Vacuum distillation and zone melting combined purification method of high-purity tin

Abstract

This invention discloses a combined vacuum distillation and zone melting method for purifying high-purity tin, belonging to the field of high-purity metal purification technology. The method comprises four progressive steps: primary vacuum distillation, primary zone melting, secondary vacuum distillation, and secondary zone melting. 4N crude tin is first vacuum distilled to obtain 5N distilled tin, then zone melted to obtain 6N zone-melted tin, followed by secondary vacuum distillation to obtain 6N5 high-purity tin. Finally, secondary zone melting is performed, and the impurity enrichment end is removed to obtain a high-purity tin product with a purity ≥7N. This invention achieves step-by-step targeted removal of impurities with different vapor pressures and segregation coefficients through deep synergy between distillation and zone melting, combined with refined control techniques such as gradient temperature distillation, variable temperature segmented condensation, and ingot-turning zone melting. This breaks through the purification limits of single methods, while the enrichment end is returned to the front end for recycling. It features high product purity, good overall recovery rate, and suitability for industrial production.

Description

Technical Field

[0001] This invention relates to the field of high-purity tin purification technology, specifically a method for the combined purification of high-purity tin by vacuum distillation and zone melting. Background Technology

[0002] High-purity tin is a key basic material in semiconductor packaging, superconducting material preparation, and integrated circuit interconnection. As high-end applications place increasingly stringent requirements on material purity, the demand for 7N-grade (purity ≥99.99999%) ultra-high purity tin is becoming increasingly urgent.

[0003] Currently, the main methods for purifying high-purity tin include vacuum distillation and zone melting. Vacuum distillation utilizes the vapor pressure difference between tin and impurity elements, allowing tin to preferentially volatilize and separate from high-boiling-point impurities under high-temperature and high-vacuum conditions, effectively removing non-volatile metals such as iron and nickel. Zone melting, on the other hand, is based on the segregation effect of impurities in the solid-liquid two-phase system. Through repeated movement of the molten zone, impurities are directionally migrated and enriched towards the ingot end, making it particularly effective for removing impurities with a distribution coefficient deviating from 1.

[0004] However, single purification methods have significant limitations in practical applications. Vacuum distillation is insufficient for separating impurities with vapor pressures close to tin (such as lead and bismuth), and even with multiple distillations, it is difficult to consistently achieve a purity above 6N. Zone melting can enrich and remove some impurities, but it is inefficient when processing large quantities of high-content impurities, and its ability to remove impurities with segregation coefficients close to 1 (such as iron and nickel) is extremely weak. Relying on only one method often requires more than ten repetitions, resulting in high energy consumption, long production cycles, and product purity hovering around the 6N level for a long time, making it difficult to break through to the 7N level.

[0005] To address the aforementioned technical bottlenecks, this invention proposes a combined purification method for high-purity tin using vacuum distillation and zone melting. Summary of the Invention

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

[0007] This invention provides a method for the combined purification of high-purity tin through vacuum distillation and zone melting, comprising the following steps:

[0008] S1 Single Vacuum Distillation: Crude tin raw material with a purity of 4N is placed in a vacuum distillation furnace and subjected to a vacuum of 1×10⁻⁶. -3 Up to 5×10 -2 A vacuum distillation is carried out under conditions of Pa and temperature of 1100 to 1300℃ to volatilize and collect the tin, thereby obtaining distilled tin with a purity of 5N, while separating and removing high-boiling-point impurities.

[0009] S2 First-stage zone melting: After casting the distilled tin ingot obtained in step S1, the zone melting is carried out 5 to 8 times under a protective atmosphere. The width of the melting zone is 8% to 15% of the ingot length, and the moving speed of the melting zone is 2 to 8 mm / h, so that impurities are enriched at the ingot end. The impurity enriched end is cut off to obtain a first-stage zone melting tin with a purity of 6N.

[0010] S3 Secondary Vacuum Distillation: The primary zone-melted tin obtained in step S2 is placed again in a vacuum distillation furnace at a vacuum degree of 5×10⁻⁶. -4 Up to 1×10 -2 A second vacuum distillation was carried out under conditions of Pa and temperature of 1050 to 1200℃ to further remove residual trace amounts of high-boiling-point and low-boiling-point impurities, resulting in a high-purity tin product with a purity of 6N5.

