Patent Application
20250215593
This application claims priority of Taiwan Patent Application No. 112151489, filed on Dec. 29, 2023, the entirety of which is incorporated by reference herein.
The present disclosure relates to a cathode for rare earth molten salt electrolysis and an electrolysis system comprising the same.
Rare earth elements have a critical impact on improving product performance and are used in a wide range of applications, including permanent magnets, ceramics and glass, optoelectronics, catalytic raw materials, superconductivity, green energy and other fields. However, in addition to the production of carbon monoxide and carbon dioxide during a rare earth fluoride molten salt electrolysis process, fluorine gas and fluorocarbons may be produced under high current density of an anode, causing greenhouse gas emissions. Therefore, it is necessary to reduce the local current density of the cathode and the current density of the anode in the molten salt electrolysis process through designing the electrode structure and arranging the electrodes in an electrolysis system to increase the yield of rare earth metals.
In accordance with one embodiment of the present disclosure, a cathode for rare earth molten salt electrolysis to prepare rare earth metals is provided. The cathode includes a column. The bottom of the column includes a cone. The peak of the cone includes a sharp tip or a flat surface. When the peak of the cone is a sharp tip, an opening angle of the sharp tip is between 5 degree and 175 degree.
In one embodiment, the cathode includes tungsten, molybdenum, tantalum or alloy thereof.
In one embodiment, when the peak of the cone is a sharp tip and the slant lengths of the cone are the same, an opening angle of the sharp tip is calculated by formula (I):
In formula (I), c is a diameter of the column, a is a slant length of the cone, and γ is an opening angle of the sharp tip.
In one embodiment, the slant lengths of the cone are different.
In accordance with one embodiment of the present disclosure, an electrolysis system is provided. The electrolysis system includes a cathode, at least one anode, and an electrolyte containing rare earth oxides. The cathode and the at least one anode are disposed in the electrolyte. The ratio of the surface area of the cathode to the surface area of the at least one anode is between 1:100 and 1:1.
In one embodiment, the cathode includes a column. In one embodiment, the bottom of the column includes a plane, an arc or a cone.
In one embodiment, the peak of the cone includes a sharp tip or a flat surface. In one embodiment, when the peak of the cone is a sharp tip, an opening angle of the sharp tip is between 5 degree and 175 degree. In one embodiment, when the peak of the cone is a sharp tip and the slant lengths of the cone are the same, the opening angle of the sharp tip is calculated by formula (I):
In formula (I), c is a diameter of the column, a is a slant length of each side of the cone, and γ is an opening angle of the sharp tip.
In one embodiment, the peak of the cone is a sharp tip and the slant lengths of the cone are different.
In one embodiment, the at least one anode surrounds the cathode.
In one embodiment, the cathode includes tungsten, molybdenum, tantalum or alloy thereof. In one embodiment, the at least one anode includes graphite.
In one embodiment, the rare earth oxides include neodymium oxide, praseodymium oxide or dysprosium oxide.
In the present disclosure, a fluoride-based/rare earth molten salt electrolyte system is utilized. The anodes are graphite. The cathode is tungsten, molybdenum, or tantalum, and its shape is columnar, conical, or a combination thereof. The cathode is placed in the center of the crucible. The anodes are disposed around the cathode or in a symmetrical position. After current is conducted, an electrolysis reaction proceeds. During the electrolysis process, since the melting point of the generated rare earth metal is lower than the melting point of the cathode, the surface of the cathode is first electrolyzed into metal droplets, and the droplets fall into the underneath crucible.
The dimension and the shape of the cathode will affect the local current density, causing the reduced rare earth metal to form droplets of different sizes. For example, when the same current density is provided, there will be an accumulation of current at the peak of the electrode which increases the local current density, causing an increase in the amount of precipitated metal droplets after the electrolysis process, and an increase in the diameter of the metal droplets, making it easier to collect the metal droplets and to achieve a high electrolysis efficiency.
When the particle size of the obtained rare earth metal droplets becomes larger, the specific surface area becomes proportionally smaller. This phenomenon can significantly reduce metal oxidation and improve the electrolysis efficiency.
The main technology of the present disclosure is to design the electrode structure in a fluorine-containing molten salt metal-electrolysis system, in order to increase the recovery rate of electrolyzed metal and reduce the anode current density, avoiding the formation of fluorine gas/fluoride which maybe produced during fluorine salt electrolyte decomposition. Rare earth metals is then precipitated and aggregated to increase metal yield.
