A method for continuous multistage vacuum distillation purification of metallic selenium

Abstract

This invention discloses a method for purifying metallic selenium through continuous multi-stage vacuum distillation: S1: Crude selenium powder is placed in a graphite crucible, the temperature of the crucible heater is set to 350-500℃, the temperature of the temperature-controlled heater is set to 250-350℃, and the vacuum degree of the distillation apparatus is controlled to 0.1-10 Pa for first-stage vacuum distillation; S2: The temperature of the crucible heater is set to 200-300℃, the temperature of the temperature-controlled heater is set to 600-900℃, and the vacuum degree of the distillation apparatus is controlled to 0.1-10 Pa for second-stage vacuum distillation. This invention, by selecting and controlling the temperatures of the crucible heater and the temperature-controlled heater during the purification process, enables continuous multi-stage vacuum distillation to purify metallic selenium. This avoids the need for multiple heating and cooling cycles and multiple material handling processes required in traditional methods, reducing energy consumption and pollution caused during handling. The process steps are simple, and the overall process time is significantly shortened.

Description

Technical Field

[0001] This invention relates to a method for purifying metallic selenium, and more particularly to a method for purifying selenium by vacuum distillation. Background Technology

[0002] Selenium possesses a high specific surface area, suitable band gap, low inherent toxicity, excellent stability, and modifiable surface chemistry, making it an important material for applications in electronics, optoelectronics, nonlinear photonics, sensors, and biomedicine. Refined selenium and high-purity selenium are widely used in the manufacture of compound semiconductors, thermoelectric conversion, photosensitive materials, thin-film materials for infrared detection, and solar cell materials. Typically, crude selenium extracted from copper anode mud via hydrometallurgical processes has a purity of approximately 99%, which is unsuitable for these applications. Therefore, crude selenium needs to be purified to achieve a purity of 4N refined selenium or higher (5N grade or higher). Currently, crude selenium purification processes mainly include chemical refining and physical refining. Chemical refining processes, such as the oxidative volatilization method, suffer from drawbacks including lengthy processes, low direct product recovery rates, high consumption of chemical reagents, significant waste emissions, equipment corrosion, high production costs, and high environmental risks. The product purity can reach 4N-5N. Physical refining processes mainly include zone melting and vacuum distillation. Zone melting has strict requirements on the composition of raw materials, and often requires multiple zone melting processes to achieve high purity, resulting in a long processing cycle. Compared with chemical refining, vacuum distillation refining has advantages such as a shorter process flow, simpler operation, and environmental friendliness. Compared with zone melting, it has advantages such as strong raw material adaptability, large output, high economic value, and great potential for sustainable development.

[0003] Patent document CN111039265 B discloses a method for preparing high-purity selenium, which involves slurry preparation, pH adjustment, oxidation, precipitation, filtration, smelting, and vacuum distillation of crude selenium slag with a selenium content of 60-95%. This process requires the addition of chemical reagents and is relatively complicated, involving multiple chemical and physical steps, and has a certain degree of operational difficulty. Patent document CN 113003548 A discloses a method for removing tellurium from crude selenium to prepare high-purity selenium. This method involves passing an oxidizing gas through crude selenium in a closed reactor to fully oxidize the tellurium in the crude selenium in the oxidizing atmosphere, followed by vacuum distillation to separate selenium and tellurium oxide, obtaining a selenium product with a tellurium content of less than 10 ppm.

[0004] Currently, vacuum distillation purification of crude selenium mainly achieves the separation of selenium from impurities through impurity oxidation modification and repeated vacuum distillation. However, chemical reagents are still required, and repeated material handling and temperature changes are necessary during repeated vacuum distillation. This results in problems such as long purification cycles, complex processes, and product purity that does not meet practical application requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for purifying metallic selenium by continuous multi-stage vacuum distillation.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for purifying metallic selenium through continuous multi-stage vacuum distillation is disclosed. The method employs a distillation apparatus comprising a distillation chamber and a condensation chamber located above the distillation chamber. A graphite crucible is disposed within the distillation chamber, and a graphite tube is sealed and connected above the graphite crucible. A conical condenser is disposed within the condensation chamber, and the graphite tube is sealed and connected to the conical condenser. The conical condenser contains detachable multi-stage condensing plates for condensing vapors volatilized within the graphite crucible. A temperature-controlled heater is disposed around the graphite tube, and a crucible heater is disposed around the graphite crucible.

