Method, equipment and system for extracting and purifying phosphoric acid from anodic oxidation wastewater

Abstract

The invention discloses a method for extracting and purifying phosphoric acid from anodized chemical casting waste liquid, a purification device, and a system. The method relates to the technical fields of waste liquid recovery and phosphoric acid purification, and solves the technical problems of poor extraction effect and need to improve the purity of existing anodized chemical casting waste phosphoric acid. The method comprises S1 pretreatment; S2: adding an impurity remover to the chemical casting waste acid liquid obtained by preliminary filtering and removing impurities from S1, and performing solid-liquid separation after mixing to obtain a clear liquid and a precipitate; S3: performing negative pressure low-temperature evaporation on the clear liquid obtained in S2 to obtain a concentrated liquid; and S4: adding phosphoric acid seed crystals to the concentrated liquid in S3 to perform crystal growth and purification to obtain purified phosphoric acid. The purification system of the invention comprises a filtering device, a precipitation tank, a storage tank, a McLaval low-temperature evaporation device, and a purification device, which are sequentially arranged. The method has the technical effects of obtaining phosphoric acid with high purity, reaching electronic grade E1.

Description

Technical Field

[0001] The invention relates to the technical field of waste liquid recovery and phosphoric acid extraction and purification, and in particular to a method, purification equipment and system for extracting and purifying phosphoric acid from anodic oxidation polishing waste liquid. Background Art

[0002] In the anodizing process, chemical polishing waste liquid is primarily generated during the chemical polishing process. Chemical polishing is a surface treatment method that removes microscopic surface irregularities on the metal through chemical reactions, resulting in a smooth, shiny finish. During the chemical polishing of aluminum and aluminum alloys, a polishing fluid containing phosphoric acid is typically used. As the polishing process progresses, aluminum on the metal surface continuously dissolves into the polishing fluid. Simultaneously, the various acids in the polishing fluid chemically react with the metal, causing the composition of the polishing fluid to gradually change. When the composition and performance of the polishing fluid fail to meet polishing requirements, a large amount of chemical polishing waste liquid is generated. Existing technologies use monoacid phosphoric acid for chemical polishing, which greatly improves product quality. However, the phosphoric acid usage is high in concentration and costly, necessitating recycling to avoid unnecessary waste. Therefore, breakthroughs in recycling technology are urgently needed.

[0003] After analyzing the components of the chemical waste liquid, it was found that it mainly contains the following components:

[0004] 1. Phosphoric acid: As one of the main components of chemical polishing liquid, phosphoric acid dissolves metals and promotes polishing reactions during the chemical polishing process.

[0005] Phosphoric acid, a key inorganic compound, plays a vital role in modern industry. In agriculture, it's a core raw material for phosphate fertilizer production, playing an indispensable role in increasing crop yields and improving soil fertility, and is a crucial component of global food security. In the food processing industry, phosphoric acid is often used as an acidulant, preservative, and moisture retainer, effectively enhancing food's taste, extending its shelf life, and maintaining the freshness and juiciness of meat products.

[0006] The content of phosphoric acid in chemical wastewater is usually high and is the main recovery target of this study.

[0007] 2. Sulfuric acid: Sulfuric acid in the chemical polishing solution can increase the acidity of the solution, accelerate the dissolution of metals, and help improve the polishing effect. The content of sulfuric acid in the chemical polishing wastewater varies depending on the process formula and generally fluctuates within a certain range.

[0008] 3. Nitric acid: Nitric acid is a strong oxidizing agent and forms an oxide film during the chemical polishing process, which protects the metal surface and improves the polishing effect. However, nitric acid produces harmful gases such as nitrogen oxides during the reaction, which can pollute the environment. With increasing environmental protection requirements, some processes are reducing or eliminating the use of nitric acid.

[0009] 4. Aluminum ions: During the chemical polishing process, aluminum metal continuously dissolves into the solution, resulting in a large amount of aluminum ions in the chemical polishing wastewater. The presence of aluminum ions affects the properties of the chemical polishing wastewater and the difficulty of subsequent treatment. However, it is also a potential resource that can be considered for recycling.

[0010] 5. Other impurities: Chemical wastewater may also contain small amounts of additives, surfactants, metal impurities, and reaction by-products. The types and contents of these impurities vary depending on the process conditions and raw materials, and may have a certain impact on the treatment of chemical wastewater and the recovery of phosphoric acid.

[0011] At present, there are mainly the following methods for treating anodizing waste liquid:

[0012] 1. Neutralization: This is a common treatment method. Alkaline substances, such as sodium hydroxide and calcium hydroxide, are added to the chemical wastewater to neutralize the acid in the wastewater, bringing the pH value of the wastewater to neutral or near-neutral. The wastewater can then be discharged or further treated. The neutralization process is simple and easy to operate, but it has some significant disadvantages. First, the neutralization reaction produces a large amount of salt precipitates, such as calcium sulfate and calcium phosphate, which require subsequent treatment, increasing the cost and difficulty of treatment. Second, neutralization only converts the acidic substances in the wastewater into salts and does not achieve resource recycling, resulting in the waste of valuable resources such as phosphoric acid. In addition, the neutralization process may cause secondary pollution. For example, excessive use of alkaline substances may cause the pH value of the water to be too high, posing a threat to the environment.

[0013] 2. Hazardous Waste Disposal: Because chemical waste liquid contains large amounts of acidic substances and heavy metal ions, it is classified as hazardous waste. Some companies choose to collect the chemical waste liquid and entrust it to professional hazardous waste disposal units for treatment. Hazardous waste disposal units typically use incineration, landfilling, and other methods for final disposal of chemical waste liquid. While these treatment methods can ensure the safe treatment of the waste liquid, they are extremely costly and require high hazardous waste disposal fees. In addition, disposal methods such as incineration and landfilling can have certain impacts on the environment. For example, incineration may produce harmful gases, and landfilling may cause soil and groundwater contamination.

[0014] 3. Evaporation and concentration: The waste liquid is concentrated by heating it to evaporate its water content. Evaporation and concentration can reduce the volume of the waste liquid, facilitating subsequent treatment or disposal. However, this method consumes a lot of energy and requires a large investment in equipment, and its effectiveness in treating high-concentration waste acid is limited. The evaporation process may also generate harmful gases such as acid mist, which require effective collection and treatment to prevent environmental pollution.

