A method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide

Abstract

A method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide comprises the following steps: uniformly mixing chromium trioxide, aluminum granules, and potassium dichromate, and adding the mixture in two batches to a smelting furnace in a vacuum smelting apparatus; adding the first batch of mixed raw materials to the smelting furnace as a base charge, adding an igniter, sealing the vacuum smelting apparatus, and evacuating the furnace; activating an igniter to ignite the igniter and igniting the first batch of mixed raw materials in the smelting furnace; and continuously adding the second batch of mixed raw materials until the first batch of mixed raw materials is molten. Smelting is continued for one minute, followed by filling with protective gas, evacuating with a vacuum pump, and then shutting off the vacuum pump, allowing the temperature to naturally cool to below 600°C. The mixture is then cooled further to below 200°C in a cooling chamber and finished to obtain low-nitrogen, low-gallium, high-purity metallic chromium. Advantages include low cost, a simple and rational process, and the ability to produce low-nitrogen, low-gallium, high-purity metallic chromium in a single step with a high product yield.

Description

Technical Field

[0001] The invention belongs to the field of metallic chromium smelting and relates to a method for producing high-yield and high-purity metallic chromium, in particular to a method for producing low-nitrogen, low-gallium, high-yield and high-purity metallic chromium by utilizing chromium trioxide. Background Art

[0002] Chromium is a lustrous, silvery-white metal with wear, corrosion, and high-temperature resistance. As an alloying additive, chromium combines with nickel, cobalt, and iron to form high-temperature alloys, electrothermal alloys, and precision alloys, finding widespread application in aviation, aerospace, electrical appliances, and instrumentation. With the advancement of projects such as the domestic production of large aircraft and the construction of warships and aircraft carriers, demand for high-purity chromium in the high-temperature alloy industry for high-end components such as engines is growing. Research has shown that even variations in nitrogen and gallium content in high-temperature alloys, even at the ppm level, can significantly impact alloy properties. Gallium has a very low melting point and is liquid at room temperature. Liquid gallium alloys with other metals, dissolving them and causing corrosion. This can lead to poor metallic properties, brittleness, ductility, and mechanical properties. High nitrogen content reduces the mechanical properties of the alloy, significantly diminishing its quality. Consequently, stringent requirements for nitrogen and gallium in high-purity chromium for high-end components are in place, with nitrogen content below 50 ppm and gallium below 100 ppm.

[0003] Currently, there are two main methods for producing high-purity metallic chromium: one is the off-furnace aluminum thermal reduction method. This method produces high-purity metallic chromium with a high nitrogen content, classifying it as low- to medium-end metallic chromium, and the product yield is low. The other is the vacuum furnace carbon reduction method. This method uses low- to medium-end metallic chromium with a high oxygen and other gas content as raw material and further carbonizes the metallic chromium in a vacuum furnace to produce high-purity metallic chromium. CN 102899511A discloses a "method for smelting high-purity metallic chromium using an off-furnace method." The method involves mixing chromium trioxide powder, aluminum powder, and sodium chlorate to obtain a mixed material. The mixed material is then divided into two batches, namely, an early stage material and a late stage material. The off-furnace method is used for smelting. The early stage material is placed in a smelting furnace, smelted, and slag removed. The late stage material and a calcium deoxidizer are then added to the smelting furnace, smelted, and slag removed to obtain low-oxygen, high-purity metallic chromium. This method performs the deoxidation process simultaneously with the smelting of metallic chromium, eliminating the need for additional energy and promoting energy conservation and environmental protection. CaO, Al2O3, SiO2, and Cr2O3 can form low-melting-point composite oxides, which facilitate the removal of combined oxygen from the molten chromium. The metallic calcium gasification process facilitates mass transfer, with the generated CaO·Al2O3(s) floating to the top of the molten metal, allowing the calcium oxide to directly form slag that floats to the slag above the molten metal for removal. This method, a typical off-furnace aluminothermic reduction method, reduces the oxygen content to 0.01% to 0.03%. The chromium produced by this method has a high nitrogen content of 2000 to 5000 ppm, requiring further carbon reduction in a vacuum furnace. CN 112605390 A discloses a method for preparing vacuum-grade, low-nitrogen chromium metal for high-temperature alloys using chromium powder. The method involves cryogenically grinding a chromium block impregnated at low temperatures to obtain chromium powder. The powder is then sprayed with a layer of chromium powder and a layer of graphite powder in a pressing mold using an adhesive as a carrier to produce a chromium powder-graphite powder mixed billet. The chromium powder-graphite powder mixed billet is then pressed into a chromium billet under a protective gas atmosphere. The billet is then placed in a vacuum sintering furnace, sealed and evacuated. After gradient sintering, the billet is air-cooled to room temperature under a protective gas atmosphere to produce vacuum-grade, low-nitrogen chromium metal. This method is a typical vacuum furnace carbon reduction method. While it can remove nitrogen from the chromium metal to a certain extent, the nitrogen content in the final chromium metal exceeds 1000 ppm, which is still very high and cannot meet the demand for high-end components with nitrogen content below 50 ppm. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide. The method uses chromium trioxide as a raw material, has low cost, simple and reasonable process, and can obtain low-nitrogen, low-gallium, high-purity metallic chromium in a one-step process. The method is suitable for use as a high-temperature alloy additive for high-end components and can improve the yield of high-purity metallic chromium products.

