KR102402182B1 - Method for refining metal through molten salt electrolysis-vacuum distillation process of various raw materials containing target metal oxide - Google Patents

Abstract

The present invention relates to a method for refining a metal through molten salt electrolysis-vacuum distillation of various raw materials containing a target metal oxide, and includes a step (S10) of putting a raw material including a primary resource or secondary resource containing a target metal oxide into an electrolytic cell provided with a liquid metal cathode at the bottom and containing electrolyte salt to form an alloy between the liquid metal cathode and a target metal through molten salt electrolysis and a step (S20) of vacuum distilling the alloy to recover the target metal (S20).

Description

METHOD FOR REFINING METAL THROUGH MOLTEN SALT ELECTROLYSIS-VACUUM DISTILLATION PROCESS OF VARIOUS RAW MATERIALS CONTAINING TARGET METAL OXIDE

The present invention relates to a metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing a target metal oxide. It relates to a method for manufacturing a metal.

Magnesium (Mg) has excellent properties of high strength relative to weight, and thus is used in various fields, and in particular, attracts attention in the automobile industry.

In addition, magnesium has a wide range of applications in the biomedical industry, and when magnesium is used in implants, it can reduce implant fractures compared to other materials such as biopolymers and bioceramics. Accordingly, a compound annual growth rate (CAGR) of 5% is expected for global magnesium consumption from 2017 to 2027.

Conventionally, as a commercial magnesium production process, primary resources such as dolomite (MgCO ₃ CaCO ₃ ), magnesite (MgCO ₃ ) and brine are used as raw materials to produce Mg metal through thermal reduction or electrolysis. . At this time, the reserve of the primary resource is sufficient to satisfy the present and future demand for Mg metal.

However, the pigeon process, which accounts for more than 80% of the thermal reduction method, is a technology for producing magnesium through thermal reduction in a vacuum atmosphere using ferrosilicon as a reducing agent at a high temperature after calcining dolomite. (batch) production capacity is low, sulfur oxide (SO _x ) gas is generated when magnesium is manufactured using coal as a heat source, and the impact on global warming is larger than other processes because of the large amount of carbon dioxide gas generated. have.

In contrast, the electrolysis method is a method of producing magnesium through a molten salt electrolysis process using anhydrous chloride such as anhydrous magnesium chloride (MgCl ₂ ) or anhydrous canalite (MgCl ₂ ·KCl) obtained from various raw materials. Although there is little greenhouse gas generation, a lot of process energy is required to manufacture anhydrous chloride, and iron is mixed into magnesium produced due to iron (Fe) used as a cathode, which causes a decrease in magnesium corrosion resistance, and chlorine (Cl ₂ ) gas during electrolysis There is a disadvantage that occurs.

In order to solve these shortcomings, several studies have been conducted to develop an eco-friendly and efficient process for producing magnesium (Mg) metal from magnesium oxide (MgO).

Among them, the most promising process is the SOM (Solid Oxide Membrane) process. The SOM process is a direct Mg metal manufacturing method using MgO using a Yttria-Stabilized-Zirconia (YSZ) membrane, and does not require an anhydrous chloride manufacturing process because magnesium oxide is used as _a raw material. ) is an eco-friendly process that generates gas.

However, the price of the YSZ membrane used as the separator is high, damage and material deterioration due to thermal shock occur during the process, and if argon (Ar) gas bubbling is not performed during electrolysis, the current efficiency is reduced from 90% to 40% It has a problem of reducing to 50%.

Republic of Korea Patent Publication No. 10-1142508

The present invention is to solve the problems of the prior art described above, and an object of the present invention is to achieve high purity through molten salt electrolysis process and vacuum distillation of raw materials using a liquid metal anode that does not require production of anhydrous chloride and does not generate chlorine gas. It is to provide a high-efficiency, eco-friendly metal smelting method that can manufacture metal of

Furthermore, in the present invention, by using the primary resource and the secondary resource including the target metal oxide as a raw material, it is possible to enhance competitiveness and satisfy the increasing demand.

In order to achieve the above object, the present invention injects a raw material including a primary resource or a secondary resource containing a target metal oxide into an electrolytic cell having an electrolytic salt provided at the bottom of the liquid metal anode, and liquid through molten salt electrolysis forming an alloy between the metal cathode and the target metal (S10); And by vacuum distilling the alloy to recover the target metal (S20) molten salt of various raw materials containing the target metal oxide - provides a metal smelting method through vacuum distillation.

Before the step S10, the target metal oxide-containing primary or secondary resource is characterized in that it undergoes a pretreatment step according to the type.

The target metal oxide is characterized in that it comprises at least one selected from the group consisting of magnesium oxide, beryllium oxide, lithium oxide, antimony oxide, zinc oxide, lead oxide, gallium oxide, tin oxide and manganese oxide.

The target metal oxide is characterized in that magnesium oxide.

The primary resource is characterized in that it includes at least one selected from the group consisting of magnesite containing magnesium oxide, seawater MgO clinker, brine MgO, and dolomite.

The secondary resource is characterized in that it includes at least one selected from the group consisting of ferronickel slag containing magnesium oxide and MgO-C refractories.

The pretreatment step is characterized in that the raw material is calcined at 1000 K to 1200 K.

The pretreatment step is characterized in that the raw material is dried at 300 K to 500 K.

The pretreatment step may include: using distilled water to react the raw material with a mineral solution concentration of 5% to 25% at 250 K to 400 K for 50 hours to 100 hours; and drying at 300 K to 500 K after the reaction is completed.

The metal of the liquid metal negative electrode is characterized in that it comprises at least one selected from the group consisting of Cu, Sn, Ag and Al.

The electrolyte salt is characterized in that it comprises at least one selected from the group consisting of alkali metal halides, alkaline earth metal halides, alkali metal oxides and alkaline earth metal oxides.

The step S10 is characterized in that a current of 0.5 A to 2 A is applied at 1000 K to 1100 K for 8 hours to 16 hours.

It is characterized in that it further comprises a preliminary electrolysis step before the step S10, and performs the step S10 using the electrolytic salt that has undergone the preliminary electrolysis step.

The preliminary electrolysis step may include: charging a crucible containing the electrolyte salt into a reactor in which a cathode and an anode are installed; and applying a current of 0.01 A to 0.3 A at 1000 K to 1150 K for 1 hour or more to remove impurities.

The step S20 is characterized in that the distillation is performed for 6 hours to 13 hours at 1100 K to 1500 K under vacuum conditions.

In addition, the present invention includes the steps of pre-treating Bukhan magnesite or MgO-C refractory material containing magnesium oxide as a raw material (S11); Forming an alloy between the liquid metal anode and the target metal through molten salt electrolysis by putting the pre-treated raw material into an electrolyzer having an electrolytic salt provided at the bottom of the liquid metal anode (S21); And separating the alloy and recovering the target metal by vacuum distillation (S31), molten salt electrolytic-vacuum distillation of North Korean magnesite or MgO-C refractory material is provided.

The step S11 is characterized in that the raw material is calcined at 1000 K to 1200 K.

The step of pulverizing the North Korean magnesite to a particle size of less than 300 μm between steps S11 and S21 may be further included.

In addition, the present invention comprises the steps of pre-treating magnesium oxide-containing ferronickel slag as a raw material (S12); Forming an alloy between the liquid metal anode and the target metal through molten salt electrolysis by inputting the pre-treated raw material into an electrolytic cell having a liquid metal anode provided at the bottom inside and containing an electrolytic salt (S22); and separating the alloy and recovering the target metal by vacuum distillation (S32).

The step S12 may include: using distilled water to react the raw material with a mineral solution concentration of 5% to 25% at 250 K to 400 K for 50 hours to 100 hours; and drying at 300 K to 500 K after the reaction is completed.

According to the method for smelting metal through electrolytic-vacuum distillation of molten salt of various raw materials containing a target metal oxide according to the present invention, molten salt is used as a raw material using primary and secondary resources that have undergone appropriate pretreatment depending on the type By manufacturing the target metal through the electrolysis and vacuum distillation steps, it is possible to manufacture a high-purity metal without problems caused by the prior art.

