JPH1053411A - Production of calcium aluminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain calcium aluminate high in curing rate, by exothermic oxidation between aluminum residual ash and a calcareous stock in a kiln in an oxidative atmosphere while keeping the system at high temperatures. SOLUTION: First, aluminum residual ash containing about >=20wt.% of metallic aluminum and 40-70wt.% of Al2 O3 and a calcareous stock such as limestone powder >=80wt.% of which is passable through a 200-mesh sieve are mixed together under agitation, and the mixture is charged into a rotary kiln, subsequently, the kiln is forcedly fed with air followed by heating while rotating the kiln to initiate the reaction. The exothermic oxidation of metallic aluminum then proceeds and the system reaches a temperature of as high as about 1,600-1,800 deg.C. By the reaction between the Al2 O3 and CaO, a high-viscosity reaction product in a semi-molten state is formed. Thereafter, the system is air-cooled to bring the in-kiln temperature to about 1.000 deg.C and the reaction product is taken out as dumpling-like lumps each about 2-100mm in size followed by forced cooling an then crushing the product, thus obtaining the objective calcium aluminate fine granules composed of >=70wt.% of 12CaO.7Al2 O3 ingredient and the rest of Al2 O3 , MgO, SiO2 and others.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing calcium aluminate, and more particularly to a method for producing calcium aluminate which can be used as a raw material for ultra-rapid hardening cement having a remarkably fast setting speed from aluminum ash and calcareous raw materials.

[0002]

2. Description of the Related Art During the smelting and refining of aluminum and / or aluminum alloy, molten slag mainly composed of aluminum oxide is generated. The molten slag contains 40 to 50 metallic aluminum.
Since it is contained in an amount of about 70% by weight, the molten slag is subjected to an ashes machine to recover metallic aluminum. However, the remaining slag from which the metallic aluminum has been recovered still contains about 30 to 40% by weight of metallic aluminum, so that it is redissolved and the metallic aluminum is further recovered. The slag remaining after such a process is generally called aluminum residual ash. This aluminum residue ash still contains metallic aluminum that cannot be recovered. Further, aluminum oxide is considerably contained in aluminum residual ash.

[0003] Accordingly, it has been practiced to effectively utilize metallic aluminum or aluminum oxide in aluminum residual ash. In the field of iron and steel, it is used as a heat insulating material or a heating material utilizing the oxidative exothermic reaction of metallic aluminum, and as a part of a raw material for cement depending on the composition of residual ash. In any case, it is provided at a considerable cost, but at present, most of it is treated as industrial waste.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing useful calcium aluminate using aluminum residual ash, which is mostly treated as industrial waste, as a raw material.

[0005]

Means for Solving the Problems The present inventors have mixed aluminum residual ash with a calcareous material such as limestone powder, and made use of the metallic aluminum contained in the aluminum residual ash to form metallic aluminum. When a rapid oxidation reaction is caused to generate heat to cause the above-mentioned aluminum residual ash to react with the calcareous raw material at a high temperature, calcium aluminate is efficiently produced, and the resulting reaction product containing calcium aluminate has a curing rate. The present invention has been found to be suitable as a raw material for ultra-rapid hardening cement, which has a remarkably high speed.

That is, according to the present invention, the aluminum residual ash and the calcareous raw material are subjected to (a) a reaction system in an oxidizing atmosphere, and (b) an exothermic oxidation reaction of metallic aluminum contained in the aluminum residual ash. By raising it,
(C) A method for producing calcium aluminate, characterized in that the reaction is carried out while maintaining the reaction system at a high temperature, the above object of the present invention is achieved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for producing a calcium aluminate of the present invention will be described. The composition of aluminum residual ash used as a raw material in the production method of the present invention changes depending on whether aluminum residual ash is obtained by melting and refining aluminum or aluminum residual ash is obtained by melting and refining an aluminum alloy. The composition of the aluminum ash also changes depending on the type of the aluminum alloy. The most abundant component is aluminum oxide, about 40%.
Accounts for ~ 70% by weight.

