A high-purity quartz sand enhanced chlorination purification method

Abstract

The present invention discloses a method for purifying high-purity quartz sand by enhanced chlorination, which belongs to the technical field of inorganic non-metallic material processing. The method comprises placing a quartz sand raw material containing crystal structure impurities in a roasting furnace, and simultaneously introducing a gaseous chlorinating agent and a gaseous reducing agent into the roasting furnace for roasting, thereby obtaining purified quartz sand. Based on conventional chlorination roasting purification, the method regulates the reaction atmosphere by introducing a gaseous reducing agent, thereby promoting the efficient dissociation and chlorination of difficult-to-remove crystal structure impurities, thereby achieving deep and efficient purification of quartz sand. The method has the advantages of simple process equipment, strong raw material applicability, and high impurity removal efficiency, and can be widely used in the production of high-purity quartz sand of grade 4N5 and above.

Description

Technical Field

[0001] The invention relates to a quartz sand purification method, in particular to a high-purity quartz sand enhanced chlorination purification method, and belongs to the technical field of processing high-purity, high-end inorganic non-metallic materials. Background Art

[0002] High-purity quartz, an indispensable foundational material, plays a crucial role in numerous high-tech and emerging industries, including the semiconductor industry, fiber-optic communications technology, photovoltaic energy, and electric light sources. It not only provides critical material support for these sectors but also serves as a core driving force behind the rapid development of emerging industries such as the next-generation information industry, new energy technologies, high-end equipment manufacturing, and new materials research and development. High-purity quartz sand, grade 4N8 and above, in particular, has become a leader among high-end, high-purity quartz products due to its stringent purity requirements. It is widely used in applications requiring extremely high purity. However, the production of high-purity quartz sand faces not only the challenges of resource scarcity but also a series of technical challenges, making its production relatively difficult.

[0003] Due to the inherent shortage of high-purity quartz mineral resources and the relatively backward purification technology, it is currently difficult to produce high-purity quartz sand of grade 4N8 and above. Impurities in quartz minerals can be categorized into three main categories based on their size, occurrence state, and physicochemical properties: gangue mineral impurities, inclusion impurities, and crystal structure impurities. Gangue mineral impurities, such as mica and feldspar, often adhere to the surface of quartz sand particles or fill the tiny gaps between particles. A series of mineral processing techniques, particularly monomer dissociation, can effectively separate and remove these impurities from quartz minerals, thereby improving quartz purity. Inclusion impurities are foreign substances or components of the media during rock and mineralization that remain within the crystals during mineral growth due to interfacial capture. They lack direct chemical bonding with the host quartz mineral. Calcination is an effective method for removing these impurities. During high-temperature treatment, the inclusions expand due to the rising temperature. When the internal pressure reaches a certain level, the inclusions undergo thermal detonation, thus separating from the host quartz crystal. However, factors such as the inclusion's composition, size, location within the quartz grain, and shape significantly influence its detonation behavior at high temperatures. Specifically, some extremely small inclusions can remain intact even at extremely high temperatures because their internal pressure rarely builds up to a level sufficient to trigger detonation. Inclusions located on the surface of quartz grains, however, are more likely to detonate at the same temperature than inclusions within the grain due to the lower external pressure. Furthermore, irregularly shaped inclusions, due to their structural asymmetry, require lower internal pressure to detonate than regular shaped inclusions, making them easier to separate from the quartz crystal. Crystalline impurities are elements such as boron (B), aluminum (Al), and titanium (Ti) that can replace silicon (Si) atoms in silicon-oxygen tetrahedra, forming new tetrahedral structural units. Because this substitution is often non-equivalent—that is, differences in charge and radius between the replacing element and the silicon atom—lead to an imbalanced charge distribution within the crystal lattice. To maintain this lattice charge balance, ions such as lithium (Li), sodium (Na), and potassium (K) are present in the channels between the tetrahedrons, acting as charge compensation. These crystal structure impurities, tightly bound by the silicon-oxygen tetrahedral structure, are difficult to remove extensively using conventional physical separation methods such as magnetic separation and flotation, as well as chemical treatments such as acid leaching. While chlorination roasting is effective for removing some elements like potassium and sodium, it is less effective for removing impurities such as boron, aluminum, titanium, and calcium. These impurities often exhibit high stability during the chlorination process, making them difficult to effectively separate from quartz sand.

