A quaternary molten salt system and a method for preparing rare earth metals and alloys thereof by electrolysis

Abstract

The present invention belongs to the technical field of rare earth metal electrolytic processing, and specifically relates to a quaternary molten salt system, and further discloses a method for preparing rare earth metals and their alloys by electrolysis based on the quaternary molten salt system. The quaternary molten salt system for producing rare earth metals and their alloys described in the present invention is a mixed system of rare earth fluorides, lithium fluoride, barium fluoride and potassium fluoride. The quaternary molten salt system described in the present invention can stabilize the stability of each component in the electrolytic molten salt, thereby improving the electrolysis efficiency of rare earth metals and their alloys and reducing production costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth metal electrolytic processing, and specifically relates to a quaternary molten salt system, and further discloses a method for electrolytically preparing rare earth metals and alloys thereof based on the quaternary molten salt system. Background Art

[0002] Rare earth metals, also known as rare earth elements, are a general term for 17 elements in the scandium, yttrium, and lanthanide series in the IIIB group of the periodic table, usually represented by R or RE. Rare earth metals are mainly used in industrial fields such as metallurgy, petrochemicals, glass ceramics, fluorescence, and electronic materials, and are currently irreplaceable raw materials in industry. At present, the extraction of rare earth metals can be carried out by molten salt electrolysis, which generally uses rare earth chlorides as electrolytic raw materials and alkali metals and alkaline earth metal chlorides as electrolytes. Molten salt electrolysis is a continuous production process with the advantages of large output, low cost, and simple equipment. It is suitable for industrial production and has been widely used in large-scale industrial production of rare earth metals and their alloys.

[0003] At present, the molten salt electrolysis process of rare earth metals (alloys) is mainly divided into two electrolyte systems: one is the chloride rare earth electrolyte system, that is, a binary system such as RECl3-KCl; the other is the fluoride-oxide rare earth electrolyte system, that is, RE2O3-REF3-LiF. Due to the high volatility of chloride molten salts and the high solubility of rare earth metals in the corresponding chloride molten salts, it is easy to cause problems such as high power consumption, low current efficiency, and low yield; and because rare earth chlorides are easy to absorb moisture, and a large amount of chlorine gas is produced during the electrolysis process, the environmental pollution is serious. The fluoride molten salt system oxide electrolysis process has become the mainstream production process.

[0004] At present, the molten salt system used in the electrolysis of rare earth metals and alloys in fluoride molten salts is lithium fluoride (LiF)-rare earth fluoride (REF) as the molten salt system, and rare earth oxide is added as the raw material into the molten salt system for electrolysis. In the traditional electrolysis process, tungsten rods are used as cathodes in the production of rare earth metals such as lanthanum, cerium, praseodymium, and neodymium. Pure iron rods are generally used as cathode materials in the electrolysis of medium and heavy rare earth metals and their alloys. The top plug-in type is mainly used for the preparation of some high-melting-point rare earth metals, such as holmium iron, gadolinium iron, dysprosium iron, terbium iron and other metals.

[0005] Chinese patent CN114635162A discloses a method for preparing aluminum rare earth multi-element alloy by molten salt electrolysis with a consumable cathode, and discloses a method for preparing aluminum rare earth multi-element alloy by molten salt electrolysis. A multi-element rare earth aluminum alloy is formed by using a high-temperature aluminum alloy rod as an upper plug-in cathode for electrolyzing rare earths. The melting point of the formed multi-element rare earth aluminum alloy is lower than the electrolysis temperature, and the alloy drips from the cathode surface into the tungsten and molybdenum crucibles at the bottom of the electrolytic cell. The electrolyte components are rare earth fluoride, and one or more of lithium fluoride, sodium fluoride, potassium fluoride, calcium fluoride, barium fluoride, rare earth chloride, potassium chloride, sodium chloride, calcium chloride, aluminum fluoride, and cryolite, wherein the content of rare earth fluoride is 10% to 80%. According to the active sequence table of elements, the sodium / calcium ions in sodium fluoride / sodium chloride / calcium fluoride / calcium chloride will be continuously discharged during the electrolysis process to form liquid metal sodium / calcium. However, due to the low density of metallic sodium / calcium, it is easy to float on the surface of the molten salt and oxidize into sodium / calcium oxide when in contact with air. The sodium / calcium oxide continues to be electrolyzed and oxidized, and the electrolysis and oxidation reactions occur repeatedly, thereby reducing the efficiency of the electrolysis current, affecting product quality and output, and thus increasing the cost of the electrolytic product.

[0006] Chinese patent CN108950605A discloses a method for preparing rare earth metals or alloys by electrolysis in a quaternary molten salt system, wherein rare earth oxides are added to a quaternary molten salt electrolyte system, and rare earth metals or rare earth alloys are prepared by electrolysis; wherein the quaternary molten salt electrolyte system is a combination of rare earth fluorides, lithium fluoride, barium fluoride and calcium fluoride. Based on the same situation, since calcium fluoride will continuously discharge during the electrolysis process to form liquid metal calcium, due to the small density of metal calcium, it is easy to float on the surface of the molten salt and oxidize to calcium oxide in contact with air, and the calcium oxide continues to be electrolyzed and oxidized, and the electrolysis and oxidation reactions occur repeatedly, thereby reducing the efficiency of the electrolysis current, affecting the product quality and output, and thus increasing the cost of the electrolysis product.

[0007] Therefore, although the production of rare earth metals using lithium fluoride (LiF)-rare earth fluoride (REF) as a molten salt system has been going on for decades, lithium fluoride helps to improve conductivity and reduce the initial crystallization temperature and electrolyte density of the melt during molten salt electrolysis. However, under electrolysis conditions, it has a dissolving effect on rare earth metals, affecting the process and efficiency of electrolysis. Moreover, with the continuous development of new energy batteries, especially the continuous rise in the price of lithium resources, the production cost of rare earth metals has continued to increase. Therefore, the art expects to develop a molten salt system with better electrolysis efficiency to improve the efficiency of the rare earth electrolysis process and improve its economic benefits. Summary of the invention

[0008] To this end, the first object of the present invention is to provide a quaternary molten salt system to solve the problem that the molten salt system in the prior art affects the rare earth electrolysis production index;

[0009] The second object of the present invention is to provide a method for preparing rare earth metals and their alloys by electrolysis based on the quaternary molten salt system.

[0010] In order to solve the above technical problems, the present invention provides a quaternary molten salt system, wherein the quaternary molten salt system comprises a mixture of rare earth fluoride (REF), lithium fluoride (LiF), potassium fluoride (KF) and barium fluoride (BaF2);

[0011] The mass ratio of the rare earth fluoride, lithium fluoride, potassium fluoride and barium fluoride is 65.0-94.8:4.0-23.0:0.2-3.0:1.0-10.0.

[0012] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of praseodymium-neodymium metal;

[0013] The quaternary molten salt system comprises a mixture of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 81.6-92.8:6.0-11.9:0.2-1.5:1.0-5.0.

[0014] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of praseodymium-neodymium metal;

[0015] The quaternary molten salt system comprises a mixture of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0-90.0:6.0-11.9:0.2-1.5:1.0-5.0.

[0016] Preferably, the mass ratio of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride is 87.0-90.0:7.3-11.0:0.3-0.5:1.4-1.7.

[0017] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of praseodymium-neodymium metal;

[0018] The quaternary molten salt system includes a mixture of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0:11.0:0.3:1.7.

