JPH062571B2 - Method for producing alkaline silicate aqueous solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an aqueous alkali silicate solution using serpentine as a starting material.

[Conventional technology]

The following two methods are known as typical methods for producing an alkali silicate aqueous solution.

(1) A method of producing a cullet of anhydrous alkali silicate glass by heating and melting a mixture of silica sand and alkali, and then hydrothermally treating in an autoclave (generally called a dry method).

(2) A method in which natural silica such as sinter or amorphous silica which is easily reactive such as ferrosilicon dust is directly reacted with an alkaline aqueous solution to produce (generally called a wet method).

Among these typical manufacturing techniques, the latter wet method has a very advantageous point in that it does not require a large amount of heat energy like the former dry method, but it has a limited silica source. There is a problem that impurities are mixed in the solution.
Therefore, at present, the dry method is exclusively used industrially.

[Problems to be Solved by the Invention] As an improvement of the wet method, there has been proposed an attempt to finely pulverize crystalline silica such as silica sand and to react it with an alkaline aqueous solution as a silica source. However, in this method, Si
It is difficult to obtain as a concentrated water glass having a high O ₂ / Na ₂ O ratio, and the yield is low. For this reason, there is no choice but to require a reaction under pressure, and in consideration of complicated process operations such as pulverization, the advantages of the dry method still fall short.

By the way, a serpentine is one of the silica-containing ores produced in large quantities in Japan. Attempts have been made for a long time to effectively utilize this serpentine as an industrial resource, but its field of use is still very limited.

For example, attempts have been made to recover magnesium and a small amount of valuable metals by decomposing serpentine with sulfuric acid, but the utilization of silica, which makes up the majority of serpentine, is used for siliceous fertilizers such as fused fertilizer. Although there are examples, they have received little attention so far.

The present inventors have found that the silica produced by the mineral acid decomposition of serpentine has a structural structure substantially including the basic structure of serpentine, and has extremely good reactivity with an alkaline component. The present invention has been completed. Therefore, an object of the present invention is to efficiently produce an alkaline silicate aqueous solution by a wet method using serpentine as a starting material.

[Means for Solving the Problems]

The method for producing an alkali silicate aqueous solution according to the present invention for achieving the above object is constituted by decomposing serpentine with mineral acid to produce silica gel of a fibrous aggregate, and then dissolving the silica gel in a caustic alkaline aqueous solution. Characteristic.

In the present invention, serpentinite (Serpentinite), which is a starting material for producing silica gel, is a siliceous rock rich in magnesium and is petrologically classified as an ultramafic rock together with a peridotite (Peridotite). The two have similar chemical compositions, but the peridotite is a forsterite (Forsteri).
te) and Enstatite are the main constituent minerals, whereas serpentinite is Chrysotile,
Lizardite, Antigorite
Serpentine Minerals consisting of (ite) are the main constituent minerals, and are completely different. In many cases, serpentinite is formed by the alteration of peridotite by hydrothermal action, so in addition to serpentine minerals, unaltered forsterite, onstatite, calcite (Calcite), chromite ( Chromite), may contain impurity minerals such as magnetite (Magnetite).

Moreover, the serpentine minerals present in serpentinite are sometimes referred to asbestos (Asbestos), which is a fibrous aggregate that is sometimes clear to the naked eye.
os).

Such serpentinite is widely distributed in Japan as a mineral resource, and large-scale rock bodies are known in the Hidaka district of Hokkaido and Shikoku, and their reserves are enormous.

The history of the starting material of the fibrous aggregate silica gel, which is a raw material for producing the aqueous solution of alkali silicate according to the present invention, is not particularly limited as long as it is the above serpentine, but it is preferable that the content of serpentine mineral is large. When impurities are present in the raw material, unaltered forsterite and enstatite can be easily removed by selective pulverization or manual selection, and magnetic minerals such as chromite and magnetite can be easily removed by magnetic separation. Iron existing in place of magnesium, which is a serpentine mineral, and impurities and trace components soluble in mineral acids, such as iron hydroxide, do not substantially remain in the generated silica gel. It is not a problem because it elutes into the inside.

The serpentine used as a raw material is a crushed product, but the particle size need not be limited so much. However, if it is too large, it takes a long time to completely react, which is not preferable.
A degree is preferable.

The silica gel of the fibrous aggregate is produced by decomposing the above serpentine raw material with mineral acid.

As the mineral acid, sulfuric acid or hydrochloric acid is preferably used, and usually,
It is used in an aqueous solution of 1N or more. However, if the concentration of the aqueous solution is too high, the desired fibrous aggregate structure cannot be maintained, so it is desirable to set the upper limit to about 12N. The amount of the mineral acid used should be at least in excess of the stoichiometric amount required to convert all the magnesium components contained in the serpentine raw material into chlorides or sulfates. The slurry concentration is not particularly limited and is set taking into consideration workability and economic efficiency, but is usually in the range of 10 to 250 g /, preferably 50 to 200 g /.

As a condition for decomposing the mineral acid, a low temperature range from room temperature to 100 ° C is sufficient, and if the concentration of the mineral acid used is high, it is better to raise the temperature rather than to give a good result. The treatment time varies depending on the mineral acid concentration, decomposition temperature, etc., but it is necessary to hold the treatment time for at least 3 hours or more. In addition, performing the treatment under stirring is a desirable requirement for the smooth progress of the reaction.

The raw material decomposed under the above conditions is separated from the mother liquor by a conventional method and then recovered as silica gel. At this time, since a large amount of magnesium chloride or magnesium sulfate is dissolved in the mother liquor, these are converted into hydroxide,
It can be converted to oxides and other forms for effective use. At the same time, valuable metal components such as nickel, cobalt, and chromium that are dissolved in a small amount can be separated and collected.

