A highly efficient method for tellurium purification by removing oxygen, sulfur, and selenium.

Abstract

A highly efficient method for removing oxygen, sulfur, and selenium from tellurium for purification includes the following steps: charging; controlling the reducing atmosphere; volatilization; distillation; and ingot casting. This method can directly obtain 4N tellurium product through a single vacuum distillation. The product has low levels of single-point-digestible impurities such as selenium, sulfur, and oxygen, providing high-quality raw materials with low levels of oxygen-containing impurities for subsequent preparation of 5N and higher purity tellurium. By controlling the vacuum degree and H2 content during the vacuum distillation process, this method efficiently removes impurities such as selenium, sulfur, and oxygen while improving tellurium recovery.

Description

Technical Field

[0001] This invention relates to a method for purifying tellurium, specifically a method for purifying tellurium by removing oxygen, sulfur, and selenium. Background Technology

[0002] Tellurium is a typical rare and dispersed metal, with an abundance of only 0.001–0.005 g / t in the Earth's crust, making its reserves scarce. It has wide applications in infrared detection, solar energy technology, semiconductors, 5G communications, and military industries. For example, CdTe is an important solar cell material, Bi₂Te₃ and PbTe are excellent cooling materials, and HgCdTe, ZnCdTe, and PbSnTe are mainly used in infrared detection and military applications. Trace impurities in tellurium directly affect material performance. For instance, in infrared detection and guidance systems for military weapons, the presence of impurities reduces detection accuracy, thereby shortening the operational radius and reducing the strike accuracy of advanced weapons. Therefore, high purification of tellurium is of great significance.

[0003] Tellurium purification techniques include chemical and physical methods. Chemical purification methods include extraction, precipitation, and electrolysis, while physical purification methods include vacuum distillation and zone melting. Currently, electrolytic refining is generally used in industry to prepare 4N tellurium, while extraction and precipitation techniques are less commonly used. For example, CN111647902A, CN107475736A, and CN116657212A all mention the use of electrolysis or electrowinning to prepare 4N tellurium. This involves first preparing a solution, then removing impurities from the tellurium-containing solution, followed by electrolysis, and then repeated washing or boiling of the tellurium powder produced during electrolysis to finally obtain 4N tellurium. The chemical method for preparing high-purity tellurium consumes a large amount of reagents, and the solution is easily contaminated during the reaction and transport processes, generating a large amount of wastewater. Tellurium is a low-melting-point, high-saturated vapor pressure metal; vacuum distillation can effectively remove most impurities from tellurium, obtaining high-purity distilled tellurium. Vacuum distillation technology can purify tellurium to a purity of 5N or higher. However, this requires multiple zone melting processes, multi-stage temperature control, multi-stage condensation, and a high-vacuum environment. Directly purifying 99% tellurium powder to 5N or higher via vacuum distillation presents challenges such as a lengthy process, difficulty in controlling individual impurities, numerous purification cycles, and high energy consumption. Existing vacuum distillation technologies generally suffer from low removal rates of single-point impurities such as oxygen, sulfur, and selenium, resulting in unstable product purity. Typically, hydrogenation for selenium removal and oxygen removal is required after vacuum distillation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a tellurium purification method that can efficiently remove oxygen, sulfur and selenium to obtain 4N tellurium.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: A highly efficient method for removing oxygen, sulfur, and selenium from tellurium for purification, comprising the following steps:

[0006] (1) Loading: Load 2N tellurium powder into a container and place it in a distillation furnace;

[0007] (2) Control the reducing atmosphere: Adjust the atmosphere in the distillation furnace to a reducing atmosphere with a vacuum of 250-500 Pa and hydrogen volume of 30%-50%;

[0008] (3) Volatilization: Control the temperature inside the distillation furnace to 450-500℃ and maintain it for 60-90 minutes; during the volatilization process, maintain the hydrogen volume in the atmosphere to be 30%-50% by supplying and exhausting gas, and the vacuum degree to be 250-500Pa.

[0009] (4) Distillation: Control the temperature inside the distillation furnace to 500-600℃ and maintain it for 3-5 hours; during the volatilization process, maintain the hydrogen volume in the atmosphere to be 30%-50% by supplying and exhausting gas, and the vacuum degree to be 250-500Pa.

