JPH0811688B2 - Method for treating alkaline silicate aqueous solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating an aqueous alkali silicate solution. More specifically, it relates to a method for treating an aqueous alkali silicate solution which is a raw material when producing high-purity silica. Those treated in the present invention, the content of the radiator such as uranium and thorium is extremely small as 0.1 ppb or less, especially the filler of the resin for the IC sealant, the raw material of the high purity glass for optical fiber and the optical glass, Furthermore, it is suitable for producing low-emissivity, high-purity silica suitable for applications such as silicon raw materials for semiconductor devices.

[Prior Art and Problems Thereof] In recent years, for example, in the electronic component manufacturing industry, semiconductor encapsulants generate α-rays that cause soft errors in computers as IC, LSI, VLSI and the like become more integrated. There is a demand for a high degree of purification by removing the trace amounts of uranium (U), thorium (Th), etc. to the limit, and to prevent corrosion of aluminum wiring on integrated circuit chips, chlorine (C)
l) It is required to reduce the content as much as possible.

The semiconductor encapsulant is a kind of compound product consisting of a mixture of resin, curing agent, silica powder, etc.
The proportion of silica powder is 20 to 90% by weight, and as the degree of integration increases, low α-emission and low chlorination for silica powder are becoming increasingly important and indispensable requirements.

In the prior art, high-purity silica originally used natural quartz or silica stone with a low content of U and Th, and if necessary, was used after acid treatment,
The production of high-purity natural raw materials is so small that it is no longer possible to meet the ever-increasing demand. So, in recent years,
The development of artificial high-purity silica manufacturing methods has become active. The method is roughly classified into a production method, a dry method and a wet method. The former is a gas phase decomposition method using silicon halide or alkoxysilane, and the latter is hydrolysis using an acid such as alkali silicate or alkoxysilane.

As a method for producing high-purity silica by the dry method, for example, the following are known.

A method for producing high-purity silica by spraying a silicon halide represented by silicon tetrachloride together with a flame onto a refractory target to cause melt fusion growth and pulverization. (JP Sho
58-140,313) A method for producing high-purity silica by further melting high-purity ultrafine particulate silica produced by gas-phase hydrolysis in a flame of silicon halide in the flame. (JP Sho 59
In the case of these dry processes, silica having a small α-emitter content can be obtained, but the following problems are mentioned.

 Silica raw materials such as silicon halide are expensive.

When a chlorosilane-based raw material is used as the silicon halide, chloro tends to remain in the product, and it is difficult to reduce the chloro content.

Chlorosilane is difficult to handle because it is corrosive and flammable.

On the other hand, as a method for producing high-purity silica by the wet method,
For example, the following precipitation method is known.

An acidic silica sol obtained by treating an aqueous solution of sodium silicate with a cation exchange resin is used as an alkaline silica sol with ammonia, and the solution is brought into contact with ammonium nitrate to produce an agglomerated precipitated silica gel, which is acid-treated, washed with water,
A method of obtaining high-purity silica gel by drying and melting. (JP-A-60-180,911).

A method in which a sodium silicate aqueous solution is gradually added to a nitric acid aqueous solution to produce precipitated silica gel, which is subjected to acid treatment, water washing, drying and firing to obtain high purity silica gel. (Japanese Patent Laid-Open No. 61-4
No.8,422) A chelating agent, a method in which sodium silicate and a mineral acid are reacted in the presence of hydrogen peroxide to produce precipitated silica, which is subjected to acid treatment, washing with water, drying, and calcination to obtain high-purity silica.
(Japanese Patent Laid-Open Nos. 61-178,414 and 62-12,608) However, in all of these methods, alkali silicate is used as a raw material, but in general, a considerable amount of U and Th etc. are contained in the alkali silicate. Since the above-mentioned α-emitter is included as impurities, the high-purity silica finally obtained tends to contain some of these impurities. In order to efficiently separate and remove the α-emitter during its production, it is necessary to remove U and Th in the reaction step in which silica is broken out from the aqueous alkali silicate solution and the acid treatment step. Therefore, the process control was complicated and troublesome. Furthermore, since the formed form of silica is precipitating silica and only fine particles can be obtained, the range of particle diameters that can be produced is narrow, and solid-liquid separation during dehydration is not good.