In the production method of the present invention, aluminum residual ash in which metallic aluminum is present is used. The proportion of metallic aluminum present in aluminum ash is 20%
It is preferred that the content be at least 10% by weight. If the amount of metallic aluminum is small, the reaction system cannot be maintained at a high temperature. The amount of metallic aluminum in the residual aluminum ash is usually at most about 30% by weight.

The aluminum residue ash contains silicon oxide, magnesium oxide, aluminum nitride and the like in addition to the above-mentioned aluminum oxide and metallic aluminum. Table 1 below shows a typical example of the composition of aluminum residual ash.

[0010]

[Table 1]

The calcareous raw material which is another raw material used in the production method of the present invention is calcium oxide and a compound which can be converted to calcium oxide under the reaction temperature conditions of the production method of the present invention. Specific examples of the calcareous raw material include calcium oxide powder, calcium hydroxide powder, limestone powder, and the like. Of these, use of limestone powder is preferred. In addition, 80% or more of the limestone powder usually passes 200 mesh.

In the production method of the present invention, the aluminum residual ash and the calcareous material are maintained while maintaining the reaction system at a high temperature due to the heat generated by the rapid oxidation reaction of the metallic aluminum contained in the aluminum residual ash represented by the following formula (1). React with raw materials. Then, the reaction system is set to an oxidizing atmosphere so that the oxidation reaction is continued.

[0013]

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In order to uniformly generate calcium aluminate in the reaction system by the exothermic oxidation reaction of metallic aluminum represented by the above formula (1) and the sintering reaction of aluminum oxide and calcium oxide described below, It is preferable that aluminum residual ash and calcareous raw material are uniformly mixed in advance and then charged into a firing furnace.

The initiation of the exothermic oxidation reaction of metallic aluminum represented by the above formula (1) depends on the composition of aluminum residual ash, particularly the ratio of metallic aluminum, the ratio of aluminum residual ash to calcareous raw material, and the like. 400-600
Start with a temperature range of ° C. Therefore, for the purpose of starting the oxidation reaction, heating is performed from outside the reaction system until the temperature reaches the above-mentioned temperature. It is preferable to stop heating from outside the reaction system after confirming that the oxidation reaction continues stably.

In the production method of the present invention, the reaction system is placed in an oxidizing atmosphere for the purpose of promoting the exothermic oxidation reaction of aluminum represented by the above formula (1) to maintain the reaction system at a high temperature. Specifically, the reaction system can be brought into an oxygen atmosphere by forcibly supplying an oxygen-containing gas, for example, air into the reactor.

The temperature of the reaction system reaches a high temperature of, for example, 1600 to 1800 ° C. due to a rapid oxidation reaction of metallic aluminum. As a result, the following elementary reactions (i) and (ii)
Occurs.

[0018]

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Of course, in the elementary reaction (i), the calcareous raw material is not calcium oxide. When the calcareous material is calcium carbonate, the elementary reaction (i) is a decarbonation reaction. By the elementary reaction (ii), calcium aluminate is produced by the involvement of the aluminum oxide originally present in the aluminum ash and the aluminum oxide produced by the oxidation reaction of the metallic aluminum. This elementary reaction (ii)
Is a sintering reaction.

Note that calcium aluminate is
That is, 12CaO.7Al_TwoO_ThreeOf the composition
Typical, but of other composition, for example 3CaO.
Al _TwoO_Three, CaO.Al_TwoO_ThreeThe one indicated by
Included in the concept of sium aluminate Production of the present invention
The calcium aluminate produced by the method has 12Ca
O ・ 7Al_TwoO_ThreeContaining calcium aluminate
Having can provide a fast setting cement material
Preferred from the point. And 12CaO.7Al _TwoO_Threeof
The calcium aluminate of the composition is produced by the production method of the present invention.
70% by weight or more in the calcium aluminate produced
Occupation gives a favorable result.

In the prepared calcium aluminate,
In order that calcium aluminate having a composition of 2CaO · 7Al ₂ O ₃ be present at the above ratio, the amount of calcareous raw material used is CaO / Al ₂ O ₃ (molar ratio) = 0.5.
It is preferable to use so as to satisfy 1.0. In the above formulas, CaO is the amount of time obtained by converting the calcareous material to CaO, Al ₂ O ₃ is Al ₂ O ₃ in the aluminum residual ash
(Mol).

