Preparation method of high-purity potassium hexafluoroaluminate crystal

Abstract

The invention discloses a preparation method of a high-purity potassium hexafluoroaluminate crystal, which comprises the following steps: (1) dissolving aluminum nitrate and / or a hydrate thereof in water to obtain an aluminum nitrate solution; dissolving potassium fluoride in water to obtain a potassium fluoride solution; and (2) mixing and stirring the aluminum nitrate solution prepared in the step (1) and the potassium fluoride solution to react, and then standing and aging to obtain the potassium hexafluoroaluminate crystal. The potassium hexafluoroaluminate crystal is prepared by taking aluminum nitrate and potassium fluoride as raw materials in a simple solution mixing mode, the high-purity potassium hexafluoroaluminate crystal can be obtained by controlling the reactant proportion and the mixing mode, the preparation method is simple, the raw materials are safe, the cost is low, the product does not need to be further purified, and the method is suitable for industrial production. The method is suitable for industrial mass production of high-purity potassium hexafluoroaluminate crystals.

Description

Technical Field

[0001] The invention relates to the technical field of potassium hexafluoroaluminate preparation, and in particular to a method for preparing high-purity potassium hexafluoroaluminate crystals. Background Art

[0002] Potassium hexafluoroaluminate is an important chemical raw material, and its main use in industry is as an aluminum electrolysis auxiliary agent, glass and ceramic industry auxiliary agent, preservative and fluorinating agent, etc. It plays an important role in improving production efficiency, improving material properties and extending material life. However, potassium hexafluoroaluminate is currently prepared with hydrofluoric acid as raw material, but hydrofluoric acid has high toxicity and is extremely harmful to the life safety of operators. For example, patent CN108190931A discloses a method for preparing potassium hexafluoroaluminate using a mixed acid containing hydrofluoric acid, wherein aluminum hydroxide solid is added to a potassium hydroxide solution for reaction, potassium metaaluminate clarified solution is generated to prepare potassium hexafluoroaluminate, and under cooling and stirring conditions, a mixed acid containing hydrofluoric acid is added to the potassium metaaluminate solution, potassium hexafluoroaluminate crystals are precipitated, and a fluorine-free acid solution is produced simultaneously, and the obtained potassium hexafluoroaluminate crystal product is separated, washed and dried to obtain a potassium hexafluoroaluminate product.

[0003] In order to avoid the use of highly dangerous hydrofluoric acid, patent CN114634196A provides a method for preparing potassium fluoroaluminate, which comprises crushing hydroxyaluminum fluoride, screening out the part with a particle size of ≤200 mesh; mixing it evenly with water to make a slurry; dissolving potassium fluoride in an acid solution to make an acidic fluorine-containing solution; mixing the acidic fluorine-containing solution with the slurry, stirring the reaction, and obtaining a suspension; filtering the suspension to obtain a filter residue, washing it with water, and drying it to remove moisture to obtain potassium fluoroaluminate. The above method not only has cumbersome synthesis steps, but also the prepared potassium fluoroaluminate is impure, mostly a mixed product of potassium pentafluoroaluminate and potassium hexafluoroaluminate, which is not easy to separate, which not only affects the yield of the target product but also increases the production cost due to the added separation process.

[0004] Based on this, there is an urgent need for a method for preparing high-purity potassium hexafluoroaluminate crystals that is green, environmentally friendly, simple to operate, and suitable for industrial mass production. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing high-purity potassium hexafluoroaluminate crystals, wherein the potassium hexafluoroaluminate crystals are prepared by using safe and easily available aluminum nitrate and potassium fluoride as raw materials through a simple solution mixing method, and the high-purity potassium hexafluoroaluminate crystals can be obtained by controlling the ratio of reactants. The above preparation method is simple, the raw materials are safe, the cost is low, and the product does not need to be further purified, and is suitable for industrial mass production of high-purity potassium hexafluoroaluminate crystals.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing potassium hexafluoroaluminate crystals, comprising the following steps:

[0008] (1) dissolving aluminum nitrate and / or its hydrate in water to obtain an aluminum nitrate solution; dissolving potassium fluoride in water to obtain a potassium fluoride solution;

[0009] (2) mixing the aluminum nitrate solution prepared in step (1) with the potassium fluoride solution, stirring and reacting, and then standing and aging to obtain the potassium hexafluoroaluminate crystals.