[0005] The technical solution of the present invention is:

[0006] A method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide, the specific steps of which are as follows:

[0007] (1) Ingredients

[0008] Chromium trioxide, aluminum particles, and potassium dichromate, a heating agent, are uniformly mixed to obtain a mixed raw material. The mass ratios of chromium trioxide to aluminum particles and potassium dichromate are 100:(50-70) and 100:(30-50), respectively. The mixed raw material is added into a smelting furnace of a vacuum smelting equipment in two batches.

[0009] (2) First batch of feeding

[0010] The first batch of mixed raw materials is added to the smelting furnace as a base material, the amount of the first batch of mixed raw materials added accounts for 1 / 3 to 1 / 2 of the volume of the smelting furnace, and an igniter is added. The igniter is a mixture of sodium chlorate and aluminum particles with a mass ratio of 2:1. The position of the igniter in the vacuum smelting equipment is adjusted so that it is completely buried in the igniter; the remaining mixed raw materials are used as the second batch of mixed raw materials in the silo of the vacuum smelting equipment for standby, ready to be added to the smelting furnace;

[0011] (3) Vacuuming before smelting

[0012] Seal the vacuum smelting equipment, turn on the vacuum pump, evacuate the vacuum smelting equipment until the pressure inside the vacuum smelting equipment is -101kPa ~ -95kPa, and ignite smelting. At this time, the vacuum pump can be turned on or off;

[0013] (4) Vacuum smelting

[0014] Start the igniter to ignite the igniter to ignite the first batch of mixed raw materials in the smelting furnace. The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace. When the first batch of mixed raw materials is in a molten state, open the discharge valve to continuously discharge the second batch of mixed raw materials in the hopper until all the second batch of mixed raw materials enter the smelting furnace. Continue refining for 1 minute, turn off the vacuum pump, and fill with protective gas for 20 minutes to 30 minutes. Then, turn on the vacuum pump to evacuate to the pressure of the vacuum smelting equipment before smelting, turn off the vacuum pump, and fill the vacuum furnace shell with protective gas to cool the smelting furnace. The temperature of the smelting furnace is reduced to below 200°C, and finishing is performed to obtain low-nitrogen and low-gallium high-purity metallic chromium.

[0015] Furthermore, the weight of the second batch of mixed raw materials is more than 1 times that of the first batch of mixed raw materials.

[0016] Furthermore, during the continuous feeding in step (4), the feeding speed is 0.3 t mixed raw material / min to 0.75 t mixed raw material / min.

[0017] Furthermore, the N content in the low-nitrogen and low-gallium high-purity metallic chromium is 5ppm-10ppm, and the Ga content is 60ppm-80ppm.

[0018] Furthermore, the Al content in the low-nitrogen and low-gallium high-purity metallic chromium is 100ppm to 200ppm.

[0019] Furthermore, the mixed raw materials in step (1) have a unit charge reaction heat of 2905 kJ / kg to 3105 kJ / kg.

[0020] Furthermore, the protective gas in step (4) is argon.

[0021] Furthermore, when the smelting furnace is cooled in step (4), the smelting furnace is first cooled to 550°C to 600°C by circulating protective gas; then the smelting furnace is pushed out of the vacuum smelting equipment and sent into a cooling chamber, and compressed air is continued to circulate and cool to below 200°C.

[0022] Beneficial effects of the present invention:

[0023] Chromium trioxide and aluminum particles are used as raw materials, and an appropriate amount of heating agent potassium dichromate is added to ensure smooth vacuum smelting. Sodium chlorate and aluminum particles are used as ignition agents. Without introducing other impurities, the raw materials react completely, resulting in a high yield of high-purity metallic chromium, with a smelting yield of over 90%. No additional heat source is required, the reaction power consumption is low, and the economic benefits are significantly improved. The obtained low-nitrogen and low-gallium high-purity metallic chromium has an N content of 5ppm to 10ppm and a Ga content of 60ppm to 80ppm. The metallic chromium is of high quality and is suitable as a high-temperature alloy additive for high-end components. In addition, no smoke is generated during the production process, and the smelting slag does not contain hexavalent chromium. This is a clean production high-purity metallic chromium technology that reduces emissions and pollution, and is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart of the present invention;

[0025] Figure 2 It is a structural schematic diagram of the high-purity metallic chromium vacuum smelting equipment of the present invention;

[0026] Figure 3 yes Figure 2 sectional view of

[0027] Figure 4 yes Figure 3 Magnified view of part A.

[0028] In the figure: 1-base; 2-vacuum furnace shell; 3-water cooling jacket; 301-water inlet; 302-water outlet; 4-furnace door; 5-insulation layer; 501-metal felt insulation layer; 502-knotted material insulation layer; 6-metal furnace lining; 7-observation window; 8-material table; 9-smelting furnace; 10-material silo; 11-screw feeder; 12-discharge chute; 13-loading scoop; 14-protective cover, 15-vacuum pump; 16-first valve; 17-second valve; 18-third valve; 19-igniter; 20-protective gas inlet hole. DETAILED DESCRIPTION

[0029] The ignition agent used in Examples 1 to 3 of the present invention is a mixture of sodium chlorate and aluminum particles in a mass ratio of 2:1. The specific structure of the high-purity metallic chromium vacuum smelting equipment used in Examples 1 to 3 and Comparative Examples 1 and 2 is as follows:

