A vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium.

Abstract

This invention discloses a vacuum distillation method for preparing 5N grade high-purity cadmium from 4N grade cadmium, belonging to the field of high-purity metal preparation technology. The method uses 4N grade cadmium obtained by ultrasonic-enhanced electrolysis as raw material. First, it undergoes pretreatment under an inert atmosphere to remove surface oxides and volatile impurities. Then, the pretreated cadmium is placed in a vacuum distillation apparatus and distilled at 10... ‑2 ~10 ‑4 Temperature-controlled distillation is performed under vacuum conditions (Pa), with the evaporation zone at 450–650°C, the distillation zone at 350–500°C, and the condensation zone at 250–320°C. This efficient separation is achieved by utilizing the vapor pressure differences between different impurities and cadmium. The purified cadmium vapor is collected and deposited in the condensation zone, yielding a 5N-grade high-purity cadmium product. Purity can be further improved through repeated distillation if necessary. This invention offers advantages such as high separation efficiency, strong impurity removal capability, low energy consumption, and high metal recovery rate. It can stably prepare high-purity cadmium with a purity ≥99.999%, making it suitable for semiconductor materials and optoelectronic functional materials.

Description

Technical Field

[0001] This invention belongs to the field of high-purity metal preparation technology, specifically relating to a method for deep purification of 4N grade crude cadmium obtained by ultrasonic electrolysis using vacuum distillation technology to prepare 5N grade high-purity cadmium. Background Technology

[0002] Currently, high-purity cadmium is widely used in cadmium telluride photovoltaic materials, infrared detectors, and nuclear radiation detection materials, requiring extremely high purity and impurity control. Existing processes mainly include zone melting and electrolytic refining, but these have the following problems: zone melting has low efficiency and long cycle time; electrolytic purification is difficult to remove low vapor pressure impurities; energy consumption is high and costs are high; and impurities (such as Pb, Zn, Tl, etc.) are difficult to separate deeply.

[0003] While ultrasonic-enhanced electrolysis can yield cadmium with a purity of approximately 4N, this is still insufficient to meet the demands of high-end applications, thus requiring further purification methods. Vacuum distillation, based on the vapor pressure differences between different elements, offers advantages such as high separation efficiency, strong continuity, and excellent impurity removal capabilities, making it an effective method for preparing 5N-grade cadmium. Summary of the Invention

[0004] The purpose of this invention is to provide a vacuum distillation purification method for high-purity cadmium. By controlling segmented distillation and zoned condensation, the method effectively separates low-boiling-point impurities, high-boiling-point impurities, and cadmium, thereby stably obtaining high-purity cadmium with a purity ≥99.999%.

[0005] One of the technical solutions of this invention is achieved through the following measures: a vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium, characterized by the following steps: Step 1: The 4N grade cadmium raw material obtained by ultrasonic-enhanced electrolysis is pretreated by heating and melting under an inert atmosphere to remove surface oxides and volatile impurities; Step 2: Load the pretreated cadmium into the evaporation zone of the vacuum distillation apparatus, seal the system, and evacuate to 10°C. -2 ~10 -4 Pa; Step 3: Perform zoned temperature control on the vacuum distillation apparatus, so that the temperature of the evaporation zone is controlled at 450~650℃, the temperature of the distillation zone is controlled at 350~500℃, and the temperature of the condensation zone is controlled at 250~320℃. Step 4: Under the above temperature and vacuum conditions, cadmium is heated and evaporated, so that the cadmium vapor undergoes multi-stage gas-liquid mass transfer separation in the rectification zone. High-boiling-point impurities are retained in the evaporation zone, while medium-volatile impurities are retained in the rectification zone. Step 5: The cadmium vapor entering the condensation zone is condensed and deposited, and the condensation products are collected to obtain 5N grade high-purity cadmium; Step 6: Depending on the purity requirements, the obtained cadmium is purified by vacuum distillation once or multiple times.

[0006] To further explain, ultrasonic waves with a frequency of 20~40kHz are introduced during the ultrasonic-enhanced electrolysis process to reduce concentration polarization and improve the purity of electrolyzed cadmium to ≥99.99%.

[0007] To further explain, the pretreatment temperature in step 1 is 350~450℃, and the holding time is 0.5~2 hours.

[0008] To further clarify, the vacuum degree mentioned in step 2 is preferably 1×10⁻⁶. -3 ~5×10 -3 Pa.

[0009] To further explain, the preferred temperature of the evaporation zone in step 3 is 550~620℃.

[0010] To further explain, the preferred temperature of the condensation zone in step 3 is 270~300℃, in order to suppress the co-deposition of impurities.

[0011] To further explain, the reflux ratio during the distillation process is 1:1 to 5:1 to improve separation efficiency.

[0012] To further clarify, the distillation time is 4 to 12 hours.

