A method for defluorination of phosphoric acid

Abstract

The present invention provides a method for defluorinating phosphoric acid, belonging to the technical field of defluorination; the method includes preparing a defluorinating agent, primary defluorination and secondary defluorination; for the preparation of the defluorinating agent, sodium silicate solution is added into a reaction device, then cetyltrimethylammonium bromide is added for ultrasonic treatment, sulfuric acid solution is added until the pH value reaches 3.4 - 3.6, then citric acid solution is added, the temperature is raised to 32 - 37 °C for heat preservation reaction, after aging, it is put into sodium hydroxide solution for soaking, and then put into potassium chloride solution for soaking. After the soaking is completed, it is filtered, washed, dried and calcined to obtain silica gel; the silica gel is placed in a pretreatment solution, the temperature is raised to 52 - 57 °C for heat preservation and stirring, after filtering and drying, it is put into a modification solution and stirred at 70 - 74 °C for reaction, and after filtering, washing and drying, a defluorinating agent is obtained; the phosphoric acid obtained by the defluorination method of the present invention has a low fluorine content, a high phosphorus-fluorine ratio, and excellent and stable defluorination effect.

Description

Technical Field

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

[0002] Phosphoric acid is an important chemical product with a relatively wide range of application fields; in the agricultural field, phosphoric acid is an important raw material for producing phosphate fertilizers and is also a raw material for producing feed additives; in the food field, it is one of the food additives, serving as an acidulant and yeast nutrient in food. Phosphoric acid is contained in Coca-Cola, and phosphates are also important food additives, which 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, etc.; in the industrial field, phosphoric acid is an important chemical raw material, which can be used to treat metal surfaces to protect metals from corrosion, and can also be mixed with nitric acid as a chemical polishing agent to improve the smoothness of the metal surface. It can also be used to produce detergents, pesticides, and flame retardants, etc.

[0003] Currently, the main source of phosphoric acid is wet-process phosphoric acid, but fluoride is one of the main impurities in wet-process phosphoric acid. Many fields and products have strict requirements for the fluorine content of phosphoric acid; therefore, studying a method for defluorinating phosphoric acid has important research significance.

[0004] The defluorination methods for wet-process phosphoric acid mainly include chemical precipitation method, vacuum concentration method, and stripping method;

[0005] The chemical precipitation method refers to using alkali metal salts (potassium salts, sodium salts, etc.) as defluorinating agents, which react with the fluorine in phosphoric acid to form potassium fluorosilicate and sodium fluorosilicate precipitates. The precipitates are separated by filtration to remove fluoride ions; however, the defluorination efficiency of this method is not high. Even if excessive potassium salts and sodium salts are added, it is still impossible to ensure complete removal of fluorine, and it will also introduce cation impurities such as sodium and potassium, and the loss of phosphorus during the removal process is relatively large; the vacuum concentration method refers to adding an excessive amount of substances containing active silica to wet-process phosphoric acid to convert F into H2FSi6. By heating and concentrating, the concentration and temperature of phosphoric acid are increased, and most of the fluorine escapes as gaseous fluorides (SiF4, HF). HF reacts with silica to form H2FSi6 again and decomposes again. Each time the generated SiF4 gas escapes, defluorination can be achieved, but its energy consumption is large, and phosphoric acid is prone to condensation during the concentration process.

[0006] At present, the stripping method is the most effective defluorination method. The stripping method mainly considers that after concentration, fluorine in wet-process phosphoric acid mainly exists in the forms of H2FSi6 and HF. During the defluorination process, fluosilicic acid decomposes into SiF4 and HF when heated; during the stripping defluorination process, high-pressure supersaturated steam enters the container and collides strongly with phosphoric acid, and the fluorine in the acid is vaporized and taken away by the vacuum pump together with water vapor, thereby achieving defluorination. And sometimes silica is also heated to convert HF into SiF4 with stronger volatility, thereby improving the defluorination efficiency of fluorine;