The disclosure can be more fully understood from the following detailed description when read with the accompanying figures. It is worth noting that in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
Various embodiments or examples are provided in the following description to implement different features of the present disclosure.
In this specification, the terms “about”, “around” and “substantially” typically mean a value is in a range of +/−15% of a stated value, typically a range of +/−10% of the stated value, typically a range of +/−5% of the stated value, typically a range of +/−3% of the stated value, typically a range of +/−2% of the stated value, typically a range of +/−1% of the stated value, or typically a range of +/−0.5% of the stated value. The stated value of the present disclosure is an approximate value. Namely, the meaning of “about”, “around” and “substantially” may be implied if there is no specific description of “about”, “around” and “substantially”.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It should be appreciated that, in each case, the term, which is defined in a commonly used dictionary, should be interpreted as having a meaning that conforms to the relative skills of the present disclosure and the background or the context of the present disclosure, and should not be interpreted in an idealized or overly formal manner unless so defined.
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In formula (I), c is a diameter of the cathode 12, a is a slant length of the side 12B′ of the bottom 12B of the cone, and γ is an opening angle of the sharp tip.
In one embodiment, the peak 12Bb of the bottom 12B of the cathode 12 is a sharp tip, and the slant length “a” of the side 12B′ is different from the slant length “b” of the side 12B″ of the bottom 12B of the cone (not shown).
As shown in
The shape of the cathode 12 of the present disclosure is not limited to the shapes shown in
In one embodiment, the rare earth oxides in the electrolyte include neodymium oxide, praseodymium oxide or dysprosium oxide.
A rare earth oxide (e.g., neodymium oxide (Nd2O3)) is added to an electrolyte containing rare earth fluoride (e.g., neodymium fluoride (NdF3)) and lithium fluoride (LiF), and the electrolyte is placed in a graphite crucible. Next, the graphite crucible is moved into a metal cavity that can be sealed and protected by inert gas, and the temperature is heated to above 1050° C. An electrolysis is performed using graphite as an anode and tungsten as a cathode, and then neodymium metal can be obtained on the tungsten electrode or in the electrolyte.
A neodymium oxide (1.5 wt %) was added to an electrolyte containing 90% neodymium fluoride and 10% lithium fluoride, and the above electrolyte was placed in a graphite crucible. Next, the graphite crucible was moved into a metal cavity that can be sealed and protected by inert gas (Ar), and was then heated to 1050° C. An electrolysis was performed using graphite as an anode and tungsten as a cathode, and then neodymium metal was obtained on the tungsten electrode or in the electrolyte.
The diameter of the anode was 10 mm, and the length was 150 mm. The diameter of the cathode was 10 mm, and the length was 150 mm. The cathode was a columnar structure with a flat bottom. The ratio of the surface area of the cathode to the surface area of the anode was 1:1. The electrodes were immersed into the electrolyte to a depth of 50 mm. The current density was 150 ASD. The electrolysis time was 2 hours. The diameter of the tungsten electrode, the maximum particle size and the specific surface area of the metal droplets are listed in Table 1 below.
According to Table 1, the electrolysis reaction carried out with the electrolysis system of t example 1 (cathode: columnar structure, flat bottom, 10 mm of diameter), the obtained maximum particle size of the neodymium metal droplets ranges from 6 mm to 7 mm, and its specific surface area ranges from 0.69 cm2/g to 1.01 cm2/g.
A neodymium oxide (1.5 wt %) was added to an electrolyte containing 90% neodymium fluoride and 10% lithium fluoride, and the above electrolyte was placed in a graphite crucible. Next, the graphite crucible was moved into a metal cavity that can be sealed and protected by inert gas (Ar), and was then heated to 1050° C. An electrolysis was performed using graphite as an anode and tungsten as a cathode, and then neodymium metal was obtained on the tungsten electrode or in the electrolyte.
The diameter of the anode was 10 mm, and the length was 150 mm. The diameter of the cathode was 3.2 mm, and the length was 150 mm. The cathode was a columnar structure with a flat bottom. The ratio of the surface area of the cathode to the surface area of the anode was 1:3.16. The electrodes were immersed into the electrolyte to a depth of 50 mm. The current density was 150 ASD. The electrolysis time was 2 hours. The diameter of the tungsten electrode, the maximum particle size and the specific surface area of the metal droplets are listed in Table 2 below.
