A crystallization process optimization method for improving the crystallization rate of ammonium paratungstate crystals

Abstract

The application discloses a crystallization process optimization method for improving the crystallization rate of ammonium paratungstate crystals, and belongs to the technical field of wet metallurgy of tungsten. The method comprises the following steps: providing an ammonium tungstate solution, heating to 80-90 DEG C, and adding a crystal face regulator A; continuing to heat to 95-105 DEG C, and performing evaporation crystallization; when the crystallization is performed to the beginning of the appearance of crystallization objects, the temperature is reduced to 70-80 DEG C, the crystal face regulator B is added, the evaporation crystallization is continuously performed to the crystallization end point, the crystallization is ended, the crystal product is collected, and ammonium paratungstate crystals are obtained. The application significantly inhibits the poisoning effect of impurities on the crystal growth by screening specific types of crystal face regulators and adopting a strategy of time-sharing batch addition and temperature coordination control, and greatly improves the crystallization rate of ammonium paratungstate crystals. The method has the advantages of improving the crystal quality, improving the production efficiency, reducing the enterprise cost, and the like, and has good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology for tungsten, and more particularly to an optimized method for improving the crystallization rate of ammonium paratungstate crystals. Background Technology

[0002] In the production of tungsten materials, the crystallinity of ammonium paratungstate (APT) crystals is a core indicator of tungsten product quality. The presence of impurity ions such as phosphorus and silicon in the crystallization system strongly adsorbs onto the crystal nucleus surface or growth interface, severely interfering with normal crystal nucleation and directional growth, leading to abnormal crystal morphology, wider grain size distribution, and ultimately a significant decrease in crystallinity. With the increasing demand for high-purity, high-performance tungsten materials in aerospace, electronics, and high-end manufacturing, the requirements for APT crystallinity and product consistency are becoming increasingly stringent. Therefore, in-depth research into the influence mechanism of phosphorus and silicon impurities and the development of efficient crystallinity improvement technologies have become key scientific issues and technological bottlenecks in promoting the upgrading of the tungsten materials industry towards high-end and green development.

[0003] To address the challenge of crystallization rates caused by phosphorus and silicon impurities, the industry has explored various technological approaches, primarily categorized into physical impurity removal and chemical regulation. Physical methods focus on deep removal of impurities at the upstream stage, such as separation using ion exchange and solvent extraction. However, these traditional methods generally suffer from lengthy processes, high energy consumption, and large wastewater generation. In particular, ion exchange processes produce large amounts of ammonia-nitrogen-containing wastewater, posing a significant environmental burden. Notably, to achieve green production, the industry is actively exploring and applying novel ammonium tungstate solution preparation technologies (such as short-process closed-loop processes) aimed at significantly reducing or even eliminating ion exchange and extraction steps, thereby substantially reducing fresh water consumption and wastewater discharge. However, while these new processes improve environmental benefits, they also bring new challenges: they may weaken or bypass traditional deep purification stages, making it easier for inherent impurities such as phosphorus, arsenic, and silicon in the raw materials to enter the subsequent ammonium tungstate crystallization system. Studies have indicated that the presence of phosphorus, arsenic, and silicon has a significant "poisoning" effect on ammonium paratungstate crystallization. Domestic research data shows that when the concentration of silicon, arsenic, and phosphorus in the solution exceeds 0.8 g / L, the crystallization rate of APT can drop sharply to around 80%, and the crystallization rate further deteriorates with increasing concentration. Therefore, in novel green process systems where these impurities must be accepted or are difficult to completely remove, how to effectively improve the crystallization rate of APT has become a research direction with great practical significance and innovative challenges.

[0004] Existing studies have shown that the essence of phosphorus and silicon impurities reducing crystallinity lies in the fact that phosphorus and silicon enter the coordination structure of WO3 and form heteropolyacids (such as phosphotungstic acid and silicotungstic acid) when the acidity of the crystallization system decreases. These heteropolyacid macromolecules are strongly adsorbed on the surface of the crystal nucleus and the growth interface through steric hindrance and electrostatic interaction, poisoning crystal growth and ultimately leading to a significant decrease in crystallinity.

