Method and device for preparing high-purity selenium

Abstract

The invention belongs to the technical field of preparation of high-purity metal materials, and particularly relates to a preparation method and device of high-purity selenium. The preparation method of the high-purity selenium comprises the following steps: under a protective atmosphere, immersing a first crystallization rod and a flow baffle into a melt of a raw material selenium, then carrying out first-stage rotary crystallization, and taking out the first crystallization rod to obtain a first-stage crystallization product; and under the protective atmosphere, immersing a second crystallization rod and a flow baffle into the melt of the primary crystallization product, and then carrying out secondary rotary crystallization to obtain high-purity selenium of more than 6N on the second crystallization rod, the crystallization rate of the first-stage rotary crystallization is 0.1-0.5 mm / h, the crystallization rate of the second-stage rotary crystallization is 0.5-1.5 mm / h, and the thickness of a solid-liquid boundary layer is less than or equal to 50 microns. The flow baffle is added in the rotary crystallization process to strengthen convection of the melt, the thickness of a boundary layer of a solid-liquid interface is reduced, and impurity diffusion is accelerated; the crystallization rate is controlled to improve the crystallization efficiency, the product purity is improved through two times of crystallization, and the obtained product is high-purity selenium of more than 6N.

Description

Technical Field

[0001] This invention belongs to the field of high-purity metal material preparation technology, specifically relating to a method and apparatus for preparing high-purity selenium. Background Technology

[0002] In the electronics industry, the selenium used is 4N to 6N high-purity selenium. 6N-grade high-purity selenium (total impurities <1ppm) is a core material for high-end optoelectronic industries: its narrow bandgap characteristics require selenium of 6N or higher to meet the conversion efficiency of CdTe solar cells; low Fe impurity content is needed for infrared transmittance to ensure the performance of ZnSe military optical components; and X-ray detectors require 6N selenium to maintain dark current stability. Due to the excellent physicochemical properties of high-purity selenium, it has become crucial for the preparation of cutting-edge materials.

[0003] Currently, physical methods for preparing high-purity selenium include vacuum distillation and zone melting. Vacuum distillation has been extensively studied, but it cannot remove substances with similar vapor pressures to selenium; impurity modification is necessary, oxidizing these impurities to achieve separation. Furthermore, this method can only produce 4N selenium. Zone melting creates a moving molten zone within a quartz tube, causing impurities to separate at the solid-liquid interface, thus improving selenium purity. However, this method is time-consuming and energy-intensive.

[0004] Crystallization, theoretically, can prepare high-purity selenium based on the equilibrium distribution coefficient at the solid-liquid interface. Traditional crystallization methods involve placing a crystallizer rod into the melt, setting a crystallization temperature, and allowing equilibrium to be reached before removing impurities or crystals. A clean crystallizer rod is then placed into the melt for recrystallization. For example, a method for preparing 6N selenium is disclosed in related technologies: immersing a crystallizer in a 4N selenium melt for rotational crystallization. However, this method requires multiple rotational crystallizations (10-30 times) to achieve the preparation of 6N selenium, resulting in a long preparation cycle. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method and apparatus for preparing high-purity selenium. The preparation method provided by this invention requires only two rotational crystallization processes to obtain 6N high-purity selenium, thus improving the preparation efficiency of 6N high-purity selenium.

[0006] This invention provides a method for preparing high-purity selenium, comprising the following steps: Under a protective atmosphere, the first crystallizing rod and the baffle plate are immersed in the melt of raw material selenium for primary rotational crystallization. The first crystallizing rod is then removed to obtain the primary crystalline product. Under a protective atmosphere, a second crystallizing rod and a baffle plate are immersed in the melt of the primary crystallization product for secondary rotational crystallization to obtain high-purity selenium on the second crystallizing rod; the high-purity selenium is 6N or higher. The crystallization rate of the first-stage rotational crystallization is 0.1~0.5 mm / h, and the crystallization rate of the second-stage rotational crystallization is 0.5~1.5 mm / h; the solid-liquid boundary layer thickness during the first-stage and second-stage rotational crystallization processes is ≤50 μm.

[0007] Preferably, the temperature of the melt of the raw material selenium is 270~290℃.

[0008] Preferably, the rotational speed of the primary rotary crystallizer is 10~60 rpm.

[0009] Preferably, the temperature of the melt of the primary crystallized product is 240~260℃.

