Preparation method of high-purity electronic-grade phosphoric acid

Abstract

The invention relates to the technical field of phosphoric acid production, in particular to a preparation method of high-purity electronic-grade phosphoric acid, which comprises the following steps: S1, preheating wet-process phosphoric acid in an arsenic removal area, mixing with hydrogen sulfide gas, and carrying out arsenic removal reaction; filtering in a first filtering area, feeding the obtained filtrate into a hydrogen sulfide removal area, removing hydrogen sulfide gas under the conditions of air blowing and negative pressure, and feeding into a second filtering area for filtering; s2, carrying out ion exchange on the phosphoric acid treated in the step S1 to obtain crystallized raw material acid; and S3, stirring and mixing the crystallized raw material acid with phosphoric acid seed crystal in a crystallization region, carrying out cooling crystallization in a process temperature control manner, and carrying out solid-liquid separation on obtained crystal mush to obtain the high-purity electronic-grade phosphoric acid. According to the method, the high-purity electronic-grade phosphoric acid is efficiently prepared with low energy consumption and low cost by adopting a means of coupling purification technologies such as chemical arsenic removal, suspension melt crystallization and ion exchange resin, and the method is less in used equipment, high in applicability and beneficial to industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid production technology, and in particular to a method for preparing high-purity electronic-grade phosphoric acid. Background Technology

[0002] Electronic-grade phosphoric acid is widely used as an etchant in semiconductor manufacturing, especially in the etching of silicon nitride (Si3N4) films. Its unique chemical properties, high etching rate, selective etching capability, and environmental friendliness make it an ideal choice for etching silicon nitride films. With the rapid development of the semiconductor industry and continuous breakthroughs in chip technology, the demand for electronic-grade phosphoric acid is increasing daily, while its quality requirements are becoming increasingly stringent, and high purification standards are being further refined to higher levels.

[0003] The preparation processes of electronic-grade phosphoric acid are mainly divided into two categories: thermal methods and wet methods. Thermal methods directly produce high-purity phosphoric acid through chemical reactions using phosphorus compounds. Wet methods involve replacing phosphate concentrate with sulfuric acid, and the resulting industrial-grade wet-process phosphoric acid is further purified using techniques such as ion exchange, electrodialysis, solvent extraction, chemical precipitation, membrane separation, and crystallization to obtain electronic-grade phosphoric acid. Compared to traditional thermal processes, these preparation processes avoid high energy consumption, making the production process more energy-efficient and cost-effective, and are gradually becoming the mainstream processes.

[0004] Existing technology proposes a method for preparing electronic-grade phosphoric acid via cooling crystallization. First, a raw acid with a concentration of 85%–90% is heated to a clear liquid state free of solid particles at high temperature. Then, 1%–10% of the mother liquor mass of seed crystals is added during cooling. Through staged temperature control, all phosphoric acid in the mother liquor is crystallized out. Finally, the frozen crystal layer on the reactor wall is peeled off by heating, and the product is discharged, centrifuged, and washed. The resulting electronic-grade phosphoric acid product has impurity content controlled below 5 ppb, with a yield of 58%. This method requires the raw acid to meet the national standard E1 for electronic-grade phosphoric acid, demanding very high purity. It also requires a large amount of seed crystals, resulting in high costs. Furthermore, the staged cooling and isothermal control leads to long operation times and low production efficiency.

[0005] Another existing technology combines nanofiltration membrane filtration with static melt crystallization to prepare electronic-grade phosphoric acid. The main process includes three steps: preheating of the raw phosphoric acid; primary purification via acid-resistant nanofiltration membrane filtration; and deep purification via static melt crystallization. This method can reduce the content of single impurities in phosphoric acid to below 30 ppb. This method is the first to couple membrane separation and crystallization technologies, producing phosphoric acid with high concentration and low metal content; however, it also has significant drawbacks. Using membrane separation for primary purification makes the membrane surface highly susceptible to fouling, requiring regular cleaning and maintenance, which can lead to membrane damage. Ultimately, discarded membranes can also pollute the environment. Furthermore, high-concentration phosphoric acid has poor fluidity, placing high demands on the nanofiltration membrane during high-pressure filtration, resulting in high membrane prices and further increasing production costs.

[0006] Another technology proposes a novel method combining chemical precipitation and suspension melt crystallization. Using industrial phosphoric acid as raw material, electronic-grade phosphoric acid is prepared through the following steps: chemical removal of arsenic from phosphorus pentasulfide; subsequent desiliconization of the arsenic-removed phosphoric acid solution; and purification of the phosphoric acid solution using a self-made crystallization tower. This method, to some extent, compensates for the shortcomings of single purification technologies; however, certain problems remain: the arsenic removal reaction efficiency of phosphorus pentasulfide is low, reagent consumption is large, the treated product is highly polluting, equipment requirements are high, costs are high, and reaction time is long. Furthermore, the purification process of phosphoric acid in the crystallization tower is extremely time-consuming, with a single treatment time of at least 20 hours and a single-batch yield of 55.1%, while the content of elements such as Na, K, and Fe after purification is still as high as 300 ppb. It barely meets the national standard for electronic-grade E1 phosphoric acid, and there is still considerable room for improvement in producing high-purity electronic-grade phosphoric acid.

[0007] In addition, there is an existing technology that uses a crystallization-electrodialysis-reverse osmosis coupled process to prepare electronic-grade phosphoric acid. The process mainly includes the following steps: First, industrial-grade phosphoric acid is pre-separated and impurities are removed using a layer-by-layer melt crystallization method to obtain purified phosphoric acid I. Then, purified phosphoric acid I is treated by electrodialysis to obtain purified phosphoric acid II, which meets the MOS-grade electronic-grade phosphoric acid standard. Finally, reverse osmosis is performed through a cross-flow flat-plate membrane filtration system to obtain BV-I grade electronic-grade phosphoric acid (the total content of metal impurities needs to be controlled to less than 1000 ppb). Specific product specifications for this existing technology are not disclosed. The electrodialysis method has the following disadvantages: high energy consumption, poor process stability, expensive electrode materials, and high maintenance costs. It is not suitable for industrial production. Summary of the Invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing high-purity electronic-grade phosphoric acid, which can prepare high-purity electronic-grade phosphoric acid efficiently, with low energy consumption and low cost.

