Complete-flow acid-free semiconductor-grade quartz sand purification process

Abstract

The invention discloses a whole-process acid-free semiconductor-grade quartz sand purification process. The process comprises the following steps: coarsely crushing raw material ores to obtain coarsely crushed ores with the average particle size of 1-3 cm; color sorting is conducted on the coarsely-broken ore, the coarsely-broken ore with the mica and / or feldspar content exceeding the detection limit is picked out, and the remaining coarsely-broken ore is washed with water and dried; roasting, water quenching and fine crushing are carried out on the dried coarsely-crushed ore to prepare quartz sand particles of 60-160 meshes; performing magnetic separation on the quartz sand particles to separate out magnetic mineral impurities; the quartz sand subjected to magnetic separation is placed in a scrubbing agent to be soaked for 1-2 hours, and then scrubbing is conducted for 3-4 hours under the assistance of microwaves; the scrubbed quartz sand is subjected to reverse flotation operation and dried; carrying out magnetic separation on the obtained quartz sand to separate out magnetic mineral impurities; the obtained quartz sand is repeatedly subjected to soaking scrubbing, reverse flotation and drying operation once; and carrying out chlorination purification on the obtained quartz sand by using an ammonium chloride solid under the condition of 1100-1200 DEG C to obtain the semiconductor-grade quartz sand.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor-grade quartz sand preparation, and particularly relates to a purification process for semiconductor-grade quartz sand without acid throughout the process. Background Art

[0002] High-purity quartz sand refers to quartz with a SiO2 purity of ≥99.99%. Due to its excellent chemical stability, high-temperature resistance, low thermal expansion coefficient, and high light transmittance, it plays an irreplaceable role in multiple high-tech industries.

[0003] In the semiconductor field, key components such as quartz crucibles for manufacturing single-crystalline silicon and quartz boats, quartz tubes, diffusion furnaces, etc. in semiconductor processing are made of ultra-high-purity quartz sand (SiO2 purity ≥99.9992%). Since the presence of metal impurities in quartz sand will significantly affect the corresponding high-precision quartz products, the semiconductor industry has extremely high requirements for the purity of quartz sand, especially the content of impurities such as Ca, Fe, and alkali metals (Na, K, Li, etc.) must be controlled within 2 ppm.

[0004] The purification process of high-purity quartz sand involves a series of links, including ore crushing, high-temperature calcination, water quenching, sand making and screening, flotation, pickling, and high-temperature chlorination. Among them, flotation, as the most important link in the purification process, can effectively remove most mineral impurities and metal impurities. Flotation is a mineral processing method that separates quartz from impurity minerals by utilizing the differences in the physical and chemical properties of the mineral surface (such as chemical adsorption, physical adsorption, and differences in hydrophilicity and hydrophobicity). Its core mechanism is to regulate the surface properties of minerals through reagents and use bubbles to selectively carry hydrophobic minerals for separation. Its high efficiency and flexibility make it an indispensable technology in modern mineral processing. However, in the current high-purity quartz purification process, the flotation efficiency is often relatively low, and it is unable to efficiently remove the mineral impurities attached to the surface of quartz. Therefore, a more efficient flotation process needs to be introduced.

[0005] In addition to the flotation process, pickling is also an important improvement link in the current purification of high-purity quartz sand. Currently, since pickling often requires the use of volatile acids (such as hydrochloric acid, hydrofluoric acid, etc.), and due to the large-scale industrial production, the demand for acid is very large, which brings more pressure to the purification process, including the transportation and storage of acid, corrosion of equipment, harm to the physical health of workers, etc. In addition, the post-treatment of waste acid needs to meet environmental protection requirements, which also brings a certain cost pressure.

[0006] After retrieval, the following prior arts are available: The patent specification with the publication number CN1562743A discloses a method for preparing ultra-pure quartz sand. The method includes preparing coarse silica sand through crushing and screening; removing surface impurities through hot acid leaching; removing bubbles and cracks inside the sand grains through cold explosion; and removing foreign substances inside the ore grains better through ultrasonic vibration acid washing.

[0007] The patent specification with the publication number CN116143133A discloses a method for preparing high-purity quartz sand. The preparation method includes multiple steps such as flotation and acid washing. Among them, the acid washing mainly uses sulfuric acid, hydrochloric acid, nitric acid or hydrofluoric acid, and the concentration of the acid is 5% - 20%. It is stirred at a constant temperature for 2 - 24 hours under the condition of 30 - 100 °C.

