A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

Abstract

The application provides a method for preparing silicon tetrafluoride by using fluorine-containing silicon slag, and belongs to the field of fluorine-containing silicon slag utilization; the method comprises the following steps: washing the fluorine-containing silicon slag with brine A, filtering to obtain silicon dioxide and filtrate; adding brine B to the obtained filtrate, filtering to obtain a silicon tetrafluoride precursor and secondary filtrate; and drying, calcining the obtained silicon tetrafluoride precursor to obtain silicon tetrafluoride. Compared with the prior art, the fluorine-containing silicon slag is washed with specific ammonium brine, so that the fluosilicic acid in the fluorine-containing silicon slag can be efficiently extracted, the yield of the silicon tetrafluoride precursor is improved, the method is more energy-saving, the raw material cost is lower, the process control is simpler, and the silicon tetrafluoride precursor is not prone to sticking to the wall during the calcining process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fluorine-containing silicon slag utilization, and particularly relates to a method for preparing silicon tetrafluoride from fluorine-containing silicon slag. BACKGROUND

[0002] As a general electronic special gas, silicon tetrafluoride is an important raw material in the production of electronics and semiconductors, and can be used for plasma etching of silicon-containing materials, doping of light-emitting diodes, epitaxial deposition growth of silicon, amorphous silicon film generation, ion implantation process, etc. In recent years, due to the rapid development of the industry, its use has also increased rapidly. With the development and maturity of the polysilicon production process using silicon tetrafluoride as an intermediate product, silicon tetrafluoride has a broader application in the semiconductor industry. Silicon tetrafluoride can also be used as a fluorine source and a reaction promoter in organic synthesis, and can also be used for casting of magnesium alloy, smoking agent, cement and artificial marble hardener, etc.

[0003] Fluorine-containing silicon slag is a kind of industrial by-product which is difficult to utilize. It is produced when anhydrous hydrogen fluoride is produced by recovering fluorine elements associated with phosphate rock, and its main components are fluorosilicic acid and silicon dioxide, and it also contains a small amount of hydrofluoric acid, which has strong acidity and corrosivity. In recent years, it has been found that fluorine-containing silicon slag can be used as a raw material for the production of silicon tetrafluoride; however, there are problems of high preparation cost and low product quality in the process of using it to produce silicon tetrafluoride.

[0004] CN116282041A discloses a method for preparing silicon tetrafluoride from fluorine-containing silicon slag, which relates to a compound of fluorine and silicon, and particularly relates to a method for preparing silicon tetrafluoride gas by using fluorine-containing silicon slag. The specific steps of the method include: (1) neutralizing the fluorine-containing silicon slag with lye; (2) filtering, and using the filtrate to prepare lye and return it to the neutralization of the fluorine-containing silicon slag; drying the filter residue to obtain modified fluorine-containing silicon slag; (3) heating and decomposing the modified fluorine-containing silicon slag in a vacuum or inert atmosphere to obtain silicon tetrafluoride gas, collecting silicon tetrafluoride liquid or compressed gas, and the by-product is mainly decomposed slag containing active silicon dioxide.

[0005] The above-mentioned invention uses a solid mixture mainly containing silicon dioxide, fluorosilicic acid and hydrogen fluoride to prepare silicon tetrafluoride, which reduces the preparation consumption and makes the preparation of fluorine-containing silicon slag more economical while improving the product value; however, since it uses lye for neutralization and a large amount of fluorine-containing silicon slag for preparing silicon tetrafluoride, the cost is high and the energy consumption is large, and a series of improvements are still needed.

[0006] Meanwhile, the inventors found in experiments that currently, non-alkaline solution is used to clean fluorine-containing silicon slag, which can easily lead to insufficient leaching of fluorosilicic acid in the fluorine-containing silicon slag, resulting in low yield of silicon tetrafluoride precursor prepared from fluorine-containing silicon slag, and reducing the treatment efficiency of fluorine-containing silicon slag.

