A quartz deep purification method based on multi-stage crystal phase transition induced grain refinement

Abstract

The present application relates to mineral processing and non-metallic material purification technical field, especially to a kind of quartz deep purification method based on multi-stage crystal phase transition induced grain refinement.The technical scheme includes the following steps, raw material pretreatment and ball milling, after the acid pickling pretreatment of quartz raw material, wet ball milling treatment is carried out, and ultrafine quartz powder is obtained;Na2CO3 roasting and first crystal phase transition, the quartz powder obtained in step S1 is mixed with Na2CO3 evenly, and is roasted at high temperature, so that quartz is converted from alpha-quartz phase to cristobalite phase;Fluorine-free acid immersion, quartz sample after roasting in step S2 is heated and leached with mixed acid solution without hydrofluoric acid, to remove surface and near-surface impurities;Chlorination roasting and second crystal phase transition.The present application has significant advantages in environmental protection, impurity removal efficiency, product purity and economy, and provides a reliable technical path for green preparation of high-purity quartz material.

Description

Technical Field

[0001] This invention relates to the field of mineral processing and non-metallic material purification technology, and in particular to a method for deep purification of quartz based on multi-level crystal phase transformation-induced grain refinement. Background Technology

[0002] High-purity quartz (SiO2 purity ≥ 99.99%) is a core basic material for high-tech industries such as semiconductors, photovoltaics, optical fiber communication, and precision optics, and its market demand continues to rise with the development of high-end manufacturing. However, high-quality crystal resources that can be directly used in nature are becoming increasingly depleted. Purifying and preparing high-purity quartz from ordinary quartz ore or quartz sand with SiO2 purity of approximately 99% has become a research focus and industrial breakthrough direction in the global mineral processing field.

[0003] Impurities in quartz can be classified into three categories based on their form: gangue minerals, inclusion impurities, and lattice impurities. Gangue minerals (such as feldspar and mica) and most inclusion impurities (such as gaseous and liquid inclusions) can be effectively removed using conventional beneficiation methods such as magnetic separation and flotation, or by combining them with conventional acid leaching processes such as hydrochloric acid and nitric acid. However, lattice impurities (such as Al)... 3+ Fe 3+ Ti 4+ (etc.) because it replaces Si in an isomorphic form 4+ Once inside the quartz lattice, its solid solution properties make it difficult for physical sorting or conventional acid leaching to work, becoming a key bottleneck restricting the improvement of quartz purity. Particularly noteworthy is aluminum (Al), the most abundant metallic element in the Earth's crust, whose ionic radius (0.053 nm) is similar to that of Si. 4+ With a wavelength of 0.041 nm, it is extremely easy to embed into the quartz lattice in an isomorphic manner, making it the most difficult quartz impurity element to remove in current industrial production.

[0004] Currently, the mainstream technology for removing quartz lattice impurities in the industry still highly depends on hydrofluoric acid (HF). HF can expose and dissolve the impurities wrapped in the lattice by its strong corrosive destruction ability to the quartz SiO2 network structure, so it is often combined with calcination, water quenching, flotation and other processes to form a combined purification scheme of "calcination-water quenching-flotation-mixed acid leaching (containing HF)", and some processes can obtain quartz products with a purity of more than 99.997%. However, the strong corrosiveness and high toxicity of HF bring serious challenges to the production process: on the one hand, HF has very high requirements for equipment materials, which need to use special corrosion-resistant alloys or polytetrafluoroethylene materials, greatly increasing the equipment investment and maintenance cost; on the other hand, the treatment of fluorine-containing waste liquid generated during the use of HF is difficult and costly, and if not properly treated, it can cause environmental problems such as soil fluorine pollution and water fluorine exceeding standard, and there is also a safety risk of poisoning for operators, and the reaction rate of the process containing HF is slow, which significantly reduces the production efficiency of quartz purification, which is contrary to the current development direction of green chemical industry and low-carbon manufacturing.

