Method and apparatus for purifying sodium metal by melt extraction

Abstract

The application provides a method and device for purifying sodium by melt extraction, the method comprising: immersing sodium crude product into molten metallic gallium under a protective atmosphere, keeping the temperature of the mixed system at 30-300 DEG C for a set time, and then cooling to 30-90 DEG C to perform solid-liquid separation, thereby obtaining high-purity metallic sodium. The device comprises a heating assembly, a reaction assembly and a filter element arranged in the reaction assembly. The application uses industrial sodium crude product as raw material, and high-purity metallic sodium can be obtained after melt extraction, which significantly reduces the content of key impurities, and the operation steps are less, the main equipment is simple to operate, low in cost, and can be large or small in specification, and is easy to realize industrialization, without the need for a vacuum system or external radiation assistance, which greatly reduces energy consumption, is low in production cost, and realizes efficient, economic and environmentally-friendly purification of metallic sodium.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and more particularly to a method for purifying sodium. Background Technology

[0002] Sodium is one of the most abundant elements on Earth, accounting for approximately 2.83% of the Earth's total crust weight, ranking sixth. Due to its highly reactive chemical properties, low melting point, high boiling point, and excellent thermal and electrical conductivity, sodium has a wide range of applications: in the chemical industry, it is used to manufacture compounds such as sodium cyanide, triphenylphosphine (TPP), sodium borohydride, sodium azide, sodium methoxide, sodium ethoxide, sodium peroxide, sodium hydride, and sodium amide, which have wide applications in metallurgy, pharmaceuticals, pesticides, and dyeing industries; in the metallurgical industry, it is used as a reducing agent to produce titanium, zirconium, and silicon. However, due to the extremely reactive nature of sodium, purification is indeed difficult.

[0003] Currently, most methods for purifying metallic sodium use industrial sodium as raw material and employ chemical methods, cold trap methods, distillation methods, and filtration methods.

[0004] For example, Chinese patent application CN202682925U discloses a high-purity sodium metal purification device, including a filter tank connected to a nitrogen source, a ceramic membrane filter, a crude liquid storage tank connected to the nitrogen source, and a clarified liquid tank. The ceramic membrane filter is designed using a cross-flow principle and is connected to the filter tank, crude liquid storage tank, and clarified liquid tank via connecting pipes. Another example is Chinese patent application CN103757435B, which discloses a method for purifying sodium metal. This method uses a sodium metal purification device consisting of a top flange, a transparent disc, a hollow flange, a vacuum distillation vessel, gaskets, and bolts. This device heats solid sodium to melt it into a liquid state, then evaporates volatile impurities contained in the liquid sodium, separating them from the liquid sodium. Simultaneously, a vacuum pump removes the volatile impurities. Afterward, a heating furnace raises the temperature of the liquid sodium, and circulating cooling water flows through the condenser tube. Radiation-assisted distillation is used, with high-purity argon gas carrying the volatile impurities. Thermal radiation raises the liquid surface temperature, accelerating the evaporation rate of the sodium. The sodium vapor rapidly condenses into solid sodium upon encountering the condenser tube, thus achieving thermal radiation-assisted distillation purification of metallic sodium. Another example is Chinese patent CN108624913B, which provides a process for industrial sodium molten electrolytic purification to high-purity sodium. This process utilizes the ion-selective permeability of a ceramic diaphragm tube to block impurities in metallic sodium through electrochemical methods. The process is simple, energy-efficient, produces high-purity metallic sodium, and is easily mass-produced.

[0005] Among the commonly used methods mentioned above, conventional filtration methods have poor purification effects, only obtaining metallic sodium with a purity of ≥99.5%. Although vacuum distillation and cold trap distillation can obtain high-purity sodium, the equipment structure and process flow are relatively complex and energy consumption is high. Chemical methods require the addition of various oxidants and reducing agents to remove metallic and non-metallic impurities from industrial sodium, which not only has long production time, but also has the problems of high energy consumption, complex equipment structure and process flow. Summary of the Invention

[0006] This invention provides a method and apparatus for purifying metallic sodium through melt extraction, thereby solving the technical problems of existing methods mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0008] A method for purifying metallic sodium by melt extraction includes the following steps: Under a protective atmosphere, crude sodium is immersed in molten gallium to obtain a mixed system. The temperature of the mixed system is maintained at 30~300℃ for a set time, and then cooled to 30~90℃ to solidify the sodium while keeping the gallium liquid. Then, solid-liquid separation is performed to obtain high-purity metallic sodium.

