Method for purifying crude tellurium

Abstract

The application provides a purification method of crude tellurium, and belongs to the field of high-purity metal preparation. The application provides a purification method of crude tellurium, which comprises the following steps: rotating crystallization is carried out by immersing a crystallizer into a tellurium melt obtained by melting the crude tellurium; and the temperature of the crystallizer is lower than the temperature of the tellurium melt during the rotating crystallization. The interface shear force generated by the rotating of the tellurium melt realizes the thinning of the solute boundary layer of the liquid-solid interface, and the impurities are forced to be removed from the boundary layer, so that high-purity tellurium is crystallized; the rotation of the crucible promotes the increase of the temperature gradient of the liquid phase zone near the liquid-solid interface, and the increase of the temperature gradient makes the crystallization faster, so that the purification efficiency is improved. The results of the examples show that the purification method provided by the application can purify 4N tellurium to 99.9999% in one step. Moreover, the process flow of the application is simple, and no waste gas, waste water and waste residue are generated.

Description

Technical Field

[0001] This invention relates to the field of high-purity metal preparation, and more particularly to a method for purifying crude tellurium. Background Technology

[0002] Tellurium, as a rare and dispersed element, is widely used in semiconductors, chemicals, metallurgy, pharmaceuticals, photovoltaics, and other fields. With the increasing demand for tellurium in emerging fields such as solar energy and semiconductors, especially in CdTe optoelectronic glasses and Bi2Te3 thermoelectric materials, high-purity tellurium has become one of the key materials supporting the development of high-tech and new products. The performance of a product largely depends on the purity of the initial material. However, tellurium extracted from anode mud is generally metallurgical-grade crude tellurium, which does not meet the requirements of new materials. Achieving green and efficient purification of crude tellurium and increasing its added value has become an urgent problem for tellurium producers worldwide.

[0003] Chemical purification of crude tellurium includes redox reactions, selective precipitation, and electrolysis. Chemical methods utilize the differences in chemical properties between tellurium and impurity elements, generating intermediate compounds by adding chemical reagents, followed by the separation of the impurities. While chemical methods can achieve satisfactory purity in the preparation of high-purity tellurium, the purification process involves repeated oxidation and reduction of elements, involving toxic and hazardous substances, and presents significant safety hazards and waste disposal issues. Therefore, current technologies increasingly utilize physical methods to prepare high-purity tellurium.

[0004] CN112408338A discloses a method and apparatus for purifying crude tellurium, which involves immersing a condenser tube into the melt for crystallization. However, this method is inefficient, and the purity of the tellurium obtained still needs to be improved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for purifying crude tellurium, which is highly efficient and yields tellurium with high purity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for purifying crude tellurium, comprising the following steps:

[0008] The crystallizer is immersed in the tellurium melt obtained from the melting of crude tellurium for rotational crystallization;

[0009] During the rotary crystallization process, the temperature of the crystallizer is lower than the temperature of the tellurium melt.

[0010] Preferably, the crude tellurium comprises Cu 1-1000ppm, Mg 5-200ppm, Bi 5-200ppm, Fe 5-40ppm, As 5-200ppm, Si 5-40ppm, Al 5-200ppm, Se 5-200ppm, Pb 5-40ppm, Na 5-200ppm, S 5-40ppm, and the balance tellurium.

[0011] Preferably, the rotational speed of the tellurium melt during rotational crystallization is 0–120 r / min.

[0012] Preferably, the temperature of the crystallizer during the rotary crystallization is 420–440°C.

[0013] Preferably, the rotational crystallization time is 60–120 min.

[0014] Preferably, the temperature of the tellurium melt is 460–500°C.

[0015] Preferably, the crystallizer is made of graphite;

[0016] The crystallizer has a shell structure, including a central layer for inputting the cooling medium and an outer shell layer for outputting the cooling medium.

[0017] Preferably, the cooling medium includes air.

[0018] Preferably, the immersion depth of the crystallizer is 45-100 mm below the surface of the tellurium melt.

[0019] The present invention provides a method for purifying crude tellurium, comprising the following steps: immersing a crystallizer in tellurium melt obtained by melting crude tellurium for rotational crystallization; wherein the temperature of the crystallizer is lower than the temperature of the tellurium melt during rotational crystallization.

[0020] This invention utilizes the interfacial shear force generated by the rotation of the tellurium melt to thin the solute boundary layer at the liquid-solid interface, forcing impurities out of the boundary layer and thus crystallizing high-purity tellurium. The rotation of the tellurium melt also increases the temperature gradient in the liquid phase region near the liquid-solid interface, accelerating crystallization and improving purification efficiency. Example results show that the purification method provided by this invention can purify 4N tellurium to 99.9999% in one step. Furthermore, the process flow of this invention is simple, generating no waste gas, wastewater, or waste residue. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0022] This invention provides a method for purifying crude tellurium, comprising the following steps:

[0023] The crystallizer is immersed in the tellurium melt obtained from the melting of crude tellurium for rotational crystallization;

[0024] During the rotary crystallization process, the temperature of the crystallizer is lower than the temperature of the tellurium melt.