[0008] The method for preparing high-purity selenium by continuous multi-stage vacuum distillation includes:

[0009] S1: Place the dried crude selenium powder in a graphite crucible, set the temperature of the crucible heater to 350-500℃ and the temperature of the temperature-controlled heater to 250-350℃, and control the vacuum degree of the distillation apparatus to 0.1-10Pa for single-stage vacuum distillation. The distilled selenium vapor reaches the conical condenser, where it condenses and deposits on the inner side to form the primary evaporation product. The unevaporated material remains in the graphite crucible to form residue. The vacuum degree is the surface vacuum degree, also known as the ultimate relative pressure.

[0010] S2: Set the crucible heater temperature to 200-300℃ and the temperature control heater temperature to 600-900℃, and control the vacuum degree of the distillation apparatus to 0.1-10Pa for two-stage vacuum distillation. The primary evaporation product formed in the conical condenser evaporates, and the selenium vapor reaches the condensing plate and deposits at the bottom of the condensing plate to form the secondary evaporation product. In this process, the material in the conical condenser is heated a second time and changes from solid to liquid, entering the graphite tube. The molten metal is distilled a second time in the graphite tube to form metal vapor. Because the temperature of the conical condenser increases at this time, the vapor does not condense on the conical condenser, but is transferred to the condensing plate at a higher position for condensation. This process can effectively remove the low saturated vapor pressure impurities (Ti, Ni, Si, Fe, Cu, Al) carried by the rapid and large-scale evaporation of selenium vapor during the primary distillation. The low saturated vapor pressure impurities eventually adhere to the inner wall of the graphite tube; while the high saturated vapor pressure impurities (Mg, Te, Na, Cd, As, S, Hg) in the conical condenser evaporate first and are finally deposited on the lower condensing plate, realizing the secondary separation of selenium.

[0011] In the continuous multi-stage vacuum distillation process for preparing high-purity selenium of this invention, the crucible heater temperature is set higher than the temperature control heater temperature during the first-stage vacuum distillation heating process. This is because the crucible heater controls the evaporation rate and volatile elements of the material, while the temperature control heater controls the condensation position of the steam in the upper conical condenser and the top condensing plate. If the temperature control heater temperature is too high, the steam will evaporate to the top condensing plate and condense, preventing the subsequent secondary distillation. If the temperature control heater temperature is set too low, the steam will condense before reaching the conical condenser, and excessive material accumulation will clog the graphite tube. Therefore, it is necessary to control a reasonable temperature range so that the material evaporates to the conical condenser but not to the top condenser. During secondary vacuum distillation, the temperature of the temperature-controlled heater must be higher than that of the crucible heater during primary distillation. This is because during primary vacuum distillation, the material is surrounded by a heater, resulting in higher heat transfer efficiency and allowing for a lower temperature setting. However, during secondary vacuum distillation, the temperature relies on heat transfer from graphite to the conical condenser, necessitating a higher temperature setting. Furthermore, the temperature of the bottom crucible heater should not be too high during secondary vacuum distillation. This is because the bottom heater's function is to maintain the temperature of the temperature-controlled heater. Excessive heat will cause impurities to volatilize, reducing product purity and wasting energy. Conversely, excessively low temperatures or the absence of a temperature setting will prevent the temperature-controlled heater from effectively maintaining the furnace temperature, leading to fluctuations in the furnace temperature.