[0005] To replace HF, researchers have carried out a lot of exploration around fluorine-free purification technology, among which the gas-phase chlorination roasting technology is widely studied for removing charge compensation ions (such as Li + , Na + , K + ) in quartz due to its good flowability, strong diffusivity and difficulty in introducing solid impurities. However, this technology has poor removal effect on Al impurities in the form of isomorphism, and the core reason is that it does not change the quartz crystal structure, and the lattice impurities lack an effective channel to migrate from the inside to the surface. Subsequent studies have found that the phase transition process of quartz is accompanied by crystal volume expansion and lattice reconstruction, which can break the stability of the original lattice and provide a potential path for impurity migration. As the most loose and open phase state among quartz variants, tridymite can provide the most space for impurity ions to escape in theory; and according to the quartz phase diagram and industrial practice, heating quartz to above 1500°C and holding for a sufficient time can realize the transition of low-temperature stable α-quartz phase to tridymite phase, and the distortion of crystal structure caused by the rupture of Si-O bonds and atomic rearrangement can further promote the escape of impurity atoms from the lattice.

[0006] However, the existing quartz purification technology based on phase transition still has many problems to be solved and is difficult to meet the needs of industrial-scale application:

[0007] The impurity removal efficiency is low, especially the poor Al removal effect: as disclosed in patent document CN102674377B, "Quartz crystal type conversion metal element gasification integrated purification method", although the transformation from a-quartz to cristobalite and the impurity gasification are realized in a mixed atmosphere of HCl and Cl2 at 1400-1700°C, the removal rate of the key impurity Al is only 4.0%-11.4%, which is far from meeting the stringent requirements of high-purity quartz on Al content (usually Al content ≤ 50 ppm).

[0008] The process temperature is too high, and the energy consumption and equipment cost are high: the above patent documents and another patent document CN115367763B ("High-temperature cyclic treatment and preparation process of high-purity quartz sand") all have the problem of high-temperature dependence. The former requires a gasification reaction temperature of 1400°C or higher, and the latter realizes the phase transition of β-quartz and cristobalite through multiple high-temperature cycles of 600-950°C and 1000-1500°C, but the subsequent chlorination treatment still requires an ultra-high temperature of 1400-1650°C. The maximum tolerance temperature of the conventional industrial chlorination equipment is only 1200°C, and the requirement of ultra-high temperature not only leads to a sharp increase in energy consumption, but also requires the customization of special ultra-high temperature corrosion-resistant equipment, significantly increasing the production cost, and the damage of corrosive gas to the equipment is intensified at high temperature, shortening the service life of the equipment.

[0009] The process design is unreasonable, and the impurities are easily re-embedded in the lattice: the phase transition process of patent document CN115367763B is completed in air, and lacks an immediate impurity removal mechanism. The Al and other impurities released from the lattice during the phase transition cannot quickly diffuse to the surface and be removed, and are easily re-embedded in the lattice when the sample cools back to the a-quartz phase, resulting in the need for subsequent ultra-high temperature chlorination to partially remove them, further increasing the process complexity and cost.

[0010] In summary, the existing quartz purification technology either relies on highly toxic HF or has defects such as low removal efficiency of lattice impurities (especially Al), high process temperature, and high equipment cost, making it difficult to balance environmental protection, high efficiency, and industrial feasibility. Therefore, developing a new type of quartz deep purification technology that does not require the use of HF, can efficiently remove lattice Al impurities, and has a process temperature suitable for industrial equipment has important industrial application value and environmental protection significance, and is also a key technical bottleneck that needs to be broken through in the current high-purity quartz material preparation field. SUMMARY

[0011] The purpose of the present application is to address the defects of the existing quartz purification technology in the background art, such as relying on highly toxic HF, or having low removal efficiency of lattice impurities (especially Al), high process temperature, and high equipment cost, and to propose a quartz deep purification method based on multi-stage crystal phase transition induced grain refinement.

[0012] The technical scheme of the present application is a quartz deep purification method based on multi-stage crystal phase transition induced grain refinement, comprising the following steps:

[0013] S1. Raw material pretreatment and ball milling, after acid pickling pretreatment of the quartz raw material, wet ball milling treatment is carried out to obtain ultrafine quartz powder;

[0014] S2. Na2CO3 roasting and first crystal phase transition, the quartz powder obtained in step S1 is mixed with Na2CO3 uniformly, and roasting is carried out at high temperature to make the quartz transform from α-quartz phase to cristobalite phase;

[0015] S3. Fluorine-free acid immersion, the quartz sample after roasting in step S2 is heated and leached with a mixed acid solution not containing hydrofluoric acid to remove surface and near-surface impurities;

[0016] S4. Chlorination roasting and second crystal phase transition, the quartz sample after acid immersion in step S3 is high-temperature roasted in an HCl atmosphere to make the quartz transform from cristobalite phase back to α-quartz phase and deeply remove residual lattice impurities;

[0017] Among them, steps S2 and S4 jointly constitute a multi-stage crystal phase transition process, which promotes impurity migration and removal through crystal phase transition induced grain refinement and lattice defect generation.

