KR20220072763A - Impurity removal method - Google Patents

Abstract

[Problem] An object of the present invention is to provide an impurity removal method capable of efficiently removing impurities that are mixed in aluminum or aluminum alloy and are difficult to remove from molten metal.
[Solution] An impurity removal method according to an aspect of the present invention comprises a step of mixing Mg or Mg alloy with aluminum or an aluminum alloy and a molten metal containing impurities, and a step of stirring the molten metal after the mixing step, , In the stirring step, an intermetallic compound is separated from the molten metal by applying a temperature gradient to the molten metal.

Description

Impurity removal method {IMPURITY REMOVAL METHOD}

The present invention relates to a method for removing impurities.

In recent years, from the social demand for carbon dioxide emission suppression, weight reduction of automobiles etc. is progressing all over the world, and it is predicted that the demand of aluminum will increase from now on. Therefore, in the future, it is expected that the emission of aluminum scrap will increase along with the increase in demand. In general, aluminum is considered to be a metal material excellent in recyclability. Many aluminum products made of aluminum wrought materials, including aluminum cans, are re-melted after being scrapped and recycled into new products. However, impurities adhere to aluminum products after disposal, and the concentration of the impurity element gradually increases by repeating recycling. Therefore, it is common that the aluminum product after retirement is cascade-recycled into the product with a looser component standard.

As a technique for suppressing mixing of impurities into aluminum, advancement of the classification technique after shredding is being pursued. However, since it is difficult to completely remove the deposit, a technique for removing impurities from aluminum or aluminum alloy molten metal is ultimately required.

There have been many reports on a technique for removing impurities from aluminum or aluminum alloy molten metal. As a technique for removing Fe, which is particularly difficult to remove, after daring to add Mn as an impurity to crystallize an Al-Fe-Mn-based intermetallic compound, A technique for removing the intermetallic compound by centrifugation, suction, or the like has been proposed (refer to Japanese Patent Laid-Open No. 8-35021 and Japanese Patent Laid-Open No. 7-70666).

Further, as a technique for reducing the impurity concentration in aluminum or aluminum alloy molten metal, a technique using a three-layer electrolytic refining method or a segregation method in the process of manufacturing aluminum metal is disclosed (Materia, Vol. 33 (1994), see No. 1).

Japanese Patent Laid-Open No. 8-35021 Japanese Patent Laid-Open No. 7-70666

Kondo et al., Materia, 1994, Vol. 33, No. 1, 62-68

However, in the technique disclosed in Patent Document 1 and Patent Document 2, there is a fear that the added Mn as an impurity increases. In addition, although the technique disclosed in Non-Patent Document 1 can in principle remove Fe, as a method for refining scrap containing a large amount of impurity elements, there is a fear that retention may become low. In addition, the three-layer electrolytic refining method has poor profitability in areas with high electric power cost, and the segregation method has a risk of lowering the yield as the impurity concentration of the raw material is higher. As such, the prior art is not sufficient as a method of recycling aluminum scrap containing a large amount of impurities recovered from the market.

Therefore, in order to realize horizontal recycling from aluminum wrought materials to wrought materials, a technique capable of efficiently removing impurities that adversely affect quality from aluminum or aluminum alloy molten metal to an allowable concentration or less is desired.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an impurity removal method capable of efficiently removing impurities that are mixed in aluminum or aluminum alloy and are difficult to remove from molten metal.

The present inventors mix Mg, which is an essential element in an aluminum alloy of JIS-A5000 series, etc., with molten aluminum or aluminum alloy containing impurities, promote eutecticization of impurities, and separate the produced intermetallic compound By doing so, it was discovered that impurities can be efficiently removed, and the present invention was completed.

An impurity removal method according to an aspect of the present invention includes a step of mixing Mg or Mg alloy with aluminum or an aluminum alloy and a molten metal containing impurities, and a step of stirring the molten metal after the mixing step, the stirring step In , by giving a temperature gradient to the molten metal, the intermetallic compound is separated from the molten metal.

