Method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder

Abstract

The present invention discloses a method for preparing high-purity quartz sand for photovoltaic crucibles from fine quartz powder. The method comprises the following steps: using fine quartz powder as a raw material, sequentially undergoing acid leaching and chlorination roasting to purify the material to a purity of 4N8 or higher; then mixing the material with a high-purity silicon-based organic solvent; vacuum extrusion molding; and drying the material to obtain high-purity quartz sand. This method is based on the production process of high-purity quartz and the granulation properties of fine quartz powder, combined with a fine powder cold pressing process. This method produces high-purity quartz sand for photovoltaic crucibles with uniform particle size without destroying the quartz crystal structure. Furthermore, the method has a simple process flow, is easy to operate, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to a method for producing high-purity quartz sand for crucibles by using quartz fine powder produced in a high-purity quartz production process as raw material, and belongs to the field of comprehensive utilization of mineral resources and processing of high-purity mineral materials. Background Art

[0002] High-purity quartz is widely used in photovoltaics, semiconductors, fiber optic communications, electro-optical sources and other fields. It is a key basic material for strategic emerging industries such as the new generation of information industry, new energy, high-end equipment, and new materials.

[0003] Quartz sand is produced from natural ore through a series of processes, including crushing, grinding, screening, sorting, and purification. Currently, vein quartz and pegmatite are the primary raw materials for high-purity quartz sand. The crushing and grinding process inevitably produces fines, which are unsuitable for use in high-purity quartz sand production. Currently, the fines produced during high-purity quartz production are mostly sold cheaply as a byproduct.

[0004] Because the mineral raw materials used to produce high-purity quartz sand are scarce and highly valuable, selling the fine powder produced during the production process at a low price not only impacts the company's economic profitability but also wastes a non-renewable, high-value resource. Producing high-purity quartz sand from high-purity fine powder can not only improve the company's economic performance but also achieve efficient and high-value utilization of mineral resources. However, related technologies are rarely reported. Therefore, the development of technologies for producing high-purity quartz sand from high-purity fine powder is urgently needed. Summary of the Invention

[0005] In response to the problems existing in the existing production process of high-purity quartz sand from quartz fine powder, the purpose of the present invention is to provide a method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder. The method is based on the high-purity quartz production process and the granulation properties of quartz fine powder, combined with the fine powder cold pressing process, to obtain quartz sand for photovoltaic crucibles with uniform particle size and high purity without destroying the quartz crystal structure.

[0006] In order to achieve the above technical objectives, the present invention provides a method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder. The method uses quartz fine powder as raw material, sequentially undergoes acid leaching and chlorination roasting to purify it to a purity of 4N8 or above, then mixes it with a high-purity silicon-based organic solvent and performs vacuum extrusion molding. After drying, high-purity quartz sand is obtained; the SiO2 mass content in the quartz fine powder is ≥99.5%, and the particle size is <150 mesh.

[0007] In the technical solution of the present invention, deep purification of quartz powder is a prerequisite, and cold pressing and forming of lumps is the key. The raw material quartz powder of the present invention is a fine-grained product of the high-purity quartz production process. Its purity is relatively high, but it still does not meet the purity requirements of quartz sand for photovoltaic crucibles, and the impurity elements therein need to be further removed. The present invention first removes impurities remaining in the grain boundaries and microcracks of the quartz fine powder by acid leaching. Increasing the acid concentration or acid dosage helps dissolve the impurities, but due to the fine particle size of the quartz powder of the present invention, the acid leaching process inevitably causes quartz dissolution, especially when the solution contains hydrofluoric acid. Therefore, it is necessary to efficiently regulate the acid leaching process. The lattice impurities in the quartz fine powder are then further removed by chlorination roasting. The finer particle size of the quartz powder of the present invention helps the full reaction and volatilization removal of impurity elements and chlorinating agents, but the quartz powder and the air flow are in a countercurrent state during the roasting process, and the movement characteristics of the fine-grained powder are difficult to regulate.