[0007] For example, CN110817820A discloses a method for catalytically improving the stripping defluorination efficiency of wet-process phosphoric acid, specifically discloses a process for removing arsenic and heavy metals from raw material 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 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 during the defluorination process, and reduce the defluorination cost; the efficiency of producing defluorinated phosphoric acid is high, the output is high, the consumption is low, the quality of phosphoric acid is good, the impurity content is low, and its phosphorus-fluorine ratio (P2O5 / F) is 315;

[0008] However, in the defluorination process of this method, the fluorine content is lower than the phosphoric acid content. After the defluorinating agent enters the phosphoric acid solution, the reaction efficiency is low. And the defluorinating agent in this patent is one or several of white carbon black, activated SiO2, diatomite, microsilica powder, etc. The defluorinating agent has strong aggregation, and it is easy to form aggregates in wet-process phosphoric acid, thereby limiting the defluorination effect of the defluorinating agent, and finally making the fluorine content of the defluorinated phosphoric acid still relatively high. Summary of the Invention

[0009] In order to solve the technical problems existing in the prior art, the present invention provides a phosphoric acid defluorination method with good defluorination effect, high phosphorus-fluorine ratio of the defluorinated phosphoric acid and low fluorine content.

[0010] In view of the above technical problems, the present invention adopts the following technical solutions:

[0011] A phosphoric acid defluorination method includes steps of preparing a defluorinating agent, preliminary defluorination and secondary defluorination, specifically as follows:

[0012] 1. Preparation of defluorinating agent

[0013] (1) Preparation of silica gel

[0014] Add sodium silicate solution to the reaction device, then add cetyltrimethylammonium bromide and perform ultrasonic treatment. The ultrasonic time is 20 - 25 min, the ultrasonic power is 64 - 70 W, and the ultrasonic frequency is 30 - 34 kHz. After the ultrasonic treatment, add sulfuric acid solution until the pH value reaches 3.4 - 3.6, then stop adding sulfuric acid solution. Next, add citric acid solution and stir at 20 - 35 °C for 28 - 32 min. Raise the temperature to 32 - 37 °C and keep the reaction for 4.8 - 5.2 h. After the reaction ends, a sol is obtained; age the sol at 58 - 62 °C for 3.4 - 3.6 h, then immerse it in sodium hydroxide solution with a mass 4 - 8 times that of the sol for 0.8 - 1.2 h. The immersion temperature is 58 - 62 °C. After the immersion ends, filter and wash, then immerse it in potassium chloride solution with a mass 4 - 8 times that of the sol for 1.0 - 1.4 h. The immersion temperature is 62 - 66 °C. After the immersion ends, filter and wash, and then dry at 63 - 68 °C for 3.8 - 4.2 h. Then, heat it at a rate of 5.7 - 6.2 °C / min to 475 - 484 °C and keep the calcination for 2.4 - 2.7 h. Wait for it to naturally return to room temperature to obtain silica gel;

[0015] The mass concentration of the sodium silicate solution is 26 - 30%;

[0016] The mass concentration of the sulfuric acid solution is 20 - 24%;

[0017] The mass ratio of cetyltrimethylammonium bromide to the sodium silicate solution is 0.2 - 0.4:8.0 - 8.5;

[0018] The mass concentration of the citric acid solution is 2.8 - 3.3%;

[0019] The mass ratio of the citric acid solution to the sodium silicate solution is 4.0 - 4.3:100;

[0020] The mass concentration of the sodium hydroxide solution is 6.3 - 6.7%;

[0021] The mass concentration of the potassium chloride solution is 9.5 - 10.4%;

[0022] (2)Modification

[0023] Place the silica gel in a pretreatment solution with a mass 6 - 10 times that of the silica gel, raise the temperature to 52 - 57 °C, keep stirring for 58 - 63 min. After the stirring ends, filter and dry, then put it into a modification solution with a mass 6 - 10 times that of the silica gel and stir and react at 70 - 74 °C for 2.8 - 3.2 h. After the stirring and reaction end, filter, wash and dry to obtain a defluorinating agent;

[0024] The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate. The mass ratio of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate is 100:2.3 - 2.8:1.5 - 1.8;

[0025] The components of the modification liquid are a 36wt% ethanol solution and KH550. The mass ratio of the 36wt% ethanol solution and KH550 is 100:1.0 - 1.4.

