KR101793471B1 - Refining Method of Metal Using Electroreduction and Electrorefining process - Google Patents

Abstract

According to the present invention, a metal refining method comprises: an electrolytic reduction step of electrolytic reducing a raw material containing a metal oxide using a liquid metal cathode forming an eutectic phase and a first metal which is metal of the metal oxide to manufacture an intermetallic alloy between the first metal and a second metal which is a metal of the liquid metal cathode; and an electrolytic refining step of electrolytic refining the solidified alloy to recover the first metal from the alloy. The present invention is able to manufacture the metal having a high quality.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal refining method using an electrolytic reduction and electrolytic refining process,

The present invention relates to a metal refining method, and more particularly, to a metal refining method capable of producing a high-purity metal by using a metal oxide as a raw material in an environment-friendly and safe manner and producing a high quality metal having a significantly low oxygen content .

A typical process for the reduction of existing zirconium and titanium metal oxides is the Kroll process (US 5,035,404). The Kroll process is a process based on a chlorination process. Since magnesium is used to reduce zirconium chloride or titanium, the process is complicated and the probability of chlorine gas generation is high, which is an environmental problem. have. The electrolytic reduction process has been studied as a substitute for the existing crawl process. It has many advantages such as maintaining the shape of the precursor material and the advantage of not generating chlorine gas. However, There is still a problem in that the oxygen concentration after the process is difficult to control since the metal is limited to some types such as titanium and tantalum and the recovered metal is limited to powder or porous form. An electrolytic reduction method using a molten oxide electrolyte has been reported as an approach to control a high oxygen concentration caused by a large surface area of such a product (Antoine Allanore, Journal of The Electrochemical Society, 162 (1) (2015) E13-E22) This process requires a high temperature of 1500 ° C or higher in order to melt the oxide raw material and has a limit to be applied to a high melting point metal having a melting point of 1700 ° C or higher like Ti and Zr. In order to overcome this problem, it is necessary to lower the specific surface area of the Ti and Zr target metals produced by the electrolytic reduction reaction in the electrolyte so as not to cause reoxidation. However, in the case of Ti and Zr, the reduction of the specific surface area due to melting is practically impossible.

United States Patent 5,035,404

Antoine Allanore, Journal of The Electrochemical Society, 162 (1) (2015) E13-E22

 It is an object of the present invention to provide a metal refining method capable of producing a high purity metal from a metal oxide by an environmentally friendly and safe method that does not require a chlorination step will be.

It is another object of the present invention to provide a metal refining method capable of producing a high-quality metal having a remarkably low oxygen content from a metal oxide.

Still another object of the present invention is to provide a metal refining method which is advantageous for commercialization because it is possible to perform a relatively low temperature process and has an energy efficient and simple process.

The metal refining method according to the present invention comprises the steps of electrolytically reducing a raw material containing a metal oxide by using a liquid metal anode forming a process phase (eutectic phase) with a first metal which is a metal of a metal oxide, An electrolytic reduction step of producing an alloy between a second metal which is a metal of the liquid metal cathode; And electrolytically refining the solidified alloy to recover the first metal from the alloy.

In the metal refining method according to an embodiment of the present invention, the metal oxide may satisfy the following formula (1).

(Formula 1)

M _x O _y

Wherein M is a metal which is a metal to be reduced and is a metal having a negative standard reduction potential with respect to a standard reduction potential of a second metal which is a metal of the liquid metal cathode, x is a natural number of 1 to 3, y is It is a natural number from 1 to 4.

In the metal refining method according to an embodiment of the present invention, the metal oxide is _{ZrO 2, TiO 2, WO 3} , Fe 2 O 3, Fe 3 O 4, NiO, ZnO, Co 3 O 4, MnO, Cr 2 O ₃ , Ta ₂ O ₅ , Ga ₂ O ₃ , Pb ₃ O ₄ , SnO and Ag ₂ O.

In the metal refining method according to an embodiment of the present invention, the second metal may be selected from Cu, Sn, Zn, Pb, Bi, Cd, and alloys thereof.

In the metal refining method according to an embodiment of the present invention, the electrolyte in the electrolytic reduction step may include a molten salt of a halide of a metal selected from the group consisting of alkali metals and alkaline earth metals.

In the metal refining method according to an embodiment of the present invention, the electrolyte in the electrolytic reduction step may further include an additive which is an oxide of one or more metals selected from the group consisting of alkali metals and alkaline earth metals.

In the metal refining method according to an embodiment of the present invention, the solidification of the alloy obtained by the electrolytic reduction is slowly cooled to a room temperature at a cooling rate of 20 DEG C / min or less at the temperature of the liquid metal cathode during the electrolytic reduction, .

In the metal refining method according to an embodiment of the present invention, the temperature of the liquid metal cathode may be 1100 ° C to 1200 ° C.

