Purification method of metal, and purification apparatus of metal

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 metal refining method and a metal refining apparatus for refining a predetermined metal from a molten metal. [Background technology]

[0002] Metal scrap is generated when industrial equipment, transportation equipment, electronic devices, etc. are discarded. This metal scrap contains a mixture of multiple metals, but recycling can be achieved by refining the most useful metals.

[0003] 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 compacting plate with multiple holes is lowered from the top of the refining vessel to apply pressure and separate the α-Al from impurities (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-054065 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-201917 Summary of the Invention [Problem to be solved by the invention]

[0005] Figure 1 is a phase diagram showing an example of eutectic solidification. When an alloy undergoing eutectic solidification has a hypoeutectic composition (i.e., a composition with a lower solute element concentration than the eutectic composition), the element with the higher concentration crystallizes first as the primary crystal. Therefore, by extracting only the primary crystal, high-purity metal can be recycled.

[0006] For example, in the case of an Al-Si alloy, when the molten alloy with the C0 composition shown in Figure 1 is cooled to T1°C, where a solid-liquid coexistence state occurs, the concentration C s of solids and concentration C lThe ratio of solid to liquid is W s :W l From this molten alloy, a low impurity concentration, concentration C s By extracting the solid, it becomes possible to purify Al.

[0007] On the other hand, when the concentration of impurities such as Si is high, for example, in the case of a molten alloy with the C1 composition in Figure 1, the amount of solid crystallization is limited to W' even when cooled to the temperature T2℃ at which the amount of solid crystallization is maximized. s / (W' l +W' s ), which reduces the amount of refined metal that can be separated.

[0008] The method described in Patent Document 1 uses electromagnetic stirring to increase the amount of purified metal separated even when the impurity concentration is high. However, because this method uses a refining vessel made of refractory material during stirring, the refining vessel is easily worn out during separation by squeezing, which creates safety and cost issues.

[0009] Furthermore, the method of Patent Document 2 described above uses a refining vessel made of graphite, which makes it impossible to perform electromagnetic stirring. Furthermore, similar to the method of Patent Document 1, the refining vessel is easily worn out during separation by squeezing.

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

[0011] One aspect of the present disclosure is a metal refining method that includes the steps of: producing a molded body having 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 contained in a stainless steel refining vessel using a rotating magnetic field; and applying pressure to the molded body in the refining vessel to separate the molded body into a purified ingot containing the metal to be refined and a concentrated molten metal.

[0012] Another aspect of the present disclosure is a metal refining device that includes a stainless steel refining vessel, a molding unit configured to produce a molded body having a solid fraction of 0.2 to 0.7 by rotating and cooling a molten metal contained in the refining vessel, the molten metal including the metal to be refined and elements other than the metal to be refined, using a rotating magnetic field, and a separation unit configured to apply pressure to the molded body within the refining vessel to separate the molded body into a purified ingot containing the metal to be refined and a concentrated molten metal.

[0013] With this configuration, the purity of the refined metal can be increased by electromagnetic stirring using a rotating magnetic field. Furthermore, since the production of the compacts and the compression separation are carried out in a stainless steel refining vessel, safety can be improved and refining costs can be reduced. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a phase diagram showing an example of eutectic solidification. [Figure 2] FIG. 2 is a schematic diagram of a metal refining apparatus according to an embodiment. [Figure 3] Figure 3A is a schematic diagram showing the state in which molten metal is contained in a refining vessel, Figure 3B is a schematic diagram showing the process for manufacturing a molded body by electromagnetic stirring, and Figures 3C and 3D are schematic diagrams showing the process for separating the molded body by squeezing. [Figure 4] FIG. 4 is a flow diagram of a method for refining a metal according to an embodiment. [Figure 5] FIG. 5A shows the solidification structure of the purified ingot in Example 1, and FIG. 5B shows the solidification structure of the concentrated molten metal in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings. [1. First embodiment] [1-1.Configuration] 2 is used to refine a target metal from a molten metal containing a plurality of elements. The refinement apparatus 1 includes a refinement vessel 2, a shaping section 3, and a separation section 4.

