JPS591216B2 - Method for producing easily soluble solid alkali silicate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing easily soluble solid alkali silicate, and its purpose is to effectively produce fine silica-containing by-products discharged from the electrothermal metallurgy industry, such as metal silicon and ferrosilicon. The present invention provides an industrially advantageous method for producing easily soluble solid alkali silicate which can be used in various fields by mixing and reacting the by-product with liquid caustic alkali.

Fine silica-rich by-products obtained during the collection of exhaust gas generated from electrothermal metallurgy industries, such as metal silicon and ferrosilicon, have recently been proposed for various effective uses as a silica source. One example of this is its use in alkali production.

For example, a method for producing an aqueous sodium silicate solution, as disclosed in Japanese Patent Publication No. 51-17519, effectively utilizes this by-product as a silica source.

On the other hand, as in Japanese Patent Publication No. 48-16438, a mixture of the above-mentioned by-products and solid caustic alkali such as powder, grains, or flakes is prepared in advance, and when actually used, water is added to heat the solution. It was proposed that an aqueous alkali silicate solution could be easily prepared using the heat of reaction.

Generally, alkali silicate is used in the form of an aqueous solution, called water glass, but it is economically disadvantageous because it must be transported and stored in drums or tank trucks.

In this respect, packaging the above-mentioned mixture in a waterproof paper bag or the like is sufficient, and the above-mentioned drawbacks were considered to be solved.

However, it has been found that a water glass solution is not as easily obtained as proposed by simply adding water to this mixture.

In other words, it takes a long time to react to form an alkali silicate, and since the reaction rate is low, there is a lot of unreacted silica, making it impossible to adjust the desired molar ratio of silica and alkali, resulting in poor quality. There are many problems such as poor quality, the danger of generating hydrogen gas when adding water and reacting, and the need for a reaction tank and dissolution tank at the site of use. Judging from the examples in which it is used, it is hardly usable.

For this reason, the present inventors have developed an easily soluble solid alkali silicate using the above-mentioned by-product and a method for producing the same.

(Refer to Japanese Patent Application Laid-Open No. 53-52299.) However, this manufacturing method involves kneading by-products such as ferrosilicon, caustic alkali, and water at a predetermined molar ratio to form a paste.
Next, the method involves heating and curing at a temperature of 70 to 130°C, but it requires at least 30 minutes from kneading to product production, and in particular, evaporation is carried out to allow the reaction to occur as much as possible and at the same time to produce a product with a predetermined moisture content. For this reason, they had to spend a long time curing under heat.

As a result, it is difficult to control the moisture content in the product, and there are large variations in quality characteristics such as the product's molar ratio, dissolution rate, and undissolved components, making it difficult to control the set quality. .

The inventors of the present invention continued to study this manufacturing method and found that there is an extremely delicate relationship between the kneading and reaction of raw materials, and that the quality of the product will always be stable if manufactured according to the specific conditions described below. The present invention was completed by discovering that it can be produced continuously and in large quantities in a surprisingly short amount of time.

That is, the present invention provides a method for producing a solid alkali silicate by reacting a fine silica-containing by-product discharged from the electrothermal metallurgy industry, such as metal silicon or ferrosilicon, with a liquid caustic alkali. is the weight of 8102 in the by-product that can be effectively used as an alkali silicate, H is the weight percent of water in the by-product (loss on heating at 500°C for 930 minutes),
C is the SiO2/R20 weight ratio (where R represents Na or K) and a is the water content (wt%) of the raw material mixture.
Concentration M calculated by [expressing a value in the range of 3 to 30]
The liquid caustic alkali (weight ratio of R20) and the effective 5102 in the by-product are combined with C (S 102/R20 weight ratio) of 1.
．． This is a method for producing easily soluble solid alkali silicate, which is characterized by rapidly kneading to a ratio of 93 to 2.9 and reacting to produce solid alkali silicate all at once.

The present invention will be explained in detail below.

First, the silica source used as a raw material is dust that is rich in fine silica and is collected during exhaust gas collection in the electrothermal metallurgy industry, which manufactures simple metals, alloys, silicides, carbides, etc. .

