Vanadium-chromium separation method for vanadium-chromium solution

Abstract

The invention relates to the technical field of hydrometallurgy, in particular to a vanadium and chromium separation method for a vanadium and chromium solution. The method comprises the following steps: adjusting the pH value of the vanadium-chromium solution to 2-4; adding a reducing agent into the vanadium-chromium solution; adding tetraalkylammonium into the obtained solution, stirring, and filtering to obtain a vanadium-containing precipitate and a chromium-containing solution; washing, drying and calcining the vanadium-containing precipitate to obtain vanadium pentoxide; adding alkali into the chromium-containing solution, stirring, filtering to obtain chromium hydroxide precipitate, washing, drying and calcining the chromium hydroxide precipitate to obtain chromium sesquioxide. According to the method, Cr (VI) is selectively reduced into Cr (III) through a reducing agent, vanadium in the solution exists in the form of polyvanadate anions and chromium exists in the form of Cr < 3 + >, then tetraalkylammonium is selected for vanadium precipitation, the radius of tetraalkylammonium ions is larger than that of NH4 < + > in a traditional vanadium precipitation agent, the tetraalkylammonium ions can be combined with the polyvanadate anions more easily to repel Cr < 3 + >, and therefore the vanadium precipitation effect is improved. Therefore, the separation of vanadium and chromium is simply, conveniently and efficiently completed.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for separating vanadium and chromium from a vanadium-chromium solution. Background Art

[0002] Vanadium is an important strategic metal resource and is widely used in the fields of steel, alloys, and chemicals. The main sources of vanadium resources are vanadium-containing ores such as vanadium-titanium magnetite and stone coal. The extraction of vanadium from vanadium-containing ores mainly involves roasting-leaching-precipitation and other steps. However, some vanadium-containing ores (such as Panzhihua Hongge magnetite) also contain a certain amount of chromium. During the leaching process, chromium will enter the solution together with vanadium to form a vanadium-chromium solution. In the acidic leaching solution, V(V) is usually expressed as HV 10 O 28 5- , H 2 V 10 O 28 4- Cr(VI) exists in the form of Cr 2 O 7 2- The polyvanadate ions and chromate ions exist in different forms. Their chemical properties are similar and they are difficult to separate. The traditional vanadium precipitation method using inorganic ammonium salts will cause a certain amount of chromium to mix into the vanadium-containing precipitate, resulting in a decrease in the purity of the final vanadium product. Therefore, it is necessary to explore and develop vanadium-chromium separation technology for vanadium-chromium solution, thereby improving the purity of the vanadium product and recovering valuable chromium at the same time.

[0003] At present, the main methods for separating vanadium and chromium from vanadium-chromium solutions are precipitation, ion exchange and extraction. The invention patent with the authorization announcement number CN116334414B proposes a method for separating vanadium and chromium using adsorption resin. The pH value of the vanadium-chromium solution is first adjusted, and the selective separation of chromium is achieved by adsorption of multi-stage anion exchange resins; after the chromium is removed, the solution is separated by vanadium extraction and back extraction crystallization to achieve the separation of vanadium and chromium. However, the resin adsorption capacity is limited, and the adsorption efficiency is low when processing a large amount of vanadium-chromium solution.

[0004] The invention patent with the authorization announcement number CN111057875B proposes a method for selectively extracting and separating vanadium and chromium using microemulsion. The vanadium-chromium solution is adjusted in pH and then NaHSO is added. 3 After the reaction is complete, adjust the pH and add H 2 O 2, heated under stirring conditions until no bubbles are generated, thereby achieving the difference in the charge of vanadium and chromium ions. Aliquat336, isoamyl alcohol, n-heptane and the inner water phase are mixed to prepare a microemulsion and a vanadium-chromium solution. Under room temperature, the mixture is mixed and shaken for extraction to achieve the separation of vanadium and chromium. The microemulsion phase and the aqueous phase are separated by stripping, and the vanadium-containing stripping solution is further subjected to alkaline ammonium salt precipitation of vanadium, and calcined to obtain vanadium pentoxide. After the pH of the separated chromium-containing solution is adjusted, chromium is converted into Cr(OH) 3 The microemulsion is precipitated in the form of chromium trioxide, and chromium trioxide is obtained after calcination. However, the preparation of the microemulsion is complicated and requires stripping, and the overall process is relatively long.

