Method for removing chromium from sodium tungstate solution

Abstract

The invention belongs to the technical field of tungsten hydrometallurgy, and particularly relates to a method for removing chromium from a sodium tungstate solution, which comprises the following steps: adjusting the pH value of the chromium-containing sodium tungstate solution to 9-12, heating to 80-90 DEG C, and keeping the temperature to obtain a pretreated sodium tungstate solution; the preparation method comprises the following steps: mixing ferrite and aluminum salt in a mass ratio of (3: 1)-(4: 1), adding a proper amount of water, and stirring until the ferrite and the aluminum salt are dissolved, so as to obtain a chromium removal reagent, and the molar ratio of ferrous ions to a chromium element is (3.15: 1)-(4.50: 1); and adding a chromium removal reagent into the pretreated sodium tungstate solution, stirring, standing and filtering to obtain the chromium-removed sodium tungstate solution. The solution is prepared from the ferrous salt and the aluminum salt, so that the usage amount of a precipitator is reduced, and the chromium removal cost is reduced; al (OH) 3 generated by introducing aluminum salt is wrapped on the surface of formed Fe (OH) 3 colloidal precipitate, so that tungsten loss is reduced; according to the technical scheme, less sludge is generated, and the treatment is simple; the purity of sodium tungstate is improved, so that the quality and the performance of a tungsten product are improved; and the method is suitable for production requirements of different scales and has relatively high adaptability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrometallurgy of tungsten, and specifically relates to a method for removing chromium from a sodium tungstate solution. BACKGROUND

[0002] Sodium tungstate, as an important tungsten compound, plays a key role in the production of tungsten materials. In view of the problems of long process flow, poor comprehensive utilization, poor applicability and the like in the traditional recycling treatment technology of waste hard alloy, a new process route of alkali roasting-water leaching process for treating waste hard alloy is gradually accepted by various manufacturers. The main component WC can be converted into soluble Na2WO4 in one step and dissolved in the solution, while cobalt, copper, iron and other components exist in the form of solid slag in the slag, realizing selective separation of tungsten. In particular, when treating waste hard alloy blades, no oxidation decomposition, physical crushing, ball milling and other pretreatments are needed to realize one-step efficient alkali fusion decomposition of waste hard alloy blades, and coarse sodium tungstate solution and cobalt slag are obtained through water leaching. However, in the production process of sodium tungstate, the existence of chromium impurities seriously affects the purity and performance of tungsten products, and also brings environmental pollution and health risks. Therefore, how to efficiently remove the chromium impurities in sodium tungstate has become an important challenge in the field of tungsten material production technology.

[0003] At present, in order to remove the chromium impurities in sodium tungstate, the main methods adopted include chemical precipitation method, ion exchange method and membrane separation method and the like. These methods can remove the chromium impurities to some extent, but have obvious deficiencies. The chemical precipitation method usually needs to add a large amount of precipitant, resulting in high cost of chromium removal and complex sludge treatment; the ion exchange method can remove chromium ions, but the exchange resin is difficult to regenerate, and the treatment efficiency is low, which is difficult to meet the demand of large-scale production; the membrane separation method has the problems of membrane pollution and short service life of membrane, and the maintenance cost is high, which limits its practical application. In patent CN114635041B, ferrous salt is used to remove chromium from sodium tungstate solution, a part of Fe 2+ The hexavalent chromium is reduced to trivalent chromium and Fe 3+ is generated, Fe 3+ is hydrolyzed to form Fe(OH)3, a part of Fe 2+ is hydrolyzed to form Fe(OH)2, and a part of Fe(OH)2 is oxidized to Fe(OH)3 by oxygen in the solution or in the air, and finally the intermediate product Fe(OH)2·2Fe(OH)3 is formed. The product has adsorption property, and the trivalent chromium is hydrolyzed to Cr(OH)3, which can form coprecipitation with Fe(OH)2·2Fe(OH)3, but the amount of ferrous salt added in the patent is too much, and a large amount of Fe 3+It can form iron tungstate with tungstate ions in sodium tungstate solution, and the precipitated ferrous hydroxide (iron) has adsorption on WO3, causing a large loss of tungsten. Patent CN106186064B proposes a method of co-precipitation, first adding aluminum salt, then adding ferrous salt, and using ion precipitation to reduce chromium in ammonium metavanadate. Although this method can deeply remove chromium, it ignores the loss of main elements.

