JPH02133311A - Production of high purity silica - Google Patents

Abstract

PURPOSE:To obtain high purity silica especially having a very low Ti content by adding ammonium persulfate as an extracting aid when Ti, etc., as impurities are removed from an aq. soln. of an alkali silicate as starting material. CONSTITUTION:An aq. soln. of an alkali silicate represented by a general formula M2O.nSiO2 (where M is an alkali metal and n is 0.5-5) is prepd. and allowed to react with a mineral acid to produce silica. This silica is treated with a mineral acid to extract and remove impurities. At this time, the silica production reaction and/or the extraction of the impurities is performed in the presence of ammonium persulfate. High purity silica especially having a very low Ti content is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing high-purity silica.

Specifically, the present invention relates to a method for producing high-purity silica containing extremely low content of radioactive impurities such as alkali metals, chlorine, and uranium, as well as particularly titanium, from an aqueous alkali silicate solution.

The high-purity silica obtained by the method of the present invention can be used as a filler, dispersant, etc. in resin compositions for encapsulating electronic components, and
In addition to being suitably used as a raw material for special ceramics,
It is expected to be used as a raw material for transparent quartz glass.

Conventionally, natural quartz has been used as a raw material for transparent quartz glass. However, as the degree of integration of electronic component elements increases in the semiconductor field, demands for higher purity of the raw materials used become stricter, and high-quality natural crystals are running out. Therefore, studies are being conducted to replace natural quartz with synthetic high-purity silica.

An object of the present invention is to provide a method for producing high-purity silica that can meet such demands.

[Prior Art] One of the methods for obtaining synthetic high-purity silica to replace natural quartz crystal is to produce high-purity silica using an alkali silicate aqueous solution as a raw material: 1) Treating an alkali silicate aqueous solution with an acid. Method of purification by: (JP-A-59-54632, JP-A-60-19101)
No. 6, etc.).

2) - When processing the above, a method has been proposed in which the treatment is carried out in the presence of 11 tO (Japanese Patent Laid-Open No. 61-286212, etc.).

(Problems to be Solved by the Invention) Silica of considerably high purity can be produced by these methods.However, method 1) has a drawback in that it is difficult to remove Ti.

Ti is a typical impurity that must be removed from the raw material of silica glass because it lowers the transmittance of silica glass in the ultraviolet region.

-C, since the solubility of T1 in mineral acids is low, multi-stage acid cleaning treatment is required to extract and remove Ti contained in the raw material to a desired concentration level, resulting in high costs. In practical terms,
Using an aqueous alkali silicate solution as a raw material, the Ti content is 59
It was difficult to obtain silica below 11M.

Furthermore, method 2) attempts to facilitate extraction and removal by converting Ti into a complex with high solubility in mineral acids using H20□. It is effective to use 1 (20□) to extract and remove trace amounts of Ti, but Hi
nt has the disadvantage that it generates highly toxic ozone upon thermal decomposition, and also has problems in practical handling, such as foaming during the Ti extraction process.

[Means for solving problems]

The present inventors conducted research to improve the above-mentioned problems in the conventional method, and found that alkaline silicate water? g 'e
Ammonium persulfate (hereinafter referred to as APS) is used as an extraction aid when removing trace amounts of Ti using , as a raw material.
They found that this is suitable and completed the present invention.

That is, the present invention provides an aqueous solution of an alkali silicate represented by the general formula: M20·n5io□ (where M is an alkali metal element and n is 0.5 to 5 because it is a mole of SiO□). A method for producing high-purity silica by reacting with an acid and treating the obtained silica with a mineral acid to extract and remove impurities, characterized in that the reaction and/or impurity extraction is performed in the presence of ammonium persulfate. The summary is ``A method for producing high-purity silica.''

In the method of the present invention, the raw alkali silicate aqueous solution includes sodium salts and potassium salts of silicic acid.

A water 18 solution such as J.S.T.M. salt can be used.

In addition, examples of ili used in each step of extracting impurities include sulfuric acid, 14 acid, and hydrochloric acid, and it is preferable to use sulfuric acid in practice.

How to add ^ps as a Ti extraction aid is i′+? ■
APS may be dissolved in the mineral acid water (8) solution, or a previously prepared AI''S aqueous solution may be mixed with the mineral acid.

The amount of APS to be used is preferably equivalent to an equimolar amount or more, preferably 10 to 100 times the molar amount of Ti present.

The Ti extraction process is performed at a temperature of 20°C or higher, preferably 50°C or higher.
It is best to perform this in the 1·n range of 140'c.

