JPH05170426A - Production of high purity synthetic kaolinite in high yield - Google Patents

Abstract

PURPOSE:To obtain a high purity synthetic kaolinite in high yield by gelating a Na2SiO3 aq. solution and an Al2(SO4)3 aq. solution with a pH controlled and hydrothermal treating after aging with aging with two steps of alkaline and acidic, filtrating and washing. CONSTITUTION:The sodium silicate aq. solution and the aluminum sulfate aq. solution are mixed and are gelated while keeping pH 4-12. The silica-alumina gel obtained is aged in the alkaline aq. solution of pH >=7, is filtrated and is washed to completely gelate an ungelated raw material and to completely remove residual SO4 ion. Next, the gel is aged in the acidic aq. solution of pH 3-4, is filtrated, is washed and sodium ion is ion exchanged with proton. And the synthetic kaolinite having <=0.1wt.% impurity content except silica, aluminum and water is obtained by hydrotherm-treating the gel in an autoclave or a pressure tight cup.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a raw material for ceramics,
The present invention relates to a production method of high-purity, high-purity synthetic kaolinite, which is widely used as a binder for molding ceramics, a filler for papermaking, and is attracting attention as a new functional material.

[0002]

2. Description of the Related Art Conventionally, natural clay containing kaolinite as a main component has been used as a raw material for ceramics. This kaolinite is the main mineral of the kaolinite group in clay minerals and is a white, gray or yellow mineral. The quality of natural clay mainly composed of kaolinite, especially the kibushi clay and frog clay produced in the Seto area of Aichi prefecture, has been declining due to long-term consumption and the recent rapid development of residential land. is doing. Therefore, research and development of artificial clay has been promoted as a novel functional material utilizing the fact that it is a plate crystal as a material replacing these natural clays.

A hydrothermal synthesis method is usually used as a method for producing the above kaolinite. This hydrothermal synthesis method is a method of obtaining a desired mineral by sealing the raw material in an autoclave in the presence of water and maintaining it at a high temperature and high pressure for a certain time, and is widely used as a synthetic means for various artificial minerals. ing. Methods for producing kaolinite by such a hydrothermal synthesis method include Shibasaki and Watamura (Clays and
Clay Minerals, 1983) and the like, a method of mixing silica sol and alumina sol as a raw material, and a method of mixing allophane, diatomaceous earth, montmorillonite, zeolite and the like and an aluminum compound as a raw material are known.

However, in the above-mentioned method, since the silica raw material and the alumina raw material are solid mixed or solid / liquid mixed, there are difficult-to-react portions, the reaction does not proceed 100% and the kaolinite content does not increase. was there. Furthermore, when a natural raw material is used, impurities such as metal oxides contained in the raw material remain in kaolinite, which causes a problem of coloring.

For example, when silica sol and alumina sol, which are synthetic products, are mixed and used as a raw material, impurities such as metal oxides are not mixed, but the kaolinite content is about 90% regardless of the hydrothermal treatment temperature and the hydrothermal treatment time. Then the reaction is completed and unreacted silica and alumina remain. This is because the silica and alumina raw materials are mixed in a solid state and therefore are not homogeneously mixed, and because these stabilizers are used in the sol or gel manufacturing process, they are fired to remove them. It is considered that this is because of the presence of non-reactive silica and alumina parts.

The remaining unreacted silica and alumina cause agglomeration of the kaolinite microcrystalline powder, resulting in deterioration of clay characteristics of the kneaded clay using the same. Further, when diatomaceous earth and aluminum chloride are mixed and used as a raw material, quartz, iron, and other metal oxides remain as impurities in kaolinite, and diatomaceous earth as a raw material also remains.

