A concentration process for fluosilicic acid

Abstract

The present invention discloses a process for concentrating fluorosilicic acid, comprising the following steps: S1, subjecting a fluorosilicic acid solution having a mass concentration of less than 25% to cyclic gas-liquid contact with a first gas-phase heat medium and separating water vapor to obtain a primary concentrated fluorosilicic acid having a temperature of 40 to 70°C and a mass concentration of 30 to 35%; S2, subjecting the primary concentrated fluorosilicic acid in S1 to cyclic gas-liquid contact with a second gas-phase heat medium and separating water vapor to obtain a secondary concentrated fluorosilicic acid having a temperature of 20 to 40°C; wherein the temperature of the primary concentrated fluorosilicic acid is greater than that of the secondary concentrated fluorosilicic acid. The present invention employs two staged concentrations, the two concentrations being process flows and process technical parameters selected based on the differences in the stability of fluorosilicic acid under different conditions, thereby achieving an overall optimal concentration concentration, concentration time, and fluorine yield.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, in particular to a process for concentrating fluosilicic acid. Background Art

[0002] Fluorosilicic acid, a byproduct of the phosphate fertilizer and phosphoric acid industries, is a raw material for the production of sodium fluosilicate, aluminum fluoride, ammonium fluoride, and other products. With the increasing maturity of the fluosilicic acid process for producing anhydrous hydrogen fluoride, fluosilicic acid has become increasingly important in the fluorine chemical industry. However, fluosilicic acid produced as a byproduct of the phosphate fertilizer and phosphoric acid industries has a low concentration, generally ranging from 10% to 18% by mass. Its high water content results in a low commercial added value. High-concentration fluosilicic acid, on the other hand, is widely used in a variety of fields, including fluorine chemical industry, metallurgical electrolysis, and electroplating, offering high economic benefits. Therefore, it is necessary to concentrate low-concentration fluosilicic acid to increase its economic value.

[0003] Existing processes often use low-temperature concentration processes to concentrate fluosilicic acid. However, due to the limitations of the heat and mass transfer processes of the low-temperature concentration process, the concentration efficiency (including concentration concentration and concentration time) will be significantly affected. Since fluosilicic acid itself has poor thermal stability, it will decompose into silicon tetrafluoride and hydrogen fluoride gas when heated, resulting in a low fluorine yield of the product. Therefore, it is often difficult to improve the concentration efficiency of fluosilicic acid while taking into account the fluorine yield of the product. Summary of the Invention

[0004] The object of the present invention is to provide a process for concentrating fluosilicic acid to solve the contradiction that fluosilicic acid concentration efficiency and product fluorine yield cannot be taken into account at the same time.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A process for concentrating fluosilicic acid comprises the following steps:

[0007] S1. subjecting a fluosilicic acid solution having a mass concentration of less than 25% to cyclic gas-liquid contact with a first gas-phase heat medium and separating water vapor to obtain a concentrated fluosilicic acid having a temperature of 40 to 70° C. and a mass concentration of 30 to 35%;

[0008] S2, subjecting the once-concentrated fluorosilicic acid in S1 to cyclic gas-liquid contact with a second gas-phase heat medium and separating water vapor to obtain a second-concentrated fluorosilicic acid having a temperature of 20 to 40° C.;

[0009] The temperature of the fluosilicic acid after the first concentration is greater than the temperature of the fluosilicic acid after the second concentration.

[0010] Preferably, the temperature of the first gas-phase heat medium is 50-120°C, and the temperature of the second gas-phase heat medium is 30-80°C.

[0011] Preferably, the water content of the first gas phase heat medium is 5.3-8.1 g / Nm 3 .

[0012] Preferably, the gas flow rate during the gas-liquid contact process between the fluorosilicic acid solution in S1 and the first gas phase heat medium is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0013] Preferably, the water content of the second gas phase heat medium is 1.9 to 2.7 g / Nm 3 .

[0014] Preferably, the gas flow rate during the gas-liquid contact process of the fluorosilicic acid concentrated once in S2 and the second gas phase heat medium is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0015] Preferably, the gas-liquid contact in S1 and S2 is countercurrent contact.