Industries that produce such dust as by-products include metal silicon, metal chromium, metal manganese, ferrosilicon, ferrochrome,
Examples include manufacturing industries of ferromanganese, silicon halides, silicon carbide, etc., and dust produced as a by-product during the production of metal silicon or ferrosilicon is particularly preferred as the silica raw material in the present invention.

Although it is of course possible to use this product as it is in the dust state, it is preferable for operation to use one that has been granulated to an appropriate particle size.

In addition, when using this dust, if necessary, silica that easily reacts with caustic alkali, such as natural amorphous silica, commercially available white carbon, silica gel, etc., may be used as an auxiliary. .

Such silica raw materials generally contain water, but when used, it is preferable that the water content is about 20 times or less.

The reason for this is due to limitations on the water content in the raw material formulation and on the applicable predetermined concentration of liquid caustic.

Next, the other raw material, caustic alkali, is caustic soda or caustic potash, and usually caustic soda is used, but liquid caustic alkali having the following formula concentration M (R 20% by weight) is used.

[In the formula, S is the weight ratio of SiO2 in the by-product that can be effectively used as an alkali silicate, H is the weight ratio of water in the by-product,
(Heating loss at 500°C for 30 minutes), C is the weight ratio of effective SiO□ in the by-product to the alkali content in the liquid caustic alkali, SiO2/R20 (R represents Na or K), and a is the weight ratio in the raw material mixture. The above formula is derived as follows.

That is, if the usage amount of the silica-containing by-product is used as the standard (1), and the usage amount of liquid caustic alkali IJ (R20) to be blended with it is X, and this is substituted for C: Moisture in liquid caustic alkali = 100-M (wt%) When the water content in the raw material mixture is a, it is expressed as: If this is transformed and expressed as M, the following formula is obtained. Applicable.

That is, the reason for this is that when the temperature is about 23 or less, the reaction of the raw material mixture becomes insufficient and the effective SiO2 decreases, leading to an increase in insoluble clusters in the product. In particular, since evaporation is required to bring the water content of the resulting alkali silicate to a predetermined value, heating is performed for a long time.

As a result, the quality of the product deteriorates, resulting in significant deterioration in manufacturing method and product quality, which is not appropriate.

Specifically, this M is, for example, M in liquid caustic soda.
The amount of a2O is in the range of 40 to 50% by weight, and due to this relationship, the blended raw material mixture can obtain easily soluble solid alkali silicate in a very short time as described below.

In other words, since the reaction with alkali silicate is an exothermic reaction, it is necessary to mix the raw materials in consideration of water evaporation during production, but there are limitations due to the reactivity of the preparation and the setting of the moisture content of the product. Although it is very difficult to do so, if the above conditions are followed, the amount of evaporation will be stabilized with a substantially constant tolerance since the kneading of the raw materials and the completion of the reaction will take just one hour, and the above equation will hold. This allows products of high design quality to be manufactured easily and in a short time.

Next, when mixing raw materials, due to the characteristics of the product, the weight ratio S
i02/R20 (R represents Na or K) is 1
．． It is necessary that the ratio is between 93 and 2.9.

The reason for this is that when it is less than 1.93, the hygroscopicity of the product tends to increase, while when it is more than about 2.9, the effective SiO2 of the silica raw material that can be effectively used as alkali silicate decreases, making the product insoluble. This is because there is a tendency to increase the number of ingredients, making them unsuitable as products.

That is, the effective S io 2 varies depending on the type of raw material, but the total silica in the raw material and the silica fraction, which is considered to be alkali silicate with a high molar ratio that is not utilized for the reaction to alkali silicate or is difficult to dissolve even if reacted, Although it is determined as a difference, it also has a correlation with the polymerization ratio, and tends to decrease as it increases, and the approximate value can be determined experimentally in advance.

Thus, if the raw materials are mixed under the control described above, the following steps can be completed within a single hour with extremely simple operations.

That is, the raw material mixture is quickly and uniformly kneaded while no substantial reaction occurs.

Whether or not a reaction has occurred can be easily determined by the presence or absence of heat generation in the kneaded material. If heat generation occurs in the cross-mixing, the reaction will proceed too much and fluidity will be lost, making it impossible to achieve uniform cross-mixing, resulting in product quality deterioration, so avoid this. Should.