[0019] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic lanthanum;

[0020] The quaternary molten salt system comprises a mixture of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 65.0-88.0:10.0-23.0:0.5-2.0:1.5-10.0.

[0021] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic lanthanum;

[0022] The quaternary molten salt system comprises a mixture of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 75.0-78.0:10.0-23.0:0.5-2.0:1.5-10.0.

[0023] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic lanthanum;

[0024] The quaternary molten salt system includes a mixture of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 75.0:17.5:1.25:6.25.

[0025] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic neodymium;

[0026] The quaternary molten salt system comprises a mixture of neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 82.0-92.8:6.0-11.0:0.2-1.5:1.0-5.5.

[0027] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic neodymium;

[0028] The quaternary molten salt system comprises a mixture of neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0-89.0:6.0-11.0:0.2-1.5:1.0-5.5.

[0029] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic neodymium;

[0030] The quaternary molten salt system includes a mixture of neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0:11.0:0.5:1.5.

[0031] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of dysprosium-iron alloy;

[0032] The quaternary molten salt system comprises a mixture of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 82.0-92.8:4.0-7.5:0.2-1.5:1.0-6.

[0033] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of dysprosium-iron alloy;

[0034] The quaternary molten salt system comprises a mixture of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 89.0-92.8:4-6:0.8-1.0:2.4-4.0.

[0035] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of dysprosium-iron alloy;

[0036] The quaternary molten salt system includes a mixture of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 91.1:6.0:0.4:2.5.

[0037] Specifically, the quaternary molten salt system of the present invention is used for preparing metallic cerium by electrolysis;

[0038] The quaternary molten salt system comprises a mixture of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 71.5-92.5:5.0-17.5:0.5-3.0:2.0-8.0.

[0039] Specifically, the quaternary molten salt system of the present invention is used for preparing metallic cerium by electrolysis;

[0040] The quaternary molten salt system comprises a mixture of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 80.0-84.0:5.0-17.5:0.5-3.0:2.0-8.0.

[0041] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic cerium;

[0042] The quaternary molten salt system includes a mixture of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 83.0:11.9:0.85:4.25.

[0043] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of lanthanum-cerium alloy;

[0044] The quaternary molten salt system comprises a mixture of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 71.5-92.5:5.0-17.5:0.5-3.0:2.0-8.0.

[0045] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of lanthanum-cerium alloy;

[0046] The quaternary molten salt system comprises a mixture of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 80.0-83.0:6.0-17.5:0.5-3.0:2.0-8.0.

[0047] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of lanthanum-cerium alloy;

[0048] The quaternary molten salt system includes a mixture of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 80.0:15.0:1.0:4.0.

[0049] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic praseodymium;

[0050] The quaternary molten salt system comprises a mixture of praseodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 77.3-92.2:6.0-15.2:0.3-1.5:1.5-6.0.

[0051] Specifically, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic praseodymium;

[0052] The quaternary molten salt system comprises a mixture of praseodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 83.0-86.5:6.0-15.2:0.3-1.5:1.5-6.0.

[0053] Preferably, the quaternary molten salt system of the present invention is used for electrolytic preparation of metallic praseodymium;

[0054] The quaternary molten salt system includes a mixture of praseodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 86.0:10.5:0.7:2.8.

[0055] The invention also discloses the use of the quaternary molten salt system for electrolytic preparation of rare earth metals and alloys thereof.

[0056] Specifically, the rare earth metal and its alloy include at least one of metal lanthanum, metal cerium, metal praseodymium, metal neodymium, lanthanum-cerium alloy, praseodymium-neodymium alloy or rare earth iron alloy;

[0057] Preferably, the rare earth iron alloy includes at least one of neodymium iron, gadolinium iron, dysprosium iron, holmium iron or terbium iron.

[0058] The present invention also discloses a method for preparing rare earth metals and alloys thereof by electrolysis based on a quaternary molten salt system, comprising the steps of adding rare earth oxides for electrolysis in the presence of the quaternary molten salt system.

[0059] Specifically, in the method for preparing rare earth metals and their alloys by electrolysis, the rare earth oxides include oxides of metal lanthanum, metal cerium, metal praseodymium, metal neodymium, lanthanum-cerium alloy, praseodymium-neodymium alloy or rare earth-iron alloy.

[0060] Specifically, in the method for preparing rare earth metals and their alloys by electrolysis, in the electrolysis step, the direct current is controlled to be 5500-6500A.

[0061] Specifically, the method for preparing rare earth metals and their alloys by electrolysis uses a molybdenum crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode.

[0062] Specifically, the method for preparing rare earth metals and their alloys by electrolysis further comprises the step of stirring with a molybdenum rod.

[0063] The quaternary molten salt system for producing rare earth metals and their alloys described in the present invention is a quaternary molten salt system formed by adding potassium fluoride and barium fluoride to the traditional REF-LiF binary system. Compared with the traditional molten salt system, the scheme of the present invention effectively avoids the situation that the fluidity of the melt is poor due to the single increase of the amount of barium fluoride, and the situation that the excessive use of potassium fluoride leads to low viscosity of the molten salt and aggravated melt flow, by adding part of potassium fluoride and barium fluoride in a synergistic manner. At the same time, it also avoids the introduction of other impurities into the product, thereby affecting the product quality.

[0064] The quaternary molten salt system of the present invention effectively ensures the reasonable usage of lithium fluoride and barium fluoride by adopting the REF-LiF-KF-BaF2 quaternary molten salt system with a suitable ratio, thereby reducing the production cost, effectively solving the defects of the traditional molten salt system, and also increasing the barium fluoride to inhibit the dissolution of rare earth metals and the volatilization of lithium fluoride. Part of the lithium fluoride in the molten salt system is replaced by potassium fluoride and barium fluoride, which stabilizes the ratio of each component in the electrolysis process.

[0065] The method for preparing rare earth metals and alloys thereof by electrolysis of the present invention adopts the quaternary molten salt system to effectively improve various electrolysis indicators, product quality is increased from 75% to 99.4%, shift production (8-hour production) is increased by 10-15%, anode unit production (weight of rare earth metals produced by 1kg anode) is increased from 4.5 to 5.79, an increase of 28%, current efficiency is increased from 60% to 85%, electricity unit consumption is reduced from 9.5 to 7.5, and product yield is increased from 95.6% to 99.2%. Due to the reduction in the use of lithium fluoride, the production cost per ton of product is reduced by 8.5-15%. Due to the improvement of current efficiency and the reduction of electricity unit consumption in the production process, carbon reduction of 25% is achieved. The implementation of the scheme effectively suppresses the volatilization of molten salt and improves the working environment of production workers. DETAILED DESCRIPTION

[0066] Example 1

[0067] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaF3-LiF-KF-BaF2 system with a mass ratio of 75.0:23.0:0.5:1.5.

[0068] During the electrolysis process, evenly mixed lanthanum oxide is added in batches to the molten LaF3-LiF-KF-BaF2 (75:23:0.5:1.5) mixed electrolyte in the electrolytic cell, the electrolysis current is controlled to 6025A, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum product is obtained by natural cooling.

[0069] In the present embodiment, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace is 96.2%, the monthly cumulative output (or monthly unit output) is 4190.2kg, the current efficiency is 76%, the unit electricity consumption is 8.54 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 96.8%.

[0070] Example 2

[0071] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaF3-LiF-KF-BaF2 system with a mass ratio of 78.0:10.0:2.0:10.0.

