A method for preparing ammonium hexafluoroferrate

Abstract

The application relates to the field of fluorinated technology, and particularly discloses a preparation method of ammonium hexafluoroferrate. The method uses ammonium fluoride and iron fluoride with a molar ratio of 3:1 as raw materials, and ammonium hexafluoroferrate is prepared by reacting under the condition of inert atmosphere or vacuum environment at room temperature for 2-3 hours through high-energy ball milling. The method is simple in operation, short in production cycle, and only needs 2-3 hours in the preparation process, so that the method is suitable for large-scale industrial production and can provide a reference for the preparation method of materials with a similar perovskite structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fluorine chemical industry, in particular to a preparation method of ammonium hexafluoroferrate. BACKGROUND

[0002] Ammonium hexafluoroferrate ((NH4)3FeF6) has dielectric properties, and a phase transition occurs at about 264K. It has a cubic cryolite structure at room temperature, and is a typical perovskite structure. By sintering (NH4)3FeF6 at 700℃ in air for 2h, iron oxide can be prepared. It is reported in the literature that (NH4)3FeF6 has good specific capacity and can be used as a new type of anode material for lithium ion batteries (LIBS) [Jie Sun et al., Materials Letters, 2012, 93, 39-41]. In addition, due to the low cost and high specific capacity of ammonium hexafluoroferrate ((NH4)3FeF6), it can be used as an electrode material for sodium ion batteries (SIB). The prepared double perovskite type (NH4)3FeF6 / graphene nanosheet ((NH4)3FeF6 / GNS) composite material has an open three-dimensional framework, which is beneficial to the rapid storage of large-size Na + , and is a very potential anode material for sodium ion batteries [Zhanghui Hao et al., Sustainable Energy Fuels, 2019, 3(10), 2828-2836]. Therefore, ammonium hexafluoroferrate ((NH4)3FeF6) has attracted widespread attention, and its preparation method is also the current research focus.

[0003] The preparation methods of fluoride mainly include traditional high-temperature solid-phase method, sol-gel method, molten salt method and hydrothermal synthesis method. Among them, HE et al. prepared (NH4)3FeF6 by hydrothermal synthesis method with Fe2O3 and NH4HF2 as main raw materials [HE Li-jie et al., Chinese Journal of Synthetic Chemistry, 2017, 4(25), 326-329]. In the preparation process, Fe2O3 and distilled water were first added into a beaker in sequence, then NH4HF2 was added until saturation, and stirring was uniform; 1 mL of HF was added dropwise to make the filling degree of the reaction kettle 80%, and then it was tightly closed and placed in an oven for crystallization at 180℃ for 3 days. After cooling to room temperature, it was poured into a beaker and washed with ethanol, and then dried at 50℃ to obtain colorless transparent crystals (NH4)3FeF6 with a yield of 35%. The problems existing in the preparation method are: 1. low yield and high cost; 2. the amount of reaction raw material NH4HF2 and the reaction temperature need to be strictly controlled during the preparation process, and the target product can be obtained only at 180℃-200℃, and the generation of the target product is not conducive at too low or too high temperature; 3. the raw material HF used is strong acid and is highly toxic, and improper operation of workers will cause serious consequences; 4. long preparation time and low production efficiency.

[0004] In addition, the literature also records a method for preparing (NH4)3FeF6 by using an electric field assisted in-situ dissolution reaction, which is realized by in-situ dissolution and hydrolysis of iron oxide. The preparation process is as follows: Fe foil is used as anode and cathode, water and ammonium fluoride ethylene glycol solution are added as electrolyte, and electrochemical reaction is carried out at a large current density for 1 second to 10 minutes, then centrifugation is carried out at 10000 r / min for 5 minutes, washing is carried out with anhydrous ethanol, and drying is carried out in air at 60℃ to obtain (NH4)3FeF6. Compared with the aforementioned hydrothermal synthesis method, the preparation process is shortened, but the preparation process is complicated [Hui Li et al., Chemical Communications, 2022, 58, 1922-1925].

[0005] The above preparation methods all use the interaction between ions in the liquid phase to realize the preparation of (NH4)3FeF6, and the common problem is that the preparation process is very complex, the production cost is high, and it is not suitable for large-scale industrial production. SUMMARY

[0006] The present application provides a preparation method of ammonium hexafluoroferrate to overcome the problems of complex preparation process, high production cost and unsuitable for large-scale industrial production in the prior art.

