JPS62278121A - Production of fused alumina - Google Patents

Abstract

PURPOSE:To obtain a high-quality fused alumina suitable as abrasive grain for grinding and polishing, etc., preventing pulverization of raw material, by melting a mixture of Al dross and scale in a furnace, completely melting the thermit reaction product, solidifying the surface layer of the molten product, adding the same composition as above to the surface of the solidified layer and repeating the reaction. CONSTITUTION:An Al dross containing AlN and a chloride and having a composition adjusted to 20-50wt% metallic Al, >=40wt% Al2O3, <=9wt% Mg (compound), <=1wt% Ca (compound), <=15wt% AlN, etc., is mixed with a scale at a ratio to give a composition satisfying the reactions of formulas I-V in proper quantities. The composition is melted in a furnace to effect the thermit reaction of metallic Al in the Al dross with iron oxide in the scale to obtain a completely molten product. After solidifying the surface layer of the molten product, the same composition as above is added upon the surface layer and subjected to the thermit reaction preventing the intrusion of metallic Al into molten dross. If necessary, the reaction is repeated to obtain high-quality fused alumina.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing molten alumina using aluminum slag and scale as raw materials.

(Prior art) Aluminum slag is the A that floats on the surface of the molten material during the refining of metallic aluminum, melting and refining of aluminum alloys, etc.
The slag, which is mainly composed of L203, is crushed, sieved, etc., and a portion of the metal aluminum is recovered.

In addition, scale is something that is grown and peeled off on the surface of a steel ingot during continuous casting, rolling, forging, etc. of steel or special steel, and is mainly composed of iron oxide.

A method for producing iron and molten alumina from scale and aluminum slag is known as seen in Japanese Patent Application Laid-Open No. 59-121153. Specifically, scale and aluminum slag are mixed and put into a melting furnace, and in the furnace a thermite reaction occurs between metallic aluminum contained in the aluminum slag and iron oxide contained in the scale. Through this Chirmint reaction, iron oxide is reduced to obtain iron, and metal aluminum is oxidized to obtain molten alumina. This technology utilizes by-products similar to two types of industrial waste (1)! /l>?
rt, x f i u-? a 宕IE
? , -; *E, ht n, : Q l-
64.

(Problems to be Solved by the Invention) The above publication only describes a method for obtaining molten alumina by charging the compound only once, but in order to actually increase production efficiency and save energy, it is necessary to Large quantities of molten alumina must be produced by additional loading of the compound in the furnace. When the inventors added the formulation onto the melt in the early stages of their research, they were bound to obtain poor quality fused alumina. Therefore, we conducted extensive research to find the cause of this quality deterioration, and came up with the method of the present invention.

(Means for Solving the Problems) The present invention has been made to solve the above problems.
The gist is a method for producing molten alumina by melting a mixture of aluminum slag and scale in a furnace, and mainly through thermite reaction between metallic aluminum in the aluminum slag and iron oxide in the scale. After the thermite reaction is completed and the compound is almost completely melted, the surface of this melt is solidified, and the above-mentioned aluminum slag and scale compound is additionally charged on top of this pseudo-solid layer. There is a method for producing fused alumina.

(Operation) After the thermite reaction is completed in the furnace and the compound is almost completely melted, the surface of this molten material is solidified, and the compound is additionally charged onto this solidified layer. Therefore, since the metal aluminum in the additionally loaded compound is blocked by the surface solidification layer, it does not melt into the molten alumina of the molten slag before the thermite reaction, and the metal aluminum is generated by the reaction between this metal aluminum and the gas. Suboxide A10. Carbide A1
．． C.

Nitride AIN and residual metallic aluminum do not precipitate into molten alumina. Therefore, high quality molten alumina can be obtained that can be used as abrasive grains for grinding and refractories, etc. It can prevent the inconvenience of reacting with moisture and turning into powder.

(Example) An embodiment of the present invention will be described below.

Aluminum slag is prepared with the following ingredients.

(a) Metal aluminum should be 20 to 50% (weight %, same hereinafter). The reason why it was set at 20% or more was to ensure that the thermite reaction occurred, and the reason why it was set at 50% or less was because
This is to suppress the thermite reaction from occurring violently enough to damage the reactor walls.

(b) Al□○ shall be 40% or more.

(c) Mg and (7Mg compounds (MgCL, MgO, etc.)
Reduce the total weight to 9% or less. The reason for setting it to 9% is to limit the content of spinel in the finally obtained molten alumina, which will be described later, to 40% or less. Mg and Mg compounds ultimately become MgO, and since this MgO is not reduced by thermite reaction and has little volatilization,
It is difficult to remove in the process of manufacturing molten alumina, and ultimately remains in the molten alumina as spinel.

