A method for the resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluorinated nitrobenzene.

Abstract

A method for the resource utilization of potassium chloride and potassium fluoride mixed salts, byproducts of polyfluorinated nitrobenzene (PFN) reactions, belongs to the field of resource utilization of potassium salts byproducts of fluorination reactions. The method is characterized by the following preparation steps: 1) removing organic pollutants from the mixed salts through heat treatment to obtain inorganic mixed salts; 2) dissolving the inorganic mixed salts in a solvent to obtain an inorganic mixed salt solution, evaporating and concentrating the solution, cooling and crystallizing, and filtering to separate primary potassium chloride solid and a mixed filtrate; 3) adding a defluorinating agent to the mixed filtrate to obtain precipitated sodium fluoride product and potassium chloride solution; 4) preparing a potassium chloride solution by dissolving the primary potassium chloride solid in distilled water and performing bipolar membrane electrodialysis to obtain a dilute KOH solution; 5) concentrating the KOH solution and then introducing HF gas to prepare potassium fluoride. This invention obtains sodium fluoride, potassium fluoride, and potassium chloride products through salt separation technology and bipolar membrane electrodialysis technology, realizing the separation, purification, and recycling of potassium and fluorine resources.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of potassium salts produced as a byproduct of fluorination reactions, and specifically relates to a method for the resource utilization of a mixed salt of potassium chloride and potassium fluoride. Background Technology

[0002] Potassium fluoride (KF) plays a crucial role in organofluorination reactions, but these reactions easily produce mixed potassium salts containing organic components, such as potassium chloride and potassium fluoride. Since these salts contain fluorine and potassium, direct disposal as solid waste not only wastes these resources and increases enterprise investment costs, but also pollutes the environment and disrupts the ecological balance.

[0003] A common treatment method is to incinerate the mixed potassium salts to remove harmful components, then dissolve them in water to obtain a mixed solution of potassium chloride and potassium fluoride. A fluorine precipitant is then added to obtain fluoride and potassium chloride. However, due to cost issues and secondary pollution problems, its application is limited.

[0004] Chinese patent application CN106006679A discloses a method for recovering high-purity potassium chloride from a byproduct of a fluorination reactor. The specific operation is as follows: first, heat treatment removes attached organic matter; then, potassium fluoride is leached using liquid ammonia under pressure, achieving separation of potassium chloride and potassium fluoride. The liquid ammonia solution used to leach potassium fluoride is then vaporized for further separation and recovery. This method requires two different solvent systems to separate potassium fluoride and potassium chloride, and it requires high temperature and high pressure conditions. Liquid ammonia can easily have an adverse environmental impact, and recovery is difficult, making it unsuitable for widespread industrial production.

[0005] Chinese patent application CN112441600A discloses a method for separating industrial mixed potassium salts. The method includes the following steps: Step (1) recrystallizing the mixed potassium salts in water and methanol to obtain potassium chloride and mother liquor A; Step (2) concentrating mother liquor A obtained in step (1) to obtain mother liquor A', recrystallizing mother liquor A' in methanol to obtain potassium chloride concentrate, and collecting and concentrating mother liquor B to obtain potassium fluoride. This separation method achieves the one-time separation of potassium chloride and potassium fluoride from the mixed potassium salts without involving any chemical reaction; however, the purity of potassium chloride is only about 98.42%, and the purity of potassium fluoride is only about 94.46%. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a simple process for the resource utilization of potassium chloride and potassium fluoride mixed salts, which are byproducts of polyfluoronitrobenzene and have high product purity.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for the resource utilization of mixed salts of potassium chloride and potassium fluoride, which are byproducts of polyfluoronitrobenzene, characterized by comprising the following steps:

[0008] 1) Remove organic pollutants from the mixed salt of potassium chloride and potassium fluoride by heat treatment at 200℃~600℃ to obtain an inorganic mixed salt;

[0009] 2) Add solvent to dissolve inorganic mixed salts to obtain inorganic mixed salt solution. After evaporation and concentration of inorganic mixed salt solution, cool and crystallize. Filter to separate into primary potassium chloride solid and mixed filtrate.