In the metal refining method according to an embodiment of the present invention, the alloy may contain at least 2.1 wt% of the first metal.

In the metal refining method according to an embodiment of the present invention, the liquid metal cathode may be a liquid copper cathode, and the metal oxide may include zirconium oxide.

The refining method according to the present invention is advantageous in that it is environment-friendly and excellent in stability because a zirconium is smelted by an electrolytic reduction process, and thus a chlorination step is not necessary.

Further, the refining method according to the present invention is advantageous in that the amount of dissolved oxygen can be reduced by recovering a target metal in the form of an alloy using a liquid metal cathode, particularly a liquid copper anode having a very low solubility of oxygen.

Further, the refining method according to the present invention uses a metal having a positive standard reduction potential higher than the standard reduction potential of a target metal, as a metal of a liquid metal cathode, The reducing potential is increased in the positive direction, so that the reduction can be performed more easily.

Further, the refining method according to the present invention provides a metal refining method which is advantageous for commercialization because it can be processed at a relatively lower temperature than a pure target metal melting temperature by a process reaction between a liquid metal cathode and a desired metal, will be.

Further, the refining method according to the present invention is advantageous in that an alloy obtained by electrolytic reduction is solidified and a refined alloy of a solid phase is electrolytically refined to produce a highly pure metal with improved efficiency.

Further, the refining method according to the present invention is a refining method of a liquid metal anode, in which a target metal is hardly dissolved and a metal that forms an intermetallic compound with a desired metal is used, so that the stable and efficient reduction And it is also possible to reduce a thick solid alloy.

1 is a process diagram showing an electrolytic reduction process in a metal refining method according to an embodiment of the present invention,
2 is a process diagram showing an electrolytic refining process in the metal refining method according to an embodiment of the present invention,
3 is a scanning electron microscope (SEM) image of an alloy obtained in an electrolytic reduction process in an embodiment of the present invention,
4 is a scanning electron microscope (SEM) image of the structure of another alloy obtained in the electrolytic reduction process according to an embodiment of the present invention,
5 is a scanning electron microscope (SEM) image of another alloy obtained in an electrolytic reduction process in an embodiment of the present invention,
6 is a scanning electron microscope (SEM) image of another alloy obtained in an electrolytic reduction process in an embodiment of the present invention,
7 is a graph showing the results of an X-ray diffraction test of an alloy obtained in an electrolytic reduction process in an embodiment of the present invention,
8 is a view showing an optical photograph, a scanning electron microscope photograph and an EDS elemental analysis result of an anode and an anode observed in an electrolytic refining step in an embodiment of the present invention,
FIG. 9 is a scanning electron microscope (SEM) image of a cathode taken along an electrolytic refining process in an embodiment of the present invention,
10 is a scanning electron microscope (SEM) image of a Cu-Zr alloy containing 1.21 wt% Cu.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a metal refining method of the present invention will be described in detail with reference to the accompanying drawings. The following drawings are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the following drawings, but may be embodied in other forms, and the following drawings may be exaggerated in order to clarify the spirit of the present invention. Hereinafter, the technical and scientific terms used herein will be understood by those skilled in the art without departing from the scope of the present invention. Descriptions of known functions and configurations that may be unnecessarily blurred are omitted.

The metal refining method according to the present invention comprises the steps of electrolytically reducing a raw material containing a metal oxide by using a liquid metal anode forming a process phase (eutectic phase) with a first metal which is a metal of a metal oxide, An electrolytic reduction step of producing an intermetallic alloy between the first metal and the second metal; And electrolytically refining the solidified alloy to recover the first metal from the alloy.

As described above, the metal refining method according to the present invention is a method of refining a raw material containing a metal oxide by electrolytically reducing the metal oxide, and a liquid metal cathode is subjected to an eutectic phase with a target metal (a first metal which is a metal of a metal oxide) The metal (metal) of the metal oxide (the first metal) is electrolytically reduced and the melting point of the metal (the first metal) is lowered by the eutectic reaction, so that the electrolytic reduction can be effectively performed at a relatively low temperature, , The reduction metal (first metal) is obtained in the form of a liquid alloy (an alloy of the first metal and the second metal) by the process reaction, so that contamination by oxygen can be remarkably prevented. Further, even if the metal oxide contained in the raw material is a substance which is difficult to be electrolytically reduced by the metal, the difference between the standard redox potential difference between the second metal which is the metal of the liquid metal cathode and the first metal, There is an advantage that the metal oxide can be easily reduced. That is, when a metal having a positive standard reduction potential than the standard reduction potential of the first metal is used as the metal of the liquid metal negative electrode, the standard reduction potential value of the first metal is shifted in the positive direction by the liquid metal negative electrode The electrolytic reduction of the metal can be made easier.

