KR800000647B1 - Process for producing magnesiun aluminate spinel - Google Patents

Abstract

High-purity spinel was produced by mixing by-product Al2O3, and MgO in a MgO:Al2O3 ratio of 0.4-0.8 and heating at 800≰C. Thus, dust 145.1 and Mg(OH)2 84.9 were mixed(MgO:Al2O3) with water 259g, milled for 4 hr, filtered, dried, and heated at 1680≰C. The resultant refractory material had trued. 3.57 g/cm3 (theor. d. of Al2MgO4 was 3.58), bulk d. 3.33 g/cm3, and contained Al2MgO4 97.4 MgO 1.9, CaO 0.47, SiO2 0.16, Fe2O3 0.05, and Na2O 0.03%

Description

Method for producing high purity magnesium aluminate spinel

The present invention relates to the manufacture of spinel, and more particularly, to an improved method for producing high purity magnesium aluminate spinel.

Pure magnesium aluminate spinel has been produced in subunits by an electromelting process and has been used as an excellent refractory material. A comparison of spinel and other common refractory materials will show why.

The spinel also shows the first deformation at a temperature of 2,000 ° C. and a pressure of ² kg / cm ² , that is, it does not react with silica until 1,735 ° C., but with magnesia or calcium oxide until it becomes a solid solution at 2,000 ° C. It does not react with α-alumina below 1,925 ° C. In addition, it can be used for all metals except alkaline earth metals, alkali resistance is better than alumina, spall resistance is better than chromium-magnesite refractory material, and resistance to basic slag is excellent.

Several attempts have been made to produce inexpensive high purity magnesium aluminate spinel ingots but have not been commercially successful. These attempts include the following typical steps: physical mixing of high purity alumina and magnesia ore, firing at 900-1,500 ° C, grinding, pelletizing, and finally sintering at 1,600-1,900 ° C. Consists of Due to the technical complexity of these processes, the use of magnesium aluminate as a refractory material is currently very limited.

The present inventors knead only the alumina in the form of an ESP electrostatic precipitator powder and the magnesia ore in the fine powder so that the magnesia: alumina weight ratio is 0.4-0.8, and the kneaded material is completed to form a sharpness. It has been found that high purity magnesium aluminate is produced by only heating at a temperature of at least about 900 ° C. for as long as possible. The kneading process includes a grinding process, and the heating process is sufficient for a time at a temperature higher than the sublimation point of sodium oxide so that spinel having a bulk density of at least 90% of theory and a sodium oxide content of 0.1 wt% or less can be produced. Preference is given to heat treatment. In this way, high-quality spinel can be produced without the use of high quality raw materials or expensive manufacturing steps.

In the process of the present invention, the kneaded material is kneaded at about 900 ° C. or higher until the ESP powder to be defined below and the fine powder magnesia ore are kneaded in a desired ratio and the kneaded is sufficiently reacted to form magnesium aluminate spinel. Heating at temperature is included.

The alumina source used in the present invention is ESP powder. "ESP powder" refers to alumina dust that is recovered as a by-product in the firing process of alumina hydrates such as gibbsite when reducing aluminum oxide to produce metal aluminum.

Although "ESP" means an electrostatic precipitator, which is a conventional dust collecting means for collecting such dust, the term ESP powder herein includes all alumina dust by-products as described above regardless of what dust collection technology has been collected. It is a term to say. These dusts are so fine that they cannot be efficiently recycled during the firing process, containing about 80-97.5% by weight of alumina and about 75-100% by weight of the particles having a particle size of 20 microns or less.

ESP powders obtained by Gibbsite firing are relatively inhomogeneous mixtures containing alpha-, eta-, delta- and chi-alumina, gibbsite, sodium carbonate and chemically bound sodium oxide. Among the untreated ESP powders, the relative composition ratios of these components are unpredictably varied, and furthermore, because of the high content of sodium oxide, the untreated ESP powder cannot be used in ceramics and heat-resistant materials. However, it has been found that this powder is excellent as a source of alumina for the production of magnesium aluminate spinel. The high reactivity of this powder makes spinel denser at lower temperatures, and the high sodium oxide content is reduced nationally as described below during normal spinel sintering processes.

ESP powders obtained from calcining gibsite in the manufacture of spinel are preferred, but other alumina ores such as, for example, nordstrandite bayerite and pseudomorphous trihydrate. Powders obtained by firing can also be used.

