JPH0364466B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing molten alumina using aluminum slag and scale as raw materials. (Prior art) Aluminum slag is slag consisting mainly of Al ₂ O ₃ that emerges on the surface of molten products during the refining of metallic aluminum, melting and refining of scrap aluminum, melting and refining of aluminum alloys, etc. This is the residual material obtained by recovering a portion of metal aluminum through processing such as crushing and sieving. Furthermore, scale is a thin layer formed 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. 121153/1983. Specifically, scale and aluminum slag are mixed and put into a melting furnace, where a thermite reaction occurs between metallic aluminum contained in the aluminum slag and iron oxide contained in the scale. Through this thermite reaction, iron oxide is reduced to obtain iron, and metal aluminum is oxidized to obtain molten alumina. This technology has the advantage of being able to obtain useful molten alumina and iron with less energy by using by-products similar to two types of industrial waste. (Problems to be Solved by the Invention) The above publication only describes a method for obtaining molten alumina by loading the compound only once.
In order to actually increase production efficiency and save energy, it is necessary to mass-produce molten alumina by using larger furnaces and additional loading of the compound. When the inventors added the formulation onto the melt in the early stages of their research, they were only able to obtain poor quality fused alumina. Therefore, we conducted extensive research to find out 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, and its gist is to melt a mixture of aluminum slag and scale in a furnace, and to melt the metal aluminum of the main aluminum slag in a furnace. In a method for producing molten alumina by a thermite reaction between iron oxide and scale, after the thermite reaction in the above compound is completed and the compound is almost completely melted, the solidified alumina is solidified on the surface of this molten material. A method for producing molten alumina, characterized in that the above-mentioned combination of aluminum slag and scale is additionally loaded onto the layer. (Operation) After the thermite reaction is completed in the furnace and the compound is almost completely melted, the surface of this melt 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 dissolve into the molten alumina of the molten slag before the thermite reaction, and the metal aluminum is generated by the reaction between the metal aluminum and the gas. suboxide AlO, carbide
Al ₄ C ₃ , nitride AlN, and residual metallic aluminum do not precipitate into molten alumina. Therefore, it is possible to obtain high-quality fused alumina that can be applied to 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. (Example) An example of the present invention will be described below. Aluminum slag Aluminum slag is prepared with the following ingredients. (a) Metal aluminum should be 20 to 50% (weight%, same below). The reason why it is set at 20% or more is to ensure that the thermite reaction occurs, and the reason why it is set at 50% or less is to use other substances to suppress the thermite reaction from occurring so violently that it damages the furnace wall. (b) Al ₂ O ₃ should be 40% or more. (c) The total weight of Mg and Mg compounds (MgCl ₂ , MgO, etc.) should be 9% or less. The reason for setting the content to 9% is to limit the content of spinel in the finally obtained kiln-fused 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 molten alumina production process, and it ultimately becomes spinel and is contained in molten alumina. remains. Therefore, when restricting the spinel content as described above, it is necessary to restrict the content in the aluminum slag. (d) The total weight of Ca and Ca compounds (CaCl ₂ , CaO, etc.) shall be 1% or less. These are ultimately
It becomes CaO, and as with Mg, it is difficult to remove in the molten alumina production process, and its eventual contamination with molten alumina is unavoidable. Since CaO has an adverse effect on the properties of molten alumina, it is necessary to strictly limit the above content. (e) AlN should be 15% or less, preferably 10% or less. (F) Reaction formulas (1), (2), (5) that describe the content of AlCl ₃ later
Adjust so that there is no excess or deficiency based on the above, and the weight ratio is adjusted to be AlN:AlCl ₃ =1:1.07.
Note that in reality, MgCl ₂ and CaCl ₂ , which undergo almost the same chemical reactions as AlCl ₃ , are included, albeit in small amounts, and considering the reaction equations (3) and (4) of these chlorides, AlN and chlorides (AlCl ₃ , CaCl ₂ ,
