Preparation method of potassium hexafluoroaluminate

Abstract

The invention discloses a preparation method of potassium hexafluoroaluminate, which effectively reduces the energy consumption in the reaction process, and comprises the following steps: S1, reaction: reacting a potassium fluoride aqueous solution and an aluminum chloride aqueous solution in an aqueous solution system, and controlling the reaction process in two temperature stages, in the first stage, adding part of the aluminum chloride solution at a first preset temperature, and in the second stage, adding the rest of the aluminum chloride solution at a second preset temperature higher than the first preset temperature and completing the reaction to obtain a potassium hexafluoroaluminate suspension; the potassium hexafluoroaluminate turbid liquid obtained in the step S1 is subjected to solid-liquid separation and gradient drying, and a potassium hexafluoroaluminate product is obtained.The potassium hexafluoroaluminate preparation method is novel in structure, ingenious in conception and easy and convenient to operate, the reaction process is effectively safer and more controllable, the probability that equipment is corroded is reduced, the reaction progress is optimized, the production efficiency is improved, and the production cost is reduced. And stable product quality is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production and relates to a method for preparing potassium hexafluoroaluminate. Background Art

[0002] Potassium hexafluoroaluminate (K3AlF6), commonly known as cryolite, is an important inorganic fluoride. Due to its unique physical and chemical properties, it is widely used as a flux in aluminum electrolysis, a filler in the ceramic and abrasive industries, a flux in metal welding, and in the preparation of various functional ceramics.

[0003] Currently, the traditional method for industrially preparing potassium hexafluoroaluminate is the high-temperature melting process. This process typically involves mixing potassium fluoride (KF) with aluminum fluoride (AlF3) or raw materials containing aluminum and fluorine in a specific proportion. The mixture is then melted at temperatures exceeding 500°C. After several hours of reaction, the melt is rapidly cooled and crushed to yield the final product.

[0004] However, this traditional method has the following defects: 1. High energy consumption: Maintaining a high-temperature melting state for a long time requires huge energy consumption, resulting in high production costs; 2. Prominent safety hazards: High-temperature melts exceeding 500°C are potentially dangerous and can easily cause melt splashing due to improper operation or equipment failure, leading to serious production safety accidents; 3. Severe equipment corrosion: High-temperature fluoride melts are extremely corrosive to reaction vessels, shortening equipment life and increasing maintenance costs; 4. Poor controllability of product quality: High-temperature reaction and rapid cooling processes are difficult to precisely control, which can easily lead to irregular product crystal morphology and the formation of fragmented aggregates, affecting its fluidity and application performance as a flux or filler.

[0005] In addition, in the purification industry of potassium chloride (KCl), fluoride ions (F - ) is a common impurity that is difficult to remove. Existing technologies lack a method for efficiently removing fluorine impurities and converting them into valuable resources. These methods typically only produce low-value fluoride sludge, which not only increases treatment costs but also wastes fluorine resources and causes secondary pollution.

[0006] Therefore, a method for preparing potassium hexafluoroaluminate with low energy consumption, high safety, low equipment loss, excellent product quality, and the ability to recover fluorine resources is needed to overcome the shortcomings of the above-mentioned prior art. Summary of the Invention

[0007] In view of the above problems, the present invention proposes a method for preparing potassium hexafluoroaluminate, which effectively solves the problems in the prior art.

[0008] In order to achieve the above object, the technical scheme adopted by the present application is as follows: A preparation method of potassium hexafluoroaluminate, comprising the following steps: Step S1, reaction step: reacting potassium fluoride aqueous solution with aluminum chloride aqueous solution in an aqueous solution system, the reaction process is controlled in two temperature stages, in the first stage, part of the aluminum chloride solution is added at a first predetermined temperature, in the second stage, the remaining aluminum chloride solution is added at a second predetermined temperature higher than the first predetermined temperature and the reaction is completed, to obtain potassium hexafluoroaluminate suspension; Step S2, post-treatment step: solid-liquid separation of the potassium hexafluoroaluminate suspension obtained in step S1 to obtain potassium hexafluoroaluminate wet paste; gradient drying of the wet paste at a first drying temperature and a second drying temperature higher than the first drying temperature to obtain potassium hexafluoroaluminate product.

[0009] Preferably, in the step S1, the first predetermined temperature is 60-65℃; the second predetermined temperature is 70-75℃.

[0010] Preferably, in the step S1, the addition amount of the part of the aluminum chloride solution is 60-80% of the total amount of the aluminum chloride solution; the molar ratio of the aluminum chloride to the potassium fluoride is 1.1-1.2:6.