[0009] This invention provides a method for preparing high-purity electronic-grade phosphoric acid, comprising the following steps:

[0010] S1. Wet phosphoric acid is preheated in the arsenic removal zone and mixed with hydrogen sulfide gas to carry out the arsenic removal reaction; then filtered in the first filtration zone, and the resulting filtrate enters the hydrogen sulfide removal zone. After removing hydrogen sulfide gas under the conditions of gas blowing and negative pressure, it enters the second filtration zone for filtration.

[0011] S2. After ion exchange, the phosphoric acid treated in step S1 is used to obtain crystalline raw material acid;

[0012] S3. The acid raw material for crystallization is stirred and mixed with phosphoric acid seed crystals in the crystallization zone, and then cooled and crystallized by process temperature control. The resulting crystal slurry is subjected to solid-liquid separation to obtain high-purity electronic-grade phosphoric acid.

[0013] Preferably, in step S1, the gas blown in is used as a carrier gas and is selected from air, nitrogen, or an inert gas.

[0014] The gas-liquid ratio of the blown gas is 3~10:1;

[0015] The duration of the inflation is 30-60 minutes.

[0016] Preferably, in step S2, the ion exchange resin used for ion exchange is a strongly acidic cation exchange resin.

[0017] The particle size of the strongly acidic cation exchange resin is 100-200 mesh.

[0018] The ion exchange residence time is 1 to 6 hours.

[0019] Preferably, in step S1, the mass content of H3PO4 in the wet-process phosphoric acid is 85%~95%.

[0020] Preferably, in step S1, the preheating temperature of the arsenic removal zone is 60~80℃.

[0021] Preferably, in step S1, the amount of hydrogen sulfide gas introduced is 10 to 25 times the molar amount of arsenic in wet-process phosphoric acid.

[0022] Preferably, in step S2, the mass concentration of phosphoric acid in the crystalline raw material acid is 85%~95%.

[0023] Preferably, in step S3, before stirring and mixing the crystallizing raw acid with the phosphoric acid seed crystals, the method further includes maintaining the temperature of the crystallizing raw acid at 15~30°C.

[0024] The stirring speed is 20~300 rpm.

[0025] Preferably, in step S3, the shape of the phosphate seed crystal is selected from rhomboid, plate-like, or spherical;

[0026] The particle size range of the phosphate seed crystals is 0.1~5 mm;

[0027] The mass ratio of the phosphate seed crystals to the crystallization raw material acid is 1:20~10000.

[0028] Preferably, in step S3, the cooling crystallization is carried out using a process temperature control method, specifically as follows:

[0029] a. First-gradient cooling: The solution after mixing the raw material acid and the phosphate seed crystals is cooled at a rate of 0.2~2℃ / h for 1~2 h;

[0030] b. Maintain the temperature for 1-4 hours until the phosphate crystals in the raw acid of the crystallization material grow to 2-7 mm;

[0031] c. Second-gradient cooling: Cooling to 0~15℃ at a rate of 0.3~7℃ / h.

[0032] This invention addresses the problems of high cost, low production efficiency, environmental pollution, high equipment requirements, and long reaction time in existing technologies by providing a method for preparing electronic-grade phosphoric acid. This process uses a combination of purification technologies such as chemical arsenic removal, suspension melt crystallization, and ion exchange resin to prepare high-purity electronic-grade phosphoric acid efficiently, with low energy consumption and low cost. It solves the shortcomings of existing technologies to a certain extent, and requires less equipment and has high applicability, which is conducive to industrialization and promotion. Attached Figure Description

[0033] Figure 1 A process flow diagram for preparing high-purity electronic-grade phosphoric acid is provided for one embodiment of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] This invention provides a method for preparing high-purity electronic-grade phosphoric acid, comprising the following steps:

[0036] S1. Wet phosphoric acid is preheated in the arsenic removal zone and mixed with hydrogen sulfide gas to carry out the arsenic removal reaction; then filtered in the first filtration zone, and the resulting filtrate enters the hydrogen sulfide removal zone. After removing hydrogen sulfide gas under the conditions of gas blowing and negative pressure, it enters the second filtration zone for filtration.

[0037] S2. After ion exchange, the phosphoric acid treated in step S1 is used to obtain crystalline raw material acid;

[0038] S3. The acid raw material for crystallization is stirred and mixed with phosphoric acid seed crystals in the crystallization zone, and then cooled and crystallized by process temperature control. The resulting crystal slurry is subjected to solid-liquid separation to obtain high-purity electronic-grade phosphoric acid.

[0039] Regarding step S1:

[0040] Wet-process phosphoric acid is preheated in the arsenic removal zone and mixed with hydrogen sulfide gas to carry out the arsenic removal reaction. It is then filtered in the first filtration zone, and the resulting filtrate enters the hydrogen sulfide removal zone. After removing the hydrogen sulfide gas under the conditions of gas blowing and negative pressure, it enters the second filtration zone for filtration.

[0041] In some embodiments of the present invention, the wet-process phosphoric acid originates from a phosphate chemical plant. The present invention does not impose any particular limitations on the composition of the wet-process phosphoric acid and is therefore universally applicable. Specifically, the mass content of H3PO4 in the wet-process phosphoric acid is 85% to 95%.

