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REDUCTION SYSTEM AND METHOD FOR HIGH-MELTING POINT METAL OXIDES, USING LIQUID METAL CRUCIBLE

20240026555 ยท 2024-01-25

    Inventors

    Cpc classification

    International classification

    Abstract

    The present disclosure provides a system and a method for reducing metal oxide to metal M.sup.1.

    Claims

    1. A system for reducing a metal oxide to metal M.sup.1, the system comprising: a cell; a liquid metal crucible accommodated at a bottom of the cell and comprising a liquid metal alloy of metal M.sup.1 and metal M.sup.2 forming a eutectic phase with each other; a liquid flux accommodated in the cell while forming a layer on the liquid metal crucible without being mixed with the liquid metal crucible; and a solid raw material module comprising a metal oxide, metal M.sup.2, and reducing metal M.sup.3, wherein the metal oxide is reduced to metal M.sup.1 by reaction with the reducing metal M.sup.3 while the solid raw material module reaches the liquid metal crucible and is melted, and the reduced metal M.sup.1 and the metal M.sup.2 are continuously incorporated into the liquid metal crucible while forming a liquid metal alloy.

    2. The system according to claim 1, further comprising an electrorefining part configured to collect and electrorefine the liquid metal alloy formed by the reduced metal M.sup.1 and the metal M.sup.2 to obtain metal M.sub.1.

    3. The system according to claim 1, wherein the metal oxide comprises at least one selected from the group consisting of M.sup.1.sub.xO.sub.z and M.sup.1.sub.xM.sup.3.sub.yO.sub.z, wherein x and y are each a real number ranging from 1 to 3, and z is a real number ranging from 1 to 4.

    4. The system according to claim 1, wherein the solid raw material module comprises: a core layer comprising the metal oxide and the reducing metal M.sup.3; and a shell layer composed of metal M.sup.2 surrounding the core layer.

    5. The system according to claim 1, wherein: the solid raw material module is a multilayer structure comprising: a core layer comprising the metal oxide; and a shell layer coated to surround an outer surface of the core layer; and the shell layer comprises an alloy phase composed of the metal M.sup.2 and the metal M.sup.3.

    6. The system according to claim 1, wherein: the solid raw material module is configured to descend vertically within the cell until it reaches the liquid metal crucible through the flux; and the solid raw material module descends at a rate of a distance corresponding to 0.1% to 10% of a depth of the cell per min.

    7. The system according to claim 1, wherein, when the metal oxide is reduced to the metal M.sup.1 by reaction with the reducing metal M.sup.3 while the solid raw material module is melted, oxide M.sup.3.sub.aO.sub.b is produced, and the oxide M.sup.3.sub.aO.sub.b has a lower specific gravity than that of the flux, wherein a and b are each a real number ranging from 1 to 3.

    8.-10. (canceled)

    11. The system according to claim 1, wherein the reaction between the metal oxide and the reducing metal is performed in an inert gas atmosphere and/or air.

    12. The system according to claim 4, wherein the core layer is composed of a powder mixture comprising powder of the metal oxide powder and powder of the reducing metal M.sup.3.

    13. The system according to claim 4, wherein the core layer is a multilayer structure comprising: a first core composed of the metal oxide; and a second core coated to surround an outer surface of the first core and composed of the metal M.sup.3.

    14. The system according to claim 4, wherein the solid raw material module further comprises an oxidation-preventing layer surrounding the shell layer and serving to prevent oxidation of the metal contained in the core layer and/or the shell layer.

    15. (canceled)

    16. The system according to claim 1, wherein the metal M.sup.1 is one selected from the group consisting of Ti, Zr, Hf, W, Fe, Ni, Zn, Co, Mn, Cr, Ta, Ga, Nb, Sn, Ag, La, Ce, Pr, Nd, Nb, Pm, Sm, Eu, Al, V, Mo, Gd, Tb, Dy, Ho, Er, Tm, Yb, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md and No.

    17. The system according to claim 1, wherein the metal M.sup.2 is at least one selected from the group consisting of Cu, Ni, Fe, Sn, Zn, Pb, Bi, Cd, and alloys thereof.

    18. The system according to claim 1, wherein the metal M.sup.3 is at least one selected from the group consisting of Ca, Mg, Al, and alloys thereof.

    19. The system according to claim 1, wherein the flux comprises a molten halide salt of at least one metal selected from the group consisting of alkali metals and alkaline earth metals.

    20. A method of reducing a metal oxide to metal M.sup.1, the method comprising: providing a cell; introducing a liquid flux into the cell; introducing metal M.sup.1 and metal M.sup.2 forming a eutectic phase with each other, thereby producing a liquid metal crucible having a specific gravity higher than that of the flux and accommodated in the cell while forming a layer under the flux without being mixed with the flux; moving a solid raw material module comprising a metal oxide, metal M.sup.2 and reducing metal M.sup.3 to the cell until it reaches the liquid metal crucible through the flux; and obtaining a liquid metal alloy comprising metal M.sup.1 derived from the metal oxide of the solid raw material module and metal M.sup.2.