In particular, since secondary resources, which are industrial wastes, are used as raw materials, mining and beneficiation processes in primary resources are not required, thereby protecting the environment. This can be prevented, and it is economical and can secure excellent competitiveness by recycling waste that has to be buried in the past.

1 shows a flow chart of a metal smelting method according to the present invention.
Figure 2 is a graph showing the theoretical decomposition voltage of the electrolytic salt and MgO in an embodiment of the present invention.
3 is a graph showing changes in the vapor pressure of Mg according to the concentration and temperature of Mg in the Mg-Cu alloy in an embodiment of the present invention together with the Mg-Cu phase diagram.
4 is a schematic diagram and a photograph of a molten salt electrolysis apparatus for performing a metal smelting method according to the present invention.
5 is a schematic diagram and a photograph of a vacuum distillation apparatus for performing a metal smelting method according to the present invention.
6 is a photograph of a raw material used in an embodiment of the present invention.
7A is an XRD measurement result before performing pretreatment of the raw material used in an embodiment of the present invention.
7B is an XRD measurement result after pretreatment of the raw material used in an embodiment of the present invention.
8 is (a) a SEM photograph of a cross-section of ferronickel slag before aging and (b) a SEM photograph of a cross-section of ferronickel slag after aging.
9 is a photograph of an Mg-Cu alloy recovered as a result of molten salt electrolysis in an embodiment of the present invention.
10 is an XRD analysis result of the Mg-Cu alloy recovered as a result of molten salt electrolysis in an embodiment of the present invention.
11 is an SEM and EDS analysis result of the Mg-Cu alloy recovered as a result of molten salt electrolysis in an embodiment of the present invention.
12 is a cross-sectional photograph of an electrolysis cell after molten salt electrolysis in an embodiment of the present invention using MgO clinker as a raw material.
13 is (a) SEM analysis results and (b) line scan results of an Al ₂ O ₃ crucible and an Mg-Cu alloy contact surface in an embodiment of the present invention using calcined Bukhan-made magnet as a raw material.
14 is a SEM analysis result and line scan result of an Al ₂ O ₃ crucible and an Mg-Cu alloy contact surface when (a), (b) an oxidized MgO-C refractory material is used as a raw material in an embodiment of the present invention, ( c), (d) SEM analysis results and line scan results of Al ₂ O ₃ crucible and Mg-Cu alloy contact surface when seawater MgO clinker is used as raw material, (e), (f) Aged ferronickel slag as raw material SEM analysis results and line scan results of the Al ₂ O ₃ crucible and the Mg-Cu alloy contact surface when used, (g), (h) The Al ₂ O ₃ crucible and the Mg-Cu alloy contact surface when ferronickel slag is used as a raw material SEM analysis results and line scan results are shown.
15 is a photograph of an electrolytic salt obtained after electrolysis in an embodiment of the present invention using an oxidized MgO-C refractory material as a raw material.
16 is a photograph of Mg metal recovered after vacuum distillation in an embodiment of the present invention.
17 is a photograph of a residue recovered after vacuum distillation in an embodiment of the present invention.

Before describing the present invention in detail, the terms or words used herein should not be construed as being unconditionally limited to their ordinary or dictionary meanings, and in order for the inventor of the present invention to explain his invention in the best way It should be understood that the concepts of various terms can be appropriately defined and used, and furthermore, these terms or words should be interpreted as meanings and concepts consistent with the technical idea of the present invention.

That is, the terms used herein are only used to describe preferred embodiments of the present invention, and are not used for the purpose of specifically limiting the content of the present invention, and these terms represent various possibilities of the present invention. It should be understood that the term has been defined taking into account.

Also, in this specification, it should be understood that, unless the context clearly indicates otherwise, the expression in the singular may include a plurality of expressions, and even if it is similarly expressed in plural, it should be understood that the meaning of the singular may be included. .

When it is stated throughout this specification that a component "includes" another component, it does not exclude any other component, but further includes any other component unless otherwise stated. It could mean that you can.

In addition, if terms such as "one side", "other side", "one side", "other side", "first", "second" are used in this specification, with respect to one component, this one component is It is used to be clearly distinguished from other components, and it should be understood that the meaning of the component is not limitedly used by such terms.

In addition, in the following, in describing the present invention, a detailed description of a configuration determined that may unnecessarily obscure the subject matter of the present invention, for example, a detailed description of a known technology including the prior art may be omitted.

Hereinafter, the present invention will be described in more detail with reference to FIGS. 1 to 17 in order to help the understanding of the present invention.

According to the present invention, there is provided a metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing a target metal oxide. In the metal smelting method, a raw material including a primary resource or a secondary resource containing a target metal oxide is put into an electrolytic cell having an electrolytic salt provided at the bottom of the liquid metal anode, and a liquid metal cathode and a target through molten salt electrolysis forming an alloy between metals (S10); and vacuum distilling the alloy to recover the target metal (S20).

According to an embodiment of the present invention, in manufacturing a high-purity metal through molten salt electrolysis and vacuum distillation, a primary resource or a secondary resource including a target metal oxide may be used as a raw material.

The target metal oxide may include at least one selected from the group consisting of magnesium oxide, beryllium oxide, lithium oxide, antimony oxide, zinc oxide, lead oxide, gallium oxide, tin oxide, and manganese oxide. For example, the target metal oxide is one selected from the group consisting of MgO, BeO, LiO ₂ , Sb ₂ O ₃ , ZnO, Pb ₃ O ₄ , Ga ₂ O ₃ , SnO, SnO ₂ , MnO, and MnO ₂ . may include more than one. As a specific example, the target metal oxide may be magnesium oxide (MgO).

The primary resource may include a raw material obtained without processing from nature, for example, the primary resource is magnesite containing magnesium oxide, seawater MgO clinker, brine MgO and at least one selected from the group consisting of dolomite may include As a specific example, the primary resource may be North Korean magnesite or MgO clinker.

The secondary resource may include by-products or wastes generated in the industry using the primary resource, for example, the secondary resource is from the group consisting of ferronickel slag and MgO-C refractories containing magnesium oxide. It may include at least one selected type. By smelting metal using such secondary resources, there is an advantage of being environmentally friendly and economical by recycling industrial by-products or wastes.

The ferronickel slag may be an industrial byproduct of a ferronickel production process. In addition, the MgO-C refractory material may be an industrial waste that is disposed of after the MgO-C refractory brick used in a high-temperature industrial process such as the steel industry is used.

Such industrial by-products or industrial wastes may contain significant amounts of magnesium oxide. For example, the MgO concentration of the ferronickel slag and the MgO-C refractory material is reported to be 34.0% and 94.5%, respectively.

In addition, 9.45 million tons of Mg metal can be produced annually from Ferronickel slag and MgO-C refractory brick, which is the current Mg metal production using the world's primary resources. This figure significantly exceeds 1.12 million tons.

As such, by pre-treating industrial by-products or wastes containing MgO at a high concentration and using them as a raw material for the metal smelting method according to the present invention, it is possible to produce Mg metal in an amount that meets the demand and to secure excellent competitiveness. In particular, the demand for the Mg metal can be sufficiently met through smelting using only secondary resources.

When a MgO-containing primary resource or a raw material (MgO-containing feedstock) including a secondary resource is used, Mg metal may be manufactured through a flow as shown in FIG. 1 . Specifically, Mg alloy (Mg-Cu) is formed through MgO molten salt electrolysis using a high-density metal (Cu) cathode and high-purity Mg metal is recovered from the Mg alloy through vacuum distillation is divided into stages.

In molten salt electrolysis, 5 mass% of potassium chloride (KCl) relative to the mass of the mixed salt may be added to the MgF ₂ -LiF mixed salt of the eutectic composition in consideration of MgO solubility, dissolution temperature and viscosity to be used as an electrolyte salt. 2 below shows the theoretical decomposition voltage of electrolyte salt and MgO, MgO electrolysis may be stably possible without decomposition of the electrolyte used for MgO and electrolyte salt at 1000 K to 1100 K.

Cu metal uses high-density Cu as a cathode as a cathode in consideration of the density of Mg-Cu alloy, solubility of Mg in Cu, and the difference in vapor pressure between Mg and Cu. formed at the bottom. Specifically, the reaction at the Cu negative electrode is shown in Scheme 1 below, and the reaction at the graphite (C) anode is shown in Scheme 2 below. As the Mg-Cu alloy is formed on the bottom of the electrolytic cell, it is possible to prevent a recombination reaction between the Mg metal of the negative electrode and a reactive gas such as oxygen gas of the positive electrode from occurring.