[0042] In some embodiments, the wet-process phosphoric acid contains 85% H3PO4 by mass and SO4. 2- The mass content of each component is less than 100 ppm. The mass content of Li is 26.3 ppb, Na is 2013 ppb, Mg is 1494 ppb, Al is 24466 ppb, K is 1505 ppb, Ca is 14084 ppb, Cr is 265 ppb, Mn is 191 ppb, Fe is 64747 ppb, Co is 14.8 ppb, Ni is 294 ppb, Cu is 40.2 ppb, Zn is 1136 ppb, Ga is 13.2 ppb, As is 32571 ppb, Ag is 58.6 ppb, Cd is 1.26 ppb, Ba is 37.6 ppb, and Pb is 3.05 ppb.

[0043] In some embodiments, the wet-process phosphoric acid contains 85.6% H3PO4 by mass and SO42-22% ... 2-The mass content of each element is less than 100 ppm, with Li at 2.15 ppb, Na at 29717 ppb, Mg at 388 ppb, Al at 398 ppb, K at 1439 ppb, Ca at 14287 ppb, Cr at 748 ppb, Mn at 172 ppb, Fe at 46058 ppb, Co at 7.36 ppb, Ni at 1525 ppb, Cu at 241 ppb, Zn at 760 ppb, Ga at 1.51 ppb, As at 2849 ppb, Ag at 413 ppb, Cd at 64 ppb, Ba at 5.16 ppb, and Pb at 315 ppb.

[0044] In some embodiments of the present invention, wet-process phosphoric acid is preheated in an arsenic removal zone and mixed with hydrogen sulfide gas to carry out an arsenic removal reaction, specifically as follows:

[0045] Wet-process phosphoric acid is preheated in the arsenic removal zone, and hydrogen sulfide gas is introduced from the bottom of the arsenic removal zone to carry out the arsenic removal reaction.

[0046] The wet-process phosphoric acid can be pumped into the arsenic removal zone.

[0047] In some embodiments of the present invention, the preheating temperature of the arsenic removal zone is 60~80°C, preferably 75~80°C, such as 75°C.

[0048] In some embodiments of the present invention, the amount of hydrogen sulfide gas introduced is 10 to 25 times the molar amount of arsenic in wet-process phosphoric acid, preferably 15 to 20 times, such as 15, 20, 17, or 25 times. The hydrogen sulfide gas needs to be introduced for 15 to 30 minutes to ensure sufficient reaction; specifically, it can be 30 minutes, 25 minutes, or 20 minutes.

[0049] The temperature of the arsenic removal reaction is 60~80℃, preferably 75~80℃, such as 75℃.

[0050] In some embodiments of the present invention, the arsenic removal zone is an arsenic removal tower, such as a spray tower or a blower tower.

[0051] In some embodiments of the present invention, the first filtration zone is a pressure filtration system.

[0052] In some embodiments of the present invention, the gas blown in is used as a carrier gas, which may be air, nitrogen, or an inert gas, preferably nitrogen. The gas-liquid ratio of the blown gas is 3 to 10:1, preferably 6:1. The duration of the blown gas is 30 to 60 minutes, preferably 40 to 50 minutes, for example, 40 minutes, 50 minutes, 45 minutes, or 60 minutes.

[0053] In some embodiments of the present invention, the negative pressure is -0.05 to -0.1 kPa, for example -0.05 kPa.

[0054] In some embodiments of the present invention, the hydrogen sulfide desulfurization zone is a hydrogen sulfide desulfurization tower.

[0055] In this invention, after the phosphoric acid is filtered to remove the filter residue, it is then pumped into the desulfurization tower. At this time, the phosphoric acid still retains residual heat. Then, carrier gas is blown into the desulfurization tower from the bottom. The top of the tower is equipped with a negative pressure system. During this period, the flow rate of the carrier gas is controlled and a stable negative pressure is maintained. The H2S gas in the phosphoric acid is efficiently lifted out by blowing and pumping.

[0056] In some embodiments of the present invention, after removing hydrogen sulfide gas under blast and negative pressure conditions, the process further includes: subjecting the hydrogen sulfide gas to alkaline washing and water washing. The gas is then discharged. The alkaline washing is performed in an alkaline washing tower. The water washing is performed in a water washing tower.

[0057] Phosphoric acid, after the removal of hydrogen sulfide gas, enters the second filtration zone for filtration.

[0058] In some embodiments of the present invention, the second filtration zone is a pressure filtration system.

[0059] The phosphoric acid after filtration in the second filtration zone is clear, dearsenic-free phosphoric acid.

[0060] Regarding step S2:

[0061] After ion exchange, the phosphoric acid treated in step S1 is concentrated to obtain crystalline raw material acid.

[0062] In some embodiments of the present invention, the ion exchange resin used for the ion exchange is an acid-resistant cation exchange resin, preferably a strongly acidic cation exchange resin type, such as hydrogen form cation exchange resin (including but not limited to DOWEX(R) 50WX2 Hydrogen Form, DOWEX(R) 50WX4 Hydrogen Form resin, etc.); the resin particle size is preferably 100~200 mesh.

[0063] Before use, the ion exchange resin is further subjected to washing with ultrapure water until the washing solution also meets the electronic grade water quality standards.

[0064] In some embodiments of the present invention, the ion exchange residence time is 1-6 h, preferably 2-4 h, such as 4 h, 2 h, 3 h, or 5 h. The ion exchange is carried out in a resin tank. The phosphoric acid treated in step S1 can be pumped into the resin tank.

[0065] In some embodiments of the present invention, the process after ion exchange further includes concentration.

[0066] In some embodiments of the present invention, the mass concentration of phosphoric acid in the crystallizing raw acid is 85% to 95%, for example, 85%. This further prepares the material for crystallization.

[0067] Regarding step S3:

[0068] The acid raw material for crystallization is stirred and mixed with phosphoric acid seed crystals in the crystallization zone, and then cooled and crystallized by process temperature control. The resulting crystal slurry is then subjected to solid-liquid separation to obtain high-purity electronic-grade phosphoric acid.

[0069] In some embodiments of the present invention, before stirring and mixing the crystallizing raw acid with the phosphoric acid seed crystal, the method further includes maintaining the temperature of the crystallizing raw acid at 15~30°C, preferably 19~25°C, such as 21°C, 23°C, or 19°C.