    21. The method according to claim 20, further comprising obtaining metal M.sup.1 by electrorefining the obtained metal alloy comprising the metals M.sup.1 and M.sup.2.

    22. The method according to claim 20, wherein oxide M.sup.3.sub.aO.sub.b is produced as a by-product in moving the solid raw material module and/or obtaining the liquid metal alloy, and the oxide M.sup.3.sub.aO.sub.b has a lower specific gravity than that of the flux, and the method further comprises continuously collecting the by-product M.sup.3.sub.aO.sub.b forming a layer on the flux, and adding and mixing M.sup.1.sub.xO.sub.z with the collected M.sup.3.sub.aO.sub.b, thereby producing a metal oxide expressed as M.sup.1.sub.xM.sup.3.sub.yO.sub.z derived from the by-product M.sup.3.sub.aO.sub.b and the added M.sup.1.sub.xO.sub.z.

    23. A metal alloy obtained by the method according to claim 20.

    24. A metal obtained by the method according to claim 21.

    25. (canceled)

    Description

    BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

    [0045] FIG. 1 is a schematic view of a system according to one example embodiment of the present disclosure;

    [0046] FIG. 2 depicts photographs showing a process of preparing a raw material module including MgTiO.sub.3 as a metal oxide according to one example embodiment of the present disclosure;

    [0047] FIG. 3 is a graph showing the results of XRD analysis of the raw material module prepared as shown in FIG. 2;

    [0048] FIG. 4 is a schematic vertical sectional view of a raw material module according to one example embodiment of the present disclosure;

    [0049] FIG. 5 is a schematic vertical sectional view of a raw material module according to another example embodiment of the present disclosure;

    [0050] FIG. 6 is a schematic vertical sectional view of a raw material module according to still another example embodiment of the present disclosure;

    [0051] FIG. 7 is a photograph of a raw material module;

    [0052] FIG. 8 is another photograph of a raw material module;

    [0053] FIG. 9 depicts photographs showing the results of comparing weight before and after removing the flux from the alloy ingot produced in an Example;

    [0054] FIG. 10 is a table showing the results of performing elemental analysis of the inside of an alloy, produced in an Example, by energy dispersive spectrometry (EDS) after cutting the alloy; and

    [0055] FIG. 11 is a table showing the results of measuring the content of oxygen present in the alloy using ELTRA ONH2000.

    DETAILED DESCRIPTION

    [0056] Hereinafter, the intentions, operations and effects of the present disclosure will be described in detail through specific descriptions and examples to assist in understanding the example embodiments of the present disclosure and to implement these example embodiments. However, the following descriptions and example embodiments are presented as examples to assist in understanding the present disclosure as described above, and the scope of the invention is neither defined thereby nor limited thereto.

    [0057] Prior to the detailed description of the present disclosure, it should be noted that the terms or words used in the present specification and claims should not be construed as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present disclosure, based on the principle according to which the inventors can appropriately define the meaning of the terms to describe their invention in the best manner.

    [0058] Accordingly, it should be understood that the example embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred example embodiments, but not cover all the technical spirits of the present disclosure, and thus there may be various equivalents and modifications capable of replacing them at the time of filing the present disclosure.

    [0059] In the present specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, it should be understood that terms such as include and have are intended to denote the existence of mentioned characteristics, numbers, operations, components, or combinations thereof, but do not exclude the possibility of existence or addition of one or more other characteristics, numbers, operations, components, or combinations thereof.

    [0060] The term charging as used in the present specification may be used interchangeably with the term feeding, introducing, flowing in, or injection, and may be understood to mean sending or putting any material, such as a raw material, into a place where it is needed.

    [0061] Hereinafter, the present disclosure will be described in detail in the order of a system for reduction to metal M.sup.1, a method for reduction to metal M.sup.1, and examples.

    1. System for Reduction to Metal M.SUP.1

    [0062] In one specific example embodiment, a system for a metal oxide to metal M.sup.1 according to the present disclosure is schematically shown in FIG. 1. Referring to FIG. 1, the system according to the present disclosure may include: a cell 400; a liquid metal crucible 100 accommodated at the bottom of the cell 400 and including a liquid metal alloy of metal M.sup.1 and metal M.sup.2 forming a eutectic phase with each other; a liquid flux 200 accommodated in the cell while forming a layer on the liquid metal crucible 100 without being mixed with the liquid metal crucible, so as to block oxygen and reaction by-products from flowing into the liquid metal crucible 100; and a solid raw material module 300 including a metal oxide, metal M.sup.2, and reducing metal M.sup.3, wherein the metal oxide may be reduced to metal M.sup.1 by reaction with the reducing metal M.sup.3 while the solid raw material module reaches the liquid metal crucible and is melted, and the reduced metal M.sup.1 and metal M.sup.2 may be continuously incorporated into the liquid metal crucible while forming a liquid metal alloy.

