A method for the production of niobium metal by molten salt electrolysis

Abstract

The present application relates to a kind of methods for preparing metallic niobium by molten salt electrolysis, comprising: taking electrolytic cell containing anode electrolysis chamber and cathode electrolysis chamber, and liquid niobium alloy is placed in the bottom of electrolytic cell, for separating the anode electrolysis chamber and the cathode electrolysis chamber;Add molten salt a to the anode electrolysis chamber, and add molten salt b to the cathode electrolysis chamber;Raw material niobium pentoxide is added to the anode electrolysis chamber, and anode and cathode are placed in anode electrolysis chamber and cathode electrolysis chamber respectively, then power operation electrolytic cell, anode precipitates CO, CO2 Gas, and cathode deposits solid metallic niobium.The method for preparing metallic niobium by molten salt electrolysis, the raw material is niobium pentoxide, not only the purity requirement of raw material is not high, but also high-purity metallic niobium can be obtained directly, other impurities are intercepted in liquid niobium alloy and molten salt;Process flow is simple, energy-efficient, and operation is continuous.

Description

Technical Field

[0001] This invention belongs to the field of niobium metallurgy, specifically relating to a method for preparing metallic niobium by molten salt electrolysis. Background Technology

[0002] Niobium is an important rare metal with advantages such as high melting point, low vapor pressure, good cold working properties, high chemical stability, and strong resistance to acid and alkali corrosion. Metallic niobium and its alloys are important functional materials, widely used in military and defense, aerospace, special materials, metallurgy, energy and other industries.

[0003] Niobium metal preparation processes can be divided into two categories. One category consists of methods that are currently in industrial application: niobium oxide carbothermic reduction, niobium oxide aluminothermic reduction, potassium sodium fluoroniobate thermal reduction, and niobium oxide molten salt electrolysis. The other category consists of methods that are still in the laboratory research stage, including niobium oxide solid-state electro-deoxidation, niobium oxide calcium thermal reduction, and niobium oxide solid-state oxygen-permeable membrane method.

[0004] The carbothermic reduction of niobium oxide is a process in which niobium pentoxide is reduced to metallic niobium using carbon under high-temperature vacuum conditions. The reduction process is as follows: Nb₂O₅ + 7C = 2NbC + 5CO; Nb₂O₅ + 12NbC = 7Nb₂C + 5CO; Nb₂O₅ + 5Nb₂C = 12Nb + 5CO. This production process is characterized by intermittent production, low mechanization, and high content of impurities C and O in the metal.

[0005] The aluminothermic reduction of niobium oxide is a process in which niobium pentoxide is reduced to metallic niobium using metallic aluminum under high-temperature vacuum conditions. The reduction process is: 3Nb₂O₅ + 10Al = 6Nb + 5Al₂O₃. This production process suffers from the same problems as the carbothermic reduction method, such as the inability to operate continuously, low degree of mechanization, and high content of impurity elements in the metal.

[0006] The basic principle of the potassium fluoroniobate sodium thermal reduction method is to prepare metallic niobium by reducing niobium compounds with active metals such as alkali metals and alkaline earth metals. For example, the method for thermal reduction of potassium fluoroniobate with molten sodium salt disclosed in US Patent 3012877 has the chemical process K2NbF7 + 5Na = Nb + 2KF + 5NaF; Chinese Patent CN1169643C discloses a method for preparing ultrafine niobium powder by reducing niobium oxides with alkali metals in molten halides of alkali metals and alkaline earth metals, with the chemical process Nb2O5 + 5CaCl2 + 10Na = 2Nb + 10NaCl + 5CaO. In the process of preparing metallic niobium powder, inert salts (such as KCl, NaCl, KF, NaF, etc. halides) need to be added as diluents. However, this process has disadvantages such as a large demand for inert salts, the inability to recycle them, and the inability to achieve continuous production.

[0007] Furthermore, US Patent 6136062 discloses a method for preparing metallic niobium powder and tantalum powder by reducing tantalum oxide and niobium oxide with metallic magnesium. This method includes two reduction processes. The first stage is (5-2x)Mg + Nb₂O₅ = (5-2x)MgO + 2NbO x (x = 0.5–1.5); Second stage, NbO x (x=0.5~1.5)+xMg=Nb+xMgO. The disadvantages of this method are: the niobium metal has a high content of impurities Mg and O, the process is complex, and continuous production is not possible.

