Ammonium paratungstate crystallization and purification method assisted by ultrasonic defoaming

Abstract

The application discloses an ultrasonic-assisted defoaming ammonium paratungstate crystallization and purification method, and belongs to the technical field of tungsten hydrometallurgy. The method comprises the following steps: placing an ammonium tungstate solution in a crystallizer, and arranging an ultrasonic transducer on the crystallizer; adding talcum powder into the solution before evaporation crystallization, and binding organic flotation agent molecules by utilizing the hydrophobic and oleophilic characteristics of the talcum powder; starting to heat for evaporation crystallization, adding a defoaming agent when the temperature rises to 50±5 DEG C, starting the ultrasonic transducer to apply ultrasonic waves when the temperature rises to 90±5 DEG C, and continuing to heat to the crystallization temperature for evaporation crystallization, so as to obtain purified ammonium paratungstate crystals. The method realizes efficient defoaming, greatly reduces the amount of chemical defoaming agent, effectively improves the product purity and crystal morphology, and has good industrial practicability.

Description

Technical Field

[0001] This invention relates to the field of tungsten hydrometallurgy, and in particular to a method for purifying ammonium paratungstate crystals using ultrasonic-assisted defoaming. Background Technology

[0002] Tungsten is an important strategic metal, widely used in electronics, aerospace, and military fields. With the massive depletion of global tungsten resources, high-quality tungsten ore resources are becoming increasingly scarce, and the tungsten smelting industry is currently facing the severe challenge of a continuous decline in ore grade. To effectively recover tungsten from low-grade, complexly associated ores, various organic flotation reagents, such as collectors (oleic acid, talc oil), frothers (pine oil), and inhibitors (starch, tannin), must be used extensively during the beneficiation process. The residues of these organic substances inevitably adhere to the surface of the tungsten concentrate and subsequently enter the hydrometallurgical system. While the ammonium tungstate solution, after ion exchange purification, theoretically removes most inorganic impurities, trace amounts of organic flotation reagents and their decomposition products from the ore still remain in the solution. These residual organic substances exhibit significant frotherly activity in the subsequent evaporation and crystallization process, resulting in a large amount of stable foam within the crystallizer, severely affecting evaporation efficiency and operational stability.

[0003] To address this foaming problem, the industry currently widely employs chemical defoamers. However, due to the volatility and complexity of residual organic flotation reagents in the raw ore, traditional defoaming strategies face an irreconcilable contradiction: On the one hand, in order to effectively eliminate stubborn foam caused by residual flotation reagents, the dosage of defoamer is often increased during production. Although defoamer can disrupt the foam structure to some extent, it is itself an organic substance such as organosilicon and polyether. Excessive use will inevitably lead to the continuous accumulation of defoamer and its reaction byproducts in the mother liquor, further increasing the total amount of organic impurities in the solution. On the other hand, these additional organic impurities, whether residual flotation reagents or defoamer added for defoaming, will seriously interfere with the normal growth of ammonium paratungstate (APT) crystals during the crystallization process. Specifically, organic matter selectively adsorbs onto specific crystal faces, inhibiting the growth of those crystal faces, resulting in abnormal crystal morphology, such as needle-like, plate-like, or aggregated crystals, rather than regular cubic crystals; the abnormal crystal growth mode makes it easier for trace impurities in the mother liquor to be encapsulated inside the crystals, causing a decrease in product purity; irregular crystal shape and impurity encapsulation will also lead to a deterioration in the physical properties of APT powder, such as flowability and bulk density, thereby affecting the production performance of downstream tungsten carbide and cemented carbide.

[0004] This demonstrates that the existing process has fallen into a vicious cycle: the more organic residue in the mineral source, the more severe the foaming, the larger the amount of defoamer needed, the higher the total amount of organic impurities in the solution, and the more significant the deterioration in the crystal form and purity of the final product. Simply increasing the amount of defoamer to address the foaming problem is tantamount to drinking poison to quench thirst.