[0016] Preferably, in S1, the hydrosilicic acid solution is mixed with an oxidant and then circulated with the first gas-phase heat medium for gas-liquid contact.

[0017] More preferably, the mass concentration of the oxidant is 20% to 40%. More preferably, the mass of the oxidant accounts for 1‰ to 2‰ of the mass of the fluosilicic acid, calculated on a pure basis.

[0018] Preferably, the obtained secondary concentrated fluorosilicic acid is subjected to arsenic removal treatment using an arsenic removal agent. More preferably, the agent used in the arsenic removal process is sulfide.

[0019] More preferably, the pressure environment for arsenic removal is a positive pressure of 10 to 60 kPa.

[0020] More preferably, the dosage of the reagent in the arsenic removal process is 2-4‰ of the mass of the fluosilicic acid solution.

[0021] More preferably, the dearsenicization reaction temperature is 20-40° C., and the residence time is 5-20 min.

[0022] Preferably, the concentrated fluorosilicic acid after the arsenic removal treatment is subjected to H2S gas treatment.

[0023] The beneficial effects of the present invention are:

[0024] The fluorosilicic acid concentration process provided by the present invention uses two staged concentrations, and the two concentrations are based on the process flow and process technology parameters selected based on the stability difference of fluorosilicic acid under different conditions, for achieving the overall optimization of concentration efficiency (concentration concentration and concentration time) and fluorine yield. Fluorosilicic acid is first concentrated under relatively high temperature conditions. Since the fluorosilicic acid concentration is relatively low at this time, even if concentrated at relatively high temperatures, the gas phase SiF4 partial pressure in equilibrium with the liquid phase is still relatively low, so that while obtaining a higher concentration efficiency, excessive decomposition of fluorosilicic acid can be avoided; After fluorosilicic acid is concentrated at high temperature, the concentration is increased. If high temperature concentration is continued at this time, the decomposition of fluorosilicic acid will be extremely significant. Therefore, after fluorosilicic acid is concentrated at high temperature, it enters low temperature concentration so that at relatively high concentrations, the decomposition of fluorosilicic acid can be controlled, so that the fluorine yield is also relatively high while the fluorosilicic acid concentration efficiency is relatively high.

[0025] Existing processes either perform concentration and impurity removal separately or only remove one impurity during concentration, resulting in high processing costs. The present invention achieves concentration and removal of multiple impurities (arsenic, iodine, and chlorine) in a single process, effectively reducing processing costs. Through oxidation, iodine ions are converted to elemental iodine and trivalent arsenic is converted to pentavalent arsenic. Iodine and chlorine are then removed through gas stripping during the concentration process, while pentavalent arsenic is removed through chemical precipitation.

[0026] Existing fluorosilicic acid arsenic removal processes mostly operate at atmospheric or negative pressure, requiring large amounts of arsenic removal agents or creating a poor operating environment. The present invention utilizes positive pressure arsenic removal, using solid-phase sulfide as the arsenic removal agent. This facilitates production control, effectively reduces arsenic removal agent usage, improves the operating environment, and achieves thorough arsenic removal.

[0027] Existing fluosilicic acid concentration processes either require high energy consumption, such as vacuum falling film evaporation, or fail to fully utilize waste heat and low-grade thermal energy resources. The present invention utilizes process exhaust and waste gases as dry air for concentration, and utilizes low-grade thermal energy produced as a by-product of various industrial processes for heating the circulating fluid, resulting in significant energy savings. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solution of the invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0029] In order to ensure high concentration efficiency of fluosilicic acid and high fluorine yield of the product, the present invention provides a fluosilicic acid concentration process, comprising the following steps:

[0030] S1. subjecting a fluosilicic acid solution having a mass concentration of less than 25% to cyclic gas-liquid contact with a first gas-phase heat medium and separating water vapor to obtain a concentrated fluosilicic acid having a temperature of 40 to 70° C. and a mass concentration of 30 to 35%;

[0031] S2, subjecting the once-concentrated fluorosilicic acid in S1 to cyclic gas-liquid contact with a second gas-phase heat medium and separating water vapor to obtain a second-concentrated fluorosilicic acid having a temperature of 20 to 40° C.;

[0032] The temperature of the fluosilicic acid after the first concentration is greater than the temperature of the fluosilicic acid after the second concentration.