[0004] The existing technology can remove chromium impurities in sodium tungstate to some extent, but still has some problems and deficiencies. Therefore, it is of great practical significance and application value to develop a new type of high-efficiency chromium removal method. SUMMARY

[0005] To solve the above problems, the present application provides a method for removing chromium from sodium tungstate solution, which uses a mixture of ferrous salt and aluminum salt in a certain proportion to prepare a chromium removal reagent. Under specific pH conditions, the chromium content is reduced through oxidation-reduction reaction and hydrolysis reaction, which can also reduce tungsten loss and improve the recovery rate of sodium tungstate.

[0006] The method for removing chromium from sodium tungstate solution provided by the present application comprises the following steps: S1, obtaining a sodium tungstate solution containing chromium elements, adjusting the pH of the sodium tungstate solution to 9-12, then heating to 80-90℃ and keeping the temperature, to obtain a pretreated sodium tungstate solution; S2, mixing ferrous salt and aluminum salt, adding appropriate amount of water and stirring to dissolve, to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.15:1-4.50:1, and the mass ratio of the ferrous salt to the aluminum salt is 3:1-4:1; S3, adding the chromium removal reagent to the pretreated sodium tungstate solution, stirring, standing, filtering, to obtain a sodium tungstate solution after chromium removal and a precipitate.

[0007] In the above technical solution, first, the chromium-containing sodium tungstate solution is adjusted to alkaline, and after adding the chromium removal reagent, the main reactions occur as follows: (1), 3Fe 2+ +CrO4 2－ +4H2O+4OH － =3Fe(OH)3↓+Cr(OH)3↓ (2), Al 3+ +3OH － =Al(OH)3↓ (3), 2Al 3+ +3CrO4 2－ =Al2(CrO4)3↓ In the above reaction (1), Fe2+ Cr(VI) is reduced to Cr(III), which is oxidized to Fe 3+ , Cr 3+ Hydrolysis occurs to form Cr(OH)3 precipitate; Fe 3+ Hydrolysis occurs to form Fe(OH)3 colloidal precipitate, which has a small particle size and thus a large specific surface area and adsorption capacity, can adsorb Cr(OH)3 to form a co-precipitate, but also has an adsorption effect on WO4 2－ in the solution; and the addition of Al 3+ can reduce tungsten loss, as in the above reaction (2), Al 3+ will form Al(OH)3 colloidal under alkaline conditions, which is wrapped on the surface of the formed Fe(OH)3 colloidal precipitate, thereby reducing the electrostatic adsorption of WO4 2－ by Fe(OH)3, in addition, Al 3+ can form a soluble complex with WO4 2－ , which has a more open crystal structure, so that the wrapping effect of the Fe(OH)3 colloidal precipitate on the tungsten-containing complex is weakened.

[0008] When designing the amount of chromium removal reagent to be added, the above reaction (1) is used as a standard for proportioning, that is, 3 mol of ferrous ions are theoretically required to consume 1 mol of chromium elements, and the molar ratio of ferrous ions to chromium elements in the sodium tungstate solution is controlled to be 3.15:1~4.50:1, that is, the amount of ferrous salt added is 1.05~1.5 times the theoretical amount, on the one hand, it can remove as much chromium as possible, and on the other hand, it will not introduce too much iron element to cause 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, and the addition of too much aluminum salt does not obviously improve the effect of chromium removal and tungsten loss reduction, but increases the cost. In addition, the ferrous salt and aluminum salt are mixed and added to the solution in the form of a chromium removal reagent, and each element can rapidly react and completely react in a dissociated state, while the chromium removal reagent in a solid state is directly added to the sodium tungstate solution, and the generated precipitate is wrapped on the surface of the chromium removal reagent, resulting in poor chromium removal effect.

[0009] Further, in step S1, the pH of the sodium tungstate solution is adjusted to 9~12 at room temperature.