[Problems and Solutions of the Invention] In view of the above situation, when the present inventor produces high-purity silica using an alkaline silicate aqueous solution as a starting material, impurities such as α-emitters such as U and Th are efficiently generated during the production. Removed, for example, if the U and Th contents are each 0.1 p
As a result of extensive studies on a method for obtaining high-purity silica of pb or less, an alkali silicate aqueous solution or a solution obtained by treating the alkali silicate aqueous solution with a cation exchange resin was adjusted under a certain specific condition and then specified. When the treatment liquid is brought into contact with the anion exchange resin, the treatment liquid does not gel and U and
The inventors have found that Th is extremely well removed, and completed the present invention.

[Summary of the Invention] That is, the gist of the present invention is to add an acid to an aqueous solution of an alkali silicate or a treatment solution after contacting it with an H ⁺ -type strongly acidic cation exchange resin to adjust pH, and then A process for producing high-purity silica having a low uranium and thorium content is characterized by carrying out a contact treatment with a strongly basic anion exchange resin.

 Hereinafter, the present invention will be described in detail.

In the present invention, alkali silicate is used as a starting material, but in the present invention, the target alkali silicate is:
Sodium silicate, potassium silicate, ammonium silicate, etc. For example, in the case of sodium silicate, commercially available sodium silicate, JIS special 1, 2, 3, 4 and sodium orthosilicate, sodium metanaiate, etc. Is mentioned. U is generally present in these alkali silicates.
And impurities such as Th and α-emitters are about several tens to several hundreds of p
About pb is included.

The concentration of the aqueous alkali silicate solution is usually 1 to 20% by weight, preferably 2 to 10% by weight, as the SiO ₂ concentration.
If this concentration is too low, the volume of the alkali silicate aqueous solution to be treated increases, and the purification operation is difficult.On the contrary, if this concentration is too high, when adding acid to the alkali silicate aqueous solution to adjust the pH. This is not preferable because the solution gels. The gelation of this solution depends on the type and amount of the acid used, so the actual concentration of the aqueous alkali silicate solution is selected from the above range depending on the treatment method.

In the present invention, the pH is adjusted by adding an acid to the alkali silicate aqueous solution as described above, or this alkali silicate aqueous solution is added.
The pH may be adjusted by adding an acid to the treatment liquid after contact with the H ⁺ type strongly acidic cation exchange resin. In the latter case, the treatment liquid is usually an acidic silica colloidal solution from which alkaline components have been removed.

In the present invention, it is necessary to add an acid to adjust the pH before treating such an aqueous solution of alkali silicate or the treatment liquid with a strongly basic anion exchange resin. In short, when contact treatment with a strongly basic anion exchange resin is performed without adjusting the pH with this acid,
Impurities such as U and Th cannot be removed well. As the acid used here, sulfuric acid or sulfuric acid is usually desirable. Among the acids, for example, when hydrochloric acid is used, it is not desirable because the alkali silicate aqueous solution is easily gelled, but in the case of sulfuric acid and nitric acid, the concentration of the alkali silicate aqueous solution is selected by selecting the concentration of the solution. It is preferable because gelation hardly occurs. The pH of the mixture after pH adjustment is usually preferably 1-2. If the pH is out of the above range, impurities such as U and Th in the solution cannot be efficiently removed in the next treatment.

Next, in the present invention, a contact treatment is carried out with a strongly basic anion exchange resin, and this resin usually contains a gel type or porous type quaternary ammonium group, for example, Amberlite IRA-400. A commercially available product (trade name of Rohm and Haas Company) or Diaion SAIOA (trade name of Mitsubishi Kasei Co., Ltd.) is suitable. The exchange ions of these resins depend on the acid of the alkaline aqueous solution of acidic silicate to be treated, for example, when acidified with sulfuric acid, SO ₄ ²⁻ type, or when acidified with nitric acid, NO ₃ ^−. It is particularly preferable to use a mold of the type from the viewpoint of removing U and Th.

