JPH01261221A - Production of aqueous solution of alkali silicate - Google Patents

Abstract

PURPOSE:To efficiently obtain an aqueous solution of an alkali silicate by wet method, by decomposing serpentine with a mineral acid to form fibrous aggregate silica gel and dissolving the gel in an aqueous solution of a caustic alkali. CONSTITUTION:Serpentine is decomposed with a mineral acid to form silica gel of fibrous aggregate. Then the silica gel is dissolved in an aqueous solution of a caustic alkali to give the aimed solution. A starting raw material of the fibrous aggregate preferably has a high content of serpentine minerals. Ground serpentine is used as serpentine of raw material, a considerable limitation of particle size is not required but too large serpentine is not preferable because it takes a long time in reaction and serpentine has preferably about -100 meshes. In the condition of the dissolution operation, stirring at normal temperature under pressure is sufficient and the dissolution reaction is smoothly advanced without especially loading pressure. As for temperature, since a little heating as accelerating effects on dissolution rate, heating is properly applied to an additional condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an aqueous alkali silicate solution using serpentinite as a starting material.

[Conventional technology]

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

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

(2) A method of manufacturing by directly reacting natural silica such as ridge grass or easily reactive amorphous silica such as ferrosilicon dust with an alkaline aqueous solution (generally referred to as a wet method).

Among these typical manufacturing techniques, the latter wet method is recognized as having a very advantageous aspect in that it does not require a large amount of thermal energy like the former dry method, or it has a limited silica source. There is a drawback that impurities get mixed into the solution.

Therefore, currently only dry methods are practiced industrially.

[Problem to be solved by the invention]

As an improvement to the wet method, it has also been proposed to ultrafinely pulverize crystalline silica such as silica sand and react it with an aqueous alkali solution as a silica source. However, with this method, Si
It is difficult to obtain a concentrated water glass with a high O/Na2O ratio, and the yield is also low.

Therefore, it is necessary to carry out the reaction under pressure, and when complicated process operations such as pulverization are taken into consideration, the advantages of the dry method are still not as good.

By the way, serpentinite is a silica-containing ore that is produced in large quantities in our country. Attempts have been made for a long time to effectively use this serpentine as an industrial resource, but the fields of use are still extremely limited.

For example, attempts to recover magnesium and small amounts of valuable metals by decomposing serpentine with sulfuric acid have been proposed, but the use of silica, which makes up the majority of serpentinite, has been proposed for use in siliceous fertilizers such as dissolved phosphorous fertilizers. Although there are examples, they have not received much attention so far.

The present inventors discovered the fact that silica produced by mineral acid decomposition of serpentinite has a structure that substantially has the basic structure of serpentine, and has good reactivity as an alkaline component. and completed the present invention. Therefore, the object of the present invention is to efficiently produce an aqueous alkali silicate solution by a wet method using serpentine as a starting material.

[Means to solve the problem]

A method for producing an alkali silicate aqueous solution according to the present invention for achieving the above object includes decomposing serpentine with mineral acid to produce a fibrous aggregate of silica gel, and then dissolving the silica gel in a caustic alkali aqueous solution. Characteristics.

In the present invention, serpentinite, which is the starting material for silica gel production, is a magnesium-rich silicate rock, petrologically known as peridotite.
It is classified as an ultramafic rock along with nitrite).

The two have similar chemical compositions, but while peridotite has forsterite and enstatite as its main constituent minerals, serpentinite has chrysotile.
i le), Lizardite (Lizard lte)
, Serpentine Minerals consisting of Antigorite
are the main constituent minerals, and are completely different. In many cases, serpentinite is formed by hydrothermal alteration of peridotite, so in addition to serpentine minerals, it also contains unaltered forsterite, enstatite, calcite, and minerals. 0 feet (C
h row ite), magnetite (Magne
It may contain impurity minerals such as tite.

In addition, the serpentine mineral present in serpentine is sometimes a fibrous aggregate that is clearly visible to the naked eye, so-called asbestos (Asb).
It may also be produced as estos.

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

The starting material of the fibrous aggregate silica gel, which is the raw material for producing the aqueous alkali silicate solution according to the present invention, is not particularly limited in its history as long as it is the above-mentioned serpentinite, but it is preferable that it has a high content of serpentine mineral.

If there are impurities in the raw materials, unaltered forsterite and enstatite can be easily removed by selective crushing or manual selection, and magnetic minerals such as chromite and magnetite can be easily removed by magnetic separation. Impurities and trace components that are soluble in mineral acids, such as iron that replaces the magnesium in serpentine minerals and iron hydroxide, do not substantially remain in the produced silica gel, and can be removed from the treatment solution. It is not considered to be much of a problem because it elutes into the water.

Pulverized serpentine is used as the raw material, but the particle size does not need to be too limited. However, if it is too large, it will take a long time to completely react, so it is undesirable.
esh level is preferable.

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

Sulfuric acid or hydrochloric acid is preferably used as the mineral acid, and usually
It can be used in an aqueous solution of IN or higher. However, if the aqueous solution concentration 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 mineral acid used must be at least in excess of the stoichiometric amount required to convert all the magnesium components contained in the serpentinite raw material into chloride or sulfate. There are no particular restrictions on the slurry concentration, and it is set solely in consideration of workability and economic efficiency.
Usually lO~250g/[, preferably 50~200g
/ff range.