[0008] The patent specification with the publication number CN102120583A discloses a purification method for high-purity quartz sand used in crucibles and lining materials for the electronic industry. The purification method includes multiple steps such as flotation and acid washing. Among them, the acid washing requires a ratio of 30% hydrochloric acid to 35% hydrofluoric acid (150 kg of hydrochloric acid and 40 kg of hydrofluoric acid are used per ton of quartz sand).

[0009] The patent specification with the publication number CN110127708A discloses a purification method for high-purity quartz sand with SiO2 purity ≥ 99.99%. The method includes multiple steps such as flotation and acid washing. Among them, flotation requires the use of hydrofluoric acid and NaOH / KOH as pH regulators, dodecylamine as a collector, and No. 2 oil as a foaming agent. Feldspar mineral impurities are floated out under the condition of pH 2.0 - 3.0.

[0010] The patent specification with the publication number CN119158691A discloses a method for preparing high-purity quartz sand, which includes using hydrochloric acid as an acid washing agent and hydrogen chloride as a roasting agent.

[0011] The patent specification with the publication number CN119080008A discloses a process for preparing high-purity quartz sand from quartz ore with high iron and aluminum content, including acid washing the quartz sand with a mixed acid and maintaining the temperature at 80 - 90 °C; the subsequent process requires chlorination purification of the quartz sand under hydrogen chloride gas and at 1100 - 1200 °C.

[0012] The above patent technologies all have the following problems: 1) The purification process of high-purity quartz sand inevitably uses volatile acids including hydrochloric acid and even hydrofluoric acid. Considering the large-scale use in industrial production, in the long run, it not only has a strong corrosive effect on equipment, but also causes certain harm to the physical health of workers. Especially, there are strict requirements for the storage and transportation of acids; 2) It has limited effect on removing metal impurities. Often, the cumulative content of Ca, Fe, and alkali metals (such as Na, K, Li, etc.) exceeds 10 ppm, which cannot meet the requirements of the semiconductor field. Summary of the Invention

[0013] In view of the above technical problems and deficiencies in the art, the present invention provides a semiconductor-grade quartz sand purification process without acid in the whole process. On the one hand, by optimizing the process (replacing the traditional pickling process with a microwave scrubbing process and selecting a suitable scrubbing agent), it avoids the use of volatile acids such as hydrochloric acid and hydrofluoric acid. On the other hand, by using a flotation reagent with higher selectivity, it improves the flotation efficiency and efficiently removes impurities on the surface of quartz, especially metal impurities, etc.

[0014] A semiconductor-grade quartz sand purification process without acid in the whole process includes the steps: S01: Coarse crushing of the raw ore to obtain a coarsely crushed ore with an average particle size of 1 - 3 cm; S02: Color sorting the coarsely crushed ore, picking out the coarsely crushed ore with mica and / or feldspar content exceeding the detection limit, and washing and drying the remaining coarsely crushed ore; S03: Roasting and water quenching the coarsely crushed ore dried in step S02, and finely crushing it into sand to obtain quartz sand particles with a mesh size of 60 - 160; S04: Magnetic separation of the quartz sand particles to separate out magnetic mineral impurities; S05: Immerse the magnetically separated quartz sand in the scrubbing agent for 1 - 2 hours, and then perform scrubbing under microwave assistance for 3 - 4 hours; the solvent of the scrubbing agent is water, and the scrubbing agent contains 5wt% - 10wt% sodium oxalate, 5wt% - 10wt% sodium citrate, and 5wt% - 10wt% disodium ethylenediaminetetraacetate; S06: Perform reverse flotation operation on the quartz sand scrubbed in step S05 and dry it; the impurity mineral flotation reagent used in the reverse flotation operation has the following structure: , where n is 7 - 11; S07: Magnetically separate the quartz sand obtained in step S06 again to separate out magnetic mineral impurities; S08: Repeat the operations of step S05 and step S06 on the quartz sand obtained in step S07 once; S09: Chlorinate and purify the quartz sand obtained in step S08 with solid ammonium chloride at 1100 - 1200 °C to obtain semiconductor-grade quartz sand.

[0015] In step S01, the raw ore may include granitic pegmatite ore, etc.

[0016] Preferably, in step S01, the ore with a particle size greater than 3 cm after coarse crushing is recycled for continuous coarse crushing.

[0017] Preferably, in step S02, a laser light source is used for the color sorting.