[0008] The traditional niobium oxide molten salt electrolysis method uses a mixed molten salt of potassium fluoroniobate, potassium chloride, and sodium chloride as the electrolyte. Niobium pentoxide is added to the electrolyte and undergoes a dissolution reaction. Niobium ions are reduced on a nickel cathode to produce metallic niobium, while oxygen ions are discharged on a graphite anode to release CO and CO2. However, this method requires high purity of the niobium oxide raw material, and the resulting metallic niobium product has a high content of impurity elements.

[0009] The core of the niobium oxide solid-state electro-deoxidation method is to use solid niobium oxide as the cathode and calcium chloride molten salt as the electrolyte. Through molten salt electrolysis, niobium ions in the cathode are reduced in situ to metallic niobium. Simultaneously, oxygen anions leave the cathode and enter the melt, migrating to the anode under the influence of the electric field and being oxidized to oxygen (when using a carbon anode, oxygen further reacts with carbon to produce CO and CO2). However, the niobium oxide briquettes at the cathode are reduced gradually from the outside in, making oxygen diffusion increasingly difficult, resulting in low-oxygen-content niobium. Furthermore, the purity of the product is limited by the purity of impurities in the raw materials.

[0010] The core of the niobium oxide solid-state oxygen-permeable membrane method is to use solid niobium oxide as the cathode, with carbon-saturated copper liquid inside a yttrium-stabilized zirconia tube as the anode, and a magnesium oxide-magnesium fluoride mixed molten salt as the electrolyte. Through molten salt electrolysis, niobium ions in the cathode are reduced in situ to metallic niobium. Simultaneously, oxygen anions leave the cathode and enter the melt, diffusing through the solid-state oxygen-permeable membrane under the influence of an electric field to the anode where they are oxidized to oxygen (when using a carbon anode, oxygen further reacts with carbon to produce CO and CO2). This method avoids the problems of side reactions and high impurity content in the metal. However, it suffers from drawbacks such as short lifespan of the solid-state oxygen-permeable membrane and high manufacturing cost, making large-scale application difficult.

[0011] The reduction of niobium pentoxide by calcium niobium oxide is carried out in stages using a calcium chloride-calcium oxide mixed molten salt as the electrolyte. Through molten salt electrolysis, oxygen ions are discharged at the graphite anode to release CO and CO2, while calcium ions are reduced on the cathode grid to form liquid metallic calcium. This liquid metallic calcium then reduces the particulate niobium pentoxide in the cathode grid to metallic niobium. The reaction process is: Nb₂O₅ + 5Ca = 2Nb + 5CaO. However, the drawback of this method is that the product, metallic niobium, contains high levels of impurity elements O and C.

[0012] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0013] To address the problems existing in the prior art, this invention provides a method for preparing metallic niobium by molten salt electrolysis. The method uses niobium pentoxide as the raw material, which not only has low requirements for raw material purity but also directly yields high-purity metallic niobium, while other impurities are retained in the liquid niobium alloy and molten salt. The process is simple, highly efficient, energy-saving, and allows for continuous operation.

[0014] The present invention provides a method for preparing metallic niobium by molten salt electrolysis, comprising the following steps:

[0015] (1) Take an electrolytic cell containing an anode electrolytic chamber and a cathode electrolytic chamber, and place liquid niobium alloy at the bottom of the electrolytic cell to separate the anode electrolytic chamber and the cathode electrolytic chamber;

[0016] (2) Add molten salt a to the anode electrolysis chamber and molten salt b to the cathode electrolysis chamber;

[0017] (3) Add the raw material niobium pentoxide to the anode electrolysis chamber, and place the anode and cathode into the anode electrolysis chamber and cathode electrolysis chamber respectively. Then, power on the electrolysis cell to run the electrolysis cell. CO and CO2 gases are generated at the anode, and solid metal niobium is deposited at the cathode.

[0018] The anode electrolysis chamber and cathode electrolysis chamber of the electrolytic cell are individually temperature controlled. The temperature control methods include the thermal effect of current, heating element heating, and water-cooled jacket cooling.

[0019] Preferably, in step (1), the liquid niobium alloy is composed of niobium and one or more of gold, palladium, rhodium, nickel, iron, cobalt, gallium, indium, and germanium.

[0020] In step (2), the molten salt a is divided into two categories. The first category of molten salt a is composed of one or more of calcium chloride, barium chloride, strontium chloride, lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, and lanthanum chloride.