[0015] 4. Membrane separation technology: Membrane technologies, such as membrane filtration, membrane evaporation, and reverse osmosis, can separate and recover solvents, metal ions, and organic matter from chemical wastewater. Membrane separation technology offers advantages such as high separation efficiency, low energy consumption, and simple operation. However, it requires significant investment in technology and equipment, and the membrane's lifespan and maintenance costs also need to be considered. Furthermore, membrane separation technology requires high pretreatment requirements for chemical wastewater, otherwise it can easily lead to membrane contamination and clogging, affecting separation effectiveness and membrane lifespan.

[0016] 5. Ion Exchange: Ion exchange resins are used to adsorb and release ions, removing metal ions and other harmful ions from chemical wastewater, thereby purifying and recycling the wastewater. Ion exchange is relatively simple to operate, offers high waste acid recovery efficiency, and effectively removes metal ions, reducing fresh acid usage and wastewater treatment costs. However, ion exchange resins are expensive and require regular regeneration and replacement, increasing treatment costs and operational complexity.

[0017] In summary, existing methods for treating waste liquid from chemical waste generally suffer from high costs, waste of resources, and environmental pollution. With increasingly stringent environmental protection requirements and growing awareness of resource recycling, developing an efficient, low-cost, environmentally friendly, and effective extraction and purification technology for treating waste liquid from chemical waste, and realizing the recycling of resources such as phosphoric acid, is of great practical significance and market demand. Summary of the Invention

[0018] The technical problem to be solved by the present invention is that the existing treatment cost of anodizing waste liquid is high and the treatment effect is poor. The present invention provides a method, purification equipment and system for extracting and purifying phosphoric acid from anodizing waste liquid.

[0019] A method for extracting and purifying phosphoric acid from anodic oxidation waste liquid comprises the following steps:

[0020] S1: Preliminary filtration and impurity removal of the waste acid solution to be treated;

[0021] S2: adding impurity remover to the waste acid liquid obtained by preliminary filtration and impurity removal in S1 and performing solid-liquid separation after mixing to obtain clear liquid and precipitate;

[0022] S3: subjecting the clear liquid obtained in S2 to negative pressure low temperature evaporation to obtain a concentrated liquid;

[0023] S4: Phosphoric acid seed crystals are added to the concentrated solution in S3 to perform multi-stage crystal growth purification to obtain purified phosphoric acid. Multi-stage crystal growth refers to multi-angle and different directions, which can accelerate the reaction process.

[0024] The present invention preferably provides a method for extracting and purifying phosphoric acid from anodized chemical waste liquid, wherein in S2, the impurity remover is a polyferric sulfate solution, the addition amount of which is 0.05%-0.2% of the volume of the chemical waste acid liquid, and the concentration of the polyferric sulfate solution is 10-20wt%.

[0025] The S3 utilizes McLaval technology for negative pressure, low-temperature evaporation. This innovative technology, based on unique fluid dynamics principles, achieves high-efficiency negative pressure, low-temperature evaporation. Its core lies in the ingenious use of specially designed vortex tubes and nozzle tube structures. By precisely controlling the flow rate and pressure of the fluid, it achieves efficient evaporation in extremely low-pressure environments.

[0026] In McLaval technology equipment, a highly efficient vacuum pump or other pressure-reducing device rapidly reduces the pressure within the system to a level far below atmospheric pressure, typically reaching negative pressures of -96kPa to -99kPa or even lower. This negative pressure significantly lowers the boiling point of the liquid, a key factor in achieving low-temperature evaporation.

[0027] The present invention preferably provides a method for extracting and purifying phosphoric acid from anodized waste liquid, wherein the negative pressure low temperature evaporation in S3 is performed twice, namely, a first negative pressure low temperature evaporation and a second negative pressure low temperature evaporation, the pressure of the negative pressure low temperature evaporation is -96~-98kPa, and the temperature of the low temperature evaporation is 25°C-36°C.

[0028] The present invention preferably provides a method for extracting and purifying phosphoric acid from anodized waste liquid, wherein the pressure of the first negative pressure low temperature evaporation is -96 kPa, the temperature of the first negative pressure low temperature evaporation is 32°C to 33°C, the pressure of the second negative pressure low temperature evaporation is -98 kPa, and the temperature of the second negative pressure low temperature evaporation is 25°C to 28°C.

[0029] Preferably, before the negative pressure low temperature evaporation, when the chemical waste liquid to be treated is introduced into the McLaval device, it is initially filtered through a stainless steel filter with a pore size of 50 μm to remove large particle impurities such as metal debris, dust, etc. that may be present in the chemical waste liquid.

[0030] Preferably, in S2, the filtered waste liquid is placed in a stirred tank for stirring, and an appropriate amount of impurity remover polyferric sulfate is slowly added. The effect of the impurity remover is to aggregate the tiny suspended particles in the waste liquid to form larger flocs, which is convenient for subsequent precipitation and separation. After stirring for a period of time, the waste liquid is allowed to stand and settle for a certain time. After precipitation is complete, the clear liquid is transferred to a clean storage container using a siphon method, and the precipitation at the bottom is further processed or properly disposed of. The impurity content of the pretreated chemical waste liquid is significantly reduced, and aluminum ions and iron ions form impurity precipitation, which is peeled off from the liquid, providing a purer raw material for subsequent evaporation and purification steps.

[0031] Preferably, negative pressure low-temperature evaporation in S3 is achieved by passing the treated chemical waste liquid in S2 into a specially designed vortex tube. This vortex tube contains multiple carefully designed spiral channels. During its high-speed flow, the waste liquid swirls along these channels, forming powerful vortices. This vortex effect imparts additional kinetic energy to the molecules in the waste liquid, while also increasing mutual collisions and friction between molecules, further promoting evaporation.

[0032] After being accelerated and boosted by the vortex tube, the waste liquid enters the nozzle tube. The nozzle tube's design accelerates the waste liquid to an extremely high velocity in a very short time, forming a high-speed jet. Upon entering the evaporation space, this high-speed jet rapidly diffuses and exchanges heat with the surrounding low-temperature environment, instantly evaporating the water in the waste liquid into water vapor.

[0033] During the evaporation process, water vapor is cooled by a condenser, causing it to recondense into liquid water, effectively separating the water from other components in the chemical waste liquid. Furthermore, by precisely controlling parameters such as temperature, pressure, and flow rate during the evaporation process, the various components in the chemical waste liquid can be fully separated and recovered, improving resource utilization and treatment effectiveness. By reducing the system pressure through vacuum pumping, the boiling point of the solution is lowered, allowing the water to evaporate rapidly at a lower temperature, thereby increasing the saturation of the salts. Using a negative pressure of -96kPa to -98kPa not only accelerates water evaporation but also prevents salts from decomposing or reacting with other substances at high temperatures, which helps specific salts reach saturation and crystallize at relatively low temperatures.