[0005] The invention patent application with the announcement number CN111041205A proposes a method for selectively precipitating vanadium with melamine, wherein the vanadium-chromium solution is adjusted to a weak acidity, then heated, and melamine is added, stirred and adjusted to a strong acidity, and after the reaction is kept warm, the vanadium precipitate and the chromium-containing solution are obtained by standing and solid-liquid separation. In the above method, melamine has low solubility and limited vanadium precipitation capacity.

[0006] The invention patent application with announcement number CN110423901A provides a method for separating sodium vanadium chromium from a vanadium chromium solution, and the steps are as follows: a. Use an organic acid to adjust the pH of the vanadium chromium solution to 2.0-4.0, then add a vanadium precipitator to react, separate the solid and liquid, and wash, dry and calcine the solid to obtain vanadium pentoxide; b. Add an organic acid to the liquid obtained by solid-liquid separation in step a and concentrate it to 1 / 3-1 / 2 volume, separate the solid and liquid, and wash, dry and calcine the solid to obtain chromium trioxide; c. The liquid obtained by solid-liquid separation in step b is concentrated and crystallized to obtain sodium carbonate. Since the separation method in the above application requires multiple solid-liquid separation, washing, drying and calcination steps, the operation is relatively complicated and time-consuming. And because it involves multiple concentration and crystallization processes, the energy consumption is relatively high. Based on this, the existing technology still needs to be improved. Summary of the invention

[0007] The present invention provides a method for separating vanadium and chromium from a vanadium-chromium solution. The method comprises adjusting the pH value of the solution, firstly using a reducing agent to selectively reduce Cr(VI) to Cr(III) under acidic conditions, and then selecting tetraalkylammonium to perform vanadium precipitation and subsequent steps. The method can at least solve the technical problem that the separation of vanadium and chromium from the existing vanadium-chromium solution is difficult.

[0008] Specifically, the method for separating vanadium and chromium from a vanadium and chromium solution of the present invention comprises the following steps: S1, adjusting the pH of the vanadium-chromium solution to 2-4; S2, adding a reducing agent to the vanadium-chromium solution, stirring sufficiently, and selectively reducing Cr(VI) to Cr(III); S3, adding tetraalkylammonium to the obtained solution, stirring, and filtering to obtain a vanadium-containing precipitate and a chromium-containing solution; S4, washing, drying and calcining the vanadium-containing precipitate to obtain vanadium pentoxide; S5, adding alkali to the chromium-containing solution, stirring and filtering to obtain chromium hydroxide precipitate, washing, drying and calcining the chromium hydroxide precipitate to obtain chromium trioxide.

[0009] In some embodiments, step S1 further comprises: if the initial vanadium-chromium solution has a pH value greater than 4, then adding acid to adjust the pH value, and if the initial vanadium-chromium solution has a pH value less than 2, then adding alkali to adjust the pH value, so that the pH value satisfies the selective reduction condition of chromium. The added acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid. The added alkali is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

[0010] In some embodiments, step S2 includes: continuously adding acid to maintain a stable pH during the reduction process.

[0011] In some embodiments, in step S3, the cation of tetraalkylammonium is tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion or tetrabutylammonium ion. The anion of tetraalkylammonium is chloride ion, bromide ion, sulfate ion or nitrate ion. The radius of these ions is larger than that of NH 4 + When vanadium is precipitated under acidic conditions, it is easier to combine with polyvanadate anions and Cr 3+ Exclusion, thus completing the selective precipitation of vanadium simply and efficiently.

[0012] In some embodiments, in step S3, the molar ratio of the added tetraalkylammonium to the vanadium in the vanadium chromium solution is 0.2 to 3: 1. By controlling the molar ratio of tetraalkylammonium to vanadium, the precipitation process can be optimized to ensure sufficient precipitation of vanadium, thereby increasing the yield of vanadium pentoxide and the purity of the chromium product extracted from the subsequent chromium solution.

[0013] In some embodiments, in step S3, the stirring time is 15 min to 2 h. Appropriate stirring time can make the precipitate purer, reduce the co-precipitation of impurities, and thus improve the purity of the product.

[0014] In some embodiments, in step S4, the calcination temperature of the vanadium-containing precipitate is 500-600° C., and the calcination time is 2-4 hours. By calcination, carbon, nitrogen, and hydrogen in the precipitate can be effectively removed to obtain a vanadium pentoxide product.