[0070] In some embodiments of the present invention, the crystallization zone is a jacketed crystallization vessel.

[0071] In some embodiments of the present invention, the crystallizing raw material acid is stirred and mixed with phosphate seed crystals, specifically as follows:

[0072] The raw material acid for crystallization is pumped into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the raw material acid for crystallization in the reactor is maintained at 15~30℃. Phosphate seed crystals are added during the stirring process.

[0073] The stirring speed is 20-300 rpm, preferably 100-200 rpm, so that the crystals are just suspended during the crystallization process. The stirring time is 25-35 minutes, for example, 30 minutes.

[0074] In some embodiments of the present invention, the shape of the phosphate seed crystals can be rhomboid, plate-like, or spherical, with a rhomboid shape being preferred. The particle size of the phosphate seed crystals ranges from 0.1 to 5 mm. The mass ratio of the phosphate seed crystals to the crystallization raw material acid is 1:20 to 10000, for example, 1:2000, 1:20, or 1:1000.

[0075] In some embodiments of the present invention, cooling crystallization is carried out by process temperature control, which is specifically cooling crystallization by gradient cooling:

[0076] a. First-gradient cooling: The solution after mixing the raw material acid and the phosphate seed crystals is cooled at a rate of 0.2~2℃ / h for 1~2 h;

[0077] b. Maintain the temperature for 1-4 hours until the phosphate crystals in the raw acid of the crystallization material grow to 2-7 mm;

[0078] c. Second-gradient cooling: Cooling to 0~15℃ at a rate of 0.3~7℃ / h.

[0079] Regarding step a:

[0080] The cooling rate is preferably 0.5~1℃ / h, such as 0.5℃ / h, 1℃ / h, or 0.75℃ / h. The cooling time is specifically 2 hours.

[0081] Step a is the secondary nucleation stage.

[0082] Regarding step b:

[0083] The isothermal stage is the crystal nucleus cultivation stage. The isothermal duration is specifically 2 hours.

[0084] In some embodiments of the present invention, after the constant temperature period ends, the method further includes:

[0085] Heat to 25~35℃ and maintain for 25~35 minutes.

[0086] This stage is for removing fine crystals to prevent them from adhering to the wall and forming a crystalline layer on the inner wall of the crystallization vessel. The heating rate is 20~40℃ / h, for example, 40℃ / h or 30℃ / h. The final temperature is 28℃. The holding time is 30 min.

[0087] Regarding step c:

[0088] Step c is the crystal growth stage.

[0089] In some embodiments of the present invention, the cooling rate is specifically 5℃ / h, 0.5℃ / h, 10℃ / h, or 7℃ / h.

[0090] In some embodiments of the present invention, the temperature after cooling is 5~15℃; specifically 13℃, 10℃, 8℃, and 9℃.

[0091] In some embodiments of the present invention, the solid-liquid separation of the crystal slurry is performed by centrifugation.

[0092] In some embodiments of the present invention, after the solid-liquid separation, the method further includes: mixing the phosphoric acid crystals after solid-liquid separation with ultrapure water to obtain high-purity electronic-grade phosphoric acid.

[0093] The mixing of the phosphate crystals after solid-liquid separation with ultrapure water is carried out in an acid-adjusting tank.

[0094] In some embodiments of the present invention, the liquid acid after solid-liquid separation is returned to the arsenic removal zone for recycling.

[0095] The ultrapure water used in the above method has an online resistivity of ≥18.2 MΩ·cm at 25℃.

[0096] Beneficial effects

[0097] 1. The high-purity electronic-grade phosphoric acid prepared according to the technical solution of the present invention has a total impurity content of <10ppb, the content of most metal ions can reach within 0.1ppb, and the content of a very small number of impurities that are difficult to completely remove, such as Fe and As, can also be controlled within 5ppb.

[0098] 2. This invention is the first to combine chemical precipitation, ion exchange and suspension crystallization methods, creating a coupling technology that can reduce the production consumption of a single technology and greatly reduce production costs.

[0099] 3. The coupling technology proposed in this invention has strong adaptability and can be adapted to wet-process phosphoric acid raw materials with different impurity compositions and contents obtained from phosphate rock of different grades through wet process.

[0100] 4. The coupling technology proposed in this invention offers high operational flexibility, allowing for adjustments to operating conditions based on actual needs, thereby improving the adaptability and flexibility of the process. It can be adjusted as required to obtain phosphoric acid of varying purities and concentrations.

[0101] 5. The suspension melting crystallization step of this invention uses a unique temperature control method to control the crystallization temperature in a gradient, making full use of the secondary nucleation mechanism, turning waste into treasure, greatly reducing the amount of seed crystals used, lowering production costs, and avoiding the difficult-to-remove crystal layers formed on the reactor wall in traditional crystallization processes. It also reduces the mother liquor inclusion between crystals, increases product yield, simplifies the process, and is more suitable for industrial production.

[0102] 6. This invention enables the recycling and continuous production of phosphoric acid, simplifies production operations, and improves production efficiency.

[0103] To further illustrate the present invention, the following detailed description of a method for preparing high-purity electronic-grade phosphoric acid provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0104] The following examples and comparative examples were all conducted in a Class 1000 cleanroom; the ultrapure water used had an online resistivity of ≥18.2 MΩ·cm at 25°C.

[0105] Example 1

[0106] The raw material, wet-process phosphoric acid, comes from a phosphate chemical plant in Guizhou Province. The wet-process phosphoric acid contains 85% H3PO4 and 0.5% SO4. 2- The mass content of each component is less than 100 ppm, with Li at 26.3 ppb, Na at 2013 ppb, Mg at 1494 ppb, Al at 24466 ppb, K at 1505 ppb, Ca at 14084 ppb, Cr at 265 ppb, Mn at 191 ppb, Fe at 64747 ppb, Co at 14.8 ppb, Ni at 294 ppb, Cu at 40.2 ppb, Zn at 1136 ppb, Ga at 13.2 ppb, As at 32571 ppb, Ag at 58.6 ppb, Cd at 1.26 ppb, Ba at 37.6 ppb, and Pb at 3.05 ppb.