[0010] Further, in step S2, the ferrous salt is a soluble ferrous salt, and the aluminum salt is a soluble aluminum salt.

[0011] Still further, the ferrous salt is ferrous sulfate, and the aluminum salt is aluminum sulfate.

[0012] Further, in step S3, the stirring time is 1~2h.

[0013] Further, the standing time in step S3 is 1-2h.

[0014] Further, in step S1, the form of existence of the chromium element in the sodium tungstate solution includes at least one of CrO4 2－ , Cr2O7 2－ .

[0015] Further, in step S1, the content of the chromium element in the sodium tungstate solution is 0.01-10g / L.

[0016] Further, the content of the chromium element in the sodium tungstate solution after the chromium removal is <10mg / L, and the content of WO3 in the precipitate is <1.5%.

[0017] The present application proposes a method for removing chromium from a sodium tungstate solution, which has the following beneficial effects: a solution of ferrous salt and aluminum salt is used to reduce the amount of precipitant used, thereby reducing the cost of chromium removal; the introduction of aluminum salt produces Al(OH)3 wrapped on the surface of the formed Fe(OH)3 colloidal precipitate, reducing tungsten loss; the amount of sludge produced by the technical solution is small and easy to handle; the purity of sodium tungstate is improved, thereby improving the quality and performance of tungsten products; it is suitable for different scale production needs and has strong adaptability. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0019] The present application proposes a method for removing chromium from a sodium tungstate solution, which includes the following steps: S1, obtaining a sodium tungstate solution containing chromium elements, adjusting the pH of the sodium tungstate solution to 9-12, then heating to 80-90℃ and holding, to obtain a pretreated sodium tungstate solution; Preferably, the pH of the sodium tungstate solution can be adjusted to 9-12 at room temperature, and the form of existence of the chromium element in the sodium tungstate solution includes at least one of CrO4 2－ , Cr2O7 2－The content of chromium element is 0.01-10 g / L; specifically, the pH of the sodium tungstate solution can be adjusted to any one of 9, 10, 11, 12 or a range between any two of them, the temperature is raised to any one of 80 DEG C, 82 DEG C, 84 DEG C, 86 DEG C, 88 DEG C, 90 DEG C or a range between any two of them, and the content of chromium element can be any one of 0.01 g / L, 1 g / L, 2 g / L, 5 g / L, 8 g / L, 10 g / L or a range between any two of them.

[0020] S2, mixing ferrous salt and aluminum salt, adding appropriate amount of water and stirring to dissolve to obtain a chromium removal reagent, wherein the molar ratio of ferrous ions in the chromium removal reagent to chromium element in the sodium tungstate solution is 3.15:1-4.50:1, and the mass ratio of ferrous salt to aluminum salt is 3:1-4:1; Preferably, the chromium removal reagent is prepared by adding water to soluble ferrous salt and soluble aluminum salt, such as ferrous sulfate and aluminum sulfate; specifically, the molar ratio of ferrous ions in the chromium removal reagent to chromium element in the sodium tungstate solution can be any one of 3.15:1, 3.30:1, 3.60:1, 3.90:1, 4.20:1, 4.50:1 or a range between any two of them, and 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 a range between any two of them.

[0021] S3, adding the chromium removal reagent to the pretreated sodium tungstate solution, stirring, standing, filtering to obtain a sodium tungstate solution after chromium removal and a precipitate; Preferably, the stirring time is 1-2 h, the standing time is 1-2 h, the content of chromium element in the sodium tungstate solution after chromium removal is <10 mg / L, and the content of WO3 in the precipitate is <1.5%.

[0022] The technical scheme of the present application is further described below in combination with specific examples.

[0023] Example 1 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1 L of sodium tungstate solution containing 0.5 g / L of chromium element, adjusting the pH of the sodium tungstate solution to 12 at room temperature, then raising the temperature to 80 DEG C and keeping the temperature, to obtain a pretreated sodium tungstate solution; S2, mixing 4.8 g of ferrous sulfate and 1.6 g of aluminum sulfate, adding 200 mL of water and stirring to dissolve to obtain a chromium removal reagent, wherein the molar ratio of ferrous ions in the chromium removal reagent to chromium element in the sodium tungstate solution is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 h, stand for 1 h, filter, to obtain the sodium tungstate solution after chromium removal and a precipitate residue.

