A method for preparing 7N tellurium

Abstract

The present invention provides a method for preparing 7N tellurium, and belongs to the field of high-purity metal preparation. The present invention provides a method for preparing 7N tellurium, comprising the following steps: mixing 2N crude tellurium with concentrated sulfuric acid and then performing oxidative roasting to obtain selenium dioxide vapor and roasting slag; mixing the roasting slag with a strong alkaline solution, electrolyzing the resulting solution to obtain 4N electrolytic tellurium; vacuum distilling the 4N electrolytic tellurium to obtain 5N tellurium; melting the 5N tellurium, immersing a crystallizer in the resulting tellurium melt and then performing crystallization to obtain 7N tellurium; the total time of the preparation method is less than 14 days. The present invention prepares 7N tellurium from 2N tellurium with a high impurity content through a combined process of oxidative roasting-electrolysis-vacuum distillation-crystallization, and the process flow is simple and the production equipment requirements are low. The results of the embodiment show that the present invention can obtain ultra-high purity tellurium with a purity of 99.99999%.

Description

Technical Field

[0001] The present invention relates to the field of high-purity metal preparation, and in particular to a method for preparing 7N tellurium. Background Art

[0002] As a rare element, tellurium is widely used in semiconductors, chemicals, metallurgy, medicine, photovoltaics and other fields. Tellurium extracted from anode mud is generally metallurgical grade crude tellurium with a purity of 98-99%, which does not meet the requirements of new materials.

[0003] Realizing green and efficient purification of crude tellurium and increasing its added value have become urgent issues that need to be solved by tellurium producers around the world. Chemical methods for purifying crude tellurium include oxidation-reduction, selective precipitation and electrolysis. The chemical method utilizes the difference in chemical properties between tellurium and impurity elements to generate intermediate compounds by adding chemical reagents, and then separates the impurities. Although the chemical method can obtain satisfactory purity, the chemical method requires repeated oxidation and reduction of elements during the purification process, involves toxic and hazardous substances, and has major safety hazards and waste disposal problems. Therefore, physical methods are more commonly used in the prior art to prepare high-purity tellurium.

[0004] The physical method for preparing high-purity tellurium is mainly the zone melting method. No reagents are added during the zone melting process, so no impurities are introduced. However, this process is very time-consuming (about 2 to 3 weeks) and has low productivity. In addition, zone melting also has requirements for the purity of crude tellurium. Only crude tellurium with a purity of 4N or above can obtain high-purity metal. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing 7N tellurium. The method of the present invention is time-saving and has low requirements on raw materials.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing 7N tellurium, comprising the following steps:

[0008] 2N crude tellurium is mixed with concentrated sulfuric acid and then oxidatively roasted to obtain selenium dioxide vapor and roasted slag;

[0009] The calcined slag is mixed with a strong alkaline solution, and the obtained solution is electrolyzed to obtain 4N electrolytic tellurium;

[0010] The 4N electrodeposited tellurium is subjected to vacuum distillation to obtain 5N tellurium;

[0011] The 5N tellurium is melted, and a crystallizer is immersed in the obtained tellurium melt for crystallization to obtain 7N tellurium;

[0012] The total time of the preparation process is less than 14 days.

[0013] Preferably, the mass ratio of the 2N crude tellurium to concentrated sulfuric acid is 1-3:1, and the mass concentration of the concentrated sulfuric acid is 98%.

[0014] Preferably, the temperature of the oxidative roasting is 350-600° C., and the holding time is 0.5-3 h.

[0015] Preferably, the concentration of tellurium element in the solution is 100-300 g / L, and the concentration of strong alkali is 90-130 g / L.

[0016] Preferably, the electrolysis temperature is 30-50°C, the time is 50-110h, and the current density is 45-55A / m 2 ;

[0017] During the electrolysis, the solution is in a circulation state, and the circulation speed of the solution is 1 to 5 mL / s.

[0018] Preferably, the temperature of the vacuum distillation is 450-600° C., and the vacuum degree is 0-100 Pa.

