Method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas produced as by-product in phosphoric acid industry

Abstract

The present invention discloses a method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical by-products, belonging to the field of wet-process phosphoric acid purification. This method is to send the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank and / or the wet-process phosphoric acid concentration evaporator into the gas absorption reaction device after condensation and gas-liquid separation to carry out a multi-stage countercurrent absorption reaction with wet-process phosphoric acid, and after filtration, wet-process purified phosphoric acid with low magnesium and aluminum contents can be obtained. This method uses the fluorine-containing tail gas from phosphorus chemical by-products as raw materials, and after simple treatment, it can be used to reduce magnesium and aluminum impurities in wet-process phosphoric acid. It can not only make full use of the fluorine resources in the fluorine-containing tail gas from phosphorus chemical by-products, greatly reduce the cost of removing impurities in wet-process phosphoric acid, but also play the role of stripping and concentration, reduce the fluorine ion content in wet-process phosphoric acid and increase the acid concentration of wet-process phosphoric acid, which is easy to realize industrialization and has obvious economic benefits.

Description

Technical Field

[0001] The present invention relates to a method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas as a by-product of phosphoric acid production, and belongs to the field of wet-process phosphoric acid purification. Background Art

[0002] The production methods of phosphoric acid are mainly divided into thermal process and wet process. Compared with the thermal process, the wet process of phosphoric acid determines that the obtained product phosphoric acid will contain many impurities such as iron, magnesium, and aluminum, and these impurities will have an extremely adverse impact on the production of downstream phosphorus chemicals. Therefore, wet-process phosphoric acid often needs to be further purified to remove iron, magnesium, aluminum and other impurities therein.

[0003] At present, there are many researches on the purification and impurity removal of wet-process phosphoric acid at home and abroad. The main methods include ion exchange method, electrodialysis method, crystallization method, membrane separation method, chemical precipitation method, solvent precipitation method, etc. Among them, the simplest and most economical purification method is the chemical precipitation method, and the most commonly used precipitant in the chemical precipitation method is fluoride. For example, Patent CN103523764A discloses a method for reducing magnesium and aluminum impurities in wet-process phosphoric acid, Patent CN106145074A discloses a wet-process phosphoric acid process for reducing the content of Al2O3 in wet-process phosphoric acid during production, Patent CN109809377A discloses a method for efficiently removing impurities from sulfuric acid-process wet-process phosphoric acid, U.S. Patent No. 4136199 describes a method for removing metal impurity ions (such as magnesium and aluminum) in wet-process phosphoric acid with sludge, U.S. Patent No. 36424399 proposes a method for removing magnesium in wet-process phosphoric acid by forming Mg-Al-F-P complex precipitate, and U.S. Patent No. 4710366 proposes adding sufficient fluorosilicic acid to dilute wet-process phosphoric acid to precipitate magnesium and aluminum impurities with fluorine. Essentially, these patents all use solid fluoride compounds as precipitants to combine magnesium and aluminum impurities in wet-process phosphoric acid with fluorine to form inorganic salt precipitates or complex precipitates for precipitation, so as to complete the purification of wet-process phosphoric acid. However, the fluorides used in these patents are solid, with a large dosage, high economic cost, and often introduce new impurity ions.

[0004] During the production process of wet-process phosphoric acid, a large amount of fluorine-containing tail gas will escape from the extraction reaction tank and the wet-process phosphoric acid concentration evaporator. Its main component is SiF4, and it contains a very small amount of phosphorus vapor and some water vapor, and does not contain other elements. Summary of the Invention

[0005] The present invention aims to provide a method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas as a by-product of phosphoric acid production. Using the fluorine-containing tail gas as a by-product of phosphoric acid production as a raw material, after simple treatment, it is directly used to reduce magnesium and aluminum impurities in wet-process phosphoric acid, so as to solve the problems of large dosage of fluoride, high economic cost and introduction of new impurity ions in the current chemical precipitation method for removing impurities in wet-process phosphoric acid.

[0006] The technical solution of the present invention is as follows: The fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank and / or the wet-process phosphoric acid concentration evaporator is condensed and subjected to gas-liquid separation, and then sent into a gas absorption reaction device to carry out a multi-stage countercurrent absorption reaction with wet-process phosphoric acid. After the reaction, filtration can obtain wet-process purified phosphoric acid with low contents of magnesium, aluminum and fluorine and high acid concentration.

