JP2023102012A - Purification method of metal, and purification apparatus of metal - Google Patents

Abstract

To provide a purification method of a metal capable of improving safety and reducing a purification cost while heightening a purification degree.SOLUTION: A purification method of a metal includes: a process of producing a molding having a solid phase rate of 0.2 or more and 0.7 or less by cooling a molten metal including a purifying-objective metal, and an element other than the purifying-objective metal housed in a purification container made of stainless steel while rotating by a rotating magnetic field; and a process of separating the molding into a purified ingot containing the purifying-objective metal and a concentrated molten metal by pressurizing the molding in the purification container.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a metal refining method and a metal refining apparatus for refining a predetermined metal from molten metal.

When discarding industrial equipment, transportation equipment, electronic equipment, etc., scrap metal is generated. This metal scrap contains a mixture of multiple types of metals, but recycling can be achieved by refining the highly useful metals.

For the refining of such metal scrap, a method has been proposed in which the molten metal contained in a refining vessel is cooled to a temperature just above the freezing point of α-Al, and then a pressing plate having a plurality of holes is lowered from the upper part of the refining vessel to apply pressure to separate α-Al from impurities (see Patent Documents 1 and 2).

JP-A-7-054065 JP 2012-201917 A

FIG. 1 is a state diagram showing an example of eutectic solidification. If the alloy undergoing eutectic solidification has a hypoeutectic composition (that is, a composition with a lower solute element concentration than the eutectic composition), the element with the higher concentration will crystallize first as the primary crystal. Therefore, by taking out only the primary crystal, the metal with high purity can be recycled.

For example, in an Al—Si alloy, when the molten alloy with the _C0 composition in FIG. 1 is cooled to T ₁ ° C., which is a solid-liquid coexistence state, it separates _into a solid with a concentration of C _s and a liquid with a concentration of _{C l .} Al can be refined by extracting a solid having a concentration _Cs with a low impurity concentration from this molten alloy.

On the other hand, when the concentration of impurities such as Si is high, _{for example ,} in _the molten alloy having the _C1 composition in FIG.

In the method of Patent Literature 1 described above, the amount of purified metal separated can be increased by using electromagnetic stirring even when the concentration of impurities is high. However, in this method, since a refractory refining vessel is used during agitation, the refining vessel is likely to be consumed during separation by compression, which poses problems in terms of safety and cost.

Further, in the method of Patent Document 2 described above, since a graphite refining container is used, electromagnetic stirring cannot be performed. In addition, as in the method of Patent Document 1, the purification container is likely to be consumed during separation by compression.

An object of one aspect of the present disclosure is to provide a metal refining method capable of improving safety and reducing refining costs while increasing refining purity.

One aspect of the present disclosure is a metal refining method comprising: a step of cooling a molten metal containing a metal to be refined and an element other than the metal to be refined contained in a stainless steel refining container while being rotated by a rotating magnetic field to produce a compact having a solid phase ratio of 0.2 to 0.7;

Another aspect of the present disclosure includes a stainless steel refining vessel, and a molten metal containing a metal to be refined and an element other than the metal to be refined contained in the refining vessel, which is rotated and cooled by a rotating magnetic field, thereby producing a compact having a solid fraction of 0.2 to 0.7. It is a refining device for metals.

According to such a configuration, the refining purity of the metal can be enhanced by electromagnetic stirring using a rotating magnetic field. In addition, since the molded body is manufactured and separated by pressure in a stainless steel refining vessel, safety can be improved and refining costs can be reduced.

FIG. 1 is a state diagram showing an example of eutectic solidification. FIG. 2 is a schematic diagram of a metal refining device according to the embodiment. FIG. 3A is a schematic diagram showing how the molten metal is stored in the refining vessel, FIG. 3B is a schematic diagram showing a process for producing a compact by electromagnetic stirring, and FIGS. 3C and 3D are schematic diagrams showing a process for separating the compact by pressing. FIG. 4 is a flow diagram of a metal refining method according to an embodiment. 5A is the solidified structure of the refined ingot in Example 1, and FIG. 5B is the solidified structure of the concentrated molten metal in Example 1. FIG.

