Purification method of high-purity tellurium

Abstract

The invention discloses a purification method of high-purity tellurium, and belongs to the technical field of non-ferrous metallurgy. The method sequentially comprises the steps of raw material ultrasonic mechanical activation, ultrasonic selective recrystallization, smelting reduction refining, vacuum rectification purification and tellurium ingot forming, and volatile impurities such as selenium and sulfur are effectively removed by oxidizing calcination of a crude tellurium raw material; then, primary separation of impurities is realized in a manner of combining alkaline dissolution and oxidation precipitation, and then repeated purification is performed through low-temperature crystallization, so that the purity of tellurium is remarkably improved; metal impurities are further removed through smelting reduction treatment under the inert atmosphere, and preliminarily purified tellurium ingots are formed; step distillation separation is carried out by utilizing vapor pressure difference between tellurium and impurities under a high vacuum condition, and a pure tellurium component is enriched; and finally, melting in an inert atmosphere, cooling and forming to obtain the high-purity tellurium ingot. The method is stable in technological process, suitable for industrial application and capable of meeting the requirements of high-end fields such as semiconductors and photoelectric materials for high-purity tellurium materials.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal metallurgy, and particularly relates to a method for purifying high-purity tellurium. Background Art

[0002] Tellurium is a rare metalloid element with excellent electrical, thermal, and optical properties, and is widely used in high-tech fields. For example, in the semiconductor industry, tellurium is a key raw material for the preparation of tellurides (such as cadmium telluride (CdTe) and bismuth telluride (Bi2Te3), among others), which can be used in the manufacture of infrared detectors, solar cells, thermoelectric converters, optoelectronic devices, and phase-change memory materials. With the rapid development of new energy, electronic information, and energy-saving and environmental protection industries, the demand for high-purity tellurium materials continues to grow, especially for electronic-grade tellurium, which must achieve a purity of 5N (i.e., 99.999%) or even higher than 6N to meet the extremely stringent impurity control requirements.

[0003] Currently, tellurium purification relies primarily on traditional methods such as zone melting, vacuum distillation, chemical replacement, and electrolytic purification. Zone melting can effectively remove some impurities, but the process is long and the equipment complex. Vacuum distillation can improve purity to a certain extent, but it requires high temperature control and vacuum systems, resulting in high energy consumption. Chemical replacement is cumbersome and prone to introducing secondary impurities. Electrolytic purification requires specific electrode materials and electrolytic conditions, consumes a lot of electricity, and has poor adaptability. Therefore, existing technologies still have significant limitations in terms of purity improvement, energy efficiency, process simplicity, and industrial feasibility.

[0004] Therefore, there is an urgent need to develop a high-purity tellurium production method with a clear process flow, significant purity improvement, strong equipment adaptability, and easy scalability to meet the growing quality and cost control demands of high-purity tellurium materials in future high-end technologies. This present invention, based on this background, provides an efficient, controllable, and industrially applicable high-purity tellurium purification process. Summary of the Invention

[0005] To solve or partially solve the problems existing in the related art, the present invention provides a method for purifying high-purity tellurium. Through a combined process of composite pretreatment + selective recrystallization + distillation purification, metallic impurities (such as Cu, Pb, Bi, Se, etc.) and non-metallic impurities (such as S, Cl, O, etc.) in crude tellurium are effectively removed, thereby producing tellurium ingots with a purity of 5N or above.

[0006] The present invention provides a method for purifying high-purity tellurium, comprising the following steps: (1) Crude tellurium is crushed with the aid of ultrasonic waves and then calcined in an air atmosphere; (2) The calcined crude tellurium is dissolved in a sodium hydroxide solution to form a mixed liquid, and then an oxidant is added. After filtering and removing the slag, the pH of the solution is adjusted to neutral. Tellurium oxide crystals are crystallized at 20-30°C under the assistance of ultrasound. The crystallization process is repeated 2-3 times. (3) Heat and melt the tellurium oxide crystals in an inert atmosphere, add a reducing agent to the molten system, remove the bottom inclusions after standing, and cool to form a tellurium ingot; (4) Heating the tellurium ingot under high vacuum conditions to perform step distillation, separating and discarding the front and back fractions, and retaining the middle fraction; (5) The intermediate fraction is melted in an inert atmosphere and cooled to form a high-purity tellurium ingot.

