Method for preparing high-purity metal chromium through carbon reduction

Abstract

The invention discloses a method for preparing high-purity chromium metal through carbon reduction, which comprises the following steps: proportioning chromic oxide, carbon powder, starch and water according to a certain proportion, and carrying out primary compaction to obtain a wet blank; adding the wet blank into an electric arc furnace, and smelting and melting to obtain bulk carbon chromium; after being manually and coarsely crushed, the molten and cooled large carbon chromium blocks are sequentially fed into a jaw crusher and a column mill to be crushed; adding chromic oxide, starch and water into the crushed carbon chromium, mixing, and carrying out secondary compaction to obtain a briquette-like material; feeding the coal-like spherical material into a drying box, gradually heating, fully drying a green body, and then cooling; and after drying, loading the blank into a vacuum reduction furnace layer by layer, and carrying out vacuum reduction on chromium sesquioxide and carbon chromium in a four-side heating manner to obtain the high-purity metal chromium. According to the method, preparation of high-purity metal chromium is achieved, and the conversion rate of preparing metal lattice powder from chromium oxide can be greatly increased; and the content of impurities in the metal chromium is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of high-purity metallic chromium smelting, and more specifically, the invention relates to a method for preparing high-purity metallic chromium by carbon reduction. Background Art

[0002] Metal chromium is mainly used in the production of nickel-based and cobalt-based high-temperature alloys, aluminum alloys, titanium alloys, resistance alloys, corrosion-resistant alloys, iron-based heat-resistant alloys and stainless steel. There are two types of industrially produced metal chromium: one is aluminothermic chromium, which is block-shaped, silver-bright, metallic, and contains Cr>98%, and has different requirements for impurities depending on the purpose; the other is electrolytic chromium, which is flake-shaped, dark brown in surface, and bright in surface after hydrogen refining, and contains Cr>99%.

[0003] Metallic chromium has the characteristics of high melting and boiling points, high hardness, strong corrosion resistance, and metallic luster. It is used as an alloying agent in the production of various nickel- or cobalt-based high-temperature alloys, titanium alloys, aluminum-based alloys, resistance alloys, etc. These materials can be widely used in sputtering coating targets, thermal spraying, powder metallurgy products, fuel cell plates, aerospace high-temperature alloys, electrical alloy contacts, automobiles, shipbuilding and other fields.

[0004] In particular, the high-temperature alloy industry, target material industry, electrical alloy contact industry, etc. currently have very strict requirements on metallic chromium, which must meet higher purity, lower gas impurities and low-melting point impurity content, lower preparation cost, higher product consistency, etc.

[0005] The existing methods for producing metallic chromium include aluminothermic method, electrolytic method and electrosilicon thermal method. At present, most of the metallic chromium produced in China is produced by mixing chromium oxide, reducing agent aluminum and heating agent sodium chlorate in a certain proportion for smelting. However, this method can only achieve a conversion rate of chromium oxide of 80-83%, resulting in low production efficiency and great waste of resources.

[0006] Another problem is that the obtained metallic chromium has a high impurity content, low purity and low yield, which makes it difficult to meet the production requirements of the high-temperature alloy industry, target material industry and electrical alloy contact industry. Summary of the invention

[0007] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0008] In order to achieve these purposes and other advantages according to the present invention, a method for preparing high-purity metallic chromium by carbon reduction is provided, comprising the following steps:

[0009] Step 1, mixing chromium trioxide, carbon powder, starch and water in a certain proportion and pressing them into a green compact to obtain a wet compact;

[0010] Step 2: Add the wet billet into an electric arc furnace to smelt and melt to obtain a large piece of carbon chromium;

[0011] Step 3: After the molten and cooled large pieces of carbon chromium are roughly crushed manually, they are successively sent to a jaw crusher and a column mill for crushing;

[0012] Step 4: adding chromium trioxide, starch and water to the crushed carbon chromium in step 3, mixing and then performing secondary compacting to obtain a material in the shape of coal balls;

[0013] Step 5: Place the coal-like spherical material into a drying oven, gradually increase the temperature, fully dry the green body, and then cool it down;

[0014] Step 6: After drying, the green bodies are loaded layer by layer into a vacuum reduction furnace, and the chromium trioxide and carbon chromium are vacuum reduced by heating on four sides to obtain high-purity metallic chromium.