[0033] The two-step concentration mechanism of the present invention:

[0034] Fluorosilicic acid readily decomposes into SiF4 and HF upon heating. One of the most important properties of the fluosilicic acid concentration process is the equilibrium partial pressure of the fluosilicic acid solution, including the partial pressures of SiF4, HF, and H2O. The equilibrium partial pressures of the gases in the fluosilicic acid solution are closely related to the fluosilicic acid concentration and liquidus temperature. Through extensive experimental research, the inventors found that when the concentration of the fluosilicic acid solution is less than 25%, and the liquidus temperature is less than 70°C, the equilibrium partial pressures of HF and SiF4 are almost nonexistent. However, when the temperature exceeds 70°C, the partial pressure of SiF4 begins to increase. Therefore, the present invention chooses to perform high-temperature concentration in the first stage to maximize the efficiency of fluosilicic acid concentration.

[0035] When the concentration of the fluosilicic acid solution is within the range of 30% to 40%, the equilibrium partial pressure of SiF4 increases rapidly. If the temperature continues to exceed 70°C, the equilibrium partial pressure of SiF4 and HF at the liquid surface of the fluosilicic acid concentrated solution rises significantly, causing a large amount of fluosilicic acid decomposition. Furthermore, the inventors found that when conducting concentration experiments, the higher the fluosilicic acid concentration in the product, the lower the average evaporation intensity of water. Therefore, the present invention selects a second low-temperature concentration treatment of the fluosilicic acid concentrate in the second stage to reduce the decomposition of fluosilicic acid and achieve an increase in fluorine yield.

[0036] The present invention carries out cyclic contact between the gas and liquid phases, and the circulation is used to achieve relative temperature stability to obtain a fluosilicic acid solution with a relatively stable mass concentration. The concentration of the fluosilicic acid during the concentration process is controlled by the temperature of the gaseous heat medium to facilitate the mass transfer and heat transfer process. Furthermore, the temperature of the first gaseous heat medium is 50 to 120°C, and the temperature of the second gaseous heat medium is 30 to 80°C. In some embodiments of the present invention, the temperature of the first gaseous heat medium is any one of 50°C, 85°C, 90°C, and 120°C, or a value between the two, and the temperature of the second gaseous heat medium is any one of 30°C, 40°C, 60°C, and 80°C, or a value between the two. In some embodiments of the present invention, the temperature of the fluosilicic acid after the first concentration is any one of 40°C, 50°C, 60°C, and 70°C, or a value between the two, and the temperature of the fluosilicic acid after the second concentration is any one of 20°C, 30°C, and 40°C, or a value between the two.

[0037] It should be noted that the initial mass concentration of the fluorosilicic acid raw material of the present invention is less than 25%. In some embodiments of the present invention, the initial mass concentration of the fluorosilicic acid raw material is 15.3%. As long as the initial mass concentration is less than 25%, the single concentration of the present invention can be carried out, and the technical effect brought about by the fluorosilicic acid raw material with a mass concentration of 15.3% in the embodiment of the present invention will not produce a significant difference. After the single concentration, in some embodiments of the present invention, the mass concentration of the fluorosilicic acid after the single concentration is any one of 30.5%, 31.1%, 31.7% and 32.4%, or a value between the two.

[0038] The first and second vapor-phase heat media of the present invention can be any conventional medium capable of separating water vapor, such as air, nitrogen, etc. To further reduce costs and energy consumption, dry air is preferred, and the air can be process tail gas or waste gas.

[0039] In the present invention, the water content of the first gas phase heat medium is 5.3-8.1 g / Nm 3 The gas flow rate during the contact between the hydrosilicic acid solution in S1 and the first gas phase heat medium is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0040] In the present invention, the water content of the second gas phase heat medium is 1.9 to 2.7 g / Nm 3 The gas flow rate during the contact process between the concentrated fluorosilicic acid in S2 and the second gas phase heat medium is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0041] For better mass and heat transfer, preferably, the contact in S1 and S2 is countercurrent contact.