[0007] In order to achieve the purpose of the present application, the technical solutions provided by the present application are as follows:

[0008] A method for preparing ammonium hexafluoroferrate involves using ammonium fluoride and iron fluoride in a molar ratio of 3:1 as raw materials, and carrying out the reaction under an inert atmosphere or vacuum at room temperature. The reaction is carried out by high-energy ball milling. The reaction formula is: 3NH4F + FeF3 → (NH4)3FeF6.

[0009] Furthermore, in the above-mentioned high-energy ball milling reaction, the milling beads are made of stainless steel or tungsten carbide, the ball-to-material mass ratio is 200:1, the milling speed is 400-500 rpm, and the milling time is 2-3 hours.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. This invention uses physical high-energy ball milling to prepare the product. High-energy ball milling is a method for material preparation and powdering that utilizes the interaction between grinding balls and materials to provide shear and impact energy. This invention selects suitable materials, ammonium fluoride and iron fluoride, and then uses high-energy ball milling to induce a reaction between the molecules of ammonium fluoride and iron fluoride. Following the specific parameters provided in this invention, high-purity ammonium hexafluoroferrate can be prepared.

[0012] 2. The method of the present invention is simple to operate and can be completed by ordinary workers; the production cycle is short, the preparation process only takes 2-3 hours, the production efficiency is high, and it is suitable for large-scale industrial production.

[0013] 3. The preparation method of ammonium hexafluoroferrate provided by the present invention can provide a reference preparation method for materials with similar perovskite structures. Attached Figure Description

[0014] Figure 1 The X-ray diffraction pattern of the ball-milled product ammonium hexafluoroferrate prepared in Example 1 is shown, and the standard PDF card of the XRD diffraction of standard ammonium hexafluoroferrate is also provided.

[0015] Figure 2 SEM image of ammonium hexafluoroferrate, the ball-milled product prepared in Example 1;

[0016] Figure 3 X-ray diffraction pattern of ammonium hexafluoroferrate, the ball-milled product prepared in Example 2;

[0017] Figure 4 X-ray diffraction pattern of the ball-milled product prepared in Comparative Example 1;

[0018] Figure 5 X-ray diffraction pattern of the ball-milled product prepared in Comparative Example 2;

[0019] Figure 6 X-ray diffraction pattern of the ball-milled product prepared in Comparative Example 3;

[0020] Figure 7 The X-ray diffraction pattern of the ball-milled product prepared in Comparative Example 4 is shown. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] The present invention provides a method for preparing ammonium hexafluoroferrate, which uses ammonium fluoride and iron fluoride in a molar ratio of 3:1 as raw materials, and carries out the process under an inert atmosphere or vacuum environment at room temperature, and then prepares ammonium hexafluoroferrate by high-energy ball milling reaction.

[0023] During ball milling, NH4F and FeF3 react as shown in reaction formula (1):

[0024] 3NH4F + FeF3 → (NH4)3FeF6 (1)

[0025] Example 1: A method for preparing ammonium hexafluoroferrate, comprising the following specific steps:

[0026] (1) Because ammonium fluoride and iron fluoride are prone to absorbing water and deteriorating in the air, ammonium fluoride and iron fluoride are mixed in a molar ratio of 3:1 and placed in a stainless steel ball mill jar in an argon atmosphere glove box and sealed. Stainless steel grinding balls are used, and the mass ratio of the balls to the material is 200:1.

[0027] (2) The ball mill containing the mixture of ammonium fluoride and ferric fluoride was ball milled at a speed of 500 rpm for 2 hours to obtain the ball milling product ammonium hexafluoroferrate.

[0028] Figure 1 The X-ray diffraction (XRD) pattern of the ball-milled product was compared with the standard PDF card of ammonium hexafluoroferrate. It was found that there were no diffraction peaks of the initial reactants ammonium fluoride and iron fluoride in the ball-milled product, only the diffraction peaks of ammonium hexafluoroferrate. Figure 2 This is a SEM image of the ball-milled product. It indicates that all the initial reactants have reacted, forming ammonium hexafluoroferrate.

[0029] Example 2, a method for preparing ammonium hexafluoroferrate, involves mixing ammonium fluoride and ferric fluoride in a molar ratio of 3:1 in an argon atmosphere glove box, sealing the mixture in a stainless steel ball mill jar, using tungsten carbide grinding balls with a ball-to-material mass ratio of 200:1, and ball milling the mixture at 400 rpm for 3 hours to obtain the ball-milled product ammonium hexafluoroferrate.

[0030] Figure 3 The image shows the XRD pattern of the ball-milled product in this embodiment. The XRD results show that only ammonium hexafluoroferrate diffraction peaks are present in the ball-milled product, indicating that after the ball milling reaction, ammonium fluoride and ferric fluoride completely react to form ammonium hexafluoroferrate.