[0026] 2. Preliminary defluorination

[0027] The clarified phosphoric acid obtained after removing heavy metals, clarification, and pressure filtration is pumped into a reaction tank, heated to 78 - 83°C using a steam coil, and a defluorinating agent is added and stirred for reaction for 42 - 48 min. Then, the steam is turned off and stirring is stopped, and it is allowed to settle naturally for 0.8 - 1.3 h. After settlement, the supernatant is pumped into a defluorination reaction tank, a potassium chloride solution is added, and stirring reaction is carried out for 28 - 32 min, and then stirring reaction is continued for 3.8 - 4.3 h. After filtration and separation, the filtrate is collected to obtain preliminarily defluorinated phosphoric acid;

[0028] The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.2 - 0.4;

[0029] The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.23 - 0.27:1;

[0030] The mass concentration of the potassium chloride solution is 10 - 12%.

[0031] 3. Secondary defluorination

[0032] The preliminarily defluorinated phosphoric acid and the defluorinating agent are introduced into a defluorination tower. After being mixed evenly, a mixed acid solution is obtained; the mixed acid solution is heated to 68 - 72°C at a rate of 1.8 - 2.2°C / min and then sent to be sprayed inside the defluorination tower. High-temperature steam is introduced at the bottom of the defluorination tower to fully contact with 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 defluorinated phosphoric acid is sent to the finished acid tank;

[0033] The mass ratio of the preliminarily defluorinated phosphoric acid to the defluorinating agent is 100:0.6 - 0.8.

[0034] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0035] 1. The present invention prepares a defluorinating agent by a specific method. First, silica gel is prepared. Specifically, cetyltrimethylammonium bromide is added as a surfactant, and then a citric acid solution is added, which helps to promote the stability of the sol, increase the number of hydroxyl groups on the surface of the silica gel, and further promote the effect of defluorination by phosphoric acid. Combining with a potassium chloride solution, potassium ions are adsorbed on the surface of the silica gel, promoting the binding of the silica gel with fluoride ions. In the modification step, the pretreatment solution can promote the dispersion of the silica gel in phosphoric acid and has good compatibility with phosphoric acid, thus avoiding the agglomeration of the defluorinating agent and enhancing the defluorination effect. Sodium styrene sulfonate contains a benzene ring, which has a large rigidity. During the high-temperature stripping process, the molecular mobility is small, reducing its viscosity in the defluorination system, thereby promoting the reaction activity and further enhancing the defluorination effect. Combining with the modification solution, the surface of the defluorinating agent contains amino groups, which have good binding with fluorine, enhancing the defluorination performance and also enhancing the stability of the defluorinating agent, ensuring the stability of the defluorination effect, resulting in a low F content in the defluorinated phosphoric acid and excellent defluorination effect.

[0036] 2. Using the method of the present invention for defluorinating phosphoric acid, in the clarified phosphoric acid in the preliminary defluorination step, the P2O5 content is 37.64 wt%, the F content is 1.95 wt%, and the solid content is 0.43 wt%. It is measured that in the defluorinated phosphoric acid, the F content is 0.13 - 0.16 wt%, the phosphorus-fluorine ratio (P2O5 / F) is 318 - 409, and the solid content is 0.12 - 0.15 wt%. Specific embodiments

[0037] In order to understand the technical features, objectives, and effects of the present invention more clearly, the specific embodiments of the present invention are described below.