In the said impurity removal method, the production|generation of the intermetallic compound containing the said impurity can be accelerated|stimulated by mixing Mg or a Mg alloy with the molten metal containing aluminum or an aluminum alloy and an impurity in the said mixing process. In particular, in the method for removing impurities, in the stirring step, a temperature gradient is applied to the molten metal, the impurities are sent to the low temperature side of the molten metal, and the intermetallic compound is crystallized from the low temperature side, and the impurities are efficiently removed from the molten metal can be removed well.

As content of Mg in the said molten metal after the said mixing process, 5 mass % or more is preferable. As described above, when the content of Mg in the molten metal after the mixing step is equal to or greater than the lower limit, eutecticization of the impurities can be promoted and the intermetallic compound can be easily and efficiently crystallized.

What is necessary is just that the said impurity contains Fe, and the said intermetallic compound contains aluminum and Fe. According to this impurity removal method, Fe, which is easily mixed and difficult to remove, can be efficiently removed from the Al-Mg-based molten metal.

What is necessary is just that the said impurity contains Si, and the said intermetallic compound contains Mg and Si. As described above, when the impurity contains Si and the intermetallic compound contains Mg and Si, Si can be efficiently removed from the Al-Mg-based molten metal.

In the stirring step, the molten metal may be partially cooled. In this way, in the stirring step, by partially cooling the molten metal, a low-temperature region can be easily formed in the molten metal, and the intermetallic compound can be easily crystallized in the low-temperature region.

In the stirring step, the cooling member may be brought into contact with the molten metal. In this way, in the stirring step, by bringing the cooling member into contact with the molten metal, it is possible to easily form the low-temperature region around the cooling member.

What is necessary is just to crystallize the said intermetallic compound on the surface of the said cooling member. The vicinity of the surface of the cooling member is easily maintained below the crystallization temperature of the intermetallic compound. Therefore, the surface of the cooling member is suitable for crystallizing the intermetallic compound. On the other hand, "crystallizing the intermetallic compound on the surface of the cooling member" means that the intermetallic compound is crystallized on at least a part of the surface of the cooling member, and a metal or compound other than the intermetallic compound is formed on the surface of the cooling member. This may be crystallized.

As a cooling temperature of the said molten metal, 640 degrees C or less is preferable. Thus, when the cooling temperature of the said molten metal is below the said upper limit, it is easy to crystallize the said intermetallic compound. On the other hand, "the cooling temperature of molten metal is 640 degrees C or less" means that the area|region of 640 degrees C or less exists in molten metal.

In the stirring step, the molten metal may be partially heated. In this way, in the stirring step, by partially heating the molten metal, it is easy to give a temperature gradient to the molten metal.

As described above, the impurity removal method according to one aspect of the present invention can efficiently remove impurities that are mixed in aluminum or aluminum alloy and are difficult to remove from the molten metal.

1 is a flowchart illustrating an impurity removal method according to an embodiment of the present invention.
FIG. 2 is a schematic diagram for explaining the stirring step of the impurity removal method of FIG. 1 .
Fig. 3 is a schematic diagram showing an apparatus for carrying out the impurity removal method of an Example.
[FIG. 4] FIG. 4 is a No. 3 is a cross-sectional image of the solid part.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is permanently described, referring drawings.

[Method of removing impurities]

In the impurity removal method of FIG. 1 , impurities mixed in aluminum or aluminum alloy and difficult to remove are removed from the molten metal using Mg (magnesium), which is an essential element of the 5000 series. The said impurity removal method removes impurities, such as a metal element, which are difficult to remove in the process of recycling aluminum from an Al-Mg type|system|group molten metal. The impurity removal method promotes eutecticization of impurities by containing Mg, which is an essential element in a JIS-A5000 series aluminum alloy or the like, in a relatively high concentration in the molten metal, and removes impurities by separating the generated intermetallic compound.

As shown in Fig. 1, the impurity removal method includes a step of mixing Mg or Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities (mixing step S1), and a step of stirring the molten metal after the mixing step S1 ( Stirring step S2) is provided. The said impurity removal method isolate|separates an intermetallic compound from the said molten metal by giving a temperature gradient to the said molten metal in the stirring step S2.