Further, the metal refining method of the present invention is a refining method of a metal according to the present invention, in which a liquid alloy obtained by electrolytic reduction is solidified and then a solid alloy is electrolytically refined to obtain a desired metal, (Productivity) can be greatly improved, which is advantageous for commercialization. In addition, electrolytic refining is performed in the form of an ingot having a good conductivity by solidifying a liquid-phase alloy, so electrolytic refining can be effectively and easily performed without any other pretreatment other than the shape processing. Particularly, when electrolytic refining is performed by solidification, it is advantageous in terms of efficiency because it is easy to raise the reaction area during refining.

In the metal refining method according to an embodiment of the present invention, the metal oxide contained in the raw material may satisfy the following chemical formula (1).

(Formula 1)

M _x O _y

Wherein M is a metal which is a metal to be reduced and is a metal having a negative standard reduction potential with respect to a standard reduction potential of a second metal which is a metal of the liquid metal cathode, x is a natural number of 1 to 3, y is It is a natural number from 1 to 4.

The metal oxide according to Formula 1 is an oxide of the first metal having a negative standard reduction potential that is lower than the standard reduction potential of the second metal that is the metal of the liquid metal cathode, Even if the standard reduction potential value is increased in the positive direction, even if the metal oxide is difficult to electrolytically reduce, it can be easily reduced to a metal.

Examples specific one, the metal oxide is _{ZrO 2, TiO 2, WO 3} , Fe 2 O 3, Fe 3 O 4, NiO, ZnO, Co 3 O 4, MnO, Cr 2 O 3, Ta 2 O 5, Ga 2 O ₃ , Pb ₃ O ₄ , SnO and Ag ₂ O. However, the present invention is not limited by the kind of the metal oxide.

In other words, the metal refining method according to an embodiment of the present invention includes the steps of: selecting a metal (first metal) to be refined; Selecting a metal (second metal) of a liquid metal cathode forming a common eutectic phase with a selected metal (first metal); And electrolytically reducing the raw material containing the oxide of the selected metal using the selected liquid metal cathode. Also, the step of selecting the second metal may include forming a eutectic phase with the first metal and, at the same time, performing a standard reduction of the first metal more than the standard reduction potential of the first metal, And selecting the metal having the dislocation as the metal (second metal) of the liquid metal cathode.

The liquid metal cathode can be used as long as it meets the above-mentioned conditions of eutectic phase formation and conditions that have a standard reduction potential higher than the standard reduction potential of the first metal. However, in order to have a process temperature as low as possible with the eutectic phase formation, it is advantageous that the second metal satisfies the above-mentioned conditions and has a low melting point.

Further, in the metal refining method according to an embodiment of the present invention, after the electrolytic reduction is performed, the liquid alloy of the first metal and the second metal obtained in the electrolytic reduction process is solidified, and electrolytic refining of the solidified alloy is performed do. Accordingly, it is advantageous that the second metal, which is the metal of the liquid metal cathode, is a metal that does not solubilize the first metal as much as possible and that forms an intermetallic compound with the first metal. This is because when the second metal forms a solid solution with the first metal or when the solubility limit of the first metal is high, the diffusion rate of the first metal from the center of the solidified alloy to the surface The speed of electrolytic refining is determined by the electrolytic refining process, and the electrolytic refining efficiency is significantly lowered.

Accordingly, the step of selecting the second metal may include forming a eutectic phase with the first metal, and performing a standard reduction of the first metal relative to the standard reduction potential of the first metal based on the standard reduction potential of the first metal. And a metal having a dislocation and forming an intermetallic compound with the first metal as a metal (second metal) of the liquid metal cathode.

 As a specific example, the metal (second metal) of the liquid metal cathode may be selected from one or more of Cu, Sn, Zn, Pb, Bi, Cd and their alloys, It is not.

As described above, the refining method according to an embodiment of the present invention is advantageous in that it can minimize the contamination of oxygen (oxygen impurities) and also reduce the metal oxide which is difficult to electrolytically reduce at a relatively low processing temperature. With these advantages, the refining process according to the present invention is particularly advantageous in replacing the method of making zirconium or titanium based on the conventional crawling process. That is, the refining method according to one embodiment of the present invention may be a refining method of zirconium or titanium, and may be replaced with a commercial crawling process, and refining of zirconium or titanium that can minimize contamination with oxygen Lt; / RTI >