[0072] During the electrolysis process, evenly mixed lanthanum oxide is added in batches to the molten LaF3-LiF-KF-BaF2 (78:10:2:10) mixed electrolyte in the electrolytic cell, the electrolysis current is controlled to be 5934A, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum product is obtained by natural cooling.

[0073] In the present embodiment, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace was 89.2%, the monthly cumulative output (or monthly unit output) was 4455.9kg, the current efficiency was 68.9%, the unit electricity consumption was 8.87 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.4%.

[0074] Example 3

[0075] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaF3-LiF-KF-BaF2 system with a mass ratio of 75.0:17.5:1.25:6.25.

[0076] During the electrolysis process, a uniformly mixed lanthanum oxide is added in batches to the molten LaF3-LiF-KF-BaF2 (75:17.5:1.25:6.25) mixed electrolyte in the electrolytic cell, the electrolysis current is controlled to be 6011A, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, a molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum product is obtained by natural cooling.

[0077] In the present embodiment, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace is 89.2%, the monthly cumulative output (or monthly unit output) is 4871.2kg, the current efficiency is 81.5%, the unit electricity consumption is 8.12 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 97.3%.

[0078] Example 4

[0079] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaF3-LiF-KF-BaF2 system with a mass ratio of 65.0:23.0:2.0:10.0.

[0080] During the electrolysis process, the mixed and uniform lanthanum oxide is added in batches to the molten LaF3-LiF-KF-BaF2 (65.0:23.0:2.0:10.0) mixed electrolyte in the electrolytic cell, the electrolysis current is controlled to 5806A, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum product is obtained by natural cooling.

[0081] In the present embodiment, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace is 63.2%, the monthly cumulative output (or monthly unit output) is 4963.2kg, the current efficiency is 61.5%, the unit electricity consumption is 8.67 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.3%.

[0082] Example 5

[0083] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaF3-LiF-KF-BaF2 system with a mass ratio of 88.0:10.0:0.5:1.5.

[0084] During the electrolysis process, the mixed and uniform lanthanum oxide is added in batches to the molten LaF3-LiF-KF-BaF2 (88.0:10:0.5:1.5)) mixed electrolyte in the electrolytic cell, the electrolysis current is controlled to be 5902A, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum product is obtained by natural cooling.

[0085] In the present embodiment, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace is 69.2%, the monthly cumulative output (or monthly unit output) is 4756.8kg, the current efficiency is 62.4%, the unit electricity consumption is 8.87 degrees, and the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride, and barium fluoride are stable during the electrolysis process, and the product yield is 96.4%.

[0086] Comparative Example 1-1

[0087] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 1-5, the only difference being that the quaternary molten salt system comprises a LaF3-LiF-KF-BaF2 system with a mass ratio of 64.0:25.0:0.3:10.7.

[0088] In this comparative scheme, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace accounted for 56.2%, the monthly cumulative output (or monthly unit output) was 4675.2kg, the current efficiency was 56.7%, the unit electricity consumption was 9.24 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 94.6%.

[0089] Comparative Example 1-2

[0090] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 1-5, the only difference being that the quaternary molten salt system comprises a LaF3-LiF-KF-BaF2 system with a mass ratio of 89.0:8.0:2.2:0.8.

[0091] In this comparative scheme, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace accounted for 60.2%, the monthly cumulative output (or monthly unit output) was 4257.5kg, the current efficiency was 52.7%, the unit electricity consumption was 10.3 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 93.8%.

[0092] Comparative Examples 1-3

[0093] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 1-5, the only difference being that the quaternary molten salt system comprises a LaF3-LiF-KF-BaF2 system with a mass ratio of 75.0:17.5:0.3:7.2.

[0094] In this comparative scheme, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace accounted for 43.5%, the monthly cumulative output (or monthly unit output) was 4657.8kg, the current efficiency was 64.5%, the unit electricity consumption was 8.82 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 95.3%.

[0095] Comparative Examples 1-4

[0096] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that of Examples 1-5, with the only difference being that the quaternary molten salt system comprises a LaF3-LiF-KF-BaF2 system with a mass ratio of 75.0:17.5:6.3:1.2.

[0097] In this comparative scheme, the C content of metallic lanthanum (C<300ppm) during the production of a single furnace accounted for 74.3%, the monthly cumulative output (or monthly unit output) was 4798.2kg, the current efficiency was 73.1%, the unit electricity consumption was 8.43 degrees, the proportions of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.8%.

[0098] Comparative Examples 1-5

[0099] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that of Examples 1-5, the only difference being that the molten salt system comprises a LaF3-LiF-BaF2 system with a mass ratio of 75.0:17.5:7.5.

[0100] In this comparative scheme, the metal lanthanum C content (C<300ppm) during the production of a single furnace accounted for 65.3%, the monthly cumulative output (or monthly unit output) was 4563.7kg, the current efficiency was 62.3%, the unit electricity consumption was 8.67 degrees, and the product yield was 95.7%.

[0101] Comparative Examples 1-6

[0102] The process for preparing rare earth metals and their alloys by electrolysis in this comparative example is the same as that in Examples 1-5, the only difference being that the molten salt system comprises a LaF3-LiF-KF system in a mass ratio of 75.0:17.5:7.5.

[0103] In this comparative scheme, the metal lanthanum C content (C<300ppm) during the production of a single furnace accounted for 36.8%, the monthly cumulative output (or monthly unit output) was 4267.9kg, the current efficiency was 55.4%, the unit electricity consumption was 11.2 degrees, and the product yield was 93.7%.

[0104] Example 6

[0105] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 89.0:9.8:0.2:1.0.

[0106] To the molten NdF3-LiF-KF-BaF2 (89:9.8:0.2:1.0) mixed electrolyte in the electrolytic cell, uniformly mixed neodymium oxide was added in batches, the electrolysis current was controlled to be 5867A, a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal neodymium product was obtained by natural cooling.

[0107] In this embodiment, the C content of metallic neodymium (C<300ppm) during the production of a single furnace is 97.6%, the monthly cumulative output (or monthly unit output) is 5707.9kg, the current efficiency is 78.3%, the unit electricity consumption is 8.34 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride are stable during the electrolysis process, and the product yield is 98.7%.

[0108] Example 7

[0109] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 88.0:6.0:1.5:5.5.

[0110] To the molten NdF3-LiF-KF-BaF2 (88:6:1.5:5.5) mixed electrolyte in the electrolytic cell, uniformly mixed neodymium oxide was added in batches, the electrolysis current was controlled to be 5778A, a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal neodymium product was obtained by natural cooling.

[0111] In this embodiment, the C content of metallic neodymium (C<300ppm) during production of a single furnace is 94.6%, the monthly cumulative output (or monthly unit output) is 5506.3kg, the current efficiency is 74.6%, the unit electricity consumption is 8.68 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride are stable during the electrolysis process, and the product yield is 98.3%.

[0112] Example 8

[0113] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 87.0:11.0:0.5:1.5.

[0114] To the molten NdF3-LiF-KF-BaF2 (87:11:0.5:1.5) mixed electrolyte in the electrolytic cell, uniformly mixed neodymium oxide was added in batches, the electrolysis current was controlled to be 5778A, a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal neodymium product was obtained by natural cooling.

[0115] In this embodiment, the C content of metallic neodymium (C<300ppm) during production of a single furnace is 99.6%, the monthly cumulative output (or monthly unit output) is 5876.9kg, the current efficiency is 82.6%, the unit electricity consumption is 8.01 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride are stable during the electrolysis process, and the product yield is 99.1%.

