Method for purifying quartz sand by laser focusing irradiation coupling supergravity acid leaching

Abstract

The application belongs to the field of high-purity material preparation, and discloses a method for purifying quartz sand by laser focusing irradiation coupled with supergravity acid leaching. The method comprises the following steps: irradiating quartz sand by pulsed laser focusing, generating thermal stress by using the difference between the thermal expansion coefficients of the quartz matrix and the internal impurity inclusions, cracking the closed inclusions, and opening the acid liquid penetration channel; forming micron-level liquid film under high-strength supergravity field by using ternary mixed acid, greatly strengthening solid-liquid mass transfer, and quickly dissolving and releasing metal impurities in deep part; and obtaining high-purity quartz sand through post-processing. The method has the dual synergistic effect of laser channel opening and supergravity enhanced leaching, and compared with single supergravity acid leaching and single laser pretreatment process, the impurity removal depth is significantly improved, the purity of SiO2 can reach more than 99.995%, and the total impurity content is less than 30 ppm; the acid leaching time is shortened to dozens of minutes, the acid consumption and energy consumption are greatly reduced, the waste acid can be recycled, the method is green and efficient, and is suitable for large-scale continuous industrial production of high-purity quartz sand for photovoltaic and semiconductor use.

Description

Technical Field

[0001] This invention belongs to the field of high-purity material preparation, specifically relating to a method for the synergistic purification of quartz sand by laser focused irradiation coupled with supergravity acid leaching. Background Technology

[0002] High-purity quartz sand is a core raw material for photovoltaic silicon wafers, optical fiber preforms, semiconductor crucibles, and high-end optical glass. The industry requires SiO2 purity ≥ 99.99%, with trace metal impurities such as Fe, Al, Ti, Ca, Mg, Na, and K totaling less than 50 ppm. Natural vein quartz and quartzite ores commonly contain fine inclusions of feldspar, mica, iron oxide, titanium oxide, and clay minerals. These impurities are embedded in microcracks, lattice defects, and grain boundaries within the quartz crystals. Existing single acid leaching processes have core drawbacks: the mineral inclusions are tightly sealed, making it difficult for acid to penetrate. While surface impurities are easy to remove, removing deeply embedded impurities is extremely difficult. To improve leaching efficiency, high-concentration strong acids and prolonged high-temperature immersion are required, resulting in high acid consumption, long leaching cycles of 6–12 hours, high energy consumption, large amounts of waste acid, and low purification limits. Conventional atmospheric pressure acid leaching makes it difficult to achieve SiO2 purity exceeding 99.97%.

[0003] Existing reinforcement methods have obvious shortcomings: 1. Simple high-temperature calcination: The energy consumption for heating and cooling is huge, which can easily cause quartz crystal transformation and generate new defects, and impurities are easy to be dissolved in solid solution again; 2. Ultrasonic / microwave-assisted acid leaching: can only enhance mass transfer on the particle surface, but cannot destroy enclosed mineral inclusions; 3. Individual supergravity acid leaching: It only improves the liquid-solid contact efficiency, but cannot open up the internal impurity channels, and the improvement in removing deeply encapsulated impurities is limited; 4. Simple laser irradiation of minerals: It can only break up inclusions, but without a matching efficient leaching system, the metal impurities released by the breakup are still adsorbed on the quartz surface, and subsequent water washing is difficult to completely remove them. Summary of the Invention

[0004] The purpose of this invention is to overcome at least one deficiency of the prior art and to provide a method for the synergistic purification of quartz sand by laser focused irradiation coupled with supergravity acid leaching.

[0005] The technical solution adopted in this invention is: The first aspect of the present invention provides a method for purifying quartz sand by supergravity acid leaching, comprising the following steps: Quartz sand is added to a high-gravity rotating bed, the high-gravity factor is controlled to be no less than 50 g, the reaction temperature is 60-120℃, and mixed acid is introduced for leaching, the acid leaching time is 10-60 min. After acid leaching, separate the quartz sand and wash it with water until neutral; After drying, purified quartz sand is obtained.

