A method for preparing ammonium paratungstate by using wolframite or mixed black and white tungsten ore

Abstract

The application belongs to the technical field of hydrometallurgy, and particularly relates to a method for preparing ammonium paratungstate by using wolframite or mixed wolframite, which comprises the following steps: ball milling the wolframite or mixed wolframite; then adding NaOH to perform first-stage alkali boiling to obtain first alkali boiling residue and first alkali boiling liquid, and then adding NaOH to the first alkali boiling residue to perform second-stage alkali boiling; adding a calcium-containing reagent into the first alkali boiling liquid and stirring to perform tungsten precipitation to obtain artificial white tungsten; using a sulfuric acid-oxalic acid mixed solution to decompose the artificial white tungsten to obtain a tungsten oxalate complex solution; then performing thermal decomposition, solid-liquid separation to obtain tungstic acid, and performing ammonia dissolution, evaporation crystallization and drying on the tungstic acid to obtain APT. The method realizes efficient decomposition of the wolframite and the mixed wolframite through a relatively short technological process, breaks through the limitation that the sulfuric acid-oxalic acid mixed system cannot treat the wolframite or the mixed wolframite, simultaneously reduces the reagent consumption and the cost, and greatly reduces the generation of high-salinity wastewater.

Description

Technical Field

[0001] This application belongs to the field of hydrometallurgical technology, specifically a method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and tungsten. Background Technology

[0002] Existing technologies for extracting tungsten from tungsten ore mainly include alkaline and acidic methods. Alkaline methods (such as NaOH decomposition) are effective for treating wolframite, but when treating high-calcium scheelite or complex mixed ores, they suffer from high reagent consumption, severe impurity co-dissolution, and lengthy subsequent purification processes. Traditional acidic methods (such as hydrochloric acid decomposition) produce a dense tungstate film that encapsulates the ore particles, leading to incomplete decomposition and low recovery rates.

[0003] To address this issue, patent CN111893327B proposes a sulfuric acid-oxalic acid mixed acid decomposition technology for scheelite concentrate, achieving efficient one-step decomposition of scheelite. This method is carried out under acidic conditions, using inexpensive, non-volatile sulfuric acid as the leaching agent, while oxalic acid acts as a complexing agent with a synergistic effect. This causes tungsten to form a highly soluble tungsten oxalate complex that enters the solution, while calcium forms calcium sulfate and enters the solid phase. The tungsten oxalate complex decomposes upon heating, with tungsten remaining in the solid phase as tungstic acid precipitate. The oxalic acid leaching agent remains in the liquid phase as a solution, and the mother liquor produced can be recycled. Because the leaching agent is recyclable, the entire process generates no wastewater, and the decomposition residue is high-quality, usable gypsum, preventing environmental pollution. Compared to traditional acid methods, the sulfuric acid-oxalic acid decomposition method is a clean, pollution-free tungsten smelting process with significant application potential. However, this process currently only processes scheelite and cannot decompose wolframite or ferruginous tungsten.

[0004] However, my country's tungsten ore is characterized by low grade and complex composition (68.7% scheelite, 20.9% wolframite, and 10.4% mixed types). High-grade scheelite is scarce and low-grade, while high-grade wolframite is abundant and high-grade. Mixed scheelite and wolframite ore are associated with other minerals, resulting in complex compositions that are difficult to beneficiate and process. For these minerals, direct treatment using a sulfuric acid-oxalic acid mixed acid process results in the wolframite not reacting at all, and all of it ending up in the leaching residue. In fact, not only is the sulfuric acid-oxalic acid mixed acid system ineffective in decomposing wolframite, but even other acids exhibit extremely slow leaching reactions with it.

[0005] Given that wolframite cannot be effectively decomposed in various acidic systems, a completely new technological approach may be needed. We envision converting wolframite into scheelite, which could potentially achieve efficient decomposition of tungsten in a sulfuric acid-oxalic acid system. In fact, patent CN102649995A proposed a method for converting wolframite into scheelite, using calcium salts to calcine wolframite at 600-1000℃ to obtain a calcined product containing scheelite. However, this conversion operation is energy-intensive and costly, especially when processing raw materials containing small amounts of wolframite, where production efficiency is very low. Summary of the Invention

[0006] To address the aforementioned problems, this application provides a method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and spodumene. This method achieves efficient decomposition of wolframite and wolframite / spodumene ...

