Method for deep removal of chloride impurities in synthetic silica

Abstract

The application discloses a method for deeply removing chloride ion impurities in synthetic silicon dioxide, which comprises the following steps: adding water to SiO2 gel and performing ultrasonic dispersion to form sol, and then performing negative pressure rotary evaporation to the gel to obtain washed SiO2 gel; drying the washed SiO2 gel under reduced pressure to obtain SiO2 particles; and calcining the SiO2 particles with a particle size of 0.2-0.45 microns at 300-600 DEG C to remove chlorine. The application has the advantages of simple process, easy operation, low cost, no pollution and the like, and greatly reduces the corrosion of the SiO2 drying process to the equipment. The minimum content of chlorine in the synthetic SiO2 obtained by the method can reach 17.05 ppm, and meets the application in various fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of synthetic silica, in particular to a method for deep removal of chloride ion impurities in synthetic silica. BACKGROUND

[0002] Silica (SiO2) is a tough, high-temperature resistant, corrosion-resistant and chemically stable inorganic compound, widely used in glass, optical fiber and semiconductor fields. Especially ultra-high purity SiO2, has become a key basic material in the fields of semiconductor, photovoltaic and high-end optics, etc., and has great strategic value. Compared with traditional purified SiO2, SiO2 prepared by chemical synthesis method with silicon-containing compounds as raw materials has higher purity, and becomes the most promising way to meet the future market demand for ultra-high purity SiO2.

[0003] Currently, the main way of chemical synthesis is to use chlorosilane as raw material, including gas phase method and sol-gel method, etc., and then to obtain SiO2 powder through further processing. However, the presence of chlorine makes it inevitable to contain chloride ion impurities in the product, and these residual chloride ions may cause equipment corrosion, and also affect the physical and chemical properties of SiO2, such as phase transition point, high temperature viscosity and softening point, etc. In addition, when manufacturing crucibles for semiconductors and photovoltaics, trace amounts of chloride ion impurities (usually in ppm level) may also cause crystallization and bubble phenomenon of the crucible, and even may 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 light transmittance and reduce the refractive index, it is generally required that the lower the content of chloride ions in SiO2, the better.

[0004] Currently, the method of washing is mostly used to remove chlorine impurities in SiO2, such as the method of washing the precursor and SiO2 with ammonia solution in document 【1】. However, the chlorine content in the prepared SiO2 is still 20-50 ppm (mg / kg), and this method takes a long time (more than 3 days) and consumes a large amount of water (60 L of water is used for 1 kg of SiO2). In addition, a plate and frame filter is often used to remove residual chlorine ion impurities in nano-oxides (such as zirconia, ceria, etc.). In document 【2】, after the plate and frame filter is used for solid-liquid separation of rare earth oxides prepared by the precipitation method, the nano-oxides are washed in sections, and the chlorine content of the nano-oxides is less than 20 ppm. However, this method needs multiple washing and filtering to achieve efficient removal of chlorine impurities, which consumes a large amount of water during the process, causing problems such as high processing cost and complicated operation. Similarly, in document 【3】, the slurry is first washed with ammonia to reduce the chlorine content, and then washed by pressure filtration, calcination and hot acid cleaning to further significantly reduce the chlorine ion content in the powder, and finally the chlorine content in the powder is less than 50 ppm. Although this method reduces the number of pressure filtration washing and the amount of water consumption by adding some complex treatment methods, the use of ammonia and hot acid in the treatment process may introduce trace amounts of impurity ions into the product, and the use of acid will bring additional processing costs and potential environmental pollution problems. Therefore, it is of great practical significance to find a simple, convenient, low-cost and pollution-free treatment method for efficient removal of chlorine ion impurities in SiO2.

[0005] Document 【1】 is Chinese patent application CN106853970A.

[0006] Document 【2】 is Chinese patent application CN109319820A.

