A process for the production of alkali and alkaline earth metals by electrolysis without chlorine gas emission

Abstract

The application discloses a method for preparing alkali metals and alkaline earth metals by electrolysis without chlorine gas emission, and steps are as follows: liquid metal tin is used as a cathode, graphite or nickel-based high-temperature alloy is used as an anode, X2CO3-XCl mixed molten salt is used as an electrolyte, and X-Sn alloy is obtained by electrolysis; the obtained X-Sn alloy is placed in XCl-MCl n mixed molten salt (X is Na, K, Rb or Cs, M is Li, Mg, Ca, Sr or Ba, and n is 1 or 2) for soaking, and M-Sn alloy is obtained by replacement; the obtained X-Sn and M-Sn alloys are subjected to vacuum distillation, and high-purity X, M and Sn are separated. The method has the advantages of low cost, low CO2 and solid waste emission, no chlorine gas emission, high current efficiency and environmental friendliness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molten salt metallurgy, in particular to a method for preparing alkali metals and alkaline earth metals by electrolysis without chlorine gas emission. BACKGROUND

[0002] Alkali metals (lithium, sodium, potassium, rubidium, cesium) and alkaline earth metals (magnesium, calcium, strontium, barium) play an indispensable role in promoting the modernization process of human society, and are widely used in metallurgy, chemistry, energy, automobiles, aerospace and atomic energy fields. At present, the methods for preparing alkali metals and alkaline earth metals in industry can be divided into two kinds: molten salt electrolysis method and thermal reduction method. In the process of preparing metals by thermal reduction method, huge energy consumption, considerable greenhouse gas CO2 emission and a large amount of solid waste are often required, and in the context of energy saving and emission reduction, this method will be gradually replaced by molten salt electrolysis method using green energy (electricity). However, the mainstream molten salt electrolysis method uses chlorides of alkali metals and alkaline earth metals as raw materials, and a large amount of environmentally harmful gas Cl2 is generated during the electrolysis of metals. Although Cl2 has certain economic value, its production is much larger than its demand. At the same time, the molten salt electrolysis has extremely strict requirements for the chlorides raw materials. For example, in the electrolytic magnesium industry, MgO impurities exist in the molten state of incompletely dried MgCl2, which will form Mg slag and precipitate at the bottom of the cathode, resulting in a sharp decrease in current efficiency. The MgO involved in electrolysis will corrode the graphite anode, which will cause the anode to be damaged, so that a complicated dehydration process is required to obtain anhydrous MgCl2, and a complex electrolysis device is used to avoid the contact of molten salt with air (introducing H2O to generate MgO), which greatly increases the cost.

[0003] Therefore, it is necessary to develop a method for preparing alkali metals and alkaline earth metals with low cost, low CO2 and solid waste emission, high current efficiency and environmental friendliness. SUMMARY

[0004] In order to solve the above technical problems, especially the problem of huge environmental harmful gas Cl2 emission in molten salt metallurgy, the purpose of the present application is to provide a method for preparing alkali metals and alkaline earth metals by electrolysis. The preparation method has the advantages of rich raw materials, low CO2 and solid waste emission, high preparation efficiency and no pollution to the environment.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A method for preparing alkali metals and alkaline earth metals by electrolysis without chlorine gas emission, comprising the following steps:

[0007] Liquid tin (Sn) is used as the cathode, graphite or nickel-based superalloy as the anode, and a mixed molten salt of X₂CO₃-XCl is used as the electrolyte to electrolyze and obtain X-Sn alloy; wherein X is Na, K, Rb or Cs.

[0008] The electrolytically obtained X-Sn alloy was placed in an XCl-MCl... n Immersion in a mixed molten salt, wherein M is Li, Mg, Ca, Sr, or Ba, and n = 1 or 2, yields an M-Sn alloy by substitution.

[0009] The obtained X-Sn and M-Sn alloys were subjected to vacuum distillation to separate high-purity X, M and Sn.