[0006] In some instances, the molar ratio of the mixed acids is hydrochloric acid: sulfuric acid: nitric acid = (3-4):(4-6):(1.5-2), with H+ as the solvent. + The total concentration is calculated to be 3–5 mol / L.

[0007] In some instances, the hypergravity factor is 50–300 g.

[0008] In some instances, the liquid-to-solid ratio of quartz sand to mixed acid is (3–8):1.

[0009] In some instances, the particle size of the quartz sand is 0.2–0.8 mm.

[0010] In some instances, the washing water is ultrapure water with a resistivity ≥18.2 MΩ·cm.

[0011] In some instances, the purity of the quartz sand raw material is not less than 98%.

[0012] A second aspect of the present invention provides a method for the synergistic purification of quartz sand by laser focused irradiation coupled with hypergravity acid leaching, comprising the following steps: Laser-modified quartz sand is obtained by irradiating quartz sand with a laser and using thermal stress to break up the metal mineral inclusions inside the quartz. The laser-modified quartz sand is further processed according to the method described in the first aspect of this invention to obtain purified quartz sand.

[0013] In some instances, the laser single-pulse energy is 50–200 mJ, and the spot diameter is 0.1–0.5 mm.

[0014] In some instances, the laser single-pulse energy is 100–150 mJ, and the spot diameter is 0.2–0.3 mm.

[0015] The above features can be combined arbitrarily as long as they do not conflict with each other.

[0016] The beneficial effects of this invention are: The methods described in some examples of this invention can significantly reduce acid leaching time, significantly improve production efficiency, and effectively improve the purity of quartz sand.

[0017] The methods in some examples of this invention utilize laser irradiation to generate thermal stress cracking that seals feldspar, mica, and iron-titanium oxide inclusions, thereby opening up acid permeation channels; hypergravity enhances liquid-solid mass transfer, rapidly dissolving internal impurities; the synergy of these two methods can stably increase the purity of SiO2 to over 99.995%, with a total impurity content of less than 30 ppm, meeting the top-grade high-purity quartz standards for photovoltaic crucibles and semiconductors. Neither a single laser nor a single hypergravity process can achieve the same purification effect.

[0018] The methods in some examples of this invention allow the inclusions to crack in advance without prolonged soaking in high-concentration strong acid, reducing acid consumption by 20% to 35%; there is no need for a high-temperature calcination process, laser instantaneous heating is used without overall temperature rise, reducing overall energy consumption by 25% to 40%, and lowering production costs.

[0019] The methods in some examples of this invention have a continuous and controllable process, stable product quality, and fully automated and adjustable laser scanning and hypergravity reaction processes. The batch impurity fluctuations of quartz sand are small, and it is applicable to vein quartz and quartzite raw materials from different origins. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments. In the following examples, only the main detectable impurities are listed for individual impurities, and not all impurities are listed. Example 1

[0021] 1) Raw ore pretreatment: Natural vein quartz blocky raw ore is coarsely crushed and finely crushed, and screened to obtain 0.2-0.8 mm quartz sand; 60 wt% slurry is prepared with water, and vertical high-speed scrubbing is performed for 20 min to remove the surface clay film and iron; it is then fed into a 1.2 T high gradient magnetic separator to remove magnetic minerals; after pretreatment, the raw material has SiO2 of 98.70%, and impurities: Fe2O3 286 ppm, Al2O3 1650 ppm, TiO2 98 ppm, CaO 210 ppm, MgO 126 ppm.

[0022] 2) Laser-focused irradiation modified pretreated quartz sand was evenly spread on a belt conveyor at a speed of 1.5 m / min; a fiber laser with a wavelength of 1064 nm, a single pulse energy of 120 mJ, and a spot diameter of 0.25 mm was continuously scanned for irradiation; local instantaneous high temperature in the particles generated thermal stress, and all the feldspar and iron oxide inclusions inside cracked to form interconnected microchannels; after irradiation, the particles were air-cooled for 5 min to room temperature to obtain laser-modified quartz sand.

