JPS6321212A - Production of high purity silica - Google Patents

Abstract

PURPOSE:To industrially produce high purity silica by subjecting an aqueous alkali silicate soln. to ion exchange, adding an acid to the resulting silica sol, subjecting the silica sol to ion exchange and using the resulting highly acidic silica sol. CONSTITUTION:An aqueous alkali silicate soln. is subjected to ion exchange with an ion exchange resin of cation type or the like and an acid is added to the resulting silica sol. This silica sol is passed through an ion exchange resin to remove impurities such as Al2O3 and Fe2O3 as well as the remaining alkali such as Na or K. The resulting silica sol of <about 1.0pH is added to an alkali soln. contg. ammonia adjusted to about 9.2-9.6pH to precipitate silica. By this method, high purity silica can be produced from inexpensive starting material. The silica is suitable for use as various fillers, a sealant for a semiconductor, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing high-purity silica.
The present invention is characterized in that the highly acidic silica sol is then obtained by ion exchange again, and further relates to a simple and inexpensive method for producing high purity silica, in which the highly acidic silica sol is added to an ammonia-containing alkaline solution to obtain silica precipitate.

[Prior art and its problems] Traditionally, silica has been widely used as a reinforcing filler for rubber, synthetic resins, etc., but recently, with the development of the electronic industry, silica has been used as a material for electronic parts, etc. There is an increasing demand for high-quality silica.

For example, high-purity silica is used as a material for protective containers for LSIs, VLSIs, etc., and a purity of 4 nines or higher is required. Furthermore, high purity silica of 6-9 class is required as a silicon raw material for amorphous solar cells.

Methods for producing such high-purity silica include methods using organic silicon compounds such as silicate esters as raw materials;
A method using silicon tetrachloride and a method using water glass (a concentrated aqueous alkali silicate solution) are known.

Among these methods, methods using organosilicon compounds or silicon tetrachloride produce high-purity silica by oxidatively decomposing high-purity silicate esters or silicon tetrachloride purified by distillation in the gas phase, or hydrolyzing it by wet reaction. This is the way to get it. According to this method, ultra-high purity silica of 7 to 9 nines grade can be obtained, but both have problems in terms of economic efficiency because the raw materials used are expensive.

In addition, as a method using inexpensive alkali silicate as a raw material, for example, the silica precipitation process is carried out so that the free m concentration is always 1.
．． The process is carried out in an acidic region of 0N or higher and at a high temperature of 70 to 90°C (Japanese Patent Application Laid-open No. 191016/1983).Easy-to-clean silica gel is made from a highly concentrated aqueous alkali silicate solution. Items that are repeatedly heated in strong acids (JP-A No. 60-204613, No. 60-204614)
Publication No.) etc. However, according to these methods, in the process of washing silica gel and forming silica precipitate,
Because it is necessary to use large amounts of acid at high temperatures, raw materials are expensive, and the equipment is made of special and expensive materials. Furthermore, in the above-mentioned Japanese Unexamined Patent Application Publication No. 60-204613, colloidal silica gel is produced simultaneously with granular silica gel, so the filtration performance with filter paper is poor and impurities cannot be sufficiently removed.

In addition, as a method using ion exchange, an aqueous alkali silicate solution is ultrafiltrated to remove colloid particles, and then an acidic silica sol is obtained by ion exchange treatment, which is made weakly alkaline, and then silica is precipitated with a coagulant. (Japanese Unexamined Patent Publication No. 60-42217, No. 60-42218)
(No. Publication), an alkali silicate aqueous solution obtained by adding an insoluble substance such as a metal hydroxide to an aqueous silicate solution and then performing solid-liquid separation is subjected to an ion exchange treatment to obtain a silica sol,
This is used to precipitate silica using a flocculant (Japanese Unexamined Patent Publication No. 6
0-90811), etc. However, these methods involve problems such as the use of a large amount of flocculants such as ammonia or ammonium salts in the flocculation process, resulting in high raw material costs and complicated wastewater treatment.

Furthermore, as a method for precipitating silica from an acidic silica sol obtained by ion-exchanging an aqueous alkali silicate solution, there is a special method in which the pH is adjusted with ammonia, then cooled and frozen, and then heated and melted to precipitate silica. Kosho 36-9
415), ammonia per mole of silica 0
．． Those that are treated with inorganic acids, acid anhydrides, acid salts, etc. during firing after adding 8 mol or more (Japanese Patent Publication No. 36-1
(Japanese Patent Publication No. 37-4304), or one in which silicic acid is precipitated by adding a quaternary ammonium salt surfactant, and then water is separated and fired (Japanese Patent Publication No. 37-4304).
According to these methods, many impurities such as AlFe and U remain, resulting in high Iil! Maro's silica cannot be obtained.