[0011] Preferably, in the step S1, the mass fraction of the potassium fluoride aqueous solution is 45%-50%; the mass fraction of the aluminum chloride aqueous solution is 35%-40%.

[0012] Preferably, in the step S1, after adding the remaining aluminum chloride solution in the second stage, stirring for 2-4 minutes to make the reaction fully completed.

[0013] Preferably, in the step S2, the solid-liquid separation mode is centrifugation while hot at a temperature of 80℃; the wet paste obtained by centrifugation is washed with distilled water for 1-2 times to obtain pure potassium hexafluoroaluminate wet paste.

[0014] Preferably, in the step S2: the first drying temperature is 120℃, and the drying time is 0.5-1.5 hours; the second drying temperature is 250℃, and the drying time is 1.5-2.5 hours.

[0015] Preferably, in the step S2, after drying is completed at the second drying temperature, the potassium hexafluoroaluminate product is naturally cooled to room temperature with the drying equipment.

[0016] Preferably, after obtaining the dried product in the step S2, a step of crushing the product is further included.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. The present invention achieves energy saving and consumption reduction effects by adopting a two-stage temperature control reaction and a low-temperature gradient drying process under an aqueous solution system.

[0018] 2. The present invention achieves a safe and controllable reaction process and reduces the probability of equipment corrosion by adopting mild reaction and drying conditions.

[0019] 3. The present invention improves the production efficiency of the product by adding materials in stages.

[0020] 4. By applying this method to the defluorination of fluorine-containing potassium chloride solutions, the present invention achieves the dual effects of "treating waste with waste" and recovering high-value resources. While efficiently purifying potassium chloride, harmful fluorine impurities are converted into the high-value potassium hexafluoroaluminate byproduct, achieving both environmental and economic benefits. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] The specific embodiments of the present invention are described in further detail below.

[0023] Example 1, as a basic implementation method, the steps are as follows: Step 1. Prepare 1 L of 45% KF aqueous solution (4.5 mol KF) and heat to 65°C. Step 2. Take a 40% by mass AlCl3 aqueous solution (the total amount corresponds to 1.32 mol AlCl3) and slowly add 70% (volume) to the KF solution at 65°C; Step 3. Heat to 75°C, add the remaining 30% AlCl3 solution, and continue stirring for 3 minutes to form a white suspension; Step 4. Centrifuge the suspension while hot at 80°C and wash the ointment twice with distilled water; Step 5. Dry the wet paste at 120°C for 1 hour and then at 250°C for 2 hours; Step 6. The product is naturally cooled to room temperature in a muffle furnace and crushed to obtain a white powder to obtain potassium hexafluoroaluminate product.

[0024] Example 2

[0025] On the basis of Example 1, the volume of the AlCl3 aqueous solution added in step 2 was modified to 60% of the total amount of the AlCl3 aqueous solution; step 5 was adjusted to: drying the wet paste at 120°C for 0.5 hours and then drying at 250°C for 1.5 hours; the other step parameters were the same as those in Example 1.

[0026] Example 3

[0027] On the basis of Example 1, the volume of the AlCl3 aqueous solution added in step 2 was modified to 80% of the total amount of the AlCl3 aqueous solution; step 5 was adjusted to: drying the wet paste at 120°C for 1.5 hours and then drying at 250°C for 2.5 hours; the other step parameters were the same as those in Example 1.

[0028] Example 4, industrial application scenario, the steps are as follows: Step 1. Take the solution containing 0.6% F - 1 ton of industrial KCl solution (equivalent to 0.32 mol / L KF); Step 2. Prepare a 40% aqueous solution of solid AlCl3·6H2O by mass and add it to the industrial KCl solution in two portions to make the final Al:F ratio 1.2:6. The specific addition method is as follows: Step 21. - The industrial KCl solution is heated to 65°C; Step 22. Slowly add 60% volume of AlCl3·6H2O solution to industrial KCl solution at 65°C; Step 23. Heat the solution to 75°C, add the remaining 40% volume of AlCl3·6H2O solution, and continue stirring for 3 minutes to form a white suspension. Step 3. Centrifuge the suspension while hot at 80°C and wash the ointment twice with distilled water; Step 4. Dry the wet paste at 120°C for 1 hour and then at 250°C for 2 hours; Step 5. The product is naturally cooled to room temperature in a muffle furnace and crushed to obtain a white powder, which is the K3AlF6 by-product.

