A method for removing chromium from a sodium tungstate solution

Abstract

The application belongs to the technical field of tungsten hydrometallurgy, and particularly relates to a method for removing chromium from a sodium tungstate solution, comprising the following steps: adjusting the pH of a chromium-containing sodium tungstate solution to 9-12, heating to 80-90 DEG C and keeping warm to obtain a pretreated sodium tungstate solution; mixing ferrous salt and aluminum salt in a mass ratio of 3:1-4:1, adding an appropriate amount of water to stir to dissolve to obtain a chromium removal reagent, and the molar ratio of ferrous ions to chromium elements is 3.15:1-4.50:1; adding the chromium removal reagent into the pretreated sodium tungstate solution, stirring, standing, filtering to obtain a sodium tungstate solution after chromium removal. The application uses a solution of ferrous salt and aluminum salt to reduce the use amount of a precipitant, thereby reducing the chromium removal cost; Al(OH)3 is generated by introducing aluminum salt to wrap on the surface of the formed Fe(OH)3 colloidal precipitate, thereby reducing tungsten loss; the generated sludge amount is small, and the treatment is simple; the purity of the sodium tungstate is improved, thereby improving the quality and performance of tungsten products; and the method is suitable for different scale production requirements and has strong adaptability.

Description

Technical Field

[0001] This application belongs to the field of hydrometallurgical technology of tungsten, specifically a method for removing chromium from sodium tungstate solution. Background Technology

[0002] Sodium tungstate, as an important tungsten compound, plays a crucial role in the production of tungsten materials. Addressing the problems of long process flows, poor comprehensive utilization, and limited applicability in traditional recycling technologies for waste cemented carbide, a novel process route of alkali fusion roasting-water leaching for treating waste cemented carbide has gradually been accepted by major manufacturers. In this process, the main component, WC, can be converted into soluble Na₂WO₄ in one step, while cobalt, copper, iron, and other components exist in the slag as solid phases, achieving selective separation of tungsten. Notably, when processing waste cemented carbide cutting tools, it can efficiently achieve alkali fusion decomposition of the tools in one step without pretreatment such as oxidation decomposition, physical crushing, or ball milling, and obtain crude sodium tungstate solution and cobalt slag through water leaching. However, the presence of chromium impurities in the sodium tungstate production process severely affects the purity and performance of tungsten products, while also posing environmental pollution and health risks. Therefore, how to efficiently remove chromium impurities from sodium tungstate has become a significant challenge in the field of tungsten material production technology.

[0003] Currently, the main methods for removing chromium impurities from sodium tungstate include chemical precipitation, ion exchange, and membrane separation. While these methods can remove chromium impurities to some extent, they have significant drawbacks. Chemical precipitation typically requires the addition of large amounts of precipitant, leading to high chromium removal costs and complex sludge treatment. Ion exchange, although effective at removing chromium ions, suffers from difficult resin regeneration and low treatment efficiency, making it unsuitable for large-scale production. Membrane separation suffers from membrane fouling and short membrane lifespan, resulting in high maintenance costs and limiting its practical application. Patent CN114635041B utilizes ferrous salts to remove chromium from sodium tungstate solutions, partially removing Fe... 2+ Hexavalent chromium is reduced to trivalent chromium, producing Fe. 3+ Fe 3+ Hydrolysis forms Fe(OH)3, and some of the Fe... 2+ Hydrolysis forms Fe(OH)₂. Oxygen in the solution or air will oxidize some of the Fe(OH)₂ to Fe(OH)₃, ultimately forming the intermediate product Fe(OH)₂·2Fe(OH)₃. This product has adsorption properties. Trivalent chromium hydrolyzes to Cr(OH)₃, which can form a co-precipitate with Fe(OH)₂·2Fe(OH)₃. However, the amount of ferrous salt added in this patent is too high, resulting in Fe... 3+It reacts with tungstate ions in sodium tungstate solution to form ferric tungstate, and the precipitated ferrous hydroxide (iron) has an adsorption capacity for WO3, causing significant tungsten loss. Patent CN106186064B proposes a co-precipitation method, first adding aluminum salt, then adding ferrous salt, using ion precipitation to reduce chromium in ammonium metavanadate. Although this method can remove chromium deeply, it neglects the loss of the main element.