As conditions for mineral acid decomposition, a low temperature range from room temperature to 100° C. is sufficient, and when the concentration of mineral acid used is high, better results are obtained by not raising the temperature too much. The treatment time varies depending on the mineral acid concentration, decomposition temperature, etc., but it is necessary to hold the treatment for at least 3 hours or more. Note that it is a desirable requirement that the treatment be performed under stirring in order to proceed with the reaction smoothly.

The raw material decomposed under the above conditions is separated from the mother liquor according to 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 can be converted into hydroxide,
It can be effectively used by converting it into oxides and other forms. At the same time, valuable metal components such as nickel, cobalt, and chromium that are dissolved in small amounts can also be separated and recovered.

The silica gel produced by mineral acid decomposition in this way has a structure that retains the basic structure of fibrous aggregates of the raw material serpentinite without being substantially destroyed, and the magnesium oxide content is It is a high purity amorphous material with a content of 0.3 wt% or less.

Next, the above fibrous aggregate silica gel is dissolved in an aqueous caustic solution.

Typical caustic materials include sodium hydroxide and potassium hydroxide, but sodium hydroxide is often used. The caustic alkali is reacted directly with the silica gel in the form of an aqueous solution. It is desirable to set the alkaline concentration of the aqueous solution in the range of 0.5 to 5N, especially 1 to 3N; if the concentration is thinner than this range, the processing capacity will increase and it will not be industrially practical, while if it is too thick, the dissolution rate will slow down. Moreover, the viscosity of the solution increases, impeding workability. In addition, it is appropriate to select the amount of caustic alkali to be used within the range of 1 to 3 in terms of the molar ratio of 5i02/M20; if this molar ratio is less than 1, there is no industrial meaning, and if it exceeds 3, there is no reaction. The silica force (leads to residual silica).

The dissolution operation can be carried out at room temperature and under normal pressure with stirring, and the dissolution reaction proceeds smoothly even without applying pressure. Regarding the temperature, since slight heating has the effect of accelerating the dissolution rate, it is applied as an additional condition as appropriate.

The aqueous alkali silicate solution obtained by dissolving in this way can be used as a product as it is, but if necessary, it can be separated and
Removal of undissolved components through post-processing such as concentration,
The concentration is adjusted and the product is made.

[For production]

Silica gel, which is produced by decomposing serpentine with mineral acids, has a main component, the SiO4 tetrahedral sheet of serpentine mineral, which maintains its original structure without being substantially decomposed, and the octahedral sheet of serpentine. The magnesium and soluble metal components therein have selectively eluted and highly reactive texture. Therefore, dissolution with a caustic alkali aqueous solution proceeds smoothly and quickly even under conditions of normal temperature and normal pressure, and is efficiently converted into an aqueous alkali silicate solution.

〔Example〕

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

Example 1 Serpentinite from the Hidaka Mine in Kochi Prefecture was crushed and classified into 1150 mesh pieces. 100 g of this serpentine was placed in a 59 beaker, 2 g of 3N hydrochloric acid was added, the beaker was covered with a petri dish, and the mixture was treated at 100° C. for 4 days with stirring. After the treatment, it was separated into a furnace, thoroughly washed with ion-exchanged water, and further purified to obtain 40 g (calculated as SiO2) of fibrous aggregate of silica gel.

Fibrous aggregate silica gel containing approximately 20% water by weight 0=
Put 9 g (in terms of S L O2) into a looml Teflon heater and heat it to 20 ml at room temperature (approximately 18°C).
An aqueous IN sodium hydroxide solution was added thereto and dissolved while stirring with a stirrer. The entire amount was dissolved in about 10 minutes, and the sodium silicate solution was separated, but no undissolved silica gel was found on the filter paper.

This solution was an aqueous sodium silicate solution with a molar ratio of SiO/Na2O of 1.5.

Example 2 The same fibrous silica gel as in Example 1. IN sodium hydroxide loml was added to Oi and dissolved at room temperature.

As a result, the solution dissolved in 3 hours, and nothing remained on the filter paper after it was removed.

The obtained mother liquor has a molar ratio SiO/N a 20 of about 3
It was a molar sodium silicate aqueous solution.

Example 3 An experiment similar to Example 2 was conducted using a melting temperature of 70°C.

As a result, the entire amount was dissolved within 30 minutes from the start of dissolution.

Comparative Example A ridge grass from Iwo Jima, Kagoshima Prefecture (310298%) used in the production of wet alkali silicate.1. Osr was dissolved under the same conditions as in Example 1. As a result, even after 10 hours of dissolution, the entire amount was not dissolved.

[Effects of the Invention] According to the present invention, since the silica source is silica gel, which is an easily reactive fibrous aggregate with a unique structure made from serpentinite as a starting material, the silica gel can be processed extremely smoothly even under normal temperature and normal pressure conditions. Moreover, an aqueous alkali silicate solution can be rapidly produced.

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

Patent applicant Director of Industrial Technology Nippon Chemical Industry Co., Ltd.

Claims (1)

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