When the desired metal is zirconium or titanium, the liquid metal cathode forms a eutectic phase with zirconium (or titanium) and has a positive standard reduction potential greater than the standard reduction potential of zirconium (or titanium) And may be a metal forming an intermetallic compound. When the target metal is zirconium or titanium, copper is one example of a specific liquid metal cathode. Copper is substantially free of zirconium (or titanium), and in a wide variety of compositions, zirconium (or titanium) and intermetallic compound Which is advantageous. In addition, copper can facilitate the electrolytic reduction reaction of zirconium oxide (or titanium oxide), which has a difference in standard reduction potential from zirconium (or titanium), which is difficult to electrolytically reduce. Furthermore, as described above, contamination with oxygen can be prevented by the common phase using the liquid metal cathode, and when the liquid metal cathode is copper, the amount of dissolved oxygen in the copper is very low, and the alloy and / It is possible to remarkably reduce the oxygen content of the metal. As a specific example, when the target metal is zirconium or titanium, the oxygen content of the metal obtained by alloying and / or electrolytic refining can be controlled to less than 1000 ppm by using the liquid metal cathode as copper

1 is a process diagram showing an electrolytic reduction step in a refining method according to an embodiment of the present invention. 1, the electrolytic reduction includes a liquid metal cathode (molten metal in FIG. 1), an electrolyte (molten salt in FIG. 1), and an anode (anode in FIG. 1) and a reference electrode Lt; / RTI > During electrolytic reduction, a raw material containing a metal oxide is contained in the electrolyte and an electrolytic reduction process can be performed. At this time, the metal oxide may be in powder form, and it is advantageous that the average particle size is 100 μm or less, specifically 1 μm to 20 μm so as to be stably dispersed in the electrolyte.

The electrolyte in the electrolytic reduction step may be a molten salt in which the halide of one or more selected metals in the alkali metal and alkaline earth metal groups is melted. More specifically, the electrolyte in the electrolytic reduction step is a halide of one or more metals 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 May be a molten molten salt. Wherein the halide may comprise chloride, fluoride, bromide, iodide or mixtures thereof. It is preferable to use a salt having a higher boiling point of the electrolyte so that the metal used as the cathode is melted (liquid-phase negative electrode). In this respect, it is advantageous that the electrolyte in the electrolytic reduction process is chloride, and calcium chloride (CaCl ₂ ) is more advantageous.

The electrolyte in the electrolytic reduction step may further comprise an additive which is an oxide of one or more metals selected from the group consisting of alkali metals and alkaline earth metals. The content of the additive may be 0.1 to 25% by weight based on the total weight of the electrolyte. As a specific example, the oxides of the metal selected from the group of alkali metals and alkaline earth metals may include Li ₂ O, Na ₂ O, SrO, Cs ₂ O, K ₂ O, CaO, BaO or mixtures thereof. The oxide of the metal contained in the electrolyte is advantageous because it enables easier reduction of the metal oxide contained in the raw material.

For example, when the metal to be produced is zirconium, the raw material contains zirconium oxide, the liquid metal cathode is copper, and the electrolyte does not contain any of the additives described above, When the electrolyte contains the above-mentioned additive, the indirect reduction reaction, which is a reaction selected from one or more of the following Reaction Schemes 2 to 4, is possible, so that the metal oxide can be more effectively reduced at a lower cathode potential.

(Scheme 1)

ZrO ₂ + Cu + 4e ^- ? CuZr + 2O ^{2 -}

At this time, the product oxygen ion after the reaction can be converted into CO ₂ , CO or O ₂ depending on the anode used.

(Scheme 2)

ZrO ₂ + CaO - > ZrCaO ₃

ZrCaO ₃ + Cu + 4e ^- ? CuZr + CaO + 2O ^{2 -}

In the reaction of the reaction formula (2), the compound is formed by the reaction of the electrolyte additive and the zirconium oxide in the first stage by the reaction of the two stages, and then the compound is electrolytically reduced at the second stage to produce the copper-zirconium alloy.

(Formula 3)

Ca ^{2 +} + 2e ^- ? Ca

2Ca + ZrO ₂ + Cu? CuZr + 2CaO

The reaction of Scheme 3 is a two-step reaction in which calcium ion is reduced to calcium in the first stage and calcium produced in the second stage is chemically reacted with the zirconium oxide to form a zirconium metal. As the reaction occurs in the liquid copper cathode, Finally, a copper-zirconium alloy can be formed.

(Scheme 4)

ZrO ₂ + CaO - > ZrCaO ₃

Ca ^{2 +} + 2e ^- ? Ca

_{3Ca + CaZrO 3 + Cu → CuZr} + 3CaO

The reaction of Reaction Scheme 4 is a three-step reaction. In Step 1, an electrolyte additive and zirconium oxide react to form a compound. In Step 2, calcium ions are reduced to calcium through an electrolytic reduction process. A zirconium metal can be produced. At this time, as the electrolytic reduction process and the chemical reduction process occur in the liquid copper cathode, the copper-zirconium alloy can be finally produced by reacting with metal zirconium and liquid metal copper.

