Metal refining method and metal refining apparatus

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

Technical Field

[0001] The present disclosure relates to a method for purifying a metal and a metal purification apparatus for purifying a predetermined metal from molten metal.

Background Art

[0002] When industrial equipment, transportation equipment, electronic equipment, etc. are discarded, metal scraps are generated. Although a plurality of types of metals are mixed in this metal scrap, recycling can be achieved by purifying a highly useful metal.

[0003] Regarding the purification of such metal scraps, after cooling the molten metal contained in a purification container to a temperature just above the freezing point of α-Al, a pressing plate having a plurality of holes is lowered from the upper part of this purification container to apply pressure, and a method of separating α-Al and impurities has been proposed (see Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] FIG. 1 is a state diagram showing an example of eutectic solidification. When the alloy in which eutectic solidification occurs has a hypoeutectic composition (that is, a composition with a lower solute element concentration than the eutectic composition), the element with a higher concentration crystallizes first as a primary crystal. Therefore, by taking out only the primary crystal, a highly pure metal can be recycled.

[0006] For example, in an Al—Si alloy, when the alloy molten metal having the composition C0 in FIG. 1 is cooled to T1° C. at which a solid-liquid coexistence state is achieved, a solid having a concentration C s and a concentration C lIt separates into liquid and solid, and the ratio of solid to liquid is W s :W l This results in a low concentration of impurities in this molten alloy, concentration C. s By extracting the solid, it becomes possible to purify Al.

[0007] On the other hand, if the concentration of impurities such as Si is high, for example, in the molten alloy with composition C1 shown in Figure 1, even when cooled to the temperature T2°C where the amount of solid crystallization is maximum, the amount of solid crystallization is W' s / (W' l +W' s ) and the amount of refined metal that can be separated decreases.

[0008] The method described in Patent Document 1 above can increase the amount of purified metal separated even when the impurity concentration is high by using electromagnetic stirring. However, since this method uses a refractory purification container during stirring, the purification container is easily consumed during separation by compression, which presents challenges in terms of safety and cost.

[0009] Furthermore, the method described in Patent Document 2 above uses a graphite refining container, making electromagnetic stirring impossible. Also, similar to the method in Patent Document 1, the refining container is easily consumed during separation by compression.

[0010] One aspect of this disclosure is to provide a method for refining metals that can improve safety and reduce refining costs while increasing the purity of the refined metal. [Means for solving the problem]

[0011] One aspect of the present disclosure is a method for purifying metal, comprising the steps of: producing a molded body with a solid fraction of 0.2 to 0.7 by cooling a molten metal containing a metal to be purified and elements other than the metal to be purified, which is contained in a stainless steel refining container, while rotating it with a rotating magnetic field; and separating the molded body into a purified ingot containing the metal to be purified and a concentrated molten metal by applying pressure to the molded body in the refining container.

[0012] Another aspect of the present disclosure is a metal refining apparatus comprising: a stainless steel refining container; a molding unit configured to produce a molded body with a solid fraction of 0.2 to 0.7 by rotating and cooling a molten metal containing the metal to be refined and elements other than the metal to be refined, contained in the refining container, using a rotating magnetic field; and 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 within the refining container.

[0013] With these configurations, the purity of the metal can be increased by electromagnetic stirring using a rotating magnetic field. Furthermore, since the molded product is manufactured and compressed within a stainless steel refining container, safety can be improved and refining costs can be reduced. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a phase diagram showing an example of eutectic solidification. [Figure 2] Figure 2 is a schematic diagram of a metal refining apparatus in an embodiment. [Figure 3] Figure 3A is a schematic diagram showing the state of molten metal storage in a refining container, Figure 3B is a schematic diagram showing the manufacturing process of a molded body by electromagnetic stirring, and Figures 3C and 3D are schematic diagrams showing the separation process of a molded body by compression. [Figure 4] Figure 4 is a flow chart of the metal refining method in an embodiment. [Figure 5] Figure 5A shows the solidification structure of the purified ingot in Example 1, and Figure 5B shows the solidification structure of the concentrated molten metal in Example 1. [Modes for carrying out the invention]

[0015] Embodiments to which this disclosure applies will be described below with reference to the drawings. [1. First Embodiment] [1-1. Structure] The metal refining apparatus 1 shown in Fig. 2 is used to refine a target metal from a molten metal containing a plurality of types of elements. The refining apparatus 1 includes a refining vessel 2, a forming section 3, and a separating section 4.

