A method for reducing the chromium content of ammonium tungstate

Abstract

The present application belongs to the technical field of hydrometallurgy of tungsten, and particularly relates to a method for reducing the chromium content in ammonium tungstate, comprising the following steps: S1, obtaining a chromium-containing ammonium tungstate solution and a chromium removal reagent, wherein the chromium removal reagent comprises: a divalent iron salt and a trivalent iron salt, and the mass ratio of ferrous ions to ferric ions is 1:(3-4); S2, adding the chromium removal reagent into the chromium-containing ammonium tungstate solution to form a reaction system, and reacting at 10-40 DEG C for 1-3 h, and then performing solid-liquid separation to obtain a post-chromium-removal solution; the present application configures a chromium removal reagent from ferrous salt and iron salt in a certain proportion, the ferric ions can destroy the stability of chromium ammonia complex, and the ferrous ions can prevent the oxidation of chromium ions in the reaction process, so that a reducing environment is created, thereby realizing the deep removal of chromium elements.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology of tungsten, specifically a method for reducing the chromium content in ammonium tungstate. Background Technology

[0002] Controlling chromium content is a key technical challenge in the preparation of ammonium tungstate. Traditional production processes often suffer from excessive chromium content, which not only affects product purity but also increases the cost and complexity of subsequent processing. Traditional ammonium tungstate preparation methods typically rely on simple chemical precipitation processes, which are ineffective at controlling chromium content. Due to the lack of precise raw material ratios and reaction condition control, the introduction of chromium is often unavoidable, leading to excessive chromium content in the final product. Some processes employ physical separation techniques to reduce chromium content, such as filtration and centrifugation. While these methods can reduce chromium content to some extent, they are inefficient and cannot fundamentally solve the problem because they cannot prevent the introduction of chromium during production. Certain chemical treatment methods, such as using reducing agents or complexing agents to remove chromium from solution, can reduce chromium content, but often require additional chemical reagents and complex operational steps, increasing production costs and environmental risks. Existing tungstate catalysts have low selectivity, resulting in the generation of numerous byproducts during the synthesis reaction. This not only increases the impurity content of the product but also makes subsequent purification processes more difficult and expensive.

[0003] Normally, chromium can be removed at the front end. However, if the chromium solution is not removed at the front end, during the ammonia dissolution process, the chromium element will react with excess ammonia to form Cr(NH3) in the normal high-pressure reaction of tungsten oxide (at which 105℃ corresponds to about 1 atmosphere). x 3+ A complex soluble in the liquid is formed, leading to the final exceedance of Cr. The reaction mechanism is as follows: Cr 3+ +3NH3H2O=3NH4 + Cr(OH)3 reacts with excess ammonia at high temperatures, and the reaction mechanism is as follows: Cr(OH)3 + xNH3H2O ​​→ Cr(NH3) x 3+ +xH₂O+3OH - Currently, there is no corresponding method to remove this complex, and a corresponding method is urgently needed to treat it.

[0004] In summary, traditional methods for preparing ammonium tungstate have significant shortcomings in controlling chromium content, necessitating optimization of production processes and the development of novel catalysts to achieve more effective chromium content control. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for reducing the chromium content in ammonium tungstate, comprising the following steps:

[0006] S1. Obtain a chromium-containing ammonium tungstate solution and a chromium removal reagent, wherein the chromium removal reagent includes: ferrous salt and ferric salt, and the mass ratio of ferrous ions to ferric ions is 1:(3-4).

[0007] S2. The chromium removal reagent is added to the chromium-containing ammonium tungstate solution to form a reaction system, and the reaction is carried out at 10-40℃ for 1-3 hours. After solid-liquid separation, the chromium-removed liquid is obtained.

[0008] In step S1, the iron element accounts for a mass fraction of 15 wt% or greater than that of the chromium removal reagent.

[0009] In step S1, the chromium content in the chromium-containing ammonium tungstate solution is less than or equal to 5000 ppm.

