Silicon tetrafluoride resource utilization method

Abstract

The invention discloses a silicon tetrafluoride resource utilization method, and relates to the field of silicon tetrafluoride resource utilization. The method comprises the following steps: S1, introducing silicon tetrafluoride into an ammonium bifluoride solution, and filtering to obtain ammonium fluosilicate precipitate and first filtrate; s2, adding a desilicication precipitator into the first filtrate, and filtering to obtain fluosilicate precipitate and second filtrate; s3, mixing the second filtrate with concentrated sulfuric acid, heating, evaporating and analyzing, absorbing the obtained gas with water to obtain hydrofluoric acid, and crystallizing and separating out the residual liquid to obtain ammonium salt. The whole process route is mild in reaction condition and high in safety coefficient; high temperature and external electric field are not needed, and energy consumption is low; no secondary waste is generated, and the comprehensive utilization degree of resources is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silicon tetrafluoride resource utilization, in particular to a silicon tetrafluoride resource utilization method. BACKGROUND

[0002] Silicon tetrafluoride, also known as silicon fluoride, has a molecular formula of SiF4, is a colorless, toxic, and irritating odor gas, and is produced by combining fluorine and silicon existing in phosphate ore or fluorite in the production process of industrial utilization.

[0003] At present, the resource utilization of silicon tetrafluoride includes converting it into fluorosilicic acid and then using fluorosilicic acid as a raw material to prepare silicon dioxide and hydrogen fluoride, or directly hydrolyzing silicon tetrafluoride under the condition of an additional electric field or high temperature to prepare silicon dioxide and hydrogen fluoride. Among them, converting silicon tetrafluoride into fluorosilicic acid and using fluorosilicic acid as a raw material for resource utilization has high energy consumption, large water consumption, produces a large amount of by-product fluorine-containing waste sulfuric acid and fluorine-containing silicon residue which is difficult to handle, and low industrial economic benefits; and the hydrolysis method still has the problems of high energy consumption and difficult handling of fluorine-containing silicon residue, which needs an additional electric field or a high temperature of 200-800℃. SUMMARY

[0004] In view of the above-mentioned deficiencies of the related art, the present application provides a silicon tetrafluoride resource utilization method, which uses silicon tetrafluoride and ammonium fluoride as the starting point of the reaction, and can directly prepare high-value-added ammonium fluorosilicate, lithium fluorosilicate, ammonium sulfate, and hydrogen fluoride through processes such as precipitation and evaporation. The reaction conditions of the entire process route are mild, which improves the safety factor; no high temperature or external electric field is needed, which reduces energy consumption; and no secondary waste is produced, which improves the degree of comprehensive utilization of resources.

[0005] The silicon tetrafluoride resource utilization method provided by the present application adopts the following technical scheme: A silicon tetrafluoride resource utilization method, comprising the following steps: S1: passing silicon tetrafluoride into an ammonium bifluoride solution to obtain ammonium fluorosilicate precipitate and a first filtrate by filtration; S2: adding a desiliconization precipitant to the first filtrate to obtain a fluorosilicate precipitate and a second filtrate by filtration; S3: mixing the second filtrate with concentrated sulfuric acid and heating and evaporating to resolve, absorbing the obtained gas with water to obtain hydrofluoric acid, and crystallizing the remaining liquid to obtain an ammonium salt.

[0006] Preferably, the concentration of the ammonium bifluoride solution is 33wt.%-38wt.%.

[0007] Preferably, the concentration of the ammonium bifluoride solution is 35wt.%.

[0008] Preferably, the desilication precipitant includes sodium sulfate or potassium sulfate.

[0009] Preferably, the precipitant is potassium sulfate.

[0010] Preferably, the fluorosilicate precipitate comprises sodium fluorosilicate and potassium fluorosilicate.

[0011] Preferably, the fluorosilicate precipitate is potassium fluorosilicate.

[0012] Preferably, the ammonium salt is ammonium sulfate.

[0013] Preferably, the weight ratio of the silicon tetrafluoride to the ammonium bifluoride solution is 1-1.1:3.

[0014] Preferably, the weight ratio of the first filtrate to the desilication precipitant is 5-10:1.

[0015] Preferably, in step S3, the concentration of sulfuric acid in the solution after mixing the second filtrate with concentrated sulfuric acid is 70wt%-80wt%.

