Phosphoric acid defluorination method

Abstract

The invention provides a phosphoric acid defluorination method, and belongs to the technical field of defluorination. The method comprises the steps of preparation of a defluorination agent, primary defluorination and secondary defluorination, the preparation of the defluorinating agent comprises the following steps: adding a sodium silicate solution into a reaction device, then adding cetyltrimethylammonium bromide for ultrasonic treatment, adding a sulfuric acid solution until the pH value is 3.4-3.6, stopping adding the sulfuric acid solution, adding a citric acid solution, raising the temperature to 32-37 DEG C, carrying out heat preservation reaction, aging, then putting into a sodium hydroxide solution for soaking, and carrying out vacuum drying to obtain the defluorinating agent. Then putting into a potassium chloride solution for soaking, and after soaking is finished, filtering, washing, drying and calcining to obtain silica gel; silica gel is placed in the pretreatment liquid, the temperature is increased to 52-57 DEG C, heat preservation and stirring are conducted, after filtering and drying, the silica gel is put into the modified liquid, stirring reaction is conducted at the temperature of 70-74 DEG C, filtering, washing and drying are conducted, and the defluorination agent is obtained; the phosphoric acid obtained by adopting the defluorination method disclosed by the invention is low in fluorine content, high in phosphorus-fluorine ratio and excellent and stable in defluorination effect.

Description

Technical Field

[0001] The invention belongs to the technical field of defluorination, and in particular relates to a method for defluorinating phosphoric acid. Background Art

[0002] Phosphoric acid is an important chemical product with a wide range of applications. In the agricultural field, phosphoric acid is an important raw material for the production of phosphate fertilizers and is also a raw material for the production of feed additives. In the food field, it is one of the food additives and is used as an acidulant and yeast nutrient in food. Coca-Cola contains phosphoric acid, and phosphates are also important food additives. They can also be used as nutritional enhancers. In the pharmaceutical field, phosphoric acid can be used to prepare phosphorus-containing drugs, such as sodium glycerophosphate. In the industrial field, phosphoric acid is an important chemical raw material. It can be used to treat metal surfaces to protect metals from corrosion. It can also be mixed with nitric acid as a chemical polishing agent to improve the smoothness of metal surfaces. It can also be used to produce detergents, pesticides, and flame retardants.

[0003] At present, the source of phosphoric acid is mainly wet-process phosphoric acid, but fluoride is one of the main impurities in wet-process phosphoric acid. Many fields and products have strict requirements on the fluorine content of phosphoric acid; therefore, studying a defluorination method for phosphoric acid is of great research significance.

[0004] The defluorination methods of wet-process phosphoric acid mainly include chemical precipitation, vacuum concentration and stripping; The chemical precipitation method refers to the use of alkali metal salts (potassium salts, sodium salts, etc.) as defluorination agents to react with fluorine in phosphoric acid to generate potassium fluorosilicate and sodium fluorosilicate precipitates, which are separated by filtration to remove fluoride ions; however, the defluorination efficiency of this method is not high, and even if excessive potassium and sodium salts are added, it still cannot guarantee complete fluorine removal, and cationic impurities such as sodium and potassium will be introduced, resulting in a large loss of phosphorus during the removal process; the vacuum concentration method refers to the addition of excessive active silica-containing substances to wet phosphoric acid to convert F into H2FSi6, and the concentration and temperature of phosphoric acid are increased by heating and concentration, and most of the fluorine escapes in the form of gaseous fluorides (SiF4, HF), and HF reacts with silica to generate H2FSi6 again, which is decomposed again. Defluorination can be achieved after the SiF4 gas generated by each decomposition escapes, but its energy consumption is large, and phosphoric acid is easily condensed during the concentration process.