[0007] Document 【3】 is Chinese patent application CN112811903A. SUMMARY

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

[0009] A method for deep removal of chlorine ion impurities in synthetic silica, comprising:

[0010] The SiO2 gel is subjected to one or repeated (for example 2 times, 3 times, 4 times, etc., preferably 3 times) water-adding-ultrasonic dispersion to form a sol, and then subjected to negative pressure rotary evaporation to form a gel, to obtain a washed SiO2 gel;

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

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

[0013] During the process of water-adding-ultrasonic dispersion to form a sol and then subjected to negative pressure rotary evaporation to form a gel, the material maintains a gel network structure, and at this time, the washing and evaporation operations are helpful for the removal of chlorine ion impurities, and thus the number of operations affects the removal effect of chlorine ion impurities. Preferably, the SiO2 gel is subjected to 3 times of water-adding-ultrasonic dispersion to form a sol and then subjected to negative pressure rotary evaporation to form a gel, which is conducive to the deep removal of chlorine ion impurities.

[0014] The purpose of the present application is to quickly reduce the chlorine impurity content in SiO2 in a gel state by using a simple multiple vacuum distillation washing method, to reduce 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 water consumption and the use of acid and alkali reagents in the existing process are solved, 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 chlorine ion impurities in synthetic silicon dioxide, the SiO2 gel can be prepared by using chlorosilane as raw material by sol-gel method;

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

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

[0018] The present application gives an exemplary preparation method of SiO2 gel, which adopts sol-gel method, specifically comprising: under stirring, chlorosilane (preferably trichlorosilane) is added to water, after the addition, stirring is continued for a period of time, and then aging is carried out 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] The ratio of the volume of water added to the SiO2 gel to the volume of SiO2 gel in a single operation can be 4-6:1, for example 4.5:1, 5.5:1, etc.

[0020] The temperature of the negative pressure rotary evaporation in the method for deep removal of chloride ion impurities in synthetic silicon dioxide can be 60-90 DEG C.

[0021] The temperature of the reduced pressure drying in the method for deep removal of chloride ion impurities in synthetic silicon dioxide can be 85-95 DEG C, for example 90 DEG C, etc., and the time can be 4-6 hours, for example 4.5 hours, 5 hours, etc.

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

[0023] The calcination time in the method for deep removal of chloride ion impurities in synthetic silicon dioxide can be 60-120 min, for example 90 min, etc.

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

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

[0026] The application is dedicated to preliminary treatment of SiO2 using a simple vacuum distillation washing method, which reduces corrosion of equipment by hydrochloric acid in a subsequent drying step, and finally removes chloride ion impurities in SiO2 through a low-temperature calcination process. Through the foregoing means, the application reduces the large consumption of water in the washing process, avoids the use of acid and alkali reagents, simplifies the operation process, reduces the processing cost, and ultimately achieves deep removal of chloride ion impurities.

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

[0028] 1) The application keeps SiO2 in a uniform sol state during the distillation washing stage, which is conducive to cleaning chloride ion impurities attached to the surface of the sol and in the skeleton, and the vacuum distillation also promotes removal of chloride ions in the form of HCl. Compared with washing and removing chlorine from a dried powder product, the method is more effective in removing chloride ion impurities, and solves the problem of large water consumption, saving water resources and reducing production costs.

[0029] 2) The present application does not add any reagent in the whole process, avoiding trace impurities possibly introduced by additional reagents and environmental pollution problems and processing costs brought by waste liquid.

[0030] 3) The present application realizes the SiO2 product meeting 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 in the calcination process. The chlorine ion content in the SiO2 obtained by the method of the present application can be as low as less than 18 ppm, which has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The macroscopic morphology photo of the dried SiO2 of Example 1.

[0032] Figure 2 The chlorine ion chromatogram in the calcined SiO2 of Example 1.

[0033] Figure 3 The macroscopic morphology photo of the dried SiO2 of Example 2.

[0034] Figure 4 The chlorine ion chromatogram in the calcined SiO2 of Example 2.

[0035] Figure 5 The chlorine ion chromatogram in the calcined SiO2 of Example 3.

[0036] Figure 6 The chlorine ion chromatogram in the calcined SiO2 of Example 4.

[0037] Figure 7 The chlorine ion chromatogram in the calcined SiO2 of Example 5.

[0038] Figure 8 The chlorine ion chromatogram in the calcined SiO2 of Example 6.

[0039] Figure 9 The chlorine ion chromatogram in the calcined SiO2 of Example 7.