[0005] Therefore, there is an urgent need to develop a new crystallization method that can effectively defoam and ensure smooth evaporation and crystallization while significantly reducing the use of chemical defoamers, cutting off the path of "defoamers introducing organic pollution" at the source, thereby achieving a breakthrough balance between defoaming effect and product purity, and meeting the production requirements of regular crystal form APT. Summary of the Invention

[0006] To address the limitations of single defoaming methods in existing technologies and the contradiction between defoamer dosage and organic pollution, this invention provides an ultrasound-assisted defoaming method for the crystallization and purification of ammonium paratungstate. This method combines adsorbent pretreatment, the addition of a trace amount of defoamer, and ultrasound-assisted crystallization. By precisely controlling the trigger temperature of each step, the three methods work sequentially at different stages, achieving highly efficient defoaming while significantly reducing the amount of chemical defoamer used. This reduces the introduction of organic impurities at the source, thereby improving product purity and crystal morphology.

[0007] The technical solution of the present invention is as follows: This invention provides a method for purifying ammonium paratungstate crystallization using ultrasound-assisted defoaming, comprising the following steps: An ammonium tungstate solution is placed in a crystallizer for evaporation and crystallization, and the crystallizer is equipped with an ultrasonic transducer. Before evaporation and crystallization, an adsorbent is added to the ammonium tungstate solution, and then the temperature is raised to carry out evaporation and crystallization. When the temperature reaches 50±5℃, add defoamer to the solution and continue heating; When the temperature rises to 90±5℃, the ultrasonic transducer is turned on to apply ultrasonic treatment to the solution, and the temperature is further raised to the crystallization temperature for evaporation and crystallization to obtain purified ammonium paratungstate crystals.

[0008] Preferably, the ammonium tungstate solution, calculated as WO3, has a concentration of 220-250 g / L.

[0009] Preferably, the adsorbent is talc, and the amount of talc added is 10-20 ppm.

[0010] In further explanation of the present invention, in the above method, by selecting talc powder as an adsorbent and adding it to the ammonium tungstate solution before evaporation and crystallization, the hydrophobic and oleophilic properties of the talc powder surface can be utilized to bind the organic flotation reagent molecules to the surface of the talc powder particles through hydrophobic interactions, making it difficult for organic molecules to migrate to the gas-liquid interface to form foam, thereby reducing the amount of foaming substances from the source.

[0011] Preferably, the defoamer is castor oil or a polyether defoamer, and the amount of the defoamer added is 50-80 ppm.

[0012] In further explanation of the present invention, in the above method, when the temperature rises to 50±5℃, the solution is in a critical state where foam is about to form but has not yet formed. At this time, adding defoamer can achieve precise interception with the minimum amount, avoiding decomposition failure caused by premature intervention or a surge in dosage caused by late intervention.

[0013] Preferably, the heating rate is 1-5℃ / min.

[0014] Preferably, the ultrasonic transducer has an ultrasonic frequency of 20-40kHz and a power of 500-1000W.

[0015] Preferably, the ultrasonic treatment is applied continuously until crystallization is complete.

[0016] In a further description of the present invention, in the above method, when the temperature rises to 90±5℃, the ultrasonic transducer is turned on to apply ultrasonic treatment to the solution. At this temperature, the viscosity of the solution has been greatly reduced. The micro-jet and shock wave generated by the ultrasonic cavitation effect can effectively break up the residual foam. At the same time, the micro-turbulence caused by cavitation can enhance the solid-liquid separation of the talc powder and organic impurity complex, so that the bound organic impurities are removed from the mother liquor.

[0017] Preferably, the evaporation and crystallization process is supplemented by stirring, and the stirring adopts propeller-shaped blades or turbine-shaped blades, with a stirring speed of 150-350 r / min.

[0018] Preferably, the evaporation and crystallization temperature is 100-120℃, and the holding time after reaching the crystallization temperature is 2-8 hours.

[0019] Preferably, the method further includes: after the evaporation and crystallization are completed, filtering, washing and drying the obtained ammonium paratungstate crystals, and detecting them using the total organic carbon method, wherein the total organic carbon is the organic carbon content after deducting inorganic carbon, and the organic residue content of the ammonium paratungstate crystals is less than 0.01 wt%.