[0005] At present, the stripping method is the most effective defluorination method. The stripping method mainly takes into account that the fluorine in the wet-process phosphoric acid after concentration mainly exists in the form of H2FSi6 and HF. During the defluorination process, fluorosilicic acid is decomposed into SiF4 and HF by heat. During the stripping defluorination process, high-pressure supersaturated steam enters the container and collides strongly with phosphoric acid, gasifying the fluorine in the acid and pumping it away with the water vapor by the vacuum pump, thereby achieving defluorination. Sometimes, silicon dioxide is also heated to convert HF into SiF4, which is more volatile, thereby improving the removal efficiency of fluorine. For example, CN110817820A discloses a method for catalytically improving the efficiency of steam stripping defluorination of wet-process phosphoric acid, specifically disclosing the steps of removing arsenic and heavy metals from raw phosphoric acid to obtain clarified, purified concentrated phosphoric acid with low impurity content; after adding a defluorination catalyst to the purified concentrated phosphoric acid, it is mixed with a defluorinating agent and heated for steam stripping defluorination, and an indirect steam heating method is adopted to finally achieve phosphoric acid defluorination; the method in this patent can effectively reduce the consumption of defluorinating agent, steam and electricity in the defluorination process, and reduce the defluorination cost; the production efficiency of defluorinated phosphoric acid is high, the output is high, the consumption is low, the phosphoric acid quality is good, the impurity content is low, and its phosphorus-fluorine ratio (P2O5 / F) is 315; However, in the defluorination process of this method, the fluorine content is lower than that of phosphoric acid, and the reaction efficiency of the defluorinating agent is low after entering the phosphoric acid solution. In addition, the defluorinating agent in this patent is one or more of white carbon black, activated SiO2, diatomaceous earth, and microsilica powder. The defluorinating agent has strong agglomeration and is easy to form aggregates in wet phosphoric acid, thereby limiting the defluorination effect of the defluorinating agent, and ultimately making the fluorine content of the defluorinated phosphoric acid still relatively high. Summary of the invention

[0006] In order to solve the technical problems existing in the prior art, the present invention provides a phosphoric acid defluorination method, which has good defluorination effect, and the phosphorus-fluorine ratio of the phosphoric acid after defluorination is high and the fluorine content is low.

[0007] In view of the above technical problems, the present invention adopts the following technical solutions: A phosphoric acid defluorination method includes the steps of preparing a defluorinating agent, primary defluorination and secondary defluorination, as follows: 1. Preparation of defluorination agent (1) Preparation of silica gel Add sodium silicate solution to the reaction device, then add hexadecyltrimethylammonium bromide for ultrasonic treatment, the ultrasonic time is 20-25 minutes, the ultrasonic power is 64-70W, and the ultrasonic frequency is 30-34kHz. After the ultrasonic treatment, add sulfuric acid solution until the pH value is 3.4-3.6, stop adding sulfuric acid solution, then add citric acid solution, stir at 20-35°C for 28-32 minutes, increase the temperature to 32-37°C, keep warm for reaction for 4.8-5.2 hours, and obtain sol after the reaction is completed; age the sol at 58-62°C for 3 .4-3.6h, then put it into 4-8 times the mass of sodium hydroxide solution and soak it for 0.8-1.2h, the soaking temperature is 58-62℃, after the soaking, filter it out and wash it, then put it into 4-8 times the mass of potassium chloride solution and soak it for 1.0-1.4h, the soaking temperature is 62-66℃, after the soaking, filter it and wash it, dry it at 63-68℃ for 3.8-4.2h, then heat it to 475-484℃ at a rate of 5.7-6.2℃ / min, keep it warm and calcine it for 2.4-2.7h, and wait for it to naturally return to room temperature to obtain silica gel; The mass concentration of the sodium silicate solution is 26-30%; The mass concentration of the sulfuric acid solution is 20-24%; The mass ratio of the hexadecyltrimethylammonium bromide to the sodium silicate solution is 0.2-0.4:8.0-8.5; The mass concentration of the citric acid solution is 2.8-3.3%; The mass ratio of the citric acid solution to the sodium silicate solution is 4.0-4.3:100; The mass concentration of the sodium hydroxide solution is 6.3-6.7%; The mass concentration of the potassium chloride solution is 9.5-10.4%; (2) Modification The silica gel is placed in a pretreatment liquid of 6-10 times its mass, the temperature is raised to 52-57°C, and the mixture is stirred for 58-63 minutes. After the stirring is completed, the mixture is filtered and dried. The silica gel is then placed in a modification liquid of 6-10 times its mass, and the mixture is stirred and reacted at 70-74°C for 2.8-3.2 hours. After the stirring reaction is completed, the mixture is filtered, washed, and dried to obtain a defluorinating agent. The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate, and the mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate is 100:2.3-2.8:1.5-1.8; The modified liquid is a mixture of 36wt% ethanol solution and kH550, and the mass ratio of the 36wt% ethanol solution to kH550 is 100:1.0-1.4.

