Preparation method of 4N high-purity chromium

Abstract

The invention discloses a preparation method of 4N high-purity chromium. The preparation method comprises the following steps that 1, concentrated sulfuric acid and water are mixed, and then metal chromium is added for leaching; step 2, a Moire salt method; 3, extracting to obtain a chromium (III) solution; 4, performing alkaline precipitation on the chromium (III) solution, and filtering to obtain chromium hydroxide; 5, roasting the chromium hydroxide to obtain chromium trioxide; and 6, the chromium trioxide is mixed with aluminum particles and a heat generating agent, vacuum aluminothermic reduction and vacuum suspension smelting are sequentially conducted, and the 4N chromium is obtained. According to the preparation method, the preparation period is shortened on the premise that the iron removal effect is guaranteed by adopting the one-time Moire salt method matched with the extraction iron removal process, then the content of gas, iron elements and other impurities is effectively reduced by adopting the vacuum aluminothermic reduction matched with the vacuum suspension smelting process, 4N chromium is obtained, and the preparation method is suitable for the technical field of high-purity metal chromium preparation.

Description

Technical Field

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

[0002] Chromium is a very hard and corrosion-resistant alloy. It can be used as an alloying element in special steels, making them corrosion-resistant, impact-resistant, extremely temperature-resistant, wear-resistant, friction-resistant, hard and strong. At the same time, since chromium forms a Cr2O3 oxide film, which produces good oxidation resistance and corrosion resistance, chromium is 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 manufacturing process of semiconductors and electronic devices to make high-purity chromium targets.

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

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

[0005] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing 4N high-purity chromium. The preparation method adopts a process of a primary Mohr salt method combined with an extraction and iron removal process to shorten the preparation cycle while ensuring the iron removal effect, and then adopts a process of vacuum aluminothermic reduction combined with a vacuum suspension smelting process to effectively reduce the content of impurities such as gas and iron elements to obtain 4N chromium, thereby solving the problem that it is difficult to obtain 4N grade chromium in the prior art.

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

[0007] Step 1, mixing concentrated sulfuric acid with water and adding the mixture to metallic chromium for leaching to obtain a leachate;

[0008] Step 2, Mohr salt method: filtering the leaching solution obtained in step 1, mixing it with a reducing agent and ammonium sulfate, and sequentially performing crystallization and filtering to obtain a filtrate;

[0009] Step 3, extracting the filtrate obtained in step 2 to obtain a chromium (III) solution;

[0010] Step 4: subjecting the chromium (III) solution obtained in step 3 to alkaline precipitation, and filtering to obtain chromium hydroxide;

[0011] Step 5: roasting the chromium hydroxide obtained in step 4 to obtain chromium trioxide;

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

[0013] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the excess coefficient of concentrated sulfuric acid in step 1 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°C to 100°C, and the leaching time is 1h to 6h.

[0014] The invention makes the excess of concentrated sulfuric acid conducive to the leaching reaction, controls the excess coefficient of concentrated sulfuric acid to be 1-1.5 to avoid excessive concentration of concentrated sulfuric acid, and controls the leaching temperature and time to improve the leaching rate of metal chromium.

[0015] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the reducing agent in step 2 is ascorbic acid, the excess coefficient of ammonium sulfate is 1 to 4, and the crystallization process is: controlling the temperature to 50°C to 90°C, the pH value to 0.2 to 2.5, then cooling to 5°C, and then crystallizing for 4h to 30h.

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

[0017] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the extraction process described in step 3 is: using a mixture of P204 and sulfonated kerosene as the extraction organic phase, under the conditions of an extraction phase ratio Vo / Va of 1 / 1, an extraction temperature of 10°C to 50°C, an oscillation time of 5min to 30min, and a pH value of 1 to 4, transferring chromium from the filtrate obtained in step 2 to the extraction organic phase; then using sulfuric acid with a concentration of 2 mol / L, under the conditions of an extraction phase ratio Vo / Va of 5 / 1, a temperature of 10°C to 50°C, and an oscillation time of 5min to 30min, the chromium is stripped.