[0107] The preparation of high-purity electronic-grade phosphoric acid uses the following methods: Figure 1 The preparation process shown; Figure 1 A process flow diagram for preparing high-purity electronic-grade phosphoric acid is provided for one embodiment of the present invention.

[0108] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 75°C. H2S gas is introduced from the bottom of the tower at a rate of 15 times the molar amount of arsenic in the wet phosphoric acid for 30 min. The arsenic removal reaction is carried out at 75°C.

[0109] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0110] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the tower from the bottom at a gas-liquid ratio of 6:1 for 40 minutes. A negative pressure of -0.05 kPa is applied at the top of the tower. The discharged tail gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0111] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, yielding clarified arsenic-free phosphoric acid.

[0112] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX4 Hydrogen Form hydrogen cation exchange resin with a particle size of 200 mesh.

[0113] The dearsenic-removed phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 4 hours.

[0114] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass.

[0115] 3) Pump the crystallizing raw acid into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the crystallizing raw acid in the reactor is maintained at 21°C. Start stirring at 100 rpm. Add rhombic phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the crystallizing raw acid is 1:2000.

[0116] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 0.5℃ / h for 2 hours, followed by a constant temperature for 2 hours, until the phosphoric acid crystals in the raw material acid grew to 2-7 mm; then the temperature was increased to 28℃ at a rate of 40℃ / h and held for 30 minutes to melt the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 5℃ / h to the final crystallization temperature of 13℃.

[0117] After crystallization, the material is discharged, and the resulting slurry is fed into a centrifuge to separate the crystals. The separated liquid acid is returned to the arsenic removal tower for recycling, and the separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare high-purity electronic-grade phosphoric acid with a mass concentration of 85%.

[0118] Example 2

[0119] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0120] Preparation of high-purity electronic-grade phosphoric acid:

[0121] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 75°C. H2S gas is introduced from the bottom of the tower at a rate of 20 times the molar amount of arsenic in the wet phosphoric acid for 25 min. The arsenic removal reaction is carried out at 75°C.

[0122] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0123] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the tower from the bottom at a gas-liquid ratio of 6:1 for 50 minutes. A negative pressure of -0.05 kPa is applied at the top of the tower. The discharged tail gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0124] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, yielding clarified arsenic-free phosphoric acid.

[0125] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX4 Hydrogen Form hydrogen cation exchange resin with a particle size of 200 mesh.

[0126] The dearsenic-removed phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 2 hours.

[0127] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass.

[0128] 3) Pump the crystallizing raw acid into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the crystallizing raw acid in the reactor is maintained at 23°C. Start stirring at 100 rpm. Add flaky phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the crystallizing raw acid is 1:2000.

[0129] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 1℃ / h for 2 hours, followed by a constant temperature for 2 hours, until the phosphoric acid crystals in the raw material acid grew to 2-7 mm; then the temperature was increased to 28℃ at a rate of 40℃ / h and held for 30 minutes to melt away the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 5℃ / h to the final crystallization temperature of 10℃.

[0130] After crystallization, the material is discharged, and the resulting slurry is fed into a centrifuge to separate the crystals. The separated liquid acid is returned to the arsenic removal tower for recycling, and the separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare high-purity electronic-grade phosphoric acid with a mass concentration of 85%.

[0131] Example 3

[0132] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0133] Preparation of high-purity electronic-grade phosphoric acid:

[0134] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 75°C. H2S gas is introduced from the bottom of the tower at a rate of 17 times the molar amount of arsenic in the wet phosphoric acid for 30 min. The arsenic removal reaction is carried out at 75°C.

[0135] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0136] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 6:1 for 45 minutes. A negative pressure of -0.05 kPa is drawn from the top of the tower. The exhaust gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0137] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, yielding clarified arsenic-free phosphoric acid.

[0138] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX4 Hydrogen Form hydrogen cation exchange resin with a particle size of 200 mesh.

[0139] The dearsenic-removed phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 3 hours.

[0140] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass.

[0141] 3) Pump the raw acid for crystallization into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the raw acid for crystallization in the reactor is maintained at 19°C. Start stirring at 100 rpm. Add spherical phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the raw acid for crystallization is 1:20.

[0142] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 0.75℃ / h for 2 hours, followed by a hold-temperature period of 2 hours, until the phosphoric acid crystals in the raw material acid grew to 2-7 mm; then the temperature was increased to 28℃ at a rate of 40℃ / h and held for 30 minutes to melt away the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 5℃ / h to reach the final crystallization temperature of 13℃.

[0143] After crystallization, the material is discharged, and the resulting slurry is fed into a centrifuge to separate the crystals. The separated liquid acid is returned to the arsenic removal tower for recycling, and the separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare high-purity electronic-grade phosphoric acid with a mass concentration of 85%.

[0144] Example 4

[0145] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0146] Preparation of high-purity electronic-grade phosphoric acid:

[0147] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 75°C. H2S gas is introduced from the bottom of the tower at a rate of 25 times the molar amount of arsenic in the wet phosphoric acid for 20 min. The arsenic removal reaction is carried out at 75°C.

[0148] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0149] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 6:1 for 60 minutes. A negative pressure of -0.05 kPa is drawn from the top of the tower. The exhaust gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0150] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, yielding clarified arsenic-free phosphoric acid.

[0151] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX4 Hydrogen Form hydrogen cation exchange resin with a particle size of 150 mesh.

[0152] The dearsenic-removed phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 4 hours.

[0153] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass.

[0154] 3) Pump the crystallizing raw acid into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the crystallizing raw acid in the reactor is maintained at 23°C. Start stirring at 100 rpm. Add flaky phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the crystallizing raw acid is 1:2000.