[0007] Therefore, how to provide a preparation method for preparing silicon tetrafluoride from fluorine-containing silicon slag with lower preparation cost, less energy consumption and higher extraction rate of fluorosilicic acid in the fluorine-containing silicon slag is an important problem for those skilled in the art to study. SUMMARY

[0008] The present application provides a method for preparing silicon tetrafluoride from fluorine-containing silicon slag, which has the advantages of high product value, energy saving, cost reduction and simple process control, can efficiently separate fluorosilicic acid from fluorine-containing silicon slag, and obtain better silicon tetrafluoride yield.

[0009] To achieve the above-mentioned object, the technical scheme adopted by the present application is as follows:

[0010] A method for preparing silicon tetrafluoride from fluorine-containing silicon slag, comprising the following steps:

[0011] S1. washing the fluorine-containing silicon slag with salt water A to obtain silica and filtrate by filtration;

[0012] S2. adding salt water B to the filtrate obtained in S1 to obtain silicon tetrafluoride precursor and secondary filtrate by filtration;

[0013] S3. drying and calcining the silicon tetrafluoride precursor obtained in S2 to obtain silicon tetrafluoride;

[0014] The fluorine-containing silicon slag in step S1 contains silica, water, hydrogen fluoride and fluorosilicic acid.

[0015] Preferably, the salt in the salt water A in step S1 includes ammonium salt.

[0016] Further preferably, the ammonium salt is selected from one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium fluoride, ammonium bifluoride and ammonium formate.

[0017] The salt water A used in step S1 of the present application generally contains an effective amount of salt, which can leach fluorosilicic acid and reduce the residual fluorosilicic acid in the fluorine-containing silicon slag; in general, the salt water A according to the present application contains salt at a concentration of 0.1wt%-10wt%, such as 0.1-5, 0.1-1, 0.1-0.5, 0.1-0.2, 1-5, 1-2 and 2-5wt%, preferably between 0.1-5wt%, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4 or 5wt%; the concentration of salt in the specific salt water A can be adjusted by those skilled in the art according to the composition of the fluorine-containing silicon slag and the concentration of fluorosilicic acid therein.

[0018] The ratio of the amount of the salt water A to the fluorine-containing silicon residue can also be adjusted by those skilled in the art according to the composition and quality of the fluorine-containing silicon residue. Generally, the ratio of the amount of the salt water A to the fluorine-containing silicon residue is 0.5-1000:1, such as 0.5-100:1, 0.5-50:1, 0.5-20:1, 0.5-10:1, 0.5-5:1, 0.5-2:1, 1-100:1, 1-50:1, 1-20:1, 1-10:1, 1-5:1 and 1-2:1, preferably 1-10:1, for example, 1-5:1, 1-2:1, 1-1.5:1, 1-1.2:1 and 1-1.1:1.

[0019] Preferably, the salt in the salt water B in step S2 is selected from inorganic sodium, potassium or barium salts with solubility at 20°C higher than 10 g / 100 g H2O.

[0020] Further preferably, the salt water B is a saturated solution of the salt.

[0021] It should be noted that whether a saturated solution of the salt is used has no obvious effect on the extraction effect, and increasing the concentration of the salt mainly plays a role in improving the processing efficiency; those skilled in the art can adjust the amount and concentration of the salt water B as needed to achieve the separation of fluorosilicic acid or its salt components.

[0022] Preferably, in step S2, the salt water B is added until no more precipitate is produced.

[0023] Preferably, the secondary filtrate in step S2 can be used to prepare the salt water B in step S2.

[0024] Preferably, the temperature of the drying in step S3 is not higher than 350°C.

[0025] Preferably, inert powder is added during the calcination in step S3.

[0026] Further preferably, the inert powder is a solid that does not participate in the reaction and is stable at the calcination temperature in step S3.