[0018] In the present 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 the 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% 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 4 is 50°C to 90°C, the pH value of the alkaline precipitation is 7 to 8, and the duration of the alkaline precipitation is 1h to 2h.

[0021] The invention controls the temperature, pH value and time in the alkaline precipitation process to ensure that the chromium ions in the solution are completely converted into chromium hydroxide precipitation as much 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 4, and the concentration of the polyacrylamide in the chromium (III) solution is 3g / L to 10g / L.

[0023] The invention adds polyacrylamide to improve the filtering performance of the generated amorphous colloidal chromium hydroxide, so that the amorphous colloidal chromium hydroxide is transformed into gel or flocculent, which is beneficial to increase the chromium hydroxide filtration amount.

[0024] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the roasting process in step 5 is: filling carbon monoxide into an atmosphere calcining furnace, heating to 500° C. to 1000° C. and roasting for 1 hour to 4 hours.

[0025] The present invention adopts a reducing carbon monoxide atmosphere for calcination, thereby avoiding the formation of hexavalent chromium during the calcination process, and better controlling the oxidation state of chromium hydroxide to form the desired chromium trioxide.

[0026] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the aluminum particles in step six are above 4N grade, the particle size of the aluminum particles is 1mm~5mm, and the mass of the aluminum particles is 90%~95% of the theoretical amount; the exothermic agent is sodium nitrate with a mass purity greater than 99%; a mixture of saltpeter, aluminum beans and magnesium chips is used as an ignition agent in the vacuum aluminothermic reduction, and the mass of the ignition agent is 0.3%~0.5% of the total mass of chromium trioxide, aluminum particles and the exothermic agent; the process of the vacuum aluminothermic reduction is: evacuate to 1Pa~100Pa, fill with argon to a pressure of 4500Pa~5000Pa, then evacuate after the reduction reaction for 0.5h~1h, and cool the furnace for more than 6h.

[0027] The present invention controls the pressure to 4500Pa-5000Pa, thereby preventing the product chromium from being heated and melted during the aluminothermic reduction process, whereby too low system pressure easily causes the chromium to volatilize, and too high pressure is not conducive to the volatilization of impurity elements; preferably, the present invention sets the mass of the heat-generating agent within the range of 2970kJ-3100kJ of unit charge reaction heat, which can heat the raw materials to a suitable temperature and effectively separate the metal liquid and slag.

[0028] The above-mentioned method for preparing 4N high-purity chromium is characterized in that the process of vacuum suspension smelting in step 6 is: evacuating to 1Pa~100Pa, filling with argon gas to a pressure of more than 1000Pa, then heating to 1950℃~2000℃, smelting for 0.5h~1h and then cooling.

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

[0030] 1. The present invention adopts a single Mohr salt method combined with an extraction and iron removal process to avoid the use of multiple Mohr salt methods for crystallization, which leads to a longer preparation cycle, while ensuring the effect of iron removal. At the same time, the single Mohr salt method combined with an extraction and iron removal process can significantly reduce the content of iron elements, thereby obtaining 4N chromium.

[0031] 2. The present invention can obtain 4N chromium with qualified composition by adopting a process of vacuum aluminothermic reduction combined with vacuum suspension smelting. Compared with the metallic chromium prepared by the aluminothermic reduction process or the electrolysis process in the prior art, the 4N chromium prepared by the present invention has a lower gas impurity content.