[0010] Furthermore, the molar ratio of X2CO3 to XCl in the X2CO3-XCl mixed molten salt is a eutectic ratio.

[0011] Furthermore, the operating temperature of the X2CO3-XCl mixed molten salt is 650-700℃, and no protective atmosphere is required. During electrolysis, the liquid Sn at the cathode transforms into a liquid X-Sn alloy, while CO2 (graphite anode) or O2, CO2 (nickel-based high-temperature alloy anode) is generated on the anode.

[0012] Furthermore, the electrolysis is constant cell voltage or constant current electrolysis, with the current density controlled between 200 and 500 mA·cm⁻¹. -2 Within the range.

[0013] Furthermore, the XCl-MCl n The working temperature of the mixed molten salt is 550–750℃.

[0014] Furthermore, the X-Sn alloy is immersed in it for 2 to 3 hours without the need for a protective atmosphere.

[0015] Furthermore, the X-Sn and M-Sn alloys are separated by vacuum distillation at a working temperature of 700–1200°C and an internal pressure of 10 kJ / L. -1 ~10 2 Pa.

[0016] Furthermore, the X-Sn alloy obtained by electrolysis is in a liquid state with a density greater than that of X2CO3-XCl molten salt, and is located in the lower part of the molten salt, isolated from the outside air atmosphere.

[0017] Furthermore, the M-Sn alloy obtained by the substitution is in a liquid state and has a density greater than that of XCl-MCl. n Molten salt, located at the bottom of the molten salt, is isolated from the outside air atmosphere.

[0018] Furthermore, the liquid Sn serves as a carrier for alkali metals and alkaline earth metals, is not consumed during the entire process, and can be recycled as an electrolytic cathode after vacuum distillation separation.

[0019] The method provided by this invention uses readily available carbonates (X2CO3), Sn, and MCl. n Using liquid metal Sn as the cathode, X-Sn alloys were prepared by electrolysis. The X-Sn alloys were then placed in XCl-MCl... n M-Sn alloys are obtained through displacement in molten salt. Finally, X-Sn and M-Sn alloys are separated by vacuum distillation to obtain high-purity X, M, and Sn. The electrolysis process consumes carbonates (alkali metal source), and the use of carbonates is fundamental to avoiding chlorine gas generation. The use of liquid tin can store alkali metals and reduce the electrolytic cell pressure. The immersion displacement process utilizes the activity differences between different alkali metals and alkaline earth metals in liquid tin to achieve the displacement reaction.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Raw materials are abundant and inexpensive;

[0022] (2) No chlorine emissions, no environmental pollution;

[0023] (3) Low CO2 and solid waste emissions;

[0024] (4) No protective atmosphere required;

[0025] (5) The preparation efficiency and metal purity are both higher than those of traditional electrolysis;

[0026] (6)XCl-MCl n Salt mixtures do not require cumbersome dehydration pretreatment. Attached Figure Description

[0027] Figure 1 This is a technical flow diagram of a method for preparing alkali metals and alkaline earth metals by electrolysis without chlorine emissions, provided in an embodiment of the present invention. Detailed Implementation

[0028] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0029] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0030] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be obtained by purchasing them from the market or by existing methods.

[0031] Example 1

[0032] Mix 300g of Na2CO3 and 200g of NaCl evenly (at this point, it is a eutectic composition with a molar ratio of 45:55) and place it in a vacuum drying oven at 200℃. After drying for 24 hours, transfer it to a resistance furnace and heat it to 800℃ and hold it for 30 minutes. After the Na2CO3-NaCl mixed salt has fully melted, cool it down to 650-700℃ and hold it. This process does not require a strict protective atmosphere.

