JPS63315514A - Method for treating aqueous solution of alkali silicate - Google Patents

Abstract

PURPOSE:To obtain high-purity silica with low U and Th contents, by adding an acid to an aqueous solution of an alkali silicate, adjusting the pH and bringing the adjusted solution into contact with a strong basic anion exchange polymer. CONSTITUTION:Sulfuric acid or nitric acid is added to an aqueous solution of an alkali silicate (e.g. sodium silicate) in 2-10wt.% concentration to adjust the pH to 1-2. The adjusted aqueous solution of alkali silicate is then heated at 10-60 deg.C, brought into contact with an SO4<2-> or NO3<-> type strong basic anion exchange polymer and then concentrated while being heated. Alternatively an alkali is added to adjust the pH to 6-8 and gelatinize the aqueous solution to afford a silica hydrogel, which is then treated with an acid, washed with deionized water and dried to afford the aimed high-purity silica with respective <=0.1ppb U and Th contents.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for treating an aqueous alkali silicate solution. Specifically, the present invention relates to a method for treating an aqueous alkali silicate solution that is a raw material when producing high-purity silica. The content of radioactive substances such as uranium and thorium in the products treated with the present invention is extremely low at 0.1 ppb or less.
In particular, it is suitable for the production of low-emissivity, high-purity silica suitable for uses such as fillers for resins for IC encapsulants, raw materials for high-purity glass for optical fibers and optical glasses, and raw materials for silicon for semiconductor devices. .

[Prior art and its problems] In recent years, for example, in the electronic component manufacturing industry, as the degree of integration of ICs, LSIs, and VLSIs increases, semiconductor encapsulants emit alpha rays that cause software errors in computers. Trace components such as uranium (U) and thorium (T
It is desired to achieve high purity by eliminating such factors as possible, and to prevent corrosion of aluminum wiring on integrated circuit chips.
There is a demand for a material with as low a chloro (CΩ) content as possible.

Semiconductor encapsulant is a type of compound product consisting of a combination of resin, curing agent, silica powder, etc. Among these, the proportion of silica powder is 20 to 90% by weight, and as the degree of integration increases, Low α-emitting copper properties and low chloride are becoming increasingly important and essential requirements for silica powders.

In the prior art, high purity silica is initially
Originally, natural crystal or silica stone with low U and Th content was used, and if necessary, it was used after acid treatment, but highly pure natural raw materials have a small production base, and the demand is increasing year by year. I can no longer do that. Therefore, in recent years, the development of artificial high-purity silica production methods has become active. The manufacturing method is roughly divided into a dry method and a wet method, the former being a gas phase decomposition method using silicon halide or alkoxysilane, and the latter being hydrolysis using an acid such as alkali silicate or alkoxysilane.

Examples of methods for producing high-purity silica using a dry method include:
The following are known.

■ A method for producing high-purity silica by spraying silicon halide, typically silicon tetrachloride, onto a refractory target along with flame, allowing it to melt and grow, and then pulverizing it. (Unexamined Japanese Patent Publication No. 5
8-14Q, No. 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. (Japanese Patent Application Laid-Open No. 59-152.215) However, although these dry methods yield silica with a low content of alpha emitters, they have the following problems.

■ Silica raw materials such as silicon halides are expensive.

■ When a chlorosilane-based raw material is used as the silicon halide, chlorine tends to remain in the product, making it difficult to reduce the amount of chlorine.

■Chlorosilane type materials are corrosive and flammable, so they are difficult to handle.

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

■ Acidic silica sol obtained by treating an aqueous sodium silicate solution with a cation exchange resin is made into an alkaline silica sol with ammonia, and this solution is brought into contact with ammonium nitrate to produce coagulated precipitated silica gel, which is then subjected to acid treatment, water washing, drying, and melting. How to obtain high purity silica gel. (Japanese Patent Application Laid-open No. 180-180-911).

■ Gradually add sodium silicate aqueous solution to nitric acid aqueous solution to produce precipitated silica gel, acid treatment, and water washing.