〔impurities〕

As said impurity, (1) Fe (iron), (2) Si (silicon), (3) Mn (manganese), Co (cobalt), Ti (titanium), V (vanadium), Zr (zirconium), Cr (chromium) or a combination thereof. As said impurity, you may contain the 1 type, or 2 or more types of arbitrary elements contained in said (1)-(3). When Fe is included as the impurity, the intermetallic compound separated in the stirring step S2 contains aluminum and Fe. When Si is included as the impurity, the intermetallic compound separated in the stirring step S2 contains Mg and Si. When Mn, Co, Ti, V, Zr, Cr, or a combination thereof is included as the impurity, the intermetallic compound separated in the stirring step S2 is aluminum and Mn, Co, Ti, V, Zr, Cr, or a combination thereof. contains a combination.

[Fe]

Fe is the most likely to be incorporated as an impurity element in the molten metal containing aluminum or an aluminum alloy, and is an element that is difficult to remove. Fe is easily incorporated from fastening parts, shredders, and the like. On the other hand, since aluminum is an element which is easy to be oxidized and oxidation refining similar to the converter in the steel industry cannot be carried out, removal of Fe is difficult. The said impurity removal method can remove Fe efficiently from the molten metal (Al-Mg type molten metal) containing aluminum and Mg. Since the said impurity removal method can reduce Fe below the prescribed concentration of A5000 series (Al-Mg series alloy) prescribed|regulated by JIS, it can implement|achieve horizontal recycling from aluminum wrought material to wrought material easily.

[Si]

Si is an impurity in the molten metal containing aluminum or an aluminum alloy, and is easily mixed after Fe and is an element difficult to remove. Si originates in the inside of a casting/die-cast product, or the scrap of the silica sand which has SiO2 as _a main component, and mixes. According to the impurity removal method, when Si is included as the impurity, an intermetallic compound containing Si and Mg can be easily generated by the stirring step S2, and Si can be efficiently removed from the Al-Mg-based molten metal. can

[Mn, Co, Ti, V, Zr, Cr, or a combination thereof]

Mn, Ti, V, Zr, and Cr are incorporated as an additive element of an aluminum alloy, or an element included in grain refinement, gold, and the like. In addition, Co is an element included in a battery, and may be mixed from scrap. According to the impurity removal method, when Mn, Co, Ti, V, Zr, Cr, or a combination thereof is contained as the impurity, aluminum and Mn, Co, Ti, V, Zr, Cr in the stirring step S2 or intermetallic compounds containing combinations thereof. Accordingly, impurities including Mn, Co, Ti, V, Zr, Cr, or a combination thereof can be efficiently removed from the Al-Mg-based molten metal.

(mixing process)

In mixing process S1, Mg or Mg alloy is added to the molten metal containing aluminum or an aluminum alloy, and an impurity, for example. In more detail, in mixing process S1, Mg or Mg alloy is added to the molten metal which melt|dissolved aluminum scrap.

In the mixing step S1, Mg, which is an essential element, is mixed with aluminum or an aluminum alloy and the molten metal containing the above impurities in an aluminum alloy of JIS-A5000 or the like. When the molten metal containing aluminum or an aluminum alloy contains Mg at a relatively high concentration, the formation of the intermetallic compound containing the impurities in the Al-Mg-based molten metal is promoted. According to the said impurity removal method, in order to generate|occur|produce an intermetallic compound, as is conventionally performed, it is not necessary to mix unnecessary impurities daringly. That is, in the mixing step S1, it is not necessary to mix Mg or a component other than the Mg alloy into the molten metal. In addition, since Mg is not an impurity, the process for removing Mg is not required in the said impurity removal method. Therefore, the molten metal after the impurities have been removed in the impurity removal method can be diluted and used for aluminum recycling. In addition, the dilution procedure (dilution process) of the molten metal after the said impurity is removed is mentioned later. As an Mg alloy mixed in mixing process S1, JIS-MC5, JIS-MDC2A, etc. are mentioned, for example.