The current density at the electrolytic reduction step is sufficient for a current density capable of stable electrolytic reduction. As a specific example, the current density at the electrolytic reduction step may be 100 to 1000 mA / cm ² , more specifically 300 to 700 mA / cm ² , but is not limited thereto. The time during which the electrolytic reduction step is performed may be the time for which all the metal oxides are reduced. For example, the electrolytic reduction step may be performed for 30 minutes to 8 hours, but the time during which the electrolytic reduction is performed may be appropriately controlled in consideration of the amount of the metal oxide to be added, It is needless to say that it can not be limited by time. In addition, the potential applied to the negative electrode during the electrolytic reduction step may be such that a stable reduction reaction can occur. As a specific example, the potential applied to the cathode may be -0.3 to -4 V relative to the hydrogen reduction potential, but is not limited thereto.

An anode or a reference electrode can be used if it is a positive electrode or a reference electrode conventionally used for electrolytic reduction of a metal oxide. As a specific and non-limiting example, graphite or the like may be used as the anode, and W (pesudo) or the like may be used as the reference electrode, but it goes without saying that the present invention can not be limited by the anode or the reference electrode material.

The process temperature of the electrolytic reduction process may be a temperature above the melting point of the electrolyte and the melting point of the liquid metal cathode. However, in terms of preventing excessive energy consumption while maintaining a stable molten phase, the temperature difference between the melting point of the electrolyte and the melting point of the metal material of the liquid metal cathode, which is relatively higher than the melting point, is 10 to 200 ° C good. As a practical example, if the electrolyte is CaCl ₂ molten salt and the metal used as the cathode is copper, the process temperature at which electrolytic reduction is performed may be from 1100 ° C to 1200 ° C.

In the refining process according to an embodiment of the present invention, the alloy (liquid alloy) obtained by electrolytic reduction preferably contains 2.1% by weight or more of the first metal, more preferably 7% by weight, It is preferable to contain at least 16% by weight of the first metal.

As described above, when the electrolytic reduction step is completed after the electrolytic reduction step, the liquid metal cathode is converted to the liquid alloy. Thereafter, as the liquid alloy solidifies and the solid alloy is electrolytically refined, when the first metal contained in the liquid alloy is 2.1% by weight or less, a continuous mass transfer path of the first metal in the solid alloy is not formed, There is a risk that it will not be done. In detail, as the liquid alloy solidifies, the solid phase alloy has a microstructure structure in which a phase of the first metal, which is the metal of the liquid metal cathode, and a phase of the intermetallic compound of the first metal and the second metal coexist (microstructure). When the content of the second metal contained in the alloy is 2.1 wt% or less, the structure of the solid-state alloy is such that the intermetallic compound of the first metal and the second metal forms a matrix of the first metal in an island- Or the like. In such a case, the second metal is trapped in the matrix during the electrolytic refining of the solid-phase alloy, so that it is difficult to escape out of the solid-state alloy.

Thus, the liquid alloy contains at least 2.1 wt% of the first metal, and in the structure structure of the solid phase alloy, intermetallic compound phases of the first metal and the second metal are continuously connected to each other, It is necessary to provide a material movement path of the metal so that the electrolytic refining can be performed.

Specifically, the liquid alloy may contain at least 2.1 wt.% Of the intermetallic compound of the first metal and the second metal such that the intermetallic compound of the first metal and the triple point of the first metal grain can stably form a continuum. The first metal is preferably contained, more preferably, at least 7 wt% of the first metal.

The intermetallic compound grains of the first metal and the second metal themselves can stably form an intermetallic compound in a continuous manner (for example, without interposing a first metal grain, a triple point, etc.) continuum, the liquid alloy preferably contains at least 16% by weight of the first metal. At this time, the upper limit of the first metal content in the substantial liquid alloy may be 70% by weight.

At this time, the first metal content in the alloy can be controlled by controlling the mass of the liquid metal cathode and the metal oxide charged into the electrolyte during the electrolytic reduction, and independently controlling the time during which the electrolytic reduction is performed . As a specific example, the metal oxide is reduced in the liquid metal cathode during electrolytic reduction, and as the liquid metal cathode is converted into the alloy, the metal oxide to be charged into the electrolyte during the electrolytic reduction is converted into the metal (first metal) (First metal) of the metal oxide is 2.1% by weight or more, preferably 7% by weight or more preferably 16% by weight or more based on the total weight of the metal (second metal) Or more, so that the first metal content in the alloy can be controlled. Alternatively, the first metal content in the alloy can be controlled by controlling the time during which electrolytic reduction is performed after a certain amount of metal oxide is input to the electrolyte.