[0007] Preferably, the crude tellurium has a tellurium content of 98-99% by mass. The crude tellurium also contains 30-80 ppm of Se, 65-300 ppm of Fe, 1200-4000 ppm of Si, 40-100 ppm of Al, 5-30 ppm of Mg, 20-100 ppm of Cu, 10-60 ppm of Bi, and 10-200 ppm of S.

[0008] Preferably, in step (1), the ultrasonic frequency of the ultrasonic-assisted method is 20 to 40 kHz, the ultrasonic power is 100 to 300 W, and the raw tellurium material is crushed to a particle size of less than 1 mm.

[0009] Preferably, the roasting temperature is 500-600°C, the duration is 2-4 hours, and the air flow rate is 5000-15000 L / min·t to promote the complete oxidation and volatilization of impurities such as selenium (Se) and sulfur (S). Excessively fast air flow rates may lead to uneven gas flow within the furnace, thereby affecting the volatilization efficiency of impurities such as selenium and sulfur, resulting in incomplete volatilization of impurities in certain areas. Excessively low air flow rates may result in insufficient oxygen supply, preventing the complete oxidation of impurities such as selenium (Se) and sulfur (S), resulting in reduced impurity removal efficiency and affecting the final purification effect. Lower air flow rates mean slower oxidation reactions, which may prolong the roasting time, thus affecting overall production efficiency.

[0010] Preferably, the concentration of the sodium hydroxide solution is 1-3 mol / L, and the solid-to-liquid ratio of the calcined crude tellurium to the sodium hydroxide solution is 1:(5-10) g / mL. Too low a concentration of sodium hydroxide solution results in insufficient dissolution of the sodium tellurate, thereby affecting the effective tellurium concentration in the solution and, in turn, the crystallization process. High-concentration sodium hydroxide solutions are highly corrosive to equipment, and long-term use may cause equipment damage, thereby increasing production costs.

[0011] Preferably, the oxidant is one or more of hydrogen peroxide, potassium permanganate, and sodium hypochlorite; the mass of the oxidant is 5%-25% of the mass of the mixed liquid. If the amount of oxidant added is too little, the oxidation reaction will be incomplete, and impurities may not be fully oxidized, which may result in impurities remaining in the final product and affect the purity of the tellurium. Excessive oxidant will cause the reaction to be too intense, potentially leading to temperature increases, bubble formation, and other phenomena, increasing operational difficulty and instability, and even posing safety risks.

[0012] Preferably, in step (2), the ultrasonic frequency of the ultrasonic-assisted method is 20 to 40 kHz, the ultrasonic power is 100 to 300 W, and the time is 12 to 48 hours to promote the sedimentation of impurities and the precipitation of crystals. Ultrasonic-assisted crystallization can significantly increase the crystallization rate and reduce the time required for crystallization. Since ultrasound can cause the vibration of tiny bubbles and particles in the solution, it enhances the local fluidity and mixing properties of the solution, making the substances in the solution more evenly distributed, promoting the formation and growth of crystals, and thus accelerating the crystallization process. Ultrasonic waves can promote the uniform distribution of solute molecules or ions in the solution, which helps to form crystals with regular structure and relatively uniform crystal shape. In addition, the action of ultrasound can also avoid the problem of irregular morphology or uneven crystal stacking caused by excessive concentration or excessive growth of crystals, thereby obtaining a more perfect crystal structure.

[0013] In step (2), the crystallization time is 12 to 48 hours. Too short a crystallization time may result in insufficient growth of tellurium oxide crystals, leading to an incomplete crystallization process; the crystals fail to fully precipitate from the solution, and impurities may be "entrained" into the crystals, resulting in reduced purity. Too long a crystallization time may result in excessive crystal growth, resulting in oversized crystal particles; oversized crystals not only increase the difficulty of subsequent processing, but may also reduce filtration efficiency, making it difficult to remove some impurities.

[0014] Preferably, in step (3), the heating and melting temperature is 700-800°C.