[0032] 3. The preparation method of the present invention has no requirement on 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 is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a process flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0035] Example 1

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

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

[0038] Step 2, Mohr salt method: the leachate obtained in step 1 is filtered and mixed with 10g ascorbic acid and 3769.6g ammonium sulfate, the temperature is controlled to 70°C, the pH value is adjusted to 0.5, the reaction container is placed in an ice-water mixture and cooled to 5°C, and then crystallized for 24 hours, and filtered to obtain a filtrate; the excess coefficient of ammonium sulfate is 3;

[0039] Step 3, extracting the filtrate obtained in step 2 to obtain a chromium (III) solution; the extraction process is: using a mixture of 30% P204 and 70% sulfonated kerosene as an extraction organic phase, transferring chromium from the filtrate obtained in step 2 to the extraction organic phase under the conditions of an extraction phase ratio Vo / Va of 1 / 1, an extraction temperature of 28°C, an oscillation time of 5 minutes, and a pH value of 2.4; then using sulfuric acid with a concentration of 2 mol / L, under the conditions of an extraction phase ratio Vo / Va of 5 / 1, a temperature of 28°C, and an oscillation time of 5 minutes, the chromium is stripped; the saponification rate of the extraction organic phase is 70%;

[0040] Step 4: Control the temperature of the chromium (III) solution obtained in step 3 to 85° C., adjust the pH value to 7-8, add polyacrylamide for alkaline precipitation for 1 hour, and obtain chromium hydroxide after filtering; the concentration of the polyacrylamide in the chromium (III) solution is 5 g / L;

[0041] Step 5: The chromium hydroxide obtained in step 4 is charged with carbon monoxide at a flow rate of 1 L / min to 2 L / min in an atmosphere calcining furnace, and roasted at a temperature of 600° C. for 2 h to obtain chromium trioxide;

[0042] Step 6: Take 100g of the chromium trioxide obtained in step 5, mix it with 36.04g of 4N grade aluminum particles with a particle size of 1mm, 6.45g of sodium nitrate with a mass purity greater than 99% and 0.428g of ignition agent, and perform vacuum aluminothermic reduction and vacuum suspension smelting in sequence to obtain 4N chromium; the unit charge reaction heat of the 6.45g sodium nitrate is 3050kJ, and the ignition agent is composed of 65% by mass of saltpeter, 5% by mass of aluminum beans, and 0.428g by mass of ignition agent. 30% magnesium chips; the vacuum aluminum thermal reduction process is: evacuate to 50Pa before ignition, fill with argon to a pressure of 4500Pa, start the igniter to discharge, carry out the reduction reaction for 0.5h, then evacuate, and cool the furnace for 6h; the vacuum suspension smelting process is: evacuate to 1Pa, fill with argon to a pressure of more than 1000Pa, then adjust the vacuum system to maintain the pressure of 1500Pa under the argon atmosphere, smelt at a temperature of 1950℃ for 0.5h and then cool.

[0043] According to the test, the concentration of iron (II) in the chromium (III) solution obtained in step three of this embodiment is 0.008 g / L, and the mass percentage of iron in the chromium trioxide obtained in step four is 0.001%.

[0044] Example 2

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

[0046] Step 1, after mixing 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, leaching at 90°C for 4h, and stirring at a speed of 300r / min during the leaching process to obtain a leachate; the chromium powder consists of 71.34% of Cr and 27.58% of Fe by mass, and the excess coefficient of concentrated sulfuric acid is 1.3;

[0047] Step 2, Mohr salt method: the leachate obtained in step 1 is filtered and mixed with 20g ascorbic acid and 4670.1g ammonium sulfate, the temperature is controlled to 70°C, the pH value is adjusted to 0.5, and then rapidly cooled to 5°C, and then crystallized for 24h, and filtered to obtain a filtrate; the excess coefficient of ammonium sulfate is 3;

[0048] Step 3, extracting the filtrate obtained in step 2 to obtain a chromium (III) solution; the extraction process is: using a mixture of 30% P204 and 70% sulfonated kerosene as an extraction organic phase, transferring chromium from the filtrate obtained in step 2 to the extraction organic phase under the conditions of an extraction phase ratio Vo / Va of 1 / 1, an extraction temperature of 28°C, an oscillation time of 5 minutes, and a pH value of 2.4; then using sulfuric acid with a concentration of 2 mol / L, under the conditions of an extraction phase ratio Vo / Va of 5 / 1, a temperature of 28°C, and an oscillation time of 5 minutes, the chromium is stripped; 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° C., adjust the pH value to 7-8, add polyacrylamide for alkaline precipitation for 1.5 hours, and obtain chromium hydroxide after filtering; the concentration of the polyacrylamide in the chromium (III) solution is 5 g / L;