[0007] A method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas produced as a by-product in the phosphoric acid industry, comprising the following steps:

[0008] (1) Sending the fluorine-containing tail gas into a gas absorption reaction device to carry out a multi-stage countercurrent absorption reaction with wet-process phosphoric acid;

[0009] (2) Filtering the wet-process phosphoric acid after the reaction in step (1) to obtain wet-process purified phosphoric acid.

[0010] The fluorine-containing tail gas is a fluorine-containing gas with a high fluorine content and a low water vapor content obtained by condensing and carrying out gas-liquid separation on the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank and / or the wet-process phosphoric acid concentration evaporator.

[0011] Among them, the fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 10-15%, the phosphorus vapor content is 2-4%, and the water vapor content is 80-90%; the fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid concentration evaporator is 30-40%, the phosphorus vapor content is 3-6%, and the water vapor content is 60-70%.

[0012] The temperature of the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank and the wet-process phosphoric acid concentration evaporator is 80-90°C. The condensation of the fluorine-containing tail gas is carried out by a condenser, and the temperature after condensation is 50-60°C; the gas-liquid separation of the fluorine-containing tail gas is carried out by a demister. The fluorine content in the fluorine-containing gas obtained after gas-liquid separation is 80-90%, the phosphorus vapor content is 6-10%, and the water vapor content is 5-10%.

[0013] In step (1), the concentration of the wet-process phosphoric acid used for impurity removal is 20-28% P2O5.

[0014] In the said step (1), the gas absorption reaction device is composed of at least two absorption towers connected in series; the volume percentage concentration of the fluorine-containing gas fed into the inlet of the first-stage absorption tower of the gas absorption reaction device is 4000-4500 ppm; the volume percentage concentration of the tail gas at the outlet of the last-stage absorption tower of the gas absorption reaction device ≤ 500 ppm; the tail gas at the outlet of the last-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling.

[0015] The wet-process phosphoric acid is added from the last-stage absorption tower of the gas absorption reaction device, and undergoes a multi-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device, and is withdrawn from the first-stage absorption tower of the gas absorption reaction device after the reaction ends.

[0016] The described gas absorption reaction device is composed of three-stage absorption towers connected in series. That is, in step (1), the gas absorption reaction device is composed of three-stage absorption towers connected in series; the volume percentage concentration of the fluorine-containing gas fed into the inlet of the first-stage absorption tower of the gas absorption reaction device is 4000 - 4500 ppm; the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device ≤ 500 ppm (the described volume percentage concentration ≤ 500 ppm is not equal to 0, generally greater than 200 and less than or equal to 500); the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device can be sent back to the inlet of the condenser for recycling.

[0017] In step (1), the wet-process phosphoric acid is added from the third-stage absorption tower of the gas absorption reaction device, and undergoes a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device, and is withdrawn from the first-stage absorption tower of the gas absorption reaction device after the reaction ends.

[0018] During the multi-stage countercurrent absorption reaction, the reaction temperature is controlled at 80 - 90 °C, the pressure is -50 - -60 kPa, and the reaction residence time is 1 - 3 hours.

[0019] In step (2), the wet-process phosphoric acid after the reaction is withdrawn from the first-stage absorption tower of the gas absorption reaction device is filtered by a filter press, and the obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) The raw material used in the present invention is the fluorine-containing tail gas as a by-product of the phosphorus chemical industry, which can be used to reduce the magnesium and aluminum impurities in the wet-process phosphoric acid after simple treatment, not only reducing or even eliminating the subsequent treatment cost of the fluorine-containing tail gas, but also reducing the reagent cost for removing metal impurities in the wet-process phosphoric acid by the chemical precipitation method, with obvious economic benefits.

[0022] (2) The present invention can not only make full use of the fluorine resources in the fluorine-containing tail gas as a by-product of the phosphorus chemical industry and recover a very small amount of phosphorus resources therein, but also will not introduce new impurity ions into the wet-process phosphoric acid during the impurity removal process.

[0023] (3) The present invention can also play a role in stripping and defluorination and concentration during the multi-stage countercurrent absorption reaction process, thereby reducing the fluorine ion content in the wet-process phosphoric acid and increasing the acid concentration of the wet-process phosphoric acid, and reducing the subsequent concentration energy consumption.