[0015] In some embodiments, the reducing agent is ethanol. 3+ , reaction formula: 2Cr 2 O 7 2- +16H + +3CH 3 CH 2 OH→4Cr3+ +11H 2 O+3CH 3 COOH, but not easy to change the valence state of V(V) in the solution, in the subsequent vanadium precipitation process to reduce the interference of chromium in the solution on vanadium precipitation, thereby improving the precipitation rate and purity of vanadium.

[0016] In some embodiments, the molar ratio of the added ethanol to the chromium in the vanadium-chromium solution is 1-3:1, that is, 0.88-2.65 g of ethanol (1.12-3.36 mL) is required to add every 1 gram of Cr reduced in the solution. The amount of ethanol added should not be lower than this range to ensure that it can fully reduce Cr(VI) to Cr(III), nor should it exceed this range to reduce the risk of V(V) being reduced.

[0017] The beneficial effects of the present invention are as follows: the present invention adjusts the pH of the vanadium-chromium solution to 2-4, at which pH, ​​V (V) is mainly in the form of HV 10 O 28 5- , H 2 V 10 O 28 4- Cr(VI) exists in the form of Cr 2 O 7 2- Since these ions have similar chemical properties, if vanadium is directly precipitated under this condition, whether the conventional inorganic ammonium salt vanadium precipitator or the tetraalkylammonium vanadium precipitator of the present invention is used, a certain amount of chromium will be entrained in the vanadium precipitate. Therefore, the present invention first uses a reducing agent to selectively reduce Cr(VI) to Cr(III), while the existence form of vanadium remains unchanged. Then, tetraalkylammonium is used to precipitate vanadium. The ion radius of tetraalkylammonium is larger than that of NH in the conventional vanadium precipitator. 4 + , more easily combined with polyvanadate anions and Cr 3+ Rejection, thus completing the selective vanadium precipitation simply and efficiently, the vanadium precipitation reaction can be carried out at room temperature, and the vanadium-containing precipitation (NR 4 ) x H y (V 10 O 28 ) z The carbon, nitrogen and hydrogen can be removed by oxidation calcination to obtain vanadium pentoxide product. The chromium-containing solution can also be precipitated under alkaline conditions to obtain chromium hydroxide, which is then calcined to obtain chromium trioxide product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A flow chart of a method for separating vanadium and chromium from a vanadium and chromium solution provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0021] The present invention provides a method for separating vanadium and chromium from a vanadium and chromium solution, comprising the following steps: S1, adjusting the pH of the vanadium-chromium solution to 2-4; S2, adding a reducing agent to the vanadium-chromium solution, stirring sufficiently, and selectively reducing Cr(VI) to Cr(III); S3, adding tetraalkylammonium to the obtained solution, stirring, and filtering to obtain a vanadium-containing precipitate and a chromium-containing solution; S4, washing, drying and calcining the vanadium-containing precipitate to obtain vanadium pentoxide; S5, adding alkali to the chromium-containing solution, stirring and filtering to obtain chromium hydroxide precipitate, washing, drying and calcining the chromium hydroxide precipitate to obtain chromium trioxide.

[0022] Compared with the prior art, the present invention first adjusts the pH to 2-4. At this pH, V (V) is mainly HV 10 O 28 5- , H 2 V 10 O 28 4- Cr(VI) exists in the form of Cr 2 O 7 2- Since these ions have similar chemical properties, if vanadium is directly precipitated under this condition, whether the conventional inorganic ammonium salt vanadium precipitator or the tetraalkylammonium vanadium precipitator of the present invention is used, a certain amount of chromium will be entrained in the vanadium precipitate. Therefore, the present invention first uses a reducing agent to selectively reduce Cr(VI) to Cr(III), while the existence form of vanadium remains unchanged. Then, tetraalkylammonium is used to precipitate vanadium. The ion radius of tetraalkylammonium is larger than that of NH in the conventional vanadium precipitator. 4 + , more easily combined with polyvanadate anions and Cr 3+Rejection, thus completing the selective vanadium precipitation simply and efficiently, the vanadium precipitation reaction can be carried out at room temperature, and the vanadium-containing precipitation (NR 4 ) x H y (V 10 O 28 ) z The carbon, nitrogen and hydrogen can be removed by oxidation calcination to obtain vanadium pentoxide product. The chromium-containing solution can also be precipitated under alkaline conditions to obtain chromium hydroxide, which is then calcined to obtain chromium trioxide product.

[0023] In some embodiments, step S1 further comprises: if the pH of the initial vanadium-chromium solution is greater than 4, then adding acid to adjust the pH; if the pH of the initial vanadium-chromium solution is less than 2, then adding alkali to adjust the pH, so as to maintain a stable pH.