[0010] (5) Casting: The purified distillation product is melted and cast into a mold under a hydrogen reducing atmosphere to obtain purified tellurium ingots.

[0011] The method of this invention can directly obtain 4N tellurium product through a single vacuum distillation. The product has low content of single-point difficult-to-remove impurities such as selenium, sulfur, and oxygen, providing high-quality raw materials with low content of oxalic impurities for subsequent preparation of 5N and higher purity tellurium.

[0012] Preferably, in step (2), the distillation furnace is first evacuated, then filled with nitrogen to atmospheric pressure, then evacuated again, then filled with hydrogen to atmospheric pressure, and then the gas supply device and the vacuum device are adjusted to make the vacuum degree in the distillation furnace 250-500Pa.

[0013] By adopting the above technical solution, a suitable atmosphere can be provided.

[0014] Preferably, in step (2), the vacuum degree in the distillation furnace is first evacuated to below 20 Pa, nitrogen is added to atmospheric pressure, then evacuated to below 20 Pa, hydrogen is added to atmospheric pressure, and then the gas supply device and the vacuum device are adjusted to make the vacuum degree in the distillation furnace 250-500 Pa.

[0015] By adopting the above technical solution, a suitable atmosphere can be provided.

[0016] Preferably, in step (5), the hydrogen flow rate is controlled at 0.1-0.3 L / min during the casting process.

[0017] By adopting the above technical solution, a good protective effect can be achieved.

[0018] Preferably, in step (1), the container is a graphite device; in step (5), the mold is a graphite device.

[0019] Graphite devices have good thermal conductivity, low coefficient of linear expansion, and good thermal and chemical stability, making them suitable for tellurium purification.

[0020] Preferably, the graphite device in steps (1) and (5) has an ash content of less than 50 ppm.

[0021] By adopting the above technical solutions, it is helpful to improve product purity.

[0022] Preferably, the purity of the hydrogen and nitrogen used is above 4N.

[0023] By adopting the above technical solutions, it is helpful to improve product purity.

[0024] Principle of this invention:

[0025] Tellurium has a melting point of approximately 452°C and a boiling point of approximately 1390°C. It begins to volatilize at 400°C under vacuum conditions. The saturated vapor pressure of impurities in tellurium at various temperatures is shown in the table below.

[0026]

[0027]

[0028] Selenium, sulfur, oxygen, and other impurities belong to the same group as metallic tellurium. Selenium and tellurium have extremely similar physicochemical properties, and the saturated vapor pressure of sulfur is also close to that of tellurium. Therefore, selenium and sulfur are difficult to remove during distillation. Although theoretically, during distillation, tellurium, selenium, sulfur, and some other impurities melt and volatilize upon heating, and the gas phase can then be separated from tellurium through fractional condensation, in practice, the fractional condensation effect of selenium, sulfur, and tellurium is poor.

[0029] Furthermore, oxygen present in the raw materials or distillation system can form oxides with tellurium and other metallic elements. For example, tellurium dioxide has a melting point of 733℃ and does not volatilize during tellurium vacuum distillation, thus reducing the distillation efficiency. Impurity oxygen also affects the separation of metallic tellurium from highly volatile impurities, reducing purification efficiency.

[0030] Considering that selenium and sulfur, upon volatilization, can react with H2 to generate hydrogen selenide and hydrogen sulfide gases respectively, thus being removed, the partial pressure of H2 is controlled during vacuum distillation to ensure sufficient reaction between H2 and impurities selenium, sulfur, and oxygen. The Gibbs free energies of the reaction of selenium, sulfur, and tellurium with H2 at 500℃ are shown in the following equation:

[0031] Se(g)+H2(g)=H2Se(g) ΔG=-32.48<0

[0032] S(g)+H2(g)=H2S(g) ΔG=-53.02<0

[0033] Te(g)+H2(g)=H2Te(g) ΔG=-9.87<0

[0034] The above analysis shows that selenium, sulfur, and tellurium can all react with H2 to generate gases. However, hydrogen telluride gas is extremely unstable and decomposes into H2 and metallic tellurium at room temperature. Therefore, metallic tellurium remains in the system and is not lost during gas flow. Simultaneously, H2 can react with metal oxides to generate elemental metals and water vapor, thus impurity oxygen can be effectively removed from this system. This also reduces the residue of tellurium dioxide in the distillation residue, increases the volatilization rate of metallic tellurium, and further improves the tellurium recovery rate.