[0023] 3) Preparation of compound acid: Mix concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid in a molar ratio of 3:4:1.5. The molar concentration of concentrated hydrochloric acid is 11.9 mol / L, concentrated sulfuric acid is 18.4 mol / L and concentrated nitric acid is 14.5 mol / L. Dilute with water to a total acid concentration of 4 mol / L and stir for 30 min until homogeneous before use.

[0024] 4) 10 kg of laser-modified quartz sand was fed into a high-gravity rotating bed and pumped into a mixed acid solution with a liquid-to-solid ratio of 5:1. The jacket was kept at a constant temperature of 90 ℃, the motor speed was 800 r / min, the high-gravity factor was 150 g, and the acid leaching was carried out continuously for 30 min. The inclusion channels created by laser cracking allowed the acid solution to quickly enter the interior and dissolve the metal impurities. High gravity continuously enhanced mass transfer.

[0025] 5) After the in-situ solid-liquid separation acid leaching is completed, keep the rotor rotating at high speed for 5 minutes, discharge the waste acid into the recovery storage tank, and discharge the solid phase quartz sand from the bottom.

[0026] 6) Countercurrent washing and drying: Three-stage ultrapure water countercurrent washing, single-stage washing for 8 min, until the effluent pH=6.5; vacuum filtration to dehydrate to a moisture content of 7%; hot air drying at 120 ℃ for 3 h, cooling and sieving to obtain the finished product.

[0027] Finished product testing indicators: SiO2 99.995%, Fe2O3 0.8 ppm, Al2O3 7.2 ppm, TiO2 7.5 ppm, CaO 6.1 ppm, MgO6.4 ppm. Example 2

[0028] 1) Raw ore pretreatment: crushing and screening of homologous quartz ore to obtain 0.1-0.6 mm fine-grained quartz sand; slurry concentration 55wt%; scrubbing for 15 min; 1.2 T magnetic separation to remove impurities; pretreated raw material SiO2 98.60%, Fe2O3 312 ppm, Al2O3 1720 ppm, TiO2 106 ppm.

[0029] 2) Laser irradiation belt travel speed 1 m / min, laser single pulse energy 100 mJ, spot size 0.2 mm, scanning irradiation, air cooling.

[0030] 3) Acid solution preparation: hydrochloric acid: sulfuric acid: nitric acid = 2:3:1, wherein the molar concentration of concentrated hydrochloric acid is 11.9 mol / L, concentrated sulfuric acid is 18.4 mol / L, concentrated nitric acid is 14.5 mol / L, and the total acid concentration is 3 mol / L.

[0031] 4) The ratio of liquid to solid in the supergravity acid leaching solution is 4:1, the constant temperature is 80 ℃, the supergravity factor is 100 g, the rotation speed is 600 r / min, and the acid leaching time is 40 min.

[0032] 5) Post-treatment: four-stage countercurrent washing until pH=6.3; drying at 110 ℃ for 4 h.

[0033] Finished product testing indicators: SiO2 99.994%, Fe2O3 1.3 ppm, Al2O3 9.8 ppm, TiO2 11.6 ppm.

[0034] Process advantages: Low temperature and low laser energy system, less acid mist volatilization, low equipment corrosion and wear, suitable for batch purification of fine-grained quartz sand. Example 3

[0035] 1) Raw ore pretreatment: 0.5-1.0 mm coarse-grained quartz sand was selected, scrubbed for 25 min and magnetically separated; the initial SiO2 content of the raw material was 99.00%, deep inclusions were developed, Fe2O3 was 243 ppm and Al2O3 was 1460 ppm.

[0036] 2) Laser irradiation enhances the fracturing of the belt at a speed of 2 m / min, with a single laser pulse of 150 mJ and a spot size of 0.3 mm. High-intensity scanning is used to fully blast open deep enclosed inclusions of coarse particles.

[0037] 3) High-concentration compound acid preparation: hydrochloric acid: sulfuric acid: nitric acid = 4:5:2, wherein the molar concentration of concentrated hydrochloric acid is 11.9 mol / L, concentrated sulfuric acid is 18.4 mol / L, concentrated nitric acid is 14.5 mol / L, and the total acid concentration is 5 mol / L.