[0009] Research has revealed that, within a specific temperature range, impurities Li, Ca, and Pb in metallic sodium have a certain solubility in metallic gallium, while metallic sodium has no solubility in metallic gallium. For example, at 300℃, the mass fractions of the main impurity elements Li, Ca, and Pb in metallic sodium in molten metallic gallium are 9 wt.%, 3 wt.%, and 2 wt.%, respectively. This difference can be utilized to extract the impurity elements Li, Ca, and Pb from sodium using molten gallium. This invention uses crude sodium as raw material and molten metallic gallium (Ga) as the extraction medium. Utilizing the aforementioned discovery that impurity elements Li, Ca, and Pb have a certain solubility in metallic gallium, while sodium is insoluble in metallic gallium, the content of impurities Li, Ca, and Pb in crude sodium is reduced. Then, based on the difference in melting points between metallic sodium and metallic gallium, and taking advantage of the low melting point of metallic gallium, a certain temperature is maintained, allowing both to exist as solid and liquid phases. Finally, high-purity metallic sodium is obtained through solid-liquid separation, achieving the purification of impurities Li, Ca, and Pb from crude sodium. Tests showed that the purification rate of Li was over 90%, the purification rate of Ca was over 94%, and the purification rate of Pb was over 70%. The high-purity sodium produced had a purity of over 99.9%. Moreover, the process was short and the equipment was simple, solving the problems of low efficiency, high energy consumption, and long process of traditional distillation and filtration.

[0010] As a further preferred embodiment of the above technical solution, the mass ratio of the crude sodium to metallic gallium is 1:(5~10).

[0011] As a further preferred embodiment of the above technical solution, the heat preservation time of the mixed system is 2~10h.

[0012] As a further preferred embodiment of the above technical solution, the holding temperature of the mixed system is 250~300℃. The higher the temperature, the more vigorous the reaction and the better the extraction effect; the above-mentioned range provides the best extraction and purification effect.

[0013] As a further preferred embodiment of the above technical solution, after solid-liquid separation, an alloyed gallium phase is obtained, and the alloyed gallium phase is returned to the molten gallium for recycling.

[0014] As a further preferred embodiment of the above technical solution, the purity of the crude sodium product is ≤99.50%, and the purity of the high-purity metallic sodium is ≥99.90%.

[0015] As a further preferred embodiment of the above technical solution, the purity of the gallium metal is ≥99.99%.

[0016] As a further preferred embodiment of the above technical solution, the protective atmosphere is argon gas with a purity of ≥99.999%.

[0017] Based on the same technical concept, the present invention also provides an apparatus for purifying metallic sodium by melt extraction. The apparatus is used to implement the above-mentioned method for purifying metallic sodium by melt extraction, and includes a heating component, a reaction component, and a filter element placed in the reaction component.

[0018] As a further preferred embodiment of the above technical solution, the filter element is a stainless steel mesh that can move in a vertical direction; the heating assembly is a pit-type resistance furnace.

[0019] The present invention has the following beneficial effects: This invention uses industrial crude sodium with a purity ≤99.50% as raw material. After melt extraction, high-purity metallic sodium with a purity ≥99.90% can be obtained, significantly reducing the content of key impurities. Compared with the complex equipment and lengthy processes required by traditional vacuum distillation, cold trap methods, or chemical methods, this method only requires immersing the crude sodium in molten gallium metal for heat preservation and cooling, followed by solid-liquid separation. The operation steps are fewer, the main equipment is simple to operate, has a lower cost, and can be scaled up or down, making it easy to industrialize. Furthermore, the overall reaction temperature is controlled at 30~300℃ (preferably 250~300℃), far lower than high-temperature processes such as distillation, and requires no vacuum system or external radiation assistance, significantly reducing energy consumption. During the process, the alloyed metallic gallium phase obtained after solid-liquid separation can be recycled back into the molten gallium, improving resource utilization and reducing production costs.

[0020] Overall, this invention overcomes the problems of poor purification effect of conventional filtration method, complex equipment structure and high energy consumption of distillation / cold trap method, and time-consuming and complicated process of chemical method, and realizes efficient, economical and environmentally friendly purification of metallic sodium.

