JPH0645454B2 - Method for producing kaolinite-like minerals - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a kaolinite-like mineral, which is used in large quantities as a ceramic raw material, a ceramics binder, a papermaking filler, and the like.

[Conventional technology]

Natural clay minerals containing kaolinite as a main component have been used in large quantities as ceramic raw materials since they are excellent in fire resistance and plasticity. In particular, Kibushi clay and frog eye clay produced in the Seto region of Aichi prefecture have excellent plasticity and are said to be the best ceramic raw materials in the world. But,
In recent years, its depletion has become a problem, and the need for materials to replace natural clay has become a problem. In addition, research and development of artificial clay is being promoted because new functions and applications can be expected by synthesizing highly pure clay minerals that are not found in nature.

As a means for producing kaolinite, which is the main component in the clay, 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. The conventional method for producing kaolinite by the hydrothermal synthesis method will be described in detail. As a raw material, Shibasaki and Watamura (Clays and Clay Minerals, 1983
, Et al.) Using commercially available silica sol and alumina sol as industrial reagents, and using natural compounds such as allophane, diatomaceous earth, montmorillonite and zeolite, and aluminum compounds. These materials are mixed and then hydrothermally treated. A method for producing kaolinite by this is generally known.

[Problems to be Solved by the Invention]

However, in the above method, the uniformity of the raw material is poor,
In the hydrothermal treatment, there is a problem that a high reaction temperature (250 to 300 ° C.) requires a long time (7 days or more). When a natural raw material is used, metal oxides such as iron and titanium contained in the raw material and impurities such as quartz remain in the product,
Not only high-purity kaolinite cannot be obtained, but also whiteness,
There is a problem that the clay properties are degraded.

An object of the present invention is to provide a method capable of producing a higher purity kaolinite-like mineral under milder conditions than conventional methods.

[Means for Solving the Problems]

As a result of diligent studies, the present inventor has used sodium silicate aqueous solution as a silica raw material and aluminum sulfate aqueous solution as an alumina raw material, respectively, to uniformly mix and gel the silicon and aluminum while maintaining pH = 4-12. We have found a method for producing a kaolinite-like mineral that can be prepared by mixing silica-alumina mixed gel at a level and then hydrothermally treating the gel to crystallize it under milder conditions than conventional methods.

The details will be described below.

The kaolinite-like mineral in the present invention has a chemical formula of {Si
₂ Al ₂ O ₅ (OH) ₄ }, which is a layered aluminosilicate in which a tetrahedral volume of silica and an octahedral layer of alumina are overlapped at a ratio of 1: 1 to form one layer, specifically, kaolinite. Kaolinite group minerals such as, halloysite and dickite.

The silica-alumina mixed gel in the present invention is obtained by mixing an aqueous solution of sodium silicate and an aqueous solution of aluminum sulfate. Mixing is pH = 4-12, preferably pH
It is performed while maintaining around = 7, and if necessary, an acid and an alkali are added. The mixing method is not particularly limited as long as it can be uniformly dispersed, but in order to improve the dispersibility of silica and alumina, it is preferable to continuously mix while stirring. Further, the mixing ratio of the raw materials is preferably in the vicinity of Si / Al = 1, which is the chemical composition of kaolinite, in order to suppress by-products in the hydrothermal treatment. The gel is excessively washed to remove by-products. The washing method is not particularly limited, but it is preferable to wash with warm water in order to efficiently remove by-products such as sodium ions and sulfate ions. The composition of the gel thus obtained was analyzed to find that Si / Al
= 1 and Na / Al = 0.01-0.5. 220 gels with different sodium contents (Na / Al = 0.1, 0.3, 0.5)
After hydrothermal treatment at ℃ for 3 days, the sodium content was N
It was found that kaolinite was not produced from the gel having a / Al = 0.3 or more, but was produced from the gel having Na / Al = 0.1 or less. That is, in hydrothermal treatment, sodium inhibits the crystallization of kaolinite, so its content must be Na / Al = 0.1 or less.