[0030] like Figures 1 to 3 As shown, the high-purity metallic chromium vacuum smelting equipment comprises a base 1 and a vacuum furnace shell 2 horizontally installed on the base 1, a water-cooling jacket 3 is provided in the vacuum furnace shell 2, a water inlet 301 of the water-cooling jacket 3 is provided at the middle and lower part of the outer wall of the vacuum furnace shell 2, and a water outlet 302 of the water-cooling jacket 3 is provided at the upper part of the outer wall of the vacuum furnace shell 2; a protective gas inlet hole 20 is provided in the circumferential direction of the vacuum furnace shell 2 and perpendicular to the vacuum furnace shell 2, and the protective gas inlet hole 20 is connected to the protective gas source through a pipeline; a furnace door 4 is provided at one end of the vacuum furnace shell 2, and an observation window 7 is provided on the furnace door 4, the observation window 7 is circular and has a diameter of 30 cm, and is used to observe the situation in the smelting furnace 9; a thermal insulation layer 5 is provided on the inner wall of the vacuum furnace shell 2, and the thermal insulation layer 5 is composed of a metal felt insulation layer 501 and a knotted material insulation layer 502 from the outside to the inside, and a metal furnace lining 6 is provided on the inner side of the thermal insulation layer 5;

[0031] An igniter 19 is softly connected to the inner wall of the vacuum furnace shell 2, a charging platform 8 is provided at the bottom of the vacuum furnace shell 2, a smelting furnace 9 is provided on the charging platform 8, the furnace wall of the smelting furnace 9 has a ductile iron layer and a magnesia brick layer with a thickness of 65 mm provided on the inner side of the ductile iron layer, and a protective cover 14 is provided just above the smelting furnace 9 and near the inner wall of the vacuum furnace shell 2; a silo 10 is provided above the vacuum furnace shell 2, and a screw feeder 11 is provided at the discharge port of the silo 10, the screw feeder 11 is connected to the vacuum furnace shell 2 through a discharge chute 12, and the discharge chute 12 passes downward through the protective cover 14, and a charging scoop 13 is installed at the outlet of the discharge chute 12; a second valve 17 is provided on the discharge port of the silo 10, and the second valve 17 in this embodiment is a vacuum valve; a third valve 18 is provided on the discharge port of the screw feeder 11;

[0032] A vacuum pump 15 is provided on one side of the vacuum furnace shell 2 , and the vacuum pump 15 is connected to the vacuum furnace shell 2 and the silo 10 through a tee pipe. A first valve 16 is provided on the pipeline between the vacuum pump 15 and the silo 10 close to the silo 10 .

[0033] The specification of the vacuum furnace shell 2 of the high-purity metallic chromium vacuum smelting equipment used in Examples 1 to 3 and Comparative Examples 1 and 2 is φ3.5m×3.5m.

[0034] Example 1 (using potassium dichromate as a heating agent and shutting down the pump for smelting)

[0035] Use high-purity chromium vacuum smelting equipment to produce low-nitrogen and low-gallium high-purity chromium metal, such as Figure 1 As shown, the specific process flow is as follows: (1) Ingredients

[0036] Weigh 3 tons of chromium trioxide and 1.5 tons of aluminum pellets as raw materials, add 0.9 tons of potassium dichromate as a heating agent based on a calorific value of 2918 kJ / kg, and mix the three materials evenly to prepare a mixed raw material; place the smelting furnace 9 on the material platform 8, push it into the vacuum furnace shell 2, add the mixed raw material to the silo 10 of the vacuum smelting equipment, and then discharge the raw material into the smelting furnace 9 of the vacuum smelting equipment in two batches through the silo 10;

[0037] (2) First batch of feeding

[0038] Open the second valve 17 and the third valve 18, start the screw feeder 11, and discharge the raw materials into the smelting furnace 9 through the discharge chute 12 into the charging hopper 13. The first batch of mixed raw materials is used as the bottom material, and the feeding amount accounts for 1 / 3 of the volume of the smelting furnace 9. At this time, the second batch of mixed raw materials is more than 1 times the first batch of mixed raw materials; close the second valve 17 and the third valve 18, and at the same time close the screw feeder 11, and then add the remaining mixed material into the silo 10, add 2kg of igniter, and adjust the position of the igniter 19 so that it is completely buried in the igniter;

[0039] (3) Vacuum smelting

[0040] The silo 10 and the vacuum furnace shell 2 are sealed, and circulating water is injected into the water-cooling jacket 3 from the water inlet 301 and discharged from the outlet 302 to water-cool the vacuum furnace shell 2. The first valve 16 is opened, and the vacuum pump 15 is started to evacuate the vacuum furnace shell 2 and the silo 10. After the pressure of the vacuum furnace shell 2 reaches -101kPa, the first valve 16 and the vacuum pump 15 are closed, and the igniter 19 is started to ignite the ignition agent to ignite the first batch of mixed raw materials in the smelting furnace 9. The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace 9. The smelting situation inside the smelting furnace 9 is observed through the observation window 7. When the first batch of mixed raw materials is in a molten state, the smelting furnace 9 is The inner bottom material emits a bright white light. The second valve 17 and the third valve 18 are opened, and the screw feeder 11 is started to feed the second batch of mixed raw materials in the silo 10 into the loading bucket 13 through the unloading chute 12 for continuous unloading. After 14 minutes, the unloading of the second batch of mixed raw materials is completed. Refining is continued for 1 minute. The pressure in the vacuum furnace shell 2 drops to -48kP. The screw feeder 11, the second valve 17, and the third valve 18 are closed in sequence. Argon is then filled into the vacuum furnace shell 2 until the pressure of the vacuum smelting equipment is 0kPa. Argon protection is carried out for 20 minutes. The vacuum pump 15 is then turned on to evacuate the vacuum furnace shell 2 to a pressure of -101kPa. The vacuum pump 15 is then turned off.