[0116] Example 9

[0117] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 82.0:11.0:1.5:5.5.

[0118] To the molten NdF3-LiF-KF-BaF2 (82.0:11.0:1.5:5.5) mixed electrolyte in the electrolytic cell, uniformly mixed neodymium oxide was added in batches, the electrolysis current was controlled to be 5846A, a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal neodymium product was obtained by natural cooling.

[0119] In this embodiment, the C content (C<300ppm) of metallic neodymium during production of a single furnace is 83.4%, the monthly cumulative output (or monthly unit output) is 5798.3kg, the current efficiency is 71.4%, the unit electricity consumption is 8.45 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride are stable during the electrolysis process, and the product yield is 97.8%.

[0120] Example 10

[0121] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 92.8:6.0:0.2:1.0.

[0122] To the molten NdF3-LiF-KF-BaF2 (92.8:6.0:0.2:1.0) mixed electrolyte in the electrolytic cell, uniformly mixed neodymium oxide was added in batches, the electrolysis current was controlled to be 5532A, a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal neodymium product was obtained by natural cooling.

[0123] In this embodiment, the C content (C<300ppm) of metallic neodymium during production of a single furnace is 81.4%, the monthly cumulative output (or monthly unit output) is 5589.1kg, the current efficiency is 69.7%, the unit electricity consumption is 8.61 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride are stable during the electrolysis process, and the product yield is 97.6%.

[0124] Comparative Example 2-1

[0125] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 6-10, the only difference being that the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 80.0:14.0:0.1:5.9.

[0126] In this comparative example, the C content of metallic neodymium (C<300ppm) during the production of a single furnace was 65.4%, the monthly cumulative output (or monthly unit output) was 5267.8kg, the current efficiency was 52.8%, the unit electricity consumption was 8.98 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride were stable during the electrolysis process, and the product yield was 95.6%.

[0127] Comparative Example 2-2

[0128] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 6-10, the only difference being that the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 93.0:5.0:1.6:0.4.

[0129] In this comparative example, the C content of metallic neodymium (C<300ppm) during the production of a single furnace was 73.2%, the monthly cumulative output (or monthly unit output) was 5267.8kg, the current efficiency was 61.3%, the unit electricity consumption was 9.12 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride were stable during the electrolysis process, and the product yield was 96.7%.

[0130] Comparative Examples 2-3

[0131] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 6-10, the only difference being that the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 87.0:11.0:1.6:0.4.

[0132] In this comparative example, the C content of metallic neodymium (C<300ppm) during the production of a single furnace was 75.1%, the monthly cumulative output (or monthly unit output) was 5743.2kg, the current efficiency was 71.6%, the unit electricity consumption was 8.43 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride were stable during the electrolysis process, and the product yield was 98.2%.

[0133] Comparative Examples 2-4

[0134] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 6-10, the only difference being that the quaternary molten salt system used includes a NdF3-LiF-KF-BaF2 system with a mass ratio of 87.0:11.0:0.1:1.9.

[0135] In this comparative example, the C content of metallic neodymium (C<300ppm) during the production of a single furnace was 85.2%, the monthly cumulative output (or monthly unit output) was 5678.4kg, the current efficiency was 74.1%, the unit electricity consumption was 8.63 degrees, and the proportions of the components of neodymium fluoride, lithium fluoride, potassium fluoride, and barium fluoride were stable during the electrolysis process, and the product yield was 97.5%.

[0136] Comparative Examples 2-5

[0137] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that of Examples 6-10, the only difference being that the quaternary molten salt system used includes a NdF3-LiF-BaF2 system with a mass ratio of 87.0:11.0:2.0.

[0138] In this comparative example, the C content (C<300ppm) of metal neodymium during production of a single furnace was 81.2%, the monthly cumulative output (or monthly unit output) was 5647.2kg, the current efficiency was 66.6%, the unit electricity consumption was 8.46 degrees, and the product yield was 97.2%.

[0139] Comparative Examples 2-6

[0140] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that of Examples 6-10, the only difference being that the quaternary molten salt system used includes a NdF3-LiF-KF system with a mass ratio of 87.0:11.0:2.0.

[0141] In this comparative example, the C content (C<300ppm) of metal neodymium during production of a single furnace was 62.7%, the monthly cumulative output (or monthly unit output) was 5697.1kg, the current efficiency was 63.8%, the unit electricity consumption was 8.65 degrees, and the product yield was 96.4%.

[0142] Embodiment 11

[0143] The molten salt system described in this embodiment includes PNF3 (praseodymium neodymium fluoride)-LiF-KF-BaF2 mixture (in different quaternary molten salt electrolyte systems), PNF3 (praseodymium neodymium fluoride)-LiF, PNF3 (praseodymium neodymium fluoride)-LiF-KF, PNF3 (praseodymium neodymium fluoride)-LiF-BaF2, PNF3 (praseodymium neodymium fluoride)-LiF-NaF-BaF2, PNF3 (praseodymium neodymium fluoride)-LiF-KF-CaF2, PNF3 (praseodymium neodymium fluoride)-LiF-BaF2-CaF2 and other systems. The specific raw material composition and ratio are shown in Table 1 below.

[0144] According to the molten salt systems listed in Table 1 below, praseodymium-neodymium oxide was added in batches to the different molten salt mixtures and electrolytes melted in the electrolytic cell, and a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir the raw materials from time to time depending on the situation in the electrolytic cell to fully diffuse and dissolve the raw materials in the molten salt. After being taken out of the furnace, the raw materials were naturally cooled to obtain metallic praseodymium-neodymium.

[0145] The production conditions of praseodymium and neodymium metals at different contents of different molten salt components in this embodiment are shown in Table 1 below. The production data of each molten salt component is collected at an interval of 1 month, which is more representative.

[0146] Table 1 The electrolytic production indicators of praseodymium and neodymium metal produced by different molten salt systems

[0147]

[0148]

[0149] In the above table, the data are calculated as follows: the shift production is the average output of 8 hours in one month; the proportion of qualified Mo content products (i.e. Mo content less than 500ppm) and the proportion of qualified C content products (i.e. C content <300ppm) are the ratios of qualified Mo and C products to the total production; the unit electricity consumption is the electricity consumption per kilogram of metal (KWH).

[0150] It can be seen from the data in the above table that in the entire molten salt system, not only the influence of the selected raw material composition varies greatly, but the ratio between the various molten salt components also has a great influence.

[0151] For example, although the molten salt system schemes in No. 1 and No. 5 in Table 1 above both use the quaternary molten salt system of PNF3-LiF-KF-BaF2, the different content of the components leads to great differences in various electrolytic production indicators. The difference in unit electricity consumption is 8.77-7.51=1.26KWH, ​​that is, the difference in electricity consumption for each kg of praseodymium-neodymium metal produced is 1.26 kWh, saving 1,260 kWh of electricity per ton of metal and reducing carbon emissions by 16.3%. The difference in yield is 99.1%-96.3%=2.8%, that is, 28 kg of praseodymium-neodymium oxide is saved for each ton of metal produced, equivalent to a market price of 14,000 yuan.