[0042] Fluorosilicic acid solutions often contain various impurities such as iodine, arsenic, and chlorine, which affect the quality of the concentrated product. In order to further achieve the effect of impurity removal while ensuring high fluosilicic acid concentration efficiency and product fluorine yield, the present invention also includes: in S1, the fluosilicic acid solution is first mixed with an oxidant and then subjected to cyclic gas-liquid contact with the first gas-phase heat medium. The mass concentration of the oxidant is 20% to 40%. The oxidant can be any oxidant in the art that can oxidize iodide ions and trivalent arsenic. The oxidant oxidizes iodine ions into iodine molecules and converts trivalent arsenic into pentavalent arsenic. Subsequent contact with the first gas-phase heat medium and the second gas-phase heat medium removes impurities such as iodine and chlorine through gas stripping. In some embodiments of the present invention, the oxidant is hydrogen peroxide with a mass concentration of 25%. The mass of the oxidant accounts for 1‰ to 2‰ of the mass of the fluosilicic acid, calculated as the mass of the pure substance.

[0043] Preferably, the secondary concentrated fluosilicic acid is subjected to arsenic removal treatment using a dearsenicizing agent. More preferably, the agent used in the dearsenicization process is a sulfide. In some embodiments of the present invention, the sulfide is selected from one or more of sodium sulfide and hydrogen sulfide. After dearsenicization, a solid and a liquid are obtained. The solid is treated as waste residue, and the liquid is the concentrated and impurity-free fluosilicic acid.

[0044] The pressure environment of the arsenic removal described in the present invention is positive pressure. The arsenic removal agent is introduced into the closed reactor to react with the fluorosilicic acid solution. The hydrogen sulfide gas produced increases the gas phase pressure. The pressure is controlled by controlling the feeding rate. At the same time, a pressure relief valve is provided to automatically release the pressure when the pressure exceeds the set value. The positive pressure arsenic removal pressure of the present invention is between 10kPa and 60kPa. In some embodiments of the present invention, the amount of the agent used in the arsenic removal process is any one of 2‰, 3‰, 4‰ of the mass of the fluorosilicic acid solution, or a value between the two. In some embodiments of the present invention, the arsenic removal reaction temperature is any one of 20°C, 30°C, 34°C and 40°C, or a value between the two. In some embodiments of the present invention, the residence time is any one of 5min, 10min and 20min, or a value between the two.

[0045] The arsenic impurity in the concentrated fluorosilicic acid can be removed by arsenic removal treatment. The present invention adopts positive pressure arsenic removal, which is convenient for production control and can effectively reduce the amount of arsenic removal agent used, is more environmentally friendly, and removes arsenic thoroughly.

[0046] Furthermore, the present invention can also subject the concentrated fluorosilicic acid after the arsenic removal treatment to H2S gas treatment to remove H2S impurities contained in the product.

[0047] The above is a detailed description of the present invention, and the following are embodiments of the present invention:

[0048] Example 1

[0049] This embodiment provides a process for concentrating fluosilicic acid, comprising the following steps:

[0050] S1. Fluorosilicic acid solution (H2SiF6 mass concentration of 15.3%, iodine concentration of 24ppm, chlorine concentration of 436ppm, arsenic content of 24ppm) and hydrogen peroxide (mass concentration of 25%, the amount added is controlled to be 1‰ of the mass of fluosilicic acid) are mixed, and the mixed solution is subjected to gas-liquid countercurrent contact with first hot air and water vapor is separated to obtain a concentrated fluosilicic acid with a mass concentration of 30.5%; the temperature of the first hot air is 50°C, the water content is 5.3g / Nm 3 The temperature of the concentrated fluorosilicic acid is 70°C, the gas flow rate is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m3 The gas-liquid contact time is 6 to 8 seconds.

[0051] S2, the fluosilicic acid after the primary concentration is contacted with the second hot air in a gas-liquid countercurrent manner and the water vapor is separated to obtain the fluosilicic acid after the secondary concentration, the mass concentration of which is 36.5%; the temperature of the second hot air is 80 ° C, the water content is 2.7 g / Nm 3 The temperature of the fluosilicic acid after the secondary concentration is 20°C, the gas flow rate is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0052] S3. Sodium sulfide was added to the secondary concentrated silicofluoric acid in an amount of 2‰ of the mass of the silicofluoric acid solution. The arsenic removal operation pressure was 45 kPa, the arsenic removal reaction temperature was 34°C, and the residence time was 10 min. After filtration, the arsenic removal acid had an As content of 0.6 ppm.