[0021] When using molten salt of type I a, the electrolysis principle is as follows:

[0022] When the electrolytic cell is powered on, niobium pentoxide (NiO2) is added to the surface of the liquid niobium alloy in the anode electrolysis chamber. Niobium ions in the niobium pentoxide are insoluble in the molten salt of the anode electrolysis chamber. Niobium ions in the niobium pentoxide are reduced to metallic niobium in situ via electro-deoxidation and dissolve in the liquid niobium alloy. Meanwhile, oxygen ions bound to niobium move to the anode surface under the influence of the electric field and are oxidized to zero-valent oxygen, which then reacts with the anode carbon to generate CO and CO2, which escape. Simultaneously, niobium atoms in the liquid niobium alloy lose electrons at the interface and are oxidized to niobium ions, which enter the molten salt of the cathode chamber. Niobium ions in the molten salt of the cathode chamber move to the cathode surface under the influence of the electric field and are reduced to solid metallic niobium.

[0023] The second type of molten salt a is composed of one of potassium fluoroniobate and sodium fluoroniobate, together with one or more of potassium chloride, potassium fluoride, sodium chloride, sodium fluoride, lithium chloride, lithium fluoride, calcium chloride, and calcium fluoride.

[0024] When using molten salt type a, the electrolysis principle is as follows:

[0025] When the electrolytic cell is powered on, niobium pentoxide is added to the anode electrolysis chamber and dissolves in the molten salt. Niobium ions in the molten salt move to the interface of the liquid niobium alloy under the influence of the electric field and are reduced to metallic niobium, dissolving in the liquid niobium alloy. Oxygen ions move to the anode surface under the influence of the electric field and are oxidized to zero-valent oxygen, then react with the anode carbon to generate CO and CO2, which escape. Simultaneously, niobium atoms in the liquid niobium alloy lose electrons at the interface and are oxidized to niobium ions, which enter the molten salt of the cathode chamber. Meanwhile, niobium ions in the molten salt of the cathode chamber move to the cathode surface under the influence of the electric field and are reduced to solid metallic niobium.

[0026] Preferably, in step (2), the molten salt b is composed of one of potassium fluoroniobate and sodium fluoroniobate, and one or more of sodium chloride, potassium chloride, lithium chloride, calcium chloride, barium chloride, lithium fluoride, sodium fluoride, and potassium fluoride.

[0027] Preferably, in step (3), the purity of the niobium pentoxide is ≥80%wt.

[0028] Preferably, in step (3), the anode is a graphite anode.

[0029] Preferably, in step (3), the cathode is a niobium cathode, a tungsten cathode, or a molybdenum cathode.

[0030] Preferably, in step (3), the operating temperature of the electrolytic cell is 700–1600°C.

[0031] Preferably, in step (3), the anolyte current density during electrolysis is 0.01–2.0 A / cm². 2 .

[0032] The beneficial effects of this invention are as follows:

[0033] The method for preparing metallic niobium by molten salt electrolysis described in this invention uses niobium pentoxide as raw material, which not only does not require high purity of raw material, but also can directly obtain high-purity metallic niobium, while other impurities are trapped in the liquid niobium alloy and molten salt; the process is simple, efficient and energy-saving, and the operation is continuous. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the electrolytic cell described in this invention.

[0036] Figure reference numerals:

[0037] 1-Anode; 2-Molten salt a; 3-Niobium pentoxide; 4-Liquid niobium alloy; 5-Molten salt b; 6-Niobium cathode product; 7-Cathode; 8-Water-cooled jacket; 9-Insulation material; 10-Heating element; 11-Refractory material; I-Anode electrolysis chamber; II-Cathode electrolysis chamber. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] Example 1

[0040] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0041] (1) A niobium-gold alloy (8% wt niobium, 92% wt gold) is placed at the bottom of the electrolytic cell beforehand. After evacuating the electrolytic cell, inert argon gas is introduced. Once the cell is filled with argon gas, a continuous flow rate of 10 mL / min is maintained for argon protection. The electrolytic cell is then heated to 1300℃ and held for 1 hour to allow the niobium-gold alloy inside the cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolysis chamber and a cathode electrolysis chamber.

