A method for preparing ammonium metatungstate and ammonium paratungstate from a crude sodium tungstate solution

Abstract

This invention discloses a method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution. The crude sodium tungstate solution is adjusted to pH 1-4, and then H₂O₂ is added and kept at a constant temperature to obtain a first solution. The first solution is then adjusted to pH 0.5-2.5, and an organic extractant is added for extraction, yielding a raffinate. The raffinate is treated to decompose the hydrogen peroxide it contains, yielding a sodium metatungstate solution. The metatungstate solution is mixed with a neutral extractant and subjected to low-temperature multi-stage countercurrent extraction to obtain a saturated loaded organic phase. The loaded organic phase is purified using an acidic solution, and then ammonia is added to the organic phase for back-extraction. After phase separation, a high-concentration ammonium metatungstate solution is obtained. The ammonium metatungstate solution is then added to ammonia and kept at a low temperature to obtain ammonium paratungstate. This invention uses less hydrogen peroxide, has a high molybdenum extraction rate, and minimizes tungsten loss. It also has low molybdenum removal costs, significantly reduces the ammonium metatungstate preparation process, and substantially lowers costs. This invention can also further prepare APT (ammonium paratungstate) without generating ammonia-containing waste gas through evaporation and crystallization.

Description

Technical Field

[0001] This invention belongs to the field of tungsten smelting technology, specifically relating to a method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution. Background Technology

[0002] The traditional process for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution is to first remove molybdenum, then purify and transform it to obtain ammonium tungstate solution, then crystallize APT, and then use APT as raw material to further prepare ammonium metatungstate. The specific method is as follows: (1) First, take advantage of the thiophilic properties of molybdenum to convert molybdenum in crude sodium tungstate solution into thiomolybdate, and then remove the molybdenum precipitate by adding acid precipitation or adding copper salt; (2) After purifying and removing molybdenum, the sodium tungstate solution is used to extract tungsten with anion exchange resin or amine extractant, and then desorbed or back-extracted with ammonia or ammonium salt to obtain ammonium tungstate solution with a concentration of about 250 g / L, and then evaporated and crystallized to obtain ammonium paratungstate (APT) crystals; (3) In order to obtain ammonium metatungstate, APT needs to be calcined at high temperature to remove ammonium, and then leached with water to obtain ammonium metatungstate solution with a concentration of about 300 g / L, and then concentrated to obtain ammonium metatungstate solution with a concentration of more than 1000 g / L, and finally obtained ammonium metatungstate crystals by spray drying. The current process presents the following problems: (1) The molybdenum removal slag is classified as hazardous waste, resulting in high environmental disposal costs, and the production process also generates toxic hydrogen sulfide gas; (2) Both ammonium paratungstate and ammonium metatungstate production processes generate ammonia-containing waste gas, requiring further treatment; (3) The production processes for ammonium paratungstate and ammonium metatungstate are lengthy, resulting in significant tungsten loss, requiring high-temperature calcination, and consuming high energy, leading to high overall production costs. Therefore, it is necessary to develop new methods for deep molybdenum removal from crude sodium tungstate solution to produce ammonium metatungstate and ammonium paratungstate.

[0003] To eliminate the hazardous waste residue generated during molybdenum removal from tungstate solutions, many researchers have conducted studies on molybdenum removal techniques using ion exchange and extraction. Among these, molybdenum removal via peroxymolybdate extraction is an effective method for deep removal of molybdenum with varying concentrations. Zelikman et al. used TBP as the extractant, adding hydrogen peroxide at 1.5–2.0 times the total molar amount of tungsten and molybdenum in the solution, then adjusting the pH to 1.5–2 for molybdenum extraction, achieving an extraction rate of over 96%. Other literature uses ammonium tungstate solution as raw material, first treating the solution with bipolar membrane electrodialysis, then adding hydrogen peroxide at 1.5 times the total molar amount of tungsten and molybdenum, followed by TBP-TRPO extraction, achieving a single-stage molybdenum extraction rate of over 63%. Both methods involve adding sufficient hydrogen peroxide (approximately 1.5 times the total molar amount of tungsten and molybdenum) to the tungstate solution, completely converting the tungsten and molybdenum in the solution into free peroxytungstate and peroxymolybdate ions, which are then removed by extraction. The solution after molybdenum removal is actually transformed into a peroxytungstate solution. According to the traditional process of extracting tungsten to prepare APT, the peroxytungstate solution needs to be converted into a tungstate solution. For example, after removing molybdenum from an ammonium tungstate solution using this method, a peroxytungstate solution needs to be converted into an ammonium tungstate solution before APT can be evaporated and crystallized. The hydrogen peroxide bound to tungsten in this process is essentially wasted, as tungsten is the main component of the tungstate solution; a large amount of hydrogen peroxide is wasted, significantly increasing the cost of molybdenum removal. Therefore, it is necessary to develop a molybdenum removal method that can significantly reduce hydrogen peroxide consumption.