[0024] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 5 mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 1.2%.

[0025] Example 2 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1 L of a sodium tungstate solution containing 0.5 g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 80℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; S2, mix 4.8 g of ferrous sulfate and 1.2 g of aluminum sulfate, add 200 mL of water and stir until dissolved, to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 4:1; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 h, stand for 1 h, filter, to obtain the sodium tungstate solution after chromium removal and a precipitate residue.

[0026] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 5 mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 1.2%.

[0027] Example 3 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1 L of a sodium tungstate solution containing 0.5 g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 80℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; S2, mix 4.8 g of ferrous sulfate and 1.2 g of aluminum sulfate, add 200 mL of water and stir until dissolved, to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 4:1; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 h, stand for 1 h, filter, to obtain the sodium tungstate solution after chromium removal and a precipitate residue.

[0028] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 5 mg / L; The precipitated slag after removing chromium is determined by X-ray fluorescence spectrometry (XRF), and the slag contains 1.2% tungsten.

[0029] Example 4 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 11 at room temperature, then heating to 80℃ and keeping the temperature, to obtain a pretreated sodium tungstate solution; S2, mixing 6.4g of ferrous sulfate and 2g of aluminum sulfate, adding 200mL of water and stirring until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 4.38:1, and the mass ratio of ferrous salt to aluminum salt is 3.2:1; S3, adding the chromium removal reagent to the pretreated sodium tungstate solution, stirring for 2h, standing for 2h, filtering, to obtain a sodium tungstate solution after removing chromium and a precipitated slag.

[0030] The chromium content in the sodium tungstate solution after removing chromium is determined by AAS method, and the result is 4mg / L; The precipitated slag after removing chromium is determined by X-ray fluorescence spectrometry (XRF), and the slag contains 1.1% tungsten.

[0031] Example 5 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 9 at room temperature, then heating to 85℃ and keeping the temperature, to obtain a pretreated sodium tungstate solution; S2, mixing 5.7g of ferrous sulfate and 1.9g of aluminum sulfate, adding 200mL of water and stirring until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.90:1, and the mass ratio of ferrous salt to aluminum salt is 3:1; S3, adding the chromium removal reagent to the pretreated sodium tungstate solution, stirring for 1.5h, standing for 1.5h, filtering, to obtain a sodium tungstate solution after removing chromium and a precipitated slag.

[0032] The chromium content in the sodium tungstate solution after removing chromium is determined by AAS method, and the result is 4mg / L; The precipitated slag after removing chromium is determined by X-ray fluorescence spectrometry (XRF), and the slag contains 1.4% tungsten.

[0033] Comparative Example 1 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 20℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; 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 in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1h, stand for 1h, filter, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0034] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 263mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 4.8%.

[0035] Comparative Example 2 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 80℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; 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 in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1h, stand for 1h, filter, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0036] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 64mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 4.8%.

[0037] Comparative Example 3 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 80℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; S2, 4.8 g of ferrous sulfate and 4.8 g of aluminum sulfate were mixed, added to 200 mL of water and stirred until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution was 3.29:1, and the mass ratio of ferrous salt and aluminum salt was 1:1; S3, the chromium removal reagent was added to the pretreated sodium tungstate solution, stirred for 1 h, stood for 1 h, filtered to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0038] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 13 mg / L; The precipitate residue after chromium removal was determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue was 0.9%.

[0039] Comparative Example 4 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 12 at room temperature, then heating to 80℃ and keeping, to obtain a pretreated sodium tungstate solution; S2, 2.4 g of ferrous sulfate and 2.4 g of aluminum sulfate were mixed, added to 200 mL of water and stirred until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution was 1.64:1, and the mass ratio of ferrous salt and aluminum salt was 1:1; S3, the chromium removal reagent was added to the pretreated sodium tungstate solution, stirred for 1 h, stood for 1 h, filtered to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0040] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 95 mg / L; The precipitate residue after chromium removal was determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue was 1.4%.

