JPS6356174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-density spherical particles containing spinel as a main component.

Spinel is a complex oxide that has been known for a long time, and despite its many excellent properties, its uses have not been developed compared to other simple oxides such as alumina and magnesium. Considering the main reason why the development of applications for spinel has been delayed compared to other oxides, it is because spinel does not exist naturally enough to be used as an industrial resource.
We have no choice but to rely on artificially synthesized materials, but in this case, the cost of synthesizing spinel is extra compared to simple oxides such as alumina and magnesia. One reason is that no outstanding properties have been found that cannot be replaced by simple oxides such as those mentioned above.

Based on this situation of spinel, the present inventors searched for a method to improve the properties of spinel and produce products with excellent characteristics. It is possible to efficiently produce high-density and nearly spherical particles, which were thought to be
A relatively inexpensive manufacturing method was discovered and the present invention was completed.

The sintered body mainly composed of spinel obtained by the method of the present invention has a high density and a nearly spherical shape, so it can be used for applications that take advantage of these properties, such as raw materials for refractories or balls for crushing ball mills. It is a very good item.

The present invention combines magnesium hydroxide and/or magnesium oxide with aluminum hydroxide and/or aluminum oxide, and
The raw material is prepared so that the total of MgO 20-70% by weight, Al ₂ O ₃ 80-30% by weight, and other components is 2% by weight or less, and the semi-dry raw material containing water is not molded. After firing as it is at a temperature of 1000℃ to 1400℃, it is press-formed, and the resulting molded body is heated at a temperature of 1500℃ or higher in a rotary kiln with an inner peripheral speed of 3m/min or more and a length of 30m or more. The present invention relates to a method for producing a high-density spherical body mainly composed of spinel, which is characterized by firing.

Spinel has a molar composition ratio of MgO and Al ₂ O ₃ of 1:1.
(MgO28.3:Al ₂ O ₃ 71.7 in weight ratio), but the spinel raw materials actually used are MgO,
The blending ratio of Al ₂ O ₃ is selected depending on the purpose. However, if this blending ratio is changed too drastically to a higher MgO content, the properties of magnesia become more pronounced than the properties of spinel.
On the other hand, if this blending ratio is changed too drastically to a higher content of Al ₂ O ₃ , the properties of alumina become more pronounced than those of spinel. Here, as a result of searching for a blending ratio of MgO and Al ₂ O ₃ that can fully utilize the properties as spinel, we found that MgO is 20 to 70% by weight,
It was found that a range of 80 to 30% by weight of Al ₂ O ₃ sufficiently exhibits the properties as a spinel as a whole. To synthesize and sinter spinel, MgO,
Components other than Al ₂ O ₃ sometimes have a large effect.
These components sometimes give great results, such as promoting sintering, but unless the content is greater than 2% by weight, the content of low-melting substances becomes large, making it difficult to perform sintering at high temperatures. Damages such as a decrease in strength and a decrease in spalling resistance appear strongly.
Therefore, it is particularly desirable to keep the amount of components other than MgO and Al ₂ O ₃ as low as possible, preferably 1% by weight or less.

Spinel MgO and Al ₂ O ₃ used in the present invention
Although the use of natural raw materials is not specifically excluded as raw materials, artificial raw materials such as seawater magnesia and Bayer process alumina are usually used because they are easy to obtain raw materials of consistent quality and high purity. These raw materials are obtained as fine powder products, so some of them do not require special treatment such as pulverization, but in order to obtain spherical bodies with high bulk specific gravity, raw materials should be as fine in particle size as possible. For example, if you want the bulk specific gravity of the spherical bodies to be 3.3 or more, the particle size of the raw material should be mostly 44μ or less,
Furthermore, it is necessary to prepare so that 60% by weight or more has a size of 15μ or less. Furthermore, when manufacturing spherical bodies with a bulk specific gravity of 3.4 or more, the portion of 15 μ or less is
% by weight or more and the average particle size is 10μ or less.

The magnesia raw material and alumina raw material are blended using a dry method that uses a crusher to simultaneously crush and mix the raw materials.
Alternatively, it may be carried out by a wet method in which water is added to the raw materials and kneaded.

The firing temperature of the blended raw materials must be 1000°C or higher. If this temperature is lower than 1000°C, it is difficult to sufficiently increase the bulk specific gravity of the resulting spherical bodies. Similarly, if the firing temperature of the raw material is raised too high, it becomes difficult to increase the bulk specific gravity of the spherical bodies. can be reached. When the firing raw material is not pulverized, it is desirable to perform the firing at a temperature of 1100°C to 1400°C, particularly preferably 1200°C to 1300°C.