In a reaction system heated to a high temperature of, for example, 1600 to 1800 ° C. by the exothermic oxidation reaction of metallic aluminum, calcium aluminate is formed according to the elementary reactions (i) and (ii) described above. The composition is 12CaO.7Al
Calcium aluminate of ₂ O ₃ has a lower melting point (1360 ° C.) than the melting point of aluminum oxide (2050 ° C.), and is molten in the above temperature range. On the other hand, calcium aluminate whose composition is not as described above has a higher melting point.

Therefore, aluminum oxide,
High melting point substances such as silicon oxide and high melting point calcium aluminate are present in a solid state and have a composition of 12CaO.7A.
l ₂ O ₃ calcium aluminate is present in the molten state. Therefore, the reaction system is in a semi-molten state with high viscosity.

In order to allow the reaction of the reaction system in the semi-molten state to proceed uniformly, it is preferable to employ a method in which a rotary baking furnace described later is used as a reaction apparatus and the furnace is rotated at least during the reaction. .

When the metallic aluminum to be oxidized substantially disappears, the heat generated by the oxidation disappears. In practice, assuming that the calcium aluminate generation reaction has stopped at the place where the temperature in the firing furnace has started to fall, in order to obtain the reaction product from the reaction apparatus as an easy-to-handle lump, for example, The number of rotations was 2-4 at the time of reaction.
It is preferable to rapidly increase the temperature by twice and rapidly cool by air cooling in order to stably obtain calcium aluminate. 1500 ° C
The reaction product cooled to below has a diameter of 2 to 100 mm
It becomes a so-called dumpling-like mass (clinker). It should be noted that the rise time of the rotation speed is not so strict, and may be any time when the reaction product is in a semi-molten state.

The high-temperature lump product is put into a cooler and forcibly cooled, and crushed into a fine-grained product. The resulting clot (the main component is calcium aluminate) is normally calcium aluminate composition of 12CaO · 7Al ₂ O ₃ containing 70 wt% or more, Al ₂ O ₃ as the remainder, MgO, SiO _2, etc. It contains.

A preferred reactor that can be used in the production method of the present invention is a rotary firing furnace lined with a high alumina refractory (SK40 or more) so as to withstand high temperatures during the reaction. Such a furnace is known and can be used as a rotary furnace for batch operation or a rotary furnace (rotary kiln) for continuous operation. By using a rotary baking furnace and rotating during the reaction, the uniformity of the heat generating portion and the uniformity of the calcium aluminate generation reaction are achieved.
In addition, by rotating at the time of heat release, the product can be formed into a dumpling-like lump that is easy to handle.

[0028]

EXAMPLES Hereinafter, the production method of the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. [Example 1] The firing furnace used in this example is a rotatable horizontal cylindrical combustion furnace (a rotary furnace for batch operation) disclosed in a patent application (Japanese Patent Application No. 8-34921) filed by the present applicant. Was used. However, in order to withstand high temperatures,
Lined with high alumina refractory (SK40).

310 kg of aluminum residual ash and 240 kg of limestone powder containing 20.2% by weight of metallic aluminum were weighed, mixed by stirring, and charged into a firing furnace. Here, 240 kg of limestone powder is equivalent to 134.4 kg in terms of CaO, which is 30.1% by weight based on aluminum residual ash.
Is the amount of The CaO / Al ₂ O ₃ (molar ratio), the amount of time is about 0.62 (where CaO is obtained by converting the limestone powder CaO (mol), Al ₂ O ₃ is Al ₂ in the aluminum residual ash the amount of O ₃ is (moles)). After charging into the firing furnace, the charge was heated with an oil burner while rotating the furnace (1 rpm) while forcing air into the furnace. 9 minutes after the burner ignition, oxidation of metallic aluminum started,
A violent exothermic reaction was observed. The exothermic reaction of metallic aluminum was terminated 17 minutes after the start of the oxidation reaction. At this point, an observation in the furnace revealed that the reaction product was in a semi-molten state having a high viscosity, and its surface temperature was as high as about 1600 ° C.
The furnace was air-cooled for 64 minutes at a rotation speed of 2.5 rpm.
It was taken out as a lumpy mass of about 100 mm, and the mass product was subsequently forcibly cooled by a cooler, and subsequently crushed into fine granules having a diameter of about 2 to 20 mm.