[0016] <molten metal> As the molten metal to be refined by the refining apparatus 1, for example, molten metal scrap is used.

[0017] The molten metal contains a target metal to be refined and elements other than the target metal to be refined (hereinafter also referred to as "impurities"). The molten metal is obtained by heating the metal of the refining material to a temperature equal to or higher than the melting temperature.

[0018] Examples of the target metal 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 with high recyclability economy is preferable. Also, it is preferable that the mass concentration of Al in the molten metal is greater than the mass concentration of other metal elements contained in the molten metal.

[0019] Examples of the impurities contained in the molten metal include, in addition to the metals described above as the target metal to be refined, manganese (Mn), chromium (Cr), zinc (Zn), titanium (Ti), silicon (Si), etc.

[0020] As the lower limit of the concentration of impurities with respect to the entire molten metal, 1.0 mass% is preferable, 1.5 mass% is more preferable, and 3.0 mass% or more is even more preferable. As the upper limit of the concentration of impurities with respect to the entire molten metal, 15.0 mass% is preferable, and 11.0 mass% is more preferable. According to the refining apparatus 1, high-purity refining of the target metal is possible for a molten metal having an impurity concentration within such a range.

[0021] The molten metal preferably contains a combination of a target metal to be refined that causes eutectic solidification and impurities. The refining apparatus 1 can effectively perform refining on such a molten metal combination. Also, the molten metal may contain one or more noble metals or rare metals in addition to the elements described above.

[0022] When the metal to be refined is Al, it is desirable for the impurities to include Si (i.e., silicon). The combination of Al and Si is widely used as a casting alloy, and a large amount is generated as metal scrap. Refining apparatus 1 can refine Al to high purity from molten metal containing such an elemental combination.

[0023] In a molten metal containing Al as the most abundant metallic element, the lower limit of the Si concentration relative to the entire molten metal is preferably 1.0 mass%, and more preferably 3.0 mass%. The upper limit of the Si concentration relative to the entire molten metal is preferably 11.0 mass%. By setting the Si concentration within this range, the efficiency of Al purification in metal scrap containing aluminum alloys can be increased. Furthermore, by setting the upper limit of the Si concentration to 11.0 mass%, a difference can be created between the crystallization temperature of α-Al and the crystallization temperature of the eutectic phase of Al and Si, making it easier to purify Al.

[0024] Furthermore, the molten metal may contain at least one of Fe, Cu, Mn, Mg, Cr, Zn, and Ti. 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% by mass, and more preferably 4.0% by mass.

[0025] By keeping the total mass concentrations of Fe, Cu, Mn, Mg, Cr, Zn, and Ti within this range, the efficiency of Al purification in metal scrap containing a mixture of casting aluminum alloy and wrought aluminum alloy can be increased.

[0026] <Purification container> The refining container 2 is a crucible with heat resistance capable of holding molten metal. Specifically, the refining container 2 is a bottomed cylindrical body made of non-magnetic stainless steel. For example, SUS304 as specified in JIS-G-4303:2015 can be used as the material for the refining container 2.

[0027] The purification container 2 allows external magnetic fields to pass through it so that the molten metal can be electromagnetically stirred by the molding unit 3. Furthermore, the purification container 2 has sufficient strength to withstand pressure from the separation unit 4 without being damaged.

[0028] As shown in Figure 3A, the molten metal M1 is contained inside the purification container 2. The temperature of the molten metal M1 is measured by a thermometer 2A.

[0029] <Forming part> The molding unit 3 is configured to produce a molded body with a solid phase ratio within a certain range by cooling molten metal containing the metal to be refined and elements other than the metal to be refined, which is contained in the refining container 2, while rotating it with a rotating magnetic field.