In view of the problems of the prior art, it is an object of the present invention to provide a simple and industrial method for producing high-purity silica using an inexpensive alkali silicate as a raw material.

[Means and Effects for Solving the Problems 1] As a result of intensive studies in accordance with the above objectives, the present inventors have found that after ion-exchanging a diluted aqueous alkali silicate solution, adding an acid and then ion-exchanging it again. It was discovered that by this method, alkalis such as sodium and potassium can be removed, and impurities such as aluminum oxide (Al2O2) and iron oxide (Fe203) can be easily removed. The present invention was achieved based on the finding that a precipitate with 8 filterability (easy cleaning) can be obtained by adding the above-mentioned additives.

That is, the present invention is a method for producing high-purity silica, which is characterized by ion-exchanging an aqueous alkali silicate solution, adding an acid, and then performing ion-exchange again.

Furthermore, the present invention provides the thus obtained pl-11,
This is a method for producing high-purity silica, which is characterized in that a silica sol having a pH of less than 0 is added to an alkaline solution containing amperanine having a pH of 9.2 to 9.6 to obtain a silica precipitate.

In the present invention, the alkali silicate aqueous solution, which is an aqueous solution of sodium silicate, potassium silicate, or a mixture thereof, used as a raw material is a commercially available JIS
Standard water glass is preferred because it is available at a low cost, and a diluted version of this is generally used, but the present invention is not limited to this, and any aqueous solution of alkali silicate can be used. In the present invention, as the aqueous alkali silicate solution, one in which the silica (Si 02 ) content is diluted to ewt% or less is preferably used.

In the present invention, this diluted aqueous alkali silicate solution is subjected to a first ion exchange treatment using a cationic ion exchange resin to obtain a silica sol from which metal ions such as sodium and potassium have been removed. This sol has l)H of 2.9
It contains impurities such as unionized Fe and AJ.

Next, an acid such as concentrated nitric acid or concentrated hydrochloric acid is added to this silica sol to make the pH less than 1.0, and the mixture is stirred and mixed to ionize and dissolve colloidal impurities such as Fe.

Next, this acidic silica sol is subjected to ion exchange treatment using a cationic ion exchange resin to remove the impurities, thereby obtaining a highly pure highly acidic silica sol.

Removal of impurities by this method is much more efficient than using conventional ultrafiltration, and the process is easier to maintain.

The highly acidic silica sol obtained in this way is filtered after adding an ammonium-containing alkaline solution (direct addition), or by adding alcohol or ketone to form a highly concentrated silica sol, which is then crushed. After that, high-purity silica can be obtained by known methods such as water washing, acid washing, drying, and calcination. However, in the present invention, this purified highly acidic silica sol is mixed with ammonium nitrate or ammonium chloride, etc. by adding ammonia to it. It is preferable to precipitate the silica by gradually adding it back into an ammonia-containing alkaline solution whose discharge value is adjusted to 9.2 to 9.6. The ammonia content at this time is desirably in the range of 0.3 to 1.0 in terms of ammonia/silica molar ratio.

By back-pouring in this manner, a precipitate with good fluidity can be obtained from the initial stage of precipitation of silica, and the obtained precipitate has good filterability and can be used with an ordinary filter. In addition, the cake after filtration has a low water content of 75 to 85%, and the cost required for drying can be reduced. Furthermore, this cake has good dispersibility in water, so it has a great cleaning effect, and the silica after drying and baking is very soft and easily pulverized, so the pulverization cost is low, and the resulting high-purity silica powder has a bulk specific gravity. small.

The easily soluble precipitate (cake) obtained is, as described above,
The mixture is placed in approximately 2N hydrochloric acid or nitric acid, stirred for 60 minutes while heating to 80° C., and then filtered and washed.

By performing such acid washing twice, impurities such as Fe in the cake are further removed. The cake is then resuspended in water, washed, dried, and baked.

The high-purity silica produced in this way can be used with various fillers,
Used for semiconductor encapsulants, quartz glass, synthetic crystals, abrasives, solar cells, etc.

[Examples] The present invention will be specifically described below based on Examples and Comparative Examples.

Examples 1 to 5 and Comparative Example 1.2 After diluting a commercially available high-purity alkali silicate concentrated aqueous solution (Water Glass No. 3, manufactured by Fuji Chemical Co., Ltd.) to a silica content of 14 wt%, a cation exchange resin (Amberlite IR) was diluted. -1203
) to obtain a silica sol. The IIH of this silica sol was about 2.9.