[0027] More preferably, the inert powder is a solid produced by the decomposition of the silicon tetrafluoride precursor after the calcination in step S3; the mass ratio of the silicon tetrafluoride precursor after drying to the inert powder in step S3 is 1:0.1-100.

[0028] Most preferably, the temperature of the calcination in step S3 is 520-800°C, and the time is 0.25-2h.

[0029] Preferably, the temperature and time of the calcination in step S3 are selected from:

[0030] 660-740℃ for 1.8-2.2h, 600-690℃ for 0.7-0.8h or 520-590℃ for 0.9-1.2h.

[0031] Further preferably, the temperature and time of the roasting in step S3 are selected from:

[0032] 700℃ for 2h, 650℃ for 0.75h or 550℃ for 1h.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] The present application uses specific ammonium salt to wash the fluorine-containing silicon slag, which can efficiently extract fluorosilicic acid from the fluorine-containing silicon slag and improve the yield of silicon tetrafluoride precursor;

[0035] The method provided by the present application is more energy-saving, and only needs to dry the separated silicon tetrafluoride precursor by using the filtrate precipitation method.

[0036] The raw material used in the present application is more economical, and the cost of preparing silicon tetrafluoride by using salt water is lower than that of using lye;

[0037] The process control of the present application is more simple, and the salt water used in the precipitation method can be excessively added, and the excessive raw material will not affect the subsequent process.

[0038] The present application uses specific roasting temperature or further connects inert powder to roast silicon tetrafluoride precursor, which can effectively avoid the deposition or caking of the generated roasting by-products in the roasting equipment, affecting the production. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a process route map of the embodiment of the present application;

[0040] Figure 2 It is the XRD characterization result of the silicon tetrafluoride precursor prepared by using sodium salt in the embodiment 1 of the present application and the standard PDF card comparison diagram of Na2SiF6.

[0041] Figure 3 It is the XRD characterization result of the silicon tetrafluoride precursor prepared by using potassium salt in the embodiment 2 of the present application and the standard PDF card comparison diagram of K2SiF6.

[0042] Figure 4 It is the XRD characterization result of the silicon tetrafluoride precursor prepared by using barium salt in the embodiment 3 of the present application and the standard PDF card comparison diagram of BaSiF6.

[0043] Figure 5 、 Figure 6 、 Figure 7 and Figure 8Fig. 1 is a graph showing the material conditions after roasting under different conditions of the embodiment of the present application. DETAILED DESCRIPTION

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The following definitions are applied to the descriptions and claims herein, and apply equally when used in the singular or plural forms, and also apply to methods employing them.

[0045] As used herein, the recitations "a" and "an" include plural referents unless the context clearly indicates otherwise.

[0046] As used herein, the term "about" means a range of ±20% of the value that follows. In some embodiments, the term "about" means a range of ±10% of the value that follows. In some embodiments, the term "about" means a range of ±5% of the value that follows.

[0047] Numerical ranges as used herein are intended to include all numbers and ranges falling within the specified range. For example, a range of 1 to 20 is intended to include any number or combination of numbers or sub-ranges falling within the range, e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.

[0048] As used herein, the terms "comprises" or "comprising" mean "including, but not limited to." This term is intended to be open-ended to designate any stated feature, element, integer, step, or component, but does not preclude the presence or addition of one or more other features, elements, integers, steps, components, or groups thereof. Therefore, the term "comprising" encompasses the more restrictive terms "consisting of" and "consisting essentially of." In one embodiment, the term "comprising" as used throughout the application, and in particular in the claims, can be replaced with the term "consisting of."

[0049] As used herein, the terms "optional," "any of," "any," or "any of" mean that the event or circumstance subsequently described can or can not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. As used herein, "a" and "an" are used in the present application to refer to one or more than one of the grammatical object of the article.

[0050] As used herein, the term "and / or" is to be taken as specific embodiments of the inclusive- or. That is, in the phrase "A and / or B" for example, A or B can be present, or A and B can be present.