[0038] Example 1

[0039] 1. Preparation of defluorinating agent

[0040] (1) Preparation of silica gel

[0041] Add a 28 wt% sodium silicate solution to the reaction device, then add cetyltrimethylammonium bromide and perform ultrasonic treatment. The ultrasonic time is 22 min, the ultrasonic power is 68 W, and the ultrasonic frequency is 32 kHz. After the ultrasonic treatment, add a 22 wt% sulfuric acid solution until the pH value reaches 3.5, then stop adding the sulfuric acid solution. Next, add a 3.0 wt% citric acid solution, stir at 23 °C for 30 min, raise the temperature to 35 °C, and keep the reaction for 5.0 h. After the reaction, a sol is obtained; age the sol at 60 °C for 3.5 h, then immerse it in a sodium hydroxide solution with 6 times the mass and a concentration of 6.5 wt% at 60 °C for 1.0 h. After the immersion, filter and wash it, then immerse it in a potassium chloride solution with 6 times the mass and a concentration of 10.0 wt% at 64 °C for 1.2 h. After the immersion, filter and wash it, dry it at 65 °C for 4.0 h, then heat it to 480 °C at a rate of 6.0 °C / min, keep the temperature for calcination for 2.5 h, and wait for it to naturally return to room temperature to obtain silica gel;

[0042] The mass ratio of the cetyltrimethylammonium bromide to the sodium silicate solution is 0.3:8.2;

[0043] The mass ratio of the citric acid solution to the sodium silicate solution is 4.2:100.

[0044] (2)Modification

[0045] Place the silica gel in a pretreatment liquid with 8 times the mass, raise the temperature to 54 °C, keep stirring for 60 min. After the stirring, filter and dry it, then put it into a modification liquid with 8 times the mass, and stir and react at 72 °C for 3.0 h. After the stirring reaction, filter, wash, and dry it to obtain a defluorinating agent;

[0046] The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate. The mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate is 100:2.5:1.7;

[0047] The components of the modification liquid are a 36 wt% ethanol solution and KH550. The mass ratio of the 36 wt% ethanol solution to KH550 is 100:1.2.

[0048] 2. Preliminary defluorination

[0049] Pump the clarified phosphoric acid obtained after removing heavy metals, clarification, and pressure filtration into the reaction tank, heat it to 80 °C using a steam coil, add the defluorinating agent and stir and react for 45 min, turn off the steam and stop stirring, and let it settle naturally for 1.0 h. After settling, pump the supernatant into the defluorination reaction tank, add an 11 wt% potassium chloride solution, stir and react for 30 min, continue to stir and react for 4.0 h, and after filtration and separation, collect the filtrate to obtain preliminarily defluorinated phosphoric acid;

[0050] The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.3;

[0051] The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.25:1.

[0052] 3. Secondary defluorination

[0053] The preliminarily defluorinated phosphoric acid and the defluorinating agent are introduced into a defluorination tower. After being mixed evenly, a mixed acid solution is obtained. 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 with the mixed acid solution. The temperature of the high-temperature steam is 160 °C and the pressure is 0.7 MPa. 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 defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the defluorinated phosphoric acid is sent to the finished acid tank;

[0054] The mass ratio of the preliminarily defluorinated phosphoric acid to the defluorinating agent is 100:0.7.

[0055] The method of Example 1 is used for defluorination of phosphoric acid. Among them, for the clarified phosphoric acid in the preliminary defluorination step, the P2O5 content is 37.64 wt%, the F content is 1.95 wt%, and the solid content is 0.43 wt%. In the measured defluorinated phosphoric acid, the F content is 0.13 wt%, the phosphorus-fluorine ratio (P2O5 / F) is 409, and the solid content is 0.12 wt%.

[0056] Example 2

[0057] 1. Preparation of defluorinating agent

[0058] (1) Preparation of silica gel

[0059] Add a 26 wt% sodium silicate solution to the reaction device, then add cetyltrimethylammonium bromide for ultrasonic treatment. The ultrasonic time is 20 min, the ultrasonic power is 64 W, and the ultrasonic frequency is 30 kHz. After the ultrasonic treatment is completed, add a 20 wt% sulfuric acid solution until the pH value reaches 3.4, then stop adding the sulfuric acid solution, and then add a 2.8 wt% citric acid solution. Stir at 20 °C for 28 min, raise the temperature to 32 °C, and keep the reaction for 4.8 h. After the reaction is completed, a sol is obtained. The sol is aged at 58 °C for 3.4 h, then put into a 4-fold mass of 6.3 wt% sodium hydroxide solution and soaked for 0.8 h. The soaking temperature is 58 °C. After the soaking is completed, filter and wash, then put into a 4-fold mass of 9.5 wt% potassium chloride solution and soak for 1.0 h. The soaking temperature is 62 °C. After the soaking is completed, after filtration and washing, dry at 63 °C for 3.8 h, then raise the temperature to 475 °C at a rate of 5.7 °C / min, keep the calcination for 2.7 h, and wait for it to naturally return to room temperature to obtain silica gel;

