A method for removing chromium from sodium tungstate solution

Abstract

The invention discloses a method for removing chromium from a sodium tungstate solution, and relates to the field of sodium tungstate purification. In a sodium tungstate solution containing chromium, a mixed gas of carbon dioxide and an inert gas is first introduced, and then the volume proportion of carbon dioxide in the mixed gas is gradually increased, and then sulfur dioxide gas is introduced, and a precipitant is added, stirred, and aged. The invention first treats sodium tungstate with a mixed gas containing carbon dioxide, and then gradually adjusts the content of carbon dioxide, so that the pH value of the sodium tungstate solution can be adjusted, and the method can effectively avoid making the solution partially over-acidic and causing tungstate colloid, and the addition of the inert gas plays a role of buffering, diluting, and stirring, reducing the loss of tungstate ions, and then sulfur dioxide and a precipitant are introduced, so that hexavalent chromium is reduced to trivalent chromium. Therefore, the method of the invention not only reduces the loss of tungsten, but also ensures high-efficiency chromium removal.

Description

Technical Field

[0001] The invention relates to the field of sodium tungstate purification, in particular to a method for removing chromium from a sodium tungstate solution. Background Art

[0002] At present, the recycling of waste tungsten has reached more than 20% of my country's tungsten consumption. Among them, the sodium carbonate smelting method for recycling waste tungsten is relatively mature and has a wide range of adaptability. Most of the recycled waste tungsten is tungsten in cemented carbide waste powder and various slags. During the leaching process of the sodium carbonate smelting method, the chromium element is leached through high-temperature smelting and enters the sodium tungstate solution in the form of hexavalent chromium, resulting in excessive chromium in the sodium tungstate solution, which cannot meet the production of high-purity tungsten products.

[0003] The main method of removing chromium in the prior art is to reduce hexavalent chromium to trivalent chromium by passing sulfur dioxide and sulfite. Strong acid is often used to adjust the pH directly. Since strong acid often produces tungstate colloid, tungstate ion is lost, thus affecting the further recovery of tungsten. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a method for removing chromium from a sodium tungstate solution.

[0005] The technical solution of the present invention is as follows:

[0006] A method for removing chromium from a sodium tungstate solution comprises the following steps: firstly introducing a mixed gas of carbon dioxide and an inert gas into a sodium tungstate solution containing chromium, then gradually increasing the volume ratio of carbon dioxide in the mixed gas, then introducing sulfur dioxide gas, adding a precipitant, stirring, and aging.

[0007] As a preferred embodiment of the present invention, the precipitant is sodium sulfite.

[0008] As a preferred embodiment of the present invention, the volume ratio of the carbon dioxide to the inert gas is 3-8:1.

[0009] As a preferred embodiment of the present invention, the inert gas is nitrogen or argon or a mixed gas of nitrogen and argon in a volume ratio of 1-3:1-5.

[0010] As a preferred embodiment of the present invention, the stepwise increase of the volume proportion of carbon dioxide in the mixed gas specifically includes four stages of adjustment:

[0011] In the first stage, the volume ratio of carbon dioxide to inert gas is 3-4:1, and the introduction time is 10-20 minutes;

[0012] The volume ratio of carbon dioxide and inert gas in the second stage is 4-5:1, and the introduction time is 5-10 minutes;

[0013] The volume ratio of carbon dioxide and inert gas in the third stage is 5-7:1, and the introduction time is 5-10 minutes;

[0014] In the fourth stage, the volume ratio of carbon dioxide to inert gas is 7-8:1, and the introduction time is 5-15 minutes.

[0015] As a preferred embodiment of the present invention, the inlet flow rate of the mixed gas is 5-10 L / min.

[0016] As a preferred embodiment of the present invention, the pH value of the sodium tungstate solution introduced with sulfur dioxide gas is 5.5-6.5.

[0017] As a preferred embodiment of the present invention, the stirring time is 3-5h.

[0018] As a preferred embodiment of the present invention, the aging time is 5-15h.

[0019] As a preferred embodiment of the present invention, modified castor oil is added to the sodium tungstate solution while the mixed gas is introduced. The preparation method of the modified castor oil is as follows: castor oil, isopropanol and fluoroboric acid are mixed in a closed container, heated to 100-110° C. under an inert atmosphere with stirring, reacted for 1-2 hours, cooled, extracted with ethyl acetate, washed, and distilled under reduced pressure to obtain a polyol substance, and then the polyol substance and the catalyst are reacted for a period of time, and propylene oxide is continuously added, maintained at 140-150° C., and reacted for 20-40 minutes to obtain the modified castor oil.

