Doping purification process of high-purity quartz sand

Abstract

The invention discloses a doping purification process of high-purity quartz sand, and relates to the technical field of quartz sand purification, and the doping purification process comprises the following steps: crushing quartz sand, putting the crushed quartz sand into a microwave reactor, and introducing ozone; immersing the quartz sand subjected to microwave treatment into bacterial liquid, stirring or oscillating, and then separating; the bacterial liquid comprises acidophilic thiobacillus thiooxidans and silicate decomposition bacteria in a mass ratio of 1: (3-10), the concentration of the bacterial liquid is 106-108 CFU / mL, and the pH value is 1.5-3.0; the separated quartz sand is sequentially subjected to high-voltage pulsed magnetic field action and nano bubble flotation; the quartz sand subjected to nano bubble flotation is subjected to acid pickling with a composite acid solution; carrying out pyrolysis film removal on the quartz sand subjected to acid pickling; removing membrane impurities from the quartz sand subjected to pyrolysis membrane removal through a subcritical water repairing process, and filtering, washing and drying; according to the method, micron-sized impurities in the quartz sand can be efficiently separated, impurities of different sizes in the quartz sand are removed step by step, the impurity removal rate is high, the removal effect is good, and the process cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of quartz sand purification, and particularly to a doping purification process for high-purity quartz sand. Background Art

[0002] As an important industrial raw material, quartz sand is widely used in many fields such as glass manufacturing, semiconductor materials, optical fiber communication, ceramics, and silicon materials. With the progress of technology and the continuous improvement of material quality requirements in various industries, the purity requirements for quartz sand are becoming increasingly strict. High-purity quartz sand not only requires a high content of silicon dioxide (SiO2), but also requires extremely low contents of metal impurities such as iron (Fe), aluminum (Al), titanium (Ti), etc. to meet the needs of high-end manufacturing fields.

[0003] Traditional quartz sand purification processes mainly include multiple steps such as mechanical crushing, scrubbing and de-sludging, magnetic separation, flotation, acid leaching, and calcination. Mechanical crushing separates non-structural impurities from quartz by reducing the particle size of minerals, but new impurities may be introduced during the process. Scrubbing and de-sludging removes film iron, adhered and muddy impurity minerals on the surface of quartz sand by means of mechanical force and abrasive force between sand grains, but the removal effect is limited. Magnetic separation is mainly used to remove magnetic minerals in quartz sand, while flotation is used to remove non-magnetic associated impurities such as feldspar and mica. Acid leaching dissolves impurity minerals with acid solution, but the type, concentration, dosage of acid, and reaction conditions all have a significant impact on the purification effect. Calcination and water quenching generate cracks in minerals through thermal stress, thereby achieving further crushing and purification of quartz.

[0004] However, while these traditional processes improve the purity of quartz sand, they are often accompanied by high process costs. For example, the acid leaching process requires the use of a large amount of chemical reagents, which not only increases the cost but also may cause environmental pollution. The flotation process requires complex equipment and high energy consumption, and the selection and use of flotation reagents also have an important impact on the purification effect and environmental impact. In addition, the multi-step purification process also increases the operation complexity and time cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a doping purification process for high-purity quartz sand, and solve the following technical problems:

[0006] How to improve the purity of quartz sand purification and reduce the cost of the purification process.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The present invention discloses a doping purification process for high-purity quartz sand, which is characterized by including the following steps:

[0009] S1. After crushing the quartz sand, place it in a microwave reactor and introduce ozone;

[0010] S2. Immerse the microwave-treated quartz sand in the bacterial solution, stir or shake it, and then separate it;

[0011] S3. Apply high-voltage pulsed magnetic field and nano-bubble flotation to the separated quartz sand in sequence;

[0012] S4. Pickle the quartz sand after nano-bubble flotation with a composite acid solution;

[0013] S5. Perform thermal de-filming on the pickled quartz sand;

[0014] S6. Remove the film impurities from the quartz sand after thermal de-filming through a subcritical water repair process, and then filter, wash, and dry it.

[0015] Further, in step S1, the particle size of the crushed quartz sand is ≤500 um. The crushed quartz sand can have a larger contact area with the treatment liquid during subsequent processing, so that the impurity removal rate can be higher.