As an effect of mixing Mg or an Mg alloy in mixing process S1, the following (a)-(c) is mentioned, for example.

(a) Since the liquidus temperature is lowered, the liquidus state can be maintained at a low temperature, and thus the produced compound can be efficiently separated.

(b) Mg increases the activity of the impurity element, thereby accelerating the production of the compound.

(c) Mg directly reacts with an impurity element to form an intermetallic compound.

For example, when Fe is included as the impurity, it is assumed that the removal of Fe is promoted by the effects of (a) and (b). In addition, when Si is included as the said impurity, it is estimated that removal of Si is accelerated|stimulated by the effect of said (a) and (c). For impurities other than Fe and Si, the formation of intermetallic compounds is promoted by the effect of any one of the above (a) to (c) or the combination of the effects of (a) to (c), and the molten metal is efficiently removed from the molten metal. can be removed with

As a lower limit of content of Mg in the said molten metal after mixing process S1, 5 mass % is preferable, 8 mass % is more preferable, 10 mass % is still more preferable. When the content of Mg is less than the lower limit, there is a possibility that the liquidus temperature cannot be sufficiently lowered. In addition, when the content of Mg is less than the lower limit, there is a fear that the intermetallic compound cannot be sufficiently formed when Si is included as the impurity. On the other hand, the upper limit of the content of Mg in the molten metal after the mixing step S1 is not particularly limited, but for example, preferably 50 mass %, more preferably 40 mass %, still more preferably 30 mass %, 25 % by mass is particularly preferred. When content of Mg exceeds the said upper limit, the dilution amount in the dilution process mentioned later increases, and there exists a possibility that the cost required for recycling of aluminum may increase.

(stirring process)

In the stirring step S2, the intermetallic compound is crystallized in the region on the low temperature side of the molten metal by providing a temperature gradient in the molten metal while stirring the molten metal. That is, as shown in FIG. 2, in the stirring process S2, the high temperature area|region H and the low temperature area|region L whose temperature is lower than the high temperature area|region H are formed in the molten metal X. In the low-temperature region L, a liquid phase L1 and a solid-liquid coexistence phase L2 are formed. In the solid-liquid coexistence phase (L2), the intermetallic compound (I) is partially crystallized.

In the stirring step S2, by stirring the molten metal X while applying a temperature gradient to the molten metal X, the impurities mixed in aluminum or aluminum alloy can be efficiently removed. More specifically, in the stirring step S2, the impurity contained in the high temperature region H is mechanically sent to the low temperature region L side by stirring the molten metal X, and the impurity is contained in the low temperature region L. Intermetallic compound (I) can be crystallized. The intermetallic compound (I) crystallized in the low-temperature region L combines with other compounds, for example, to form a solid phase S, and is removed from the molten metal X. As a result, the concentration of the impurity in the molten metal X can be reduced.

In the stirring step S2, it is preferable to partially cool the molten metal X as a means for imparting a temperature gradient to the molten metal X. According to this method, the low-temperature region L can be easily formed in the molten metal X, and the intermetallic compound (I) can be easily crystallized by mechanically sending the impurities to the low-temperature region L. have.

It does not specifically limit as means for cooling the molten metal X partially, For example, the method of making the molten metal X contact a cooling member is mentioned. According to this method, the low-temperature region L can be easily formed around the cooling member. As said cooling member, a cooling plate, a cooling tube, a cooling rod, etc. are mentioned, for example. The said cooling member may be inserted in the molten metal X, for example, and may be provided in the furnace wall or furnace bottom in which the molten metal X is accommodated.

When the cooling member is brought into contact with the molten metal (X), it is preferable to crystallize the intermetallic compound (I) on the surface of the cooling member. The vicinity of the surface of the cooling member is easily maintained below the crystallization temperature of the intermetallic compound (I). Therefore, the surface of the cooling member is suitable for crystallizing the intermetallic compound (I). Further, by crystallizing the intermetallic compound (I) on the surface of the cooling member, the intermetallic compound (I) is fixed to the cooling member, and the intermetallic compound (I) can be easily removed from the molten metal (X) .