[0007] This application discloses a method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wollastonite, comprising the following steps: S1. The tungsten-containing raw material is wet-milled to obtain a slurry, wherein the mass fraction of WO3 in the tungsten-containing raw material is 40%~70% and the mass fraction of Ca is 0.2%~20%; S2. The slurry is subjected to two-stage countercurrent alkaline boiling. The secondary countercurrent alkaline cooking process specifically involves adding sodium hydroxide to the slurry for the first-stage alkaline cooking, followed by solid-liquid separation to obtain the first alkaline cooking residue and the first alkaline cooking solution. Sodium hydroxide is added to the first alkaline residue for a second alkaline boiling process, and solid-liquid separation is performed to obtain a second alkaline residue and a second alkaline boiling solution. S3. Add a calcium-containing reagent to the first alkaline boiling solution and stir to precipitate tungsten. Separate the solid and liquid to obtain artificial scheelite and tungsten-precipitated liquid. S4. The artificial scheelite is decomposed using a sulfuric acid-oxalic acid mixed solution to obtain a tungsten oxalate complex solution; S5. The oxalate-tungsten complex solution is thermally decomposed and the solid-liquid separation is performed to obtain tungstic acid. The tungstic acid is then subjected to ammonia dissolution, evaporation crystallization, and drying to obtain the national standard grade zero ammonium paratungstate product.

[0008] Furthermore, in step S1, the tungsten-containing raw material includes wolframite or a mixture of wolframite and wolframite; the ball-to-material mass ratio of the wet ball mill is (2.0~5.0):1, the liquid-to-solid ratio is 1L:(1~4)kg, and the proportion of particles with a particle size of less than 300 mesh in the slurry is ≥96%.

[0009] Furthermore, in step S2, the liquid-to-solid ratio of the secondary countercurrent alkaline boiling process is (0.8~3) L:1 kg, the concentration of sodium hydroxide is 2~8 mol / L, the reaction temperature is 100~200℃, the time is 1~5 h, and the pressure is 1.0~2.5 MPa.

[0010] Furthermore, in step S2, the sodium hydroxide concentration in the first alkaline boiling solution is less than 1 mol / L, and the WO3 mass fraction in the second alkaline boiling residue is less than 0.5%. According to formula 1-(m2ω2 / m1ω1)×100%, the decomposition rate of wolframite using the technical solution of this application reaches over 98%, and the decomposition rate of mixed wolframite and tungsten ore reaches over 97%; where m1 is the mass of wolframite or mixed wolframite and tungsten ore, ω1 is the WO3 content in wolframite or mixed wolframite and tungsten ore, m2 is the mass of the second alkali leaching residue, and ω2 is the WO3 content in the second alkali leaching residue.

[0011] Furthermore, in step S3, the calcium-containing reagent includes calcium chloride, calcium oxide, calcium hydroxide, calcium sulfate, calcium hydrogen phosphate, calcium dihydrogen phosphate, or calcium citrate, and the molar ratio of the calcium-containing reagent to WO3 in the first alkaline boiling solution is (1~3):1.

[0012] Furthermore, in step S3, the reaction temperature for tungsten precipitation is 10~100℃, the time is 0.5~5h, and the stirring rate is 100~500rpm.

[0013] Furthermore, in step S4, the concentration of oxalic acid in the sulfuric acid-oxalic acid mixed solution is 0.5~2.5 mol / L, and the concentration of sulfuric acid is 0.5~2.0 mol / L.

[0014] Furthermore, in step S4, the liquid-to-solid ratio of the decomposition is (1~25) L:1 kg, the reaction temperature is 20~100℃, and the time is 1~6 h.

[0015] Furthermore, in step S5, the thermal decomposition temperature is 80~100℃ and the time is 0.5~3h; the liquid-to-solid ratio of the ammonia solution is (2~4)L:1kg, the time is 0.5~2h, the temperature is 20~50℃, and the concentration of the ammonia solution used is 5~9mol / L.