[0035] In this invention, under vacuum conditions, tellurium begins to volatilize at 400℃, and simultaneously, highly volatile impurities such as selenium and sulfur also begin to volatilize. By adjusting the temperature and atmosphere, the removal rate of highly volatile impurities such as selenium and sulfur can be improved. When the temperature is 500℃, the saturated vapor pressure difference between tellurium and impurities is relatively large, making it easier for metallic tellurium to separate from impurities during vacuum distillation. Therefore, the distillation temperature is controlled at or above 500℃. During the distillation process, the hydrogen content is maintained throughout, and the vacuum degree of the system is controlled at 250-500 Pa, allowing impurities such as selenium, sulfur, and oxygen to fully react with H2 and be removed.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) The method of the present invention can directly obtain 4N tellurium product through a single vacuum distillation. The product has low content of single-point difficult-to-remove impurities such as selenium, sulfur, and oxygen, providing high-quality raw materials with low content of oxalic impurities for subsequent preparation of 5N and above purity tellurium.

[0038] (2) The method of the present invention improves the recovery rate of tellurium by controlling the vacuum degree and H2 content in the vacuum distillation process, effectively removing impurities such as selenium, sulfur, and oxygen. Detailed Implementation

[0039] The present invention will be further described below with reference to embodiments. The following are only some embodiments of the present technology, and the present invention can be implemented in many different ways as defined and covered by the claims.

[0040] The raw materials used in the various embodiments and comparative examples of this invention were all obtained through conventional commercial means.

[0041] The composition of the 2N tellurium powder used in each embodiment and comparative example is shown in Table 1.

[0042] Table 1 Raw material testing data

[0043]

[0044] Example 1

[0045] This embodiment of the efficient tellurium purification method for removing oxygen, sulfur, and selenium includes the following steps:

[0046] (1) Loading: Clean the graphite boat, weigh 600g of 2N tellurium powder and load it into the graphite boat, then load the loaded graphite boat into the distillation furnace.

[0047] (2) Control the reducing atmosphere: First, the vacuum in the system is reduced to below 20 Pa, and then nitrogen is added to atmospheric pressure; then the vacuum in the system is reduced to below 20 Pa, and then hydrogen is added to atmospheric pressure; finally, the vacuum device is turned on, the hydrogen valve is adjusted, and the hydrogen volume in the system atmosphere is controlled to be 30% and the vacuum is 300 Pa.

[0048] (3) Volatilization: The evaporation temperature is controlled at 450℃ and the evaporation time is controlled at 60min; during the evaporation process, the hydrogen volume in the atmosphere is maintained at 30% by gas supply and exhaust, and the vacuum degree is 300Pa.

[0049] (4) Distillation: The distillation temperature is controlled at 550℃ and the distillation time is controlled at 4h; during the volatilization process, the hydrogen volume in the atmosphere is maintained at 30% by gas supply and exhaust, and the vacuum degree is 300Pa; the distillation rate is 86.7%;

[0050] (5) Casting: The purified distillation product is melted and cast into a graphite mold under a hydrogen reducing atmosphere (hydrogen flow rate controlled at 0.2 L / min) to obtain purified tellurium ingot.

[0051] The graphite boat in step (1) and the graphite mold in step (5) are both graphite devices with an ash content of less than 50 ppm; the purity of the hydrogen and nitrogen used is above 4N.

[0052] The test data of the purified tellurium ingot product obtained in this embodiment are shown in Table 2. It can be seen that the purified tellurium ingot obtained meets the 4N tellurium standard.

[0053] Table 2 Product Detection Data from Example 1

[0054]

[0055] Example 2

[0056] This embodiment of the efficient tellurium purification method for removing oxygen, sulfur, and selenium includes the following steps:

[0057] (1) Loading: Clean the graphite boat, weigh 700g of 2N tellurium powder and load it into the graphite boat, then load the loaded graphite boat into the distillation furnace.

