JPH049730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a silicon dioxide raw material, and particularly to a method for producing a high purity SiO ₂ raw material.

[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 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 produce silicon that can be used in solar cells by reducing high-purity silicon dioxide with high-purity carbon without contamination. 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. Therefore, there is a need for a technology to purify the abundant silica sand and other low-purity silicate raw materials and turn them into high-purity silicon dioxide that can be used in the production of solar cells.

In addition, as a general method for producing silicon dioxide raw materials,
A method of reacting a silicate of an alkali metal or alkaline earth metal with a mineral acid under conditions of a hydrogen ion concentration of 1.5 or less to precipitate hydrated silicic acid, and washing, drying, and calcining the precipitate of hydrated silicic acid (for example, as described in JP-A No. Showa 59-
54632) and a method for obtaining silica gel by reacting an alkali silicate with a mineral acid (e.g.
232911) etc. are known.

[Problems to be solved by the invention] However, although the above-mentioned silica gel and hydrated silicic acid are made of highly pure _SiO2 ,
In the case of silica gel, its purity is usually around 99.5wt%.
It is said to be highly pure, and in the case of hydrated silicic acid, it has a purity of about 99.95 wt%, and it could not be used as it is for producing silicon for solar cells by the above-mentioned direct reduction.

This is usually due to the fact that impurity components (Al, Fe, Ti, Zr, etc.) contained in silica gel or hydrated silicic acid are difficult to escape from the silica gel or hydrated silicic acid, and in particular, it is caused by a large amount of Ti components remaining. was.

[Means for solving problems]

In order to solve the above problems, the present invention aims to produce a silicon dioxide raw material by reacting an alkali silicate with a mineral acid to obtain silica gel or hydrated silicic acid, and then washing the obtained silica gel or hydrated silicic acid with a cleaning solution. In the method, the reaction and/or the washing are performed in a heated liquid containing hydrogen peroxide in an amount equivalent to or more than the amount of Ti contained as an impurity in the alkali silicate.

Specific ways to add hydrogen peroxide include adding and mixing hydrogen peroxide to an alkali silicate and/or mineral acid, and adding hydrogen peroxide to a mixture of an alkali silicate and mineral acid. Examples include a method in which hydrogen peroxide is used as the cleaning liquid or hydrogen peroxide is added to the cleaning liquid. Moreover, instead of adding hydrogen peroxide solution, hydrogen peroxide gas may be blown into each liquid, or metal peroxide may be added to the acidic solution and hydrogen peroxide may be generated by reaction.

As the alkali silicate, alkali metal and alkaline earth silicates can be used, but alkali silicates containing water and usually called water glass are preferably used. As the alkali silicate, sodium silicic acid is preferably included because it is economical, and those having a SiO ₂ /Na ₂ O ratio of 2 to 3.5 are preferred because they are easy to handle.

It is preferable to use sulfuric acid as the mineral acid, and the term "cleaning liquid" in the present invention refers to a liquid in which impurities such as Al and Ti are washed away, and includes not only pure water but also liquids such as mineral acids.

The amount of hydrogen peroxide to be present during the reaction and/or cleaning is determined by the amount of impurities (especially the amount of titanium) contained in the raw materials such as alkali silicates and mineral acids and the desired purity of the silicon dioxide raw material. It is necessary that hydrogen peroxide be present in an amount equal to or more than the amount of impurities (particularly the amount of titanium) in the material. When hydrogen peroxide is present in the solution during reaction or cleaning,
The reaction solution or cleaning solution is heated in order to quickly form a soluble complex with strong binding strength with metal impurities such as Ti and Al. As the liquid is heated, more of the hydrogen peroxide added reacts with impurity metals without being adsorbed by silica gel or hydrated silicic acid, creating more soluble complexes. This complex can be easily separated from silica gel and hydrated silicic acid using a washing solution of water or mineral acid, so that highly pure silicon dioxide can be obtained.