[0008] 2. Initial defluorination The clarified phosphoric acid obtained after heavy metal removal, clarification and filter pressing is pumped into a reaction tank, heated to 78-83°C by a steam coil, a defluorinating agent is added and stirred for reaction for 42-48 minutes, the steam is turned off and stirring is stopped, and the mixture is naturally settled for 0.8-1.3 hours. After settling, the supernatant is pumped into a defluorination reaction tank, potassium chloride solution is added, and the mixture is stirred for reaction for 28-32 minutes. The mixture is stirred for reaction for 3.8-4.3 hours. After separation by filtration, the filtrate is collected to obtain preliminary defluorinated phosphoric acid; The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.2-0.4; The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.23-0.27:1; The mass concentration of the potassium chloride solution is 10-12%.

[0009] 3. Secondary defluorination The preliminary defluorinated phosphoric acid and the defluorinating agent are introduced into the defluorination tower, and mixed evenly to obtain a mixed acid solution; the mixed acid solution is heated to 68-72°C at a rate of 1.8-2.2°C / min and then sent to the defluorination tower for spraying; high-temperature steam is introduced into the bottom of the defluorination tower to fully contact the mixed acid solution; the temperature of the high-temperature steam is 158-162°C and the pressure is 0.6-0.8MPa; the high-temperature steam heats the mixed acid solution, and the temperature of the mixed acid solution after heating is controlled to be 123-127°C; after the defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the phosphoric acid after defluorination is sent to the finished acid tank; The mass ratio of the preliminary defluorinated phosphoric acid to the defluorinating agent is 100:0.6-0.8.

[0010] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. The present invention adopts a specific method to prepare a defluorinating agent. First, silica gel is prepared, specifically, hexadecyl trimethyl ammonium bromide is added as a surfactant, and then a citric acid solution is added, which is helpful to promote the stability of the sol, increase the number of hydroxyl groups on the surface of the silica gel, and then promote the defluorination effect of phosphoric acid. In combination with a potassium chloride solution, potassium ions are adsorbed on the surface of the silica gel, and the binding property of the silica gel and fluoride ions is promoted. In the modification step, the pretreatment liquid can promote the dispersibility of silica gel in phosphoric acid and has good compatibility with phosphoric acid, thereby avoiding the agglomeration of the defluorinating agent and enhancing the defluorination effect. Sodium p-styrene sulfonate contains benzene rings, which have greater rigidity. In the high-temperature stripping process, the molecular mobility is small, and its viscosity in the defluorination system is weakened, thereby promoting the reaction activity and further enhancing the defluorination effect. In combination with a modified liquid, the surface of the defluorinating agent contains amino groups, which have good binding property with fluorine, enhance the defluorination performance, and can also enhance the stability of the defluorinating agent, ensure the stability of the defluorination effect, make the F content of the defluorinated phosphoric acid low, and have an excellent defluorination effect.

[0011] 2. The method of the present invention is used to defluorinate phosphoric acid, wherein the clarified phosphoric acid in the preliminary defluorination step has a P2O5 content of 37.64wt%, a F content of 1.95wt%, and a solid content of 0.43wt%; the defluorinated phosphoric acid is measured to have a F content of 0.13-0.16wt%, a phosphorus-fluorine ratio (P2O5 / F) of 318-409, and a solid content of 0.12-0.15wt%. DETAILED DESCRIPTION

[0012] In order to more clearly understand the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described.