According to Table 2, the electrolysis reaction carried out with the electrolysis system of example 2 (cathode: columnar structure, flat bottom, 3.2 mm of diameter), the obtained maximum particle size of the neodymium metal droplets ranges from 15 mm to 16 mm, and its specific surface area ranges from 0.48 cm2/g to 0.51 cm2/g.
It can be seen from the results shown in Table 1 and Table 2 that when the diameter of the tungsten electrode in the electrolysis system is reduced from 10 mm to 3.2 mm, the maximum particle size of the obtained neodymium metal droplets becomes significantly larger and the specific surface area becomes significantly smaller, which will reduce the oxidation of the neodymium metal and improve the electrolysis efficiency.
A neodymium oxide (1.5 wt %) was added to an electrolyte containing 90% neodymium fluoride and 10% lithium fluoride, and the above electrolyte was placed in a graphite crucible. Next, the graphite crucible was moved into a metal cavity that can be sealed and protected by inert gas (Ar), and was then heated to 1050° C. An electrolysis was performed using graphite as an anode and tungsten as a cathode, and then a neodymium metal was obtained on the tungsten electrode or in the electrolyte.
The diameter of the anode was 10 mm, and the length was 150 mm. The diameter of the cathode was 3.2 mm, and the length was 150 mm. The cathode was a columnar structure with a sharp tip bottom, and the opening angle of the cone was calculated by formula (I). The ratio of the surface area of the cathode to the surface area of the anode was 1:3.42. The electrodes were immersed into the electrolyte to a depth of 50 mm. The current density was 150 ASD. The electrolysis time was 2 hours. The diameter of the tungsten electrode, the maximum particle size, and the specific surface area of the metal droplets are listed in Table 3 below.
According to Table 3, the electrolysis reaction carried out with the electrolysis system of example 3 (cathode: a combination of columnar and conical structures, tip bottom, 3.2 mm of diameter), the obtained maximum particle size of the neodymium metal droplets ranges from 16 mm to 18 mm, and its specific surface area ranges from 0.37 cm2/g to 0.48 cm2/g.
It can be seen from the results shown in Table 2 and Table 3 that when the bottom structure of the tungsten electrode in the electrolysis system is changed from a flat surface to a sharp tip, since the electrode tip can induce current accumulation and produce an increase in local current density, the diameter of the obtained metal droplets can be further increased and the specific surface area can be further reduced. In this way, the amount of precipitated metal after electrolysis can be increased, the metal droplets can be collected more easily, and a high electrolysis efficiency can be achieved.
A neodymium oxide (2.0 wt %) was added to an electrolyte containing 76% neodymium fluoride, 20% lithium fluoride and 4% barium fluoride, and the above electrolyte was placed in a graphite crucible. Next, the graphite crucible was moved into a metal cavity that can be sealed and protected by inert gas (Ar), and was then heated to 1050° C. An electrolysis was performed using graphite as an anode and tungsten as a cathode, and then a neodymium metal was obtained on the tungsten electrode or in the electrolyte.
The diameter of the anode was 10 mm, and the length was 150 mm. The diameter of the cathode was 6.5 mm, and the length was 150 mm. The cathode was a columnar structure with a flat bottom. The ratio of the surface area of the cathode to the surface area of the anode was 1:1.58. The electrodes were immersed into the electrolyte to a depth of 30 mm. The current density was 120 ASD. The electrolysis time was 2 hours. The diameter of the tungsten electrode, the maximum particle size, and the specific surface area of the metal droplets are listed in Table 4 below.
According to Table 4, the electrolysis reaction carried out with the electrolysis system of example 4 (cathode: columnar structure, flat bottom, 6.5 mm of diameter), the obtained maximum particle size of the neodymium metal droplets ranges from 7 mm to 9 mm, and its specific surface area ranges from 0.96 cm2/g to 1.24 cm2/g.
A neodymium oxide (2.0 wt %) was added to an electrolyte containing 76% neodymium fluoride, 20% lithium fluoride and 4% barium fluoride, and the above electrolyte was placed in a graphite crucible. Next, the graphite crucible was moved into a metal cavity that can be sealed and protected by inert gas (Ar), and was then heated to 1050° C. An electrolysis was performed using graphite as an anode and tungsten as a cathode, and then a neodymium metal was obtained on the tungsten electrode or in the electrolyte.