[0016] <Molten metal> The molten metal refined in the refining device 1 is, for example, melted metal scrap.

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

[0018] Metals contained in the molten metal that can be refined include, for example, aluminum (Al), iron (Fe), copper (Cu), magnesium (Mg), tin (Sn), and lead (Pb). Among these, Al is preferred because it is highly economical to recycle. It is also desirable that the mass concentration of Al in the molten metal be greater than the mass concentrations of other metal elements contained in the molten metal.

[0019] Impurities contained in the molten metal include, for example, manganese (Mn), chromium (Cr), zinc (Zn), titanium (Ti), silicon (Si), and the like, in addition to the metals mentioned above as the metals to be refined.

[0020] The lower limit of the impurity concentration relative to the entire molten metal is preferably 1.0 mass%, more preferably 1.5 mass%, and even more preferably 3.0 mass% or more. The upper limit of the impurity concentration relative to the entire molten metal is preferably 15.0 mass%, more preferably 11.0 mass%. The refining apparatus 1 enables high-purity refining of the target metal from molten metal with an impurity concentration in this range.

[0021] The molten metal preferably contains a combination of the metal to be refined and impurities that undergo eutectic solidification. The refinement device 1 can effectively refine the molten metal with such a combination. In addition to the elements described above, the molten metal may also contain one or more precious metals or rare metals.

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

[0023] In a molten metal containing Al most abundantly as a metallic element, the lower limit of the Si concentration relative to the entire molten metal is preferably 1.0 mass%, 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 refining Al in metal scrap containing aluminum alloys can be improved. 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 refine Al.

[0024] Furthermore, the molten metal preferably contains 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 setting the total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn, and Ti within this range, the refining efficiency of Al in metal scrap containing a mixture of casting aluminum alloy and wrought aluminum alloy can be increased.

[0026] <Refining vessel> The refining vessel 2 is a heat-resistant crucible capable of holding the molten metal. Specifically, the refining vessel 2 is a cylindrical body with a bottom made of non-magnetic stainless steel. The refining vessel 2 can be made of, for example, SUS304 as specified in JIS-G-4303:2015.

[0027] The refining vessel 2 allows external magnetism to pass through to the interior so that the molten metal can be electromagnetically stirred by the forming section 3. The refining vessel 2 also has sufficient strength to withstand the pressure from the separating section 4.

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

[0029] <Molding section> The forming section 3 is configured to produce a formed body with a certain range of solid fraction by rotating and cooling a molten metal contained in the refining vessel 2, which contains the metal to be refined and elements other than the metal to be refined, using a rotating magnetic field.

[0030] As shown in FIG. 3B, the molding unit 3 has a rotating magnetic field applying device 31. The rotating magnetic field applying device 31 generates a rotating magnetic field around the refining vessel 2, the polarity of which changes so that pairs of south and north poles rotate around 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 applying 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 applying device 31 passes through the interior of the refining vessel 2. 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 refining vessel 2.

[0032] The lower limit of the frequency of the rotating magnetic field is preferably 1 Hz, and 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 morphology of the primary crystals generated by cooling the molten metal can be efficiently controlled.

[0033] The maximum magnetic flux density on the surface of the molten metal along the circumferential direction of the rotating magnetic field (i.e., the outermost surface) is preferably 20 mT or more and 120 mT or less. By keeping the magnetic flux density in this range, the molten metal can be stirred sufficiently while suppressing power consumption. The magnetic flux density can be measured not only by direct measurement but also by electromagnetic field analysis, etc.

