Method for deeply removing chloride ion impurities in synthetic silicon dioxide

Abstract

The invention discloses a method for deeply removing chloride ion impurities in synthetic silicon dioxide, which comprises the following steps: carrying out one-time or repeated operations of adding water, carrying out ultrasonic dispersion to form sol and carrying out negative pressure rotary evaporation to obtain gel on SiO2 gel to obtain washed SiO2 gel; drying the washed SiO2 gel under reduced pressure to obtain SiO2 particles; siO2 particles with the particle size of 0.2-0.45 micrometer are taken and calcined at the temperature of 300-600 DEG C for dechlorination. The method has the advantages of being simple in process, easy to operate, low in cost, free of pollution and the like, and corrosion to equipment in the SiO2 drying process is greatly reduced. The minimum value of chlorine content in the synthesized SiO2 obtained by the method can reach 17.05 ppm, and the method can be applied to various fields.

Description

Technical Field

[0001] The invention relates to the field of synthetic silicon dioxide, and in particular to a method for deeply removing chloride ion impurities in synthetic silicon dioxide. Background Art

[0002] Silicon dioxide (SiO2) is a tough, high temperature resistant, corrosion resistant, and chemically stable inorganic compound, which is widely used in glass, optical fiber, semiconductors and other fields. In particular, ultra-high purity SiO2 has become a key basic material in cutting-edge technology fields such as semiconductors, photovoltaics and high-end optics, and has great strategic value. Compared with traditional purified SiO2, SiO2 prepared by chemical synthesis using silicon-containing compounds as raw materials has higher purity and has become the most promising way to meet the future market demand for ultra-high purity SiO2.

[0003] At present, the main method of chemical synthesis is to use chlorosilane as raw material, including gas phase method and sol-gel method, and then further process to obtain SiO2 powder. However, the presence of chlorine makes it inevitable that the product contains chloride ion impurities, and these residual chloride ions may cause equipment corrosion and affect the physical and chemical properties of SiO2, such as phase change point, high temperature viscosity and softening point. In addition, when manufacturing crucibles for semiconductors and photovoltaics, trace chloride ion impurities (usually at the ppm level) may also cause crystallization and bubbling of the crucible, and may even escape during high-temperature use, affecting the final quality of the product. When SiO2 is used for optical quartz glass, in order to improve the transmittance and reduce the refractive index, it is generally required that the chloride ion content in SiO2 is as low as possible.

[0004] At present, washing methods are mostly used to remove chlorine impurities in SiO2. For example, literature [1] uses ammonia solution to wash the precursor and SiO2. However, the chlorine content in the prepared SiO2 is still 20-50ppm (mg / kg), and this method is time-consuming (more than 3 days) and consumes a lot of water (60L of water for 1kg SiO2). In addition, a plate and frame filter press method is often used to remove residual chloride ion impurities in nano-oxides (such as zirconium oxide, cerium oxide, etc.). In literature [2], rare earth oxides prepared by precipitation method are separated from solids and liquids by plate and frame filter press, and then washed in stages to obtain nano-oxides with a chlorine content of less than 20ppm. However, this method requires multiple washing and filtration to achieve efficient removal of chlorine impurities, and the water consumption during the process is huge, resulting in problems such as increased processing costs and cumbersome operations. Similarly, literature [3] first reduces the chlorine content in the slurry by washing with ammonia water, and then significantly reduces the chloride ion content in the powder by filter press washing, calcination and hot acid cleaning, and the final powder chlorine content is less than 50ppm. Although this method reduces the number of filter press washing and water consumption by adding some complex treatment methods, the use of ammonia water and hot acid during the treatment process may introduce trace impurity ion contamination to the product, and the use of acid solution will bring additional treatment costs and potential environmental pollution problems. Therefore, finding a treatment method with simple process, convenient operation, low cost and no pollution is of great production practical significance for achieving efficient removal of chloride ion impurities in SiO2.

[0005] Document [1] Chinese patent application with publication number CN106853970A.

[0006] Document [2] Chinese patent application with publication number CN109319820A.

[0007] Document [3] Chinese patent application with publication number CN112811903A. Summary of the invention

[0008] The present invention provides a method for deep removal of chloride ion impurities in synthetic silicon dioxide, including vacuum distillation washing of SiO2 gel, reduced pressure drying and low-temperature calcination to remove chlorine, etc., which has the advantages of simple process, easy operation, low cost and no pollution, and greatly reduces the corrosion of SiO2 drying process to equipment. The minimum chlorine content in the synthetic SiO2 obtained by the method of the present invention can reach 17.05ppm, which can meet the application in various fields.