Therefore, when restricting the spinel content as described above, it is necessary to restrict the content in the aluminum slag.

(d) Ca and Ca compounds (CaCl□, CaO, etc.)
The total weight shall be 1% or less. These are finally CaO
As in the case of MH, it is difficult to remove in the molten alumina production process, and its contamination with the molten alumina is unavoidable.Since CaO has a negative effect on the properties of molten alumina, the above content rate is strictly limited. There is a need to.

(,k) AIN is 15% or less, preferably 10% or less.

(to) Reaction formula (1) below, the content of A ICI,
(Adjust so that there is no excess or deficiency based on 2L (5), and the weight ratio is AIN: AlC1p = 1: 1.0
Make it 7. In fact, M gCl : r Ca which undergoes almost the same chemical reaction as A Ic L
Cl: is included, although in a small amount, and considering the reaction formulas (3) and (4) of these chlorides, the above reaction should be carried out so that AIN and chloride (A Ic Is, CaC12゜MgCl2) are not too much or too little. Determine the weight ratio.

When scraping, the AIN and the total weight of the chlorides may be adjusted to be approximately equal.

(g) Impurities other than the above (Si, Ti, Fe, Cu, C
r, Zn and its compounds, NaCl, KCI and A
1. C.

etc.) to 5% or less.

As mentioned above, aluminum slag contains AIN,
Some contain A Ic+, and others contain both.Usually, by blending two or more of these three types of aluminum slag, the above weight ratio of AIN and chlorides such as AICL can be achieved. Prepare as follows.

Scale The scale may be made of either ordinary steel or special steel. In large-scale factories, on production lines such as continuous casting, rolling, and forging, scale is collected by water transportation and stored in water tanks, so when taken out from the water tank, it contains 20 to 30% water. As it is, there is too much moisture, so dry it with a powder containing an appropriate amount.

Here, the appropriate amount is determined based on the reaction formulas (1) to (5) described later, so that there is almost no excess or deficiency, and specifically, in a mixture obtained by mixing aluminum slag and scale, A
The amount is 85% of the total weight of IN and AlCl.

The above-mentioned aluminum slag and scale are thoroughly mixed in a mixer to prepare a mixture. At this time, even when using two or more types of aluminum slag, it is preferable in terms of work efficiency to mix them together with the scale without mixing them in advance. The weight ratio of aluminum slag and scale is determined based on thermite reaction equations (7) to (16) described below. If there is much scale, Fe2O remains in the slag, and if there is little scale, A1 will enter the ferroalloy. In order to ensure the quality of the slag, it is also possible to simultaneously perform 5-b processing based on the calculated amount of scale.

Heat Treatment Next, the material is heated at 100 to 300'C in a drying furnace or a melting furnace that causes the thermite reaction described below. As a result, as shown in equation (1) below, AIN contained in the aluminum slag reacts with the water contained in the scale to produce ammonia, and as shown in equations (2) to (4) below. As shown, A Ic + in the aluminum slag and smaller amounts of MgCl2 and CaCl2 react with moisture to generate hydrogen chloride, and as shown in equation (5), the ammonia and hydrogen chloride finally react. ammonium chloride is produced.

AIN+3H20=NH,+Al(OH), (
i) AICL+3820=38C++AI(OHL
(2) or 2 AlCl, +(3+X)H20=68
C++Al2O, -XH20(2)'MgC1=+28
20=28C1+Mg(OH)2 (3)CaCl
2 + 2 H20=2HCI+Ca(OHL (4
)NH,+HC1=NH,CI'
(5) Moisture and aluminum metal in aluminum slag react as shown below, and this reaction occurs in (1) to
Since this reaction is much slower than the reaction of formula (5), only a small amount of metallic aluminum is lost.

2AI+6820=38. +2AI(OH), (
6) Furthermore, since the water content is adjusted to be almost exact by pre-drying the scale, the remaining water will not react with the metal aluminum and cause metal aluminum to be lost as shown in equation (6).

In addition, as mentioned above, since the weight ratio of chlorides such as AIN and A I CI 3 and water is adjusted as described above, almost all of the ammonia and hydrogen chloride generated in equations (1) to (4) are Since ammonium chloride is formed by the reaction (5), ammonia and hydrogen chloride are hardly scattered alone, or even if only in small amounts, they do not cause pollution.