[0020] The present invention has the following beneficial effects: 1. Compared with existing technologies, this invention pre-adds talc powder as an adsorbent before evaporation and crystallization, utilizing its hydrophobic and oleophilic properties to bind organic flotation reagent molecules to the particle surface, thus reducing the concentration of foaming substances at the source. Based on this, the precise addition of defoamer at 50±5℃ achieves effective control of residual foam with minimal dosage. Simultaneously, the propeller stirring continuously provides physical breaking action during crystallization, further reducing the total amount of foam. These three steps are sequentially linked and complementary, achieving stable foam control throughout the evaporation and crystallization process, avoiding problems such as overflow and decreased heat transfer efficiency caused by foam. At the same time, it significantly reduces the amount of chemical defoamer used, avoiding the organic pollution problems caused by excessive defoamer introduction in traditional processes. The organic residue content of the obtained ammonium paratungstate crystals is significantly lower than that of existing processes, effectively improving product purity.

[0021] 2. Compared to existing technologies, this invention initiates ultrasonic treatment when the solution temperature reaches 90±5℃. At this point, the solution viscosity has significantly decreased. The microjets and shock waves generated by the ultrasonic cavitation effect not only effectively break up residual foam but also enhance the solid-liquid separation of the talc-organic impurity complex through micro-turbulence caused by cavitation, thus removing the bound organic impurities from the mother liquor. Simultaneously, the microscopic disturbances generated by the ultrasonic cavitation effect promote uniform mixing of the solution and inhibit the selective adsorption of organic matter on specific crystal faces, resulting in crystals with regular morphology, good flowability, and high bulk density. Furthermore, the process modification of this invention is simple; only the addition of an ultrasonic transducer to existing crystallization equipment and optimization of the operating sequence are needed to achieve a dual improvement in defoaming effect and product quality, demonstrating good industrial applicability and economic efficiency. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0023] Figure 1 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Example 1 of the present invention; Figure 2 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Example 2 of the present invention; Figure 3 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Example 3 of the present invention; Figure 4 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 1 of this invention. Figure 5 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 2 of this invention. Figure 6 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 3 of the present invention. Figure 7 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 4 of this invention. Figure 8 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 5 of the present invention. Figure 9 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 6 of this invention. Figure 10 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 7 of this invention. Figure 11 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 8 of this invention. Figure 12 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 9 of this invention. Figure 13 This is a SEM image of the purified ammonium paratungstate crystal product obtained in Comparative Example 10 of this invention.

[0024] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] 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.

[0026] This invention provides a method for purifying ammonium paratungstate crystallization using ultrasound-assisted defoaming, comprising the following steps: An ammonium tungstate solution is placed in a crystallizer for evaporation and crystallization, and the crystallizer is equipped with an ultrasonic transducer. Before evaporation and crystallization, an adsorbent is added to the ammonium tungstate solution, and then the temperature is raised to carry out evaporation and crystallization. When the temperature reaches 50±5℃, add defoamer to the solution and continue heating; When the temperature rises to 90±5℃, the ultrasonic transducer is turned on to apply ultrasonic treatment to the solution, and the temperature is further raised to the crystallization temperature for evaporation and crystallization to obtain purified ammonium paratungstate crystals.

[0027] Preferably, the ammonium tungstate solution, calculated as WO3, has a concentration of 220-250 g / L.

[0028] Preferably, the adsorbent is talc, and the amount of talc added is 10-20 ppm.

[0029] Specifically, the amount of talc added can be any one of 10ppm, 12ppm, 14ppm, 15ppm, 16ppm, 18ppm, 20ppm, or a range between two of them.

[0030] Preferably, the defoamer is castor oil or a polyether defoamer, and the amount of the defoamer added is 50-80 ppm.

[0031] Specifically, the amount of defoamer added can be any one of 50ppm, 55ppm, 60ppm, 65ppm, 70ppm, 75ppm, 80ppm, or a range between two of them.

[0032] Preferably, the heating rate is 1-5℃ / min.

[0033] Specifically, the heating rate can be any one of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, or a range between two of them.