[0018] Optionally, the parameters of the ball milling in step S1 are: zirconia balls are used as grinding medium, the slurry concentration is 50%-70%, the ball milling speed is 500-700 rpm, and the ball milling time is 1-5 hr.

[0019] Optionally, the preferred parameters of the ball milling in step S1 are: the slurry concentration is 60%, the ball milling speed is 600 rpm, and the ball milling time is 2 hr.

[0020] Optionally, the addition amount of Na2CO3 in step S2 is 0.5%-2% of the mass of the quartz powder; the roasting temperature is 900-1200°C, and the time is 5-25 hr.

[0021] Optionally, the addition amount of Na2CO3 in step S2 is 1%, the roasting temperature is 1100°C, and the roasting time is 15 hr.

[0022] Optionally, the fluorine-free mixed acid in step S3 is a mixed solution of HCl and HNO3, wherein the HCl concentration is 4-6 mol / L and the HNO3 concentration is 3-5 mol / L; the liquid-solid ratio of the acid immersion is 4:1-6:1 mL / g, the temperature is 80-100°C, and the time is 4-8 hr.

[0023] Optionally, the mixed acid in step S3 is a mixed solution of 5 mol / L HCl and 4 mol / L HNO3, the liquid-solid ratio is 5:1, the temperature is 90°C, and the time is 6 hours.

[0024] Optionally, the chlorination roasting in step S4 is performed at a temperature of 500-1200°C for 1-6 hours, and the HCl gas flow rate is 100-200 mL / min.

[0025] Optionally, the preferred parameters of the chlorination roasting in step S4 are a temperature of 1200°C, a time of 4 hours, and an HCl gas flow rate of 150 mL / min.

[0026] Optionally, the SiO2 purity of the quartz raw material in step S1 is not less than 99%.

[0027] Compared with the prior art, the present application has at least one of the following beneficial technical effects:

[0028] The use of highly toxic and strongly corrosive hydrofluoric acid (HF) is completely avoided, the entire process flow is fluorinated, the environmental risk, equipment corrosion and safety hazards are significantly reduced, and the green chemical requirements are met.

[0029] Through the synergistic strategy of high-energy ball milling and two times of crystal phase transformation, grain refinement and defect generation are induced, and impurity migration channels are constructed. The aluminum removal rate is more than 90%, and the total impurity removal rate reaches 98%, which is better than the traditional fluorine-free acid immersion and fluorine-containing acid immersion process.

[0030] The purity of quartz can be increased from 99.7% to more than 99.994%, the total impurity content is less than 60 ppm, and the material requirements of high-purity quartz for high-end fields such as semiconductors and photovoltaics are met.

[0031] It is suitable for various quartz raw materials, including ordinary quartz ore, the chlorination temperature is significantly reduced (≤1200°C) compared with the prior art, no super-high temperature equipment is needed, the energy consumption and cost are controllable, and it has industrial application potential.

[0032] In summary, the present application has significant advantages in environmental protection, impurity removal efficiency, product purity and economy, and provides a reliable technical path for the green preparation of high-purity quartz materials. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a specific embodiment of the present application. The specific embodiment of the present application is a specific embodiment of the present application.

[0034] Figure 2 is an XRD pattern of a quartz sample after different process treatments in the embodiment of the present application. DETAILED DESCRIPTION

[0035] Following, the embodiments of the present application will be described in detail by specific examples. Other advantages and effects of the present application can be easily understood by those skilled in the art from this disclosure. The present application can also be implemented or applied by other different embodiments, and the details in this specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict.