[0018] Preferably, in steps S04 and S07, an electromagnetic magnetic separator is used for the magnetic separation. More preferably, the background magnetic field intensity of the electromagnetic magnetic separator is 5000 - 6000 GS.

[0019] Preferably, in steps S04 and S07, the time for the magnetic separation is 2 - 4 h.

[0020] Preferably, in step S05, the dosage ratio of the quartz sand to the scrubbing agent is 1 - 1.5 kg / L.

[0021] Preferably, in step S05, the temperature of the soaking is 50 - 60 °C.

[0022] Preferably, in step S05, the microwave is in pulse mode.

[0023] Preferably, in step S05, the frequency of the microwave is 2 - 2.45 GHz.

[0024] Preferably, in step S06, the reverse flotation operation specifically includes: Transfer the quartz sand scrubbed in step S05 to a flotation machine, and add water to prepare a quartz sand pulp; Add sodium citrate to the quartz sand pulp and stir, then add a quartz depressant and stir, then add the impurity mineral flotation agent and stir, and then add a foaming agent, and blow air for reverse flotation of quartz. During this period, stir and scrape the foam, and the impurities float out with the foam, and wash the quartz sand remaining in the flotation machine.

[0025] Preferably, in step S06, the temperature of the water used to prepare the quartz sand pulp is 50 - 60 °C.

[0026] Preferably, in step S06, the mass concentration of quartz sand in the quartz sand pulp is 45% - 55%, such as 50%, etc.

[0027] Preferably, in step S06, based on the solid mass in the quartz sand pulp, the addition amount of sodium citrate is 20 - 25 g / 500 kg.

[0028] Preferably, in step S06, the stirring time after adding sodium citrate is 20 - 30 minutes.

[0029] Preferably, in step S06, the quartz depressant includes sodium fluorosilicate.

[0030] Preferably, in step S06, based on the solid mass in the quartz sand pulp, the addition amount of the quartz inhibitor is 20 - 25 g / 500 kg.

[0031] Preferably, in step S06, the stirring time after adding the quartz inhibitor is 20 - 30 minutes.

[0032] Preferably, in step S06, based on the solid mass in the quartz sand pulp, the addition amount of the impurity mineral flotation agent is 60 - 70 g / 500 kg.

[0033] Preferably, in step S06, the stirring time after adding the impurity mineral flotation agent is 20 - 30 minutes.

[0034] Preferably, in step S06, the foaming agent includes pine oil.

[0035] Preferably, in step S06, based on the solid mass in the quartz sand pulp, the addition amount of the foaming agent is 10 - 15 g / 500 kg.

[0036] Preferably, in step S06, the time for air - bubbling for quartz reverse flotation is 20 - 30 minutes.

[0037] Preferably, in step S09, based on the mass of the quartz sand obtained in step S08, the dosage of ammonium chloride solid is 100 - 120 g / 500 kg.

[0038] Preferably, in step S09, the heat - preservation time at 1100 - 1200 °C is 5 - 6 h.

[0039] Preferably, in step S09, the quartz sand after chlorination purification is quenched with water and dried to obtain semiconductor - grade quartz sand.

[0040] Taking the quartz content in the raw ore as a comparison, the recovery rate of the semiconductor - grade quartz sand obtained by the all - process acid - free semiconductor - grade quartz sand purification process of the present invention is greater than 73%.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The purification process of the present invention does not use dangerous chemicals such as acids (including acid solutions, acidic gases, etc.), especially avoiding the use of volatile acids and chlorine gas, greatly reducing the production cost and potential safety hazards of enterprises.

[0042] 2. The addition of the microwave scrubbing process and the improvement of the flotation process in the present invention can effectively reduce the impurity content in the final finished sand. Especially, the content of impurities such as Fe, Ca, and alkali metals (Na, K, Li, etc.) is less than 2 ppm, meeting the usage requirements of semiconductor - grade high - purity quartz sand. Detailed implementation manners

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

[0044] Embodiment 1:

[0045] Mineral raw materials: Taking a certain batch of ore from a granitic pegmatite in a certain area of India as an example for material analysis, the mass content of quartz in the raw ore is 44.23%, the mass content of feldspar is 26.40%, the mass content of mica is 16.78%, the mass content of hematite / magnetite is 6.32%, the mass content of kyanite is 5.29%, and the mass content of the remaining impurity minerals such as rutile and ilmenite is less than 1%.