[0010] Preferably, the rotational speed of the secondary rotary crystallization is 60~120 rpm.

[0011] Preferably, during the first-stage rotary crystallization process, the first crystallizer undergoes a gradient cooling process, wherein the gradient cooling is as follows: first, the temperature is reduced to 230°C at a rate of 50°C / h, then reduced to 225°C at a rate of 5°C / h, and finally reduced to 219°C at a rate of 1°C / h, and held at that temperature for 2 hours. During the secondary rotational crystallization process, the second crystallizer rod undergoes a gradient cooling process. The gradient cooling is as follows: first, the temperature is reduced to 210°C at a rate of 50°C / h, then to 205°C at a rate of 5°C / h, and finally to 199°C at a rate of 1°C / h, and held at that temperature for 2 hours.

[0012] Preferably, the raw material selenium is 4N selenium, and the content of impurity elements in the 4N selenium is as follows: mercury and copper ≤3ppm independently; boron, bismuth, lead, nickel, arsenic, antimony, and tin ≤5ppm independently; magnesium and aluminum ≤8ppm independently; silicon ≤9ppm; tellurium and iron ≤40ppm independently; and sulfur ≤40ppm.

[0013] Preferably, the protective atmosphere is an inert gas, including argon; the protective atmosphere is under slight negative pressure, which is 6000~90000 Pa.

[0014] The present invention also provides a high-purity selenium preparation apparatus, including an intelligent gas flow control module, a furnace shell, a heating element disposed in the furnace shell, a crucible disposed in the heating element, a liftable baffle plate and a crystallizing rod; The intelligent gas flow control module includes an inlet pipe and an outlet pipe, which are connected to a crystallizing rod. An intelligent gas flow meter is installed on the inlet pipe.

[0015] Preferably, the baffle is triangular prism-shaped.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing high-purity selenium, comprising the following steps: under a protective atmosphere, immersing a first crystallizing rod and a baffle plate into a melt of raw selenium for primary rotational crystallization, removing the first crystallizing rod to obtain a primary crystalline product; under a protective atmosphere, immersing a second crystallizing rod and a baffle plate into a melt of the primary crystalline product for secondary rotational crystallization, obtaining high-purity selenium on the second crystallizing rod; wherein the high-purity selenium is 6N or higher high-purity selenium; the crystallization rate of the primary rotational crystallization is 0.1~0.5 mm / h, and the crystallization rate of the secondary rotational crystallization is 0.5~1.5 mm / h; the solid-liquid boundary layer thickness during the primary and secondary rotational crystallization processes is ≤50 μm.

[0017] This invention incorporates baffles into the melt during rotary crystallization. These baffles induce forced eddies, increasing the Reynolds number of the melt and compressing the solute boundary layer thickness to ≤50μm. This improves the impurity diffusion coefficient and the diffusion rate of impurity elements, shortening the liquid-solid equilibrium time to <30min (compared to >90min in traditional methods) and suppressing component supercooling. This invention stabilizes the crystallization rate of the first-stage rotary crystallization at 0.1~0.5mm / h and the second-stage rotary crystallization at 0.5~1.5mm / h. Dynamic thermal field control reduces the solute boundary layer thickness, and the actual impurity equilibrium distribution coefficient Keff is close to the equilibrium distribution coefficient K, facilitating impurity removal. Furthermore, this invention employs two rotary crystallization processes: in the first-stage process, impurity elements with K>1 are enriched on the crystal rod and removed; in the second-stage process, impurity elements with K<1 are enriched in the melt, and high-purity selenium is distributed on the crystal rod. Compared to the first-stage crystallization, impurity removal is faster and more thorough.

[0018] This invention also provides a device for preparing high-purity selenium, wherein an intelligent gas flow control module dynamically adjusts the flow rate of argon or air (0.1~50m³) through PID closed-loop control. 3 / h), establish an axial temperature gradient (from the solid-liquid interface to the crystal rod, with an accuracy of ±0.5℃), and combine it with the growth rate-flow rate model to achieve continuous directional crystallization. Compared with traditional rotary crystallization which uses a single temperature crystallization, the production capacity is increased by more than 50%.