[0041] (4) Cooling treatment

[0042] Argon gas was filled into the vacuum furnace shell 2 to perform argon circulation cooling on the smelting furnace 9. After the temperature in the vacuum smelting equipment dropped to 600° C., the smelting furnace 9 was pushed out of the vacuum smelting equipment into a cooling chamber and further cooled to 200° C. by compressed air. The smelting furnace 9 was pushed out of the cooling chamber and refined to obtain low-nitrogen, low-gallium, high-purity metallic chromium. Sample analysis showed that the Cr mass content of the metallic chromium was 99.70%, the N mass content was 10 ppm, the Ga mass content was 80 ppm, and the Al mass content was 200 ppm. The other components met the JCr99.2 standard. This batch of low-nitrogen, low-gallium, high-purity metallic chromium was weighed and packaged, and the chromium yield was 90.75%.

[0043] Example 2 (using potassium dichromate as a heating agent and operating a pump for smelting)

[0044] (1) Ingredients

[0045] Weigh 3 tons of chromium trioxide and 2.1 tons of aluminum pellets as raw materials, add 1.5 tons of potassium dichromate as a heating agent based on a calorific value of 2905 kJ / kg, and mix the three materials evenly to prepare a mixed raw material; place the smelting furnace 9 on the material platform 8, push it into the vacuum furnace shell 2, add the mixed raw material to the silo 10 of the vacuum smelting equipment, and then discharge the raw material into the smelting furnace 9 of the vacuum smelting equipment in two batches through the silo 10;

[0046] (2) First batch of feeding

[0047] Open the second valve 17 and the third valve 18, start the screw feeder 11, and discharge the raw materials into the smelting furnace 9 through the discharge chute 12 into the charging scoop 13. The first batch of mixed raw materials is used as the bottom material, and the feeding amount accounts for 1 / 3 of the volume of the smelting furnace 9. At this time, the second batch of mixed raw materials is more than 1 times the first batch of mixed raw materials; close the second valve 17 and the third valve 18, and close the screw feeder 11 at the same time, and then add the remaining mixed material into the silo 10. Close the second valve 17 and the third valve 18, and close the screw feeder 11 at the same time, and then add the remaining mixed material into the silo 10. Add 2 kg of igniter and adjust the position of the igniter 19 so that it is completely buried in the igniter.

[0048] (3) Vacuum smelting

[0049] The silo 10 and the vacuum furnace shell 2 are sealed, and circulating water is injected into the water-cooling jacket 3 from the water inlet 301 and discharged from the outlet 302 to water-cool the vacuum furnace shell 2. The first valve 16 is opened, and the vacuum pump 15 is started to evacuate the vacuum furnace shell 2 and the silo 10. After the pressure of the vacuum furnace shell 2 reaches -95kpa, the igniter 19 is started to ignite the igniter to ignite the first batch of mixed raw materials in the smelting furnace 9. The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace 9. The smelting situation inside the smelting furnace 9 is observed through the observation window 7. When the first batch of mixed raw materials is in a molten state, the bottom material in the smelting furnace 9 emits a bright White light, open the second valve 17 and the third valve 18, start the screw feeder 11 to feed the second batch of mixed raw materials in the silo 10 into the feeding hopper 13 through the feeding chute 12 for continuous feeding. After 8 minutes, the second batch of mixed raw materials is fed. After continuing to refine for 1 minute, close the screw feeder 11, the first valve 16, the second valve 17, the third valve 18 and the vacuum pump 15 in sequence, and then fill the vacuum furnace shell 2 with argon gas until the vacuum smelting equipment pressure is 0kpa. Argon protection is carried out for 30 minutes, and then the vacuum pump 15 is turned on. After the vacuum furnace shell 2 is evacuated to a pressure of -95kpa, the vacuum pump 15 is turned off.

[0050] (4) Cooling treatment

[0051] Argon gas was filled into the vacuum furnace shell 2 to perform argon circulation cooling on the smelting furnace 9. After the temperature in the vacuum smelting equipment dropped to 550°C, the smelting furnace 9 was pushed out of the vacuum smelting equipment into a cooling chamber and continued to be cooled to 190°C by compressed air. The smelting furnace 9 was pushed out of the cooling chamber and refined to obtain low-nitrogen, low-gallium, high-purity metallic chromium. Sample analysis showed that the Cr mass content of the metallic chromium was 99.72%, the N mass content was 5ppm, the Ga mass content was 70ppm, and the Al mass content was 100ppm. The other components met the JCr99.2 standard. The batch of metallic chromium was weighed and packaged, and the chromium yield was 90.82%.

[0052] Example 3 (using potassium dichromate as a heating agent and shutting down the pump for smelting)

[0053] Use high-purity chromium vacuum smelting equipment to produce low-nitrogen and low-gallium high-purity chromium metal, such as Figure 1 As shown, the specific process flow is as follows: (1) Ingredients

[0054] Weigh 3 tons of chromium trioxide and 1.8 tons of aluminum pellets as raw materials, add 1.2 tons of potassium dichromate as an exothermic agent based on a calorific value of 2911 kJ / kg, and mix the three materials evenly to prepare a mixed raw material; place the smelting furnace 9 on the material platform 8, push it into the vacuum furnace shell 2, add the mixed raw material to the silo 10 of the vacuum smelting equipment, and then discharge the raw material into the smelting furnace 9 of the vacuum smelting equipment in two batches through the silo 10;