[0046] Specific operation process of the purification process: (1) Pretreatment process: Use a crusher to roughly crush the raw ore to obtain roughly crushed ore with an average particle size of 1 - 3 cm. The ore with a particle size greater than 3 cm after rough crushing is returned to the crusher for continued crushing; the roughly crushed ore with an average particle size of 1 - 3 cm is color - sorted. The color - sorter uses a laser light source to remove the roughly crushed ore with more impurities such as mica and feldspar, and the screened roughly crushed ore is washed and dried with water; the dried roughly crushed ore is roasted, water - quenched, finely broken and made into sand to obtain quartz sand particles with a mesh size of 60 - 160; use an electromagnetic magnetic separator to perform magnetic separation on the obtained quartz sand particles. The background magnetic field intensity of the electromagnetic magnetic separator is 6000 GS, and the magnetic separation time is 2 h to separate magnetic mineral impurities.

[0047] (2) Microwave - assisted scrubbing process: Put 500 kg of the magnetically separated quartz sand into the scrubbing agent in the scrubbing machine. The scrubbing agent is a 500 L water mixture of 5% sodium oxalate, 5% sodium citrate, and 5% disodium ethylenediaminetetraacetate. Control the temperature at 50 °C and soak for 1 hour, and then perform scrubbing assisted by microwave for 3 hours. The microwave is in pulse mode, and the microwave frequency is 2.45 GHz; after scrubbing, rinse with clean water to wash the quartz sand clean.

[0048] (3) Flotation process: Pour the scrubbed quartz sand into the flotation machine, stir and rinse the preliminarily purified raw sand once with 50℃ warm water, and prepare it into quartz sand slurry with a mass concentration of 50%; add sodium citrate to the quartz sand slurry in the flotation machine in an amount of 20g / 500kg (500kg is based on the solid mass in the quartz sand slurry, the same below), and stir for 20 minutes; continue to add quartz inhibitor sodium fluorosilicate 20g / 500kg to the slurry and stir for 20 minutes; then add impurity mineral flotation agent ODA in an amount of 60g / 500kg and stir for 20 minutes; then add pine oil 10g / 500kg as a frother, and perform quartz reverse flotation for 30 minutes with aeration, stirring and scraping bubbles during the period, and impurities float out with the foam. After flotation, rinse the obtained quartz sand with deionized water for two to three times to clean the agent residue on the surface of the mineral to obtain fine quartz sand. The dried quartz sand is subjected to the aforementioned magnetic separation, scrubbing and flotation again.

[0049] The impurity mineral flotation agent ODA has the following structure: , where n=7.

[0050] (4) Chlorination roasting process: The quartz sand dried after flotation is sent to a roasting furnace, and solid ammonium chloride is added. The amount of solid ammonium chloride is 100g / 500kg quartz sand. The temperature is controlled at 1100°C for roasting for 5 hours, and then the roasted quartz sand is placed in water for quenching, rapidly cooled with cooling water, and then dried as the final semiconductor-grade high-purity quartz sand.

[0051] The test results show that semiconductor-grade quartz sand can be obtained according to the above-mentioned process parameters and conditions, with a recovery rate of 73.25% (compared with the quartz content in the original ore), and the obtained grade (purity) of product quartz sand is 99.9992%. The main metal content indicators are shown in Table 1 below (in ppm, by mass).

[0052] Table 1

[0053] Embodiment 2: Mineral raw materials: Taking a batch of granite pegmatite ore from a certain area in India as an example for material analysis, the mass content of quartz in the original ore is 54.81%, the mass content of feldspar is 18.94%, the mass content of mica is 10.22%, the mass content of hematite / magnetite / ilmenite is 11.96%, the mass content of kyanite is 3.08%, and the mass content of other impurity minerals such as rutile and apatite is less than 1%.

[0054] The specific operation process of the purification process is the same as that of Example 1.

[0055] The test results show that semiconductor-grade quartz sand can be obtained according to the above process parameters and conditions. The recovery rate is 79.86% (compared with the quartz content in the original ore), and the product quartz sand with a grade (purity) of 99.9993% is obtained. The main metal content indexes are shown in Table 2 below (unit: ppm, by mass).

[0056] Table 2

[0057] Example 3: Mineral raw materials: Taking a batch of ore from a granite pegmatite in a certain area of India as an example for material analysis, the mass content of quartz in the original ore is 50.12%, the mass content of feldspar is 23.91%, the mass content of mica is 12.21%, the mass content of kyanite is 5.72%, the mass content of hematite / magnetite / ilmenite is 5.11%, and the mass content of the remaining impurity minerals such as rutile and apatite is less than 3%.