Embodiments to which the present disclosure is applied will be described below with reference to the drawings.
[1. First Embodiment]
[1-1. composition]
A metal refining apparatus 1 shown in FIG. 2 is used for refining a target metal from a molten metal containing a plurality of types of elements. The refining device 1 includes a refining container 2 , a molding section 3 and a separation section 4 .

<Molten metal>
As the molten metal to be refined in the refining device 1, for example, a melted metal scrap is used.

The molten metal contains metals to be refined and elements other than the metals to be refined (hereinafter also referred to as "impurities"). Molten metal is obtained by heating the metal of the refining material above its melting temperature.

Examples of metals to be refined contained in the molten metal include aluminum (Al), iron (Fe), copper (Cu), magnesium (Mg), tin (Sn), and lead (Pb). Among these, Al is preferable because of its high economic efficiency in recycling. Also, the mass concentration of Al in the molten metal is preferably higher than the mass concentrations of other metal elements contained in the molten metal.

Impurities contained in the molten metal include, for example, manganese (Mn), chromium (Cr), zinc (Zn), titanium (Ti), silicon (Si), etc., in addition to the metals mentioned above as metals to be refined.

The lower limit of the impurity concentration relative to the entire molten metal is preferably 1.0% by mass, more preferably 1.5% by mass, and even more preferably 3.0% by mass or more. The upper limit of the impurity concentration in the entire molten metal is preferably 15.0% by mass, more preferably 11.0% by mass. According to the refining apparatus 1, high-purity refining of the metal to be refined is possible for the molten metal with the concentration of impurities in such a range.

The melt may contain a combination of the metal to be refined and impurities that undergo eutectic solidification. The refiner 1 can effectively refine such a combination of molten metals. Moreover, the molten metal may contain one or more kinds of noble metals or rare metals in addition to the elements described above.

When the metal to be refined is Al, the impurity preferably contains Si (that is, silicon). A combination of Al and Si is widely used as a casting alloy, and a large amount of metal scrap is generated. The refining apparatus 1 can refine Al with high purity from the molten metal containing such a combination of elements.

In the molten metal containing the most Al as the metal element, the lower limit of the concentration of Si in the entire molten metal is preferably 1.0% by mass, more preferably 3.0% by mass. The upper limit of the concentration of Si in the entire molten metal is preferably 11.0% by mass. By setting the concentration of Si in such a range, the efficiency of refining Al in scrap metal containing an aluminum alloy can be increased. In addition, by setting the upper limit of the Si concentration to 11.0% by mass, a difference is provided between the crystallization temperature of α-Al and the crystallization temperature of the eutectic phase between Al and Si, so that Al can be easily purified.

Furthermore, the molten metal may contain at least one of Fe, Cu, Mn, Mg, Cr, Zn and Ti. Also, the lower limit of the total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn and Ti in the molten metal is preferably 0.5% by mass. The upper limit of the total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn and Ti in the molten metal is preferably 6.0 mass %, more preferably 4.0 mass %.

By setting the sum of the mass concentrations of Fe, Cu, Mn, Mg, Cr, Zn, and Ti within such a range, the efficiency of refining Al in metal scrap in which a casting aluminum alloy and a wrought aluminum alloy are mixed can be increased.

<Purification container>
The refining container 2 is a heat-resistant crucible capable of holding molten metal. Specifically, the refining container 2 is a bottomed cylindrical body made of non-magnetic stainless steel. As the material of the refining container 2, for example, SUS304 defined in JIS-G-4303:2015 can be used.

The refining vessel 2 allows external magnetism to pass through the inside so that the molding section 3 can electromagnetically stir the molten metal. Further, the refining container 2 has a strength that does not break when pressure is applied from the separation unit 4 .

As shown in FIG. 3A, the molten metal M1 is accommodated inside the refining container 2 . Also, the temperature of the molten metal M1 is measured by a thermometer 2A.

<Molding part>
The forming unit 3 is configured to cool the molten metal containing the metal to be refined and elements other than the metal to be refined contained in the refining vessel 2 while being rotated by a rotating magnetic field, thereby producing a compact having a solid fraction within a certain range.

The molding section 3 has a rotating magnetic field imparting device 31 as shown in FIG. 3B. The rotating magnetic field imparting device 31 generates a rotating magnetic field around the refining vessel 2 whose polarity changes so that the pairs of S and N poles rotate about the central axis. The molten metal to which the rotating magnetic field is applied rotates within the refining vessel 2 . As the rotating magnetic field imparting device 31, for example, a known device having three stator coils can be used.