[0010] Step S2 further includes: when the chromium content in the ammonium chromium tungstate solution is less than or equal to 1000 ppm, the solid-liquid ratio of the chromium removal reagent to the ammonium chromium tungstate solution is (0.5-1):100 g / mL; when the chromium content in the ammonium chromium tungstate solution is greater than 1000 ppm and less than or equal to 5000 ppm, the solid-liquid ratio of the mass of the chromium removal reagent to the volume of the ammonium chromium tungstate solution is (2-3):100 g / mL.

[0011] In step S1, the mass fraction of tungsten trioxide in the ammonium chromium tungstate solution is 180-280 g / L.

[0012] Step S1 further includes: adding the chromium removal reagent to the chromium-containing ammonium tungstate solution to form a reaction system, reacting at 10-40℃ for 1-3 hours, and continuously stirring during the reaction, with the stirring speed being 300-500 r / min.

[0013] In step S2, the pH value of the reaction system is 9-11, and the pressure of the reaction system is 1 atm.

[0014] The method further includes the following after step S2:

[0015] S3. Add ammonium sulfide to the chromium-removed liquid, filter, and then evaporate and crystallize the filtrate to obtain ammonium paratungstate crystals, wherein the mass fraction of the ammonium sulfide is 16wt%-20wt%.

[0016] In step S3: when the chromium content in the ammonium chromium tungstate solution is less than or equal to 1000 ppm, the amount of ammonium sulfide added is 0.5% of the volume of the ammonium chromium tungstate solution; when the chromium content in the ammonium chromium tungstate solution is greater than 1000 ppm but less than or equal to 5000 ppm, the amount of ammonium sulfide added is 1%-1.5% of the volume of the ammonium chromium tungstate solution.

[0017] The ammonium tungstate crystal contains less than or equal to 5 ppm of chromium and less than or equal to 10 ppm of iron.

[0018] This invention uses ferrous salt and ferric salt in a specific ratio to prepare a chromium removal reagent. Ferric ions can disrupt the stability of chromium-ammonia complexes, while ferrous ions can prevent chromium ions from being oxidized during the reaction, creating a reducing environment. This achieves deep removal of chromium, solving the problem of excessive impurities caused by the instability of chromium complexes. Moreover, the system has low cost and is a low-carbon, energy-saving hydrometallurgical production system. It also solves the problem of excessive impurity fluctuations after acid process treatment, removing chromium salts without causing excessive impurities in the final product. Detailed Implementation

[0019] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a method for reducing the chromium content in ammonium tungstate, comprising the following steps:

[0021] S1. Obtain a chromium-containing ammonium tungstate solution and a chromium removal reagent, wherein the chromium removal reagent includes: ferrous salt and ferric salt, and the mass ratio of ferrous ions to ferric ions is 1:(3-4);

[0022] This method mainly uses ferric salts as the main component, which disrupt the stability of the complex in this system and solve the root cause of excessive Cr. The excess ferrous salts prevent chromium ions from being oxidized during the process and create a reducing environment. If oxidized chromium ions are present, ferrous salts can be reduced to ferric ions to further disrupt the stability of the complexed chromium and improve the effect.

[0023] S2. The chromium removal reagent is added to the chromium-containing ammonium tungstate solution to form a reaction system, and the reaction is carried out at 10-40℃ for 1-3 hours. After solid-liquid separation, the chromium-removed liquid is obtained.

[0024] Example 1

[0025] Obtain 300 mL of ammonium chromium tungstate solution, with a mass fraction of 180 g / L based on tungsten trioxide, containing 4000 ppm of chromium.

[0026] To obtain the chromium removal reagent, which is composed of ferrous chloride and ferric chloride, wherein the mass ratio of ferrous ions to ferric ions is 1:3 and the amount used is 6g, that is, the solid-liquid ratio of the mass of the chromium removal reagent to the volume of the chromium-containing ammonium tungstate solution is 2:100g / mL.