    [0063] In the system of the present disclosure, the desired metal M.sup.1 is not particularly limited, but may be specifically one selected from the group consisting of Ti, Zr, Hf, W, Fe, Ni, Zn, Co, Mn, Cr, Ta, Ga, Nb, Sn, Ag, La, Ce, Pr, Nd, Nb, Pm, Sm, Eu, Al, V, Mo, Gd, Tb, Dy, Ho, Er, Tm, Yb, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md and No. More specifically, the desired metal M.sup.1 may be one selected from the group consisting of Ti, Zr, W, Fe, Ni, Zn, Co, Mn, Cr, Ta, Er and No, and more specifically, may be one selected from the group consisting of Ti, Zr, W, Fe, Ni, Zn, Co, Mn, and Cr. Even more specifically, it may be Ti, Zr or W.

    [0064] In the system of the present disclosure, metal M.sup.2 is not particularly limited as long as it can form a liquid metal alloy by a eutectic reaction with metal M.sup.1. Specifically, metal M.sup.2 may be at least one selected from the group consisting of Cu, Ni, Fe, Sn, Zn, Pb, Bi, Cd, and alloys thereof, and more specifically, may be Cu, Ni, or an alloy thereof.

    [0065] In the system of the present disclosure, metal M.sup.3 is not particularly limited as long as it can reduce the metal oxide to M.sup.1. Specifically, metal M.sup.3 may be at least one selected from among Ca, Mg, Al, and alloys thereof, and more specifically, may be Ca or Mg, in particular, Mg.

    [0066] In the system of the present disclosure, the metal oxide may include at least one selected from the group consisting of M.sup.1.sub.xO.sub.z and M.sup.1.sub.xM.sup.3.sub.yO.sub.z, wherein x and y are each a real number ranging from 1 to 3, and z is a real number ranging from 1 to 4.

    [0067] In one specific example embodiment, the metal oxide may include one or a combination of two or more selected from the group consisting of ZrO.sub.2, TiO.sub.2, MgTiO.sub.3, HfO.sub.2, Nb.sub.2O.sub.5, Dy.sub.2O.sub.3, Tb.sub.4O.sub.7, WO.sub.3, Co.sub.3O.sub.4, MnO, Cr.sub.2O.sub.3, MgO, CaO, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, Ga.sub.2O.sub.3, Pb.sub.3O.sub.4, SnO, NbO and Ag.sub.2O, without being limited thereto.

    [0068] The system according to the present disclosure is different from the conventional Kroll process in that it uses a metal oxide instead of a metal chloride as a raw material. Raw materials usually found in nature include an oxide of metal M.sup.1, and in order to use this metal oxide in the Kroll process, a pretreatment process of substituting the metal oxide with a chloride needs to be performed. If this pretreatment process is performed, it itself will cause an increase in process cost. Moreover, hydrochloric acid is used in the pretreatment process of substituting the metal oxide with a chloride, and in this case, corrosion of production equipment may be promoted due to the strong acidity of the hydrochloric acid, and toxic chlorine gas may be generated during the process, which may cause environmental problems. The system according to the present disclosure has advantages over the Kroll process in that it does not require the pretreatment process of substituting the metal oxide with a chloride, and thus it incurs a lower cost than the Kroll process cost and does not cause environmental problems.

    [0069] The cell 400 is preferably made of a material that has a high melting point in terms of durability and does not cause side reactions with the flux and the liquid metal crucible. The material of the cell may include at least one selected from the group consisting of MgO, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, SiO.sub.2, CaO, SiC, WO.sub.3, W, C, and Mo, without being limited thereto.

    [0070] The cell 400 may include a tapping hole 410 for continuously tapping the liquid metal alloy produced at the bottom thereof.

    [0071] As used herein, the term liquid metal crucible may refer to a reaction region capable of providing an environment in which at least one metal may be accommodated in, for example, the cell in a molten state while forming one layer, and the raw material module of the present disclosure may be melted within and the layer surface of the melted metal so that the metal oxide may be reduced.

    [0072] The system according to the present disclosure has the advantage of using this liquid metal crucible.

    [0073] Specifically, in the system of the present disclosure, as the liquid metal crucible including the liquid metal alloy of metal M.sup.1 and metal M.sup.2 forming a eutectic phase with each other is used, melting point of metal M.sup.1 may be lowered by the eutectic reaction while the metal oxide of the raw material module is reduced to metal M.sup.1, and thus electrolytic reduction may be effectively performed at a relatively low temperature. That is, in the system of the present disclosure, it is possible to obtain a liquid metal alloy while operating a liquid metal crucible in which metals are melted, and it is possible to operate the process at a lower temperature than the melting point of metal M.sup.1, thereby significantly reducing energy consumption. This temperature may vary depending on the types of M.sup.1 and M.sup.2, but may preferably be 900 C. to 1,600 C.

    [0074] What is also noteworthy about the liquid metal crucible is that a liquid alloy (M.sup.1 and M.sup.2 form a liquid metal alloy) may be obtained based on the eutectic reaction induced in the system of the present disclosure, and the metal alloy itself may be used as a final product. M.sup.1 is often used industrially in the form of an alloy. When M.sup.1 can be produced as only a single metal as in the conventional Kroll process, a post-processing process for forming an alloy with another metal may be required. However, the present disclosure has high process efficiency in that it is possible to obtain a final product in the form of a metal alloy of M.sup.1 and M.sup.2 through reduction reaction without the above-described post-treatment process. In addition, when the liquid metal crucible is formed, there are advantages in that it is possible to adjust the ratio between M.sup.1 and M.sup.2, it is also possible to adjust the ratio between the metal oxide and M.sup.2 in the module, and thus it is possible to the ratio between M.sup.1 and M.sup.2 in the metal alloy as a final product. It is to be understood that, if necessary, metal M.sup.1 may be obtained by electrorefining the obtained metal alloy, and a method known in the art may be used for such electrolytic refining.