[0016] Furthermore, after step S2, the method further includes returning the second alkaline boiling solution to perform the first-stage alkaline boiling. The step S3 is followed by returning the tungsten-precipitated liquid to be used for the first-stage alkaline boiling.

[0017] This application proposes a method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite, which produces the following beneficial effects: 1. Compared with the traditional alkaline leaching process, this application adopts a two-stage countercurrent alkaline leaching method, which achieves a decomposition rate of over 98% for wolframite and over 97% for mixed wolframite and wolframite. 2. During the two-stage countercurrent alkaline boiling process, parameter control can ensure that the alkali in the first-stage alkaline boiling is basically exhausted, significantly reducing the amount of alkali used and greatly reducing the discharge of high-salt wastewater; at the same time, the tungsten content in the alkaline boiling residue is kept as low as possible, reducing the waste of tungsten resources. 3. It overcomes the limitation that the sulfuric acid-oxalic acid mixed acid system cannot process wolframite and mixed wolframite, and achieves efficient decomposition of wolframite and mixed wolframite in this system. The process is easy to operate and can be easily industrialized. Detailed Implementation

[0018] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] This application discloses a method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wollastonite, comprising the following steps: S1. The tungsten-containing raw material is wet-milled to obtain a slurry. The tungsten-containing raw material contains 40%~70% WO3 and 0.2%~20% Ca by mass. Preferably, the tungsten-containing raw material includes wolframite or a mixture of wolframite and wolframite; the ball-to-material mass ratio of the wet ball mill is (2.0~5.0):1, the liquid-to-solid ratio is 1L:(1~4)kg, and the proportion of particles smaller than 300 mesh in the slurry is ≥96%. Specifically, the ball-to-material mass ratio can be any one of 2.0:1, 3.0:1, 4.0:1, 5.0:1 or any range between two of them, and the liquid-to-solid ratio can be any one of 1L:1kg, 1L:2kg, 1L:3kg, 1L:4kg or any range between two of them.

[0020] S2. The slurry undergoes a two-stage countercurrent alkaline boiling process. The secondary countercurrent alkaline cooking process specifically involves adding sodium hydroxide to the slurry for the first-stage alkaline cooking, followed by solid-liquid separation to obtain the first alkaline cooking residue and the first alkaline cooking liquid. Sodium hydroxide is added to the first alkaline cooking residue for a second alkaline cooking process, and solid-liquid separation is performed to obtain the second alkaline cooking residue and the second alkaline cooking solution. Preferably, the liquid-to-solid ratio of the secondary countercurrent alkaline boiling process is (0.8~3)L:1kg, the concentration of sodium hydroxide is 2~8mol / L, the reaction temperature is 100~200℃, the time is 1~5h, and the pressure is 1.0~2.5MPa; the concentration of sodium hydroxide in the first alkaline boiling solution is less than 1mol / L, and the mass fraction of WO3 in the second alkaline boiling residue is less than 0.5%. Specifically, in the two-stage countercurrent alkaline boiling process, the liquid-to-solid ratio of the first-stage and second-stage alkaline boiling can be any one of 0.8L:1kg, 1.5L:1kg, 2L:1kg, 2.5L:1kg, or 3L:1kg, or any combination thereof; the concentration of sodium hydroxide can be any one of 2mol / L, 4mol / L, 6mol / L, or 8mol / L, or any combination thereof; the reaction temperature can be any one of 100℃, 120℃, 140℃, 160℃, 180℃, or 200℃, or any combination thereof; the reaction time can be any one of 1h, 2h, 3h, 4h, or 5h, or any combination thereof; and the pressure can be any one of 1.0MPa, 1.5MPa, 2.0MPa, or 2.5MPa, or any combination thereof.