[0050] Step 5: The chromium hydroxide obtained in step 4 is charged with carbon monoxide at a flow rate of 1 L / min to 2 L / min in an atmosphere calcining furnace, and roasted at a temperature of 600° C. for 2 h to obtain chromium trioxide;

[0051] Step 6: Take 500g of the chromium trioxide obtained in step 5, mix it with 180.2g of 4N grade aluminum particles with a particle size of 1mm, 32.25g of sodium nitrate with a mass purity greater than 99% and 0.428g of ignition agent, and perform vacuum aluminothermic reduction and vacuum suspension smelting in sequence to obtain 4N chromium; the unit charge reaction heat of the 32.25g sodium nitrate is 3050kJ, and the ignition agent is composed of 62% by mass of saltpeter, 2% by mass of aluminum beans, and 0.428g by mass of ignition agent. 36% magnesium chips; the vacuum aluminum thermal reduction process is: evacuate to 50Pa before ignition, fill with argon to a pressure of 4500Pa, start the igniter to discharge, carry out the reduction reaction for 0.5h, then evacuate, and cool the furnace for 6h; the vacuum suspension smelting process is: evacuate to 100Pa, fill with argon to a pressure of more than 1000Pa, then adjust the vacuum system to maintain the pressure of 1500Pa under argon atmosphere, smelt at 1950℃ for 0.5h and then cool.

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

[0053] Example 3

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

[0055] Step 1, 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 are mixed, and leached at 25°C for 6h, and stirred at a speed of 100r / min during the leaching process to obtain a leachate; the excess coefficient of concentrated sulfuric acid is 1;

[0056] Step 2, Mohr salt method: the leachate obtained in step 1 (with obvious insoluble matter) is filtered and mixed with 10g ascorbic acid and 1256.5g ammonium sulfate, the temperature is controlled to 50°C, the pH value is adjusted to 0.2, and then rapidly cooled to 5°C, and then crystallized for 30h, and filtered to obtain a filtrate; the excess coefficient of ammonium sulfate is 1;

[0057] Step 3, extracting the filtrate obtained in step 2 to obtain a chromium (III) solution; the extraction process is: using a mixture of 30% by mass of P204 and 70% by mass of sulfonated kerosene as an extraction organic phase, transferring chromium from the filtrate obtained in step 2 to the extraction organic phase under the conditions of an extraction phase ratio Vo / Va of 1 / 1, an extraction temperature of 10°C, an oscillation time of 30min, and a pH value of 4; then using sulfuric acid with a concentration of 2 mol / L, under the conditions of an extraction phase ratio Vo / Va of 5 / 1, a temperature of 10°C, and an oscillation time of 30min, to strip the chromium; the saponification rate of the extraction organic phase is 20%;

[0058] Step 4: Control the temperature of the chromium (III) solution obtained in step 3 to 50° C., adjust the pH value to 7-8, add polyacrylamide for alkaline precipitation for 1.5 hours, and obtain chromium hydroxide after filtering; the concentration of the polyacrylamide in the chromium (III) solution is 10 g / L;

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

[0060] Step 6: Take 100g of the chromium trioxide obtained in step 5, mix it with 36.04g of 4N grade aluminum particles with a particle size of 3mm, 7.02g of sodium nitrate with a purity greater than 99% by mass, and 0.38g of ignition agent, and perform vacuum aluminothermic reduction and vacuum suspension smelting in sequence to obtain 4N chromium; the unit charge reaction heat of the 7.02g of sodium nitrate is 3100kJ, and the ignition agent is composed of 66% by mass of saltpeter, 5% by mass of aluminum beans, and 1.3% by mass of aluminum nitrate. 29% magnesium chips; the vacuum aluminum thermal reduction process is: evacuate to 1Pa before ignition, fill with argon to a pressure of 4600Pa, start the igniter to discharge, carry out the reduction reaction for 0.6h, then evacuate, and cool the furnace for 6h; the vacuum suspension smelting process is: evacuate to 50Pa, fill with argon to a pressure of more than 1000Pa, then adjust the vacuum system to maintain the pressure of 1000Pa under the argon atmosphere, smelt at a temperature of 1960℃ for 0.6h and then cool.