An object of the present invention is to provide a method capable of producing kaolinite having a higher production rate and a higher purity that does not contain impurities and unreacted substances as compared with the conventional methods.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have obtained a method for producing a synthetic kaolinite having a high production rate and a high purity according to the present invention. That is, the present invention gels while maintaining the sodium silicate aqueous solution and the aluminum sulfate aqueous solution at pH 4 to 12, and then ages in an alkaline aqueous solution having a pH of 7 or more,
A method for producing a high-purity, high-purity synthetic kaolinite, which comprises subjecting the gel, which has been filtered and washed and then aged, filtered and washed in an acidic aqueous solution of pH 3 to 4, to a hydrothermal treatment.

[0009]

The present invention will be described in detail below. The synthetic kaolinite in the present invention is a chemical formula {Al ₂ Si ₂ produced mainly by hydrothermal treatment from a silica raw material and an alumina raw material.
O ₅ (OH) ₄ }, which is a tetrahedral sheet consisting of silicon and 4 oxygens, and aluminum is surrounded by 6 oxygens 8
The face sheet is a layered hydrous aluminosilicate composed of 1: 1. The particle shape has a granular, spherical, or plate-like shape depending on the manufacturing method.

The synthetic kaolinite of the present invention is a kaolinite having a high production rate and high purity. The production rate is calculated by measuring the weight loss of kaolinite with dehydration of the structured water by thermogravimetric analysis (TG). The present invention provides a high production rate of 90% or more, preferably 95% or more. Provide synthetic kaolinite. Next, what is high purity?
The content of impurities other than silica, alumina and water is 0.1wt
% Means less than or equal to%. Examples of the impurities include alkali metals such as sodium and calcium, alkaline earth metals, and heavy metals such as iron and titanium.

As described above, the silica-alumina gel of the present invention can be prepared by using an aqueous sodium silicate solution and an aluminum sulfate aqueous solution as raw materials and gelling these. Gelation is pH 4-12, preferably pH
It is carried out at 10 to 12, and an alkali and an acid can be added if necessary. The gelling method is not particularly limited, but continuous mixing is preferably performed with stirring in order to uniformly mix the silica and alumina particles in the gel. Further, the Si / Al molar ratio in the synthetic gel is preferably close to Si / Al = 1 in order to suppress by-products in the hydrothermal reaction.

In the present invention, the silica-alumina gel prepared as described above is first aged, filtered and washed in an alkaline solution having a pH of 7 or higher to completely gelate the unreacted gelled raw material and the residual SO. Remove ₄ ions. At this time, the aging temperature and time are not particularly limited, but it is preferable to heat to accelerate the reaction. If necessary, an alkali such as sodium hydroxide or ammonia can be added to adjust the pH.

Then, aging, filtration and washing are carried out in an acidic solution having a pH of 3 to 4 to carry out ion exchange between sodium ions and protons. When the aging is less than pH3, aluminum is dissolved to cause a change from the optimum composition of gel, and when the aging is more than pH4, ion exchange becomes insufficient. The pH is adjusted by adding hydrochloric acid, nitric acid, sulfuric acid and an organic acid, and is not particularly limited. For example, after aging at a temperature of room temperature to 100 ° C for 1 hour or more, Na ⁺ eluted by filtration / washing is added. Remove. The amount of residual Na is not particularly limited,
To promote crystallization, the Na / Al molar ratio is preferably 0.1 or less.

The hydrothermal reaction in the present invention can be carried out by using an ordinary autoclave or pressure cup. The slurry concentration, reaction temperature, and reaction time in the hydrothermal reaction are not particularly limited, but it is preferable that the slurry concentration is 1 to 20 wt%, the reaction temperature is 100 ° C. or higher, and the reaction time is 1 hour or longer. If necessary, the reaction time can be shortened by performing stirring and / or adding seed crystals.

By such a hydrothermal treatment, kaolinite can be synthesized with a production rate close to 100% as compared with the production rate of about 90% in the conventional method.

[0016]

The present invention is described in detail below with reference to examples, but the present invention is not limited to these.

(Example 1) No. 3 water glass (S
iO ₂ = 29.3 wt%, Na ₂ O = 9.35 wt%) and aluminum sulfate (Al ₂ O ₃ = 8.02 wt%),
The raw materials were continuously mixed while stirring so that the molar ratio was Si / Al = 1. At the same time, a silica-alumina gel was prepared by adding and mixing sodium hydroxide so that the reaction pH became 10-12.