[0010] In step (2) of the present invention, the ratio of the molar amount of aluminum nitrate in the aluminum nitrate solution to the molar amount of potassium fluoride in the potassium fluoride solution is 1:(10-20), such as 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, etc., including but not limited to the ratios listed above; preferably, the ratio of the molar amount of aluminum nitrate in the aluminum nitrate solution to the molar amount of potassium fluoride in the potassium fluoride solution is 1:(16-18), and the molar ratio of the two is controlled within the range of 1:(16-18), and the product prepared by the above method does not contain other impurities; more preferably, the ratio of the molar amount of aluminum nitrate in the aluminum nitrate solution to the molar amount of potassium fluoride in the potassium fluoride solution is 1:17, and at this molar ratio, the crystallinity of the prepared product potassium hexafluoroaluminate is optimal.

[0011] Furthermore, in step (2), the stirring reaction temperature is 10-40°C, such as 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, etc., and the stirring reaction time is 1-6h, such as 1h, 2h, 3h, 4h, 5h, 6h, etc.

[0012] Furthermore, in step (2), the temperature of the static aging is 10-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, etc., and the static aging time is 12-48h, for example, 12h, 18h, 24h, 30h, 36h, 42h, 48h, etc.

[0013] Furthermore, the preparation method also includes the process of centrifuging the system after static aging to collect precipitation and drying; preferably, the drying temperature is 80-120°C, for example, drying at 100°C for 4 hours.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The invention provides a method for preparing high-purity potassium hexafluoroaluminate crystals, wherein aluminum nitrate and potassium fluoride, which are safe and readily available, are used as raw materials, and water is used as a solvent, and potassium hexafluoroaluminate crystals can be prepared by a simple solution mixing method, and high-purity potassium hexafluoroaluminate crystals free of impurities can be obtained by controlling the ratio of reactants and the mixing method. The preparation method is simple and efficient, with safe raw materials and low cost, and high-purity potassium hexafluoroaluminate crystals can be obtained without further purification, and is suitable for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the XRD pattern of the solid powder 1 prepared in Example 1;

[0017] Figure 2 is the XRD pattern of the solid powder 2 prepared in Example 2;

[0018] Figure 3 is the XRD pattern of solid powder 3 prepared in Example 3;

[0019] Figure 4 is the XRD pattern of solid powder 4 prepared in Example 4;

[0020] Figure 5 This is a SEM image of the solid powder 4 prepared in Example 4, with a magnification of 10000 times;

[0021] Figure 6 This is a surface scan of the K element in the solid powder 4 prepared in Example 4;

[0022] Figure 7 This is a surface scan of the Al element in the solid powder 4 prepared in Example 4;

[0023] Figure 8 This is a surface scan of the F element in the solid powder 4 prepared in Example 4;

[0024] Fig. 9 is the XRD pattern of solid powder 5 prepared in Example 5;

[0025] Fig.10 is the XRD pattern of solid powder 6 prepared in Example 6;

[0026] Fig.11 The XRD pattern of the solid powder prepared in Comparative Example 1;

[0027] Fig.12 The XRD pattern of the solid powder prepared in Comparative Example 2;

[0028] Fig.13 The XRD pattern of the solid powder prepared in Comparative Example 3;

[0029] Fig.14This is the XRD pattern of the solid powder prepared in Comparative Example 4. DETAILED DESCRIPTION

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "includes" or "comprising" described in the present invention means that it may include or contain other components in addition to the components described. The term "includes" or "comprising" described in the present invention may also be replaced by the closed form "for" or "consisting of..."

