Preparation method of 4n high-purity chromium

Abstract

The application discloses a preparation method of 4N high-purity chromium, and comprises the following steps: step one, adding metal chromium into concentrated sulfuric acid mixed with water for leaching; step two, adopting a Mohr salt method; step three, obtaining a chromium (III) solution through extraction; step four, performing alkaline precipitation on the chromium (III) solution, and obtaining chromium hydroxide through filtration; step five, performing roasting on the chromium hydroxide, and obtaining chromium trioxide; step six, mixing the chromium trioxide with aluminum particles and a heating agent, and sequentially performing vacuum aluminothermic reduction and vacuum suspension smelting to obtain 4N chromium. The preparation method shortens the preparation period under the premise of ensuring the iron removal effect by adopting the process of the Mohr salt method combined with extraction of iron, and effectively reduces the impurity content of gas, iron and the like by adopting the process of vacuum aluminothermic reduction combined with vacuum suspension smelting, so that 4N chromium is obtained, and the method is suitable for the technical field of high-purity metal chromium preparation.

Description

Technical Field

[0001] This invention belongs to the field of high-purity metallic chromium preparation technology, and in particular relates to a method for preparing 4N high-purity chromium. Background Technology

[0002] Chromium is an alloying element with extremely high hardness and corrosion resistance, used in special steels to impart properties such as corrosion resistance, impact resistance, resistance to extreme temperatures, wear resistance, friction hardness, and strength. Furthermore, because chromium forms a Cr₂O₃ oxide film, it provides excellent oxidation and corrosion resistance, making it essential for various types of high-temperature alloys. Chromium is also used in tanned leather, wood preservatives, pigments, refractory materials, chromium plating, and in the manufacture of high-purity chromium sputtering targets in semiconductor and electronic device manufacturing.

[0003] Currently, the commonly used production processes for elemental chromium are mainly divided into the aluminothermic reduction method and the electrolysis method. The aluminothermic reduction method uses metallurgical-grade chromium oxide as raw material, combined with aluminum powder and a heating agent, and can obtain metallic chromium with a yield of 89% and a purity of over 98%. The molten salt (KCl-AlCl3-CrCl3) electrolysis method has higher current efficiency. Since solution electrolysis mainly uses chromium(III) solution for electrolysis, chromium with a purity greater than 99.9% can be obtained under different control conditions. However, the content of impurities such as gaseous impurities and iron is difficult to meet the standard of 4N chromium.

[0004] Therefore, there is an urgent need for a method to prepare 4N high-purity chromium. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing 4N high-purity chromium. This method employs a single Mohr's salt process combined with extraction for iron removal, shortening the preparation cycle while ensuring effective iron removal. Then, by using vacuum aluminothermic reduction combined with vacuum suspension melting, the content of impurities such as gases and iron is effectively reduced, yielding 4N chromium and solving the problem of obtaining 4N-grade chromium using existing technologies.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing 4N high-purity chromium, characterized in that the preparation method includes the following steps:

[0007] Step 1: Mix concentrated sulfuric acid with water and then add it to metallic chromium for leaching to obtain a leachate;

[0008] Step 2, Mohr's salt method: After filtering the leachate obtained in Step 1, mix it with a reducing agent and ammonium sulfate, and then crystallize and filter it to obtain the filtrate.

[0009] Step 3: Extract the filtrate obtained in Step 2 to obtain a chromium(III) solution;

[0010] Step 4: The chromium(III) solution obtained in Step 3 is subjected to alkaline precipitation, and after filtration, chromium hydroxide is obtained;

[0011] Step 5: Calcining the chromium hydroxide obtained in Step 4 yields chromium trioxide;

[0012] Step 6: Mix the chromium trioxide obtained in Step 5 with aluminum granules and a heating agent, and then perform vacuum aluminothermic reduction and vacuum suspension melting in sequence to obtain 4N chromium.

[0013] The above-mentioned method for preparing 4N high-purity chromium is characterized in that, in step one, the excess coefficient of concentrated sulfuric acid is 1 to 1.5, the mass concentration of concentrated sulfuric acid is greater than 98%, the particle size of metallic chromium is 200 mesh to 500 mesh, the stirring during the leaching process is carried out at a speed of 100 r / min to 500 r / min, the leaching temperature is 25℃ to 100℃, and the leaching time is 1 h to 6 h.