[0010] 3) Add a defluorinating agent to the mixed filtrate to obtain the precipitated sodium fluoride product and potassium chloride solution;

[0011] 4) Prepare a potassium chloride solution with a concentration of 8wt% to 10wt% by mixing potassium chloride solid with distilled water. Use this solution as an electrodialysis solvent for bipolar membrane electrodialysis to obtain dilute KOH solution, dilute HCl solution and dilute potassium chloride brine, respectively.

[0012] 5) After concentrating the KOH solution, KOH concentrate is obtained. HF gas is then introduced into the KOH concentrate to prepare potassium fluoride.

[0013] This invention provides a method for the resource recovery of potassium chloride and potassium fluoride mixed salts. By using salt separation technology and bipolar membrane electrodialysis technology, pure KCl, pure KF, pure NaF and dilute HCl solution with purity meeting the group standard requirements are obtained, realizing the separation, purification and recovery of potassium and fluorine resources in potassium salts produced as a by-product of fluorination reaction.

[0014] The potassium chloride and potassium fluoride mixed salt contains 70wt% to 80wt% potassium chloride, 15wt% to 20wt% potassium fluoride, and a small amount of organic components.

[0015] In step 1), the heat treatment is carried out at 200℃ to 600℃ for 2 to 6 hours. The volatilized organic gases are absorbed and treated by a waste gas treatment system. Preferably, in the above method for the resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene, the heat treatment temperature in step 1) is 400℃ to 550℃ for 2 to 4 hours. The equipment used for heat treatment can be a muffle furnace, a high-temperature rotary kiln, an energy-saving box furnace, etc. More preferably, the heat treatment is carried out at 550℃ in a muffle furnace for 4 hours.

[0016] Preferably, in the above method for resource utilization of potassium chloride and potassium fluoride mixed salt byproducts of polyfluoronitrobenzene, the solvent in step 2) is water or potassium chloride aqueous solution, and the dissolution temperature is 20℃~50℃.

[0017] Preferably, in the above-mentioned method for the resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene, the inorganic mixed salt solution in step 2) contains 10% to 50% by mass; more preferably, the inorganic mixed salt contains 35% by mass. The evaporation and concentration process removes 30% to 60% of the original water volume. The preferred evaporation rate, combined with the crystallization temperature, allows for more thorough crystallization of potassium chloride and the removal of lower amounts of impurities, enabling the mixed filtrate to undergo desorption treatment directly without further processing, thus simplifying the process. This method effectively guarantees both single-batch yield and product purity. The distillate evaporated during the evaporation and concentration process is collected, condensed, and used to prepare the potassium chloride solution in step 4).

[0018] Preferably, the inorganic mixed salt solution described in step 2) can be pre-decolorized and adsorbed using activated carbon before concentration and crystallization, which can further improve the purity of the product.

[0019] Preferably, recrystallization is performed after cooling and crystallization in step 2), using a solvent of 90 wt% ethanol, acetone, or hydrochloric acid. Recrystallization significantly improves product purity. More preferably, the solvent is 90 wt% ethanol, and the ethanol is recycled within the system. This preferred recrystallization solvent minimizes material loss and maximizes product purity during recrystallization.

[0020] The filtration method in step 2) is at least one of vacuum filtration, pressure filtration, membrane filtration, centrifugation, and sedimentation. Preferably, in the above method for resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene, the filtration method in step 2) is vacuum filtration; the filter paper used for vacuum filtration is 0.22 μm aqueous filter paper, and the vacuum degree is -0.089 MPa to -0.098 MPa. Vacuum filtration uses a diaphragm pump or a circulating water pump, preferably a circulating water pump.

[0021] Preferably, in the above-mentioned method for the resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene, the molar ratio of the defluorinating agent to the potassium fluoride contained in the mixed filtrate in step 3) is 0.9-1.2:1, and the defluorinating agent is sodium chloride. The purity of the co-produced sodium fluoride reaches ≥98.5%, meeting the group standard for sodium fluoride byproducts of fluorobenzene products, and there is no waste generation or emission during the entire process.

[0022] Because the bipolar membrane system can detect Ca in the water... 2+ Mg 2+ The requirement for divalent cation content is <1ppm. This invention uses NaCl to precipitate fluoride ions instead of the commonly used CaCl2, effectively avoiding the problem caused by Ca... 2+ The problem is that the water hardness caused by residues does not meet the standards and hardness removal is required before it can enter the bipolar membrane electrodialysis system.