[0005] While existing control methods have some effect, they have significant limitations. Physical impurity removal methods often only address the symptoms, failing to achieve efficient and deep removal of impurities, and are also economically unsound. Chemical methods often involve adding crystallization modifiers such as surfactants and amino acids to attempt to inhibit the adsorption of impurities on crystal faces. However, these additives generally suffer from low selectivity and limited inhibition efficiency, and may introduce new foreign substances, affecting the final purity of the product. In particular, the crystallization modifiers disclosed in existing technologies are mostly surfactants or polymers with large molecular sizes, much larger than phosphorus-silicon heteropolyacids, making it difficult to effectively enter the microscopic adsorption sites on crystal faces occupied by heteropolyacids. Furthermore, existing technologies all employ single additives or one-time addition methods, failing to recognize the need to add small-molecule regulators with different functional groups at different stages of crystallization (before nucleation and during crystal growth) to achieve phased synergistic protection of crystal faces. Overall, current technologies struggle to effectively solve the problem of low crystallization rates caused by the coexistence of phosphorus, silicon, and arsenic impurities in novel green processes while simultaneously considering both economic efficiency and environmental friendliness. Therefore, developing a new method for improving the crystallization rate of APT that can accurately adapt to complex impurity systems and is both efficient and environmentally friendly is not only of urgent practical significance for breaking through the current technological bottlenecks in the industry, but also of important strategic value for promoting the transformation of the entire tungsten smelting industry towards a sustainable development model characterized by low carbon, short process, and high value. Summary of the Invention

[0006] To address the technical problems existing in the prior art, namely that phosphorus and silicon impurities are strongly adsorbed at the crystal growth interface during the crystallization of ammonium paratungstate, leading to a significant decrease in crystallization rate, and that existing physical impurity removal and chemical precipitation methods are lengthy and energy-intensive, while existing crystallization additives have poor selectivity and easily introduce new impurities, this invention provides an optimized crystallization process method to improve the crystallization rate of ammonium paratungstate crystals. This invention, by screening specific types of crystal facet modifiers and employing a strategy of time-phased and batch-added addition combined with temperature control, effectively suppresses the poisoning effect of phosphorus and silicon impurities on the growth interface of ammonium paratungstate crystals without introducing additional impurities, thus significantly improving the crystallization rate.

[0007] The technical solution of the present invention is as follows: This invention provides an optimized method for improving the crystallization rate of ammonium paratungstate crystals, comprising the following steps: Step 1: Provide an ammonium tungstate solution; heat the ammonium tungstate solution to 80-90°C and add crystal facet modifier A; Step 2: Continue heating to 95-105℃ to carry out evaporation and crystallization; Step 3: When crystallization begins to occur, lower the temperature to 70-80℃, add crystal surface regulator B, and continue evaporation and crystallization at 70-80℃ until the crystallization endpoint is reached. End the crystallization, collect the crystal product, and obtain ammonium paratungstate crystals.

[0008] Preferably, the ammonium tungstate solution contains phosphorus and / or silicon impurities, and the total concentration of the impurities, calculated as silicate ions and / or phosphate ions, is 0.8 g / L or higher.

[0009] Preferably, the ammonium tungstate solution contains phosphorus and / or silicon impurities, and the total concentration of the impurities, calculated as silicate ions and / or phosphate ions, is 0.8-1.5 g / L.

[0010] Preferably, the concentration of the ammonium tungstate solution, calculated as WO3, is 220-250 g / L.

[0011] Preferably, the amount of crystal plane modifier A added is 0.1-1% of the volume of the ammonium tungstate solution.

[0012] Preferably, the crystal plane regulator A is a hydroxyl-containing small organic molecule compound.

[0013] Preferably, the hydroxyl-containing small organic molecule compound is selected from at least one of C2-C4 polyols.

[0014] Preferably, the hydroxyl-containing small organic molecule compound is selected from at least one of ethylene glycol, glycerol, and 1,2-propanediol.

[0015] More preferably, the hydroxyl-containing small organic molecule compound is ethylene glycol.

[0016] Preferably, the amount of crystal plane regulator B added is 0.05-0.5% of the volume of the ammonium tungstate solution.

[0017] Preferably, the crystal plane regulator B is a small organic molecule compound containing a carboxyl group.

[0018] Preferably, the carboxyl-containing small organic molecule compound is selected from at least one of C4-C6 carboxyl-containing organic acids.

[0019] Preferably, the carboxyl-containing small organic molecule compound is selected from at least one of tartaric acid, citric acid, and malic acid.

[0020] More preferably, the carboxyl-containing small organic molecule compound is tartaric acid.

[0021] Preferably, the crystallization endpoint is a solution pH of 6.6-7.0.

[0022] Preferably, the heating rate in step 1 is 10-15℃ / min, the heating rate in step 2 is 2-4℃ / min, and the cooling rate in step 3 is 2-4℃ / min.