From the observation of the appearance and fracture surface of the obtained fine particles, it was clear that the product had undergone the process of sintering, semi-melting and solidification. Further, the fine particles were measured by X-ray diffraction (Cu-Kα ray).
The spectra shown in FIGS. 2 and 3 were obtained, and clear diffraction peaks were observed at the positions shown in Table 2 below.

[0031]

[Table 2]

The above diffraction peak is 12CaO · 7Al
_This peak was characteristic of ₂ O ₃ , and it was confirmed that calcium aluminate having the above composition was present as a main component in the product. As a result of quantitative analysis by X-ray diffraction, it was confirmed that about 70% by weight of calcium aluminate having the above composition was present in the product.

Next, in accordance with JIS R5201 (physical test method for cement), a setting test was performed using the obtained fine particles as a sample, and the curing speed was measured. At this time, W /
A cement paste was prepared with a C ratio of 0.4 (where W is the weight of water and C is the weight of the sample). The result is shown in FIG. In FIG. 1, the distance from the bottom is
This is the distance between the tip of the needle and the bottom plate of the Vicat needle device used in the above JIS test method, and the value increases as the cement paste hardens.

From FIG. 1, it can be seen that curing started 3 minutes after water injection into the sample, and was completed 50 minutes later. This means that the curing rate of the calcium aluminate produced in this example is extremely high, and it is suitable as a raw material for ultra-hard cement.

[0035]

According to the production method of the present invention, calcium aluminate having a remarkably high curing rate can be obtained from aluminum residual ash which has been conventionally treated as industrial waste. Therefore, the above-mentioned calcium aluminate can be used as a raw material of ultra-hard cement. Further, the above-mentioned calcium aluminate is suitably used as a slag-making agent in the field of steel because of its low melting point.

[0036]

[Brief description of the drawings]

FIG. 1 is a graph showing the curing rate of calcium aluminate produced in Example 1.

FIG. 2 is an X-ray diffraction spectrum of the calcium aluminate produced in Example 1.

FIG. 3 is an X-ray diffraction spectrum of the calcium aluminate produced in Example 1.

Claims (7)

[Claims] 1. An aluminum exothermic ash and a calcareous raw material are converted into: (a) a reaction system in an oxidizing atmosphere, and (b) an exothermic oxidation reaction of metallic aluminum contained in the aluminum residual ash. C) A method for producing calcium aluminate, wherein the reaction is carried out while maintaining the reaction system at a high temperature. 2. The method according to claim 1, wherein the calcareous material is limestone powder. 3. The method according to claim 3, wherein the calcium aluminate contains 12CaO.
· 7Al calcium proportion of aluminate composition ₂ O ₃ is 70 wt% or more, the production method according to claim 1 or 2. 4. The production method according to claim 1, wherein the reaction between the aluminum residual ash and the calcareous raw material is performed using a rotatable firing furnace. 5. A (1) rotatable firing furnace is charged with a mixture of aluminum residual ash and calcareous raw material. (2) The firing furnace is rotated under forced air supply, and the firing furnace is The exothermic oxidation reaction of the metallic aluminum contained in the aluminum residual ash starts, and heating is performed until the exothermic oxidation reaction stably continues. (3) The heat generated in the exothermic oxidation reaction causes While raising the temperature, the aluminum residual ash reacts with the calcareous raw material, and the inside of the reaction system which is in a semi-molten state by the rotation of the firing furnace is made uniform. (4) After the end of the exothermic oxidation reaction While rotating the firing furnace, the reaction product is cooled and solidified to form a reaction product into a lump, and (5) the lump is further pulverized to obtain fine-grained calcium aluminate. Made of calcium aluminate Method. 6. An ultra-hard cement containing calcium aluminate produced by the method according to claim 1. Description: 7. A slag-making agent for iron-making, comprising calcium aluminate produced by the method according to any one of claims 1 to 5.