[0016] Preferably, the heating and evaporation in step S3 includes controlling the temperature at 110-135°C under negative pressure.

[0017] Preferably, step S3 is followed by step S4: taking ammonium fluorosilicate precipitate and mixing it with ammonia water, filtering to obtain silica precipitate and a third filtrate; S5: The third filtrate is evaporated to remove ammonia, and ammonium bifluoride is obtained and reused in step S1. Ammonia gas is used to prepare ammonia water and reused in step S4.

[0018] Preferably, the hydrofluoric acid obtained in step S3 has an ammonia nitrogen content of less than 10 ppm and a fluorosilicic acid content of less than 1%.

[0019] In summary, the present invention has the following beneficial technical effects: This invention utilizes ammonium bifluoride at room temperature and pressure, without the need for an external electric field, to directly convert low-value-added silicon tetrafluoride into high-value-added fluorosilicates and hydrogen fluoride. The ammonium fluorosilicate in the fluorosilicate is directly separated by filtration. The remaining fluorosilicate ions in the solution are converted into fluorosilicate precipitates with lower solubility than ammonium fluorosilicate by a desilication precipitant and then separated by filtration. This secondary precipitation improves the utilization rate of fluorosilicate ions. Simultaneously, the addition of the desilication precipitant in the second filtrate disrupts the azeotropic point of hydrogen fluoride and water through a salting-out effect. Combined with the removal of impurities by concentrated sulfuric acid, the purity of the hydrogen fluoride product is improved. Furthermore, the entire process generates no secondary waste, demonstrating high resource utilization and being both economical and environmentally friendly. Attached Figure Description

[0020] Figure 1 This is the process flow diagram of Example 1. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the following embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the methods used are conventional methods known in the art, and the consumables and reagents used are commercially available. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be applied to the present invention.

[0022] Example 1 Embodiment 1 of the present invention provides a method for the resource utilization of silicon tetrafluoride, referring to... Figure 1 The steps are as follows: S1: 200g of silicon tetrafluoride was passed into 600g of ammonium bifluoride solution (35wt.%) at 20℃. After the reaction was complete, the mixture was filtered to obtain 286g of ammonium fluorosilicate precipitate (water content 12.5%) and 514g of the first filtrate. S2: Add 69g of potassium sulfate as a precipitant to the first filtrate to carry out the silica precipitation reaction. After the reaction is complete, filter to obtain 90g of potassium fluorosilicate precipitate (water content 10.0%) and 490g of the second filtrate. S3: Add concentrated sulfuric acid (98wt%) to the second filtrate until the sulfuric acid concentration is 75wt%. Heat to 110-135℃ under a negative pressure of -0.08KPa to -0.06KPa for evaporation and desorption. The resulting gas is absorbed by water to obtain 178g of 40% hydrofluoric acid. The remaining liquid is cooled, crystallized, and filtered to obtain 49g of ammonium sulfate. The filtrate is reused in concentrated sulfuric acid. S4: Mix ammonium fluorosilicate precipitate with ammonia water to carry out ammonolysis reaction, and filter to obtain silica precipitate and third filtrate; S5: The third filtrate is evaporated to remove ammonia, and ammonium bifluoride is obtained and reused in step S1. Ammonia gas is used to prepare ammonia water and reused in step S4.

[0023] Example 2 Embodiment 2 of the present invention provides a method for the resource utilization of silicon tetrafluoride, the steps of which are as follows: S1: 210g of silicon tetrafluoride was passed into 600g of ammonium bifluoride solution (35wt.%) at 20℃. After the reaction was complete, the mixture was filtered to obtain 287g of ammonium fluorosilicate precipitate (water content 12.3%) and 523g of the first filtrate. S2: Add 69g of potassium sulfate as a precipitant to the first filtrate to carry out the silica precipitation reaction. After the reaction is complete, filter to obtain 91g of potassium fluorosilicate precipitate (water content 9.9%) and 500g of the second filtrate. S3: Add concentrated sulfuric acid (98wt%) to the second filtrate until the sulfuric acid concentration is 75wt%. Heat to 110-135℃ under a negative pressure of -0.08KPa to -0.06KPa for evaporation and desorption. The resulting gas is absorbed by water to obtain 176g of hydrofluoric acid with a concentration of 40.1%. The remaining liquid is cooled, crystallized, and filtered to obtain 49g of ammonium sulfate. The filtrate is reused in concentrated sulfuric acid. S4: Mix ammonium fluorosilicate precipitate with ammonia water to carry out ammonolysis reaction, and filter to obtain silica precipitate and third filtrate; S5: The third filtrate is evaporated to remove ammonia, and ammonium bifluoride is obtained and reused in step S1. Ammonia gas is used to prepare ammonia water and reused in step S4.