The following table shows the general ranges of analytical data and ESP powder properties of ESP powders obtained from typical firing of gibbsite.

Preferred fine powder magnesia sources include magnesium carbonate and especially magnesium hydroxide, all of which can be easily converted to active magnesia by heating. The analysis data and general characteristics of representative samples of magnesium hydroxide in the form of fine powder are as follows.

Other sources of magnesia include magnesium acetate, magnesium oxalate, magnesium nitrate, magnesium sulfate and magnesium oxide itself. Magnesia sources in the form of fine powder must pass through a 50-mesh screen (US standard: 300 microns maximum particle size).

The ESP powder and the fine powder magnesia source are kneaded so that the MgO: Al ₂ O ₃ weight ratio in the kneaded product is 0.4-0.8. Using the weight ratio in this range, the bulk density of the refractory spinel prepared according to the procedure described below is high and the content of sodium oxide is low. A more preferable kneading ratio is that the stoichiometric ratio of M 僅 and Al ₂ O ₃ is 0.395, which forms a heat resistant aggregate with a minimum amount of secondary phases suppressed.

Adopting lower stoichiometric ratios results in lower bulk density in the formed heat resistant aggregates and relatively high sodium oxide content. The kneading may be carried out in a dry process or in a wet process so long as the particle-particle contact of sub-micron units can be made intimately after kneading. The kneading is carried out in the presence of moisture, and preferably, the mixing step and the grinding step are included therein. Suitable equipment for both dry and wet kneading include ball mills, rod mills, muller mixers and turbine mixers. The kneading time can vary depending on the nature of the alumina and magnesia source, the kneading method and the type of equipment used, for example up to about 4 hours when wet kneading in a ball mill using ESP powder and magnesium hydroxide as described above, dry kneading If it takes about 24 hours. In the case of wet kneading, it is necessary to at least partially dry it before firing the kneaded material. Suitable drying means include, for example, drum drying in air. This drying step may include a method of removing excess water from the kneaded material by pre-filtering the wet kneaded material by means such as rotary drum filtration.

As described above, the production of magnesium aluminate spinel using ESP powder results in a low soda (Na ₂ O) content in the product, i.e., the soda content of the spinel kneader is 2 weights during the sintering process described below. From 0.1 to less than 0.1% by weight. This reduction in soda content is very useful when the product is used in refractory materials or high grade ceramic products. In fact, alumina manufacturers are trying to reduce the soda content of high grade alumina products to this level. A technique for reducing the soda content of alumina is to add a compound containing boron, fluorine or chlorine to alumina, which reacts with soda at high temperature to form a volatile sodium compound, and then heats the sodium compound to alumina. To remove it. If omitted, the soda content of calcined alumina is usually about 0.3-0.8% by weight. This soda is very difficult to remove because it is in the form of very stable sodium aluminate.

Thus, magnesium aluminate spinel prepared from alumina containing sodium retains a significant amount of sodium even in products calcined at high temperatures. However, this is the case when the soda content of spinel is not reduced by 0.1% by weight without using adducts.

A mechanism proposed to reduce the soda content is to substitute sodium in sodium aluminate with magnesium, and volatilize the resulting soda at temperatures above the sublimation point of the soda (about 1,275 ° C.) at atmospheric pressure.

In this way sodium aluminate is converted to magnesium aluminate spinel. The reaction that can be made at this time is as follows.

The proposal for such a reactor is based on the experimental results when the mixture of ESP powder, a mixture of ESP powder and magnesium hydroxide, and a mixture of sodium aluminate and magnesium hydroxide were separated and calcined at 1,680 ° C. for 1 hour as shown in the following table. Can be demonstrated.