[0152] For example, although the molten salt system schemes in No. 5 and No. 27 in Table 1 above use different quaternary systems of PNF3-LiF-KF-BaF2 and PNF3-LiF-BaF2-CaF2, the differences in the system and component content will also lead to greater differences in various electrolytic production indicators. For example, the difference in electricity consumption is 8.87-7.51=1.36KWH, ​​that is, the difference in electricity consumption for each kg of praseodymium-neodymium metal produced is 1.36 degrees of electricity, and the production of 1 ton of metal saves 1360 degrees of electricity and reduces carbon emissions by 16.8%; for example, the difference in yield is 99.1%-95.4%=3.7%, that is, the production of ton of metal saves 37kg of praseodymium-neodymium oxide, which is equivalent to a market price of 18,500 yuan; for example, the difference in anode yield is 5.79-4.89=0.9, that is, the anode is saved by 15% for each ton of metal produced, and the anode carbon emission is reduced by 15.5%.

[0153] For example, the existing molten salt systems of No. 11, 12, and 13 in the above table and the quaternary molten salt system of No. 5 reduce the use of lithium fluoride to a certain extent. For example, No. 11 and No. 5 can save 20kg of lithium fluoride for every ton of molten salt used, saving about 10,000 yuan in costs (the current market price of lithium fluoride is 550 yuan / kg, the price of barium fluoride is 30 yuan / kg, and the price of potassium fluoride is 32 yuan / kg).

[0154] In summary, from the production index data listed in Table 1 above, it can be seen that the quaternary molten salt system formed by barium fluoride, potassium fluoride, sodium fluoride and rare earth fluoride in the present invention has a great influence on product quality (carbon, Mo), current efficiency, power consumption, shift production, anode yield, yield, etc. Although the various production indicators do not seem to be very significant, in the actual production process, if calculated by converting into tons of metal, the improvement of the entire production index is a considerable number for carbon emissions, energy conservation and product cost reduction, and has important production significance.

[0155] Example 12

[0156] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 94.8:4.0:0.2:1.0.

[0157] To the molten DyF3-LiF-KF-BaF2 (94.8:4:0.2:1.0) mixed electrolyte in the electrolytic cell, add uniformly mixed dysprosium oxide in batches, use a pure iron crucible as a collecting crucible, a pure iron rod as a cathode, and graphite as an anode. During the electrolysis process, the pure iron rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain a dysprosium-iron alloy product.

[0158] In the present embodiment, the content of dysprosium-iron alloy products (C<300ppm) during the production of a single furnace accounted for 58.4%, the monthly cumulative output (or monthly single output) was 5213.6g, the current efficiency was 62.3%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 95.6%.

[0159] Example 13

[0160] In the process for electrolytic preparation of rare earth metals and their alloys described in this embodiment, the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 85.0:7.5:1.5:6.0.

[0161] To the molten DyF3-LiF-KF-BaF2 (85.0:7.5:1.5:6.0) mixed electrolyte in the electrolytic cell, add uniformly mixed dysprosium oxide in batches, use a pure iron crucible as a collecting crucible, a pure iron rod as a cathode, and graphite as an anode. During the electrolysis process, the pure iron rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain a dysprosium-iron alloy product.

[0162] In the present embodiment, the content of dysprosium-iron alloy products (C < 300ppm) during the production of a single furnace accounted for 62.3%, the monthly cumulative output (or monthly single output) was 5222.7 kg, the current efficiency was 58.6%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 95.4%.

[0163] Embodiment 14

[0164] In the process for electrolytic preparation of rare earth metals and their alloys described in this embodiment, the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 91.1:6.0:0.4:2.5.

[0165] To the molten DyF3-LiF-KF-BaF2 (91.1:6.0:0.4:2.5) mixed electrolyte in the electrolytic cell, add uniformly mixed dysprosium oxide in batches, use a pure iron crucible as a collecting crucible, a pure iron rod as a cathode, and graphite as an anode. During the electrolysis process, the pure iron rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain a dysprosium-iron alloy product.

[0166] In the present embodiment, the content of dysprosium-iron alloy products (C < 300ppm) during the production of a single furnace is 88.3%, the monthly cumulative output (or monthly single output) is 5608.4 kg, the current efficiency is 75.4%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 97.5%.

[0167] Embodiment 15

[0168] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 89.7:6.0:0.3:4.0.

[0169] To the molten DyF3-LiF-KF-BaF2 (89.7:6.0:0.3:4.0) mixed electrolyte in the electrolytic cell, add uniformly mixed dysprosium oxide in batches, use a pure iron crucible as a collecting crucible, a pure iron rod as a cathode, and graphite as an anode. During the electrolysis process, the pure iron rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain a dysprosium-iron alloy product.

[0170] In the present embodiment, the content of dysprosium-iron alloy products (C<300ppm) during the production of a single furnace accounted for 69.4%, the monthly cumulative output (or monthly single output) was 5723.4 kg, the current efficiency was 61.5%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.5%.

[0171] Example 16

[0172] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 92.8:4.0:0.8:2.4.

[0173] To the molten DyF3-LiF-KF-BaF2 (92.8:4.0:0.8:2.4) mixed electrolyte in the electrolytic cell, add uniformly mixed dysprosium oxide in batches, use a pure iron crucible as a collecting crucible, a pure iron rod as a cathode, and graphite as an anode. During the electrolysis process, the pure iron rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain a dysprosium-iron alloy product.

[0174] In the present embodiment, the content of dysprosium-iron alloy products (C < 300ppm) during the production of a single furnace accounted for 76.4%, the monthly cumulative output (or monthly single output) was 5582.1 kg, the current efficiency was 60.7%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.7%.

[0175] Comparative Example 3-1

[0176] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 11-16, with the only difference being that the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 83.0:9.0:0.1:6.9.

[0177] In this comparative scheme, the dysprosium-iron alloy product content (C<300ppm) during the production of a single furnace accounted for 34.5%, the monthly cumulative output (or monthly single output) was 5524.1 kg, the current efficiency was 58.4%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 93.4%.

[0178] Comparative Example 3-2

[0179] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 11-16, with the only difference being that the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 95.0:3.0:1.6:0.4.

[0180] In this comparative scheme, the dysprosium-iron alloy product content (C<300ppm) during the production of a single furnace accounted for 43.6%, the monthly cumulative output (or monthly single output) was 5491.0kg, the current efficiency was 54.9%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride components were stable during the electrolysis process, and the product yield was 94.5%.

[0181] Comparative Example 3-3

[0182] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 11-16, with the only difference being that the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 91.1:6.0:0.1:2.8.

[0183] In this comparative scheme, the dysprosium-iron alloy product content (C<300ppm) during the production of a single furnace accounted for 40.2%, the monthly cumulative output (or monthly single output) was 5346.1 kg, the current efficiency was 49.8%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 94.2%.

[0184] Comparative Examples 3-4

[0185] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 11-16, the only difference being that the quaternary molten salt system used includes a DyF3-LiF-KF-BaF2 system with a mass ratio of 91.1:6.0:2.0:0.9.

[0186] In this comparative scheme, the dysprosium-iron alloy product content (C<300ppm) during the production of a single furnace accounted for 43.5%, the monthly cumulative output (or monthly single output) was 5213.6kg, the current efficiency was 59.2%, the proportions of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 93.6%.

[0187] Comparative Examples 3-5

[0188] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 11-16, with the only difference being that the quaternary molten salt system used includes a DyF3-LiF-BaF2 system with a mass ratio of 91.1:6.0:2.9.

[0189] In this comparative example, the dysprosium-iron alloy product content (C<300ppm) during the production of a single furnace accounted for 65.3%, the monthly cumulative output (or monthly single output) was 5023.1 kg, the current efficiency was 55.4%, and the product yield was 95.3%.