[0014] This invention improves the leaching rate of metallic chromium by using an excess of concentrated sulfuric acid to facilitate the leaching reaction, controlling the excess sulfuric acid coefficient to 1-1.5 to avoid excessive concentration of concentrated sulfuric acid, and controlling the leaching temperature and time.

[0015] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the reducing agent in step two is ascorbic acid, the excess coefficient of ammonium sulfate is 1 to 4, and the crystallization process is as follows: the temperature is controlled at 50℃ to 90℃ and the pH value is 0.2 to 2.5, then cooled to 5℃, and then crystallized for 4h to 30h.

[0016] This invention controls the excess ammonium sulfate coefficient, temperature, pH value, and crystallization time during the Mohr salt process to ensure that chromium ions in the solution are converted into ammonium salts as much as possible; preferably, the reaction vessel is placed in an ice-water mixture during cooling to accelerate the cooling rate.

[0017] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the extraction process in step three is as follows: a mixture of P204 and sulfonated kerosene is used as the extraction organic phase, and chromium is transferred from the filtrate obtained in step two to the extraction organic phase under the conditions of an extraction ratio of Vo / Va of 1 / 1, an extraction temperature of 10℃~50℃, a shaking time of 5min~30min, and a pH value of 1~4; then, chromium is back-extracted using sulfuric acid with a concentration of 2mol / L under the conditions of an extraction ratio of Vo / Va of 5 / 1, a temperature of 10℃~50℃, and a shaking time of 5min~30min.

[0018] In this invention, P204 is dioctyl phosphate, Vo represents the volume of the organic phase, and Va represents the volume of the aqueous phase.

[0019] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the mass of P2O4 is 30% of the total mass of the extracted organic phase, the mass of sulfonated kerosene is 70% of the total mass of the extracted organic phase, and the saponification rate of the extracted organic phase is 20% to 90%.

[0020] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the temperature of the alkaline precipitation in step four is 50℃~90℃, the pH value of the alkaline precipitation is 7~8, and the duration of the alkaline precipitation is 1h~2h.

[0021] This invention controls the temperature, pH value, and time during the alkaline precipitation process to ensure that chromium ions in the solution are converted into chromium hydroxide precipitate as completely as possible.

[0022] The above-mentioned method for preparing 4N high-purity chromium is characterized in that polyacrylamide is added before the alkaline precipitation in step four, and the concentration of polyacrylamide in the chromium(III) solution is 3 g / L to 10 g / L.

[0023] This invention improves the filtration performance of the generated amorphous colloidal chromium hydroxide by adding polyacrylamide, transforming the amorphous colloidal chromium hydroxide into a gel or flocculent state, which is beneficial to increasing the chromium hydroxide filtration rate.

[0024] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the calcination process in step five is as follows: carbon monoxide is introduced into an atmosphere calcination furnace, and the temperature is raised to 500℃~1000℃ for calcination for 1h~4h.

[0025] This invention employs a reducing carbon monoxide atmosphere for calcination, which avoids the formation of hexavalent chromium during the calcination process and better controls the oxidation state of chromium hydroxide, thereby forming the desired chromium trioxide.

[0026] The above-mentioned method for preparing 4N high-purity chromium is characterized in that, in step six, the aluminum particles are of grade 4N or higher, the particle size is 1mm to 5mm, and the mass of the aluminum particles is 90% to 95% of the theoretical amount; the heating agent is sodium nitrate with a mass purity greater than 99%; in the vacuum aluminothermic reduction, a mixture of saltpeter, aluminum granules, and magnesium shavings is used as the igniter, and the mass of the igniter is 0.3% to 0.5% of the total mass of chromium trioxide, aluminum particles, and heating agent; the vacuum aluminothermic reduction process is as follows: vacuum is drawn to 1Pa to 100Pa, argon gas is introduced to a pressure of 4500Pa to 5000Pa, and then the reduction reaction is carried out for 0.5h to 1h before vacuuming again, followed by furnace cooling for more than 6h.