[0058] (2) Control the reducing atmosphere: First, the vacuum in the system is reduced to below 20 Pa, and then nitrogen is added to atmospheric pressure; then the vacuum in the system is reduced to below 20 Pa, and then hydrogen is added to atmospheric pressure; finally, the vacuum device is turned on, the hydrogen valve is adjusted, and the hydrogen volume in the system atmosphere is controlled to be 40% and the vacuum is 400 Pa.

[0059] (3) Volatilization: The evaporation temperature is controlled at 480℃ and the evaporation time is controlled at 70min; during the evaporation process, the hydrogen volume in the atmosphere is maintained at 40% by gas supply and exhaust, and the vacuum degree is 400Pa.

[0060] (4) Distillation: The distillation temperature was controlled at 580℃ and the distillation time was controlled at 4.5h; during the volatilization process, the hydrogen volume in the atmosphere was maintained at 40% by gas supply and exhaust, and the vacuum degree was 400Pa; the distillation rate was 89.3%;

[0061] (5) Casting: The purified distillation product is melted and cast into a graphite mold under a hydrogen reducing atmosphere (hydrogen flow rate controlled at 0.1 L / min) to obtain purified tellurium ingot.

[0062] The graphite boat in step (1) and the graphite mold in step (5) are both graphite devices with an ash content of less than 50 ppm; the purity of the hydrogen and nitrogen used is above 4N.

[0063] The test data of the purified tellurium ingot product obtained in this embodiment are shown in Table 3. It can be seen that the purified tellurium ingot obtained meets the 4N tellurium standard.

[0064] Table 3 Product Detection Data from Example 2

[0065]

[0066]

[0067] Example 3

[0068] This embodiment of the efficient tellurium purification method for removing oxygen, sulfur, and selenium includes the following steps:

[0069] (1) Loading: Clean the graphite boat, weigh 800g of 2N tellurium powder and load it into the graphite boat, then load the loaded graphite boat into the distillation furnace.

[0070] (2) Control the reducing atmosphere: First, the vacuum in the system is reduced to below 20 Pa, and then nitrogen is added to atmospheric pressure; then the vacuum in the system is reduced to below 20 Pa, and then hydrogen is added to atmospheric pressure; finally, the vacuum device is turned on, the hydrogen valve is adjusted, and the hydrogen volume in the system atmosphere is controlled to be 35% and the vacuum is 350 Pa.

[0071] (3) Volatilization: The evaporation temperature is controlled at 460℃ and the evaporation time is controlled at 80min; during the evaporation process, the hydrogen volume in the atmosphere is maintained at 35% by gas supply and exhaust, and the vacuum degree is 350Pa.

[0072] (4) Distillation: The distillation temperature is controlled at 600℃ and the distillation time is controlled at 3h; during the volatilization process, the hydrogen volume in the atmosphere is maintained at 35% by gas supply and exhaust, and the vacuum degree is 350Pa; the distillation rate is 91.8%;

[0073] (5) Casting: The purified distillation product is melted and cast into a graphite mold under a hydrogen reducing atmosphere (hydrogen flow rate controlled at 0.2 L / min) to obtain purified tellurium ingot.

[0074] The graphite boat in step (1) and the graphite mold in step (5) are both graphite devices with an ash content of less than 50 ppm; the purity of the hydrogen and nitrogen used is above 4N.

[0075] The test data of the purified tellurium ingot product obtained in this embodiment are shown in Table 4. It can be seen that the purified tellurium ingot obtained meets the 4N tellurium standard.

[0076] Table 4 Product Detection Data from Example 3

[0077]

[0078] Comparative Example

[0079] This comparative example uses nitrogen as a protective atmosphere, and is identical to Example 1 in all aspects except for the different atmosphere composition.

[0080] The purification process in this comparative example includes the following steps:

[0081] (1) Loading: Clean the graphite boat, weigh 600g of 2N tellurium powder and load it into the graphite boat, then load the loaded graphite boat into the distillation furnace.