[0019] Traditional crystallization methods only consider one crystallization process, resulting in limited impurity removal. This invention combines dynamic temperature gradients with enhanced convection to reduce boundary layer thickness, achieving a purity of 6N-level, meeting the material's application requirements. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the rotary crystallizer used in the embodiment; Figure 2 This is a schematic diagram illustrating the regulation of the crystallization process by the intelligent gas flow control module in this embodiment. Figure 3 This is a schematic diagram of the two-stage rotational crystallization process in the embodiment. Detailed Implementation

[0022] This invention provides a method for preparing high-purity selenium, comprising the following steps: Under a protective atmosphere, the first crystallizing rod and the baffle plate are immersed in the melt of raw material selenium for primary rotational crystallization. The first crystallizing rod is then removed to obtain the primary crystalline product. Under a protective atmosphere, a second crystallizing rod and a baffle plate are immersed in the melt of the primary crystallization product for secondary rotational crystallization to obtain high-purity selenium on the second crystallizing rod; the high-purity selenium is 6N or higher. The crystallization rate of the first-stage rotational crystallization is 0.1~0.5 mm / h, and the crystallization rate of the second-stage rotational crystallization is 0.5~1.5 mm / h; the solid-liquid boundary layer thickness during the first-stage and second-stage rotational crystallization processes is ≤50 μm.

[0023] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0024] In this invention, under a protective atmosphere, a first crystallizing rod and a baffle plate are immersed in the melt of raw material selenium for primary rotational crystallization. The first crystallizing rod is then removed to obtain the primary crystalline product.

[0025] In this invention, the protective atmosphere is preferably an inert gas, and the inert gas preferably includes argon. The protective atmosphere is preferably under a slight negative pressure, preferably 6000~90000 Pa, more preferably 8000~9000 Pa. The slight negative pressure is preferably obtained by repeatedly evacuating and purging with argon; the pressure after evacuation is preferably 1 Pa, and the pressure after purging with argon is preferably 8000~9000 Pa; the number of repetitions is preferably 3~8 times, specifically 4 or 5 times.

[0026] In this invention, the raw material selenium is preferably 4N selenium, which conforms to the industry standard YS / T 223-2009. The content of impurity elements in the 4N selenium is preferably as follows: mercury and copper ≤3ppm independently; boron, bismuth, lead, nickel, arsenic, antimony, and tin ≤5ppm independently; magnesium and aluminum ≤8ppm independently; silicon ≤9ppm; tellurium and iron ≤40ppm independently; and sulfur ≤40ppm. The impurity elements in the 4N selenium preferably also include silver, cadmium, and titanium, with silver and cadmium ≤5ppm independently and titanium ≤40ppm.

[0027] In this invention, the preferred method for preparing the melt of the raw material selenium includes the following steps: placing 4N selenium in a rotating crucible of a rotating crystallization furnace, removing air from the rotating crystallization furnace, filling it with a protective gas, and then heating to melt. The temperature of the melt of the raw material selenium is preferably 270~290℃, specifically 270℃, 280℃, or 290℃; specifically, it can be rapidly heated to melt at 300~350℃ and then cooled to 270~290℃.

[0028] In this invention, the melt of the raw material selenium is contained within a rotating crucible, preferably made of high-purity quartz (purity > 4N), and the baffle plate is preferably made of high-purity graphite (purity > 4N). The bottom of the first crystallizing rod is preferably 0.5-5 cm from the bottom of the rotating crucible, specifically 0.5 cm or 1 cm. This invention uses a baffle plate to increase melt flowability, improve impurity diffusion rate, and reduce the solid-liquid boundary layer thickness.

[0029] In this invention, the rotational speed of the rotating crucible during the primary rotational crystallization process is preferably 10 to 60 rpm, specifically 15 rpm, 20 rpm, or 30 rpm.

[0030] In this invention, the first crystallizing rod preferably undergoes gradient cooling during the primary rotary crystallization process. The gradient temperature is as follows: first, cooling to 230°C at a rate of 50°C / h; then cooling to 225°C at a rate of 5°C / h; and finally cooling to 219°C at a rate of 1°C / h, and holding at that temperature for 2 hours. This invention can precisely control the gas flow rate from 0.1 to 50 m³ / h using an intelligent gas flow control module. 3 / h, thereby enabling precise temperature control of the crystallizing rod within ±0.5℃ range, allowing impurities to continuously crystallize on the first crystallizing rod, and the gas can be argon or purified air.

[0031] In this invention, after removing the first crystallizing rod, the process preferably further includes: cooling the melt after the first-stage rotary crystallization to room temperature to facilitate the transfer of the crystallizing rod. During the first-stage rotary crystallization process, impurity elements with K>1 are enriched on the crystallizing rod and removed.