[0027] By controlling the pressure to 4500Pa to 5000Pa, this invention avoids the problem that excessively low system pressure can cause chromium to volatilize after it is heated and melted during the aluminothermic reduction process, while excessively high pressure can hinder the volatilization of impurity elements. Preferably, the mass of the exothermic agent is set in the range of 2970kJ to 3100kJ per unit furnace charge reaction heat, which can heat the raw materials to a suitable temperature and effectively separate the molten metal and slag.

[0028] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the vacuum suspension melting process in step six is ​​as follows: evacuate to 1 Pa to 100 Pa, fill with argon gas to a pressure of over 1000 Pa, then heat to 1950℃ to 2000℃ for melting for 0.5 h to 1 h and then cool.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. This invention employs a single Mohr's salt process combined with extraction for iron removal, which ensures the effectiveness of iron removal while avoiding the increased preparation cycle caused by multiple Mohr's salt crystallization processes. At the same time, the single Mohr's salt process combined with extraction for iron removal can significantly reduce the iron content, thereby obtaining 4N chromium.

[0031] 2. This invention uses a process of vacuum aluminothermic reduction combined with vacuum suspension melting to obtain 4N chromium with the required composition. Compared with metallic chromium obtained by aluminothermic reduction or electrolysis in the prior art, the 4N chromium prepared by this invention has a lower content of gaseous impurities.

[0032] 3. The preparation method of the present invention does not require the purity of the raw material chromium, which greatly reduces the production cost of 4N chromium and broadens the range of raw material selection.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the preparation method of the present invention. Detailed Implementation

[0035] Example 1

[0036] like Figure 1 As shown, the preparation method of this embodiment includes the following steps:

[0037] Step 1: Mix 1000g of 3N grade chromium powder with a particle size of 300 mesh, 3749.9g of concentrated sulfuric acid with a mass fraction greater than 98%, and 7.5L of water, and leach at 90℃ for 4 hours, stirring at 300r / min during the leaching process to obtain the leachate; the excess coefficient of the concentrated sulfuric acid is 1.3.

[0038] Step 2, Mohr's salt method: After filtering the leachate obtained in Step 1, mix it with 10g ascorbic acid and 3769.6g ammonium sulfate. Control the temperature at 70℃, adjust the pH to 0.5, and then place the reaction vessel in an ice-water mixture to cool to 5℃. Then crystallize for 24 hours, and filter to obtain the filtrate; the excess coefficient of the ammonium sulfate is 3.

[0039] Step 3: Extract the filtrate obtained in Step 2 to obtain a chromium(III) solution. The extraction process is as follows: a mixture of 30% P2O4 and 70% sulfonated kerosene is used as the extraction organic phase. Under the conditions of an extraction ratio of Vo / Va of 1 / 1, an extraction temperature of 28°C, a shaking time of 5 min, and a pH of 2.4, chromium is transferred from the filtrate obtained in Step 2 to the extraction organic phase. Then, chromium is back-extracted using 2 mol / L sulfuric acid under the conditions of an extraction ratio of Vo / Va of 5 / 1, a temperature of 28°C, and a shaking time of 5 min. The saponification rate of the extraction organic phase is 70%.

[0040] Step 4: The temperature of the chromium(III) solution obtained in Step 3 is controlled at 85℃, the pH is adjusted to 7-8, and then polyacrylamide is added for alkaline precipitation for 1 hour. After filtration, chromium hydroxide is obtained; the concentration of polyacrylamide in the chromium(III) solution is 5 g / L.

[0041] Step 5: The chromium hydroxide obtained in Step 4 is charged into an atmosphere calcination furnace with carbon monoxide at a flow rate of 1L / min to 2L / min, and calcined at a temperature of 600℃ for 2 hours to obtain chromium trioxide.