[0015] Preferably, in step 1, the molar ratio of chromium trioxide to carbon powder is 1:3.00-3.09, starch accounts for 0.05%-3% of the mass of chromium trioxide, and water accounts for 1%-20% of the mass of chromium trioxide.

[0016] Preferably, in the step 2, during the arc furnace smelting process, a transformer is used to generate a high current to cause arc discharge heating between the three carbon rods. After the arc is generated, a small amount of wet blanks are added to the special crucible of the arc furnace for melting reaction. The carbon rods are raised and lowered according to the current displayed on the instrument to ensure normal smelting. A small amount of wet blanks are added every 10 minutes during the arc process until the entire crucible is filled with material layers.

[0017] Preferably, in the step 2, the arc smelting is carried out under normal pressure, the current is controlled at 300A-400A, the smelting temperature is 1800°C-2200°C, and the carbon rod is lifted up when the current increases, and vice versa.

[0018] Preferably, in the step 2, indoor induced draft bag type dust removal is used during the smelting process.

[0019] Preferably, in step three, the large pieces of carbon chromium are ground to a fineness that allows them to pass through an 80-mesh sieve.

[0020] Preferably, in step 4, the mass ratio of carbon chromium to chromium trioxide is 10:1-1.6, the amount of starch used accounts for 1%-1.5% of the mass of the carbon chromium, and the amount of water used accounts for 1%-10% of the mass of the carbon chromium.

[0021] Preferably, in the step five, the final drying temperature is 300-600° C., the drying time is 3 h-5 h, the green body is fully dried, and then cooled.

[0022] Preferably, in step six, the dried blanks are loaded layer by layer into a vacuum reduction furnace, and a four-sided heating method is adopted. The blanks cannot contact the carbon rods. Then the seal is closed, the furnace cooling water is turned on, and the rotary vane vacuum pump is started to operate at negative pressure and gradually increase the temperature. After the moisture of the material in the blank is further dried, the rotary vane vacuum pump oil is replaced. The oil contains a small amount of moisture. When changing the oil, refer to the vacuum gauge pressure. When the vacuum pump pressure reaches -0.1MPa, 3h to 6h after heating, the Roots vacuum pump is turned on to reach the highest vacuum.

[0023] Preferably, in step six, the reduction temperature is between 1400°C and 1500°C, the final vacuum is below 100Pa, the control time is 10h to 12h of heating, 15h of constant temperature, and a total of 25h to 27h; after the reduction is completed, the temperature begins to drop, and the final temperature is required to be between 180°C and 220°C. During the cooling process, the vacuum must be operated normally. After the cooling is completed, the vacuum pump is turned off and the furnace door is opened to discharge the material.

[0024] The metallic chromium prepared in step 6 is subjected to ultrafine treatment to obtain ultrafine metallic chromium powder, wherein the ultrafine treatment method comprises the following steps:

[0025] Step 1: put high-purity chromium metal and steel balls into a ball mill, the mass ratio of high-purity chromium metal to steel balls is 1-2:4-5, the steel balls include large steel balls with a diameter of 80-120 mm and small steel balls with a diameter of 40-60 mm, and the mass ratio of large steel balls to small steel balls is 1:3-4; the vacuum degree of the ball mill is pumped to 1.5×10 -2 Pa, then argon is introduced to stabilize the pressure in the ball mill to 120-600 Pa; during ball milling, the speed of the ball mill is 400-800 rpm, and the ball milling time is 6-18 hours to obtain metallic chromium powder;

[0026] Step 2, washing and drying the metal chromium powder after dry ball milling, then putting the metal chromium powder into deionized water, stirring at a speed of 600-900rpm, and adding a dispersant in small amounts multiple times. After the dispersant is added, the stirring speed is increased to 1200-2000rpm, and then the temperature is increased to 60-80°C, the dispersion time is 1-3h, and then solid-liquid separation is performed, and the dispersed metal chromium powder is obtained after washing and drying; wherein the mass ratio of the metal chromium powder, deionized water, and the dispersant is 5-10:250-500:0.01-1;