[0023] More preferably, the defluorinating agent is in a 1:1 molar ratio with potassium fluoride in the mixed filtrate, and sodium chloride is added and the mixture is stirred for 4 hours. The resulting sodium fluoride has higher purity.

[0024] Preferably, in the above-mentioned method for resource utilization of potassium chloride and potassium fluoride mixed salt byproducts of polyfluoronitrobenzene, the concentration of KOH solution generated by bipolar membrane electrodialysis in step 4) is 8wt% to 10wt%, the concentration of HCl solution is 6wt% to 8wt%, the acid and alkali are recycled into the relevant synthesis reaction, and the generated potassium chloride dilute brine is recycled back into the potassium chloride solution preparation in this step.

[0025] Step 4) describes a bipolar membrane electrodialysis system using a three-compartment experimental bipolar membrane electrodialysis system: one bipolar membrane, one alkali compartment partition, one cation exchange membrane, one feed compartment partition, one anion exchange membrane, and one acid compartment partition are stacked alternately to form one membrane pair, for a total of 10 membrane pairs. After obtaining HCl and KOH solutions of the above concentrations, the electrodialysis reaction is terminated.

[0026] Preferably, in the above method for the resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene, the concentration of the KOH concentrate in step 5) is 40wt% to 80wt%.

[0027] The KOH concentrate is obtained by two-stage concentration of KOH solution through reverse osmosis and evaporation. The concentration of KOH solution after reverse osmosis concentration is 30wt% to 40wt%, and the concentration after evaporation concentration is 40wt% to 80wt%. The reverse osmosis membrane used for reverse osmosis concentration is a polyethylene membrane, polyethersulfone membrane, polypropylene membrane, or polyamide membrane with a magnesium sulfate rejection rate of 35%.

[0028] Preferably, in the above-mentioned method for resource utilization of potassium chloride and potassium fluoride mixed salt byproducts of polyfluoronitrobenzene, the specific process for preparing potassium fluoride by introducing HF gas in step 5) is: crystallization drying method or spray drying method.

[0029] 5.1) Crystallization drying method

[0030] Maintain the reaction temperature at 30℃~60℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 6.5~7.0. After standing for 6h~24h, separate the supernatant, concentrate the supernatant to crystallize out potassium fluoride. Filter the supernatant and wash the filter cake 1~3 times with a saturated potassium fluoride aqueous solution, and then dry it under vacuum to obtain the potassium fluoride product.

[0031] The resulting potassium fluoride product is recycled into the polyfluoronitrobenzene process to achieve the recycling of potassium fluoride.

[0032] Preferably, in the above process for preparing potassium fluoride, the vacuum drying temperature is 60℃~80℃ and the time is 4h~8h, and the purity of the obtained potassium fluoride product is ≥99.65%.

[0033] More preferably, the reaction temperature in step 5.1) is 40°C, the pH is 7.0, and the mixture is kept at this temperature for 8 hours. More preferably, the vacuum drying temperature is 70°C and the drying time is 4 hours.

[0034] 5.2) Spray drying method

[0035] Maintain the reaction temperature at 30℃~60℃, and introduce HF gas into the KOH concentrate until the solution pH is 6.5~7.0 to obtain potassium fluoride solution. Add the potassium fluoride solution into the spray dryer at a constant feed rate, and control the spray drying and inlet air temperature at 200~250℃ and the outlet air temperature at 100~150℃. Under these conditions, potassium fluoride is prepared.

[0036] The concentrations of KOH and HCl solutions were calculated by titration with standard acid-base solutions; the purity of potassium chloride and sodium fluoride was detected by ion chromatography; and the mass percentage of KCl and KF was determined according to national standard methods.