[0024] (4) The process of the present invention can be directly reformed on the existing wet-process phosphoric acid device, which is simple and easy to implement and easy to industrialize. Detailed Embodiments

[0025] To deepen the understanding of those skilled in the art of the present invention, the present invention will be further described in detail below in conjunction with specific embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0026] Example 1-1

[0027] A method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphoric acid production by-products includes the following steps:

[0028] (1) The fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank has a fluorine content of 10.9%, a phosphorus vapor content of 2.6%, a water vapor content of 86.5%, and a temperature of 87°C. It is sent to the inlet of the condenser and passes through the condenser and the demister in sequence. A fluorine-containing gas with a fluorine content of 86.3%, a phosphorus vapor content of 7.6%, a water vapor content of 6.1%, and a temperature of 54°C is obtained from the outlet of the demister;

[0029] (2) The fluorine-containing gas obtained in step (1) is sent to the inlet of the first-stage absorption tower of the gas absorption reaction device. The volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower is controlled to be 4100 ppm, and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device is 450 ppm. The tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling; The wet-process phosphoric acid with a P2O5 concentration of 25.8% for impurity removal is added from the third-stage absorption tower of the gas absorption reaction device, and a three-stage countercurrent absorption reaction is carried out with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, it is taken out from the first-stage absorption tower of the gas absorption reaction device. The reaction temperature is controlled to be 88°C, the pressure is -55 kPa, and the reaction residence time is 2 hours;

[0030] (3) The wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) is filtered by a filter press, and the obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0031] Example 1-2

[0032] The method and steps are the same as those in Example 1-1. Only in step (1), the fluorine-containing tail gas with a fluorine content of 35.8%, a phosphorus vapor content of 4.1%, a water vapor content of 60.1%, and a temperature of 87°C escaping from the wet-process phosphoric acid concentration evaporator is sent to the inlet of the condenser and passes through the condenser and the demister in sequence. A fluorine-containing gas with a fluorine content of 84.1%, a phosphorus vapor content of 7.2%, a water vapor content of 8.7%, and a temperature of 56°C is obtained from the outlet of the demister.

[0033] Example 1-3

[0034] The method and steps are the same as those in Example 1-1, except that in step (1), the fluorine-containing tail gases escaping from the wet-process phosphoric acid extraction reaction tank and the wet-process phosphoric acid concentration evaporator are mixed and then sent together to the inlet of the condenser, and are successively passed through the condenser and the demister. A fluorine-containing gas with a fluorine content of 87.5%, a phosphorus vapor content of 6.4%, a water vapor content of 6.1%, and a temperature of 57°C is obtained from the outlet of the demister.

[0035] Example 2

[0036] A method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical industry by-products, comprising the following steps:

[0037] (1) The fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank has a fluorine content of 10.9%, a phosphorus vapor content of 2.6%, a water vapor content of 86.5%, and a temperature of 87°C. Without condensation and gas-liquid separation, this fluorine-containing tail gas is directly sent to the inlet of the first-stage absorption tower of the gas absorption reaction device. The volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower is controlled to be 4400 ppm, and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower is 400 ppm. The tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling; The wet-process phosphoric acid with a P2O5 concentration of 25.5% for impurity removal is added from the third-stage absorption tower of the gas absorption reaction device, and a three-stage countercurrent absorption reaction is carried out with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, it is taken out from the first-stage absorption tower of the gas absorption reaction device. The reaction temperature is controlled to be 87°C, the pressure is -58 kPa, and the reaction residence time is 2 hours;

[0038] (2) The wet-process phosphoric acid after the reaction completed in step (1) and taken out from the first-stage absorption tower of the gas absorption reaction device is filtered by a filter press, and the obtained filtrate is the wet-process purified phosphoric acid with lower magnesium, aluminum, and fluorine contents and higher acid concentration.