[0036] Example 1:

[0037] Step 1: Take a quartz raw material from East China, the main chemical components are shown in Table 1 (quartz powder raw material), the purity of SiO2 is 99.704%. First, use 5wt.% HCl solution to stir and clean at room temperature for 24 hours to remove acid-soluble impurities and surface contaminants. After drying, the cleaned quartz powder is ball milled by a planetary ball mill. The mill pot is made of agate, and the grinding medium is 300g of zirconia balls. Each time 20g of quartz powder is put in, and ultrapure water is used as a grinding aid. The optimal ball milling parameters are determined by optimization experiments: slurry concentration 60%, ball milling speed 600 rpm, ball milling time 2 hr. The key data of particle size distribution of the quartz powder after ball milling are shown in Table 1, D50 decreases from 33.42 μm to 1.185 μm, and the specific surface area increases from 0.0862 m 2 / g to 12.3584 m 2 / g (see Figure 1 ).

[0038] Table 1 Key particle size data of quartz powder before and after ball milling

[0039] Sample D10 (pm) D50 (pm) D90 (pm) Quartz powder 16.54 33.42 62.79 After ball milling 0.308 1.185 7.41

[0040] Step 2: Take 20g of the ball-milled quartz powder and place it in a high-purity quartz crucible with a lid. Add 0.2g (1% of the mass of the quartz powder) of Na2CO3 (super-purity grade) and mix evenly by mechanical stirring. Place the sample in a muffle furnace and calcine at 1100°C for 15 hours. After natural cooling, take it out. Through XRD analysis (XRD analysis) Figure 2 ), it is confirmed that most of the α-quartz phase has been converted to cristobalite phase.

[0041] Step 3: Take 10g of the calcined quartz sample treated in Step 2 and place it in a fluorinated ethylene propylene (FEP) beaker. Add 50mL of a fluoride-free mixed acid solution composed of 5mol / L HCl and 4mol / L HNO3, with a liquid-to-solid ratio of 5:1. Place the beaker in a 90°C constant-temperature water bath and stir for 6 hours. After the reaction is complete, wash the quartz sample repeatedly with ultrapure water until it is neutral, and then dry it for use. The impurity content of the quartz powder after this stage is shown in Table 3 (the row labeled "ball milling + Na2CO3 calcination + fluoride-free acid leaching").

[0042] Step 4: Weigh 5g of the quartz sample treated in Step 3 and evenly spread it in a quartz boat, placing it in the middle of a tube furnace. Connect the HCl gas generation and purification system: Add 250mL of concentrated H2SO4 to a round-bottom flask and 250mL of concentrated HCl to a separatory funnel. By controlling the drip rate of the separatory funnel, generate HCl gas at a flow rate of 150mL / min. The generated HCl gas is first dehydrated and dried by passing it through a concentrated H2SO4 washing bottle, and then introduced into the tube furnace. The tail gas is absorbed with saturated NaOH solution. All system sealing interfaces are coated with high-vacuum silicone grease to ensure airtightness. Heat the tube furnace to 1200°C at a rate of 5°C / min, and react with dried HCl gas at this temperature for 4 hours. After the reaction is complete, stop heating, continue to purge residual HCl gas with high-purity argon gas, and remove the sample after cooling to room temperature. Analyze by XRD (…). Figure 2 It was confirmed that most of the cristobalite phase reverted to the α-quartz phase.

[0043] Table 2 shows the internal grain size of quartz powder calculated using XRD (101) diffraction peaks.

[0044] Table 2. Internal grain size of quartz powder under different treatment conditions (XRD).

[0045] Treatment condition Grain size nm Crystal phase Quartz powder 78.9 a-quartz After ball milling 50.8 a-quartz Na2CO3 after calcination 43.5 cristobalite After chlorination roasting 38.2 a-quartz cristobalite

[0046] The purified quartz powder obtained was analyzed by ICP-OES, and the results are shown in the last row of Table 3. The Al content decreased from the initial 327.8 ppm to 31.1 ppm, with an Al removal rate of 90.5%; the total impurity content decreased from 2955.8 ppm to 58.3 ppm, with a total impurity removal rate of 98.0%; and the SiO2 purity increased from 99.704% to 99.994%.

[0047] Example 2:

[0048] Step 1: Take a quartz raw material from East China. First, wash it with a 5wt.% HCl solution at room temperature for 24 hours to remove acid-soluble impurities and surface contaminants. After drying, the washed quartz powder is ball-milled using a planetary ball mill. The mill jar is made of agate, the grinding media is 300g of zirconia balls, 20g of quartz powder is added each time, and ultrapure water is used as the grinding aid. The optimal ball milling parameters were determined through optimization experiments: slurry concentration 60%, milling speed 600rpm, and milling time 2 hours.