[0034] Preferably, the ultrasonic transducer has an ultrasonic frequency of 20-40kHz and a power of 500-1000W.

[0035] Specifically, the ultrasonic frequency of the ultrasonic transducer can be any one of 20kHz, 25kHz, 30kHz, 35kHz, 40kHz or a range between two of them, and the power can be any one of 500W, 600W, 700W, 800W, 900W, 1000W or a range between two of them.

[0036] Preferably, the ultrasonic treatment is applied continuously until crystallization is complete.

[0037] Preferably, the evaporation and crystallization process is supplemented by stirring, and the stirring adopts propeller-shaped blades or turbine-shaped blades, with a stirring speed of 150-350 r / min.

[0038] Specifically, the stirring speed can be any one of 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, or a range between two of them.

[0039] Preferably, the evaporation and crystallization temperature is 100-120℃, and the holding time after reaching the crystallization temperature is 2-8 hours.

[0040] Specifically, the evaporation and crystallization temperature can be any one of 100℃, 105℃, 110℃, 115℃, 120℃ or a range between two of them, and the time can be any one of 2h, 3h, 4h, 5h, 6h, 7h, 8h or a range between two of them.

[0041] Preferably, the method further includes: after the evaporation and crystallization are completed, filtering, washing and drying the obtained ammonium paratungstate crystals, and detecting them using the total organic carbon method, wherein the total organic carbon is the organic carbon content after deducting inorganic carbon, and the organic residue content of the ammonium paratungstate crystals is less than 0.01 wt%.

[0042] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0043] Example 1

[0044] A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: An ammonium tungstate solution with a concentration of 220 g / L (WO3) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirrer with propeller-shaped blades. The stirrer was turned on and stirred at a speed of 150 r / min. Before the start of evaporation crystallization, 10 ppm of talc powder was added to the solution, and then the temperature was increased at a rate of 3 °C / min. When the solution temperature reached 50 °C, 50 ppm of castor oil was added to the solution, and the temperature was increased further. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, the ultrasonic frequency was set to 20 kHz, and the power was set to 500 W. The temperature was increased further to the crystallization temperature of 100 °C, and the evaporation crystallization reaction was maintained at this temperature for 2 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain the purified ammonium paratungstate crystal product.

[0045] Testing showed that no significant foam was generated in the crystallizer during the entire crystallization process in this embodiment, the crystallization process was stable, and the evaporation efficiency was stable. Figure 1 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this embodiment. As can be seen from the image, the crystals have a regular cubic morphology, smooth surface, and uniform particle size. This indicates that the method of the present invention effectively inhibits the selective adsorption of organic matter on specific crystal faces, resulting in crystals with regular morphology. The total organic carbon (TOC) content of the ammonium paratungstate crystals obtained in this embodiment is 0.005 wt%.

[0046] Example 2

[0047] A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: A 250 g / L ammonium tungstate solution (WO3 concentration) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirrer with propeller-shaped blades. The stirrer was turned on and stirred at 350 r / min. Before the start of evaporation crystallization, 20 ppm of talc was added to the solution, and then the temperature was increased at a rate of 3 °C / min. When the solution temperature reached 50 °C, 80 ppm of castor oil was added, and the temperature was increased further. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, the ultrasonic frequency was set to 40 kHz, and the power was set to 1000 W. The temperature was increased further to the crystallization temperature of 120 °C, and the evaporation crystallization reaction was maintained at this temperature for 8 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain purified ammonium paratungstate crystal product.

[0048] Testing showed that no significant foam was generated in the crystallizer during the entire crystallization process in this embodiment, the crystallization process was stable, and the evaporation efficiency was stable. Figure 2 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this embodiment. As can be seen from the image, the crystals have clear boundaries, no obvious adhesion, smooth surfaces, and uniform particles. This indicates that the method of the present invention effectively inhibits the selective adsorption of organic matter on specific crystal planes, resulting in crystals with regular morphology and uniform particles. The total organic carbon (TOC) analysis showed that the organic residue content of the ammonium paratungstate crystals obtained in this embodiment was 0.008 wt%.