The hydrothermal treatment in the present invention can be carried out using a normal autoclave or a high-pressure reaction vessel as a reaction vessel. The slurry concentration, reaction temperature, and time in the hydrothermal treatment are not particularly limited, but the slurry concentration is 1 to 40 wt% and the reaction temperature is
It is preferable to carry out the reaction at 100 ° C. or higher and the reaction time for 1 hour or longer.
Further, the reaction temperature and the reaction time can be shortened by stirring or adding a seed crystal if necessary.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 Sodium silicate aqueous solution (No. 3 water glass; SiO ₂ = 29.3 wt%, Na ₂ O = 9.35 wt%) was used as a silica source as a raw material.
Aluminum sulfate aqueous solution (Al ₂ O ₃ = 8.
02 wt%), and the raw materials were continuously mixed and gelled while stirring so that Si / Al = 1. At that time, an aqueous sodium hydroxide solution was added so that the pH of the reaction solution was always maintained at 4 to 12. By-products such as sodium ions and sulfate ions were removed by passing and washing the gel. The compositional analysis values of this gel were Si / Al = 1 and Na / Al = 0.1.

A 5 wt% slurry was prepared using the gel, charged into an autoclave, and hydrothermally treated at 220 ° C. for 5 days. After cooling, the product was obtained by washing with water, filtering and drying. The obtained product was subjected to powder X-ray diffraction measurement and thermogravimetric analysis (TG). The result of powder X-ray diffraction is shown in FIG.

As is clear from FIG. 1, the X-ray diffraction pattern of the product shows only kaolinite-like minerals, and since there is no impurity peak, the product may be crystallized from high-purity kaolinite-like minerals. Recognize. In addition, the weight loss of kaolinite along with the dehydration reaction of the structural water of kaolinite at around 500 ° C was measured by thermogravimetric analysis (TG) to calculate the kaolinite production rate. Met.

Example 2 Using the gel synthesized in Example 1, the same operation as in Example 1 was performed except that hydrothermal treatment was performed at 200 ° C. for 5 days to obtain a product.

The product was a high-purity kaolinite-like mineral as in Example 1. Kaolinite content in the product was 75% by thermogravimetric analysis.

Comparative Example 1 Using silica-alumina gel in which colloidal silica and alumina sol were mixed so that Si / Al = 1 and calcined at 600 ° C. to remove the stabilizer, the conditions of Example 1 were used.
When hydrothermal treatment was performed at 0 ° C. for 3 days, kaolinite was formed, but its content was about 50%.

Comparative Example 2 An aqueous solution of aluminum sulfate was dropped into an aqueous solution of sodium silicate and mixed and gelled. Then, the gel was hydrothermally treated at 220 ° C. for 3 days in accordance with the conditions of Example 1, and kaolinite was not formed.

〔The invention's effect〕

As described above, according to the present invention, an aqueous solution of sodium silicate and an aqueous solution of aluminum sulfate are used to prepare a uniform gel by mixing while keeping the pH at 4 to 12, and the gel is hydrothermally treated to obtain a conventional method. High-purity kaolinite-like minerals can be synthesized at lower reaction temperature and shorter reaction time.

[Brief description of drawings]

FIG. 1 shows the result of X-ray diffraction measurement of the kaolinite-like mineral obtained in Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaki Maeda 49-1, Kusagi, Akui-cho, Chita-gun, Aichi Prefecture (72) Inventor Shigeo Satokawa 2-14-8 Tabata, Kita-ku, Nagoya, Aichi (72) Inventor Wataru Inaoka 4-6-1, Shinnanyo-shi, Yamaguchi Prefecture 306 (72) Inventor Kyo Osaki 1-26-22, Ogami, Shinnanyo-shi, Yamaguchi Prefecture Inventor Soichiro Samejima 2 in front of Miya, Shinnanyo-shi, Yamaguchi Prefecture Katsuki Yamagishi, Examiner, Tosoh Jitsurai Dormitory, No. 6-10

Claims (1)

[Claims] 1. A process for producing a kaolinite-like mineral, which comprises uniformly mixing an aqueous solution of sodium silicate and an aqueous solution of aluminum sulfate in the range of pH = 4 to 12, gelling the mixture, and then hydrothermally treating the gel. Method.