[0025] In this invention, the crude tellurium preferably comprises Cu 1-1000ppm, Mg 5-200ppm, Bi 5-200ppm, Fe 5-40ppm, As 5-200ppm, Si 5-40ppm, Al 5-200ppm, Se 5-200ppm, Pb 5-40ppm, Na 5-200ppm, S 5-40ppm, and the balance tellurium.

[0026] In this invention, the melting is preferably carried out under protective gas and negative pressure conditions; the pressure of the negative pressure is preferably 60,000 to 70,000 Pa, more preferably 65,000 to 68,000 Pa.

[0027] The melting is preferably carried out in a crystallization furnace; the conditions for obtaining the protective gas and negative pressure preferably include evacuating the crystallization furnace to 100 Pa, then introducing the protective gas, repeating the steps of evacuating and introducing the protective gas multiple times, purging the air in the crystallization furnace, and introducing the protective gas to make the vacuum degree in the crystallization furnace reach the negative pressure.

[0028] In this invention, the temperature of the tellurium melt is preferably 460–500°C, more preferably 470–480°C.

[0029] In this invention, the crystallizer is preferably made of graphite;

[0030] The crystallizer in this invention has a shell-type structure, including a central layer for inputting the cooling medium and an outer shell layer for outputting the cooling medium; the cooling medium preferably includes air. The temperature of the crystallizer is controlled during the crystallization process by inputting and outputting the cooling medium.

[0031] In this invention, the rotational crystallization is preferably carried out under protective gas and negative pressure conditions; the pressure of the negative pressure is preferably 60,000 to 70,000 Pa, more preferably 65,000 to 68,000 Pa.

[0032] In this invention, the rotational crystallization is preferably performed by a crucible driving the tellurium melt to rotate, and the rotational speed of the rotational crystallization is preferably less than 120 r / min; the rotation of the tellurium melt is preferably driven by a tellurium melt container, and the speed of the tellurium melt container is the rotational speed. The tellurium melt container preferably includes a graphite crucible.

[0033] In this invention, the purification method preferably further includes: immersing the crystallizer in the tellurium melt obtained by melting crude tellurium, wherein part of the tellurium melt solidifies on the surface of the crystallizer to form a solid; after the solid is remelted, the temperature of the crystallizer is adjusted to the temperature of the crystallizer during the rotary crystallization.

[0034] In this invention, after the crystallizer is immersed in the tellurium melt, due to the temperature difference between the crystallizer and the tellurium melt, the crystallizer will solidify metal.

[0035] In this invention, the immersion depth of the crystallizer is preferably 45-100 mm below the surface of the tellurium melt, more preferably 60-90 mm, and even more preferably 70-80 mm.

[0036] In this invention, the temperature of the crystallizer during rotational crystallization is preferably 420–440°C; the crystallizer is stationary during rotational crystallization; and the rotational crystallization time is preferably 60–120 min, more preferably 80–100 min. The rotational crystallization time is calculated from the point after the solid melts.

[0037] The process flow diagram of Embodiment 1 of the present invention is as follows: Figure 1 As shown: 4N tellurium is heated and melted, then crystallized to obtain 6N high-purity tellurium and residue. The residue can be reused in the heating and melting process.

[0038] The following detailed description of the crude tellurium purification method provided by the present invention, in conjunction with embodiments, should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1

[0040] 1510g of tellurium with a purity of 4N was weighed. The impurity element content in the crude tellurium is shown in Table 1. The crude tellurium was placed in a crucible, which was then placed in a crystallization furnace. A stainless steel furnace shell was placed over the crucible, and the furnace was evacuated to 100Pa. A protective gas was then introduced, and the evacuation and protective gas introduction steps were repeated several times to purge the air from the furnace. Argon gas was then introduced to bring the vacuum level in the furnace to 70000Pa. The raw material was then heated and melted. After melting, a graphite crystallizer (including a central layer for inputting the cooling medium and an outer shell layer for outputting the cooling medium) was immersed in the tellurium melt at a temperature of 490℃. The immersion depth was 50 mm below the surface of the tellurium melt. After the solid solidified in the crystallizer melted, compressed air was introduced into the crystallizer to adjust the temperature to 430℃. The graphite crucible was kept rotating at a uniform speed of 60 r / min for crystallization. The crystallization time was controlled at 60 min. After the high-purity tellurium on the surface of the columnar crystallizer was fully crystallized, the crystallizer was removed from the tellurium melt. Finally, 120 g of high-purity tellurium was obtained. Under these conditions, the purity of the prepared tellurium was 99.99997%, and its impurity content is shown in Table 4.