[0027] Step 3, wet ball milling the metal chromium powder dispersed in step 2, specifically using anhydrous ethanol as the ball milling medium, zirconium oxide as the grinding balls, and KH550 as the coupling agent; wherein the mass ratio of the metal chromium powder, anhydrous ethanol, zirconium oxide grinding balls and the coupling agent is 10-50:20-200:80-120:0.5-5; the ball milling speed is 200-600rpm, the metal chromium powder, anhydrous ethanol, zirconium oxide grinding balls and the coupling agent are mixed and added into a ball milling jar, the ball milling time is 5-12h, and after the ball milling is completed, the ultrafine metal chromium powder is separated, washed and dried to obtain.

[0028] Wherein, the dispersant used in step 2 is a modified polyacrylic acid dispersant, and its preparation method comprises:

[0029] Dissolve polyacrylic acid and polyvinyl pyrrolidone in deionized water to obtain polyacrylic acid solution and polyvinyl pyrrolidone solution respectively; wherein the concentration of the polyacrylic acid solution is 200-400 mg / mL, the relative molecular weight of polyacrylic acid is 300-600 g / mol, and the concentration of the polyvinyl pyrrolidone solution is 20-100 mg / mL; stir the polyacrylic acid solution at a speed of 80-140 rpm while heating to 50-80°C, pour an equal volume of polyvinyl pyrrolidone solution into the polyacrylic acid solution, keep warm for 2-12 hours, cool to room temperature, add sodium hydroxide to adjust the pH to 7-8; add sodium tartrate powder, then heat to 70-90°C, keep warm for 5-20 minutes, cool to room temperature, stand for 6-12 hours, evaporate and concentrate, wash and dry to obtain a modified polyacrylic acid dispersant. wherein the mass ratio of sodium tartrate powder to polyacrylic acid is 1-5:5-16.

[0030] The present invention includes at least the following beneficial effects: the present invention realizes the preparation of high-purity metallic chromium by adopting the preparation process of batching → primary compacting → one-step electric arc furnace smelting → primary crushing → secondary batching and compacting → drying → vacuum reduction → packaging, and can greatly improve the conversion rate of metal grid powder prepared by chromium oxide; and reduce the impurity content in the metallic chromium powder.

[0031] The present invention obtains ultrafine metal chromium powder by ultrafine treatment of prepared metal chromium. The particle size of the ultrafine metal chromium powder is concentrated in 13.5-45.7 μm, and it has a smaller particle size and a smaller particle size distribution range. The ultrafine metal chromium powder can be used in industrial production such as coatings, welding materials, sputtering target manufacturing, alloy powder metallurgy, etc., which can greatly improve the quality of the product. Among them, the ultrafine treatment of metal chromium includes three main steps: dry ball milling → slurry dispersion → wet ball milling. High-purity metal chromium is pre-milled by dry ball milling to obtain metal chromium powder, and then the metal chromium powder is dispersed by using a modified polyacrylic acid dispersant, which improves the dispersion performance of the metal chromium powder and reduces the agglomeration between the metal chromium powders, which is convenient for the final wet ball milling. The metal chromium powder with extremely high dispersion performance is subjected to the final homogenization ball milling by wet ball milling, thereby preparing an ultrafine metal chromium powder with a smaller particle size and a more concentrated particle size distribution range.

[0032] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0033] The present invention is described in further detail below so that those skilled in the art can implement it according to the description.

[0034] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0035] Example 1

[0036] This embodiment provides a method for preparing high-purity metallic chromium by carbon reduction, comprising the following steps:

[0037] Step 1: 200 kg of chromium trioxide, 47.2 kg of carbon powder, 1.25 kg of starch and 5 kg of water are mixed in a certain proportion and pressed into a green compact to obtain a wet compact; wherein the molar ratio of chromium trioxide to carbon powder is determined by the reaction equation Cr2O3+3C=2Cr+3CO, and the carbon powder is in excess;

