Purification method of high-purity quartz sand

Abstract

The invention belongs to the technical field of quartz sand treatment, and particularly relates to a purification method of high-purity quartz sand. The method comprises the following steps: carrying out vacuum roasting treatment on high-purity quartz sand to obtain quartz sand subjected to vacuum roasting treatment; carrying out acid leaching treatment on the quartz sand subjected to vacuum roasting treatment by adopting a pickling solution to obtain acid-leached quartz sand; and sequentially washing and drying the quartz sand subjected to acid leaching treatment. Volatile impurities in the quartz sand can be effectively removed through vacuum roasting, impurities such as residual metal oxides can be further removed in combination with acid leaching treatment, the purity of the quartz sand is remarkably improved, the inclusion state in the quartz sand is improved, and the requirements of high-end industries are met. Meanwhile, the purification method provided by the invention is simple and clear in process steps, simple and convenient to operate and easy to control and operate; meanwhile, the acid consumption and energy consumption can be greatly reduced, and the method is suitable for industrial production and application.

Description

Technical Field

[0001] This invention belongs to the field of quartz sand treatment technology, specifically relating to a method for purifying high-purity quartz sand. Background Technology

[0002] High-purity silica sand (SiO2 purity ≥ 99.99%) is an indispensable key material in high-end manufacturing, widely used in semiconductor single-crystal silicon growth, photovoltaic cells, optical fiber preforms, and precision optical devices. With integrated circuit manufacturing processes entering the 3nm era and the photovoltaic industry's pursuit of higher conversion efficiency, the market's purity requirements for silica sand have increased to over 99.998%, while imposing more stringent standards on impurity content and microstructure. In particular, the submicron-sized inclusions within silica sand, with residual metallic impurities such as Al, Fe, and Ti, significantly affect the material's optical properties and thermal stability. The core challenge currently facing the industry is how to achieve deep removal of inclusions within the crystal lattice without damaging the silica crystal structure.

[0003] Traditional quartz sand purification processes primarily rely on a combination of physical sorting and chemical acid leaching, but these methods have significant limitations when dealing with inclusions within the crystal lattice. While conventional acid leaching effectively removes surface impurities, its penetration into closed fluid inclusions is insufficient. High-temperature calcination, although promoting the rupture of some inclusions, easily leads to re-encapsulation of impurities or a phase transformation of the quartz under normal pressure. Especially for deeply buried inclusions with a particle size less than 1 μm, existing technologies often require repeated processing, resulting in high energy consumption and introducing new pollution risks. Furthermore, the excessive use of highly corrosive reagents such as hydrofluoric acid not only increases production costs but also causes a severe environmental burden. Summary of the Invention

[0004] The purpose of this invention is to provide a purification method for high-purity quartz sand. The purification method provided by this invention can significantly improve the purity of quartz sand, improve the state of inclusions in quartz sand, and meet the requirements of high-end industries. At the same time, the purification steps are simple, easy to control and operate, and suitable for industrial production applications.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for purifying high-purity quartz sand, comprising the following steps: High-purity quartz sand is subjected to vacuum calcination to obtain vacuum-calcined quartz sand, wherein the purity of the high-purity quartz sand is ≥99.99% and the holding temperature of the vacuum calcination is ≥1000℃. The vacuum-calcined quartz sand is then subjected to acid leaching with an acid washing solution to obtain acid-leached quartz sand. The acid washing solution is a mixed solution of hydrofluoric acid and hydrochloric acid. The acid-treated quartz sand was then washed with water and dried in sequence.

[0006] Preferably, the vacuum degree of the vacuum calcination process is ≤0.5 mbar.

[0007] Preferably, the holding temperature for the vacuum calcination treatment is 1000~1500℃, and the holding time is 2~4 h.

[0008] Preferably, the heating rate from room temperature to the holding temperature of the vacuum calcination treatment is 5~15℃ / min.

[0009] Preferably, the HF content in the hydrofluoric acid is 2-8 wt%; the HCl content in the hydrochloric acid is 10-20 wt%; and the mass ratio of hydrofluoric acid to hydrochloric acid in the pickling solution is 1:1-5.

[0010] Preferably, the mass ratio of the vacuum-calcined quartz sand to the pickling solution during the acid leaching treatment is 1:(3~6).

[0011] Preferably, the acid leaching treatment is carried out at a temperature of 60~110℃ for 8~24 h.

[0012] Preferably, the acid leaching treatment is carried out under stirring conditions, and the stirring speed is 20~80 r / min.

[0013] Preferably, the reagent used for washing is ultrapure water with a resistivity ≥18 MΩ·cm; the washing is performed until the pH value is 6.5~7.5.