[0037] In summary, the method for resource utilization of potassium chloride and potassium fluoride mixed salts, a byproduct of polyfluoronitrobenzene, according to the present invention comprises the following steps: The potassium chloride and potassium fluoride mixed salts are heat-treated at 200℃ to 600℃ for 2 to 6 hours to obtain an inorganic mixed salt solution. This solution is then prepared using water / potassium chloride mother liquor to achieve a content of 10% to 50% and a temperature of 20℃ to 50℃. 30% to 60% of the water is removed by evaporation, followed by cooling and crystallization, and recrystallization to obtain primary potassium chloride solid, evaporated water, and a mixed filtrate of potassium chloride and potassium fluoride. Sodium chloride is added to the mixed filtrate, and sodium fluoride and potassium chloride solutions with a purity ≥98.5% are separated. The potassium chloride solution is recycled for dissolving the heat-treated potassium salts. The purity of the separated primary potassium chloride solid meets the group standard requirements. It is mixed with the evaporated water to prepare an 8%–10% concentrated potassium chloride brine solution, which is then subjected to bipolar membrane electrodialysis to convert the potassium chloride into an 8%–10% dilute KOH solution and a 6%–8% HCl solution. The HCl solution is recycled into the synthesis process. The dilute KOH solution undergoes a two-stage concentration process to become a 30%–80% concentrated KOH solution, which is then purged with HF gas to prepare KF, which is recycled into the polyfluoronitrobenzene process. This invention features a simple separation process, high waste salt resource utilization rate, and meets the environmental protection requirements of green chemistry.

[0038] Compared with the prior art, the method of resource utilization of potassium chloride and potassium fluoride mixed salt byproducts of polyfluoronitrobenzene according to the present invention has the following beneficial effects:

[0039] The KCl produced by this invention meets the group standard in purity and can also be used as a raw material to prepare high-purity KF products for reuse in fluorination reactions. The HCl produced in the electrodialysis process can also be reused in related reactions, making full use of existing fluorine and potassium resources and reducing waste emissions.

[0040] This invention combines current bipolar membrane electrodialysis technology to convert salts into acids and bases for resource recycling, reducing the purchase costs of KCl and KF. By integrating salt separation and bipolar membrane electrodialysis technologies, this invention successfully achieves the separation, purification, and recycling of potassium and fluorine resources, improving the resource utilization rate of waste salts. This aligns with the environmental requirements of green chemistry, supports the environmentally friendly development of the chemical industry and other related sectors, promotes carbon reduction in the circular economy, reduces salt emissions, and drives the resource utilization of waste salts, providing a feasible path for the circular economy of chemical waste salt treatment. Attached Figure Description

[0041] Figure 1 Flowchart for potash resource utilization

[0042] Figure 2 Schematic diagram of bipolar membrane electrodialysis Detailed Implementation

[0043] The present invention will be specifically described below through examples. Unless otherwise stated, all raw materials used are commercially available. For ease of comparison between examples, the mixed salts used in each example are from the same batch of material, and the mass fraction of potassium chloride in the mixed salts is 77.4 wt%, the mass fraction of potassium fluoride is 18.4 wt%, and the balance is organic impurities.

[0044] Example 1

[0045] 1) An inorganic mixed salt was obtained by heat-treating 200g of potassium chloride and potassium fluoride mixed salt in a muffle furnace at 550℃ for 4h.

[0046] 2) Prepare an inorganic mixed salt solution at 35℃ using 180mL of water. Evaporate 46% of the water to obtain evaporated water and concentrated liquid. After cooling and crystallizing the concentrated liquid, recrystallize it once with 90wt% ethanol. Vacuum filter to obtain potassium chloride solid and a mixed filtrate of potassium chloride and potassium fluoride. The filter paper used for vacuum filtration is 0.22μm aqueous filter paper, and the vacuum degree is -0.095MPa.

[0047] 3) Add sodium chloride to the mixed filtrate and stir for 4 hours. The molar ratio of sodium chloride to potassium fluoride is 1:1. After solid-liquid separation, sodium fluoride product with a purity of 99.1% and potassium chloride solution are obtained. The potassium chloride solution is recycled to dissolve the inorganic mixed salt after heat treatment. The yield of sodium fluoride product is calculated to be 98.7% after weighing.

[0048] 4) The separated primary potassium chloride solid is washed three times with saturated potassium chloride solution and dried at 60°C. It is then mixed with the evaporated water from step 2) to prepare a 9% potassium chloride concentrated brine solution for bipolar membrane electrodialysis. This process converts the potassium chloride into a 9% dilute KOH solution, a 7% HCl solution, and a dilute potassium chloride brine solution. The HCl solution is then reused in the synthesis process.