[0016] Further, in step S1, the microwave power of the microwave reactor is set to 300 - 800 W, the frequency is 2.45 GHz, and the radiation mode is intermittent radiation. It stops for 15 s every 30 s of radiation; Microwaves induce lattice vibration of quartz sand through dielectric polarization, thereby generating local high temperature, and promoting the migration of impurities such as iron ions and aluminum ions in the quartz sand lattice to the lattice surface; Intermittent irradiation avoids microcracks caused by local overheating of quartz, and at the same time allows ozone to fully diffuse to the newly formed surface.

[0017] After multiple tests, it is determined that the optimal microwave power is between 300 - 800 W. If it is less than 300 W, the electrode activation is insufficient. If it is greater than 800 W, it is easy to cause phase transformation of quartz sand, and the optimal microwave power is selected as 500 W; The radiation time is determined to be 5 - 20 min. If it is less than 5 min, the activation reaction is insufficient. If it is greater than 20 min, the energy consumption is too high and the cost increases, and the optimal radiation time is selected as 10 min.

[0018] Further, in step S1, the inlet concentration of ozone is 50 - 200 mg / L, and the gas flow rate is 0.5 - 2 L / min; Ozone can oxidize the organic matter on the surface of quartz sand to generate small carboxylic acid molecules, thereby enhancing the accessibility of subsequent bioleaching;

[0019] Preferably, the inlet concentration of ozone is 100 mg / L, and the gas flow rate is 1 L / min.

[0020] Further, in step S2, the bacterial solution includes a mixed bacterium composed of Acidithiobacillus thiooxidans and silicate-decomposing bacteria in a mass ratio of 1:(3 - 10), and the concentration of the bacterial solution is 10 6 -108 CFU / mL, with a pH of 1.5 - 3.0; Acidithiobacillus thiooxidans metabolizes to produce H2SO4, which can lower the pH to 1.0, thereby dissolving metal oxide impurities; silicate decomposing bacteria secrete extracellular polysaccharides (EPS), which can strip layered silicate impurities through coordination, and the removal rate of iron ions and aluminum ions can reach over 90%;

[0021] Preferably, the bacterial solution is a mixed bacterial solution composed of Acidithiobacillus thiooxidans and silicate decomposing bacteria in a mass ratio of 1:5, and the concentration of the bacterial solution is 10 7 CFU / mL, with a pH of 2.

[0022] Furthermore, the preparation method of the bacterial solution is: mixing Acidithiobacillus thiooxidans and silicate decomposing bacteria in a mass ratio of 1:(3 - 10), and adding 0.1 - 0.5 g / L of Fe 3+ as an electron acceptor to accelerate sulfur metabolism, and at the same time adding 2 - 5 g / L of sodium thiosulfate as an energy substrate to avoid autolysis of the bacteria, and obtaining the bacterial solution after stirring evenly;

[0023] Preferably, the mass ratio of Acidithiobacillus thiooxidans to silicate decomposing bacteria is 1:5; the addition amount of Fe 3+ is 0.3 g / L, and the concentration of sodium thiosulfate is 3 g / L.

[0024] Furthermore, in step S2, the conditions for immersing the quartz sand in the bacterial solution and stirring or oscillating are: stirring or oscillating at 35 - 45 °C for 12 - 20 h;

[0025] Preferably, stirring or oscillating at 40 °C for 16 h.

[0026] Furthermore, in step S3, the magnetic field intensity of the high - voltage pulsed magnetic field action is 2 - 5 T, the pulse frequency is 10 - 100 Hz, and the action time is 5 - 30 min;

[0027] Preferably, the magnetic field intensity is 4 T, the pulse frequency is 50 Hz, and the action time is 20 min.

[0028] Furthermore, in step S3, the nano - bubble flotation uses micro - nano - bubbles with a particle size ≤200 nm and surface - loaded with 0.1 wt% of modified carboxymethyl chitosan, and the flotation pH is 4.0 - 6.0, preferably pH = 5.

[0029] Furthermore, the preparation method of the modified carboxymethyl chitosan is as follows: Carboxymethyl chitosan and dodecyl primary amine are reacted at a molar ratio of 1:(0.5 - 2) at 60 °C for 2 - 4 hours. The combination at this molar ratio can balance its hydrophilic and hydrophobic capabilities; after the reaction, the pH is adjusted to 8.0 - 9.0 to ensure the stable form of zwitterions, and thus the modified carboxymethyl chitosan is obtained; the -NH2 / -COOH groups of carboxymethyl chitosan selectively adsorb to the hydroxyl groups (-OH) on the quartz surface, and the dodecyl chains form a hydrophobic film. Nano-bubbles capture hydrophobic impurities through the surface tension effect, which can improve the impurity removal rate and reduce the dosage of flotation liquid, achieving the purpose of reducing the treatment cost.