[0190] Comparative Examples 3-6

[0191] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 11-16, the only difference being that the quaternary molten salt system used includes a DyF3-LiF-KF system with a mass ratio of 91.1:6.0:2.9.

[0192] In this comparative scheme, the content of dysprosium-iron alloy products (C<300ppm) during the production of a single furnace accounted for 50.2%, the monthly cumulative output (or monthly single output) was 5480.6 kg, the current efficiency was 61.2%, and the product yield was 94.7%.

[0193] Embodiment 17

[0194] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 80.0:17.5:0.5:2.0.

[0195] Add uniformly mixed cerium oxide to the molten CeF3-LiF-KF-BaF2 (80:17.5:0.5:2.0) mixed electrolyte in the electrolytic cell, use a molybdenum crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain the metallic cerium product.

[0196] In this embodiment, the C content of metallic cerium (C<300ppm) during the production of a single furnace is 85.9%, the monthly cumulative output (or monthly single output) is 4987.5kg, the current efficiency is 64.5%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.6%.

[0197] Embodiment 18

[0198] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 84.0:5.0:3.0:8.0.

[0199] Add uniformly mixed cerium oxide to the molten CeF3-LiF-KF-BaF2 (84.0:5.0:3.0:8.0) mixed electrolyte in the electrolytic cell, use a molybdenum crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode. During the electrolysis process, stir with a molybdenum rod from time to time depending on the situation in the electrolytic cell to make the raw materials fully diffuse and dissolve in the molten salt. After being taken out of the furnace, cool naturally to obtain the metallic cerium product.

[0200] In this embodiment, the C content of metallic cerium (C<300ppm) during the production of a single furnace is 76.7%, the monthly cumulative output (or monthly single output) is 4800.7kg, the current efficiency is 62.8%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.1%.

[0201] Embodiment 19

[0202] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 83.0:11.9:0.85:4.25.

[0203] Add uniformly mixed cerium oxide to the molten CeF3-LiF-KF-BaF2 (83:11.9:0.85:4.25) mixed electrolyte in the electrolytic cell, use a molybdenum crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain the metallic cerium product.

[0204] In this embodiment, the C content of metallic cerium (C<300ppm) during the production of a single furnace is 96.3%, the monthly cumulative output (or monthly single output) is 5123.3kg, the current efficiency is 78.3%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 98.2%.

[0205] Embodiment 20

[0206] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 71.5:17.5:3.0:8.0.

[0207] Add uniformly mixed cerium oxide to the molten CeF3-LiF-KF-BaF2 (71.5:17.5:3.0:8.0) mixed electrolyte in the electrolytic cell, use a molybdenum crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain the metallic cerium product.

[0208] In this embodiment, the C content of metallic cerium (C<300ppm) during the production of a single furnace is 78.6%, the monthly cumulative output (or monthly single output) is 4965.3kg, the current efficiency is 63.4%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.7%.

[0209] Embodiment 21

[0210] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 92.5:5.0:0.5:2.0.

[0211] Add uniformly mixed cerium oxide to the molten CeF3-LiF-KF-BaF2 (92.5:5.0:0.5:2.0) mixed electrolyte in the electrolytic cell, use a molybdenum crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode. During the electrolysis process, the molybdenum rod is used to stir from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, it is naturally cooled to obtain the metallic cerium product.

[0212] In this embodiment, the C content of metallic cerium (C<300ppm) during the production of a single furnace is 81.6%, the monthly cumulative output (or monthly single output) is 4567.8kg, the current efficiency is 58.4%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 96.4%.

[0213] Comparative Example 4-1

[0214] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 17-21, the only difference being that the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 71.0:19.0:0.3:9.7.

[0215] In this comparative example, the C content of metallic cerium (C<300ppm) during the production of a single furnace accounted for 53.4%, the monthly cumulative output (or monthly single output) was 4895.6kg, the current efficiency was 65.3%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 94.5%.

[0216] Comparative Example 4-2

[0217] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 17-21, the only difference being that the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 93.0:2.5:3.5:1.0.

[0218] In this comparative example, the C content of metallic cerium (C<300ppm) during the production of a single furnace accounted for 76.8%, the monthly cumulative output (or monthly single output) was 4952.8kg, the current efficiency was 63.6%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.4%.

[0219] Comparative Example 4-3

[0220] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 17-21, the only difference being that the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 83.0:11.9:3.85:1.25.

[0221] In this comparative example, the C content of metallic cerium (C<300ppm) during the production of a single furnace accounted for 85.2%, the monthly cumulative output (or monthly single output) was 5012.1kg, the current efficiency was 71.2%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.8%.

[0222] Comparative Example 4-4

[0223] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 17-21, the only difference being that the quaternary molten salt system used includes a CeF3-LiF-KF-BaF2 system with a mass ratio of 83.0:11.9:0.35:4.75.

[0224] In this comparative example, the C content of metallic cerium (C<300ppm) during the production of a single furnace accounted for 83.6%, the monthly cumulative output (or monthly single output) was 4999.5kg, the current efficiency was 68.7%, the proportions of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.9%.

[0225] Comparative Examples 4-5

[0226] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that in Examples 17-21, the only difference being that the quaternary molten salt system used includes a CeF3-LiF-BaF2 system with a mass ratio of 83.0:11.9:5.1.

[0227] In this comparative example, the metal cerium C content (C<300ppm) during the production of a single furnace accounted for 66.3%, the monthly cumulative output (or monthly single output) was 4798.1 kg, the current efficiency was 63.1%, and the product yield was 93.8%.

[0228] Comparative Examples 4-6

[0229] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 17-21, the only difference being that the quaternary molten salt system used includes a CeF3-LiF-KF system with a mass ratio of 83.0:11.9:5.1.

[0230] In this comparative example, the metal cerium C content (C<300ppm) during the production of a single furnace accounted for 46.2%, the monthly cumulative output (or monthly single output) was 4523.1 kg, the current efficiency was 55.3%, and the product yield was 92.2%.

[0231] Embodiment 22

[0232] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 80.0:17.5:0.5:2.0.

[0233] The uniformly mixed lanthanum oxide and cerium are added to the molten LaCeF3-LiF-KF-BaF2 (80:17.5:0.5:2.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum cerium product is obtained by natural cooling.

[0234] In this embodiment, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace was 88.4%, the monthly cumulative output (or monthly single output) was 4965.8kg, the current efficiency was 70.3%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 95.7%.

[0235] Embodiment 23

[0236] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 83.0:6.0:3.0:8.0.

[0237] The uniformly mixed lanthanum oxide and cerium are added to the molten LaCeF3-LiF-KF-BaF2 (83:6.0:3.0:8.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum cerium product is obtained by natural cooling.

[0238] In this embodiment, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace is 83.2%, the monthly cumulative output (or monthly single output) is 4879.4kg, the current efficiency is 62.5%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.4%.

[0239] Embodiment 24

[0240] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 80.0:15.0:1.0:4.0.

[0241] The uniformly mixed lanthanum oxide and cerium are added to the molten LaCeF3-LiF-KF-BaF2 (80.0:15.0:1.0:4.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell to allow the raw materials to fully diffuse and dissolve in the molten salt. After being taken out of the furnace, the metal lanthanum cerium product is obtained by natural cooling.

[0242] In this embodiment, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace is 98.3%, the monthly cumulative output (or monthly single output) is 5107.2kg, the current efficiency is 75.3%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 97.8%.

[0243] Embodiment 25

[0244] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 71.5:17.5:3.0:8.0.