[0020] The beneficial effects of the present invention are:

[0021] (1) The present invention first treats the sodium tungstate solution with a mixed gas containing carbon dioxide, and then gradually adjusts the content of carbon dioxide to adjust the pH value of the sodium tungstate solution. In addition, the method can effectively avoid the solution from being partially over-acidic and causing tungstate colloid to appear. The addition of inert gas plays a role in buffering, diluting and stirring, thereby reducing the loss of tungstate ions. Then, sulfur dioxide and a precipitant are introduced to reduce hexavalent chromium to trivalent chromium. Therefore, the method of the present invention not only reduces the loss of tungsten, but also ensures high-efficiency chromium removal.

[0022] (2) The present invention adds modified castor oil while introducing the mixed gas. This is mainly because other impurities may remain in the sodium tungstate solution, such as the surfactant used in the process. The introduction of the mixed gas will cause the solution to foam, which will affect the contact between the subsequent added precipitant and the chromium ions. Therefore, the addition of modified castor oil can inhibit the influence of the foaming of the surfactant, thereby improving the chromium removal efficiency. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0024] Example 1

[0025] Take 200g / L sodium tungstate solution, in which the chromium content is 1.1g / L, the WO3 content is 85g / L, and the pH is 8, and heat it to 60℃. Then, introduce a mixed gas of carbon dioxide and inert gas (nitrogen) with a volume ratio of 3:1 into the sodium tungstate solution for 5 minutes, and then gradually increase the volume proportion of carbon dioxide in the mixed gas. Specifically, it includes four stages of adjustment:

[0026] In the first stage, the volume ratio of carbon dioxide to inert gas is 4:1, and the introduction time is 15 minutes;

[0027] The volume ratio of carbon dioxide and inert gas in the second stage is 5:1, and the introduction time is 5 minutes;

[0028] The volume ratio of carbon dioxide and inert gas in the third stage is 7:1, and the introduction time is 7 minutes;

[0029] In the fourth stage, the volume ratio of carbon dioxide to inert gas is 8:1, and the introduction time is 10 minutes.

[0030] The flow rate of the mixed gas and sulfur dioxide gas is 5 L / min.

[0031] Then, sulfur dioxide gas is introduced until the pH value of the sodium tungstate solution reaches 5.5, and a precipitant is added at the same time, stirred for 4 hours, and aged for 10 hours. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0032] Example 2

[0033] Take 200g / L sodium tungstate solution, in which the chromium content is 1.3g / L, the WO3 content is 83g / L, and the pH is 8, and heat it to 60℃. Then, introduce a mixed gas of carbon dioxide and inert gas (argon) with a volume ratio of 3:1 into the sodium tungstate solution for 5 minutes, and then gradually increase the volume proportion of carbon dioxide in the mixed gas. Specifically, it includes four stages of adjustment:

[0034] In the first stage, the volume ratio of carbon dioxide to inert gas is 4:1, and the introduction time is 20 minutes;

[0035] The volume ratio of carbon dioxide and inert gas in the second stage is 5:1, and the introduction time is 10 minutes;

[0036] The volume ratio of carbon dioxide and inert gas in the third stage is 6:1, and the introduction time is 10 minutes;

[0037] In the fourth stage, the volume ratio of carbon dioxide to inert gas is 8:1, and the introduction time is 15 minutes.

[0038] The flow rate of the mixed gas and sulfur dioxide gas is 7 L / min.

[0039] Then, sulfur dioxide gas is introduced until the pH value of the sodium tungstate solution reaches 5.5, and a precipitant is added at the same time, stirred for 4 hours, and aged for 15 hours. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0040] Example 3

[0041] Take 200g / L sodium tungstate solution, in which the chromium content is 1.6g / L, the WO3 content is 89g / L, and the pH is 9, and heat it to 60℃. Then, introduce a mixed gas of carbon dioxide and inert gas (nitrogen and argon with a volume ratio of 1:1) with a volume ratio of 3:1 into the sodium tungstate solution for 5 minutes, and then gradually increase the volume proportion of carbon dioxide in the mixed gas. Specifically, it includes four stages of adjustment:

[0042] In the first stage, the volume ratio of carbon dioxide to inert gas is 3:1, and the introduction time is 15 minutes;

[0043] The volume ratio of carbon dioxide and inert gas in the second stage is 5:1, and the introduction time is 6 minutes;

[0044] The volume ratio of carbon dioxide and inert gas in the third stage is 7:1, and the introduction time is 7 minutes;

[0045] In the fourth stage, the volume ratio of carbon dioxide to inert gas is 8:1, and the introduction time is 15 minutes.

[0046] The flow rate of the mixed gas and sulfur dioxide gas is 9 L / min.