[0008] The key to using quartz sand for photovoltaic crucibles is to further shape the quartz powder into the required particle size after purification. Powder molding methods include sintering and pressing. The temperature of the sintering process in the prior art is relatively high, which will cause changes in the quartz crystal structure and affect subsequent use, while the pressing molding process generally requires the use of a binder, which inevitably introduces impurities and affects the purity of the quartz. In addition, quartz sand for photovoltaic crucibles requires dense particles to avoid the introduction of bubbles during the crucible production process, which affects the quality of the crucible. Therefore, it is necessary to ensure that the quartz fine powder is densely and efficiently molded in a non-high temperature state. The present invention uses a high-purity silicone solvent to infiltrate the surface of the particles to promote adhesion between the particles, while not causing impurity components and being easy to dry and remove. In addition, the particle size and density of the quartz sand can be guaranteed by vacuum extrusion molding.

[0009] The inventors found that if chlorination roasting is performed first and then acid leaching is used to remove impurities, repeated deacidification and drying are required in the subsequent process, which not only makes the process steps cumbersome and increases costs, but also may cause the product yield to decrease during the repeated deacidification process.

[0010] As a preferred solution, SiO2 mass content ≥99.5% in the quartz fine powder, and particle size <150 mesh. The impurity content of the quartz fine powder particles and the internal residues used in the present invention is too high, and subsequent acid leaching and chlorination need to increase acid concentration, consumption and extend the acid leaching time, as well as increase the chlorinating agent flow, increase the chlorination roasting temperature, etc., which not only causes the chemical medium and energy consumption to increase, but also causes the problems of increased acid-soluble loss of quartz sand and reduced production efficiency. Meanwhile, the particle size of the quartz fine powder used in the present invention is relatively small, and it is difficult to directly utilize it in the prior art, and its particle size must be regulated by the cold-pressed agglomerate forming process of the present invention.

[0011] As a preferred embodiment, the high-purity silicon-based organic solvent is at least one of tetrachlorosilane, trichlorosilane, and vinyl silicone oil, with a purity of ≥99.999%. The high-purity silicon-based organic solvent employed in the present invention can infiltrate the surface of the fine quartz powder particles at low temperatures without destroying the quartz sand's crystal structure, promoting adhesion between the quartz particles. It also maintains the purity of the quartz sand without introducing impurities and is easily removed by drying.

[0012] As a preferred solution, the amount of high-purity silicon-based organic solvent used is 3.5-8% of the mass of the quartz powder. The amount of high-purity silicon-based organic solvent used has a significant impact on the fine powder's shape. A large amount facilitates fine powder formation, but when the dried and prepared quartz sand is used in crucible production, volatilization of organic matter can cause bubbles, affecting the quality of the quartz crucible. On the other hand, too little solvent can fail to form sufficient bonding between the quartz powders, making the subsequent vacuum extrusion molding process impossible or the resulting quartz sand grain size unsatisfactory for crucible production.

[0013] As a preferred embodiment, the chlorination roasting temperature is 900-1150°C, the time is 5-30 minutes, and the HCl roasting atmosphere is 2-15 ml / min of gas flow rate. Chlorination roasting is the key to deep impurity removal of fine quartz powder, and the impurity removal effect is affected by factors such as temperature, chlorinating agent dosage, and time. Increasing the temperature and increasing the chlorinating agent dosage are both beneficial to the removal of impurity elements, but at the same time, it will lead to high energy consumption and heavy pollution during the roasting process. Conversely, it is not conducive to the chlorination removal of impurities. In addition, the fine particle size of fine quartz powder can cause it to be entrained into the exhaust gas by the airflow due to a large gas flow rate, resulting in the loss of quartz resources. A small gas flow rate cannot meet the impurity removal requirements. A roasting time that is too long can easily lead to powder consolidation, affecting subsequent molding. A roasting time that is too short can lead to incomplete impurity removal and substandard purity. A further preferred gas flow rate is 5-15 ml / min.