[0155] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 0.5℃ / h for 2 hours, followed by a constant temperature for 2 hours, until the phosphoric acid crystals in the raw material acid grew to 2-7 mm; then the temperature was increased to 30℃ at a rate of 30℃ / h and held for 30 minutes to melt away the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 6℃ / h to reach the final crystallization temperature of 6℃.

[0156] After crystallization, the material is discharged, and the resulting slurry is fed into a centrifuge to separate the crystals. The separated liquid acid is returned to the arsenic removal tower for recycling, and the separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare high-purity electronic-grade phosphoric acid with a mass concentration of 85%.

[0157] Example 5

[0158] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0159] Preparation of high-purity electronic-grade phosphoric acid:

[0160] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 75°C. H2S gas is introduced from the bottom of the tower at a rate of 20 times the molar amount of arsenic in the wet phosphoric acid for 30 min. The arsenic removal reaction is carried out at 75°C.

[0161] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0162] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 6:1 for 60 minutes. A negative pressure of -0.05 kPa is drawn from the top of the tower. The exhaust gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0163] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, yielding clarified arsenic-free phosphoric acid.

[0164] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX4 Hydrogen Form hydrogen cation exchange resin with a particle size of 200 mesh.

[0165] The dearsenic-degraded phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 5 hours.

[0166] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass.

[0167] 3) Pump the crystallizing raw acid into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the crystallizing raw acid in the reactor is maintained at 19°C. Start stirring at 100 rpm. Add rhomboid phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the crystallizing raw acid is 1:1000.

[0168] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 1℃ / h for 2 hours, followed by a constant temperature for 2 hours, until the phosphoric acid crystals in the raw material acid grew to 2-7 mm; then the temperature was increased to 35℃ at a rate of 40℃ / h and held for 30 minutes to melt away the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 15℃ / h to the final crystallization temperature of 5℃.

[0169] After crystallization, the material is discharged, and the resulting slurry is fed into a centrifuge to separate the crystals. The separated liquid acid is returned to the arsenic removal tower for recycling, and the separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare high-purity electronic-grade phosphoric acid with a mass concentration of 85%.

[0170] Example 6

[0171] The raw material, wet-process phosphoric acid, comes from a phosphate chemical plant in Hubei Province. The wet-process phosphoric acid contains 85.6% H3PO4 and 0.5% SO4. 2- The mass content of each element is less than 100 ppm, with Li at 2.15 ppb, Na at 29717 ppb, Mg at 388 ppb, Al at 398 ppb, K at 1439 ppb, Ca at 14287 ppb, Cr at 748 ppb, Mn at 172 ppb, Fe at 46058 ppb, Co at 7.36 ppb, Ni at 1525 ppb, Cu at 241 ppb, Zn at 760 ppb, Ga at 1.51 ppb, As at 2849 ppb, Ag at 413 ppb, Cd at 64 ppb, Ba at 5.16 ppb, and Pb at 315 ppb.

[0172] Preparation of high-purity electronic-grade phosphoric acid:

[0173] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 75°C. H2S gas is introduced from the bottom of the tower at a rate of 15 times the molar amount of arsenic in the wet phosphoric acid for 30 min. The arsenic removal reaction is carried out at 75°C.

[0174] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0175] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 6:1 for 60 minutes. A negative pressure of -0.05 kPa is drawn from the top of the tower. The exhaust gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0176] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, yielding clarified arsenic-free phosphoric acid.

[0177] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX4 Hydrogen Form hydrogen cation exchange resin with a particle size of 200 mesh.

[0178] The dearsenic-removed phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 3 hours.

[0179] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass.

[0180] 3) Pump the crystallizing raw acid into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the crystallizing raw acid in the reactor is maintained at 21°C. Start stirring at 100 rpm. Add rhombic phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the crystallizing raw acid is 1:2000.

[0181] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 0.5℃ / h for 2 hours, followed by a constant temperature for 2 hours, until the phosphoric acid crystals in the raw material acid grew to 2-7 mm; then the temperature was increased to 28℃ at a rate of 30℃ / h and held for 30 minutes to melt the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 7℃ / h to the final crystallization temperature of 13℃.

[0182] After crystallization, the material is discharged, and the resulting slurry is fed into a centrifuge to separate the crystals. The separated liquid acid is returned to the arsenic removal tower for recycling, and the separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare high-purity electronic-grade phosphoric acid with a mass concentration of 85%.

[0183] The final product acid (high-purity electronic-grade phosphoric acid) obtained from each embodiment was analyzed by ICP-MS, and the mass content of each metal impurity is shown in Table 1. The detection method used was inductively coupled plasma mass spectrometry (ICP-MS), and the ultrapure water used had an online resistivity ≥18.2 MΩ·cm at 25℃.

[0184] Table 1. Mass content of various metal impurities in the acid products of Examples 1-6

[0185]

[0186] As shown in Table 1, the total impurity content in the high-purity electronic-grade phosphoric acid obtained in the examples is <10 ppb, the content of most metal ions can be reduced to less than 0.1 ppb, and the content of a very small number of impurities that are difficult to completely remove, such as Fe and As, can also be controlled to less than 5 ppb.

[0187] Refer to the national standard document GB / T 28159-2011. The E1 standard is for ordinary electronic-grade phosphoric acid, with a relatively high impurity content, suitable for some electronic applications where purity requirements are not particularly stringent. The E2 standard represents high-purity electronic-grade phosphoric acid, meaning that the impurity content in the phosphoric acid is extremely low, meeting the manufacturing requirements of high-end electronic products. The impurity content requirements for national standard E1 ordinary electronic-grade phosphoric acid and national standard E2 high-purity electronic-grade phosphoric acid are shown in Table 2.