[0012] The reason why temperature control is not performed during the first-stage vacuum distillation in this invention is that the crude selenium contains many and varied impurities, making it difficult to achieve precise temperature control. The types and amounts of impurities in the first-stage distillation product in the conical condenser are greatly reduced. In the secondary distillation process of this invention, the precise removal of specific impurities can be effectively achieved by controlling the temperature setting range of the temperature-controlled heater according to the differences in the types and contents of impurities in different batches of materials. Specifically, when the temperature range of the heater is controlled at 600-700℃, it is beneficial for the precise removal of impurities such as Ti, Ni, Si, Fe, Cu, and Al, because the evaporation rate of the material is slower at lower temperatures, and it can carry less low-saturated vapor pressure impurities. When the temperature range of the heater is controlled at 700-800℃, it is beneficial for the precise removal of impurities such as Sn, In, Bi, Pb, Sb, and Mg, because selenium will preferentially volatilize and deposit on the lower condenser plate in this temperature range, while medium-saturated vapor pressure impurities will volatilize later and deposit on the upper condenser plate. When the temperature range of the heater is controlled at 800-900℃, it is beneficial for the precise removal of impurities such as Te, Na, Cd, Al, S, and Hg, because the higher temperature is conducive to the rapid evaporation of high-saturated vapor pressure impurities and their deposition on the lower condenser plate. Therefore, by controlling the temperature of the second distillation, specific impurity sets can be precisely removed to meet specific product requirements, thereby further improving product quality.

[0013] In the above-described method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, in step S1, the holding time for the first-stage vacuum distillation is 2-4 hours.

[0014] In the above-described method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, the holding time for the second-stage vacuum distillation in step S2 is 2-4 hours.

[0015] In the above-mentioned method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, in S1 and S2, the heating rate and cooling rate in the heating and cooling processes are both 4℃-8℃ / min.

[0016] In the above-described method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, the crude selenium powder is of the 2N grade, and the impurities in the crude selenium powder include Te 4000-4100ppm, S 1500-3000ppm, Na 300-500ppm, Fe 100-300ppm, Cu 20-50ppm and Pb 10-50ppm.

[0017] In the above-described method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, the evaporation products are collected, the condensed products collected on the condenser plate are high-purity selenium, and the products collected on the inner wall of the conical condenser are refined selenium, wherein the purity of the refined selenium is 99.995%-99.998%, and the purity of the high-purity selenium is 99.9993%-99.9997%.

[0018] In the above-described method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, the outer wall of the condensation chamber has a double-layer structure, and an inlet and an outlet are connected in the cavity between the double layers.

[0019] In the above-described method for preparing high-purity selenium through continuous multi-stage vacuum distillation, preferably, during the first-stage vacuum distillation process, a cooling water machine is used to circulate cooling water through the double-layer cavity on the outer wall of the condenser chamber.

[0020] In the above-described method for preparing high-purity selenium through continuous multi-stage vacuum distillation, preferably, the cooling water pump is turned off during the second-stage vacuum distillation process. Secondary evaporation requires heat transfer from the graphite tube to the conical condenser. Evaporation can only occur after the temperature of the conical condenser rises to a certain level, at which point the cooling water pump must be turned off; otherwise, secondary evaporation of the material cannot be achieved, and energy will be wasted.

[0021] In the above-described method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, both the crucible heater and the temperature control heater are resistance heaters; and the crucible, conical condenser, and condensing plate are all made of high-purity graphite with an ash content of ≤5ppm.

[0022] In the above-mentioned method for preparing high-purity selenium by continuous multi-stage vacuum distillation, preferably, in step S1, the drying temperature of the crude selenium powder is 40-80℃, the drying time is 2-6 hours, and the drying is vacuum drying.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] (1) The present invention purifies metallurgical grade crude selenium powder by distillation device. At the same time, by selecting and controlling the temperature of crucible heater and temperature control heater during the purification process, the present invention can continuously purify metallic selenium by multi-stage vacuum distillation, avoiding the need for multiple heating and cooling and multiple material handling in the traditional process, reducing energy consumption and pollution caused during handling, simplifying the process steps, and significantly shortening the overall process time.

[0025] (2) The present invention purifies metallurgical grade crude selenium powder by distillation device. At the same time, by selecting and controlling the temperature of crucible heater and temperature control heater during the purification process, metallurgical grade crude selenium powder can be purified to obtain 4N grade refined selenium and 5N grade or higher high-purity selenium products. The purity of refined selenium reaches 99.993%-99.996%, and the purity of high-purity selenium reaches 99.9993%-99.9998%.

[0026] In summary, the present invention provides a continuous multi-stage vacuum distillation method for purifying metallic selenium, which enables efficient, low-energy-consumption, short-process, and environmentally friendly preparation of high-purity selenium. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the distillation apparatus used in the embodiments of the present invention.

[0028] Figure 2 This is a photograph of the evaporation products in the first-stage vacuum distillation conical condenser of Embodiment 1 of the present invention.