[0014] As a preferred embodiment, the extrusion pressure during vacuum extrusion molding is 0.8-3.2 MPa, and the vacuum level is 5,000-50,000 Pa. Quartz sand compaction is one factor that affects crucible quality. Poor quartz sand compaction and high porosity lead to numerous bubbles in the crucible, significantly reducing the crucible's service life. Therefore, the apparent porosity of quartz sand is generally less than 0.2%. Extrusion pressure and vacuum level are key parameters for forming fine quartz powder. Moderately increasing the pressure helps the fine powder particles agglomerate and compact, but excessively high pressure can cause the fine powder to pulverize during the molding process, placing high demands on equipment and production energy. Conversely, low pressure can lead to weak bonding between particles, causing breakage during subsequent drying or transportation, making them unsuitable for subsequent production use. Maintaining a low pressure during the extrusion process allows gas between particles to be extracted, helping to strengthen the compactness between particles and reducing the adverse effects on the porosity of the quartz crucible during use. However, excessively high vacuum levels not only place high demands on the equipment but can also cause fine powder or silicone solvent to be extracted during the molding process, affecting particle formation.

[0015] As a preferred embodiment, the acid leaching process uses at least one of hydrofluoric acid, nitric acid, sulfuric acid, and oxalic acid as the leaching medium; the volume fraction of the acid in the leaching medium is 5-30%. During the acid leaching process, the mass ratio of fine quartz powder to leaching medium is (0.5-1):1, the acid leaching temperature is 20-80°C, and the acid leaching time is 2-9 hours. Acid leaching is an important method for removing surface and interstitial impurities and has a significant impact on product quality. The reaction process primarily involves acid diffusion on the particle surface and within the particle, dissolution of impurity components, and diffusion and migration of dissolved ions. High acid concentrations or large amounts help remove impurities, but they can cause dissolution of fine particles and reduce yield. Conversely, low acid concentrations hinder the removal of impurities, affecting product quality. Appropriately increasing the temperature during the acid leaching process can accelerate dissolution and diffusion, promote impurity removal, and shorten the reaction time. However, excessively high temperatures can cause quartz dissolution. Furthermore, high-temperature acid leaching requires high equipment requirements and increases production costs.

[0016] As a preferred solution, the drying conditions are: temperature of 90-135°C and time of 30-100 minutes. Vacuum extrusion products contain moisture and organic matter, which are easily deformed or crushed during storage or transportation. Drying can remove excess moisture or organic matter, thereby improving the mechanical properties of the extrudate. The drying process is affected by temperature and actual conditions. High temperature helps the volatilization of moisture and organic matter, but if the temperature is too high, the uneven heating of the moisture in the inner and outer layers of the extrudate can easily cause cracking. Low temperature helps to slowly remove moisture or organic matter, but it results in long drying times and low production efficiency.

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0018] 1) The technical solution of the present invention realizes the efficient and high-value utilization of fine-grained quartz powder, and at the same time broadens the source of high-purity quartz sand raw materials for crucibles.

[0019] 2) The present invention is based on the high-purity quartz production process and the granulation performance of quartz fine powder, combined with the fine powder cold pressing process, to obtain quartz sand for photovoltaic crucibles with uniform particle size and high purity without destroying the quartz crystal structure.

[0020] 3) The process of the present invention is simple, easy to operate, and suitable for large-scale industrial production.

[0021] 4) The present invention adopts a purification method of first acid leaching and then chlorination roasting to quartz fine powder, which can first remove impurities in the grain boundaries and microcracks of the quartz fine powder, and then remove lattice impurities in the quartz fine powder, thereby significantly improving the purity of the quartz fine powder; at the same time, a high-purity silicon-based organic solvent is introduced to infiltrate the surface of the quartz fine powder particles under low temperature conditions without destroying the crystal structure of the quartz sand, thereby promoting the adhesion between the quartz particles. The particle size of the prepared quartz sand is controlled by a subsequent cold pressing and forming process, and the density between the particles is enhanced, making it more suitable for use in photovoltaic crucibles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the microstructure of the product in Example 1.