[0040] Figure 10 The chlorine ion chromatogram in the calcined SiO2 of Example 8.

[0041] Figure 11 The chlorine ion chromatogram in the calcined SiO2 of Example 9.

[0042] Figure 12 The pore distribution graph of the samples of Example 1 and Example 6. DETAILED DESCRIPTION

[0043] The application will be further described in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application. The operation methods in the following examples without specific conditions are usually according to the conventional conditions or the conditions suggested by the manufacturers.

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

[0045] The size of the quartz crucible is 60 mm in length, 30 mm in width and 20 mm in height.

[0046] The SiO2 gel is prepared by the following process: 10 mL of trichlorosilane is added dropwise into 50 mL of water under stirring at room temperature, the dropwise addition is completed in 6 min, the stirring is continued for 30 min, and then the gel is aged for 2 hours to obtain a freshly prepared SiO2 gel.

[0047] Example 1:

[0048] Vacuum distillation washing of the SiO2 gel: 60 mL of the freshly prepared SiO2 gel is roughly measured with a beaker, then transferred into a round-bottom flask and a certain amount of water is added, the volume ratio of water to gel is 4.5:1, then the gel aqueous solution is uniformly mixed by means of ultrasonic and shaking; the above-mentioned round-bottom flask is placed on a rotary evaporator, water is evaporated at 60-90°C, and the rotary evaporator is kept in a negative pressure state by a circulating water vacuum pump during the evaporation, after the gel is evaporated, the initial volume is added again, and the washing is repeated for 3 times, finally the washed SiO2 gel is obtained.

[0049] Reduced pressure drying to obtain SiO2 particles: the above-mentioned washed wet gel is collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4 h to obtain the dried SiO2 as shown in Figure 1 .

[0050] Low-temperature calcination to remove chlorine: the dried SiO2 is ground into different particle sizes, 0.7 g of SiO2 with a particle size range of 0.35-0.45 μm is uniformly laid in a quartz crucible, the crucible is placed in a tube furnace, and calcined at 400°C for 60 min in an air atmosphere. Figure 2 The ion chromatogram of the chlorine ion in the calcined SiO2 is shown, and the chlorine ion content is calculated according to the peak area, and the result is 17.05 ppm.

[0051] Example 2:

[0052] Vacuum distillation washing of SiO2 gel: 50 mL of freshly prepared SiO2 gel was roughly measured with a beaker, then transferred to a round-bottom flask and a certain amount of water was added, the volume ratio of water to gel was 4.5:1, then the gel aqueous solution was mixed uniformly by means of ultrasonic and shaking; the above-mentioned round-bottom flask was placed on a rotary evaporator, and water was evaporated at 60-90°C, during which the rotary evaporator was kept in a negative pressure state by a circulating water vacuum pump, and after evaporation to the gel state, the washed SiO2 gel was obtained.

[0053] Vacuum drying to obtain SiO2 particles: the above-mentioned washed wet gel was collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4h, and the dried SiO2 was obtained as shown in Figure 3 .

[0054] Low-temperature calcination to remove chlorine: the dried SiO2 was ground into different particle sizes, 0.7 g of SiO2 with a particle size range of 0.35-0.45 μm was uniformly laid in a quartz crucible, the crucible was placed in a tube furnace, and calcined at 400°C for 60 min in air atmosphere. Figure 4 The ion chromatogram of chlorine ions in the calcined SiO2 is shown, and the chlorine ion content is calculated according to the peak area, the result is 89.43 ppm.

[0055] Example 3:

[0056] Vacuum distillation washing of SiO2 gel: 45 mL of freshly prepared SiO2 gel was roughly measured with a beaker, then transferred to a round-bottom flask and a certain amount of water was added, the volume ratio of water to gel was 4.5:1, then the gel aqueous solution was mixed uniformly by means of ultrasonic and shaking; the above-mentioned round-bottom flask was placed on a rotary evaporator, and water was evaporated at 60-90°C, during which the rotary evaporator was kept in a negative pressure state by a circulating water vacuum pump, and after evaporation to the gel state, the initial volume was added again, and the washing was repeated for 3 times, and finally the washed SiO2 gel was obtained.