[0049] Step 2: Take 10 g of the quartz powder sample obtained in Step 1 and place it in a FEP beaker. Add 50 mL of a fluoride-free mixed acid solution composed of 5 mol / L HC1 and 4 mol / L HNO3, with a liquid-to-solid ratio of 5:1. Place the beaker in a 90°C constant-temperature water bath and stir for 6 hours. After the reaction is complete, wash the sample repeatedly with ultrapure water until it is neutral, and then dry it for use. The analysis results of the sample after treatment are shown in Table 3 (the row labeled “ball milling + fluoride-free acid leaching”), with an Al removal rate of 78.2%, a total impurity removal rate of 94.5%, and a SiO2 purity of 99.983%.

[0050] Example 3:

[0051] Step 1: Take a certain quartz raw material from East China, first stir and clean it with a 5wt.% HC1 solution at room temperature for 24 hours to remove acid-soluble impurities and surface contaminants. After drying, the cleaned quartz powder is ball milled using a planetary ball mill. The ball mill tank is made of agate, and the grinding medium is 300 g of zirconia balls. Each time, 20 g of quartz powder is added, and ultrapure water is used as a grinding aid. The optimal ball milling parameters are determined through optimization experiments: slurry concentration 60%, ball milling speed 600 rpm, and ball milling time 2 hours.

[0052] Step 2: Take 10 g of the ball-milled quartz powder sample obtained in Step 1 and place it in a FEP beaker. Add 50 mL of a mixed acid solution composed of 5 mol / L HC1, 4 mol / L HNO3, and 0.5 mol / L HF, with a liquid-to-solid ratio of 5:1. Place the beaker in a 90°C constant-temperature water bath and stir for 6 hours. After the reaction is complete, wash the sample repeatedly with ultrapure water until it is neutral, and then dry it for use. The analysis results of the sample after treatment are shown in Table 3 (the row labeled “ball milling + fluoride-containing acid leaching”), with an Al removal rate of 84.0%, a total impurity removal rate of 96.4%, and a SiO2 purity of 99.989%.

[0053] Example 4:

[0054] Step 1: Take a certain quartz raw material from East China, first stir and clean it with a 5wt.% HC1 solution at room temperature for 24 hours to remove acid-soluble impurities and surface contaminants. After drying, the cleaned quartz powder is ball milled using a planetary ball mill. The ball mill tank is made of agate, and the grinding medium is 300 g of zirconia balls. Each time, 20 g of quartz powder is added, and ultrapure water is used as a grinding aid. The optimal ball milling parameters are determined through optimization experiments: slurry concentration 60%, ball milling speed 600 rpm, and ball milling time 2 hours.

[0055] Step 2: Take 10 g of the quartz powder sample obtained in Step 1 and place it in a FEP beaker. Add 50 mL of a fluoride-free mixed acid solution composed of 5 mol / L HCl and 4 mol / L HNO3, with a liquid-to-solid ratio of 5:1. Place the beaker in a 90°C constant-temperature water bath and stir for 6 hours. After the reaction is complete, wash the sample repeatedly with ultrapure water until it is neutral, and then dry it for use.

[0056] Step 3: Take 5 g of the quartz sample treated in Step 2 and evenly spread it in a quartz boat in the middle of a tube furnace. Connect the HCl gas generation and purification system: add 250 mL of concentrated H2SO4 to a round-bottom flask and 250 mL of concentrated HCl to a separatory funnel. Control the drop rate of the separatory funnel to generate HCl gas at a flow rate of 150 mL / min. The generated HCl gas is first passed through a concentrated H2SO4 gas washing bottle to remove water and dry, and then introduced into the tube furnace. The tail gas is absorbed with saturated NaOH solution. All system sealing interfaces are coated with high-vacuum silicone grease to ensure airtightness. Heat the tube furnace to 1200°C at a rate of 5°C / min, and introduce HCl gas at this temperature for 4 hours. After the reaction is complete, stop heating and continue to introduce high-purity argon to sweep away residual HCl gas. After cooling to room temperature, remove the sample. The analysis results of the treated sample are shown in Table 3 (one row of ball milling, fluoride-free acid leaching, and chlorination roasting). The Al removal rate is 85.3%, the total impurity removal rate is 96.8%, and the SiO2 purity is 99.990%. The effect is better than that of Examples 2 and 3, but significantly lower than that of the complete process of the present application (90.5%), which proves that the first crystal phase transformation induced by Na2CO3 roasting is crucial for deep impurity removal.