[0014] Preferably, the drying temperature is 100~130℃ and the time is 1~4 h.

[0015] This invention provides a method for purifying high-purity quartz sand, comprising the following steps: vacuum roasting the high-purity quartz sand to obtain vacuum-roasted quartz sand, wherein the purity of the high-purity quartz sand is ≥99.99%, and the holding temperature of the vacuum roasting is ≥1000℃; acid leaching the vacuum-roasted quartz sand with an acid washing solution to obtain acid-leached quartz sand, wherein the acid washing solution is a mixed solution of hydrofluoric acid and hydrochloric acid; and sequentially washing and drying the acid-leached quartz sand. This invention first employs vacuum roasting for purification, while simultaneously optimizing the temperature of the vacuum roasting process. During vacuum roasting, the high-temperature environment promotes the volatilization of volatile impurities (such as moisture, organic matter, and some low-boiling-point metal compounds) inside the quartz sand. The vacuum conditions not only inhibit high-temperature oxidation reactions but also utilize the pressure difference to promote the vaporization and escape of inclusion components. Furthermore, the volatile impurities in the vacuum environment are promptly discharged from the furnace, preventing them from re-adsorbing onto the surface of the quartz sand, thereby improving the impurity removal effect. After vacuum roasting, this invention uses an acid leaching solution composed of hydrofluoric acid and hydrochloric acid for purification. Because this invention optimizes the vacuum roasting temperature to ≥1000℃, the quartz sand lattice undergoes crystal transformation and volume expansion during vacuum roasting, which not only facilitates the directional breakage of inclusions but also opens the lattice channels of the quartz sand at the micro-nano scale, allowing the acid leaching solution to directly reach the inclusion core. The acid leaching solution can chemically react with residual metal oxides and other impurities in the quartz sand to generate water-soluble substances, thereby further removing impurities. Therefore, this invention effectively removes volatile impurities from quartz sand through vacuum roasting, and the combined acid leaching further removes residual metal oxides and other impurities, significantly improving the purity of the quartz sand and the state of inclusions, meeting the requirements of high-end industries. Furthermore, the purification method provided by this invention has simple and clear process steps, is easy to operate and control; it also significantly reduces acid consumption and energy consumption, making it suitable for industrial production applications. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the purification method for high-purity quartz sand provided by this invention; Figure 2 These are microscopic images comparing the quartz sand samples before and after treatment in Example 1 of this invention. Figure 3 These are microscopic images comparing the quartz sand samples before and after treatment in Comparative Example 1 of this invention. Figure 4 These are microscopic images comparing the quartz sand samples before and after treatment in Example 2 of this invention. Figure 5 These are microscopic images comparing the quartz sand samples before and after treatment in Example 3 of this invention. Detailed Implementation

[0017] This invention provides a method for purifying high-purity quartz sand, comprising the following steps: High-purity quartz sand is subjected to vacuum calcination to obtain vacuum-calcined quartz sand, wherein the purity of the high-purity quartz sand is ≥99.99% and the holding temperature of the vacuum calcination is ≥1000℃. The vacuum-calcined quartz sand is then subjected to acid leaching with an acid washing solution to obtain acid-leached quartz sand. The acid washing solution is a mixed solution of hydrofluoric acid and hydrochloric acid. The acid-treated quartz sand was then washed with water and dried in sequence.

[0018] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0019] This invention involves vacuum calcining high-purity quartz sand to obtain vacuum-calcined quartz sand with a purity ≥99.99% and a holding temperature ≥1000℃ during the vacuum calcination process. In this invention, the purity of the high-purity quartz sand can be 99.99~99.996%.

[0020] In this invention, the vacuum calcination process is carried out in a vacuum calcination furnace. During the vacuum calcination process, the present invention maintains the required vacuum level by evacuating the vacuum calcination furnace through a vacuum pump. The vacuum level of the vacuum calcination process is preferably ≤0.5 mbar. The holding temperature of the vacuum calcination process is preferably 1000~1500℃, and in the embodiments, it can be 1000, 1100, 1200, 1300, 1400, or 1500℃. The holding time of the vacuum calcination process is preferably 2~4 h, and in the embodiments, it can be 2, 2.5, 3, 3.5, 4, 4.5, or 5 h. The heating rate from room temperature to the holding temperature of the vacuum calcination process is preferably 5~15℃ / min, more preferably 8~12℃ / min, and in the embodiments, it can be 10, 11, 11.5, 12, or 12.5℃ / min.

[0021] In this invention, after the vacuum calcination process is completed, the vacuum calcination furnace is stopped from heating, the vacuum conditions are maintained and cooled to room temperature, and then the pressure is restored to normal to obtain the vacuum-calcined quartz sand.