[0034] The principle and technology of the above-mentioned negative pressure low temperature evaporation can be found in patent CN214617244U - a vacuum generator, and the negative pressure low temperature evaporation equipment can be found in patent CN114573493B - a method for purifying methyl pyrrolidone waste liquid.

[0035] Chemical waste liquid contains a variety of components, some of which are sensitive to temperature and prone to decomposition, oxidation, or other chemical reactions under high temperature conditions, thus affecting the quality and efficiency of phosphoric acid recovery. The low-temperature evaporation characteristics of the McLaval technology provide mild conditions for the treatment of chemical waste liquid, effectively avoiding the occurrence of these adverse reactions. Throughout the treatment process, key components such as phosphoric acid can maintain relatively stable chemical properties, reducing the generation of impurities and improving the purity and recovery rate of phosphoric acid. These mild treatment conditions enable the McLaval technology to better retain valuable components when treating chemical waste liquid, achieving maximum resource recovery.

[0036] In the actual operation of purifying phosphoric acid from anodized chemical blasting liquid, the wastewater can be concentrated and the salt crystals collected in a relatively short time, improving treatment efficiency and meeting the processing speed and output requirements of industrial production. Compared with other traditional separation technologies, the McLaval technology can more quickly and thoroughly separate the various components in the chemical blasting wastewater, providing a purer raw material for subsequent phosphoric acid purification.

[0037] The present invention preferably provides a method for extracting and purifying phosphoric acid from anodized waste liquid. In S4, the amount of phosphoric acid seed crystals added is 2-10% of the mass of the concentrated liquid, the crystal growth temperature is 8-12° C., and the crystal growth time is 10-30 h.

[0038] The present invention preferably provides a method for extracting and purifying phosphoric acid from anodized waste liquid. In S4, ultrasonic-assisted stirring is also used during the crystallization process. When ultrasonic-assisted stirring is used, the amount of phosphoric acid seed crystals added is 6-10% of the mass of the concentrated liquid, the crystal growth temperature is 8-10°C, and the crystal growth time is 11-12h.

[0039] The present invention preferably provides a method for extracting and purifying phosphoric acid from anodized wastewater, further comprising further purifying the phosphoric acid obtained in S4 to obtain electronic-grade phosphoric acid, the steps being as follows:

[0040] S5: The solid phosphoric acid that has been grown in S4 is subjected to solid-liquid separation. After the solid crystalline phosphoric acid is heated to liquefaction, it is stirred. The growth temperature is stabilized at 8-12°C, and pre-prepared electronic grade pure phosphoric acid seed crystals are slowly added in an amount of 2% of the liquid mass.

[0041] S6: Repeat S5 to obtain electronic grade phosphoric acid.

[0042] Preferably, in S5 and S6, the phosphate seed crystals are first subjected to particle size control and pre-dispersion, wherein the seed crystal particle size control range is 1~5μm, and the pre-dispersion method is: the seed crystals are first dissolved in a small amount of pure phosphoric acid to make a low-concentration suspension, and then pre-treated with low-frequency ultrasound 20~50kHz for 10~30 minutes (low-frequency ultrasound has a weak cavitation effect but more uniform vibration, which is suitable for fine particle dispersion), so that the seed crystal particles are deagglomerated into a monodisperse state, and then added to the main crystallization system.

[0043] Preferably, ultrasonic assisted crystallization is further added in S5 and S6, wherein low frequency and medium-high power are used in the seed addition stage, wherein the low frequency range is 20~40kHz, and the medium-high power range is 500~800W; and high frequency and medium-low power are switched in the crystal growth stage, wherein the high frequency range is 60~100kHz, and the medium-low power range is 300~500W.

[0044] In ultrasound-assisted crystallization, the ultrasonic cavitation effect and mechanical vibration can promote nucleation (increasing the seed population) and shorten the induction period. However, if the seed population is not dispersed promptly, localized high concentrations can easily lead to agglomeration, resulting in uneven crystal size and impurity inclusion (affecting the purity and crystal morphology of electronic-grade phosphoric acid). Therefore, achieving high-purity phosphoric acid crystals requires a dual optimization approach: "dispersion enhancement" and "growth regulation."

[0045] An extraction and purification device for phosphoric acid in anodized waste liquid, used for growing crystals in the above method, comprises a tank body and a stirring assembly. The tank body is provided with a jacket structure for inputting and discharging cooling medium to provide temperature conditions for cooling crystallization.

[0046] The stirring assembly includes a drive motor, a stirring shaft and a stirring paddle. One end of the stirring shaft is connected to the drive motor at the top of the tank body, and the other end penetrates into the tank body and is connected to the stirring paddle. The stirring paddle is provided with three layers of blades along the axial direction of the stirring shaft. From top to bottom, the first layer of blades is longer than the second layer of blades, and the second layer of blades is longer than the third layer of blades.

[0047] A channel is provided on the outer wall of the stirring shaft, a through hole is provided in the middle of the blade, one end of the through hole extends to the free end of the blade, the other end of the through hole is connected to the stirring shaft, one end of the channel extends outwardly to the outside of the tank body, and the other end of the channel is connected to the through hole, providing a channel for adding seed crystals.

[0048] A system for extracting and purifying phosphoric acid from anodized wastewater is provided, which is used to implement the above method and comprises a filtering device, a precipitation tank, a storage tank, a McLaval low-temperature evaporation device and a jacketed purification device connected in sequence.

[0049] The present invention has the following beneficial effects:

[0050] (1) The present invention aims to achieve large-scale mass production and recycling through a new process, greatly saving the cost of treating waste liquid and improving the feasibility of recycling; by adopting innovative technical means, phosphoric acid is successfully extracted and purified from anodizing waste liquid to obtain phosphoric acid products that meet industrial-grade standards and electronic-grade high-purity phosphoric acid.

[0051] (2) The present invention utilizes the McLaval technique to achieve efficient evaporation and extraction of water from wastewater and crystallization separation of salts by precisely controlling vacuum pressure and temperature conditions, laying the foundation for the subsequent purification of electronic-grade phosphoric acid. Subsequently, by introducing a unique ice-induced flip-chip technology, homemade phosphoric acid seed crystals are used to slowly stimulate the ice-induced crystal growth of the concentrated solution from multiple angles, achieving efficient separation of phosphoric acid and water within a specific temperature range, thereby obtaining high-purity industrial-grade phosphoric acid, which is then further purified through crystallization to obtain electronic-grade phosphoric acid.