[0009] A method for deep removal of chloride ion impurities in synthetic silicon dioxide, comprising:

[0010] The SiO2 gel is subjected to the operation of adding water - ultrasonic dispersion to form a sol - vacuum rotary evaporation to form a gel once or repeatedly (for example, 2 times, 3 times, 4 times, etc., preferably 3 times) to obtain a washed SiO2 gel;

[0011] The washed SiO2 gel is dried under reduced pressure to obtain SiO2 particles;

[0012] SiO2 particles with a particle size of 0.2 to 0.45 microns, preferably 0.35 to 0.45 microns, are calcined at 300 to 600° C., such as 400° C., 500° C., etc., preferably 400° C. to remove chlorine. The preferred particle size is conducive to the deep removal of chloride ion impurities.

[0013] In the process of adding water - ultrasonic dispersion to form sol - negative pressure rotary evaporation to gel, the material maintains a gel network structure. At this time, the washing and evaporation operations are helpful for the removal of chloride ion impurities. Therefore, the number of operations in this process affects the removal effect of chloride ion impurities. It is preferred to perform the operation of adding water - ultrasonic dispersion to form sol - negative pressure rotary evaporation to gel three times, which is conducive to the deep removal of chloride ion impurities.

[0014] The purpose of the present invention is to firstly use a simple vacuum distillation washing method for multiple times in a gel state to quickly reduce the chlorine impurity content in SiO2, thereby reducing the corrosion of volatile hydrochloric acid to equipment in the subsequent drying step. Finally, the removal of chlorine ion impurities in SiO2 is achieved through a low-temperature calcination process. Through this method, the problems of large-scale water consumption and the use of acid and alkali reagents in the existing process are solved, while the operation process is simplified, the processing cost is reduced, and finally the efficient removal of chlorine ion impurities is achieved.

[0015] The method for deep removal of chloride ion impurities in synthetic silicon dioxide, SiO2 gel can be prepared by using chlorosilane as raw material by sol-gel method;

[0016] The chemical expression of the chlorosilane is SiCl x H 4-x , 0 <x≤4。

[0017] Furthermore, the chlorosilane may be a mixture of one or more of monochlorosilane, dichlorosilane, trichlorosilane and silicon tetrachloride.

[0018] The present invention provides an exemplary preparation method of SiO2 gel, using a sol-gel method, specifically comprising: adding chlorosilane (preferably trichlorosilane) to water under stirring, continuing to stir for a period of time after the addition, and then standing for aging to obtain SiO2 gel. The above preparation process can be carried out at room temperature, and the volume ratio of chlorosilane to water can be 1:5.

[0019] In the method for deep removal of chloride ion impurities in synthetic silica, in a single operation, the ratio of the volume of water added to the SiO2 gel to the volume of the SiO2 gel can be 4 to 6:1, such as 4.5:1, 5.5:1, etc.

[0020] In the method for deeply removing chloride ion impurities in synthetic silicon dioxide, the temperature of the negative pressure rotary evaporation can be 60-90°C.

[0021] In the method for deep removal of chloride ion impurities in synthetic silica, the temperature of reduced pressure drying can be 85 to 95° C., such as 90° C., and the time can be 4 to 6 hours, such as 4.5 hours, 5 hours, etc.

[0022] The method for deep removal of chloride ion impurities in synthetic silicon dioxide can achieve a laying density of SiO2 particles of 0.03 to 0.15 g / cm during calcination. 2 , preferably 0.035 to 0.04 g / cm 2 , which is beneficial to the deep removal of chloride ion impurities.

[0023] The method for deeply removing chloride ion impurities in synthetic silicon dioxide can have a calcination time of 60 to 120 minutes, such as 90 minutes.

[0024] In the method for deep removal of chloride ion impurities in synthetic silicon dioxide, the calcination atmosphere can be one or more combinations of nitrogen atmosphere, air atmosphere, and helium atmosphere.

[0025] As a general inventive concept, the present invention also provides the application of the deep removal method in the deep removal of chloride ion impurities in synthetic silicon dioxide.