[0042] (2) A molten salt of (10 at%) LiCl-(40 at%) NaCl-CaCl2 (50 at%) was used as the electrolyte in the anode electrolysis chamber of the electrolytic cell, and a molten salt of Na2NbF7 (22 wt%)-NaCl (40 wt%)-KCl (38 wt%) was used as the electrolyte in the cathode electrolysis chamber. Niobium pentoxide (80% wt% purity) was added to the interface of the liquid niobium alloy in the anode electrolysis chamber. The molten salt temperature in both the anode and cathode electrolysis chambers was controlled at 750℃, and the temperature of the liquid niobium alloy at the bottom of the electrolytic cell was controlled at 1300℃. Once the temperatures of each section of the electrolytic cell stabilized, the graphite anode was inserted into the electrolyte in the anode electrolysis chamber, and the niobium cathode was inserted into the molten salt in the cathode electrolysis chamber. Electrolysis was performed for 12 hours, with the anode current density controlled at 0.01 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was tested to be 99.95%).

[0043] Example 2

[0044] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0045] (1) A niobium-indium alloy (15% wt niobium, 85% wt indium) is placed at the bottom of the electrolytic cell beforehand. After the electrolytic cell is evacuated, inert argon gas is introduced. Once the cell is filled with argon gas, a continuous flow rate of 20 mL / min is maintained to provide argon protection. The electrolytic cell is then heated to 740°C and held at that temperature for 2 hours to allow the niobium-indium alloy inside the cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0046] (2) A K₂NbF₇ (17.5% wt)-KF (27.5% wt)-KCl (50.0% wt)-LiCl (5% wt) molten salt was used as the electrolyte for the anode electrolysis chamber of the electrolytic cell, and a K₂NbF₇ (22 wt%)-NaCl (40 wt%)-KCl (38 wt%) molten salt was used as the electrolyte for the cathode electrolysis chamber. The molten salt temperature in both the anode and cathode electrolysis chambers was controlled at 740℃, as was the temperature of the liquid niobium alloy at the bottom of the electrolytic cell. Once the temperatures of each section of the electrolytic cell stabilized, the graphite anode was inserted into the electrolyte of the anode electrolysis chamber, and the niobium cathode was inserted into the molten salt of the cathode electrolysis chamber. Niobium pentoxide (80% wt) was added to the anode electrolysis chamber at 1.5% of the total mass of the molten salt. Electrolysis was performed for 12 hours, with the anode current density controlled at 0.05 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was found to be 99.96%).

[0047] Example 3

[0048] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0049] (1) A niobium-iron alloy (74% wt niobium, 26% wt iron) is placed at the bottom of the electrolytic cell beforehand. The electrolytic cell is evacuated and then inert argon gas is introduced. After the argon gas is filled, a continuous argon gas supply is maintained at a flow rate of 30 mL / min. The electrolytic cell is then heated to 1500℃ and held at that temperature for 1 hour to allow the niobium-iron alloy in the electrolytic cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0050] (2) Using a molten salt of (46.7 at%) NaCl-CaCl2 (53.3 at%) as the electrolyte in the anode electrolysis chamber and a molten salt of K2NbF7 (40% wt)-NaCl (40% wt)-KCl (20% wt) as the electrolyte in the cathode electrolysis chamber, niobium pentoxide raw material (85% purity) was added to the interface of the liquid niobium alloy in the anode electrolysis chamber. The temperature of the anode electrolysis chamber and the cathode electrolysis chamber was then controlled at 750℃, and the temperature of the liquid niobium alloy at the bottom of the electrolysis chamber was controlled at 1500℃. After the temperature of each section of the electrolysis chamber stabilized, the graphite anode was inserted into the molten salt in the anode electrolysis chamber, and the tungsten cathode was inserted into the molten salt in the cathode electrolysis chamber. Electrolysis was carried out for 12 hours, with the anode current density controlled at 0.5 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was tested to be 99.95%).

[0051] Example 4

[0052] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0053] (1) A niobium-cobalt alloy (25% wt niobium, 75% wt cobalt) is placed at the bottom of the electrolytic cell beforehand. The electrolytic cell is then evacuated and inert argon gas is introduced. After the argon gas is filled, a continuous flow rate of 40 mL / min is maintained to provide argon protection. The electrolytic cell is then heated to 1300℃ and held for 1 hour to allow the niobium-cobalt alloy in the electrolytic cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0054] (2) A molten salt of Na₂NbF₇ (17.5% wt) - KF (27.5% wt) - KCl (55.0% wt) was used as the electrolyte in the anode electrolysis chamber of the electrolytic cell, and a molten salt of K₂NbF₇ (40% wt) - NaCl (40% wt) - KCl (20% wt) was used as the electrolyte in the cathode electrolysis chamber. The molten salt temperature in both the anode and cathode electrolysis chambers was controlled at 750℃, and the temperature of the liquid niobium alloy at the bottom of the electrolytic cell was controlled at 1300℃. After the temperatures of each section of the electrolytic cell stabilized, the graphite anode was inserted into the molten salt in the anode electrolysis chamber, and the molybdenum cathode was inserted into the molten salt in the cathode electrolysis chamber. Niobium pentoxide (purity 97% wt) was added to the anode electrolysis chamber at 1.6% of the total mass of the molten salt in the anode electrolysis chamber. Electrolysis was performed for 20 hours, and the anode current density was controlled at 2.0 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was tested to be 99.95%).