A method of producing 1 q of high-purity silica gel by drying and firing.

(Unexamined Japanese Patent Publication No. 61-48,422) ■ Chelating agent Furthermore, precipitated silica is produced by reacting sodium silicate and mineral acid in the presence of hydrogen peroxide, and is then subjected to acid treatment, water washing, drying, and calcination. How to obtain high purity silica. (
JP-A-61-178.414 and JP-A-62-12,60
(No. 8) However, in all of these methods, alkali silicate is used as a raw material, but in general, alkali silicate contains a considerable amount of impurities consisting of alpha emitters such as U and Th. There is a tendency for these impurities to be contained to some extent even in the high purity silica that is used as a material. and,
During the manufacturing process, this αti! In order to efficiently separate and remove i projectiles, it is necessary to remove U and Th during the reaction process in which silica is precipitated from the aqueous alkali silicate solution and during the acid treatment process, so the process management is critical. It was very complicated and troublesome. Furthermore, since the form of silica produced is precipitated silica, and only fine particles can be obtained, the range of particle sizes that can be produced is narrow, and solid-liquid separation during dehydration is poor.

[Problems to be solved by the invention and means for solving the problem] In view of the above-mentioned circumstances, the present inventors produced high-purity silica using an aqueous alkali silicate solution as a starting material, and during the production, impurities consisting of α emitters such as U and Hh were introduced. For example, U and Th contents are each 0.
．． As a result of extensive research into methods for obtaining high-purity silica of 1 ppb or less, we have determined that an aqueous alkali silicate solution or a solution obtained by treating this with a cation exchange resin must be adjusted under certain conditions. The present invention was completed by devising that when the treatment solution is brought into contact with an anion exchange resin, the glue and Th in the solution are removed extremely well without gelation.

[Summary of the Invention 1 That is, the gist of the present invention is to add Shun to an aqueous alkali silicate solution or a treatment solution obtained by contacting this with a strongly acidic cation exchange resin of type A to adjust the pH, and then to The present invention relates to a method for producing high-purity silica with low uranium and thorium content, which is characterized by contact treatment with a basic anion exchange resin.

The present invention will be explained in detail below.

In the present invention, an alkali silicate is used as a starting material, and examples of the alkali silicate targeted by the present invention include sodium silicate and potassium silicate.

For example, in the case of sodium silicate, commercially available sodium silicate, JIS special 1.1
．． No. 2.3.4, sodium orthosilicate, sodium metasilicate, and the like. These alkali silicates generally contain impurities consisting of α emitters such as U and Th in an amount of about several tens to several 1 ooppb.

Further, the concentration of the aqueous alkali silicate solution is usually 1 to 20% by weight, preferably 2 to 10% by weight in terms of SiO2 concentration. If this concentration is too low, the volume of the aqueous alkali silicate solution to be treated will increase, making the purification process difficult; on the other hand, if it is too high, it will be difficult to adjust the pH by adding acid to the aqueous alkali silicate solution. This is not preferable because the solution will gel. Since the gelation of this solution differs depending on the type of acid and the amount used, the actual concentration of the aqueous alkali silicate solution is selected from the above range depending on the treatment method.

In the present invention, an acid is added to the above-mentioned aqueous alkali silicate solution to adjust the pH, or the aqueous alkali silicate solution is brought into contact with an H-type strongly acidic cation exchange resin, and then an acid is added to the treatment solution. - may be adjusted. In the latter case, the treatment liquid is usually an acidic silica colloid solution from which alkaline components have been removed.

In the present invention, prior to treating such aqueous alkali silicate solution or the treatment liquid with a strongly basic anion exchange resin, it is required to adjust the pH by adding an acid. In short, if the contact treatment with a strongly basic anion exchange resin is performed without adjusting the pH using this acid, impurities such as U and dust cannot be removed satisfactorily.