[0022] After obtaining vacuum-calcined quartz sand, the present invention further treats the vacuum-calcined quartz sand with an acid leaching solution to obtain acid-leached quartz sand. The acid leaching solution is a mixed solution of hydrofluoric acid and hydrochloric acid. In this invention, the acid leaching treatment can be carried out in an acid leaching tank. The HF content in the hydrofluoric acid is preferably 2-8 wt%, and in the examples, it can be 2, 3, 4, 5, 6, 7, or 8 wt%. The HCl content in the hydrochloric acid is preferably 10-20 wt%, and in the examples, it can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 wt%. The mass ratio of hydrofluoric acid to hydrochloric acid in the acid leaching solution is preferably 1:1-5, and in the examples, it can be 1:2, 1:3, 1:4, or 1:5.

[0023] In this invention, the mass ratio of the quartz sand after vacuum calcination and the pickling solution (i.e., the solid-liquid ratio of the acid leaching treatment) is preferably 1:(3~6), and in the embodiments it can be 1:4, 1:5 or 1:6.

[0024] In this invention, the acid leaching temperature is preferably 60-110°C, and in the embodiments, it can be 60, 70, 80, 90, 100, or 110°C. The acid leaching time is preferably 8-24 h, and in the embodiments, it can be 8, 12, 16, or 24 h. The acid leaching is preferably carried out under stirring conditions. The stirring speed is preferably 20-80 r / min, and in the embodiments, it can be 20, 30, 40, 50, 60, 70, or 80 r / min.

[0025] The present invention preferably optimizes the temperature, time and stirring speed of the acid leaching treatment to further remove residual metal oxides and other impurities, significantly improve the purity of quartz sand, and improve the state of inclusions in quartz sand.

[0026] After obtaining the acid-leached quartz sand, the present invention sequentially washes and dries the acid-leached quartz sand. In this invention, the reagent used for washing is preferably ultrapure water, and the resistivity of the ultrapure water is preferably ≥18 MΩ·cm, which can be 18.2 MΩ·cm in the embodiment. The pH value of the water washing is preferably 6.5~7.5, which can be 7.0±0.5 in the embodiment. The pH value of the water washing is the pH value of the washing solution obtained from the water washing.

[0027] In this invention, the drying can be oven drying. The drying temperature is preferably 100~130℃, and in the embodiments, it can be 120±5℃. The drying time is preferably 1~4 h, and in the embodiments, it can be 2, 3, or 4 h. The purified quartz sand obtained after drying has the following properties: Moisture content ≤0.02%; Purity ≥99.9975%, and in the embodiments, it can be 99.9978%; Transparency >50%, and in the embodiments, it can be 56%, 52%, or 51%.

[0028] This invention reveals that when quartz sand reaches a temperature of 573℃, it undergoes a transformation from α-quartz to β-quartz. At 846℃, a transformation from β-quartz to tridymite occurs, resulting in significant expansion of the quartz lattice, with an expansion rate reaching 16%–18%. At approximately 1400℃, it transforms into cristobalite. These crystal transformations and volume expansion characteristics provide a theoretical basis for the directional fracture of inclusions in quartz sand. However, conventional high-temperature treatment under normal pressure or inert gas environments easily induces sintering on the quartz surface and impurity diffusion, which reduces the purification effect. This invention, by introducing a vacuum environment, not only suppresses high-temperature oxidation reactions but also utilizes pressure differences to promote the vaporization and escape of inclusion components. Simultaneously, the high-temperature conditions open lattice channels at the micro- and nano-scale, allowing the pickling solution to directly reach the inclusion core, effectively removing residual metal oxides and other impurities, and significantly improving the purity of the quartz sand.

[0029] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. The following embodiments and comparative examples are based on... Figure 1 The flowchart shown illustrates the purification of high-purity quartz sand.

[0030] Example 1 1. Raw material preparation and pretreatment High-purity quartz sand with a SiO2 content of 99.9961% was selected.

[0031] 2. Vacuum calcination treatment High-purity quartz sand was loaded into a vacuum calcining furnace, and the vacuum pump was started to evacuate the furnace. Once the vacuum level reached below 0.5 mbar, heating began at an average rate of 11.5 °C / min. The furnace was then held at 1400 °C for 3 hours under a vacuum of 0.5 mbar. Heating was then stopped, and the furnace was allowed to cool to room temperature while maintaining the vacuum. Afterward, the pressure was restored to normal, and the quartz sand was removed for later use.