[0019] Preferably, the temperature of the melt is 460-560°C.

[0020] Preferably, the immersion depth of the crystallizer is 50 to 100 mm below the melt surface.

[0021] Preferably, the initial temperature of the crystallizer is 460-500° C.; after immersion, the temperature of the crystallizer decreases to 420-440° C. after 10-60 minutes.

[0022] Preferably, the crystallization includes static crystallization and rotational crystallization, and the rotation speed of the rotational crystallization is lower than 120 r / min.

[0023] The present invention provides a method for preparing 7N tellurium, comprising the following steps: mixing 2N crude tellurium with concentrated sulfuric acid and then performing oxidation roasting to obtain selenium dioxide vapor and roasting slag; mixing the roasting slag with a strong alkaline solution, electrolyzing the obtained solution to obtain 4N electrolytic tellurium; vacuum distilling the 4N electrodeposited tellurium to obtain 5N tellurium; melting the 5N tellurium, immersing a crystallizer in the obtained tellurium melt and then performing crystallization to obtain 7N tellurium; the total time of the preparation method is less than 14 days. The present invention prepares 7N tellurium from 2N tellurium with high impurity content through a combined process of oxidation roasting-electrolysis-vacuum distillation-crystallization, and the process flow is simple and the production equipment requirements are low. The results of the embodiment show that the present invention can obtain ultra-high purity tellurium with a purity of 99.99999%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing 7N tellurium, comprising the following steps:

[0026] 2N crude tellurium is mixed with concentrated sulfuric acid and then oxidatively roasted to obtain selenium dioxide vapor and roasted slag;

[0027] The calcined slag is mixed with a strong alkaline solution, and the obtained solution is electrolyzed to obtain 4N electrolytic tellurium;

[0028] The 4N electrodeposited tellurium is subjected to vacuum distillation to obtain 5N tellurium;

[0029] The 5N tellurium is melted, and a crystallizer is immersed in the obtained tellurium melt for crystallization to obtain 7N tellurium.

[0030] The invention mixes 2N crude tellurium with concentrated sulfuric acid and then performs oxidation roasting to obtain selenium dioxide vapor and roasting slag.

[0031] In the present invention, the mass ratio of the 2N crude tellurium to concentrated sulfuric acid is preferably 1 to 3:1, more preferably 1.5 to 2:1; the mass concentration of the concentrated sulfuric acid is preferably 98%.

[0032] In the present invention, the temperature of the oxidation roasting is preferably 350-600°C, more preferably 400-550°C, and further preferably 450-500°C; the holding time is preferably 0.5-3h, more preferably 1-2.5h, and further preferably 1.5-2h. The purpose of oxidation roasting is to remove selenium in the raw material and obtain low-selenium tellurium dioxide.

[0033] In the present invention, the oxidation roasting is preferably carried out in a rotary roasting furnace. Roasting in a rotating state can make the materials fully mixed and improve the deselenization efficiency.

[0034] After obtaining the calcined slag, the present invention mixes the calcined slag with a strong alkaline solution, and electrolyzes the obtained solution to obtain 4N electrolytic tellurium.

[0035] In the present invention, the concentration of tellurium element in the solution is preferably 100-300 g / L, more preferably 150-250 g / L, further preferably 180-220 g / L; the concentration of strong base is preferably 90-130 g / L, more preferably 100-120 g / L; the strong base preferably includes sodium hydroxide.

[0036] In the present invention, the electrolysis temperature is preferably 30-50°C, more preferably 40-45°C; the time is preferably 50-110h, more preferably 60-100h, and further preferably 80-90h; the current density is preferably 45-55A / m 2 , more preferably 48 to 50 A / m 2; The anode for electrolysis is a common steel plate, and the cathode is preferably stainless steel;

[0037] During the electrolysis, the solution is preferably in a circulating state, and the circulation speed of the solution is preferably 1-5 mL / s, more preferably 2-4 mL / s; the solution flows into the anode chamber through the cathode chamber and the diaphragm, then flows out of the electrolytic cell, and is collected and sent to the liquid purification system to be adjusted to convert the electrolyzed solution back into the original solution before entering the cathode chamber for circulation.