[0029] Figure 3 This is a photograph of the evaporation products on the condenser plate of the two-stage vacuum distillation in Embodiment 1 of the present invention.

[0030] Figure 4 This is a photograph of the evaporation products in the first-stage vacuum distillation conical condenser of Comparative Example 2 of this invention.

[0031] Figure 5 This is a photograph of the evaporation products on the condenser plate of the secondary vacuum distillation in Comparative Example 2 of this invention.

[0032] Figure 6 This is a SEM-Mapping image of the condensation products in the condenser plate and conical condenser in Embodiment 1 of the present invention.

[0033] Figure 7 This is a process flow diagram of the continuous multi-stage vacuum distillation process for preparing high-purity selenium according to the present invention.

[0034] Legend:

[0035] 1. Distillation chamber; 2. Condensation chamber; 3. Graphite crucible; 4. Crucible heater; 5. Graphite tube; 6. Conical condenser; 7. Condensing plate; 8. Temperature control heater; 9. Water inlet; 10. Water outlet; 11. Vacuum port. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0039] The main elemental composition of the crude selenium mud to be purified in the following examples and comparative examples is shown in Table 1.

[0040] Table 1. Content of major elements in coarse selenium mud

[0041]

[0042] The cross-sectional view of the distillation apparatus used in the continuous multi-stage vacuum distillation purification of metallic selenium in the following embodiments is shown in the figure. Figure 1 As shown, the distillation apparatus includes a distillation chamber 1 and a condensation chamber 2 located above the distillation chamber 1. A graphite crucible 3 is placed inside the distillation chamber 1, and a graphite tube 5 is sealed above the graphite crucible 3. A conical condenser 6 is placed inside the condensation chamber 2, and the graphite tube 5 is sealed to the conical condenser 6. A detachable multi-stage condensing plate 7 is placed inside the conical condenser 6. The multi-stage condensing plate 7 is used for condensing the volatile vapors inside the graphite crucible 3. A temperature-controlled heater 8 is placed around the graphite tube 5, and a crucible heater 4 is placed around the graphite crucible 3. The outer wall of the condensation chamber 2 has a double-layer structure, and an inlet 9 and an outlet 10 are connected in the cavity between the two layers. The inlet 9 is connected to a cooling water pump. A vacuum port 11 is placed on the condensation chamber 2 and is connected to a vacuum pump.

[0043] Example 1:

[0044] A method for purifying metallic selenium through continuous multi-stage vacuum distillation according to the present invention is shown in the process flow diagram below. Figure 7 As shown, the steps are as follows:

[0045] (1) The coarse selenium mud was placed in a vacuum drying oven and dried at 50°C and 1000Pa for 2 hours to obtain coarse selenium powder with an average particle size of 85.73 μm.

[0046] (2) Take 500g of the crude selenium powder obtained in step (1) and place it in the graphite crucible 3 of the distillation apparatus. Turn on the vacuum pump to make the vacuum degree in the distillation apparatus reach 0.1-1Pa. Set the temperature of the crucible heater 4 to 450℃ and the temperature control heater 8 to 300℃, with a heating rate of 6℃ / min. Start the heating program and keep the temperature at the set temperature for 3 hours to perform first-stage vacuum distillation. During this vacuum distillation process, cooling water is circulated in the double-layer cavity on the outer wall of the condensing chamber 2 using a cooling water pump. The cooling water temperature is 25℃. During this process, as the temperature gradually increases, the material in the graphite crucible 3 evaporates, and the selenium vapor reaches the conical condenser 6 of the condensing chamber 2. The vapor condenses and deposits on the inner side of the conical condenser 6 to form the primary evaporation product. See the product photo. Figure 2 As shown, its SEM-Mapping diagram is shown below. Figure 6 As shown in (a) and (b), the evaporated material remains in the graphite crucible, forming a residue.

[0047] (3) Set the temperature of crucible heater 4 to 300℃ and the cooling rate to 6℃ / min; set the temperature of temperature control heater 8 to 650℃ and the heating rate to 6℃ / min, maintain the vacuum degree in the distillation apparatus at 0.1-1Pa, and hold the temperature for 2 hours after reaching the set temperature to perform secondary vacuum distillation. During this process, the cooling water is turned off. In this process, the material in the conical condenser 6 evaporates, and the metal vapor reaches the condenser plate 7 and deposits at the bottom of the condenser plate 7 to form secondary evaporation products. See the product photograph. Figure 3 As shown, its SEM-Mapping diagram is shown below. Figure 6 As shown in (c) and (d).

