Art] Currently, solar energy is attracting attention as a next-generation energy resource, and research on solar power generation is progressing. In particular, silicon solar cells are considered to be the most promising, and there is an urgent need to improve their quality and develop inexpensive manufacturing methods. The silicon used in silicon solar cells is required to be highly pure, so silicon produced 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. On the other hand, a method is known in which silica gel is obtained by reacting an alkali silicate (commonly known as water glass) with an acid. [Problem to be solved by the invention] The silica gel is made of highly pure SiO ₂ , and it is possible to use such silica gel for the above-mentioned direct reduction, but these silica gels usually have a SiO ₂ purity of 99.5wt. %, and even those that are said to have high purity have a purity of about 99.95 wt %, and in that state, they could not be used in the production of silicon for solar cells by the above-mentioned direct reduction. This is because with ordinary silica gel, impurities other than SiO ₂ contained in the silica gel (Na ⁺ , Ca ²⁺ , Mg ²⁺ , etc.) are difficult to escape into the silica gel external cleaning solution.
This was due to the difficulty of achieving high purity. An object of the present invention is to provide a method for producing high-purity hydrated silicic acid that can be used in the production of silicon for solar cells from a silicate raw material with poor purity, particularly a method that can be mass-produced. [Means for Solving the Problems] In order to solve the above problems, the present invention supplies a liquid hydrated silicate raw material from a raw material supply port to a buffer liquid provided between the mineral acid phase and the raw material supply port. A liquid hydrated silicate raw material is supplied into the mineral acid phase through the buffer liquid phase, and a condensation reaction of silanol groups is caused from the surface of the liquid silicate raw material within the mineral acid phase to form a liquid. A method for producing hydrated silicic acid is used in which a porous hydrated silicate raw material is changed into 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 having a specific gravity smaller than that of 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 transferred from the buffer liquid phase to the mineral acid phase by its own weight. This is preferable because it can be supplied to As a buffer liquid with a specific gravity smaller than that of mineral acids, n-
Examples include organic liquids such as pentane and n-hexane. The method of supplying the liquid hydrated silicate raw material to the mineral acid phase through the buffer liquid phase is as follows: (a) The buffer liquid phase is provided above the mineral acid phase () The raw material is dropped into the buffer liquid phase from a nozzle or the like. () Pour the raw material into the buffer liquid phase using a toy or nozzle. () Dip the nozzle into the buffer liquid phase and pour the raw material through the nozzle. (b) A buffered liquid phase is provided below or to the side of the mineral acid phase. () The raw material is ejected or forced through a nozzle immersed in the buffered liquid phase. Examples of methods include: Among the above methods, methods (a) to () are preferred because they allow accurate control of the shape of the raw material fed into the mineral acid. The smallest size for the shape of the raw material fed into the mineral acid
50μm to 10mm (more preferably minimum dimension
100 μm to 2 mm) is preferable in order to efficiently obtain high purity silicon dioxide. Here, the shape with the minimum dimension of 50 μm to 10 mm is
For example, if it is plate-like or flake-like, the thickness is
50 μm to 10 mm, if it is a square bar or round bar, the side or diameter is 50 μm to 10 mm, if it is a particle shape, the short side of the particle is
Refers to the shape of an object whose shortest distance from the surface layer of the center of the object is 25 μm to 5 mm, such as 50 μm to 10 mm. 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 72wt of the total weight.
%, and the _SiO2 content is 21~37wt of the total weight
% is preferred. Moisture content is more than 72wt% or SiO ₂
If the content is less than 21 wt%, the hydrated silicate raw material will be dissolved in the mineral acid, making it difficult to obtain porous silicon dioxide, and if the water content is less than 50 wt% or the SiO ₂ content is 37 wt%. When it becomes more,