The mixture is kneaded at about 70° C. or below, then kept above this temperature for reaction, cooled, solidified, and coarsely crushed or ground to an appropriate particle size to produce a product.

Note that the change in physical properties from the kneaded product to the reaction product is continuous and there are no clear boundaries, but at first the solid silicon dust is wet with liquid caustic soda (plasticity), and as the reaction progresses, the physical properties change. As the temperature begins to rise, it becomes fluid, and the reaction gradually becomes more intense.As the temperature rises further, it reaches a boiling state while generating water vapor, etc., and as the reaction approaches the end, the viscosity of the highly concentrated alkali silicate increases and it becomes rubbery. (When it cools, it solidifies and becomes glass-like.)

This change occurs over a short period of time, and it is technically difficult to maintain it in a stopped state midway through.

In addition, it is difficult to cover this change with one process (equipment), so we have taken into account the change as much as possible and divided it into two processes, kneading and reaction, and we have created a process that directly connects the two processes. is desirable.

However, if there is a device that can effectively perform kneading and reaction, there is no need to distinguish between kneading and reaction since they are simple operations.

The kneading step is carried out to the extent that the reaction progresses and becomes fluid, in other words, until no substantial reaction occurs.
To do this, a water-cooled double-screw feeder, for example, is required, which is equipped with a cooling mechanism that allows the kneaded material to be at 70°C or lower (preferably 60°C or lower) and homogeneously kneaded in a short time. is suitable.

In addition, in the reaction process, if the reaction is slow, water will not evaporate sufficiently as planned, so it is necessary to heat the initial temperature to about 70°C at the start of the operation, but once the reaction has started, As this process progresses, a significant amount of heat is generated, so this amount of heat is sufficient, and in the case of continuous operation, hardly any heat source is required thereafter.

As a reactor, a flaker drum, a belt conveyor, etc. are suitable, but in view of the tendency of the reaction product to stick to metal, the belt conveyor is preferably made of Teflon or polypropylene.

Thus, according to the present invention, easily soluble solid alkali silicate can be produced continuously in an extremely short period of time, from the time of crosstalk to the end of the reaction, which is a few minutes or less.The following characteristic advantages are pointed out. be able to.

(1) The drying process, which requires a long time, is omitted.

(Time is saved and the equipment is compact).

(2) Since the heat of reaction is effectively used, almost no heat source is required.

(3) Less uneven drying of the product.

Since there is no need for drying by applying heat from the outside, there is almost no drying unevenness on the surface and inside of the material to be dried.

In particular, the quality characteristic is that the product has a fast dissolution rate and is easily soluble.

(4) Product moisture can be controlled by the initial kneaded product moisture.

The alkali silicate produced by the method of the present invention has a limited moisture content of 18 to 28 weight percent, preferably 20 to 25 weight percent (this value is the value of loss on heating at 500°C for 1 hour). It is a solid alkali silicate having SiO2/R20 in the range of 1.93 to 2.9 and having a black-gray appearance that can be rapidly dissolved in coarse to powdery water to prepare a water glass liquid.

Therefore, the product according to the present invention can be applied to conventional fields where water glass is applied, such as civil engineering as a soil stabilizer and soil improver, metals as a binder or refractory binder in mold making, and ceramics. Due to its solidity, it can be used advantageously for its handling and functional advantages.

Next, the present invention will be specifically explained by giving Examples and Comparative Examples.

Examples 1 and 2 and Comparative Examples 1 and 2 Easily soluble solid sodium silicate having the product target values shown in Table 1 is produced using ferrosilicon dust and liquid caustic soda according to the above formula.

On the other hand, for comparison, commercially available liquid caustic soda having a weight ratio of 50% was used and produced in the same manner regardless of the formula.

Water-cooled double screw with rotation speed 10 Or, p, m.
Continuously feed predetermined starting materials to each kneader, and
Knead homogeneously while keeping the temperature below 0'C.

The average residence time for this kneading was about 20 seconds.

When the continuously discharged contaminant is placed on a Teflon-lined belt conveyor and heated to an initial temperature of 70°C or higher, the reaction starts, and the reaction occurs rapidly with intense evaporation, resulting in an average reaction. The reaction was completed in about 60 seconds.

The conveyor was heated only for about 1 minute at the beginning, and after that, no heating was required and continuous operation was performed using only the heat of reaction.