[0004] Given the complexity and difficulty of removing crystalline impurities from quartz sand, developing efficient, targeted deep removal technologies is crucial. This requires not only in-depth research into the occurrence and migration patterns of these impurity elements in quartz sand, as well as their interaction mechanisms with silicon-oxygen tetrahedrons, but also the exploration of new treatment methods and technologies to achieve efficient, energy-efficient, and environmentally friendly removal of these impurity elements, thereby meeting the stringent purity requirements of high-end quartz materials. Summary of the Invention

[0005] The conventional chlorination roasting method in the existing high-purity quartz sand production process has difficulty in achieving deep removal of crystal structure impurities (such as boron, aluminum, titanium, calcium, and other impurity elements) in quartz sand. The purpose of the present invention is to provide a method for enhanced chlorination purification of high-purity quartz sand. This method is based on the occurrence form and chemical bond characteristics of impurity elements such as B, Al, Ti, and Ca in quartz sand crystals during the chlorination purification process, and analyzes the chemical bond breakage and recombination mechanism of the chlorination reaction of difficult-to-remove impurities. Extensive experimental studies have shown that the chemical bonds formed by these difficult-to-remove impurities with oxygen in the quartz sand lattice are stable. Conventional chlorination roasting processes break chemical bonds slowly, making it difficult to deeply remove these impurity elements doped in the lattice. The present invention innovatively proposes introducing a reducing medium to promote the breakage of the chemical bonds between the difficult-to-remove impurity elements and oxygen, thereby enhancing the formation of chlorides by the impurity elements for efficient volatilization and removal. This method specifically achieves the simultaneous dissociation and chlorination of difficult-to-remove impurity elements, effectively enhancing their removal. Only a gaseous reducing agent is required to be introduced into the existing chlorination process. The method has the advantages of simple process, strong operability, wide raw material applicability, and high removal efficiency.

[0006] To achieve the above technical objectives, the present invention provides a method for purifying high-purity quartz sand by enhanced chlorination. The method comprises placing a quartz sand raw material containing crystal structure impurities in a roasting furnace, and simultaneously introducing a gaseous chlorinating agent and a gaseous reducing agent into the roasting furnace for roasting to obtain purified quartz sand. The amount of the gaseous chlorinating agent is 0.9 to 1.3 times the total molar amount of impurity elements in the quartz sand; the amount of the gaseous reducing agent is 0.3 to 1.2 times the total molar amount of impurity elements in the quartz sand. The roasting conditions are: a temperature of 900 to 1200° C. and a time of 5 to 30 minutes.

[0007] The quartz sand raw material containing crystal structure impurities involved in the present invention is preferably preliminarily purified quartz sand, such as quartz sand of grade 4N or above, which contains almost no associated mineral impurities and mainly retains trace crystal structure impurities.

[0008] The present invention targets the occurrence morphology and chemical bond characteristics of impurity elements in the crystal structure of quartz sand. For example, impurity elements such as B, Al, Ti, and Ca have strong oxygen binding capacity and stable chemical bond properties. This is the key to the difficulty of conventional chlorination roasting in achieving deep removal of impurity elements such as B, Al, Ti, and Ca in the quartz lattice. The present invention cleverly introduces a reducing medium simultaneously during the chlorination roasting process, utilizing the characteristic that the reducing medium can promote the breaking of the chemical bond between the impurity elements and oxygen at high temperature, thereby promoting the impurity elements to combine with the chlorinating agent and then volatilize and remove. This method significantly improves the dissociation degree and removal effect of difficult-to-remove impurity elements in the quartz lattice, achieving deep and efficient removal of impurity elements.

[0009] As a preferred embodiment, the gaseous chlorinating agent comprises at least one of hydrogen chloride and chlorine. Commonly used chlorinating agents in the prior art are divided into gaseous chlorinating agents and solid chlorinating agents. Solid chlorinating agents, such as potassium chloride (KCl) and calcium chloride (CaCl2), decompose at high temperatures to release chlorine gas (Cl2), which then participates in the subsequent chlorination reaction. However, during the high-temperature decomposition process of these solid chlorinating agents, residual elements such as potassium and calcium may remain in the reaction system, leading to increased potassium and calcium content in the quartz sand, thereby affecting the purity and performance of the product. In contrast, gaseous chlorinating agents offer significant advantages. They not only effectively avoid the elemental residue issues associated with solid chlorinating agents, but also, due to their small molecular weight and rapid diffusion rate, they can rapidly react with impurity elements in the quartz sand, thereby improving the reaction efficiency and product quality of the chlorination purification process. Therefore, conventional gaseous chlorinating agents such as hydrogen chloride and chlorine are preferred in the present invention.