[0031] The present invention is further described below in conjunction with specific embodiments and drawings so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0032] Example 1

[0033] This embodiment relates to the preparation of potassium hexafluoroaluminate crystals, and the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:10; the details are as follows:

[0034] (1) Dissolve 7.5 g of aluminum nitrate nonahydrate (20 mmol) in 110 ml of deionized water and stir for 30 minutes to obtain an aluminum nitrate nonahydrate aqueous solution;

[0035] A potassium fluoride aqueous solution was prepared by dissolving 11.62 g of potassium fluoride (200 mmol) in 90 ml of deionized water and stirring for 30 minutes until the potassium fluoride was completely dissolved;

[0036] (2) mixing the aluminum nitrate nonahydrate aqueous solution and the potassium fluoride aqueous solution prepared in step (1) at room temperature for 2 hours, and then standing for 24 hours for aging, centrifuging the aged solution to collect the precipitate, and drying the obtained precipitate at 100° C. for 4 hours to obtain a solid powder 1;

[0037] The XRD pattern of the solid powder 1 prepared in this example is as follows: Figure 1 As shown in the figure, most of the diffraction peaks in the product can be attributed to potassium hexafluoroaluminate, but it also contains a small amount of impurity peaks (such as Figure 1 (as indicated by the triangle in the middle).

[0038] Example 2

[0039] This embodiment relates to the preparation of potassium hexafluoroaluminate crystals, and the only difference from Embodiment 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:13; specifically as follows:

[0040] (1) Dissolve 7.5 g of aluminum nitrate nonahydrate (20 mmol) in 110 ml of deionized water and stir for 30 minutes to obtain an aluminum nitrate nonahydrate aqueous solution;

[0041] A potassium fluoride aqueous solution was prepared by dissolving 15.11 g of potassium fluoride (260 mmol) in 90 ml of deionized water and stirring for 30 minutes until the potassium fluoride was completely dissolved;

[0042] (2) mixing the aluminum nitrate nonahydrate aqueous solution and the potassium fluoride aqueous solution prepared in step (1) at room temperature for 2 hours, and then standing for 24 hours for aging, centrifuging the aged solution to collect the precipitate, and drying the obtained precipitate at 100° C. for 4 hours to obtain a solid powder 2;

[0043] The XRD pattern of the solid powder 2 prepared in this example is as follows: Figure 2 As shown in the figure, most of the diffraction peaks in the product can be attributed to potassium hexafluoroaluminate, but it also contains a small amount of impurity peaks (such as Figure 2 In the middle triangle, compared to Figure 1 , Figure 2 The peak intensity of the impurity peak is weakened.

[0044] Example 3

[0045] This embodiment relates to the preparation of potassium hexafluoroaluminate crystals, and the only difference from Embodiment 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:16; specifically as follows:

[0046] (1) Dissolve 7.5 g of aluminum nitrate nonahydrate (20 mmol) in 110 ml of deionized water and stir for 30 minutes to obtain an aluminum nitrate nonahydrate aqueous solution;

[0047] A potassium fluoride aqueous solution was prepared by dissolving 18.59 g of potassium fluoride (320 mmol) in 90 ml of deionized water and stirring for 30 minutes until the potassium fluoride was completely dissolved;

[0048] (2) mixing the aluminum nitrate nonahydrate aqueous solution and the potassium fluoride aqueous solution prepared in step (1) at room temperature for 2 hours, and then standing for 24 hours for aging, centrifuging the aged solution to collect the precipitate, and drying the obtained precipitate at 100° C. for 4 hours to obtain a solid powder 3;

[0049] The XRD pattern of the solid powder 3 prepared in this example is as follows: Figure 3 As shown in the figure, it can be seen that the diffraction peaks in the product are all attributed to potassium hexafluoroaluminate, and there are no other impurity peaks; thus, it can be seen that the product solid powder 3 prepared in this embodiment is a high-purity potassium hexafluoroaluminate crystal.