[0030] Preferably, carboxymethyl chitosan and dodecyl primary amine are reacted at a molar ratio of 1:1 at 60 °C for 3 hours, and after the reaction, the pH is adjusted to 8.5.

[0031] Furthermore, in step S4, the composite acid solution is a mixed acid solution composed of organic acids (such as citric acid, oxalic acid, etc.) and inorganic acids (such as hydrochloric acid, sulfuric acid, etc.) at a molar ratio of 1:(1 - 3).

[0032] Preferably, the composite acid solution is a mixed acid solution composed of citric acid and hydrochloric acid at a molar ratio of 1:2.

[0033] Furthermore, in step S4, the pickling method is as follows: multi-stage countercurrent pickling is carried out under the assistance of ultrasonic waves with a frequency of 20 - 40 kHz and a power density of 0.5 - 2 W / cm 2 , and the pickling time for each stage is 10 - 30 min, and the pickling temperature is 60 - 80 °C.

[0034] Preferably, multi-stage countercurrent pickling is carried out under the assistance of ultrasonic waves with a frequency of 30 kHz and a power density of 1 W / cm 2 , the pickling time for each stage is 20 min, and the pickling temperature is 70 °C.

[0035] Furthermore, the acid solution is recycled. The recycling method is as follows: The waste acid solution is regenerated through an adsorption column filled with biomass charcoal (BC) loaded with nano-zero-valent iron (nZVI), and the flow rate is controlled at 1 - 3 BV / h. The regenerated acid solution is supplemented to the fresh acid solution to reach the initial concentration and then reused; nZVI precipitates metal ions such as iron ions and aluminum ions in the waste acid as hydroxides through a reduction reaction (Fe 0 →Fe 2+ ), and BC adsorbs organic substances, which can restore the quality of the acid solution, making the acid solution reuse rate exceed 80%, reducing the waste liquid discharge by 70%, saving costs and being beneficial to environmental protection.

[0036] Further, in step S5, the method of thermal desorption film removal is as follows: After pickling the quartz sand, under nitrogen protection, it is heated to 800 - 1000 °C at a rate of 5 - 10 °C / min and held for 1 - 2 hours, and then rapidly cooled to below 200 °C at a rate of 50 - 100 °C / s. During the above treatment process, organic and inorganic impurities remain on the surface of the quartz sand. High-temperature treatment causes these impurities to form a carbonized film or an oxidized film attached to the surface of the quartz sand after pyrolysis. Since the thermal expansion coefficients of quartz sand and impurities such as iron oxide, aluminum oxide, and mica are significantly different, high-temperature treatment also generates different interfacial stresses between these impurities and the quartz sand matrix. Quenching further amplifies the stress due to the difference in shrinkage rates, resulting in microcracks and peeling at the grain boundaries, thus achieving film removal;

[0037] Preferably, after pickling the quartz sand, under nitrogen protection, it is heated to 900 °C at a rate of 8 °C / min and held for 1.5 hours, and then rapidly cooled to below 200 °C at a rate of 80 °C / s.

[0038] Further, in step S6, the subcritical water remediation process is as follows: The quartz sand after thermal desorption film removal and supercritical CO2 are placed together in a subcritical water reactor and treated for 1 - 3 hours under the conditions of a pressure of 8 - 15 MPa and a temperature of 200 - 300 °C, with 0.1 - 0.5 wt% of sodium metasilicate dissolved in the water; in the subcritical water environment, supercritical CO2 acts as a solvent to enhance the penetration ability of water to polar impurities. Sodium metasilicate preferentially reacts with the remaining Al 3+ 、Fe 3+ to form soluble complexes, further dissolving trace impurities; then conventional filtration, washing, and drying are carried out to obtain high-purity quartz sand.

[0039] Preferably, the quartz sand after thermal desorption film removal and supercritical CO2 are placed together in a subcritical water reactor and treated for 2 hours under the conditions of a pressure of 12 MPa and a temperature of 150 °C, with 0.3 wt% of sodium metasilicate dissolved in the water.