[0049] Example 3

[0050] A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: An ammonium tungstate solution with a concentration of 235 g / L (WO3) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirrer with propeller-shaped blades. The stirrer was turned on and stirred at a speed of 250 r / min. Before the start of evaporation crystallization, 15 ppm of talc powder was added to the solution, and then the temperature was increased at a rate of 3 °C / min. When the solution temperature reached 50 °C, 70 ppm of castor oil was added to the solution, and the temperature was increased further. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, the ultrasonic frequency was set to 40 kHz and the power to 1000 W, and the temperature was increased further to the crystallization temperature of 110 °C. The evaporation crystallization reaction was maintained at this temperature for 5 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain the purified ammonium paratungstate crystal product.

[0051] Testing showed that no significant foam was generated in the crystallizer during the entire crystallization process in this embodiment, the crystallization process was stable, and the evaporation efficiency was stable. Figure 3The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this embodiment. As can be seen from the image, the crystals have a regular cubic morphology, clear and complete crystal faces, a smooth and dense surface, and a uniform particle size distribution, with no obvious agglomeration or fragmentation. This indicates that the method of the present invention effectively controls the crystal growth rate, effectively inhibits the selective adsorption of organic matter on specific crystal faces, eliminates anisotropic growth caused by the adsorption layer, and results in crystals with regular morphology, sharp edges, and extremely low organic residue on the surface. The total organic carbon (TOC) method shows that the organic residue content of the ammonium paratungstate crystals obtained in this embodiment is 0.008 wt%.

[0052] Comparative Example 1 The only difference between this comparative example and Example 1 is that it does not use a mechanical stirring device with blades designed as propellers, but only conventional magnetic stirring.

[0053] Tests showed that a small amount of foam was generated in the crystallizer during the entire crystallization process in this comparative example. Figure 4 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, the crystal morphology is irregular, a few crystals have slight adhering substances on their surface, and some of the matrix shows dispersion. The total organic carbon (TOC) method shows that the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.023 wt%.

[0054] Comparative Example 2 The only difference between this comparative example and Example 1 is that castor oil was not added.

[0055] Tests showed that a significant amount of foam was generated in the crystallizer during the entire crystallization process in this comparative example. Figure 5 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, the crystal surface is rough, with a large amount of adhering substances and obvious adhesion between particles, which seriously affects the formation of crystal nucleation. The total organic carbon (TOC) method shows that the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.75 wt%.

[0056] Comparative Example 3 A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: An ammonium tungstate solution with a concentration of 220 g / L (WO3) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirring device with propeller-shaped blades. The stirring device was turned on and stirred at a speed of 150 r / min. Before the start of evaporation crystallization, 10 ppm of talc powder and 50 ppm of castor oil were added to the solution, and then the temperature was increased at a rate of 3 °C / min. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, the ultrasonic frequency was set to 20 kHz and the power to 500 W, and the temperature was continued to rise to the crystallization temperature of 100 °C. The evaporation crystallization reaction was maintained at this temperature for 2 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain the purified ammonium paratungstate crystal product.

[0057] Tests showed that this comparative example produced relatively little foam in the crystallizer throughout the entire crystallization process. Figure 6 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, the crystal surface is rough, with a large amount of adhering substances and obvious adhesion between particles, which seriously affects the formation of crystal nucleation. The total organic carbon (TOC) method shows that the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.038 wt%.

[0058] Comparative Example 4 A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: An ammonium paratungstate solution with a concentration of 220 g / L (calculated as WO3) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirring device with propeller-shaped blades. The stirring device was turned on and stirred at a speed of 150 r / min. Before the start of evaporation crystallization, 10 ppm of talc powder was added to the solution, and then the temperature was increased at a rate of 3 °C / min. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, and the ultrasonic frequency was set to 20 kHz and the power to 500 W. The temperature was continued to rise to the crystallization temperature of 100 °C. At this time, 50 ppm of castor oil was added to the solution, and the evaporation crystallization reaction was maintained at this temperature for 2 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain the purified ammonium paratungstate crystal product.