[0057] Table 3 Effect of different processes on impurity content (ppm) of quartz samples

[0058]

[0059] Effect analysis of the examples

[0060] As can be seen from the comparison between Example 1 and Examples 2-4, the complete process of high-energy ball milling, Na2CO3 roasting, fluoride-free acid leaching, and chlorination roasting provided by the present application achieves optimal removal of quartz impurities, especially lattice Al impurities, without using HF at all. The grain refinement and defect generation induced by the two crystal phase transformation processes of Na2CO3 roasting and chlorination roasting are the key to significantly improving the impurity removal efficiency.

[0061] The method of the present application completely avoids the use of hydrofluoric acid (HF) in the whole purification process. As a key reagent for removing lattice impurities in traditional quartz purification, HF has strong corrosiveness and toxicity, which not only requires high equipment material quality and is easy to cause equipment corrosion damage, but also produces fluoride pollution in the use and waste liquid treatment process, threatening the ecological environment, and there is a safety risk of poisoning for the operators. The present application completely abandons the use of HF through the innovative process design of multi-stage crystal phase transformation and fluoride-free acid immersion, completely eliminates the above safety and environmental risks from the source, conforms to the current green chemical industry and low-carbon manufacturing industry development direction, and reduces the environmental protection treatment cost and production safety management difficulty.

[0062] Through the synergistic effect of the first crystal phase transformation (alpha-quartz→cristobalite) induced by high-energy ball milling and Na2CO3 roasting and the second crystal phase transformation (cristobalite→alpha-quartz) induced by chlorination roasting, the two crystal phase transformation processes will continuously induce quartz grain refinement (the final grain size is reduced from the initial 78.9 nm to 38.2 nm) and produce a large number of lattice defects (such as vacancies, dislocations, grain boundaries, and phase boundaries). These defects provide a fast channel for the internal migration of lattice impurities (especially Al impurities which are the most difficult to remove) to the surface, and the HCl atmosphere in the chlorination roasting stage can react with the impurities migrated to the surface to generate volatile chlorides, achieving deep removal. The final Al impurity removal rate is as high as 90.5%, and the total impurity removal rate is 98%, which is much higher than that of the traditional fluoride-free acid immersion process (Al removal rate 78.2%) and the HF-containing acid immersion process (Al removal rate 84.0%). Unlike existing technologies that perform phase transformation and chlorination treatment in stages, the second crystal phase transformation (cristobalite→alpha-quartz) and chlorination impurity removal in the present application are performed simultaneously. During the phase transformation process, Al and other impurities released from the lattice can immediately diffuse to the particle surface through the defect channel and be quickly removed by the HCl atmosphere, avoiding the problem of impurities re-embedding into the quartz lattice during the cooling process, and further ensuring the stability of the impurity removal effect.

[0063] Among them, the method of the present application can stably purify the quartz raw material with an initial SiO2 purity of not less than 99% to a level of SiO2 purity ≥99.99% (reaching 4N level), and the total impurity content is reduced to below 100 ppm. High-purity quartz is the core basic material of high-tech industries such as semiconductors, photovoltaics, optical fiber communication, and precision optics, and these fields have strict requirements for quartz purity (usually ≥99.99%). The high-purity quartz powder prepared by the present application fully meets the use standards of the above high-end fields, providing reliable technical support for the preparation of high-performance quartz materials, and breaking the limitation of high-quality crystal resources exhaustion on the supply of high-end quartz materials.

[0064] The purification method is suitable for high-quality quartz crystal raw materials, and also has excellent purification effect for ordinary quartz ore or quartz sand with SiO2 purity close to 99% as alternative raw materials. The traditional high-purity quartz preparation technology has high requirements for the purity of raw materials, which limits the range of available resources. The universality of the present application provides the possibility for the expansion of high-purity quartz raw materials, reduces the dependence on scarce high-quality crystal resources, helps to alleviate the situation of tight supply of high-purity quartz raw materials, and improves the industrial resource guarantee capability. Some existing quartz purification technologies based on crystal phase transition, such as 1400-1700°C ultra-high temperature chlorination process, need to customize special ultra-high temperature corrosion-resistant equipment, which has high equipment investment and maintenance cost. In the present application, the chlorination roasting temperature is controlled at 1200°C, which is compatible with the highest tolerance temperature (1200°C) of conventional industrial chlorination equipment, without the need for additional modification or customization of equipment, reducing the equipment investment cost and subsequent maintenance difficulty. Compared with the existing technology which needs 2-50 times of high-temperature cycle treatment, the present application can realize efficient impurity removal through only two times of crystal phase transition, simplifying the process flow, reducing the energy loss caused by repeated heating and cooling, and reducing the labor and material investment, further controlling the total production cost.