[0058] The specific operation process of the purification process is the same as that of Example 1.

[0059] The test results show that semiconductor-grade quartz sand can be obtained according to the above process parameters and conditions. The recovery rate is 76.96% (compared with the quartz content in the original ore), and the product quartz sand with a grade (purity) of 99.9992% is obtained. The main metal content indexes are shown in Table 3 below (unit: ppm, by mass).

[0060] Table 3

[0061] Comparative Example 1: The mineral raw materials are the same as those in Example 1.

[0062] The difference in the specific operation process of the purification process from that of Example 1 is that the microwave-assisted scrubbing process is replaced by an acid-washing process. The acid-washing process is as follows: Add 500 kg of quartz sand after magnetic separation and screening to the reaction kettle, and prepare 300 L of mixed acid by mixing hydrochloric acid with a mass concentration of 38% and hydrofluoric acid with a mass concentration of 49% in a volume ratio of 2:1 for acid-washing. The temperature of the reaction kettle is maintained at 80-90 °C for 8 hours of acid-washing; after acid-washing, rinse the residues on the surface of the quartz sand with water and proceed to the next flotation. And, the quartz sand after the first flotation and drying is subjected to the aforementioned magnetic separation, acid-washing, and flotation again. The remaining operation processes are the same as those in Example 1.

[0063] The test results show that high-purity quartz sand can be obtained according to the above process parameters and conditions. The recovery rate is 88.72% (compared with the quartz content in the original ore), and the product quartz sand with a grade (purity) of 99.991% is obtained. According to various indicators, the quartz sand product of this comparative example cannot meet the requirements of semiconductor-grade quartz sand, and its main metal content indicators are shown in Table 4 below (unit: ppm, by mass).

[0064] Table 4

[0065] Comparative Example 2: The mineral raw material is the same as that in Example 1.

[0066] The difference in the specific operation process of the purification process from that of Example 1 lies in the following specific flotation process: Using sulfuric acid as a regulator under the condition of pH 2-4, a combination of 600 g / 500 kg of dodecylamine, sodium dodecylsulfonate and sodium oleate (mass combination ratio 3:2:1) is used as a collector to float the quartz sand; The collector is added in a segmented manner. The addition amount in the initial flotation is controlled at 60% of the total amount, and the remaining 20% and 20% of the collector are gradually added later, which can make the flotation process more uniform and stable, prevent the excessive consumption of the collector in the initial stage, and ensure that the collector concentration in the whole flotation process is always at the optimal level. Immediately after flotation, multi-stage water washing is carried out, and deionized water is used to thoroughly remove the collector residue. The dried quartz sand is magnetically separated, scrubbed and floated again as described above. The rest of the operation process is the same as that in Example 1.

[0067] The test results show that high-purity quartz sand can be obtained according to the above process parameters and conditions. The recovery rate is 80.13% (compared with the quartz content in the original ore), and the product quartz sand with a grade (purity) of 99.97% is obtained. According to various indicators, the quartz sand product of this comparative example cannot meet the requirements of semiconductor-grade quartz sand, and its main metal content indicators are shown in Table 5 below (unit: ppm, by mass).

[0068] Table 5

[0069] In summary, the all-acid-free semiconductor-grade quartz sand purification process of the present invention has the following characteristics: First, a color sorting operation is introduced in the quartz sand pretreatment process, and mica and feldspar in the coarse sand are effectively removed through a laser light source; Second, a microwave-assisted scrubbing process is introduced to replace the traditional acid washing process. Through microwave treatment at a specific frequency and in combination with a specific scrubbing agent, the scrubbing agent can penetrate into the interior of the sand grains to achieve a better acid leaching effect; Third, the flotation process is optimized, and the flotation effect is improved by using more efficient flotation reagents.

[0070] Fourth, the whole process is safe and environmentally friendly, without using volatile acids such as hydrochloric acid, hydrofluoric acid, and highly hazardous acidic gases such as hydrogen chloride and chlorine.

[0071] Fifth, the impurity removal effect of the purification process is obvious, and the cumulative content of key metal element indexes Fe, Ca, Ti, and alkali metals (such as Na, K, Li, etc.) is less than 2 ppm, meeting the requirements of the semiconductor industry for quartz sand.