[0023] Figure 2 The microstructure of the product of Comparative Example 1 is shown. DETAILED DESCRIPTION

[0024] In order to facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed manner below in conjunction with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0026] Unless otherwise specified, all reagents and raw materials used in the present invention are commercially available products or products that can be prepared by known methods.

[0027] Comparative Example 1

[0028] Compared with Example 1, the only difference is that no tetrachlorosilane is added during extrusion molding.

[0029] The final product has a particle size of <200 mesh and a SiO2 content of 99.9982%. Figure 2 ,contrast Figure 1 and Figure 2 From the microstructure, it can be seen that when silicone solvent is not used, the adhesion effect of silicone solvent is lost during the cold pressing process, resulting in uneven product particle size and poor crystal structure.

[0030] Comparative Example 2

[0031] Compared with Example 1, the only difference is that the HCl flow rate during the roasting process is 20 ml / min.

[0032] The final product has a particle size of <200 mesh and a SiO2 content of 99.9963%.

[0033] Comparative Example 3

[0034] Compared with Example 2, the only difference is that the acid solution is a mixture of hydrofluoric acid and sulfuric acid, wherein the volume concentration of hydrofluoric acid is 1% and the volume concentration of sulfuric acid is 3%.

[0035] The final product has a particle size of 80-120 mesh and a SiO2 content of 99.94%.

[0036] Comparative Example 4

[0037] Compared with Example 4, the only difference is that the extrusion molding is carried out under normal pressure.

[0038] The final product has a particle size of <170 mesh, a SiO2 content of 99.9980%, and an apparent porosity of 1.1%.

[0039] Example 1

[0040] Quartz fine powder with a particle size of ≤300 mesh and a SiO2 content of 99.5% is mixed with 10 vol% hydrofluoric acid in a mass ratio of quartz fine powder to acid solution of 1:1. The mixture is acid-leached at 25°C for 3 hours. After the acid-leached sample is cleaned and dried, it is chlorinated and roasted at 1050°C for 15 minutes. The HCl flow rate during the roasting process is 15 ml / min. The roasted sample is evenly mixed with 5N grade tetrachlorosilane in an amount of 5% of the mass of the quartz fine powder. The mixture is then extruded under a pressure of 1 MPa and a vacuum of 10,000 Pa, and dried at 100°C for 45 minutes to obtain a quartz sand product.

[0041] The particle size distribution was detected to be 70-100 mesh. According to the national standard GB / T 32650-2016, the sample was digested and the contents of 13 impurity components were measured. The SiO2 content of the product was calculated to be 99.9983%.

[0042] Example 2

[0043] Quartz fine powder with a particle size of ≤300 mesh and a SiO2 content of 99.9% is mixed with acid, wherein the acid solution is a mixture of hydrofluoric acid and sulfuric acid, wherein the volume concentration of hydrofluoric acid is 5%, the volume concentration of sulfuric acid is 15%, and the mass ratio of quartz fine powder to acid solution is 0.5:1. The acid is leached at 45°C for 9 hours. After the acid-leached sample is cleaned and dried, it is chlorinated and roasted at 900°C for 30 minutes. The HCl flow rate during the roasting process is 5ml / min. The roasted sample is evenly mixed with 5N grade vinyl silicone oil, and the amount of vinyl silicone oil is 5% of the mass of the quartz fine powder. Then, the sample is extruded under a pressure of 3.2MPa and a vacuum degree of 8000Pa, and dried at 120°C for 30 minutes to obtain a quartz sand product.

[0044] The particle size distribution was detected to be 80-120 mesh. According to the national standard GB / T 32650-2016, the sample was digested and the contents of 13 impurity components were measured. The SiO2 content of the product was calculated to be 99.9981%.