[Scheme 1]

Mg ²⁺ (in molten salt) + 2 e ^- + Cu (s) = Mg-Cu (s,l)

[Scheme 2]

C (s) + O ² - (in molten salt) = CO ₂ (g) + 2 e ^-

According to an embodiment of the present invention, before the step S10, the target metal oxide-containing primary resource or the secondary resource may be subjected to a pretreatment step according to the type. Specifically, the pretreatment step may be a step of treating the primary resource or the secondary resource in an optimal state for use as a raw material of the metal smelting method according to the present invention.

As an example, in the pretreatment step, the raw material may be calcined at 1000 K to 1200 K, 1000 K to 1150 K, or 1000 K to 1100 K. For example, the calcination step may be performed using a box-type electric furnace.

Through the calcination step, it is possible to increase the MgO concentration of the primary resource or the secondary resource. For example, when magnesite from North Korea is used as a raw material, most of the magnesite from North Korea is composed of magnesium carbonate (MgCO ₃ ), and MgO is generated through calcination to increase the concentration of MgO. In particular, when calcining at a temperature within the above range, the reaction occurs smoothly to promote the production of MgO, and through this, a high-purity target metal can be manufactured through molten salt electrolysis and vacuum distillation according to the present invention.

In addition, in the case of MgO-C refractories, MgO and C are the main phases, and may be physically mixed. In addition, when the MgO refractory material is calcined in the above temperature range, the concentration of MgO relative to the same weight may be increased by reducing the amount of C through oxidation.

It may further include the step of pulverizing the raw material after the calcination. For example, the pulverizing step may be selectively performed on a raw material having a large particle size, and the pulverizing step may pulverize the particle size to 300 μm or less.

As another example, in the pretreatment step, the raw material may be dried at 300 K to 500 K, 320 K to 450 K, or 340 K to 400 K. By drying the raw material in the above range, moisture contained in the raw material can be removed, thereby removing the impeding factor during molten salt electrolysis. For example, in the case of seawater MgO clinker, the MgO concentration is very high and there are almost no impurities, so there is no significant difference between before and after pretreatment, so pretreatment is not necessary. may be

As another example, the pretreatment step may include: using distilled water to react the raw material with a mineral solution concentration of 5% to 25% at 250 K to 400 K for 50 hours to 100 hours; and drying at 300 K to 500 K after the reaction is completed.

The step of reacting the raw material using the distilled water is, for example, 280 K to 380 K or 300 K to 380 K for 60 hours to 100 hours or from 65 hours to 85 hours. In addition, the drying step may be dried at 320 K to 450 K or 340 K to 400 K.

By using the distilled water to react the raw material and drying it, Mg(OH) ₂ may be generated from Mg-containing components in the primary resource or secondary resource, and current efficiency may be increased. For example, in the case of ferronickel slag, the concentration of MgO is relatively low, and MgSiO ₃ and Mg ₂ SiO ₄ are contained as main components. Free MgO, MgSiO ₃ and Mg ₂ SiO ₄ in the slag Mg(OH) ₂ that can be used as an electrolytic raw material can be generated.

The pre-processing step may be selectively performed in consideration of the type, characteristic, component, etc. of the primary or secondary resource. For example, when the concentration of MgO is high and there is almost no impurity, so that there is no significant difference between before and after pretreatment, from an economic point of view, pretreatment is not necessary and a pretreatment step of heating at a relatively low temperature for drying may be performed.

According to an embodiment of the present invention, a preliminary electrolysis step may be further included before the step S10, and the step S10 may be performed using the electrolyte salt that has undergone the preliminary electrolysis step. In this case, it is possible to reduce the reduction of impurities other than the reduction of the target metal oxide during electrolysis by performing molten salt electrolysis using the electrolytic salt prepared by reducing impurities.

The preliminary electrolysis step may include: charging a crucible containing the electrolyte salt into a reactor in which a cathode and an anode are installed; and applying a current of 0.01 A to 0.3 A or 0.1 A to 0.2 A at 1000 K to 1150 K or 1050 K to 1100 K for 1 hour or more to remove impurities. At this time, the current may be applied until the impurities are removed.

The crucible containing the electrolyte salt may be an alumina crucible, an iron (Fe) crucible, or a graphite (C) crucible. For example, the crucible used in the preliminary electrolysis step may be an iron crucible.

The crucible may further include silver (Ag) granules in addition to the electrolytic salt. When the silver granules are put in a crucible together with an electrolytic salt for preliminary electrolysis, the silver granules may absorb impurities.

The preliminary electrolysis step may be performed in a state maintained at 0.5 atm to 2 atm, 0.8 atm to 1.5 atm, or 1 atm.

The molten salt prepared in the preliminary electrolysis step can be used in step S10 after storage.

According to an embodiment of the present invention, the step S10 is a step for performing molten salt electrolysis of a raw material including a primary resource or a secondary resource pretreated according to the type, and a liquid metal cathode is provided at the bottom inside and the An alloy between the liquid metal cathode and the target metal can be formed through molten salt electrolysis by putting the pretreated raw material into an electrolytic bath containing sea salt.

The metal of the liquid metal negative electrode may include at least one selected from the group consisting of Cu, Sn, Ag and Al. As such, by performing molten salt electrolysis using a high-density metal as a cathode, a high current efficiency can be maintained throughout the electrolysis because an Mg alloy is generated at the bottom of the electrolytic cell. In addition, high purity magnesium metal can be produced by vacuum distillation after electrolysis.

The electrolyte salt may include at least one selected from the group consisting of alkali metal halides, alkaline earth metal halides, alkali metal oxides and alkaline earth metal oxides.

The electrolytic salt during the electrolysis may be a molten salt, and the molten salt may include at least one selected from the group consisting of alkali metal halides, alkaline earth metal halides, alkali metal oxides and alkaline earth metal oxides.

As a specific example, the electrolyte salt may be a mixed salt of MgF ₂ -LiF-KCl. In the case of electrolyzing the conventional reagent grade MgO, MgF ₂ -CaF ₂ -NaF-based or MgF ₂ -LiF-based mixed salt was used due to MgO solubility. In comparison, when using MgO-containing primary and secondary resources as raw materials in the present invention, it is necessary to control the viscosity of the salt, and by using the MgF ₂ -LiF-KCl mixed salt, the effect of lowering the viscosity of the salt due to KCl can be obtained

When the raw material is a MgO-containing primary or secondary resource, the average cell potential in step S10 may be greater than the theoretical decomposition voltage of MgO and lower than the theoretical decomposition voltage of the electrolyte salt. For example, when the electrolytic salt is a mixed salt of a plurality of electrolytic salts, it may be compared with a component having the lowest theoretical decomposition voltage among components constituting the mixed salt. In this case, the electrochemical reduction of MgO can be effectively performed without consumption of the electrolyte.

Step S10 may be performed by applying a current of 0.5 A to 2 A at 1000 K to 1100 K for 8 hours to 16 hours. For example, step S10 may be performed by applying a current of 0.5 A to 1.8 A or 0.5 A to 1.5 A at 1000 K to 1080 K or 1000 K to 1500 K for 8 hours to 15 hours or 10 hours to 15 hours. can

In step S10, the electrolytic salt should be capable of melting the target metal oxide, and the decomposition voltage must be greater than the decomposition voltage of the target metal oxide so that the electrolysis can proceed stably, and it is advantageous in terms of process energy to have a low melting temperature. .

In addition, during the electrolysis, the cathode has a greater density than the target metal, is non-toxic, must not be a rare metal or a noble metal, has a wide range in which the target metal can be dissolved, is liquid at the corresponding process temperature, or when forming an alloy with the target metal It should be a liquid metal, and it should be a metal that is easy to separate from the target metal during vacuum distillation due to a large difference in vapor pressure from the target metal.

The molten salt electrolysis may be performed by chronopotentiometry.

After the molten salt electrolysis, the electrolytic cell is cooled to room temperature, the alloy of the target metal is removed from the alumina electrolysis crucible, and the salt on the surface of the alloy of the target metal is removed for component analysis.