In addition, in stirring process S2, you may heat the molten metal X partially as a means of giving a temperature gradient to the molten metal X. Also by this method, it is easy to give a temperature gradient to the molten metal X. As a means to partially heat the molten metal X, heating by a burner etc. are mentioned, for example. In addition, in stirring process S2, in parallel with cooling molten metal X partially, you may heat this molten metal X partially. As such a method, while heating the central part of the molten metal X, the method of cooling the peripheral part of the molten metal X is mentioned, for example.

As an upper limit of the cooling temperature of the molten metal X in stirring process S2, 640 degreeC is preferable, 610 degreeC is more preferable, and 550 degreeC is still more preferable. In other words, a low-temperature region L of 640° C. or lower is preferably formed in the molten metal X, more preferably a low-temperature region L of 610° C. or lower is formed, and a low-temperature region L of 550° C. or lower. ) is more preferably formed. When the cooling temperature of molten metal (X) exceeds the said upper limit, there exists a possibility that it may become difficult to crystallize intermetallic compound (I).

As the maximum temperature of the high temperature region H of the molten metal X, it is higher than the crystallization temperature of the intermetallic compound (I) and higher than the cooling temperature (that is, the temperature gradient can be given to the molten metal X) a) It is not particularly limited. As a lower limit of the said highest temperature, it can be set as 630 degreeC, for example, and 700 degreeC may be sufficient.

The stirring means of the molten metal X in the stirring step S2 is not particularly limited as long as it can be stirred while applying a temperature gradient to the molten metal X. As said stirring means, mechanical stirring by a rod or stirring blade, electromagnetic stirring by a stirrer, gas bubbling, etc. are mentioned, for example.

(dilution process)

Molten metal X after removing impurities by stirring step S2 can be diluted and used for aluminum recycling. The recycling method of aluminum which added the dilution process to mixing process S1 and stirring process S2 mentioned above is one Embodiment of this invention. In the dilution step, the molten metal X from which the impurities have been removed by the stirring step S2 is mixed with industrial pure aluminum or aluminum scrap having a low Mg concentration (for example, 1000 series), and the A5000 series (Al -Mg-based alloy) is diluted to the Mg standard concentration.

In the dilution step, the Mg concentration of the molten metal (X) containing a high concentration of Mg is diluted below the standard concentration according to JIS-A5000. Since Mg is not an impurity, it is not required to remove it from the molten metal X. In the aluminum recycling method, the diluted molten metal (X) can be used for aluminum products by lowering the concentration of Mg in the dilution step. Further, in the dilution step, it is possible to evaporate Mg having a high vapor pressure by maintaining the molten metal X containing a high concentration of Mg under vacuum to lower the concentration of Mg in the molten metal X. Moreover, in the said dilution process, it is also possible to remove Mg by the method of blowing chlorine into the molten metal X, or using a flux.

On the other hand, the molten metal X containing a high concentration of Mg after the stirring step S2 can also be used as an Mg intermediate alloy by separating and recovering it by suction or the like, or by hardening it in a mold or the like.

<Advantage>

The said impurity removal method can accelerate|stimulate the production|generation of the intermetallic compound containing the said impurity by mixing Mg or Mg alloy with the molten metal containing aluminum or an aluminum alloy and an impurity in the mixing process S1. In particular, in the method for removing impurities, in the stirring step S2, a temperature gradient is applied to the molten metal, the impurities are sent to the low temperature side of the molten metal, the intermetallic compound is crystallized at the low temperature side, and the impurities are efficiently removed from the molten metal can be removed well.

In this impurity removal method, Mg, which is an essential element in an aluminum alloy of JIS-A5000 series, etc., is contained in the molten metal to promote compounding of the impurities, and the generated intermetallic compound is separated to remove the impurity. . In this impurity removal method, it is not necessary to mix unnecessary impurities in order to generate an intermetallic compound as was conventionally performed, and retention can also be improved.

According to the said impurity removal method, since the metal element which is considered to be difficult to remove in the recycling process of aluminum can be efficiently reduced below the allowable concentration of a wrought material, horizontal recycling from an aluminum wrought material to an aluminum wrought material can be implement|achieved.