[0033] The cathode is 100g of metallic Sn, placed in an alumina (Al₂O₃) crucible and then placed at the bottom of a Na₂CO₃-NaCl molten salt. A molybdenum (Mo) wire with a diameter of φ = 2mm is used as the current collector and connected to a DC power supply. The anode is a graphite rod with a diameter of φ = 10mm, inserted into the molten salt and spaced 3-5cm away from the cathode. The current density is controlled at 200-500mA·cm⁻¹. -2 Within a certain range, constant cell voltage or constant current electrolysis is performed to obtain a product with the composition Na. 10 Sn and Na 20 Sn alloys. The composition of the Na-Sn alloy obtained by electrolysis was determined and the current efficiency was calculated. 10 Sn and Na 20 The current efficiencies of the Sn alloys were 96.0% and 89.2%, respectively.

[0034] Example 2

[0035] The treatment method for the Na2CO3-NaCl mixed salt and metallic Sn cathode is the same as in Example 1. The anode is a 10mm×3mm×100mm nickel-based superalloy (GH 738 type nickel alloy), with the upper end connected to a φ=2mm 316 # Stainless steel welding is used as a current collector, inserted deep into the molten salt and spaced 3-5 cm away from the cathode. The current density is controlled at 200-500 mA·cm. -2 Within a certain range, constant cell voltage or constant current electrolysis is performed to obtain a product with the composition Na. 10 Sn and Na 20 Sn alloys. The composition of the Na-Sn alloy obtained by electrolysis was determined and the current efficiency was calculated. 10 Sn and Na 20 The current efficiencies of the Sn alloys were 90.5% and 82.8%, respectively.

[0036] Example 3

[0037] Weigh out a total of 300g of NaCl and LiCl at a molar ratio of 27:73 and mix thoroughly. Place the mixture in a vacuum drying oven at 200℃ and dry for 24 hours. Then transfer it to a resistance furnace and heat to 750℃, holding for 30 minutes. After the NaCl-LiCl mixed salt is fully melted, cool to 600-700℃ and hold. This process does not require a strictly protective atmosphere. (The last sentence appears to be incomplete and possibly refers to a different process.) 10 Sn and Na 20 Sn was immersed in NaCl-LiCl molten salt for 180 min, and then the contents of Li and Na in the alloy were measured and the displacement efficiency was calculated. 10 Sn and Na 20 The substitution efficiency of Sn reached 99.5%.

[0038] Example 4

[0039] Weigh out a total of 300g of NaCl and MgCl2 at a molar ratio of 57:43 and mix thoroughly. Place the mixture in a vacuum drying oven at 200℃ and dry for 24 hours. Then transfer it to a resistance furnace and heat to 650℃, holding for 30 minutes. After the NaCl-MgCl2 mixed salt has fully melted, cool it to 500-600℃ and hold. This process does not require a strictly protective atmosphere. (The last sentence appears to be incomplete and possibly refers to a different process.) 10 Sn and Na 20 Sn was immersed in NaCl-MgCl2 molten salt for 180 min, and then the contents of Mg and Na in the alloy were measured and the displacement efficiency was calculated. 10 Sn and Na 20 The substitution efficiencies for Sn were 98.2% and 98.4%, respectively.

[0040] Example 5

[0041] Weigh out a total of 300g of NaCl and CaCl2 at a molar ratio of 47:53 and mix thoroughly. Place the mixture in a vacuum drying oven at 200℃ and dry for 24 hours. Then transfer it to a resistance furnace and heat to 700℃, holding for 30 minutes. After the NaCl-CaCl2 mixed salt has fully melted, cool it to 550-650℃ and hold. This process does not require a strictly protective atmosphere. (The last sentence appears to be incomplete and possibly refers to a different process.) 10 Sn and Na 20 Sn was immersed in NaCl-CaCl2 molten salt for 180 min, and then the contents of Ca and Na in the alloy were measured and the displacement efficiency was calculated. 10 Sn and Na 20 The substitution efficiencies for Sn were 96.1% and 97.8%, respectively.