[0011] S4 Secondary Zone Melting: After casting the high-purity tin product with a purity of 6N5 obtained in step S3 into an ingot, it is subjected to 3 to 5 zone meltings under a protective atmosphere. The width of the melting zone is 5% to 10% of the ingot length, and the melting zone moving speed is 1 to 3 mm / h. The impurity enriched end is cut off to obtain a high-purity tin product with a purity of 7N and above.

[0012] As a preferred technical solution of the present invention, the vacuum distillation furnace in step S1 is a multi-stage tray vacuum distillation furnace with 3 to 6 tray stages, and the crude tin raw material is acid-washed to remove the surface oxide layer before distillation.

[0013] As a preferred technical solution of the present invention, the condensation collection temperature in step S1 is 350 to 500°C, and a staged condensation method is adopted, first collecting high-boiling-point impurity condensate in the first condensation zone, and then collecting target tin condensate in the second condensation zone.

[0014] As a preferred technical solution of the present invention, the protective atmosphere in step S2 is high-purity argon gas with a purity of not less than 99.999%, and the boat used for zone melting is a high-purity graphite boat or a high-purity quartz boat. The boat is acid-washed and high-temperature vacuum baked before use.

[0015] As a preferred technical solution of the present invention, in step S2, the melting zone moving speed of the zone melting is 2 to 3 mm / h at the beginning and end, and 5 to 8 mm / h in the middle pass. The ingot is flipped up and down between each pass so that impurities are symmetrically enriched at both ends of the ingot.

[0016] As a preferred technical solution of the present invention, in step S2, the length of the impurity enriched end to be cut off is 10% to 20% of the total length of the ingot, and the cut-off end is returned to step S1 as crude tin raw material for vacuum distillation again.

[0017] As a preferred technical solution of the present invention, the secondary vacuum distillation in step S3 adopts a gradient heating method. First, the temperature is raised to 800 to 900°C at a rate of 5 to 8°C / min and held for 20 to 40 min to remove low-boiling-point impurities. Then, the temperature is raised to 1050 to 1200°C at a rate of 3 to 5°C / min to allow the tin to volatilize and be condensed and collected.

[0018] As a preferred technical solution of the present invention, the condensation and collection of the secondary vacuum distillation in step S3 adopts a variable temperature segmented condensation method, collecting the main tin condensate in the 350 to 400°C range and collecting the trace amounts of high-boiling-point impurities that may be entrained in the 400 to 450°C range, thereby achieving secondary deep separation.

[0019] As a preferred technical solution of the present invention, in step S4, the melting zone moving rate of the secondary zone melting is 1 to 1.5 mm / h at the beginning and end, and 2 to 3 mm / h in the middle pass. The ingot is rotated 180° axially between every two passes so that the residual impurities are fully and symmetrically enriched at both ends.

[0020] As a preferred technical solution of the present invention, in step S4, the length of the impurity enriched end to be cut off is 8% to 12% of the total length of the ingot. The cut-off end is returned to step S1 as crude tin raw material for vacuum distillation again, thereby realizing the closed-loop recycling of materials.

[0021] As a preferred technical solution of the present invention, in the regional melting process described in steps S2 and S4, the heating method of the melting zone adopts high-frequency induction heating, and the temperature fluctuation is controlled within ±1℃ to ensure the stability of the melting zone width and temperature field.

[0022] The beneficial effects of this invention are as follows: This method for combined vacuum distillation and zone melting of high-purity tin organically combines vacuum distillation and zone melting. Through a four-stage progressive purification path of "primary distillation - zone melting - secondary distillation - secondary zone melting," and refined control techniques such as gradient temperature distillation, variable temperature segmented condensation, and ingot-turning zone melting, it overcomes the bottleneck of poor separation of impurities with similar vapor pressures or similar segregation coefficients achieved by single methods. The steps are synergistic and complementary: primary distillation removes high-boiling-point impurities, primary zone melting enriches and removes impurities with segregation coefficients deviating from 1, secondary distillation deeply removes residual high and low-boiling-point impurities, and secondary zone melting refines and removes residual trace impurities. Ultimately, a high-purity tin product with a purity ≥7N can be obtained. Simultaneously, the enriched end is returned to the front end for recycling, improving the overall tin recovery rate. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0024] Figure 1This is a process flow diagram of a method for the combined purification of high-purity tin by vacuum distillation and zone melting according to the present invention. Detailed Implementation