[0032] 3. Acid leaching treatment A pickling solution was prepared using hydrofluoric acid with 4 wt% HF and hydrochloric acid with 15 wt% HCl, with a mass ratio of hydrofluoric acid to hydrochloric acid of 1:3. The high-purity quartz sand after vacuum calcination was transferred to a pickling tank. The pickling solution was added to the tank at a solid-liquid ratio of 1:4, ensuring the high-purity quartz sand was completely submerged. The pickling tank was placed in a thermostatic stirrer, and the reaction was carried out at 90℃ and 40 r / min for 12 h.

[0033] 4. Drying treatment After acid leaching, the high-purity quartz sand treated with acid leaching was removed from the pickling solution and washed with 18.2 MΩ·cm ultrapure water until pH=7.0±0.5. Then it was dried at 120±5℃ for 2 h, with the moisture content controlled at ≤0.02%. Its purity was tested to be 99.9978%.

[0034] Figure 2 These are microscopic images comparing the quartz sand samples before and after treatment in Example 1. Figure 2 It can be seen that the inclusion state of the quartz sand sample after treatment in Example 1 is better. The permeability of the quartz sand raw material before treatment in Example 1 is 31%, and the permeability of the purified quartz sand obtained after drying treatment is 56%.

[0035] Comparative Example 1 1. Raw material preparation and pretreatment High-purity quartz sand with a SiO2 content of 99.9961% was selected.

[0036] 2. Calcination treatment High-purity quartz sand is loaded into a muffle furnace and heated to 1400℃, then held at that temperature for 3 hours. Heating is then stopped, and the mixture is cooled to room temperature before being removed for later use.

[0037] 3. Acid leaching treatment A pickling solution was prepared using hydrofluoric acid with a HF content of 4 wt% and hydrochloric acid with a HCl content of 15 wt%, wherein the mass ratio of hydrofluoric acid to hydrochloric acid was 1:3. The calcined high-purity quartz sand was transferred to a pickling tank, and the pickling solution was added to the tank at a solid-liquid ratio of 1:4, ensuring that the calcined high-purity quartz sand was completely submerged in the pickling solution. The pickling tank was placed in a thermostatic stirrer, and the reaction was carried out at 90℃ and 40 r / min for 12 h.

[0038] 4. Drying treatment After acid leaching, the high-purity quartz sand treated with acid leaching was removed from the pickling solution and washed with 18.2 MΩ·cm ultrapure water until pH=7.0±0.5. Then it was dried at 120±5℃ for 2 h, with the moisture content controlled at ≤0.02%. Its purity was tested to be 99.9965%.

[0039] Figure 3 These are microscopic images comparing the quartz sand samples before and after treatment in Comparative Example 1. Figure 3 It can be seen that the inclusion state of the quartz sand sample after treatment in Comparative Example 1 is also better, but the improvement effect is worse than that in Example 1. The permeability of the quartz sand raw material before treatment in Comparative Example 1 is 31%, and the permeability of the purified quartz sand obtained after drying treatment is 45%.

[0040] Example 2 1. Raw material preparation and pretreatment High-purity quartz sand with a SiO2 content of 99.9961% was selected.

[0041] 2. Vacuum calcination treatment High-purity quartz sand was loaded into a vacuum calcining furnace, and the vacuum pump was started to evacuate the furnace. When the vacuum level reached below 0.5 mbar, heating was initiated at an average rate of 11.5 °C / min. The furnace was then held at 1200 °C for 3 hours under a vacuum of below 0.5 mbar. Heating was then stopped, and the furnace was allowed to cool to room temperature while maintaining the vacuum. Afterward, the pressure was restored to normal, and the quartz sand was removed for later use.

[0042] 3. Acid leaching treatment A pickling solution was prepared using hydrofluoric acid with 4 wt% HF and hydrochloric acid with 15 wt% HCl, with a mass ratio of hydrofluoric acid to hydrochloric acid of 1:3. The high-purity quartz sand after vacuum calcination was transferred to a pickling tank. The pickling solution was added to the tank at a solid-liquid ratio of 1:4, ensuring the high-purity quartz sand was completely submerged. The pickling tank was placed in a thermostatic stirrer, and the reaction was carried out at 90℃ and 40 r / min for 12 h.

[0043] 4. Drying treatment After acid leaching, the high-purity quartz sand treated with acid leaching was removed from the acid washing solution and washed with 18.2 MΩ·cm ultrapure water until pH=7.0±0.5. Then it was dried at 120±5℃ for 2 h, with the moisture content controlled at ≤0.02%. Its purity was tested to be 99.9965%.