[0051] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with examples. If specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturers are adopted. If the manufacturers of all reagents or instruments are not specified, they are all the conventional products that can be purchased in the market. In order to better illustrate the present application, numerous specific details are given in the following specific embodiments. The specific embodiments described herein are only used to explain the present application and do not constitute any limitation on the present application. In addition, in the following description, the description of the well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application. Such structures and technologies are also described in many publications.

[0052] The moisture content is determined according to GB / T 35924-2018 "Determination of Moisture Content in Solid Chemical Products-Thermogravimetric Method";

[0053] The silicon dioxide content is determined according to GB / T 4209-2022 "Industrial Sodium Silicate";

[0054] The fluorine content is determined according to GB / T 21057-2007 "General Method for Determination of Fluorine Content in Inorganic Chemical Products-Ion Selective Electrode Method";

[0055] The main components of the fluorine-containing silicon slag obtained by determination are as follows:

[0056] Item Test result Method used Moisture (%) 55.40 GB / T 35924-2018 Silicon dioxide (%) 34.21 GB / T4209-2008 Fluorine content (%) 6.7360 GB / T21057-2007

[0057] It should be noted that due to the stability of the chemical properties of the chemical components in the fluorine-containing silicon slag, the adjustment of the component content of the above fluorine-containing silicon slag will not affect the chemical process involved and the technical effects that can be achieved by the present application.

[0058] The process route of the present application is shown in Figure 1 .

[0059] The amount of fluorine-containing silicon slag used in the examples and comparative examples is the same, which is 66.7g.

[0060] Example 1 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0061] S1. The fluorine-containing silicon slag is washed with an ammonium chloride aqueous solution with a concentration of 5wt%, and filtration is performed to obtain silicon dioxide and a filtrate;

[0062] S2. A saturated aqueous solution of sodium sulfate is added to the filtrate obtained in S1 until no precipitate is generated, and filtration is performed to obtain a silicon tetrafluoride precursor and a secondary filtrate;

[0063] S3. The silicon tetrafluoride precursor obtained in S2 is dried at 300℃, and is calcined at 650℃ under a vacuum condition of 20Pa for 0.75h to obtain silicon tetrafluoride.

[0064] Example 2 A method for preparing silicon tetrafluoride by using fluorine-containing silicon residue

[0065] S1. washing the fluorine-containing silicon residue with an aqueous solution of ammonium sulfate having a concentration of 10 wt%, and filtering to obtain silica and a filtrate;

[0066] S2. adding a 10 wt% aqueous solution of potassium chloride to the filtrate obtained in S1 until no precipitate is produced, and filtering to obtain a silicon tetrafluoride precursor and a secondary filtrate;

[0067] S3. drying the silicon tetrafluoride precursor obtained in S2 at 120°C, and calcining at 700°C under a vacuum of 20 Pa for 2 h to obtain silicon tetrafluoride.

[0068] Example 3 A method for preparing silicon tetrafluoride by using fluorine-containing silicon residue

[0069] S1. washing the fluorine-containing silicon residue with an aqueous solution of ammonium nitrate having a concentration of 0.1 wt%, and filtering to obtain silica and a filtrate;

[0070] S2. adding a 20 wt% aqueous solution of barium chloride to the filtrate obtained in S1 until no precipitate is produced, and filtering to obtain a silicon tetrafluoride precursor and a secondary filtrate;

[0071] S3. drying the silicon tetrafluoride precursor obtained in S2 at 300°C, and calcining at 550°C under a vacuum of 20 Pa for 1 h to obtain silicon tetrafluoride.