[0057] Vacuum drying to obtain SiO2 particles: the above-mentioned washed wet gel was collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4h, and the dried SiO2 was obtained.

[0058] Low-temperature calcination to remove chlorine: the dried SiO2 was ground into different particle sizes, 2.1 g of SiO2 with a particle size range of 0.35-0.45 μm was uniformly laid in a quartz crucible, the crucible was placed in a tube furnace, and calcined at 300°C for 60 min in air atmosphere. Figure 5 The ion chromatogram of chlorine ions in the calcined SiO2 is shown, and the chlorine ion content is calculated according to the peak area, the result is 39.15 ppm.

[0059] Example 4:

[0060] Vacuum distillation washing of SiO2 gel: 50 mL of freshly prepared SiO2 gel was roughly measured with a beaker, then transferred to a round-bottom flask and a certain amount of water was added, the volume ratio of water to gel was 4.5:1, then the gel aqueous solution was mixed uniformly by means of ultrasonic and shaking; the above-mentioned round-bottom flask was placed on a rotary evaporator, water was evaporated at 60-90°C, during which the rotary evaporator was kept in a negative pressure state by a circulating water vacuum pump, after evaporation to the gel state, the initial volume was added again, and the washing was repeated for 3 times, finally the washed SiO2 gel was obtained.

[0061] Vacuum drying to obtain SiO2 powder: the above-mentioned washed wet gel was collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4h, and the dried SiO2 was obtained.

[0062] Low-temperature calcination to remove chlorine: the dried SiO2 was ground into different particle sizes, 2.1 g of SiO2 with a particle size range of 0.35-0.45 μm was uniformly laid in a quartz crucible, the crucible was placed in a tube furnace, and calcined at 400°C for 60 min in air atmosphere. Figure 6 The ion chromatogram of chlorine ions in the calcined SiO2 was displayed, and the chlorine ion content was calculated according to the peak area, the result was 33.86 ppm.

[0063] Example 5:

[0064] Vacuum distillation washing of SiO2 gel: 50 mL of freshly prepared SiO2 gel was roughly measured with a beaker, then transferred to a round-bottom flask and a certain amount of water was added, the volume ratio of water to gel was 4.5:1, then the gel aqueous solution was mixed uniformly by means of ultrasonic and shaking; the above-mentioned round-bottom flask was placed on a rotary evaporator, water was evaporated at 60-90°C, during which the rotary evaporator was kept in a negative pressure state by a circulating water vacuum pump, after evaporation to the gel state, the initial volume was added again, and the washing was repeated for 3 times, finally the washed SiO2 gel was obtained.

[0065] Vacuum drying to obtain SiO2 powder: the above-mentioned washed wet gel was collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4h, and the dried SiO2 was obtained.

[0066] Low-temperature calcination to remove chlorine: the dried SiO2 was ground into different particle sizes, 2.1 g of SiO2 with a particle size range of 0.35-0.45 μm was uniformly laid in a quartz crucible, the crucible was placed in a tube furnace, and calcined at 400°C for 60 min in air atmosphere. Figure 7 The ion chromatogram of chlorine ions in the calcined SiO2 was displayed, and the chlorine ion content was calculated according to the peak area, the result was 33.86 ppm.

[0067] Example 6:

[0068] Vacuum distillation washing of SiO2 gel: The freshly prepared SiO2 gel was roughly measured with a beaker, 40 mL, then transferred to a round-bottom flask and added with a certain amount of water, the volume ratio of water to gel was 4.5:1, then the gel aqueous solution was mixed uniformly by means of ultrasonic and shaking; the above-mentioned round-bottom flask was placed on a rotary evaporator, heated to evaporate water at 60-90°C, during which the rotary evaporator was kept in a negative pressure state by a circulating water vacuum pump, after evaporated to the gel state, the initial volume was added with water again, repeated washing for 3 times, finally the washed SiO2 gel was obtained.

[0069] Vacuum drying to obtain SiO2 particles: the above-mentioned washed wet gel was collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4h, to obtain dried SiO2.