[0055] (2) First batch of feeding

[0056] Open the second valve 17 and the third valve 18, start the screw feeder 11, and discharge the raw materials into the smelting furnace 9 through the discharge chute 12 into the charging hopper 13. The first batch of mixed raw materials is used as the bottom material, and the feeding amount accounts for 1 / 2 of the volume of the smelting furnace 9. At this time, the second batch of mixed raw materials is more than 1 times the first batch of mixed raw materials; close the second valve 17 and the third valve 18, and at the same time close the screw feeder 11, and then add the remaining mixed material into the silo 10, add 3kg of igniter, and adjust the position of the igniter 19 so that it is completely buried in the igniter;

[0057] (3) Vacuum smelting

[0058] The sealed silo 10 and the vacuum furnace shell 2 are provided with circulating water injected into the water-cooling jacket 3 from the water inlet 301 and discharged from the outlet 302 to water-cool the vacuum furnace shell 2. The first valve 16 is opened and the vacuum pump 15 is started to evacuate the vacuum furnace shell 2 and the silo 10. After the pressure of the vacuum furnace shell 2 reaches -98 kPa, the first valve 16 and the vacuum pump 15 are closed and the igniter 19 is started to ignite the igniter to ignite the first batch of mixed raw materials in the smelting furnace 9. The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace 9. The smelting situation inside the smelting furnace 9 is observed through the observation window 7. When the first batch of mixed raw materials is in a molten state, the smelting furnace 9 is in a molten state. The inner bottom material emits a bright white light. The second valve 17 and the third valve 18 are opened, and the screw feeder 11 is started to feed the second batch of mixed raw materials in the silo 10 into the loading bucket 13 through the unloading chute 12 for continuous unloading. After 11 minutes, the unloading of the second batch of mixed raw materials is completed. The refining is continued for 1 minute. The pressure in the vacuum furnace shell 2 drops to -45kP. The screw feeder 11, the second valve 17, and the third valve 18 are closed in sequence. Argon is then filled into the vacuum furnace shell 2 until the pressure of the vacuum smelting equipment is 0kPa. Argon protection is carried out for 25 minutes. The vacuum pump 15 is then turned on to evacuate the vacuum furnace shell 2 to a pressure of -98kPa. The vacuum pump 15 is then turned off.

[0059] (4) Cooling treatment

[0060] Argon gas was filled into the vacuum furnace shell 2 to perform argon circulation cooling on the smelting furnace 9. After the temperature in the vacuum smelting equipment dropped to 565° C., the smelting furnace 9 was pushed out of the vacuum smelting equipment into a cooling chamber and continued to be cooled to 170° C. by compressed air. The smelting furnace 9 was pushed out of the cooling chamber and refined to obtain low-nitrogen, low-gallium, high-purity metallic chromium. Sample analysis showed that the mass content of Cr in the metallic chromium was 99.75%, the mass content of N was 7 ppm, the mass content of Ga was 60 ppm, and the mass content of Al was 100 ppm. Other components met the JCr99.2 standard. This batch of low-nitrogen, low-gallium, high-purity metallic chromium was weighed and packaged, and the chromium yield was 91.02%.

[0061] Example 4 (using potassium dichromate as a heating agent and shutting down the pump for smelting)

[0062] Use high-purity chromium vacuum smelting equipment to produce low-nitrogen and low-gallium high-purity chromium metal, such as Figure 1 As shown, the specific process flow is as follows: (1) Ingredients

[0063] Weigh 3 tons of chromium trioxide and 1.5 tons of aluminum pellets as raw materials, add 1.3 tons of potassium dichromate as an exothermic agent based on a calorific value of 3105 kJ / kg, and mix the three materials evenly to prepare a mixed raw material; place the smelting furnace 9 on the material platform 8, push it into the vacuum furnace shell 2, add the mixed raw material to the silo 10 of the vacuum smelting equipment, and then discharge the raw material into the smelting furnace 9 of the vacuum smelting equipment in two batches through the silo 10;

[0064] (2) First batch of feeding

[0065] Open the second valve 17 and the third valve 18, start the screw feeder 11, and discharge the raw materials into the smelting furnace 9 through the discharge chute 12 into the charging hopper 13. The first batch of mixed raw materials is used as the bottom material, and the feeding amount accounts for 1 / 2 of the volume of the smelting furnace 9. At this time, the second batch of mixed raw materials is more than 1 times the first batch of mixed raw materials; close the second valve 17 and the third valve 18, and at the same time close the screw feeder 11, and then add the remaining mixed material into the silo 10, add 3kg of igniter, and adjust the position of the igniter 19 so that it is completely buried in the igniter;

[0066] (3) Vacuum smelting

[0067] The sealed silo 10 and the vacuum furnace shell 2 are provided with circulating water injected into the water cooling jacket 3 from the water inlet 301 and discharged from the outlet 302 to water-cool the vacuum furnace shell 2. The first valve 16 is opened and the vacuum pump 15 is started to evacuate the vacuum furnace shell 2 and the silo 10. After the pressure of the vacuum furnace shell 2 reaches -100kPa, the first valve 16 and the vacuum pump 15 are closed and the igniter 19 is started to ignite the igniter to ignite the first batch of mixed raw materials in the smelting furnace 9. The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace 9. The smelting situation inside the smelting furnace 9 is observed through the observation window 7. When the first batch of mixed raw materials is in a molten state, the smelting furnace 9 is in a molten state. The inner bottom material emits a bright white light. The second valve 17 and the third valve 18 are opened, and the screw feeder 11 is started to feed the second batch of mixed raw materials in the silo 10 into the loading hopper 13 through the unloading chute 12 for continuous unloading. After 9 minutes, the unloading of the second batch of mixed raw materials is completed. Refining is continued for 1 minute. The pressure in the vacuum furnace shell 2 drops to -47kP. The screw feeder 11, the second valve 17, and the third valve 18 are closed in sequence. Argon is then filled into the vacuum furnace shell 2 until the pressure of the vacuum smelting equipment is 0kPa. Argon protection is carried out for 28 minutes. The vacuum pump 15 is then turned on to evacuate the vacuum furnace shell 2 to a pressure of -100kPa. The vacuum pump 15 is then turned off.