[0038] 4) High-temperature, high-gravity rapid acid leaching with a liquid-to-solid ratio of 6:1, reaction temperature of 100 ℃, hypergravity factor of 200 g, rotation speed of 1000 r / min, and leaching for only 20 min.

[0039] 5) Post-treatment: two-stage rapid washing at pH 6.8, followed by drying at 140 ℃ for 2 h.

[0040] Finished product testing indicators: SiO2 99.996%, Fe2O3 0.6 ppm, Al2O3 5.3 ppm, TiO2 7.1 ppm.

[0041] Process advantages: High-energy laser + high-strength supergravity coupling, short-time deep removal of coarse particles and deep-seated insoluble impurities, suitable for high-end high-purity sand continuous production lines for photovoltaic crucibles. Comparative Example 1: Traditional atmospheric pressure stirring ternary acid leaching process (without laser irradiation or hypergravity enhancement)

[0042] This comparative example uses the same source and batch of pretreated quartz sand as Example 1. It only uses the industry-standard stirred tank atmospheric pressure acid leaching, does not include the laser focusing irradiation to break up inclusions, and does not use the high gravity rotating bed equipment. The remaining acid solution ratio, temperature, liquid-solid ratio, and post-treatment washing and drying conditions are consistent with those of Example 1. It is used to compare the purification effect of existing conventional processes.

[0043] 1) The raw material pretreatment process uses the same vein quartz ore as in Example 1. It is coarsely crushed, finely crushed, and screened using a double-layer vibrating screen to obtain 0.2–0.8 mm quartz sand. A 60 wt% slurry is prepared and scrubbed at high speed in a vertical scrubber for 20 minutes to remove surface clay and thin-film iron. It is then fed into a 1.2 T high-gradient magnetic separator to remove magnetic iron oxide minerals. After drying, pretreated quartz sand is obtained. Raw material testing indicators: SiO2 98.80%, Fe2O3 286 ppm, Al2O3 1650 ppm, TiO2 98 ppm, CaO 210 ppm, MgO 126 ppm. No laser focusing irradiation treatment is performed, and the feldspar and iron-titanium oxide inclusions within the quartz remain intact.

[0044] 2) Preparation of the ternary mixed acid leaching solution: Concentrated hydrochloric acid, concentrated sulfuric acid, and concentrated nitric acid are mixed in a volume ratio of 3:4:1.5, wherein the molar concentration of concentrated hydrochloric acid is 11.9 mol / L, concentrated sulfuric acid is 18.4 mol / L, and concentrated nitric acid is 14.5 mol / L. Water is added to dilute and adjust the total hydrogen ion concentration to 4 mol / L. The mixture is stirred for 30 min and then used for preparation. The acid solution formula is exactly the same as that in Example 1.

[0045] 3) Atmospheric Pressure Stirred Acid Leaching Reaction: 10 kg of pretreated quartz sand (without laser treatment) was added to an atmospheric pressure stirred reactor with a heating jacket. The prepared mixed acid solution was pumped in, and the liquid-to-solid volume ratio was strictly controlled at 5:1. Heat transfer oil was turned on to maintain the system reaction temperature at 90 ℃. A mechanical stirrer was used for continuous stirring at 300 r / min, and leaching was carried out at atmospheric pressure for 8 hours. Due to the lack of laser-pre-cracked inclusions, the acid solution could only contact the outer surface of the quartz particles and could not penetrate into the crystal to seal the inclusions, making it difficult to dissolve deep metallic impurities. Without enhanced mass transfer due to gravity, the solid-liquid interface renewal was slow, resulting in extremely poor leaching reaction kinetics.

[0046] 4) After the conventional solid-liquid separation and acid leaching are completed, heating and stirring are stopped, and the mixture is allowed to settle naturally for 30 minutes. Solid-liquid separation is then carried out using a plate and frame filter press. The separated waste acid is stored directly without any efficient recycling or regeneration equipment.