[0042] Step Six: Take 100g of chromium trioxide obtained in Step Five, mix it with 36.04g of 4N grade aluminum granules with a particle size of 1mm, 6.45g of sodium nitrate with a purity greater than 99%, and 0.428g of igniter, and perform vacuum aluminothermic reduction and vacuum suspension melting sequentially to obtain 4N chromium; the unit charge reaction heat of the 6.45g sodium nitrate is 3050kJ, and the igniter consists of 65% saltpeter, 5% aluminum granules, and 0.428g of [unspecified ingredient]. The composition is 30% magnesium shavings; the vacuum aluminothermic reduction process is as follows: before ignition, the vacuum is drawn to 50 Pa, argon gas is introduced to a pressure of 4500 Pa, the igniter is started to discharge, the reduction reaction is carried out for 0.5 h, then the vacuum is drawn again, and the furnace is cooled for 6 h; the vacuum suspension melting process is as follows: the vacuum is drawn to 1 Pa, argon gas is introduced to a pressure of more than 1000 Pa, then the vacuum system is adjusted to maintain the pressure under the argon atmosphere at 1500 Pa, and the furnace is melted at 1950℃ for 0.5 h and then cooled.

[0043] Upon testing, the iron (II) concentration in the chromium (III) solution obtained in step three of this embodiment was found to be 0.008 g / L, and the iron element mass percentage in the chromium trioxide obtained in step four was 0.001%.

[0044] Example 2

[0045] The preparation method of this embodiment includes the following steps:

[0046] Step 1: Mix 1000g of chromium powder with a particle size of 300 mesh, 3319g of concentrated sulfuric acid with a mass fraction greater than 98%, and 6.64L of water. Leach at 90℃ for 4 hours, stirring at 300r / min during the leaching process to obtain a leachate. The chromium powder consists of 71.34% Cr and 27.58% Fe by mass, and the excess coefficient of the concentrated sulfuric acid is 1.3.

[0047] Step 2, Mohr's salt method: After filtering the leachate obtained in Step 1, mix it with 20g ascorbic acid and 4670.1g ammonium sulfate. Control the temperature at 70℃, adjust the pH to 0.5, and then rapidly cool it to 5℃. Then crystallize for 24 hours, and filter to obtain the filtrate; the excess coefficient of the ammonium sulfate is 3.

[0048] Step 3: Extract the filtrate obtained in Step 2 to obtain a chromium(III) solution. The extraction process is as follows: a mixture of 30% P2O4 and 70% sulfonated kerosene is used as the extraction organic phase. Under the conditions of an extraction ratio of Vo / Va of 1 / 1, an extraction temperature of 28°C, a shaking time of 5 min, and a pH of 2.4, chromium is transferred from the filtrate obtained in Step 2 to the extraction organic phase. Then, chromium is back-extracted using 2 mol / L sulfuric acid under the conditions of an extraction ratio of Vo / Va of 5 / 1, a temperature of 28°C, and a shaking time of 5 min. The saponification rate of the extraction organic phase is 70%.

[0049] Step 4: Control the temperature of the chromium(III) solution obtained in Step 3 to 85℃, adjust the pH to 7-8, add polyacrylamide for alkaline precipitation for 1.5h, filter to obtain chromium hydroxide; the concentration of polyacrylamide in the chromium(III) solution is 5g / L;

[0050] Step 5: The chromium hydroxide obtained in Step 4 is charged into an atmosphere calcination furnace with carbon monoxide at a flow rate of 1L / min to 2L / min, and calcined at a temperature of 600℃ for 2 hours to obtain chromium trioxide.

[0051] Step Six: Take 500g of chromium trioxide obtained in Step Five, mix it with 180.2g of 4N grade aluminum granules with a particle size of 1mm, 32.25g of sodium nitrate with a purity greater than 99%, and 0.428g of igniter, and perform vacuum aluminothermic reduction and vacuum suspension melting sequentially to obtain 4N chromium; the unit furnace charge reaction heat of the 32.25g sodium nitrate is 3050kJ, and the igniter consists of 62% saltpeter, 2% aluminum granules, and 0.428g of [unspecified ingredient]. The composition is 36% magnesium shavings; the vacuum aluminothermic reduction process is as follows: before ignition, the vacuum is drawn to 50 Pa, argon gas is introduced to a pressure of 4500 Pa, the igniter is started to discharge, the reduction reaction is carried out for 0.5 h, then the vacuum is drawn again, and the furnace is cooled for 6 h; the vacuum suspension melting process is as follows: the vacuum is drawn to 100 Pa, argon gas is introduced to a pressure of more than 1000 Pa, then the vacuum system is adjusted to maintain the pressure under the argon atmosphere at 1500 Pa, and the furnace is melted at 1950℃ for 0.5 h and then cooled.