[0049] 5) The dilute KOH solution is concentrated in two stages to obtain a 60% KOH concentrate;

[0050] 5.1) Crystallization and Drying Method: Maintain the reaction temperature at 40℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 7.0. After standing for 8 hours, separate the supernatant, concentrate the supernatant to crystallize out potassium fluoride. Filter the supernatant and wash the filter cake three times with a saturated potassium fluoride aqueous solution. Dry under vacuum at 70℃ for 4 hours to obtain the potassium fluoride product. The purity of the potassium fluoride product is 99.74%, and the yield of potassium fluoride is calculated to be 98.4% after weighing.

[0051] Example 2

[0052] 1) An inorganic mixed salt was obtained by heat-treating 200g of potassium chloride and potassium fluoride mixed salt in a muffle furnace at 400℃ for 3.5h.

[0053] 2) Prepare an inorganic mixed salt solution at 40℃ using 180mL of water. Evaporate 50% of the water to obtain evaporated water and concentrated liquid. After cooling and crystallizing the concentrated liquid, recrystallize it once with 90wt% ethanol. Vacuum filter to obtain potassium chloride solid and a mixed filtrate of potassium chloride and potassium fluoride. The filter paper used for vacuum filtration is 0.22μm aqueous filter paper, and the vacuum degree is -0.096MPa.

[0054] 3) Sodium chloride was added to the mixed filtrate and stirred for 4 hours. The molar ratio of sodium chloride to potassium fluoride was 1.1:1. Solid-liquid separation yielded sodium fluoride product with a purity of 98.7% and potassium chloride solution. The potassium chloride solution was recycled to dissolve the inorganic mixed salt after heat treatment. The yield of sodium fluoride product was calculated to be 99.2%.

[0055] 4) The separated primary potassium chloride solid is washed three times with saturated potassium chloride solution and dried at 60°C. It is then mixed with the evaporated water from step 2) to prepare a 9% potassium chloride concentrated brine solution for bipolar membrane electrodialysis. This process converts the potassium chloride into a 9% dilute KOH solution, a 7% HCl solution, and a dilute potassium chloride brine solution. The HCl solution is then reused in the synthesis process.

[0056] 5) The dilute KOH solution is concentrated in two stages to obtain a 70% KOH concentrate;

[0057] Spray drying method: Maintain the reaction temperature at 50℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 6.9 to obtain potassium fluoride solution. The potassium fluoride solution is added to the spray dryer at a constant feed rate. The spray drying and inlet air temperature are controlled at 250℃ and the outlet air temperature at 150℃. Under these conditions, potassium fluoride is prepared with a purity of 99.66% and a yield of 98.5%.

[0058] Example 3

[0059] 1) An inorganic mixed salt was obtained by heat-treating 200g of potassium chloride and potassium fluoride mixed salt at 2550℃ for 2h in a rotary kiln.

[0060] 2) Prepare an inorganic mixed salt solution at 300℃ using 180mL of water / potassium chloride mother liquor. Evaporate 40% of the water to obtain evaporated water and concentrated liquid. After cooling and crystallizing the concentrated liquid, recrystallize it once with 90wt% ethanol. Vacuum filter to obtain primary potassium chloride solid and a mixed filtrate of potassium chloride and potassium fluoride. The filter paper used for vacuum filtration is 0.22μm aqueous filter paper, and the vacuum degree is -0.092MPa.

[0061] 3) Sodium chloride was added to the mixed filtrate and stirred for 4 hours. The molar ratio of sodium chloride to potassium fluoride was 1:1. Solid-liquid separation was performed to obtain sodium fluoride product with a purity of 99.1% and potassium chloride solution. The potassium chloride solution was recycled to dissolve the inorganic mixed salt after heat treatment. The yield of sodium fluoride product was calculated to be 98.4%.

[0062] 4) The separated primary potassium chloride solid is washed three times with saturated potassium chloride solution and dried at 60°C. It is then mixed with the evaporated water from step 2) to prepare a 9% potassium chloride concentrated brine solution for bipolar membrane electrodialysis. This process converts the potassium chloride into a 9% dilute KOH solution, a 7% HCl solution, and a dilute potassium chloride brine solution. The HCl solution is then reused in the synthesis process.