[0041] Comparative Example 5 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 12 at room temperature, then heating to 80℃ and keeping, to obtain a pretreated sodium tungstate solution; S2, 1.6 g of ferrous sulfate and 4.8 g of aluminum sulfate were mixed, added to 200 mL of water and stirred until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution was 1.09:1, and the mass ratio of ferrous salt and aluminum salt was 1:3; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 h, stand for 1 h, filter, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0042] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 181 mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 0.9%.

[0043] Comparative Example 6 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1 L of a sodium tungstate solution containing 0.5 g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 80℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; S2, mix 0.8 g of ferrous sulfate and 2.4 g of aluminum sulfate, add 200 mL of water and stir until dissolved, to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 0.55:1, and the mass ratio of ferrous salt to aluminum salt is 1:3; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 h, stand for 1 h, filter, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0044] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 263 mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 1.0%.

[0045] Comparative Example 7 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtain 1 L of a sodium tungstate solution containing 0.5 g / L of chromium elements, adjust the pH of the sodium tungstate solution to 12 at room temperature, then heat to 80℃ and keep the temperature, to obtain a pretreated sodium tungstate solution; S2, use 12 g of sodium sulfide as a chromium removal reagent; S3, add the chromium removal reagent to the pretreated sodium tungstate solution, stir for 1 h, stand for 1 h, filter, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0046] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 381 mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 0.4%.

[0047] Comparative Example 8 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 14 at room temperature, then heating to 80℃ and keeping, to obtain a pretreated sodium tungstate solution; S2, mixing 4.8g of ferrous sulfate and 1.6g of aluminum sulfate, adding 200mL of water and stirring until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution is 3.29:1, and the mass ratio of ferrous salt to aluminum salt is 3:1; S3, adding the chromium removal reagent to the pretreated sodium tungstate solution, stirring for 1h, standing for 1h, filtering, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0048] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 37mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 1.2%.

[0049] Comparative Example 9 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 12 at room temperature, then heating to 80℃ and keeping, to obtain a pretreated sodium tungstate solution; S2, adding 4.8g of ferrous sulfate to 100mL of water and stirring until dissolved to obtain a chromium removal reagent one, the molar ratio of ferrous ions in the chromium removal reagent one to chromium elements in the sodium tungstate solution is 3.29:1, adding 1.6g of aluminum sulfate to 100mL of water and stirring until dissolved to obtain a chromium removal reagent two, and the mass ratio of ferrous salt to aluminum salt is 3:1; S3, adding the chromium removal reagent one to the pretreated sodium tungstate solution, stirring for 1h, then adding the chromium removal reagent two to the solution, stirring for 1h, standing for 1h, filtering, to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0050] The chromium content in the sodium tungstate solution after chromium removal is determined by AAS method, and the result is 5mg / L; The precipitate residue after chromium removal is determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue is 9.5%.

[0051] Comparative Example 10 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1L of a sodium tungstate solution containing 0.5g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 12 at room temperature, then heating to 80℃ and keeping, to obtain a pretreated sodium tungstate solution; S2, 4.8 g ferrous sulfate was added into 100 mL water and stirred until dissolved to obtain a chromium removal reagent one, the molar ratio of ferrous ions in the chromium removal reagent one to chromium elements in the sodium tungstate solution was 3.29:1, 1.6 g aluminum sulfate was added into 100 mL water and stirred until dissolved to obtain a chromium removal reagent two, the mass ratio of ferrous salt to aluminum salt was 3:1; S3, the chromium removal reagent two was added into the pretreated sodium tungstate solution, stirred for 1 h, filtered to obtain a filtrate, then the chromium removal reagent one was added into the filtrate, stirred for 1 h, stood for 1 h, filtered to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0052] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L; The precipitate residue after chromium removal was determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue after the second filtration was 10.6%.