[0004] Through detailed research on the coordination reaction characteristics of tungsten-molybdenum ions with hydrogen peroxide in acidic sodium tungstate solution, we found that in acidic solution, the stability of tungsten is greatly enhanced after it transforms into true metatungstate, and hydrogen peroxide cannot coordinate with it. Furthermore, we also discovered that under acidic conditions, tungsten-molybdenum polymeric heteropolyions can undergo the following reaction with hydrogen peroxide:

[0005] Mo3W4O 24 6- +6H₂O₂ + H⁺ + =3 / 2[Mo2O] 11 (H2O)] 2- +1 / 3[H2W 12 O 40 ] 6- +14 / 3H2O

[0006] Mo4W3O 24 6- +8H₂O₂ + 1 / 2H₂ + =2[Mo2O] 11 (H2O)] 2- +1 / 4[H2W 12 O 40 ] 6- +6H2O

[0007] Mo5W2O 24 6- +10H₂O₂=5 / 2[Mo₂O₂] 11 (H2O)] 2- +1 / 6[H2W 12 O 40 ] 6- +7 / 3H2O

[0008] Through the above reaction, molybdenum is coordinated to form peroxymolybdate ions, while tungsten under these conditions is transformed into metatungstate ions, which cannot be coordinated by hydrogen peroxide. These two findings provide a theoretical basis for reducing hydrogen peroxide consumption while ensuring sufficient coordination of molybdenum with hydrogen peroxide. Our further research revealed that metatungstate ions not coordinated by hydrogen peroxide cannot be extracted by TBP / TRPO. This provides the conditions for selective molybdenum removal. The tungsten solution after molybdenum removal is actually a sodium metatungstate solution. Through transformation, it can be converted into ammonium metatungstate, which can then be used to prepare APT. Transformation is crucial in this process.

[0009] Based on this, the present invention provides a method for retrieving ammonium metatungstate and ammonium paratungstate from a crude sodium tungstate solution. Summary of the Invention

[0010] In view of the above shortcomings, this invention proposes a method for preparing ammonium metatungstate and ammonium paratungstate that is simple in process, requires less hydrogen oxide, has a high molybdenum extraction rate, and significantly reduces production costs. This invention is achieved through the following technical means:

[0011] This invention discloses a method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution, comprising:

[0012] (1) Adjust the pH of the crude sodium tungstate solution to 1-4, then add H2O2 and keep it warm at low temperature to obtain the first solution;

[0013] (2) The pH of the first solution is adjusted to 0.5-2.5, and then an organic extractant is added for low-temperature extraction. After multi-stage countercurrent extraction, the raffinate is obtained.

[0014] (3) Decompose the hydrogen peroxide in the raffinate to obtain a sodium metatungstate solution;

[0015] (4) Mix the metatungstic acid solution with a neutral extractant at a ratio (O / A) of 0.2 to 4, and perform multi-stage countercurrent extraction at low temperature. During the extraction process, adjust the pH of the solution to -0.5 to 1.0, wait for phase separation, and obtain a saturated loaded organic phase.

[0016] (5) The saturated loaded organic phase was purified by using an acidic solution to obtain a purified organic phase;

[0017] (6) Add ammonia water to the purified organic phase for back-extraction. After phase separation is completed, a high-concentration ammonium metatungstate solution is obtained.

[0018] (7) A high-concentration ammonium metatungstate solution is spray-dried to obtain ammonium metatungstate powder;

[0019] (8) Add ammonia to a high-concentration ammonium paratungstate solution and keep it warm to obtain ammonium paratungstate.

[0020] Further, the amount of H2O2 used in step (1) is 1 to 4 times the molar amount of molybdenum in the solution; the low-temperature insulation condition is 0.5 to 6 hours at 20 to 70°C.

[0021] Further, the organic extractant in step (2) is a mixed solution of TBP, TRPO and sulfonated kerosene; the low-temperature extraction temperature is 25℃~60℃; and the ratio (O / A) of the multi-stage countercurrent extraction is 0.5~4.

[0022] Further, the method of decomposing hydrogen peroxide in the raffinate in step (3) includes: heating to 90-100°C, or adding an appropriate amount of Na2SO3, or introducing SO2.

[0023] Further, the neutral extractant in step (4) is prepared by the following method:

[0024] Take one or more of the following: isooctyl alcohol, sec-octyl alcohol, isoamyl alcohol, ethyl acetate, MIBK, diethyl ether, TBP, TOPO, and TRPO, and mix them with sulfonated kerosene to obtain the product.

[0025] Furthermore, the extraction temperature in step (4) is 25℃~60℃.