[0053] S4. The fluorosilicic acid after arsenic removal in S3 is sent to a H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0054] The total fluorine yield during the concentration process is 96.8%, the concentration of the finished product iodine fluorosilicate is 2.1ppm, and the chlorine concentration is 40.3ppm; the tail gas is discharged after being defoamed and washed to meet the standards.

[0055] Example 2

[0056] This embodiment provides a process for concentrating fluosilicic acid, comprising the following steps:

[0057] S1, a fluosilicic acid solution (fluosilicic acid mass concentration of 15.3%, iodine concentration of 24ppm, chlorine concentration of 436ppm, arsenic content of 24ppm) and hydrogen peroxide (its mass concentration is 25%, and the amount added is controlled to be 2‰ of the mass of the fluosilicic acid) are mixed, and the mixed solution is subjected to gas-liquid countercurrent contact with a first hot air and water vapor is separated to obtain a concentrated fluosilicic acid with a mass concentration of 31.1%; the temperature of the first hot air is 85°C, and the water content is 8.1g / Nm 3 The temperature of the concentrated fluorosilicic acid is 60°C, the gas flow rate is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0058] S2, the fluosilicic acid after the primary concentration is contacted with the second hot air in a gas-liquid countercurrent manner and the water vapor is separated to obtain the fluosilicic acid after the secondary concentration, the mass concentration of which is 36.2%; the temperature of the second hot air is 60 ° C, the water content is 2.1g / Nm 3The temperature of the fluosilicic acid after secondary concentration is 40°C, the gas flow rate is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0059] S3. Sodium sulfide was added to the secondary concentrated fluosilicic acid in an amount of 4‰ of the fluosilicic acid solution mass. The arsenic removal operating pressure was 45 kPa, the arsenic removal reaction temperature was 34°C, and the residence time was 10 min. After filtration, the arsenic removal acid had an As content of 0.5 ppm.

[0060] S4. The fluorosilicic acid after arsenic removal in S3 is sent to a H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0061] The total fluorine yield during the concentration process is 94.5%, the concentration of the finished product iodine fluorosilicate is 1.7ppm, and the chlorine concentration is 36.3ppm; the tail gas is discharged after being defoamed and washed to meet the standards.

[0062] Example 3

[0063] This embodiment provides a process for concentrating fluosilicic acid, comprising the following steps:

[0064] S1, a fluosilicic acid solution (fluosilicic acid mass concentration of 15.3%, iodine concentration of 24ppm, chlorine concentration of 436ppm, arsenic content of 24ppm) and hydrogen peroxide (its mass concentration is 25%, and the amount added is controlled to be 1.5‰ of the mass of fluosilicic acid) are mixed, and the mixed solution is subjected to gas-liquid countercurrent contact with a first hot air and water vapor is separated to obtain a concentrated fluosilicic acid with a mass concentration of 31.7%; the temperature of the first hot air is 120°C, and the water content is 6.4g / Nm 3 The temperature of the concentrated fluorosilicic acid is 50°C, the gas flow rate is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0065] S2, the fluosilicic acid after the primary concentration is contacted with the second hot air in a gas-liquid countercurrent manner and the water vapor is separated to obtain the fluosilicic acid after the secondary concentration, the mass concentration of which is 39.6%; the temperature of the second hot air is 30 ° C, the water content is 1.9 g / Nm 3 The temperature of the fluosilicic acid after the secondary concentration is 30°C, the gas flow rate is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0066] S3. Sodium sulfide was added to the secondary concentrated silicofluoric acid in an amount of 3‰ of the mass of the silicofluoric acid solution. The arsenic removal operation pressure was 45 kPa, the arsenic removal reaction temperature was 30°C, and the residence time was 10 min. After filtration, the arsenic removal acid had an As content of 0.5 ppm.