[0052] Upon testing, the iron (II) concentration in the chromium (III) solution obtained in step three of this embodiment was found to be 0.0085 g / L, and the iron element mass percentage in the chromium trioxide obtained in step four was 0.0018%.

[0053] Example 3

[0054] The preparation method of this embodiment includes the following steps:

[0055] Step 1: Mix 1000g of 3N grade chromium powder with a particle size of 200 mesh, 2884.5g of concentrated sulfuric acid with a mass fraction greater than 98%, and 5.8L of water, and leach at 25℃ for 6 hours, stirring at 100r / min during the leaching process to obtain the leachate; the excess coefficient of the concentrated sulfuric acid is 1.

[0056] Step 2, Mohr's salt method: After filtering the leachate obtained in Step 1 (with obvious undissolved matter), mix it with 10g ascorbic acid and 1256.5g ammonium sulfate. Control the temperature at 50℃, adjust the pH to 0.2, and then rapidly cool it to 5℃. Then crystallize for 30 hours, and filter to obtain the filtrate; the excess coefficient of the ammonium sulfate is 1.

[0057] Step 3: Extract the filtrate obtained in Step 2 to obtain a chromium(III) solution. The extraction process is as follows: a mixture of 30% P2O4 and 70% sulfonated kerosene is used as the extraction organic phase. Under the conditions of an extraction ratio of Vo / Va of 1 / 1, an extraction temperature of 10℃, a shaking time of 30 min, and a pH of 4, chromium is transferred from the filtrate obtained in Step 2 to the extraction organic phase. Then, chromium is back-extracted using 2 mol / L sulfuric acid under the conditions of an extraction ratio of Vo / Va of 5 / 1, a temperature of 10℃, and a shaking time of 30 min. The saponification rate of the extraction organic phase is 20%.

[0058] Step 4: The temperature of the chromium(III) solution obtained in Step 3 is controlled at 50℃, the pH is adjusted to 7-8, and then polyacrylamide is added for alkaline precipitation for 1.5 hours. After filtration, chromium hydroxide is obtained; the concentration of polyacrylamide in the chromium(III) solution is 10 g / L.

[0059] Step 5: The chromium hydroxide obtained in Step 4 is charged into an atmosphere calcination furnace with carbon monoxide at a flow rate of 1L / min to 2L / min, and calcined at a temperature of 500℃ for 4 hours to obtain chromium trioxide.

[0060] Step Six: Take 100g of chromium trioxide obtained in Step Five, mix it with 36.04g of 4N grade aluminum granules with a particle size of 3mm, 7.02g of sodium nitrate with a purity greater than 99%, and 0.38g of igniter, and perform vacuum aluminothermic reduction and vacuum suspension melting sequentially to obtain 4N chromium; the unit charge reaction heat of the 7.02g sodium nitrate is 3100kJ, and the igniter consists of 66% saltpeter, 5% aluminum granules, and 0.38g of [unspecified ingredient]. The composition is 29% magnesium shavings; the vacuum aluminothermic reduction process is as follows: before ignition, the vacuum is drawn to 1 Pa, argon gas is introduced to a pressure of 4600 Pa, the igniter is started to discharge, the reduction reaction is carried out for 0.6 h, then the vacuum is drawn again, and the furnace is cooled for 6 h; the vacuum suspension melting process is as follows: the vacuum is drawn to 50 Pa, argon gas is introduced to a pressure of more than 1000 Pa, then the vacuum system is adjusted to maintain the pressure under the argon atmosphere at 1000 Pa, and the furnace is melted at 1960℃ for 0.6 h and then cooled.

[0061] Upon testing, the iron (II) concentration in the chromium (III) solution obtained in step three of this embodiment was found to be 0.012 g / L, and the iron element mass percentage in the chromium trioxide obtained in step four was 0.0012%.