In the case of molten salt electrolysis, when a MgO-containing primary or secondary resource is used as a raw material and Cu is used as a cathode, an Mg-Cu alloy is produced. Referring to FIG. 3 below, changes in the vapor pressure of Mg according to the concentration and temperature of Mg in the Mg-Cu alloy are shown together with the Mg-Cu phase diagram.

At atmospheric pressure, when p _Mg in the Mg-Cu alloy is 0.01 atm or more, Mg evaporation occurs actively. In addition, the maximum concentration of Mg that can be electrodeposited on the Cu cathode at 1 atm and 1043 K is 33.2 mass%. This is because the current efficiency decreases due to Mg evaporation when the Mg concentration in the alloy is greater than 33.2 mass%.

According to an embodiment of the present invention, the step S20 may be performed to recover the target metal in high yield and high purity from the target metal alloy after the molten salt electrolysis.

In step S20, vacuum distillation may be performed by distilling at 1100 K to 1500 K, 1100 K to 1400 K, or 1200 K to 1350 K under vacuum conditions for 6 hours to 13 hours or 8 hours to 12 hours.

The vacuum distillation temperature may be controlled to be higher than the temperature at which the target metal is distilled and at the same time to be lower than the temperature at which the liquid metal anode is distilled.

The vacuum distillation may be performed using a vacuum distillation column, and an alloy melt of the liquid metal cathode and the target metal is provided at the bottom of the vacuum distillation column, and a temperature gradient may be formed in the distillation region.

3, when vacuum distillation is performed on the Mg-Cu alloy, the pressure of the reaction system may be less than 1 atm. In this case, it is expected that Mg in the Mg-Cu alloy will be actively evaporated even at 0.0001~0.001 atm, where p _Mg is lower than 0.01 atm.

When p _Mg is 0.0001 to 0.001 atm at 1300 K, the Mg concentration in the alloy is 0.09 to 0.94 mass%, so it is expected that most of the Mg in the Mg-Cu alloy will be recovered during vacuum distillation at 1300 K.

In addition, as shown in FIG. 3 below, since the vapor pressure of pure Cu metal at 1300 K is 1.58 x 10 ^-7 atm, it may be possible to produce high-purity Mg metal without contamination of Cu metal through vacuum distillation at 1300 K.

According to the present invention, there is provided a method for smelting metal through electrolytic-vacuum distillation of molten salt of magnesite or MgO-C refractory from Bukhan. The metal smelting method of Bukhan magnesite or MgO-C refractory material includes the steps of pre-treating Bukhan magnesite or MgO-C refractory material containing magnesium oxide as a raw material (S11); Forming an alloy between the liquid metal anode and the target metal through molten salt electrolysis by putting the pre-treated raw material into an electrolyzer having an electrolytic salt provided at the bottom of the liquid metal anode (S21); and separating the alloy and vacuum distilling to recover the target metal (S31).

In step S11, the raw material may be calcined at 1000 K to 1200 K, 1000 K to 1150 K, or 1000 K to 1100 K. For example, the calcination step may be performed using a box-type electric furnace.

Through the calcination step, it is possible to increase the MgO concentration of the primary resource or the secondary resource. For example, when magnesite from North Korea is used as a raw material, most of the magnesite from North Korea is composed of magnesium carbonate (MgCO ₃ ), and MgO is generated through calcination to increase the concentration of MgO. In particular, when calcining at a temperature within the above range, the reaction occurs smoothly to promote the production of MgO, and through this, a high-purity target metal can be manufactured through molten salt electrolysis and vacuum distillation according to the present invention.

The North Korean magnesite may further include a step of pulverizing to a size of less than 300 μm after the pre-treatment step. In the case of the northern magnesite, by pulverizing the particle size to less than 300 μm, the reactivity during alloy formation may be improved.

In addition, in the case of MgO-C refractories, MgO and C are the main phases, and may be physically mixed. In addition, when the MgO refractory material is calcined in the above temperature range, the concentration of MgO relative to the same weight may be increased by reducing the amount of C through oxidation.

According to the present invention, there is provided a method for smelting metal through molten salt electrolytic-vacuum distillation of ferronickel slag. The metal smelting method of the ferronickel slag includes the steps of pretreating magnesium oxide-containing ferronickel slag as a raw material (S12); Forming an alloy between the liquid metal anode and the target metal through molten salt electrolysis by inputting the pre-treated raw material into an electrolytic cell having a liquid metal anode provided at the bottom inside and containing an electrolytic salt (S22); and separating the alloy and vacuum distilling to recover the target metal (S32).

Conventionally, ferronickel slag was vacuum reduced using silicon (Si) at 1573 K for Mg metal production using ferronickel slag. However, this process still has the problem of requiring high energy consumption.

In addition, conventionally, ferronickel slag was carbon-thermal reduction at 1773-1823 K for the production of Mg metal using ferronickel slag. However, pure Mg metal has a problem in that pure Mg metal cannot be produced because all Mg gas is re-oxidized by silicon monoxide (SiO) and carbon monoxide (CO) gas generated from slag.

In comparison, the metal smelting method through molten salt electrolytic-vacuum distillation of ferronickel slag according to the present invention saves energy compared to the conventional process and improves the current efficiency during molten salt electrolysis It can be possible to manufacture high-purity Mg metal .

The step S12 may include: using distilled water to react the raw material with a mineral solution concentration of 5% to 25% at 250 K to 400 K for 50 hours to 100 hours; and drying at 300 K to 500 K after the reaction is completed.

The step of reacting the raw material using the distilled water is, for example, 280 K to 380 K or 300 K to 380 K for 60 hours to 100 hours or from 65 hours to 85 hours. In addition, the drying step may be dried at 320 K to 450 K or 340 K to 400 K.

By using the distilled water to react the raw material and drying it, Mg(OH) ₂ may be generated from Mg-containing components in the primary resource or secondary resource, and current efficiency may be increased. For example, in the case of ferronickel slag, the concentration of MgO is relatively low, and MgSiO ₃ and Mg ₂ SiO ₄ are contained as main components. Free MgO, MgSiO ₃ and Mg ₂ SiO ₄ in the slag Mg(OH) ₂ that can be used as an electrolytic raw material can be generated.

In the above, the metal smelting method of various raw materials containing the target metal oxide according to the present invention has been shown in the base material and drawings, but the description and drawings above describe and show only the essential components for understanding the present invention, In addition to the processes and apparatus shown in the above description and drawings, processes and apparatus not separately described and not shown may be appropriately applied and used for carrying out the metal smelting method according to the present invention.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the following examples are intended to illustrate the present invention, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

<Example>

1. Raw material

As raw materials, primary resources such as magnesite and seawater MgO clinker and secondary resources such as MgO-C refractories and ferronickel slag were used as raw materials.

Since MgO-C refractories have the same composition before and after use, the refractory materials before use were used in the experiment.

Bukhan magnesite was used for magnesite, MgO-C refractory material provided by Korea refractory material was used for MgO-C refractory material, MgO clinker provided by POSCO Chemical was used for MgO clinker, and ferronickel slag was ferronickel slag provided by SNNC. Nickel slag was used.

2. Pre-electrolysis

MgF ₂ , LiF and KCl were used after drying for 72 hours or more at 453 K using a vacuum oven (model: VOS-601SD, EYELA).

The reduction of the Fe crucible used for preliminary electrolysis was performed at 1073 K in an Ar gas atmosphere (purity: 99.9999%) for 5 hours using a Ti sponge.

Thereafter, 51 mass% MgF ₂ -44 mass% LiF-5 mass% KCl mixed salt was charged into the reduced Fe crucible for preliminary electrolysis. In this case, the mass of MgF ₂ is 256.0 g, the mass of KCl is 25.0 g, and the mass of LiF is 219.0 g. In addition, the MgF ₂ , LiF and KCl purity is 99.9%, 99.9% and 99%, respectively, Kojundo Chemicals Lab. Co., Ltd. purchased.

In addition, an Ag shot (Ag shot, purity: 99.99 %; Φ 1 to 3 mm; Sungeel Himal) was charged into the crucible together to absorb the metal impurities generated in the preliminary electrolysis process.