[0032] After obtaining the primary crystalline product, the present invention, under a protective atmosphere, immerses a second crystallizing rod and a baffle plate into the melt of the primary crystalline product for secondary rotational crystallization, thereby obtaining high-purity selenium on the second crystallizing rod; the high-purity selenium is 6N or higher.

[0033] In this invention, the protective atmosphere is preferably the same as that used for primary rotational crystallization, and will not be described in detail here.

[0034] In this invention, the method for preparing the melt of the primary crystalline product is preferably the same as the method for preparing the melt of the raw material selenium, and will not be repeated here. The temperature of the melt of the primary crystalline product is preferably 240~260℃, specifically 240℃, 250℃ or 260℃.

[0035] In this invention, the second crystal rod is preferably made of the same material and has the same height as the first crystal rod, which will not be described in detail here.

[0036] In this invention, the rotational speed of the rotating crucible during the secondary rotational crystallization process is preferably 60~120 rpm, specifically 90 rpm or 120 rpm.

[0037] In this invention, the second crystallizing rod preferably undergoes gradient cooling during the secondary rotary crystallization process. The gradient cooling is as follows: first, cooling to 210°C at a rate of 50°C / h; then cooling to 205°C at a rate of 5°C / h; and finally cooling to 199°C at a rate of 1°C / h, and holding at that temperature for 2 hours. This invention can precisely control the gas flow rate from 0.1 to 50 m³ / h using an intelligent gas flow control module. 3 / h, thereby enabling precise temperature control of the crystallizing rod within ±0.5℃ range, allowing high-purity selenium to continuously crystallize on the second crystallizing rod. The gas can be argon or purified air.

[0038] In the two-stage rotational crystallization process, impurity elements with K < 1 are enriched in the melt, while high-purity selenium is distributed on the second crystallizing rod, resulting in high-purity selenium with a purity of 6N or higher. This invention achieves more thorough and efficient impurity removal through a two-stage rotational crystallization method.

[0039] This invention provides a high-purity selenium preparation apparatus, including an intelligent gas flow control module, a furnace shell, a heating element disposed within the furnace shell, a crucible disposed within the heating element, a liftable baffle plate, and a crystallizing rod. The intelligent gas flow control module includes an inlet pipe and an outlet pipe, which are connected to a crystallizing rod. An intelligent gas flow meter is installed on the inlet pipe.

[0040] In this invention, the intelligent gas flow control module can provide a stable gas flow rate, thereby continuously cooling the crystallizer and accurately controlling its temperature.

[0041] In this invention, the baffle is preferably triangular prism-shaped, with its upper edge extending 20-80 mm above the rotating crucible. The edge of the baffle closest to the crucible wall is 5-10 mm away from the inner wall of the crucible. The triangular prism-shaped baffle provides better stability.

[0042] This invention utilizes an intelligent gas flow meter coupled with an intelligent temperature control module. Based on real-time crystal growth rate (0.1~1.5 mm / h) and crystal rod temperature sensing data, it dynamically adjusts the gas intake to establish an axial temperature gradient (from the solid-liquid interface to the crystal rod), achieving steady-state segregation of impurity elements. A triangular prism-shaped baffle plate, placed inside the crucible, compresses the solid-liquid boundary layer thickness to ≤50 μm to accelerate impurity diffusion. This invention, through the synergistic effect of the intelligent gas flow control module and the baffle plate, suppresses non-equilibrium impurity inclusion at the crystallization interface, resulting in selenium crystals with a purity of 6N or higher (total impurities <1 ppm).

[0043] To further illustrate the present invention, the method and apparatus for preparing high-purity selenium provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0044] Figure 1 This is a schematic diagram of the rotary crystallizer used in the embodiment (illustrated as a single-stage rotary crystallization process), including an intelligent gas flow control module, a furnace shell, a heating element, a crucible, a baffle plate, and a crystallizing rod. The inlet and outlet of the intelligent gas flow control module are connected to the crystallizing rod to regulate its temperature; the inlet is connected to an intelligent gas flow meter. The furnace shell encloses the heating element, and the crucible is inside the heating element, with an inner diameter of 130mm and a height of 200mm. The baffle plate and the crystallizing rod are placed inside the crucible and can be raised and lowered. The crystallizing rod is located at the central axis of the crucible. The baffle plate is a triangular prism (with an isosceles triangle base, 50mm high, and horizontally placed), with one edge (passing through the vertex of the isosceles triangle) close to the crystallizing rod, and the opposite face close to the crucible wall and parallel to the crystallizing rod, 5-10mm from the crucible wall; the baffle plate protrudes 20mm from the crucible.