The contact treatment with an anion exchange resin is usually a method in which a liquid to be treated is passed through a column filled with a resin in a downward flow or an upward flow, or after the resin is added to the liquid to be treated and stirred and held,
A method of separating the resin can be adopted. The contact temperature is usually 10 to 60 ° C., and generally room temperature is acceptable.

By the above-mentioned treatment, α-emitters such as U and Th can be efficiently separated and removed.
Since U and Th are changed into the form of complex anion by adjusting the pH, they are favorably adsorbed and removed by the subsequent treatment of the anion exchange resin. For example, when pH is adjusted with sulfuric acid, U
Becomes [UO ₂ (SO ₄ ) ₂ ] ²⁻ or [UO ₂ (SO ₄ ) ₃ ] ⁴⁻ , so it can be easily adsorbed by the SO ₄ ²⁻ type strongly basic anion exchange resin. .

Therefore, in the present invention, the U and Th contents are each 0.1 ppb.
Since the following aqueous alkali silicate solution can be obtained,
When high-purity silica is produced using this by a known method, the U and Th contents in the obtained product are naturally 0.1 ppb or less. Therefore, since it is not necessary to remove U and Th in the subsequent steps, complicated and strict process control is not required in the reaction process and the acid treatment process unlike the conventional wet process for producing high-purity silica.

To produce high-purity silica by a known method or various methods having flexibility based on the acidified alkaline alkali silicate solution or acidic silica colloid solution containing no α-emitter impurities such as U and Th obtained above. Is possible.

For example, as a method for producing silica from an acidified alkali silicate aqueous solution that does not contain α-emitter impurities, the aqueous solution is allowed to flow down a column filled with a strongly acidic cation exchange resin whose ion exchange ions are H ⁺ type, An acidic colloidal silica solution from which alkali components have been removed is obtained as an effluent, and by heating this solution to dryness, it is possible to obtain bulk amorphous amorphous silica from which alkali components and other impurity metals have been removed. .

Further, the acidified alkali silicate aqueous solution is heated and concentrated, or
Adjust the pH to 6-8 with an alkaline aqueous solution such as NaOH or NH ₄ OH, gelate, and treat the resulting silica hydrogel with acid.
After washing with deionized water and drying, it is possible to obtain high-purity silica in the form of lumps, and the pulverizer
Size reduction can be performed to a desired particle size. Alternatively, the aqueous solution on the verge of gelation may be dispersed in a hydrophobic organic solvent after the concentration process or adjustment to pH 6 to 8 with an alkali, or dispersed in the gas phase to cause gelation to form spherical hydrosilica gel and acid A high-purity spherical silica having a desired particle size can be obtained by treating, washing with deionized water, and then drying.

On the other hand, as a method for producing silica from an acidic silica colloidal solution containing no α-emitter impurity, it is possible to obtain massive amorphous silica having a high purity simply by heating and drying the aqueous solution. By subjecting the acidified alkali silicate aqueous solution and the acidic silica colloidal solution to the known precipitation treatment and water washing treatment, it is possible to obtain high-purity precipitated silica in the form of particles.

[Effect of the Invention] According to the present invention, it is possible to easily remove impurities such as U and Th that are formed from α-emitters during the production thereof. Therefore, by using this, high-purity silica having U and Th contents of 0.1 ppb or less can be obtained, and various silica shapes can be produced. And the high-purity silica is extremely effective as a filler for the resin for IC encapsulant, and from the viewpoint of high purity,
It is suitable for use as a raw material for optical fibers and optical glass, and as a silicon raw material for semiconductor devices, and is of great significance in a wide range of industries.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to the description of the following examples unless it exceeds the gist.