[0047] 5) The filter cake quartz sand from the countercurrent washing, dehydration, and drying process is fed into a three-stage countercurrent washing tower. It is washed in reverse with ultrapure water with a resistivity of 18.25 MΩ·cm for 8 minutes per stage until the pH of the effluent stabilizes at 6.5. After washing, the material is dehydrated by vacuum filtration, and the moisture content of the filter cake is about 10%. It is then spread out and sent into a hot air drying oven and dried at a constant temperature of 120 ℃ for 3 hours. After cooling, it is sieved to obtain purified quartz sand samples.

[0048] Finished product testing indicators: The purity of SiO2 is only 99.920%, and the total impurity content is 420 ppm; individual impurities are: Fe2O3 38.0 ppm, Al2O3 210.0 ppm, TiO2 42.0 ppm, CaO 76.0 ppm, and MgO 54.0 ppm.

[0049] Comparison of process defects: The leaching cycle is as long as 8 hours, resulting in extremely low production efficiency; a large number of deep inclusions cannot be removed, and the product purity does not meet the standards for high-purity quartz raw materials for photovoltaics and semiconductors; the acid consumption is 32% higher than that of the synergistic process of this invention under the same processing capacity, resulting in a large amount of waste acid and high environmental treatment costs. Comparative Example 2: High-gravity acid leaching process only (without laser focused irradiation pretreatment)

[0050] The raw materials, acid system, parameters of the hypergravity equipment, reaction temperature, leaching time, liquid-solid ratio, and subsequent washing and drying process of this comparative example are all consistent with those of Example 1. The only difference is that the laser focusing irradiation to break up the inclusions is omitted, and mass transfer is enhanced solely by the hypergravity field. This is used to verify the synergistic effect of laser pretreatment and hypergravity acid leaching.

[0051] 1) The raw material pretreatment process uses the same batch of pretreated quartz sand as in Example 1. The crushing, screening, scrubbing, and magnetic separation process parameters are exactly the same, resulting in 0.2-0.8 mm quartz sand with an initial purity of 98.80% SiO2 and a large number of complete and closed mineral inclusions inside. It is directly sent to the storage tank for use without laser focusing scanning irradiation or air-cooled thermal stress cracking process.

[0052] 2) The mixed acid leaching solution is prepared with hydrochloric acid, sulfuric acid and nitric acid in a volume ratio of 3:4:1.5, wherein the concentration of concentrated hydrochloric acid is 11.9 mol / L, concentrated sulfuric acid is 18.4 mol / L and concentrated nitric acid is 14.5 mol / L, and the total hydrogen ion concentration is 4 mol / L. The preparation process and stirring time are the same as in Example 1.

[0053] 3) Single-stage high-gravity acid leaching reaction: 10 kg of unmodified pretreated quartz sand was weighed and fed into a high-gravity rotating bed reactor with a heat-conducting oil insulation jacket. Mixed acid solution was pumped in, and the liquid-to-solid volume ratio was controlled at 5:1. The temperature was raised and stabilized at 90 ℃, and the motor speed was adjusted to 800 r / min, corresponding to a high-gravity factor of 150 g. The acid leaching was carried out continuously at a constant temperature for 30 min. Although the high-gravity field can tear the acid solution to form a thin liquid film and enhance mass transfer on the particle surface, the feldspar and titanium-iron oxide inclusions inside the quartz did not crack to form a permeation channel. The acid solution could not penetrate into the inclusions to dissolve the buried impurities and could only remove impurities attached to the surface of the quartz.

[0054] 4) After the in-situ solid-liquid separation and acid leaching by gravity is completed, the rotor is kept rotating at high speed for 5 minutes. The waste acid and quartz solid phase are separated by centrifugal force, and the waste acid is collected into the recycling tank. This step is exactly the same as in Example 1.

[0055] 5) The quartz sand solid phase, after being washed, dehydrated, dried, and sieved, was fed into a three-stage countercurrent ultrapure water washing tower. Each stage of washing lasted 8 minutes, and the final pH value was 6.5. After vacuum filtration and dehydration, the sample was dried with hot air at 120 °C for 3 hours and then cooled and sieved to obtain the sample.