[0062] Example 4

[0063] The preparation method of this embodiment includes the following steps:

[0064] Step 1: Mix 1000g of 3N grade chromium powder with a particle size of 500 mesh, 4236.75g of concentrated sulfuric acid with a mass fraction greater than 98%, and 8.65L of water. Leach at 100℃ for 1 hour, stirring at 500r / min during the leaching process to obtain the leachate. The excess coefficient of the concentrated sulfuric acid is 1.5, and the stirring speed is 500r / min.

[0065] Step 2, Mohr's salt method: After filtering the leachate obtained in Step 1, mix it with 10g ascorbic acid and 5026g ammonium sulfate. Control the temperature at 90℃, adjust the pH to 2.5, and then rapidly cool it to 5℃. Then crystallize for 4 hours and filter to obtain the filtrate. The excess coefficient of the ammonium sulfate is 4.

[0066] Step 3: Extract the filtrate obtained in Step 2 to obtain a chromium(III) solution. The extraction process is as follows: a mixture of 30% P2O4 and 70% sulfonated kerosene is used as the extraction organic phase. Under the conditions of an extraction ratio of Vo / Va of 1 / 1, an extraction temperature of 50°C, a shaking time of 25 min, and a pH of 4, chromium is transferred from the filtrate obtained in Step 2 to the extraction organic phase. Then, chromium is back-extracted using 2 mol / L sulfuric acid under the conditions of an extraction ratio of Vo / Va of 5 / 1, a temperature of 50°C, and a shaking time of 25 min. The saponification rate of the extraction organic phase is 90%.

[0067] Step 4: The temperature of the chromium(III) solution obtained in Step 3 is controlled at 90℃, the pH is adjusted to 7-8, and then polyacrylamide is added for alkaline precipitation for 2 hours. After filtration, chromium hydroxide is obtained; the concentration of polyacrylamide in the chromium(III) solution is 3 g / L.

[0068] Step 5: The chromium hydroxide obtained in Step 4 is charged into an atmosphere calcination furnace with carbon monoxide at a flow rate of 1L / min to 2L / min, and calcined at a temperature of 1000℃ for 1 hour to obtain chromium trioxide.

[0069] Step Six: Take 100g of chromium trioxide obtained in Step Five, mix it with 36.04g of 4N grade aluminum granules with a particle size of 5mm, 5.56g of sodium nitrate with a purity greater than 99%, and 0.38g of igniter, and perform vacuum aluminothermic reduction and vacuum suspension melting sequentially to obtain 4N chromium; the unit furnace charge reaction heat of the 5.56g sodium nitrate is 2970kJ, and the igniter consists of 65% saltpeter, 5% aluminum granules, and 0.38g of other materials. It consists of 30% magnesium shavings; the vacuum aluminothermic reduction process is as follows: before ignition, the vacuum is drawn to 100Pa, argon is introduced to a pressure of 5000Pa, the igniter is started to discharge, the reduction reaction is carried out for 1 hour, then the vacuum is drawn again, and the furnace is cooled for 6 hours; the vacuum suspension melting process is as follows: the vacuum is drawn to 50Pa, argon is introduced to a pressure of more than 1000Pa, then the vacuum system is adjusted to maintain the pressure under the argon atmosphere at 2000Pa, and the furnace is melted at 2000℃ for 1 hour and then cooled.

[0070] Upon testing, the iron (II) concentration in the chromium (III) solution obtained in step three of this embodiment was found to be 0.007 g / L, and the iron element mass percentage in the chromium trioxide obtained in step four was 0.0008%.

[0071] Impurity composition was analyzed in all 4N chromium samples prepared in Examples 1-4, and the results are shown in Table 1. Table 1: Impurity element mass content (%) of 4N chromium in Examples 1-4 and the impurity element mass content (%) requirements for 4N chromium in "High Purity Metallic Chromium" (GB / T28908-2012).

[0072]

[0073] As shown in Table 1, the content of each impurity element in the 4N chromium prepared in Examples 1 to 4 meets the range requirements in "High Purity Metallic Chromium", indicating that the preparation method of the present invention can effectively reduce the impurity content in chromium and improve the purity of chromium. At the same time, when using chromium powder composed of 71.34% Cr and 27.58% Fe by mass as raw materials, the preparation method of the present invention can also effectively reduce the iron content to prepare 4N chromium, which greatly reduces the requirements for raw materials in the preparation of 4N chromium.