[0026] Furthermore, the concentration of the acidic solution in step (5) is 0.2–2 mol / L.

[0027] Further, in step (6), the molar ratio of ammonia water to tungsten on the organic phase is 0.5:1; and the back-extraction time is 2 to 20 minutes.

[0028] Further, in step (8), the molar ratio of the added ammonia water to the molar ratio of the tungsten in the solution is 1:3; the heat preservation temperature is 30-80℃.

[0029] The present invention also discloses an ammonium metatungstate prepared according to any of the methods described above.

[0030] The present invention also discloses an ammonium paratungstate prepared according to any of the above methods.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) The present invention uses less hydrogen peroxide, has a high molybdenum extraction rate and less tungsten loss, and has low molybdenum removal cost.

[0033] (2) High-concentration ammonium metatungstate solution can be prepared directly from sodium tungstate solution, which greatly reduces the preparation process of ammonium metatungstate and significantly lowers the cost.

[0034] (3) APT can be further prepared without the need for evaporation and crystallization to generate ammonia-containing waste gas. Detailed Implementation

[0035] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0038] Example 1

[0039] A method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution

[0040] (1) The crude sodium tungstate solution was acidified to pH=1 with sulfuric acid to obtain an acidic tungsten-molybdenum mixed solution with a tungsten concentration of 100 g / L and a molybdenum concentration of 10 g / L. Then, H2O2 with a molar amount of molybdenum was added to the solution, and the solution was kept at 70℃ for 6 h to obtain the first solution;

[0041] (2) Adjust the pH of the first solution to pH=0.5, then add organic extractant (TBP+TRPO+sulfonated kerosene) and extract at 25℃. According to the ratio (O / A)=0.5, the extraction is carried out through multi-stage countercurrent extraction to obtain the raffinate.

[0042] (3) Heat the raffinate after molybdenum removal to 90°C to decompose the small amount of hydrogen peroxide in the solution and obtain sodium metatungstate solution.

[0043] (4) The treated metatungstic acid solution was mixed with a neutral extractant (isooctanol + TBP + sulfonated kerosene) at a ratio (O / A) = 1, and multi-stage countercurrent extraction was carried out at a temperature of 25°C. During the extraction process, acid (sulfuric acid, hydrochloric acid and nitric acid) was added to adjust the pH to 1.0, and the saturated loaded organic phase after phase separation was obtained.

[0044] (5) The supported organic phase was washed with a 0.2 mol / L acidic solution to remove impurities;

[0045] (6) The washed loaded organic phase was back-extracted by adding ammonia water. The ratio of the molar amount of ammonia water to the molar amount of tungsten on the organic phase was 0.5. The back-extraction time was 2 min. After the phase separation was completed, a high concentration ammonium metatungstate solution with a concentration of 1215 g / L was obtained.

[0046] (7) High-concentration ammonium metatungstate solution is directly spray-dried to obtain ammonium metatungstate powder.

[0047] Example 2

[0048] A method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution

[0049] (1) The crude sodium tungstate solution was acidified to pH 1.5 with hydrochloric acid to obtain an acidic tungsten-molybdenum mixed solution with a tungsten concentration of 100 g / L and a molybdenum concentration of 0.5 g / L. Then, 2.5 times the molar amount of molybdenum in H2O2 was added to this solution, and the mixture was kept at 65℃ for 6 h to obtain the first solution;

[0050] (2) Adjust the pH of the first solution to pH=2.5, then add organic extractant (TBP+TRPO+sulfonated kerosene) and extract at 25℃. According to the ratio (O / A)=2, perform multi-stage countercurrent extraction to obtain the raffinate.

[0051] (3) Pass SO2 through the raffinate after molybdenum removal to decompose the small amount of hydrogen peroxide in the solution and obtain sodium metatungstate solution.

[0052] (4) The treated metatungstic acid solution was mixed with a neutral extractant (ethyl acetate + diethyl ether + sulfonated kerosene) at a ratio (O / A) = 4, and multi-stage countercurrent extraction was carried out at a temperature of 40°C. During the extraction process, acid (sulfuric acid, hydrochloric acid and nitric acid) was added to adjust the pH to 0, and the saturated loaded organic phase after phase separation was obtained.

[0053] (5) The supported organic phase was washed with an acidic solution of 0.5 mol / L to remove impurities;

[0054] (6) The washed loaded organic phase was back-extracted by adding ammonia water. The ratio of the molar amount of ammonia water to the molar amount of tungsten on the organic phase was 0.5. The back-extraction time was 4 min. After the phase separation was completed, a high concentration ammonium metatungstate solution with a concentration of 960 g / L was obtained.

