JPH06102538B2 - Production method of highly dispersed synthetic kaolinite - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a raw material for ceramics,
The present invention relates to a synthetic kaolinite production method, which is widely used as a binder for ceramics, a filler for papermaking, etc., and is attracting attention as a new functional material. It relates to the manufacturing method.

[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 production of high-quality natural clay mainly composed of kaolinite, especially Kibushi Clay and Frogme Clay produced in the Seto area of Aichi Prefecture, has decreased due to long-term consumption and rapid housing development in recent years. is doing. Therefore, research and development of artificial clay has been promoted as a new functional material utilizing the fact that it is a plate crystal as a material replacing these natural clays.

As a method for producing the above kaolinite, a hydrothermal synthesis method is usually used. This hydrothermal synthesis method is a method of obtaining a desired mineral by hermetically sealing raw materials in an autoclave in the presence of water and maintaining a high temperature and high pressure for a certain time, and is widely used as a synthetic means for various artificial minerals. ing. As a method for producing kaolinite by such a hydrothermal synthesis method, a method in which silica sol and alumina sol are mixed and used as a raw material, a method in which allophane, diatomaceous earth, montmorillonite, a zeolite or the like and an aluminum compound are mixed and used as a raw material are known. ing.

However, in the above-mentioned method, although the raw material can be purified or purified to some extent by the effect of removing impurities by dissolving the raw material during hydrothermal treatment as compared with natural clay, the obtained kaolinite is agglomerated and has surface characteristics. As a result, the characteristics of the kneaded clay, the characteristics of the slurry, and the like are deteriorated.
In addition, physical treatment such as pulverization of kaolinite obtained as an improvement of dispersibility and chemical treatment such as dissolution and dispersion may be considered.However, kaolinite crystal is changed by amorphization of the crystal surface due to pulverization and change in chemical composition due to dissolution. It also has a problem of deterioration in purity.

An object of the present invention is to provide a method capable of producing synthetic kaolinite having a higher dispersibility and a higher purity than conventional methods.

[0006]

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 highly dispersed synthetic kaolinite according to the present invention. That is, in the present invention, when producing high-purity kaolinite from uniformly mixed silica-alumina gel, the average particle size is 1 μm.
A method for producing a highly dispersed synthetic kaolinite, which comprises subjecting the gel having a size of m or less to a hydrothermal treatment.

[0007]

The present invention will be described in detail below. The synthetic kaolinite in the present invention means a chemical formula {Al ₂ S produced mainly from a silica raw material and an alumina raw material by hydrothermal treatment.
i ₂ O ₅ (OH) ₄ } is a layered hydrous aluminosilicate composed of a 1: 1 tetrahedral sheet consisting of silicon and four oxygens and an octahedral sheet surrounding aluminum with six oxygens. . The particle shape may have a granular shape, a spherical shape, a plate shape, or the like depending on the manufacturing method.

Further, the high dispersion of the present invention means that the aggregation of kaolinite crystals is small, which can be confirmed by particle size distribution measurement, microscopic observation and the like. Generally, the crystal size of kaolinite is 0.2 to 0.8 μm, and it is necessary that the average particle diameter is 1 μm or less for high dispersion.

The silica-alumina gel in the present invention is a gel-like silica-alumina mixture obtained by uniformly mixing a solid or liquid silica raw material and the same solid or liquid alumina raw material. As the solid or liquid silica raw material, silica gel, colloidal silica, water glass,
Examples thereof include acidic silicic acid solutions, and solid or liquid alumina raw materials include aluminum hydroxide, aluminum oxide,
Examples thereof include an aluminum salt aqueous solution and an aluminate aqueous solution. Then, one or more of these are combined and mixed to obtain a silica-alumina gel.

Although the mixing method is not particularly limited, it is necessary that silica and alumina are uniformly mixed. Therefore, when a solid raw material is used, it is mixed while being pulverized if necessary. . When a liquid raw material is used, it is preferable to add an acid or an alkali for pH adjustment in order to promote gelation. Further, the composition ratio of silica and alumina in the gel is preferably close to Si / Al = 1 in terms of molar ratio in order to suppress by-products in hydrothermal treatment. Furthermore, it is preferable that the cations and anions of the impurities that are mixed in are removed by ion exchange, washing, calcination, etc., since they inhibit the production of kaolinite.

Next, in the present invention, in order to produce a highly dispersed kaolinite, a silica-alumina gel having an average particle size of 1 μm or less is hydrothermally treated. As a result of intensive studies, the present inventors have found that the dispersibility of the kaolinite produced depends on the average particle size of the gel used for hydrothermal treatment. Therefore, a highly dispersed kaolinite can be obtained by hydrothermally treating a silica-alumina gel having an average particle diameter of 1 μm or less. The silica-alumina gel having an average particle diameter of 1 μm or less can be obtained by adjusting pH, adjusting stirring, etc. at the time of gel adjustment, but simply obtained by physically pulverizing with a ball mill or the like. The milling conditions are not particularly limited, but for example, a gel prepared from sodium silicate and aluminum sulfate has an average particle size of 0.5 μm after 24 hours of ball milling.

The hydrothermal treatment in the present invention can be carried out by using a usual autoclave or pressure cup.
The slurry concentration, reaction temperature, and reaction time in the hydrothermal treatment are not particularly limited, but the slurry concentration is preferably 1 to 30 wt%, the reaction temperature is 100 ° C. or higher, and the reaction time is 1 hour or longer. By such a hydrothermal treatment, highly dispersed kaolinite can be synthesized as compared with the aggregated kaolinite by the conventional method.