[0024] Example 3 Embodiment 3 of the present invention provides a method for the resource utilization of silicon tetrafluoride, the steps of which are as follows: S1: 220g of silicon tetrafluoride was passed into 600g of ammonium bifluoride solution (35wt.%) at 20℃. After the reaction was complete, the mixture was filtered to obtain 290g of ammonium fluorosilicate precipitate (water content 12.1%) and 528g of the first filtrate. S2: Add 69g of potassium sulfate as a precipitant to the first filtrate to carry out the silica precipitation reaction. After the reaction is complete, filter to obtain 92g of potassium fluorosilicate precipitate (water content 10.2%) and 503g of the second filtrate. S3: Add concentrated sulfuric acid (98wt%) to the second filtrate until the sulfuric acid concentration is 75wt%. Heat to 110-135℃ under a negative pressure of -0.08KPa to -0.06KPa for evaporation and desorption. The resulting gas is absorbed by water to obtain 182g of hydrofluoric acid with a concentration of 40.5%. The remaining liquid is cooled, crystallized, and filtered to obtain 49g of ammonium sulfate. The filtrate is reused in concentrated sulfuric acid. S4: Mix ammonium fluorosilicate precipitate with ammonia water to carry out ammonolysis reaction, and filter to obtain silica precipitate and third filtrate; S5: The third filtrate is evaporated to remove ammonia, and ammonium bifluoride is obtained and reused in step S1. Ammonia gas is used to prepare ammonia water and reused in step S4.

[0025] Comparative Example 1 Comparative Example 1 provides a method for the resource utilization of silicon tetrafluoride, the steps of which are as follows: S1: 200g of silicon tetrafluoride was passed into 600g of ammonium hydrogen fluoride solution (35wt.%) at 20℃. After the reaction was complete, the mixture was filtered to obtain 287g of ammonium fluorosilicate precipitate (water content 12.4%) and 513g of the first filtrate. S2: Add concentrated sulfuric acid (98wt%) to the first filtrate until the sulfuric acid concentration is 75wt%. Heat to 110-135℃ under a negative pressure of -0.08KPa to -0.06KPa for evaporation and desorption. After absorbing the gas with water, 180g of a mixed solution of hydrogen fluoride and fluorosilicic acid is obtained, of which 72g is pure hydrogen fluoride and 13.5g is fluorosilicic acid. S3: Mix ammonium fluorosilicate precipitate with ammonia water to carry out ammonolysis reaction, and filter to obtain silica precipitate and third filtrate; S4: The third filtrate is evaporated to remove ammonia, and ammonium bifluoride is recycled to step S1. Ammonia gas is used to prepare ammonia water, which is then recycled to step S3.

[0026] Testing and Inspection (1) The silicon utilization rate in Examples 1-3 and Comparative Example 1 was calculated based on the total amount of ammonium fluorosilicate and potassium fluorosilicate products. The results are shown in Table 1. The fluorine utilization rate in Examples 1-3 and Comparative Example 1 was calculated based on the total amount of ammonium fluorosilicate, potassium fluorosilicate and hydrogen fluoride. The results are shown in Table 1.

[0027] Table 1:

[0028] (2) Take water samples of the hydrofluoric acid obtained in step S3 of Example 1 and the mixed solution of hydrogen fluoride and fluorosilicic acid obtained in step S2 of Comparative Example 1, and test the ammonia nitrogen content and fluorosilicic acid content in the water samples respectively. The results are shown in Table 2.

[0029] Table 2:

[0030] Results Analysis The present invention will be described in detail below with reference to the experimental results provided in Tables 1-2.