[0055] Example 5

[0056] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0057] (1) A niobium-palladium alloy (50%wt niobium, 50%wt palladium) is placed at the bottom of the electrolytic cell beforehand. The electrolytic cell is evacuated and then inert argon gas is introduced. After the argon gas is filled, a continuous flow rate of 35 mL / min is maintained to provide argon protection. The electrolytic cell is then heated to 1600℃ and held for 2 hours to allow the niobium-palladium alloy in the electrolytic cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0058] (2) Using a molten salt of (46.7 at%) NaCl-CaCl2 (53.3 at%) as the electrolyte in the anode electrolysis chamber and a molten salt of K2NbF7 (40% wt)-NaCl (40% wt)-KCl (20% wt) as the electrolyte in the cathode electrolysis chamber, niobium pentoxide raw material (purity 88% wt) was added to the interface of the liquid niobium alloy in the anode electrolysis chamber. The temperature of the anode electrolysis chamber and the cathode electrolysis chamber was then controlled at 750℃, and the temperature of the liquid niobium alloy at the bottom of the electrolysis chamber was controlled at 1600℃. After the temperature of each section of the electrolysis chamber stabilized, the graphite anode was inserted into the molten salt in the anode electrolysis chamber, and the niobium cathode was inserted into the molten salt in the cathode electrolysis chamber. Electrolysis was performed for 12 hours, with the anode current density controlled at 0.8 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was tested to be 99.95%).

[0059] Example 6

[0060] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0061] (1) A niobium-germanium alloy (10% wt niobium, 90% wt germanium) is placed at the bottom of the electrolytic cell beforehand. The electrolytic cell is then evacuated and inert argon gas is introduced. After the argon gas is filled, a continuous argon gas supply is maintained at a flow rate of 20 mL / min. The electrolytic cell is then heated to 1400℃ and held for 2 hours to allow the niobium-germanium alloy in the electrolytic cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0062] (2) A K2NbF7 (17.5% wt)-KF (27.5% wt)-KCl (55.0% wt) molten salt was used as the electrolyte in the anode electrolysis chamber of the electrolytic cell, and a K2NbF7 (22 wt%)-NaCl (40 wt%)-KCl (38 wt%) molten salt was used as the electrolyte in the cathode electrolysis chamber. The molten salt temperatures in both the anode and cathode electrolysis chambers were controlled at 750℃, and the temperature of the liquid niobium alloy at the bottom of the electrolytic cell was controlled at 1400℃. After the temperatures of each section of the electrolytic cell stabilized, the graphite anode was inserted into the molten salt in the anode electrolysis chamber, and the niobium cathode was inserted into the molten salt in the cathode electrolysis chamber. Niobium pentoxide (purity 95% wt) was added to the anode electrolysis chamber at 2% of the total mass of the molten salt in the anode electrolysis chamber. Electrolysis was performed for 24 hours, and the anode current density was controlled at 1.5 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was found to be 99.96%).

[0063] Example 7

[0064] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0065] (1) A niobium-rhodium alloy (55%wt niobium, 45%wt rhodium) is placed at the bottom of the electrolytic cell beforehand. The electrolytic cell is evacuated and then inert argon gas is introduced. After the argon gas is filled, a continuous argon gas supply is maintained at a flow rate of 50 mL / min. The electrolytic cell is then heated to 1600℃ and held for 2 hours to allow the niobium-rhodium alloy in the electrolytic cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0066] (2) A K₂NbF₇ (40% wt)-NaCl (40% wt)-KCl (20% wt) molten salt was used as the electrolyte for the anode electrolysis chamber of the electrolytic cell, and a K₂NbF₇ (22 wt%)-NaCl (40 wt%)-KCl (38 wt%) molten salt was used as the electrolyte for the cathode electrolysis chamber. The molten salt temperature in both the anode and cathode electrolysis chambers was controlled at 700℃, and the temperature of the liquid niobium alloy at the bottom of the electrolytic cell was controlled at 1600℃. After the temperatures of each section of the electrolytic cell stabilized, the graphite anode was inserted into the molten salt in the anode electrolysis chamber, and the niobium cathode was inserted into the molten salt in the cathode electrolysis chamber. Niobium pentoxide (90% wt) was added to the anode electrolysis chamber at 1.5% of the total mass of the molten salt in the anode electrolysis chamber. Electrolysis was performed for 20 hours, and the anode current density was controlled at 0.05 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was found to be 99.96%).