[0004] Existing technologies can remove chromium impurities from sodium tungstate to some extent, but some problems and shortcomings still exist. Therefore, developing a new and efficient chromium removal method has significant practical importance and application value. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a method for removing chromium from sodium tungstate solution. A chromium removal reagent is prepared by mixing ferrous salt and aluminum salt in a certain proportion. Under specific pH conditions, through redox reactions and hydrolysis reactions, the chromium content is reduced while tungsten loss is also reduced, thereby improving the recovery rate of sodium tungstate.

[0006] This application discloses a method for removing chromium from a sodium tungstate solution, comprising the following steps:

[0007] S1. Obtain a sodium tungstate solution containing chromium. Adjust the pH of the sodium tungstate solution to 9-12, then heat it to 80-90°C and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0008] S2. Mix ferrous salt and aluminum salt, add an appropriate amount of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.15:1 to 4.50:1, and the mass ratio of ferrous salt to aluminum salt is 3:1 to 4:1.

[0009] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir, let stand, and filter to obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0010] In the above technical solution, the chromium-containing sodium tungstate solution is first adjusted to alkaline. After adding the chromium removal reagent, the chemical equations for the main reactions that occur are as follows:

[0011] (1) 3Fe 2+ +CrO4 2－ +4H₂O+4OH － =3Fe(OH)3↓+Cr(OH)3↓

[0012] (2) Al 3+ +3OH － =Al(OH)3↓

[0013] (3) 2Al3+ +3CrO4 2－ =Al2(CrO4)3↓

[0014] In the above reaction (1), Fe 2+ Cr(VI) is reduced to Cr(III), and the Cr(VI) itself is oxidized to Fe. 3+ Cr 3+ Hydrolysis will occur to form Cr(OH)3 precipitate; Fe 3+ Hydrolysis produces Fe(OH)3 colloidal precipitate. This precipitate has small particles, thus possessing a large specific surface area and adsorption capacity. It can adsorb Cr(OH)3 to form a coprecipitate, but it will also affect WO4 in the solution. 2－ Adsorption occurs; and the addition of Al 3+ This can reduce tungsten loss, as shown in reaction (2) above, Al 3+ Under alkaline conditions, Al(OH)3 colloids will form, coating the surface of the formed Fe(OH)3 colloid precipitate, thereby reducing the effect of Fe(OH)3 on WO4. 2－ Electrostatic adsorption, in addition to Al 3+ It can also be used with WO4 2－ The formation of soluble complexes with a more open crystal structure weakens the encapsulation effect of Fe(OH)3 colloidal precipitates on tungsten-containing complexes.

[0015] When designing the amount of chromium removal reagent to be added, the above reaction (1) is used as the standard for the ratio. That is, 1 mol of chromium element theoretically requires 3 mol of ferrous ions. The molar ratio of ferrous ions to chromium element in sodium tungstate solution is controlled to be 3.15:1~4.50:1, that is, the amount of ferrous ions added is 1.05~1.5 times the theoretical amount. On the one hand, it can remove chromium precipitation as much as possible, and on the other hand, it will not introduce too much iron element, resulting in too much tungsten loss. When the mass ratio of ferrous salt to aluminum salt is controlled to be 3:1~4:1, the introduced aluminum salt can achieve the corresponding effect. Adding too much aluminum salt will not significantly improve the effect of chromium removal and tungsten loss reduction, and will also increase the cost. In addition, when the chromium removal reagent is mixed with ferrous salt and aluminum salt and added to an appropriate amount of water to form a solution, it can be added to sodium tungstate solution. Each element can react quickly and completely in the dissociated state. However, when the solid state of the chromium removal reagent is added directly to sodium tungstate solution, the precipitate generated will coat the surface of the chromium removal reagent, resulting in a poorer chromium removal effect.

[0016] Furthermore, in step S1, the pH of the sodium tungstate solution is adjusted to 9-12 at room temperature.