[0021] In step S2 above, an appropriate amount of solid sodium hydroxide or a sodium hydroxide solution is first added to the slurry. After adjusting to a suitable liquid-solid ratio, a first-stage alkaline leaching is performed to obtain a first alkaline leaching residue and a first alkaline leaching solution, the first alkaline leaching solution being mainly a sodium tungstate solution. Then, sodium hydroxide is added to the first alkaline leaching residue for a second-stage alkaline leaching, further leaching out the tungsten in the first alkaline leaching residue and improving the tungsten decomposition rate. In addition, since the tungsten content in the first alkaline leaching residue is low, the WO3 mass fraction in the obtained second alkaline leaching residue is less than 0.5%, which can be treated as tailings. However, the sodium hydroxide concentration in the second alkaline leaching solution is still relatively high. Therefore, in the embodiments of this application, it is usually reused for the first-stage alkaline leaching of the slurry, so that the small amount of tungsten in the second alkaline leaching solution can continue to be enriched, while the sodium hydroxide in the first alkaline leaching solution can also be exhausted, avoiding the alkali recovery process. From a long-term perspective, this two-stage countercurrent alkaline leaching process only requires the addition of sodium hydroxide during the second-stage alkaline leaching, and the entire process can significantly reduce the amount of alkali used compared to the traditional alkaline leaching process.

[0022] S3. Add a calcium-containing reagent to the first alkaline boiling solution and stir to precipitate tungsten. Separate the solid and liquid to obtain artificial scheelite and the precipitated tungsten solution. Preferably, the calcium-containing reagent includes calcium chloride, calcium oxide, calcium hydroxide, calcium sulfate, calcium hydrogen phosphate, calcium dihydrogen phosphate, or calcium citrate. The molar ratio of the calcium-containing reagent to WO3 in the first alkaline boiling solution is (1~3):1. The reaction temperature for tungsten precipitation is 10~100℃, the time is 0.5~5h, and the stirring rate is 100~500rpm. Specifically, the molar ratio of the calcium-containing reagent to WO3 in the first alkaline boiling solution can be any one or a range between 1:1, 1.5:1, 2:1, 2.5:1, and 3:1; the reaction temperature for tungsten precipitation can be any one or a range between 10℃, 30℃, 50℃, 70℃, 90℃, and 100℃; the reaction time can be any one or a range between 0.5, 1.5, 3, 4.5, and 5h; and the stirring rate can be any one or a range between 100rpm, 200rpm, 300rpm, 400rpm, and 500rpm.

[0023] In step S3 above, the first alkaline boiling solution is a mixed solution of sodium tungstate and a small amount of residual alkali. After adding a calcium-containing reagent, calcium tungstate precipitate (artificial scheelite) is generated. The liquid after tungsten precipitation is a sodium hydroxide solution. In some preferred embodiments, when other calcium-containing reagents besides calcium chloride are used for precipitation, the calcium ion content in the solution can be maintained at a relatively low concentration, and the liquid after tungsten precipitation can be reused for the first-stage alkaline boiling of the slurry.

[0024] S4. Artificial scheelite is decomposed using a sulfuric acid-oxalic acid mixed solution to obtain a tungsten oxalate complex solution; Preferably, the concentration of oxalic acid in the sulfuric acid-oxalic acid mixed solution is 0.5~2.5 mol / L, and the concentration of sulfuric acid is 0.5~2.0 mol / L; the liquid-to-solid ratio of decomposition is (1~25) L:1 kg, the reaction temperature is 20~100℃, and the time is 1~6 h. Specifically, the concentration of oxalic acid can be any one or any two of 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, and 2.5 mol / L; the concentration of sulfuric acid can be any one or any two of 0.5 mol / L, 1 mol / L, 1.5 mol / L, and 2 mol / L; the liquid-to-solid ratio of decomposition can be any one or any two of 1 L:1 kg, 5 L:1 kg, 10 L:1 kg, 15 L:1 kg, 20 L:1 kg, and 25 L:1 kg; the reaction temperature can be any one or any two of 20℃, 40℃, 60℃, 80℃, and 100℃; and the reaction time can be any one or any two of 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h.

[0025] S5. The oxalate-tungsten complex solution is thermally decomposed, and tungstic acid is obtained by solid-liquid separation. The tungstic acid is then dissolved in ammonia, evaporated and crystallized, and dried to obtain the national standard grade zero ammonium paratungstate product.