The above weight ratio is determined so that the amount of MgCl ₂ ) is not too much or too little. During operation, the total weight of AlN and the chloride may be adjusted to be approximately equal. (g) Impurities other than the above (Si, Ti, Fe, Cu, Cr,
Zn and its compounds NaCl, KCl and Al ₄ C ₃
etc.) to 5% or less. As mentioned above, there are some aluminum slags that contain AlN, some that contain _AlCl3 , and some that contain both.Usually, by blending two or more of these three types of aluminum slag, the above-mentioned
AlN and a chloride such as AlCl ₃ are prepared in the above weight ratio. Scale The scale may be made of either ordinary steel or special steel. In large-scale factories, scale is collected by water transport on production lines such as continuous casting, rolling, and forging, and stored in water tanks, so when taken out from the water tank, it is
Contains ~30% water. As it is, there is too much moisture, so dry it until it contains 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, AlN and AlCl The amount is 85% of the total weight of ₃ . Mixing Mix the above aluminum slag and scale well with a mixer to make 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 by the Thermite reaction equations (7) to (16) described below.
Determined based on. If there is a lot of scale, Fe ₂ O ₃ will remain in the slag, and if there is little scale, Al will enter the ferroalloy. To ensure the quality of the slag, the amount of scale should be 5-10% less than the calculated value. Note that this mixing can also be performed simultaneously with the heat treatment described below. 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, AlN contained in the aluminum slag reacts with the water contained in the scale to produce ammonia, and
As shown in equations (2) to (4), AlCl ₃ in aluminum slag
A smaller amount of MgCl ₂ or CaCl ₂ reacts with moisture to produce hydrogen chloride, and as shown in equation (5), the ammonia and hydrogen chloride finally react to produce aluminum chloride. AlN+3H ₂ O=NH ³ +Al(OH) ₃ (1) AlCl ₃ +3H ₂ O=3HCl+Al(CH) ₃ (2) or 2AlCl ₃ +(3+X)H ₂ O =6HCl+Al ₂ O ₃ −XH ₂ O (2 )′ MgCl ₂ +2H ₂ O=2HCl+Mg(OH) ₂ (3) CaCl ₂ +2H ₂ O=2HCl+Ca(OH) ₂ (4) NH ₃ +HCl=NH ₄ Cl (5) Note that the relationship between water and metallic aluminum in aluminum slag reacts as shown below, but this reaction is similar to the above
Since this reaction is much slower than the reactions of equations (1) to (5), only a small amount of metallic aluminum is lost. 2Al + 6H ₂ O = 3H ₂ + 2Al(OH) ₃ (6) Also, since the water content is adjusted to almost no excess or deficiency by pre-drying the scale, the remaining water reacts with metal aluminum as shown in equation (6). No metal aluminum is lost. In addition, as mentioned above, since the weight ratio of AlN and chlorides such as AlCl ₃ and water is adjusted as described above, almost all of the ammonia and hydrogen chloride generated in equations (1) to (4) are (5 Since ammonium chloride is formed by the reaction of (2), ammonia and hydrogen chloride are rarely scattered, or only in small amounts, and do not cause any pollution. White smoke is produced by the reactions of equations (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-mentioned compound contains the metallic aluminum necessary for the thermite reaction with scale in its entirety and does not contain AlN, AlCl _{3 ,} etc., so it is optimal as a raw material for the production of molten alumina, which will be described later. During this heat treatment, the scale is almost completely dried. Thermite Reaction When the above heat treatment 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. and,
A small amount of electrode scrap is placed on the surface of the compound in the melting furnace, and electricity is supplied to gently ignite it with an arc.
First, the reactions of formulas (1) to (5) above occur between the small amount of remaining AlN and chlorides such as AlCl ₃ and the steam in the furnace, producing some white smoke. Eventually the temperature of the compound reaches 1000
When the temperature reaches ℃, the following thermite reaction occurs mainly between the metallic aluminum contained in the aluminum slag and the iron oxide contained in the scale. Al+Fe ₂ O ₃ =2Fe+Al ₂ O ₃ −194800 (7) 2Al+3/4Fe ₃ O ₄ =9/4Fe +Al ₂ O ₃ −189800 (8) 2Al+3FeO=3Fe+Al ₂ O ₃ −197900 (9) In the case of special scale The following thermite reaction occurs between the metal aluminum and other metal oxides in the scale. 2Al+Cr ₂ O ₃ =2Cr+Al ₂ O ₃ −123800 (10) 2Al+3NiO+3Ni+Al ₂ O ₃ −216000 (11) 2Al+3/2MoO ₂ =3/2Mo+Al ₂ O ₃ −192900 (12) 2Al+3/2WO ₂ 3/2W+Al ₂ O ₃ − 196800 (13) 2Al+3/2SiO ₂ =3/2Si+Al ₂ O ₃ −81600 (14) 2Al+3/2TiO ₂ =3/2Ti+Al ₂ O ₃ −68850 (15) △H (Cal/molAl ₂ O ₃ ) Other than the above A thermite reaction similar to the above occurs between a trace amount of metal oxide and metal aluminum. Furthermore, a thermite reaction occurs between Al ₄ C ₃ in the aluminum slag and iron oxide in the scale, as exemplified below. 3/2Fe ₂ O ₃ + 1/2Al ₄ O ₃ = 3Fe + Al ₂ O ₃ + 3/2CO−△H (16) Furthermore, SiO ₂ contained in the aluminum slag and