[0013]

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 an aluminum sulfate aqueous solution (Al ₂ O ₃ = 8.02 wt%) are used while stirring so that the molar ratio becomes Si / Al = 1. The raw materials were mixed continuously. At the same time the reaction pH is 10-1
A uniformly mixed silica-alumina gel was prepared by adding and neutralizing sodium hydroxide so as to be 1. When the composition of this gel was analyzed, the molar ratio of Si
/ Al = 1 and Na / Al = 0.8.

Next, in order to remove sodium, ion exchange was carried out with ammonium nitrate, and then ammonium was removed by baking treatment at 600 ° C. for 1 hour. The results of particle size distribution measurement of this gel are shown in FIG. From FIG. 1, the average particle diameter was 3.0 μm.

Further, in order to control the particle diameter, wet milling was carried out for 24 hours with a ball mill. The results of particle distribution measurement of this gel are shown in FIG. 2. From FIG. 2, the average particle diameter was 0.6 μm.

The above-mentioned raw material gel was charged into an autoclave so that the slurry concentration was 10 wt%, and hydrothermal treatment was carried out at 250 ° C. for 5 days. After cooling, the product 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 shows only the X-ray pattern of kaolinite, and the weight loss of kaolinite along with dehydration of the structural water was measured by thermogravimetric analysis (TG) to calculate the production amount of kaolinite. Kaolinite production rate is 96%
Met.

The result of particle size distribution measurement of the obtained product is shown in FIG. It can be seen from FIG. 4 that the kaolinite has an average particle diameter of 0.8 μm and has a narrow particle size distribution and weak cohesiveness.

(Example 2) Colloidal silica (Snowtex N manufactured by Nissan Chemical) and alumina sol (Alumina sol-200 manufactured by Nissan Chemical) were used as raw materials, and S was used in a molar ratio.
The mixture was stirred and mixed so that i / Al = 1. Then, it was dried and further calcined at 600 ° C. for 1 hour to remove acetic acid, which is a gel and sol stabilizer, to obtain a uniformly mixed silica-alumina gel.

In the same manner as in Example 1 below, the product was pulverized and hydrothermally treated to obtain a product. The average particle size of the gel before pulverization was 2.6 μm, and the average particle size of the gel after pulverization was 0.
It was 5 μm.

As a result of X-ray diffraction, the product showed a pattern of only kaolinite, and the product rate was 92% as a result of quantification by thermogravimetric analysis. Further, the average particle size of the product is 0.7 μm, which indicates that it is kaolinite having weak cohesiveness as in Example 1.

Example 3 As a raw material, an acidic silicic acid solution obtained by carrying out proton ion exchange between aluminum hydroxide and an aqueous solution of sodium silicate whose average particle size was adjusted to 0.5 μm by milling was used as a raw material, and the molar ratio was changed. Then, by stirring and mixing so that Si / Al = 1, silicic acid was adsorbed to aluminum hydroxide to obtain a silica-alumina gel slurry. The average particle size of this gel was 0.5 μm.

The gel slurry was adjusted to a concentration of 10% by weight, charged into an autoclave, and hydrothermally treated at 220 ° C. for 7 days. After cooling, the product was washed with water, filtered and dried to obtain a product.
As a result of X-ray diffraction, this product showed a pattern of only kaolinite, and as a result of quantification by thermogravimetric analysis, the production rate was 95%. Further, it can be seen that the average particle size of the product is 0.5 μm, which is kaolinite having weak cohesiveness as in Example 1.

(Comparative Example 1) A product was obtained in the same manner as in Example 1 except that wet milling was not carried out by a ball mill. The result of particle size distribution measurement of the obtained product is shown in FIG. This product has a production rate of 95 as in Example 1.
Although it was a kaolinite with a high production rate of not less than%, the average particle size was 2.8 μm from FIG. 5, and the kaolinite had a strong cohesive property.

(Comparative Example 2) A product was obtained in the same manner as in Example 2 except that wet milling was not performed by a ball mill. The production rate of this product was 92% as in Example 2, but it was kaolinite having an average particle diameter of 2.5 μm and strong cohesiveness. Table 1 is a summary of the above results.
Shown in.

[0026]

[Table 1]

[0027]

As described above, according to the present invention, in producing high-purity kaolinite from the homogeneously mixed silica-alumina gel, the gel having an average particle diameter of 1 μm or less is hydrothermally treated to obtain a conventional product. It is possible to synthesize highly dispersed kaolinite which is superior in moldability and slurry characteristics by the method.

[Brief description of drawings]

FIG. 1 is an actual measurement diagram showing measurement results of gel particle size distribution before milling in Example 1.

FIG. 2 is an actual measurement diagram showing a measurement result of a particle size distribution of a gel after milling in Example 1.

FIG. 3 is an actual measurement diagram showing the result of X-ray diffraction measurement of the product obtained in Example 1.

FIG. 4 is an actual measurement diagram showing the measurement results of the particle size distribution of the product obtained in Example 1.

5 is an actual measurement diagram showing the measurement results of the particle size distribution of the product obtained in Comparative Example 1. FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Soichiro Samejima 2-6-10 Miyanomae, Shinnanyo-shi, Yamaguchi Prefecture East Source Jiyo Dormitory (72) Inventor Shigeo Satogawa 2-14-8 Tabata, Kita-ku, Nagoya, Aichi Prefecture issue

Claims (1)

[Claims] 1. A method for producing a highly dispersed synthetic kaolinite, which comprises subjecting a gel having an average particle size of 1 μm or less to a hydrothermal treatment when producing high-purity kaolinite from a homogeneously mixed silica-alumina gel.