[0048] (4) After the heat preservation is completed, stop heating. After the temperature in the graphite crucible 3 cools down to below 50°C, turn off the vacuum pump, introduce high-purity nitrogen to restore normal pressure, remove the conical condenser 6 and condenser plate 9, weigh and sample in a clean room and clean the graphite parts.

[0049] from Figure 6 It can be seen that the material deposited at the condenser plate has a dense and smooth surface. This is because the temperature of the condenser plate has been heated to a certain level during the second distillation, and the metal vapor cannot be condensed quickly. Instead, it is condensed through a relatively slow gas-liquid-solid condensation process. On the other hand, the material deposited at the conical condenser shows obvious plate-like condensation. This is because the temperature of the conical condenser is lower during the first distillation, and the metal vapor can be converted directly from the gaseous state to the solid state for condensation more quickly. The plate-like condensation results in a larger specific surface area, which is beneficial for the material to be heated, thus facilitating the second distillation.

[0050] According to the types of impurities in high-purity selenium specified in the People's Republic of China Nonferrous Metals Industry Standard YS / T816-2012, and in accordance with the People's Republic of China National Standard GB / T 26289-2010, inductively coupled plasma mass spectrometry (ICP-MS) was used to detect and analyze the impurity components. The content of selenium and various impurities in the distillation product can be determined. The detection results are shown in Table 2.

[0051] Table 2. Impurity content in distillation products from different locations (unit: ppm)

[0052] 4N Selenium Quality Standard 5N selenium quality standard Conical condenser inner wall Condensing plate Product selenium purity / % 99.99 99.999 99.9978 99.99964 Cu 3.0 0.2 0.6510 0.0943 Mg 8.0 0.5 0.0638 0.9383 Ni 5.0 0.2 0.0679 0.1058 Bi 5.0 0.5 0.5546 0.2124 Fe 10.0 0.5 7.1404 0.4291 Pb 5.0 0.5 0.3491 0.2060 Te 10.0 1.0 6.3782 0.6421 Sb 5.0 0.5 0.5430 0.0687 Hg 3.0 1.0 0.7671 0.1950 As 5.0 0.0 0.4844 0.9277 S 4.0 0.0 3.2813 2.8926 Si 9.0 0.0 0.5602 0.1413 Al 8.0 0.5 0.7071 0.2923 Ag 0.0 0.2 0.1627 0.1697 In 0.0 0.5 0.3593 0.0265 Cd 0.0 0.2 0.0533 0.0762 Ti 0.0 0.5 0.4006 0.1336

[0053] According to the weighing results, the mass of high-purity selenium obtained on the condenser plate in this embodiment is 298.8g, and the mass of refined selenium obtained on the conical condenser is 116.1g.

[0054] The yield, volatility, and overall time of refined selenium and high-purity selenium are calculated according to the following formulas (1)(2)(3)(4):

[0055]

[0056]

[0057]

[0058] Total time (min) = heating time + holding time + cooling time (4).

[0059] Calculations show that in this embodiment, the selenium recovery rate is 23.24%, the high-purity selenium recovery rate is 59.76%, the volatility rate is 82.98%, the first-stage distillation heating time is 75 min, the holding time is 180 min, the second-stage distillation heating time is 60 min, the holding time is 120 min, the cooling time is 360 min, and the total time is 795 min.

[0060] Comparative Example 1:

[0061] This comparative example uses a common method in the prior art for preparing high-purity selenium through repeated vacuum distillation. The raw materials used have the same composition as the crude selenium powder used in the example, and the distillation apparatus used is a tubular vacuum distillation furnace. The specific steps are as follows:

[0062] (1) First, place the coarse selenium mud in a vacuum drying oven and dry it for 2 hours at 50°C and 1000Pa to obtain coarse selenium powder with an average particle size of 85.73 μm.