[0025] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] Example 1: As Figure 1 As shown, a method for purifying high-purity tin by a combination of vacuum distillation and zone melting includes the following steps:

[0027] A method for combined vacuum distillation and zone melting purification of high-purity tin includes the following steps:

[0028] S1 Single Vacuum Distillation: Crude tin raw material with a purity of 4N is placed in a vacuum distillation furnace and subjected to a vacuum of 1×10⁻⁶. -3 Up to 5×10 -2 A vacuum distillation is carried out under conditions of Pa and temperature of 1100 to 1300℃ to volatilize and collect the tin, thereby obtaining distilled tin with a purity of 5N, while separating and removing high-boiling-point impurities.

[0029] S2 First-stage zone melting: After casting the distilled tin ingot obtained in step S1, the zone melting is carried out 5 to 8 times under a protective atmosphere. The width of the melting zone is 8% to 15% of the ingot length, and the moving speed of the melting zone is 2 to 8 mm / h, so that impurities are enriched at the ingot end. The impurity enriched end is cut off to obtain a first-stage zone melting tin with a purity of 6N.

[0030] S3 Secondary Vacuum Distillation: The primary zone-melted tin obtained in step S2 is placed again in a vacuum distillation furnace at a vacuum degree of 5×10⁻⁶. -4 Up to 1×10 -2 A second vacuum distillation was carried out under conditions of Pa and temperature of 1050 to 1200℃ to further remove residual trace amounts of high-boiling-point and low-boiling-point impurities, resulting in a high-purity tin product with a purity of 6N5.

[0031] S4 Secondary Zone Melting: After casting the high-purity tin product with a purity of 6N5 obtained in step S3 into an ingot, it is subjected to 3 to 5 zone meltings under a protective atmosphere. The width of the melting zone is 5% to 10% of the ingot length, and the melting zone moving speed is 1 to 3 mm / h. The impurity enriched end is cut off to obtain a high-purity tin product with a purity of 7N and above.

[0032] The vacuum distillation furnace mentioned in step S1 is a multi-stage tray vacuum distillation furnace with 3 to 6 tray stages. The crude tin raw material is acid-washed to remove the surface oxide layer before distillation.

[0033] In step S1, the condensation collection temperature is 350 to 500°C, and a staged condensation method is adopted. First, high-boiling-point impurity condensates are collected in the first condensation zone, and then the target tin condensates are collected in the second condensation zone.

[0034] The protective atmosphere described in step S2 is high-purity argon gas with a purity of not less than 99.999%. The boat used for zone melting is a high-purity graphite boat or a high-purity quartz boat. The boat is acid-washed and high-temperature vacuum baked before use.

[0035] In step S2, the melting zone moving rate of the zone melting is 2 to 3 mm / h at the beginning and end, and 5 to 8 mm / h in the middle pass. The ingot is flipped up and down between each pass so that impurities are symmetrically enriched at both ends of the ingot.

[0036] In step S2, the length of the impurity-rich end to be cut off is 10% to 20% of the total length of the ingot. The cut-off end is returned to step S1 as crude tin raw material for vacuum distillation again.

[0037] In step S3, the secondary vacuum distillation adopts a gradient heating method. First, the temperature is raised to 800 to 900℃ at a rate of 5 to 8℃ / min and held for 20 to 40 min to remove low-boiling-point impurities. Then, the temperature is raised to 1050 to 1200℃ at a rate of 3 to 5℃ / min to allow the tin to volatilize and be condensed and collected.

[0038] In step S3, the condensation and collection of the secondary vacuum distillation adopts a variable temperature segmented condensation method. The main tin condensate is collected in the 350 to 400°C range, and trace amounts of high-boiling-point impurities that may be entrained are collected in the 400 to 450°C range.

[0039] In step S4, the melting zone moving rate of the secondary zone melting is 1 to 1.5 mm / h at the first and last two passes, and 2 to 3 mm / h in the middle pass. The ingot is rotated 180° axially between every two passes.

[0040] In step S4, the length of the impurity-enriched end to be cut off is 8% to 12% of the total length of the ingot. The cut-off end is returned to step S1 as crude tin raw material for vacuum distillation again.

[0041] In the zone melting process described in steps S2 and S4, the heating method of the melting zone adopts high-frequency induction heating, and the temperature fluctuation is controlled within ±1℃.