[0010] As a preferred embodiment, the gaseous reducing agent includes at least one of H2, CO, and CH4. Gaseous reducing agents such as hydrogen (H2), methane (CH4), and carbon monoxide (CO) are ash-free and leave virtually no residue under high-temperature reduction conditions, making them preferred. Furthermore, the selection of a gaseous reducing agent must also consider its molecular characteristics and chemical properties. If the medium has a high molecular weight or a high carbon content, its ability to diffuse within the crevices of the quartz sand particles will be limited, which will affect its effectiveness in reducing the product. In particular, when the carbon content is high, carbon deposition may occur during the calcination process, causing carbon particles to adhere to the quartz sand surface. This not only reduces the purity of the product but may also adversely affect its optical properties. Therefore, among gaseous reducing media, hydrogen (H2), carbon monoxide (CO), and methane (CH4) are preferred reducing media due to their moderate molecular weight, relatively low carbon content, and ease of diffusion and reaction. They can be used alone or in combination to achieve optimal results.

[0011] The consumption of the gaseous chlorinating agent of the present invention is 0.9 to 1.3 times the total molar amount of the impurity elements in the quartz sand. The consumption of the gaseous chlorinating agent directly determines the degree to which the impurity elements are removed. In order to ensure that the impurity elements in the quartz sand can be effectively removed, the consumption of the gaseous chlorinating agent must at least reach a critical value, which refers to the theoretical molar amount required to fully convert all the impurity elements in the quartz sand into the corresponding metal chloride. On this basis, appropriately increasing the consumption of the chlorinating agent can produce positive effects. It can accelerate the process of the chlorination reaction, so that the impurity elements are converted into metal chlorides faster, thereby improving the chlorination removal efficiency of impurities. However, it is worth noting that when the consumption of the chlorinating agent is too high, although the removal efficiency may be further improved, the production cost will also be increased accordingly, resulting in a waste of resources. Therefore, in actual operation, it is necessary to find a balance point. The preferred chlorinating agent consumption is usually set to 0.9 to 1.3 times the total molar amount of the impurity metals in the quartz sand, so that effective removal efficiency can be guaranteed while controlling production costs.

[0012] The amount of the gaseous reducing agent of the present invention is 0.3 to 1.2 times the total molar amount of the impurity elements in the quartz sand. The amount of the gaseous reducing medium is a key factor affecting the degree of chemical bond breaking between the impurity elements and oxygen. If the amount of the reducing medium is insufficient, the number of chemical bonds between the impurity elements and oxygen that can be broken will be limited, resulting in a poor reduction effect and the impurity elements cannot be effectively removed. In order to increase the degree of chemical bond breaking, it is necessary to increase the amount of the reducing medium. However, this also brings new problems. Too much gaseous reducing medium may trigger other unnecessary chemical reactions. Therefore, when determining the amount of reducing medium, it is necessary to comprehensively consider the type and content of the impurity elements in the quartz sand. Generally speaking, the preferred amount of reducing medium is 0.3 to 1.2 times the total molar amount of the impurity elements in the quartz sand. This range can ensure both an effective reduction effect and the quality of the quartz.

[0013] The calcination conditions of the present invention are: a temperature of 900-1200°C and a time of 5-30 minutes. The calcination temperature is a key factor influencing the reaction behavior of impurity elements with the chlorinating and reducing gases. As the calcination temperature increases, the reaction between the impurity elements, the chlorinating and reducing gases accelerates, significantly improving the efficiency of impurity removal. However, higher temperatures require the heating elements and lining materials of the furnace to withstand higher temperatures, placing more stringent requirements on their heat resistance and increasing energy consumption throughout the entire process. Furthermore, when the temperature is too high, solid-phase sintering is likely to occur between the quartz sand particles, which not only disrupts the particle size distribution of the product but also adversely affects its overall quality. Conversely, if the temperature is set too low, the reaction rate will be significantly slowed, resulting in low production efficiency. Specifically, if the reaction time is too short, the reaction may not proceed completely, or the generated impurity chlorides may not be able to fully diffuse from the interior of the quartz sand particles and be removed. If the reaction time is too long, overall production efficiency will be affected.