[0030] As shown in Figure 3B, the molding unit 3 has a rotating magnetic field generating device 31. The rotating magnetic field generating device 31 generates a rotating magnetic field around the refining container 2, in which the polarity changes so that pairs of S poles and N poles rotate around a central axis. The molten metal, subjected to the rotating magnetic field, rotates within the refining container 2. As the rotating magnetic field generating device 31, for example, a known device equipped with three stator coils can be used.

[0031] The central axis of the rotating magnetic field generated by the rotating magnetic field generating device 31 passes through the inside of the purification container 2. Furthermore, 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.

[0032] The lower limit of the rotating magnetic field frequency is preferably 1 Hz, and more preferably 5 Hz. The upper limit of the rotating magnetic field frequency is preferably 100 Hz. By setting the frequency within this range, the morphology of the primary crystal generated by the cooling of the molten metal can be efficiently controlled.

[0033] The maximum magnetic flux density at the surface (i.e., the outermost surface) along the circumferential direction of the rotating magnetic field of the molten metal is preferably between 20 mT and 120 mT. By keeping the magnetic flux density within this range, the molten metal can be sufficiently stirred while suppressing power consumption. The magnetic flux density can be measured directly or by electromagnetic field analysis.

[0034] The rotational speed of the rotating magnetic field on the surface along the circumferential direction of the molten metal is preferably between 0.5 m / s and 10 m / s. By setting the rotational speed within this range, the amount of primary crystals generated by the cooling of the molten metal can be efficiently increased.

[0035] When molten metal is cooled without stirring, the metal to be purified has a dendritic structure. In contrast, by cooling the molten metal while electromagnetically stirring it with a rotating magnetic field, the variation in the temperature of the molten metal in the purification container 2 is reduced, and the primary crystals become fine and nearly spherical in shape. Therefore, the pressure loss in the separation process is reduced compared to the case with a dendritic structure. As a result, the metal to be purified and the concentrated molten metal (i.e., the concentrated liquid phase) can be efficiently separated.

[0036] The molding unit 3 continues stirring and cooling the molten metal until it becomes a molded body M2 in a solid-liquid coexistence state with a solid fraction of 0.2 or more and 0.7 or less. The molded body M2 contains solid S crystallized by the decrease in temperature and molten liquid L. The cooling method is not particularly limited, and known methods such as air cooling, wind cooling, and cooling with a refrigerant can be used.

[0037] By setting the solid phase fraction of the molded body M2 within the above range, the purification efficiency (i.e., the recovery rate of the target metal) can be increased while simultaneously improving the separation efficiency by reducing the pressure loss in the separation section 4. A lower limit of 0.4 is preferred for the solid phase fraction of the molded body M2. The "solid phase fraction of the molded body" refers to the mass ratio of the total crystallized solid phase to the entire molded body, which includes both the liquid and solid phases.

[0038] Furthermore, the molding section 3 is designed to produce a molded body in which the solid phase ratio of the metal to be refined (e.g., Al) is 0.2 or more and 0.7 or less. This makes it possible to obtain a molded body M2 with a high concentration of the metal to be refined that crystallizes as the primary crystal. Note that "solid phase ratio of the metal to be refined" refers to the mass ratio of the crystallized metal to be refined (i.e., the primary crystal) to the entire molded body, which includes both the liquid and solid phases.

[0039] <Separation part> The separation unit 4 is configured to separate the molded body M2 produced by the molding unit 3 into a purified ingot I1 containing the metal to be purified and a concentrated molten metal I2 with a high concentration of solute elements by applying pressure to the molded body M2 in the refining container 2.

[0040] As shown in Figure 3C, the separation unit 4 includes a press machine 41 and a filter 42. The press machine 41 presses the filter 42 downward, thereby pressing the filter 42 against the molded body M2 from above.

[0041] The filter 42 is a compaction plate having multiple holes. As shown in Figure 3D, the filter 42, pressed against the molded body M2 from above, presses the purified ingot I1 downwards while allowing the concentrated molten metal I2 to pass upwards. As a result, the molded body M2 is compressed, and the concentrated molten metal I2 is separated from the purified ingot I1 above the filter 42.