When the composition of this gel was analyzed, the molar ratios were Si / Al = 1, Na / Al = 0.8, and SO ₄ ions = 2 wt% (calculated as anhydrous gel). Silica above
The alumina gel is filtered and washed to remove sodium sulfate as a by-product and excess sodium hydroxide, and then pH = 10.
Slurry is adjusted to 100 ° C. and heat-treated for 1 hour
_Four ions were dissolved.

Next, after filtering and washing again to remove the eluted SO ₄ ions, 0.5N nitric acid was added dropwise to bring the final pH to 3
By adjusting to -4, the sodium ion and the proton were ion-exchanged to elute the sodium ion.
After aging for 24 hours at room temperature, the sodium ions were removed by filtration and washing to obtain a silica-alumina gel for hydrothermal treatment. When the composition of this gel was analyzed again, the molar ratios of Si / Al = 1, Na / Al = 0.005 and SO
₄ ions = 0.1 wt% (anhydrous gel equivalent).

The above-mentioned raw material gel was charged into an autoclave so that the slurry concentration would be 10 wt%, and hydrothermal reaction was carried out at 220 ° C. for 10 days. After cooling, it was washed with water, filtered, and dried to obtain a product. The X-ray-diffraction result of the obtained product is shown in FIG.

The product showed only the X-ray pattern of kaolinite. Further, the weight loss of kaolinite due to dehydration of structured water was measured by thermogravimetric analysis (TG) to quantify the amount of kaolinite produced, and the content of kaolinite in the product was 98%.

The results of the chemical composition analysis are shown in Table 1 below. Impurities other than silica, alumina, and water are 0.1 wt% or less, which indicates that the purity is high.

[0023]

[Table 1]

Example 2 Example 1 was repeated except that the gel prepared in Example 1 was used and hydrothermal treatment was carried out at 250 ° C. for 5 days.
The same operation was performed to obtain a product. X of the obtained product
The line diffraction result is shown in FIG.

The product showed only the X-ray pattern of kaolinite. When the weight loss of kaolinite with dehydration of the structured water was measured by thermogravimetric analysis (TG) and the amount of kaolinite produced was quantified, the kaolinite content in the product was 97%.

(Example 3) Example 1 was repeated except that the reaction pH during mixed gelation was adjusted to 4 to 6.
The same operation was performed to obtain a product. The composition analysis result of the gel before aging treatment shows that Si / Al = 1 in molar ratio,
Na / Al = 0.2, SO ₄ ion 4 wt% (anhydrous gel equivalent), and the composition analysis result of the gel after aging treatment was Si / Al = 1 and Na / Al = 0.005 in terms of molar ratio, SO _Four
Ion = 0.2 wt% (converted to anhydrous gel). The X-ray-diffraction result of the obtained product is shown in FIG.

It can be seen that the product is only kaolinite as in Example 1. Further, the thermogravimetric analysis revealed that the kaolinite content in the product was 97%.

Comparative Example 1 A product was obtained by the same procedure as in Example 1 except that the aging in the alkaline solution and the aging in the acidic solution were not performed. The X-ray-diffraction result of the obtained product is shown in FIG.

As is clear from FIG. 2, the peak of the kaolinite-like mineral does not appear in the X-ray diffraction pattern, indicating that the kaolinite-like mineral is not formed.

(Comparative Example 2) A product was obtained in the same manner as in Example 1, except that the aging in an acidic solution was carried out at pH 1-2. The composition of the hydrothermally treated gel was analyzed and the molar ratios were Si / Al = 1.8 and Na / Al = 0.1.
It is 0, which means that melting of aluminum is occurring. The X-ray-diffraction result of the obtained product is shown in FIG.

It can be seen that the product is only kaolinite-like mineral as in Example 1. Further, the thermogravimetric analysis revealed that the kaolinite content in the product was 45%.