[0027] The above-mentioned chromium removal reagent was added to the above-mentioned chromium-containing ammonium tungstate solution, and the reaction was carried out at 25°C, 1 atm, pH 10, and stirring speed of 300 r / min for 3 hours. After filtration, the chromium-removed liquid was obtained.

[0028] Add 3 mL of ammonium sulfide to the chromium-removed solution, which is 1% of the volume of the chromium-containing ammonium tungstate solution. After filtering again, evaporate the filtrate to crystallize and obtain ammonium tungstate crystals.

[0029] The ammonium tungstate crystals were analyzed, and the calculated chromium content in the solution after chromium removal was 4 ppm and the iron content was 5 ppm.

[0030] Example 2

[0031] Obtain 300 mL of ammonium chromium tungstate solution, with a mass fraction of 200 g / L based on tungsten trioxide, containing 4000 ppm of chromium.

[0032] To obtain the chromium removal reagent, which is composed of ferrous chloride and ferric chloride, wherein the mass ratio of ferrous ions to ferric ions is 1:4 and the amount used is 6g, that is, the solid-liquid ratio of the mass of the chromium removal reagent to the volume of the chromium-containing ammonium tungstate solution is 2:100g / mL.

[0033] The above-mentioned chromium removal reagent was added to the above-mentioned chromium-containing ammonium tungstate solution, and the reaction was carried out at 25°C, 1 atm, pH 10, and stirring speed of 300 r / min for 3 hours. After filtration, the chromium-removed liquid was obtained.

[0034] Add 4.5 mL of ammonium sulfide to the chromium-removed solution, which is 1.5% of the volume of the chromium-containing ammonium tungstate solution. After filtering again, evaporate the filtrate to crystallize and obtain ammonium tungstate crystals.

[0035] The ammonium tungstate crystals were analyzed, and the calculated chromium content in the solution after chromium removal was 2 ppm and the iron content was 3 ppm.

[0036] Example 3

[0037] Obtain 300 mL of ammonium chromium tungstate solution, with a mass fraction of 200 g / L based on tungsten trioxide, containing 500 ppm of chromium.

[0038] The chromium removal reagent is prepared by means of ferrous chloride and ferric chloride, wherein the mass ratio of ferrous ions to ferric ions is 1:3 and the amount used is 1.5g, that is, the solid-liquid ratio of the mass of the chromium removal reagent to the volume of the chromium-containing ammonium tungstate solution is 0.5:100g / mL.

[0039] The above-mentioned chromium removal reagent was added to the above-mentioned chromium-containing ammonium tungstate solution, and the reaction was carried out at 25°C, 1 atm, pH 10, and stirring speed of 300 r / min for 3 hours. After filtration, the chromium-removed liquid was obtained.

[0040] Add 1.5 mL of ammonium sulfide to the chromium-removed solution, which is 0.5% of the volume of the chromium-containing ammonium tungstate solution. After filtering again, evaporate the filtrate to crystallize and obtain ammonium tungstate crystals.

[0041] The ammonium tungstate crystals were tested, and the calculated chromium content in the solution after chromium removal was 2 ppm and the iron content was 5 ppm.

[0042] Example 4

[0043] Obtain 300 mL of ammonium chromium tungstate solution, with a mass fraction of 280 g / L based on tungsten trioxide, containing 500 ppm of chromium.

[0044] The chromium removal reagent is composed of ferrous chloride and ferric chloride, wherein the mass ratio of ferrous ions to ferric ions is 1:4, and the amount used is 1.5g, that is, the solid-liquid ratio of the mass of the chromium removal reagent to the volume of the chromium-containing ammonium tungstate solution is 0.5:100g / mL.