[0026] The present invention is committed to using a simple vacuum distillation washing method to preliminarily treat SiO2, reduce the corrosion of hydrochloric acid to equipment in the subsequent drying step, and finally remove chloride ion impurities in SiO2 through a low-temperature calcination process. Through the above means, the large amount of water consumption in the washing process is reduced, the use of acid and alkali reagents is avoided, the operation process is simplified, the processing cost is reduced, and the deep removal of chloride ion impurities is finally achieved.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The present invention keeps SiO2 in a uniform sol state during the distillation and washing stage, which is beneficial for cleaning chloride ion impurities attached to the surface of the sol and in the skeleton, and vacuum distillation also promotes the volatilization and removal of chloride ions in the form of HCl. Compared with washing and dechlorinating the dried powder product, this method is easier to remove chloride ion impurities, and solves the problem of high water consumption, saves water resources and reduces production costs.

[0029] 2) The present invention does not add any reagents in the whole process, thus avoiding the trace impurities that may be introduced by additional reagents and the environmental pollution problems and treatment costs caused by waste liquid.

[0030] 3) The present invention achieves the goal of obtaining SiO2 finished products that meet the requirements in a shorter time and at a lower cost by regulating the material laying density and particle size range, calcination temperature, time and atmosphere during the calcination process. The chloride ion content in SiO2 obtained by the method of the present invention can be as low as less than 18ppm, which has a wide range of application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a photo of the macroscopic morphology of SiO2 after drying in Example 1.

[0032] Figure 2 This is the chromatogram of chloride ions in SiO2 after calcination in Example 1.

[0033] Figure 3 This is a photo of the macroscopic morphology of SiO2 after drying in Example 2.

[0034] Figure 4 This is the chromatogram of chloride ions in SiO2 after calcination in Example 2.

[0035] Figure 5 This is the chromatogram of chloride ions in SiO2 after calcination in Example 3.

[0036] Figure 6 This is the chromatogram of chloride ions in SiO2 after calcination in Example 4.

[0037] Figure 7 This is the chromatogram of chloride ions in SiO2 after calcination in Example 5.

[0038] Figure 8 This is the chromatogram of chloride ions in SiO2 after calcination in Example 6.

[0039] Fig. 9 This is the chromatogram of chloride ions in SiO2 after calcination in Example 7.

[0040] Fig.10 This is the chromatogram of chloride ions in SiO2 after calcination in Example 8.

[0041] Fig.11 This is the chromatogram of chloride ions in SiO2 after calcination in Example 9.

[0042] Fig.12 This is the pore distribution diagram of the samples in Example 1 and Example 6. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0044] Unless otherwise specified, in the following examples:

[0045] The dimensions of the quartz crucible are 60 mm long × 30 mm wide × 20 mm high;

[0046] The SiO2 gel was prepared by the following process: 10 mL of trichlorosilane was added dropwise to 50 mL of water under stirring at room temperature, the addition was completed within 6 minutes, stirring was continued for 30 minutes, and then the mixture was allowed to stand and aged for 2 hours to obtain a newly prepared SiO2 gel.

[0047] Embodiment 1:

[0048] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 60 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the above round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0049] The washed wet gel was collected in a beaker and then placed in a vacuum drying oven and dried at 90°C for 4 h to obtain SiO2 particles. Figure 1 The dried SiO2 is shown.

[0050] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 0.7g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 400℃ for 60min in an air atmosphere. Figure 2 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 17.05 ppm.

[0051] Embodiment 2:

[0052] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 50 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, the washed SiO2 gel is obtained.

[0053] The washed wet gel was collected in a beaker and then placed in a vacuum drying oven and dried at 90°C for 4 h to obtain SiO2 particles. Figure 3 The dried SiO2 is shown.

[0054] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 0.7g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 400℃ for 60min in an air atmosphere. Figure 4 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 89.43 ppm.

[0055] Embodiment 3:

[0056] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 45 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the above round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, the rotary evaporator is kept in a negative pressure state with a circulating water vacuum pump. After evaporation to a gel state, add water again to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0057] Dry under reduced pressure to obtain SiO2 particles: collect the washed wet gel into a beaker, then place it in a vacuum drying oven and dry it at 90°C for 4 hours to obtain dried SiO2.

[0058] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 2.1g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 300℃ for 60min in an air atmosphere. Figure 5 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 39.15 ppm.