After loading the crucible into a stainless steel reactor, using ultra-torr vacuum fitting, nickel (Ni, purity > 99.5 %; Φ 2 mm; Alfa Aesar Chemical Co. Ltd.) anode and graphite (C, Φ 8 mm; SGL Carbon) Group) The upper flange where the anode was installed and the reactor were assembled.

After maintaining the reactor in a vacuum state for 10 minutes, Ar gas was injected until the internal pressure of the reactor became 1 atm. In addition, Ar gas was flowed using a MFC (Mass flow controller) to maintain the internal pressure at 1 atm during the preliminary electrolysis experiment.

And the reactor was placed in a vertical electric furnace. The reactor temperature was raised to 773 K and maintained for 24 hours to remove residual moisture in the reactor. After the temperature was raised from 773 K to 1083 K, a preliminary electrolysis experiment was performed.

After immersing the electrode in molten salt, apply a current of 0.15 A to the electrolytic cell for at least 1 hour using a potentiometer (model: VMP3, booster: VMP3B, 2 A - 20 V, Biologic Science Instruments) until impurities are removed. did

After the preliminary electrolysis was completed, the electrode was removed from the molten salt and the reactor temperature was cooled to room temperature. MgF ₂ -LiF-KCl molten salt was separated from the Fe crucible and stored in a glove box (model: MB-200MOD, MBRAUN).

Examples 1 to 5

(1) Raw material pretreatment

Bukhan magnesite was calcined at 1073 K using a box-type electric furnace, and after pulverization, the particle size was selected to be less than 300 μm through sieving. MgO-C refractories were oxidized by calcining at 1073 K using a box-type electric furnace.

MgO clinker was dried at 383 K using a high-temperature dryer to remove moisture.

The ferronickel slag was put in distilled water and a glass bottle so that the mineral solution concentration (pulp density, w/v) was 12.5%, and 72 at 353 K using a shaking water bath (shaking water bath, model: BS-21, JEIO TECH CO., Ltd). After the time reaction, it was dried and aged at 383 K using an air oven.

(2) Molten salt electrolysis

Molten salt electrolysis of the pretreated MgO-containing raw material was carried out at 1043 K after preliminary electrolysis using a copper (Cu) anode and graphite (C) anode, and then put into an electrolytic cell containing MgF ₂ -LiF-KCl molten salt.

As the feedstock, calcined North Korean magnesite in Example 1, Seawater MgO clinker in Example 2, and oxidized MgO-C refractory bricks in Example 3 ( Oxidized MgO-C refractory brick), in the case of Example 4, aged ferronickel slag, in the case of Example 5, ferronickel slag before aging (Ferronickel slag) was used. In this case, the particle size of the raw materials of Examples 1 to 5 is less than 300 μm.

It was carried out under the experimental conditions shown in Table 1 below using the experimental apparatus shown in FIG. 4 .

Exp. no. Raw material Raw material mass (g) Reaction time (ton/hr) Average current (A) Cathode mass (g) Example 1 210224 Calcined North Korean magazine 30.00 12.5 1.44 45.06 Example 2 210318 Seawater MgO clinker 30.00 12.5 1.44 45.07 Example 3 210228 Oxidized MgO-C refractory brick 40.00 12.5 1.44 44.99 Example 4 210321 Aged ferronickel slag 95.72 12.5 1.44 45.02 Example 5 210331 Ferronickel slag 95.72 12.5 1.44 45.04

Figure 4 (a) is a schematic diagram of an apparatus for performing a metal smelting method according to the present invention, Figure 4 (b) is a photograph of copper metal pellets, Figure 4 (c) is a photograph showing the cathode.

Specifically, the Cu anode was prepared by loading copper metal pellets into an alumina crucible (Al ₂ O ₃ crucible), and was connected to a C (Graphite) rod shielded with a boron nitride tube (BN tube). At this time, the C rod was connected to the Al ₂ O ₃ protective tube (Al ₂ O ₃ tube), the shielded Ni wire (Ni wire) as a lead wire for the cathode. The boron nitride tube and the Al ₂ O ₃ protection tube were fixed with C bolts (Graphite bolt). The size of the copper metal pellets was 3 mm, the purity was 99.995%, and it was purchased from RND KOREA Corp.

The Al ₂ O ₃ crucible containing the copper metal pellets for the negative electrode was charged to the bottom of the C crucible (Graphite crucible). In crucible C, a Ni wire shielded with an Al ₂ O ₃ protective tube was connected as a lead wire for the anode. Thereafter, the C crucible was placed inside a stainless steel reactor (SUS reactor), and the reactor was assembled with an upper stainless steel flange (SUS flange).

The upper part of the Al ₂ O ₃ protective tube of the cathode and the anode is sealed with a silicone plug, and a water cooling unit for temperature control is installed at the upper part of the SUS reactor, and between the SUS reactor and the C crucible An alumina ball (Al ₂ O ₃ ball) was positioned.

The gas inside the reactor was discharged as exhaust gas, and the atmosphere inside the reactor was replaced with an Ar gas atmosphere by repeating the vacuum process and charging Ar gas twice. After the final Ar gas filling, Ar gas was flowed so that the internal pressure of the reactor was maintained at 1 atm. Thereafter, the temperature was raised to 1043 K for electrolysis after the reactor was charged into a vertical electric furnace.

Molten salt electrolysis was performed using chronopotentiometry to control the current density. During the molten salt electrolysis reaction, a current of 0.5 A to 1.5 A was applied for 12.5 hours using a potentiostat. After the molten salt electrolysis reaction, the C rod assembled into the BN tube from the copper negative electrode was removed from the negative electrode, and 1 hour after the C rod was removed, the reactor temperature was cooled to room temperature, and the Mg alloy was recovered. Salts attached to the surface of the recovered Mg alloy were removed for component analysis.

(3) vacuum distillation

5 (a) is a schematic diagram of a vacuum distillation apparatus, FIGS. 5 (b) and (c) are photographs of crucible C, and FIG. 5 (d) is a photograph of a stainless steel reactor of the vacuum distillation apparatus. .

Vacuum distillation was performed using a stainless steel reactor as shown in FIGS. 5(a) and 5(d) below.

Specifically, the Mg alloy obtained after molten salt electrolysis was positioned at the bottom of a C crucible with one side blocked as shown in FIG. 5(c) below. Then, C crucibles with both open sides were stacked on top of the C crucible with one closed as shown in FIG.

A steel lid was fastened to the upper portion of the steel holder, and a cooling water was installed outside the reactor for temperature control.

The opposite side of the reactor was blocked with a viton plug, and the inside of the reactor was substituted with Ar three times using a vacuum pump, and then a vacuum atmosphere was maintained. After the reactor in which the vacuum was maintained was charged into a vertical electric furnace preheated to 1300 K, a temperature gradient was allowed from Z7 at the bottom to Z1 at the top, and distillation was carried out for 10 hours.

After completion of the reaction, the reactor was immediately separated from the electric furnace, cooled to room temperature, and Mg metal and the residue were recovered from the C crucible.

<Experimental example>

(characterization method)

Component analysis was performed using inductively coupled plasma optical emission spectroscopy (ICP-OES: PerkinElmer, Optima 5300DV and Thermo Fisher Scientific, iCAP 6500) and inductively coupled plasma mass spectrometry (ICP-MS: PerkinElmer, DRC-II quadrupole).

The purity of the Mg metal recovered through vacuum distillation was analyzed using a glow discharge mass spectrometer (GD-MS: MSI, GD90RF).

The crystal phase was analyzed using an X-ray diffraction analyzer (XRD: Philips X'Pert MPD, Cu-Kα radiation).

Microstructures were analyzed using a field emission scanning electron microscope (FE-SEM/EDS: TESCAN, CLARA/Oxford instruments, Ultim Max).

Experimental Example 1: Raw material analysis

1. Analysis of raw material components

Photographs of the raw materials used in Examples 1 to 5 were taken and shown in FIGS. 6 (a) to (e), respectively.