TiO ₂ also undergoes a thermite reaction with metallic aluminum as shown in equations (14) and (15). The thermite reaction mentioned above is rapid and produces high temperatures, but
The reaction is alleviated by substances that do not participate in the thermite reaction, that is, Al ₂ O ₃ contained in the aluminum slag and Al ₂ O ₃ obtained by the above reaction, preventing damage to the furnace. can. At the high temperature of the thermite reaction, chlorides such as NaCl and KCl float to the surface, are almost completely volatilized at 1500℃ due to arc heat, and are collected by a dust collector. When the slag is heated to 2100°C by the high heat of the thermite reaction and arc heat, and becomes 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. Solidification of the surface of the melt When the surface is completely melted and the temperature reaches 2100℃, the electricity is temporarily stopped and the electrode is raised. Three minutes after the electricity stops, the slag surface solidifies and becomes a thin crust. 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 mixture is heat-treated in the drying furnace in the same manner as described above to remove AlN, AlCl ₃ , etc., and then loaded into the melting furnace again. Then, as described above, some white smoke is generated, and furthermore, several minutes after loading, a thermite reaction occurs 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 electrode Scrap is placed on the surface and heated by an arc to cause a thermite reaction. The ferroalloy produced by the thermite reaction penetrates the slag produced in the previous step due to its weight, descends, and dissolves into the ferroalloy obtained in the previous step. Since the surface of the molten slag has been solidified in advance as described above, this solidified layer can prevent the metal aluminum in the additionally charged compound from penetrating into the molten slag before the thermite reaction begins. When a part of metallic aluminum dissolves into the molten alumina of the molten slag before the thermite reaction, 2Al
-3Al ₂ O ₃ , and this metallic aluminum becomes suboxide AlO, carbide Al ₄ C ₃ nitride AlN by reaction with gas generated during slow solidification, which will be described later. 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. AlN+3H ₂ O=Al(OH) ₃ +NH ₃ (17) Al ₄ C ₃ +12H ₂ O=4Al(OH) ₃ +3CH ₄ (18) 3AlO+3H ₂ O=2Al(OH) ₃ +Al (19) 2Al+6H ₂ O=2Al (CH) ₃ +3H ₂ (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 metal can be obtained. Alumina can be obtained. Note that the above additional loading may be performed multiple times. Further, the heating and drying treatment of the compound that involves the production of ammonium chloride is preferably carried out in a drying oven as described above, but in order to reduce the equipment cost, it may be carried out in a melting furnace. In this case, the additionally loaded compound is heated and dried using the heat of the melt in the melting furnace. Collection of ferroalloy When the temperature reaches 2100℃, stop the power supply and raise the electrode. Then, before the electricity is turned off, the plug 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). Alternatively, it may be poured into a mold and sold as an ingot for use in steel production or cast iron melting. Slow cooling of slag After the electricity is turned off, cover the top of the furnace with a heat insulating cover and slowly cool the slag. 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, the content of Al ₂ O ₃ in the above slag was 91% or more,
MgO 8% or less, others (CaO, Fe ₂ O ₃ , SiO ₂ ,
TiO ₂ , Cr ₂ O ₃ , Na ₂ O, K ₂ O) can be reduced to 1.5% or less. Note that since the surface of the molten material is solidified before additional charging as described above, the amount of contamination of aluminum nitrides, carbides, and suboxides is extremely small. Almost all MgO is bonded with Al ₂ O ₃ to form spinel crystals. Furthermore, almost all of the remaining Al ₂ O ₃ is in the form of α-alumina crystals. The alpha alumina crystals are surrounded by spinel crystals. In addition, more than 60% alpha alumina crystal and spinel crystal
It can be 40% or less. Comparing the porosity and bulk specific gravity of molten alumina with a particle size of 3.36 to 1.68 mm obtained by crushing and sifting the above slag with white alumina abrasive material with the same particle size, the porosity is as shown in the table below. is small and bulk specific gravity is large, making it excellent as an abrasive material. Also,
The hardness and toughness are also at least the same as white alumina abrasives.