[0045] Figure 2 This diagram illustrates how an intelligent gas flow control module regulates the crystallization process. The temperature of the crystallizer is fed back to the intelligent control module, which adjusts the gas flow rate based on the input temperature. This, in turn, controls the axial temperature gradient from the solid-liquid interface to the crystallizer, thereby achieving efficient crystallization.

[0046] Figure 3 This is a schematic diagram of the two-stage rotational crystallization process. In the first-stage rotational crystallization process, impurity elements with K>1 are enriched on the crystallizing rod and removed. In the second-stage rotational crystallization process, impurity elements with K<1 are enriched in the melt, and high-purity selenium is obtained on the crystallizing rod.

[0047] Example 1 Weigh 500g of 4N selenium and place it in a quartz crucible. The content of impurity elements in 4N selenium is shown in Table 1.

[0048] Table 1. Impurity element content in 4N selenium (ppm)

[0049] The furnace was evacuated to 1 Pa, then argon gas was introduced to 8000 Pa, repeated 5 times until the furnace was almost entirely filled with argon. The mixture was heated to 280°C, the baffle plate was lowered, and the rotation speed was increased to 15 rpm. The crystallizing rod was lowered so that its bottom was 0.5 cm from the bottom of the crucible. Gas was continuously introduced into the crystallizing rod through the intelligent gas flow control module at a cooling rate of 50°C / h for 1 hour (to 230°C), then reduced to 5°C / h for 1 hour (to 225°C), and finally reduced to 1°C / h for 6 hours (to 219°C), followed by a 2-hour holding period. The crystallizing rod and baffle plate were then raised. Once the furnace temperature had cooled to room temperature, the primary crystalline product was obtained. The crystallizing rod was then removed and replaced with a new one.

[0050] The furnace was evacuated to 1 Pa, then argon gas was introduced to 8000 Pa, and this process was repeated 5 times until the furnace was almost entirely filled with argon gas. The mixture was heated to 260℃, the baffle plate was lowered, and the rotation speed was increased to 90 rpm. The crystallizing rod was lowered so that its bottom was 0.5 cm from the bottom of the crucible. Gas was continuously introduced into the crystallizing rod through an intelligent gas flow control module at a cooling rate of 50℃ / h for 1 hour (cooling to 210℃), then changed to 5℃ / h for 1 hour (cooling to 205℃), and finally changed to 1℃ / h for 6 hours (cooling to 199℃), followed by a 2-hour holding period. Finally, a 6N selenium purity was obtained on the crystallizing rod, and the impurity element content is shown in Table 4.

[0051] Example 2 Weigh 2 kg of 4N selenium and place it in a quartz crucible. The content of impurity elements in 4N selenium is shown in Table 2.

[0052] Table 2. Impurity element content in 4N selenium (ppm)

[0053] The furnace was evacuated to 1 Pa, then argon gas was introduced to 8000 Pa, and this process was repeated 5 times. The furnace was almost entirely filled with argon gas. The mixture was heated to 280°C, the baffle was lowered, and the rotation speed was increased to 20 rpm. The crystallizing rod was lowered so that its bottom was 1 cm from the bottom of the crucible. Gas was continuously introduced into the crystallizing rod through the intelligent gas flow control module at a cooling rate of 50°C / h for 1 hour (until the temperature dropped to 230°C), then the rate was changed to 5°C / h for 1 hour (until the temperature dropped to 225°C), and finally the rate was changed to 1°C / h for 6 hours (until the temperature dropped to 219°C), followed by a 2-hour holding period. The crystallizing rod and baffle were then raised. Once the furnace temperature had cooled to room temperature, the primary crystalline product was obtained. The crystallizing rod was then removed and replaced with a new one.