[0059] Tests showed that this comparative example produced relatively little foam in the crystallizer throughout the entire crystallization process. Figure 7 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, there are many needle-like and plate-like crystals in the crystal, with obvious differences in particle size. Some crystal surfaces are covered with fine particles. According to the total organic carbon (TOC) method, the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.17 wt%.

[0060] Comparative Example 5 The only difference between this comparative example and Example 1 is that the amount of castor oil added is 40 ppm.

[0061] Tests showed that this comparative example produced relatively little foam in the crystallizer throughout the entire crystallization process. Figure 8 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, a few particles in the crystal have irregular morphology, and there is a certain degree of agglomeration and cracking in the crystal. The total organic carbon (TOC) method shows that the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.024 wt%.

[0062] Comparative Example 6 The only difference between this comparative example and Example 1 is that the amount of castor oil added is 90 ppm.

[0063] Tests showed that this comparative example produced relatively little foam in the crystallizer throughout the entire crystallization process. Figure 9 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, some particles in the crystal have rough surfaces and contain adhering substances, and the crystal edges are not clear enough. According to the total organic carbon (TOC) method, the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.13 wt%.

[0064] Comparative Example 7 The only difference between this comparative example and Example 1 is that it did not undergo ultrasonic treatment.

[0065] Tests showed that a small amount of foam was generated in the crystallizer during the entire crystallization process in this comparative example. Figure 10 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, the crystal morphology is irregular, with a large number of crystals growing in a plate-like manner. The particles are poorly dispersed and have many fine particles attached to the surface. According to the total organic carbon (TOC) method, the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.26 wt%.

[0066] Comparative Example 8 The only difference between this comparative example and Example 1 is that talc was not added.

[0067] Tests showed that a significant amount of foam was generated in the crystallizer during the entire crystallization process in this comparative example. Figure 11 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, there are many irregular particles in the crystal, some crystals grow in a needle-like shape, and there are deposits on the crystal surface. According to the total organic carbon (TOC) method, the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.25 wt%.

[0068] Comparative Example 9 A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: A 220 g / L ammonium tungstate solution (WO3 concentration) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirrer with propeller-shaped blades. The stirrer was turned on and stirred at 150 r / min. The temperature was increased at a rate of 3 °C / min. When the solution temperature reached 50 °C, 50 ppm castor oil and 10 ppm talc were added to the solution, and the temperature was increased further. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, and the ultrasonic frequency was set to 20 kHz and the power to 500 W. The temperature was increased further to the crystallization temperature of 100 °C, and the evaporation crystallization reaction was maintained at this temperature for 2 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain the purified ammonium paratungstate crystal product.

[0069] Tests showed that a significant amount of foam was generated in the crystallizer during the entire crystallization process in this comparative example. Figure 12 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, the particle size distribution in the crystal is uneven and there are adhering substances on the surface. According to the total organic carbon (TOC) method, the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.14 wt%.

[0070] Comparative Example 10 A method for purifying ammonium paratungstate by ultrasound-assisted defoaming crystallization includes the following steps: A 220 g / L ammonium tungstate solution (WO3 concentration) was placed in a crystallizer equipped with an ultrasonic transducer and a mechanical stirrer with propeller-shaped blades. The stirrer was turned on and stirred at 150 r / min. The temperature was increased at a rate of 3 °C / min. When the solution temperature reached 50 °C, 50 ppm of castor oil was added to the solution, and the temperature was increased further. When the solution temperature reached 90 °C, the ultrasonic transducer was turned on, and the ultrasonic frequency was set to 20 kHz and the power to 500 W. The temperature was increased further to the crystallization temperature of 100 °C, and 10 ppm of talc was added to the solution. The evaporation crystallization reaction was then maintained at this temperature for 2 hours. After the reaction was completed, heating and ultrasonication were stopped, the crystallized product was filtered, and the obtained ammonium paratungstate crystals were washed with pure water and dried to obtain the purified ammonium paratungstate crystal product.