[0042] The purified ingot I1 is a solid phase containing a large amount of the metal to be refined. The concentration of the metal to be refined in the purified ingot I1 is greater 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 a large amount of impurities. The concentrated molten metal I2 becomes a concentrated ingot upon cooling.

[0043] The pressure applied by the separation unit 4 to the molded body M2 is preferably 0.5 MPa to 30.0 MPa. Furthermore, the temperature of the molded body M2 when pressure is applied is preferably 500°C to 700°C.

[0044] <Methods for refining metals> Figure 4 shows the flow chart of the metal refining method using the refining apparatus 1. The metal refining method of this embodiment includes a melting step S10, a molded body manufacturing step S20, and a compression separation step S30. Each step is performed as a batch process on one refining container 2.

[0045] (Melting process) In this process, the material to be refined (for example, metal scrap containing aluminum alloy) is placed in the refinement container 2 and heated to the melting temperature. Molten metal is obtained by melting the material to be refined.

[0046] (Molded object manufacturing process) In this process, a molded body with a solid fraction of 0.2 to 0.7 is produced by cooling the molten metal contained in the purification container 2 while rotating it with a rotating magnetic field.

[0047] (Pressing and separation process) In this process, pressure is applied to the molded body in the refining container 2, separating it into a purified ingot containing the metal to be refined and a concentrated molten metal.

[0048] [1-2. Effects] According to the embodiments described in detail above, the following effects can be obtained. (1a) The purity of the metal can be increased by electromagnetic stirring using a rotating magnetic field. In addition, since the molded product is manufactured and compressed and separated within the stainless steel refining container 2, safety can be improved and refining costs can be reduced.

[0049] [2. Other Embodiments] While embodiments of this disclosure have been described above, it goes without saying that this disclosure is not limited to the embodiments described above and can take various forms.

[0050] (2a) In the metal refining apparatus of the above embodiment, the configuration of the separation section is an example and is not limited to those described above.

[0051] (2b) The functions of one component in the above embodiment may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, some parts of the configuration of the above embodiment may be omitted. Also, at least some parts of the configuration of the above embodiment may be added to, substituted for, or otherwise used in the configuration of other above embodiments. Any aspect of the technical concept specified by the wording of the claims is an embodiment of the present disclosure.

[0052] [3. Examples] The following describes the details of the tests conducted to confirm the effectiveness of this disclosure and their evaluation.

[0053] <Examples 1-3> 100g of Al-4%Si alloy with the composition shown in Table 1 was placed in a refining container as the refining material. This alloy is intended to represent metal scrap that is a mixture of casting aluminum alloy and wrought aluminum alloy. The values ​​in Table 1 represent mass percentages relative to the total molten metal.

[0054] [Table 1]

[0055] Next, the purification container was heated to 680°C to melt the purification material and obtain 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 and the molten metal was electromagnetically stirred.

[0056] A coil from a three-phase AC motor was used as the rotating magnetic field application device. The frequency of the rotating magnetic field, the maximum value of the magnetic flux density on the surface of the molten metal along the circumferential direction of the rotating magnetic field, and the rotational speed of the rotating magnetic field on the surface of the molten metal along the circumferential direction of the rotating magnetic field are as shown in Table 2. The rotating magnetic field was continuously applied until the temperature of the molten metal reached 610°C.

[0057] [Table 2]

[0058] After the application of the rotating magnetic field was stopped (i.e., after the electromagnetic stirring was completed), the refining container was placed in a press machine equipped with a filter (i.e., a compaction plate). Subsequently, when the compression temperature shown in Table 2 was reached, the solid fraction of the molded body was measured. The molded body in the refining container was then pressurized using the compression pressure shown in Table 2, separating it into purified ingot and concentrated molten metal.

[0059] Figure 5A shows the solidification structure of the purified ingot obtained in Example 1. Figure 5B shows the solidification structure of the concentrated molten metal obtained in Example 1. In the solidification structure of the purified ingot, white α-Al constituted the majority of the structure, indicating that α-Al was purified. On the other hand, in the solidification structure of the concentrated molten metal, a gray Al-Si eutectic structure constituted the majority. From these results, it was confirmed that α-Al was purified by the purification method of this disclosure.