[0060] The mass ratio of the cetyltrimethylammonium bromide to the sodium silicate solution is 0.2:8.0;

[0061] The mass ratio of the citric acid solution to the sodium silicate solution is 4.0:100.

[0062] (2)Modification

[0063] Place the silica gel in a pretreatment solution with a mass 6 times that of the silica gel, raise the temperature to 52 °C, keep stirring for 58 min. After the stirring ends, filter and dry, and then put it into a modification solution with a mass 6 times that of the silica gel, and stir and react at 70 °C for 2.8 h. After the stirring reaction ends, filter, wash and dry to obtain the defluorinating agent;

[0064] The pretreatment solution is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate. The mass ratio of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate is 100:2.3:1.5;

[0065] The components of the modification solution are a mixture of 36 wt% ethanol solution and KH550. The mass ratio of the 36 wt% ethanol solution to KH550 is 100:1.0.

[0066] 2. Preliminary defluorination

[0067] Pump the clarified phosphoric acid obtained after removing heavy metals, clarification, and pressure filtration into a reaction tank, heat it to 78 °C using a steam coil, add the defluorinating agent and stir and react for 42 min, turn off the steam and stop stirring, and let it settle naturally for 0.8 h. After settlement, pump the supernatant into a defluorination reaction tank, add a 10 wt% potassium chloride solution, stir and react for 28 min, continue to stir and react for 3.8 h, and after filtration and separation, collect the filtrate to obtain preliminarily defluorinated phosphoric acid;

[0068] The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.2;

[0069] The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.23:1.

[0070] 3. Secondary defluorination

[0071] Feed the preliminarily defluorinated phosphoric acid and the defluorinating agent into a defluorination tower, and obtain a mixed acid solution after mixing evenly; heat the mixed acid solution to 72 °C at a rate of 1.8 °C / min and then send it to be sprayed inside the defluorination tower. High-temperature steam is introduced at the bottom of the defluorination tower to fully contact with the mixed acid solution. The temperature of the high-temperature steam is 158 °C and the pressure is 0.8 MPa. The high-temperature steam heats the mixed acid solution, and control the temperature of the mixed acid solution after heating to 123 °C. After defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the defluorinated phosphoric acid is sent to the finished acid tank;

[0072] The mass ratio of the preliminary defluorinated phosphoric acid to the defluorinating agent is 100:0.6.

[0073] The method of Example 2 was used to defluorinate phosphoric acid. Among them, for the clarified phosphoric acid in the preliminary defluorination step, the P2O5 content was 37.64 wt%, the F content was 1.95 wt%, and the solid content was 0.43 wt%. In the measured defluorinated phosphoric acid, the F content was 0.16 wt%, the phosphorus-fluorine ratio (P2O5 / F) was 318, and the solid content was 0.15 wt%.

[0074] Example 3

[0075] 1. Preparation of defluorinating agent

[0076] (1) Preparation of silica gel

[0077] Add 30 wt% sodium silicate solution to the reaction device, then add cetyltrimethylammonium bromide and perform ultrasonic treatment. The ultrasonic time is 25 min, the ultrasonic power is 70 W, and the ultrasonic frequency is 34 kHz. After the ultrasonic treatment, add 24 wt% sulfuric acid solution until the pH value reaches 3.6, then stop adding sulfuric acid solution, and then add 3.3 wt% citric acid solution. Stir at 25 °C for 32 min, raise the temperature to 37 °C, and keep the reaction for 5.2 h. After the reaction, a sol is obtained. The sol is aged at 62 °C for 3.6 h, then put into 8 times the mass of 6.7 wt% sodium hydroxide solution and soaked for 1.2 h at 62 °C. After soaking, filter and wash, then put into 8 times the mass of 10.4 wt% potassium chloride solution and soak for 1.4 h at 66 °C. After soaking, filter and wash, dry at 68 °C for 4.2 h, then raise the temperature to 484 °C at a rate of 6.2 °C / min, keep the temperature for calcination for 2.4 h, and wait for it to naturally return to room temperature to obtain silica gel;