[0039] Example 3-1

[0040] (1) The fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank has a fluorine content of 12.4%, a phosphorus vapor content of 2.2%, a water vapor content of 85.4%, and a temperature of 87°C. It is sent to the inlet of the condenser and successively passed through the condenser and the demister. A fluorine-containing gas with a fluorine content of 85.1%, a phosphorus vapor content of 8.2%, a water vapor content of 6.7%, and a temperature of 58°C is obtained from the outlet of the demister;

[0041] (2) Feed the fluorine-containing gas obtained in step (1) into the inlet of the first-stage absorption tower of the gas absorption reaction device. Control the volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower to be 3000 ppm and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower to be 410 ppm. Send the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device back to the inlet of the condenser for recycling. Add wet-process phosphoric acid with a concentration of 26.7% P2O5 for impurity removal from the third-stage absorption tower of the gas absorption reaction device, and carry out a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, take out the product from the first-stage absorption tower of the gas absorption reaction device. Control the reaction temperature to be 82 °C, the pressure to be -51 kPa, and the reaction residence time to be 2 hours.

[0042] (2) Filter the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (1) using a filter press. The obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0043] Example 3-2

[0044] (1) The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 13.7%, the phosphorus vapor content is 3.6%, the water vapor content is 82.7%, and the temperature is 82 °C. Feed it into the inlet of the condenser, and let it pass through the condenser and the demister in sequence. Obtain a fluorine-containing gas with a fluorine content of 86.6%, a phosphorus vapor content of 7.5%, a water vapor content of 5.9%, and a temperature of 53 °C from the outlet of the demister.

[0045] (2) Feed the fluorine-containing gas obtained in step (1) into the inlet of the first-stage absorption tower of the gas absorption reaction device. Control the volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower to be 5500 ppm and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower to be 410 ppm. Send the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device back to the inlet of the condenser for recycling. Add wet-process phosphoric acid with a concentration of 27.1% P2O5 for impurity removal from the third-stage absorption tower of the gas absorption reaction device, and carry out a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, take out the product from the first-stage absorption tower of the gas absorption reaction device. Control the reaction temperature to be 88 °C, the pressure to be -53 kPa, and the reaction residence time to be 2 hours.

[0046] (2) Filter the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (1) using a filter press. The obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0047] Example 4-1

[0048] (1)The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 14.1%, the phosphorus vapor content is 2.8%, the water vapor content is 83.1%, and the temperature is 86°C. It is sent to the inlet of the condenser and passes through the condenser and the demister in sequence. A fluorine-containing gas with a fluorine content of 82.6%, a phosphorus vapor content of 7.5%, a water vapor content of 9.9%, and a temperature of 58°C is obtained from the outlet of the demister;

[0049] (2)The fluorine-containing gas obtained in step (1) is sent to the inlet of the first-stage absorption tower of the gas absorption reaction device. The volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower is controlled at 4100 ppm, and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower is 450 ppm. The tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling; Wet-process phosphoric acid with a P2O5 concentration of 27.8% for impurity removal is added from the third-stage absorption tower of the gas absorption reaction device and undergoes a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction, it is taken out from the first-stage absorption tower of the gas absorption reaction device. The reaction temperature is controlled at 84°C, the pressure is -57 kPa, and the reaction residence time is 0.5 hour;

[0050] (3)The wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) is filtered by a filter press, and the obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0051] Example 4-2

[0052] (1)The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 10.8%, the phosphorus vapor content is 3.1%, the water vapor content is 86.1%, and the temperature is 84°C. It is sent to the inlet of the condenser and passes through the condenser and the demister in sequence. A fluorine-containing gas with a fluorine content of 84.9%, a phosphorus vapor content of 6.6%, a water vapor content of 8.5%, and a temperature of 59°C is obtained from the outlet of the demister;

[0053] (2)The fluorine-containing gas obtained in step (1) is sent to the inlet of the first-stage absorption tower of the gas absorption reaction device. The volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower is controlled at 4200 ppm, and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower is 690 ppm. The tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling; Wet-process phosphoric acid with a P2O5 concentration of 24.5% for impurity removal is added from the third-stage absorption tower of the gas absorption reaction device and undergoes a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction, it is taken out from the first-stage absorption tower of the gas absorption reaction device. The reaction temperature is controlled at 84°C, the pressure is -55 kPa, and the reaction residence time is 3 hours;

[0054] (3) Filter the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) using a filter press. The obtained filtrate is the wet-process purified phosphoric acid with low contents of magnesium, aluminum and fluorine and high acid concentration.