[0050] Example 4

[0051] This embodiment relates to the preparation of potassium hexafluoroaluminate crystals, and the only difference from Embodiment 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:17; specifically as follows:

[0052] (1) Dissolve 7.5 g of aluminum nitrate nonahydrate (20 mmol) in 110 ml of deionized water and stir for 30 minutes to obtain an aluminum nitrate nonahydrate aqueous solution;

[0053] A potassium fluoride aqueous solution was prepared by dissolving 19.75 g of potassium fluoride (340 mmol) in 90 ml of deionized water and stirring for 30 minutes until the potassium fluoride was completely dissolved;

[0054] (2) mixing the aluminum nitrate nonahydrate aqueous solution and the potassium fluoride aqueous solution prepared in step (1) at room temperature for 2 hours, and then standing for 24 hours for aging, centrifuging the aged solution to collect the precipitate, and drying the obtained precipitate at 100° C. for 4 hours to obtain a solid powder 4;

[0055] The XRD pattern of the solid powder 4 prepared in this example is as follows: Figure 4 As shown in the figure, it can be seen that the diffraction peaks in the product are all attributed to potassium hexafluoroaluminate, and there are no other impurity peaks. It can be seen that the product solid powder 4 prepared in this embodiment is a high-purity potassium hexafluoroaluminate crystal, and compared with the product prepared in Example 3, the crystallinity is better.

[0056] The SEM image of the solid powder 4 prepared in this example is as follows: Figure 5 As shown, it has a pyramidal morphology. Figure 6-8 The surface scanning images corresponding to the K, Al, and F elements in the product solid powder 4 further illustrate that high-purity potassium hexafluoroaluminate crystals are successfully prepared.

[0057] Example 5

[0058] This embodiment relates to the preparation of potassium hexafluoroaluminate crystals, and the only difference from Example 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:18; specifically as follows:

[0059] (1) Dissolve 7.5 g of aluminum nitrate nonahydrate (20 mmol) in 110 ml of deionized water and stir for 30 minutes to obtain an aluminum nitrate nonahydrate aqueous solution;

[0060] A potassium fluoride aqueous solution was prepared by dissolving 20.88 g of potassium fluoride (360 mmol) in 90 ml of deionized water and stirring for 30 minutes until the potassium fluoride was completely dissolved;

[0061] (2) mixing the aluminum nitrate nonahydrate aqueous solution and the potassium fluoride aqueous solution prepared in step (1) at room temperature for 2 hours, and then standing for 24 hours for aging, centrifuging the aged solution to collect the precipitate, and drying the obtained precipitate at 100° C. for 4 hours to obtain a solid powder 5;

[0062] The XRD pattern of the solid powder 5 prepared in this example is as follows: Fig. 9 As shown in the figure, it can be seen that the diffraction peaks in the product are all attributed to potassium hexafluoroaluminate, and there are no other impurity peaks.

[0063] Example 6

[0064] This embodiment relates to the preparation of potassium hexafluoroaluminate crystals, and the only difference from Embodiment 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:20; specifically as follows:

[0065] (1) Dissolve 7.5 g of aluminum nitrate nonahydrate (20 mmol) in 110 ml of deionized water and stir for 30 minutes to obtain an aluminum nitrate nonahydrate aqueous solution;

[0066] A potassium fluoride aqueous solution was prepared by dissolving 23.24 g of potassium fluoride (400 mmol) in 90 ml of deionized water and stirring for 30 minutes until the potassium fluoride was completely dissolved;

[0067] (2) mixing the aluminum nitrate nonahydrate aqueous solution and the potassium fluoride aqueous solution prepared in step (1) at room temperature for 2 hours, and then standing for 24 hours for aging, centrifuging the aged solution to collect the precipitate, and drying the obtained precipitate at 100° C. for 4 hours to obtain a solid powder 6;

[0068] The XRD pattern of the solid powder 6 prepared in this example is as follows: Fig.10 As shown in the figure, most of the diffraction peaks in the product can be attributed to potassium hexafluoroaluminate, but a small amount of impurity peaks (such as Fig.10 (as indicated by the triangle in the middle).