[0038] Step 2: Add the wet blank into the electric arc furnace, smelt and melt to obtain a large piece of carbon chromium; during the smelting process of the electric arc furnace, use a transformer to generate a high current to generate arc discharge heating between three carbon rods. After the arc is generated, add a small amount of the wet blank of the primary batching into the special crucible of the electric arc furnace for melting reaction. Adjust the lifting of the carbon rod according to the current displayed by the instrument to ensure normal smelting. Add a small amount of wet blank every 10 minutes during the arc process until the entire crucible material layer is full; arc smelting is carried out under normal pressure, the current is controlled at 400A, the smelting temperature is 2000℃, the carbon rod is lifted when the current increases, and vice versa; 1 crucible is produced every 4 hours, about 350kg of carbon chromium; indoor induced draft bag type sedimentation dust removal is used during the smelting process;

[0039] Step 3: After the molten cooled large pieces of carbon chromium are coarsely crushed manually, they are successively sent to a jaw crusher and a column mill for crushing, and the crushing fineness is required to pass through an 80-mesh sieve;

[0040] Step 4: Add 10 kg of chromium trioxide, 1.2 kg of starch and 5 kg of water to the 100 kg of carbon chromium crushed in step 3, mix and perform secondary compacting to obtain a material in the shape of coal balls;

[0041] Step 5: Place the coal-like spherical material into a drying oven, gradually increase the temperature to 400°C, dry for 5 hours, fully dry the body, and then cool it down;

[0042] Step 6: After drying, the blanks are loaded layer by layer into the vacuum reduction furnace, and the four-sided heating method is adopted. The blanks cannot contact the carbon rods. Then the seal is closed, the furnace cooling water is turned on, and the rotary vane vacuum pump is started to operate under negative pressure and gradually increase the temperature. After the moisture in the material in the blank is further dried, the rotary vane vacuum pump oil is replaced. The oil contains a small amount of moisture. When changing the oil, refer to the vacuum gauge pressure, which is generally close to -0.1MPa. The time is 3h after heating, and then the Roots vacuum pump is turned on to make the vacuum reach the highest. The reduction temperature is 1450℃, and the final vacuum degree is below 100Pa. The control time is 10h for heating, 15h for constant temperature, and a total of 25h; after the reduction is completed, the temperature is lowered, and the final temperature is required to be 200℃. The normal operation of the vacuum must be guaranteed during the cooling process. After the cooling is completed, the vacuum pump is turned off, and the furnace door is opened to discharge the material to obtain high-purity metallic chromium with a purity of 99.5%.

[0043] Step 7: Packaging: Pack qualified products into packaging barrels based on the appearance of the output and the test results.

[0044] Example 2

[0045] Step 1: 2000 kg of chromium trioxide, 472 kg of carbon powder, 12.5 kg of starch and 50 kg of water are mixed in a certain proportion and pressed into a green compact to obtain a wet compact; wherein the mass ratio of chromium trioxide to carbon powder is determined by the reaction equation Cr2O3+3C=2Cr+3CO, and the carbon powder is in excess;

[0046] Step 2: Add the wet blank into the electric arc furnace, smelt and melt to obtain a large piece of carbon chromium; during the smelting process of the electric arc furnace, use a transformer to generate a high current to generate arc discharge heating between three carbon rods. After the arc is generated, add a small amount of the wet blank of the primary batching into the special crucible of the electric arc furnace for melting reaction. Adjust the lifting of the carbon rod according to the current displayed by the instrument to ensure normal smelting. Add a small amount of wet blank every 10 minutes during the arc process until the entire crucible material layer is full; arc smelting is carried out under normal pressure, the current is controlled at 400A, the smelting temperature is 2000℃, the carbon rod is lifted when the current increases, and vice versa; 1 crucible is produced every 4 hours, about 350kg of carbon chromium; indoor induced draft bag type sedimentation dust removal is used during the smelting process;

[0047] Step 3: After the molten cooled large pieces of carbon chromium are coarsely crushed manually, they are successively sent to a jaw crusher and a column mill for crushing. The crushing fineness is required to pass through an 80-mesh sieve, and about 1350k carbon chromium is produced;

[0048] Step 4: Add 160kg of chromium trioxide, 16kg of starch and 60kg of water to the 1300kg of carbon chromium crushed in step 3, and then perform secondary compaction to obtain a material in the shape of coal balls;