[0059] Embodiment 4:

[0060] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 50 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0061] Dry under reduced pressure to obtain SiO2 powder: collect the washed wet gel into a beaker, then place it in a vacuum drying oven and dry it at 90°C for 4 hours to obtain dried SiO2.

[0062] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 2.1g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 400℃ for 60min in an air atmosphere. Figure 6 The ion chromatogram shows the chloride ion in SiO2 after calcination. The chloride ion content was calculated based on the peak area, and the result was 33.86 ppm.

[0063] Embodiment 5:

[0064] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 50 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0065] Dry under reduced pressure to obtain SiO2 particles: collect the washed wet gel into a beaker, and then place it in a vacuum drying oven and dry it at 90°C for 4 hours.

[0066] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 0.7g of SiO2 with a particle size range of 0.1-0.2μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 600℃ for 60min in an air atmosphere. Figure 7 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 64.14 ppm.

[0067] Embodiment 6:

[0068] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 40 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0069] Dry under reduced pressure to obtain SiO2 particles: collect the washed wet gel into a beaker, then place it in a vacuum drying oven and dry it at 90°C for 4 hours to obtain dried SiO2.

[0070] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 0.7g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 600℃ for 60min in an air atmosphere. Figure 8 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 18.96 ppm.

[0071] Embodiment 7:

[0072] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 50 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0073] Dry under reduced pressure to obtain SiO2 particles: collect the washed wet gel into a beaker, then place it in a vacuum drying oven and dry it at 90°C for 4 hours to obtain dried SiO2.

[0074] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 2.1g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 400℃ for 120min in an air atmosphere. Fig. 9 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 32.14 ppm.

[0075] Embodiment 8:

[0076] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 40 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0077] Dry under reduced pressure to obtain SiO2 particles: collect the washed wet gel into a beaker, then place it in a vacuum drying oven and dry it at 90°C for 4 hours to obtain dried SiO2.

[0078] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 0.7g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 400℃ for 60min in a He atmosphere. Fig.10 The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 25.99 ppm.

[0079] Embodiment 9:

[0080] Vacuum distillation washing of SiO2 gel: Use a beaker to roughly measure 50 mL of the newly prepared SiO2 gel, then transfer it to a round-bottom flask and add a certain amount of water, with the volume ratio of water to gel being 4.5:1. Then, use ultrasound and vibration to mix the gel-water solution evenly; place the round-bottom flask on a rotary evaporator and heat at 60-90°C to evaporate the water. During this period, use a circulating water vacuum pump to keep the rotary evaporator in a negative pressure state. After evaporation to a gel state, add water back to the initial volume, repeat washing 3 times, and finally obtain the washed SiO2 gel.

[0081] Dry under reduced pressure to obtain SiO2 particles: collect the washed wet gel into a beaker, then place it in a vacuum drying oven and dry it at 90°C for 4 hours to obtain dried SiO2.

[0082] Low-temperature calcination to remove chlorine: Grind the dried SiO2 into different particle sizes, weigh 0.7g of SiO2 with a particle size range of 0.35-0.45μm and evenly spread it in a quartz crucible, place the crucible in a tubular furnace, and calcine at 400℃ for 60min in a N2 atmosphere. Fig.11The ion chromatogram of chloride ions in SiO2 after calcination is shown. The chloride ion content is calculated based on the peak area, and the result is 46.19 ppm.

[0083] Table 1 Summary of treatment conditions and chlorine content of final products in Examples 1-5

[0084] Example 1 2 3 4 5 Washing times 3 1 3 3 3 Material mass / g 0.7 0.7 2.1 2.1 0.7 Particle size range / μm 0.35-0.45 0.35-0.45 0.35-0.45 0.35-0.45 0.1-0.2 Calcination temperature / ℃ 400 400 300 400 600 Calcination time / min 60 60 60 60 60 Calcination atmosphere Air Air Air Air Air Chlorine content / ppm 17.05 89.43 39.15 33.86 64.14

[0085] Table 2 Summary of treatment conditions and final product chlorine content in Examples 6-9

[0086] Example 6 7 8 9 Washing times 3 3 3 3 Material mass / g 0.7 2.1 0.7 0.7 Particle size range / μm 0.35-0.45 0.35-0.45 0.35-0.45 0.35-0.45 Calcination temperature / ℃ 600 400 400 400 Calcination time / min 60 120 60 60 Calcination atmosphere Air Air He <![CDATA[N2]]> Chlorine content / ppm 18.96 32.14 25.99 46.19