[0069] Comparative Example 1

[0070] This comparative example involves the preparation of potassium hexafluoroaluminate crystals. The only difference from Example 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:4; the other operations are the same, and the XRD characteristics of the prepared solid powder are as follows: Fig.11 As shown, no diffraction peak attributable to potassium hexafluoroaluminate was found.

[0071] Comparative Example 2

[0072] This comparative example involves the preparation of potassium hexafluoroaluminate crystals. The only difference from Example 1 is that the molar ratio of the reaction raw materials aluminum nitrate nonahydrate to potassium fluoride is 1:7; the other operations are the same, and the XRD characteristics of the prepared solid powder are as follows: Fig.12 As shown, no diffraction peak attributable to potassium hexafluoroaluminate was found.

[0073] Comparative Example 3

[0074] This comparative example involves the preparation of potassium hexafluoroaluminate crystals. The only difference from Example 4 is that the reaction raw materials aluminum nitrate nonahydrate and potassium fluoride are added to 200 mL of deionized water and stirred at the same time; the other operations are the same, and the XRD characteristics of the prepared solid powder are as follows: Fig.13 As shown, most of the diffraction peaks in the product can be attributed to potassium hexafluoroaluminate, but a small amount of impurity peaks (such as Fig.13 (as indicated by the triangle in the middle).

[0075] Comparative Example 4

[0076] This comparative example involves the preparation of potassium hexafluoroaluminate crystals. The only difference from Example 4 is that the type of aluminum source is different, aluminum fluoride trihydrate is used as the aluminum source, and the molar ratio of the reaction raw materials aluminum fluoride trihydrate to potassium fluoride is controlled to be 1:17; the potassium fluoride content and other operations are the same, and the XRD characteristics of the prepared solid powder are as follows: Fig.14 As shown, no diffraction peak attributable to potassium hexafluoroaluminate was found.

[0077] The types of aluminum sources used in the above examples and comparative examples, the molar ratios of aluminum sources to potassium fluoride, and the products are summarized in the following Table 1:

[0078] Table 1

[0079]

[0080]

[0081] In summary, the present invention uses safe and easily available aluminum nitrate and potassium fluoride as raw materials and water as solvent, and can prepare potassium hexafluoroaluminate crystals by a simple solution mixing method, and can obtain high-purity potassium hexafluoroaluminate crystals without impurities by controlling the ratio of reactants and the mixing method.

[0082] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for preparing potassium hexafluoroaluminate crystals, characterized in that: The following steps are involved: (1) dissolving aluminum nitrate and / or its hydrate in water to obtain an aluminum nitrate solution; dissolving potassium fluoride in water to obtain a potassium fluoride solution; (2) mixing the aluminum nitrate solution prepared in step (1) with the potassium fluoride solution for reaction, and then standing and aging to obtain the potassium hexafluoroaluminate crystals; the ratio of the molar amount of aluminum nitrate in the aluminum nitrate solution to the molar amount of potassium fluoride in the potassium fluoride solution is 1:(10-20).

2. The preparation method according to claim 1, characterized in that: The ratio of the molar amount of aluminum nitrate in the aluminum nitrate solution to the molar amount of potassium fluoride in the potassium fluoride solution is 1:(16-18).

3. The preparation method according to claim 2, characterized in that: The ratio of the molar amount of aluminum nitrate in the aluminum nitrate solution to the molar amount of potassium fluoride in the potassium fluoride solution is 1:

17.

4. The preparation method according to claim 1, characterized in that: In step (2), the stirring reaction temperature is 10-40° C., and the stirring reaction time is 1-6 h.

5. The preparation method according to claim 1, characterized in that: In step (2), the temperature of the static aging is 10-40° C., and the static aging time is 12-48 hours.

6. The preparation method according to claim 1, characterized in that: The preparation method also includes the process of centrifuging the system after static aging to collect precipitation and drying.

7. The preparation method according to claim 6, characterized in that: The drying temperature is 80-120°C.

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