    [0075] The liquid alloy obtained according to the present disclosure may be completely isolated from an environment in which oxygen may exist, and thus contamination thereof by oxygen may be significantly prevented. That is, according to the above aspect, it is possible to obtain a high-purity metal alloy and metal M.sup.1.

    [0076] Furthermore, the use of the liquid metal crucible including the liquid metal alloy of metal M.sup.1 and metal M.sup.2 forming a eutectic phase with each other has an advantage in that, even if the metal oxide contained in the raw material module is a material that is difficult to electrolytically reduce to metal, it is possible to more easily reduce the metal oxide in the raw material module using the standard oxidation-reduction potential difference between the liquid metal alloy and the desired metal M.sup.1. That is, when metal M.sup.2 having a more positive standard reduction potential that of metal M.sup.1 is used, the standard reduction potential value of M.sup.1 may move in a positive direction due to the liquid metal crucible, so that electrolytic reduction of the metal may be more easily achieved.

    [0077] In one major aspect of the present disclosure, in the system of the present disclosure, a metal oxide as a raw material, another metal as a reducing agent, and other additive metals are not introduced, but they constitute a raw material module like a single part, and based on this raw material module, it is possible to obtain a higher-quality metal alloy and metal.

    [0078] For example, in a process of continuously introducing a plurality of raw materials into a cell, like the Kroll process, the raw materials are likely to be oxidized before being introduced, but the raw material module according to the present disclosure includes a structure treated to be prevented from oxidation, and thus has a more enhanced oxygen barrier effect compared to the Kroll process. Accordingly, the metal alloy and metal obtained according to the present disclosure may have a significantly low oxygen content.

    [0079] Additionally, as described above, the system of the present disclosure includes a configuration for doubly blocking oxygen, because the flux serves as a barrier layer for blocking oxygen, and the raw material module itself can also block oxygen. Accordingly, the system of the present disclosure has significant advantages in that it is possible to perform the reaction between the metal oxide and the reducing metal under an inert gas atmosphere, which has been commonly recognized in the art, and it is also possible to perform the reaction between the metal oxide and the reducing metal in air. Even if the system of the present disclosure is operated in air, the metal alloy and metal produced thereby are of high purity with little oxygen. This will be clearly demonstrated through examples to be described later. In some cases, in the system of the present disclosure, the reaction between the metal oxide and the reducing metal may be performed in a combination of an inert gas atmosphere and a normal air atmosphere.

    [0080] In addition, the system of the present disclosure uses a raw material module in which raw materials necessary for the reaction are gathered into one body, and thus has an advantage in that it is easy to induce the reaction at the most optimal location in the cell.

    [0081] Photographs showing a process of preparing a raw material module according to the present disclosure are depicted in FIG. 2, and FIG. 4 shows a schematic view of a raw material module according to one example embodiment of the present disclosure. Incidentally, the photographs shown in FIG. 2 are only for helping understanding of the preparation of the raw material module as a non-limiting example, and the scope of the present disclosure is not limited thereto.

    [0082] Referring to FIG. 4, the solid raw material module 300 may include: a core layer 30 including the metal oxide 10 and the reducing metal M.sup.3 30; and a shell layer 320 composed of metal M.sup.2 surrounding the core layer 310. As shown in FIG. 4, the core layer 310 may have a multilayer structure including: a first core 311 composed of the metal oxide 10; and a second core 312 coated to surround the outer surface of the first core 311 and composed of the reducing metal M.sup.3 30.

    [0083] In some cases, a raw material module 300a as shown in FIG. 5 in which a core layer is shown as another example of the present disclosure may be used. The core layer 310a of the raw material module 300a may be composed of a powdery mixture including metal oxide powder 10a and reducing metal M.sup.3 powder 30a.

    [0084] Alternatively, the structure shown in FIG. 6 may also be preferable as the raw material module. Referring to FIG. 6, the raw material module 300b is similar to the above-described example in terms of a multilayer structure, but is different from the above-described example in that it includes the core layer 310b including the metal oxide 10b and the shell layer 320b coated to surround the outer surface of the core layer 310b, wherein the shell layer 320b is a coating layer including an alloy phase 330b composed of the metal M.sup.2 20b and the metal M.sup.3 30b.

    [0085] The above-described solid raw material module may further include an oxidation-preventing layer (330 in FIG. 4) surrounding the shell layer and serving to prevent oxidation of metal included in the core layer and/or the shell layer by blocking oxygen from contacting the metal. The oxidation-preventing layer 330 may include at least one selected from the group consisting of LiF, MgF.sub.2, CaF.sub.2, BaF.sub.2, CaCl.sub.2, MgCl.sub.2, MgO, CaO, BaO, Al.sub.2O.sub.3 and SiO.sub.2, but the scope of the present disclosure is not limited thereto. Although the oxidation-preventing layer is shown only in FIG. 4, it is to be understood that the oxidation-preventing layer may also be applied to the other example embodiments shown in FIGS. 5 and 6.