[0049] Step 5: Place the coal-like spherical material into a drying oven, gradually increase the temperature to 400°C, dry for 5 hours, fully dry the body, and then cool it down;

[0050] Step 6: After drying, the blanks are loaded into the vacuum reduction furnace layer by layer, and the four-sided heating method is adopted. The blanks cannot contact the carbon rods. Then the seal is closed, the furnace cooling water is turned on, and the rotary vane vacuum pump is started to operate under negative pressure and gradually increase the temperature. After the moisture in the material in the blank is further dried, the rotary vane vacuum pump oil is replaced. The oil contains a small amount of moisture. When changing the oil, refer to the vacuum gauge pressure, which is generally close to -0.1MPa. The time is 3h after heating, and then the Roots vacuum pump is turned on to make the vacuum reach the highest. The reduction temperature is 1450℃, the final vacuum degree is below 100Pa, and the control time is 10h for heating, 25h for constant temperature, and a total of 35h; after the reduction is completed, the temperature is lowered, and the final temperature is required to be below 200℃. The normal operation of the vacuum must be guaranteed during the cooling process. After the cooling is completed, the vacuum pump is turned off, and the furnace door is opened to discharge the material, and 1300kg of high-purity metallic chromium with a purity of 99.5% is obtained.

[0051] Example 3

[0052] In this embodiment, the high-purity metallic chromium prepared in embodiment 1 is subjected to ultrafine treatment, and the steps of ultrafine treatment include:

[0053] Step 1: Put 20kg of high-purity chromium and 50kg of steel balls into the ball mill. The steel balls include 10kg of large steel balls with a diameter of 80mm and 40kg of small steel balls with a diameter of 40mm. Pump the vacuum of the ball mill to 1.5×10 -2 Pa, and then argon gas was introduced to stabilize the air pressure in the ball mill to 500 Pa; during ball milling, the speed of the ball mill was 400 rpm, the ball milling time was 6 h, and after the ball milling was completed, the metal chromium powder was sieved;

[0054] Step 2: Wash and dry the metal chromium powder after ball milling in step 1, then weigh 20g of the metal chromium powder and put it into 500mL of deionized water, stir it at a speed of 600rpm, and add 1g of modified polyacrylic acid dispersant in small amounts and multiple times. After the modified polyacrylic acid dispersant is added, the stirring speed is increased to 1500rpm, and then the temperature is increased to 60°C, the dispersion time is 2h, and then the solid-liquid separation is performed, and the dispersed metal chromium powder is obtained after washing and drying. The method of modifying the polyacrylic acid dispersant comprises:

[0055] Dissolve polyacrylic acid and polyvinyl pyrrolidone with a relative molecular weight of 300-600 g / mol in deionized water to obtain 200 mg / mL polyacrylic acid solution and 50 mg / mL polyvinyl pyrrolidone solution respectively; stir the polyacrylic acid solution at a rotation speed of 120 rpm and heat it to 80°C; pour 200 mL of the polyvinyl pyrrolidone solution into 200 mL of the polyacrylic acid solution, keep it warm for 6 hours, cool it to room temperature, add sodium hydroxide to adjust the pH to 8; add 8 g of sodium tartrate powder, then heat it to 90°C, keep it warm for 10 minutes, cool it to room temperature, let it stand for 12 hours, evaporate and concentrate, wash and dry to obtain a modified polyacrylic acid dispersant.

[0056] Step 3: wet-milling 10 kg of the metal chromium powder dispersed in step 2, specifically using 20 kg of anhydrous ethanol as the ball milling medium, 80 kg of zirconium oxide as the grinding balls, and 0.5 kg of KH550 as the coupling agent; mixing the metal chromium powder, anhydrous ethanol, zirconium oxide grinding balls and the coupling agent and adding them into a ball milling jar, with a ball milling speed of 600 rpm and a ball milling time of 6 hours. After the ball milling is completed, separating, washing and drying to obtain ultrafine metal chromium powder.