Pressure molding of the firing raw material is carried out using a powder molding means such as a briquette machine, and the higher the molding pressure, the greater the effect of increasing the bulk specific gravity of the spherical bodies. The molding pressure is at least 200Kg/cm ²
The above is necessary, and if the pressing force is lower than this pressure, the bulk specific gravity of the resulting spherical bodies will be significantly lower. The molding pressure is preferably 500Kg/cm ² or more.
It is particularly desirable that it be 800Kg/cm ² or more. The firing raw material that produces spinel, which is the main component, is molded under high pressure because the powder has low adhesive strength, and it is not recommended to add substances that improve moldability such as water and oil to the firing raw material. This is a particularly desirable method.

The length of the forming raw material is 30 m or more, and the peripheral speed in the furnace is 3.
Fired at a temperature of 1500°C or higher in a rotary kiln at a speed of 1500°C or higher. If the length of the rotary kiln is shorter than 30 m and the circumferential speed in the furnace is slower than 3 m/min, the shape of the molded product will remain as it is, and it will not be sufficient to be used as a spherical product. In order to obtain spherical bodies, it is particularly desirable that the length of the rotary kiln be 40 m or more, and the inner peripheral speed of the rotary kiln be 5 m/min or more. The maximum temperature of the rotary kiln must be 1500℃ or higher. The higher the maximum temperature, the greater the bulk specific gravity of the resulting spherical bodies, but when firing in a rotary kiln, if the temperature is 1900°C or higher, the adherent to the rotary kiln becomes severe and continuous firing becomes difficult. Therefore, the maximum temperature of the rotary kiln is 1750℃ to 1850℃.
It is particularly desirable that

Hereinafter, the effects of the present invention will be explained with reference to Examples.

Example 1 Magnesium oxide and aluminum oxide raw materials were mixed at a weight ratio of 55:45 in terms of fired product,
This mixed raw material was pulverized and mixed using a ball mill. The particle size of the obtained raw material was such that 98% by weight passed through a 44μ sieve, and further 70% by weight passed through a 15μ sieve. Approximately 20% by weight of water is added to this pulverized raw material to make it semi-dry, and then the ore is fed to a rotary kiln with a maximum temperature of 1200°C, and the resulting fired product is processed using a briquette machine.
It was molded into an almond shape under a pressure of 2 tons/cm ² . This compact was fed into a rotary kiln with a length of 45 m, an internal furnace peripheral speed of 4 m/min, and a maximum temperature of 1750° C., and was fired, resulting in the spherical particles shown in the micrograph of FIG. 1. moreover,
The chemical analysis values and bulk specific gravity values of these spherical particles were as follows.

MgO 55.4% Al ₂ O ₃ 42.8 CaO 0.5 Fe ₂ O ₃ 0.2 SiO ₂ 0.4 Bulk specific gravity 3.34 Example 2 98% by weight passes through a 15μ sieve Magnesium hydroxide cake also has 98% by weight passed through a 15μ sieve Aluminum hydroxide powder was blended and kneaded in a clay mixer while adding water. This kneaded material was fed into a rotary kiln with a maximum temperature of 1400°C, and about 7% by weight of water was added to the resulting baked product, which was then shaped into an almond shape using a briquette machine at a pressure of 1 ton/cm ² . Molded. This molded product has a length of 45 m and a circumferential speed of 5 m/
Fired in a rotary kiln at a maximum temperature of 1800°C. The obtained spherical bodies are shown in the micrograph of FIG. Furthermore, the chemical analysis values and bulk specific gravity values of these spherical particles were as follows.

MgO 34.7% Al ₂ O ₃ 64.6 CaO 0.3 Fe ₂ O ₃ 0.1 SiO ₂ 0.2 Bulk specific gravity 3.46

[Brief explanation of drawings]

FIGS. 1 and 2 are micrographs showing examples of the particle structure of spherical particles containing spinel as a main component obtained by the method of the present invention.

Claims (1)

[Claims] 1 Blend magnesium hydroxide and/or magnesium oxide with aluminum hydroxide and/or aluminum oxide, and the total amount of MgO 20 to 70% by weight, Al ₂ O ₃ 80 to 30% by weight, and other components is 2 in terms of fired product. % by weight or less, and the semi-dry raw material containing water is fired as it is at a temperature of 1000°C to 1400°C without being molded, and then pressure molded, resulting in a molded body. A method for producing high-density spherical bodies mainly composed of spinel, which is characterized by firing in a rotary kiln with a length of 30 m or more at a temperature of 1500°C or more, an inner peripheral speed of 3 m/min or more, and a length of 30 m or more.