[0013] Example 1 1. Preparation of defluorination agent (1) Preparation of silica gel Add 28wt% sodium silicate solution to the reaction device, then add hexadecyltrimethylammonium bromide for ultrasonic treatment, the ultrasonic time is 22min, the ultrasonic power is 68W, the ultrasonic frequency is 32kHz, after the ultrasonic treatment, add 22wt% sulfuric acid solution until the pH value is 3.5, stop adding sulfuric acid solution, then add 3.0wt% citric acid solution, stir at 23°C for 30min, increase the temperature to 35°C, keep warm for reaction for 5.0h, and obtain sol after the reaction is completed; Aged at 60°C for 3.5h, then immersed in 6 times the mass of 6.5wt% sodium hydroxide solution for 1.0h, the immersion temperature is 60°C, filtered out and washed after the immersion, immersed in 6 times the mass of 10.0wt% potassium chloride solution for 1.2h, the immersion temperature is 64°C, after the immersion, filtered and washed, dried at 65°C for 4.0h, then heated to 480°C at a rate of 6.0°C / min, kept warm and calcined for 2.5h, and naturally recovered to room temperature to obtain silica gel; The mass ratio of the hexadecyltrimethylammonium bromide to the sodium silicate solution is 0.3:8.2; The mass ratio of the citric acid solution to the sodium silicate solution is 4.2:100.

[0014] (2) Modification The silica gel was placed in a pretreatment liquid of 8 times the mass, the temperature was raised to 54°C, the mixture was kept warm and stirred for 60 minutes, after the stirring was completed, it was filtered and dried, and then placed in a modification liquid of 8 times the mass, stirred and reacted at 72°C for 3.0 hours, after the stirring reaction was completed, it was filtered, washed and dried to obtain a defluorinating agent; The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate, and the mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate is 100:2.5:1.7; The modified liquid is a mixture of 36wt% ethanol solution and kH550, and the mass ratio of the 36wt% ethanol solution to kH550 is 100:1.2.

[0015] 2. Initial defluorination The clarified phosphoric acid obtained after heavy metal removal, clarification and filter pressing is pumped into a reaction tank, heated to 80°C by a steam coil, a defluorinating agent is added and stirred for 45 minutes, the steam is turned off and stirring is stopped, and the mixture is naturally settled for 1.0 hour. After settling, the supernatant is pumped into a defluorination reaction tank, 11wt% potassium chloride solution is added, and the mixture is stirred for 30 minutes. The mixture is stirred for 4.0 hours, and the filtrate is collected after separation by filtration to obtain preliminary defluorinated phosphoric acid; The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.3; The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.25:1.

[0016] 3. Secondary defluorination The preliminary defluorinated phosphoric acid and the defluorinating agent are introduced into the defluorination tower, and mixed evenly to obtain a mixed acid solution; the mixed acid solution is heated to 70°C at a rate of 2.0°C / min and then sent to the defluorination tower for spraying; high-temperature steam is introduced into the bottom of the defluorination tower to fully contact the mixed acid solution; the temperature of the high-temperature steam is 160°C and the pressure is 0.7MPa; the high-temperature steam heats the mixed acid solution, and the temperature of the mixed acid solution after heating is controlled to be 125°C; after the defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the phosphoric acid after defluorination is sent to the finished acid tank; The mass ratio of the preliminary defluorinated phosphoric acid to the defluorinating agent is 100:0.7.

[0017] Phosphoric acid was defluorinated by the method of Example 1, wherein the clarified phosphoric acid in the preliminary defluorination step had a P2O5 content of 37.64wt%, a F content of 1.95wt%, and a solid content of 0.43wt%. The defluorinated phosphoric acid was measured to have a F content of 0.13wt%, a phosphorus-to-fluorine ratio (P2O5 / F) of 409, and a solid content of 0.12wt%.