[0057] Example 4

[0058] In this embodiment, the high-purity metallic chromium prepared in embodiment 1 is subjected to ultrafine treatment, and the steps of ultrafine treatment include:

[0059] Step 1: Put 30kg of high-purity chromium metal and 120kg of steel balls into the ball mill, including 30kg of large steel balls with a diameter of 100mm and 90kg of small steel balls with a diameter of 60mm; vacuum the ball mill to 1.5×10 -2 Pa, and then argon gas was introduced to stabilize the air pressure in the ball mill to 600 Pa; during ball milling, the speed of the ball mill was 800 rpm, and the ball milling time was 12 h to obtain metallic chromium powder;

[0060] Step 2: Wash and dry the metal chromium powder after dry ball milling, then put 50g of the metal chromium powder into 500mL of deionized water, stir at a speed of 900rpm, and add 5g of modified polyacrylic acid dispersant in small amounts and multiple times. After the modified polyacrylic acid dispersant is added, the stirring speed is increased to 2000rpm, and then the temperature is increased to 80°C, the dispersion time is 3h, and then the solid-liquid separation is performed, and the dispersed metal chromium powder is obtained after washing and drying; wherein the preparation method of the modified polyacrylic acid dispersant comprises:

[0061] Dissolve polyacrylic acid and polyvinyl pyrrolidone in deionized water to obtain 300 mg / mL polyacrylic acid solution and 50 mg / mL polyvinyl pyrrolidone solution respectively; the relative molecular weight of polyacrylic acid is 300-600 g / mol; stir the polyacrylic acid solution at a speed of 140 rpm and heat it to 80°C; pour 200 mL of polyvinyl pyrrolidone solution into 200 mL of polyacrylic acid solution, keep it warm for 5 hours, cool it to room temperature, add sodium hydroxide to adjust the pH to 8; add 12 g of sodium tartrate powder, then heat it to 90°C, keep it warm for 10 minutes, cool it to room temperature, stand it for 12 hours, evaporate and concentrate it, wash and dry it to obtain a modified polyacrylic acid dispersant.

[0062] Step 3: wet-milling 10 kg of the metal chromium powder dispersed in step 2, specifically using 30 kg of anhydrous ethanol as the ball milling medium, 80 kg of zirconium oxide as the grinding balls, and 3 g of KH550 as the coupling agent; mixing the metal chromium powder, anhydrous ethanol, zirconium oxide grinding balls and the coupling agent and adding them into a ball milling jar, with a ball milling speed of 600 rpm and a ball milling time of 6 h. After the ball milling is completed, separating, washing and drying to obtain ultrafine metal chromium powder.

[0063] Comparative Example 1

[0064] In this comparative example, the metallic chromium prepared in Example 1 is subjected to ultrafine treatment. Compared with Example 3, the high-purity metallic chromium prepared in Example 1 is only subjected to dry ball milling without subsequent slurry dispersion and wet ball milling, wherein the process parameters of dry ball milling are the same as those in Example 3.

[0065] Comparative Example 2

[0066] In this comparative example, the metallic chromium prepared in Example 1 is subjected to ultrafine treatment. Compared with Example 3, the metallic chromium powder prepared in Example 1 is directly subjected to wet ball milling, and the process parameters of the wet ball milling are the same as those in Example 3, and dry ball milling and slurry dispersion are not performed.

[0067] Comparative Example 3

[0068] In this comparative example, the metallic chromium prepared in Example 1 is subjected to ultrafine treatment. Compared with Example 3, the metallic chromium powder prepared in Example 1 is subjected to step 1 dry ball milling, step 2 slurry dispersion and step 3 wet ball milling, wherein the process parameters of dry ball milling and wet ball milling are the same as those in Example 3, except that the dispersant used in the slurry dispersion in this comparative example is 8 g of commercially available polyacrylic acid with a relative molecular mass of 300 to 600 g / mol, and the process parameters of the remaining steps are the same as those in Example 3.