[0026] Preferably, the thermal decomposition temperature is 80~100℃ and the time is 0.5~3h; the liquid-to-solid ratio of ammonia solution is (2~4)L:1kg, the time is 0.5~2h, the temperature is 20~50℃, and the concentration of ammonia water used is 5~9mol / L. Specifically, the thermal decomposition temperature can be any one or any two of 80℃, 85℃, 90℃, 95℃, and 100℃, and the time can be any one or any two of 0.5h, 1.5h, 2.5h, and 3h; the liquid-to-solid ratio of ammonia solution can be any one or any two of 2L:1kg, 2.5L:1kg, 3L:1kg, 3.5L:1kg, and 4L:1kg, the time can be any one or any two of 0.5h, 1h, 1.5h, and 2h, the temperature can be any one or any two of 20℃, 30℃, 40℃, and 50℃, and the concentration of ammonia solution used can be any one or any two of 5mol / L, 6mol / L, 7mol / L, 8mol / L, and 9mol / L.

[0027] In step S5 above, the tungsten oxalate complex solution is thermally decomposed to obtain tungstic acid solid. The filtrate after solid-liquid separation is an oxalic acid solution, which can be added with sulfuric acid to obtain a sulfuric acid-oxalic acid mixed solution, which can then be reused in step S4 as a leaching agent.

[0028] The entire technical solution of this application has a short process flow and requires less reagents in actual operation. It only requires adding alkali during the second-stage alkaline boiling and adding sulfuric acid to the leaching agent to a suitable concentration in step S4.

[0029] The technical solution of this application will be further described below with reference to specific embodiments.

[0030] Example 1

[0031] A method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite includes the following steps: S1. The tungsten-containing raw material is subjected to wet ball milling, wherein the WO3 content in the tungsten-containing raw material is 50wt% and the Ca content is 1.56wt%. The ball-to-material mass ratio of the wet ball milling is 2.5:1 and the liquid-to-solid ratio is 1L:1.0kg, to obtain a slurry with a particle size of less than 325 mesh. S2. The slurry undergoes a two-stage countercurrent alkaline boiling process. The secondary countercurrent alkaline cooking process specifically involves adding NaOH to the slurry for the first-stage alkaline cooking, followed by solid-liquid separation to obtain the first alkaline cooking residue and the first alkaline cooking liquid. Sodium hydroxide is added to the first alkaline cooking residue for a second alkaline cooking process, and solid-liquid separation is performed to obtain the second alkaline cooking residue and the second alkaline cooking solution. The liquid-to-solid ratio in both the first and second stage alkaline boiling processes was 1 L: 1.0 kg, the initial NaOH concentration was 4 mol / L, the temperature was 180℃, the time was 2 h, and the pressure was 1.0 MPa. The residual NaOH concentration in the first alkaline boiling solution was 0.05 mol / L. After the two-stage countercurrent alkaline boiling process, the decomposition rate of tungsten was 98.88%. S3. Add calcium oxide to the first alkaline boiling solution and stir to precipitate tungsten. Separate the solid and liquid to obtain artificial scheelite and tungsten-precipitated liquid. The molar ratio of calcium oxide to WO3 in the first alkaline boiling solution was 2:1, the reaction temperature for tungsten precipitation was 90℃, and the reaction time was 2 h. S4. Artificial scheelite is decomposed using a sulfuric acid-oxalic acid mixed solution to obtain a tungsten oxalate complex solution; In this mixture of sulfuric acid and oxalic acid, the concentration of oxalic acid was 0.5 mol / L, the concentration of sulfuric acid was 0.5 mol / L, the liquid-to-solid ratio was 15 L: 1 kg, the temperature was 50 °C, and the time was 4 h. During this process, the leaching rate of WO3 was 98.46%. S5. The oxalate-tungsten complex solution was thermally decomposed at 85℃ for 3 hours, and tungstic acid was obtained by solid-liquid separation. The tungstic acid was then ammonia-dissolved in 7 mol / L ammonia water for 2 hours, with a liquid-to-solid ratio of 2.5 L: 1 kg and a temperature of 40℃. Subsequently, the solution was evaporated and crystallized at 85℃ and a vacuum of 0.075 MPa. The resulting crystallized product was then dried at 60℃, 80℃, and 100℃ for 1 hour each to obtain ammonium paratungstate product, in which the WO3 content was 88.66 wt%, and other impurities met the requirements of grade 0 of the national standard GB / T 10116-2007.