[0245] The uniformly mixed lanthanum oxide and cerium are added to the molten LaCeF3-LiF-KF-BaF2 (71.5:17.5:3.0:8.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum cerium product is obtained by natural cooling.

[0246] In this embodiment, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace was 81.7%, the monthly cumulative output (or monthly single output) was 5024.7kg, the current efficiency was 67.8%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 95.1%.

[0247] Embodiment 26

[0248] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 92.5:5.0:0.5:2.0.

[0249] The uniformly mixed lanthanum oxide and cerium are added to the molten LaCeF3-LiF-KF-BaF2 (92.5:5.0:0.5:2.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal lanthanum cerium product is obtained by natural cooling.

[0250] In this embodiment, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace was 65.4%, the monthly cumulative output (or monthly single output) was 4798.1kg, the current efficiency was 61.7%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 94.8%.

[0251] Comparative Example 5-1

[0252] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 22-26, with the only difference being that the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 70.5:19.0:0.3:10.2.

[0253] In this comparative example, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace accounted for 62.1%, the monthly cumulative output (or monthly single output) was 4856.8kg, the current efficiency was 59.3%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 93.3%.

[0254] Comparative Example 5-2

[0255] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 22-26, with the only difference being that the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 93.0:2.5:3.5:1.0.

[0256] In this comparative example, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace accounted for 78.2%, the monthly cumulative output (or monthly single output) was 4523.1kg, the current efficiency was 53.2%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 92.6%.

[0257] Comparative Example 5-3

[0258] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 22-26, with the only difference being that the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 80.0:15.0:3.5:1.5.

[0259] In this comparative example, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace accounted for 78.3%, the monthly cumulative output (or monthly single output) was 5000.4kg, the current efficiency was 63.5%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.7%.

[0260] Comparative Example 5-4

[0261] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 22-26, with the only difference being that the quaternary molten salt system used includes a LaCeF3-LiF-KF-BaF2 system with a mass ratio of 80.0:15.0:0.3:4.7.

[0262] In this comparative example, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace accounted for 68.9%, the monthly cumulative output (or monthly single output) was 4987.5kg, the current efficiency was 62.4%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.5%.

[0263] Comparative Example 5-5

[0264] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 22-26, with the only difference being that the quaternary molten salt system used includes a LaCeF3-LiF-BaF2 system with a mass ratio of 80.0:15.0:5.0.

[0265] In this comparative example, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace accounted for 67.2%, the monthly cumulative output (or monthly single output) was 5012.4kg, the current efficiency was 60.2%, and the product yield was 96.8%.

[0266] Comparative Examples 5-6

[0267] The process for preparing rare earth metals and their alloys by electrolysis described in this comparative example is the same as that of Examples 22-26, the only difference being that the quaternary molten salt system used includes a LaCeF3-LiF system with a mass ratio of 80.0:15.0:5.0.

[0268] In this comparative example, the C content of metallic lanthanum cerium (C<300ppm) during the production of a single furnace accounted for 66.4%, the monthly cumulative output (or monthly single output) was 5010.7kg, the current efficiency was 59.9%, and the product yield was 96.7%.

[0269] Embodiment 27

[0270] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 83.0:15.2:0.3:1.5.

[0271] The mixed praseodymium oxide was added to the molten PrF3-LiF-KF-BaF2 (83.0:15.2:0.3:1.5) mixed electrolyte in the electrolytic cell, and a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal praseodymium product was obtained by natural cooling.

[0272] In this embodiment, the metal praseodymium C content (C<300ppm) during the production of a single furnace is 98.3%, the monthly cumulative output (or monthly single output) is 5864.7kg, the current efficiency is 78.9%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 96.7%.

[0273] Embodiment 28

[0274] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 86.5:6.0:1.5:6.0.

[0275] The mixed praseodymium oxide is added uniformly to the molten PrF3-LiF-KF-BaF2 (86.5:6.0:1.5:6.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal praseodymium product is obtained by natural cooling.

[0276] In this embodiment, the metal praseodymium C content (C<300ppm) during the production of a single furnace is 88.3%, the monthly cumulative output (or monthly single output) is 5698.7kg, the current efficiency is 74.3%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.8%.

[0277] Embodiment 29

[0278] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 86.0:10.5:0.7:2.8.

[0279] The mixed praseodymium oxide was added to the molten PrF3-LiF-KF-BaF2 (86.0:10.5:0.7:2.8) mixed electrolyte in the electrolytic cell, and a molybdenum crucible was used as a collecting crucible, a tungsten rod was used as a cathode, and graphite was used as an anode. During the electrolysis process, the molybdenum rod was used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials were fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal praseodymium product was obtained by natural cooling.

[0280] In this embodiment, the metal praseodymium C content (C<300ppm) during the production of a single furnace is 99.5%, the monthly cumulative output (or monthly single output) is 6025.7kg, the current efficiency is 83.2%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 97.4%.

[0281] Embodiment 30

[0282] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 77.3:15.2:1.5:6.0.

[0283] The mixed praseodymium oxide is added uniformly to the molten PrF3-LiF-KF-BaF2 (77.3:15.2:1.5:6.0) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell, so that the raw materials can be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal praseodymium product is obtained by natural cooling.

[0284] In this embodiment, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 86.4%, the monthly cumulative output (or monthly single output) was 6123.4kg, the current efficiency was 78.7%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride, and barium fluoride were stable during the electrolysis process, and the product yield was 96.4%.

[0285] Embodiment 31

[0286] In the process for preparing rare earth metals and their alloys by electrolysis described in this embodiment, the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 92.2:6.0:0.3:1.5.

[0287] The mixed praseodymium oxide is added uniformly to the molten PrF3-LiF-KF-BaF2 (92.2:6.0:0.3:1.5) mixed electrolyte in the electrolytic cell, a molybdenum crucible is used as a collecting crucible, a tungsten rod is used as a cathode, and graphite is used as an anode. During the electrolysis process, the molybdenum rod is used to stir the raw materials from time to time depending on the situation in the electrolytic cell to allow the raw materials to be fully diffused and dissolved in the molten salt. After being taken out of the furnace, the metal praseodymium product is obtained by natural cooling.

[0288] In this embodiment, the metal praseodymium C content (C<300ppm) during the production of a single furnace is 81.2%, the monthly cumulative output (or monthly single output) is 5946.1kg, the current efficiency is 71.8%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride are stable during the electrolysis process, and the product yield is 95.8%.

[0289] Comparative Example 6-1

[0290] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 27-31, with the only difference being that the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 75.0:18.0:0.1:6.9.

[0291] In this comparative example, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 67.8%, the monthly cumulative output (or monthly single output) was 5826.4kg, the current efficiency was 68.2%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 93.8%.

[0292] Comparative Example 6-2

[0293] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 27-31, the only difference being that the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 93.0:5.0:1.6:0.4.

[0294] In this comparative example, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 69.8%, the monthly cumulative output (or monthly single output) was 5568.7kg, the current efficiency was 65.7%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 93.3%.

[0295] Comparative Example 6-3

[0296] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 27-31, with the only difference being that the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 86.0:10.5:2.5:1.0.

[0297] In this comparative example, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 82.3%, the monthly cumulative output (or monthly single output) was 5963.1kg, the current efficiency was 72.1%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.1%.

[0298] Comparative Example 6-4

[0299] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 27-31, with the only difference being that the quaternary molten salt system used includes a PrF3-LiF-KF-BaF2 system with a mass ratio of 86.0:10.5:0.1:3.4.