    [0086] This solid raw material module may be configured to descend vertically within the cell until it reaches the liquid metal crucible through the flux. The solid raw material module may descend at a rate of a distance corresponding to 0.1% to 10% of the depth of the cell per min.

    [0087] When the descending direction of the solid raw material module is set as an imaginary axis, rotating the solid raw material module about the axis is preferable in terms of stirring the liquid metal crucible and improving reactivity thereby. The rotation may be performed during the descent into the cell and/or until completion of the descent.

    [0088] Accordingly, the system according to the present disclosure may further include a rotation unit to which the solid raw material module is mounted and which rotates the same.

    [0089] Meanwhile, the solid raw material module descends to the liquid metal crucible and is melted, and at the same time or partially simultaneously, the metal oxide and the reducing metal M.sup.3 react to reduce the metal oxide to M.sup.1, and the reduced M.sup.1 forms a liquid metal alloy with M.sup.2 contained in the solid raw material module.

    [0090] As an example, when M.sup.1 is Ti, the metal oxide (M.sup.1.sub.xO.sub.z) is TiO.sub.2, M.sup.2 is Ni, and M.sup.3 is Mg, according to Reaction Formulas 1-1 and 1-2 below, the metal oxide may be reduced to metal Ti, and then an M.sup.3 oxide (M.sup.3.sub.aO.sub.b) may be separated while the liquid metal alloy TiNi is obtained.


    2Mg+TiO.sub.2->Ti+2MgO[Reaction Formula 1-1]


    Ti+Ni+2MgO.fwdarw.TiNi (alloy)+2MgO (separated)[Reaction Formula 1-2]

    [0091] As another example, when M.sup.1 is Ti, the metal oxide (M.sup.1.sub.xM.sup.3.sub.yO.sub.z) is MgTiO.sub.3, M.sup.2 is Ni, and M.sup.3 is Mg, according to Reaction Formulas 2-1 and 2-2 below, the metal oxide may be reduced to metal Ti, and then an M.sup.3 oxide (M.sup.3.sub.aO.sub.b) may be separated while the liquid metal alloy TiNi is obtained.


    2Mg+MgTiO.sub.3->Ti+3MgO[Reaction Formula 2-1]


    Ti+Ni+3MgO.fwdarw.TiNi (alloy)+3MgO (separated)[Reaction Formula 2-2]

    [0092] M.sub.3aO.sub.b produced according to the above-described reaction is a kind of by-product and may have a lower specific gravity that that of the flux of the present disclosure. The M.sup.3.sub.aO.sub.b may float on the flux due to its density difference from the flux to form a by-product layer. Therefore, the by-product M.sup.3.sub.aO.sub.b does not mix with the liquid metal crucible present as a layer under the flux and with the formed liquid metal alloy. In addition, the by-product layer may serve to prevent the flux from being lost by vaporization while being positioned on the flux, and to prevent oxygen in the air from penetrating into the reactor.

    [0093] Meanwhile, since the by-product floats on the cell as the liquid metal alloy is produced, the by-product needs to be continuously removed from the cell in order to continuously perform the process in the cell having a limited volume. Thus, the system according to the present disclosure may be configured to enable a continuous process by using this by-product. Specifically, the system of the present disclosure may further include a recycling device that continuously collects the layered by-product floating on the flux through the top of the cell and mixes the collected by-product with, for example, M.sup.1.sub.xO.sub.z to produce metal oxide M.sup.1.sub.xM.sup.3.sub.yO.sub.z. At this time, when the produced M.sup.1.sub.xM.sup.3.sub.yO.sub.z is used, the reduction reaction rate may be further increased compared to when M.sup.1.sub.xO.sub.z is used.

    [0094] The flux preferably has a specific gravity which is intermediate between the specific gravity of the liquid metal crucible and the specific gravity of the by-product M.sup.3.sub.aO.sub.b so as to prevent the liquid metal crucible and the by-product M.sup.3.sub.aO.sub.b from mixing with each other, and at the same time, the flux is preferably insoluble in the by-product M.sup.3.sub.aO.sub.b. The flux is preferably a material such as a non-chlorine-based material, which does not cause environmental problems while being capable of preventing prevent oxygen from penetrating into the liquid metal crucible and the liquid metal alloy containing the desired metal M.sup.1.

    [0095] This flux may include a molten halide salt of at least one metal selected from the group consisting of alkali metals and alkaline earth metals, but does not contain chloride. More specifically, the flux in the system of the present disclosure may be a molten halide salt of at least one metal selected from the group consisting of alkali metals including Li, Na, K, Rb, and Cs, and alkaline earth metals including Mg, Ca, Sr, and Ba. In this case, the halide may include fluoride, bromide, iodide, or a mixture thereof.