[0018] Example 2 1. Preparation of defluorination agent (1) Preparation of silica gel A 26 wt % sodium silicate solution was added to the reaction device, and then hexadecyl trimethyl ammonium bromide was added for ultrasonic treatment. The ultrasonic time was 20 min, the ultrasonic power was 64 W, and the ultrasonic frequency was 30 kHz. After the ultrasonic treatment, a 20 wt % sulfuric acid solution was added until the pH value was 3.4, and then the addition of the sulfuric acid solution was stopped. Then, a 2.8 wt % citric acid solution was added, and the mixture was stirred at 20 ° C for 28 min, and the temperature was increased to 32 ° C. The reaction was kept warm for 4.8 h. After the reaction was completed, a sol was obtained; the sol The gel was aged at 58°C for 3.4h, then immersed in 4 times the mass of 6.3wt% sodium hydroxide solution for 0.8h, the immersion temperature was 58°C, filtered out and washed, and then immersed in 4 times the mass of 9.5wt% potassium chloride solution for 1.0h, the immersion temperature was 62°C, after the immersion, filtered and washed, dried at 63°C for 3.8h, then heated to 475°C at a rate of 5.7°C / min, kept warm and calcined for 2.7h, and naturally recovered to room temperature to obtain silica gel; The mass ratio of the hexadecyltrimethylammonium bromide to the sodium silicate solution is 0.2:8.0; The mass ratio of the citric acid solution to the sodium silicate solution is 4.0:100.

[0019] (2) Modification The silica gel was placed in a pretreatment liquid of 6 times the mass, the temperature was raised to 52°C, and the mixture was stirred for 58 minutes. After the stirring was completed, the mixture was filtered and dried. Then, the silica gel was placed in a modification liquid of 6 times the mass, and the mixture was stirred and reacted at 70°C for 2.8 hours. After the stirring reaction was completed, the mixture was filtered, washed, and dried to obtain a defluorinating agent. The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate, and the mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate is 100:2.3:1.5; The modified liquid is a mixture of 36wt% ethanol solution and kH550, and the mass ratio of the 36wt% ethanol solution to kH550 is 100:1.0.

[0020] 2. Initial defluorination The clarified phosphoric acid obtained after heavy metal removal, clarification and filter pressing is pumped into a reaction tank, heated to 78°C by a steam coil, a defluorinating agent is added and stirred for reaction for 42 minutes, the steam is turned off and stirring is stopped, and the mixture is naturally settled for 0.8 hours. After settling, the supernatant is pumped into a defluorination reaction tank, 10wt% potassium chloride solution is added, and the mixture is stirred for reaction for 28 minutes. The mixture is stirred for reaction for 3.8 hours, and the filtrate is collected after separation by filtration to obtain preliminary defluorinated phosphoric acid; The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.2; The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.23:1.

[0021] 3. Secondary defluorination The preliminary defluorinated phosphoric acid and the defluorinating agent are introduced into the defluorination tower, and mixed evenly to obtain a mixed acid solution; the mixed acid solution is heated to 72°C at a rate of 1.8°C / min and then sent to the defluorination tower for spraying; high-temperature steam is introduced into the bottom of the defluorination tower to fully contact the mixed acid solution; the temperature of the high-temperature steam is 158°C and the pressure is 0.8MPa; the high-temperature steam heats the mixed acid solution, and the temperature of the mixed acid solution after heating is controlled to be 123°C; after the defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the phosphoric acid after defluorination is sent to the finished acid tank; The mass ratio of the preliminary defluorinated phosphoric acid to the defluorinating agent is 100:0.6.

[0022] Phosphoric acid was defluorinated by the method of Example 2, wherein the clarified phosphoric acid in the preliminary defluorination step had a P2O5 content of 37.64wt%, a F content of 1.95wt%, and a solid content of 0.43wt%. The defluorinated phosphoric acid was measured to have a F content of 0.16wt%, a phosphorus-to-fluorine ratio (P2O5 / F) of 318, and a solid content of 0.15wt%.

[0023] Example 3 1. Preparation of defluorination agent (1) Preparation of silica gel Add 30wt% sodium silicate solution to the reaction device, then add hexadecyltrimethylammonium bromide for ultrasonic treatment, the ultrasonic time is 25min, the ultrasonic power is 70W, the ultrasonic frequency is 34kHz, after the ultrasonic treatment, add 24wt% sulfuric acid solution until the pH value is 3.6, stop adding sulfuric acid solution, then add 3.3wt% citric acid solution, stir at 25°C for 32min, increase the temperature to 37°C, keep warm for 5.2h, and obtain sol after the reaction is completed; Aged at 62°C for 3.6h, then immersed in 8 times the mass of 6.7wt% sodium hydroxide solution for 1.2h, the immersion temperature is 62°C, filtered out and washed after the immersion, immersed in 8 times the mass of 10.4wt% potassium chloride solution for 1.4h, the immersion temperature is 66°C, after the immersion, filtered and washed, dried at 68°C for 4.2h, then heated to 484°C at a rate of 6.2°C / min, kept warm and calcined for 2.4h, and naturally recovered to room temperature to obtain silica gel; The mass ratio of the hexadecyltrimethylammonium bromide to the sodium silicate solution is 0.4:8.5; The mass ratio of the citric acid solution to the sodium silicate solution is 4.3:100.