[0068] (4) Cooling treatment

[0069] Argon gas was filled into the vacuum furnace shell 2 to perform argon circulation cooling on the smelting furnace 9. After the temperature in the vacuum smelting equipment dropped to 580°C, the smelting furnace 9 was pushed from the vacuum smelting equipment into a cooling chamber and continued to be cooled to 190°C by compressed air. The smelting furnace 9 was pushed out of the cooling chamber and refined to obtain low-nitrogen, low-gallium, high-purity metallic chromium. Sample analysis showed that the mass content of Cr in the metallic chromium was 99.73%, the mass content of N was 9 ppm, the mass content of Ga was 70 ppm, and the mass content of Al was 200 ppm. The other components met the JCr99.2 standard. This batch of low-nitrogen, low-gallium, high-purity metallic chromium was weighed and packaged, and the chromium yield was 91.51%.

[0070] Comparative Example 1 (using sodium chlorate as a heating agent and shutting down the pump for smelting)

[0071] (1) Ingredients

[0072] Weigh 3 tons of chromium trioxide and 1.05 tons of aluminum pellets as raw materials, add 0.09 tons of sodium chlorate as a heating agent based on a calorific value of 2918 kJ / kg, and mix the three materials evenly to prepare a mixed raw material; place the smelting furnace 9 on the material platform 8, push it into the vacuum furnace shell 2, add the mixed raw material to the silo 10 of the vacuum smelting equipment, and then discharge the raw material into the smelting furnace 9 of the vacuum smelting equipment in two batches through the silo 10;

[0073] (2) First batch of feeding

[0074] Open the second valve 17 and the third valve 18, start the screw feeder 11, and discharge the raw materials into the smelting furnace 9 through the discharge chute 12 into the charging hopper 13. The first batch of mixed raw materials is used as the bottom material, and the feeding amount accounts for 1 / 2 of the volume of the smelting furnace 9. At this time, the second batch of mixed raw materials is more than 1 times the first batch of mixed raw materials; close the second valve 17 and the third valve 18, and at the same time close the screw feeder 11, and then add the remaining mixed material into the silo 10, and adjust the position of the igniter 19 so that it is completely buried in the mixed material;

[0075] (3) Vacuum smelting

[0076] The sealed silo 10 and the vacuum furnace shell 2 are provided with circulating water, which is injected into the water-cooling jacket 3 from the water inlet 301 and discharged from the outlet 302 to water-cool the vacuum furnace shell 2. The first valve 16 is opened, and the vacuum pump 15 is started to evacuate the vacuum furnace shell 2 and the silo 10. After the pressure of the vacuum furnace shell 2 reaches -101 kPa, the first valve 16 and the vacuum pump 15 are closed, and the igniter 19 is started to ignite the first batch of mixed raw materials in the smelting furnace 9. (When sodium chlorate is used as the exothermic agent, the heat released by the reaction is relatively high, and the mixture can react continuously by self-heating without the need for an external ignition agent.) The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace 9. The observation window 7 is used to observe the smelting situation inside the smelting furnace 9. When the first batch of mixed raw materials is in a molten state, the bottom material in the smelting furnace 9 emits a bright white light. The second valve 17 and the third valve 18 are opened, and the screw feeder 11 is started to feed the second batch of mixed raw materials in the silo 10 into the loading chute 13 through the unloading chute 12 for continuous unloading. After 4 minutes and 28 seconds, the pressure in the vacuum furnace reaches 80kPa, triggering the explosion-proof vent to explode. The pressure in the furnace quickly returns to 0kPa. Smelting is continued for 6 minutes. After the unloading of the second batch of mixed raw materials is completed, the screw feeder 11, the second valve 17 and the third valve 18 are closed in sequence, and refining is carried out for 1 minute. The smelting furnace is placed in the vacuum furnace shell to cool naturally.

[0077] (4) Cooling treatment

[0078] Argon gas was filled into the vacuum furnace shell 2 to perform argon circulation cooling on the smelting furnace 9. After the temperature in the vacuum smelting equipment dropped to 600°C, the smelting furnace 9 was pushed out of the vacuum smelting equipment into a cooling chamber and further cooled to 200°C using compressed air. The smelting furnace 9 was pushed out of the cooling chamber and refined. The obtained metallic chromium was sampled and analyzed: the Cr mass content of the metallic chromium was 99.1%, the N mass content was 80ppm, the Ga mass content was 120ppm, and the Al mass content was 2000ppm. The other components met the JCr99-A standard. The batch of metallic chromium was weighed and packaged, and the chromium yield was 88.24%.