[0024] Since vanadium and chromium have different redox properties under different pH conditions, by controlling the pH value of the solution between 2 and 4, the selective reduction conditions of chromium can be guaranteed, and this pH is conducive to the subsequent direct precipitation of vanadium using tetraalkylammonium.

[0025] In some embodiments, the acid for adjusting pH is one or more of hydrochloric acid, sulfuric acid, and nitric acid. The base for adjusting pH is one or more of ammonia water, sodium hydroxide, and potassium hydroxide. Specifically, the corresponding acid or alkaline solution is selected according to the pH value to be adjusted and the characteristics of the reaction system. The acid solution or alkaline solution is added dropwise to the reaction system, and the pH value is monitored in real time with a pH meter until the target value is reached.

[0026] In some embodiments, step S2 includes: continuously adding acid to maintain a stable pH during the reduction process.

[0027] In some embodiments, in step S3, the cation of tetraalkylammonium is tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion or tetrabutylammonium ion, and the anion of tetraalkylammonium is chloride ion, bromide ion, sulfate ion or nitrate ion. The radius of these ions is larger than that of NH 4 + , more easily combined with polyvanadate anions and Cr 3+ Exclusion, thus completing the selective precipitation of vanadium simply and efficiently.

[0028] In some embodiments, in step S3, the molar ratio of the added tetraalkylammonium to the vanadium in the vanadium chromium solution is 0.2 to 3: 1. By controlling the molar ratio of tetraalkylammonium to vanadium, the precipitation process can be optimized to ensure sufficient precipitation of vanadium, thereby increasing the yield of vanadium pentoxide and the purity of the chromium product extracted from the subsequent chromium solution.

[0029] In some embodiments, in step S3, the stirring time is 15 min to 2 h. During the precipitation process, the length of the stirring time will also affect the effect of the precipitation. An appropriate stirring time can make the precipitate purer, reduce the co-precipitation of impurities, and thus improve the purity of the product.

[0030] In some embodiments, step S4, the vanadium-containing precipitate (NR 4 ) x H y (V 10 O 28 ) z The calcination temperature is 500-600℃ and the calcination time is 2-4h. Through calcination, carbon, nitrogen and hydrogen in the precipitate can be effectively removed to obtain vanadium pentoxide product.

[0031] In some embodiments, the reducing agent is ethanol. 3+ , reaction formula: 2Cr 2 O 7 2- +16H + +3CH 3 CH 2 OH→4Cr 3+ +11H 2 O+3CH 3 COOH. Ethanol can selectively reduce Cr(VI) to Cr(III) without easily changing the valence state of V(V) in the solution, thus reducing the interference of chromium in the solution on the vanadium precipitation process, thereby improving the precipitation rate and purity of vanadium.

[0032] In some embodiments, the molar ratio of the added ethanol to the chromium in the vanadium-chromium solution is 1-3:1, that is, 0.88-2.65 g of ethanol (1.12-3.36 mL) is required to add every 1 gram of Cr reduced in the solution. The amount of ethanol added should not be lower than this range to ensure that it can fully reduce Cr(VI) to Cr(III), nor should it exceed this range to reduce the risk of V(V) being reduced.

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Example 1 Use laboratory prepared Na 2 Cr 2 O 7 and NaVO 3Mixed solution, in which the V concentration is 1g / L and the Cr concentration is 1g / L. Take 500mL of the solution, first add sulfuric acid to it to adjust the pH to 2.5, then add 1mL of ethanol to the solution to selectively reduce chromium, and add a small amount of sulfuric acid during the process to maintain the pH at 2.5. After the chromium is reduced, add 2.5g of tetrabutylammonium bromide, stir and precipitate for 1h, and filter to separate the vanadium-containing precipitate and the chromium-containing solution. After the precipitate is acid-washed and dried, it is calcined at 600℃ for 2h to obtain a vanadium pentoxide product with a purity of 99.0%. Add sodium hydroxide to the chromium-containing solution to obtain chromium hydroxide, wash, dry and calcine the chromium hydroxide to obtain a chromium trioxide product with a purity of 99.2%.