It is difficult to become a liquid with fluidity. Glass containing alkali metals and alkaline earth metals (R ₂ O-RO-RnOm-SiO ₂ glass) can be used as a silicate raw material for hydrated silicate, but glass containing a large amount of water is usually called water glass. Alkali silicates are preferably used. These alkali silicates are preferable for obtaining hydrated silicic acid with a purity of 99.99 wt % or more because they contain less alkaline earth metals, which are relatively difficult to clean, and are also preferable because they are easily available. As the alkali silicate, sodium silicate is economically preferable, and when preparing the alkali silicate, a SiO ₂ /Na ₂ O ratio in the range of 2 to 3.5 is preferable because it is easy to melt. 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 acids is 1 to 12 in the case of hydrochloric acid.
1 to 14 N for nitric acid, 1 to 36 N for sulfuric acid, 1 to 36 N for mixed acids, and 6 to 18 N for mixed acids.
Standard sulfuric acid is preferred. These mineral acids are available at room temperature to 100%
Used as temperature in °C. The ratio of mineral acid to the raw material added to the mineral acid is determined by considering the amount of hydrated silicic acid and mineral acid produced.
It is preferable to use 150 parts by weight or more of mineral acid per 100 parts by weight. The raw material is preferably supplied to the mineral acid in the form of a minimum dimension of 50 μm to 10 mm, but plate-shaped bodies of less than 50 μm,
In the case of granular, rod-shaped, and fibrous bodies, the silicon dioxide produced becomes small particles, resulting in poor filtration performance.For plates, granules, and rod-shaped bodies larger than 10 mm, the silicon dioxide produced becomes large particles, so it takes time to clean. It takes. [Function] 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 reduces the amount of raw materials or blocks the raw material supply port. (b) 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 disadvantages, the present invention proposes a method of extruding the raw material from a nozzle into mineral acid in a direction that is approximately the same as the flow rate of the raw material and at a speed that is 1 to 20 times the flow rate, which was conventionally required. Patent application 1986-61742
There is no need to perform special operations such as the described method. [Example] 25% sulfuric acid 4 was placed in a long and narrow cylindrical container with a volume of 5, and then 0.5 of n-pentane was added.
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. Then, make 15 holes with a diameter of 0.794 mm at a pitch of 5 mm.
A separate shower-like nozzle was inserted into the buffer liquid phase near the interface between the buffer liquid phase and the mineral acid phase 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. ,
Further, 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 a nozzle immersed in the buffered liquid phase;
JIS standard No. 3 water glass (moisture content 60-63wt%,
500 g of SiO ₂ (water content 28-30 wt%) was forced into the buffer liquid phase over approximately 1 minute (500 g/min) using pressure from a roller pump. At this time, the outflow velocity at the nozzle outlet was estimated to be approximately 90 cm/sec. When the water glass was extruded into the organic layer through the nozzle, it became fibrous with a diameter of about 1 mm and sank into the mineral acid layer. At this time, the nozzle outlet was extremely stable, as phenomena such as clogging of the nozzle outlet and the formation of lump-shaped water glass due to water glass getting around the nozzle outlet, which occur when the nozzle outlet is directly submerged in the mineral acid layer, did not occur. Water glasses were being supplied. The water glass supplied in mineral acid in fibrous form became porous fibrous hydrated silicic acid through the condensation reaction. , heat to 90℃, and
It kept time. After that, let it cool and remove the sulfuric acid.
1 portion of 20% hydrochloric acid was added and the same 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 reached around 4.5. The solid content was taken out and dried at 150° C. for 6 hours to obtain 150 g of silicon dioxide with a water content of about 3%. The amount of impurities in this hydrated silicic acid was as shown in Table 1.

〔Effect of the invention〕

According to the present invention, a buffered liquid phase is provided adjacent to the mineral acid phase, and the liquid hydrated silicate raw material is supplied through the buffered liquid phase. No raw materials are generated. Therefore, hydrous silicic acid can be produced with the raw material supply port and the mineral acid kept stationary.

Claims (1)

[Claims] 1. A liquid hydrated silicate raw material is supplied into the mineral acid phase from a raw material supply port, and a condensation reaction of silanol groups is caused from the surface of the liquid hydrated silicate raw material to form the liquid hydrated silicate. 1. A method for producing hydrated silicic acid that converts a raw material into porous hydrated silicic acid, the method comprising providing a buffer liquid phase 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 method for producing hydrated silicic acid according to claim 1 or 2, wherein the buffer liquid phase is n-pentane and/or n-hexane.