[Table] In addition, in the present invention, the particle size ratio (ratio of short axis to long axis, based on microscopic observation) of molten alumina with a particle size of 0.5 to 2.0 mm is as shown in the table below. Excellent as an abrasive material.

[Table] Experiment 1 Aluminum slag produced when melting and refining aluminum alloy using the active gas method and aluminum slag produced when melting and refining aluminum alloy using the inert gas method were mixed in a mixer to produce 20 kg of aluminum slag. was prepared. The chemical composition (unit weight %, same hereinafter) is as shown in the table below.

[Table] The content of other chlorides is 0.9%. Stainless steel scale with the following chemical composition containing 8% moisture pre-dried with 20 kg of the above aluminum slag.
42Kg of formulation was prepared by mixing 22Kg in a mixer.

[Table] 42 kg of the above formulation was loaded into a drying oven preheated to 300°C and held at 100 to 300°C for 15 minutes. The white smoke generated during this period was collected by a dust collector. The amount of dust collected by the dust collector was 1.8 kg, and its chemical composition was as shown in the table below.

[Table] Therefore, it was confirmed that this dust can be used as a flux when melting fertilizer or aluminum alloy scrap. The mixture that has been treated to be non-polluting in the furnace weighs 38.5 kg and has no moisture.
0.2%, metallic aluminum 16%, and no AlN and _AlCl3 were observed, confirming that it is an excellent formulation for producing high quality molten alumina by utilizing thermite reaction as described below. . Next, 38.5 kg of the above-mentioned compound was loaded into a three-phase Eleu crystal compact electric furnace (130 KVA), electrode scraps were placed on the surface of the furnace, and electric power was supplied, whereby the compound melted while causing a thermite reaction. When the temperature of the melt in the furnace reaches 2100°C, the power supply to the furnace is stopped and the surface of the melt is solidified. 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 placed on the surface in the same manner as above, and electricity was supplied until the temperature of the molten material reached 2100℃. The power supply will be stopped when the Next, the electrode is raised and the top is covered with a heat insulating cover to gradually cool the molten material. 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.

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

[Table] When the above slag was analyzed by X-ray diffraction, almost all of the MgO was chemically combined with Al ₂ O ₃ to form spinel, and almost all of the remaining Al ₂ O ₃ was formed into α-alumina crystals. It's summery. As a result of observation with a microscope, α
Spinel crystals were observed surrounding the alumina crystals, and there were few impurities. Experiment 2 Ferroalloy and slag were manufactured using 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. The slag obtained in Experiment 1 (hereinafter referred to as slag A) and the slag obtained in Experiment 2 (hereinafter referred to as slag A)
(referred to as slag B) were prepared in an amount of 1 kg each, pulverized and sized in the same manner, and steam at 3 atm was supplied in an autoclave for 3 hours to measure the weight increase rate and pulverization rate. The results are shown in the table below.

[Table] In slag A, the weight increase and pulverization due to the reactions of equations (17) to (20) are very small compared to slag B, and harmful substances such as metal aluminum and aluminum carbides, nitrides, suboxides, etc. It was found that there was almost no residual substance. Therefore, it was confirmed that it is effective to solidify the surface of the melt before additional loading. In the case of Experiment 1, the production amount of slag A was 36.6 kg,
The production amount of ferroalloy was 38.4Kg, and in the case of Experiment 2, slag B was 35.9Kg and ferroalloy was 37.9Kg.
The reason why the total amount of slag B and alloy iron obtained in Experiment 2 was smaller than in Experiment 1 can be presumed to be because the mixture was blown up by the high-temperature air flow in the furnace and reached the dust collector. Therefore, it was confirmed that solidifying the surface of the molten material before additional loading is effective in increasing production efficiency. Experiment 3 Briquettes were formed from slag A obtained in Experiment 1 and white molten alumina under the same conditions. That is, the particle size distribution obtained by crushing and sieving is as shown in the table below, and the briquettes were molded at a pressure of 700 Kg/cm ² and fired at a temperature of 1800°C to obtain 100 x 100 briquettes.
The shape was a rectangular parallelepiped of 65 mm.

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

[Table] 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 is particularly superior in compression and bending strength. It showed the following characteristics. 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 still 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] 1. A mixture of aluminum slag and scale is melted in a furnace, and the thermite reaction between the metallic aluminum of the aluminum slag and the iron oxide of the scale is carried out.
In the method for producing molten alumina, after the thermite reaction in the above-mentioned compound is completed and the compound is almost completely melted, the surface of this molten material is solidified, and the above-mentioned combination of aluminum slag and scale is deposited on the solidified layer. A method for producing molten alumina, characterized by additionally charging a substance.