[0188] Table 2. Mass content of impurities in national standard E1 ordinary electronic grade phosphoric acid and national standard E2 high-purity electronic grade phosphoric acid

[0189]

[0190] As can be seen from Tables 1 and 2, the results of Examples 1 to 6 all far exceed the national standard E2, indicating that the phosphoric acid prepared by this invention has extremely high purity, far exceeding the requirements for high-purity electronic-grade phosphoric acid, which provides strong support for the production of higher-performance electronic products.

[0191] Comparative Example 1

[0192] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0193] Preparation of phosphoric acid:

[0194] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 80°C. H2S gas is introduced from the bottom of the tower at a rate of 5.0 L / min, which is 100 times the molar amount of arsenic in the wet phosphoric acid. The arsenic removal reaction is carried out at 80°C.

[0195] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0196] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 20:1 for 2 hours. A negative pressure of -0.05 kPa is drawn from the top of the tower. The exhaust gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0197] After hydrogen sulfide gas is removed, the phosphoric acid enters the second pressure filtration system for filtration, resulting in purified phosphoric acid.

[0198] Comparative Example 2

[0199] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0200] Preparation of phosphoric acid:

[0201] The ion exchange resin was washed with ultrapure water until the washing solution also met the electronic grade water standards. The selected resin was DOWEX® 50WX4 Sodium Form sodium cation exchange resin with a particle size of 100 mesh.

[0202] 150 kg of wet-process phosphoric acid was pumped into a resin tank for ion exchange, and the ion exchange residence time was 12 h.

[0203] The ion exchange solution after ion exchange is purified phosphoric acid.

[0204] Comparative Example 3

[0205] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0206] Preparation of phosphoric acid:

[0207] Wet-process phosphoric acid is pumped into a jacketed crystallizer. The initial temperature of the raw material acid for crystallization is maintained at 20°C by controlling the temperature of the medium in the jacket. Stirring is started at 100 rpm. Flaky phosphoric acid seed crystals (particle size range of 0.1~5 mm) are added and stirred for 30 min. The mass ratio of the phosphoric acid seed crystals to the raw material acid for crystallization is 1:2000.

[0208] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 1℃ / h for 2 hours, followed by a hold at that temperature for 1 hour; then the temperature was increased to 28℃ at a rate of 40℃ / h and held for 30 minutes to dissolve the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 5℃ / h to the final crystallization temperature of 8℃.

[0209] After crystallization, the material is discharged into a centrifuge to separate the crystals. The resulting liquid acid is returned to the arsenic removal tower for recycling. The separated phosphoric acid crystals are transferred to an acid conditioning tank and ultrapure water is added to prepare purified phosphoric acid with a mass concentration of 85%.

[0210] Comparative Example 4

[0211] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0212] Preparation of phosphoric acid:

[0213] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 70°C. H2S gas is introduced from the bottom of the tower at a rate of 2.5 L / min, which is 50 times the molar amount of arsenic in the wet phosphoric acid. The arsenic removal reaction is carried out at 70°C.

[0214] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0215] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 8:1 for 2 hours. A negative pressure of -0.05 kPa is drawn at the top of the tower. The exhaust gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0216] Phosphoric acid after the removal of hydrogen sulfide gas enters the second pressure filtration system for filtration, yielding arsenic-free phosphoric acid.

[0217] 2) Wash the ion exchange resin with ultrapure water until the washing solution also meets the electronic grade water standards. The selected resin is DOWEX® 50WX2 Hydrogen Form hydrogen cation exchange resin with a particle size of 100 mesh.

[0218] The dearsenic-degraded phosphoric acid is pumped into a resin tank for ion exchange, and the ion exchange residence time is 6 hours.

[0219] The ion-exchange solution was then concentrated; the resulting crystalline raw acid contained 85% phosphoric acid by mass, which is the purified phosphoric acid.

[0220] Comparative Example 5

[0221] The raw material, wet-process phosphoric acid, is the same as in Example 1;

[0222] Preparation of phosphoric acid:

[0223] 1) Pump 150 kg of wet phosphoric acid into the arsenic removal tower. The preheating temperature inside the tower is maintained at 80°C. H2S gas is introduced from the bottom of the tower at a rate of 2.5 L / min, which is 50 times the molar amount of arsenic in the wet phosphoric acid. The arsenic removal reaction is carried out at 80°C.

[0224] After the reaction is complete, the phosphoric acid enters the first pressure filtration system for filtration.

[0225] The obtained filtrate is pumped into the H2S removal tower. Nitrogen gas is blown into the H2S removal tower from the bottom at a gas-liquid ratio of 10:1 for 2 hours. A negative pressure of -0.05 kPa is drawn at the top of the tower. The discharged tail gas containing H2S enters the alkaline washing tower for neutralization and absorption, then enters the water washing tower for washing, and finally is discharged.

[0226] Phosphoric acid after hydrogen sulfide gas removal enters the second pressure filtration system for filtration to obtain arsenic-free phosphoric acid; it is then concentrated; the mass concentration of phosphoric acid in the resulting crystalline raw acid is 85%.

[0227] 2) Pump the crystallizing raw acid into the jacketed crystallizer. By controlling the temperature of the medium in the jacket, the initial temperature of the crystallizing raw acid in the reactor is maintained at 20°C. Start stirring at 300 rpm. Add rhombic phosphate seed crystals (particle size range of 0.1~5 mm) and stir for 30 min. The mass ratio of the phosphate seed crystals to the crystallizing raw acid is 1:2000.

[0228] Next, the jacketed crystallizer was subjected to gradient cooling: the first gradient was applied at a rate of 1℃ / h for 2 hours, followed by a hold at that temperature for 1 hour; then the temperature was increased to 28℃ at a rate of 40℃ / h and held for 30 minutes to dissolve the fine crystals in the phosphoric acid solution. The second gradient was applied at a rate of 10℃ / h to the final crystallization temperature of 8℃.

[0229] After crystallization, the material is discharged into a centrifuge to separate the crystals. The resulting liquid acid is returned to the arsenic removal tower for recycling. The separated phosphoric acid crystals are transferred to an acid conditioning tank and mixed with ultrapure water to prepare phosphoric acid with a mass concentration of 85%, which is the purified phosphoric acid.