[Other embodiments]

The said embodiment does not limit the structure of this invention. Accordingly, in the above embodiments, it is natural to be construed as being able to omit, substitute, or add components of each part of the above embodiments based on the description and technical common sense of the present specification, and all of them fall within the scope of the present invention.

Example

Hereinafter, the present invention will be described in detail based on Examples, but the present invention should not be construed as being limited based on the description of these Examples.

[Example]

[No. 1 to No. 4]

Alloy A having the composition of Table 1 was prepared in an Ar (argon) atmosphere in a CCIM furnace (cold crucible induction melting apparatus) 10 in FIG. 3 having a water-cooled copper crucible 11 with cooling members disposed on the furnace wall and furnace bottom was dissolved to obtain a molten metal containing Fe and Si as impurities. This molten metal was heated by electromagnetic induction and stirred by electromagnetic repulsion. Table 1 shows the holding temperature on the high temperature side of the molten metal during this stirring. By this stirring, the solid phase containing an intermetallic compound is formed in the contact part with the water-cooled copper crucible 11 on the low-temperature side. After that, the furnace was turned off to solidify the molten metal. No. The cross-sectional image of the solid-phase part in 3 is shown in FIG. A part was taken from the central part of the solidified ingot, and the concentration of Fe was measured by ICP emission spectroscopy. Table 1 shows the results of this measurement.

[Comparative example]

[No. 5]

The molten alloy having the composition of Table 1 was maintained at the temperature of Table 1. No. In 5, partial cooling or heating of the molten metal was not performed, and the molten metal was not stirred. Next, the crucible containing the molten metal was taken out of the furnace, left to cool, and after solidifying the molten metal, the lower part of the ingot was cut. The concentration of Fe in the upper cut surface was measured by ICP emission spectroscopy. Table 1 shows the results of this measurement.

As shown in Table 1, No. 1 to No. No. 4 sufficiently removes Fe, which is an impurity, even if the holding temperature on the high temperature side is relatively high. In addition, as shown in FIG. 4, No. In 3, the intermetallic compound containing aluminum and Fe, and the intermetallic compound containing Mg and Si are produced|generated in a solid-phase part, and in addition to Fe, it has fully removed also about Si. In contrast, No. 5 does not sufficiently remove Fe, which is an impurity.

As described above, the method for removing impurities according to an aspect of the present invention can efficiently reduce metal elements, etc., which are difficult to remove in the recycling process of aluminum to below the allowable concentration of the wrought material. It is suitable for realization of recycling.

with 10 CCIM
11 water cooling copper crucible
A alloy
H hot zone
I Intermetallics
L low temperature zone
L1 liquid
L2 solid-liquid coexistence phase
S solid
X Molten

Claims (9)

A step of mixing Mg or Mg alloy with molten metal containing aluminum or aluminum alloy and impurities;
A step of stirring the molten metal after the mixing step
to provide
An impurity removal method for separating an intermetallic compound from the molten metal by applying a temperature gradient to the molten metal in the stirring step. The method of claim 1,
The impurity removal method in which content of Mg in the said molten metal after the said mixing process is 5 mass % or more. 3. The method of claim 1 or 2,
The impurities include Fe,
A method for removing impurities wherein the intermetallic compound contains aluminum and Fe. 4. The method according to any one of claims 1 to 3,
The impurity contains Si,
A method for removing impurities wherein the intermetallic compound contains Mg and Si. 5. The method according to any one of claims 1 to 4,
In the stirring step, an impurity removal method for partially cooling the molten metal. 6. The method of claim 5,
In the stirring step, a method for removing impurities in which a cooling member is brought into contact with the molten metal. 7. The method of claim 6,
An impurity removal method for crystallizing the intermetallic compound on the surface of the cooling member. 8. The method according to any one of claims 5 to 7,
A method for removing impurities wherein the cooling temperature of the molten metal is 640° C. or less. 9. The method according to any one of claims 1 to 8,
In the stirring step, an impurity removal method of partially heating the molten metal.

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