[0031] Comparative Example 1

[0032] (1) In an argon atmosphere glove box, ammonium fluoride and iron fluoride are mixed at a molar ratio of 3:1 and placed in a stainless steel ball mill jar and sealed. Stainless steel grinding balls are used, and the ball-to-material ratio is 200:1.

[0033] (2) The ball mill containing the mixture of ammonium fluoride and iron fluoride was ball milled at 300 rpm for 6 hours to obtain the ball milled product.

[0034] Figure 4 The XRD pattern of the ball-milled product is shown. It can be seen that diffraction peaks of ammonium hexafluoroferrate are present, but a small number of diffraction peaks of ferric fluoride are also present. This indicates that even after 6 hours of ball milling at 300 rpm, the reactants cannot be completely converted into the products. Further increasing the ball milling time is not conducive to improving production efficiency.

[0035] Comparative Example 2

[0036] In an argon atmosphere glove box, ammonium fluoride and iron fluoride were mixed at a molar ratio of 3:1 and placed in a stainless steel ball mill jar and sealed. Stainless steel grinding balls were used with a ball-to-material mass ratio of 100:1. The mixture was ball-milled at 500 rpm for 2 hours to obtain the ball-milled product.

[0037] Figure 5 This is the XRD pattern of the ball-milled product in this comparative example. The figure shows the formation of ammonium hexafluoroferrate, as well as unreacted ammonium fluoride and ferric fluoride. This indicates that under low ball-to-material ratio conditions, insufficient ball milling efficiency resulted in the complete conversion of reactants into the product ammonium hexafluoroferrate.

[0038] Comparative Example 3

[0039] In an argon atmosphere glove box, ammonium fluoride and iron fluoride were mixed at a molar ratio of 2:1 and placed in a stainless steel ball mill jar and sealed. Tungsten carbide grinding balls were used with a ball-to-material ratio of 200:1, and the mixture was ball-milled at 500 rpm for 2 hours to obtain the ball-milled product.

[0040] Figure 6 The XRD pattern of the ball-milled product of this comparative example is shown. It can be seen that there are diffraction peaks of ammonium hexafluoroferrate in the pattern, but there are also a large number of diffraction peaks of ferric fluoride. This indicates that when the molar ratio of ammonium fluoride to ferric fluoride is 2:1, according to chemical reaction formula (1), ferric fluoride is in excess, and there is residual ferric fluoride after the ball milling reaction.

[0041] Comparative Example 4

[0042] In an argon atmosphere glove box, ammonium fluoride and iron fluoride were mixed at a molar ratio of 4:1 and placed in a stainless steel ball mill jar and sealed. Tungsten carbide grinding balls were used with a ball-to-material ratio of 200:1, and the mixture was ball-milled at 500 rpm for 2 hours to obtain the ball-milled product.

[0043] Figure 7 The XRD pattern of the ball-milled product of this comparative example is shown. It can be seen that there are diffraction peaks of ammonium hexafluoroferrate in the pattern, but there are also diffraction peaks of unreacted ammonium fluoride and iron fluoride. This indicates that when the molar ratio of ammonium fluoride to iron fluoride is 4:1, the reaction cannot proceed effectively according to chemical reaction formula (1), and there are unreacted ammonium fluoride and iron fluoride after the ball milling reaction.

[0044] Comparative Example 5

[0045] In an argon atmosphere glove box, ammonium fluoride and iron fluoride were mixed at a molar ratio of 3:1 and placed in a stainless steel ball mill jar and sealed. The ball-to-material ratio was 200:1. The mixture was ball-milled at 500 rpm for 1 hour to obtain the ball-milled product.

[0046] The XRD pattern of the ball-milled product in this comparative example is similar to that in Comparative Example 2, both showing the formation of ammonium hexafluoroferrate and unreacted ammonium fluoride and ferric fluoride. This indicates that insufficient ball milling time led to incomplete reaction, and the reactants did not completely form the product ammonium hexafluoroaluminate.

[0047] The embodiments 1 and 2 described above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ammonium hexafluoroferrate, characterized in that, Ammonium hexafluoroferrate was prepared by high-energy ball milling of ammonium fluoride and ferric fluoride in a molar ratio of 3:1 at room temperature under an inert atmosphere or vacuum. The reaction formula is as follows: ; The high-energy ball milling reaction uses stainless steel or tungsten carbide balls, with a ball-to-material mass ratio of 200:1, a milling speed of 400-500 rpm, and a milling time of 2-3 hours.

Images