[0063] 5) The dilute KOH solution is concentrated in two stages to obtain a 50% KOH concentrate;

[0064] 5.1) Crystallization and Drying Method: Maintain the reaction temperature at 35℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 6.8. After standing for 15 hours, separate the supernatant. Concentrate the supernatant to crystallize out potassium fluoride. Filter the supernatant and wash the filter cake three times with a saturated potassium fluoride aqueous solution. Dry under vacuum at 70℃ for 6 hours to obtain the potassium fluoride product. The purity of the potassium fluoride product is 99.71%, and the yield of potassium fluoride is calculated to be 98.5%.

[0065] Example 4

[0066] 1) An inorganic mixed salt was obtained by heat-treating 200g of potassium chloride and potassium fluoride mixed salt in a muffle furnace at 200℃ for 6h.

[0067] 2) Prepare an inorganic mixed salt solution at 50℃ using 180mL of water / potassium chloride mother liquor. Evaporate 60% of the water to obtain evaporated water and concentrated liquid. After cooling and crystallizing the concentrated liquid, recrystallize it once with acetone. Vacuum filter to obtain primary potassium chloride solid and a mixed filtrate of potassium chloride and potassium fluoride. The filter paper used for vacuum filtration is 0.22μm aqueous filter paper, and the vacuum degree is -0.098MPa.

[0068] 3) Sodium chloride was added to the mixed filtrate and stirred for 4 hours. The molar ratio of sodium chloride to potassium fluoride was 0.9:1. Solid-liquid separation yielded sodium fluoride product with a purity of 98.5% and potassium chloride solution. The potassium chloride solution was recycled to dissolve the inorganic mixed salt after heat treatment. The yield of sodium fluoride product was calculated to be 99.3%.

[0069] 4) The separated primary potassium chloride solid is washed three times with saturated potassium chloride solution and dried at 60°C. It is then mixed with the evaporated water from step 2) to prepare an 8% potassium chloride concentrated brine solution for bipolar membrane electrodialysis. This process converts the potassium chloride into an 8% dilute KOH solution, a 6% HCl solution, and the dilute potassium chloride brine solution. The HCl solution is then reused in the synthesis process.

[0070] 5) The dilute KOH solution is concentrated in two stages to obtain an 80% KOH concentrate; 5.1)

[0072] Spray drying method: Maintain the reaction temperature at 30℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 6.5 to obtain potassium fluoride solution. Add the potassium fluoride solution to the spray dryer at a constant feed rate, and control the spray drying and inlet air temperature at 200℃ and the outlet air temperature at 100℃. Under these conditions, potassium fluoride is prepared with a purity of 99.57% and a yield of 95.5%.

[0073] Example 5

[0074] 1) An inorganic mixed salt was obtained by heat-treating 200g of potassium chloride and potassium fluoride mixed salt at 600℃ in an electric furnace for 2 hours.

[0075] 2) Prepare an inorganic mixed salt solution at 20℃ using 180mL of water / potassium chloride mother liquor. Evaporate 30% of the water to obtain evaporated water and concentrated liquid. After cooling and crystallizing the concentrated liquid, recrystallize it once with hydrochloric acid. Vacuum filter to obtain primary potassium chloride solid and a mixed filtrate of potassium chloride and potassium fluoride. The filter paper used for vacuum filtration is 0.22μm aqueous filter paper, and the vacuum degree is -0.089MPa.

[0076] 3) Sodium chloride was added to the mixed filtrate and stirred for 4 hours. The molar ratio of sodium chloride to potassium fluoride was 1.2:1. Solid-liquid separation yielded sodium fluoride product with a purity of 99.4% and potassium chloride solution. The potassium chloride solution was recycled to dissolve the inorganic mixed salt after heat treatment. The yield of sodium fluoride product was calculated to be 91.3%.

[0077] 4) The separated primary potassium chloride solid is washed three times with saturated potassium chloride solution and dried at 60°C. It is then mixed with the evaporated water from step 2) to prepare a 10% potassium chloride concentrated brine solution for bipolar membrane electrodialysis to convert potassium chloride into a 10% dilute KOH solution, an 8% HCl solution, and a dilute potassium chloride brine solution. The HCl solution is recycled to the synthesis process.

