JPS606907B2 - Method for producing synthetic magnesia/alumina clinker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for producing synthetic magnesia-alumina (mineral name: spinel) clinker.

Traditionally, this type of clinker has poor densification and sintering properties,
Furthermore, it was brittle and therefore not suitable as a raw material for refractories.

Therefore, in order to obtain a clinker with a dense structure, the inventors first developed a new method for producing a synthetic magnesia/alumina clinker (Tsubaki Kosho No. 56-31314). The outline is that when first mixing the magnesia raw material and the alumina raw material, they are mixed so that the molar ratio of Mg0 and A203 after mixing is 1:1 (theoretical composition AZ20372%, Mg028%), and then this mixture is mixed. In addition, a calcination reaction accelerator (
Add silicic acid and iron oxide (or solid phase reaction accelerator) so that each component after addition is 0.5 to 5.0 (wt)%, and then add water to the mixture to form a slurry. , mud mixing, dehydration molding, drying, high temperature firing (175
000 or more).

According to this method, the structural, mineralogical, and physical properties of the clinker can be improved.

However, subsequent detailed studies by the inventors revealed that further improvements can be expected mainly in the following points.

Since magnesia has better corrosion resistance than alumina for steels, it is expected that the corrosion resistance of synthetic magnesia/alumina materials will be improved by enriching the composition with magnesia. '2' In the previous application, a competitive colloid reaction accelerator was added to the mixture of magnesia raw materials and alumina raw materials, but when the amount added was increased, the purity of the clinker decreased, and especially when the amount of iron oxide added was increased. , low-melting minerals are produced, creating a problem of lowering the melting temperature of the clinker.

t3} In the slurry-forming step, the mineral reaction during the continuous process is promoted by increasing the surface area of the synthetic raw material and increasing the amount of fine particles.

This invention was made based on the above knowledge, and in producing a synthetic magnesia/alumina clinker with a delicate structure, it is possible to achieve high purity and corrosion resistance while satisfying the properties of easy-sintering silk. To provide a manufacturing method for obtaining quality clinker.

The manufacturing method of the present invention is such that when mixing tomagnesia raw materials and alumina raw materials, the A〆203/Mg○ composition ratio (weight ratio) after mixing is greater than 1.86 and less than 2.54. Furthermore, a sintering reaction accelerator such as silicic acid is added to this mixture, so that the Si02 after addition is 0.5 to 3.
After adjusting the content to 0% and Fe203 to 1.5% or less, the mixture is subjected to a slurrying process, a mud-mixing process, a dehydration molding process, a drying process, and a high-temperature firing process of 1750 qo or more.

This will be explained in detail below.

The magnesia raw material and alumina raw material used in this invention are:
Both are preferably in the form of fine powder; an example of the former is magnesium hydroxide, and an example of the latter is aluminum hydroxide produced by the Bayer process.

Traditionally, seawater magnesia, natural magnesia, etc. have been known as raw materials for magnesia, and calcined alumina, hazy alumina, etc. have been known as raw materials for alumina.
They require post-processing such as pulverization and chemical purification, and are often expensive, so they are not practical. In this invention, the above-mentioned magnesia raw material and alumina raw material are mixed together and
3/Mg○ It is mixed so that the composition ratio is greater than 1.86 and less than 2.56. However, if the above molar ratio is 1.86 or less, bericlese mineral (magnesia other than spinel mineral) is produced. In addition to structural deterioration, physical properties such as porosity and high specific gravity also become inferior.

On the other hand, when the composition ratio of A203/Mg0 is 2.56 or more, even if a spinel mineral is obtained, the physical and structural properties tend to be slightly inferior. In this invention, the composition ratio of A203/Mg○ to obtain high quality clinker is as follows:
A magnesia enrichment range of less than 2.56 and greater than 2.08 is considered preferred.

After mixing magnesia raw materials and alumina raw materials, the sintering reaction accelerators added to this mixture include silicic acid (raw materials include silica stone and silica sand), iron oxide (raw materials include iron ore,
Converter dust, etc.) are known, but the former is preferred. However, Si02 in the mixture after addition is 0.5 to 3
．． It is necessary to adjust the Fe203 content to 0% and 1.5% or less. If the respective upper limits are exceeded, not only will the purity of the clinker be lowered, but especially in the case of iron oxide, the amount of Mg◯.Fe203 produced will increase, reducing the corrosion resistance of the clinker.

After adjusting the mixed raw materials in this way, the slurry process, mud bran mixing process, dehydration molding process, drying process, and high-temperature firing process begin.

Generally, in order to produce synthetic minerals from powdered raw materials, a method is being explored in which a reaction is carried out under high temperature and pressure in a closed container using water as a solvent, and this is called hydrothermal synthesis or hydrothermal synthesis.