The central axis of the rotating magnetic field generated by the rotating magnetic field imparting device 31 passes through the inside of the purification container 2 . Also, the central axis of the rotating magnetic field is parallel to the vertical direction. It is preferable that the central axis of the rotating magnetic field coincides with the central axis of the purification container 2 .

The lower limit of the frequency of the rotating magnetic field is preferably 1 Hz, more preferably 5 Hz. The upper limit of the frequency of the rotating magnetic field is preferably 100 Hz. By setting the frequency within this range, the form of primary crystals generated by cooling the molten metal can be efficiently controlled.

The maximum value of the magnetic flux density on the surface (that is, the outermost surface) along the circumferential direction of the rotating magnetic field of the molten metal is preferably 20 mT or more and 120 mT or less. By setting the magnetic flux density within this range, it is possible to sufficiently stir the molten metal while suppressing power consumption. The magnetic flux density can be measured not only by direct measurement but also by electromagnetic field analysis or the like.

The rotation speed of the rotating magnetic field on the surface along the circumferential direction of the rotating magnetic field of the molten metal is preferably 0.5 m/s or more and 10 m/s or less. By setting the rotation speed within this range, the amount of primary crystals generated by cooling the molten metal can be efficiently increased.

When the molten metal is cooled without stirring, the metal to be refined has a dendritic structure. On the other hand, by cooling the molten metal while electromagnetically stirring it with a rotating magnetic field, the variation in temperature of the molten metal in the refining vessel 2 is reduced, and the primary crystals become fine and nearly spherical. Therefore, the pressure loss in the separation process is reduced as compared with the case of dendrites. As a result, the metal to be refined and the concentrated molten metal (that is, the concentrated liquid phase) can be efficiently separated.

The molding unit 3 continues stirring and cooling the molten metal until the molten metal becomes a compact M2 in a solid-liquid coexistence state with a solid fraction of 0.2 or more and 0.7 or less. The compact M2 contains a solid S crystallized by a temperature drop and a liquid L in a molten state. The cooling method is not particularly limited, and known methods such as air cooling, wind cooling, and cooling with a refrigerant can be used.

By setting the solid fraction of the compact M2 within the range described above, it is possible to increase the separation efficiency by reducing the pressure loss in the separation section 4 while increasing the refining efficiency (that is, the recovery rate of the target metal). The lower limit of the solid fraction of the compact M2 is preferably 0.4. The "solid phase ratio of the compact" means the mass ratio of the entire crystallized solid phase to the entire compact including the liquid phase and the solid phase.

In addition, the molding section 3 preferably manufactures a molded body in which the solid fraction of the metal to be refined (for example, Al) is 0.2 or more and 0.7 or less. As a result, it is possible to obtain the compact M2 having a high concentration of the metal to be refined that crystallizes as the primary crystal. The "solid ratio of the metal to be refined" means the mass ratio of the crystallized metal to be refined (that is, primary crystals) to the entire molded body including the liquid phase and the solid phase.

<Separation part>
The separation unit 4 is configured to apply pressure to the compact M2 produced by the molding unit 3 in the refining vessel 2, thereby separating the compact M2 into a purified ingot I1 containing the metal to be refined and a concentrated molten metal I2 having a high concentration of solute elements.

The separation unit 4 has a press 41 and a filter 42 as shown in FIG. 3C. The press machine 41 presses the filter 42 downward to press the filter 42 against the molded body M2 from above.

Filter 42 is a compaction plate with a plurality of holes. As shown in FIG. 3D, the filter 42 pressed against the molded body M2 from above pushes the refined ingot I1 downward and allows the thickened molten metal I2 to pass upward. As a result, the compact M2 is squeezed, and the thickened molten metal I2 is separated from the refined ingot I1 above the filter 42. As shown in FIG.

The purified ingot I1 is a solid phase containing a large amount of metal to be purified. The concentration of the metal to be refined in the refined ingot I1 is higher than the concentration of the metal to be refined in the concentrated molten metal I2. The concentrated molten metal I2 is a liquid phase containing many impurities. The thickened molten metal I2 becomes a thickened ingot by cooling.