[0087] It can be seen from Table 1 and Table 2 that the SiO2 product prepared by Example 1 of the present invention has the lowest chloride ion impurity content (17.05ppm). Combining the results of Example 1 and Example 2, it can be seen that vacuum washing significantly affects the removal effect of chloride ion impurities. This is because SiO2 is in a sol state during the washing process. Under heating and vacuum conditions, the chloride ions in the sol are more likely to volatilize in the form of HCl, and multiple washings reduce the agglomeration of SiO2. At the same time, combined with Figure 1 and Figure 3 The results show that the number of washing times will significantly affect the particle size structure of the dried sample. Specifically, compared with the dried sample of Example 2, the dried SiO2 obtained in Example 1 is a small-sized and loose particle, which will be more conducive to removing chloride ion impurities during the calcination process. Comparing the chlorine content results of the final samples of Example 4 and Example 7, it can be found that extending the calcination temperature can only slightly improve the chloride ion removal effect. From the perspective of energy consumption and processing efficiency, choosing a calcination time of 60 minutes is the most reasonable and efficient.

[0088] By comparing the results of Example 1 and Example 4, it can be seen that the amount of material added during calcination has a significant effect on the chlorine content of the final product. Since the crucible size is consistent in each embodiment, this means that the material laying density will inhibit the escape of HCl. Therefore, in order to prepare a SiO2 product with a low chlorine content, the material laying density must be precisely controlled during the calcination process. By comparing the results of Example 1, Example 8 and Example 9, it is found that the atmosphere during the calcination process will also affect the chloride ion content of the final product. Ultimately, considering both cost and effect, using air as the reaction atmosphere is the best choice. In addition, by comparing the results of Example 5 and Example 6, it is found that the particle size range has a certain effect on the calcination dechlorination effect. When the particle size range is very small (<0.2μm), the residual chlorine content in the product increases significantly. This is because the small-particle SiO2 powder is more densely stacked, which is not conducive to the volatilization and escape of HCl. At the same time, according to the comparison results of Example 1 and Example 6 and Example 3 and Example 4, it can be seen that the increase and decrease of temperature will have a certain effect on the dechlorination effect. Among them, the volatilization of HCl will be weakened at a lower temperature, and the increase in temperature will affect the pore distribution on the surface of the material (such as Fig.12 As shown), the small pores account for a larger proportion, which is not conducive to the volatilization of HCl inside the particles, thereby reducing the removal effect of chloride ions. The preferred calcination temperature is 400°C.

[0089] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for deep removal of chloride ion impurities in synthetic silicon dioxide, characterized in that: include: The SiO2 gel is subjected to the operation of adding water once or repeatedly dispersing by ultrasound to form a sol and then rotary evaporating under negative pressure to form a gel, thereby obtaining a washed SiO2 gel; The washed SiO2 gel is dried under reduced pressure to obtain SiO2 particles; SiO2 particles with a particle size of 0.2 to 0.45 microns, preferably 0.35 to 0.45 microns, are calcined at 300 to 600°C, preferably 400°C to remove chlorine.

2. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: SiO2 gel was prepared by sol-gel method using chlorosilane as raw material; The chemical expression of the chlorosilane is SiCl x H 4-x , 0 <x≤4。 3. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: In a single operation, the ratio of the volume of water added to the SiO2 gel to the volume of the SiO2 gel is 4 to 6:1, and further 4.5:

1.

4. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: The temperature of the negative pressure rotary evaporation is 60-90°C.

5. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: The temperature for the reduced pressure drying is 85 to 95° C., preferably 90° C., and the time is 4 to 6 hours.

6. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: The laying density of SiO2 particles during calcination is 0.03-0.15 g / cm 2 , preferably 0.035 to 0.04 g / cm 2 .

7. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: The calcination time is 60 to 120 minutes.

8. The method for deep removal of chloride ion impurities in synthetic silicon dioxide according to claim 1, characterized in that: The calcination atmosphere is a nitrogen atmosphere, an air atmosphere, a helium atmosphere or a combination of one or more of the following.

9. Use of the deep removal method according to any one of claims 1 to 8 in deep removal of chloride ion impurities in synthetic silicon dioxide.

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