[0067] S4. The fluorosilicic acid after arsenic removal in S3 is sent to a H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0068] The total fluorine yield during the concentration process is 95.3%, the concentration of the finished product iodine fluorosilicate is 1.9 ppm, and the chlorine concentration is 37.9 ppm; the tail gas is discharged after being defoamed and washed to meet the standards.

[0069] Example 4

[0070] This embodiment provides a process for concentrating fluosilicic acid, comprising the following steps:

[0071] S1, a fluosilicic acid solution (fluosilicic acid mass concentration of 15.3%, iodine concentration of 24ppm, chlorine concentration of 436ppm, arsenic content of 24ppm) and hydrogen peroxide (its mass concentration is 25%, and the amount added is controlled to be 1.5‰ of the mass of the fluosilicic acid) are mixed, and the mixed solution is subjected to gas-liquid countercurrent contact with a first hot air and water vapor is separated to obtain a concentrated fluosilicic acid with a mass concentration of 32.4%; the temperature of the first hot air is 90°C, and the water content is 6.4g / Nm 3 The temperature of the concentrated fluorosilicic acid is 40°C, the gas flow rate is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0072] S2, the fluosilicic acid after the primary concentration is contacted with the second hot air in a gas-liquid countercurrent manner and the water vapor is separated to obtain the fluosilicic acid after the secondary concentration, the mass concentration of which is 42.1%; the temperature of the second hot air is 40 ° C, the water content is 1.9 g / Nm 3 The temperature of the fluosilicic acid after the secondary concentration is 30°C, the gas flow rate is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0073] S3. Sodium sulfide was added to the secondary concentrated silicofluoric acid in an amount of 3‰ of the mass of the silicofluoric acid solution. The arsenic removal operation pressure was 45 kPa, the arsenic removal reaction temperature was 30°C, and the residence time was 10 min. After filtration, the arsenic removal acid had an As content of 0.6 ppm.

[0074] S4. The fluorosilicic acid after arsenic removal in S3 is sent to a H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0075] The total fluorine yield during the concentration process was 94.7%, the content of arsenic fluorosilicate in the finished product was 0.6 ppm, the iodine concentration was 1.8 ppm, and the chlorine concentration was 35.4 ppm; the tail gas was discharged after being defoamed and washed to meet the standards.

[0076] Comparative Example 1

[0077] A process for concentrating fluosilicic acid comprises the following steps:

[0078] S1. Mix a fluosilicic acid solution (fluosilicic acid mass concentration of 15.3%, iodine concentration of 24 ppm, chlorine concentration of 436 ppm, arsenic content of 24 ppm) and hydrogen peroxide (its mass concentration is 25%, and the amount added is controlled to be 2‰ of the mass of the fluosilicic acid in terms of pure value), and contact the mixed solution with hot air in countercurrent flow for mass and heat transfer to obtain concentrated fluosilicic acid with a mass concentration of 35.7%; the temperature of the hot air is 80°C, and the water content is <20 g / Nm 3 The temperature of the concentrated fluorosilicic acid is 70°C, the gas flow rate is 3m / s, and the liquid-gas ratio is ≤8L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0079] S2. Sodium sulfide is added to the concentrated fluosilicic acid to perform arsenic removal at normal pressure. The amount of arsenic removal agent used is 2‰ of the mass of the fluosilicic acid solution. The arsenic removal reaction temperature is 58°C and the residence time is 10 minutes. After filtration, the As content of the dearsenicated acid is 5 ppm.

[0080] S3. The fluorosilicic acid after dearsenification of S2 is sent to an H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0081] The total fluorine yield during the concentration process is 63.4%, the concentration of the finished iodine fluorosilicate is 1.2ppm, and the chlorine concentration is 28.4ppm; the tail gas is discharged after being defoamed and washed to meet the standards.