The pressure applied by the separation unit 4 to the compact M2 is preferably 0.5 MPa or more and 30.0 MPa or less. Moreover, the temperature of the compact M2 when the pressure is applied is preferably 500° C. or higher and 700° C. or lower.

<Metal refining method>
FIG. 4 shows a flow of a metal refining method using the refining apparatus 1 . The metal refining method of the present embodiment includes a melting step S10, a compact manufacturing step S20, and a compression separation step S30. Each step is a batch process performed on one refining container 2 .

(melting process)
In this step, a refining material (for example, scrap metal containing an aluminum alloy) is put into a refining vessel 2 and heated to a melting temperature. A molten metal is obtained by melting the refined material.

(Molded body manufacturing process)
In this step, the molten metal contained in the refining vessel 2 is cooled while being rotated by a rotating magnetic field to produce a compact having a solid fraction of 0.2 or more and 0.7 or less.

(Compression separation process)
In this step, pressure is applied to the molded body in the refining vessel 2 to separate the molded body into a refined ingot containing the metal to be refined and a concentrated molten metal.

[1-2. effect]
According to the embodiment detailed above, the following effects are obtained.
(1a) The refining purity of the metal can be enhanced by electromagnetic stirring with a rotating magnetic field. In addition, since the molded product is produced and separated by pressure in the stainless steel purification container 2, safety can be improved and the purification cost can be reduced.

[2. Other embodiments]
Although the embodiments of the present disclosure have been described above, it is needless to say that the present disclosure is not limited to the above embodiments and can take various forms.

(2a) In the metal refining apparatus of the above-described embodiment, the configuration of the separation section is an example, and is not limited to the configuration described above.

(2b) The function of one component in the above embodiment may be distributed as multiple components, or the functions of multiple components may be integrated into one component. Also, part of the configuration of the above embodiment may be omitted. Also, at least a part of the configuration of the above embodiment may be added, replaced, etc. with respect to the configuration of the other above embodiment. It should be noted that all aspects included in the technical idea specified by the wording in the claims are embodiments of the present disclosure.

[3. Example]
The following describes the details of the test conducted to confirm the effects of the present disclosure and the evaluation thereof.

<Example 1-3>
100 g of an Al-4% Si alloy having the composition shown in Table 1 was put into a refining container as a refining material. This alloy is intended for scrap metal, which is a mixture of casting and wrought aluminum alloys. In addition, the numerical value in Table 1 is the mass % with respect to the whole molten metal.

Next, the refining container was heated to 680° C. to melt the refining material to obtain a molten metal. This molten metal was air-cooled, and when the temperature of the molten metal reached 630° C., a rotating magnetic field was applied to stir the molten metal electromagnetically.

A coil of a three-phase AC motor was used as the rotating magnetic field imparting device. Table 2 shows the frequency of the rotating magnetic field, the maximum value of the magnetic flux density on the surface of the rotating magnetic field of the molten metal along the circumferential direction, and the rotational speed of the rotating magnetic field on the surface of the rotating magnetic field of the molten metal along the circumferential direction. The rotating magnetic field was continuously applied until the temperature of the molten metal reached 610°C.

After stopping the application of the rotating magnetic field (that is, after the end of the electromagnetic stirring), the purification vessel was placed in a press fitted with a filter (ie, compaction plate). After that, when the compression temperature shown in Table 2 was reached, the solid fraction of the compact was measured. In addition, the molded body in the refining vessel was pressurized by the compression pressure shown in Table 2 to separate the refined ingot and the thickened molten metal.

5A shows the solidified structure of the purified ingot obtained in Example 1. FIG. 5B shows the solidified structure of the concentrated molten metal obtained in Example 1. As shown in FIG. In the solidified structure of the purified ingot, white α-Al occupied most of the structure, and the α-Al was purified. On the other hand, the gray Al—Si eutectic structure occupies most of the solidified structure of the concentrated molten metal. From this result, it was confirmed that α-Al was purified by the purification method of the present disclosure.

<Comparative Example 1-3>
100 g of the same Al-4% alloy as in Example 1-3 was melted in a refining vessel to obtain a molten metal. This molten metal was air-cooled, and a purification vessel was placed in a press equipped with a filter.