[0300] In this comparative example, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 80.2%, the monthly cumulative output (or monthly single output) was 5897.7kg, the current efficiency was 70.2%, the proportions of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride were stable during the electrolysis process, and the product yield was 96.0%.

[0301] Comparative Example 6-5

[0302] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 27-31, the only difference being that the quaternary molten salt system used includes a PrF3-LiF-BaF2 system with a mass ratio of 86.0:10.5:3.5.

[0303] In this comparative example, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 73.5%, the monthly cumulative output (or monthly single output) was 5768.4kg, the current efficiency was 63.2%, and the product yield was 95.8%.

[0304] Comparative Example 6-6

[0305] The process for electrolytic preparation of rare earth metals and their alloys described in this comparative example is the same as that of Examples 27-31, the only difference being that the quaternary molten salt system used includes a PrF3-LiF-KF system with a mass ratio of 86.0:10.5:3.5.

[0306] In this comparative example, the metal praseodymium C content (C<300ppm) during the production of a single furnace accounted for 77.4%, the monthly cumulative output (or monthly single output) was 5891.4kg, the current efficiency was 61.7%, and the product yield was 95.5%.

[0307] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A quaternary molten salt system, characterized in that: The quaternary molten salt system comprises a mixture of rare earth fluoride (REF), lithium fluoride (LiF), potassium fluoride (KF) and barium fluoride (BaF2); wherein, The quaternary molten salt system is used for preparing praseodymium-neodymium metal by electrolysis; the quaternary molten salt system comprises a mixture of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 81.6-92.8:6.0-11.9:0.2-1.5:1.0-5.0; or, The quaternary molten salt system is used for preparing metallic lanthanum by electrolysis; the quaternary molten salt system comprises a mixture of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 65.0-88.0:10.0-23.0:0.5-2.0:1.5-10.0; or, The quaternary molten salt system is used for preparing metallic neodymium by electrolysis; the quaternary molten salt system comprises a mixture of neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 82.0-92.8:6.0-11.0:0.2-1.5:1.0-5.5; or, The quaternary molten salt system is used for electrolytic preparation of dysprosium-iron alloy; the quaternary molten salt system comprises a mixture of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 85.0-94.8:4.0-7.5:0.2-1.5:1.0-6.0; or, The quaternary molten salt system is used for preparing metallic cerium by electrolysis; the quaternary molten salt system comprises a mixture of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 71.5-92.5:5.0-17.5:0.5-3.0:2.0-8.0; or, The quaternary molten salt system is used for preparing lanthanum-cerium alloy by electrolysis; the quaternary molten salt system comprises a mixture of lanthanum-cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 71.5-92.5:5.0-17.5:0.5-3.0:2.0-8.0; or, The quaternary molten salt system is used for preparing metallic praseodymium by electrolysis; the quaternary molten salt system comprises a mixture of praseodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 77.3-92.2:6.0-15.2:0.3-1.5:1.5-6.

0.

2. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system is used for electrolytic preparation of praseodymium-neodymium metal; The quaternary molten salt system comprises a mixture of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0-90.0:6.0-11.9:0.2-1.5:1.0-5.

0.

3. The quaternary molten salt system according to claim 2, characterized in that: The quaternary molten salt system is used for electrolytic preparation of praseodymium-neodymium metal; The quaternary molten salt system includes a mixture of praseodymium-neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0:11.0:0.3:1.

7.

4. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system of the present invention is used for preparing metallic lanthanum by electrolysis; The quaternary molten salt system comprises a mixture of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 75.0-78.0:10.0-23.0:0.5-2.0:1.5-10.

0.

5. The quaternary molten salt system according to claim 4, characterized in that: The quaternary molten salt system is used for electrolytic preparation of metallic lanthanum; The quaternary molten salt system includes a mixture of lanthanum fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 75.0:17.5:1.25:6.

25.

6. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system of the present invention is used for preparing metallic neodymium by electrolysis; The quaternary molten salt system comprises a mixture of neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0-89.0:6.0-11.0:0.2-1.5:1.0-5.

5.

7. The quaternary molten salt system according to claim 6, characterized in that: The quaternary molten salt system is used for preparing metallic neodymium by electrolysis; The quaternary molten salt system includes a mixture of neodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 87.0:11.0:0.5:1.

5.

8. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system of the present invention is used for preparing dysprosium-iron alloy by electrolysis; The quaternary molten salt system comprises a mixture of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 89.7-92.8:4.0-6.0:0.3-0.8:2.4-4.

0.

9. The quaternary molten salt system according to claim 8, characterized in that: The quaternary molten salt system is used for electrolytic preparation of dysprosium-iron alloy; The quaternary molten salt system includes a mixture of dysprosium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 91.1:6.0:0.4:2.

5.

10. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system of the present invention is used for preparing metallic cerium by electrolysis; The quaternary molten salt system comprises a mixture of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 80.0-84.0:5.0-17.5:0.5-3.0:2.0-8.

0.

11. The quaternary molten salt system according to claim 10, characterized in that: The quaternary molten salt system is used for preparing metallic cerium by electrolysis; The quaternary molten salt system includes a mixture of cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 83.0:11.9:0.85:4.

25.

12. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system of the present invention is used for preparing lanthanum-cerium alloy by electrolysis; The quaternary molten salt system comprises a mixture of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 80.0-83.0:6.0-17.5:0.5-3.0:2.0-8.

0.

13. The quaternary molten salt system according to claim 12, characterized in that: The quaternary molten salt system is used for electrolytic preparation of lanthanum-cerium alloy; The quaternary molten salt system includes a mixture of lanthanum cerium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 80.0:15.0:1.0:4.

0.

14. The quaternary molten salt system according to claim 1, characterized in that: The quaternary molten salt system of the present invention is used for preparing metallic praseodymium by electrolysis; The quaternary molten salt system comprises a mixture of praseodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 83.0-86.5:6.0-15.2:0.3-1.5:1.5-6.

0.

15. The quaternary molten salt system according to claim 14, characterized in that: The quaternary molten salt system is used for electrolytic preparation of metallic praseodymium; The quaternary molten salt system includes a mixture of praseodymium fluoride, lithium fluoride, potassium fluoride and barium fluoride in a mass ratio of 86.0:10.5:0.7:2.

8.

16. Use of the quaternary molten salt system according to any one of claims 1 to 15 for electrolytic preparation of rare earth metals and alloys thereof, characterized in that: The rare earth metal and its alloy include at least one of metal lanthanum, metal cerium, metal praseodymium, metal neodymium, lanthanum-cerium alloy, praseodymium-neodymium alloy or rare earth iron alloy.

17. A method for preparing rare earth metals and their alloys by electrolysis based on a quaternary molten salt system, characterized in that: The method comprises the steps of adding the rare earth oxide to be treated and conducting electrolysis in the presence of the quaternary molten salt system according to any one of claims 1 to 15.

18. The method for preparing rare earth metals and their alloys by electrolysis according to claim 17, characterized in that: The method for preparing rare earth metals and alloys thereof by electrolysis adopts a molybdenum crucible, a tungsten crucible or an iron crucible as a collecting crucible, a tungsten rod as a cathode, and graphite as an anode.

19. The method for electrolytically preparing rare earth metals and alloys thereof according to claim 17 or 18, characterized in that: The method for preparing rare earth metals and alloys thereof by electrolysis also includes the step of stirring with a molybdenum rod.

Images