White smoke is produced by the reactions of formulas (1) to (5) accompanying the heating, and when this white smoke is collected by a dust collector, a powder containing ammonium chloride as a main component is obtained. This powder is useful as a fertilizer or as a flux used for melting and refining aluminum alloys.

In addition, the above formulation contains almost all the metallic aluminum necessary for the Chilmitsu F reaction with scale, and A
Since it does not contain IN, AlC1, etc., it is optimal as a raw material for producing fused alumina, which will be described later. During this heat treatment, the scale is almost completely dried.

Thermite Reaction When the heat treatment described above is carried out in a drying oven, the treated mixture is transferred to a melting oven. When carried out in a melting furnace, the formulation may be used as is. Then, when a small amount of electrode scrap is placed on the surface of the compound in the melting furnace, electricity is supplied, and the arc is gently ignited, the remaining AIN and A
The above (1) to (
5) The reaction of formula occurs and some white smoke is generated. When the temperature of the mixture eventually reaches 000°C, the following thermite reaction occurs mainly between the metallic aluminum contained in the aluminum slag and the iron oxide contained in the scale.

AI+Fe:01=2Fe+AI=○s -194,8
00(7)2A I+3/'4F el○, =9/4F
e+ A I. 0, -189,800(8)2Al+
'3Feo =3Fe+Al2O, -197,900(
9) In the case of special steel scale, the following thermite reaction occurs between the metal aluminum and the metal oxide in the scale.

2AI+Cr2O>=2Cr+Al2O, -123. −
800 (10)2Al+3NiO”3Ni+AI
□○, -216,000 (11) 2A I + 372
MoO2= 3/2M o + AI20 *-19
2,900 (12) 2A I+372W O2=3/2
Vi' + A l□O, -196,800(13)2
Al+3/2Si○2=3/2S i+ A I□O,
-81,600 (14) 2A I + 3/2T io
2=3/2T I + A I203-68,850
(15) ΔH (Cal/mol AIzo-) Note that the same thermite reaction as above occurs between trace amounts of metal oxides other than those mentioned above and metal aluminum.

Further, a thermite reaction as exemplified below occurs between ALC in the aluminum slag and iron oxide in the scale.

3/2Fe20z+1/2A14Cz=3Fe+Al□
Oi 1372CO-ΔH (16) In addition, Sin and TiO contained in the aluminum slag
2 also causes a thermite reaction with metal aluminum as shown in equations (14) and (15).

The thermite reaction is rapid and generates high temperatures, but the reaction is moderated by substances that do not participate in the thermite reaction, that is, A1□03 contained in the aluminum slag and A 120 obtained by the above reaction. It can prevent damage to the furnace.

At the high temperature of the thermite reaction, chlorides such as NaCl and KCI float to the surface, are almost completely volatilized at 1500°C by arc heat, and are collected by a dust collector.

Due to the high heat of the thermite reaction and arc heat, the slag becomes 21
When heated to 00°C and completely molten, the reduced ferroalloy sinks to the bottom due to the difference in specific gravity. This completely separates the slag from the ferroalloy.

The thermite reaction and melting may be carried out in any type of electric furnace, such as a resistance furnace, an arc furnace, or an induction furnace.

When the solidified surface of the melt surface completely melts and reaches 2100°C, the electricity supply is temporarily stopped and the electrode is raised. After 3 minutes of positive electricity, the slag surface becomes i! The skin will be hard and thin. It is even better if a thin skin of sintered alumina is formed by pouring a small amount of Bayer alumina onto this thin skin and sintering it with the heat of the molten material.

Additional loading The formulation was heat-treated in the above drying oven in the same manner as described above, and the AI
The material from which N, AlCl, etc. have been removed is loaded into the melting furnace again. Then, as described above, some white smoke is generated, and furthermore, after several minutes have passed after loading, a thermite reaction is generated from the lower part of the compound due to the heat of the melt and spreads to the upper part. Once the surface has melted, the electrode is lowered and electric power is supplied by the arc to completely melt the surface. If the aluminum slag contains 20% or more of metallic aluminum, the thermite reaction will naturally occur due to the heat of the melt as described above, but if this thermite reaction does not occur naturally, the same as in the previous case will occur. Electrode scraps are placed on the surface and heated by an arc to cause a thermite reaction. Due to its weight, the ferroalloy formed by the Chirmint reaction passes through the lag formed in the previous step, descends, and melts into the ferroalloy obtained in the previous step.