[0072] Example 4 A method for preparing silicon tetrafluoride by using fluorine-containing silicon residue

[0073] S1. washing the fluorine-containing silicon residue with an aqueous solution of ammonium chloride having a concentration of 3 wt%, and filtering to obtain silica and a filtrate;

[0074] S2. adding a saturated aqueous solution of sodium chloride to the filtrate obtained in S1 until no precipitate is produced, and filtering to obtain a silicon tetrafluoride precursor and a secondary filtrate;

[0075] S3. drying the silicon tetrafluoride precursor obtained in S2 at 300°C, and mixing with sodium fluoride powder having a mass of 200% of the mass of the dried silicon tetrafluoride precursor, and calcining at 750°C under a vacuum of 20 Pa for 0.25 h to obtain silicon tetrafluoride.

[0076] Example 5 A method for preparing silicon tetrafluoride by using fluorine-containing silicon residue

[0077] S1. washing the fluorine-containing silicon residue with an aqueous solution of ammonium sulfate having a concentration of 6 wt%, and filtering to obtain silica and a filtrate;

[0078] S2. To the filtrate obtained in S1, a saturated aqueous solution of potassium sulfate was added until no precipitate was formed, and the obtained silicon tetrafluoride precursor and secondary filtrate were filtered.

[0079] S3. The silicon tetrafluoride precursor obtained in S2 was dried at 120°C, mixed with 10,000% of silicon dioxide powder by weight of the dried silicon tetrafluoride precursor, and calcined at 800°C under a vacuum of 20 Pa for 0.75 h to obtain silicon tetrafluoride.

[0080] Example 6 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0081] S1. The fluorine-containing silicon slag was washed with an aqueous solution of 0.5 wt% ammonium sulfate, and the obtained silicon dioxide and filtrate were filtered.

[0082] S2. To the filtrate obtained in S1, a saturated aqueous solution of barium chloride was added until no precipitate was formed, and the obtained silicon tetrafluoride precursor and secondary filtrate were filtered.

[0083] S3. The silicon tetrafluoride precursor obtained in S2 was dried at 300°C, mixed with 10% of barium fluoride powder by weight of the dried silicon tetrafluoride precursor, and calcined at 520°C under a vacuum of 20 Pa for 1.5 h to obtain silicon tetrafluoride.

[0084] Comparative Example 1 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0085] The only difference between this comparative example and Example 1 is that in step S1, an equal amount of water was used instead of salt water.

[0086] Comparative Example 2 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0087] The only difference between this comparative example and Example 1 is that in step S1, an aqueous solution of 5 wt% sodium hydroxide was used instead of salt water.

[0088] Comparative Example 3 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0089] The only difference between this comparative example and Example 1 is that in step S1, 0.5 wt% of sodium chloride salt water was used for washing.

[0090] Comparative Example 4 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0091] The only difference between this comparative example and Example 1 is that the calcination temperature used in step S3 was 700°C.

[0092] Comparative Example 5 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0093] The only difference between this comparative example and Example 2 is that the calcination temperature used in step S3 was 750°C.

[0094] Comparative Example 6 A method for preparing silicon tetrafluoride using fluorine-containing silicon slag

[0095] The difference between this comparative example and Example 3 is that the calcination temperature used in step S3 is 600°C.

[0096] Comparative Example 7

[0097] The difference between this comparative example and Example 4 is that no sodium fluoride powder is added in step S3.

[0098] Test Example 1 Yield and purity of silicon tetrafluoride precursor

[0099] The silicon tetrafluoride precursor (mainly composed of sodium fluorosilicate, potassium fluorosilicate or barium fluorosilicate) prepared in Examples 1-3 is first analyzed by XRD, and by comparison with the standard PDF card (such as Figure 2-Figure 4 ), it can be seen that the silicon tetrafluoride precursor is successfully prepared.