The acid used here is usually preferably sulfuric acid or nitric acid. Among acids, for example, when hydrochloric acid is used, it is undesirable because an aqueous alkali silicate solution tends to gel, but in the case of sulfuric acid and nitric acid, the concentration of the aqueous alkali silicate solution can be selected. This is preferable because gelation hardly occurs. The pH of the mixture after pH adjustment is usually
It is desirable that the pH is 1 to 2. If this pH is outside 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, contact treatment is carried out with a strongly basic anion exchange resin, which usually contains a gel type or porous type quaternary ammonium group, such as Amberlite IRA-400. (ROHM・
& Haas company product name) or Diaion 5AIOA
(trade name of Mitsubishi Chemical Industries, Ltd.) is suitable. The exchange ions of these resins depend on the acid of the acidic alkali silicate aqueous solution to be treated, for example, SO42- type when acidified with sulfuric acid, or NO3- type when acidified with nitric acid. It is particularly desirable to use this from the standpoint of removing U and Th.

Contact treatment with an anion exchange resin is usually carried out by passing the liquid to be treated through a column filled with resin in a downward flow or an upward flow.
Alternatively, a method may be adopted in which a resin is added to the liquid to be treated, stirred and maintained, and then the resin is filtered off. Further, the contact temperature is usually 10 to 60'C, and generally room temperature is sufficient.

Through the above-mentioned treatment, alpha emitters such as U and Hh can be efficiently separated and removed. It is effectively adsorbed and removed by treatment with the exchange resin.

For example, when the pH is adjusted with sulfuric acid, the beam becomes [UC2(
SO4) 212-'' or [UC2(SO4)3]4
-, so it can be easily adsorbed by SO4'-type strongly basic anion exchange resin.

Therefore, in the present invention, the beam and Th content are respectively ○ and "
Since it is possible to produce 1q of aqueous alkali silicate solution of +ppb or less, when high ITi degree silica is produced using this in accordance with a known method, the U and Th contents in the resulting product will naturally vary, respectively. It is 0.1 pp6 or less. Therefore, since there is no need to remove U and Th in subsequent steps, complicated and strict process control is not required in the reaction step, acid treatment step, etc., unlike the conventional wet method manufacturing process of high-purity silica.

High-purity silica can be produced by known methods or various flexible methods based on the acidified alkaline silicate aqueous solution or acidic silica colloidal solution obtained above and containing no alpha emitter impurities such as Th. It is possible.

For example, a method for producing silica from an acidified alkaline silicate aqueous solution that does not contain α-emitting impurities is to flow the aqueous solution down a column filled with a strongly acidic cation exchange resin whose ion exchange ions are H-type, and to By heating and drying 1 q of acidic colloidal silica solution from which components have been removed as an effluent, it is possible to obtain a lumpy, amorphous, highly pure wrinkle strength from which alkaline components and impurity metals have been removed. .

In addition, the acidified alkaline silicate aqueous solution can be heated and concentrated, or N
pH 6 with alkaline aqueous solution such as a○H or NH4OH
By adjusting the silica hydrogel to ~8 and gelling it, treating the obtained silica hydrogel with an acid, washing with deionized water, and drying it, it is possible to obtain a blocky, amorphous silica with high purity. Size reduction can be achieved even to a particle size of . Alternatively, pH 6-8 by concentration process or alkali
After adjusting the aqueous solution to a gel state, the aqueous solution on the verge of gelation is dispersed in a hydrophobic organic solvent or dispersed in a gas phase to form a gel.
By preparing spherical hydrosilica gel, acid treatment, washing with deionized water, and drying, 1 q of highly pure spherical silica having a desired particle size can be obtained.

On the other hand, as a method for producing silica from an acidic silica colloidal solution that does not contain alpha emitter impurities, it is possible to obtain amorphous, highly pure silica by simply heating and drying the aqueous solution. In addition, by subjecting the acidified alkaline silicate aqueous solution and acidic silica colloidal solution to known precipitation treatment and water washing treatment, fine particulate high purity precipitated silica can be obtained.
! 7.