Example 1 14.3 ml of a commercially available sodium silicate aqueous solution (SiO ₂ concentration 27.1% by weight, Na ₂ O concentration 8.4% by weight, U content 51.9 ppb) was diluted with about 50 ml of deionized water, and then sulfuric acid (1: 4) was added. Solution pH at
Was adjusted to 1.2 and the volume was adjusted to 100 ml.
SO ₄ ^2- type strongly basic anion exchange resin (Rohm and Haas Co., trade name Amberlite IRA400) 10 ml packed column (diameter 8 mm × height 20 cm) at room temperature in downward flow , U and Th in the aqueous solution were removed.

The operability in this liquid-passing treatment is good, and when U in the outflow solution was quantified by a fluorometric method,
It was less than 0.1 ppb.

Then, the pH of this solution was adjusted to 8 with 0.1N NaOH and gelled at room temperature.

The silica hydrogel was immersed in 1N H ₂ SO ₄ for 3 hours, washed with deionized water to remove the contained salts such as Na ₂ SO ₄ , and dried in an oven dryer.

The U and Th contents in the obtained dried silica gel were each quantified by activation analysis and found to be 0.1 ppb or less.

Example 2 In Example 1, the effluent having a U content of 0.1 ppb or less obtained by the liquid-flowing treatment of a strongly basic anion exchange resin column was used as an H ⁺ -type strongly acidic cation exchange resin (made by Rohm and Haas Co.). : Amberlite IR-120) was passed through the column in the same manner, and then the flowing out acidic silicic acid colloidal solution was concentrated in a water bath and gelled,
Rinse with deionized water until neutral and then add 180
Silica gel was produced by drying at a temperature of ° C.
When U in the silica gel obtained here was quantified by an activation analysis method, each was 0.1 ppb or less.

Example 3 A commercially available sodium silicate aqueous solution (SiO ₂ concentration 27.1% by weight, Na ₂ O concentration 8.4% by weight, U content 51.9 ppb) was diluted with 5 times the amount of demineralized water to prepare an H-type strongly acidic cation exchange solution. The solution was passed through a column packed with resin (Amberlite IR-120, manufactured by Rohm and Haas Company).

Next, add sulfuric acid (1: 4) to the effluent to add p
After adjusting H to 1.2, the solution was passed through a column of SO ₄ ^2- type strongly basic anion exchange resin similar to that in Example 1 to remove U and Th from the aqueous solution.

Subsequently, silica gel was produced by evaporating the above effluent to dryness.

When the contents of U and Th in the silica gel obtained here were quantified by activation analysis, they were each 0.1 ppb or less.

In the method of Example 4 Example 1 was diluted with a commercially available aqueous solution of sodium silicate at 10 times the amount of demineralized water, it was adjusted to 1.2 and the pH of the solution was added concentrated nitric acid 12.7 ml, then this NO ₃ ^It was passed through a column of a strongly basic anion exchange resin of the same type as-, and treated according to Example 1, and as a result, the U and Th contents were 0.1 ppb.
The following high purity silica gel was obtained.

Claims (6)

[Claims] 1. An alkali silicate aqueous solution or a treatment liquid obtained by contacting the same with an H ⁺ -type strongly acidic cation exchange resin is added with an acid to adjust the pH, and then this is used as a strongly basic anion exchange resin. A method for treating an aqueous alkali silicate solution, which comprises a contact treatment. 2. The treatment method according to claim 1, wherein the acid is sulfuric acid or nitric acid. 3. The treatment method according to claim 1, wherein the pH of the mixture adjusted by the acid is 1-2. 4. The treatment method according to claim 1, wherein the concentration of the aqueous alkali silicate solution is ₂ to 10% by weight as SiO ₂ . 5. The exchange ion of the strongly basic anion exchange resin is
Processing method of the claims claim 1 wherein characterized in that it is a type ^- SO ₄ ^2-type or NO _3. 6. The production method according to claim 1, wherein the recovered high-purity silica has a uranium content and a thorium content of 0.1 ppb or less, respectively.