After the electrolytic reduction is completed, cooling for solidification of the liquid alloy can be performed. At this time, since the first metal and the second metal are homogeneously mixed in the liquid alloy, the structure of the alloy obtained after solidification by the cooling rate of the liquid alloy is greatly influenced. The cooling rate can be controlled by controlling the temperature of the liquid metal cathode (electrolysis) so that an intermetallic compound phase can be stably formed and a structure of intermetallic compound phases of the first metal and the second metal are continuously connected to each other. Cooling process temperature) to room temperature and a cooling rate of 20 DEG C / min or less. If the cooling rate is excessively fast out of the range suggested, an intermetallic compound may not be formed or a structure in which fine intermetallic compound particles are embedded in the first metal matrix in a large amount may be obtained, and a continuous and fast first metal substance There is a risk that the movement path can not be formed. At this time, if the cooling of the liquid metal cathode is excessively slow, the advantages over the microstructure are negligible, but as the time required for the process becomes excessively long, the cooling rate is substantially 1 DEG C / min or more, more practically 5 DEG C / min Or more.

However, the present invention is not limited to solidification by direct slow cooling of the liquid alloy obtained by electrolytic reduction. As a specific example, the liquid alloy obtained by electrolytic reduction is solidified, and then the alloy is cast into a designed shape suitable for electrolytic refining through molding and heat treatment using powder of solidified alloy or casting using a melt (reflow) of solidified alloy And cooling may be performed at a cooling rate of 20 DEG C / min or less in this forming step. That is, the above-described slow cooling may be performed at the stage of producing a solid phase alloy used for electrolytic refining.

After the electrolytic reduction step described above, an electrolytic refining step may be performed in which the alloy is solidified to obtain a solid-phase alloy, electrolytically refining the solid-phase alloy, and recovering the first metal from the alloy. At this time, a step of removing the remaining electrolyte from the product obtained in the electrolytic reduction step may be further performed before the electrolytic refining of the product (solidified alloy) obtained in the electrolytic reduction step. The residual electrolyte removal step may include a step of subjecting the product obtained in the electrolytic reduction step to heat treatment in a vacuum or an inert gas atmosphere to distill off the electrolyte. The distillation temperature (heat treatment temperature) should be at least the melting point of the electrolyte used in the electrolytic reduction step. As a specific example, the distillation temperature may be 780 to 900 ° C, but is not limited thereto. In order to more effectively prevent the product obtained in the electrolytic reduction step from being oxidized again, it is preferable to use an inert gas to facilitate the distillation process in a vacuum atmosphere. The residual electrolyte removal process is a process in which the product (solidified alloy) obtained in the electrolytic reduction step is carried out in the solid phase state, so that the cooling rate is not particularly controlled in the case of performing the residual electrolyte removal process on the product obtained by the above- You do not have to.

2 is a process diagram showing a process of electrolytic refining in the refining method according to an embodiment of the present invention. As shown in Fig. 2, the electrolytic refining is performed in the same manner as in Example 1 except that the anode (anode of Fig. 1), the electrolyte (the molten salt of Fig. 2) and the cathode 2 < / RTI > reference electrode).

The electrolyte during electrolytic refining may be a molten salt in which a halide of one or more metals selected from the group of alkali metals and alkaline earth metals is melted independently of the electrolyte in the above electrolytic reduction step. More specifically, the electrolyte of the electrolytic refining process is a mixture of an alkali metal containing Li, Na, K, Rb and Cs and a halide of one or more metals selected from the group of alkaline earth metals including Mg, Ca, Sr and Ba May be a molten molten salt. Wherein the halide may comprise chloride, fluoride, bromide, iodide or mixtures thereof.

In order to lower the electrolytic refining process temperature, one or more of the electrolytes of the electrolytic refining process may be selected from LiCl, KCl, SrCl ₂ , CsCl, NaCl, LiF, KF, SrF ₂ , CsF, CaF ₂ and NaF . At this time, two or more salts may form a eutectic salt. More specifically, the electrolyte in the electrolytic refining process may comprise lithium halide and sodium halide, and more specifically, the electrolyte in the electrolytic refining process may comprise lithium fluoride and potassium fluoride. The temperature of the electrolytic refining step may be equal to or higher than the melting temperature of the electrolytic refining step. As a specific example, the temperature of the electrolytic refining process may be 600 to 800 ° C, but is not limited thereto. At this time, the electrolyte of the electrolytic refining process may further include an additive such as zirconium fluoride (ZrF ₄ ), and the additive may be contained in an amount of 1 to 10 wt% based on the total weight of the electrolyte.

The current density at the electrolytic refining step may be a current density at which stable electrodeposition of the first metal can occur. As a specific example, the current density at the electrolytic refining step may be 10 to 500 mA / cm ² , more specifically 50 to 200 mA / cm ² , but is not limited thereto. The time at which the electrolytic refining step is performed is not particularly limited, but may be performed for 1 to 20 hours.