[0032] Example 2

[0033] A method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite includes the following steps: S1. The tungsten-containing raw material is subjected to wet ball milling, wherein the WO3 content in the tungsten-containing raw material is 50wt% and the Ca content is 4.56wt%. The ball-to-material mass ratio of the wet ball milling is 2.5:1 and the liquid-to-solid ratio is 1L:1.0kg, to obtain a slurry with a particle size of less than 325 mesh. S2. The slurry undergoes a two-stage countercurrent alkaline boiling process. The secondary countercurrent alkaline cooking process specifically involves adding NaOH to the slurry for the first-stage alkaline cooking, followed by solid-liquid separation to obtain the first alkaline cooking residue and the first alkaline cooking liquid. Sodium hydroxide is added to the first alkaline cooking residue for a second alkaline cooking process, and solid-liquid separation is performed to obtain the second alkaline cooking residue and the second alkaline cooking solution. The liquid-to-solid ratio in both the first and second stage alkaline boiling processes was 1 L:1.0 kg, the initial NaOH concentration was 6 mol / L, the temperature was 190℃, the time was 3 h, and the pressure was 1.2 MPa. The residual NaOH concentration in the first alkaline boiling solution was 0.05 mol / L. After the two-stage countercurrent alkaline boiling process, the decomposition rate of tungsten was 99.02%. S3. Add calcium oxide to the first alkaline boiling solution and stir to precipitate tungsten. Separate the solid and liquid to obtain artificial scheelite and tungsten-precipitated liquid. The molar ratio of calcium oxide to WO3 in the first alkaline boiling solution was 3:1, the reaction temperature for tungsten precipitation was 80℃, and the reaction time was 2h. S4. Artificial scheelite is decomposed using a sulfuric acid-oxalic acid mixed solution to obtain a tungsten oxalate complex solution; In this sulfuric acid-oxalic acid mixed solution, the concentration of oxalic acid was 1.0 mol / L, the concentration of sulfuric acid was 0.75 mol / L, the liquid-to-solid ratio was 25 L: 1 kg, the temperature was 45℃, and the time was 2 h; the leaching rate of WO3 in this process was 99.03%. S5. The oxalate-tungsten complex solution was thermally decomposed at 95℃ for 2 hours, and tungstic acid was obtained by solid-liquid separation. The tungstic acid was then ammonia-dissolved in 6 mol / L ammonia water for 0.5 hours at a liquid-to-solid ratio of 3 L: 1 kg at 40℃. After that, it was evaporated and crystallized at 85℃ and a vacuum of 0.075 MPa. The resulting crystallized product was then dried at 60℃, 80℃, and 100℃ for 1 hour each to obtain ammonium paratungstate product, in which the WO3 content was 88.79 wt%, and other impurities met the requirements of grade 0 of national standard GB / T 10116-2007.