[0023] Further explanation of this invention: This invention screens hydroxyl-containing small organic molecules as crystal facet modifier A and carboxyl-containing small organic molecules as crystal facet modifier B. These two types of small organic molecules possess specific functional group structures and suitable molecular sizes, enabling selective adsorption onto active sites on the surface of ammonium paratungstate crystals through weak interactions such as hydrogen bonds and van der Waals forces. They competitively and preferentially occupy adsorption sites for phosphorus and silicon impurities on the ammonium paratungstate crystal surface, forming steric hindrance and effectively preventing impurities from interfering with crystal growth. Compared with macromolecular surfactants or polymeric modifiers used in the prior art, the small organic molecules selected in this invention exhibit higher selectivity, stronger crystal facet affinity, and a lower risk of introducing impurities.

[0024] Further explanation of this invention: This invention employs a batch-addition method, first adding crystal surface regulator A and then adding crystal surface regulator B, combined with a segmented temperature control strategy for the entire crystallization process. In the early stage of crystallization, crystal surface regulator A is added first, allowing it to rapidly form a preliminary adsorption layer on the surface of the ammonium paratungstate crystal, preemptively occupying adsorption sites for phosphorus and silicon impurities. Once crystallization begins to occur, crystal surface regulator B is added, working synergistically with crystal surface regulator A to further block impurity adsorption sites on newly exposed growth interfaces. This time-phased, batch-addition strategy maintains an effective regulator concentration in the solution, achieving continuous inhibition of impurity adsorption. Simultaneously, by controlling different temperatures at different stages, adding crystal surface regulator A at 80-90℃ promotes crystal surface activity, facilitating rapid adsorption and evaporation concentration; lowering the temperature from 95-105℃ to 70-80℃ and adding crystal surface regulator B slows crystal growth, prolongs the regulator's action time, and further enhances the adsorption effect of the crystal surface regulator.

[0025] The present invention has the following beneficial effects: 1. Compared with existing technologies, this invention employs a combination of hydroxyl-containing small organic molecule compounds as crystal facet modifier A and carboxyl-containing small organic molecule compounds as crystal facet modifier B. It utilizes a time-phased, batch-addition strategy, adding crystal facet modifier A first, and then adding crystal facet modifier B only after crystallization begins. Combined with a segmented temperature control process, this effectively and competitively occupies the adsorption sites of phosphorus and silicon impurities on the ammonium paratungstate crystal facets, significantly inhibiting the poisoning effect of impurities on crystal growth, thereby greatly improving the crystallinity of ammonium paratungstate crystals. Experimental results show that the method of this invention significantly improves the crystallinity in ammonium paratungstate solutions containing phosphorus and / or silicon impurities compared to traditional processes without adding any crystal facet modifiers, processes that simultaneously add crystal facet modifiers A and B without batch addition, and processes that add only a single crystal facet modifier, achieving unexpected technical effects.

[0026] 2. Compared with existing technologies, the method of this invention also has multiple advantages such as improving crystal quality, increasing production efficiency, reducing enterprise costs, and being simple and environmentally friendly. By effectively inhibiting the adsorption of impurities on the crystal face, defects and morphological anomalies inside the crystal are reduced, making the crystal growth more uniform and complete, thus improving the overall quality of ammonium paratungstate crystals; a higher crystallization rate means that more qualified products can be obtained from the same raw materials per unit time, reducing the time required for repeated processing or rework due to low crystallization rate, and improving overall production efficiency; the improvement in crystallization rate and product quality directly reduces raw material loss and energy consumption, reducing waste costs and subsequent purification costs; at the same time, the crystal face regulators used in this invention are all common small organic molecule compounds, which are widely available, inexpensive, and added in extremely small amounts, without introducing heavy metals or other harmful impurities, eliminating the need for additional impurity removal processes, and making the process simple and environmentally friendly. Detailed Implementation

[0027] 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.

[0028] This invention provides an optimized method for improving the crystallization rate of ammonium paratungstate crystals, comprising the following steps: Step 1: Provide an ammonium tungstate solution; heat the ammonium tungstate solution to 80-90°C and add crystal facet modifier A; Step 2: Continue heating to 95-105℃ to carry out evaporation and crystallization; Step 3: When crystallization begins to occur, lower the temperature to 70-80℃, add crystal surface regulator B, and continue evaporation and crystallization at 70-80℃ until the crystallization endpoint is reached. End the crystallization, collect the crystal product, and obtain ammonium paratungstate crystals.