The cathode or the reference electrode can be used as a cathode or a reference electrode which is commonly used for electrolytic refining of a metal. For example, stainless steel or the like may be used as the cathode and W (pesudo) or the like may be used as the reference electrode. However, it is needless to say that the present invention can not be limited by the cathode or the reference electrode material.

Hereinafter, zirconium is used as a target metal to provide an example of the actual metal refining according to the present invention, but the present invention is not limited to the embodiment shown.

(Example)

20 g of zirconium oxide (average particle size 4.5 탆) was used as a raw material, 30 g of copper was used as a negative electrode, and CaCl ₂ containing 5 wt% CaO was used as an electrolyte using an electrolytic reduction tank similar to that of Fig. 1 Graphite as the anode, and tungsten as the reference electrode. The reducing bath was heated to 1110 DEG C to melt the copper and the electrolyte of the negative electrode. The current density of the electrolytic reduction process was 500 mA / cm ^{2. The} anode potential was -1.3 to -1.5 V versus the tungsten reduction potential, and the electrolytic reduction process was performed for 0.9 hours, 1.6 hours, 3.3 hours, or 6.5 hours. After completion of the electrolytic reduction process, the crucible was slowly cooled at a rate of 15 캜 / min to obtain a solidified Zr-Cu alloy. After that, the Zr-Cu alloy was heat-treated at 850 캜 in an argon gas atmosphere of 10 ^-3 torr The remaining electrolyte was removed.

The Zr-Cu alloy containing 3.2% by weight of zirconium (hereinafter referred to as 3% Zr-Cu alloy) was subjected to electrolytic reduction for 0.9 hours as a result of measurement of the content of Zr contained in the Zr- (Hereinafter referred to as 7% Zr-Cu alloy) containing 7.49% by weight of zirconium was produced when electrolytic reduction was performed for 1.6 hours, and it was confirmed that the Zr- (Hereinafter referred to as a 16% Zr-Cu alloy) containing 16.42% by weight of zirconium was produced when electrolytic reduction was performed during the electrolytic reduction for 6.5 hours, and 27.47% by weight Zr-Cu alloy containing zirconium (hereinafter referred to as 27% Zr-Cu alloy) was produced.

Oxygen concentration of the 3% Zr-Cu alloy was 142 ppm, the oxygen concentration of the 7% Zr-Cu alloy was 132 ppm, and the oxygen content of the 16% Zr-Cu alloy was measured using the ELTRA ONH2000 apparatus. It was confirmed that the oxygen concentration of all the alloys prepared with 223 ppm of oxygen concentration and 249 ppm of 27% Zr-Cu alloy was less than 300 ppm, and it was confirmed that alloys substantially free from oxygen were produced regardless of the electrolytic reduction process time .

FIG. 3 is a scanning electron microscope (SEM) image of a structure of a 3% Zr-Cu alloy, FIG. 4 is a scanning electron microscope photograph showing a structure of a 7% Zr- 6 is a scanning electron microscope (SEM) image of a structure of 27% Zr-Cu alloy. In the scanning electron microscope photographs of FIGS. 3 to 6, an EDS (Energy Dispersive Spectrometer) element analysis result of a spot indicated by a red dot is also shown. As can be seen from the EDS elemental analysis, in the scanning electron microscope photographs of FIGS. 3 to 6, it can be seen that the deep gray is Cu grain and the light gray is the Cu-Zr intermetallic compound.

As can be seen from FIGS. 3 to 6, Cu-Zr intermetallic compounds are formed in the grain boundaries of copper, and when the content of zirconium in the alloy is not less than 3% by weight, a continuum connecting the copper grains is formed. Further, when the content of zirconium in the alloy is 16 wt% or more, it can be confirmed that Cu-Zr intermetallic compound grains themselves are in contact with each other to produce a continuum of Cu-Zr intermetallic compound.

7 is a graph showing the results of X-ray diffraction analysis of a 7% Zr-Cu alloy (red graph in FIG. 7) and a 27% Zr-Cu alloy (black graph in FIG. 7). As can be seen from FIG. 7, an alloy consisting of intermetallic compound phases of Cu-Zr (CuZr, Cu ₅ Zr ₁ , Cu _0.44 Zr _0.565 ) was produced together with copper.

Thereafter, a solidified Cu-Zr alloy (3% Zr-Cu alloy, 7% Zr-Cu alloy, 16% Zr-Cu alloy or 27% Zr-Cu alloy) , A LiF-KF eutectic salt containing 2.5 wt% of ZrF ₄ was used as an electrolyte, stainless steel was used as a cathode, and tungsten was used as a reference electrode. The electrolytic refining process temperature was 650 ° C and electrolytic refining was performed at a current density of 100 mA / cm ² for 10 hours.