[0013] This invention discloses a vacuum distillation method for preparing 5N grade high-purity cadmium from 4N grade cadmium. This method employs a segmented distillation strategy, resulting in more thorough separation of low-boiling-point and high-boiling-point impurities. It avoids cadmium solidification and blockage in the condenser tubes through zoned temperature-controlled condensation. The method clarifies the separation mechanism of high-boiling-point impurities remaining in the residue, improving the technical rationality. It can stably obtain high-purity cadmium with a purity ≥99.999%. The process is highly continuous and suitable for large-scale industrial production. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the vacuum distillation apparatus of the present invention. Detailed Implementation

[0015] This invention is not limited to the following embodiments; specific implementation methods can be determined according to the technical solution of this invention and actual circumstances. The invention will be further described below with reference to embodiments: Implementation Case 1 4N grade cadmium with a purity of 99.99% obtained by ultrasonic-enhanced electrolysis will be used as raw material for future use. First, the above-mentioned 4N grade cadmium was pretreated under an inert atmosphere (argon) by heating the cadmium to 380°C and holding it at that temperature for 1 hour to remove surface oxides and low-boiling-point volatile impurities. Then, the pretreated cadmium was added to the evaporation zone of a quartz vacuum distillation apparatus, with a loading of 2 kg, and the apparatus was sealed. A vacuum was then created by combining a mechanical pump and a molecular pump, achieving a vacuum level of 5 × 10⁻⁶. -3 Pa; Next, the vacuum distillation unit was heated in zones, with the evaporation zone temperature set at 580℃, the distillation zone temperature set at 420℃, and the condensation zone temperature set at 290℃. Quartz packing was also added to the distillation zone to enhance gas-liquid contact. Under the above conditions, vacuum distillation was carried out, with the reflux ratio controlled at 3:1 and the distillation time at 8 hours. Cadmium was evaporated in the evaporation zone to form metal vapor, and multi-stage gas-liquid separation was carried out in the distillation zone. High-boiling-point impurities Pb and Bi were retained in the evaporation zone, while medium-volatile impurities Zn and Tl were retained in the distillation zone. Subsequently, the purified cadmium vapor enters the condensation zone and condenses and deposits at 290°C to form a high-purity cadmium crystalline layer; After distillation, the cadmium deposited in the condensation zone was removed and collected under an inert atmosphere to obtain a high-purity cadmium product. Finally, the obtained cadmium was analyzed for its composition. The results showed that the cadmium purity reached 99.9990%, the Pb content was less than 1 ppm, the Zn content was less than 2 ppm, and the metal recovery rate was 96%.

[0016] Implementation Case 2 Using 4N grade cadmium with a purity of 99.99% as raw material, the materials were treated under the same pretreatment conditions. The loading amount is 2kg, and the vacuum distillation unit is evacuated to 1×10⁻³Pa; The evaporation zone temperature was controlled at 620℃, the rectification zone temperature at 450℃, the condensation zone temperature at 270℃, the reflux ratio at 4:1, and the rectification time at 10 hours. After the first distillation, the obtained cadmium was subjected to a second vacuum distillation process. The final product was high-purity cadmium with a purity of 99.9995%.

Claims

1. A vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium, characterized in that... Follow these steps in sequence: Step 1: The 4N grade cadmium raw material obtained by ultrasonic-enhanced electrolysis is pretreated by heating and melting under an inert atmosphere to remove surface oxides and volatile impurities; Step 2: Load the pretreated cadmium into the evaporation zone of the vacuum distillation apparatus, seal the system, and evacuate to 10°C. -2 ~10 -4 Pa; Step 3: Perform zoned temperature control on the vacuum distillation apparatus, so that the temperature of the evaporation zone is controlled at 450~650℃, the temperature of the distillation zone is controlled at 350~500℃, and the temperature of the condensation zone is controlled at 250~320℃. Step 4: Under the above temperature and vacuum conditions, cadmium is heated and evaporated, so that the cadmium vapor undergoes multi-stage gas-liquid mass transfer separation in the rectification zone. High-boiling-point impurities are retained in the evaporation zone, while medium-volatile impurities are retained in the rectification zone. Step 5: The cadmium vapor entering the condensation zone is condensed and deposited, and the condensation products are collected to obtain 5N grade high-purity cadmium; Step 6: Depending on the purity requirements, the obtained cadmium is purified by vacuum distillation once or multiple times.

2. The vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium according to claim 1, characterized in that, The ultrasonic-enhanced electrolysis process introduces ultrasonic waves with a frequency of 20~40kHz to reduce concentration polarization and improve the purity of electrolyzed cadmium to ≥99.99%.

3. The method according to claim 1, characterized in that, The pretreatment temperature in step 1 is 350~450℃, and the holding time is 0.5~2 hours.

4. The vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium according to claim 1, characterized in that, The vacuum degree mentioned in step 2 is preferably 1×10⁻⁶. -3 ~5×10 -3 Pa.

5. The vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium according to claim 1, characterized in that, In step 3, the preferred temperature for the evaporation zone is 550~620℃.

6. The vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium according to claim 1, characterized in that, In step 3, the preferred temperature of the condensation zone is 270~300℃ to suppress the co-deposition of impurities.

7. The vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium according to claim 1, characterized in that, The reflux ratio during the distillation process is 1:1 to 5:1 to improve separation efficiency.

8. The vacuum distillation method for preparing 5N high-purity cadmium from 4N-grade cadmium according to claim 1, characterized in that, The distillation time is 4 to 12 hours.

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