[0071] Tests showed that a significant amount of foam was generated in the crystallizer during the entire crystallization process in this comparative example. Figure 13 The image shows a scanning electron microscope (SEM) image of the purified ammonium paratungstate crystal product obtained in this comparative example. As can be seen from the image, the crystal morphology is irregular, the surface of the crystal is obviously covered with deposits, and there is agglomeration between the particles. The total organic carbon (TOC) method shows that the organic residue content of the ammonium paratungstate crystal obtained in this comparative example is 0.21 wt%.

[0072] In summary, this invention provides an ultrasonic-assisted defoaming method for the crystallization and purification of ammonium paratungstate. By pre-adding talc powder before evaporation and crystallization, organic flotation reagent molecules are bound at the source, reducing the concentration of foaming substances. Defoamer is precisely added at 50±5℃ to achieve foam control with minimal dosage. Ultrasonic treatment is initiated when the temperature is continuously raised to 90±5℃, utilizing cavitation to break up residual foam and promote the removal of organic impurities. Simultaneously, propeller stirring is used during evaporation and crystallization to continuously provide physical breaking action, further reducing the total amount of foam. The above steps are sequentially linked and synergistically coordinated, achieving highly efficient defoaming while significantly reducing the amount of chemical defoamer used. This avoids the organic pollution problems caused by excessive defoamer introduction in traditional processes, resulting in significantly improved purity and crystal morphology of the obtained ammonium paratungstate crystals. This invention's method features simple process modification and good industrial applicability and economy.

[0073] 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 for purifying ammonium paratungstate by ultrasonic-assisted defoaming, characterized in that, Includes the following steps: An ammonium tungstate solution is placed in a crystallizer for evaporation and crystallization, and the crystallizer is equipped with an ultrasonic transducer. Before evaporation and crystallization, an adsorbent is added to the ammonium tungstate solution, and then the temperature is raised to carry out evaporation and crystallization. When the temperature reaches 50±5℃, add defoamer to the solution and continue heating; When the temperature rises to 90±5℃, the ultrasonic transducer is turned on to apply ultrasonic treatment to the solution, and the temperature is further raised to the crystallization temperature for evaporation and crystallization to obtain purified ammonium paratungstate crystals.

2. The method for purifying ammonium paratungstate crystallization with ultrasound-assisted defoaming according to claim 1, characterized in that, The ammonium tungstate solution, calculated as WO3, has a concentration of 220-250 g / L.

3. The method for purifying ammonium paratungstate by ultrasonic-assisted defoaming according to claim 1, characterized in that, The adsorbent is talc powder, and the amount of talc powder added is 10-20 ppm.

4. The method for purifying ammonium paratungstate crystallization with ultrasound-assisted defoaming according to claim 1, characterized in that, The defoamer is castor oil or a polyether defoamer, and the amount of the defoamer added is 50-80 ppm.

5. The method for purifying ammonium paratungstate crystallization with ultrasound-assisted defoaming according to claim 1, characterized in that, The heating rate is 1-5℃ / min.

6. The method for purifying ammonium paratungstate crystallization with ultrasound-assisted defoaming according to claim 1, characterized in that, The ultrasonic transducer has an ultrasonic frequency of 20-40kHz and a power of 500-1000W.

7. The method for purifying ammonium paratungstate by ultrasonic-assisted defoaming according to claim 1, characterized in that, The ultrasonic treatment is continued until crystallization is complete.

8. The method for purifying ammonium paratungstate crystallization with ultrasound-assisted defoaming according to claim 1, characterized in that, The evaporation and crystallization process is supplemented by stirring, which uses propeller-shaped blades or turbine-shaped blades, and the stirring speed is 150-350 r / min.

9. The method for purifying ammonium paratungstate by ultrasonic-assisted defoaming according to claim 1, characterized in that, The evaporation and crystallization temperature is 100-120℃, and the reaction time after reaching the crystallization temperature is 2-8 hours.

10. The method for purifying ammonium paratungstate by ultrasonic-assisted defoaming according to any one of claims 1-9, characterized in that, Also includes: After evaporation and crystallization, the obtained ammonium paratungstate crystals were filtered, washed, and dried. The total organic carbon content of the ammonium paratungstate crystals was less than 0.01 wt%.

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