As mentioned above, since the surface of the molten slag is pre-solidified, this solidified layer can prevent the metal aluminum in the additionally charged compound from melting or penetrating into the lag before the thermite reaction starts. .

When a part of metallic aluminum melts into the molten alumina of the molten slag before the thermite reaction, 2A1-3AI□0
3, and this metallic aluminum becomes suboxide AIO, carbide A1. Cs, nitride AIN) knee. These compounds and residual metallic aluminum precipitate at the grain boundaries of α-alumina crystals and spinel crystals.

Then, as shown in the following formula, these react with moisture in the air to form hydroxide compounds and are powdered, resulting in deterioration of properties as abrasive grains for grinding and polishing and as refractories.

AIN+38=O=AI(OHL+NH'-(17)A
LC, +12H20=4AI(OH),+3CH4(I
s) 3AIO+3H20=2AI(OH),+AI
(19) 2AI+6820=2AI(OH)3+
382 (20) However, in this example, the metal aluminum in the additionally charged compound does not enter the molten slag before the thermite reaction, so the above disadvantage can be prevented and high quality molten alumina can be obtained. It comes off. Note that the above additional loading may be performed multiple times.

In addition, it is preferable that the heat drying treatment of the compound that involves the production of ammonium chloride is carried out in a drying oven as described above.
In order to reduce the equipment cost, a melting furnace may be used. In this case, the additionally loaded compound is heated and dried using the heat of the melt in the melting furnace.

Moxibustion meeting! When the temperature reaches 2100°C, the power supply is stopped and the electrode is raised. Then, before this positive charge is applied, the stopper at the bottom of the furnace is removed (tapping), the ferroalloy is allowed to flow out of the furnace, received in a ladle, and then fed in its molten state to the steel melting furnace (hot charge). It can also be cast into a mold and made into an ingot.
It may be sold as A or for melting cast iron.

Slowly cooling the slag After applying positive electricity, a heat insulating cover is placed on the top of the furnace and the slag is slowly cooled. The slowly cooled slag is pulverized and sized to be used as abrasive grains for grinding and polishing tools or as a refractory material.

Since the content of impurities in the aluminum slag was restricted, in the above slag, A I20 was 91% or more, Mg
8% or less of O, its 1ljj, (Cao, F e2
0 ISi○2+ T io 21Cr20ffl N
a201 K 20) can be made 1.5% or less. Note that since the surface of the melt is solidified before additional charging as described above, the amount of aluminum nitrides, carbides, and suboxides mixed in is extremely small. Almost all MgO is A
It combines with 12O to form a spinel crystal. Also,
Almost all of the remaining Al2O3 is alpha alumina crystal.

The alpha alumina crystals are surrounded by spinel crystals. Further, the α-alumina crystal content can be 60% or more, and the spinel crystal content can be 40% or less.

Particle size 3.3 obtained by crushing and dividing the above slag
When the porosity and bulk specific gravity of fused alumina of 6 to 1,68 nv are compared with white alumina abrasive material of the same particle size, as shown in the table below, the porosity is small and the bulk specific gravity is large, and the abrasive material has a low porosity and a large bulk specific gravity. It is excellent as. In addition, its hardness and toughness are equal to or higher than white alumina abrasives.

In addition, in the present invention, particle size (), 5 to 2, O+Il+
The particle size ratio (ratio of short axis to long axis, based on microscopic observation) of the fused alumina of No. o is as shown in the table below, and many of the particles have a small particle size ratio, making them excellent as abrasive materials.

Experiment 1 20 kg of aluminum slag was prepared by mixing aluminum slag produced when melting and refining an aluminum alloy using an active gas method and aluminum slag produced when melting and refining an aluminum alloy using an inert gas method. . The chemical composition (unit weight %, same hereinafter) is as shown in the table below.

Note that the chloride content in the pond is 0.9%.

8 kg of pre-dried water to 20 kg of the above aluminum slag
Stainless steel scale 22Kg with the following chemical composition including %
were mixed in a mixer to prepare 42 Kg of formulation.

42 kg of the above blend was loaded into a drying oven preheated to 300''C and held at 100-300°C for 15 minutes. White smoke generated during this time was collected by a dust collector.

The amount of dust collected in the dust collector was 1.8 kg, and its chemical composition was as shown in the table below.

Therefore, it has been confirmed that this dust can be used as 7 lux when melting fertilizer or aluminum alloy scrap.

The mixture that was treated to be pollution-free in the furnace weighed 38.5 kg, had a moisture content of 0.2%, and metallic aluminum of 16%, with no AIN or AlC1, and as described below, the compound was of high quality using the thermite reaction. was found to be an excellent formulation for producing fused alumina.