[0070] Low-temperature calcination to remove chlorine: the dried SiO2 was ground into different particle sizes, 0.7g of SiO2 with particle size range of 0.35-0.45μm was uniformly laid in a quartz crucible, the crucible was placed in a tube furnace, calcined at 600°C for 60min in air atmosphere. Figure 8 The ion chromatogram of chlorine ion in SiO2 after calcination was shown, the chlorine ion content was calculated according to the peak area, the result was 18.96ppm.

[0071] Example 7:

[0072] Vacuum distillation washing of SiO2 gel: The freshly prepared SiO2 gel was roughly measured with a beaker, 40 mL, then transferred to a round-bottom flask and added with a certain amount of water, the volume ratio of water to gel was 4.5:1, then the gel aqueous solution was mixed uniformly by means of ultrasonic and shaking; the above-mentioned round-bottom flask was placed on a rotary evaporator, heated to evaporate water at 60-90°C, during which the rotary evaporator was kept in a negative pressure state by a circulating water vacuum pump, after evaporated to the gel state, the initial volume was added with water again, repeated washing for 3 times, finally the washed SiO2 gel was obtained.

[0073] Vacuum drying to obtain SiO2 particles: the above-mentioned washed wet gel was collected in a beaker, then placed in a vacuum drying oven, dried at 90°C for 4h, to obtain dried SiO2.

[0074] Low-temperature calcination to remove chlorine: the dried SiO2 was ground into different particle sizes, 0.7g of SiO2 with particle size range of 0.35-0.45μm was uniformly laid in a quartz crucible, the crucible was placed in a tube furnace, calcined at 600°C for 60min in air atmosphere. Figure 9 The ion chromatogram of chlorine ion in SiO2 after calcination was shown, the chlorine ion content was calculated according to the peak area, the result was 18.96ppm.

[0075] Example 8:

[0076] Vacuum distillation washing of SiO2 gel: A beaker was used to roughly measure 40 mL of freshly prepared SiO2 gel, which was then transferred to a round-bottom flask and a certain amount of water was added, with a water-to-gel volume ratio of 4.5:1. The gel water solution was then mixed uniformly using ultrasonic and shaking methods. The round-bottom flask was placed on a rotary evaporator, and water was evaporated at 60-90°C while maintaining a negative pressure in the rotary evaporator using a circulating water vacuum pump. After the gel was evaporated, the initial volume was restored by adding water, and the washing was repeated three times. Finally, the washed SiO2 gel was obtained.

[0077] Vacuum drying to obtain SiO2 particles: The washed wet gel was collected in a beaker, which was then placed in a vacuum drying oven and dried at 90°C for 4 h to obtain dried SiO2.

[0078] Low-temperature calcination to remove chlorine: The dried SiO2 was ground into different particle sizes, and 0.7 g of SiO2 with a particle size range of 0.35-0.45 μm was uniformly placed in a quartz crucible. The crucible was placed in a tube furnace and calcined at 400°C for 60 min under a He gas atmosphere. Figure 10 The ion chromatogram of chlorine ions in the calcined SiO2 is shown, and the chlorine ion content is calculated according to the peak area, with a result of 25.99 ppm.

[0079] Example 9:

[0080] Vacuum distillation washing of SiO2 gel: A beaker was used to roughly measure 40 mL of freshly prepared SiO2 gel, which was then transferred to a round-bottom flask and a certain amount of water was added, with a water-to-gel volume ratio of 4.5:1. The gel water solution was then mixed uniformly using ultrasonic and shaking methods. The round-bottom flask was placed on a rotary evaporator, and water was evaporated at 60-90°C while maintaining a negative pressure in the rotary evaporator using a circulating water vacuum pump. After the gel was evaporated, the initial volume was restored by adding water, and the washing was repeated three times. Finally, the washed SiO2 gel was obtained.

[0081] Vacuum drying to obtain SiO2 particles: The washed wet gel was collected in a beaker, which was then placed in a vacuum drying oven and dried at 90°C for 4 h to obtain dried SiO2.