[0038] After obtaining 4N electrolytic tellurium, the present invention performs vacuum distillation on the 4N electrodeposited tellurium to obtain 5N tellurium.

[0039] In the present invention, the temperature of the vacuum distillation is preferably 450-600°C, more preferably 500-550°C; the time is preferably 120-180 min, more preferably 150-160 min; the vacuum degree is preferably 0-100 Pa, more preferably 20-80 Pa, further preferably 40-60 Pa.

[0040] After obtaining 5N tellurium, the present invention melts the 5N tellurium, immerses a crystallizer in the obtained tellurium melt, and then performs crystallization to obtain 7N tellurium.

[0041] In the present invention, the melting is preferably carried out under anaerobic conditions. Melting under anaerobic conditions can prevent tellurium from being oxidized. The melting is preferably carried out under slightly negative pressure or normal pressure; the slightly negative pressure is preferably 60,000 to 80,000 Pa.

[0042] In the present invention, the temperature of the melt is preferably 460-560°C.

[0043] In the present invention, the immersion depth of the crystallizer is preferably 50 to 100 mm below the melt surface, more preferably 60 to 80 mm; the initial temperature of the crystallizer is preferably 460 to 500°C, more preferably 470 to 480°C; after immersion, the temperature of the crystallizer is preferably reduced to 420 to 440°C after 10 to 60 minutes, more preferably 20 to 50 minutes, and further preferably 30 to 40 minutes. After the crystallizer is immersed in the melt, there is a temperature difference between the crystallizer and the melt, at which time the melt will solidify on the crystallizer, and the solidified solid can be completely melted after 10 to 60 minutes.

[0044] In the present invention, the crystallization preferably includes stationary crystallization and rotational crystallization; the rotation speed of the crystallizer in the stationary crystallization is 0; the rotational crystallization is preferably melt rotation, and the rotation speed of the rotational crystallization is preferably lower than 120r / min; the melt rotation is preferably driven by the melt container to rotate the melt, and the speed of the melt container is the rotation speed. The melt container preferably includes a graphite crucible.

[0045] In the present invention, the rotational crystallization time is preferably 65 to 130 min, more preferably 80 to 120 min, and further preferably 90 to 100 min.

[0046] In the present invention, the rotational crystallization is preferably carried out under anaerobic conditions; the rotational crystallization is preferably also carried out under a slight negative pressure or normal pressure; the pressure of the slight negative pressure is preferably 60000-80000 Pa.

[0047] In the present invention, the structure of the crystallizer preferably includes a central layer for inputting a cooling medium and an outer shell layer for outputting a cooling medium; the cooling medium preferably includes air.

[0048] The process flow chart of the method of the embodiment of the present invention is as follows Figure 1 As shown: 2N crude tellurium is subjected to oxidative roasting to obtain roasted slag; the roasted slag is mixed with a strong alkaline solution, and the resulting solution is electrolyzed to obtain 4N electrolytic tellurium; the 4N electrodeposited tellurium is vacuum distilled and then subjected to rotary crystallization to obtain 7N tellurium.

[0049] The preparation method of 7N tellurium provided by the present invention is described in detail below in conjunction with the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] 1000 g of 2N crude tellurium was weighed and placed in a rotary roasting furnace, 500 mL of 98% sulfuric acid was added, protective gas was introduced, and oxidation roasting was started (temperature was 550° C., holding time was 2 h).

[0052] After the roasting, the tellurium dioxide with low selenium content was taken out as a raw material and mixed with sodium hydroxide to make a solution (the concentration of tellurium element was 120 g / L and the concentration of sodium hydroxide was 96 g / L) for electrolysis (the electrolysis temperature was 30 ° C, the time was 48 h, and the current density was 55 A / m 2 The circulation speed of the solution is 5 mL / s. The solution flows into the anode chamber through the cathode chamber and the diaphragm, then flows out of the electrolytic cell, and is collected and sent to the liquid purification system. After adjustment, the electrolyzed solution is converted back into the original solution and then enters the cathode chamber for circulation. The anode used for electrolysis is ordinary steel plate, and the cathode is stainless steel. After electrolysis, electrolytic tellurium with a purity of 99.99% can be obtained.