[0042] Specific experimental conditions in Example 1

[0043] Single vacuum distillation: Take 500g of crude tin raw material with a purity of 4N, remove the surface oxide layer by acid washing, and place it in a multi-stage tray vacuum distillation furnace with 5 tray stages and a vacuum degree of 8×10⁻⁶. -3Pa, distillation temperature 1200℃, condensation collection temperature 420℃, staged condensation, the first condensation zone removes high-boiling-point impurities, the second condensation zone collects the target tin condensate, the evaporation rate is controlled to make the direct tin recovery rate 93.2%, and distilled tin with a purity of 5N2 is obtained.

[0044] First-stage zone melting: Distilled tin ingots are cast into 300mm long ingots and placed in high-purity graphite boats that have been pickled and baked at high temperature and vacuum. 99.999% high-purity argon gas is introduced for protection, and seven zone meltings are carried out. The width of the melting zone is 12% of the ingot length. The melting zone movement rate is 2.5 mm / h for the first and last two melting zones and 6 mm / h for the middle five melting zones. The ingot is flipped up and down between each pass, and the impurity-rich ends, which account for 15% of the ingot length, are cut off at both ends to obtain 6N1 pure first-stage zone-melted tin.

[0045] Secondary vacuum distillation: The primary zone-melted tin is placed in a vacuum distillation furnace, and a gradient heating method is used. First, the temperature is increased to 850℃ at 6℃ / min and held for 30min to remove low-boiling-point impurities. Then, the temperature is increased to 1150℃ at 4℃ / min, with a vacuum degree of 2×10⁻⁶. -3 Pa uses variable temperature segmented condensation, collecting the main tin condensate in the 370℃ segment and the tail gas condensate in the 420℃ segment to obtain high-purity tin with a purity of 6N5.

[0046] Secondary zone melting: The secondary distilled tin ingot is cast into a 250mm long ingot and subjected to four zone melting processes under a protective atmosphere. The width of the melting zone is 7% of the ingot length. The melting rate is 1.2 mm / h for the first and last two melting processes and 2.5 mm / h for the middle two melting processes. The ingot is flipped between every two passes, and the enriched ends, each accounting for 10% of the ingot length, are cut off. The final product is analyzed by glow discharge mass spectrometry (GDMS) and the total impurity content is <0.08 ppm, with a purity of 99.999992% (7N2).

[0047] Compare with Example 1

[0048] Vacuum distillation (triple distillation, without zone melting) was used, with all other conditions the same as in the previous example. The final product contained 0.5 ppm of lead and 0.35 ppm of bismuth, with a purity of only 5N8, which could not reach 7N.

[0049] Compare with Example 2

[0050] Only zone melting (12 melting cycles, without distillation pretreatment) was used, with all other conditions remaining the same. The final product contained 0.7 ppm of iron and 1.0 ppm of nickel, with a purity of only 5N5, and the total process time was nearly twice that of the previous example. The experimental data are shown in the table below:

[0051]

[0052] The experimental data shows that Example 1 uses a four-stage combined process of "single distillation-zone melting-secondary distillation-secondary zone melting" to achieve a product purity of 7N2. High-boiling-point impurities such as iron and nickel, as well as impurities with vapor pressures similar to tin such as lead and bismuth, are effectively removed to the ppb level.

[0053] Compared with Example 1, which relies solely on three vacuum distillations, the separation effect of impurities such as lead and bismuth with vapor pressures close to tin is poor, and the product purity is only 5N8, which cannot meet the high purity requirements.

[0054] Compared with Example 2, which relies solely on multiple zone melting processes, although it has a certain enrichment and removal effect on lead and bismuth, it does not completely remove impurities such as iron and nickel with segregation coefficients close to 1. Even after 12 zone melting processes, the product purity is only 5N5, and the multiple operations are energy-intensive and time-consuming.

[0055] Experimental results show that the combined method of the present invention fully leverages the synergistic advantages of distillation and zone melting, and is significantly superior to single methods in terms of comprehensive impurity removal capability and product purity, successfully achieving stable preparation of 7N grade high-purity tin.

