A method for purifying high-purity cadmium by suspension zone melting
By employing a two-stage zone melting process and high-purity protective gas treatment, the problem of the traditional zone melting method being unable to deeply purify cadmium has been solved. This process achieves efficient separation of coarse and trace impurities, resulting in high-purity cadmium suitable for infrared detection, nuclear radiation detection, and aerospace photovoltaic applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGXI UNIV
- Filing Date
- 2026-05-12
- Publication Date
- 2026-06-19
AI Technical Summary
Existing technologies cannot stably obtain 6N-grade high-purity cadmium through traditional zone melting methods, and cannot effectively remove coarse and trace impurities, resulting in low purification efficiency and insufficient purity.
A two-stage zone melting process is adopted. The primary zone melting rapidly separates coarse impurities, while the secondary zone melting precisely removes trace impurities. Combined with high-purity protective gas and controlled heating parameters, it is ensured that cadmium is not oxidized during the smelting process in the suspended zone. Surface contaminants are removed through mechanical processing and anhydrous ethanol treatment.
It achieves efficient separation of coarse and trace impurities, stably obtaining 99.9999% 6N grade high-purity cadmium. It has high purification efficiency, low energy consumption, and is suitable for industrial mass production.
Smart Images
Figure CN122235486A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of high-purity metal purification technology, specifically relating to a method for smelting and purifying high-purity 6N cadmium in a suspension zone, which is particularly suitable for purifying 5N-grade high-purity cadmium to 99.9999% (6N) grade ultra-high-purity cadmium. Background Technology
[0002] Cadmium is a key raw material in infrared detection, nuclear radiation detection, and aerospace photovoltaics. Cadmium zinc telluride detectors and cadmium telluride thin-film batteries both require ultra-high purity cadmium as a raw material. With the development of high-end devices, the requirements for cadmium purity are becoming increasingly stringent, and 6N-grade products have become a necessity in high-end fields.
[0003] Currently, high-purity cadmium purification mainly involves vacuum distillation, electrolysis, and traditional zone melting. Vacuum distillation has limited removal capabilities for impurities with similar vapor pressures; electrolysis suffers from hydrogen evolution and electrolyte contamination; traditional zone melting uses limited parameters, making it difficult to deeply remove trace impurities and consistently obtain 6N-grade products. Optimizing the zone melting process to achieve efficient separation of trace impurities is a pressing technical challenge in this field. Summary of the Invention
[0004] The technical solution of this invention is achieved through the following measures: A method for purifying high-purity 6N cadmium through suspension zone melting, characterized by the following steps: Step 1: Raw material pretreatment: Select high-purity cadmium with a purity ≥99.999% (5N) as raw material, and process it into rod-shaped blanks with a diameter of 20-30mm and a length of 100-150mm through mechanical processing. Wipe the surface with anhydrous ethanol to remove the surface oxide layer, oil and contaminants, and dry it for later use to avoid the introduction of impurities that may affect the purification effect. Step 2: Charging and Atmosphere Protection: The pretreated rod-shaped billet is loaded into a sealed quartz tube, and both ends of the billet are firmly fixed to ensure stable position during the melting process; a high-purity protective gas is introduced into the quartz tube, which can be one of high-purity argon, nitrogen or hydrogen, with the gas flow rate controlled at 1.0-1.5 L / min, and bubbled continuously for 15-20 min to purge the air and oxygen inside the tube. Then, a positive pressure (0.105-0.110 MPa) is maintained inside the quartz tube to prevent cadmium from being oxidized at high temperatures; Step 3: Primary Zone Melting: Turn on the zone melting device and adjust the heating system to form a local melting zone with a width of 25-60mm. Control the temperature of the melting zone at 350-450℃ to ensure that cadmium remains in a stable molten state and avoids violent evaporation. At a uniform speed of 20-40mm / h, slowly advance the melting zone from one end of the rod-shaped billet with cadmium seed crystals to the other end to complete one primary zone melting. Repeat the above primary zone melting process 2-7 times. Utilize the difference in segregation of impurities in the solid and liquid phases to gradually enrich coarse impurities such as lead, copper, and iron towards the end of the melting zone, achieving the initial separation of coarse impurities. Step 4: Secondary Zone Melting: After the primary zone melting is completed, the width of the heating zone is reduced to 15-35mm to further improve the temperature control accuracy of the melting zone. The moving speed of the melting zone is reduced to 10-30mm / h to allow the melting zone to advance stably along the billet axis at a slower speed, thereby enhancing the segregation effect of trace impurities. This secondary zone melting process is repeated 1-6 times to remove residual trace impurities such as boron, selenium, and tellurium from the raw materials, thereby further improving the purity of the product. Step 5: Post-processing: After the secondary zone melting is completed, the heating device is turned off, and the protective gas is continuously introduced to allow the billet to cool naturally to room temperature under an inert atmosphere. After cooling, 15-25% of the impurity-rich section at the tail end of the billet is cut off by wire cutting. The remaining part is the 6N grade (99.9999%) high-purity cadmium product. According to the test, the total cadmium recovery rate of this method is ≥88%.