[0082] Low-temperature calcination to remove chlorine: The dried SiO2 was ground into different particle sizes, and 0.7 g of SiO2 with a particle size range of 0.35-0.45 μm was uniformly placed in a quartz crucible. The crucible was placed in a tube furnace and calcined at 400°C for 60 min under a He gas atmosphere. Figure 11The ion chromatogram of chloride ions in calcined SiO2 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 Number of washes 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 / °C 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 chlorine content of final products in Examples 6-9

[0086] Example 6 7 8 9 Number of washes 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 / °C 600 400 400 400 Calcination time / min 60 120 60 60 Calcination atmosphere Air Air He [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 washes significantly affects the particle size structure of the dried sample. Specifically, compared to the dried sample in Example 2, the dried SiO2 obtained in Example 1 is small and loose particles, which is 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, selecting a calcination time of 60 minutes is the most reasonable and efficient.

[0088] From the results of Comparative 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, and since the crucible size is consistent in each example, this means that the packing density of the material inhibits the escape of HCl, and therefore the packing density of the material during calcination must be precisely controlled in order to produce a low-chlorine SiO2product. From the results of Comparative Example 1, Example 8 and Example 9, it can be seen that the atmosphere during calcination also affects the chlorine ion content of the final product, and taking both cost and effectiveness into account, the use of air as the reaction atmosphere is the optimal choice. Furthermore, from the results of Comparative Example 5 and Example 6, it can be seen that the particle size range has a certain effect on the chlorine removal effect of calcination, and when the particle size range is very small (<0.2 pm), the residual chlorine content in the product is significantly increased, which is because the small-particle-size SiO2powder is more densely packed, which is not conducive to the volatilization and escape of HCl. At the same time, from the comparison 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 chlorine removal effect. Among them, lower temperatures will weaken the volatilization of HCl, and at the same time, the increase of temperature will affect the pore distribution on the surface of the material (as shown in FIG. 1), resulting in a larger proportion of small pores, which is not conducive to the volatilization of HCl inside the particles, thereby reducing the removal effect of chlorine ions, and the preferred calcination temperature is 400°C. Figure 12

[0089] It should also be understood that various changes and modifications can be made to the application described herein, and that it is intended to cover all such changes and modifications that fall within the scope of the application, as defined by the appended claims.​

Claims

1. A method for the deep removal of chloride impurities in synthetic silica, characterized in that, The method comprises the following steps: adding water to the SiO2 gel to form a sol, and performing negative pressure rotary evaporation to obtain a washed SiO2 gel; drying the washed SiO2 gel under reduced pressure to obtain SiO2 particles; The SiO2 particles with a particle size of 0.35-0.45 microns are calcined at 400°C to remove chlorine; the laying density of the SiO2 particles during calcination is 0.035-0.04 g / cm 2 .

2. The method for the depth removal of chloride impurities in synthetic silica according to claim 1, characterized in that, the SiO2 gel is prepared by a sol-gel method using chlorosilane as a raw material; The chemical formula of the chlorosilane is SiCl x H 4-x , 0 < x < 4.

3. The method for the depth removal of chloride impurities in synthetic silica according to claim 1, characterized in that, in a single operation, the volume ratio of water added to the SiO2 gel to the volume of the SiO2 gel is 4-6:

1.

4. The method for the depth removal of chloride impurities in synthetic silica according to claim 3, characterized in that, in a single operation, the volume ratio of water added to the SiO2 gel to the volume of the SiO2 gel is 4.5:

1.

5. The method for the depth removal of chloride impurities in synthetic silica according to claim 1, characterized in that, The temperature of the negative pressure rotary evaporation is 60-90°C.

6. The method for the depth removal of chloride impurities in synthetic silica according to claim 1, characterized in that, The temperature of the reduced pressure drying is 85-95°C, and the time is 4-6 hours.

7. The method for the depth removal of chloride impurities in synthetic silica according to claim 6, characterized in that, The temperature of the reduced pressure drying is 90°C.

8. The method for the depth removal of chloride impurities in synthetic silica according to claim 1, characterized in that, The calcination time is 60-120 min.

9. The method for the depth removal of chloride impurities in synthetic silica according to claim 1, characterized in that, The calcination atmosphere is one or a combination of nitrogen atmosphere, air atmosphere, and helium atmosphere.

10. The use of the deep removal method according to any one of claims 1-9 for removing chloride impurities in synthetic silicon dioxide.

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