[0061] According to the test, the concentration of iron (II) in the chromium (III) solution obtained in step 3 of this embodiment is 0.012 g / L, and the mass percentage of iron in the chromium trioxide obtained in step 4 is 0.0012%.

[0062] Example 4

[0063] The preparation method of this embodiment comprises 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, and leach at 100°C for 1h, and stir at a speed of 500r / min during the leaching process to obtain a leachate; the excess coefficient of concentrated sulfuric acid is 1.5, and the stirring speed is 500r / min;

[0065] Step 2, Mohr salt method: the leachate obtained in step 1 is filtered and mixed with 10g ascorbic acid and 5026g ammonium sulfate, the temperature is controlled to 90°C, the pH value is adjusted to 2.5, and then rapidly cooled to 5°C, and then crystallized for 4h, and filtered to obtain a filtrate; the excess coefficient of ammonium sulfate is 4;

[0066] Step 3, extracting the filtrate obtained in step 2 to obtain a chromium (III) solution; the extraction process is: using a mixture of 30% by mass of P204 and 70% by mass of sulfonated kerosene as an extraction organic phase, transferring chromium from the filtrate obtained in step 2 to the extraction organic phase under the conditions of an extraction phase ratio Vo / Va of 1 / 1, an extraction temperature of 50°C, an oscillation time of 25min, and a pH value of 4; then using sulfuric acid with a concentration of 2 mol / L, under the conditions of an extraction phase ratio Vo / Va of 5 / 1, a temperature of 50°C, and an oscillation time of 25min, to strip the chromium; the saponification rate of the extraction organic phase is 90%;

[0067] Step 4: Control the temperature of the chromium (III) solution obtained in step 3 to 90° C., adjust the pH value to 7-8, add polyacrylamide for alkaline precipitation for 2 hours, and obtain chromium hydroxide after filtering; the concentration of the polyacrylamide in the chromium (III) solution is 3 g / L;

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

[0069] Step 6: Take 100g of the chromium trioxide obtained in step 5, mix it with 36.04g of 4N grade aluminum particles with a particle size of 5mm, 5.56g of sodium nitrate with a mass purity greater than 99% and 0.38g of ignition agent, and perform vacuum aluminothermic reduction and vacuum suspension smelting in sequence to obtain 4N chromium; the unit charge reaction heat of the 5.56g sodium nitrate is 2970kJ, and the ignition agent is composed of 65% by mass of saltpeter, 5% by mass of aluminum beans, and 0.38% by mass of ignition agent. The vacuum aluminum thermal reduction process is as follows: evacuate to 100Pa before ignition, fill with argon to a pressure of 5000Pa, start the igniter to discharge, carry out the reduction reaction for 1 hour, then evacuate, and cool the furnace for 6 hours; the vacuum suspension smelting process is as follows: evacuate to 50Pa, fill with argon to a pressure of more than 1000Pa, then adjust the vacuum system to maintain the pressure of 2000Pa under the argon atmosphere, smelt at 2000℃ for 1 hour, and then cool.

[0070] According to the test, the concentration of iron (II) in the chromium (III) solution obtained in step three of this embodiment is 0.007 g / L, and the mass percentage of iron in the chromium trioxide obtained in step four is 0.0008%.