The diameter of the anode was 10 mm, and the length was 150 mm. The diameter of the cathode was 3.2 mm, and the length was 150 mm. The cathode was a columnar structure with a flat bottom. The ratio of the surface area of the cathode to the surface area of the anode was 1:3.29. The electrodes were immersed into the electrolyte to a depth of 30 mm. The current density was 120 ASD. The electrolysis time was 2 hours. The diameter of the tungsten electrode, the maximum particle size, and the specific surface area of the metal droplets are listed in Table 5 below.
According to Table 5, the electrolysis reaction carried out with the electrolysis system of example 5 (cathode: columnar structure, flat bottom, 3.2 mm of diameter), the obtained maximum particle size of the neodymium metal droplets ranges from 14 mm to 15 mm, and its specific surface area ranges from 0.58 cm2/g to 0.62 cm2/g.
It can be seen from the results shown in Table 4 and Table 5 that when the electrolyte composition is adjusted (for example, barium fluoride is added), if the diameter of the tungsten electrode is reduced from 6.5 mm to 3.2 mm, the maximum particle size of the resulting neodymium metal will still increase, and the specific surface area will still decrease. That is, during the electrolysis process, adjusting the electrolyte composition will have little impact on the electrolysis efficiency. In contrast, the dimension of the cathode should be one of the mains factors in determining whether the electrolysis efficiency can be further improved.
The Relationship Between the Particle Size of Metal Droplet Obtained from Different Electrolysis Systems (with Different Dimensions and Shapes of Cathode) and the Corresponding Current Efficiency
In example 6, different electrolysis systems (I, II, III, and IV) were used to perform electrolysis reactions. The relationship between the particle size of the metal droplets obtained and the corresponding current efficiency is shown in Table 6 below and
Electrolysis system I: the electrolysis system as shown in Example 1 (cathode: columnar structure, flat bottom, 10 mm of diameter).
Electrolysis system II: the electrolysis system as shown in Example 4 (cathode: columnar structure, flat bottom, 6.5 mm of diameter).
Electrolysis system III: the electrolysis system as shown in Example 5 (cathode: columnar structure, flat bottom, 3.2 mm of diameter).
Electrolysis system IV: the electrolysis system as shown in Example 3 (cathode: a combination of columnar and conical structures, sharp tip bottom, 3.2 mm in diameter).
It can be seen from the results shown in Table 6 and
In the present disclosure, a fluoride-based/rare earth molten salt electrolyte system is utilized. The anodes are graphite. The cathode is tungsten, molybdenum, or tantalum, and its shape is columnar, conical, or a combination thereof. The cathode is placed in the center of the crucible. The anodes are disposed around the cathode or in a symmetrical position. After current is conducted, a electrolysis reaction proceeds. During the electrolysis process, since the melting point of the generated rare earth metal is lower than the melting point of the cathode, the surface of the cathode is first electrolyzed into metal droplets, and the droplets fall into the underneath crucible.
The dimension and the shape of the cathode will affect the local current density, causing the reduced rare metal to form droplets of different sizes. For example, when the same current density is provided, there will be an accumulation of current at the peak of the electrode which increases the local current density, causing an increase in the amount of precipitated metal droplets after electrolysis and an increase in its diameter, making it easier to collect the metal droplets and to achieve a high electrolysis efficiency.
When the particle size of the obtained rare earth metal becomes larger, the specific surface area becomes proportionally smaller. This phenomenon can significantly reduce metal oxidation and improve electrolysis efficiency.
The main technology of the present disclosure is to design electrode structure in a fluorine-containing molten salt metal-electrolysis system, in order to increase the recovery rate of the electrolyzed metal and to reduce the anode current density, avoiding the formation of fluorine gas/fluoride produced from the decomposition of fluorine salt electrolyte. Rare earth metals is then precipitated and aggregated to increase rare earth metal yield.
Although some embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. The features of the various embodiments can be used in any combination as long as they do not depart from the spirit and scope of the present disclosure. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods or steps. In addition, each claim constitutes an individual embodiment, and the claimed scope of the present disclosure includes the combinations of the claims and embodiments. The scope of protection of present disclosure is subject to the definition of the scope of the appended claims. Any embodiment or claim of the present disclosure does not need to meet all the purposes, advantages, and features disclosed in the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 112151489 | Dec 2023 | TW | national |