[0054] The furnace was evacuated to 1 Pa, then argon gas was introduced to 8000 Pa, and this process was repeated 5 times until the furnace was almost entirely filled with argon gas. The mixture was heated to 260℃, the baffle plate was lowered, and the rotation speed was increased to 90 rpm. The crystallizing rod was lowered so that its bottom was 1 cm from the bottom of the crucible. Gas was continuously introduced into the crystallizing rod through an intelligent gas flow control module at a cooling rate of 50℃ / h for 1 hour (cooling to 210℃), then changed to 5℃ / h for 1 hour (cooling to 205℃), and finally changed to 1℃ / h for 6 hours (cooling to 199℃), followed by a 2-hour holding period. Finally, a 6N selenium purity was obtained on the crystallizing rod, and the impurity element content is shown in Table 4.

[0055] Example 3 Weigh 4 kg of 4N selenium and place it in a quartz crucible. The content of impurity elements in 4N selenium is shown in Table 3.

[0056] Table 3. Impurity element content in 4N selenium / ppm

[0057] The furnace was evacuated to 1 Pa, then argon gas was introduced to 8000 Pa, repeated 5 times until the furnace was almost entirely filled with argon. The mixture was heated to 280°C, the baffle was lowered, and the rotation speed was increased to 30 rpm. The crystallizing rod was lowered until its bottom was 1 cm from the bottom of the crucible. Gas was continuously introduced into the crystallizing rod through the intelligent gas flow control module at a cooling rate of 50°C / h for 1 hour (to 230°C), then reduced to 5°C / h for 1 hour (to 225°C), and finally reduced to 1°C / h for 6 hours (to 219°C), followed by a 2-hour holding period. The crystallizing rod and baffle were then raised. Once the furnace temperature had cooled to room temperature, the primary crystalline product was obtained. The crystallizing rod was then removed and replaced with a new one.

[0058] The furnace was evacuated to 1 Pa, then argon gas was introduced to 8000 Pa, and this process was repeated 5 times until the furnace was almost entirely filled with argon gas. The mixture was heated to 260℃, the baffle plate was lowered, and the rotation speed was increased to 120 rpm. The crystallizing rod was lowered so that its bottom was 1 cm from the bottom of the crucible. Gas was continuously introduced into the crystallizing rod through an intelligent gas flow control module at a cooling rate of 50℃ / h for 1 hour (cooling to 210℃), then changed to 5℃ / h for 1 hour (cooling to 205℃), and finally changed to 1℃ / h for 6 hours (cooling to 199℃), followed by a 2-hour holding period. Finally, a 6N selenium purity was obtained on the crystallizing rod, and the impurity element content is shown in Table 4.

[0059] Table 4. Selenium impurity element content / ppm in the secondary crystallization products of Examples 1, 2, and 3

[0060] Comparative Example 1 The experiment was conducted according to the method described in Example 3 of Chinese Patent Publication No. CN 117963851 A: the raw material selenium was placed in a rotating crucible, a vacuum was drawn to remove air from the furnace and repeated several times, then nitrogen was introduced, and then heated to 310°C to make the selenium solid molten. The crystallization temperature was controlled at 240°C, and the crystallizer at 240°C was quickly immersed in the melt. The crucible rotation speed was controlled at 120 r / min, and rotational crystallization was carried out for 120 min.

[0061] The results showed that, under this process, the rotational crystallization process needed to be repeated 30 times, with each crystallization lasting 2 hours (120 minutes), to achieve the 6N standard for the 11 impurity elements in selenium. The results are shown in Table 5.

[0062] Table 5. Selenium impurity element content in raw materials and 30 crystallization products (ppm)

[0063] It can be seen that Comparative Example 1, without using baffles, intelligent gas flow control, and secondary crystallization, requires a large number of rotational crystallization cycles; the preparation of 6N selenium from 4N selenium requires 30 rotational crystallization cycles. This invention, by employing baffles, intelligent gas flow control, and secondary crystallization, completes the preparation of 6N high-purity selenium in a shorter time (20 hours), significantly shortening the preparation time and improving the efficiency of high-purity selenium preparation.