[0005] This invention solves the problem of traditional zone melting's difficulty in balancing purification efficiency and depth by using a two-stage zone melting coupled process. The primary zone melting rapidly separates coarse impurities and improves purification efficiency, while the secondary zone melting precisely removes trace impurities and ensures purity. This step-by-step process achieves efficient separation of coarse and trace impurities, stably obtaining 6N-grade products that meet the requirements of high-end fields. Moreover, the process is simple to operate, has low energy consumption, and can be industrialized for mass production, demonstrating significant practical value. Attached Figure Description
[0006] Figure 1 is a process flow diagram of a method for smelting and purifying high-purity cadmium in a suspension zone according to the present invention.
Claims
1. A method for purifying high-purity cadmium through suspension zone melting, characterized in that, Follow these steps in sequence: Step 1: Pre-treatment of raw materials: Select high-purity cadmium with a purity of 99.999% (5N) as raw material, process it into rod-shaped blanks, remove the surface oxide layer and contaminants, and obtain cadmium rods to be purified; Step 2: Loading and Atmosphere Protection: Load the pretreated cadmium rod into a high-purity quartz boat and push it into a sealed quartz tube; first, purge the air in the tube with a high-purity protective gas at a flow rate of 1.0-1.5 L / min for 20-30 min; during the process, continuously purge the protective gas to maintain a positive pressure environment and prevent oxidation contamination. Step 3: Primary Suspension Zone Melting: Turn on the zone melting device to form a local melting zone; using a heating zone with a width of 25-60mm, move the cadmium rod with seed crystal steadily from one end to the other at a moving speed of 20-40mm / h to complete a single zone melting process; repeat this stage 2-7 times, with the melting zone temperature controlled at 350-450℃, and use the impurity segregation effect to achieve preliminary impurity separation, so that the impurities are enriched at the end of the rod; Step 4: Secondary Suspension Zone Melting: After completing the primary zone melting, adjust the heating device parameters, reduce the width of the heating zone to 15-35mm, and reduce the moving speed of the melting zone to 10-30mm / h; repeat this stage 1-6 times, maintain the melting zone temperature at 350-450℃, further enhance the mass transfer efficiency of impurity segregation, and deeply remove residual trace impurities. Step 5: Post-processing and product acquisition: After zone melting, the cadmium rod is cooled to room temperature, and 15-25% of the impurity-enriched section at the tail end is cut off to obtain purified cadmium ingots. The purity of the product reaches 99.9999% (6N) or higher by glow discharge mass spectrometry, with the total content of key impurity elements ≤1ppm, Fe≤0.05ppm, Cu≤0.03ppm, Pb≤0.05ppm, Zn≤0.05ppm, and S≤0.05ppm.
2. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, In step 2, the protective gas is one or a mixture of high-purity argon, nitrogen, or hydrogen, with a purity of ≥99.999%. It must be purified by a purifier before use, with a dew point below -70℃ and an oxygen content below 0.1ppm to prevent cadmium oxidation at high temperatures.
3. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, In step 3, the width of the heating zone in the primary melting zone is preferably 30-50 mm, the melting zone moving speed is preferably 25-35 mm / h, and the melting zone is preferably repeated 3-5 times to achieve efficient separation of coarse impurities.
4. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, In step 3, the melting zone temperature of the primary melting zone is preferably 380-420℃, which is slightly higher than the melting point of cadmium, 321℃, to ensure stable melting of cadmium and avoid excessive volatilization loss of cadmium.
5. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, In step 4, the width of the heating zone in the secondary zone melting is preferably 20-30 mm, the moving speed of the melting zone is preferably 15-25 mm / h, and the number of zone melting repetitions is preferably 2-4 times, so as to enhance the removal of trace impurities through segregation.
6. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, In step 1, the raw material pretreatment process includes: vacuum remelting 5N grade cadmium ingots and casting them into rod-shaped billets with a diameter of 10-20mm, removing the surface oxide layer by pickling, washing with deionized water 3-5 times, and drying for later use.
7. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, In step 5, the removal ratio of the impurity-enriched segment is adjusted according to the number of zone meltings. When the total number of zone meltings is ≥8, 20-25% of the segment at the tail end is removed to ensure that the impurities are completely removed.
8. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, Step 5 is followed by a product testing step: glow discharge mass spectrometry is used to detect the content of more than 70 impurity elements in the product, including Li, Be, B, Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Th, and U, to ensure that the total content of all impurity elements is ≤1ppm and the product purity reaches the 6N grade standard.
9. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, Throughout the entire process, the total cadmium recovery rate is ≥88%, and the steps are closely linked, enabling continuous industrial production.
10. The method for purifying high-purity 6N cadmium by suspension zone melting according to claim 1, characterized in that, The method can flexibly prepare cadmium products of different purities (5N-7N) by adjusting the number of zone melting cycles and process parameters according to downstream application needs, adapting to the application requirements of different scenarios such as infrared detection, nuclear radiation detection, and aerospace photovoltaics.