[0082] (2) Control the reducing atmosphere: First, evacuate the vacuum in the system to below 20 Pa, and then fill it with nitrogen to atmospheric pressure; then evacuate the vacuum in the system to below 20 Pa, and then fill it with nitrogen to atmospheric pressure; finally, turn on the vacuum device, adjust the nitrogen valve, and control the vacuum in the system to 300 Pa.

[0083] (3) Volatilization: The volatilization temperature is controlled at 450℃ and the volatilization time is controlled at 60min; during the volatilization process, the vacuum degree is maintained at 300Pa by supplying nitrogen and exhausting gas.

[0084] (4) Distillation: The distillation temperature was controlled at 550℃ and the distillation time was controlled at 4h; during the volatilization process, the vacuum degree was maintained at 300Pa by supplying nitrogen and exhausting gas; the distillation rate was 75.7%; the main component of the distillation residue was tellurium dioxide, and a large amount of tellurium could not be distilled out.

[0085] (5) Casting: The purified distillation product is melted and cast into a graphite mold under a nitrogen atmosphere (nitrogen flow rate controlled at 0.2 L / min) to obtain purified tellurium ingots.

[0086] The graphite boat in step (1) and the graphite mold in step (5) are both graphite devices with an ash content of less than 50 ppm; the purity of the nitrogen gas used is above 4N.

[0087] The test data of the purified tellurium ingot obtained in this comparative example are shown in Table 5. It can be seen that the purified tellurium ingot obtained did not meet the 4N tellurium standard, and the main elements exceeding the standard were Se, S and Na.

[0088] Table 5. Detection data of comparative product

[0089]

Claims

1. A highly efficient method for tellurium purification by removing oxygen, sulfur, and selenium, characterized in that, The following steps are involved: (1) Loading: Load 2N tellurium powder into a container and place it in a distillation furnace; (2) Control the reducing atmosphere: Adjust the atmosphere in the distillation furnace to a reducing atmosphere with a vacuum of 250-500 Pa and a hydrogen volume of 30%-50%; (3) Volatilization: Control the temperature inside the distillation furnace to 450-500℃ and maintain it for 60-90 min; During the volatilization process, maintain the hydrogen volume in the atmosphere to be 30%~50% through gas supply and exhaust, and the vacuum degree to be 250-500 Pa; (4) Distillation: Control the temperature inside the distillation furnace to 500-600℃ and maintain it for 3-5 hours; during the volatilization process, maintain the hydrogen volume in the atmosphere to be 30%~50% through gas supply and exhaust, and the vacuum degree to be 250-500 Pa; (5) Casting: The purified distillation product is melted and cast into a mold under a hydrogen reducing atmosphere to obtain purified tellurium ingots.

2. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to claim 1, characterized in that, In step (2), the distillation furnace is first evacuated, then filled with nitrogen to atmospheric pressure, then evacuated again, then filled with hydrogen to atmospheric pressure, and then the gas supply device and the vacuum device are adjusted to make the vacuum degree in the distillation furnace 250 – 500 Pa.

3. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to claim 2, characterized in that, In step (2), the vacuum in the distillation furnace is first evacuated to below 20 Pa, nitrogen is then introduced to atmospheric pressure, then evacuated to below 20 Pa, hydrogen is introduced to atmospheric pressure, and then the gas supply device and the vacuum device are adjusted to make the vacuum in the distillation furnace 250-500 Pa.

4. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to any one of claims 1 to 3, characterized in that, In step (5), the hydrogen flow rate is controlled at 0.1 – 0.3 L / min during the casting process.

5. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to any one of claims 1 to 3, characterized in that, In step (1), the container is a graphite device; in step (5), the mold is a graphite device.

6. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to claim 4, characterized in that, In step (1), the container is a graphite device; in step (5), the mold is a graphite device.

7. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to claim 5, characterized in that, The graphite devices in steps (1) and (5) have an ash content of less than 50 ppm.

8. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to claim 6, characterized in that, The graphite devices in steps (1) and (5) have an ash content of less than 50 ppm.

9. The efficient tellurium purification method for removing oxygen, sulfur, and selenium according to any one of claims 1 to 3, characterized in that, The purity of the hydrogen and nitrogen used is above 4N.

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