    [0096] In the system of the present disclosure, the flux may also be present in an amount of 10 wt % to 50 wt %, specifically 10 wt % to 20 wt %, more specifically 10 wt % to 15 wt %, even more specifically 12 wt % to 13 wt %, relative to the metal oxide involved in the overall reduction reaction, that is, the metal oxide contained in the raw material module and capable of being reduced to the desired metal M.sup.1.

    [0097] The flux may further contain, as an additive, at least one metal oxide selected from the group of alkali metals and alkaline earth metals. The content of the additive may be 0.1 to 25 wt % based on the total weight of the flux. The additive may include Li.sub.2O, Na.sub.2O, SrO, Cs.sub.2O, K.sub.2O, CaO, BaO, or a mixture thereof, without being limited thereto. The additive contained in the flux may enable easier reduction of the metal oxide contained in the raw material module.

    [0098] The system according to the present disclosure may further include an electrorefining part configured to continuously collect the liquid metal alloy formed by M.sup.1 and M.sup.2 through the bottom of the cell and to electrorefine the collected liquid metal alloy to obtain metal M.sub.1.

    [0099] The electrorefining part may solidify the collected liquid metal alloy to obtain a solid metal alloy, and electrorefine the solid metal alloy, thereby recovering metal M.sup.1 from the metal alloy.

    [0100] In some cases, a flux that may remain in the liquid metal alloy may be removed before electrorefining of the solid metal alloy, and this removal may be achieved, for example, by heat-treating the liquid metal alloy in a vacuum or inert gas atmosphere, causing the flux to be removed by distillation. The distillation temperature (heat treatment temperature) is not particularly limited as long as it is a temperature equal to or higher than the melting point of the flux used in the system of the present disclosure, and it may be, for example, 780 to 1,000 C. In order to effectively prevent the liquid metal alloy from being oxidized again, it may be advantageous to carry out the distillation in a vacuum atmosphere and under an inert gas atmosphere.

    [0101] The electrorefining part may include a flux including a molten halide salt of at least one metal selected from the group consisting of alkali metals and alkaline earth metals, independently of the flux used in the above-described reduction reaction.

    2. Production Method

    [0102] The method according to the present disclosure may include the operations of: providing a cell; introducing a liquid flux into the cell; introducing metal M.sup.1 and metal M.sup.2 forming a eutectic phase with each other, thereby producing a liquid metal crucible having a specific gravity higher than that of the flux and accommodated in the cell while forming a layer under the flux without being mixed with the flux; moving a solid raw material module including a metal oxide, metal M.sup.2 and reducing metal M.sup.3 to the cell until it reaches the liquid metal crucible through the flux; and obtaining a liquid metal alloy including metal M.sup.1 derived from the metal oxide of the solid raw material module and metal M.sup.2.

    [0103] In the operation of moving the solid raw material module, when the solid raw material module is melted when it reaches the liquid metal crucible. In this case, the metal oxide and the reducing metal M.sup.3 may react with each other to reduce the metal oxide to metal M.sup.1, and the reduced metal M.sup.1 and metal M.sup.2 may be continuously incorporated into the liquid metal crucible while forming a liquid metal alloy.

    [0104] In the method of the present disclosure, the desired metal M.sup.1 is not particularly limited, but may be specifically one selected from the group consisting of Ti, Zr, Hf, W, Fe, Ni, Zn, Co, Mn, Cr, Ta, Ga, Nb, Sn, Ag, La, Ce, Pr, Nd, Nb, Pm, Sm, Eu, Al, V, Mo, Gd, Tb, Dy, Ho, Er, Tm, Yb, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md and No. More specifically, the desired metal M.sup.1 may be one selected from the group consisting of Ti, Zr, W, Fe, Ni, Zn, Co, Mn, Cr, Ta, Er and No, and more specifically, may be one selected from the group consisting of Ti, Zr, W, Fe, Ni, Zn, Co, Mn, and Cr. Even more specifically, it may be Ti, Zr or W.

    [0105] In the method of the present disclosure, metal M.sup.2 is not particularly limited as long as it can form a liquid metal alloy by a eutectic reaction with metal M.sup.1. Specifically, metal M.sup.2 may be at least one selected from the group consisting of Cu, Ni, Fe, Sn, Zn, Pb, Bi, Cd, and alloys thereof, and more specifically, may be Cu, Ni, or an alloy thereof.

    [0106] In the method of the present disclosure, metal M.sup.3 is not particularly limited as long as it can reduce the metal oxide to M.sup.1. Specifically, metal M.sup.3 may be at least one selected from among Ca, Mg, Al, and alloys thereof, and more specifically, may be Ca or Mg, in particular, Mg.

    [0107] In the method of the present disclosure, the metal oxide may include at least one selected from the group consisting of M.sup.1.sub.xO.sub.z and M.sup.1.sub.xM.sup.3.sub.yO.sub.z, wherein x and y are each a real number ranging from 1 to 3, and z is a real number ranging from 1 to 4.

    [0108] In one specific example embodiment, the metal oxide may include one or a combination of two or more selected from the group consisting of ZrO.sub.2, TiO.sub.2, MgTiO.sub.3, HfO.sub.2, Nb.sub.2O.sub.5, Dy.sub.2O.sub.3, Tb.sub.4O.sub.7, WO.sub.3, Co.sub.3O.sub.4, MnO, Cr.sub.2O.sub.3, MgO, CaO, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, Ga.sub.2O.sub.3, Pb.sub.3O.sub.4, SnO, NbO and Ag.sub.2O, without being limited thereto.