[0056] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for combined vacuum distillation and zone melting purification of high-purity tin, characterized in that, Includes the following steps: S1 Single Vacuum Distillation: Crude tin raw material with a purity of 4N is placed in a vacuum distillation furnace and subjected to a vacuum of 1×10⁻⁶. -3 Up to 5×10 -2 A vacuum distillation is carried out under conditions of Pa and temperature of 1100 to 1300℃ to volatilize and collect the tin, thereby obtaining distilled tin with a purity of 5N, while separating and removing high-boiling-point impurities. S2 First-stage zone melting: After casting the distilled tin ingot obtained in step S1, the zone melting is carried out 5 to 8 times under a protective atmosphere. The width of the melting zone is 8% to 15% of the ingot length, and the moving speed of the melting zone is 2 to 8 mm / h, so that impurities are enriched at the ingot end. The impurity enriched end is cut off to obtain a first-stage zone melting tin with a purity of 6N. S3 Secondary Vacuum Distillation: The primary zone-melted tin obtained in step S2 is placed again in a vacuum distillation furnace at a vacuum degree of 5×10⁻⁶. -4 Up to 1×10 -2 A second vacuum distillation was carried out under conditions of Pa and temperature of 1050 to 1200℃ to further remove residual trace amounts of high-boiling-point and low-boiling-point impurities, resulting in a high-purity tin product with a purity of 6N5. S4 Secondary Zone Melting: After casting the high-purity tin product with a purity of 6N5 obtained in step S3 into an ingot, it is subjected to 3 to 5 zone meltings under a protective atmosphere. The width of the melting zone is 5% to 10% of the ingot length, and the melting zone moving speed is 1 to 3 mm / h. The impurity enriched end is cut off to obtain a high-purity tin product with a purity of 7N and above.

2. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, The vacuum distillation furnace mentioned in step S1 is a multi-stage tray vacuum distillation furnace with 3 to 6 tray stages. The crude tin raw material is acid-washed to remove the surface oxide layer before distillation.

3. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, In step S1, the condensation collection temperature is 350 to 500°C, and a staged condensation method is adopted. First, high-boiling-point impurity condensates are collected in the first condensation zone, and then the target tin condensates are collected in the second condensation zone.

4. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, The protective atmosphere described in step S2 is high-purity argon gas with a purity of not less than 99.999%. The boat used for zone melting is a high-purity graphite boat or a high-purity quartz boat. The boat is acid-washed and high-temperature vacuum baked before use.

5. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, In step S2, the melting zone moving rate of the zone melting is 2 to 3 mm / h at the beginning and end, and 5 to 8 mm / h in the middle pass. The ingot is flipped up and down between each pass so that impurities are symmetrically enriched at both ends of the ingot.

6. The method according to claim 1, wherein the vacuum distillation and zone melting combined purification method of high purity tin is characterized by, In step S2, the length of the impurity-rich end to be cut off is 10% of the total ingot length. 20% of the cut-off end is returned to step S1 as crude tin raw material for vacuum distillation again.

7. The method according to claim 1, wherein the vacuum distillation and zone melting combined purification method of high purity tin is characterized by, In step S3, the secondary vacuum distillation adopts a gradient temperature method, first at 5... Increase from 8℃ / min to 800 900℃ heat preservation for 20 Remove low-boiling-point impurities in 40 minutes, then use 3 Increase to 1050 at 5℃ / min The tin is evaporated and collected at 1200℃.

8. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, In step S3, the condensation and collection of the secondary vacuum distillation adopts a variable temperature segmented condensation method. The main tin condensate is collected in the 350 to 400°C range, and trace amounts of high-boiling-point impurities that may be entrained are collected in the 400 to 450°C range, thus achieving secondary deep separation.

9. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, In step S4, the melting zone moving speed of the secondary zone melting is 1 to 1.5 mm / h at the first and last two passes, and 2 to 3 mm / h in the middle pass. The ingot is rotated 180° axially between every two passes to ensure that the residual impurities are fully and symmetrically enriched at both ends. In step S4, the length of the impurity-rich end is cut off by 8% to 12% of the total length of the ingot. The cut-off end is returned to step S1 as crude tin raw material for vacuum distillation again, realizing the closed-loop recycling of materials.

10. The method for combined vacuum distillation and zone melting purification of high-purity tin according to claim 1, characterized in that, In the zone melting process described in steps S2 and S4, the heating method of the melting zone adopts high-frequency induction heating, and the temperature fluctuation is controlled within ±1℃ to ensure the stability of the melting zone width and temperature field.

Images