[0063] (2) Take 500g of crude selenium powder prepared in step (1) and place it in a crucible. Set the heating rate to 6℃ / min, the crucible heater temperature to 450℃, and the temperature control heater temperature to 300℃. Turn on the vacuum pump. After the vacuum degree in the furnace reaches 0.1-1Pa, start the heating program and hold for 2 hours to perform the first vacuum distillation. As the temperature gradually rises, the material in the crucible evaporates, and the metal vapor reaches the condenser. The vapor condenses and deposits on the inside of the condenser to form evaporation products, while the unevaporated material remains in the crucible to form residue.

[0064] (3) After the heat preservation is completed, stop heating and let the crucible cool down naturally. When the temperature drops below 50°C, turn off the mechanical vacuum pump, introduce high-purity nitrogen to restore normal pressure, remove the condenser, take out the material in the clean room, weigh and sample it, and clean the graphite parts.

[0065] (4) Place the first distillation product in a crucible, set the heating rate to 6℃ / min, the crucible heater temperature to 350℃, and the temperature control heater temperature to 300℃. Turn on the mechanical vacuum pump, and after the vacuum degree in the furnace reaches 0.1-1 Pa, start the heating program and hold for 2 hours to carry out the second vacuum distillation. As the temperature gradually rises, the material in the crucible evaporates, and the metal vapor reaches the condenser. The vapor condenses and deposits on the inside of the condenser to form the evaporation product, while the unevaporated material remains in the crucible to form residue.

[0066] (5) After the heat preservation is completed, stop heating and let the crucible cool down naturally. When the temperature drops below 50°C, turn off the mechanical vacuum pump, introduce high-purity nitrogen to restore normal pressure, remove the condenser, take out the material in the clean room, weigh and sample it, and clean the graphite parts.

[0067] (6) Place the second distillation product in a crucible, set the heating rate to 6℃ / min, the crucible heater temperature to 300℃, and the temperature control heater temperature to 300℃. Turn on the mechanical vacuum pump, and after the vacuum degree in the furnace reaches 0.1-1Pa, start the heating program and hold for 2 hours to perform the third vacuum distillation. As the temperature gradually rises, the material in the crucible evaporates, and the metal vapor reaches the condenser. The vapor condenses and deposits on the inside of the condenser to form the evaporation product, while the unevaporated material remains in the crucible to form residue.

[0068] (7) After the heat preservation is completed, stop heating and let the crucible cool down naturally. When the temperature drops below 50°C, turn off the mechanical vacuum pump, introduce high-purity nitrogen to restore normal pressure, remove the condenser, take out the material in the clean room, weigh and sample it, and clean the graphite parts.

[0069] According to the types of impurities in high-purity selenium specified in the People's Republic of China Nonferrous Metals Industry Standard YS / T816-2012, and in accordance with the People's Republic of China National Standard GB / T 26289-2010, inductively coupled plasma mass spectrometry (ICP-MS) was used to detect and analyze the impurity components. The content of selenium and various impurities in the distillation product can be determined. The detection results are shown in Table 3.

[0070] Table 3. Impurity content in distillation products after different distillation times (unit: ppm)

[0071]

[0072] After three vacuum distillations, 5N grade high-purity selenium was obtained, but the purity was still different from that of the product obtained in Example 1, and the content of the impurity tellurium was slightly excessive. According to the weighing, the mass of high-purity selenium collected in the condenser in this comparative example was 272g.

[0073] The yield, volatility, and total time of refined selenium and high-purity selenium were calculated according to the above formula. The calculation showed that the high-purity selenium yield in this comparative example was 54.4%, the heating time for the first distillation was 75 min, the holding time was 120 min, the cooling time for the first distillation was 360 min, the heating time for the second distillation was 60 min, the holding time was 120 min, the cooling time was 320 min, the heating time for the third distillation was 50 min, the holding time was 120 min, the cooling time was 180 min, and the total time was 1405 min.

[0074] As can be seen from the comparison between Example 1 and Comparative Example 1, the method for preparing high-purity selenium provided by the present invention achieves efficient removal of impurity elements from crude selenium powder in a single batch, greatly shortens the overall time, and requires no chemical reagents. It has the advantages of being green and pollution-free, low-energy consumption, short process, and simple process. The two products, refined selenium and high-purity selenium, prepared using the method provided by the present invention, meet the 4N standard for refined selenium purity and the 5N standard for high-purity selenium purity, which can meet the needs of multiple fields for high-purity selenium products and have good economic and industrial application value.