Next, the acids shown in Table 1 were added to this silica sol so that the M/silica molar ratio was 0.25 or more, and the mixture was stirred for 1 hour. Table 1 shows the acid/silica molarization and l)H after stirring at this time.

Next, this silica sol was passed through the same cation exchange resin as above to perform a second ion exchange treatment. The contents of AJ and [e in the silica sol after this treatment are shown in Table 1.

In addition, as a comparison, in Example 1, a sodium silicate solution diluted to 4 wt% (Comparative Example 1) and Example 1
The contents of AJ and Fe are also shown in Table 1 for the silica sol (Comparative Example 2) that was subjected to only the first ion exchange.

As is clear from Table 1, Fe and AJ are significantly removed by performing ion exchange, addition of acid, and ion exchange again.

Example 6 Fuchi ammonia water was added to 150 xl of a 1 mol/ml ammonium nitrate aqueous solution so that the ammonia/silica molar ratio was 0.5 to prepare an ammonia-containing alkaline solution.
This is the silica sol 2001 obtained in Example 1! was gradually added (reverse addition) to precipitate silica, and then aged for 1 hour. The obtained precipitate had very good filterability and low water content.

Next, this precipitate was filtered and washed with water, then redispersed in 2N nitric acid, heated to 80°C and stirred for 1 hour, and then filtered and washed with water twice.

Next, the precipitate was dried and then calcined at 800° C. for 4 hours to obtain high purity silica. The AJ content in this silica is 10
．． 6 ppm, and the Fe content was 2.0 ppm.

Example 7 Silica was precipitated in the same manner as in Example 6, except that ammonium chloride was used instead of ammonium nitrate. This precipitate also had very good filterability and low water content.

Next, this precipitate was subjected to repeated filtration, water washing, and acid washing in the same manner as in Example 6, and then calcined to obtain silica. The AJ content in this silica was 11.0 +)I1mFe content was 2.0 ppm.

Comparative Example 3 A solution was prepared by adding concentrated ammonia water to 200 xl of the silica sol of Comparative Example 2 so that the molar ratio of ammonia/silica was 1.0, and this was gradually added to a 1 mol/j ammonium nitrate aqueous solution 15031f. (direct addition) to precipitate silica.

Next, after aging this for 1 hour, in the same manner as in Example 6,
After repeating filtration, water washing, and acid washing, silica was obtained by firing. The AJ content in this silica is 90 ppm, Fe
The content was 5.6 ppm.

Note that even if the same silica sol as above is used to precipitate by the reverse addition method, A,! , the content of Fe was almost the same.

Comparative Example 4 Silica was obtained in the same manner as in Example 6 using the silica sol in which only the first ion exchange and acid were added in Example 1. The AU content in this silica is 9911p111
．． The Fe content was 5.6 ppm, indicating that a second ion exchange was necessary.

[Effects of the Invention] As explained above, the following effects can be obtained by ion-exchanging the aqueous alkali silicate solution, adding an acid, and then performing ion-exchange again.

1. High purity silica can be obtained from inexpensive raw materials (alkali silicate).

2. Compared to purification by ultrafiltration, ion exchange has a large throughput, and the process is easy to maintain and manage.

Further, by adding this highly acidic silica sol to an ammonia-containing alkaline aqueous solution to obtain a silica precipitate, the following effects can be obtained.

3. Because the filterability of the precipitate is very good, ordinary filters can be used, and equipment and operating costs are low.

4. The moisture content in the cake is low at 75-85%, and the energy cost required for drying is low.

5. Dried gel is easily pulverized, so the pulverization cost is low.

6. Due to its low bulk specific gravity, it is suitable for use as various fillers.

Therefore, the silica obtained by the present invention can be used with various fillers,
Suitable for applications such as semiconductor encapsulants.

Claims (1)

[Scope of Claims] 1. A method for producing high-purity silica, which comprises ion-exchanging an aqueous alkali silicate solution, adding an acid, and then performing ion-exchange again to obtain a silica sol having a pH of less than 1.0. 2. The silica concentration in the alkali silicate aqueous solution is 6wt.
% or less, the method for producing high-purity silica according to claim 1. 3. P obtained by ion-exchanging an aqueous alkali silicate solution, adding an acid, and then ion-exchanging it again.
A method for producing high-purity silica, which comprises adding silica sol having an H of less than 1.0 to an ammonia-containing alkaline solution having a pH of 9.2 to 9.6 to obtain a silica precipitate. 4. The silica concentration in the aqueous alkali silicate solution is 6wt.
% or less, the method for producing high-purity silica according to claim 3. 5. The method for producing high-purity silica according to claim 3 or 4, wherein the content of ammonia is in the range of 0.3 to 1.0 in molar ratio of ammonia/silica.