KR102502681B1 - Anode for electrolysis, electrolytic cell comprising the same, and electrolysis process using the electrolytic cell - Google Patents

Abstract

The present invention provides an anode included in an electrolytic cell for electrolysis of an aluminum-scandium master alloy, an electrolysis anode having a concavo-convex portion formed on the surface of the anode, an electrolytic cell including the same, and the electrolytic cell. In the scandium master alloy electrolytic recovery process, it is effective in improving the recovery rate and reaction efficiency of the aluminum-scandium alloy by preventing the problem that the recovery rate of the aluminum-scandium mother alloy is lowered due to the presence of molten aluminum in the electrolyte in the form of droplets.

Description

Anode for electrolysis, an electrolytic cell including the same, and an electrolysis method using the electrolytic cell

The present invention relates to an electrolytic anode for electrolysis of an aluminum-scandium mother alloy, an electrolytic bath including the same, and an electrolysis method using the electrolytic bath.

Rare earths are essential resources used in various fields such as magnets, phosphors, catalysts, and abrasives. China accounts for most of the world's rare earth exports. In 2010, due to the Senkaku conflict between China and Japan, China restricted exports of rare earths for reasons of environmental and nature conservation. Let's face it, in 2011 the price of some rare earths soared more than fivefold. On the other hand, scandium (Sc, Scandium) with atomic number 21, which is classified as a similar rare earth element, is an alloy element that is added in small amounts to aluminum (Al, Aluminum) alloys. When the scandium is added in small amounts to aluminum alloys, mechanical properties of aluminum alloys It is reported to greatly improve weldability, corrosion resistance and elongation.

With this scandium metal reduction technology, a research team led by Professor Okabe of Tokyo University in Japan has recently proposed a scandium-containing aluminum alloy manufacturing process through electrolysis (electrolysis) (http://www.okabe.iis.u-tokyo.ac.jp/core-to -core/rmw/RMW3/slide/RMW3_20_Harata_T.pdf). In the case of electrolysis, the target metal to be reduced is obtained at the cathode by the electrochemical reaction of the cathode and anode in a molten salt state, and carbon dioxide or chlorine gas is generated at the anode. The main characteristics of the electrolysis process proposed by Professor Okabe are that scandium oxide (Sc ₂ O ₃ ) is used as a raw material, calcium chloride (CaCl ₂ ) and a eutectic salt of scandium oxide are used as the electrolyte, and molten aluminum is used as the cathode. And, the electrolysis process proceeds at a process temperature of 900 ° C.

1 is a view showing a cross section of an electrolytic cell used in a typical electrolysis process. The density of molten aluminum 40 used as the negative electrode is 2.375 g/cm ³ and the density of chloride used as the electrolyte 70 is typically 2.0 to 2.1 g/cm ³ . Although the density of the molten aluminum is higher than that of the electrolyte, the density difference is not large. Therefore, the flow of molten aluminum occurs due to carbon dioxide, which is a by-product gas 60 generated from the anode 10 during the electrolytic reaction. Due to this, a part of the molten aluminum is mixed into the electrolyte, and the mixed molten aluminum exists in the form of droplets due to surface tension to generate molten aluminum droplets 50 . Due to the generation of the molten aluminum droplets, the content of molten aluminum used as the negative electrode decreases, and finally, there is a problem in that the recovery rate of the aluminum-scandium alloy recovered from the negative electrode including molten aluminum is very low.

An object of the present invention is to provide an electrolytic anode with improved recovery rate and reaction efficiency, an electrolytic cell including the same, and an electrolysis method using the electrolytic cell.

According to one embodiment of the present invention, in an anode included in an electrolytic cell for electrolysis of an aluminum-scandium mother alloy, an electrolytic anode having concavo-convex portions formed on a surface of the anode is provided.

The concavo-convex portion may include a plurality of valleys and crests.

The valleys and crests may be formed in a longitudinal direction or a transverse direction of the anode.

The troughs and crests may form threads.

The trough and crest may be formed in a curved shape, a straight shape, or a combination of these shapes.

According to another embodiment of the present invention, an electrolytic cell including the anode for electrolysis is provided.

The electrolytic cell may further include an electrolytic cell body filled with electrolyte, and an aluminum cathode disposed at the bottom of the electrolytic cell.

The electrolyte may be fluoride, chloride or a mixture thereof.

According to another embodiment of the present invention, providing an electrolysis method comprising the steps of supplying scandium oxide and an electrolyte to the electrolytic bath, heating the electrolytic bath, and applying a current to the electrolytic bath to perform an electrolysis process. do.

The heating may have a temperature of 1000 to 1100 °C.

According to the present invention, in the aluminum-scandium master alloy electrolytic recovery process, the recovery rate and reaction efficiency of the aluminum-scandium alloy are improved by preventing the problem that the recovery rate of the aluminum-scandium mother alloy is lowered due to the presence of molten aluminum in the electrolyte in the form of droplets. has an enhancing effect.