[0047] Then, sulfur dioxide gas is introduced until the pH value of the sodium tungstate solution reaches 6.5, and a precipitant is added at the same time, stirred for 3 hours, and aged for 12 hours. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0048] Example 4

[0049] Take 200g / L sodium tungstate solution, in which the chromium content is 1.5g / L, the WO3 content is 85g / L, and the pH is 8.5, and heat it to 60°C. Then, introduce a mixed gas of carbon dioxide and inert gas (nitrogen and argon with a volume ratio of nitrogen:argon = 3:5) with a volume ratio of 3:1 into the sodium tungstate solution for 5 minutes, and then gradually increase the volume ratio of carbon dioxide in the mixed gas. Specifically, it includes four stages of adjustment:

[0050] In the first stage, the volume ratio of carbon dioxide to inert gas was 3:1, and the introduction time was 16 min.

[0051] The volume ratio of carbon dioxide and inert gas in the second stage is 5:1, and the introduction time is 8 minutes;

[0052] The volume ratio of carbon dioxide and inert gas in the third stage is 7:1, and the introduction time is 7 minutes;

[0053] In the fourth stage, the volume ratio of carbon dioxide to inert gas is 8:1, and the introduction time is 10 minutes.

[0054] The flow rate of the mixed gas and sulfur dioxide gas is 10 L / min.

[0055] Then, sulfur dioxide gas is introduced until the pH value of the sodium tungstate solution reaches 6, and a precipitant is added at the same time, stirred for 5 hours, and aged for 12 hours. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0056] Example 5

[0057] Take 200g / L sodium tungstate solution, in which the chromium content is 1.2g / L, the WO3 content is 83g / L, and the pH is 8, and heat it to 60℃. Then, introduce a mixed gas of carbon dioxide and inert gas (nitrogen) with a volume ratio of 3:1 into the sodium tungstate solution for 5 minutes, and then gradually increase the volume proportion of carbon dioxide in the mixed gas. Specifically, it includes four stages of adjustment:

[0058] In the first stage, the volume ratio of carbon dioxide to inert gas is 4:1, and the introduction time is 15 minutes;

[0059] The volume ratio of carbon dioxide and inert gas in the second stage is 5:1, and the introduction time is 9 minutes;

[0060] The volume ratio of carbon dioxide and inert gas in the third stage is 7:1, and the introduction time is 8 minutes;

[0061] In the fourth stage, the volume ratio of carbon dioxide to inert gas is 8:1, and the introduction time is 7 minutes.

[0062] The flow rate of the mixed gas and sulfur dioxide gas is 6 L / min.

[0063] Then, sulfur dioxide gas is introduced until the pH value of the sodium tungstate solution reaches 6.5, and a precipitant is added at the same time, stirred for 4 hours, and aged for 10 hours. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0064] Example 6

[0065] This embodiment is a change made on the basis of Embodiment 5, specifically, castor oil is added to the sodium tungstate solution while the mixed gas is introduced, and the castor oil is castor oil with an addition amount of 0.1 mg / L.

[0066] Example 7

[0067] This embodiment is a change made on the basis of Embodiment 5, specifically, modified castor oil is added to the sodium tungstate solution while the mixed gas is introduced, and the preparation method of the modified castor oil is as follows: castor oil and isopropanol in a molar ratio of 1:1 and 5wt% of fluoroboric acid by weight of the reactants are mixed in a closed container, stirred and heated to 110°C under an inert atmosphere (nitrogen), reacted for 2h, cooled, extracted with ethyl acetate, washed, and distilled under reduced pressure to obtain a polyol substance, and then the polyol substance and Zn3[Co(CN)6]2·0.08ZnCl2·1.0H2O·1.5DME in a mass ratio of 1:0.03 are reacted for 5h, and then 20wt% of propylene oxide by weight of the reactants is added, maintained at 140°C, and reacted for 20min to obtain the obtained product.

[0068] Comparative Example 1 (without introduction of mixed gas)

[0069] Take 200g / L sodium tungstate solution, in which the chromium content is 1.2g / L, the WO3 content is 83g / L, and the pH is 8, heat it to 60°C, then pass sulfur dioxide gas into the sodium tungstate solution until the pH value of the sodium tungstate solution is 6.5, the flow rate of sulfur dioxide gas is 6L / min, and add a precipitant at the same time, stir for 4h, and age for 10h. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0070] Comparative Example 2 (No adjustment of the mixed gas)

[0071] Take 200g / L sodium tungstate solution, in which the chromium content is 1.2g / L, the WO3 content is 83g / L, and the pH is 8, heat it to 60°C, and then pass a mixed gas of carbon dioxide and inert gas (nitrogen) with a volume ratio of 3:1 into the sodium tungstate solution for 5 minutes, and the flow rate of the mixed gas and sulfur dioxide gas is 6L / min. Then pass sulfur dioxide gas until the pH value of the sodium tungstate solution is 6.5, add a precipitant at the same time, stir for 4 hours, and age for 10 hours. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0072] Comparative Example 3 (directly using strong acid to adjust pH)

[0073] Take 200g / L sodium tungstate solution, in which the chromium content is 1.2g / L, the WO3 content is 83g / L, and the pH is 8, heat it to 60°C, then add sulfuric acid to the sodium tungstate solution, adjust the pH value to 6.5, add a precipitant at the same time, stir for 4h, and age for 10h. The precipitant is sodium sulfite. The molar ratio of the precipitant to the chromium content is 5:1.