[0024] (2) Modification The silica gel was placed in a pretreatment liquid with a mass of 10 times, the temperature was raised to 57°C, and the mixture was stirred for 63 minutes. After the stirring was completed, the mixture was filtered and dried. Then, the silica gel was placed in a modification liquid with a mass of 10 times, and the mixture was stirred and reacted at 74°C for 3.2 hours. After the stirring reaction was completed, the mixture was filtered, washed, and dried to obtain a defluorinating agent. The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate, and the mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate is 100:2.8:1.8; The modified liquid is a mixture of 36wt% ethanol solution and kH550, and the mass ratio of the 36wt% ethanol solution to kH550 is 100:1.4.

[0025] 2. Initial defluorination The clarified phosphoric acid obtained after heavy metal removal, clarification and filter pressing is pumped into a reaction tank, heated to 83°C by a steam coil, a defluorinating agent is added and stirred for 48 minutes, the steam is turned off and stirring is stopped, and the mixture is naturally settled for 1.3 hours. After settling, the supernatant is pumped into a defluorinating reaction tank, a 12wt% potassium chloride solution is added, and the mixture is stirred for 32 minutes. The mixture is stirred for 4.3 hours, and the filtrate is collected after separation by filtration to obtain preliminary defluorinated phosphoric acid; The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.4; The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.27:1.

[0026] 3. Secondary defluorination The preliminary defluorinated phosphoric acid and the defluorinating agent are introduced into the defluorination tower, and mixed evenly to obtain a mixed acid solution; the mixed acid solution is heated to 68°C at a rate of 2.2°C / min and then sent to the defluorination tower for spraying; high-temperature steam is introduced into the bottom of the defluorination tower to fully contact the mixed acid solution; the temperature of the high-temperature steam is 162°C and the pressure is 0.6MPa; the high-temperature steam heats the mixed acid solution, and the temperature of the mixed acid solution after heating is controlled to be 127°C; after the defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the phosphoric acid after defluorination is sent to the finished acid tank; The mass ratio of the preliminary defluorinated phosphoric acid to the defluorinating agent is 100:0.8.

[0027] Phosphoric acid was defluorinated by the method of Example 3, wherein the clarified phosphoric acid in the preliminary defluorination step had a P2O5 content of 37.64wt%, a F content of 1.95wt%, and a solid content of 0.43wt%. The defluorinated phosphoric acid was measured to have a F content of 0.14wt%, a phosphorus-to-fluorine ratio (P2O5 / F) of 374, and a solid content of 0.14wt%.

[0028] Comparative Example 1 Based on Example 1, the changes are as follows: In the step of preparing silica gel, the operation of "immersing in 6 times the mass of 10.0wt% potassium chloride solution for 1.2h at a soaking temperature of 64°C" was omitted; In the modification step, the pretreatment solution was replaced with deionized water in equal amounts; The rest of the operations are the same.

[0029] Phosphoric acid was defluorinated by the method of Comparative Example 1, wherein the clarified phosphoric acid in the preliminary defluorination step had a P2O5 content of 37.64wt%, a F content of 1.95wt%, and a solid content of 0.43wt%; the defluorinated phosphoric acid was measured to have a F content of 0.35wt%, a phosphorus-fluorine ratio (P2O5 / F) of 127, and a solid content of 0.27wt%.

[0030] Comparative Example 2 Based on Example 1, the changes are as follows: In the step of preparing silica gel, the operation of "adding 3.0 wt % citric acid solution and stirring at 23° C. for 30 min" was omitted; In the modification step, the modification liquid was replaced with an equal amount of 36 wt % ethanol solution; The rest of the operations are the same.