    [0109] The method according to the present disclosure is different from the conventional Kroll process in that it uses a metal oxide instead of a metal chloride as a raw material. Raw materials usually found in nature include an oxide of metal M.sup.1, and in order to use this metal oxide in the Kroll process, a pretreatment process of substituting the metal oxide with a chloride needs to be performed. If this pretreatment process is performed, it itself will cause an increase in process cost. Moreover, hydrochloric acid is used in the pretreatment process of substituting the metal oxide with a chloride, and in this case, corrosion of production equipment may be promoted due to the strong acidity of the hydrochloric acid, and toxic chlorine gas may be generated during the process, which may cause environmental problems. The method according to the present disclosure has advantages over the Kroll process in that it does not require the pretreatment process of substituting the metal oxide with a chloride, and thus it incurs a lower cost than the Kroll process cost and does not cause environmental problems.

    [0110] The raw material module that is used in the method of the present disclosure may include: a core layer including a metal oxide and reducing metal M.sup.3; and a shell layer composed of metal M.sup.2 surrounding the core layer. As shown in FIG. 4, the core layer 310 may have a multilayer structure including: a first core composed of the metal oxide; and a second core coated to surround the outer surface of the first core and composed of the reducing metal M.sup.3. In some cases, as shown in FIG. 5 in which a core layer is shown as another example of the present disclosure. The core layer 310a of the raw material module 300a may be composed of a powdery mixture including metal oxide powder and reducing metal M.sup.3 powder.

    [0111] Alternatively, the raw material module shown in FIG. 6 may also be used. This raw material module may include the core layer including the metal oxide and the shell layer coated to surround the outer surface of the core layer, wherein the shell layer may be a coating layer including an alloy phase composed of metal M.sup.2 and metal M.sup.3.

    [0112] The solid raw material module may further include an oxidation-preventing layer surrounding the shell layer and serving to prevent oxidation of metal included in the core layer and/or the shell layer by blocking oxygen from contacting the metal. The oxidation-preventing layer may include at least one selected from the group consisting of LiF, MgF.sub.2, CaF.sub.2, BaF.sub.2, CaCl.sub.2, MgCl.sub.2, MgO, CaO, BaO, Al.sub.2O.sub.3 and SiO.sub.2, but the scope of the present disclosure is not limited thereto.

    [0113] In the operation of moving the solid raw material module, the solid raw material module may be descended at a rate of a distance corresponding to 0.1% to 10% of the depth of the cell per min, until it reaches the liquid metal crucible through the flux.

    [0114] In the operation of obtaining a liquid metal alloy including metals M.sup.1 and M.sup.2, when the solid raw material module reaches the liquid metal crucible and is melted, the metal oxide may be reduced to metal M.sup.1 by reaction with the reducing metal M.sup.3, and the reduced M.sup.1 may form a liquid metal alloy with the metal M.sup.2 contained in the solid raw material module.

    [0115] As an example, when M.sup.1 is Ti, the metal oxide (M.sup.1.sub.xO.sub.z) is TiO.sub.2, M.sup.2 is Ni, and M.sup.3 is Mg, according to Reaction Formulas 1-1 and 1-2 below, the metal oxide may be reduced to metal Ti, and then an M.sup.3 oxide (M.sup.3.sub.aO.sub.b) may be separated while the liquid metal alloy TiNi is obtained.


    2Mg+TiO.sub.2->Ti+2MgO[Reaction Formula 1-1]


    Ti+Ni+2MgO.fwdarw.TiNi (alloy)+2MgO (separated)[Reaction Formula 1-2]

    [0116] As another example, when M.sup.1 is Ti, the metal oxide (M.sup.1.sub.xM.sup.3.sub.yO.sub.z) is MgTiO.sub.3, M.sup.2 is Ni, and M.sup.3 is Mg, according to Reaction Formulas 2-1 and 2-2 below, the metal oxide may be reduced to metal Ti, and then an M.sup.3 oxide (M.sup.3.sub.aO.sub.b) may be separated while the liquid metal alloy TiNi is obtained.


    2Mg+MgTiO.sub.3->Ti+3MgO[Reaction Formula 2-1]


    Ti+Ni+3MgO.fwdarw.TiNi (alloy)+3MgO (separated)[Reaction Formula 2-2]

    [0117] M.sub.3aO.sub.b produced according to the above-described reaction is a kind of by-product and may have a lower specific gravity that that of the flux of the present disclosure. The M.sup.3.sub.aO.sub.b may float on the flux due to its density difference from the flux to form a by-product layer. Therefore, the by-product M.sup.3.sub.aO.sub.b does not mix with the liquid metal crucible present as a layer under the flux and with the formed liquid metal alloy. In addition, the by-product layer may serve to prevent the flux from being lost by vaporization while being positioned on the flux, and to prevent oxygen in the air from penetrating into the reactor.