[0045] The above-mentioned chromium removal reagent was added to the above-mentioned chromium-containing ammonium tungstate solution, and the reaction was carried out at 25°C, 1 atm, pH 10, and stirring speed of 300 r / min for 3 hours. After filtration, the chromium-removed liquid was obtained.

[0046] Add 1.5 mL of ammonium sulfide to the chromium-removed solution, which is 0.5% of the volume of the chromium-containing ammonium tungstate solution. After filtering again, evaporate the filtrate to crystallize and obtain ammonium tungstate crystals.

[0047] The ammonium tungstate crystals were tested, and the calculated chromium content in the solution after chromium removal was 2 ppm and the iron content was 5 ppm.

[0048] Comparative Example 1

[0049] The difference from Example 1 is that the chromium removal reagent consists only of ferric chloride;

[0050] Analysis of ammonium tungstate crystals revealed that the chromium content in the solution after chromium removal was 22 ppm, and the iron content was 4 ppm.

[0051] Comparative Example 2

[0052] The difference from Example 1 is that the chromium removal reagent consists only of ferrous chloride;

[0053] Analysis of ammonium tungstate crystals revealed that the chromium content in the solution after chromium removal was 45 ppm, and the iron content was 4 ppm.

[0054] Comparative Example 3

[0055] The difference from Example 1 is that the chromium content in the ammonium chromate solution is 6000 ppm;

[0056] The chromium removal reagent is composed of ferrous chloride;

[0057] The ammonium tungstate crystals were analyzed, and the calculated chromium content in the solution after chromium removal was 11 ppm and the iron content was 4 ppm.

[0058] Comparative Example 4

[0059] The difference from Example 3 is that the chromium removal reagent is composed of ferric chloride, and the amount added is 1.5g;

[0060] The ammonium tungstate crystals were analyzed, and the calculated chromium content in the solution after chromium removal was 16 ppm and the iron content was 4 ppm.

[0061] Comparative Example 5

[0062] The difference from Example 3 is that the chromium removal reagent is composed of ferrous chloride, and the amount added is 1.5g;

[0063] Analysis of ammonium tungstate crystals revealed that the chromium content in the solution after chromium removal was 78 ppm, and the iron content was 4 ppm.

[0064] Comparative Example 6

[0065] The difference from Example 1 is that the chromium removal reagent is composed of ferrous chloride and ferric chloride, wherein the mass ratio of ferrous ions to ferric ions is 1:5;

[0066] The ammonium tungstate crystals were analyzed, and the calculated chromium content in the solution after chromium removal was 16 ppm and the iron content was 4 ppm.

[0067] Comparative Example 7

[0068] The difference from Example 1 is that the chromium removal reagent is composed of ferrous chloride and ferric chloride, wherein the mass ratio of ferrous ions to ferric ions is 1:2;

[0069] Analysis of ammonium tungstate crystals revealed that the chromium content in the solution after chromium removal was 67 ppm, and the iron content was 5 ppm.

[0070] Compared with Comparative Example 1, Example 1 shows that when the chromium content is greater than 1000 ppm and less than or equal to 5000 ppm, ferric chloride alone cannot achieve the technical effect of the present invention; compared with Comparative Example 2, Example 1 shows that when the chromium content is greater than 1000 ppm and less than or equal to 5000 ppm, ferrous chloride alone cannot achieve the technical effect of the present invention; compared with Comparative Example 3, Example 1 shows that when the chromium content is greater than 5000 ppm, the technical effect of the present invention cannot be achieved; compared with Comparative Example 4, Example 3 shows that when the chromium content is less than or equal to 1000 ppm, ferric chloride alone cannot achieve the technical effect of the present invention; compared with Comparative Example 5, Example 3 shows that when the chromium content is less than or equal to 1000 ppm, ferrous chloride alone cannot achieve the technical effect of the present invention; compared with Comparative Examples 6 and 7, Example 1 shows that when the mass ratio of ferrous ions to ferric ions in the chromium removal reagent is not within the range of 1:(3-4), the technical effect of the present invention cannot be achieved.