(Comparative Example 3) Colloidal shikari (Nissan Chemical's Snowtex N) and alumina sol (Nissan Chemical's alumina sol-200) were used as raw materials, and S was used in a molar ratio.
Mixing and stirring were performed so that i / Al = 1. Then dry and 600 to remove the stabilizer acetic acid.
A raw material gel used for hydrothermal treatment was obtained by performing a baking treatment at 1 ° C. for 1 hour.

The above-mentioned raw material gel was charged into an autoclave so that the slurry concentration was 5 wt%, and hydrothermal treatment was carried out at 220 ° C. for 10 days. After cooling, it was washed with water, filtered, and dried to obtain a product. The X-ray-diffraction result of the obtained product is shown in FIG.

The product showed an X-ray diffraction pattern of a kaolinite-like mineral and a trace amount of aluminum sulfate hydrate. Further, the thermogravimetric analysis revealed that the kaolinite content in the product was 90%.

(Comparative Example 4) Comparative Example 1 except that the gel prepared in Comparative Example 3 was used and hydrothermal treatment was carried out at 250 ° C. for 5 days.
The same operation was performed to obtain a product. X of the obtained product
The line diffraction result is shown in FIG.

The product showed an X-ray pattern of kaolinite and an X-ray diffraction pattern of a trace amount of aluminum sulfate hydrate. Further, the weight reduction of kaolinite due to dehydration of the structured water was measured by thermogravimetric analysis (TG) to quantify the amount of kaolinite produced, and the content of kaolinite in the product was 92%.

(Comparative Example 5) Diatomaceous earth and aluminum chloride were used as raw materials and mixed and stirred so that the molar ratio was Si / Al = 1. Then, put it in the autoclave, and
Hydrothermal treatment was performed at 0 ° C for 10 days. After cooling, it was washed with water, filtered, and dried to obtain a product. The X-ray-diffraction result of the obtained product is shown in FIG.

The product showed an X-ray diffraction pattern of kaolinite and quartz as an impurity. Further, the thermogravimetric analysis revealed that the kaolinite content in the product was 50%.
The above results are summarized in Table 2.

[0039]

[Table 2]

[0040]

As described above, according to the present invention, the sodium silicate aqueous solution and the aluminum sulfate aqueous solution are adjusted to pH 4
Gelation while maintaining at ~ 12, then aging in an alkaline aqueous solution of pH 7 or above, filtering and washing, then further pH
By subjecting the gel that has been aged, filtered and washed in an acidic aqueous solution of 3 to 4 to hydrothermal treatment, kaolinite having a higher production rate and a higher purity than conventional can be synthesized.

[Brief description of drawings]

FIG. 1 is an actual measurement diagram showing a result of X-ray diffraction measurement of a product obtained in an example of the present invention.

FIG. 2 is an actual measurement diagram showing a result of X-ray diffraction measurement of a product obtained in a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Watamura 1-70, Heiwagaoka, Meito-ku, Nagoya, Aichi (72) Inventor Ritsuro Miyawaki 199, Sunahara, Nishi-ku, Nagoya, Aichi (72) Inventor, Kyo Ohsaki Shinnanyo, Yamaguchi Prefecture 4-10-3-306 (72) Inventor Setsuo Yoshida 23-3, Nagata-cho, Shinnanyo-shi, Yamaguchi (72) Inventor Soichiro Samejima 2-6-10, East, Shinnanyo-shi, Yamaguchi Prefecture Sorojirai (72) Inventor Shigeo Satokawa 2-14-8 Tabata, Kita-ku, Nagoya-shi, Aichi

Claims (1)

[Claims] 1. A sodium silicate aqueous solution and an aluminum sulfate aqueous solution are gelled while maintaining a pH of 4 to 12, then aged in an alkaline aqueous solution having a pH of 7 or more, filtered and washed, and then further aged in an acidic aqueous solution having a pH of 3 to 4. A method for producing a high-purity, high-purity synthetic kaolinite, which comprises subjecting the filtered and washed gel to hydrothermal treatment.