[0052] (3) The present invention is a breakthrough in phosphoric acid purification technology. On the basis of producing industrial-grade phosphoric acid, the second stage of electronic-grade purification is carried out. This greatly reduces the cost of purifying phosphoric acid and solves the problem of over-reliance on the cost of imported electronic-grade phosphoric acid and the constraints and costs of foreign companies.

[0053] (4) The present invention achieves uniform dispersion of seed crystals while increasing the amount of seed crystals and shortening the crystallization time, thereby ultimately improving the crystallization quality of electronic-grade phosphoric acid, by combining strategies such as seed crystal pretreatment and step-by-step addition, ultrasonic parameter optimization process, coordinated ultrasonic stirring, and reasonable setting of temperature gradient during the crystallization process.

[0054] (5) The present invention improves the dispersion performance of seed crystals by adjusting the purification equipment, thereby improving the crystallization quality of phosphoric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0056] Figure 1 It is a flowchart of the overall process of the present invention;

[0057] Figure 2 This is a schematic cross-sectional view of the purification equipment structure of the present invention;

[0058] Figure 3 This is a schematic diagram of the structure of the stirring assembly of the purification equipment structure of the present invention;

[0059] Figure 4 This is a schematic diagram of the structure of the stirring assembly of the purification equipment of the present invention viewed from below the feeding hopper.

[0060] In the accompanying drawings, the names of the components are as follows:

[0061] 1-tank body, 2-jacket, 3-stirring shaft, 4-drive motor, 5-stirring paddle, 501-first layer of paddle blades, 502-second layer of paddle blades, 503-third layer of paddle blades, 504-through hole, 6-channel, 7-hopper, 8-discharge port, 9-feed port. DETAILED DESCRIPTION

[0062] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0063] 1. Experimental Materials

[0064] The anodizing wastewater used in the present embodiment was obtained from an anodizing production line. Its main components, including phosphoric acid content, sulfuric acid content, and aluminum ion concentration, were precisely tested. Specific data are shown in Table 1 below. To ensure the accuracy and reliability of the experiment, 99.9% pure phosphoric acid seed crystals (for industrial-grade phosphoric acid crystal growth) and electronic-grade phosphoric acid seed crystals were prepared as key materials for the subsequent ice-shock separation step. Other chemical reagents, such as sodium hydroxide and calcium hydroxide, were also used to adjust the pH and aid the reaction.

[0065] Table 1. Composition of anodizing wastewater (based on one ton of wastewater)

[0066]

[0067] 2. Experimental Equipment

[0068] The McLaval low-temperature evaporation equipment is equipped with advanced vortex tubes and nozzle tubes, which can achieve a stable negative pressure environment and precise temperature control. It ensures that the waste liquid temperature is stably controlled between 25°C and 33°C under negative pressure conditions of -96kPa to -98kPa, meeting the experimental requirements for negative pressure low-temperature evaporation. In addition, a high-precision electronic balance is used to accurately weigh the waste liquid, chemical reagents, and experimental products, with an accuracy of up to 0.001g, effectively ensuring the accuracy of the experimental data. At the same time, it is equipped with a digital thermometer that can monitor temperature changes during the reaction in real time with an accuracy of ±0.1°C, ensuring that the experiment is carried out within the set temperature range. To detect the purity and concentration of the product, advanced ion chromatographs, plasma mass spectrometers, graphite furnace atomic absorption spectrometers, and spectrophotometers are used, and the Karl Fischer coulometric method is used for moisture determination.

[0069] Example 1

[0070] A method for extracting and purifying phosphoric acid from anodizing waste liquid comprises the following steps:

[0071] S1: Collection and pretreatment of chemical waste liquid

[0072] Use corrosion-resistant plastic tanks to collect chemical polishing waste liquid from the anodizing production line's discharge outlet. Ensure the tanks are tightly sealed during the collection process to prevent leakage and volatilization. Once collected, the waste liquid is transferred to a pretreatment unit. Initially, it undergoes preliminary filtration through a 50μm stainless steel filter to remove any large impurities, such as metal debris and dust.

[0073] S2: The waste acid liquid obtained by preliminary filtration and impurity removal of S1 is added with an impurity remover and mixed, and then solid-liquid separation is performed to obtain a clear liquid and a precipitate.

[0074] The filtered waste liquid was placed in a stirring tank and stirred at a speed of 150r / min. At the same time, a scavenger was slowly added. The scavenger was polyferric sulfate (PFS), and the addition amount was 0.1% of the waste liquid volume. The polyferric sulfate (PFS) was configured to a concentration of 20%. The scavenger's function was to aggregate the tiny suspended particles in the waste liquid into larger flocs, which facilitated subsequent precipitation and separation. 3+ and Fe 3+ With PO4 3-Phosphate precipitates, such as AlPO4 and FePO4, form. After stirring for 15 minutes, stop stirring and allow the wastewater to settle for 2 hours. Once precipitation is complete, the clear liquid is transferred to a clean storage container by siphoning, while the precipitate at the bottom is further processed or properly disposed of. This pre-treated wastewater significantly reduces its impurity content, providing a purer feedstock for subsequent evaporation and purification steps.

[0075] Due to the small amount of sulfate and calcium ions in the anodizing process, the present invention uses polyferric sulfate PFS as an impurity remover. The principle is:

[0076] Due to the strong acidity of chemical waste liquid, it is necessary to avoid the introduction of harmful impurities (such as Cl - ), requires efficient removal of metal ions and suspended particles, the recommended impurity remover polyferric sulfate (PFS) has the following advantages: wide applicable pH range (1-11), can still be efficiently hydrolyzed to form Fe (OH) 3 colloid under strong acidic conditions, with large and dense body and fast sedimentation rate, and has no effect on metal ions (such as Fe 3+ 、Cu 2+ 、Al 3+ ) has a strong adsorption and removal capacity. The introduced sulfate ion (SO4 2- ), rather than chloride ions, which have little impact on the purity of phosphoric acid (sulfate can be separated from the phosphoric acid in a subsequent crystallization step or partially removed with water during evaporation). The sediment has good dehydration properties and contains no chloride ions, minimizing the risk of secondary contamination.