[0034] Example 3

[0035] A method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite includes the following steps: S1. The tungsten-containing raw material is subjected to wet ball milling, wherein the WO3 content in the tungsten-containing raw material is 60wt% and the Ca content is 8.95wt%. The ball-to-material mass ratio of the wet ball milling is 2.5:1 and the liquid-to-solid ratio is 1L:1.0kg, to obtain a slurry with a particle size of less than 325 mesh. S2. The slurry undergoes a two-stage countercurrent alkaline boiling process. The secondary countercurrent alkaline cooking process specifically involves adding NaOH to the slurry for the first-stage alkaline cooking, followed by solid-liquid separation to obtain the first alkaline cooking residue and the first alkaline cooking liquid. Sodium hydroxide is added to the first alkaline cooking residue for a second alkaline cooking process, and solid-liquid separation is performed to obtain the second alkaline cooking residue and the second alkaline cooking solution. The liquid-to-solid ratio in both the first and second stage alkaline boiling processes was 2L:1kg, the initial NaOH concentration was 4mol / L, the temperature was 200℃, the time was 4h, and the pressure was 1.4MPa. The residual NaOH concentration in the first alkaline boiling solution was 1.83mol / L. After the two-stage countercurrent alkaline boiling process, the decomposition rate of tungsten was 99.28%. S3. Add calcium oxide to the first alkaline boiling solution and stir to precipitate tungsten. Separate the solid and liquid to obtain artificial scheelite and tungsten-precipitated liquid. The molar ratio of calcium oxide to WO3 in the first alkaline boiling solution was 2.5:1, the reaction temperature for tungsten precipitation was 70℃, and the reaction time was 3h. S4. Artificial scheelite is decomposed using a sulfuric acid-oxalic acid mixed solution to obtain a tungsten oxalate complex solution; In this mixture of sulfuric acid and oxalic acid, the concentration of oxalic acid was 1.0 mol / L, the concentration of sulfuric acid was 1.0 mol / L, the liquid-to-solid ratio was 15 L:1 kg, the temperature was 60℃, and the time was 6 h. The leaching rate of WO3 during this process was 98.03%. S5. The oxalate-tungsten complex solution was thermally decomposed at 90℃ for 1 hour, and tungstic acid was obtained by solid-liquid separation. The tungstic acid was ammonia-dissolved in 7 mol / L ammonia water for 1.5 hours, with a liquid-to-solid ratio of 2 L: 1 kg and a temperature of 30℃. Then, it was evaporated and crystallized at 85℃ and a vacuum of 0.075 MPa. The resulting crystallized product was further dried at 60℃, 80℃, and 100℃ for 1 hour each to obtain ammonium paratungstate product, in which the WO3 content was 88.59 wt%, and other impurity elements met the requirements of grade 0 of national standard GB / T 10116-2007.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that steps S2 and S3 are omitted, and the slurry is directly decomposed using a sulfuric acid-oxalic acid mixed solution. During this process, the leaching rate of WO3 is only 48.52%. The final ammonium paratungstate product has a WO3 content of 88.53 wt%. However, because the slurry is directly decomposed using a sulfuric acid-oxalic acid mixed solution, iron will enter the solution, resulting in an Fe content of 0.027 wt%, which does not meet the requirements of the national standard GB / T 10116-2007 Grade 0.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that: in step S2, only one alkaline boiling is performed; the liquid-to-solid ratio of the alkaline boiling is 2L:1.0kg, the initial NaOH concentration is 4mol / L, the temperature is 180℃, the time is 4h, and the pressure is 1.0MPa; the residual NaOH concentration in the alkaline boiling solution is 1.83mol / L; the decomposition rate of tungsten after alkaline boiling is only 96%; the WO3 content in the final ammonium paratungstate product is 88.62wt%, and other impurity elements meet the requirements of the national standard GB / T 10116-2007 Grade 0 product.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that: in step S2, only one alkaline boiling is performed; the liquid-to-solid ratio of the alkaline boiling is 1L:1.0kg, the initial NaOH concentration is 8mol / L, the temperature is 180℃, the time is 4h, and the pressure is 1.0MPa; the residual NaOH concentration in the alkaline boiling solution is 4.12mol / L; the decomposition rate of tungsten after alkaline boiling is only 95.6%; the WO3 content in the final ammonium paratungstate product is 88.56wt%, and other impurity elements meet the requirements of the national standard GB / T 10116-2007 Grade 0 product.

[0039] In Comparative Example 2, twice the volume of sodium hydroxide as in Example 1 was used for a single alkaline boiling process. In Comparative Example 3, twice the concentration of sodium hydroxide as in Example 1 was used for a single alkaline boiling process. Although the amount of sodium hydroxide used in both examples was the same as that used in the two alkaline boiling processes in Example 1, the decomposition rate of tungsten was significantly reduced. This demonstrates that the technical solution of this application can not only save alkaline solution (the secondary alkaline boiling solution can be recovered) but also achieve a higher leaching rate.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that: in step S2, only one alkaline boiling is performed; the liquid-to-solid ratio of the alkaline boiling is 1L:1.0kg, the initial NaOH concentration is 4mol / L, the temperature is 180℃, the time is 2h, and the pressure is 1.0MPa; the residual NaOH concentration in the alkaline boiling solution is 0.05mol / L; the decomposition rate of tungsten after alkaline boiling is 92%; the WO3 content in the final ammonium paratungstate product is 88.78wt%, and other impurity elements meet the requirements of national standard GB / T 10116-2007 Grade 0.