[0072] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A semiconductor-grade quartz sand purification process without acid throughout the whole process, characterized in that, Including the steps: S01: Coarsely crushing the raw ore to obtain coarsely crushed ore with an average particle size of 1 - 3 cm; S02: Conducting color sorting on the coarsely crushed ore, picking out the coarsely crushed ore with mica and / or feldspar content exceeding the detection limit, and washing and drying the remaining coarsely crushed ore; S03: Subjecting the coarsely crushed ore dried in step S02 to roasting and water quenching, and finely crushing and making sand to obtain quartz sand particles of 60 - 160 mesh; S04: Conducting magnetic separation on the quartz sand particles to separate out magnetic mineral impurities; S05: Immersing the magnetically separated quartz sand in a scrubbing agent for 1 - 2 hours, and then conducting scrubbing assisted by microwave for 3 - 4 hours; the solvent of the scrubbing agent is water, and the scrubbing agent contains 5wt% - 10wt% sodium oxalate, 5wt% - 10wt% sodium citrate, and 5wt% - 10wt% disodium ethylenediaminetetraacetate; S06: Perform reverse flotation operation on the quartz sand scrubbed in step S05 and dry it; the impurity mineral flotation agent used in the reverse flotation operation has the following structure: , where n is 7-11; S07: Conducting magnetic separation on the quartz sand obtained in step S06 again to separate out magnetic mineral impurities; S08: Repeating the operations of step S05 and step S06 on the quartz sand obtained in step S07 once; S09: Conducting chlorination purification on the quartz sand obtained in step S08 with solid ammonium chloride at 1100 - 1200 °C to obtain semiconductor - grade quartz sand.

2. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that In step S01, the ore with a particle size greater than 3 cm after coarse crushing is recycled for continuous coarse crushing.

3. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that, In step S02, a laser light source is used for the color sorting.

4. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that, In step S04 and step S07, the magnetic separation is carried out using an electromagnetic magnetic separator, the background magnetic field intensity of the electromagnetic magnetic separator is 5000 - 6000 GS, and the time for the magnetic separation is 2 - 4 h.

5. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that, In step S05: The dosage ratio of the quartz sand to the scrubbing agent is 1 - 1.5 kg / L; The temperature of the immersion is 50 - 60 °C; The microwave is in pulse mode, and the frequency of the microwave is 2 - 2.45 GHz.

6. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that In step S06, the reverse flotation operation specifically includes: Transferring the quartz sand scrubbed in step S05 to a flotation machine, adding water to prepare a quartz sand pulp; Adding sodium citrate to the quartz sand pulp and stirring, then adding a quartz depressant and stirring, then adding the impurity mineral flotation agent and stirring, and then adding a foaming agent, blowing air for reverse flotation of quartz, stirring and skimming the foam during this period, and the impurities float out with the foam, and washing the quartz sand remaining in the flotation machine.

7. The acid-free semiconductor-grade quartz sand purification process according to claim 6, characterized in that, In step S06: The temperature of the water used to prepare the quartz sand pulp is 50 - 60 °C; The mass concentration of quartz sand in the quartz sand pulp is 45% - 55%; Based on the solid mass in the quartz sand pulp, the addition amount of sodium citrate is 20 - 25 g / 500 kg; The stirring time after adding sodium citrate is 20 - 30 minutes; The quartz depressant includes sodium fluorosilicate; Based on the solid mass in the quartz sand pulp, the addition amount of the quartz depressant is 20 - 25 g / 500 kg; The stirring time after adding the quartz depressant is 20 - 30 minutes; Based on the solid mass in the quartz sand pulp, the addition amount of the impurity mineral flotation agent is 60 - 70 g / 500 kg; The stirring time after adding the impurity mineral flotation agent is 20 - 30 minutes; The foaming agent includes pine oil; Based on the solid mass in the quartz sand pulp, the addition amount of the foaming agent is 10 - 15 g / 500 kg; The time for quartz reverse flotation by blowing air is 20 - 30 minutes.

8. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that, In step S09, based on the mass of the quartz sand obtained in step S08, the dosage of the ammonium chloride solid is 100 - 120 g / 500 kg.

9. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that, In step S09, the heat preservation time at 1100 - 1200 °C is 5 - 6 h.

10. The acid-free semiconductor-grade quartz sand purification process according to claim 1, characterized in that, In step S09, the quartz sand after chlorination purification is quenched and dried with water to obtain semiconductor - grade quartz sand.

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