[0040] The beneficial effects of the present invention:

[0041] (1) In the doping and purification process of the high-purity quartz sand of the present invention, in the early stage, by combining microwave treatment with ozone, the organic matter on the surface of the quartz sand can be oxidized to generate small carboxylic acid molecules, thereby enhancing the accessibility of subsequent biological leaching; the sulfur-oxidizing acidophilic bacteria in the composite bacterial solution can metabolize to produce H2SO4, which can lower the pH to 1.0, thus dissolving metal oxide impurities, and the generated H2SO4; the extracellular polysaccharide (EPS) secreted by the silicate-decomposing bacteria can strip layered silicate impurities through coordination, and the removal rate of iron ions and aluminum ions can reach more than 90%; by combining the non-equilibrium separation of pulsed magnetic fields with the spatial confinement effect of nanobubble flotation, the efficient separation of micron-scale impurities is realized, so that the quartz sand is gradually removed of impurities of different scales, with a high impurity removal rate and good removal effect.

[0042] (2) In the doping and purification process of the high-purity quartz sand of the present invention, a recycling mechanism is set up during the pickling process, so that the pickling waste liquid can be recycled, which not only reduces the acid liquid cost, but also is more environmentally friendly; the sulfur-oxidizing acidophilic bacteria in the composite bacterial solution can metabolize to produce H2SO4, which can supplement the pickling system and reduce energy consumption; at the same time, during the microwave treatment in the early stage, the energy consumption of subsequent biological leaching can also be reduced, further reducing the process cost. Specific embodiments

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0044] The experimental methods in the following embodiments are all conventional methods, unless otherwise specified, in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0045] Example 1

[0046] Prepare the bacterial solution: Mix the sulfur-oxidizing acidophilic bacteria and the silicate-decomposing bacteria in a mass ratio of 1:5, and add 0.3 g / L of Fe 3+ as an electron acceptor, and at the same time add 3 g / L of sodium thiosulfate as an energy substrate, stir evenly to obtain the bacterial solution; the concentration of the bacterial solution is 10 7 CFU / mL and the pH is 2.

[0047] Example 2

[0048] Preparation of micro-nano bubbles with surface-loaded modified carboxymethyl chitosan: Carboxymethyl chitosan and dodecyl primary amine were reacted at a molar ratio of 1:1 at 60 °C for 3 hours. After the reaction, the pH was adjusted to 8.5 to obtain modified carboxymethyl chitosan. An aqueous solution of modified carboxymethyl chitosan containing 0.1 wt% was added to a bubble generator to generate micro-nano bubbles with a particle size ≤ 200 nm, and its pH = 5.

[0049] Example 3

[0050] Preparation of composite acid solution: Citric acid and hydrochloric acid were mixed at a molar ratio of 1:2 and stirred evenly to obtain the composite acid solution.

[0051] Example 4

[0052] Step 1: Quartz sand was crushed to a particle size ≤ 500 um, then placed in a microwave reactor. The microwave power was set to 500 W and the frequency was 2.45 GHz. It was irradiated for 30 s and then stopped for 15 s, and the total radiation time was 10 min. At the same time, ozone with a concentration of 100 mg / L was introduced into the microwave reactor at a speed of 1 L / min.

[0053] Step 2: The quartz sand was taken out of the microwave reactor and transferred to the bacterial solution in Example 1, stirred at 40 °C for 16 h, and then filtered and separated.

[0054] Step 3: The separated quartz sand was placed in a pulsed magnetic field with a magnetic field strength of 4 T and a pulse frequency of 50 Hz for 20 min, and then transferred to the micro-nano bubbles in Example 2 for flotation for 3 h.

[0055] Step 4: The flotation-treated quartz sand was filtered and washed with water. The washed quartz sand was transferred to the composite acid solution prepared in Example 3, and multi-stage countercurrent pickling was carried out under ultrasonic assistance at a frequency of 30 kHz and a power density of 1 W / cm 2 The pickling time for each stage was 20 min and the pickling temperature was 70 °C. During this process, the waste acid solution was regenerated through an adsorption column filled with biomass charcoal (BC)-loaded nano-zero-valent iron (nZVI), and the flow rate was controlled at 2 BV / h. The regenerated acid solution was replenished to the fresh acid solution to reach the initial concentration and then reused.

[0056] Step 5: Under nitrogen protection, the pickled quartz sand was heated to 900 °C at a rate of 8 °C / min and held for 1.5 hours, and then quickly cooled to below 200 °C at a rate of 80 °C / s.

[0057] Step 6: The thermally demembraned quartz sand and supercritical CO2 were co-placed in a subcritical water reaction kettle and treated at a pressure of 12 MPa and a temperature of 150 °C for 2 hours. Sodium metasilicate with a solubility of 0.3 wt% was dissolved in the water. Finally, it was subjected to conventional filtration, washing, and drying to obtain high-purity quartz sand.