[0031] Referring to Tables 1 and 2, it can be seen that the silicon and fluorine utilization rates of Examples 1-3 are much higher than those of Comparative Example 1. Furthermore, the ammonia nitrogen in the water sample originates from ammonia in the evaporated gas, and the fluorosilicic acid originates from silicon tetrafluoride in the evaporated gas. This indicates that the content of ammonia and silicon tetrafluoride in the evaporated gas in step S3 of Example 1 is much lower than that in step S2 of Comparative Example 1. The analysis suggests that, firstly, the use of potassium sulfate as a precipitant dissolves fluorosilicate ions in the form of potassium fluorosilicate, which has a lower solubility than ammonium fluorosilicate, thus improving the utilization rate of fluorine and silicon. Simultaneously, the reduction of fluorosilicate ions in the filtrate also lowers the silicon tetrafluoride impurity content in the subsequent evaporated gas. Secondly, the sulfate ions derived from potassium sulfate and sulfuric acid in the second filtrate not only disrupt the azeotropic point of hydrogen fluoride and water, reducing the water content in the evaporated gas, but also combine with ammonium ions to reduce the ammonia impurity content in the evaporated gas. Under these combined effects, not only is the utilization rate of silicon and fluorine improved, but the purity of hydrogen fluoride in the evaporated gas is also increased, reducing purification costs. In Examples 2 and 3, the silicon and fluorine utilization rates continuously decrease compared to Example 1. This is attributed to the limited amount of ammonium fluoride in the ammonium bifluoride solution, while the amount of silicon tetrafluoride is excessive.

[0032] In this invention, silicon tetrafluoride and ammonium bifluoride are used as the starting point for the reaction. Compared to the silicon tetrafluoride hydrolysis process, this reduces the amount of water used in the system and the amount of concentrated sulfuric acid used in step 3. Furthermore, the concentrated sulfuric acid can be reused after filtering out ammonium sulfate, reducing costs. Through precipitation and evaporation processes, high-value-added products such as ammonium fluorosilicate, lithium fluorosilicate, ammonium sulfate, and hydrogen fluoride can be directly prepared. If the ammonium fluorosilicate is not used as a product, it can be further reacted with ammonia to produce silicon dioxide and ammonium fluoride solution. The ammonium bifluoride and ammonia obtained from the evaporation and deammoniation of the ammonium fluoride solution can be recycled back to the aforementioned steps, fully meeting the ammonium bifluoride consumption at the reaction starting point, significantly reducing raw material purchase costs. Excess ammonium bifluoride can also be sold as a product, acting as a catalyst. The entire process route features mild reaction conditions and a high safety factor; it requires no high temperature or external electric field, resulting in low energy consumption; and it generates no secondary waste, demonstrating a high degree of resource utilization.

[0033] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of the present invention.

Claims

1. A method for the resource utilization of silicon tetrafluoride, characterized in that: Includes the following steps: S1: Silicon tetrafluoride is passed into an ammonium bifluoride solution and filtered to obtain ammonium fluorosilicate precipitate and the first filtrate; S2: Add a desilication precipitant to the first filtrate, filter to obtain fluorosilicate precipitate and second filtrate; S3: Take the second filtrate and mix it with concentrated sulfuric acid, then heat and evaporate it to obtain hydrofluoric acid. The remaining liquid is crystallized to obtain ammonium salt.

2. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The concentration of the ammonium bifluoride solution is 33wt.%-38wt.%.

3. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The desilication precipitant includes sodium sulfate or potassium sulfate.

4. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The fluorosilicate precipitate includes sodium fluorosilicate or potassium fluorosilicate.

5. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The weight ratio of the silicon tetrafluoride to the ammonium bifluoride solution is 1-1.1:

3.

6. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The weight ratio of the first filtrate to the desilication precipitant is 5-10:

1.

7. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: In step S3, the concentration of sulfuric acid in the solution after mixing the second filtrate with concentrated sulfuric acid is 70wt%-80wt%.

8. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The heating and evaporation in step S3 includes controlling the temperature at 110-135℃ under negative pressure.

9. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: After step S3, step S4 is also included: taking ammonium fluorosilicate precipitate and mixing it with ammonia water, filtering to obtain silica precipitate and third filtrate; S5: The third filtrate is evaporated to remove ammonia, and ammonium bifluoride is obtained and reused in step S1. Ammonia gas is used to prepare ammonia water and reused in step S4.

10. The method for resource utilization of silicon tetrafluoride according to claim 1, characterized in that: The hydrofluoric acid obtained in step S3 has an ammonia nitrogen content of less than 10 ppm and a fluorosilicic acid content of less than 1%.

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