If the treatment is carried out at a temperature higher than the boiling point of the treated solution at normal pressure (F), the time required for the Ti extraction process can be shortened. Considering corrosion and energy costs, 11
The range from 0 to +40'C is typical for actual JT.

The time for the Ti extraction process is about 5 minutes to 5 hours in the case of a batch method, and about 30 seconds to 30 minutes in the case of a continuous method, preferably about 1 to 10 minutes.

The silica obtained by acid treatment is then filtered using water at a temperature of +IT, followed by a filtration operation if necessary, and subjected to deoxidation and dehydration treatment.

In addition, the acid used in the present invention is purified or a highly pure modified product called Uzu grade, and the water used for diluting the raw material and the acid used or for washing the silica is pure water with few impurities. It is preferable.

Note that alkali metal persulfates also have a function as a T1 extraction aid, but it is desirable that the silica targeted by the present invention has a low content of alkali metals.
The persulfate compound used as a Ti extraction aid in the method of the present invention is preferably an ammonium salt.

[Effects of the Invention] According to the method of the present invention, using an alkali silicate hex solution as a raw material, the impurity content is alkali metal: 10 pp
m or less, chlorine: 3 ppm or less, radioactive elements such as uranium =
It is possible to obtain highly pure silica particles with an extremely low impurity noise rate of 3 ρ pb or less, and titanium: 5 pp+m or less.

The ^ps used in the method of the present invention is easily available, highly safe, and easy to remove, so it can be used in the silica manufacturing process without any problems.

The silica particles obtained by the method of the present invention have an extremely low impurity content compared to those obtained by the conventional technique, so they are particularly used as a filler for resin compositions for encapsulating highly integrated circuits, and are also used for transparent quartz glass. It is expected to be used as a raw material for products such as ceramics and special ceramics.

〔Example〕

The method of the present invention will be specifically explained below using Examples and Comparative Examples.

Example-1 Sodium silicate No. 13 CJIS [equivalent to No. 1408, 3].

SiJ: 2B%+ NazO: 9%, Ti
: 60 ppm) 6 kg was heated to 50° C. under reduced pressure and dehydrated and concentrated to obtain a stock solution for fiberization of 5 iOz: 32%. The viscosity of this stock solution was about 100 voids at 30°C, and the stringability was also good.

After filtering this stock solution, use an extruder to make a pore size of 0.2 mmφ.
, through a gold-platinum alloy nozzle with 200 holes.
Reaction bath held at 50 °C at a rate of 1 min. APS:
13% by weight aqueous solution of sulfuric acid 2O in which 17.1g was dissolved
I pushed him into N.

The extruded stock solution was neutralized by Na 20 reacting with acid and solidified, turning into a transparent fibrous gel.

The fibrous gel was taken out from the reaction bath using a belt conveyor at a speed of 1 m/min, and the immersion time of the fibrous gel in the reaction bath was about 1 minute.

40g of the obtained fibrous gel was preliminarily treated with APS O,41
13% by weight sulfuric acid water in which g is dissolved? 8 liquid: 50
0 mfl and heated at 100"C for 30 minutes without stirring.
Processed for minutes. The fibrous gel is cleaved finely and has a length of 2~
It became short fibrous silica with 5 sides.

Next, the obtained short fibrous silica was soaked in deionized water at 500%
d and stirred for 10 minutes, then dehydrated using a Nusoche.

After repeating this extraction process with acid and washing with water three times, and further repeating the congestion with water five times, the concentration of sulfate groups in the silica was 1 ppI11 or less.

The obtained silica was dried at 150"C overnight and then heated to 1200°C.
It was heat-treated at C for 1 hour.

As shown in Table 1, the impurity content in the obtained silica was 1 ppm or less in all cases.

Example 2 Silica was obtained by processing in the same manner as in Example 1, except that the amount of APS used was changed as shown in Table 2. The impurity content in the obtained silica is as shown in Table 1, and the Ti content was less than 5 pl)lf1 in all cases.

Comparative Example-1 Silica was obtained in the same manner as in Example-1 except that APS was not used.

The impurity content in the obtained silica was as shown in Table 1, and Ti was 5.0 ppm+.

Table-1゜ Impurity content in silica: Table-2゜ Nitto Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1) General formula: M_2O・nSiO_2 (where M is an alkali metal element, n is the number of moles of SiO_2, 0.5 to 5
In a method for producing high-purity silica by reacting an aqueous solution of an alkali silicate represented by ) with a mineral acid and treating the obtained silica with the mineral acid to extract and remove impurities, the reaction and/or Alternatively, a method for producing high-purity silica, characterized in that impurity extraction is performed in the presence of ammonium persulfate.