[0071] This invention uses ferrous salt and ferric salt in a specific ratio to prepare a chromium removal reagent. Ferric ions can disrupt the stability of chromium-ammonia complexes, while ferrous ions can prevent chromium ions from being oxidized during the reaction, creating a reducing environment. This achieves deep removal of chromium, solving the problem of excessive impurities caused by the instability of chromium complexes. Moreover, the system has low cost and is a low-carbon, energy-saving hydrometallurgical production system. It also solves the problem of excessive impurity fluctuations after acid process treatment, removing chromium salts without causing excessive impurities in the final product.

[0072] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method of reducing the chromium content of ammonium tungstate, characterized in that, The method comprises the following steps: S1, obtaining an ammonium tungstic acid solution containing chromium and a chromium removal reagent, the chromium removal reagent comprising: a divalent iron salt and a trivalent iron salt, the mass ratio of ferrous ions and ferric ions being 1: (3-4), the ammonium tungstic acid solution containing chromium comprising Cr(NH3) x 3+ ; S2, the chromium removal reagent is added into the chromium-containing ammonium tungstate solution to form a reaction system, and the reaction is carried out at 10-40℃ for 1-3h, and then solid-liquid separation is carried out to obtain a chromium-removed solution; S3, ammonium sulfide is added into the chromium-removed solution, and then filtration is carried out, and the filtrate is evaporated and crystallized to obtain ammonium tungstate crystals; In the step S1, the mass fraction of the iron element in the chromium removal reagent is greater than or equal to 15wt%. In the step S2, when the content of the chromium element in the chromium-containing ammonium tungstate solution is less than or equal to 1000ppm, the solid-liquid ratio of the chromium removal reagent to the chromium-containing ammonium tungstate solution is (0.5-1):100g / mL; when the content of the chromium element in the chromium-containing ammonium tungstate solution is greater than 1000ppm and less than or equal to 5000ppm, the solid-liquid ratio of the mass of the chromium removal reagent to the volume of the chromium-containing ammonium tungstate solution is (2-3):100g / mL. The pH value of the reaction system is 9-11. The content of the chromium element in the ammonium tungstate crystals is less than or equal to 5ppm.

2. The method of claim 1, wherein the ammonium tungstate is prepared by the method comprising: In the step S1, the mass fraction of tungsten trioxide in the chromium-containing ammonium tungstate solution is 180-280g / L. ​ 3. The method for reducing the chromium content in ammonium tungstate according to claim 1, characterized in that, In the step S1, the chromium removal reagent is added into the chromium-containing ammonium tungstate solution to form a reaction system, and the reaction is carried out at 10-40℃ for 1-3h, and the stirring is continuously carried out during the reaction, and the stirring speed is 300-500r / min.

4. The method for reducing the chromium content in ammonium tungstate according to claim 1, characterized in that, In the step S2, the pressure of the reaction system is 1atm.

5. The method for reducing the chromium content in ammonium tungstate according to claim 1, characterized in that, In the step S3, the mass fraction of the ammonium sulfide is 16wt%-20wt%.

6. The method for reducing the chromium content in ammonium tungstate according to claim 5, characterized in that, In the step S3, when the content of the chromium element in the chromium-containing ammonium tungstate solution is less than or equal to 1000ppm, the addition amount of the ammonium sulfide is 0.5% of the volume of the chromium-containing ammonium tungstate solution; when the content of the chromium element in the chromium-containing ammonium tungstate solution is greater than 1000ppm and less than or equal to 5000ppm, the addition amount of the ammonium sulfide is 1%-1.5% of the volume of the chromium-containing ammonium tungstate solution.

7. The method of claim 6, wherein the ammonium tungstate is prepared by the method of claim 1, and the ammonium tungstate has a chromium content of less than 1 ppm. The content of the iron element in the ammonium tungstate crystals is less than or equal to 10ppm.