The obtained reaction product is cooled as it is and then pulverized, resulting in a product with the target product composition value.On the other hand, the product of the comparative example has a lot of water and lacks desirable product characteristics by itself, so it is dried. Although necessary, significant heating was not caused when compared with the example until the same moisture content was reached.

Table 1 summarizes the results along with the conditions.

As a result, uneven drying occurs inside and on the surface of the dried product, and there are probably areas that are locally overdried, and this phenomenon is unavoidable.

Examples 3 and 4 and Comparative Examples 3 and 4 Similarly, using ferrosilicon dust and liquid caustic soda according to the above formula, the weight ratio of soluble components SiO2/Na
Easily soluble solid sodium silicate having an 2O content of 2.7 and a water content of 21% by weight is produced in the same manner as in the previous example.

For comparison, commercially available liquid caustic soda having a weight ratio of 50% was used for comparison, and the preparation conditions and production results are shown in Table 2.

In addition, in the manufacturing method, the kneading of the raw materials is the same as in Example 1, but the reaction is performed by continuously discharging the kneaded material at a drum rotation speed of 0.5.
The sample was dropped onto a double flaker drum of r, p, m (the drum surface was heated through steam of 1-5 to 9/4 G inside the drum).

The product was produced by a very short reaction time in which the contaminant reacted violently on the drum surface and was continuously scraped off with a scraper.

Heating of the drum surface is required only at the beginning of operation and after continuous operation.Reference ExamplesIn order to examine the dissolution characteristics of the products obtained in Example 1, Comparative Example 1, Example 3, and Comparative Example 3, the following method was used. The dissolution rate was determined.

10g of a sample ground to a particle size within a certain range (44μ to 210μ, 95% or more) was mixed with 200g of water at 20°C.
After stirring and dissolving for 5 minutes and 10 minutes at a temperature of 50°C, it was immediately filtered, and the S io 2 and Na 2 O in the P solution were analyzed to determine the soluble components (S iO 2 + Na 20 ) in the product.
When the dissolution rate was determined by calculating the amount of (Si02+Na20) eluted in the p solution, the results shown in Table 3 were obtained.

From the above results, it can be seen that the insolid sodium silicate obtained by the method according to the present invention has few insoluble clusters and has good solubility in water.

Therefore, this product can be used as a so-called instant alkali silicate.

Claims (1)

[Claims] 1. In producing solid alkali silicate by reacting fine silica-containing by-products discharged from the electrothermal metallurgy industry, such as metal silicon and ferrosilicon, with liquid caustic alkali, the following formula: [Formula In the middle, S is the weight ratio of SiO2 in the by-product that can be effectively used as an alkali silicate, and H is the weight percentage of water in the by-product (
500°C, loss on heating for 30 minutes], C is the weight ratio of effective 5102 in the by-product to the alkaline content in the liquid caustic alkali [SiO□/R20 (where R represents Na or K)
] and a is the water content (by weight) in the raw material mixture from 23 to
represents a value in the range of 30] The liquid alkali with a concentration M (R20 weight ratio) calculated as follows and the effective SiO2 in the by-product are 1. A method for producing an easily soluble solid alkali silicate, which comprises rapidly kneading the ingredients in the same proportions and reacting to produce a solid alkali silicate all at once. 2. The method for producing easily soluble solid alkali silicate according to claim 1, wherein the reaction is carried out on a belt conveyor. 3. Claim 1 in which the reaction is carried out in a drum flaker
A method for producing an easily soluble solid alkali silicate as described in 1. 4. The method for producing easily soluble solid alkali silicate according to claims 1 to 3, wherein the liquid caustic alkali is caustic soda having a concentration of 40 to 50% by weight as R20 (R represents Na). 5. Production of easily soluble solid alkali silicate according to any one of claims 1 to 4, wherein the fine silica-containing by-product has a water content (500°C, loss on heating for 30 minutes) of 20% by weight or less. Law. 6 Weight ratio S of easily soluble solid alkali silicate to soluble components
The easy-to-understand method according to claims 1 to 5, which is a powdered sodium silicate having a t 02 / Na 20 of 1.93 to 2.9 and a moisture content of 18 to 28 by weight. Method for producing soluble solid alkali silicate.