[0035] Example 2 A vanadium-chromium solution was selected, in which the V concentration was 12.3 g / L and the Cr concentration was 15.6 g / L. Take 200 mL of the solution, first add sulfuric acid to adjust the pH to 3, then add 10 mL of ethanol to the solution to selectively reduce chromium, and add a small amount of sulfuric acid during the process to maintain the pH at 3. After the chromium is reduced, add 8.2 g of tetraethylammonium bromide, stir and precipitate for 1 hour, and filter and separate the vanadium-containing precipitate and the chromium-containing solution. After the precipitate is acid-washed and dried, it is calcined at 500 ° C for 4 hours to obtain a vanadium pentoxide product with a purity of 98.8%. Sodium hydroxide is added to the chromium-containing solution to obtain chromium hydroxide, which is washed, dried, and calcined to obtain a chromium trioxide product with a purity of 99.1%.

[0036] Example 3 A vanadium-chromium solution was selected, in which the V concentration was 5.6 g / L and the Cr concentration was 3.4 g / L. Take 500 mL of the solution, first add hydrochloric acid to adjust the pH to 3.5, then add 5 mL of ethanol to the solution to selectively reduce chromium, and add a small amount of hydrochloric acid during the process to maintain the pH at 3.5. After the chromium is reduced, add 4 g of tetraethylammonium bromide, stir and precipitate for 30 minutes, and filter and separate the vanadium-containing precipitate and the chromium-containing solution. After the precipitate is acid-washed and dried, it is calcined at 550 ° C for 3 hours to obtain a vanadium pentoxide product with a purity of 99.1%. Sodium hydroxide is added to the chromium-containing solution to obtain chromium hydroxide, which is washed, dried, and calcined to obtain a chromium trioxide product with a purity of 99.3%.

[0037] Example 4 A vanadium-chromium solution was selected, in which the V concentration was 5g / L and the Cr concentration was 8.2g / L. Take 500mL of the solution, first add hydrochloric acid to adjust the pH to 3, then add 12mL of ethanol to the solution to selectively reduce chromium, and add a small amount of hydrochloric acid to maintain the pH at 3 during the process. After the chromium is reduced, add 4g of tetraethylammonium bromide, stir and precipitate for 1h, and filter to separate the vanadium-containing precipitate and the chromium-containing solution. After the precipitate is acid-washed and dried, it is calcined at 550℃ for 3h to obtain a vanadium pentoxide product with a purity of 99.0%. Sodium hydroxide is added to the chromium-containing solution to obtain chromium hydroxide, which is washed, dried, and calcined to obtain a chromium trioxide product with a purity of 99.3%.

[0038] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0039] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for separating vanadium and chromium from a vanadium and chromium solution, characterized in that: The following steps are involved: S1, adjusting the pH of the vanadium-chromium solution to 2-4; S2, adding a reducing agent to the vanadium-chromium solution, stirring sufficiently, and selectively reducing Cr(VI) to Cr(III); S3, adding tetraalkylammonium to the obtained solution, stirring, and filtering to obtain a vanadium-containing precipitate and a chromium-containing solution; S4, washing, drying and calcining the vanadium-containing precipitate to obtain vanadium pentoxide; S5, adding alkali to the chromium-containing solution, stirring and filtering to obtain chromium hydroxide precipitate, washing, drying and calcining the chromium hydroxide precipitate to obtain chromium trioxide.

2. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: Step S1 further comprises: if the pH value of the initial vanadium-chromium solution is greater than 4, then acid is added to adjust the pH value; if the pH value of the initial vanadium-chromium solution is less than 2, then alkali is added to adjust the pH value.

3. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 2, characterized in that: The added acid is one or more of hydrochloric acid, sulfuric acid and nitric acid, and the added alkali is one or more of ammonia water, sodium hydroxide and potassium hydroxide.

4. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: Step S2 includes: continuously adding acid to maintain pH stability during the reduction process.

5. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: In step S3, the cation of the tetraalkylammonium is tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion or tetrabutylammonium ion; the anion of the tetraalkylammonium is chloride ion, bromide ion, sulfate ion or nitrate ion.

6. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: In step S3, the molar ratio of the added tetraalkylammonium to the vanadium in the vanadium-chromium solution is 0.2-3:

1.

7. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: In step S3, the stirring time is 15 minutes to 2 hours.

8. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: In step S4, the calcination temperature of the vanadium-containing precipitate is 500-600° C., and the calcination time is 2-4 hours.

9. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 1, characterized in that: The reducing agent is ethanol.

10. The method for separating vanadium and chromium from a vanadium and chromium solution according to claim 9, characterized in that: The molar ratio of the added ethanol to the chromium in the vanadium-chromium solution is 1-3:1.

Images