[0045] Example 3

[0046] Quartz fine powder with a particle size of ≤300 mesh and a SiO2 content of 99.94% is mixed with acid, wherein the acid solution is a mixture of hydrofluoric acid and oxalic acid, wherein the volume concentration of hydrofluoric acid is 5%, the volume concentration of oxalic acid is 25%, and the mass ratio of quartz fine powder to acid solution is 0.8:1. The acid is leached at 80°C for 2 hours. After the acid-leached sample is cleaned and dried, it is chlorinated and roasted at 900°C for 30 minutes. The HCl flow rate during the roasting process is 5ml / min. The roasted sample is evenly mixed with 5N grade tetrachlorosilane, and the amount of tetrachlorosilane used is 3.5% of the mass of the quartz fine powder. Then, it is extruded under a pressure of 0.8MPa and a vacuum degree of 5000Pa, and dried at 90°C for 100min to obtain a quartz sand product.

[0047] The particle size distribution was detected to be 60-100 mesh. According to the national standard GB / T 32650-2016, the sample was digested and the contents of 13 impurity components were measured. The SiO2 content of the product was calculated to be 99.9986%.

[0048] Example 4

[0049] Quartz fine powder with a particle size of ≤300 mesh and a SiO2 content of 99.97% is mixed with sulfuric acid with a volume concentration of 20% and a mass ratio of quartz fine powder to acid solution of 0.6:1. The mixture is acid-leached at 20°C for 8 hours. After the acid-leached sample is cleaned and dried, it is chlorinated and roasted at 1150°C for 15 minutes. The HCl flow rate during the roasting process is 2ml / min. The roasted sample is evenly mixed with 5N grade trichlorosilane in an amount of 8% of the mass of the quartz fine powder. The mixture is then extruded under a pressure of 1.5MPa and a vacuum of 50000Pa, and dried at 135°C for 60 minutes to obtain a quartz sand product.

[0050] The particle size distribution was detected to be 70-100 mesh. The contents of 13 impurity components were measured after the sample was digested according to the national standard GB / T 32650-2016. The SiO2 content of the product was calculated to be 99.9982%. The apparent porosity of the quartz sand measured by the gas replacement method was 0.1%.

Claims

1. A method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder, characterized in that: Quartz powder is used as raw material, which is purified by acid leaching and chlorination roasting to a purity of 4N8 or above, and then mixed with high-purity silicon-based organic solvent and vacuum extruded. After drying, high-purity quartz sand is obtained. The SiO2 mass content in the quartz fine powder is ≥99.5%, and the particle size is <150 mesh; The chlorination roasting temperature is 900-1150°C, the time is 5-30 minutes, and the HCl gas flow rate is 2-15 ml / min as the roasting atmosphere; The acid leaching uses at least one of hydrofluoric acid, nitric acid, sulfuric acid and oxalic acid as a leaching medium; and the volume fraction of the acid in the leaching medium is 5-30%; During the acid leaching process, the mass ratio of quartz fine powder to leaching medium is (0.5-1):1, the acid leaching temperature is 20-80° C., and the acid leaching time is 2-9 hours.

2. The method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder according to claim 1, characterized in that: The high-purity silicon-based organic solvent is at least one of tetrachlorosilane, trichlorosilane and vinyl silicone oil, and has a purity of ≥99.999%.

3. The method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder according to claim 2, characterized in that: The amount of the high-purity silicon-based organic solvent used is 3.5-8% of the mass of the quartz fine powder.

4. The method for preparing high-purity quartz sand for photovoltaic crucibles from a quartz fine powder according to any one of claims 1 to 3, characterized in that: The extrusion pressure of the vacuum extrusion molding is 0.8~3.2MPa, and the vacuum degree is 5000~50000Pa.

5. The method for preparing high-purity quartz sand for photovoltaic crucibles from quartz fine powder according to claim 1, characterized in that: The drying conditions are: temperature of 90-135° C. and time of 30-100 min.

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