[0053] Comparative Example 11 A method for removing chromium from a sodium tungstate solution, comprising the following steps: S1, obtaining 1 L of a sodium tungstate solution containing 0.5 g / L of chromium elements, adjusting the pH of the sodium tungstate solution to 12 at room temperature, then heating to 80℃ and keeping the temperature, to obtain a pretreated sodium tungstate solution; S2, 4.8 g ferrous sulfate was added into 200 mL water and stirred until dissolved to obtain a chromium removal reagent, the molar ratio of ferrous ions in the chromium removal reagent to chromium elements in the sodium tungstate solution was 3.29:1; S3, the chromium removal reagent was added into the pretreated sodium tungstate solution, stirred for 1 h, stood for 1 h, and filtered to obtain a sodium tungstate solution after chromium removal and a precipitate residue.

[0054] The chromium content in the sodium tungstate solution after chromium removal was determined by AAS method, and the result was 5 mg / L; The precipitate residue after chromium removal was determined by X-ray fluorescence spectrometry (XRF), and the tungsten content in the residue after the second filtration was 10.6%.

[0055] From the above examples and comparative examples, it can be seen that the chromium removal reagent is not prepared into a solution (Comparative Example 2), the conventional excess sodium sulfide treatment process (Comparative Example 7) or the reaction parameters are not within the scope of the technical scheme of the present application (such as the reaction temperature is too low in Comparative Example 1, the mass ratio of ferrous salt to aluminum salt is too high, too low or the addition amount of ferrous salt is insufficient in Comparative Examples 3, 4, 5, 6 and 8, and the pH is too high in Comparative Example 8) cannot achieve the ideal chromium removal effect, while although the separate addition of ferrous salt and aluminum salt or the addition of no aluminum salt in Comparative Examples 9, 10 and 11 can achieve the ideal chromium removal effect, a high tungsten loss will be caused.

[0056] The application provides a method for removing chromium from a sodium tungstate solution, and has the beneficial effects that: a solution is prepared by using a ferrous salt and an aluminum salt, the use amount of a precipitant is reduced, and the chromium removal cost is reduced; Al(OH)3 is generated by introducing the aluminum salt and is wrapped on the surface of Fe(OH)3 colloidal precipitate formed, and tungsten loss is reduced; the amount of sludge generated by the technical scheme is small, and the sludge is simple to handle; the purity of the sodium tungstate is improved, and the quality and performance of tungsten products are improved; and the method is suitable for production requirements of different scales and has strong adaptability.

[0057] The above merely describes the preferred embodiments of the application, and does not limit the patent scope of the application, and any equivalent structural transformation made by using the content of the application specification, or direct / indirect application in other related technical fields is included in the patent protection scope of the application.

Claims

1. A method for removing chromium from a sodium tungstate solution, characterized in that: The following steps are involved: 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 warm to obtain a pretreated sodium tungstate solution; S2. Mix the ferrous salt and the aluminum salt, add an appropriate amount of water and stir until dissolved to obtain a chromium removal reagent, wherein the molar ratio of the ferrous ion in the chromium removal reagent to the chromium element in the sodium tungstate solution is 3.15:1-4.50:1, and the mass ratio of the ferrous salt to the aluminum salt is 3:1-4:1; S3, adding the chromium removal reagent to the pretreated sodium tungstate solution, stirring, standing, and filtering to obtain the sodium tungstate solution after chromium removal and precipitated residue.

2. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In step S1, the pH of the sodium tungstate solution is adjusted to 9-12 at room temperature.

3. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In the step S2, the ferrous salt is a soluble ferrous salt, and the aluminum salt is a soluble aluminum salt.

4. The method for removing chromium from a sodium tungstate solution according to claim 3, wherein: The ferrous salt is ferrous sulfate, and the aluminum salt is aluminum sulfate.

5. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In step S3, the stirring time is 1 to 2 hours.

6. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In step S3, the standing time is 1 to 2 hours.

7. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In the step S1, the chromium element in the sodium tungstate solution exists in the form of CrO4 2－ , Cr2O7 2－ At least one of .

8. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In the step S1, the content of the chromium element in the sodium tungstate solution is 0.01-10 g / L.

9. The method for removing chromium from a sodium tungstate solution according to claim 1, wherein: In the step S2, the content of chromium in the sodium tungstate solution after chromium removal is less than 10 mg / L, and the content of WO3 in the precipitated residue is less than 1.5%.