[0055] (7) Ammonia water is added to a high-concentration ammonium metatungstate solution. The ratio of the molar amount of ammonia water added to the molar amount of tungsten in the solution is 1:3. Then the temperature is controlled at 80℃ and kept warm to directly produce APT crystals.

[0056] Example 3

[0057] A method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution

[0058] (1) The crude sodium tungstate solution was acidified to pH 3.5 with nitric acid to obtain an acidic tungsten-molybdenum mixed solution with a tungsten concentration of 30 g / L and a molybdenum concentration of 30 g / L. Then, twice the molar amount of molybdenum in H2O2 was added to this solution, and the mixture was kept at 20℃ for 0.5 h to obtain the first solution;

[0059] (2) Adjust the pH of the first solution to pH=1, then add organic extractant (TBP+TRPO+sulfonated kerosene) and extract at 40℃. According to the ratio (O / A)=0.5, the extraction is carried out through multi-stage countercurrent extraction to obtain the raffinate.

[0060] (3) Add an appropriate amount of Na2SO3 to the raffinate after molybdenum removal to decompose the small amount of hydrogen peroxide in the solution and obtain sodium metatungstate solution.

[0061] (4) The treated metatungstic acid solution and the neutral extractant (MIBK+TRPO+sulfonated kerosene) were mixed at a ratio (O / A) = 0.2 and subjected to multi-stage countercurrent extraction at 25°C. During the extraction process, acid (sulfuric acid, hydrochloric acid and nitric acid) was added to adjust the pH to -0.5 and waited until the saturated loaded organic phase after phase separation was obtained.

[0062] (5) The supported organic phase was washed with a 0.2 mol / L acidic solution to remove impurities;

[0063] (6) The washed loaded organic phase was back-extracted by adding ammonia water. The ratio of the molar amount of ammonia water to the molar amount of tungsten on the organic phase was 0.5. The back-extraction time was 6 min. After the phase separation was completed, a high concentration ammonium metatungstate solution with a concentration of 1528 g / L was obtained.

[0064] (7) High-concentration ammonium metatungstate solution is directly spray-dried to obtain ammonium metatungstate powder.

[0065] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing ammonium metatungstate and ammonium paratungstate from crude sodium tungstate solution, comprising: (1) Adjust the pH of the crude sodium tungstate solution to 1~4, then add H2O2. The amount of H2O2 used is 1~4 times the molar amount of molybdenum in the solution. Keep it at 20~70℃ for 0.5h~6h to obtain the first solution; (2) The pH of the first solution is adjusted to 0.5~2.5, and then an organic extractant is added for low-temperature extraction at 25℃~60℃. After multi-stage countercurrent extraction, the raffinate is obtained. (3) Decompose the hydrogen peroxide in the raffinate to obtain a sodium metatungstate solution; (4) Mix the metatungstic acid solution with a neutral extractant at a ratio of O / A = 0.2~4, and perform multi-stage countercurrent extraction at 25℃~60℃. During the extraction process, adjust the pH of the solution to -0.5~1.0, wait for phase separation, and obtain a saturated loaded organic phase. (5) The saturated loaded organic phase was purified by using an acidic solution to obtain a purified organic phase; (6) Add ammonia water to the purified organic phase and back-extract for 2~20 min. The ratio of the molar amount of ammonia water to the molar amount of tungsten on the organic phase is 0.5:

1. After the phase separation is completed, a high-concentration ammonium metatungstate solution is obtained. (7) A high-concentration ammonium metatungstate solution is spray-dried to obtain ammonium metatungstate powder; (8) Add ammonia to a high-concentration ammonium paratungstate solution and keep it at 30~80℃. The ratio of the molar amount of ammonia added to the molar amount of tungsten in the solution is 1:3, and ammonium paratungstate is obtained.

2. The method for preparing ammonium metatungstate and ammonium paratungstate according to claim 1, wherein: The organic extractant in step (2) is a mixed solution of TBP, TRPO, and sulfonated kerosene; The ratio of O / A in the multi-stage countercurrent extraction is 0.5~4.

3. The method for preparing ammonium metatungstate and ammonium paratungstate according to claim 1, wherein: The method for decomposing hydrogen peroxide in the raffinate in step (3) includes: Heat to 90~100℃, or add an appropriate amount of Na2SO3, or introduce SO2.

4. The method for preparing ammonium metatungstate and ammonium paratungstate according to claim 1, wherein: The neutral extractant in step (4) is prepared by the following method: Take one or more of isooctanol, sec-octanol, isoamyl alcohol, ethyl acetate, MIBK, diethyl ether, TBP, TOPO, and TRPO, and mix them with sulfonated kerosene to obtain the product.

5. The method for preparing ammonium metatungstate and ammonium paratungstate according to claim 1, wherein: The concentration of the acidic solution in step (5) is 0.2~2 mol / L.