[0021] The present invention will now be described in further detail with reference to specific embodiments. Attached Figure Description

[0022] Figure 1 The flowcharts are for the melt extraction and purification methods of metallic sodium in Examples 2-4; Figure 2 This is a schematic diagram of the apparatus for purifying metallic sodium by melt extraction in Example 1.

[0023] Legend: 1. Well-type vacuum resistance furnace; 2. Reaction vessel; 3. Extraction medium; 4. Stainless steel mesh. Detailed Implementation

[0024] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0025] Example 1: like Figure 2 As shown, the apparatus for purifying metallic sodium by melt extraction in this embodiment includes an atmosphere control component, a heating component, a reaction component, and a filter element placed within the reaction component. The heating component is a well-type vacuum resistance furnace 1, the reaction component is a reaction vessel 2 disposed within the heating component, the extraction medium 3 is placed within the reaction vessel 2, and the filter element is a stainless steel mesh 4 that can move vertically. The crude sodium to be purified is located within the stainless steel mesh 4.

[0026] Example 2: like Figure 1 As shown in this embodiment, the method for purifying metallic sodium by melt extraction uses crude metallic sodium as the impurity element, which includes elements such as Li, Ca, and Pb. The mass percentage of Li is 203 × 10⁻⁶. -3 The mass percentage of Ca is 582 × 10⁻⁶. -3 The mass percentage of Pb is 102 × 10⁻⁶. -3 Specifically, the following operations are included (Examples 2-4 are all performed using the apparatus of Example 1; in other embodiments, any other apparatus capable of implementing the method of the present invention may also be used): Before use, the reaction vessel was cleaned sequentially with 3% hydrochloric acid and deionized water, rinsed with ethanol, and then dried. First, a vacuum-sealed bag containing metallic sodium was transferred to an argon-protected glove box. The bag was opened, and 10g of a 99.0% pure sodium block was placed inside a porous, liftable stainless steel mesh. Next, 50g of 99.99% pure gallium was transferred to the reaction vessel. The reaction vessel and stainless steel mesh were then placed together in a well-type resistance vacuum furnace. The heating system was started, and the temperature was raised to 300°C and held for 6 hours. After the holding period, the temperature was immediately lowered to 70°C. The two materials were separated using a lifting device. After the lifting was completed, the temperature was lowered to room temperature, and the materials were removed. Alloyed gallium was obtained in the reaction vessel, and high-purity metallic sodium was obtained inside the porous stainless steel mesh. In this embodiment and other embodiments, when the impurity metal in the alloyed gallium reaches a certain level, metallic gallium can be obtained for reuse through vacuum distillation.

[0027] After closing the valve of the reaction vessel, the porous stainless steel mesh was removed and then re-melted in the glove box for dispensing and sampling analysis. The results are shown in Table 1. Table 1 shows the impurity content of the high-purity sodium metal collected in the reaction vessel after following the above process. The purity of the sodium metal after impurity removal was increased to 99.9%.

[0028] Table 1: Test results of impurity content in high-purity metallic sodium in Example 2

[0029] Example 3: like Figure 1 As shown in this embodiment, the method for purifying metallic sodium by melt extraction uses crude metallic sodium as the impurity element, which includes elements such as Li, Ca, and Pb. The mass percentage of Li is 298 × 10⁻⁶. -3 The mass percentage of Ca is 597 × 10⁻⁶. -3 The mass percentage of Pb is 213 × 10⁻⁶. -3 %. Specifically, this includes the following operations: Before use, the reaction vessel was cleaned sequentially with 3% hydrochloric acid and deionized water, rinsed with ethanol, and then dried. First, a vacuum-sealed bag containing metallic sodium was transferred to an argon-protected glove box. The bag was then opened, and 10g of a sodium block (98.5% purity) was placed inside a porous, liftable stainless steel mesh. Next, 70g of metallic gallium (99.99% purity) was transferred to the reaction vessel. The reaction vessel and stainless steel mesh were then placed together in a well-type resistance vacuum furnace. The heating system was started, and the temperature was raised to 250℃ and held for 8 hours. After the holding period, the temperature was immediately lowered to 90℃. The two materials were separated using a lifting device. After the lifting was completed, the temperature was lowered to room temperature, and the materials were removed. Alloyed gallium was obtained in the reaction vessel, and high-purity metallic sodium was obtained inside the porous stainless steel mesh.