[0029] Preferably, the ammonium tungstate solution contains phosphorus and / or silicon impurities, and the total concentration of the impurities, calculated as silicate ions and / or phosphate ions, is 0.8 g / L or higher.

[0030] Preferably, the ammonium tungstate solution contains phosphorus and / or silicon impurities, and the total concentration of the impurities, calculated as silicate ions and / or phosphate ions, is 0.8-1.5 g / L.

[0031] Preferably, the concentration of the ammonium tungstate solution, calculated as WO3, is 220-250 g / L.

[0032] Specifically, the concentration of the ammonium tungstate solution, calculated as WO3, can be any one of 220 g / L, 230 g / L, 240 g / L, 250 g / L, or a range between two of them.

[0033] Preferably, the amount of crystal plane modifier A added is 0.1-1% of the volume of the ammonium tungstate solution.

[0034] Specifically, the amount of crystal plane regulator A added can be any one of 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, or 1% of the volume of the ammonium tungstate solution, or a range between two of these.

[0035] Preferably, the crystal plane regulator A is a hydroxyl-containing small organic molecule compound.

[0036] Preferably, the hydroxyl-containing small organic molecule compound is selected from at least one of C2-C4 polyols.

[0037] Preferably, the hydroxyl-containing small organic molecule compound is selected from at least one of ethylene glycol, glycerol, and 1,2-propanediol.

[0038] More preferably, the hydroxyl-containing small organic molecule compound is ethylene glycol.

[0039] Preferably, the amount of crystal plane regulator B added is 0.05-0.5% of the volume of the ammonium tungstate solution.

[0040] Specifically, the amount of crystal plane regulator B added can be any one of 0.05%, 0.1%, 0.2%, 0.4%, or 0.5% of the volume of the ammonium tungstate solution, or a range between two of these.

[0041] Preferably, the crystal plane regulator B is a small organic molecule compound containing a carboxyl group.

[0042] Preferably, the carboxyl-containing small organic molecule compound is selected from at least one of C4-C6 carboxyl-containing organic acids.

[0043] Preferably, the carboxyl-containing small organic molecule compound is selected from at least one of tartaric acid, citric acid, and malic acid.

[0044] More preferably, the carboxyl-containing small organic molecule compound is tartaric acid.

[0045] Preferably, the crystallization endpoint is a solution pH of 6.6-7.0.

[0046] Specifically, the crystallization endpoint is a solution pH value that can be any one of 6.6, 6.7, 6.8, 6.9, 7.0, or a range between two of them.

[0047] Preferably, the heating rate in step 1 is 10-15℃ / min, the heating rate in step 2 is 2-4℃ / min, and the cooling rate in step 3 is 2-4℃ / min.

[0048] Specifically, in step 1, the heating rate can be any one of 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, or 15℃ / min, or a range between two of them; in step 2, the heating rate can be any one of 2℃ / min, 3℃ / min, or 4℃ / min, or a range between two of them; and in step 3, the cooling rate can be any one of 2℃ / min, 3℃ / min, or 4℃ / min, or a range between two of them.

[0049] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0050] Example 1

[0051] An optimization method for improving the crystallization rate of ammonium paratungstate crystals includes the following steps: Step 1: Take silicate ion-containing (SiO3) 2- 200 mL of an ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 80°C at a heating rate of 10°C / min, and ethylene glycol is added to mix, thereby obtaining a mixed solution, wherein the amount of ethylene glycol added is 0.1% of the volume of the ammonium tungstate solution; Step 2: Then, the mixed solution is heated to 100°C at a heating rate of 2°C / min, and the temperature is kept constant for evaporation and crystallization. Step 3: When crystallization progresses to the point where crystals begin to appear in the solution, the temperature is lowered to 80°C at a cooling rate of 2°C / min. Tartaric acid is then added and mixed, and evaporation and crystallization continue at 80°C. The amount of tartaric acid added is 0.05% of the volume of the ammonium paratungstate solution. The pH value of the solution is continuously monitored during the crystallization process. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0052] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 90.12%.