[0058] Example 5

[0059] Compared with Example 4, the only difference is that in Step 1, the microwave power is set to 300 W, the frequency is 2.45 GHz, radiation stops for 15 s every 30 s of radiation, the total radiation duration is 20 min, and ozone with a concentration of 200 mg / L is introduced into the microwave reactor at a rate of 0.5 L / min; other steps and conditions are exactly the same, and high-purity quartz sand is finally obtained.

[0060] Example 6

[0061] Compared with Example 4, the only difference is that in Step 1, the microwave power is set to 800 W, the frequency is 2.45 GHz, radiation stops for 15 s every 30 s of radiation, the total radiation duration is 5 min, and ozone with a concentration of 50 mg / L is introduced into the microwave reactor at a rate of 2 L / min; other steps and conditions are exactly the same, and high-purity quartz sand is finally obtained.

[0062] Example 7

[0063] Compared with Example 4, the only difference is that in Step 3, the magnetic field strength is 2 T, the pulse frequency is 10 Hz, and the action time is 30 min; other steps and conditions are exactly the same, and high-purity quartz sand is finally obtained.

[0064] Example 8

[0065] Compared with Example 4, the only difference is that in Step 3, the magnetic field strength is 5 T, the pulse frequency is 100 Hz, and the action time is 5 min; other steps and conditions are exactly the same, and high-purity quartz sand is finally obtained.

[0066] Example 9

[0067] Compared with Example 4, the only difference is that in Step 4, multi-stage countercurrent pickling is carried out under the assistance of ultrasonic waves with a frequency of 20 kHz and a power density of 2 W / cm 2 , and the pickling time for each stage is 10 min, and the pickling temperature is 80 °C; other steps and conditions are exactly the same, and high-purity quartz sand is finally obtained.

[0068] Example 10

[0069] Compared with Example 4, the only difference is that in Step 4, multi-stage countercurrent pickling is carried out under the assistance of ultrasonic waves with a frequency of 40 kHz and a power density of 0.5 W / cm 2 , and the pickling time for each stage is 30 min, and the pickling temperature is 60 °C; other steps and conditions are exactly the same, and high-purity quartz sand is finally obtained.

[0070] Comparative Example 1

[0071] Using the existing technology to purify quartz sand, the specific steps are as follows: ball-mill the quartz sand to a particle size ≤ 500um, then pickle it with a sulfuric acid solution with a mass fraction of 20% at 80°C for 4h. Apply ultrasonic waves during the pickling process for assistance. After pickling, filter it. Place the quartz sand in a heating furnace and calcine it at 900°C for 2h. After standing and cooling, obtain the purified quartz sand.

[0072] Comparative Example 2

[0073] Compared with Example 1, the only difference is that: change Step 1 to: crush the quartz sand to a particle size ≤ 500um, and then perform hot air drying; other steps and conditions are exactly the same., obtain the purified quartz sand.

[0074] Comparative Example 3

[0075] Compared with Example 1, the only difference is that: in Step 2, replace the bacterial solution with Acidithiobacillus thiooxidans; the concentration of the bacterial solution is 10 7 CFU / mL and the pH is 2; other steps and conditions are exactly the same, obtain the purified quartz sand.

[0076] Detect various indicators involved in the process of Examples 4 - 10 and Comparative Examples 1 - 3, including the purity of the purified quartz sand, the contents of iron oxide (Fe2O3) and aluminum oxide (Al2O3) in the quartz sand, acid consumption, energy consumption, and calculate and statistically analyze the treatment cycle, and list the statistical results in Table 1 as follows:

[0077] Table 1

[0078]

[0079] Analyzing the data in Table 1, it can be known that compared with Comparative Examples 1 - 3, the purified quartz sand obtained in Examples 4 - 10 has a higher purity, and the purity is all above 99.99, reaching the high-purity level; the impurity contents of iron oxide and aluminum oxide decrease; the acid consumption and energy consumption are significantly reduced, which can reduce the process cost, and the treatment cycle becomes shorter, which can improve the process efficiency.