[0075] Comparative Example 2:

[0076] This comparative example uses the same distillation equipment as Example 1, and the raw materials used have the same composition as the crude selenium powder used in Example 1. The specific steps are as follows:

[0077] (1) The coarse selenium mud was placed in a vacuum drying oven and dried at 50°C and 1000Pa for 2 hours to obtain coarse selenium powder with an average particle size of 85.73 μm.

[0078] (2) Take 500g of the crude selenium powder obtained in step (1) and place it in the graphite crucible 3 of the distillation apparatus. Turn on the vacuum pump to make the vacuum degree in the distillation apparatus reach 0.1-1Pa. Set the temperature of the crucible heater 4 to 450℃ and the temperature control heater 8 to 450℃, with a heating rate of 6℃ / min. Start the heating program and keep the temperature for 3 hours after it reaches the set temperature to perform first-stage vacuum distillation. During this vacuum distillation process, cooling water is circulated in the double-layer cavity on the outer wall of the condensing chamber 2 using a cooling water pump. The cooling water temperature is 25℃. During this process, as the temperature gradually increases, the material in the graphite crucible 3 evaporates, and the selenium vapor reaches the conical condenser 6 of the condensing chamber 2. The vapor condenses and deposits on the inner side of the conical condenser 6 to form the primary evaporation product. See the product photo. Figure 4 As shown, unevaporated material remains in the graphite crucible, forming residue.

[0079] (3) Set the temperature of crucible heater 4 to 450℃ and the temperature of temperature control heater 8 to 650℃, with a heating rate of 6℃ / min. Maintain a vacuum of 0.1-1 Pa in the distillation apparatus. After the set temperature is reached, hold the temperature for 2 hours to perform secondary vacuum distillation. During this process, the cooling water is turned off. In this process, the material in the conical condenser 6 evaporates, and the metal vapor reaches the condensing plate 7 and deposits at the bottom of the condensing plate 7 to form secondary evaporation products. See the product photograph. Figure 5 As shown.

[0080] (4) After the heat preservation is completed, stop heating. After the temperature in the graphite crucible 3 cools down to below 50°C, turn off the vacuum pump, introduce high-purity nitrogen to restore normal pressure, remove the conical condenser 6 and condenser plate 9, weigh and sample in a clean room and clean the graphite parts.

[0081] According to the types of impurities in high-purity selenium specified in the People's Republic of China Nonferrous Metals Industry Standard YS / T816-2012, and in accordance with the People's Republic of China National Standard GB / T 26289-2010, inductively coupled plasma mass spectrometry (ICP-MS) was used to detect and analyze the impurity components. The content of selenium and various impurities in the distillation product can be determined. The detection results are shown in Table 4.

[0082] Table 4. Impurity content in distillation products from different locations (unit: ppm)

[0083] 4N Selenium Quality Standard 5N selenium quality standard Conical condenser inner wall Condensing plate Product selenium purity / % 99.99 99.999 99.9924 99.9971 Cu 3.0 0.2 2.7165 0.4758 Mg 8.0 0.5 6.7404 0.6787 Ni 5.0 0.2 0.2102 0.3005 Bi 5.0 0.5 0.8788 0.8146 Fe 10.0 0.5 19.3271 8.723 Pb 5.0 0.5 0.3096 0.4457 Te 10.0 1.0 15.7664 8.7706 Sb 5.0 0.5 0.3776 0.2352 Hg 3.0 1.0 0.4803 0.9851 As 5.0 0.0 0.9934 0.9552 S 4.0 0.0 21.6449 3.5917 Si 9.0 0.0 3.5523 0.2193 Al 8.0 0.5 0.3286 0.5853 Ag 0.0 0.2 0.2893 0.2095 In 0.0 0.5 0.6477 0.5734 Cd 0.0 0.2 0.005 0.0642 Ti 0.0 0.5 0.9089 0.7358

[0084] The mass of the product obtained on the condenser plate in this comparative example was 302.05 g, and the mass of the product obtained on the inner wall of the conical condenser was 176.07 g.