[0029] Comparative Example 1: Traditional melting method, the specific steps are as follows: Step 1. Mix anhydrous KF and AlF3 powder in a molar ratio of 3:1; Step 2. Melt reaction at 550°C for 3 hours; Step 3. The melt is quenched and cooled by water, and then crushed to obtain K3AlF6 product.

[0030] The production processes and products of the above embodiments and comparative examples were tested to obtain the following table: Evaluation indicators Example 1 Example 2 Example 3 Example 4 Comparative Example 1 (Traditional Melting Method) Maximum process temperature 250℃ 250℃ 250℃ 250℃ 500℃ Reaction time 3 minutes 3 minutes 3 minutes 3 minutes 3 hours Specific energy consumption (kWh / kg) 0.82 0.85 0.95 0.84 3.61 Product purity 99.52% 99.48% 99.45% 99.10% 99.52% Moisture content 0.05% 0.09% 0.06% 0.08% 0.12% Crystal morphology Uniform hexagonal crystal Uniform hexagonal crystal Uniform hexagonal crystal Uniform hexagonal crystal Irregular aggregates Equipment corrosion none none none none Severe pitting, with pits deeper than 0.5 mm Security No high temperature splashing No high temperature splashing No high temperature splashing No high temperature splashing There is a risk of high temperature splashing Through the above examples and test results, we can obtain: Example 1 is a preparation method disclosed in the present invention, which reduces the maximum temperature during the process, thereby reducing energy consumption during the process, and improving reaction efficiency, thereby obtaining stable product quality; In Example 2, the reduced feed ratio and the shortest drying time only resulted in a slight increase in energy consumption, but the key quality indicators of product purity and moisture content did not change much; In Example 3, increasing the feed ratio and the longest drying time did not lead to deterioration of product quality, and the key quality indicators of product purity and moisture content did not change much; In Example 4, the industrial application value of the preparation method is demonstrated in an industrial scenario. Even when the raw material grade is low, it can still operate stably and simultaneously achieve the dual purposes of purifying potassium chloride and recovering potassium hexafluoroaluminate by-products, demonstrating the huge industrial application potential and economic benefits of the preparation method.

[0031] The present invention has an ingenious concept and is simple and convenient to operate. The design effectively reduces energy consumption during the reaction process, makes the reaction process safer and more controllable, reduces the probability of equipment corrosion, optimizes the reaction process, improves production efficiency, and obtains stable product quality.

[0032] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing potassium hexafluoroaluminate, characterized in that: The following steps are involved: Step S1, a reaction step: reacting a potassium fluoride aqueous solution and an aluminum chloride aqueous solution in an aqueous solution system, wherein the reaction process is controlled in two temperature stages, wherein a portion of the aluminum chloride solution is added at a first predetermined temperature, and a second stage wherein the remaining aluminum chloride solution is added at a second predetermined temperature higher than the first predetermined temperature and the reaction is completed to obtain a potassium hexafluoroaluminate suspension; Step S2, post-processing step: performing solid-liquid separation on the potassium hexafluoroaluminate suspension obtained in step S1 to obtain a potassium hexafluoroaluminate wet paste; performing gradient drying on the wet paste at a first drying temperature and a second drying temperature higher than the first drying temperature in sequence to obtain a potassium hexafluoroaluminate product.

2. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S1, the first predetermined temperature is 60-65°C; the second predetermined temperature is 70-75°C.

3. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S1, the amount of the partial aluminum chloride solution added is 60-80% of the total amount of the aluminum chloride solution; and the molar ratio of the aluminum chloride to potassium fluoride is 1.1-1.2:

6.

4. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S1, the mass fraction of the potassium fluoride aqueous solution is 45%-50%; the mass fraction of the aluminum chloride aqueous solution is 35%-40%.

5. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S1, after the remaining aluminum chloride solution is added in the second stage, stirring is performed for 2-4 minutes to fully complete the reaction.

6. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S2, the solid-liquid separation method is to centrifuge while hot at a temperature of 80°C; the wet paste obtained by centrifugation is washed 1-2 times with distilled water to obtain a pure potassium hexafluoroaluminate wet paste.

7. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S2, the first drying temperature is 120° C., and the drying time is 0.5-1.5 hours; the second drying temperature is 250° C., and the drying time is 1.5-2.5 hours.

8. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: In step S2, after drying at the second drying temperature is completed, the potassium hexafluoroaluminate product is naturally cooled to room temperature along with the drying equipment.

9. The method for preparing potassium hexafluoroaluminate according to claim 1, wherein: After the dry product is obtained in step S2, the method further includes a step of crushing the product.