1 is a diagram schematically showing a cross section of a conventional electrolytic cell for electrolytically depositing an aluminum alloy.
2 is a perspective view showing a conventional electrolytic anode.
3 to 5 are perspective views showing an anode for electrolysis according to an embodiment of the present invention.
6 is a view schematically showing a cross section of an electrolytic cell according to an embodiment of the present invention.
7 is a graph showing the results of analysis using X-ray diffraction (XRD) of the metal produced on the surface of the cathode of the electrolytic cell in Example.
8 is a photograph of a solidified aluminum droplet produced by solidifying a molten aluminum droplet in a comparative example.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

The present invention relates to an electrolytic anode for electrolysis of an aluminum-scandium mother alloy, an electrolytic bath including the same, and an electrolysis method using the electrolytic bath.

3 to 5 are perspective views showing an anode for electrolysis according to an embodiment of the present invention.

The anode 10 for electrolysis according to an embodiment of the present invention is an anode included in an electrolytic bath for electrolysis of an aluminum-scandium mother alloy, and an uneven portion 20 may be formed on a surface of the anode.

In general, since an electrolysis process for recovering an aluminum-scandium alloy is performed at a high temperature of 700° C. or more, the electrolyte 70 and the aluminum cathode 40 included in the electrolysis bath are in a molten state. The density difference between the molten electrolyte and the molten aluminum is not large, and the flow of the molten aluminum cathode is caused by carbon dioxide, which is a by-product gas 60 generated from the anode 10 during the electrolytic reaction. Due to this, a part of the molten aluminum is mixed into the electrolyte to generate aluminum droplets 50, and since the aluminum droplets cannot function as a cathode, they cannot participate in the electrolysis reaction, resulting in a problem in that the reaction efficiency of the electrolysis process is lowered. .

In addition, when the aluminum droplet 50 rises and is positioned on the surface of the electrolyte 70, it reacts with oxygen in the air to produce aluminum oxide (Al ₂ O ₃ ), so it cannot participate in the reaction any longer. Therefore, there is a problem in that the recovery rate and reaction efficiency of the aluminum-scandium alloy are very low because the content of the aluminum anode 40 is reduced.

However, the anode 10 for electrolysis according to an embodiment of the present invention prevents the problem that the recovery rate of the aluminum-scandium mother alloy is lowered due to the presence of molten aluminum in the form of liquid droplets in the electrolyte in the electrolytic recovery process of the aluminum-scandium mother alloy. This has the effect of improving the recovery rate and reaction efficiency of the aluminum-scandium alloy.

First, since the uneven portion 20 is formed on the surface of the anode 10 for electrolysis, the reaction area is significantly increased compared to the conventional anode having a flat surface, and as a result, reaction efficiency can be improved.

In addition, since the uneven portion 20 is formed on the surface of the anode 10 for electrolysis, the size of bubbles of by-product gas generated on the surface of the anode is controlled to a micrometer level (approximately 1,000 μm or less) to minimize the flow of electrolyte. can do. Therefore, by minimizing the flow of the electrolyte, it is possible to prevent a phenomenon in which a part of the molten aluminum is mixed into the electrolyte and the aluminum droplet 50 is generated, thereby improving the recovery rate and reaction efficiency of the aluminum-scandium alloy. there is

The uneven portion 20 of the anode 10 for electrolysis according to an embodiment of the present invention may include a plurality of valleys and crests. Due to the formation of many valleys and crests on the surface of the anode, the flow of the electrolyte is minimized by controlling the bubble size of the by-product gas generated on the surface of the anode to 1,000㎛ or less, thereby preventing some of the molten aluminum from being mixed into the electrolyte. can do.

The valleys and crests formed on the surface of the anode 10 may be formed in a longitudinal direction or a transverse direction of the anode. The valleys and crests formed in the longitudinal or transverse direction of the anode may be formed parallel or oblique to the longitudinal or transverse direction of the anode, and may be manufactured by cutting the surface of the anode.

Meanwhile, the valleys and crests formed on the surface of the anode 10 may form a screw thread. When a screw thread is formed on the surface of the anode, the trough may be a trough and the ridge may be a ridge of the screw thread.

2 is a perspective view showing a conventional electrolytic anode 10, and FIG. 2 is a typical cylindrical anode. An electrolytic anode according to an embodiment of the present invention may be manufactured by processing the cylindrical anode of FIG. 2 . Specifically, by processing the cylindrical anode in the transverse direction, it is possible to manufacture an anode in which valleys and peaks are formed in the transverse direction of the anode of FIG. 3 . In addition, by processing the cylindrical anode in the longitudinal direction, it is possible to manufacture an anode in which valleys and peaks are formed in the longitudinal direction of the anode of FIG. 4 . Further, the threaded anode of FIG. 5 may be manufactured by processing the cylindrical anode to form a thread.