[0077] S3: subjecting the clear liquid obtained in S2 to negative pressure low temperature evaporation to obtain a concentrated liquid;

[0078] S31: First negative pressure low temperature evaporation

[0079] The pretreated chemical waste liquid is slowly injected into the evaporation chamber of the McLaval low-temperature evaporation system. The vacuum pump is activated to rapidly reduce the system pressure to -96 kPa. Under negative pressure, the heating device is activated, indirectly heating the evaporation chamber through a hot water circulation system, gradually raising the waste liquid temperature to 32°C-33°C. Under these temperature and pressure conditions, the water in the waste liquid begins to evaporate rapidly, forming water vapor. As the water vapor rises, it passes through the high-efficiency condenser inside the system, where it is cooled to around 20°C. It then condenses back into liquid water and is collected in a condensate storage tank. As the water evaporates, the salt in the waste liquid gradually crystallizes and adheres to the inner walls and bottom of the evaporation chamber. When the evaporation process reduces the waste liquid volume to approximately 50% of its original volume, the heating and vacuum pump are stopped. The central coil inside the evaporator fully transfers heat to the waste liquid, raising its temperature. The pump flow rate can be adjusted to control heat absorption by the liquid, thereby minimizing evaporation energy consumption. After the first negative pressure low-temperature evaporation, most of the water and salt in the waste liquid were effectively separated, laying the foundation for the next step of concentration and purification.

[0080] S32: Second negative pressure low temperature evaporation

[0081] The concentrated liquid collected after the first evaporation is reinjected into the secondary McLaval low-temperature evaporation equipment, and the vacuum pump is restarted to reduce the pressure to -98kPa. At this lower pressure, the heating device is turned on again to maintain the temperature of the concentrated liquid at 25°C to 28°C, allowing the remaining water to continue evaporating. Similar to the first evaporation, the water vapor is cooled by the condenser and collected in the condensate storage tank. As the water evaporates further, the ratio of phosphoric acid to water in the concentrated liquid gradually increases, and the liquid specific gravity gradually approaches 1.80 to 1.88. When the liquid specific gravity reaches approximately 1.80, the evaporation process is stopped. At this point, the concentration of phosphoric acid in the resulting concentrated liquid has increased significantly. The results of multiple tests have shown that the corresponding parameters are as follows:

[0082] When the specific gravity of phosphoric acid is 1.8, the mass fraction concentration of phosphoric acid (H3PO4) is about 90%;

[0083] When the specific gravity of phosphoric acid is 1.834, the mass fraction concentration of phosphoric acid (H3PO4) is about 95%;

[0084] When the specific gravity of phosphoric acid is 1.88, the mass fraction concentration of phosphoric acid (H3PO4) is about 98%.

[0085] This provides suitable raw materials for subsequent ice-shock separation. The second negative pressure low-temperature evaporation further improves the purity and concentration of phosphoric acid in the concentrate, reduces the water content, and creates favorable conditions for achieving efficient separation of phosphoric acid and water. Here are some notes on the experimental analysis data:

[0086] In the second stage of low-temperature evaporation purification of phosphoric acid (-98kPa, 25℃), when the phosphoric acid concentration is increased to above 80%, a small amount of Al 3+ and Fe 3+ With PO4 3- The process of combining to form phosphate precipitation involves the following key reference data and mechanisms:

[0087] 1. Reaction mechanism of phosphate precipitation Al 3+ With PO4 3- The aluminum ions react with phosphate to form aluminum phosphate (AlPO4) precipitation. The reaction equation is: Al 3+ + PO4 3- →AlPO4↓.

[0088] The solubility product (Ksp) of AlPO4 is about 1×10 -22 In high concentration phosphoric acid, due to H + Higher concentrations can inhibit PO4 3- dissociation, but Al 3+ Can still be obtained by mixing with H2PO4 - or HPO4 2- Combine to form a precipitate.

[0089] Fe 3+ With PO4 3- The reaction of iron ions and phosphate to form iron phosphate (FePO4) precipitation, the reaction equation is: Fe 3+ + PO4 3- →FePO4↓.

[0090] The Ksp of FePO4 is about 9.91×10 -29 , its solubility is extremely low and it is easier to precipitate under acidic conditions.

[0091] 2. Key influencing factors and data

[0092] Effect of phosphoric acid concentration

[0093] When the phosphoric acid concentration exceeds 80%, the ionic strength of the solution increases significantly, resulting in a further decrease in the solubility of phosphate.

[0094] For example: In 85% phosphoric acid, the solubility of AlPO4 can be reduced to <0.01 g / L, and the solubility of FePO4 is even lower, usually below <0.001 g / L.

[0095] The effect of temperature and negative pressure

[0096] Temperature: At 25°C, the solubility of phosphate is low, which is conducive to the formation of precipitation.

[0097] Negative pressure (-98kPa): Promotes water evaporation by lowering the boiling point and accelerates the concentration of phosphoric acid.

[0098] pH value control In high concentration phosphoric acid, the pH value of the solution is low (usually < 1), at this time PO4 3- Mainly H2PO4 - Form exists.

[0099] The reference data is summarized in Table 2 below:

[0100] Table 2. Phosphate characteristic data

[0101]

[0102] Due to the negative pressure and low temperature evaporation concentration of the McLaval, the phosphate removal effect is very good.

[0103] S4: adding phosphoric acid seed crystals to the concentrated solution in S3 and performing multi-stage crystal growth purification to obtain purified phosphoric acid.

[0104] The concentrate from the second evaporation was transferred to a jacketed reactor, which was filled with a low-temperature coolant to precisely control the reaction temperature. The agitator was activated and stirred at 80 rpm. When the temperature of the concentrate stabilized at 10°C, pre-prepared phosphoric acid seed crystals were slowly added, at a rate of 5% of the concentrate's mass. With the addition of the phosphoric acid seed crystals, the phosphoric acid molecules in the concentrate began to crystallize around the seed crystals, forming a solid structure similar to ice cream, while the water was gradually displaced into the liquid phase. During this process, the reaction temperature was strictly controlled between 8°C and 10°C by adjusting the flow rate and temperature of the coolant in the jacket to ensure sufficient crystallization of the phosphoric acid and prevent the water from freezing. Stirring and reaction were continued for 22 hours to allow the ice cream to fully develop and stabilize. During this period, the reactor was regularly observed, and changes in parameters such as temperature and stirring time were recorded. After a period of reaction, the phosphoric acid and water were effectively separated, with the phosphoric acid existing as a solid ice cream in the reactor, while the water remained in the liquid phase.

[0105] After the ice-shock separation reaction is complete, stop stirring and discontinue the coolant supply. Slowly drain the liquid from the tank through the discharge valve at the bottom and collect it in a waste liquid collection bucket. This liquid, primarily water containing a small amount of phosphoric acid, can be further mixed with the primary treatment liquid for purification or recycling. The solid ice-shock from the tank is then removed and placed in a vacuum drying oven at 40°C for 2 hours to remove any residual surface moisture. The dried solid is the purified phosphoric acid. Accurately weigh the phosphoric acid using an electronic balance, and record the yield data. Next, analyze and test the phosphoric acid for impurities, such as sulfate ions, aluminum ions, trace metals, and arsenic, to determine whether their content meets the standard requirements for electronic-grade phosphoric acid.