[0053] Example 2

[0054] An optimization method for improving the crystallization rate of ammonium paratungstate crystals includes the following steps: Step 1: Take silicate ion-containing (SiO3) 2- 200 mL of an ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 90°C at a heating rate of 15°C / min, and ethylene glycol is added to mix, thereby obtaining a mixed solution, wherein the amount of ethylene glycol added is 0.1% of the volume of the ammonium tungstate solution; Step 2: Then, the mixed solution is heated to 100°C at a heating rate of 4°C / min and kept at a constant temperature for evaporation and crystallization. Step 3: When crystallization progresses to the point where crystals begin to appear in the solution, the temperature is lowered to 70°C at a cooling rate of 4°C / min. Tartaric acid is then added and mixed, and evaporation and crystallization continue at 70°C. The amount of tartaric acid added is 0.05% of the volume of the ammonium paratungstate solution. The pH value of the solution is continuously monitored during the crystallization process. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0055] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 90.28%.

[0056] Comparative Example 1 A method for crystallizing ammonium paratungstate crystals includes the following steps: Take silicate ions (SiO3) 2-200 mL of ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 100°C at a heating rate of 10°C / min, and evaporation crystallization is carried out at a constant temperature; the pH value of the solution is continuously monitored during the crystallization process, and when the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed and dried to obtain ammonium paratungstate crystals.

[0057] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 79.98%.

[0058] Comparative Example 2 An optimization method for improving the crystallization rate of ammonium paratungstate crystals includes the following steps: Step 1: Take silicate ion-containing (SiO3) 2- 200 mL of an ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 80°C at a heating rate of 10°C / min; ethylene glycol and tartaric acid are added and mixed to obtain a mixed solution, wherein the amount of ethylene glycol added is 0.1% of the volume of the ammonium tungstate solution, and the amount of tartaric acid added is 0.05% of the volume of the ammonium tungstate solution; Step 2: Then, the mixed solution is heated to 100°C at a heating rate of 2°C / min, and the temperature is kept constant for evaporation and crystallization. Step 3: When crystallization proceeds to the point where crystals begin to appear in the solution, the temperature is lowered to 80℃ at a cooling rate of 2℃ / min, and then evaporation and crystallization continue at 80℃. During the crystallization process, the pH value of the solution is continuously monitored. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0059] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 85.44%.

[0060] Comparative Example 3 An optimization method for improving the crystallization rate of ammonium paratungstate crystals includes the following steps: Step 1: Take silicate ion-containing (SiO3) 2- 200 mL of ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 100°C at a heating rate of 5°C / min, and then kept at the temperature for evaporation and crystallization. Step 2: When crystallization progresses to the point where crystals begin to appear in the solution, the temperature is lowered to 70°C at a cooling rate of 1°C / min. Tartaric acid is then added and mixed, and evaporation and crystallization continue at 70°C. The amount of tartaric acid added is 0.05% of the volume of the ammonium paratungstate solution. The pH value of the solution is continuously monitored during the crystallization process. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0061] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 81.23%.

[0062] Comparative Example 4 An optimization method for improving the crystallization rate of ammonium paratungstate crystals includes the following steps: Step 1: Take silicate ion-containing (SiO3) 2- 200 mL of an ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 90°C at a heating rate of 10°C / min, and ethylene glycol is added to mix, thereby obtaining a mixed solution, wherein the amount of ethylene glycol added is 0.1% of the volume of the ammonium tungstate solution; Step 2: The mixed solution is then heated to 100°C at a heating rate of 2°C / min and kept at a constant temperature for evaporation and crystallization. The pH value of the solution is continuously monitored during the crystallization process. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0063] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 82.45%.

[0064] Comparative Example 5 An optimized crystallization process method for improving the crystallization rate of ammonium paratungstate crystals involves replacing ethylene glycol in step 1 with a 4 mol / L ammonium hydroxide solution and replacing tartaric acid in step 3 with a 2 mol / L hydrochloric acid solution.

[0065] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 83.16%.

[0066] Comparative Example 6 An optimized crystallization process method for improving the crystallization rate of ammonium paratungstate crystals differs from Example 1 in that step 3 is different. Step 3 is as follows: When crystallization proceeds to the point where crystals begin to appear in the solution, tartaric acid is added and mixed. The mixture is then evaporated and crystallized again at 100°C. The amount of tartaric acid added is 0.05% of the volume of the ammonium paratungstate solution. The pH value of the solution is continuously monitored during the crystallization process. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0067] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 86.58%.