[0015] Preferably, the reducing agent includes reducing agent 1 and reducing agent 2; the reducing agent 1 is one or more of hydrogen, water gas, and natural gas, and the rate of reducing agent 1 per ton of tellurium oxide crystals is 100 L / (t·min)~1000 L / (t·min), and the blowing time is 1~2 h; the reducing agent 2 is zinc powder or magnesium powder, and the mass of reducing agent 2 is 0.01%~0.1% of the mass of the tellurium oxide crystals.

[0016] Preferably, the reducing agent 2 is zinc powder or magnesium powder, with a mass of 0.01% to 0.1% of the crude tellurium mass, used to further reduce and remove metallic impurities from the molten tellurium. If the amount of reducing agent added is too low, it may not be sufficient to effectively reduce the metallic impurities in the molten tellurium. This means that metallic impurities (such as iron, copper, and lead) cannot be completely converted into removable compounds, ultimately resulting in high impurity levels during the purification process and affecting the quality of the high-purity tellurium. Excessive reducing agent may contaminate the molten system, especially if byproducts of the reduction reaction are not completely removed. These byproducts may react with the tellurium to form insoluble impurities, making further removal difficult and reducing the purity of the final product.

[0017] Preferably, the step distillation specifically comprises: placing the tellurium ingot under high vacuum conditions and performing three-stage heating, wherein the temperature of the first stage is set at 300-350°C and maintained at this temperature for 30-60 minutes, during which low-boiling-point impurities sublime and are condensed and discarded, i.e., the front-end fraction. The temperature of the second stage is set at 420-470°C and maintained at this temperature for 30-60 minutes, during which tellurium sublimes and vapor is deposited in the condensation zone, i.e., the middle fraction. The temperature of the third stage is set at 550-600°C and maintained at this temperature for 30-60 minutes, during which high-boiling-point impurities sublime or remain, i.e., the back-end fraction.

[0018] High vacuum conditions require a pressure no higher than 1×10⁻³ Pa to achieve efficient evaporation of tellurium and separation of impurities. Under high vacuum conditions, the vapor pressure of tellurium increases significantly, promoting efficient evaporation. Tellurium has a high melting point (approximately 450°C), making evaporation inefficient at normal pressure. However, lowering the ambient pressure to 1×10⁻³ Pa significantly reduces the evaporation temperature, making it easier for tellurium to evaporate. This evaporation effect facilitates the rapid separation of high-purity tellurium during the distillation process while removing low-volatility impurities from the molten tellurium.

[0019] Preferably, in step (5), the melting temperature is 460-550°C, the time is 1-3 hours, and the cooling rate of the cooling molding is 1-5°C / min.

[0020] Preferably, the inert atmosphere is high-purity argon or high-purity nitrogen, and the entire melting and cooling process is carried out under this inert atmosphere to prevent tellurium oxidation and the reintroduction of impurities. If oxygen is present in the environment, tellurium dioxide (TeO2) may form on the tellurium surface, reducing its purity. Therefore, using an inert atmosphere (such as high-purity argon or high-purity nitrogen) can effectively prevent oxygen from coming into contact with the tellurium, preventing tellurium oxidation and ensuring that the final product is high-purity metallic tellurium. As inert gases, argon and nitrogen do not participate in the reduction reaction, thus providing a stable environment, ensuring that the reducing agent (such as zinc powder or magnesium powder) reacts with the metal impurities and removes them from the molten tellurium without interference from external gases that could affect the reaction process.

[0021] The technical solution provided by the present invention can have the following beneficial effects: (1) Ultrasonic assistance improves crushing efficiency. In the ultrasonic mechanical activation step of raw materials, the use of ultrasonic waves can effectively improve the crushing effect of crude tellurium raw materials, crushing them to a particle size of less than 1 mm. The action of ultrasound not only accelerates the crushing process of the material, but also increases the surface activity of the material, promoting the subsequent roasting and oxidation processes. This method has obvious energy efficiency advantages over traditional mechanical crushing and can quickly obtain particles suitable for subsequent processing.

[0022] (2) Ultrasonic-assisted multiple crystallization to optimize purity. In the ultrasonic-assisted crystallization step, the effect of ultrasound helps the uniform growth of crystals and more efficient precipitation of impurities. This method can significantly improve crystallization efficiency and reduce crystal defects, making the purity improvement process more precise and controllable. By repeating the crystallization 2-3 times, the impurity removal effect is obvious, and the content of harmful impurities such as selenium (Se) and sulfur (S) in tellurium can be significantly reduced.