[0030] After closing the valve of the reaction vessel, the porous stainless steel mesh was removed and then re-melted in the glove box for dispensing and sampling analysis. The results are shown in Table 2. Table 2 is a table of impurity content of high-purity sodium metal collected in the reaction vessel after the above process. The purity of the sodium metal after impurity removal is increased to 99.9%.

[0031] Table 2: Test results of impurity content in high-purity metallic sodium in Example 3

[0032] Example 4: like Figure 1 As shown in this embodiment, the method for purifying metallic sodium by melt extraction uses crude metallic sodium as the impurity element, which includes elements such as Li, Ca, and Pb. The mass percentage of Li is 185 × 10⁻⁶. -3 The mass percentage of Ca is 359 × 10⁻⁶. -3 The mass percentage of Pb is 174 × 10⁻⁶. -3 %. Specifically, this includes the following operations: Before use, the reaction vessel was cleaned sequentially with 3% hydrochloric acid and deionized water, rinsed with ethanol, and then dried. First, a vacuum-sealed bag containing metallic sodium was transferred to an argon-protected glove box. The bag was then opened, and 10g of a sodium block (99.1% purity) was placed inside a porous, liftable stainless steel mesh. Next, 80g of metallic gallium (99.99% purity) was transferred to the reaction vessel. The reaction vessel and stainless steel mesh were then placed together in a well-type resistance vacuum furnace. The heating system was started, and the temperature was raised to 300℃ and held for 8 hours. After the holding period, the temperature was immediately lowered to 80℃. The two materials were separated using a lifting device. After the lifting was completed, the temperature was lowered to room temperature, and the materials were removed. Alloyed gallium was obtained in the reaction vessel, and high-purity metallic sodium was obtained inside the porous stainless steel mesh.

[0033] After closing the valve of the reaction vessel, the porous stainless steel mesh was removed and then re-melted in the glove box for dispensing and sampling analysis. The results are shown in Table 3. Table 3 shows the impurity content of the high-purity sodium metal collected in the reaction vessel after following the above process. The purity of the sodium metal after impurity removal was increased to 99.95%.

[0034] Table 3: Test results of impurity content in high-purity metallic sodium in Example 4

[0035] The above are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

[0036] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for purifying metallic sodium through melt extraction, characterized in that, Includes the following operations: Under a protective atmosphere, crude sodium is immersed in molten gallium to obtain a mixed system. The temperature of the mixed system is maintained at 30~300℃ for a set time, and then cooled to 30~90℃ to solidify the sodium while keeping the gallium liquid. Then, solid-liquid separation is performed to obtain high-purity metallic sodium.

2. The method for purifying metallic sodium by melt extraction according to claim 1, characterized in that, The mass ratio of crude sodium to metallic gallium is 1:(5~10).

3. The method for purifying metallic sodium by melt extraction according to claim 1, characterized in that, The heat preservation time for the mixture is 2 to 10 hours.

4. The method for purifying metallic sodium by melt extraction according to claim 1, characterized in that, The insulation temperature of the mixture is 250~300℃.

5. The method for purifying metallic sodium by melt extraction according to any one of claims 1-4, characterized in that, After solid-liquid separation, an alloyed gallium phase is obtained, which is then recycled back into the molten gallium.

6. The method for purifying metallic sodium by melt extraction according to any one of claims 1-4, characterized in that, The purity of the crude sodium product is ≤99.50%, and the purity of the high-purity metallic sodium is ≥99.90%.

7. The method for purifying metallic sodium by melt extraction according to any one of claims 1-4, characterized in that, The purity of the gallium metal is ≥99.99%.

8. The method for purifying metallic sodium by melt extraction according to any one of claims 1-4, characterized in that, The protective atmosphere is argon gas with a purity of ≥99.999%.

9. An apparatus for purifying metallic sodium by melt extraction, characterized in that, The apparatus is used to implement the melt extraction and purification method for metallic sodium according to any one of claims 1-8, and includes a heating assembly, a reaction assembly, and a filter element placed within the reaction assembly.

10. The apparatus for purifying metallic sodium by melt extraction according to claim 9, characterized in that, The filter element is a stainless steel mesh that can move vertically; the heating assembly is a pit-type resistance furnace.

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