[0069] The particle size distribution of the ultrafine metallic chromium powder prepared in Example 3, Example 4, and Comparative Examples 1 to 3 was measured respectively, and the following table was obtained:

[0070] D10(μm) D50(μm) D90(μm) Example 3 13.5 28.1 45.7 Example 4 14.6 30.9 51.3 Comparative Example 1 48.3 122.5 165.4 Comparative Example 2 42.0 90.4 142.8 Comparative Example 3 29.9 63.2 77.2

[0071] As can be seen from the above table, the ultrafine metallic chromium powder obtained by dry ball milling → slurry dispersion → wet ball milling ultrafine treatment in Examples 3 and 4 has a smaller particle size and a smaller particle size distribution range, which is significantly better than Comparative Examples 1 to 3.

[0072] Step 7: Packaging: Pack qualified products into packaging barrels based on the appearance of the output and the test results.

[0073] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0074] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. A method for preparing high-purity metallic chromium by carbon reduction, characterized in that: The following steps are involved: Step 1: mixing chromium trioxide, carbon powder, starch and water in a certain proportion and pressing them into a green compact to obtain a wet compact; Step 2: Add the wet billet into an electric arc furnace to smelt and melt to obtain a large piece of carbon chromium; Step 3: After the molten and cooled large pieces of carbon chromium are roughly crushed manually, they are successively sent to a jaw crusher and a column mill for crushing; Step 4: adding chromium trioxide, starch and water to the crushed carbon chromium in step 3, mixing and performing secondary compacting to obtain a material in the shape of coal balls; Step 5: Place the coal-like spherical material into a drying oven, gradually increase the temperature, fully dry the green body, and then cool it down; Step 6: After drying, the green bodies are loaded layer by layer into a vacuum reduction furnace, and the chromium trioxide and carbon chromium are vacuum reduced by heating on four sides to obtain high-purity metallic chromium.

2. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 1, the molar ratio of chromium trioxide to carbon powder is 1:3.00-3.09, starch accounts for 0.05%-3% of the mass of chromium trioxide, and water accounts for 1%-20% of the mass of chromium trioxide.

3. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 2, during the arc furnace smelting process, a transformer is used to generate a high current to cause arc discharge heating between the three carbon rods. After the arc is generated, a small amount of primary batch wet blank is added into a special crucible of the arc furnace for melting reaction. The carbon rod is raised and lowered according to the current displayed on the instrument to ensure normal smelting. During the arc process, a small amount of wet blank is added every 10 minutes until the entire crucible is filled with material layers.

4. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 2, arc smelting is carried out under normal pressure, the current is controlled at 300A-400A, the smelting temperature is 1800°C-2200°C, and the carbon rod is lifted up when the current increases, and vice versa.

5. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 2, indoor induced draft bag type dust removal is used during the smelting process.

6. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 3, the large pieces of carbon chromium are required to be crushed to a fineness that allows them to pass through an 80-mesh sieve.

7. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 4, the mass ratio of carbon chromium to chromium trioxide is 10:1-1.6, the amount of starch used accounts for 1%-1.5% of the mass of the carbon chromium, and the amount of water used accounts for 1%-10% of the mass of the carbon chromium.

8. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step 5, the final drying temperature is 300-600° C., the drying time is 3h-5h, the green body is fully dried, and then cooled.

9. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step six, the dried green bodies are loaded layer by layer into the vacuum reduction furnace, and a four-sided heating method is adopted. The green bodies cannot contact the carbon rods. Then, the seal is closed, the furnace cooling water is turned on, and the rotary vane vacuum pump is started to operate under negative pressure and gradually increase the temperature. After the moisture of the material in the green body is further dried, the rotary vane vacuum pump oil is replaced. The oil contains a small amount of moisture. When changing the oil, refer to the vacuum gauge pressure. When the vacuum pump pressure reaches -0.1MPa, 3h to 6h after heating, the Roots vacuum pump is turned on to make the vacuum reach the highest.

10. The method for preparing high-purity metallic chromium by carbon reduction according to claim 1, characterized in that: In the step six, the reduction temperature is between 1400°C and 1500°C, the final vacuum degree is below 100Pa, the control time is 10h to 12h of heating, 15h of constant temperature, and a total of 25h to 27h; after the reduction is completed, the temperature begins to drop, and the final temperature is required to be between 180°C and 220°C. During the cooling process, the normal operation of the vacuum must be ensured. After the cooling is completed, the vacuum pump is turned off and the furnace door is opened to discharge the material.