[0056] Finished product testing indicators: The purity of SiO2 is 99.990%, with the following individual impurities: Fe2O3 4.2 ppm, Al2O3 32.0 ppm, TiO2 16.0 ppm, CaO 9.1 ppm, and MgO 6.7 ppm.

[0057] The process defects show that relying solely on hypergravity to enhance surface mass transfer cannot break deep-seated encapsulated impurity inclusions, resulting in poor removal of lattice-encapsulated impurities such as aluminum and titanium. The total impurity content is much higher than that of the synergistic process in Example 1, which can only meet the requirements of ordinary fused silica raw materials and cannot be adapted to high-purity silica high-end application scenarios such as semiconductor crucibles and optical fiber preforms. The purification limit under the same leaching time is significantly lower than that of the laser-hypergravity synergistic process, proving that the two processes cannot achieve synergistic effects when used alone.

[0058] Comparative Example 1: Traditional atmospheric pressure acid leaching has neither laser-assisted channel opening nor gravity-enhanced mass transfer, resulting in extremely long leaching time, extremely low impurity removal efficiency, and product purity that cannot meet the standards for high-purity quartz. Comparative Example 2 only uses supergravity-enhanced acid leaching and lacks the laser thermal stress fragmentation process, which can only remove impurities on the surface of particles. Deeply embedded metal minerals are difficult to dissolve, and there is a clear bottleneck in the purification depth. This invention utilizes laser focused irradiation to pre-stress and fracture internal mineral inclusions, opening up acid penetration channels. Coupled with a hypergravity field, this significantly enhances the solid-liquid mass transfer rate. The two processes work synergistically, achieving deep removal of all components (Fe, Al, Ti, Ca, Mg) in a short leaching time of only 30 minutes. SiO2 purity exceeds 99.995%, and total impurities are below 30 ppm. Simultaneously, it reduces acid consumption and shortens processing time, demonstrating significantly superior technical effects compared to existing single-process methods. This proves the invention's outstanding inventiveness and industrial application value.

[0059] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A method for purifying quartz sand by supergravity acid leaching, characterized in that, Includes the following steps: Quartz sand is added to a high-gravity rotating bed, the high-gravity factor is controlled to be no less than 50 g, the reaction temperature is 60-120℃, and mixed acid is introduced for leaching, the acid leaching time is 10-60 min. After acid leaching, separate the quartz sand and wash it with water until neutral; After drying, purified quartz sand is obtained.

2. The method according to claim 1, characterized in that, The molar ratio of the mixed acids is hydrochloric acid: sulfuric acid: nitric acid = (3-4):(4-6):(1.5-2), with H+ as the solvent. + The total concentration is calculated to be 3–5 mol / L.

3. The method according to claim 1, characterized in that, The supergravity factor is 50–300 g.

4. The method according to claim 1, characterized in that, The liquid-solid ratio of quartz sand to mixed acid is (3-8):

1.

5. The method according to claim 1, characterized in that, The particle size of the quartz sand is 0.2–0.8 mm.

6. The method according to claim 1, characterized in that, The washing water is ultrapure water with a resistivity ≥18.2 MΩ・cm.

7. The method according to claim 1, characterized in that, The purity of the quartz sand raw material is not less than 98%.

8. A method for the synergistic purification of quartz sand by laser focused irradiation coupled with high gravity acid leaching, characterized in that, Includes the following steps: Laser-modified quartz sand is obtained by irradiating quartz sand with a laser and using thermal stress to break up the metal mineral inclusions inside the quartz. The laser-modified quartz sand is further processed according to the method described in any one of claims 1 to 7 to obtain purified quartz sand.

9. The method according to claim 8, characterized in that, The laser single pulse energy is 50–200 mJ, and the spot diameter is 0.1–0.5 mm.

10. The method according to claim 9, characterized in that, The laser single pulse energy is 100–150 mJ, and the spot diameter is 0.2–0.3 mm.