Next, the above-mentioned compound 38.5KFl is loaded into a three-phase electric furnace (130 KVA), electrode scraps are placed on the surface of the furnace, and when power is supplied, the compound melts while causing a thermite reaction. The temperature of the melt in the furnace is 2100
When 'C is reached, the power supply to the furnace is stopped and the surface of the melt is allowed to solidify. Next, 38.5 kg of the above-mentioned compound that had been heat-treated in the drying furnace was loaded into the electric furnace again, and electrode scraps were then placed on the surface in the same manner as above, and electricity was supplied until the temperature of the molten material reached 21 oo'c. The power supply will be stopped when the limit is reached.

Next, the electrode is raised, the top of the furnace is covered with a heat insulating cover, and the molten material is slowly cooled.

In the product solidified in the furnace, the upper slag and the lower ferroalloy are completely separated. The chemical composition of the produced ferroalloy is as follows.

The chemical composition of the produced slag is shown in the table below.

When the above slag was analyzed by X-ray diffraction, almost all of the M
gO is chemically combined with Al2O to form spinel, and almost all of the remaining AI=Os is α-alumina crystal. As a result of microscopic observation, spinel crystals were observed surrounding the α-alumina crystals, and there were few impurities.

Experiment 2 Ferroalloy and slag are produced by the same process as in Experiment 1.

However, this experiment differed from Experiment 1 in that the compound was added without temporarily stopping the power supply and without solidifying the surface of the melt.

Slag obtained in Experiment 1 (hereinafter referred to as slag A)
and the slag obtained in Experiment 2 (hereinafter referred to as slag B), 1 kg each were prepared, pulverized and sized using the same method, and steam at 3 atm was supplied in an autoclave for 3 hours to determine the weight increase rate and The powderization rate was measured.

The results are shown in the table below.

In slag A, the weight increase and powdering caused by the reactions of equations (17) to (20) are extremely small compared to slag B, and harmful substances such as metal aluminum and aluminum carbides, nitrides, and suboxides remain. It was found that there were almost no

Therefore, it was confirmed that it is effective to solidify the surface of the molten material before additional charging.

In Experiment 1, the production amount of slag A was 36.6 kg and the production amount of ferroalloy was 38.4 kg, and in the case of Experiment 2, slag B was 35.9 kg and the ferroalloy force was 137.9 kg. Ta. The total amount of slag B and ferroalloy obtained in Experiment 2 was smaller than that in Experiment 1. It can be assumed that this is because the mixture was blown up by the high temperature air flow in the furnace and reached the dust collector. With a welding force of C, it was confirmed that it is effective to bypass the surface of the molten material before additional charging in order to increase production efficiency.

Experiment 3 Briquettes were formed from slag A obtained in Experiment 1 and white molten alumina under the same conditions. i.e. crushing,
The particle size distribution obtained by sieving is as shown in the table below, and the briquettes were molded at a pressure of 700 Kg/cIf12 and then fired at a temperature of 1800°C to obtain 100X100X65
It was made into a rectangular parallelepiped shape of IIu++.

Various comparative tests were conducted using the above briquettes. The results are shown in the table below.

As is clear from the table above, slag A has the same water absorption, apparent porosity, bulk specific gravity, and apparent specific gravity as white fused alumina, and exhibits particularly excellent properties in terms of compression and bending strength. Ta.

The present invention is not limited to the above embodiments, and various embodiments are possible. For example, even if most or almost all of the slag is spinel crystals, this is within the technical scope of the present invention; in other words, the product made of spinel crystals is also considered to be molten alumina.

(Effects of the Invention) As explained above, in the present invention, after the thermite reaction is completed in the furnace and the compound is almost completely melted, the surface of this molten material is solidified, and the compound is placed on the solidified layer. Since the material is additionally loaded, it is possible to obtain high-quality molten alumina that can be used as abrasive grains for grinding and polishing, refractories, etc., and it is possible to prevent the inconvenience of reacting with moisture in the air and turning it into powder.

Claims (1)

[Claims] In a method of producing molten alumina by melting a mixture of aluminum slag and scale in a furnace and mainly through a thermite reaction between the metallic aluminum of the aluminum slag and iron oxide of the scale, the thermite reaction in the above mixture is completed. A method for producing molten alumina, which comprises solidifying the surface of the melt after the mixture is almost completely melted, and additionally charging the above-mentioned aluminum slag and scale mixture onto the solidified layer.