Fig. 8 is a graph showing the optical photographs of the cathodes and the positive electrodes (27% Zr-Cu alloy) observed after completion of the electrolytic refining, the electrolytic refining 2 hours and 10 hours after electrolytic refining, A scanning electron microscope photograph of a red region observed with a scanning electron microscope and an analysis result of an EDS element analysis of a red region.

As can be seen from FIG. 8, as the electrolytic refining progresses, it can be seen that pure Zr is electrodeposited and recovered to the cathode. As a result of measuring the mass of total Zr recovered through electrodeposition, the theoretically possible recovery amount (27% Zr-Cu Alloy) was recovered.

9 is a scanning electron microscope (SEM) image of a section of the anode after completion of electrolytic refining for 10 hours. As can be seen from FIG. 9, as the zirconium depletion region is formed from the surface to the center as the zirconium escapes, and the electrolytic refining progresses, the zirconium depletion region gradually progresses to the center of the anode. This means that continuum of the zirconium-copper alloy (zirconium-copper intermetallic compound) that provides a stable pathway of the zirconium between the centers at the surface in the zirconium lean area continues to remain even though the zirconium escapes from the anode surface do. Zirconium The composition of the surface region and the inner central region, which is a lean region of zirconium, was analyzed by EDS elemental analysis of arbitrary 10 regions in the anode cross section of Figure 9. As a result, the average zirconium content of the zirconium lean region was 2.1 wt% And the average zirconium content in the inner central region, which is relatively light gray, was 25.98 wt%. As a result, it can be seen that the minimum zirconium content in the solidified alloy for electrolytic refining of zirconium is 2.1 wt%. As a result of the electrolytic refining test using 3% Zr-Cu alloy, 7% Zr-Cu alloy or 16% Zr-Cu alloy, it was confirmed that the electrodeposition of zirconium was continued, similar to the result of 27% Zr- , It was confirmed that the content of zirconium in the surface region, which is a zirconium lean region, was 2.1 wt% within the error range. In order to experimentally confirm the effect of the zirconium migration route by the zirconium-copper intermetallic compound on electrolytic refining, the Zr-Cu alloy containing 1.2 wt% zirconium was obtained by controlling the process time of the electrolytic reduction process , And electrolytic refining tests were carried out in the same manner. 10 is a scanning electron microscopic (SEM) image of a Zr-Cu alloy containing 1.2% by weight of zirconium. As shown in FIG. 10, the intermetallic compounds of zirconium-copper are not connected to each other, The electrolytic refining test showed that the Zr-Cu alloy containing 1.21% by weight of zirconium did not recover the zirconium by electrodeposition even during the electrolytic refining process for 10 hours Respectively.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Those skilled in the art will recognize that many modifications and variations are possible in light of the above teachings.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (9)

A raw material containing the metal oxide is electrolytically reduced by using a liquid metal cathode forming a eutectic phase with a first metal which is a metal of a metal oxide to form a second metal which is a metal of the liquid metal cathode An electrolytic reduction step of producing an intermetallic alloy; And
An electrolytic refining step of electrolytically refining the solidified alloy, and recovering a first metal from the alloy;
/ RTI >
Wherein the electrolyte in said electrolytic reduction step comprises an additive that is a molten salt of a halide of one or more metals selected from the group of alkali metals and alkaline earth metals and an oxide of one or more metals selected from the group of alkali metals and alkaline earth metals, Metal refining method. The method according to claim 1,
Wherein the metal oxide satisfies the following formula (1).
(Formula 1)
M _x O _y
Wherein M is a metal which is a metal to be reduced and is a metal having a negative standard reduction potential relative to a standard reduction potential of a second metal which is a metal of the liquid metal cathode, x is a natural number of 1 to 3, and y Is a natural number from 1 to 4.) The method according to claim 1,
The metal oxide is _{ZrO 2, TiO 2, WO 3} , Fe 2 O 3, Fe 3 O 4, NiO, ZnO, Co 3 O 4, MnO, Cr 2 O 3, Ta 2 O 5, Ga 2 O 3, Pb ₃ O ₄ , SnO, and Ag ₂ O. delete delete The method according to claim 1,
Wherein the solidification of the alloy obtained in the electrolytic reduction is slowly cooled to a solidified state at a cooling rate of 20 DEG C / min or less at a temperature of the liquid metal cathode at the electrolytic reduction. The method according to claim 6,
Wherein the temperature of the liquid metal cathode is between 1100 ° C and 1200 ° C. 7. The method according to any one of claims 1 to 3 and 6 to 7,
Wherein the alloy contains at least 2.1 wt% of the first metal. 9. The method of claim 8,
Wherein the liquid metal cathode is a liquid copper cathode, and the metal oxide comprises zirconium oxide.

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