[0060] <Comparative Example 1-3> Same Al-4% as in Examples 1-3 Si 100g of alloy was melted in a refining container to obtain molten metal. This molten metal was air-cooled, and the refining container was placed in a press machine equipped with a filter.

[0061] Subsequently, the solid fraction of the molded body was measured when the compression temperature shown in Table 2 was reached. The molded body in the refining container was then pressurized using the compression pressure shown in Table 2, separating it into purified ingot and concentrated molten metal.

[0062] <Rating> Table 2 shows the Si concentration and recovery rate of the purified ingots obtained in Examples 1-3 and Comparative Examples 1-3. The Si concentration is the mass percentage of Si in the entire purified ingot. The recovery rate is the mass percentage of the purified ingot in the entire molten metal (i.e., the purified material).

[0063] Table 2 shows that the Si concentration is lower in Examples 1-3 than in Comparative Examples 1-3. In other words, in Examples 1-3, the concentrated liquid phase is efficiently separated, resulting in the purification of α-Al with a Si concentration of 3.0% by mass or less. [Explanation of symbols]

[0064] 1... Purification equipment, 2... Purification container, 2A... Thermometer, 3... Molding section, 4... Separation section, 31... Rotating magnetic field application device, 41... Press machine, 42... Filter.

Claims

1. A process for producing a molded body with a solid phase ratio of 0.5 to 0.7 by cooling a molten metal containing the metal to be refined and elements other than the metal to be refined, which is contained in a stainless steel refining container, while rotating it with a rotating magnetic field, The process involves applying pressure to the molded body within the refining container to separate the molded body into a purified ingot containing the metal to be refined and a concentrated molten metal. Equipped with, The frequency of the rotating magnetic field is between 1 Hz and 100 Hz. 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 method for refining metal, wherein the rotational speed of the rotating magnetic field at the surface of the molten metal along the circumferential direction of the rotating magnetic field is 0.5 m / s or more and 10 m / s or less.

2. A method for refining a metal according to claim 1, A method for refining metal, wherein the manufacturing process involves producing a molded body having a solid phase ratio of 0.5 or more and 0.7 or less of the metal to be refined.

3. A method for refining a metal according to claim 1 or claim 2, The molten metal contains aluminum (Al), A method for purifying metals, wherein the mass concentration of Al in the molten metal is greater than the mass concentration of other metal elements contained in the molten metal.

4. A method for refining a metal according to claim 3, The molten metal contains silicon (Si), A method for refining metal, wherein the mass concentration of Si in the molten metal is 1.0% by mass or more and 11.0% by mass or less.

5. A method for refining a metal according to any one of claims 1 to 4, The molten metal comprises at least one of iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), and titanium (Ti). A method for purifying metals, 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.

6. A stainless steel refining container, A molding unit is configured to produce a molded body with a solid phase ratio of 0.5 to 0.7 by cooling a molten metal containing the metal to be refined and elements other than the metal to be refined, which is contained in the refining container, while rotating it with a rotating magnetic field. A separation unit configured to separate the molded body into a purified ingot containing the metal to be purified and a concentrated molten metal by applying pressure to the molded body within the purification container, Equipped with, The frequency of the rotating magnetic field is between 1 Hz and 100 Hz. 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 apparatus in which the rotational speed of the rotating magnetic field at the surface of the molten metal along the circumferential direction of the rotating magnetic field is 0.5 m / s or more and 10 m / s or less.

7. A metal refining apparatus according to claim 6, The molding section is a metal refining apparatus that produces a molded body having a solid phase ratio of 0.5 or more and 0.7 or less of the metal to be refined.

8. A metal refining apparatus according to claim 6 or claim 7, The molten metal contains aluminum (Al), A metal refining apparatus in which the mass concentration of Al in the molten metal is greater than the mass concentration of other metal elements contained in the molten metal.

9. A metal refining apparatus according to claim 8, The molten metal contains silicon (Si), A metal refining apparatus in which the mass concentration of Si in the molten metal is 1.0% by mass or more and 11.0% by mass or less.

10. A metal refining apparatus according to any one of claims 6 to 9, The molten metal comprises at least one of iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), and titanium (Ti). A metal refining apparatus in which 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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