[0079] Comparative Example 2 (using sodium chlorate as a heating agent and smelting with a pump)

[0080] (1) Ingredients

[0081] Weigh 3 tons of chromium trioxide and 1.05 tons of aluminum pellets as raw materials, add 0.09 tons of sodium chlorate as a heating agent based on a calorific value of 2918 kJ / kg, and mix the three materials evenly to prepare a mixed raw material; place the smelting furnace 9 on the material platform 8, push it into the vacuum furnace shell 2, add the mixed raw material to the silo 10 of the vacuum smelting equipment, and then discharge the raw material into the smelting furnace 9 of the vacuum smelting equipment in two batches through the silo 10;

[0082] (2) First batch of feeding

[0083] Open the second valve 17 and the third valve 18, start the screw feeder 11, and discharge the raw materials into the smelting furnace 9 through the discharge chute 12 into the charging hopper 13. The first batch of mixed raw materials is used as the bottom material, and the feeding amount accounts for 1 / 3 of the volume of the smelting furnace 9. At this time, the second batch of mixed raw materials is more than 1 times the first batch of mixed raw materials; close the second valve 17 and the third valve 18, and at the same time close the screw feeder 11, and then add the remaining mixed materials into the silo 10, and adjust the position of the igniter 19 so that it is completely buried in the igniter;

[0084] (3) Vacuum smelting

[0085] The sealed silo 10 and the vacuum furnace shell 2 are provided with circulating water, which is injected into the water-cooling jacket 3 from the water inlet 301 and discharged from the outlet 302 to water-cool the vacuum furnace shell 2. The first valve 16 is opened, and the vacuum pump 15 is started to evacuate the vacuum furnace shell 2 and the silo 10. After the pressure of the vacuum furnace shell 2 reaches -101 kPa, the igniter 19 is started to ignite the first batch of mixed raw materials in the smelting furnace 9 (when sodium chlorate is used as the exothermic agent, the heat released by the reaction is relatively high, and the self-heating can make the mixed materials react continuously without the need for an external ignition agent). The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace 9, and the smelting situation inside the smelting furnace 9 is observed through the observation window 7. When the first batch The mixed raw materials are in a molten state. At this time, the bottom material in the smelting furnace 9 emits a bright white light. The second valve 17 and the third valve 18 are opened, and the screw feeder 11 is started to feed the second batch of mixed raw materials in the silo 10 into the loading hopper 13 through the unloading chute 12 for continuous unloading. After 10 minutes and 10 seconds, the unloading of the second batch of mixed raw materials is completed. The screw feeder 11, the first valve 16, the second valve 17, the third valve 18 and the vacuum pump 15 are closed in sequence. Argon is then filled into the vacuum furnace shell 2 until the pressure of the vacuum smelting equipment is 0 kPa. Argon protection is carried out for 20 minutes. The vacuum pump 15 is then turned on. After the vacuum smelting equipment is evacuated to a pressure of -101 kPa, the vacuum pump 15 is turned off.

[0086] (4) Cooling treatment

[0087] Argon gas was filled into the vacuum furnace shell 2 to perform argon circulation cooling on the smelting furnace 9. After the temperature in the vacuum smelting equipment dropped to 600° C., the smelting furnace 9 was pushed out of the vacuum smelting equipment into a cooling chamber and further cooled to 200° C. by compressed air. The smelting furnace 9 was pushed out of the cooling chamber and refined to obtain high-purity metallic chromium. Sample analysis showed that the Cr mass content of the metallic chromium was 99.65%, the N mass content was 8 ppm, the Ga mass content was 110 ppm, and the Al mass content was 200 ppm. The other components met the JCr99.2 standard. The batch of metallic chromium was weighed and packaged, and the chromium yield was 90.85%.

[0088] Comparative Example 3: Smelting of metallic chromium by aluminothermic method outside the furnace

[0089] Weigh 3 tons of chromium trioxide and 1.05 tons of aluminum particles as raw materials, and add 0.15 tons of sodium chlorate as a heating agent according to a calorific value of 3105 kJ / kg, and mix the above three materials evenly to obtain a mixed raw material; place a smelting furnace on a charging platform, push it into a smelting room, and add the mixed raw materials into the smelting furnace in two batches. The first batch of mixed raw materials is used as a bottom material and is fed into the smelting furnace through a charging scoop from the hopper (the smelting furnace has the same specifications as in Example 1). After the remaining mixed raw materials in the furnace are added to the hopper, the dust collecting fan is turned on to collect dust from the smelting equipment, and then a half-shovel of magnesium bars loaded with a medium flat shovel is ignited and placed in the middle of the upper part of the bottom material of the smelting furnace, and the bottom material is observed through the observation hole. When the reaction emits bright white light, the screw feeder is started for continuous feeding. After 7 minutes, the second batch of mixed raw materials is fed. Smelting is continued for 1 minute and the dust collection fan is turned off. Argon protective gas is then introduced into the smelting furnace for 20 minutes. After natural cooling and the temperature drops to 200°C, the smelting furnace is pushed out of the smelting room and refined. The obtained metallic chromium is sent for sample analysis: the Cr content in the metallic chromium is 98.61%, the N content by mass is 300ppm, the Ga content by mass is 130ppm, and the Al content by mass is 6000ppm. The other components meet the JCr98.5 standard. The batch of metallic chromium is weighed and packaged, and the chromium yield is 85.5%.

[0090] Comparative Example 4: Smelting of metallic chromium by aluminothermic method outside the furnace

[0091] Weigh 3 tons of chromium trioxide and 1.5 tons of aluminum particles as raw materials, and add 0.35 tons of sodium chlorate as a heating agent according to a calorific value of 3366 kJ / kg, and mix the above three materials evenly to obtain a mixed raw material; place the smelting furnace on a charging platform, push it into the smelting room, and add the mixed raw materials into the smelting furnace in two batches. The first batch of mixed raw materials is used as a bottom material and enters the smelting furnace from the hopper through a charging scoop (the smelting furnace has the same specifications as Example 1). After the remaining mixed raw materials in the furnace are added to the hopper, the dust collecting fan is turned on to collect dust from the smelting equipment, and then a half-shovel of magnesium bars is loaded with a medium flat shovel and ignited and placed in the middle of the upper part of the bottom material of the smelting furnace, and the bottom material is observed through the observation hole. When the reaction emits bright white light, the screw feeder is started for continuous feeding. After 9 minutes, the second batch of mixed raw materials is fed. Smelting is continued for 1 minute and the dust collection fan is turned off. Argon protective gas is then introduced into the smelting furnace for 20 minutes. After natural cooling and the temperature drops to 200°C, the smelting furnace is pushed out of the smelting room and refined. The obtained metallic chromium is sent for sample analysis: the Cr content in the metallic chromium is 98.50%, the N content by mass is 200ppm, the Ga content by mass is 120ppm, and the Al content by mass is 8000ppm. The other components meet the JCr98 standard. The batch of metallic chromium is weighed and packaged, and the chromium yield is 86.12%.