[0055] Example 5-1

[0056] (1) The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 11.1%, the phosphorus vapor content is 3.5%, the water vapor content is 85.4%, and the temperature is 83°C. Send it into the inlet of the condenser, and make it pass through the condenser and the demister in sequence. Obtain a fluorine-containing gas with a fluorine content of 85.1%, a phosphorus vapor content of 6.0%, a water vapor content of 8.9%, and a temperature of 53°C from the outlet of the demister;

[0057] (2) Send the fluorine-containing gas obtained in step (1) into the inlet of the first-stage absorption tower of the gas absorption reaction device. Control the volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower to be 4450 ppm and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower to be 380 ppm. Send the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device back to the inlet of the condenser for recycling; Add the wet-process phosphoric acid with a P2O5 concentration of 27.1% for impurity removal from the third-stage absorption tower of the gas absorption reaction device, and carry out a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, take it out from the first-stage absorption tower of the gas absorption reaction device. Control the reaction temperature to be 65°C, the pressure to be -57 kPa, and the reaction residence time to be 2 hours;

[0058] (3) Filter the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) using a filter press. The obtained filtrate is the wet-process purified phosphoric acid with low contents of magnesium, aluminum and fluorine and high acid concentration.

[0059] Example 5-2

[0060] (1) The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 14.3%, the phosphorus vapor content is 3.3%, the water vapor content is 82.4%, and the temperature is 81°C. Send it into the inlet of the condenser, and make it pass through the condenser and the demister in sequence. Obtain a fluorine-containing gas with a fluorine content of 88.7%, a phosphorus vapor content of 6.1%, a water vapor content of 5.2%, and a temperature of 56°C from the outlet of the demister;

[0061] (2) Feed the fluorine-containing gas obtained in step (1) into the inlet of the first-stage absorption tower of the gas absorption reaction device. Control the volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower to be 4250 ppm and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower to be 400 ppm. Send the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device back to the inlet of the condenser for recycling. Feed wet-process phosphoric acid with a concentration of 25.5% P2O5 for impurity removal into the third-stage absorption tower of the gas absorption reaction device, and carry out a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, take it out from the first-stage absorption tower of the gas absorption reaction device. Control the reaction temperature to be 107 °C, the pressure to be -58 kPa, and the reaction residence time to be 2 hours;

[0062] (3) Filter the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) using a filter press. The obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0063] Example 6-1

[0064] (1) The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 10.8%, the phosphorus vapor content is 3.2%, the water vapor content is 86.0%, and the temperature is 89 °C. Feed it into the inlet of the condenser, and make it pass through the condenser and the demister in sequence. Obtain a fluorine-containing gas with a fluorine content of 82.7%, a phosphorus vapor content of 7.4%, a water vapor content of 9.9%, and a temperature of 51 °C from the outlet of the demister;

[0065] (2) Feed the fluorine-containing gas obtained in step (1) into the inlet of the first-stage absorption tower of the gas absorption reaction device. Control the volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower to be 4100 ppm and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower to be 390 ppm. Send the tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device back to the inlet of the condenser for recycling. Feed wet-process phosphoric acid with a concentration of 27.7% P2O5 for impurity removal into the third-stage absorption tower of the gas absorption reaction device, and carry out a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, take it out from the first-stage absorption tower of the gas absorption reaction device. Control the reaction temperature to be 83 °C, the pressure to be -20 kPa, and the reaction residence time to be 2 hours;

[0066] (3) Filter the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) using a filter press. The obtained filtrate is the wet-process purified phosphoric acid with low magnesium, aluminum, and fluorine contents and high acid concentration.

[0067] Example 6-2

[0068] (1) The fluorine content in the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank is 14.3%, the phosphorus vapor content is 2.7%, the water vapor content is 83.0%, and the temperature is 84°C. It is sent to the inlet of the condenser and passes through the condenser and the demister in sequence. A fluorine-containing gas with a fluorine content of 84.4%, a phosphorus vapor content of 8.9%, a water vapor content of 6.7%, and a temperature of 59°C is obtained from the outlet of the demister;

[0069] (2) The fluorine-containing gas obtained in step (1) is sent to the inlet of the first-stage absorption tower of the gas absorption reaction device. The volume percentage concentration of the fluorine-containing gas at the inlet of the first-stage absorption tower is controlled to be 4300 ppm, and the volume percentage concentration of the tail gas at the outlet of the third-stage absorption tower is 480 ppm. The tail gas at the outlet of the third-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling; Wet-process phosphoric acid with a P2O5 concentration of 24.9% for impurity removal is added from the third-stage absorption tower of the gas absorption reaction device and undergoes a three-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device. After the reaction is completed, it is taken out from the first-stage absorption tower of the gas absorption reaction device. The reaction temperature is controlled to be 87°C, the pressure is -80 kPa, and the reaction residence time is 2 hours;