After that, when the compression temperature shown in Table 2 was reached, the solid fraction of the compact was measured. In addition, the molded body in the refining vessel was pressurized by the compression pressure shown in Table 2 to separate the refined ingot and the thickened molten metal.

<Evaluation>
Table 2 shows the Si concentration in the purified ingots obtained in Example 1-3 and Comparative Example 1-3 and the recovery rate of the purified ingots. The Si concentration is the mass ratio of Si in the entire purified ingot. The recovery rate is the mass percentage of refined ingot in the total molten metal (ie refined material).

From Table 2, Example 1-3 has a lower Si concentration than Comparative Example 1-3. In other words, in Example 1-3, α-Al with a Si concentration of 3.0% by mass or less was purified by efficiently separating the concentrated liquid phase.

DESCRIPTION OF SYMBOLS 1... Purification apparatus, 2... Purification container, 2A... Thermometer, 3... Molding part, 4... Separation part,
31... Rotating magnetic field imparting device, 41... Press machine, 42... Filter.

Claims (14)

A step of cooling a molten metal containing a metal to be refined and an element other than the metal to be refined contained in a stainless steel refining container while being rotated by a rotating magnetic field to produce a compact having a solid fraction of 0.2 or more and 0.7 or less;
a step of separating the molded body into a purified ingot containing the metal to be refined and a concentrated molten metal by applying pressure to the molded body in the refining vessel;
A method for refining a metal, comprising: A method for refining a metal according to claim 1,
The metal refining method, wherein in the manufacturing step, the compact is manufactured in which the solid fraction of the metal to be refined is 0.2 or more and 0.7 or less. The metal refining method according to claim 1 or 2,
The metal refining method, wherein the rotating magnetic field has a frequency of 1 Hz or more. A metal refining method according to any one of claims 1 to 3,
The metal refining method, wherein the maximum value of the magnetic flux density on the surface of the molten metal along the circumferential direction of the rotating magnetic field is 20 mT or more. A metal refining method according to any one of claims 1 to 4,
The molten metal contains aluminum (Al),
A metal refining method, wherein the mass concentration of Al in the molten metal is higher than the mass concentration of other metal elements contained in the molten metal. A method for refining a metal according to claim 5,
The molten metal contains silicon (Si),
The metal refining method, wherein the mass concentration of Si in the molten metal is 1.0% by mass or more and 11.0% by mass or less. A method for refining a metal according to any one of claims 1 to 6,
the molten metal contains at least one of iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), and titanium (Ti);
A metal refining method, wherein the total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn and Ti in the molten metal is 0.5% by mass or more and 6.0% by mass or less. a stainless steel refining vessel;
a forming unit configured to produce a compact having a solid phase ratio of 0.2 or more and 0.7 or less by cooling the molten metal containing the metal to be refined and elements other than the metal to be refined contained in the refining vessel while being rotated by a rotating magnetic field;
a separation unit configured to separate the molded body into a purified ingot containing the metal to be refined and a concentrated molten metal by applying pressure to the molded body in the refining vessel;
A metal refiner comprising: The metal refining apparatus according to claim 8,
The metal refining apparatus, wherein the molding unit manufactures the molded product having a solid fraction of the metal to be refined of 0.2 or more and 0.7 or less. The metal refining apparatus according to claim 8 or 9,
A metal refiner, wherein the rotating magnetic field has a frequency of 1 Hz or higher. The metal refiner according to any one of claims 8 to 10,
A metal refining apparatus, wherein the maximum value of the magnetic flux density on the surface of the molten metal along the circumferential direction of the rotating magnetic field is 20 mT or more. The metal refiner according to any one of claims 8 to 11,
The molten metal contains aluminum (Al),
A metal refining apparatus, wherein the mass concentration of Al in the molten metal is higher than the mass concentration of other metal elements contained in the molten metal. A metal refining apparatus according to claim 12,
The molten metal contains silicon (Si),
The metal refining apparatus, wherein the mass concentration of Si in the molten metal is 1.0% by mass or more and 11.0% by mass or less. The metal refiner according to any one of claims 8 to 13,
the molten metal contains at least one of iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), and titanium (Ti);
A metal refining apparatus, wherein the total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn and Ti in the molten metal is 0.5% by mass or more and 6.0% by mass or less.

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