[0080] The above has described multiple embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. Any equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A doping and purification process for high-purity quartz sand, characterized in that, It includes the following steps: S1. Crush the quartz sand and place it in a microwave reactor, and introduce ozone; S2. Immerse the microwave-treated quartz sand in the bacterial solution, stir or oscillate it, and then separate it; the bacterial solution includes Acidithiobacillus thiooxidans and silicate decomposing bacteria with a mass ratio of 1:(3 - 10), the concentration of the bacterial solution is 10 6 -10 8 CFU / mL, and the pH is 1.5 - 3.0; S3. Subject the separated quartz sand to high-voltage pulsed magnetic field action and nano-bubble flotation in sequence; S4. Pickle the quartz sand after nano-bubble flotation with a composite acid solution; S5. Perform thermal demoulding on the pickled quartz sand; S6. Remove the mould impurities from the quartz sand after thermal demoulding through a subcritical water repair process, and then filter, wash, and dry it.

2. The doping and purification process of high-purity quartz sand according to claim 1, wherein, In step S1, the microwave power of the microwave reactor is set to 300 - 800 W, the frequency is 2.45 GHz, the radiation mode is intermittent radiation, it stops for 15 s every 30 s of radiation, and the total radiation duration is 5 - 20 min.

3. The doping and purification process of high-purity quartz sand according to claim 2, characterized in that, In step S1, the inlet concentration of the ozone is 50 - 200 mg / L, and the gas flow rate is 0.5 - 2 L / min.

4. The doping and purification process of high-purity quartz sand according to claim 1, wherein, The preparation method of the bacterial solution is as follows: mixing Acidithiobacillus thiooxidans and silicate-decomposing bacteria according to a mass ratio of 1:(3-10), and adding 0.1-0.5 g / L of Fe 3+ as an electron acceptor, and simultaneously adding 2-5 g / L of sodium thiosulfate as an energy substrate, and stirring evenly to obtain the bacterial solution.

5. The doping and purification process of high-purity quartz sand according to claim 4, characterized in that, In step S2, the conditions for immersing the quartz sand in the bacterial solution and stirring or oscillating are: stirring or oscillating at 35 - 45 °C for 12 - 20 h.

6. The doping and purification process of high-purity quartz sand according to claim 1, characterized in that, In step S3, the magnetic field intensity of the high-voltage pulsed magnetic field action is 2 - 5 T, the pulse frequency is 10 - 100 Hz, and the action time is 5 - 30 min.

7. The doping and purification process of high-purity quartz sand according to claim 6, characterized in that, In step S3, the nano-bubble flotation uses micro-nano bubbles with a particle size ≤ 200 nm and surface-loaded with 0.1 wt% of modified carboxymethyl chitosan, and the flotation pH is 4.0 - 6.

0.

8. The doping and purification process of high-purity quartz sand according to claim 7, characterized in that, The preparation method of the modified carboxymethyl chitosan is: react carboxymethyl chitosan with dodecyl primary amine at a molar ratio of 1:(0.5 - 2) at 60 °C for 2 - 4 hours, and adjust the pH to 8.0 - 9.0 after the reaction to obtain the modified carboxymethyl chitosan.

9. The doping and purification process of high-purity quartz sand according to claim 1, wherein In step S4, the composite acid solution is a mixed acid solution composed of an organic acid and an inorganic acid in a molar ratio of 1:(1 - 3); the pickling method is: under the ultrasonic assistance with a frequency of 20 - 40 kHz and a power density of 0.5 - 2 W / cm 2 , multi-stage countercurrent pickling is carried out, the pickling time for each stage is 10 - 30 min, and the pickling temperature is 60 - 80 °C.

10. The doping and purification process of high-purity quartz sand according to claim 9, characterized in that, In step S4, the acid solution is recycled, and the recycling method is: regenerate the waste acid solution through an adsorption column filled with biomass carbon-supported nano-zero-valent iron, control the flow rate at 1 - 3 BV / h, and supplement the regenerated acid solution to the fresh acid solution to reach the initial concentration and then reuse it.

11. The doping and purification process of high-purity quartz sand according to claim 1, characterized in that, In step S5, the thermal demoulding method is: under nitrogen protection, heat the pickled quartz sand to 800 - 1000 °C at a rate of 5 - 10 °C / min, hold for 1 - 2 hours, and then quickly cool to below 200 °C at a rate of 50 - 100 °C / s, so that the residual impurity phase and the quartz sand matrix generate grain boundary peeling to achieve demoulding.

12. The doping and purification process of high-purity quartz sand according to claim 1, characterized in that, In step S6, the subcritical water repair process is: place the quartz sand after thermal demoulding and supercritical CO2 in a subcritical water reaction kettle, and treat it at a pressure of 8 - 15 MPa and a temperature of 200 - 300 °C for 1 - 3 hours, and 0.1 - 0.5 wt% of sodium metasilicate is dissolved in the water.

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