Spinel prepared by firing kneaded material is used as a refractory material or quenching. In the case of refractory materials, the kneaded material is granulated, pelleted or briquettes with or without water and / or with an organic binder to form a feed suitable for the furnace. Then, this is sintered at 1,600-2,100 DEG C by a sintering technique used to sinter the fire retardant magnesia aggregate. The sintering time depends on the sintering temperature, but is usually 0.5-20 hours. The sintered material is pulverized into small chunks (aggregates) used in refractory products. A typical spinel aggregate prepared by sintering a mixture of ESP powder and magnesium hydroxide having a stoichiometric ratio as described above at 1,680 ° C. for 1 hour is about 99.3% by weight of magnesium aluminate (MgAl ₂ O ₄ ), 0.47 Composed of wt% CaO, 0.16 wt% SiO ₂ , 0.05 wt% Fe ₂ O ₃ and 0.03 wt% Na ₂ O with true density of 3.58 g / cc, bulk density of 3.30-3.44 g / cc, total The porosity is 5-8% by volume and the average grain size is expected to be less than 10 microns. In this way, magnesium aluminate spinel, which has excellent structural integrity due to its high purity, high bulk density, low porosity and its grain size, is produced.

Calcined magnesium aluminate spinel, which is used to make ceramic products or as an adjunct to fire-resistant products, is prepared by calcining kneaded mixtures at 900-1,600 ° C. by standard quenching, usually for 0.5-4 hours. The reacted spinel may be used as it is or may be pulverized into a powder state. Since quenching has a low firing temperature and a low rate of decrease in soda content, it is less pure than the corresponding fire-resistant aggregates. The amount of all other impurities is about the same as in the hot calcined aggregate. Stoichiometric spinel quenching typically contains about 0.04-1.7 weight percent Na ₂ O. Even with this relatively high soda content, if the matting is subjected to high temperatures in subsequent processing or in the field of refractory products, this content level is reduced to about 0.1% by weight or less. As such, the inexpensive matting produced by the process of the present invention exhibits the excellent reactivity needed to produce dense and pure spinel products, and the calcined at higher temperatures exhibits the inertness required in the field of refractory products.

If necessary, a solvent may be added during kneading to promote faster densification even at lower sintering temperatures. As the flux, inorganic fluorine compounds, in particular cryolite (Na ₃ AlF ₆ ) and aluminum fluoride (AlF ₃ ), are preferable. The amount of flux can vary considerably, but about 0.6-2.5% by weight of the kneaded material for cryolite and 0.5-2.0% by weight for aluminum fluoride is preferred. Hereinafter, the present invention will be described in detail through examples. The following examples are, of course, intended to illustrate the invention and do not limit the scope thereof.

Example 1

The electrostatic precipitator powder (ESP powder) and the magnesium hydroxide powder sample obtained from the dust collector of the rotary quencher for alumina manufacture were air-dried at 105 degreeC. The analysis results of the dried material are as follows.

The dried materials and water were charged to a 0.3 gallon ball mill in the following amounts.

The charge (MgO: Al ₂ O ₃ = 0.423) was ground for 4 hours. The resulting slurry is filtered in a laboratory filtration funnel to obtain a cake having a water content of 30% by weight. The bulk density after air drying this cake at 105 degreeC was about 1.35 g / cc. The cake thus dried was sintered at 1,680 ° C. for 1 hour and then the resulting material was crushed into small chunks (aggregates) for cooling and use in refractory products.

The stoichiometric magnesium aluminate spinel had a theoretical density of 3.58 g / cc, while the true density of the aggregate was 3.57 g / cc, the bulk density was 3.33 / gcc (93% of theory), and the average grain size was 10 microns. Was less. X-ray diffraction analysis revealed that spinel was completely formed, and the chemical composition was as follows.

Example 2

The refractory aggregate was produced by repeating the process of Example 1 except that the grinding time of the contents of the contents was changed to only 0.5 hours so that the kneading process could be performed with a minimum degree of grinding. The properties of the aggregates thus prepared were equivalent to those in Example 1, except that the bulk density was 3.10 g / cc (87% of theory).

Example 3

A series of refractory aggregates were prepared according to the process of Example 1 while varying the amounts of ESP powder and magnesium hydroxide charged into the ball mill so that the ratio of MgO: Al ₂ O ₃ was 0.200-0.800 to obtain the following results.

Example 4

The components of Example 1 and aluminum fluoride crystals were charged to a 0.3 gallon ball mill in the following amounts.

The charge (MgO: Al ₂ O ₃ = 0.437) was ground for 4 hours and air dried at 105 ° C. The dried cake was sintered and cooled at 1,680 ° C. for 1 hour and then ground. The aggregate thus prepared was found to contain slightly excess MgO as a fully reacted spinel by X-ray diffraction analysis. The bulk density was 3.39 g / cc (95% of theory) and the chemical composition was as follows. .