In addition, the component analysis results of the raw materials used in Examples 1 to 5 are shown in Table 2 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Component concentration (mass%) MgO 97.4 98.3 87.2 34.8 31.3 Al ₂ O ₃ 0.19 0.25 8.22 3.40 4.67 Fe ₂ O ₃ 0.19 0.22 0.64 6.76 7.26 Li ₂ O N.D. N.D. N.D. N.D. N.A. Na ₂ O 0.03 0.01 0.03 0.06 1.05 K ₂ O 0.02 N.D. 0.08 0.06 0.34 CaO 1.75 0.42 1.03 1.03 0.90 Cr ₂ O ₃ N.D. 0.01 0.18 0.75 1.17 MnO 0.01 0.05 0.04 0.42 0.43 NiO N.D. N.D. N.D. 0.03 0.04 CuO N.D. N.D. 0.01 N.D. N.D. SiO ₂ 0.38 0.79 2.59 N.A. 48.4

2. XRD measurement before/after pre-treatment of raw materials

The XRD measurement results before performing the pretreatment of the raw material are shown in FIG. 7a ((a) Bukhan magnesite, (b) seawater MgO clinker, (c) MgO-C refractory brick, (d) ferronickel slag).

In addition, the XRD measurement results after performing the pretreatment of the feedstock are shown in FIG. 7b ((a) calcined Bukhan magnesite, (b) oxidized MgO-C refractory brick, (c) aged ferronickel slag) .

Referring to (a) of FIG. 7a, it can be confirmed that the crystalline phase of magnesite from North Korea is magnesium carbonate (MgCO ₃ ), MgO is produced through calcination according to the following Reaction Formula 3, and the result is shown in (a) of FIG. 7b below. can be checked through

The concentration of MgO in the calcined Bukhan magnesite is 97.4 mass%, and the main impurity is calcium oxide (CaO), but the concentration is only 1.75 mass%.

[Scheme 3]

MgCO ₃ (s) = MgO (s) + CO ₂ (g)

7a (b), seawater MgO clinker was not pre-treated because only MgO was confirmed, the concentration of MgO in seawater MgO clinker was 98.3 mass%, and the main impurities were CaO 0.42 mass% and SiO ₂ 0.79 It was confirmed as mass%.

MgO and C were identified when MgO-C fire bricks were analyzed as shown in FIG. 7a (c). In addition, MgO and C were still confirmed despite oxidation at 1073 K as shown in (b) of FIG. 7b. These results may mean that MgO and C are physically mixed in MgO-C fire bricks. The concentration of MgO in the MgO-C fire bricks was 87.2 mass%, and Al ₂ O ₃ was identified as 8.22 mass% as the main impurity.

Referring to (d) of FIG. 7a, it can be seen that the main components of the ferronickel slag are MgSiO ₃ and Mg ₂ SiO ₄ . These compounds are generally present in ferronickel slag because they are produced during the manufacturing process of ferronickel. Referring to Table 2, ferronickel slag contains 31.3 mass% MgO, and 7.26 mass% iron oxide and 4.67 mass% Al ₂ O ₃ are included as major impurities.

In the case of the ferronickel slag, the concentration of MgO is considerably lower than that of other raw materials used in this experiment, but considering the amount of slag generated annually and the Mg content, it has high potential as a raw material for Mg production using the electrolysis process.

However, for Mg production using ferronickel slag, dissolution of MgSiO ₃ and Mg ₂ SiO ₄ in molten salt is required, but the solubility of MgSiO ₃ and Mg ₂ SiO ₄ in MgF ₂ -LiF-KCl molten salt at 1043 K was not reported. . As a way to overcome this, in this study, in order to increase the MgO concentration of ferronickel slag, free MgO and water in ferronickel slag were used for aging.

When ferronickel slag is aged using water, free MgO, MgSiO ₃ and Mg ₂ SiO ₄ are converted into Mg(OH) ₂ that can be used as an electrolytic raw material by the reactions shown in Schemes 4 to 6 below. . However, as shown in the XRD analysis result of FIG. 7b (c), the generation of Mg(OH) ₂ in the slag after aging was not confirmed.

However, differences were confirmed in the microstructure of ferronickel slag before and after aging. Specifically, in (a) of FIG. 8 is an SEM photograph of a cross-section of ferronickel slag before aging, and in FIG. 8(b) is an SEM photograph of a cross-section of ferronickel slag after aging. It can be confirmed that the microstructure of the cross-section of the slag before aging is uniform, but in the cross-section of the slag after aging, an annular microstructure was observed in the outer region of the cross-section. Mg concentrations in the annular region of the outer region and the inner region were 15.7 mass% and 21.3 mass%, respectively. This means that Mg inside the slag diffused outward through the particle surface. Therefore, it can be seen that Mg(OH) ₂ was probably generated from ferronickel slag through aging using water.

[Scheme 4]

MgO (s) + H ₂ O (l) = Mg(OH) ₂ (s)

ΔG°r = -25.2 kJ at 353 K

[Scheme 5]

2 Mg ₂ SiO ₄ (s) + 3 H ₂ O (l) = Mg ₃ Si ₂ O ₅ (OH) ₄ (s) + Mg(OH) ₂ (s)

ΔG°r = -43.4 kJ at 353 K

[Scheme 6]

4 MgSiO ₃ (s) + 2 H ₂ O (l) = Mg ₃ Si ₄ O ₁₀ (OH) ₂ (s) + Mg(OH) ₂ (s)

ΔG°r = -49.9 kJ at 353 K

Experimental Example 2: Analysis of molten salt electrolysis results of raw materials

In Examples 1 to 5, the components of the Mg-Cu alloy recovered as a result of molten salt electrolysis at 1043 K were analyzed, and the results are shown in Table 3 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Average cell potential (V) 2.43 2.67 2.48 2.75 2.55 Current Efficiency (%) 89.6 92.4 92.3 78.1 59.3 Component concentration (mass%) Mg 14.0 14.4 14.3 12.2 9.20 Si 0.04 0.02 0.03 0.18 0.16 Li 0.09 0.03 0.10 0.16 0.01 Al 0.05 0.06 0.08 0.10 0.24 Ca N.D. N.D. N.D. N.D. N.D. K 0.01 N.D. 0.02 N.D. N.D. Cr N.D. N.D. N.D. N.D. 0.01 Mn N.D. N.D. N.D. 0.01 N.D. Fe N.D. N.D. N.D. 0.03 0.31 Ni N.D. N.D. N.D. N.D. N.D. Cu Bal. Bal. Bal. Bal. Bal.

[Experimental conditions] Cathode current density: 0.220 A cm ^-2

The effective surface area for calculating the current density was determined by subtracting the cross-sectional area of the BN tube from the inner cross-sectional area of the alumina crucible.

Current efficiency: (actual weight of recovered Mg x 100) / theoretical weight of recovered Mg

In addition, in Examples 1 to 5, photographs of the Mg-Cu alloy recovered as a result of molten salt electrolysis under 1043 K conditions are shown in FIGS. 9 (a) to (e) below.

In addition, in Examples 1 to 5, XRD analysis results of the Mg-Cu alloy recovered as a result of molten salt electrolysis under 1043 K conditions are shown in FIGS. 10 (a) to (e) below.

In addition, in Examples 1 to 5, SEM and EDS analysis results of the Mg-Cu alloy recovered as a result of molten salt electrolysis under 1043 K conditions are shown in FIGS. 11 (a) to (e) below.

1. Analysis of molten salt electrolysis results of primary resources

Referring to Table 3 above, it is possible to confirm the component analysis results of the Mg-Cu alloy recovered through electrolysis using various MgO-containing primary resources using Cu anodes at 1043 K as raw materials.

Molten salt electrolysis was performed by applying an average current of 1.44 A to calcined Bukhan magnesite and seawater MgO clinker at 1043 K for 12.5 hours. As a result, the average cell potentials were 2.43 V and 2.67 V, respectively. The measured cell voltage is higher than the theoretical decomposition voltage of MgO when using the C anode at 1043 K, but is lower than the theoretical decomposition voltage of KCl used as an electrolyte salt as shown in FIG. 2 . In addition, in the previous study, the decomposition voltage of MgO in MgF ₂ -LiF molten salt was confirmed to be 2.01 V at 1083 K. Therefore, when electrolysis of MgO-containing primary resources in MgF ₂ -LiF-KCl molten salt is performed using Cu anode and C anode at 1043 K, it can be seen that the electrochemical reduction of MgO can proceed without consumption of electrolyte. have.