[0053] The obtained electrolytic tellurium is added into a quartz crucible, and the crucible is placed into a vacuum distillation furnace at a temperature of 500°C, and the vacuum is evacuated to 5Pa and vacuum distillation is started for 120 minutes. After the distillation is completed, high-purity tellurium with a purity of 99.9995% can be obtained.

[0054] 5N tellurium obtained by vacuum distillation is used as raw material, and the 5N tellurium raw material is added to a graphite crucible. The crucible is placed in a rotary crystallization furnace and heated and melted under a protective gas atmosphere, and rotary crystallization is performed under a slightly negative pressure of 70000Pa (the depth of the crystallizer immersed in the melt is 50mm; the temperature of the melt is 482°C. After the crystallizer with an initial temperature of 470°C is immersed in the melt, 20°C compressed air is introduced into the crystallizer within 45 minutes to cool it to the required crystallization temperature of 425°C. The rotation speed of the graphite crucible is 60r / min, and the time is 120 minutes). After the rotary crystallization is completed, 7N ultra-high purity metallic tellurium is peeled off from the crystallizer.

[0055] Example 2

[0056] Weigh 1260 g of 2N metallurgical grade crude tellurium and put it into a rotary roaster, add 600 mL of 98% sulfuric acid, introduce protective gas, and start oxidative roasting (temperature is 550°C, holding time is 180 min) (tellurium element concentration is 150 g / L, sodium hydroxide concentration is 90 g / L).

[0057] After the roasting, the tellurium dioxide with low selenium content was taken out as a raw material and added with sodium hydroxide to make a solution for electrolysis (the electrolysis temperature was 32°C, the time was 48h, and the current density was 55A / m 2 The circulation speed of the solution is 5 mL / s. The solution flows into the anode chamber through the cathode chamber and the diaphragm, then flows out of the electrolytic cell, and is collected and sent to the liquid purification system. After adjustment, the electrolyzed solution is converted back into the original solution and then enters the cathode chamber for circulation. The anode used for electrolysis is ordinary steel plate, and the cathode is stainless steel. After electrolysis, electrolytic tellurium with a purity of 99.996% can be obtained.

[0058] The obtained electrolytic tellurium is added into a quartz crucible, and the crucible is placed into a vacuum distillation furnace at a temperature of 450°C, and the vacuum is evacuated to 10Pa and vacuum distillation is started for 150 minutes. After the distillation is completed, high-purity tellurium with a purity of 99.9997% can be obtained.

[0059] 5N tellurium obtained by vacuum distillation is used as raw material, and the 5N tellurium raw material is added to a graphite crucible. The crucible is placed in a rotary crystallization furnace and heated and melted under a protective gas atmosphere, and rotary crystallization is performed under a slightly negative pressure of 75000Pa (the depth of the crystallizer immersed in the melt is 60mm; the temperature of the melt is 482°C. After the crystallizer with an initial temperature of 470°C is immersed in the melt, 20°C compressed air is introduced into the crystallizer within 45 minutes to cool it to the required crystallization temperature of 430°C, and the rotation speed of the graphite crucible is 65r / min, and the time is 90min). After the rotary crystallization is completed, 6N8 ultra-high purity metallic tellurium is peeled off from the crystallizer to obtain.

[0060] Example 3

[0061] 1164 g of 2N metallurgical grade crude tellurium was weighed and placed in a rotary roasting furnace, 550 mL of 98% sulfuric acid was added, protective gas was introduced, and oxidation roasting was started (temperature was 550° C., holding time was 120 min).