[0014] As a preferred solution, the roasting furnace is a static roasting furnace or a dynamic roasting furnace. As a more preferred solution, when the roasting furnace is a dynamic roasting furnace, the horizontal inclination angle of the roasting furnace during the roasting process is 5~25 °, and the rotating speed is 3~30r / min. Relative to the crystalline roasting furnace, the present invention more preferably adopts a dynamic roasting furnace, which can better promote the gas-solid reaction between quartz sand and the gas chlorinating agent and the gas reducing agent, and has a better effect on the deep removal of impurities in the quartz sand. During the dynamic roasting process of quartz sand, the inclination angle and rotation speed of the roasting furnace act together on the flow state of quartz sand, thereby affecting its motion trajectory and residence time in the furnace. Specifically, the inclination angle and rotation speed of the dynamic roasting furnace are two key factors determining the flow rate of quartz sand. When the inclination angle is too large and the rotation speed is too fast, the residence time of quartz sand in the roasting furnace will be greatly shortened, which may lead to insufficient roasting and incomplete impurity removal. Conversely, a smaller inclination angle and slower rotational speed ensures sufficient time for the quartz sand to roast in the furnace, thereby improving impurity removal. However, this also reduces operational efficiency and is only suitable for processing raw materials with high impurity content. Therefore, in actual operation, it is necessary to find the optimal combination of roaster inclination angle and rotational speed. Practical experience has shown that the optimal roaster inclination angle ranges from 5 to 25° and the rotational speed ranges from 3 to 30 rpm, which ensures good impurity removal while maintaining high production efficiency. Dynamic roasters, such as rotary kilns, are an example.

[0015] As a preferred solution, the SiO2 content of the quartz sand raw material containing crystal structure impurities is ≥99.99%, and the SiO2 content of the chlorinated product quartz sand is ≥99.995%.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0017] 1) The quartz sand purification method provided by this invention is primarily based on the chemical bonding characteristics and reaction mechanisms of the impurity elements in quartz sand. Through the synergistic effect of a chlorinating agent and a reducing agent, it effectively regulates the breakage of the chemical bonds of the impurity elements and the formation of chlorides, achieving efficient and deep removal of the impurity elements. Compared with traditional chlorination roasting processes, this technology not only significantly improves the removal efficiency of impurity elements, but also achieves a deeper level of purification. This provides a higher-quality high-purity quartz sand production method for high-tech fields such as semiconductors and photovoltaics.

[0018] 2) The quartz sand purification method provided by the present invention exhibits extremely high flexibility and operability in application, and has a high degree of raw material applicability. It can be used for deep purification of high-quality quartz resources or quality upgrading of quartz resources of different grades. It can well adapt to different production needs and provide more options and possibilities for the processing of quartz resources.

[0019] 3) The quartz sand purification method provided by this invention has the advantages of a concise and clear process flow, easy operation and control, and significant purification effects. These features make this technical solution very suitable for large-scale industrial production, effectively improving production efficiency and reducing production costs while ensuring product quality.

[0020] Therefore, the technical solution of the present invention has broad application prospects and significant economic value in the field of quartz sand purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD diagram of the quartz sand raw material in Example 1; it can be seen from the figure that the mineral phase of the quartz sand sample is pure quartz phase, and almost no associated mineral impurity phase can be seen, indicating that its impurity elements are mainly present in the quartz sand lattice. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to specific embodiments. However, the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without creative work are still within the scope of protection of the present invention.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0024] The dynamic roasting furnace involved in the following embodiments is a rotary kiln.

[0025] Example 1

[0026] Quartz sand with a SiO2 content of 99.9941% was loaded into a roasting furnace. XRD analysis showed that the sample mineral phase was pure quartz phase, without associated mineral impurities, that is, the impurity elements were present in the quartz sand lattice. H2 and Cl2 were introduced into the furnace, with their contents being 0.3 and 1.1 times the total molar amount of impurity elements in the quartz sand, respectively. The sample was roasted at 1050°C for 30 minutes. After the roasting product was collected and cooled, the sample was digested according to the requirements of the national standard GB∕T 32650-2016 and the contents of 13 impurity components were measured. The SiO2 content of the roasting product was calculated to be 99.9966%.

[0027] Example 2

[0028] Quartz sand with a SiO2 content of 99.9963% was loaded into a roasting furnace. XRD analysis showed that the sample mineral phase was pure quartz phase, without associated mineral impurities, that is, the impurity elements were present in the quartz sand lattice. CH4 and Cl2 were introduced into the furnace, with their contents being 1.0 and 0.9 times the total molar amount of impurity elements in the quartz sand, respectively. The furnace was roasted at 900°C for 20 minutes. After the roasting product was collected and cooled, the sample was digested according to the requirements of the national standard GB∕T 32650-2016 and the contents of 13 impurity components were measured. The SiO2 content of the roasting product was calculated to be 99.9982%.