[0042] Example 6

[0043] Weigh out a total of 300g of NaCl and SrCl2 at a molar ratio of 48:52 and mix thoroughly. Place the mixture in a vacuum drying oven at 200℃ and dry for 24 hours. Then transfer it to a resistance furnace and heat to 750℃, holding for 30 minutes. After the NaCl-SrCl2 mixed salt has fully melted, cool it to 600-700℃ and hold. This process does not require a strictly protective atmosphere. Add 50g of NaCl... 10 Sn and Na 20 Sn was immersed in NaCl-SrCl2 molten salt for 180 min, and then the contents of Sr and Na in the alloy were measured and the substitution efficiency was calculated. 10 Sn and Na 20 The substitution efficiencies of Sn were 96.1% and 96.6%, respectively.

[0044] Example 7

[0045] Weigh out a total of 300g of NaCl and BaCl2 at a molar ratio of 60:40 and mix thoroughly. Place the mixture in a vacuum drying oven at 200℃ and dry for 24 hours. Then transfer it to a resistance furnace and heat to 850℃, holding for 30 minutes. After the NaCl-BaCl2 mixed salt has fully melted, cool it to 700-800℃ and hold. This process does not require a strictly protective atmosphere. (The last sentence appears to be incomplete and possibly refers to a different process.) 10 Sn and Na 20 Sn was immersed in NaCl-BaCl2 molten salt for 180 min, and then the contents of Ba and Na in the alloy were measured and the displacement efficiency was calculated. 10 Sn and Na 20 The substitution efficiencies for Sn were 96.0% and 96.3%, respectively.

[0046] Example 8

[0047] 235g of K₂CO₃ and 275g of KCl were mixed evenly (eutectic composition) and placed in a vacuum drying oven at 200°C for 24 hours. After drying, the mixture was transferred to a resistance furnace and heated to 800°C for 30 minutes. Once the K₂CO₃-KCl mixed salt was fully melted, the temperature was lowered to 650–750°C and held. This process does not require a strictly protective atmosphere. 100g of metallic Sn cathode was treated according to the method described in Example 1, with the current density controlled at 200–500 mA·cm⁻¹. -2 Within the specified range, constant cell voltage or constant current electrolysis is performed. The anode is graphite, K... 10 Sn and K 20 The current efficiencies of Sn were 79.7% and 68.2%, respectively; the anode was GH 738 type nickel alloy, K 10 Sn and K 20 The current efficiencies of Sn are 78.7% and 65.9%, respectively.

[0048] Example 9

[0049] 20g of Na 20 Sn is placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 50–200 Pa. The temperature is increased to 700 °C at a rate of 10–15 °C / min and held for 120 min. After cooling, the Na deposit and the Sn residue are collected, and the Na content in Sn is determined to calculate the separation efficiency. The Na content under these vacuum distillation parameters is... 20 The Sn separation efficiency was 98.4%.

[0050] Example 10

[0051] 20g of K 20 Sn is placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 50–200 Pa. The temperature is increased to 650 °C at a rate of 10–15 °C / min and held for 90 min. After cooling, the precipitate K and the residue Sn are collected, and the K content in Sn is determined to calculate the separation efficiency. The K content under these vacuum distillation parameters is... 20 The Sn separation efficiency is 99.1%.

[0052] Example 11

[0053] 20g of Li 20 Sn is placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 1–20 Pa. It is heated to 900 °C at a heating rate of 10–15 °C / min and held at that temperature for 90 min. After cooling, the precipitate Li and the residue Sn are collected, and the Li content in Sn is determined to calculate the separation efficiency. The Li content under these vacuum distillation parameters is... 20 The Sn separation efficiency is 99.4%.

[0054] Example 12

[0055] 20g of Mg 10 Sn was placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 50–200 Pa. The mixture was heated to 1100 °C at a heating rate of 10–15 °C / min and held at that temperature for 180 min. After cooling, the precipitate (Mg) and the residue (Sn) were collected, and the Mg content in Sn was determined to calculate the separation efficiency. The Mg content under these vacuum distillation parameters was... 10 The Sn separation efficiency was 96.3%.