[0017] Furthermore, in step S2, the ferrous salt is a soluble ferrous salt, and the aluminum salt is a soluble aluminum salt.

[0018] Furthermore, the ferrous salt is ferrous sulfate, and the aluminum salt is aluminum sulfate.

[0019] Furthermore, in step S3, the stirring time is 1-2 hours.

[0020] Furthermore, in step S3, the settling time is 1 to 2 hours.

[0021] Furthermore, in step S1, the chromium element in the sodium tungstate solution exists in the form of CrO4. 2－ Cr2O7 2－ At least one of them.

[0022] Furthermore, in step S1, the chromium content in the sodium tungstate solution is 0.01~10 g / L.

[0023] Furthermore, the chromium content in the sodium tungstate solution after chromium removal is <10 mg / L, and the WO3 content in the precipitate residue is <1.5%.

[0024] This application proposes a method for removing chromium from sodium tungstate solution, which produces the following beneficial effects: The use of ferrous and aluminum salts to prepare the solution reduces the amount of precipitant used, thereby lowering the cost of chromium removal; the introduction of aluminum salts generates Al(OH)3, which coats the surface of the formed Fe(OH)3 colloidal precipitate, reducing tungsten loss; this technical solution produces less sludge and is simple to treat; it improves the purity of sodium tungstate, thereby enhancing the quality and performance of tungsten products; and it is suitable for production needs of different scales, exhibiting strong adaptability. Detailed Implementation

[0025] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] This application discloses a method for removing chromium from a sodium tungstate solution, comprising the following steps:

[0027] S1. Obtain a sodium tungstate solution containing chromium. Adjust the pH of the sodium tungstate solution to 9-12, then heat it to 80-90℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0028] Preferably, the pH of the sodium tungstate solution can be adjusted to 9-12 at room temperature, and the chromium in the sodium tungstate solution exists in the form of CrO4. 2－ Cr2O7 2－At least one of the following, the chromium content is 0.01~10 g / L; specifically, the pH of the sodium tungstate solution can be adjusted to any one or a range between 9, 10, 11, and 12, and the temperature can be raised to any one or a range between 80℃, 82℃, 84℃, 86℃, 88℃, and 90℃, and the chromium content can be any one or a range between 0.01 g / L, 1 g / L, 2 g / L, 5 g / L, 8 g / L, and 10 g / L.

[0029] S2. Mix ferrous salt and aluminum salt, add an appropriate amount of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.15:1 to 4.50:1, and the mass ratio of ferrous salt to aluminum salt is 3:1 to 4:1.

[0030] Preferably, the chromium removal reagent is prepared by adding water to soluble ferrous salts and soluble aluminum salts, such as ferrous sulfate and aluminum sulfate. Specifically, the molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent can be any one of 3.15:1, 3.30:1, 3.60:1, 3.90:1, 4.20:1, 4.50:1, or any range between two of these values. The mass ratio of ferrous salt to aluminum salt can be any one of 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, or any range between two of these values.

[0031] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir, let stand, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0032] Preferably, the stirring time is 1-2 hours; the settling time is 1-2 hours; the chromium content in the sodium tungstate solution after chromium removal is <10 mg / L, and the WO3 content in the precipitate is <1.5%.

[0033] The technical solution of this application will be further described below with reference to specific embodiments.

[0034] Example 1

[0035] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0036] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0037] S2. Mix 4.8g of ferrous sulfate and 1.6g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1.

[0038] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0039] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L;

[0040] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.2% tungsten.

[0041] Example 2

[0042] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0043] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0044] S2. Mix 4.8g of ferrous sulfate and 1.2g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 4:1.

[0045] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0046] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 3 mg / L.

[0047] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.3% tungsten.

[0048] Example 3

[0049] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0050] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 90℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0051] S2. Mix 4.8g of ferrous sulfate and 1.6g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1.

[0052] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0053] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L;

[0054] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.2% tungsten.

[0055] Example 4

[0056] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0057] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 11 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0058] S2. Mix 6.4g of ferrous sulfate and 2g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 4.38:1, and the mass ratio of ferrous salt to aluminum salt is 3.2:1.

