System and method for purifying molten salt at front end of metal electrolytic refining

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a metal electrorefining front-end molten salt purification system and method. The system comprises a physical purification treatment device and an electrochemical purification treatment device, the physical purification treatment device and the electrochemical purification treatment device are connected in series; the physical purification treatment device is used for purifying the introduced molten salt in a baking and / or hydrolysis manner; and the electrochemical purification treatment device is used for carrying out secondary purification on the molten salt purified by the physical purification treatment device in an electrolysis manner. The molten salt combined purification method is adopted, the result shows that the content of water, oxygen and impurities in the molten salt is obviously reduced, and the use requirement of metal electrolytic refining is met.

Description

Technical Field

[0001] The present application belongs to the field of metallurgical technology, and specifically relates to a molten salt purification system and method at the front end of metal electrolytic refining. Background Art

[0002] Molten salt electrolytic refining and purification of metals is a purification method in which metals are electrolyzed to remove impurities in a certain molten salt system. It has become one of the effective processes for preparing high-purity rare earth metals. At the same time, the application of molten salt electrolytic refining technology in dry post-processing, especially in the fields of nuclear fuel post-processing and metal purification, has demonstrated its unique advantages and wide application potential. With the continuous advancement of technology, this technology will play a more important role in future sustainable development. The purity of molten salt is crucial to the control of impurity content of electrolytic refining and purification of metals in the hundreds of ppm level. Commonly used molten salts such as fluoride salts and chloride salts usually contain oxides, carbides, silicides, iron-nickel compounds, etc.; such as KF, KCl, LiCl, etc. are very easy to absorb water, so the electrolyte molten salt often needs to be pretreated before electrolysis to remove impurities and water oxygen in it to reduce the impact of side reactions on the experiment. Summary of the invention

[0003] The purpose of this application is to provide a molten salt purification system and method at the front end of metal electrolytic refining to solve the problem of how to remove impurities in molten salt in the prior art.

[0004] Technical solution to achieve the purpose of this application:

[0005] In a first aspect, an embodiment of the present application provides a molten salt purification system at the front end of metal electrolytic refining, the system comprising: a physical purification treatment device and an electrochemical purification treatment device;

[0006] The physical purification treatment device and the electrochemical purification treatment device are connected in series;

[0007] The physical purification treatment device is used to purify the introduced molten salt by baking and / or hydrolysis;

[0008] The electrochemical purification treatment device is used to perform secondary purification on the molten salt purified by the physical purification treatment device by means of electrolysis.

[0009] Optionally, the physical purification treatment device comprises: a gas cylinder, a tubular furnace and a vacuum pump;

[0010] The gas cylinder is connected to the inlet of the tube furnace through a gas pipe, and the molten salt to be treated is placed in the tube furnace;

[0011] The outlet of the tube furnace is connected to a vacuum pump.

[0012] Optionally, the physical purification treatment device further includes: a first concentrated sulfuric acid bottle, an empty bottle, a second concentrated sulfuric acid bottle and a sodium hydroxide solution bottle;

[0013] The trachea is connected in series with a first concentrated sulfuric acid bottle;

[0014] The outlet of the tubular furnace is also connected in series with an empty bottle, a second concentrated sulfuric acid bottle and a sodium hydroxide solution bottle; the outlet of the sodium hydroxide solution bottle discharges tail gas.

[0015] Optionally, the physical purification treatment device further includes: a valve;

[0016] The valve is connected in series to the air pipe.

[0017] Optionally, the electrochemical purification treatment device comprises: a power supply, an electrolytic cell, a cathode and an anode;

[0018] The electrolytic cell is used to place the molten salt purified by the physical purification treatment device;

[0019] The cathode and anode of the power supply are connected to the cathode rod and the anode rod respectively; the cathode rod and the anode rod are both placed in the electrolytic cell, and the molten salt purified by the physical purification treatment device is inserted.

[0020] Optionally, the power supply is a constant voltage power supply.

[0021] Optionally, the cathode rod is a nickel foam sheet and the anode rod is graphite.

[0022] A second aspect of the embodiment of the present application provides a method for purifying molten salt at the front end of metal electrolytic refining, characterized in that it is applied to any one of the molten salt purification systems at the front end of metal electrolytic refining provided in the first aspect of the embodiment of the present application; the method comprises:

[0023] Purifying the molten salt to be treated by the physical purification treatment device;

[0024] The purified molten salt is passed into the electrochemical purification device for secondary purification.