[0071] The 4N chromium prepared in Examples 1 to 4 was tested for impurity components, and the results are shown in Table 1. Table 1 The mass content (%) of impurity elements in 4N chromium in Examples 1 to 4 and the mass content (%) of impurity elements in 4N chromium in "High Purity Metallic Chromium" (GB / T28908-2012) Requirements

[0072]

[0073] It can be seen from Table 1 that the contents of various impurity elements in the 4N chromium prepared in Examples 1 to 4 meet 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% by mass of Cr and 27.58% by mass of Fe as a raw material, 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 for the preparation of 4N chromium.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing 4N high-purity chromium, characterized in that: The preparation method comprises the following steps: Step 1, mixing concentrated sulfuric acid with water and adding metallic chromium to obtain a leachate; Step 2, Mohr salt method: filtering the leaching solution obtained in step 1, mixing it with a reducing agent and ammonium sulfate, and sequentially performing crystallization and filtering to obtain a filtrate; Step 3, extracting the filtrate obtained in step 2 to obtain a chromium (III) solution; Step 4: subjecting the chromium (III) solution obtained in step 3 to alkaline precipitation, and filtering to obtain chromium hydroxide; Step 5: roasting the chromium hydroxide obtained in step 4 to obtain chromium trioxide; Step 6: Mix the chromium trioxide obtained in step 5 with aluminum particles and a heating agent, and perform vacuum aluminothermic reduction and vacuum suspension smelting in sequence to obtain 4N chromium.

2. The method for preparing 4N high-purity chromium according to claim 1, characterized in that: In step 1, the excess coefficient of 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° C. to 100° C., 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: In step 2, the reducing agent is ascorbic acid, the excess coefficient of ammonium sulfate is 1 to 4, and the crystallization process is: controlling the temperature to 50° C. to 90° C., the pH value to 0.2 to 2.5, then cooling to 5° C., and then crystallizing for 4 h to 30 h.

4. The method for preparing 4N high-purity chromium according to claim 1, characterized in that: The extraction process in step 3 is as follows: using a mixture of P204 and sulfonated kerosene as an extraction organic phase, transferring chromium from the filtrate obtained in step 2 to the extraction organic phase under the conditions of an extraction phase ratio Vo / Va of 1 / 1, an extraction temperature of 10°C to 50°C, an oscillation time of 5min to 30min, and a pH value of 1 to 4; and then using sulfuric acid with a concentration of 2 mol / L to strip the chromium under the conditions of an extraction phase ratio Vo / Va of 5 / 1, a temperature of 10°C to 50°C, and an oscillation time of 5min to 30min.

5. The method for preparing 4N high-purity chromium according to claim 4, characterized in that: The mass of the 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% to 90%.

6. The method for preparing 4N high-purity chromium according to claim 1, characterized in that: The temperature of the alkaline precipitation in step 4 is 50° C. to 90° C., the pH value of the alkaline precipitation is 7 to 8, and the duration of the alkaline precipitation is 1 h to 2 h.

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

8. The method for preparing 4N high-purity chromium according to claim 1, characterized in that: The calcination process in step 5 is as follows: carbon monoxide is charged into an atmosphere calcining furnace, and the temperature is raised to 500° C. to 1000° C. for calcination for 1 h to 4 h.

9. The method for preparing 4N high-purity chromium according to claim 1, characterized in that: The aluminum particles described in step six are of 4N grade or above, the particle size of the aluminum particles is 1mm~5mm, and the mass of the aluminum particles is 90%~95% of the theoretical amount; the exothermic agent is sodium nitrate with a mass purity greater than 99%; a mixture of saltpeter, aluminum beans and magnesium chips is used as an ignition agent in the vacuum aluminothermic reduction, and the mass of the ignition agent is 0.3%~0.5% of the total mass of chromium trioxide, aluminum particles and the exothermic agent; the process of the vacuum aluminothermic reduction is: evacuate to 1Pa~100Pa, fill with argon to a pressure of 4500Pa~5000Pa, then evacuate after the reduction reaction is carried out for 0.5h~1h, and cool the furnace for more than 6h.

10. The method for preparing 4N high-purity chromium according to claim 1, characterized in that: The process of vacuum suspension melting in step six is: evacuate to 1Pa-100Pa, fill with argon gas to a pressure of more than 1000Pa, then heat to 1950°C-2000°C, melt for 0.5h-1h, and then cool.

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