[0082] Comparative Example 2

[0083] A process for concentrating fluosilicic acid comprises the following steps:

[0084] S1. Mix a fluosilicic acid solution (fluosilicic acid mass concentration of 15.3%, iodine concentration of 24 ppm, chlorine concentration of 436 ppm, arsenic content of 24 ppm) and hydrogen peroxide (its mass concentration is 25%, and the amount added is controlled to be 1.5‰ of the mass of the fluosilicic acid), and contact the mixed solution with hot air in countercurrent flow for mass and heat transfer to obtain concentrated fluosilicic acid with a mass concentration of 35.8%; the temperature of the hot air is 100°C, and the water content is <20 g / Nm 3 The temperature of concentrated fluorosilicic acid is 60°C, the gas flow rate is 3m / s, and the liquid-gas ratio is ≤8L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0085] S2. Sodium sulfide is added to the concentrated fluosilicic acid to perform arsenic removal at normal pressure. The amount of arsenic removal agent used is 2‰ of the mass of the fluosilicic acid solution. The arsenic removal reaction temperature is 49°C and the residence time is 10 minutes. After filtration, the As content of the dearsenicated acid is 7 ppm.

[0086] S3. The fluorosilicic acid after dearsenification of S2 is sent to an H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0087] The total fluorine yield during the concentration process is 75.1%, the concentration of the finished iodine fluorosilicate is 2.3ppm, and the chlorine concentration is 37.1ppm; the tail gas is discharged after being defoamed and washed to meet the standards.

[0088] Comparative Example 3

[0089] A process for concentrating fluosilicic acid comprises the following steps:

[0090] S1, a fluosilicic acid solution (fluosilicic acid mass concentration of 15.3%, iodine concentration of 24ppm, chlorine concentration of 436ppm, arsenic content of 24ppm) and hydrogen peroxide (its mass concentration is 25%, and the amount added is controlled to be 1.5‰ of the mass of the fluosilicic acid) are mixed, and the mixed solution is contacted with a first hot air in a gas-liquid circulation countercurrent manner and water vapor is separated to obtain a concentrated fluosilicic acid with a mass concentration of 30.2%; the temperature of the first hot air is 100°C, and the water content is 8.3g / Nm 3 The temperature of the concentrated fluorosilicic acid is 30°C, the gas flow rate is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

[0091] S2, the fluosilicic acid after the primary concentration is contacted with the second hot air in countercurrent to perform mass transfer and heat transfer, to obtain the fluosilicic acid after secondary concentration, the mass concentration of which is 39.1%; the temperature of the second hot air is 80 ° C, the water content is 1.9 g / Nm 3 The temperature of the fluosilicic acid after the secondary concentration is 50°C, the gas flow rate is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 The gas-liquid contact time is 5 to 6 seconds.

[0092] S3. Sodium sulfide was added to the secondary concentrated fluosilicic acid in an amount of 2.5‰ of the mass of the fluosilicic acid solution. The dearsenication operating pressure was 45 kPa, the dearsenication reaction temperature was 50°C, and the residence time was 10 minutes. After filtration, the dearsenicated acid had an As content of 0.6 ppm.

[0093] S4. The fluorosilicic acid after arsenic removal in S3 is sent to a H2S gas removal tower to remove H2S gas, thereby obtaining finished fluorosilicic acid.

[0094] The total fluorine yield during the concentration process is 78.4%, the concentration of the finished product iodine fluorosilicate is 1.5ppm, and the chlorine concentration is 29.4ppm; the tail gas is discharged after being defoamed and washed to meet the standards.

[0095] Comparative Example 4

[0096] The comparative example process is provided by patent CN 113800524 A "A method for concentrating fluorosilicic acid", which includes the following steps:

[0097] S1. Clean air is passed into the packed tower and 98wt% concentrated sulfuric acid is used for circulating spray drying. The gas flow rate in the packed tower is controlled at 1.m / s to 1.5m / s, and the concentrated sulfuric acid washing liquid-gas ratio is 4L / m 3 ~5L / m 3 , the temperature is 50℃ and the water content is 0.5g / Nm 3 of dry air.

[0098] S2, the dry air obtained in step S1 is passed into the spray concentration tower, and countercurrent exchange is carried out with 30°C, 15.3wt% concentration of fluorosilicic acid, the superficial gas velocity is 3m / s to 4m / s, and the washing liquid-gas ratio is controlled at 5L / m 3 ~6L / m 3 , the residence time is 7s to 8s, and a concentration of 35.6wt% of fluorosilicic acid (≤40°C) is obtained, and the total fluorine yield is 97.7%.