The shape of the trough and crest is not limited thereto, but may include, for example, a curved shape, a straight shape, or a combination of these shapes. Specifically, when the valleys and crests are formed in a curved shape, wave-shaped valleys and crests may be formed on the surface of the anode 10 . Further, when the valleys and crests are formed in a straight line, valleys and crests having trapezoidal cross sections or valleys and crests having rectangular cross sections may be formed on the surface of the anode. Furthermore, when the trough and the ridge are formed in a curved shape and a straight shape, the part where the trough and the crest are connected may be curved and the remaining part may be straight, or the part where the trough and the crest are connected may be straight and the remaining part may be curved.

Meanwhile, the concavo-convex portion 20 of the anode 10 for electrolysis according to an embodiment of the present invention may include a plurality of protrusions protruding from the surface of the anode. Due to the formation of a large number of protrusions on the surface of the anode, the flow of the electrolyte is minimized by controlling the bubble size of the byproduct gas generated on the surface of the anode to 1,000 μm or less, thereby preventing a phenomenon in which some of the molten aluminum is mixed into the electrolyte. there is. The shape of the protrusion is not particularly limited, but may be a hemisphere, a cone, a square prism, or the like.

The material of the anode 10 is not particularly limited as long as it is an inert electrode that conducts electricity well, is easy to process, and does not melt in a high temperature electrolyte, but is, for example, carbon (C), iron (Fe), and nickel (Ni). It may be made of one or more materials selected from the group consisting of. In particular, it is preferable to use an anode made of carbon.

According to another embodiment of the present invention, it is possible to provide an electrolytic cell including the anode 10 for electrolysis. 6 is a view schematically showing a cross section of an electrolytic cell according to an embodiment of the present invention.

The electrolytic bath may include an electrolytic bath body 30 filled with electrolyte 70, an aluminum cathode 40 disposed on the bottom of the electrolytic bath, and the anode 10 for electrolysis. Since the electrolysis process performed in the electrolytic bath is performed at a high temperature of 700° C. or higher, the electrolyte and the aluminum cathode included in the electrolytic bath may be in a molten state.

As the electrolysis process progresses, in the anode 10 for electrolysis, an oxidation reaction proceeds in the electrolyte solution to generate by-product gas 60 such as chlorine gas, fluorine gas, carbon dioxide or carbon monoxide. Meanwhile, scandium oxide is supplied to the electrolytic cell body 30, and the scandium oxide undergoes a reduction reaction at the interface between molten aluminum, which is a negative electrode, and the electrolyte 70, thereby producing an aluminum-scamdium alloy.

The electrolyte 70 is not particularly limited as long as it is generally used in an electrolytic cell for electrolytically depositing an aluminum-scandium alloy, but may be, for example, fluoride, chloride, or a mixture thereof.

The fluoride is sodium hexafluoroaluminate (Na ₃ AlF ₆ ), potassium hexafluoroaluminate (K ₃ AlF ₆ ), aluminum fluoride (AlF ₃ ), calcium fluoride (CaF ₂ ), sodium fluoride (NaF ), potassium fluoride (KF), potassium bromine fluoride (KBrF ₄ ), potassium hydrogen fluoride (KHF ₂ ), calcium hexafluorophosphate (KPF ₆ ), potassium hexafluorosilicate (K ₂ SiF ₆ ), It may be at least one selected from the group consisting of lithium hexafluoroaluminate (Li ₃ AlF ₆ ), ammonium hexafluoroaluminate ((NH ₄ ) ₃ AlF ₆ ), and potassium fluorophosphate (KPO ₂ F ₂ ). Meanwhile, the chloride may be at least one selected from the group consisting of lithium chloride (LiCl), potassium chloride (KCl), chromium chloride (CrCl ₂ ), calcium chloride (CaCl ₂ ), and bromine chloride (BrCl).

The present invention can provide an electrolysis method for electrolyzing an aluminum-scandium alloy using the electrolytic cell.

An electrolytic method according to an embodiment of the present invention includes supplying scandium oxide and an electrolyte 70 to the electrolytic bath, heating the electrolytic bath, and applying a current to the electrolytic bath to perform an electrolysis process. can do.

Specifically, the electrolysis process may be performed by supplying scandium oxide and the electrolyte 70 to the electrolytic bath, heating the scandium oxide and the electrolyte, and applying current to the cathode and anode 10 included in the electrolysis bath. Through this electrolysis method, in the anode, chlorine ions or fluorine ions in the electrolyte may be oxidized to generate by-product gases 60 such as chlorine gas, fluorine gas, carbon dioxide, and carbon monoxide. Meanwhile, the scandium oxide supplied to the electrolytic cell may be reduced at the interface between molten aluminum, which is a negative electrode, and the electrolyte to form an aluminum-scandium alloy.