[0056] Example 13

[0057] Add 20g of Ca 10 Sn is placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 1–20 Pa. It is heated to 950 °C at a heating rate of 10–15 °C / min and held at that temperature for 90 min. After cooling, the precipitate (Ca) and the residue (Sn) are collected, and the Ca content in Sn is determined to calculate the separation efficiency. The Ca content under these vacuum distillation parameters is...10 The Sn separation efficiency was 93.8%.

[0058] Example 14

[0059] 20g of Sr 10 Sn was placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 1–20 Pa. The temperature was increased to 950 °C at a rate of 10–15 °C / min and held for 120 min. After cooling, the precipitate Sr and the residue Sn were collected, and the Sr content in Sn was determined to calculate the separation efficiency. The Sr content under these vacuum distillation parameters was... 10 The Sn separation efficiency was 95.1%.

[0060] Example 15

[0061] Add 20g of Ba 10 Sn was placed in a vacuum distillation apparatus, with the internal pressure controlled within the range of 0.1–1 Pa. The mixture was heated to 900 °C at a heating rate of 10–15 °C / min and held at that temperature for 180 min. After cooling, the precipitate Ba and the residue Sn were collected, and the Ba content in Sn was determined to calculate the separation efficiency. The Ba content under these vacuum distillation parameters was... 10 The Sn separation efficiency is 95.5%.

[0062] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the invention.

Claims

1. A method for the electrolytic preparation of alkali metals and alkaline earth metals without chlorine emissions, characterized in that, Includes the following steps: Liquid tin (Sn) is used as the cathode, graphite or nickel-based superalloy as the anode, and an X₂CO₃-XCl mixed molten salt as the electrolyte to electrolyze and obtain an X-Sn alloy; wherein X is Na, K, Rb, or Cs; the molar ratio of X₂CO₃ to XCl in the X₂CO₃-XCl mixed molten salt is a eutectic ratio; the operating temperature of the X₂CO₃-XCl mixed molten salt is 650~700℃, and no protective atmosphere is required; The electrolytically obtained X-Sn alloy was placed in an XCl-MCl... n Immersion in a mixed molten salt, wherein M is Li, Mg, Ca, Sr, or Ba, and n = 1 or 2, yields an M-Sn alloy by displacement; the XCl-MCl... n The operating temperature of the mixed molten salt is 550 ~ 750℃; The obtained X-Sn and M-Sn alloys were subjected to vacuum distillation to separate high-purity X, M and Sn.

2. The method according to claim 1, characterized in that: The electrolysis is performed under constant cell voltage or constant current conditions, with the current density controlled between 200 and 500 mA·cm⁻¹. -2 Within the range.

3. The method according to claim 1, characterized in that: The X-Sn alloy is immersed in it for 2 to 3 hours without the need for a protective atmosphere.

4. The method according to claim 1, characterized in that: The X-Sn and M-Sn alloys are separated by vacuum distillation at a working temperature of 700~1200 ℃ and an internal pressure of 10 ℃. -1 ~ 10 2 Pa.

5. The method according to claim 1, characterized in that: The X-Sn alloy obtained by electrolysis is in a liquid state with a density greater than that of X2CO3-XCl molten salt, and is located in the lower part of the molten salt, isolated from the outside air atmosphere.

6. The method according to claim 1, characterized in that: The M-Sn alloy obtained by the substitution is in a liquid state with a density greater than that of XCl-MCl. n Molten salt, located at the bottom of the molten salt, is isolated from the outside air atmosphere.

7. The method according to claim 1, characterized in that: The liquid Sn serves as a carrier for alkali metals and alkaline earth metals, is not consumed during the entire process, and can be recycled as an electrolytic cathode after vacuum distillation separation.

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