[0067] Example 8

[0068] This embodiment provides a method for preparing metallic niobium by molten salt electrolysis, including the following steps:

[0069] (1) A niobium-nickel alloy (50% wt niobium, 50% wt nickel) is placed at the bottom of the electrolytic cell beforehand. The electrolytic cell is evacuated and then inert argon gas is introduced. After the argon gas is filled, a continuous flow rate of 10 mL / min is maintained to provide argon protection. The electrolytic cell is then heated to 1400℃ and held for 1.5 hours to allow the niobium-nickel alloy in the electrolytic cell to completely melt. The resulting liquid niobium alloy divides the electrolytic cell into an anode electrolytic chamber and a cathode electrolytic chamber.

[0070] (2) A CaCl2 (95% wt)-CaO (5%) molten salt was used as the electrolyte in the anode electrolysis chamber of the electrolytic cell, and a K2NbF7 (40% wt)-NaCl (40% wt)-KCl (20% wt) molten salt was used as the electrolyte in the cathode electrolysis chamber. Niobium pentoxide (92% wt purity) was added to the interface of the liquid niobium alloy in the anode electrolysis chamber. The molten salt temperature in both the anode and cathode electrolysis chambers was controlled at 800℃, and the liquid niobium alloy temperature at the bottom of the electrolytic cell was controlled at 1400℃. After the temperatures of each section of the electrolytic cell stabilized, the graphite anode was inserted into the molten salt in the anode electrolysis chamber, and the niobium cathode was inserted into the molten salt in the cathode electrolysis chamber. Electrolysis was performed for 20 hours, with the anode current density controlled at 1.2 A / cm². 2 The cathode product, metallic niobium, was obtained in the cathode electrolysis chamber (the purity of niobium was found to be 99.96%).

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing metallic niobium by molten salt electrolysis, characterized in that, Includes the following steps: (1) Take an electrolytic cell containing an anode electrolytic chamber and a cathode electrolytic chamber, and place liquid niobium alloy at the bottom of the electrolytic cell to separate the anode electrolytic chamber and the cathode electrolytic chamber; (2) Add molten salt a to the anode electrolysis chamber and molten salt b to the cathode electrolysis chamber; (3) Add the raw material niobium pentoxide to the anode electrolysis chamber, and place the anode and cathode into the anode electrolysis chamber and cathode electrolysis chamber respectively. Then, turn on the power to run the electrolysis cell. CO and CO2 gases are generated at the anode, and solid metal niobium is deposited at the cathode. Wherein: the molten salt a is composed of one or more of calcium chloride, barium chloride, strontium chloride, lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, and lanthanum chloride; or, the molten salt a is composed of one of potassium fluoroniobate and sodium fluoroniobate, together with one or more of potassium chloride, potassium fluoride, sodium chloride, sodium fluoride, lithium chloride, lithium fluoride, calcium chloride, and calcium fluoride; The molten salt b is composed of one of potassium fluoroniobate and sodium fluoroniobate, and one or more of sodium chloride, potassium chloride, lithium chloride, calcium chloride, barium chloride, lithium fluoride, sodium fluoride, and potassium fluoride. The liquid niobium alloy is composed of niobium and one of the following: gold, palladium, rhodium, nickel, iron, cobalt, indium, and germanium. The operating temperature of the electrolytic cell is 700~1600℃ o C.

2. The method for preparing metallic niobium by molten salt electrolysis according to claim 1, characterized in that, In step (3), the purity of the niobium pentoxide is ≥80%wt.

3. The method for preparing metallic niobium by molten salt electrolysis according to claim 1, characterized in that, In step (3), the anode is a graphite anode.

4. The method for preparing metallic niobium by molten salt electrolysis according to claim 1, characterized in that, In step (3), the cathode is a niobium cathode, a tungsten cathode, or a molybdenum cathode.

5. The method for preparing metallic niobium by molten salt electrolysis according to claim 1, characterized in that, In step (3), the anolyte current density during electrolysis is 0.01~2.0 A / cm². 2 .

Images