[0106] Example 2

[0107] The difference between this embodiment and embodiment 1 is that ultrasonic-assisted stirring is added in S4 to improve the ice-induced crystal growth speed and efficiency. At 8°C - 10°C and 39 kHz ultrasonic wave, the optimized seed amount is 7% (mass ratio), and the crystal growth time can be shortened to 11 hours. The ultrasonic-assisted stirring is set at the bottom of the tank, and the ultrasonic power is 400 W.

[0108] Example 3

[0109] This embodiment differs from Example 2 in that it further includes step S5, wherein the solid phosphoric acid, having completed crystal growth, is collected and heated until liquefied. The stirring device is then turned on again, and the industrial-grade phosphoric acid obtained in step S4 is stirred at a speed of 50 r / min. When the temperature stabilizes at 10°C, pre-prepared pure phosphoric acid seed crystals are slowly added. The seed crystals have a particle size of 5 μm and are added in an amount equivalent to 2% of the mass of the liquid. With the addition of the phosphoric acid seed crystals, the phosphoric acid molecules in the liquid begin to crystallize around the seed crystals, rapidly forming a solid structure similar to ice cream. Water and trace amounts of heavy metals and arsenic are gradually expelled into the liquid phase. After S5, crystallization is repeated once more, i.e., S6.

[0110] After the ice-shock separation reaction is complete, stirring and the supply of coolant are stopped. The liquid in the tank is slowly drained through the discharge valve at the bottom and collected in a waste liquid collection bucket. This liquid, primarily water containing a small amount of phosphoric acid, can be further mixed with the primary treatment liquid for purification or recycling. The solid ice-shock in the tank is then removed and placed in a vacuum drying oven at 40°C for 2 hours to remove any residual surface moisture. The dried solid is ultrapure phosphoric acid. The phosphoric acid is accurately weighed using an electronic balance, and the yield data is recorded. The phosphoric acid is then analyzed for impurity ions, such as sulfate ions, aluminum ions, and trace amounts of heavy metals and arsenic, to determine whether their levels meet the standard requirements for electronic-grade phosphoric acid.

[0111] Example 4

[0112] The difference between this embodiment and embodiment 3 is that in S5 and S6, the phosphoric acid seed crystals are slowly added to the tank after particle size control and pre-dispersion. The specific processing method is as follows:

[0113] Seed crystal size control:

[0114] Control the seed crystal particle size for grinding and classification to 2μm. Fine-grained seed crystals have a large specific surface area and are easier to disperse under ultrasound. Avoid using coarse-grained seed crystals, as they have large inertia and it is difficult for ultrasound to overcome the agglomeration force.

[0115] Pre-dispersion:

[0116] The seed crystals were first dissolved in a small amount of pure phosphoric acid at a mass ratio of 1:10 to form a low-concentration suspension. The suspension was then pretreated with 30kHz low-frequency ultrasound for 10 minutes. The low-frequency ultrasound had a weak cavitation effect but more uniform vibration, which was suitable for fine particle dispersion. The seed crystals were deagglomerated into a monodisperse state before being added to the main crystallization system.

[0117] Example 5

[0118] This Example differs from Example 4 in that the phosphoric acid seed crystals were added in a different manner. Specifically, the total seed crystal suspension was added in three separate additions, with 15-minute intervals between each addition. An initial addition of 30% of the total amount triggered initial nucleation. In the subsequent two additions, ultrasonic vibrations were applied at a power of 700 W and a frequency of 30 kHz to rapidly disperse the newly added seed crystals and maintain their dispersion until the seeds were completely and evenly distributed, and then until crystal growth was complete.

[0119] Example 6

[0120] The difference between this embodiment and embodiment 5 is that the ultrasonic parameters are different. Specifically, the ultrasonic power is 400W and the frequency is 80kHz. Ultrasonic vibration is used to quickly disperse the newly added seeds and maintain the dispersion until the seeds are completely evenly distributed, and then until the crystal growth is completed.

[0121] Example 7

[0122] The difference between this embodiment and embodiment 6 is that the ultrasonic power and frequency parameters are set differently, specifically:

[0123] Low-frequency ultrasound (20-40kHz) has a strong cavitation effect and is suitable for breaking up agglomerated seed crystals. High-frequency ultrasound (60-100kHz) provides more uniform vibration and is suitable for maintaining a dispersed state. Experimental results show that low frequency combined with medium-to-high power (500-800W) during the seeding phase provides rapid dispersion. During the crystal growth phase, switching to high frequency combined with medium-to-low power (300-500W) reduces impact on the crystal while maintaining uniformity. Specifically, in this embodiment, 30kHz was selected for the low frequency, 80kHz for the high frequency, 700W for the medium-to-high power, and 400W for the medium-to-low frequency.

[0124] Example 8

[0125] The difference between this embodiment and embodiment 7 is that the ultrasound mode is different, specifically:

[0126] Continuous ultrasound can easily lead to local heating of the system and excessive crystal fragmentation. The local heating will affect the crystallization equilibrium. The intermittent mode of "ultrasound for 5 to 10 seconds + pause for 10 to 20 seconds" is adopted to ensure the dispersion of crystal seeds, leave time for crystal growth, and reduce non-stable agglomeration.

[0127] Example 9

[0128] The difference between this embodiment and embodiment 8 is that the stirring speed of the crystallization is 150 r / min.

[0129] Example 10

[0130] The difference between this embodiment and embodiment 8 is that the temperature gradient control is different: when the seed crystals are added, the temperature is controlled to be slightly higher than the crystallization temperature, which can be 14°C, to reduce agglomeration caused by instantaneous precipitation of the seed crystals; after ultrasonic dispersion, the temperature is slowly lowered at 0.5°C / min to provide a uniform growth driving force for the dispersed seed crystals, thereby avoiding local secondary nucleation caused by rapid cooling.

[0131] Example 11

[0132] The difference between this embodiment and embodiment 10 is that the seeds are added from different angles through the modified purification equipment, such as Figure 2-Figure 4 In the equipment shown, the position of the seed crystals below the liquid surface is also different. Specifically, the seed crystals are added in three batches with a difference of 120° and an interval of 15 minutes.