[0230] The final acid products obtained from Comparative Examples 1-5 were analyzed by ICP-MS, and the mass content of each metal impurity is shown in Table 3. The detection method used was inductively coupled plasma mass spectrometry (ICP-MS), and the ultrapure water used had an online resistivity ≥18.2 MΩ·cm at 25℃.

[0231] Table 3. Mass content of various metal impurities in the acid of Comparative Examples 1-5

[0232]

[0233] As can be seen from Table 3:

[0234] After purification using chemical precipitation technology, the wet-process phosphoric acid in Comparative Example 1 yielded a product acid in which the As content was significantly reduced to below 10 ppb, but the SO4 content was significantly reduced. 2- The content of metallic impurities such as Na, Mg, Al, K, Ca, and Fe is still relatively high, exceeding several hundred ppb, and does not meet the electronic grade standard.

[0235] In Comparative Example 2, the wet-process phosphoric acid was purified using ion exchange technology to obtain the product acid. The content of metal cation impurities was significantly reduced, but the content of SO4 was... 2- Sodium-based ion exchange resins have a weaker impurity removal effect and do not meet electronic grade standards. Furthermore, sodium-type ion exchange resins can introduce sodium elemental impurities.

[0236] After the wet-process phosphoric acid in Comparative Example 3 was purified by recrystallization, the product acid was obtained. Similarly, the content of metal cation impurities was significantly reduced, but the removal effect on As was weak, and the removal of metal cations such as Ca and Fe did not meet the electronic grade standard.

[0237] Comparative Example 4's wet-process phosphoric acid was purified using a combination of chemical precipitation and ion exchange technology to obtain the product acid. It can be seen that all impurity indicators were significantly reduced, reaching the standard of ordinary electronic-grade phosphoric acid, but still falling short of high-purity electronic-grade phosphoric acid. Simultaneously, this process increased H2S consumption during chemical precipitation and overdrawn the capacity of the ion exchange resin, thus increasing post-processing costs.

[0238] Comparative Example 5's wet-process phosphoric acid was purified using a combination of chemical precipitation and crystallization techniques to obtain the product acid. Similarly, all impurity indicators were significantly reduced, meeting the standards for ordinary electronic-grade phosphoric acid, but still falling short of high-purity electronic-grade phosphoric acid. Furthermore, the chemical precipitation process resulted in higher H2S consumption and greater energy consumption.

[0239] As shown in Tables 2 and 3, the optimal results of Comparative Examples 4 and 5 only meet the national standard E1, indicating that the phosphoric acid purity obtained by the traditional method is relatively low and cannot meet the requirements of high-purity applications. This comparison allows the audience to clearly see the significant effectiveness of this invention in improving phosphoric acid purity, as well as its enormous potential and value in practical applications.

[0240] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high-purity electronic-grade phosphoric acid, comprising the following steps: S1. Wet phosphoric acid is preheated in the arsenic removal zone and mixed with hydrogen sulfide gas to carry out the arsenic removal reaction; then filtered in the first filtration zone, and the resulting filtrate enters the hydrogen sulfide removal zone. After removing hydrogen sulfide gas under the conditions of gas blowing and negative pressure, it enters the second filtration zone for filtration. S2. After ion exchange, the phosphoric acid treated in step S1 is used to obtain crystalline raw material acid; S3. The acid raw material for crystallization is stirred and mixed with phosphoric acid seed crystals in the crystallization zone, and then cooled and crystallized by process temperature control. The resulting crystal slurry is subjected to solid-liquid separation to obtain high-purity electronic-grade phosphoric acid.

2. The preparation method according to claim 1, characterized in that, In step S1, the gas blown in is used as a carrier gas and is selected from air, nitrogen or an inert gas. The gas-liquid ratio of the blown gas is 3~10:1; The duration of the inflation is 30-60 minutes.

3. The preparation method according to claim 1, characterized in that, In step S2, the ion exchange resin used in the ion exchange is a strongly acidic cation exchange resin. The particle size of the strongly acidic cation exchange resin is 100-200 mesh. The ion exchange residence time is 1 to 6 hours.

4. The preparation method according to claim 1, characterized in that, In step S1, the mass content of H3PO4 in the wet-process phosphoric acid is 85%~95%.

5. The preparation method according to claim 1, characterized in that, In step S1, the preheating temperature of the arsenic removal zone is 60~80℃.

6. The preparation method according to claim 1, characterized in that, In step S1, the amount of hydrogen sulfide gas introduced is 10 to 25 times the molar amount of arsenic in wet-process phosphoric acid.

7. The preparation method according to claim 1, characterized in that, In step S2, the mass concentration of phosphoric acid in the crystalline raw material acid is 85%~95%.

8. The preparation method according to claim 1, characterized in that, In step S3, before stirring and mixing the crystallizing raw acid with the phosphate seed crystals, the method further includes maintaining the temperature of the crystallizing raw acid at 15~30℃. The stirring speed is 20~300 rpm.

9. The preparation method according to claim 1, characterized in that, In step S3, the shape of the phosphate seed crystals is selected from rhomboid, plate-like, or spherical. The particle size range of the phosphate seed crystals is 0.1~5 mm; The mass ratio of the phosphate seed crystals to the crystallization raw material acid is 1:20~10000.

10. The preparation method according to claim 1, characterized in that, In step S3, the cooling crystallization is carried out using a process temperature control method, specifically as follows: a. First-gradient cooling: The solution after mixing the raw material acid and the phosphate seed crystals is cooled at a rate of 0.2~2℃ / h for 1~2 h; b. Maintain the temperature for 1-4 hours until the phosphate crystals in the raw acid of the crystallization material grow to 2-7 mm; c. Second-gradient cooling: Cooling to 0~15℃ at a rate of 0.3~7℃ / h.

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