[0064] The device of the present invention is equipped with an intelligent gas flow control module and a baffle. The former achieves precise control of the temperature gradient of the crystallizer at the ±0.5℃ level by dynamically adjusting the gas flow, while the baffle enhances the convection of the melt, reduces the thickness of the solid-liquid interface boundary layer, and accelerates the diffusion of impurities. The preparation method includes the following steps: (1) First-stage rotational crystallization: 4N selenium is placed in a high-purity quartz crucible and melted in a crystallization furnace (270~290℃); baffles generate vortices in the melt; a smart gas flow meter establishes a stable temperature gradient; the gas flow rate is dynamically adjusted according to the crystal growth rate (0.1~0.5mm / h) to maintain the stability of the crystallization interface and carry out continuous crystallization; after the crystallization cycle (about 10h), the crystal rod containing impurities is taken out; (2) Second-stage rotational crystallization: The first-stage crystallization product is placed in a high-purity quartz crucible and melted in a crystallization furnace (240~260℃); baffles generate vortices in the melt; a smart gas flow meter establishes a stable temperature gradient; the gas flow rate is dynamically adjusted according to the crystal growth rate (0.5~1.5mm / h) to maintain the stability of the crystallization interface and carry out continuous crystallization; after the crystallization cycle (about 10h), the crystal rod containing high-purity selenium is taken out. This invention employs stepwise crystallization to improve crystallization efficiency, and two-stage crystallization to improve product purity; coupled control of gas flow rate, temperature and growth rate enables continuous directional crystallization, and the product purity reaches 6N level or above (total impurities <1ppm).

[0065] This invention relates to a method and apparatus for directional crystallization of high-purity selenium based on dynamic thermal field control and fluid optimization. It is applicable to the industrial preparation of 6N-grade (99.9999%) high-purity selenium and solves key problems in traditional crystallization methods, such as boundary layer impurity enrichment and crystallization defects caused by temperature field fluctuations.

[0066] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity selenium, characterized in that, Includes the following steps: Under a protective atmosphere, the first crystallizing rod and the baffle plate are immersed in the melt of raw material selenium for primary rotational crystallization. The first crystallizing rod is then removed to obtain the primary crystalline product. Under a protective atmosphere, a second crystallizing rod and a baffle plate are immersed in the melt of the primary crystallization product for secondary rotational crystallization to obtain high-purity selenium on the second crystallizing rod; the high-purity selenium is 6N or higher. The crystallization rate of the first-stage rotational crystallization is 0.1~0.5 mm / h, and the crystallization rate of the second-stage rotational crystallization is 0.5~1.5 mm / h; the solid-liquid boundary layer thickness during the first-stage and second-stage rotational crystallization processes is ≤50 μm.

2. The preparation method according to claim 1, characterized in that, The temperature of the melt of the raw material selenium is 270~290℃.

3. The preparation method according to claim 1 or 2, characterized in that, The rotational speed of the first-stage rotary crystallizer is 10~60 rpm.

4. The preparation method according to claim 1, characterized in that, The temperature of the melt of the primary crystallized product is 240~260℃.

5. The preparation method according to claim 1 or 4, characterized in that, The rotational speed of the secondary rotational crystallization is 60~120 rpm.

6. The preparation method according to claim 1, characterized in that, During the first-stage rotary crystallization process, the first crystallizing rod undergoes a gradient cooling process, which is as follows: first, the temperature is reduced to 230°C at a rate of 50°C / h, then to 225°C at a rate of 5°C / h, and finally to 219°C at a rate of 1°C / h, and held at that temperature for 2 hours. During the secondary rotational crystallization process, the second crystallizer rod undergoes a gradient cooling process. The gradient cooling is as follows: first, the temperature is reduced to 210°C at a rate of 50°C / h, then to 205°C at a rate of 5°C / h, and finally to 199°C at a rate of 1°C / h, and held at that temperature for 2 hours.

7. The preparation method according to claim 1, characterized in that, The raw material selenium is 4N selenium, and the content of impurity elements in the 4N selenium is as follows: mercury and copper ≤3ppm independently; boron, bismuth, lead, nickel, arsenic, antimony, and tin ≤5ppm independently; magnesium and aluminum ≤8ppm independently; silicon ≤9ppm; tellurium and iron ≤40ppm independently; and sulfur ≤40ppm.

8. The preparation method according to claim 1, characterized in that, The protective atmosphere is an inert gas, including argon; the protective atmosphere is under a slight negative pressure, which is 6000~90000 Pa.

9. An apparatus for preparing high-purity selenium, characterized in that, It includes an intelligent gas flow control module, a furnace shell, a heating element installed inside the furnace shell, a crucible installed inside the heating element, a liftable baffle plate, and a crystallizing rod; The intelligent gas flow control module includes an inlet pipe and an outlet pipe, which are connected to a crystallizing rod. An intelligent gas flow meter is installed on the inlet pipe.

10. The preparation apparatus according to claim 9, characterized in that, The baffle is triangular prism-shaped.

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