[0041] Table 14. Tellurium impurity elements and their contents / ppm

[0042] element Cu Mg Bi Fe As Si Al Se Pb Na S content 10 9 9 9 5 10 9 20 20 30 10

[0043] Example 2

[0044] 4667g of tellurium with a purity of 4N2 was weighed out. The impurity element content in the crude tellurium is shown in Table 2. The crude tellurium was placed in a crucible, which was then placed in a crystallization furnace. A stainless steel furnace shell was placed over the crucible, and the furnace was evacuated to a vacuum of 100Pa. A protective gas was then introduced, and the evacuation and protective gas introduction steps were repeated several times to purge the air from the furnace. Argon gas was then introduced to bring the vacuum level in the furnace to 75000Pa. The raw material was then heated and melted. After melting, a graphite crystallizer (including a central layer for inputting the cooling medium and an outer shell layer for outputting the cooling medium) was immersed in the tellurium melt at a temperature of 495℃. The immersion depth was 45 mm below the surface of the tellurium melt. After the solid solidified in the crystallizer melted, compressed air was introduced into the crystallizer to adjust the temperature to 430℃. The graphite crucible was kept rotating at a uniform speed of 60 r / min for crystallization. The crystallization time was controlled at 90 min. After the high-purity tellurium on the surface of the columnar crystallizer was fully crystallized, the crystallizer was removed from the tellurium melt. Finally, 150 g of high-purity tellurium was obtained. Under these conditions, the purity of the prepared tellurium was 99.99997%, and its impurity content is shown in Table 4.

[0045] Table 24. N2 tellurium impurity elements and their contents / ppm

[0046]

[0047]

[0048] Example 3

[0049] Weigh 5000g of tellurium with a purity of 3N5. The impurity element content in the crude tellurium is shown in Table 3. Place the crude tellurium in a crucible, then place the crucible in a crystallization furnace, cover it with a stainless steel furnace shell, evacuate the furnace to 100Pa, and then introduce protective gas. Repeat the evacuation and protective gas introduction steps several times to purge the air from the furnace. Then, introduce argon gas to bring the vacuum level in the furnace to 65000Pa. Then, heat and melt the raw material. After melting, immerse a graphite crystallizer (including a central layer for inputting the cooling medium and an outer shell layer for outputting the cooling medium) into the tellurium melt at a temperature of 490℃. The immersion depth was 50 mm below the surface of the tellurium melt. After the solid solidified in the crystallizer melted, compressed air was introduced into the crystallizer to adjust the temperature to 430℃. The graphite crucible was kept rotating at a uniform speed of 60 r / min for crystallization. The crystallization time was controlled at 120 min. After the high-purity tellurium on the surface of the columnar crystallizer was fully crystallized, the crystallizer was removed from the tellurium melt. Finally, 200 g of high-purity tellurium was obtained. Under these conditions, the purity of the prepared tellurium was 99.9997%, and its impurity content is shown in Table 4.

[0050] Table 33. Tellurium impurity elements and their contents (ppm)

[0051] element Cu Mg Bi Fe As Si Al Se Pb Na S content 20 20 20 40 10 20 30 150 40 60 40

[0052] Table 4. Impurity content after crystallization in Examples 1-4

[0053] Cu Mg Bi Fe As Si Al Se Pb Na S Example 1 0.01 0.05 / 0.05 / / 0.05 0.1 0.05 / / Example 2 0.01 0.04 / 0.05 / 0.08 0.04 0.05 0.03 / / Example 3 0.01 0.05 / 0.05 / 0.08 0.07 2 0.1 / /

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for purifying crude tellurium, characterized in that, The steps are as follows: The crystallizer is immersed in the tellurium melt obtained from the melting of crude tellurium for rotational crystallization; During the rotary crystallization process, the temperature of the crystallizer is lower than the temperature of the tellurium melt. The purification method further includes: immersing the crystallizer in the tellurium melt obtained by melting crude tellurium, and some of the tellurium melt solidifies on the surface of the crystallizer to form a solid. After the solid has remelted, the temperature of the crystallizer is adjusted to the temperature of the crystallizer during the rotary crystallization. The rotational speed of the tellurium melt during rotational crystallization is less than 120 r / min.

2. The purification method according to claim 1, characterized in that, The crude tellurium comprises Cu 1~1000ppm, Mg 5~200ppm, Bi 5~200ppm, Fe 5~40ppm, As 5~200ppm, Si 5~40ppm, Al 5~200ppm, Se 5~200ppm, Pb 5~40ppm, Na 5~200ppm, S 5~40ppm, and the balance tellurium.

3. The purification method according to claim 1, characterized in that, The temperature of the crystallizer during the rotary crystallization process is 420~440℃.

4. The purification method according to claim 1 or 3, characterized in that, The rotational crystallization time is 60~120 min.

5. The purification method according to claim 1, characterized in that, The temperature of the tellurium melt is 460~500℃.

6. The purification method according to claim 1, characterized in that, The crystallizer is made of graphite; The crystallizer has a shell structure, including a central layer for inputting the cooling medium and an outer shell layer for outputting the cooling medium.

7. The purification method according to claim 6, characterized in that, The cooling medium includes air.

8. The purification method according to claim 1, characterized in that, The immersion depth of the crystallizer is 45~100mm below the surface of the tellurium melt.

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