[0025] Optionally, the molten salt to be treated is purified by the physical purification treatment device, specifically comprising:

[0026] For molten salts that are not easily hydrolyzed, removing water vapor adsorbed by the molten salt to be treated by baking;

[0027] For easily hydrolyzed chloride salts, a mixed gas of hydrogen chloride and argon is introduced while the temperature is kept high to remove oxides produced by the hydrolysis of the molten salt to be treated.

[0028] Optionally, the step of passing the purified molten salt into the electrochemical purification device for secondary purification specifically includes:

[0029] Any one of carbides, silicides and iron-nickel compounds in the purified molten salt is removed by electrolysis.

[0030] The beneficial technical effects of this application are:

[0031] A molten salt purification system and method for the front end of metal electrolytic refining provided in an embodiment of the present application, the system comprising: a physical purification treatment device and an electrochemical purification treatment device; the physical purification treatment device and the electrochemical purification treatment device are connected in series; the physical purification treatment device is used to purify the introduced molten salt by baking and / or hydrolysis; the electrochemical purification treatment device is used to perform secondary purification on the molten salt purified by the physical purification treatment device by electrolysis. The embodiment of the present application adopts a molten salt combined purification method, and the results show that the water, oxygen and impurity content in the molten salt are significantly reduced, meeting the use requirements of metal electrolytic refining. The active metal chemical properties are active, and electrolytic refining needs to be carried out under low water and oxygen conditions. At the same time, the molten salt used for metal electrolytic refining contains a small amount of water, oxygen and impurities. A small amount of water and impurities in the molten salt should be removed as much as possible before use, and then it can be used for metal electrolytic refining, providing favorable conditions for reducing the impurity content of the final product from the source. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the structure of a physical purification treatment device in a molten salt purification system at the front end of metal electrolytic refining provided in an embodiment of the present application;

[0033] Figure 2 A schematic diagram of the structure of an electrochemical purification treatment device in a molten salt purification system at the front end of metal electrolytic refining provided in an embodiment of the present application.

[0034] In the figure:

[0035] 1-gas cylinder; 2-valve; 3-gas pipe; 4-first concentrated sulfuric acid bottle; 5-tube furnace; 6-vacuum pump; 7-empty bottle; 8-second concentrated sulfuric acid bottle; 9-sodium hydroxide solution bottle; 10-tail gas; 11-power supply; 12-electrolytic cell; 13-cathode rod; 14-anode rod. DETAILED DESCRIPTION

[0036] In order to make those skilled in the art better understand the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the embodiments described below are only a part of the embodiments of the present application, not all. Based on the embodiments recorded in the present application, all other embodiments obtained by those skilled in the art without paying creative work are within the scope of protection of the present application.

[0037] The inventors of this application have found in their research that there are two types of molten salt purification methods: chemical purification and physical purification. Chemical purification methods include acid-base reaction, halogenation reaction, chemical replacement reaction, hydrogen reduction, electrochemical redox reaction, etc.; physical purification methods include drying, vacuum dehydration, recrystallization, distillation, sublimation, and zone smelting, etc. The appropriate method should be selected according to the properties of the molten salt and the process requirements.

[0038] The active metals targeted by the embodiments of the present application have active chemical properties and need to be electrolytically refined under low water and oxygen conditions. At the same time, the molten salt used for metal electrolytic refining contains a small amount of water, oxygen and impurities. Before use, the small amount of water and impurities in the molten salt should be removed as much as possible, and then it can be used for metal electrolytic refining, providing favorable conditions for reducing the impurity content of the final product from the source.

[0039] Based on the above content, in order to clearly and in detail illustrate the above advantages of the present application, the specific implementation methods of the present application will be described below in conjunction with the accompanying drawings.

[0040] See also Figure 1 , which is a structural schematic diagram of a physical purification treatment device in a molten salt purification system at the front end of metal electrolytic refining provided in an embodiment of the present application.

[0041] A molten salt purification system for the front end of metal electrolytic refining provided in an embodiment of the present application includes: a physical purification treatment device and an electrochemical purification treatment device;

[0042] The physical purification treatment device and the electrochemical purification treatment device are connected in series;

[0043] The physical purification treatment device is used to purify the introduced molten salt by baking and / or hydrolysis;

[0044] The electrochemical purification treatment device is used to perform secondary purification on the molten salt purified by the physical purification treatment device by means of electrolysis.

[0045] In some possible implementations of the present application, such as Figure 1 As shown, the physical purification treatment device may include: a gas cylinder 1, a tubular furnace 5 and a vacuum pump 6;

[0046] The gas cylinder 1 is connected to the inlet of the tubular furnace 5 through the gas pipe 3, and the molten salt to be treated is placed in the tubular furnace 5;

[0047] The outlet of the tube furnace 5 is connected to a vacuum pump 6 .