[0059] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 2 hours, let stand for 2 hours, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0060] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 4 mg / L;

[0061] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.1% tungsten.

[0062] Example 5

[0063] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0064] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 9 at room temperature, then heat it to 85℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0065] S2. Mix 5.7g of ferrous sulfate and 1.9g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.90:1, and the mass ratio of ferrous salt to aluminum salt is 3:1.

[0066] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1.5 h, let stand for 1.5 h, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0067] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 4 mg / L;

[0068] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.4% tungsten.

[0069] Comparative Example 1

[0070] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0071] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 20℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0072] S2. Mix 4.8g of ferrous sulfate and 1.6g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1.

[0073] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0074] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 263 mg / L.

[0075] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 4.8% tungsten.

[0076] Comparative Example 2

[0077] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0078] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0079] S2. Mix 4.8g of ferrous sulfate and 1.6g of aluminum sulfate to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1.

[0080] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0081] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 64 mg / L;

[0082] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 4.8% tungsten.

[0083] Comparative Example 3

[0084] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0085] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0086] S2. Mix 4.8g of ferrous sulfate and 4.8g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 1:1.

[0087] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0088] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 13 mg / L;

[0089] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 0.9% tungsten.

[0090] Comparative Example 4

[0091] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0092] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0093] S2. Mix 2.4g of ferrous sulfate and 2.4g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in sodium tungstate solution in the chromium removal reagent is 1.64:1. Using the above reaction (3) as the standard, the amount of aluminum ions added in the chromium removal reagent is about 1.1 times the theoretical amount, and the mass ratio of ferrous salt to aluminum salt is 1:1.

[0094] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0095] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 95 mg / L;

[0096] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.4% tungsten.

[0097] Comparative Example 5

[0098] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0099] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0100] S2. Mix 1.6g of ferrous sulfate and 4.8g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 1.09:1, and the mass ratio of ferrous salt to aluminum salt is 1:3.

[0101] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0102] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 181 mg / L.

[0103] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 0.9% tungsten.

[0104] Comparative Example 6

[0105] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0106] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0107] S2. Mix 0.8g of ferrous sulfate and 2.4g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 0.55:1, and the mass ratio of ferrous salt to aluminum salt is 1:3.

[0108] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0109] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 263 mg / L.

[0110] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.0% tungsten.

[0111] Comparative Example 7

[0112] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0113] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0114] S2. Use 12g of sodium sulfide as a chromium removal reagent;

[0115] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0116] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 381 mg / L.

[0117] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 0.4% tungsten.

[0118] Comparative Example 8

[0119] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0120] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 14 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0121] S2. Mix 4.8g of ferrous sulfate and 1.6g of aluminum sulfate, add 200mL of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1.

[0122] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0123] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 37 mg / L;

[0124] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 1.2% tungsten.

[0125] Comparative Example 9

[0126] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0127] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0128] S2. Add 4.8g of ferrous sulfate to 100mL of water and stir until dissolved to obtain chromium removal reagent one. The molar ratio of ferrous ions to chromium in sodium tungstate solution in chromium removal reagent one is 3.29:1. Add 1.6g of aluminum sulfate to 100mL of water and stir until dissolved to obtain chromium removal reagent two. The mass ratio of ferrous salt to aluminum salt is 3:1.

[0129] S3. Add chromium removal reagent one to the pretreated sodium tungstate solution and stir for 1 hour. Then add chromium removal reagent two to the solution and stir for 1 hour. Let stand for 1 hour and filter to obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0130] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L;

[0131] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 9.5% tungsten.

[0132] Comparative Example 10

[0133] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0134] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0135] S2. Add 4.8g of ferrous sulfate to 100mL of water and stir until dissolved to obtain chromium removal reagent one. The molar ratio of ferrous ions to chromium in sodium tungstate solution in chromium removal reagent one is 3.29:1. Add 1.6g of aluminum sulfate to 100mL of water and stir until dissolved to obtain chromium removal reagent two. The mass ratio of ferrous salt to aluminum salt is 3:1.