In the heating step, heating is preferably performed in a temperature range of 900 to 1300 ° C. If the heating temperature is less than 900 ° C, it is difficult to perform the electrolysis process because the salt does not melt, and if it exceeds 1300 ° C, it is difficult to operate the high-temperature electrolysis process. It is uneconomical due to increased energy costs for

Meanwhile, in the step of applying current to the cathode and anode 10 to perform the electrolysis process, the current applied to the cathode and anode is preferably -1.0 to -2.0A. If the applied current is less than -1.0A or exceeds -2.0A, the reduction reaction of the aluminum-scandium alloy does not occur in the electrolytic bath, and the recovery rate of the alloy may be reduced.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are merely examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

Example

An electrolytic cell body 30 filled with sodium fluoride, aluminum fluoride, and calcium fluoride as electrolyte 70, a carbon anode 10 impregnated with the electrolyte, and an aluminum cathode 40 disposed on the bottom of the electrolytic cell body. An electrolytic cell was prepared, and scandium oxide was supplied to the electrolytic cell body. The carbon anode is the anode of FIG. 3 in which a plurality of valleys and crests are formed on the surface in the transverse direction of the anode. After heating the scandium oxide and the electrolyte included in the electrolytic cell body to 1000 ° C, an electrolysis process was performed by applying a current of -1.5 A to the cathode and anode.

The density of molten aluminum is 2.975 g/m ³ and the weight is 80 g. Meanwhile, the electrolyte 70 is 38% by weight of sodium fluoride, 26% by weight of aluminum fluoride, and 36% by weight of calcium fluoride, and has a density of 2.12 g/m ³ . After the electrolytic process, the recovered aluminum-scandium alloy weighed 79.3 g, the recovery rate was 99%, and no solidified aluminum droplets were found. 7 is a graph showing the results of analysis using X-ray diffraction (XRD) of metal generated on the surface of the cathode, and it was confirmed that the aluminum-scandium alloy was prepared.

comparative example

An electrolytic cell body 30 filled with sodium fluoride, aluminum fluoride, and calcium fluoride as electrolyte 70, a carbon anode 10 impregnated with the electrolyte, and an aluminum cathode 40 disposed on the bottom of the electrolytic cell body. An electrolytic cell was prepared, and scandium oxide was supplied to the electrolytic cell body. The carbon anode is the anode of FIG. 2 having a flat surface. After heating the scandium oxide and the electrolyte included in the body of the electrolytic cell to 1000° C., an electrolysis process was performed by applying a current of -1.5 A to the cathode and anode.

The density of molten aluminum is 2.975 g/m ³ and the weight is 80 g. Meanwhile, the electrolyte 70 is 38% by weight of sodium fluoride, 26% by weight of aluminum fluoride, and 36% by weight of calcium fluoride, and has a density of 2.12 g/m ³ . After the electrolytic process, the recovered aluminum-scandium alloy weighs 50 g, and the recovery rate is very low at 62%. In addition, solidified aluminum droplets produced by solidification of the molten aluminum droplet 50 have been found. 8 is a photograph of the solidified aluminum droplet, confirming that the diameter is approximately 3 to 8 mm.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible without departing from the technical spirit of the present invention described in the claims. It will be obvious to those skilled in the art.

10: anode
20: uneven part
30: Electrolyzer body
40: aluminum cathode
50: aluminum droplet
60: by-product gas
70: electrolyte

Claims (11)

an anode for electrolysis of an aluminum-scandium master alloy;
Electrolyzer body filled with electrolyte; and
Including; an aluminum cathode disposed at the bottom of the electrolytic cell,
The anode has a cylindrical shape consisting of a bottom and a side surface,
An uneven portion is formed on the side surface of the anode,
An electrolytic cell in which an uneven portion is not formed on a bottom surface where the anode faces the cathode.
According to claim 1,
The uneven portion includes a plurality of valleys and crests.
According to claim 2,
The valleys and crests are formed in the longitudinal or transverse direction of the anode.
According to claim 2,
The trough and the ridge form a screw thread.
According to claim 2,
The trough and the crest are curved, straight, or both of these shapes.
According to claim 1,
The uneven portion includes a plurality of protrusions formed to protrude from the surface of the anode.
delete delete According to claim 1,
The electrolyte is fluoride, chloride or a mixture thereof.
supplying scandium oxide and an electrolyte to the electrolytic cell of claim 1;
heating the electrolyzer; and
An electrolysis method comprising the step of applying a current to the electrolysis cell to perform an electrolysis process.
According to claim 10,
The heating is an electrolysis method in which the temperature is 1000 to 1100 ° C.

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