[0048] In one example, the physical purification treatment device may further include: a first concentrated sulfuric acid bottle 4, an empty bottle 7, a second concentrated sulfuric acid bottle 8 and a sodium hydroxide solution bottle 9;

[0049] The trachea 3 is connected in series with a first concentrated sulfuric acid bottle 4;

[0050] The outlet of the tubular furnace 5 is also connected in series with an empty bottle 7 , a second concentrated sulfuric acid bottle 8 and a sodium hydroxide solution bottle 9 ; the outlet of the sodium hydroxide solution bottle 9 discharges tail gas 10 .

[0051] In another example, the physical purification treatment device may further include: a valve 2;

[0052] The valve 2 is connected in series to the air pipe 3.

[0053] In some possible implementations of the present application, such as Figure 2 As shown, the electrochemical purification treatment device may include: a power supply 11, an electrolytic cell 12, a cathode 13 and an anode 14;

[0054] The electrolytic cell 12 is used to place the molten salt purified by the physical purification treatment device;

[0055] The cathode and anode of the power source 11 are connected to the cathode rod 13 and the anode rod 14 respectively; the cathode rod 13 and the anode rod 14 are both placed in the electrolytic cell 12, and the molten salt purified by the physical purification treatment device is inserted.

[0056] In one example, the power source 11 is a constant voltage power source.

[0057] In another example, the cathode rod 13 is a nickel foam sheet, and the anode rod 14 is graphite.

[0058] In the embodiment of the present application, the physical purification treatment device can realize functions such as vacuuming, heating, and passing working gas. For molten salts of different properties, corresponding pretreatment processes can be designed. For molten salts that are not easily hydrolyzed, they can be vacuumed and baked at 300°C for 12 hours to remove the water vapor adsorbed by the molten salt; for chlorine salts that are easily hydrolyzed, a mixed gas of hydrogen chloride and argon needs to be passed while keeping warm to remove the oxides produced by the hydrolysis of the molten salt. The electrochemical purification treatment system removes impurities such as carbides, silicides, and iron-nickel compounds in the molten salt. A Φ10mm graphite rod is used for the anode, and a foam nickel sheet with a larger specific surface area is used for the cathode. Constant voltage electrolysis is used for impurity removal, and the electrolysis voltage is within the electrochemical window of the molten salt system. Generally, a cell voltage of about 0.3V below the theoretical decomposition voltage of the molten salt system used for electrolysis is selected. As the electrolytic decontamination proceeds, flowing argon is used to carry the generated gas out of the system, and the current gradually decreases and stabilizes below 5mA. After the common chloride salt background current is less than 5mA, the molten salt purification is very thorough and fully meets the needs of metal electrolytic refining.

[0059] The embodiment of the present application adopts a molten salt combined purification method. The results show that the water, oxygen and impurity content in the molten salt is significantly reduced, meeting the use requirements of metal electrolytic refining. The active metal has active chemical properties and needs to be electrolytically refined under low water and oxygen conditions. At the same time, the molten salt used for metal electrolytic refining contains a small amount of water, oxygen and impurities. Before use, a small amount of water and impurities in the molten salt should be removed as much as possible, and then it can be used for metal electrolytic refining, providing favorable conditions for reducing the impurity content of the final product from the source.

[0060] Based on the molten salt purification system at the front end of metal electrolytic refining provided in the above embodiment, the embodiment of the present application also provides a molten salt purification method at the front end of metal electrolytic refining, which is applied to any one of the molten salt purification systems at the front end of metal electrolytic refining provided in the above embodiment.

[0061] The present application provides a method for purifying molten salt at the front end of metal electrolytic refining, comprising:

[0062] Step S101: purifying the molten salt to be treated by the physical purification treatment device;

[0063] Step S102: passing the purified molten salt into the electrochemical purification device for secondary purification.

[0064] In some possible implementations of the embodiments of the present application, step S101 may specifically include:

[0065] For molten salts that are not easily hydrolyzed, removing water vapor adsorbed by the molten salt to be treated by baking;

[0066] For easily hydrolyzed chloride salts, a mixed gas of hydrogen chloride and argon is introduced while the temperature is kept high to remove oxides produced by the hydrolysis of the molten salt to be treated.

[0067] In some possible implementations of the embodiments of the present application, step S102 may specifically include:

[0068] Any one of carbides, silicides and iron-nickel compounds in the purified molten salt is removed by electrolysis.

[0069] A method for purifying molten salt at the front end of metal electrolytic refining provided by an embodiment of the present application is described in detail below with reference to a specific example.