[0136] S3. Add chromium removal reagent II to the pretreated sodium tungstate solution, stir for 1 hour, filter to obtain filtrate, then add chromium removal reagent I to the filtrate, stir for 1 hour, let stand for 1 hour, filter to obtain chromium-removed sodium tungstate solution and precipitate residue.

[0137] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L;

[0138] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue after the second filtration contained 10.6% tungsten.

[0139] Comparative Example 11

[0140] A method for removing chromium from a sodium tungstate solution includes the following steps:

[0141] S1. Obtain 1L of sodium tungstate solution containing 0.5g / L of chromium. Adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat it to 80℃ and keep it at that temperature to obtain a pretreated sodium tungstate solution.

[0142] S2. Add 4.8g of ferrous sulfate to 200mL of water and stir until dissolved. The molar ratio of ferrous ions in the chromium removal reagent to chromium in the sodium tungstate solution is 3.29:1, thus obtaining the chromium removal reagent.

[0143] S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 hour, let stand for 1 hour, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue.

[0144] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L;

[0145] The precipitate residue after chromium removal was analyzed by X-ray fluorescence spectrometry (XRF), and the residue contained 10.4% tungsten.

[0146] As can be seen from the above examples and comparative examples, if the chromium removal reagent is not prepared into a solution (Comparative Example 2), or if the conventional excess sodium sulfide treatment process is used (Comparative Example 7), or if the reaction parameters are not within the range of the technical solution of this application (such as the reaction temperature being too low in Comparative Example 1, the mass ratio of ferrous salt to aluminum salt being too high or too low in Comparative Examples 3, 4, 5, and 6, or the amount of ferrous salt added being insufficient, or the pH being too high in Comparative Example 8), the ideal chromium removal effect cannot be achieved. Although the ferrous salt and aluminum salt are added separately or no aluminum salt is added in Comparative Examples 9, 10, and 11, the ideal chromium removal effect can be achieved, but a high tungsten loss will occur.

[0147] This application proposes a method for removing chromium from sodium tungstate solution, which produces the following beneficial effects: The use of ferrous and aluminum salts to prepare the solution reduces the amount of precipitant used, thereby lowering the cost of chromium removal; the introduction of aluminum salts generates Al(OH)3, which coats the surface of the formed Fe(OH)3 colloidal precipitate, reducing tungsten loss; this technical solution produces less sludge and is simple to treat; it improves the purity of sodium tungstate, thereby enhancing the quality and performance of tungsten products; and it is suitable for production needs of different scales, exhibiting strong adaptability.

[0148] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the inventive concept of this application and using the content of this application specification, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for removing chromium from a sodium tungstate solution, characterized in that, Includes the following steps: S1. Obtain a sodium tungstate solution containing chromium. The chromium content in the sodium tungstate solution is 0.01~10 g / L, and the chromium exists in the sodium tungstate solution in the form of CrO4. 2－ Cr2O7 2－ At least one of the following: adjust the pH of the sodium tungstate solution to 11-12, then heat to 80-90°C and keep warm to obtain a pretreated sodium tungstate solution; S2. Mix ferrous sulfate and aluminum sulfate, add an appropriate amount of water and stir until dissolved to obtain a chromium removal reagent. The molar ratio of ferrous ions to chromium in the sodium tungstate solution in the chromium removal reagent is 3.15:1 to 4.50:1, and the mass ratio of ferrous sulfate to aluminum sulfate is 3:1 to 4:

1. S3. Add the chromium removal reagent to the pretreated sodium tungstate solution, stir, let stand, filter, and obtain the chromium-removed sodium tungstate solution and precipitate residue. The chromium content in the sodium tungstate solution after chromium removal is <10 mg / L, and the WO3 content in the precipitate is <1.5%.

2. The method for removing chromium from sodium tungstate solution according to claim 1, characterized in that, In step S1, the pH of the sodium tungstate solution is adjusted to 11-12 at room temperature.

3. The method for removing chromium from sodium tungstate solution according to claim 1, characterized in that, In step S3, the stirring time is 1-2 hours.

4. The method for removing chromium from sodium tungstate solution according to claim 1, characterized in that, In step S3, the settling time is 1 to 2 hours.