[0023] (3) Melt reduction refining improves the removal rate of metal impurities. In the melt reduction refining step, by adding trace reducing agents such as zinc powder or magnesium powder, metal impurities in tellurium can be further removed. This step uses an inert atmosphere to avoid oxidation reactions. The static clarification and bottom inclusion removal during the melting process make the final tellurium ingot purer. This process greatly improves the impurity removal effect during the refining process and effectively reduces the residual metal impurities.

[0024] (4) High-efficiency vacuum distillation purification. By performing step distillation under high vacuum conditions, the high vapor pressure of tellurium can be utilized to selectively separate impurities and retain a high-purity tellurium fraction. The vacuum distillation process effectively improves the purity of tellurium and minimizes cross-contamination of impurities by precisely controlling the temperature gradient and optimizing the distillation process. This step ensures the production of high-purity tellurium with a purity of 99.999%, providing high-quality raw materials for high-end electronic equipment and other fields.

[0025] (5) Energy-saving and efficient molding and preparation. During the final tellurium ingot molding process, slow cooling under an inert atmosphere ensures stable crystallization of high-purity tellurium. Due to the use of an efficient purification process, the final tellurium ingot purity reaches over 99.999%, meeting the high standards of electronic-grade materials. This process avoids tellurium oxidation and the reintroduction of impurities, ensuring the stability and performance consistency of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of the purification method of high-purity tellurium. DETAILED DESCRIPTION

[0027] The crude tellurium used in the examples and comparative examples has a tellurium content of 98% by mass and further contains 80 ppm of Se, 6 ppm of Fe, 4000 ppm of Si, 100 ppm of Al, 20 ppm of Mg, 60 ppm of Cu, 40 ppm of Bi and 100 ppm of S.

[0028] Example 1 like Figure 1 As shown, a method for purifying high-purity tellurium comprises the following steps: (1) Crude tellurium was placed in an ultrasonic device and crushed to a particle size of less than 1 mm using an ultrasonic frequency of 30 kHz and a power of 250 W. The crushed crude tellurium was then calcined in an air atmosphere at 500°C for 3 hours with an air flow rate of 10,000 L / min·t to ensure that volatile impurities such as selenium (Se) and sulfur (S) were fully oxidized and volatilized.

[0029] (2) 100 g of calcined crude tellurium was dissolved in 600 ml of 1.5 mol / L sodium hydroxide solution (i.e., the solid-to-liquid ratio of calcined crude tellurium to sodium hydroxide solution was 1:6) to produce sodium tellurate. 80 ml of 0.1 mol / L hydrogen peroxide (H2O2) was added to the solution as an oxidant, and the impurities were oxidized and precipitated. After filtration, the pH of the solution was adjusted to 7.0 with dilute hydrochloric acid, and slow crystallization was carried out at 20°C using ultrasonic waves at a frequency of 25 kHz and a power of 200 W. The crystallization process lasted for 36 hours.

[0030] (3) The crystals were dissolved in a 1.5 mol / L sodium hydroxide solution at a solid-liquid ratio of 1:6 g / ml. 0.1 mol / L hydrogen peroxide (H2O2) was then added as an oxidant at a volume 0.13 times that of the sodium hydroxide solution to oxidize the impurities and precipitate them. After filtration, the pH of the solution was adjusted to 7.0 with dilute hydrochloric acid. Ultrasonic waves at a frequency of 25 kHz and a power of 200 W were used to slowly crystallize the tellurium oxide crystals at 20°C.

[0031] (4) The crystallized tellurium oxide crystals are heated to 700°C in a high-purity argon atmosphere to melt. Hydrogen is then blown into the melt at a rate of 300 L / (t·min) per ton of tellurium oxide crystals for 1 hour. Zinc powder, at a concentration of 0.05% by mass of the tellurium oxide crystals, is then added as a reducing agent to remove metallic impurities. After standing to clarify, the bottom inclusions are removed and the melt is formed into a tellurium ingot after cooling.