[0070] A method for purifying molten salt at the front end of metal electrolytic refining provided in an embodiment of the present application may include:

[0071] Open valve 2 to ventilate the molten salt pretreatment system, and heat up the tubular furnace 5 to keep it warm; electrolytic decontamination of molten salt: the pretreated molten salt is transferred to the electrolytic cell 12, and flowing argon gas is introduced to heat the electrolytic cell 12 to melt the molten salt, and keep it warm at a certain temperature, insert the cathode rod 13 and the anode rod 14 to perform electrolytic decontamination until the current gradually decreases and stabilizes below 5mA, and lift the cathode rod 13 and the anode rod 14 above the molten salt liquid level; stop the furnace for cooling, take it out of the furnace, and collect the molten salt for later use.

[0072] The embodiment of the present application innovatively adopts a molten salt combined purification method before the electrolytic refining experiment process. The results show that the water, oxygen and impurity contents in the molten salt are significantly reduced, meeting the requirements for metal electrolytic refining.

[0073] The present application is described in detail above in conjunction with the accompanying drawings and embodiments, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present application. Any content not described in detail in the present application can adopt the existing technology.

Claims

1. A molten salt purification system for the front end of metal electrolytic refining, characterized in that: The system comprises: a physical purification treatment device and an electrochemical purification treatment device; The physical purification treatment device and the electrochemical purification treatment device are connected in series; The physical purification treatment device is used to purify the introduced molten salt by baking and / or hydrolysis; The electrochemical purification treatment device is used to perform secondary purification on the molten salt purified by the physical purification treatment device by means of electrolysis.

2. The metal electrolytic refining front-end molten salt purification system according to claim 1, characterized in that: The physical purification treatment device comprises: a gas cylinder (1), a tubular furnace (5) and a vacuum pump (6); The gas cylinder (1) is connected to the inlet of a tubular furnace (5) through a gas pipe (3), and the tubular furnace (5) contains molten salt to be treated; The outlet of the tube furnace (5) is connected to a vacuum pump (6).

3. The metal electrolytic refining front-end molten salt purification system according to claim 2, characterized in that: The physical purification treatment device also includes: a first concentrated sulfuric acid bottle (4), an empty bottle (7), a second concentrated sulfuric acid bottle (8) and a sodium hydroxide solution bottle (9); The trachea (3) is connected in series with a first concentrated sulfuric acid bottle (4); The outlet of the tubular furnace (5) is also connected in series to an empty bottle (7), a second concentrated sulfuric acid bottle (8) and a sodium hydroxide solution bottle (9); the outlet of the sodium hydroxide solution bottle (9) discharges tail gas (10).

4. The metal electrolytic refining front-end molten salt purification system according to claim 2, characterized in that: The physical purification treatment device further comprises: a valve (2); The valve (2) is connected in series to the air pipe (3).

5. The front-end molten salt purification system for metal electrolytic refining according to any one of claims 1 to 4, characterized in that: The electrochemical purification treatment device comprises: a power source (11), an electrolytic cell (12), a cathode (13) and an anode (14); The electrolytic cell (12) is used to place the molten salt purified by the physical purification treatment device; The cathode and anode of the power source (11) are connected to the cathode rod (13) and the anode rod (14) respectively; the cathode rod (13) and the anode rod (14) are both placed in the electrolytic cell (12), and the molten salt purified by the physical purification treatment device is inserted.

6. The metal electrolytic refining front-end molten salt purification system according to claim 5, characterized in that: The power supply (11) is a constant voltage power supply.

7. The metal electrolytic refining front-end molten salt purification system according to claim 5, characterized in that: The cathode rod (13) is a nickel foam sheet, and the anode rod (14) is graphite.

8. A method for purifying molten salt at the front end of metal electrolytic refining, characterized in that: The method is applied to the molten salt purification system at the front end of metal electrolytic refining according to any one of claims 1 to 7; the method comprises: Purifying the molten salt to be treated by the physical purification treatment device; The purified molten salt is passed into the electrochemical purification device for secondary purification.

9. The method for purifying molten salt at the front end of metal electrolytic refining according to claim 8, characterized in that: Purifying the molten salt to be treated by the physical purification treatment device specifically includes: For molten salts that are not easily hydrolyzed, removing water vapor adsorbed by the molten salt to be treated by baking; For easily hydrolyzed chloride salts, a mixed gas of hydrogen chloride and argon is introduced while the temperature is kept high to remove oxides produced by the hydrolysis of the molten salt to be treated.

10. The method for purifying molten salt at the front end of metal electrolytic refining according to claim 8, characterized in that: The step of passing the purified molten salt into the electrochemical purification device for secondary purification specifically includes: Any one of carbides, silicides and iron-nickel compounds in the purified molten salt is removed by electrolysis.

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