[0078] The mass ratio of the cetyltrimethylammonium bromide to the sodium silicate solution is 0.4:8.5;

[0079] The mass ratio of the citric acid solution to the sodium silicate solution is 4.3:100.

[0080] (2) Modification

[0081] Put the silica gel into 10 times the mass of the pretreatment solution, raise the temperature to 57 °C, keep stirring for 63 min. After stirring, filter and dry, then put into 10 times the mass of the modification solution, stir and react at 74 °C for 3.2 h. After the stirring reaction, filter, wash and dry to obtain the defluorinating agent;

[0082] The pretreatment liquid is a mixture of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate. The mass ratio of deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium p-styrenesulfonate is 100:2.8:1.8;

[0083] The components of the modification liquid are a mixture of 36 wt% ethanol solution and KH550. The mass ratio of the 36 wt% ethanol solution to KH550 is 100:1.4.

[0084] 2. Preliminary defluorination

[0085] The clarified phosphoric acid obtained after removing heavy metals, clarification, and pressure filtration is pumped into a reaction tank, heated to 83 °C using a steam coil, and a defluorinating agent is added and stirred for reaction for 48 min. The steam is turned off and stirring is stopped, and natural sedimentation is carried out for 1.3 h. After sedimentation, the supernatant is pumped into a defluorination reaction tank, and a 12 wt% potassium chloride solution is added and stirred for reaction for 32 min, and stirring is continued for reaction for 4.3 h. After filtration and separation, the filtrate is collected to obtain preliminarily defluorinated phosphoric acid;

[0086] The mass ratio of the clarified phosphoric acid to the defluorinating agent is 100:0.4;

[0087] The volume ratio of the potassium chloride solution to the clarified phosphoric acid is 0.27:1.

[0088] 3. Secondary defluorination

[0089] The preliminarily defluorinated phosphoric acid and the defluorinating agent are introduced into a defluorination tower, and after being mixed evenly, a mixed acid solution is obtained; the mixed acid solution is heated to 68 °C at a rate of 2.2 °C / min and then sent to be sprayed inside the defluorination tower. High-temperature steam is introduced at the bottom of the defluorination tower to fully contact with the mixed acid solution. The temperature of the high-temperature steam is 162 °C and the pressure is 0.6 MPa. 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 defluorination is completed, the fluorine-containing gas is discharged from the top of the defluorination tower, and the defluorinated phosphoric acid is sent to the finished acid tank;

[0090] The mass ratio of the preliminarily defluorinated phosphoric acid to the defluorinating agent is 100:0.8.

[0091] The method of Example 3 is used for defluorinating phosphoric acid. Among them, for the clarified phosphoric acid in the preliminary defluorination step, the P2O5 content is 37.64 wt%, the F content is 1.95 wt%, and the solid content is 0.43 wt%; it is measured that in the defluorinated phosphoric acid, the F content is 0.14 wt%, the phosphorus-fluorine ratio (P2O5 / F) is 374, and the solid content is 0.14 wt%.

[0092] Comparative Example 1

[0093] On the basis of Example 1, the difference is that

[0094] In the step of preparing silica gel, the operation of "re-adding it into a 10.0 wt% potassium chloride solution with 6 times the mass and soaking for 1.2 h at a soaking temperature of 64 °C" is omitted;

[0095] In the modification step, the pretreatment liquid is replaced with deionized water in equal amount;

[0096] All other operations are the same.