[0062] After the roasting, the tellurium dioxide with low selenium content was taken out as a raw material and added with sodium hydroxide to make a solution (the concentration of tellurium element was 140 g / L and the concentration of sodium hydroxide was 93 g / L) for electrolysis (the electrolysis temperature was 35 ° C, the time was 48 h, and the current density was 55 A / m 2 The circulation speed of the solution is 5 mL / s. The solution flows into the anode chamber through the cathode chamber and the diaphragm, and then flows out of the electrolytic cell. It is collected and sent to the liquid purification system. After adjustment, the electrolyzed solution is converted back into the original solution and then enters the cathode chamber for circulation. The anode used for electrolysis is ordinary steel plate, and the cathode is stainless steel. After electrolysis, electrolytic tellurium with a purity of 99.98% can be obtained.

[0063] The obtained electrolytic tellurium is added into a quartz crucible, and the crucible is placed into a vacuum distillation furnace at a temperature of 500°C, and the vacuum is evacuated to 10Pa and vacuum distillation is started for 180 minutes. After the distillation is completed, high-purity tellurium with a purity of 99.9999% can be obtained.

[0064] 5N tellurium obtained by vacuum distillation is used as raw material, and the 5N tellurium raw material is added to a graphite crucible. The crucible is placed in a rotary crystallization furnace and heated and melted under a protective gas atmosphere, and rotary crystallization is performed under a slightly negative pressure of 70000Pa (the depth of the crystallizer immersed in the melt is 55mm; the temperature of the melt is 482°C. After the crystallizer with an initial temperature of 470°C is immersed in the melt, 20°C compressed air is introduced into the crystallizer within 45 minutes to cool it down to the required crystallization temperature of 425°C, and the rotation speed of the graphite crucible is 60r / min, and the time is 120min). After the rotary crystallization is completed, 7N ultra-high purity metallic tellurium is peeled off from the crystallizer.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing 7N tellurium, characterized in that: The steps are: 2N crude tellurium is mixed with concentrated sulfuric acid and then oxidatively roasted to obtain selenium dioxide vapor and roasted slag; The calcined slag is mixed with a strong alkaline solution, and the obtained solution is electrolyzed to obtain 4N electrolytic tellurium; the concentration of the tellurium element in the solution is 100 to 140 g / L; The 4N electrolytic tellurium is subjected to vacuum distillation to obtain 5N tellurium; The 5N tellurium is melted, and a crystallizer is immersed in the obtained tellurium melt for crystallization to obtain 7N tellurium; the crystallization is rotational crystallization, and the rotational crystallization is performed under a slight negative pressure; the pressure of the slight negative pressure is 60000-80000 Pa; The total time of the preparation process is less than 14 days.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the 2N crude tellurium to the concentrated sulfuric acid is 1-3:1, and the mass concentration of the concentrated sulfuric acid is 98%.

3. The preparation method according to claim 1 or 2, characterized in that: The temperature of the oxidation roasting is 350-600° C., and the heat preservation time is 0.5-3 hours.

4. The preparation method according to claim 1, characterized in that: The concentration of the strong alkali in the solution is 90-130 g / L.

5. The preparation method according to claim 1 or 4, characterized in that: The electrolysis temperature is 30-50°C, the time is 50-110 hours, and the current density is 45-55A / m 2 ; During the electrolysis, the solution is in a circulation state, and the circulation speed of the solution is 1 to 5 mL / s.

6. The preparation method according to claim 1, characterized in that: The temperature of the vacuum distillation is 450-600° C., and the vacuum degree is 0-100 Pa.

7. The preparation method according to claim 1, characterized in that: The temperature of the melt is 460-560°C.

8. The preparation method according to claim 1 or 7, characterized in that: The immersion depth of the crystallizer is 50 to 100 mm below the melt surface.

9. The preparation method according to claim 1 or 7, characterized in that: The initial temperature of the crystallizer is 460-500° C.; after immersion, the temperature of the crystallizer decreases to 420-440° C. after 10-60 minutes.

10. The preparation method according to claim 1 or 7, characterized in that: The rotation speed of the rotational crystallization is lower than 120 r / min.

Images