[0031] The method of Comparative Example 2 was adopted to defluorinate phosphoric acid, wherein the clarified phosphoric acid in the preliminary defluorination step had a P2O5 content of 37.64wt%, a F content of 1.95wt%, and a solid content of 0.43wt%; it was measured that the F content in the defluorinated phosphoric acid was 0.30wt%, the phosphorus-fluorine ratio (P2O5 / F) was 158, and the solid content was 0.21wt%.

[0032] The invention adopts a specific method to prepare a defluorinating agent. First, silica gel is prepared, specifically, hexadecyl trimethyl ammonium bromide is added as a surfactant, and then a citric acid solution is added, which is helpful to promote the stability of the sol, increase the number of hydroxyl groups on the surface of the silica gel, and further promote the defluorination effect of phosphoric acid. In combination with a potassium chloride solution, potassium ions are adsorbed on the surface of the silica gel, and the binding property of the silica gel and fluoride ions is promoted. In the modification step, a pretreatment liquid can promote the dispersibility of silica gel in phosphoric acid, and has good compatibility with phosphoric acid, thereby avoiding the agglomeration of the defluorinating agent and enhancing the defluorination effect. Sodium p-styrene sulfonate contains a benzene ring, which has a large rigidity. In the high-temperature stripping process, the molecular mobility is small, and the viscosity of the defluorinating agent in the defluorination system is weakened, thereby promoting the reaction activity and further enhancing the defluorination effect. In combination with a modified liquid, the surface of the defluorinating agent contains an amino group, which has good binding property with fluorine, and enhances the defluorination performance. In addition, the stability of the defluorinating agent can be enhanced, and the stability of the defluorination effect is guaranteed, so that the F content of the defluorinated phosphoric acid is low and the defluorination effect is excellent.

[0033] Comparative Example 1 omits the pretreatment liquid component in the modification step, which makes the dispersibility of the defluorinating agent poor, the agglomeration force in phosphoric acid is strong, the reaction activity of the defluorinating agent is low, and the defluorination effect is greatly affected. In addition, Comparative Example 1 omits the potassium chloride solution immersion process, which also weakens the binding property with fluoride ions, and ultimately the fluorine content of the defluorinated phosphoric acid is still high; Comparative Example 2 omits the modification liquid component in the modification step, which on the one hand reduces the binding property of the defluorinating agent with fluorine, and on the other hand, the stability of the defluorinating agent is weak. During the high-temperature stripping process, the defluorination effect is unstable. In addition, Comparative Example 2 omits the citric acid solution immersion process, which reduces the number of hydroxyl groups on the surface of the silica gel, affects the binding property with the potassium chloride solution, and further affects the defluorination performance.

[0034] Unless otherwise specified, all ratios and percentages described in the present invention are by mass ratios and percentages are by mass percentages.

[0035] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for defluorinating phosphoric acid, characterized in that: The method includes the steps of preparing a defluorinating agent, preliminary defluorinating and secondary defluorinating, as follows: The preparation of the defluorinating agent comprises the steps of preparing silica gel and modifying the silica gel; The step of preparing silica gel is to add sodium silicate solution to a reaction device, then add hexadecyltrimethylammonium bromide for ultrasonic treatment, add sulfuric acid solution until the pH value is 3.4-3.6, then add citric acid solution, raise the temperature to 32-37°C, and keep the temperature for reaction for 4.8-5.2 hours to obtain sol; after aging the sol, soak it in sodium hydroxide solution, and then soak it in potassium chloride solution, and after soaking, filter, wash, dry and calcine to obtain silica gel; The modification step is to place silica gel in a pretreatment liquid, raise the temperature to 52-57°C, keep warm and stir for 58-63 minutes, filter and dry after the stirring is completed, then put it into the modification liquid, stir and react at 70-74°C for 2.8-3.2 hours, and after the stirring reaction is completed, filter, wash and dry to obtain a defluorinating agent; The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate; The modified liquid is composed of a mixture of 36 wt % ethanol solution and KH550.