[0074] The performance of the aged solutions of the above embodiments and comparative examples was tested, and the test results are shown in Table 1.

[0075] Chromium removal rate = (initial concentration of hexavalent chromium in the solution - final concentration) / initial concentration;

[0076] Tungsten loss rate = (initial concentration of tungstate ion - final concentration) / initial concentration.

[0077]

[0078]

[0079] From the above table, it can be seen that the performance of the embodiment is better than that of the comparative example. The main reasons may be as follows: from the analysis of comparative example 1, it can be seen that the embodiment adopts a mixed gas containing carbon dioxide for pre-introduction, which can slowly and gradually adjust the acidity of the solution. At the same time, the inert gas is mixed, which can play a role of buffering and dilution, avoiding local over-acidification of the sodium tungstate solution, thereby generating tungstic acid colloid and reducing the loss of tungsten; from the analysis of comparative example 2, it can be seen that the embodiment gradually adjusts the content of carbon dioxide in the mixed gas, which can further slowly adjust the pH of the solution to avoid local over-acidification, that is, adjust the uniformity of the pH value; from the analysis of comparative example 3, it can be seen that directly using strong acid for adjustment may result in the generation of tungstic acid colloid and a large tungsten loss rate. Therefore, the present invention can effectively ensure the tungsten content while having a high chromium removal rate; in addition, the performance of Examples 6 and 7 is better, which may be due to the fact that the introduction of the mixed gas will cause the solution to generate foam, which affects the contact between the subsequent addition of the precipitant and the chromium ions. Therefore, the addition of castor oil and modified castor oil can inhibit the influence of the foaming of the surfactant, thereby improving the chromium removal efficiency. Among them, the modified castor oil (the best performance in Example 7) has better dispersion performance in the sodium tungstate solution, which may be because the distribution of the hydrophobic chains and hydrophilic chains on the castor oil is changed after modification, thereby ensuring the dispersibility in the solution and improving the foam suppression effect.

[0080] Under the premise that no conflict occurs, those skilled in the art may freely combine and superimpose the above-mentioned additional technical features.

[0081] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for removing chromium from a sodium tungstate solution, characterized in that: In the sodium tungstate solution containing chromium, first introduce a mixed gas of carbon dioxide and inert gas, then gradually increase the volume ratio of carbon dioxide in the mixed gas, then introduce sulfur dioxide gas, and at the same time add sodium sulfite, stir, and age; The stepwise increase in the volume proportion of carbon dioxide in the mixed gas specifically includes four stages of adjustment: In the first stage, the volume ratio of carbon dioxide to inert gas is 3-4:1, and the introduction time is 10-20 minutes; The volume ratio of carbon dioxide and inert gas in the second stage is 4-5:1, and the introduction time is 5-10 minutes; The volume ratio of carbon dioxide and inert gas in the third stage is 5-7:1, and the introduction time is 5-10 minutes; In the fourth stage, the volume ratio of carbon dioxide to inert gas is 7-8:1, and the introduction time is 5-15 minutes; Adding modified castor oil to the sodium tungstate solution while introducing the mixed gas; The preparation method of the modified castor oil is as follows: castor oil, isopropanol and fluoroboric acid are mixed in a closed container, stirred and heated to 100-110° C. under an inert atmosphere, reacted for 1-2 hours, cooled, extracted with ethyl acetate, washed, and distilled under reduced pressure to obtain a polyol substance, and then the polyol substance and the catalyst are reacted for a period of time, and propylene oxide is continuously added, maintained at 140-150° C., and reacted for 20-40 minutes to obtain the modified castor oil.

2. The method for removing chromium from a sodium tungstate solution according to claim 1, characterized in that: The volume ratio of the carbon dioxide to the inert gas is 3-8:

1.

3. The method for removing chromium from a sodium tungstate solution according to claim 1, characterized in that: The inert gas is nitrogen or argon or a mixed gas of nitrogen and argon in a volume ratio of 1-3:1-5.

4. The method for removing chromium from a sodium tungstate solution according to claim 1, characterized in that: The flow rate of the mixed gas is 5-10 L / min.

5. The method for removing chromium from a sodium tungstate solution according to claim 1, characterized in that: The pH value of the sodium tungstate solution is 5.5-6.5 when sulfur dioxide gas is introduced.

6. The method for removing chromium from a sodium tungstate solution according to claim 1, characterized in that: The stirring time is 3-5h.

7. The method for removing chromium from a sodium tungstate solution according to claim 1, characterized in that: The aging time is 5-15h.

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