[0078] 5) The dilute KOH solution is concentrated in two stages to obtain a 40% KOH concentrate;

[0079] 5.1) Maintain the reaction temperature at 60℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 7.0. After standing for 6 hours, separate the supernatant. Concentrate the supernatant to crystallize out potassium fluoride. Filter the supernatant and wash the filter cake three times with a saturated potassium fluoride aqueous solution. Dry under vacuum at 80℃ for 4 hours to obtain the potassium fluoride product. The purity of the potassium fluoride product is 99.65%, and the yield of potassium fluoride is calculated to be 98.6%.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for the resource utilization of potassium chloride and potassium fluoride mixed salts, a byproduct of polyfluoronitrobenzene, characterized in that, Includes the following steps: 1) Remove organic pollutants from the mixed salt of potassium chloride and potassium fluoride by heat treatment at 200℃~600℃ to obtain an inorganic mixed salt; 2) Add solvent to dissolve inorganic mixed salts to obtain inorganic mixed salt solution. After evaporation and concentration of inorganic mixed salt solution, cool and crystallize. Filter to separate into primary potassium chloride solid and mixed filtrate. 3) Add a defluorinating agent to the mixed filtrate to obtain the precipitated sodium fluoride product and potassium chloride solution; 4) Prepare a potassium chloride solution with a concentration of 8wt%~10wt% by mixing potassium chloride solid with distilled water. Use this solution as an electrodialysis solvent for bipolar membrane electrodialysis to obtain dilute KOH solution, dilute HCl solution and dilute potassium chloride brine, respectively. 5) After concentrating the KOH solution, a concentrated KOH solution is obtained. HF gas is then passed through the concentrated KOH solution to prepare potassium fluoride. The inorganic mixed salt solution in step 2) has an inorganic mixed salt mass fraction of 10% to 50%; the evaporation and concentration process removes 30% to 60% of the original water volume. The molar ratio of the defluorinating agent to the potassium fluoride contained in the mixed filtrate in step 3) is 0.9~1.2:1, and the defluorinating agent is sodium chloride; The concentration of the KOH concentrate mentioned in step 5) is 50wt%~80wt%; the KOH concentrate is obtained by two-stage concentration of KOH solution through reverse osmosis concentration and evaporation concentration. The concentration of the KOH solution after reverse osmosis concentration is 30wt%~40wt%, and the concentration after evaporation concentration is 50wt%~80wt%.

2. The method for resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene according to claim 1, characterized in that: The heat treatment in step 1) is carried out at a temperature of 400℃~550℃ for 2h~3h.

3. The method for resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene according to claim 1, characterized in that: The solvent mentioned in step 2) is water or potassium chloride aqueous solution, and the dissolution temperature is 20℃~50℃.

4. The method for resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene according to claim 1, characterized in that: The filtration method described in step 2) is at least one of vacuum filtration, pressure filtration, and membrane filtration; the selected filter paper is 0.22μm water-based filter paper; the vacuum degree of vacuum filtration is -0.089MPa to -0.098MPa.

5. The method for resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene according to claim 1, characterized in that, The specific process for preparing potassium fluoride by introducing HF gas in step 5) is as follows: 5.1) Crystallization drying method Maintain the reaction temperature at 30℃~60℃, and introduce HF gas into the KOH concentrate until the solution pH reaches 6.5~7.

0. After standing for 6h~24h, separate the supernatant, concentrate the supernatant to crystallize out potassium fluoride; filter and wash the filter cake 1~3 times with saturated potassium fluoride aqueous solution, and vacuum dry to obtain the potassium fluoride product; or 5.2) Spray drying method Maintain the reaction temperature at 30℃~60℃, and introduce HF gas into the KOH concentrate until the solution pH is 6.5~7.0 to obtain potassium fluoride solution. Add the potassium fluoride solution into the spray dryer at a constant feed rate, and control the spray drying and inlet air temperature at 200~250℃ and the outlet air temperature at 100~150℃. Under these conditions, potassium fluoride is prepared.

6. The method for resource utilization of potassium chloride and potassium fluoride mixed salts as byproducts of polyfluoronitrobenzene according to claim 5, characterized in that: The vacuum drying temperature is 60℃~80℃ and the time is 4h~8h, and the purity of the obtained potassium fluoride product is >99.65%.

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