[0032] (5) The tellurium ingot was placed in a graphite crucible and heated to 800°C under vacuum conditions. The vacuum pressure was controlled at 1×10⁻³Pa and a step distillation was performed. The temperature of the first stage was set at 320°C and kept constant for 50 minutes. The low-boiling-point impurities sublimed and were discarded after condensation, which was the front fraction. The temperature of the second stage was set at 450°C and kept constant for 40 minutes. Tellurium sublimed and the vapor was deposited in the condensation zone, which was the middle fraction. The temperature of the third stage was set at 550°C and kept constant for 60 minutes. The high-boiling-point impurities sublimated or remained, which was the back fraction. The front and back fractions were separated and discarded, and the middle fraction was retained as the high-purity tellurium fraction. The middle fraction was melted at 480°C in a high-purity argon atmosphere and slowly cooled at a cooling rate of 2°C / min. Finally, a high-purity tellurium ingot with a purity of 99.993% was obtained.

[0033] Example 2 A method for purifying high-purity tellurium comprises the following steps: (1) Crude tellurium was placed in an ultrasonic device and crushed to a particle size of less than 1 mm using an ultrasonic frequency of 35 kHz and a power of 300 W. The crushed crude tellurium was then calcined in an air atmosphere at 600°C for 2 hours with an air flow rate of 12,000 L / min·t to ensure that volatile impurities such as selenium (Se) and sulfur (S) were fully oxidized and volatilized.

[0034] (2) 100 g of calcined crude tellurium was dissolved in 500 ml of 2 mol / L sodium hydroxide solution to produce sodium tellurite. 70 ml of 0.15 mol / L potassium permanganate (KMnO4) was added to the solution as an oxidant, oxidizing the impurities and precipitating them. After filtration, the pH of the solution was adjusted to 6.8 with dilute hydrochloric acid. Slow crystallization was carried out at 30°C using ultrasonic waves at a frequency of 30 kHz and a power of 250 W for 48 hours.

[0035] (3) Repeat the crystallization process of step (2) three times with the crystals obtained in step (2).

[0036] (4) The crystallized tellurium oxide crystals are heated to 750°C in a high-purity argon atmosphere to melt. Hydrogen is then blown into the melt at a rate of 300 L / (t·min) per ton of tellurium oxide crystals for 1 hour. Zinc powder (0.03% by weight of the tellurium oxide crystals) is then added as a reducing agent to remove metallic impurities. After standing to clarify, the bottom inclusions are removed and the melt is formed into a tellurium ingot after cooling.

[0037] (5) The tellurium ingot was placed in a graphite crucible and heated to 850°C under vacuum conditions. The vacuum pressure was controlled at 0.5×10⁻³ Pa and a step distillation was performed. The temperature of the first stage was set at 300°C and kept constant for 60 minutes. The low-boiling-point impurities sublimed and were discarded after condensation, which was the front fraction. The temperature of the second stage was set at 470°C and kept constant for 30 minutes. Tellurium sublimed and the vapor was deposited in the condensation zone, which was the middle fraction. The temperature of the third stage was set at 600°C and kept constant for 30 minutes. The high-boiling-point impurities sublimated or remained, which was the back fraction. The front and back fractions were separated and discarded, and the middle fraction was retained as the high-purity tellurium fraction. The middle fraction was melted at 500°C in a high-purity argon atmosphere and slowly cooled at a cooling rate of 3°C / min. Finally, a high-purity tellurium ingot with a purity of 99.998% was obtained.

[0038] Example 3 A method for purifying high-purity tellurium comprises the following steps: (1) Crude tellurium was placed in an ultrasonic device and crushed to a particle size of less than 1 mm using an ultrasonic frequency of 20 kHz and a power of 100 W. The crushed crude tellurium was then calcined in an air atmosphere at 500°C for 4 hours with an air flow rate of 15,000 L / min·t to ensure that volatile impurities such as selenium (Se) and sulfur (S) were fully oxidized and volatilized.

[0039] (2) 100 g of calcined crude tellurium was dissolved in 750 ml of 1 mol / L sodium hydroxide solution to produce sodium telluride. 80 ml of 0.15 mol / L sodium hypochlorite (NaClO) was added to the solution as an oxidant, oxidizing the impurities and precipitating them. After filtration, the pH of the solution was adjusted to 6.5 with dilute hydrochloric acid, and slow crystallization was carried out at 30°C for 12 hours using ultrasonic waves at a frequency of 20 kHz and a power of 200 W. (3) Repeat the crystallization process of step (2) twice with the crystals obtained in step (2).