[0097] The phosphoric acid is defluorinated by the method of Comparative Example 1. Among them, for the clarified phosphoric acid in the preliminary defluorination step, the P2O5 content is 37.64 wt%, the F content is 1.95 wt%, and the solid content is 0.43 wt%; in the measured defluorinated phosphoric acid, the F content is 0.35 wt%, the phosphorus-fluorine ratio (P2O5 / F) is 127, and the solid content is 0.27 wt%.

[0098] Comparative Example 2

[0099] Based on Example 1, the changes are as follows:

[0100] 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" is omitted;

[0101] In the modification step, the modification liquid is replaced with 36 wt% ethanol solution in equal amount;

[0102] All other operations are the same.

[0103] The phosphoric acid is defluorinated by the method of Comparative Example 2. Among them, for the clarified phosphoric acid in the preliminary defluorination step, the P2O5 content is 37.64 wt%, the F content is 1.95 wt%, and the solid content is 0.43 wt%; in the measured defluorinated phosphoric acid, the F content is 0.30 wt%, the phosphorus-fluorine ratio (P2O5 / F) is 158, and the solid content is 0.21 wt%.

[0104] The present invention uses a specific method to prepare a defluorinating agent. First, silica gel is prepared. Specifically, cetyltrimethylammonium bromide is added as a surfactant, and then a citric acid solution is added, which helps to promote the stability of the sol, increase the number of hydroxyl groups on the surface of the silica gel, and further promote the effect of defluorination by phosphoric acid. Combining with a potassium chloride solution, potassium ions are adsorbed on the surface of the silica gel, promoting the binding of the silica gel to fluoride ions. In the modification step, the pretreatment solution can promote the dispersion of the silica gel in phosphoric acid and has good compatibility with phosphoric acid, thus avoiding the agglomeration of the defluorinating agent and enhancing the defluorination effect. Sodium styrene sulfonate contains a benzene ring, which has a large rigidity. During the high-temperature stripping process, the molecular mobility is small, weakening its viscosity in the defluorination system, thereby promoting the reaction activity and further enhancing the defluorination effect. Combining with the modification solution, the surface of the defluorinating agent contains amino groups, which have good binding properties with fluorine, enhancing the defluorination performance and also enhancing the stability of the defluorinating agent, ensuring the stability of the defluorination effect, resulting in a low F content in the defluorinated phosphoric acid and excellent defluorination effect.

[0105] In Comparative Example 1, the component of the pretreatment solution in the modification step was omitted, which made the dispersion of the defluorinating agent poor, with a strong agglomeration force in phosphoric acid and low reaction activity of the defluorinating agent, greatly affecting the defluorination effect. Moreover, Comparative Example 1 also omitted the process of soaking in the potassium chloride solution, which also weakened the binding with fluoride ions, ultimately resulting in a still relatively high fluoride content in the defluorinated phosphoric acid. In Comparative Example 2, the component of the modification solution in the modification step was omitted. On the one hand, it reduced the binding performance of the defluorinating agent with fluorine, and on the other hand, the stability of the defluorinating agent was weak, and the defluorination effect was unstable during the high-temperature stripping process. Moreover, Comparative Example 2 also omitted the process of soaking in the citric acid solution, which reduced the number of hydroxyl groups on the surface of the silica gel, affecting the binding with the potassium chloride solution and thus affecting the defluorination performance.

[0106] Unless otherwise specified, the ratios described in the present invention are all mass ratios, and the percentages are all mass percentages.

[0107] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within 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 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 ℃ for aging 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 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 styrene sulfonate; the mass ratio of the deionized water, fatty alcohol polyoxyethylene ether AEO-9, and sodium 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; The preliminary defluorination step comprises: injecting the clarified phosphoric acid obtained after heavy metal removal, clarification and pressure filtration 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 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, filtering and separating, and collecting the filtrate 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 secondary defluorination step comprises: 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 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.

2. A phosphoric acid defluorination method according to claim 1, 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%.

3. 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.

4. A phosphoric acid defluorination method according to claim 1, characterized in that: In the preliminary defluorination step, 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%.