In addition, in electrolysis using calcined Bukhan magnesite and seawater MgO clinker as raw materials, the current efficiency was 89.6% and 92.4%, respectively. This is similar to the current efficiency of 84.9 to 88.0% when the Mg concentration in the Mg alloy is 12.9 to 20.1 mass% when the reagent grade MgO is electrolyzed in MgF ₂ -LiF molten salt at 1053 K using a Cu anode. This is confirmed because the MgO purity of the raw material according to the present invention is high as shown in Table 2 above.

9 (a) and (b) are photographs of Mg-Cu alloy recovered after molten salt electrolysis of MgO-containing primary resources at 1043 K. Through this, as shown in the phase diagram of FIG. 3, while the concentration of Mg in the Mg alloy reaches 14.0 to 14.4 mass%, the solid Cu anode changes to Cu (Mg) + liquid, liquid, and liquid + MgCu ₂ phase, so bulk form It was confirmed that the Mg alloy can be recovered.

10A and 10B are XRD analysis results of Mg alloys recovered using calcined magnesite and seawater MgO clinker as raw materials, respectively. In the Mg alloy recovered through electrolysis, a MgCu ₂ phase and a Cu(Mg) phase were formed. In addition, referring to FIGS. 11 (a) and (b), which are the results of analyzing the cross section of the Mg alloy recovered through the electrolysis of MgO-containing primary resources using SEM, the recovered Mg alloy is in the Mg-rich phase and Cu It is classified as a -rich phase, which is consistent with the results expected from the Mg-Cu phase diagram when the Mg concentration in the Mg alloy is 14.0 to 14.4 mass%.

As shown in Table 3, the Mg alloy recovered through electrolysis contains a small amount of impurities such as silicon (Si), lithium (Li), aluminum (Al), and potassium (K). However, although calcium (Ca) is one of the main impurities in the raw material, it was not included in the recovered Mg alloy. These results suggest that the electrolysis of CaO was limited under the experimental conditions and that there was no reaction between Mg and CaO in the Mg alloy because CaO was more stable than MgO.

On the other hand, it is expected that Si and Al are formed and mixed with the side reaction between Mg and oxide in the Mg alloy, acting as an impurity in the Mg alloy. This result is one of the reasons why the current efficiency did not reach 100% in the electrolysis process because Mg reacts with impurities and is consumed.

As shown in Table 3 above, Al was identified as an impurity in the Mg alloy, which indicates that Mg and Al ₂ O ₃ crucibles in the Mg alloy during electrolysis at 1043 K may be formed by Mg _x AlO _y through the reaction of Reaction Formula 7 below. it means.

Specifically, referring to FIG. 13 showing (a) SEM analysis results and (b) line scan results of the Al ₂ O ₃ crucible of Example 1 and the contact surface of the Mg-Cu alloy, Al ₂ O ₃ crucible after electrolysis in (a) A dense layer was observed on the contact surface of the Mg-Cu alloy. In addition, it can be seen that the microstructure region including the pores in (b) below is Al ₂ O ₃ , and the dense layer is Mg _x AlO _y . In addition, referring to FIG. 14 below, regardless of the type of raw material, the thickness of the Mg _x AlO _y layer was about 10 μm. As such, the loss of Mg due to the reaction with the Al ₂ O ₃ crucible is one of the reasons that the current efficiency does not reach 100% during electrolysis.

[Scheme 7]

3 Mg (l, in Mg alloy) + Al ₂ O ₃ (s) = 3 MgO (s, in MgAl ₂ O ₄ ) + 2Al (l)

12, it is a cross-sectional photograph of an electrolysis cell after molten salt electrolysis using MgO clinker as a raw material. In the experiment, since a sufficient amount of MgO clinker was supplied as a raw material, a raw material that was not decomposed even after electrolysis was confirmed at the bottom of the crucible. This is because the density of MgO is greater than that of the electrolyte, and the densities of MgO and the electrolyte are 3.58 g/cm ³ and 2.87 g/cm ³ , respectively. Through this, it can be seen that Mg metal can be produced through direct reduction of MgO when MgO is in direct contact with the anode according to the configuration of the anode as shown in Scheme 8.

[Scheme 8]

MgO (s) + 2 e ^- + Cu (s) = Mg-Cu (s,l) + O ^2- (in molten salt)

2. Analysis of molten salt electrolysis results of secondary resources

Referring to Table 3 above, it can be seen the compositional analysis results of the Mg-Cu alloy recovered through electrolysis using various MgO-containing secondary resources using Cu anodes at 1043 K as raw materials.

When an oxidized MgO-C refractory material was electrolyzed by applying an average current of 1.44 A at 1043 K for 12.5 hours before/after aging treatment, the cell potentials were 2.48 V, 2.55 V, and 2.75 V, respectively. The measured cell potential was lower than the theoretical decomposition voltage of KCl at 1043 K, confirming that the electrolysis proceeded without decomposition of the electrolyte, MgF ₂ -LiF-KCl.

In addition, a current efficiency of 92.3% was obtained through the electrolysis of the oxidized MgO-C refractory material. Specifically, high current efficiency was obtained due to the high concentration of MgO in the oxidized MgO-C refractory material. In addition, it could be seen that the electrochemical reduction of MgO proceeded through the reactions shown in Schemes 1 and 2 at the cathode and the anode.

15, after the electrolysis of the oxidized MgO-C refractory material, a black layer was observed on the upper part of the electrolyte. It didn't happen. This is because the MgO-C refractory material is physically mixed with MgO and C, so the C of the residue is separated and floated during the electrolysis process to form a black layer on the top of the electrolyte. Through this, when molten salt electrolysis of MgO-C refractory material using a metal cathode is performed, since the Mg alloy is formed at the bottom of the crucible, contamination of the Mg alloy by C can be prevented.

In addition, referring to Table 3, when ferronickel slag before and after aging treatment was used as a raw material, the current efficiency was 59.3% and 78.1%, respectively. Although the current efficiency during electrolysis of the aging-treated ferronickel slag was relatively higher than when ferronickel slag was used as a raw material, it showed a low result when compared with the current efficiency using other MgO raw materials. In the Mg alloy recovered using ferronickel slag, impurity concentrations such as Si, Al, and Fe were higher than those of the Mg alloy recovered using other MgO raw materials. This is expected because the Mg metal generated through the electrolysis of ferronickel slag reacted with impurities in the raw material or the impurities in the raw material participated in the electrolysis reaction. For this reason, it can be seen that the current efficiency when using ferronickel slag as a raw material is lower than when using North Korean magnesite, MgO clinker, and MgO-C refractory material as raw materials.

However, it can be seen that the current efficiency increased from 59.3% to 78.1% when aging-treated ferronickel slag was used as a raw material. This is because, as mentioned above, Mg(OH) ₂ was generated through the aging treatment of free MgO, MgSiO ₃ and Mg ₂ SiO ₄ in ferronickel slag.

In addition, the impurity concentrations of Al and Fe in the Mg alloy manufactured using ferronickel slag before aging treatment were higher than when ferronickel slag was used after aging treatment. The possibility of direct reduction of Al ₂ O ₃ crucibles through physical contact with the cathode during electrolysis is also expected because the high Al concentration in the manufactured Mg alloy and the average cell voltage measured during electrolysis are lower than the cell voltage during electrolysis using aged slag. do.

(c), (d) and (e) of FIG. 9 are photographs of Mg alloys recovered after electrolysis of MgO-containing secondary resources at 1043 K. When the Mg concentration in the Mg alloy was 9.20 to 14.3 mass%, it was possible to recover the Mg alloy in bulk form.

In addition, (c), (d) and (e) of FIG. 10 are XRD analysis results of the Mg alloy recovered using the MgO-containing secondary resource. As a result of the analysis, the recovered Mg alloy contains MgCu ₂ and Cu(Mg) phase, and as shown in (c), (d), (e) of FIG. It was confirmed that the Cu-rich phase was mixed. This is consistent with the results predicted through the Mg-Cu phase diagram of FIG. 3 below.