[0040] (4) The crystallized tellurium oxide crystals are heated to 750°C in a high-purity argon atmosphere to melt. Hydrogen is then blown into the melt at a rate of 150 L / (t·min) per ton of tellurium oxide crystals for 1.5 hours. Zinc powder, 0.1% by weight of the tellurium oxide crystals, is then added as a reducing agent to remove metallic impurities. After standing to clarify, the bottom inclusions are removed and the melt is formed into a tellurium ingot after cooling.

[0041] (5) The tellurium ingot was placed in a graphite crucible and heated to 750°C under vacuum conditions. The vacuum pressure was controlled at 1×10⁻³Pa and a step distillation was performed. The temperature of the first stage was set at 350°C and kept constant for 30 minutes. The low-boiling-point impurities sublimed and were discarded after condensation, which was the front fraction. The temperature of the second stage was set at 450°C and kept constant for 60 minutes. Tellurium sublimed and the vapor was deposited in the condensation zone, which was the middle fraction. The temperature of the third stage was set at 580°C and kept constant for 50 minutes. The high-boiling-point impurities sublimated or remained, which was the back fraction. The front and back fractions were separated and discarded, and the middle fraction was retained as the high-purity tellurium fraction. The middle fraction was melted at 550°C in a high-purity argon atmosphere and slowly cooled at a cooling rate of 1°C / min. Finally, a high-purity tellurium ingot with a purity of 99.997% was obtained.

[0042] Example 4 A method for purifying high-purity tellurium comprises the following steps: (1) Crude tellurium was placed in an ultrasonic device with an ultrasonic frequency of 40 kHz and a power of 300 W, and pulverized to a particle size of less than 1 mm. The pulverized crude tellurium was then calcined in an air atmosphere at 550°C for 2 hours with an air flow rate of 8000 L / min·t to ensure that volatile impurities such as selenium (Se) and sulfur (S) were fully oxidized and volatilized.

[0043] (2) 100 g of calcined crude tellurium was dissolved in 550 ml of 1.8 mol / L sodium hydroxide solution to produce sodium telluride. 40 ml of hydrogen peroxide (H2O2) and 30 ml of sodium hypochlorite (NaClO) were added to the solution as oxidants, oxidizing the impurities and precipitating them. After filtration, the pH of the solution was adjusted to 7.2 with dilute hydrochloric acid, and slow crystallization was carried out at 30°C for 48 hours using ultrasonic waves at a frequency of 35 kHz and a power of 250 W.

[0044] (3) Repeat the crystallization process of step (2) twice with the crystals obtained in step (2).

[0045] (4) The crystallized tellurium oxide crystals are heated to 725°C in a high-purity argon atmosphere to melt. Hydrogen is then blown into the melt at a rate of 150 L / (t·min) per ton of tellurium oxide crystals for 1.5 hours. Zinc powder, 0.05% by weight of the tellurium oxide crystals, is then added as a reducing agent to remove metallic impurities. After standing to clarify, the bottom inclusions are removed and the melt is formed into a tellurium ingot after cooling.

[0046] (5) The tellurium ingot was placed in a graphite crucible and heated to 820°C under vacuum conditions. The vacuum pressure was controlled at 0.7×10⁻³ Pa and a step distillation was performed. The temperature of the first stage was set at 300°C and kept constant for 60 minutes. The low-boiling-point impurities sublimed and were discarded after condensation, which was the front fraction. The temperature of the second stage was set at 470°C and kept constant for 30 minutes. Tellurium sublimed and the vapor was deposited in the condensation zone, which was the middle fraction. The temperature of the third stage was set at 600°C and kept constant for 30 minutes. The high-boiling-point impurities sublimated or remained, which was the back fraction. The front and back fractions were separated and discarded, and the middle fraction was retained as the high-purity tellurium fraction. The middle fraction was melted at 500°C in a high-purity argon atmosphere and slowly cooled at a cooling rate of 2°C / min. Finally, a high-purity tellurium ingot with a purity of 99.995% was obtained.