[0100] Test method:

[0101] The sodium fluorosilicate content refers to “GB / T 23936-2018 Industrial Sodium Fluorosilicate”

[0102] The potassium fluorosilicate content refers to “HG / T 4693-2014 Industrial Potassium Fluorosilicate”

[0103] The barium fluorosilicate content refers to the detection method of sodium fluorosilicate and potassium fluorosilicate in “GB / T 23936-2018 Industrial Sodium Fluorosilicate” and “HG / T 4693-2014 Industrial Potassium Fluorosilicate”;

[0104] The main difference is that the barium fluorosilicate content is calculated in terms of the mass fraction ω1 of barium fluorosilicate (BaSiF6) according to the following formula:

[0105]

[0106] In the formula:

[0107] V - the value of the volume of the sodium hydroxide standard titration solution consumed by the titration test solution, in milliliters (mL);

[0108] C - the accurate value of the concentration of the sodium hydroxide standard titration solution, in moles per liter (mol / L);

[0109] M - the value of the molar mass of sodium fluorosilicate (1 / 4 BaSiF6), in grams per mole (g / mol) (M = 69.85);

[0110] m - the value of the mass of the sample, in grams (g);

[0111] 1.9158 - coefficient of free acid (as HC1) to barium fluosilicate;

[0112] ω2 - mass fraction of free acid (as HC1);

[0113] Silicon tetrafluoride precursor purity Silicon tetrafluoride precursor yield Example 1 99.2％ 2.12g Example 2 97.5％ 2.51g Example 3 98.1％ 3.21g Example 4 99.3％ 2.10g Example 5 97.7％ 2.53g Example 6 98.7％ 3.18g Comparative Example 1 99.1％ 1.71g Comparative Example 2 / 0.12g Comparative Example 3 99.1％ 1.83g

[0114] It can be seen that the purity of the silicon tetrafluoride precursor in Example 1 is consistent with that in Comparative Examples 1-3. The yield of the silicon tetrafluoride precursor in Example 1 is 2.12 g, which is 15.85% higher than the yield of 1.83 g in Comparative Example 1 with the highest yield in the comparative examples, which can illustrate that the selection of the ammonium salt in the present application significantly improves the utilization rate of the fluorine-containing silicon residue.

[0115] Deposition of silicon tetrafluoride in Test Example 2

[0116] The deposition of silicon tetrafluoride before and after the calcination equipment is examined, and the deposition is divided into the following three types:

[0117] ① As shown in FIG. 1: After calcination, the material presents a powder shape, and in the container, it presents a loose powder boundary. There is only a small amount of deposited solid on the side wall and bottom surface of the container, which is easy to peel off. The peeled material presents a powder shape. Figure 5 ② As shown in FIG. 2: After calcination, the material presents a powder-like accumulation, and in the container, it presents a relatively round boundary. There is obvious deposition of solid on the side wall and bottom surface of the container, which is relatively easy to peel off. The peeled material is combined loosely, and the debris is in the form of loose chunks or powder.

[0118] Figure 6 ③ As shown in FIG. 3: After calcination, the material presents a smooth surface without powder texture and with small pores, and in the container, it presents a round boundary. The bottom surface of the container is fully covered with solid, and the unpeeled material is combined very tightly with the container, which is extremely difficult to peel off. Or as shown in FIG. 4: After calcination, the material presents a solid with a large number of pores without powder texture, and the bottom surface of the container is fully covered with solid and is difficult to peel off. The unpeeled material is combined tightly with the container, and the peeled material debris is in the form of a sheet.

[0119] Figure 7 Figure 8

[0120] The results are shown as follows:

[0121] Deposition after calcination Example 1 ① Example 2 ① Example 3 ① Example 4 ① Example 5 ① Example 6 ① Comparative Example 4 ② Comparative Example 5 ② Comparative Example 6 ② Comparative Example 7 ③

[0122] ​​​​It can be seen that in the test results of the embodiments of the present application, the materials after roasting all remain in powder form, compared with the block or dense solid in the comparative examples, maintaining the powder form can effectively maintain the material state during roasting in actual production, prevent the insufficient utilization of silicon tetrafluoride precursor caused by block or dense solid, and the residual material powder can be further used as inert powder, thereby maintaining the material state during roasting, so that long-time continuous production can be carried out.