In addition, the reaction between Mg and Al ₂ O ₃ in the Mg alloy was investigated by analyzing the contact surface of the Mg alloy and the Al ₂ O ₃ crucible. Through this, it was possible to confirm the formation of the Mg _x AlO _y layer, and the thickness of the Mg _x AlO _y layer was about 10 μm regardless of the type of MgO raw material used in this experiment.

Experimental Example 3: Analysis of vacuum distillation results of Mg alloy

Table 4 below shows the component analysis results of Mg metal recovered after vacuum distillation of the Mg-Cu alloy in Examples 1 to 4 under the experimental conditions of vacuum distillation at 1300 K for 10 hours and the residues in the reactor.

Photographs of the recovered Mg metal and the residue at the bottom of the reactor are shown in FIGS. 16 and 17, respectively.

As shown in Table 4, Mg metal with a purity of 99.994% or more was recovered from the low temperature part of the reactor through vacuum distillation of the Mg alloy. When vacuum distillation of Mg alloy manufactured using aging-treated ferronickel slag as a raw material, the concentration of impurities in Mg metal is less than the GD-MS detection limit, so the actual purity of Mg metal is expected to be 99.999% or more.

Meanwhile, after vacuum distillation at 1300 K for 10 hours, the Mg concentration in the Mg alloy decreased from 12.2 to 14.4 mass% to 1.29 to 1.51 mass%, and the Mg recovery rate was 90.7 to 91.5%.

In addition, the concentration of impurities in the residue after vacuum distillation was not significantly different from that of the Mg alloy before distillation, except for Li. At 1300 K, the vapor pressure of Li was 0.07 atm, and it was found that Li also evaporated along with Mg during the vacuum distillation process. However, the purity of the recovered Mg metal was 99.994% or higher regardless of the evaporation of Li. This is because the dissolution temperature of Li and Mg differs by 470 K, so the Li metal is expected to be recovered in a region different from that in which the Mg metal is recovered.

Example 1 Example 2 Example 3 Example 4 Exp. no. 210405 210408 210406 210409 Mg metal purity (%) 99.994 99.999 99.994 99.999 Mg recovery (%) 91.4 91.5 90.8 90.7 residue
Component concentration (mass%) Mg 1.40 1.41 1.51 1.29 Si 0.05 0.03 0.04 0.21 Li N.D. N.D. N.D. N.D. Al 0.05 0.07 0.10 0.10 K N.D. N.D. N.D. N.D. Cr N.D. N.D. N.D. N.D. Mn N.D. N.D. N.D. 0.01 Fe N.D. 0.01 N.D. 0.03 Ni N.D. N.D. N.D. N.D. Cu Bal. Bal. Bal. Bal.

As a result, in the present invention, high-purity Mg metal is produced through an eco-friendly and novel Mg metal production process that electrolyzes and vacuum-distills MgO-containing primary or secondary resources in MgF ₂ -LiF-KCl molten salt using a Cu cathode. could be smelted

Specifically, after electrolyzing various MgO-containing primary or secondary resources by applying a current of 1.44 A at 1043 K for 12.5 hours, MgCu ₂ and Mg-Cu on Cu (Mg) having an average cell potential of 2.43 to 2.75 V alloy could be obtained. At this time, the Mg concentration of the Mg-Cu alloy was found to be 9.20 to 14.4 mass%.

When calcined Bukhan magnesite and seawater MgO clinker were used as raw materials, the current efficiency during electrolysis was 89.6-92.4% due to the high purity of MgO in the raw material.

In addition, in the case of using ferronickel slag, the current efficiency was 59.3%, but by aging, the current efficiency increased to 78.1%.

In addition, after vacuum distillation of an Mg-Cu alloy having an Mg concentration of 12.2 to 14.4 mass% at 1300 K for 10 hours, Mg metal having a purity of 99.994% or more was obtained, and the recovery efficiency was 90.7 to 91.5%.

Claims (20)

A raw material including a primary resource or a secondary resource containing a target metal oxide is subjected to a pretreatment step;
Forming an alloy between the liquid metal anode and the target metal through molten salt electrolysis by inputting the pre-treated raw material into an electrolytic cell having a liquid metal anode provided at the bottom inside and containing a mixed salt of MgF ₂ -LiF-KCl as an electrolyte salt (S10); and
and vacuum distilling the alloy under vacuum conditions at a temperature of 1100 K to 1500 K for 6 hours to 13 hours to recover the target metal (S20),
The target metal oxide-containing primary resource includes at least one selected from the group consisting of magnesite containing magnesium oxide, seawater MgO clinker, brine MgO and dolomite,
The target metal oxide-containing secondary resource includes at least one selected from the group consisting of ferronickel slag and MgO-C refractories containing magnesium oxide,
The metal of the liquid metal negative electrode comprises at least one selected from the group consisting of Cu, Sn, Ag and Al,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
delete delete delete delete delete The method of claim 1,
The pretreatment step, characterized in that the raw material is calcined at 1000 K to 1200 K,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
According to claim 1,
The pretreatment step, characterized in that the raw material is dried at 300 K to 500 K,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
According to claim 1,
The pretreatment step may include: using distilled water to react the raw material with a mineral solution concentration of 5% (w/v) to 25% (w/v) at 250 K to 400 K for 50 hours to 100 hours; and
After the reaction is completed, characterized in that it comprises the step of drying at 300 K to 500 K,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
delete delete According to claim 1,
In the step S10, a current of 0.5 A to 2 A at 1000 K to 1100 K is applied for 8 hours to 16 hours,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
The method of claim 1,
Further comprising a preliminary electrolysis step before the step S10, characterized in that the step S10 is performed using the electrolytic salt that has undergone the preliminary electrolysis step,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
14. The method of claim 13,
The preliminary electrolysis step is
charging the crucible containing the electrolyte salt into a reactor in which a cathode and an anode are installed; and
It characterized in that it comprises the step of removing impurities by applying a current of 0.01 A to 0.3 A at 1000 K to 1150 K for 1 hour or more,
Metal smelting method through electrolytic-vacuum distillation of molten salt of various raw materials containing target metal oxides.
delete Pre-treating magnesium oxide-containing magnesite or MgO-C refractory material as a raw material (S11);
Forming an alloy between the liquid metal anode and magnesium through molten salt electrolysis by injecting the pre-treated raw material into an electrolytic bath having a liquid metal anode provided at the bottom of the interior and containing a mixed salt of MgF ₂ -LiF-KCl as an electrolyte salt ( S21); and
Separating the alloy and recovering magnesium by vacuum distillation at a temperature of 1100 K to 1500 K under vacuum conditions for 6 hours to 13 hours (S31),
The metal of the liquid metal negative electrode comprises at least one selected from the group consisting of Cu, Sn, Ag and Al,
Method for metal smelting through electro-vacuum distillation of molten salts of magnesite or MgO-C refractories.
17. The method of claim 16,
The step S11, characterized in that the raw material is calcined at 1000 K to 1200 K,
Method for metal smelting through electro-vacuum distillation of molten salts of magnesite or MgO-C refractories.
17. The method of claim 16,
The magnesite characterized in that it further comprises the step of pulverizing to a particle size of less than 300 μm between steps S11 and S21,
Method for metal smelting through electro-vacuum distillation of molten salts of magnesite or MgO-C refractories.
Pre-treating magnesium oxide-containing ferronickel slag as a raw material (S12);
Forming an alloy between the liquid metal anode and magnesium through molten salt electrolysis by injecting the pre-treated raw material into an electrolytic bath having a liquid metal anode provided at the bottom of the interior and containing a mixed salt of MgF ₂ -LiF-KCl as an electrolyte salt ( S22); and
Separating the alloy and recovering magnesium by vacuum distillation at a temperature of 1100 K to 1500 K under vacuum conditions for 6 hours to 13 hours (S32),
The metal of the liquid metal negative electrode comprises at least one selected from the group consisting of Cu, Sn, Ag and Al,
A method for metal smelting through electro-vacuum distillation of molten salt of ferronickel slag.
20. The method of claim 19,
The step S12 is, using distilled water, the raw material is reacted at 250 K to 400 K for 50 to 100 hours at a light solution concentration of 5% (w/v) to 25% (w/v); and
After the reaction is completed, characterized in that it comprises the step of drying at 300 K to 500 K,
A method for metal smelting through electro-vacuum distillation of molten salt of ferronickel slag.

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