    [0118] Meanwhile, since the by-product floats on the cell as the liquid metal alloy is produced, the by-product needs to be continuously removed from the cell in order to continuously perform the process in the cell having a limited volume. Thus, the method according to the present disclosure may be configured to use this by-product. Specifically, the method according to the present disclosure may further include the operation of continuously collecting the layered by-product (i.e., M.sup.3.sub.aO.sub.b) floating on the flux through the top of the cell, and adding and mixing, for example, M.sup.1.sub.xO.sub.z with the collected M.sup.3.sub.aO.sub.b, thereby producing the metal oxide M.sup.1.sub.xM.sup.3.sub.yO.sub.z derived from the by-product M.sup.3.sub.aO.sub.b and the added M.sup.1.sub.xO.sub.z.

    [0119] When M.sup.1.sub.xM.sup.3.sub.yO.sub.z obtained as described above is used, in some cases, the reduction reaction rate may be further increased compared to when M.sup.1.sub.xO.sub.z is used. The operation of producing M.sup.1.sub.xM.sup.3.sub.yO.sub.z may be performed at a temperature of 1,000 C. to 1,500 C., specifically 1,200 C. to 1,400 C., more specifically, 1,250 C. to 1,350 C.

    [0120] The type of the flux is not particularly limited unless it is a chlorine-based material, and is preferably as defined in the previous example embodiment.

    [0121] The method according to the present disclosure may further include, after the operation of obtaining the alloy including metals M.sup.1 and M.sup.2, the operation of obtaining metal M.sup.1 by electrorefining the obtained alloy.

    [0122] The operation of obtaining metal M.sup.1 by electrorefining may be the operation of solidifying the obtained liquid metal alloy to obtain a solid alloy, and electrorefining the solid alloy, thereby recovering metal M.sup.1 from the alloy.

    3. Examples

    [0123] Hereinafter, example will be described in detail with reference to FIGS. 3 to 5 and 6a to 6c, whereby the action and effect of the present disclosure will be demonstrated. However, the following examples are only presented as examples of the present disclosure, and the scope of the present disclosure is not defined thereby.

    Example

    [0124] The system shown in FIG. 1 was used. Flux MgF.sub.2 (0.2 kg)-BaF.sub.2 (1.5 kg) in a resistance heating furnace was weighed, introduced into a cell, and then heated to about 1,200 C. to form a flux layer.

    [0125] Cu (20 g) and Ti (200 g) were weighed, introduced into the cell, and melted, thereby producing a liquid metal crucible positioned at the bottom of the cell and forming a layer under the flux.

    [0126] As shown in FIG. 2, 630 g of MgTiO.sub.3 (average particle size of 300 m) as a metal oxide and 250 g of Mg powder as metal M.sup.3 were mixed together, charged into a cylindrical copper container (250 g), and dried, thus preparing a raw material module. Incidentally, photographs of the actually prepared raw material module are shown in FIGS. 7 and 8.

    [0127] The prepared raw material module was charged into the cell and descended vertically at a rate of about 6 cm/min until it reached the layer of the liquid metal crucible. At this time, the module was rotated for 10 minutes to stir the flux and the liquid metal crucible. The melting and reduction reaction of the raw material module was performed for 2 hours, and a CuTi liquid metal alloy as a reaction product was collected through an outlet provided at the bottom of the cell and was solidified to finally obtain a CuTi alloy shown in FIG. 9. In addition, after completion of the reaction, the crucible was cooled at a rate of 10 C./min to prevent damage to the crucible.

    Experimental Example

    [0128] The properties of the alloy obtained in Example 1 were evaluated using the following methods. [0129] Recovery: 100{(first weightsecond weight)/second weight100%} [0130] Residual impurity content: the produced alloy was cut and the inside of the alloy was analyzed by energy dispersive spectrometry. [0131] Oxygen content: the oxygen content in the alloy was measured using an ELTRA ONH2000.

    TABLE-US-00001 TABLE 1 Energy dispersive First Second Recov- spectrometry results Oxygen weight* weight** ery Ti Cu content (g) (g) (%) (wt %) (wt %) (ppm) Example 500 488.56 97.7% 40.29 59.71 980.35 *First weight: total weight of liquid metal crucible of CuTi initially charged into cell + stoichiometric reduction amount of Ti contained in metal oxide **Second weight: total weight of CuTi obtained

    [0132] From the results in Table 1 above, it can be seen that the alloy of the Example, produced according to the present disclosure, exhibited a high recovery rate which is much higher than 90%, and contained oxygen as a contaminant at an extremely low level. The results for this low oxygen content are clearly demonstrated in FIG. 11.

    [0133] In addition, FIG. 10 shows the results obtained by cutting the alloy produced in the Example and analyzing the residual impurity content in the inside of the alloy by energy dispersion spectrometry. Referring to FIG. 10, it can be seen that the alloy is composed only of the desired metal Ti and Cu, and Mg used as the reducing metal does not exist at all.

    [0134] These experimental results suggest that, according to the present disclosure, it is possible to obtain a high-purity alloy which has a very low oxygen content and has no other impurities used in the process.

    [0135] The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications, and publications to provide yet further embodiments.

    [0136] These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.