[0092] The difference between Comparative Example 1 and Example 1 is that the exothermic agents used are different. Example 1 uses potassium dichromate and Comparative Example 1 uses sodium chlorate. When the pump is turned off, the gas expansion of sodium chlorate instantly breaks through the explosion-proof port due to the violent reaction, causing the vacuum furnace to break the vacuum, the vacuum smelting fails, and the generated metallic chromium product does not meet the expected target; Comparative Example 2 is smelted in the pump-on state, and the generated metallic chromium product has a low N content, but a high Al and Ga content, which cannot meet the low nitrogen and low gallium high purity metallic chromium standard; The difference between Comparative Example 3 and Comparative Example 2 is that Comparative Example 3 is conventional The off-furnace method is to smelt under contact with air at normal pressure; the product obtained in Comparative Example 3 has low purity, high impurity content, and low yield; and, although Comparative Example 3 is added with the exothermic agent according to the highest heat distribution of the present invention, the reaction is still incomplete due to the off-furnace method, the product yield is low, and the impurity N, Ga, and Al content are high; Comparative Example 4 is smelted according to the conventional off-furnace method, that is, sufficient aluminum particles and sodium chlorate are added to ensure the heat generation and the smelting reaction is relatively complete, but due to the characteristics of the off-furnace method itself, the yield is still very low, and the impurity content in the metallic chromium is high.

[0093] The above are merely specific embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide, characterized by: Specific steps as follows: (1) Mixing chromium trioxide, aluminum particles, and potassium dichromate as a heating agent to obtain a mixed raw material. The mass ratios of chromium trioxide to aluminum particles and potassium dichromate are 100:(50-70) and 100:(30-50), respectively. The unit charge reaction heat of the mixed raw material is 2905 kJ / kg to 3105 kJ / kg. (2) The first batch of mixed raw materials is added to the smelting furnace of the vacuum smelting equipment in two batches; wherein, the first batch of mixed raw materials is added to the smelting furnace as the base material, and the amount of the first batch of mixed raw materials added accounts for 1 / 3 to 1 / 2 of the volume of the smelting furnace, and an ignition agent is added. The ignition agent is a mixture of sodium chlorate and aluminum particles with a mass ratio of 2:

1. The position of the igniter in the vacuum smelting equipment is adjusted so that it is completely buried in the ignition agent; the remaining mixed raw materials are kept in the silo of the vacuum smelting equipment as the second batch of mixed raw materials for standby use, ready to be added to the smelting furnace; (3) Before smelting, vacuumize the vacuum smelting equipment and seal it. Turn on the vacuum pump and evacuate the vacuum smelting equipment until the pressure inside the vacuum smelting equipment is -101kpa~-95kpa. Ignition smelting is carried out. At this time, the vacuum pump can be turned on or off. (4) The vacuum smelting starts with the igniter to ignite the first batch of mixed raw materials in the smelting furnace. The first batch of mixed raw materials undergoes a self-heating reaction in the smelting furnace. When the first batch of mixed raw materials is in a molten state, the discharge valve is opened to continuously discharge the second batch of mixed raw materials in the hopper until all the second batch of mixed raw materials enter the smelting furnace. Continue refining for 1 minute, turn off the vacuum pump, and fill with protective gas for 20 minutes to 30 minutes. Then, turn on the vacuum pump to evacuate to the pressure of the vacuum smelting equipment before smelting. Turn off the vacuum pump and fill the vacuum furnace shell with protective gas to cool the smelting. The temperature of the smelting furnace is reduced to below 200℃. Finishing is carried out to obtain low-nitrogen and low-gallium high-purity metallic chromium.

2. The method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide according to claim 1, characterized in that: The weight of the second batch of mixed raw materials is more than 1 times that of the first batch of mixed raw materials.

3. The method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide according to claim 1, characterized in that: When the material is continuously discharged in step (4), the discharge speed is 0.3 t mixed raw material / min to 0.75 t mixed raw material / min.

4. The method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide according to claim 1, characterized in that: The low-nitrogen and low-gallium high-purity metallic chromium has an N content of 5ppm to 10ppm and a Ga content of 60ppm to 80ppm.

5. The method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide according to claim 1, characterized in that: The Al content in the low-nitrogen and low-gallium high-purity metallic chromium is 100ppm to 200ppm.

6. The method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide according to claim 1, characterized in that: The protective gas in step (4) is argon.

7. The method for producing low-nitrogen, low-gallium, high-yield, high-purity metallic chromium using chromium trioxide according to claim 1, characterized in that: When the smelting furnace is cooled in step (4), the smelting furnace is first cooled to 550°C to 600°C by circulating protective gas; then the smelting furnace is pushed out of the vacuum smelting equipment and sent into the cooling chamber, and the compressed air is continued to circulate and cool to below 200°C.

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