[0099] Effect Example 1

[0100] The concentration effects obtained by the processes of Examples 1 to 4 and Comparative Examples 1 to 4 are compared, as shown in Table 1:

[0101] Table 1. Concentration effects of Examples and Comparative Examples

[0102]

[0103] By comparing Example 1, Example 2, Example 3 with Comparative Example 1 and Comparative Example 2, it can be seen that under the same conditions, the two-stage concentration method of the present invention is selected, and the concentration of the fluosilicic acid after the first concentration is reasonably controlled before the second concentration is performed. This can ensure that the concentration of the concentrated product is high, the concentration time is short, and the fluorine yield is also high. Otherwise, as shown in Comparative Examples 1 and 2, it will easily cause a large amount of decomposition of fluosilicic acid, and the product fluorine yield is low.

[0104] By comparing Example 3 of the present invention and Comparative Example 3, it can be seen that the liquid phase temperature of fluorosilicic acid after gas-liquid contact has an important influence on the technical effect of the present invention. As shown in Comparative Example 3, if the temperature is not within the range described in the present invention, it will significantly affect the fluorine yield. Even if a two-stage concentration method is adopted, the fluorine yield obtained will be low.

[0105] Comparative Example 4, a low-temperature concentration process commonly used in the prior art, demonstrates that while Comparative Example 4 achieves a high fluorine yield, the concentration time is significantly longer than that of the present invention, resulting in lower concentration efficiency. The present invention significantly shortens the concentration time while maintaining both product concentration and fluorine yield. Concentration time represents concentration efficiency, and the present invention significantly improves concentration efficiency while maintaining product quality, thereby increasing the company's economic benefits.

[0106] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for concentrating fluosilicic acid, characterized in that: The following steps are involved: S1. subjecting a fluosilicic acid solution having a mass concentration of less than 25% to cyclic gas-liquid contact with a first gas-phase heat medium and separating water vapor to obtain a concentrated fluosilicic acid having a temperature of 50-70° C. and a mass concentration of 30.5-32.4%. S2, subjecting the once-concentrated fluorosilicic acid in S1 to cyclic gas-liquid contact with a second gas-phase heat medium and separating water vapor to obtain a second-concentrated fluorosilicic acid having a temperature of 20-30° C.; wherein the temperature of the fluosilicic acid after the first concentration is greater than the temperature of the fluosilicic acid after the second concentration; In S1, the hydrosilicic acid solution is mixed with an oxidant and then brought into contact with a first gaseous heat medium.

2. The process for concentrating fluorosilicic acid according to claim 1, wherein: The temperature of the first gas-phase heat medium is 50-120°C, and the temperature of the second gas-phase heat medium is 30-80°C.

3. The concentration process of fluorosilicic acid according to claim 2, characterized in that, The water content of the first gas phase heat medium is 5.3-8.1 g / Nm 3 .

4. The process for concentrating fluorosilicic acid according to claim 3, wherein: The gas flow rate during the contact between the fluorosilicic acid solution in S1 and the first gas phase heat medium is 4-4.5 m / s, and the liquid-gas ratio is 6-7 L / m 3 The gas-liquid contact time is 6 to 8 seconds.

5. The process for concentrating fluorosilicic acid according to claim 2, wherein: The water content of the second gas phase heat medium is 1.9-2.75 g / Nm 3 .

6. The process for concentrating fluorosilicic acid according to claim 5, wherein: The gas flow rate during the contact between the concentrated fluorosilicic acid in S2 and the second gas phase heat medium is 3-3.5 m / s, and the liquid-gas ratio is 5-6 L / m 3 , the gas-liquid contact time is 5 to 6 seconds.

7. The process for concentrating fluorosilicic acid according to any one of claims 1 to 6, characterized in that: The obtained secondary concentrated fluorosilicic acid is subjected to arsenic removal treatment using an arsenic removal agent.

8. The process for concentrating fluorosilicic acid according to claim 7, wherein: The pressure environment for arsenic removal is a positive pressure of 10 to 60 kPa.

9. The process for concentrating fluorosilicic acid according to claim 8, wherein: The concentrated fluorosilicic acid after the arsenic removal treatment is subjected to H2S gas treatment.

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