[0074] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing 4N high-purity chromium, characterized in that, The preparation method includes the following steps: Step 1: Mix concentrated sulfuric acid with water and then add metallic chromium for leaching to obtain a leachate; Step 2, Mohr's salt method: After filtering the leachate obtained in Step 1, mix it with a reducing agent and ammonium sulfate, and then crystallize and filter it sequentially to obtain a filtrate; the reducing agent is ascorbic acid, the excess coefficient of the ammonium sulfate is 1~4, and the crystallization process is as follows: control the temperature at 50℃~90℃ and the pH value at 0.2~2.5, then cool to 5℃, and then crystallize for 4h~30h; Step 3: Extract the filtrate obtained in Step 2 to obtain a chromium (III) solution; Step 4: The chromium(III) solution obtained in Step 3 is subjected to alkaline precipitation, and after filtration, chromium hydroxide is obtained; Step 5: Calcining the chromium hydroxide obtained in Step 4 yields chromium trioxide; Step 6: Mix the chromium trioxide obtained in Step 5 with aluminum granules and a heating agent, and then perform vacuum aluminothermic reduction and vacuum suspension melting in sequence to obtain 4N chromium.

2. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, In step one, the excess coefficient of the concentrated sulfuric acid is 1 to 1.5, the mass concentration of the concentrated sulfuric acid is greater than 98%, the particle size of the metallic chromium is 200 mesh to 500 mesh, the stirring speed is 100 r / min to 500 r / min during the leaching process, the leaching temperature is 25℃ to 100℃, and the leaching time is 1 h to 6 h.

3. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, The extraction process described in step three is as follows: a mixture of P204 and sulfonated kerosene is used as the extraction organic phase. Under the conditions of an extraction ratio of Vo / Va of 1 / 1, an extraction temperature of 10℃~50℃, a shaking time of 5min~30min, and a pH value of 1~4, chromium is transferred from the filtrate obtained in step two to the extraction organic phase. Then, chromium is back-extracted using sulfuric acid with a concentration of 2mol / L under the conditions of an extraction ratio of Vo / Va of 5 / 1, a temperature of 10℃~50℃, and a shaking time of 5min~30min.

4. The method for preparing 4N high-purity chromium according to claim 3, characterized in that, The mass of P204 is 30% of the total mass of the extracted organic phase, the mass of the sulfonated kerosene is 70% of the total mass of the extracted organic phase, and the saponification rate of the extracted organic phase is 20%~90%.

5. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, The alkaline precipitation in step four is carried out at a temperature of 50℃ to 90℃, with a pH value of 7 to 8, and a precipitation time of 1 to 2 hours.

6. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, In step four, polyacrylamide is added before alkaline precipitation, and the concentration of polyacrylamide in chromium (III) solution is 3 g / L to 10 g / L.

7. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, The roasting process described in step five is as follows: carbon monoxide is introduced into an atmosphere calcination furnace, and the temperature is raised to 500℃~1000℃ for roasting for 1h~4h.

8. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, In step six, the aluminum granules are of grade 4N or higher, with a particle size of 1mm to 5mm and a mass of 90% to 95% of the theoretical amount. The heating agent is sodium nitrate with a purity greater than 99%. In the vacuum aluminothermic reduction, a mixture of saltpeter, aluminum granules, and magnesium shavings is used as the igniter, with the igniter's mass being 0.3% to 0.5% of the total mass of chromium trioxide, aluminum granules, and heating agent. The vacuum aluminothermic reduction process is as follows: vacuum is applied to 1Pa to 100Pa, argon gas is introduced to a pressure of 4500Pa to 5000Pa, and then the reduction reaction is carried out for 0.5 to 1 hour before vacuuming again, followed by furnace cooling for more than 6 hours.

9. The method for preparing 4N high-purity chromium according to claim 1, characterized in that, The vacuum suspension melting process described in step six is ​​as follows: evacuate to 1 Pa to 100 Pa, fill with argon gas to a pressure of over 1000 Pa, then heat to 1950℃ to 2000℃ and melt for 0.5 h to 1 h before cooling.

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