[0068] Comparative Example 7 An optimized crystallization process method for improving the crystallization rate of ammonium paratungstate crystals differs from Example 2 in that step 3 is different. Step 3 is as follows: When crystallization progresses to the point where crystals begin to appear in the solution, the temperature is lowered to 70°C at a cooling rate of 4°C / min. Then, dodecyltrimethylammonium chloride is added and mixed. Evaporation and crystallization continue at 70°C. The amount of dodecyltrimethylammonium chloride added is 1% of the volume of the ammonium tungstate solution. The pH value of the solution is continuously monitored during the crystallization process. When the pH value of the solution drops to 6.7, the crystallization is stopped, the crystallized product is collected, filtered, washed, and dried to obtain ammonium paratungstate crystals.

[0069] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 81.56%.

[0070] Comparative Example 8 An optimized crystallization process method for improving the crystallization rate of ammonium paratungstate crystals differs from Example 2 in that step 1 is different. Step 1 is as follows: Take silicate ions (SiO3) 2- 200 mL of ammonium tungstate solution with a concentration of 0.8 g / L, wherein the concentration of WO3 in the ammonium tungstate solution is 240 g / L; the ammonium tungstate solution is placed in a crystallizer and heated to 90°C at a heating rate of 15°C / min, and dodecyltrimethylammonium chloride is added and mixed to obtain a mixed solution, wherein the amount of ethylene glycol added is 1% of the volume of the ammonium tungstate solution.

[0071] The obtained ammonium paratungstate crystals were converted into WO3 by high-temperature calcination and weighed. The crystallization rate was calculated to be 82.10%.

[0072] In summary, this invention provides an optimized crystallization process method to improve the crystallinity of ammonium paratungstate crystals. This method addresses the technical challenge in existing technologies where phosphorus and silicon impurities are strongly adsorbed onto the crystal growth interface during ammonium paratungstate crystallization, leading to a significant decrease in crystallinity. By screening hydroxyl-containing small organic molecule compounds as crystal facet modifier A and carboxyl-containing small organic molecule compounds as crystal facet modifier B, and employing a time-phased, batch-addition strategy—adding crystal facet modifier A first, and then adding crystal facet modifier B after crystallization begins—combined with a segmented temperature control process, the crystal facet modifiers can effectively and competitively occupy the adsorption sites of phosphorus and silicon impurities on the ammonium paratungstate crystal faces, significantly inhibiting the poisoning effect of impurities on crystal growth, thereby greatly improving the crystallinity of ammonium paratungstate crystals. Simultaneously, this invention also offers multiple advantages such as improved crystal quality, increased production efficiency, reduced enterprise costs, and a simple and environmentally friendly process. Compared with existing technologies, this invention achieves significant technological progress in ammonium tungstate solutions containing phosphorus and / or silicon impurities, possessing outstanding substantive features and significant advancements, and demonstrating promising industrial application prospects. 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 optimizing the crystallization process to improve the crystallinity of ammonium paratungstate crystals, characterized in that, Includes the following steps: Step 1: Provide an ammonium tungstate solution; heat the ammonium tungstate solution to 80-90°C and add crystal facet modifier A; Step 2: Continue heating to 95-105℃ to carry out evaporation and crystallization; Step 3: When crystallization begins to occur, lower the temperature to 70-80℃, add crystal surface regulator B, and continue evaporation and crystallization at 70-80℃ until the crystallization endpoint is reached. Then, stop the crystallization, collect the crystal product, and obtain ammonium paratungstate crystals.

2. The method according to claim 1, characterized in that, The ammonium tungstate solution contains phosphorus and / or silicon impurities, and the total concentration of the impurities, calculated as silicate ions and / or phosphate ions, is above 0.8 g / L.

3. The method according to claim 1, characterized in that, The concentration of the ammonium tungstate solution, calculated as WO3, is 220-250 g / L.

4. The method according to claim 1, characterized in that, The amount of crystal plane modifier A added is 0.1-1% of the volume of the ammonium tungstate solution.

5. The method according to claim 1, characterized in that, The crystal plane regulator A is a hydroxyl-containing small organic molecule compound.

6. The method according to claim 5, characterized in that, The hydroxyl-containing small organic molecule compound is selected from at least one of C2-C4 polyols.

7. The method according to claim 1, characterized in that, The amount of crystal facet modifier B added is 0.05-0.5% of the volume of the ammonium tungstate solution.

8. The method according to claim 1, characterized in that, The crystal plane regulator B is a small organic molecule compound containing a carboxyl group.

9. The method according to claim 8, characterized in that, The carboxyl-containing small organic molecule compound is selected from at least one of C4-C6 carboxyl-containing organic acids.

10. The method according to claim 1, characterized in that, The crystallization endpoint is when the solution pH is 6.6-7.0.