[0133] Example 12

[0134] A device for extracting and purifying phosphoric acid from anodized polishing liquid comprises a tank body 1 and a stirring assembly. The tank body 1 is provided with a jacket 2 structure for inputting and discharging a cooling medium to provide temperature conditions for cooling and crystallization. The stirring assembly comprises a drive motor 4, a stirring shaft 3, and a stirring paddle 5. One end of the stirring shaft 3 is connected to the drive motor 4 at the top of the tank body 1, and the other end penetrates the interior of the tank body 1 and is connected to the stirring paddle 5. The stirring paddle 5 is provided with three layers of blades along the axial direction of the stirring shaft 3. Each layer of blades includes two symmetrical blades. From top to bottom, the first layer of blades 501 is the longest, the second layer of blades 502 is the second longest, and the third layer of blades 503 is the shortest.

[0135] A channel 6 is provided on the outer wall of the stirring shaft 3, and a cylindrical through hole 504 is provided in the middle of the blade. One end of the through hole 504 extends to the free end of the blade, and the other end of the through hole 504 is connected to the stirring shaft 3. One end of the channel 6 extends outward to the outside of the tank body 1 and is connected to the feeding hopper 7, and the other end of the channel 6 is communicated with the through hole 504, providing a channel 6 for adding seed crystals.

[0136] In this embodiment, the length of the second layer of blades 502 is 2 / 3 of the length of the first layer of blades 501 , and the length of the third layer of blades 503 is 1 / 3 of the length of the first layer of blades 501 .

[0137] This extraction equipment arranges stirring paddles 5 at different axial positions, connected to the through-holes 504 of the stirring paddles 5 via channels 6. Phosphoric acid seed crystals added from a hopper 7 can enter the through-holes 504 of the stirring paddles 5 at different layers through the channels 6. Under the action of gravity and the centrifugal force of the rotation of the stirring paddles 5, the phosphoric acid seed crystals are distributed at different locations within the tank body 1. (Due to the different lengths of the stirring paddles 5 at different layers, the seed crystals are dispersed not only in depth but also in the radial direction.) This facilitates uniform seed crystal dispersion and improves the quality of phosphoric acid crystallization. Furthermore, by arranging the stirring paddles 5 at different axial positions and lengths, the concentrated liquid is uniformly stirred. Finally, combined with ultrasonic treatment, the purification equipment achieves a shortened crystallization time and improved crystallinity even when a large amount of seed crystals is added.

[0138] Example 13

[0139] The invention discloses an extraction and purification device for phosphoric acid in anodizing polishing liquid, comprising a filtering device, a precipitation tank, a storage tank, a McLaval low-temperature evaporation device and a purification device which are arranged in sequence.

[0140] The McLaval low-temperature evaporation equipment includes a first-level McLaval low-temperature evaporation equipment and a second-level McLaval low-temperature evaporation equipment connected to each other, wherein the concentrated liquid obtained from the first-level McLaval low-temperature evaporation equipment enters the second-level McLaval low-temperature evaporation equipment for secondary low-temperature evaporation.

[0141] Comparative Example 1

[0142] The difference between this embodiment and embodiment 1 is that conventional low-pressure distillation technology is used instead of the McLaval low-temperature distillation technology, wherein the concentration of phosphoric acid after distillation is the same as the Laval concentration at the time of purchase. Except for the equipment and parameters of the low-pressure distillation step, the rest are the same.

[0143] The phosphoric acid prepared in Examples 1 to 11 and the comparative example was tested, and the results were as follows:

[0144] Table 3. Preparation and test results of different examples and comparative examples

[0145] serial number Different processing methods Impurity content Crystallization time Seed addition amount Example 1 Stirring crystallization Sulfate content: ≤0.1%, aluminum ion content ≤0.1%, the total content of other metal ions and organic impurities is within 0.1%. 22h 5% of the concentrate mass Example 2 Stirring + ultrasound assisted crystallization Sulfate content: ≤0.7%, aluminum ion content ≤0.8%, the total content of other metal ions and organic impurities is within 0.08%. 11h 7% of the concentrate mass Example 3 Recrystallization twice Arsenic ≤ 0.5 ppm Other metal impurities ≤ 6.8 ppm The first crystallization time was 11 h, and the second and third crystallization times were both 6 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the second and third crystallizations was 2%. Example 4 Phosphoric acid seeds are slowly added to the tank after particle size control and pre-dispersion. Arsenic ≤ 0.3ppm Other metal impurities ≤ 5.4ppm The first crystallization time was 11 h, and the second and third crystallization times were 5.5 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the second and third crystallizations was 2.5%. Example 5 Phosphoric acid seeds were added in three batches at intervals with a power of 700W and a frequency of 30kHz. Arsenic ≤ 0.2 ppm Other metal impurities ≤ 4.9 ppm The first crystallization time was 11 h, and the second and third crystallization times were 5.0 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the second and third crystallizations was 3%. Example 6 Ultrasonic power is 400W and frequency is 80kHz Arsenic ≤ 0.18 ppm Other metal impurities ≤ 4.6 ppm The first crystallization time was 11 h, and the second and third crystallization times were 5.0 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the second and third crystallizations was 3%. Example 7 Optimization of ultrasonic parameter combinations during seed addition and crystal growth stages Arsenic ≤ 0.10ppm Other metal impurities ≤ 3.9ppm The first crystallization time was 11 h, and the second and third crystallization times were 4 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the subsequent two crystallizations was 3.5%. Example 8 Interstitial ultrasound Arsenic ≤ 0.08ppm Other metal impurities ≤ 3.5ppm The first crystallization time was 11 h, and the second and third crystallization times were 4 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the subsequent two crystallizations was 3.5%. Example 9 Stirring speed 150r / min Arsenic ≤ 0.21ppm Other metal impurities ≤ 5.2ppm The first crystallization time was 11 h, and the second and third crystallization times were 5.0 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the subsequent two crystallizations was 3.5%. Example 10 Temperature gradient optimization Arsenic ≤ 0.07ppm Other metal impurities ≤ 3.1ppm The first crystallization time was 11 h, and the second and third crystallization times were 4.0 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the subsequent two crystallizations was 3.5%. Example 11 Optimization of purification equipment enables optimal seed stirring and dispersion Arsenic ≤ 0.05ppm Other metal impurities ≤ 2.7ppm in total The first crystallization time was 11 h, and the second and third crystallization times were 3.5 h. The amount of seed crystals added for the first crystallization was 7%; the amount of seed crystals added for the subsequent two crystallizations was 4.0%. Comparative Example 1 Conventional low-pressure distillation with a low pressure of 0.3 MPa and a temperature of 150°C is used instead of the McLaval technology. Sulfate content: ≤1.2%, aluminum ion content ≤0.8%, the total content of other metal ions and organic impurities is within 1%. 22h 5% of the concentrate mass

[0146] Note: 1. The above ≤ indicates that the data detected multiple times are no higher than this value; 2. Crystallization time indicates the shortest time required for complete crystallization obtained through experiments.