[Effect]

According to the present invention, since silica gel or hydrated silicic acid is brought into contact with hydrogen peroxide and reacted, the titanium compound in the silica gel or hydrated silicic acid becomes a soluble complex and flows out into the mineral acid or into the cleaning solution, and as a result, the silica gel or hydrated silica The content of titanium in the hydrous silicate decreases.

Hydrogen peroxide and titanium are thought to form a soluble complex in approximately equimolar ratios.

In addition, heating a liquid in the presence of hydrogen peroxide quickly forms a soluble complex with a strong bond between impurities such as metals such as Ti and Al and hydrogen peroxide.

〔Example〕

Example 1 JIS No. 3 water glass (moisture content 60-63wt%,
SiO ₂ content 28-30wt%) 400g and 480ml of pure water were mixed to prepare a sodium silicate aqueous solution. While stirring this solution, 80 ml of 25 wt% sulfuric acid was slowly added. The solution solidified into a gel during stirring. This gel was continued to be stirred to form a fine gel. 25wt% of the obtained gel
It was added to a mixture of 800 ml of sulfuric acid and 30 ml of 30 wt% hydrogen peroxide solution and held at 90°C for 60 minutes. The mixed solution of sulfuric acid and hydrogen peroxide solution turned yellow-orange due to the above treatment, indicating that impurities such as Fe and Ti in the silica gel were extracted into the mixed solution and the silica gel was washed. Thereafter, the silica gel was filtered off, transferred to 800 ml of 20 wt% hydrochloric acid, and maintained at 90°C for 30 minutes.

Thereafter, the obtained silica gel was separated by filtration, washed with water, and then dried.

Analysis of the composition of the silica gel obtained
Al2.0ppm, Ti3.3ppm, Fe less than 0.07ppm,
The Zr value was 1.3ppm.

Comparative Example 1 Silica gel was obtained by carrying out the same operation as in Example 1 except that hydrogen peroxide solution was not added to the sulfuric acid. The obtained silica gel was analyzed in the same manner as in Example 1.
Al2.0ppm, Ti13ppm, Fe less than 0.08ppm,
The Zr value was 1.4ppm.

When compared with the above examples, the Ti value is higher, and it can be seen that Ti has been removed in the examples.

Example 2 100 g of the above JIS No. 3 water glass was slowly poured into a mixed solution of 200 ml of 25 wt% sulfuric acid and 5 ml of 30 wt% hydrogen peroxide through a nozzle having a hole with a diameter of 0.794 mm.
The injected No. 3 water glass became string-like white hydrated silicic acid with a diameter of about 1 mm in the mineral acid.

Thereafter, this mixed solution and hydrated silicic acid were heated to 90°C and maintained for 30 minutes. Thereafter, the hydrated silicic acid was filtered off, washed with water, and then dried.

Analysis of the composition of the obtained hydrated silicic acid revealed that
The contents were 30ppm Al, 1.4ppm Ti, 2.6ppm Fe, and 2.6ppm Zr.

Comparative Example 2 Hydrous silicic acid was obtained by carrying out the same operation as in Example 2, except that hydrogen peroxide solution was not mixed with sulfuric acid. The composition of the obtained hydrated silicic acid was analyzed in the same manner as in Example 2, and it was found that Al45ppm, Ti25ppm, Fe3.1ppm,
Zr was 4.6ppm.

When compared with the above examples, the values of Al and Ti are higher, and it can be seen that Al and Ti are removed in the examples.

〔Effect of the invention〕

According to the present invention, the content of Ti contained as an impurity in the obtained silicon dioxide raw material can be reduced to 1/10 or less of the conventional amount by a simple operation, thereby easily producing highly pure silicon dioxide. raw materials can be obtained.

Claims (1)

[Claims] 1. A method for producing a silicon dioxide raw material in which silica gel or hydrated silicic acid is obtained by reacting an alkali silicate and a mineral acid, and then the obtained silica gel or hydrated silicic acid is washed with a cleaning liquid, in which the reaction and/or the washing is performed. A method for producing a silicon dioxide raw material, characterized in that the process is carried out in a heated liquid containing hydrogen peroxide in an amount equal to or more than the mole of Ti contained as an impurity in the alkali silicate.