Example 5

The process of Example 1 was repeated except that the dried filter cake was quenched at 1,425 ° C. for 4 hours without sintering at 1,680 ° C. for 1 hour. At this time, the prepared matt cake could be easily pulverized. As a result of analysis, it was found that the spinel reacted completely and contained a slight excess of MgO, the true density was 3.56 g / cc, and the Na ₂ O content was 0.58 weight. It was%.

Example 6

The components of Example 1 and cryolite were charged to a 0.3 gallon ball mill in the following amounts.

The charge (MgO: Al ₂ O ₃ = 0.423) was triturated, filtered and dried according to the process of Example 1. The dried cake was quenched at 900 ° C. for 4 hours and the resulting matte was dry milled for 3 hours in a ball mill. X-ray diffraction analysis of the pulverized mineral thus obtained showed that spinel was completely formed and there was a slight excess of MgO. The Na ₂ O content of this matte was 1.70 wt%.

The pulverized matte was treated with 5% by weight of water and then pressed to a pressure of 10,000 psi (703 kg / cm ² ) to make 1 ″ × 1 ″ × 2 ″ (2.5 cm × 2.5 cm × 5.1 cm) slugs, This slug was baked at 1,680 degreeC for 1 hour. The calcined slug had a bulk density of 3.37 g / cc (94% of theory) and a Na ₂ O content of 0.6% by weight.

Example 7

A fire resistant aggregate was produced by repeating the process of Example 1 except that the sintering time was 4 hours and the sintering temperature was 1,600 占 폚 instead of 1680 占 폚. The bulk density of the aggregate was 3.09 g / cc (86% of theory) and the Na ₂ O content was 0.04 wt%.

Example 8

A sample was prepared by repeating the process of Example 7 except that the calcined cake was treated as a 1,600 ° C. matt mineral. This calcined cake was ground and kneaded in a ball mill for 8 hours. The powder thus produced contained 0.04% by weight of soda, and X-ray diffraction analysis revealed that it was a spinel containing a slight excess of MgO. This matte is then treated with 5% by weight of water and compressed to a pressure of 10,000 psi (703 kg / cm ² ) to make slugs of 1 ″ × 1 ″ × 2 ″ (2.5cm × 2.5cm × 5.1cm), This slug was baked at 1,680 degreeC for 1 hour.

The calcined slug had a bulk density of 3.42 g / cc (96% of theory) and a Na ₂ O content of 0.02% by weight.

Example 9

The dry ESP powder described in Example 1 and the calcined nesquehonite shown in the following table were charged into a 0.3 gallon ball mill with water.

This charge (MgO: Al ₂ O ₃ = 0.781) was treated in accordance with the process of Example 1 to produce a fire-resistant aggregate, the results are as follows.

Example 10

The components of Example 1 were charged to a 300 gallon ball mill in the following amounts.

The charge (MgO: Al ₂ O ₃ = 0.44) was ground for 10 hours, and the resulting slurry was placed in a pan and air dried at 105 ° C. The dried material was ground and pelletized in a high speed mixed-pelleting machine with water as binder. The particle size distribution of the spherical pellets thus produced is as follows.

^* U.S. Standard (ASTM E-11-61).

Lange, Handbook of Chemistry, 11th Edition (1973), p. 11, p. 11.

The bulk density of the dried pellets was 1.56 g / cc, and the pellets were calcined at 1,680 ° C. for 1 hour to yield a product having the following characteristics.

Example 11

The contents containing water were crushed for 24 hours and then pressed at 10,000 psi (703 kg / cm ² ) to make slug, and the process of Example 1 was repeated except that it was calcined at 2,100 ° C. for 1 hour. Nate spinel was prepared. Fire-resistant aggregates of good quality were obtained from the ground slugs.

Claims (1)

As described above, the alumina in the form of an electrostatic precipitator (ESP) powder and finely ground magnesia raw material are kneaded so that the weight ratio of magnesia to alumina is about 0.4-0.8, and the kneaded material is about 1,600-2,000. High purity magnesium aluminate spinel, characterized in that the mixture is heated for a time sufficient to fully react the kneaded mixture to produce a spinel having a bulk density of at least about 90% of theory and a sodium oxide content of 0.1% by weight or less. Manufacturing method.