[0044] Figure 4 These are microscopic images comparing the quartz sand samples before and after treatment in Example 2. Figure 4It can be seen that the permeability of the quartz sand raw material before treatment in Example 2 was 31%, and the permeability of the purified quartz sand obtained after drying treatment was 52%.

[0045] Example 3 1. Raw material preparation and pretreatment High-purity quartz sand with a SiO2 content of 99.9961% was selected.

[0046] 2. Vacuum calcination treatment High-purity quartz sand was loaded into a vacuum calcining furnace, and the vacuum pump was started to evacuate the furnace. When the vacuum level reached below 0.5 mbar, heating was initiated at an average rate of 11.5 °C / min. The furnace was then held at 1400 °C for 1 hour at a vacuum level below 0.5 mbar. Heating was then stopped, and the furnace was allowed to cool to room temperature while maintaining the vacuum. Afterward, the pressure was restored to normal, and the quartz sand was removed for later use.

[0047] 3. Acid leaching treatment A pickling solution was prepared using hydrofluoric acid with 4 wt% HF and hydrochloric acid with 15 wt% HCl, with a mass ratio of hydrofluoric acid to hydrochloric acid of 1:3. The high-purity quartz sand after vacuum calcination was transferred to a pickling tank. The pickling solution was added to the tank at a solid-liquid ratio of 1:4, ensuring the high-purity quartz sand was completely submerged. The pickling tank was placed in a thermostatic stirrer, and the reaction was carried out at 90℃ and 40 r / min for 12 h.

[0048] 4. Drying treatment After acid leaching, the high-purity quartz sand treated with acid leaching was removed from the pickling solution and washed with 18.2 MΩ·cm ultrapure water until pH=7.0±0.5. Then it was dried at 120±5℃ for 2 h, with the moisture content controlled at ≤0.02%. Its purity was tested to be 99.9972%.

[0049] Figure 5 These are microscopic images comparing the quartz sand samples before and after treatment in Example 3. Figure 5 It can be seen that the inclusion state of the quartz sand sample after treatment in Example 3 also improved accordingly. The permeability of the quartz sand raw material before treatment in Example 3 was 31%, and the permeability of the purified quartz sand obtained after drying treatment was 51%.

[0050] As can be seen from the above embodiments, the purification effect of the method provided by the present invention is significant (especially the permeability): the present invention can effectively remove volatile impurities in quartz sand through vacuum calcination, and further remove residual metal oxides and other impurities by combining acid leaching treatment, thus significantly improving the purity of quartz sand and meeting the requirements of high-end industries; at the same time, the method provided by the present invention is simple to operate: the whole process steps are clear, easy to control and operate, and suitable for industrial production applications.

[0051] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for purifying high-purity quartz sand, characterized in that, Includes the following steps: High-purity quartz sand is subjected to vacuum calcination to obtain vacuum-calcined quartz sand, wherein the purity of the high-purity quartz sand is ≥99.99% and the holding temperature of the vacuum calcination is ≥1000℃. The vacuum-calcined quartz sand is then subjected to acid leaching with an acid washing solution to obtain acid-leached quartz sand. The acid washing solution is a mixed solution of hydrofluoric acid and hydrochloric acid. The acid-treated quartz sand was then washed with water and dried in sequence.

2. The purification method according to claim 1, characterized in that, The vacuum degree of the vacuum roasting process is ≤0.5mbar.

3. The purification method according to claim 1 or 2, characterized in that, The vacuum calcination process is carried out at a temperature of 1000~1500℃ for 2~4 hours.

4. The purification method according to claim 3, characterized in that, The heating rate from room temperature to the holding temperature of the vacuum calcination treatment is 5~15℃ / min.

5. The purification method according to claim 1, characterized in that, The hydrofluoric acid contains 2-8 wt% HF; the hydrochloric acid contains 10-20 wt% HCl; and the mass ratio of hydrofluoric acid to hydrochloric acid in the pickling solution is 1:1-5.

6. The purification method according to claim 1 or 5, characterized in that, The mass ratio of the vacuum-calcined quartz sand to the pickling solution during the acid leaching process is 1:(3~6).

7. The purification method according to claim 1 or 5, characterized in that, The acid leaching treatment is carried out at a temperature of 60~110℃ for a time of 8~24 h.

8. The purification method according to claim 7, characterized in that, The acid leaching treatment is carried out under stirring conditions, and the stirring speed is 20~80 r / min.

9. The purification method according to claim 1, characterized in that, The reagent used for the water washing is ultrapure water with a resistivity ≥18 MΩ·cm; the water washing is performed until the pH value is 6.5~7.

5.

10. The purification method according to claim 1 or 9, characterized in that, The drying temperature is 100~130℃, and the time is 1~4 h.

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