2. A phosphoric acid defluorination method according to claim 1, characterized in that: The step of preparing silica gel comprises: adding sodium silicate solution to a reaction device, then adding hexadecyltrimethylammonium bromide for ultrasonic treatment, wherein the ultrasonic time is 20-25 minutes, the ultrasonic power is 64-70W, and the ultrasonic frequency is 30-34kHz; after the ultrasonic treatment, adding sulfuric acid solution until the pH value is 3.4-3.6, then stopping adding sulfuric acid solution, adding citric acid solution, stirring at 20-35°C for 28-32 minutes, raising the temperature to 32-37°C, and keeping the temperature for reaction for 4.8-5.2 hours; after the reaction is completed, obtaining sol; and heating the sol at 58-62 The silica gel is aged at 4-8 times the mass of sodium hydroxide solution for 0.8-1.2 hours at a soaking temperature of 58-62°C. After the soaking, it is filtered out and washed, and then immersed in 4-8 times the mass of potassium chloride solution for 1.0-1.4 hours at a soaking temperature of 62-66°C. After the soaking, it is filtered and washed, and then dried at 63-68°C for 3.8-4.2 hours, and then heated to 475-484°C at a rate of 5.7-6.2°C / min, and calcined at this temperature for 2.4-2.7 hours. After it is naturally restored to room temperature, silica gel is obtained.

3. A phosphoric acid defluorination method according to claim 2, characterized in that: In the step of preparing silica gel, the mass concentration of the sodium silicate solution is 26-30%; The mass concentration of the sulfuric acid solution is 20-24%; The mass ratio of the hexadecyltrimethylammonium bromide to the sodium silicate solution is 0.2-0.4:8.0-8.5; The mass concentration of the citric acid solution is 2.8-3.3%; The mass ratio of the citric acid solution to the sodium silicate solution is 4.0-4.3:100; The mass concentration of the sodium hydroxide solution is 6.3-6.7%; The mass concentration of the potassium chloride solution is 9.5-10.4%.

4. A phosphoric acid defluorination method according to claim 1, characterized in that: In the modification step, the mass ratio of the silica gel to the pretreatment liquid and the modification liquid is 1:6-10:6-10.

5. A phosphoric acid defluorination method according to claim 1, characterized in that: In the modification step, in the pretreatment solution, the mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrene sulfonate is 100:2.3-2.8:1.5-1.8; In the modified liquid, the mass ratio of the 36wt% ethanol solution to kH550 is 100:1.0-1.

4.

6. A phosphoric acid defluorination method according to claim 1, characterized in that: The preliminary defluorination step comprises: injecting the clarified phosphoric acid obtained after heavy metal removal, clarification and filter pressing into a reaction tank, heating the temperature to 78-83° C. by using a steam coil, adding a defluorinating agent and stirring the reaction for 42-48 minutes, turning off the steam and stopping the stirring, and naturally settling for 0.8-1.3 hours. After the settling, injecting the supernatant into a defluorination reaction tank, adding a potassium chloride solution, stirring the reaction for 28-32 minutes, continuing the stirring reaction for 3.8-4.3 hours, and collecting the filtrate after filtering and separation to obtain preliminary defluorinated phosphoric acid.

7. A phosphoric acid defluorination method according to claim 6, characterized in that: In the preliminary defluorination step, the mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.2-0.4; The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.23-0.27:1; The mass concentration of the potassium chloride solution is 10-12%.

8. A phosphoric acid defluorination method according to claim 1, characterized in that: The secondary defluorination step comprises the following steps: introducing the preliminary defluorinated phosphoric acid and the defluorinating agent into the defluorination tower, mixing them evenly to obtain a mixed acid solution; heating the mixed acid solution to 68-72° C. at a rate of 1.8-2.2° C. / min and then sending it to the defluorination tower for spraying; introducing high-temperature steam into the bottom of the defluorination tower to fully contact the mixed acid solution; the temperature of the high-temperature steam is 158-162° C. and the pressure is 0.6-0.8 MPa; the high-temperature steam heats the mixed acid solution; and the temperature of the mixed acid solution after heating is controlled to be 123-127° C. After defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the phosphoric acid after defluorination is sent to the finished acid tank.

9. A method for defluorinating phosphoric acid according to claim 8, characterized in that: In the secondary defluorination step, the mass ratio of the preliminary defluorinated phosphoric acid to the defluorinating agent is 100:0.6-0.8.