[0085] Calculations show that in this comparative example, the products on the inner wall of the conical condenser and the condensing plate volatilized due to temperature, resulting in product purities of 99.9924% and 99.9971%, respectively. However, the impurity contents of Fe, Te, and S were high, failing to meet the 4N selenium standard. The volatilization rate was 95.62%. The first-stage distillation heating time was 75 min, and the holding time was 180 min. The second-stage distillation heating time was 60 min, the holding time was 120 min, and the cooling time was 360 min, for a total time of 795 min.

Claims

1. A method of purifying metallic selenium by continuous multistage vacuum distillation, characterized in that, Metallic selenium is purified using a distillation apparatus, which includes a distillation chamber and a condensation chamber located above the distillation chamber. A graphite crucible is disposed within the distillation chamber, and a graphite tube is sealed above the graphite crucible. A conical condenser is disposed within the condensation chamber, and the graphite tube is sealed to the conical condenser. The conical condenser contains detachable multi-stage condensing plates for condensing volatile vapors within the graphite crucible. The multi-stage condensing plates include multiple spaced-apart L-shaped condensing plates at the top and multiple spaced-apart wedge-shaped condensing plates at the bottom. A temperature-controlled heater is located around the graphite tube, and a crucible heater is located around the graphite crucible. The method for purifying metallic selenium through continuous multi-stage vacuum distillation includes: S1: Place the dried crude selenium powder in a graphite crucible, set the temperature of the crucible heater to 350-500℃ and the temperature of the temperature control heater to 250-350℃, control the vacuum degree of the distillation apparatus to 0.1-10Pa, and carry out first-stage vacuum distillation. The distilled selenium vapor reaches the conical condenser, where it condenses and deposits on the inner side of the conical condenser to form the primary evaporation product. The unevaporated material remains in the graphite crucible to form residual residue. S2: Set the crucible heater temperature to 200-300℃ and the temperature control heater temperature to 600-900℃, control the vacuum degree of the distillation apparatus to 0.1-10Pa, and perform two-stage vacuum distillation. The primary evaporation product formed in the conical condenser evaporates, and the selenium vapor reaches the condensing plate and deposits at the bottom of the condensing plate to form the secondary evaporation product. Collect the evaporation products. The condensed product collected on the multi-stage condensing plate is high-purity selenium, and the product collected on the inner wall of the conical condenser is refined selenium. The purity of the refined selenium is 99.995%-99.998%, and the purity of the high-purity selenium is 99.9993%-99.9997%. By selecting and controlling the temperatures of the crucible heater and the temperature control heater during the purification process, continuous multi-stage vacuum distillation purification of metallic selenium can be achieved.

2. The method of continuously multistage vacuum distillation purification of metallic selenium as claimed in claim 1, characterized in that, In S1, the holding time for the first-stage vacuum distillation is 2-4 hours.

3. The method of continuously multistage vacuum distillation purification of metallic selenium as claimed in claim 1, characterized in that, In S2, the holding time for the second-stage vacuum distillation is 2-4 hours.

4. The method for purifying metallic selenium by continuous multi-stage vacuum distillation as described in claim 1, characterized in that, The crude selenium powder is of grade 2N, and the impurities in the crude selenium powder include Te 4000-4100ppm, S 1500-3000ppm, Na 300-500ppm, Fe 100-300ppm, Cu 20-50ppm and Pb 10-50ppm.

5. The method for purifying metallic selenium by continuous multi-stage vacuum distillation as described in claim 1, characterized in that, The outer wall of the condensation chamber has a double-layer structure, and the cavity between the two layers is connected to the water inlet and the water outlet.

6. The method for purifying metallic selenium by continuous multi-stage vacuum distillation as described in claim 5, characterized in that, During the first-stage vacuum distillation process, cooling water is circulated through the double-layered cavity on the outer wall of the condenser chamber using a cooling water machine.

7. The method for purifying metallic selenium by continuous multi-stage vacuum distillation as described in claim 6, characterized in that, During the secondary vacuum distillation process, the cooling water pump is turned off.

8. The method for purifying metallic selenium by continuous multi-stage vacuum distillation as described in claim 1, characterized in that, In S1, the drying temperature of the crude selenium powder is 40-80℃, the drying time is 2-6 hours, and the drying is carried out under vacuum.

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