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

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

[0036] The forming unit 3 continues stirring and cooling the molten metal until the molten metal becomes a formed body M2 in a solid-liquid coexistence state with a solid fraction of 0.2 to 0.7. The formed body M2 contains a solid S that has crystallized due to a decrease in temperature and a 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 fraction of the compact M2 within the above range, it is possible to improve the purification efficiency (i.e., the recovery rate of the target metal) while improving the separation efficiency by reducing the pressure loss in the separation section 4. The lower limit of the solid fraction of the compact M2 is preferably 0.4. The "solid fraction 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.

[0038] Furthermore, the forming unit 3 preferably produces a formed body having a solid fraction of the target metal (e.g., Al) of 0.2 to 0.7. This makes it possible to obtain a formed body M2 having a high concentration of the target metal crystallized as primary crystals. Note that the "solid fraction of the target metal" refers to the mass ratio of the crystallized target metal (i.e., primary crystals) to the entire formed body including the liquid phase and solid phase.

[0039] <Separation part> The separation section 4 is configured to apply pressure to the formed body M2 produced by the forming section 3 within the refining vessel 2, thereby separating the formed body 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.

[0040] 3C, the separating section 4 has a press 41 and a filter 42. The press 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 with multiple holes. As shown in Fig. 3D, the filter 42 is pressed against the compact M2 from above, pressing the purified ingot I1 downward while allowing the concentrated molten metal I2 to pass upward. This compresses the compact M2, 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 when cooled.

[0043] The pressure applied to the molded body M2 by the separating section 4 is preferably 0.5 MPa or more and 30.0 MPa or less. The temperature of the molded body M2 when the pressure is applied is preferably 500°C or more and 700°C or less.

[0044] <Metal refining method> 4 shows a flow of a metal refining method using the refining apparatus 1. The metal refining method of this 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 vessel 2.

[0045] (Melting process) In this step, the refined material (for example, metal scrap containing an aluminum alloy) is placed in the refinement vessel 2 and heated to a melting temperature. The refined material is melted to obtain a molten metal.

[0046] (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, thereby producing a compact having a solid fraction of 0.2 or more and 0.7 or less.

[0047] (Compression separation process) In this step, pressure is applied to the compact in the refining vessel 2 to separate the compact into a purified ingot containing the metal to be refined and a concentrated molten metal.

[0048] [1-2.Effects] According to the embodiment described above in detail, the following effects can be obtained. (1a) The refining purity of metals can be increased by electromagnetic stirring using a rotating magnetic field. In addition, the production of compacts and compression separation are carried out in a stainless steel refining vessel 2, which improves safety and reduces refining costs.

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

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

[0051] (2b) The function of one component in the above embodiments may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. All aspects included in the technical idea identified by the wording of the claims are embodiments of the present disclosure.

[0052] 3. Working Example The following describes the content of the tests conducted to confirm the effects of the present disclosure and their evaluation.

[0053] <Examples 1-3> 100 g of an Al-4%Si alloy with the composition shown in Table 1 was placed in a refining vessel as a refining material. This alloy was assumed to be a metal scrap mixture of aluminum alloy for casting and aluminum alloy for wrought use. The values ​​in Table 1 are in mass% relative to the total molten metal.

[0054] [Table 1]

[0055] Next, the refining vessel was heated to 680°C to melt the refined material, obtaining 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 the molten metal, causing electromagnetic stirring.

[0056] The rotating magnetic field applying device used was a coil of a three-phase AC motor. 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 rotation speed of the rotating magnetic field on the surface of the molten metal along the circumferential direction of the rotating magnetic field were set as shown in Table 2. The rotating magnetic field was applied continuously 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 vessel was placed in a press equipped with a filter (i.e., a compacting plate). After that, when the pressing temperature shown in Table 2 was reached, the solid fraction of the green body was measured. The green body in the refining vessel was pressurized with the pressing pressure shown in Table 2, and separated into a purified ingot and a concentrated molten metal.

[0059] FIG. 5A shows the solidification structure of the purified ingot obtained in Example 1. FIG. 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 occupied the majority of the structure, indicating that α-Al was purified and refined. On the other hand, in the solidification structure of the concentrated molten metal, a gray Al-Si eutectic structure occupied the majority. These results confirmed that α-Al was purified and refined by the refining method of the present disclosure.