[0041] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wollastonite, characterized in that, Includes the following steps: S1. The tungsten-containing raw material is wet-milled to obtain a slurry, wherein the mass fraction of WO3 in the tungsten-containing raw material is 50%~70% and the mass fraction of Ca is 0.2%~20%; S2. The slurry is subjected to two-stage countercurrent alkaline boiling. The secondary countercurrent alkaline cooking process specifically involves adding sodium hydroxide to the slurry for the first-stage alkaline cooking, followed by solid-liquid separation to obtain the first alkaline cooking residue and the first alkaline cooking solution. Sodium hydroxide is added to the first alkaline residue for a second alkaline boiling process, and solid-liquid separation is performed to obtain a second alkaline residue and a second alkaline boiling solution. S3. Add a calcium-containing reagent to the first alkaline boiling solution and stir to precipitate tungsten. Separate the solid and liquid to obtain artificial scheelite and tungsten-precipitated liquid. S4. The artificial scheelite is decomposed using a sulfuric acid-oxalic acid mixed solution to obtain a tungsten oxalate complex solution; S5. The oxalate-tungsten complex solution is thermally decomposed, and tungstic acid is obtained by solid-liquid separation. The tungstic acid is then dissolved in ammonia, evaporated and crystallized, and dried to obtain the national standard grade zero ammonium paratungstate product.

2. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, In step S1, the tungsten-containing raw material includes wolframite or a mixture of wolframite and wolframite; the ball-to-material mass ratio of the wet ball mill is (2.0~5.0):1, the liquid-to-solid ratio is 1L:(1~4)kg, and the proportion of particles with a particle size of less than 300 mesh in the slurry is ≥96%.

3. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, In step S2, the liquid-to-solid ratio of the secondary countercurrent alkaline boiling process is (0.8~3) L:1 kg, the concentration of sodium hydroxide is 2~8 mol / L, the reaction temperature is 100~200℃, the time is 1~5 h, and the pressure is 1.0~2.5 MPa.

4. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 3, characterized in that, In step S2, the sodium hydroxide concentration in the first alkaline boiling solution is less than 1 mol / L, and the WO3 mass fraction in the second alkaline boiling residue is less than 0.5%.

5. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, In step S3, the calcium-containing reagent includes calcium chloride, calcium oxide, calcium hydroxide, calcium sulfate, calcium hydrogen phosphate, calcium dihydrogen phosphate, or calcium citrate, and the molar ratio of the calcium-containing reagent to WO3 in the first alkaline solution is (1~3):

1.

6. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, In step S3, the reaction temperature for tungsten precipitation is 10~100℃, the time is 0.5~5h, and the stirring rate is 100~500rpm.

7. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, In step S4, the concentration of oxalic acid in the sulfuric acid-oxalic acid mixed solution is 0.5~2.5 mol / L, and the concentration of sulfuric acid is 0.5~2.0 mol / L.

8. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 3, characterized in that, In step S4, the liquid-to-solid ratio of the decomposition is (1~25)L:1kg, the reaction temperature is 20~100℃, and the time is 1~6h.

9. The method for preparing ammonium paratungstate using wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, In step S5, the thermal decomposition temperature is 80~100℃ and the time is 0.5~3h; the liquid-to-solid ratio of the ammonia solution is (2~4)L:1kg, the time is 0.5~2h, the temperature is 20~50℃, and the concentration of the ammonia solution used is 5~9mol / L.

10. The method for preparing ammonium paratungstate from wolframite or a mixture of wolframite and wolframite according to claim 1, characterized in that, After step S2, the method further includes returning the second alkaline boiling solution to perform the first-stage alkaline boiling. The step S3 is followed by returning the tungsten-precipitated liquid to be used for the first-stage alkaline boiling.