[0029] Example 3

[0030] Quartz sand with a SiO2 content of 99.9952% was passed into a calcination furnace. XRD analysis showed that the sample mineral phase was pure quartz phase, without associated mineral impurities, that is, the impurity elements were present in the quartz sand lattice. H2 and HCl were introduced into the furnace at the same time, and their contents were 0.9 and 1.3 times the total molar amount of impurity elements in the quartz sand, respectively. The dynamic calcination furnace was horizontally inclined at 20° and rotated at 5r / min. It was roasted at 1200℃ for 15min. After the roasting product was collected and cooled, the sample was digested according to the requirements of the national standard GB∕T 32650-2016 and the contents of 13 impurity components were measured. The SiO2 content of the roasting product was calculated to be 99.9981%.

[0031] Example 4

[0032] Quartz sand with a SiO2 content of 99.9944% was passed into a calcination furnace. XRD analysis showed that the sample mineral phase was pure quartz phase, without associated mineral impurities, that is, the impurity elements were present in the quartz sand lattice. CO and HCl were introduced into the furnace at the same time, and their contents were 1.2 and 1.1 times the total molar amount of impurity elements in the quartz sand, respectively. The dynamic calcination furnace was horizontally tilted at 25° and rotated at 15r / min. It was roasted at 1100℃ for 5min. After the roasting product was collected and cooled, the sample was digested according to the requirements of the national standard GB∕T 32650-2016 and the contents of 13 impurity components were measured. The SiO2 content of the roasting product was calculated to be 99.9962%.

[0033] Example 5

[0034] Quartz sand with a SiO2 content of 99.9961% was passed into a calcination furnace. XRD analysis showed that the sample mineral phase was pure quartz phase, without associated mineral impurities, that is, the impurity elements were present in the quartz sand lattice. H2 and Cl2 were introduced into the furnace at the same time, and their contents were 0.8 and 1.1 times the total molar amount of impurity elements in the quartz sand, respectively. The dynamic calcination furnace was horizontally inclined at 5° and rotated at 30r / min. It was calcined at 1050℃ for 25min. After the calcined product was collected and cooled, the sample was digested according to the requirements of the national standard GB∕T 32650-2016 and the contents of 13 impurity components were measured. The SiO2 content of the calcined product was calculated to be 99.9993%.

[0035] Example 6

[0036] Quartz sand with a SiO2 content of 99.9941% was loaded into a roasting furnace. XRD analysis of the sample showed a pure quartz phase, free of associated mineral impurities, i.e., impurity elements were present within the quartz sand lattice. H2 and Cl2 were introduced into the furnace at concentrations of 0.3 and 1.1 times the total molar amount of impurity elements in the quartz sand, respectively. The dynamic roasting furnace was tilted horizontally at 20° and rotated at 30 rpm for 30 min at 1050°C. The roasted product was collected and cooled, and the contents of 13 impurity components were measured after sample digestion according to the national standard GB / T 32650-2016. The SiO2 content of the roasted product was calculated to be 99.9972%. Compared with Example 1, this example illustrates that the use of a dynamic roasting furnace is more conducive to the deep removal of lattice impurities in quartz sand.

[0037] Comparative Example 1

[0038] Compared with Example 1, the only difference is that the amount of H2 used is 0.1 times the total molar amount of impurity elements in the quartz sand, and the SiO2 content of the final calcined product is 99.9949%.

[0039] Comparative Example 2

[0040] Compared with Example 3, the only difference is that the calcination temperature is 750°C and the SiO2 content of the final calcined product is 99.9961%.

[0041] Comparative Example 3

[0042] Compared with Example 4, the only difference is that the calcination time is 3 minutes and the SiO2 content of the final calcined product is 99.9946%.

Claims

1. A high-purity quartz sand enhanced chlorination purification method, characterized in that: The quartz sand raw material with crystal structure impurities of grade 4N or above is placed in a roasting furnace, and a gaseous chlorinating agent and a gaseous reducing agent are simultaneously introduced into the roasting furnace for roasting to obtain purified quartz sand; The gas reducing agent is CH4; the roasting furnace is a dynamic roasting furnace; when the roasting furnace is a dynamic roasting furnace, the horizontal inclination angle of the roasting furnace during the roasting process is 5~25°, and the rotation speed is 3~30 r / min; The amount of the gaseous chlorinating agent is 0.9 to 1.3 times the total molar amount of impurity elements in the quartz sand; The amount of the gas reducing agent is 0.3 to 1.2 times the total molar amount of impurity elements in the quartz sand; The calcination conditions are: temperature of 900-1200° C. and time of 5-30 min.

2. A high-purity quartz sand enhanced chlorination purification method according to claim 1, characterized in that: The gaseous chlorinating agent includes at least one of hydrogen chloride and chlorine.

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