[0065] In summary, the quartz deep purification method based on multi-stage crystal phase transition induced grain refinement has multiple advantages such as green and environmental protection, efficient impurity removal, high product purity, strong raw material adaptability, low cost and energy consumption, etc. It not only solves the safety and environmental protection problem of HF use in traditional quartz purification and the core pain point of difficult removal of lattice impurities (especially Al), but also can stably produce high-purity quartz products meeting the needs of high-end fields, and the process is compatible with existing industrial equipment and raw material conditions, has strong industrial application value and promotion prospect, and provides an important solution for the technical breakthrough in the field of high-purity quartz material preparation.

[0066] The above specific embodiments are only several optional embodiments of the present application, and based on the technical solutions of the present application and the related inspiration of the above embodiments, those skilled in the art can make various alternative improvements and combinations on the above specific embodiments.

Claims

1. A method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement, characterized in that, The method comprises the following steps: S1. Raw material pretreatment and ball milling, the quartz raw material is pretreated by acid washing and then treated by wet ball milling to obtain superfine quartz powder; S2. Na2CO3 roasting and first crystal phase transformation, the quartz powder obtained in step S1 is mixed with Na2CO3 uniformly and then roasted at high temperature to transform the quartz from α-quartz phase to cristobalite phase, the addition amount of Na2CO3 is 0.5%-2% of the mass of the quartz powder, the roasting temperature is 900-1200°C, and the time is 5-25 hr; S3. Fluorine-free acid immersion, the quartz sample after roasting in step S2 is immersed in a mixed acid solution without hydrofluoric acid to remove surface and near-surface impurities, the fluorine-free mixed acid is a mixed solution of HCl and HNO3, the liquid-solid ratio of the acid immersion is 4:1-6:1 mL / g, the temperature is 80-100°C, and the time is 4-8 hr; S4. Chlorination roasting and second crystal phase transformation, the quartz sample after acid immersion in step S3 is roasted at high temperature in an HCl atmosphere to transform the quartz from cristobalite phase back to α-quartz phase and deeply remove residual lattice impurities, the chlorination roasting temperature is 500-1200°C, and the time is 1-6 hr; In the method, steps S2 and S4 jointly constitute a multi-stage crystal phase transformation process, the crystal phase transformation induces grain refinement and lattice defect generation, and promotes impurity migration and removal.

2. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 1, characterized in that, In step S1, the ball milling parameters are as follows: zirconia balls are used as grinding medium, the slurry concentration is 50%-70%, the ball milling speed is 500-700 rpm, and the ball milling time is 1-5 hr.

3. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 2, characterized in that, In step S1, the ball milling parameters are as follows: the slurry concentration is 60%, the ball milling speed is 600 rpm, and the ball milling time is 2 hr.

4. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 3, characterized in that, In step S2, the addition amount of Na2CO3 is 1%, the roasting temperature is 1100°C, and the roasting time is 15 hr.

5. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 1, characterized in that, In step S3, the HCl concentration is 4-6 mol / L, and the HNO3 concentration is 3-5 mol / L.

6. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 5, characterized in that, In step S3, the mixed acid is a mixed solution of 5 mol / L HCl and 4 mol / L HNO3, the liquid-solid ratio is 5:1 mL / g, the temperature is 90°C, and the time is 6 hr.

7. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 1, characterized in that, In step S4, the HCl gas flow is 100-200 mL / min.

8. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 7, characterized in that, In step S4, the chlorination roasting parameters are as follows: the temperature is 1200°C, the time is 4 hr, and the HCl gas flow is 150 mL / min.

9. The method for deep purification of quartz based on multi-stage crystalline phase transition induced grain refinement according to claim 1, characterized in that, In step S1, the SiO2 purity of the quartz raw material is not less than 99%.

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