The silica gel produced by decomposing mineral acids in this way has a structural morphology that retains the basic structure of the fibrous aggregate of the raw material serpentine without being substantially destroyed. Is 0.3 wt% or less of a high-purity amorphous body.

Next, the above-mentioned fibrous aggregate silica gel is dissolved in a caustic aqueous solution.

Although substances such as bent sodium hydroxide and potassium hydroxide are commonly used for caustic, sodium hydroxide is often used. Caustic reacts directly with silica gel in the form of an aqueous solution. The alkali concentration of the aqueous solution is preferably set in the range of 0.5 to 5 N, particularly 1 to 3 N. When it becomes thinner than this concentration range, the treatment capacity increases and it becomes unindustrial, while when it is too thick, the dissolution rate slows down. Further, the solution viscosity increases and the workability is impaired. The amount of caustic used is appropriately selected from the range of 1 to 3 as the molar ratio of SiO ₂ / M ₂ O. If this molar ratio is less than 1, it has no industrial significance and exceeds 3. And causes a situation where unreacted silica remains.

It suffices that the dissolution operation is carried out at room temperature under normal pressure with stirring, and the dissolution reaction proceeds smoothly even if no pressure is applied. Regarding the temperature, some heating has the effect of increasing the dissolution rate, so it is appropriately applied as an additional condition.

The alkali silicate aqueous solution obtained by dissolving in this manner can be directly used as a product, but if necessary, separated,
Removal of insoluble components mixed by post-treatment such as concentration,
The product shall not be adjusted in concentration.

[Action]

Silica gel, which is produced by decomposing serpentine with mineral acid, maintains the original structure of the serpentine mineral SiO ₄ tetrahedron sheet, which is the main constituent, and maintains the original texture. The magnesium and the soluble metal component in the sheet have a very reactive texture property that is selectively eluted. Therefore, the dissolution with the caustic aqueous solution proceeds smoothly and quickly even under the conditions of room temperature and atmospheric pressure, and is efficiently converted into the alkaline silicate aqueous solution.

〔Example〕

Hereinafter, the present invention will be described based on Examples and Comparative Examples.

Example 1 Serpentine from Hidaka Mine, Kochi Prefecture, was crushed and classified to -150 mesh. 100 g of this serpentine rock was placed in a 5 beaker, 3N hydrochloric acid 2 was further added, the lid was put on a petri dish, and the mixture was treated at 100 ° C. for 4 days while stirring. After the treatment, the product was separated, thoroughly washed with ion-exchanged water, and further filtered to obtain 40 g of silica gel (as SiO ₂ ) as a fibrous aggregate.

Approximately 20% by weight of water was added to the fibrous aggregate silica gel 0.9 g
Put iO ₂ equivalent) in a Teflon beaker 100 ml, are dissolved with stirring in a stirrer was added a 1N aqueous sodium hydroxide solution 20ml at room temperature (approximately 18 ° C). The total amount dissolved in about 10 minutes, and this sodium silicate solution was separated,
No undissolved silica gel was found on the paper.

The solution was aqueous sodium silicate solution in a molar ratio _SiO 2 / _Na 2 O1.5.

Example 2 To 1.0 g of the same fibrous silica gel as in Example 1, 10 ml of 1N sodium hydroxide was added and dissolved at room temperature. As a result, it was dissolved in 3 hours and nothing was left on the paper after separation.

The obtained mother liquor was a sodium silicate aqueous solution having a molar ratio of SiO ₂ / Na ₂ O of about 3 mol.

Example 3 The same experiment as in Example 2 was conducted with the melting temperature at 70 ° C.

As a result, the total amount was dissolved within 30 minutes after the dissolution was started.

Comparative Example 1.0 g of sinter (SiO ₂ 98%) from Iwo Jima, Kagoshima Prefecture, which is used for the production of wet-process alkali silicate, was dissolved under the same conditions as in Example 1. As a result, the total amount was not dissolved even after the dissolution time of 10 hours.

〔The invention's effect〕

According to the present invention, since the silica source is a highly reactive fibrous aggregate silica gel having a unique texture property from serpentine as a starting material, the alkali silicate can be extremely smoothly and rapidly even under normal temperature and normal pressure conditions. An aqueous solution can be produced.

Therefore, it greatly contributes to the industrial production of water glass.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Shiraishi Minority No. 16-3 Onogawa, Tsukuba City, Ibaraki Prefecture, Institute of Pollution Resources, Institute of Industrial Technology (72) Shin Makoto Takemori No. 16-3 Onogawa, Tsukuba City, Ibaraki Industrial Technology Pollution Resource Research Institute (72) Inventor Ryohei Otsuka 3-4-1, Okubo, Shinjuku-ku, Tokyo Inside Faculty of Science and Engineering, Waseda University (72) Inventor Naofumi Sakamoto 1-1, University of Science, Okayama City, Okayama Prefecture (72) Inventor Hitoshi Koshimizu 9-15-1, Kameido, Koto-ku, Tokyo Katsuyoshi Yamagishi, Examiner, Research & Development Department, Nippon Kagaku Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A method for producing an aqueous solution of alkali silicate, which comprises decomposing serpentine with a mineral acid to produce silica gel of a fibrous aggregate, and then dissolving the silica gel in an aqueous solution of caustic alkali. 2. The method for producing an aqueous alkali silicate solution according to claim 1, wherein silica gel is dissolved in an aqueous caustic alkali solution under normal pressure.