[0047] Comparative Example 1 The only difference between the purification method of high-purity tellurium in this comparative example and that in Example 1 is: The present invention replaces gradient distillation with vacuum distillation at a temperature of 500°C, a holding time of 2 hours, and a vacuum pressure controlled at 1×10⁻³ Pa. The front-end fraction (the fraction during the heating process) and the back-end fraction (the fraction during the cooling process) are separated and discarded, and the middle fraction (500°C) is retained as the high-purity tellurium fraction.

[0048] The final tellurium ingot has a purity of 99.987%.

[0049] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for purifying high-purity tellurium, characterized in that: The steps include: (1) Crude tellurium is crushed with the aid of ultrasonic waves and then calcined in an air atmosphere; (2) The calcined crude tellurium is dissolved in a sodium hydroxide solution to form a mixed liquid, and then an oxidant is added. After filtering and removing the slag, the pH of the solution is adjusted to neutral. Tellurium oxide crystals are crystallized at 20-30°C under the assistance of ultrasound. The crystallization process is repeated 2-3 times. (3) Heat and melt the tellurium oxide crystals in an inert atmosphere, add a reducing agent to the molten system, remove the bottom inclusions after standing, and cool to form a tellurium ingot; (4) Heating the tellurium ingot under high vacuum conditions to perform step distillation, separating and discarding the front and back fractions, and retaining the middle fraction; (5) The intermediate fraction is melted in an inert atmosphere and cooled to form a high-purity tellurium ingot.

2. The method for purifying high-purity tellurium according to claim 1, characterized in that: The mass percentage of tellurium in the crude tellurium is 98-99%.

3. The method for purifying high-purity tellurium according to claim 1, characterized in that: In the steps (1) and (2), the ultrasonic frequency of the ultrasonic assistance is 20 to 40 kHz, and the ultrasonic power is 100 to 300 W; in step (1), the ultrasonic assistance is performed until the particle size of the coarse tellurium is less than 1 mm; and in step (2), the ultrasonic assistance time is 12 to 48 hours.

4. The method for purifying high-purity tellurium according to claim 1, characterized in that: The calcination temperature is 500-600° C., the calcination time is 2-4 hours, and the air flow rate is 5000-15000 L / min·t.

5. The method for purifying high-purity tellurium according to claim 1, characterized in that: The concentration of the sodium hydroxide solution is 1-3 mol / L, and the solid-liquid ratio of the calcined crude tellurium to the sodium hydroxide solution is 1:(5-10) g / mL.

6. The method for purifying high-purity tellurium according to claim 1, characterized in that: The oxidant is one or more of hydrogen peroxide, potassium permanganate, and sodium hypochlorite; the mass of the oxidant is 5%-25% of the mass of the mixed liquid.

7. The method for purifying high-purity tellurium according to claim 1, characterized in that: In the step (3), the heating and melting temperature is 700-800°C.

8. The method for purifying high-purity tellurium according to claim 1, characterized in that: The reducing agent includes reducing agent 1 and reducing agent 2; the reducing agent 1 is one or more of hydrogen, water gas, and natural gas, and the rate of passing reducing agent 1 through each ton of tellurium oxide crystals is 100 L / (t·min) to 1000 L / (t·min), and the blowing time is 1 to 2 hours; the reducing agent 2 is zinc powder or magnesium powder, and the mass of reducing agent 2 is 0.01% to 0.1% of the mass of the tellurium oxide crystals.

9. The method for purifying high-purity tellurium according to claim 1, characterized in that: The step distillation specifically includes: placing the tellurium ingot under high vacuum conditions and performing three-stage heating, wherein the temperature of the first stage is set at 300-350°C and kept constant for 30-60 minutes; the temperature of the second stage is set at 420-470°C and kept constant for 30-60 minutes; the temperature of the third stage is set at 550-600°C and kept constant for 30-60 minutes; the pressure of the high vacuum conditions is not higher than 1×10⁻³ Pa; the first stage heating and distillation produces the front-end fraction, the second stage heating and distillation produces the middle fraction, and the third stage heating and distillation produces the back-end fraction.

10. The method for purifying high-purity tellurium according to claim 1, characterized in that: In the step (5), the melting temperature is 460-550°C, the time is 1-3 hours, and the cooling rate of the cooling molding is 1-5°C / min.

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