[Effects of the Invention] According to the present invention, impurities consisting of α emitters such as U and Th can be easily removed during the manufacturing process. Therefore, using this, the U and 7-h contents are each 0.1 p.
High $T below PB! It is possible to produce 1 q of silica, and various shapes of the silica can be produced. The high-purity silica is extremely effective as a filler material of 1!3XvJ for IC encapsulant resin.Furthermore, due to its high purity, it can be used as a raw material for optical fibers and optical glasses, and as a silicon raw material for semiconductor devices. It is suitable for many uses and is of significance in a wide range of industries.

[Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example 1 Commercially available sodium silicate aqueous solution (SiOz 5 degrees 27.1
Weight %, NazO 1 degree 8.4 weight %, U content 51.9
After diluting 14.3 mΩ of ppb) with about 50 mΩ of deionized water, the pH of the solution was adjusted to 1.2 with sulfuric acid (1:4),
Furthermore, the volume was adjusted to 100 mΩ, and then this was adjusted to 5042-
Strong basic anion exchange resin (manufactured by Rohm and Haas, trade name Amberlite IRA400) 10 mΩ
The solution was passed through a packed column (diameter 8 mm x height 20 cm) in a downward flow at room temperature to remove glue and Th from the aqueous solution.

The operability in this liquid flow treatment was good, and when the amount of soybean in the effluent was quantified by fluorescence photometry, it was found that 0
．． It was less than 1 ppb.

Next, the pH of this solution was adjusted to 8 with 0.1N NaOH, and gelation was performed at room temperature.

This silica hydrogel was washed with ionized water immersed in 1N, Hz 304 for 3 hours to remove the Na contained in it.
Salts such as 2SO4 were removed and dried in an oven dryer.

When the glue and Th-containing ω in the obtained dry silica gel were quantified by activation analysis, they were each 091 ppb or less.

Example 2 In Example 1, the effluent obtained by passing through the strongly basic anion exchange resin column and having a content of 0.1 ppb or less was treated with an H-type strongly acidic cation exchange resin (Rohm &Haas'!). A: After passing the solution in the same manner through a column packed with Amberlite IR-120), the acidic silicate colloid solution that flowed out was concentrated and gelled in a water bath, and then poured with deionized water until it became neutral. Silica gel was produced by washing with water and drying this at a temperature of 180'C. When the concentrations of glue in the silica gel (jq) were determined by activation analysis, they were each 0.1 ppb or less.

Example 3 Commercially available sodium silicate aqueous solution (SIOza degree 27.
An aqueous solution prepared by diluting 1% FF, NazOm content 8.41ffi%, U-containing FF 151.9Dpb) with 5 times the volume of demineralized water was added to an H-type strongly acidic cation exchange resin (manufactured by Rohm and Haas, trade name Amber). The solution was passed through a column packed with Light IR-120>.

Next, the pH of this effluent was adjusted to 1.2 by adding sulfuric acid (1:4), and then the pH was adjusted to 1.2 in the same manner as in Example 1.
The solution was passed through a column of 042-type strongly basic anion exchange resin to remove glue and Th from the aqueous solution.

Subsequently, silica gel was prepared 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.

Example 4 In the method of Example 1, after diluting a commercially available sodium silicate aqueous solution with 100 times the amount of demineralized water, 112.7 m of concentrated nitric acid was added.
Ω was added to adjust the pH of the solution to 1.2, and then the solution was passed through a column of a similar NO3-type strongly basic anion exchange resin and treated as described in Example 1 (11). , U
and 1q of high purity silica gel with a 1'-h content of 0°1 ppb or less.

Claims (6)

[Claims] (1) After contact-treating the alkaline silicate aqueous solution or this with an H-type strongly acidic cation exchange resin, add acid to the treatment solution to adjust the pH, and then contact-treating this with a strongly basic anion exchange resin. A method for treating an aqueous alkali silicate solution, characterized by: (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 with an acid is 1 to 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 SO_
4^2^-type or NO_3^- type, the processing method according to claim 1. (6) The manufacturing method according to claim 1, wherein the uranium and thorium contents in the recovered high-purity silica are each 0.1 ppb or less.