This method is said to promote the decomposition and crystallization of minerals, but it has disadvantages such as being dangerous to implement due to the high temperature and pressure, being unsuitable for mass production, and being expensive. be pointed out.

The inventors conducted various studies to improve the above-mentioned situation, and as a result, they selected fresh water or sea water as the solvent, and using this, boiled and synthesized the powdered mixed raw material into a slurry,
It has been found that it is most preferable to supply this slurry to a subsequent process.

In other words, this method not only avoids the problems of conventional hydrothermal synthesis, but also "increases the surface area of the synthetic raw materials, encourages an increase in the amount of fine particles, accelerates mineral reactions, and creates a more delicate structure." Clinker is obtained.The solvent used for preparing the slurry is preferably seawater rather than fresh water, and boiling synthesis using the latter method yields a clinker with better physical and structural properties than the former method. When using synthesis, even if the content of iron oxide in the powder mixture is low, easy sinterability and properties can be maintained, and a clinker with improved structure can be obtained.

Finally, regarding the conditions for high temperature firing, in order to satisfy both clinker properties and energy economy, the firing temperature is preferably 1750 to 1850 qC.

The clinker produced by the method of this invention has a uniform spinel crystal structure and a fine texture, low porosity, and high bulk specific gravity. Moreover, it is of excellent quality with a high degree of purity and corrosion resistance. Therefore, important uses are emerging for firebricks and other molding materials that require corrosion resistance and thermal shock resistance.

Next, an example will be explained.

Example 1 Magnesium hydroxide and aluminum hydroxide were mixed as raw materials, and 2% silicic acid and 1% iron oxide were added as sintering reaction accelerators.The mixture was made into a slurry with fresh water, mixed with slurry, and dehydrated. Molding, drying, firing (180,000)
A synthetic magnesia-alumina clinker was produced through the following steps.

In this clinker, Table 1 shows the physical properties and X-ray diffraction mineral measurement results depending on the composition ratio of magnesia and alumina, and Table 2 shows the chemical composition.

Table 1 (Note 1) ◎ mark is clear, 〇 mark is somewhat clear, △EO unclear table -
2 The main mineral in each composition ratio is spinel mineral (Mg0/A〆203), and the composition ratio of Aso203/Mg0 is 1.50.1
．． In 86, verikleise mineral (Mg0) is recognized, but when the composition ratio becomes 2.33, 2.57, and 3.00, verikleze mineral is not recognized.

In addition, minerals that appear to be forsterite (2MgOSj02) and mullite (3Aso203/$i02) were observed, and in particular, the composition ratio of A203/Mg0 was 2.57,
In the case of a magnesia-enriched composition of 2.33, a clinker of good physical and structural quality is obtained.

Example 2 Magnesium hydroxide and aluminum hydroxide were mixed, 2% oxalic acid was added as a molten acid reaction accelerator, this mixture was made into a slurry by changing the treatment conditions, mixed with mud, dehydrated, molded, dried, and fired at high temperature (1800 oo ) to produce clinker.

However, the Aso203/Mg○ composition ratio was unified to 2.33.

Table 3 shows the slurry processing conditions and physical properties of the clinker, and Table 4 shows the chemical composition of the clinker.

Table 3 (Note 2) This is the dry base strength (compressive strength) before high temperature firing.

Since it varies depending on the length of the mud-competition time and the compaction force, these were measured under intermediate conditions.

Table 4 X-ray diffraction minerals are all spinel minerals, with some traces of what appears to be forsterite.

Slurry formation by boiling synthesis can improve the physical and structural properties of clinker, and boiling synthesis using seawater is particularly effective. This is due to the increase in the surface area of the synthetic raw material and the increase in the amount of fine particles, but the improvement in the strength of the base material is also thought to be due to the strength increase due to ion reaction. Furthermore, since iron oxide is not added in this example, the purity of the clinker is improved, and a clinker with a small amount of magnesia ferrite (Mg00Fe203) produced mineralogically is obtained.

Claims (1)

[Claims] 1 Powdered magnesia raw material and alumina raw material are mixed so that the Al_2O_3/MgO weight composition ratio after mixing is greater than 1.86 and smaller than 2.54, and a sintering reaction accelerator such as silicic acid is added to this mixture. After adjusting SiO_2 in the mixture to 0.5 to 3.0% by weight and Fe_2O_3 to 1.5% by weight or less, the mixture is subjected to a slurry process, a slurry mixing process, a dehydration molding process, a drying process, and a high temperature. A method for producing synthetic magnesia/alumina clinker, which includes a firing process.