[0060] <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. The molten metal was air-cooled, and the refining vessel was placed in a press equipped with a filter.

[0061] Thereafter, the solid fraction of the green body was measured when the pressing temperature shown in Table 2 was reached. The green body in the refining vessel was pressurized at the pressing pressure shown in Table 2, and separated into a purified ingot and a concentrated molten metal.

[0062] <Evaluation> Table 2 shows the Si concentration in the purified ingots obtained in Examples 1-3 and Comparative Examples 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 ratio of the purified ingot in the entire molten metal (i.e., refined material).

[0063] As can be seen from Table 2, the Si concentration in Example 1-3 is lower than that in Comparative Example 1-3. That is, in Example 1-3, the concentrated liquid phase is efficiently separated, and α-Al having a Si concentration of 3.0 mass% or less is refined. [Explanation of symbols]

[0064] 1... Purification equipment, 2... Purification container, 2A... Thermometer, 3... Molding section, 4... Separation section, 31...rotating magnetic field applying device, 41...press machine, 42...filter.

Claims

1. a step of producing a compact having a solid fraction of 0.2 to 0.7 by rotating and cooling a molten metal containing a metal to be refined and elements other than the metal to be refined, the molten metal being contained in a stainless steel refining vessel, using a rotating magnetic field; a step of applying pressure to the compact in the refining vessel to separate the compact into a purified ingot containing the metal to be refined and a concentrated molten metal; A method for refining a metal, comprising:

2. 2. The method for refining a metal according to claim 1, In the producing step, the molded body is produced in which the solid fraction of the metal to be refined is 0.2 or more and 0.7 or less.

3. The method for refining a metal according to claim 1 or claim 2, A method for refining a metal, wherein the frequency of the rotating magnetic field is 1 Hz or more.

4. A method for refining a metal according to any one of claims 1 to 3, A method for refining a metal, 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.

5. A method for refining a metal according to any one of claims 1 to 4, The molten metal contains aluminum (Al), The method for refining a metal, wherein the mass concentration of Al in the molten metal is greater than the mass concentrations of other metal elements contained in the molten metal.

6. 6. The method for refining a metal according to claim 5, The molten metal contains silicon (Si), The method for refining a metal, wherein the mass concentration of Si in the molten metal is 1.0 mass% or more and 11.0 mass% or less.

7. 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 total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn, and Ti in the molten metal is 0.5 mass% or more and 6.0 mass% or less.

8. A stainless steel refining vessel, a forming unit configured to produce a formed body having a solid fraction of 0.2 or more and 0.7 or less by rotating and cooling a molten metal, which is contained in the refining vessel and includes a metal to be refined and elements other than the metal to be refined, using a rotating magnetic field; a separation unit configured to apply pressure to the compact in the refining vessel to separate the compact into a purified ingot containing the metal to be refined and a concentrated molten metal; A metal refining apparatus comprising:

9. The metal refining apparatus according to claim 8, The forming unit is configured to produce the formed body having a solid fraction of the metal to be refined of 0.2 to 0.

7.

10. The metal refining apparatus according to claim 8 or claim 9, A metal refining apparatus, wherein the frequency of the rotating magnetic field is 1 Hz or more.

11. The metal refining apparatus according to any one of claims 8 to 10, A metal refining device, 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.

12. The metal refining apparatus according to any one of claims 8 to 11, The molten metal contains aluminum (Al), The metal refining apparatus, wherein the mass concentration of Al in the molten metal is greater than the mass concentrations of other metal elements contained in the molten metal.

13. The 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 mass% or more and 11.0 mass% or less.

14. The metal refining apparatus 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 total mass concentration of Fe, Cu, Mn, Mg, Cr, Zn, and Ti in the molten metal is 0.5 mass% or more and 6.0 mass% or less.

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