[0123] Test Example 3: Silicon tetrafluoride yield and purity

[0124] The silicon tetrafluoride obtained in Examples 1-8 was characterized, specifically:

[0125] The purity of silicon tetrafluoride was detected according to the 4 test method in GB / T 31058-2014 Electronic Industry Gas Silicon Tetrafluoride using a double-helium ion gas chromatograph;

[0126] The actual yield of silicon tetrafluoride in the product was further calculated using the purity of silicon tetrafluoride, and the yield of silicon tetrafluoride was obtained.

[0127] The results are as follows:

[0128] Silicon tetrafluoride yield Silicon tetrafluoride purity Example 1 98.65％ 99.931％ Example 2 98.33％ 99.911％ Example 3 98.12％ 99.923％ Example 4 98.72％ 99.915％ Example 5 98.25％ 99.907％ Example 6 98.72％ 99.911％ Comparative Example 4 94.87％ 98.857％ Comparative Example 5 92.51％ 98.553％ Comparative Example 6 93.43％ 98.752％ Comparative Example 7 87.76％ 97.933％

[0129] According to the data in the above table, the embodiments of the present application can well ensure the product yield and purity of silicon tetrafluoride, and the purity is more than 99.9%; while the comparative examples change the roasting temperature or the condition of inert powder during roasting, resulting in the purity of silicon tetrafluoride being less than 99%.

[0130] Further combining Test Example 2, it can be seen that the deposition after roasting is closely related to the yield and purity of silicon tetrafluoride, and Comparative Example 7 with roasting condition ③ has the lowest yield and purity of silicon tetrafluoride.

[0131] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application, and simple modifications or equivalent replacements of the technical solutions of the present application by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing silicon tetrafluoride using fluorinated silicon slag, comprising the following steps: S1. Wash the fluorinated silicon slag with brine A, and filter to obtain silicon dioxide and filtrate; S2. Add brine B to the filtrate obtained in S1, and filter to obtain silicon tetrafluoride precursor and secondary filtrate; S3. Dry and calcine the silicon tetrafluoride precursor obtained in S2 to obtain silicon tetrafluoride; The fluorinated silicon slag mentioned in step S1 contains silicon dioxide, water, hydrogen fluoride and fluorosilicic acid; The salt in the brine A mentioned in step S1 includes ammonium salts; The salt in the brine B mentioned in step S2 is selected from inorganic sodium, potassium or barium salts with a solubility of more than 10g / 100gH2O at 20℃.

2. The method according to claim 1, characterized in that, The ammonium salt is selected from one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium fluoride, ammonium bifluoride, and ammonium formate.

3. The method according to claim 1, characterized in that, An inert powder is added during the calcination process described in step S3; the inert powder is a solid that does not participate in the reaction and is stable at the calcination temperature described in step S3.

4. The method according to claim 3, characterized in that, The inert powder is a solid product generated from the decomposition of the silicon tetrafluoride precursor after the calcination process described in step S3.

5. The method according to claim 3, characterized in that, In step S3, the mass ratio of the dried silicon tetrafluoride precursor to the inert powder is 1:0.1-100.

6. The method according to claim 3, characterized in that, The roasting temperature in step S3 is 520-800℃, and the time is 0.25-2h.

7. The method according to claim 1, characterized in that, The roasting temperature and time mentioned in step S3 are selected from: roasting at 660-740℃ for 1.8-2.2h, roasting at 600-690℃ for 0.7-0.8h, or roasting at 520-590℃ for 0.9-1.2h.

8. The method according to claim 7, characterized in that, The roasting temperature and time mentioned in step S3 are selected from: roasting at 700℃ for 2 hours, roasting at 650℃ for 0.75 hours, or roasting at 550℃ for 1 hour.

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