[0147] From Table 3 above we can see that:

[0148] 1. Ultrasonic-assisted crystallization is beneficial for increasing the amount of seed crystals and shortening the crystallization time. However, the amount of seed crystals added increases the difficulty of uniformly dispersing the seed crystals. Therefore, when ultrasonic-assisted crystallization alone is used to increase the amount of seed crystals, although crystallization time can be saved, the crystallization quality of phosphoric acid cannot be optimized.

[0149] 2. After adding ultrasonic assistance, by improving the method of adding seed crystals, the amount of seed crystals added can be increased and the quality of phosphoric acid crystals can be improved;

[0150] 3. After multiple crystallizations, the purity of phosphoric acid is improved. By selecting high-quality seed crystals, improving the seed addition method, and stirring and ultrasonic mixing during the crystallization process, it is upgraded from industrial-grade phosphoric acid to electronic-grade phosphoric acid.

[0151] 4. The present invention adopts a combination of strategies such as seed pretreatment and step-by-step addition, ultrasonic parameter optimization process, ultrasonic stirring coordination, and reasonable setting of temperature gradient, which can increase the amount of seed crystals, shorten the crystallization time, and achieve uniform seed dispersion, thereby ultimately improving the crystallization quality of electronic-grade phosphoric acid.

[0152] 5. The present invention improves the dispersion and addition method of seed crystals by improving the purification equipment, thereby further improving the crystallization efficiency and crystallization quality;

[0153] 6. The present invention has a good removal effect on sulfate and phosphate in waste liquid by selecting appropriate impurity removers and dosages and combining with McLaval low-pressure and low-temperature evaporation technology;

[0154] 7. During the crystallization process, the stirring speed should not be too high, otherwise it will easily resonate with the ultrasound and cause the crystal to break, affecting the product quality;

[0155] 8. Through the above-mentioned purification process and equipment optimization, the obtained phosphoric acid reaches the electronic grade phosphoric acid E1 level.

[0156] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for extracting and purifying phosphoric acid from anodized wastewater, characterized in that: The steps include: S1: Preliminary filtration and impurity removal of the anodized waste acid solution to be treated; S2: adding impurity remover to the waste acid liquid obtained by preliminary filtration and impurity removal in S1 and performing solid-liquid separation after mixing to obtain clear liquid and precipitate; S3: subjecting the clear liquid obtained in S2 to negative pressure low temperature evaporation to obtain a concentrated liquid; The negative pressure low temperature evaporation in S3 is performed twice, namely a first negative pressure low temperature evaporation and a second negative pressure low temperature evaporation, wherein the pressure of the first negative pressure low temperature evaporation is -96 kPa and the temperature of the first negative pressure low temperature evaporation is 32°C to 33°C, and the pressure of the second negative pressure low temperature evaporation is -98 kPa and the temperature of the second negative pressure low temperature evaporation is 25°C to 28°C; S4: adding phosphoric acid seed crystals to the concentrated solution in S3 and performing multi-stage crystal growth purification to obtain purified phosphoric acid; The phosphoric acid obtained in S4 is further purified to obtain electronic grade phosphoric acid, and the steps are as follows: S5: The solid phosphoric acid that has been grown in S4 is subjected to solid-liquid separation. After the solid crystalline phosphoric acid is heated to liquefaction, it is stirred. The growth temperature is stabilized at 8-12°C, and pre-prepared electronic grade pure phosphoric acid seed crystals are slowly added; S6: Repeat S5 to obtain electronic grade phosphoric acid; Electronic grade phosphoric acid is obtained through the separation process of crystal growth, re-liquefaction, and re-crystallization; The phosphoric acid seed crystals are first subjected to particle size control and pre-dispersion, wherein the seed crystal particle size control range is 1-5 μm; Ultrasonic assisted crystallization is also added to S5 and S6, wherein low frequency and medium-high power are used in the seed addition stage, wherein the low frequency range is 20~40kHz, and the medium-high power range is 500~800W; and high frequency and medium-low power are switched to in the crystal growth stage, wherein the high frequency range is 60~100kHz, and the medium-low power range is 300~500W.

2. The method for extracting and purifying phosphoric acid from anodized wastewater according to claim 1, wherein: In the S2, the impurity remover is a polyferric sulfate solution, the addition amount of which is 0.05%-0.2% of the volume of the waste acid solution, and the concentration of the polyferric sulfate solution is 10-20wt%.

3. A method for extracting and purifying phosphoric acid from anodized wastewater according to claim 1 or 2, characterized in that: In the step S4, the amount of phosphoric acid seed crystals added is 2-10% of the mass of the concentrated solution, and the crystal growth temperature is 8-12°C.

4. A method for extracting and purifying phosphoric acid from anodized wastewater according to claim 1 or 2, characterized in that: In the step S4, ultrasonic-assisted stirring is also used during the crystallization process. When ultrasonic-assisted stirring is used, the amount of phosphoric acid seed crystals added is 6-10% of the mass of the concentrated solution, and the crystal growth temperature is 8-10°C.

5. An extraction and purification device for phosphoric acid in anodized waste water, characterized by: The method according to claim 4 comprises a tank body (1) and a stirring assembly, wherein the tank body (1) is provided with a jacket (2) structure for inputting and discharging a cooling medium to provide temperature conditions for cooling crystallization. The stirring assembly comprises a driving motor (4), a stirring shaft (3) and a stirring paddle (5), one end of the stirring shaft (3) is connected to the driving motor (4) at the top of the tank body (1), and the other end penetrates into the tank body (1) and is connected to the stirring paddle (5), and the stirring paddle (5) is provided with three layers of blades along the axial direction of the stirring shaft (3), wherein, from top to bottom, the first layer of blades (501) is longer than the second layer of blades (502), and the second layer of blades (502) is longer than the third layer of blades (503); A channel (6) is provided on the outer wall of the stirring shaft (3), a through hole (504) is provided in the middle of the paddle, one end of the through hole (504) extends to the free end of the paddle, the other end of the through hole (504) is connected to the stirring shaft (3), one end of the channel (6) extends outward to the outside of the tank body (1), and the other end of the channel (6) is connected to the through hole (504).

6. A system for extracting and purifying phosphoric acid from anodizing wastewater, characterized by: The method for implementing any one of claims 1 to 4 comprises a filtering device, a precipitation tank, a storage tank, a McLaval low-temperature evaporation device and a purification device connected in sequence.

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