[0070] (3) The wet-process phosphoric acid after the reaction completed and taken out from the first-stage absorption tower of the gas absorption reaction device in step (2) is filtered by a filter press, and the obtained filtrate is the wet-process purified phosphoric acid with low contents of magnesium, aluminum, and fluorine and high acid concentration.

[0071] The contents of P2O5, Al2O3, MgO, and F in the wet-process phosphoric acid before and after impurity removal in Examples 1 to 6 are detected and compared. The purification and impurity removal effects of the wet-process phosphoric acid are shown in Table 1.

[0072] Table 1 Purification and impurity removal effects of wet-process phosphoric acid in Examples 1 to 6

[0073] .

Claims

1. A method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical by-products, characterized in that, It includes the following steps: (1) Feed the fluorine-containing tail gas into a gas absorption reaction device to carry out a multi-stage countercurrent absorption reaction with wet-process phosphoric acid; a demister is used for the gas-liquid separation of the fluorine-containing tail gas. After the gas-liquid separation, the fluorine content in the obtained fluorine-containing gas is 80-90%, the phosphorus vapor content is 6-10%, and the water vapor content is 5-10%; the volume percentage concentration of the fluorine-containing gas fed into the inlet of the first-stage absorption tower of the gas absorption reaction device is 4000-4500 ppm; the volume percentage concentration of the tail gas at the outlet of the last-stage absorption tower of the gas absorption reaction device ≤ 500 ppm. During the multi-stage countercurrent absorption reaction, control the reaction temperature at 80-90 °C, the pressure at -50 to -60 kPa, and the reaction residence time at 1-3 hours; (2) Filter the wet-process phosphoric acid after the reaction in step (1) to obtain wet-process purified phosphoric acid.

2. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphoric chemical by-products according to claim 1, wherein, The fluorine-containing tail gas is the tail gas escaping from a wet-process phosphoric acid extraction reaction tank and / or a wet-process phosphoric acid concentration evaporator; In the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank, the fluorine content is 10-15%, the phosphorus vapor content is 2-4%, the water vapor content is 80-90%, and the temperature is 80-90 °C; In the fluorine-containing tail gas escaping from the wet-process phosphoric acid concentration evaporator, the fluorine content is 30-40%, the phosphorus vapor content is 3-6%, the water vapor content is 60-70%, and the temperature is 80-90 °C.

3. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical by-products according to claim 2, characterized in that, In step (1), for the fluorine-containing tail gas escaping from the wet-process phosphoric acid extraction reaction tank and the wet-process phosphoric acid concentration evaporator, a condenser is used, and the temperature after condensation is 50-60 °C.

4. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical by-products according to claim 1, wherein In step (1), the concentration of the wet-process phosphoric acid is 20-28%.

5. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphoric chemical by-products according to claim 1, characterized in that, In step (1), the gas absorption reaction device is composed of at least two stages of absorption towers connected in series; the tail gas at the outlet of the last-stage absorption tower of the gas absorption reaction device is sent back to the inlet of the condenser for recycling.

6. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical by-products according to claim 5, wherein, In step (1), the wet-process phosphoric acid is added from the last-stage absorption tower of the gas absorption reaction device and carries out a multi-stage countercurrent absorption reaction with the fluorine-containing gas in the gas absorption reaction device, and is taken out from the first-stage absorption tower of the gas absorption reaction device after the reaction ends.

7. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphorus chemical by-products according to claim 6, characterized in that, The gas absorption reaction device is composed of three stages of absorption towers connected in series.

8. The method for reducing magnesium and aluminum impurities in wet-process phosphoric acid by using fluorine-containing tail gas from phosphoric chemical by-products according to claim 1, characterized in that, In step (2), the wet-process phosphoric acid after the reaction taken out from the first-stage absorption tower of the gas absorption reaction device is filtered by a filter press, and the obtained filtrate is the wet-process purified phosphoric acid with low contents of magnesium, aluminum, and fluorine and high acid concentration.