High-purity quartz is extensively used in industries such as electronics and information technology, photovoltaics, optical communication, and electric light sources. It holds a significant position and plays a crucial role in strategic emerging industries like new materials and new energy. The production of high-purity quartz relies on an integrated technological system encompassing four main aspects: raw material selection, purification processing, processing equipment—such as the specialized high purity quartz jet mill—and quality detection. These components are interdependent yet function as a cohesive whole. Among them, the identification, evaluation, and selection of high-purity quartz raw materials remain the most critical foundational step.
I. Raw Material Selection Technology
The quality of high-purity quartz is not simply a linear function of impurity content; rather, it depends on the process mineralogy characteristics of its impurities. Different quartz ores have varying impurity characteristics and contents. Therefore, for high-purity quartz raw materials, analyzing their impurity features is a prerequisite for determining the purification process and application direction.
Purity
Describing the purity of high-purity quartz siliceous raw materials should include both the percentage of SiO2 and the content of key impurity elements affecting purification. Thus, the content of SiO2, Al, and (Ti+Li) can serve as evaluation indices. High-purity siliceous raw materials can be classified into two grades:
High-Purity Grade: SiO2 ≥ 99.9%, Al ≤ 700×10⁻⁶, Li+Ti ≤ 200×10⁻⁶.
Ultra-Pure Grade: SiO2 ≥ 99.995%, Al ≤ 35×10⁻⁶, Li+Ti ≤ 10×10⁻⁶.
Gangue Mineral Impurities
Gangue minerals primarily affect the initial ore grade and beneficiation yield. Compared to difficult-to-remove impurities like inclusions and lattice impurities, gangue minerals and grain boundary impurities are relatively easier to eliminate during purification. After removal by appropriate methods, they generally do not impact the final purity.
Inclusion Impurities
Since inclusions exist within natural quartz minerals, only a small portion of large-sized inclusions can be removed without destroying the quartz crystal structure. Inclusions are one of the most critical factors affecting raw ore quality. An excessive amount of inclusions, especially fine-grained fluid/gas-liquid inclusions and mineral inclusions, can severely impact product performance. Impurity elements within inclusions (e.g., Ti, Li, K, Na) can reduce purity, while tiny fluid inclusions in the final product can gradually expand and coalesce under high temperatures, affecting performance. Evaluating raw ore necessitates studying the type, morphology, size, and quantity of inclusions.
Melt Inclusions primarily composed of major elements like Si, Al, Fe, Ca, Na, K, Mg. They are generally considered a main source of B and P impurities in granite-pegmatite quartz and one source of Li impurities.
Fluid Inclusions contain impurities like Na, K, Al, Ca and are a major source of alkali metal impurities in quartz. Therefore, selecting quartz raw material with few or no fluid inclusions is key to producing high-purity quartz.
Common lattice impurity elements in quartz include Al, Ti, Li, Na, K, Ge, OH, etc. Their content typically exceeds 1×10⁻⁶, making them very difficult to remove economically via conventional beneficiation or chemical purification. They are a significant factor affecting purity and product performance.
Aluminum is the most important impurity element for research and analysis, serving as a key indicator of raw material quality. Its content is often the highest and easiest to analyze. High Al content is often associated with increased levels of Li, K, Na.
Titanium is another key indicator. The Ti-O bond is extremely stable, making Ti—whether in the lattice or within Ti-bearing minerals in inclusions—very difficult to remove economically. Quartz with Ti content above a certain threshold is hard to process into high-purity quartz.
II. Purification & Processing Technology
Quartz beneficiation and purification technology can be divided into two stages: physical purification and chemical purification. Different techniques target specific impurity types.
Physical Purification
Aims to separate quartz from associated/gangue minerals and remove surface films/argillaceous minerals, addressing external impurities. It serves as preliminary purification and the foundation for chemical purification. Key technologies include: washing-classification-desliming, scrubbing, gravity separation, magnetic separation, flotation, calcination-water quenching, and color sorting.
Purificación química
Aims to remove internal micro mineral inclusions, fluid inclusions, and lattice impurities, addressing internal mineral impurities. It represents deep purification. Key technologies include: acid leaching, chlorination roasting, thermal shock (high-temperature bursting), microwave radiation, and microbial methods.
Thermal shock y calcination-water quenching (physical) create cracks to facilitate acid leaching of inclusion interiors. Acid leaching is a common foundational chemical technique. Chlorination roasting is highly effective for removing lattice impurities, a key deep purification technology. Microwave radiation targets fluid inclusion removal. Microbial methods target surface impurity separation.
III. Processing Equipment Technology
Quartz processing and purification rely on specialized equipment. Key equipment types include:
Washing and Classification
Equipment such as spiral classifiers, hydrocyclones, air classifiers, and vibrating screens is used for precise grading and separation of silica sand across various industries.
Crushing and Grinding
This stage utilizes grinding equipment including ball mills, rod mills, vertical planetary ball mills, sand mills, vibrating mills, and jet mills.
Separación por gravedad
This method separates target minerals from impurities by exploiting differences in particle shape, size, and density, which cause minerals to move at different speeds and trajectories in a medium like water or air. Common equipment for quartz sand includes spiral concentrators, shaking tables, and sluices.
Clasificación por colores
Color sorters separate impurities by detecting color differences—pure quartz sand is white, while impurities are typically other colors. These systems consist of a feeding system, an optical detection system, a signal processing system, and a separation execution system.
Flotación
This process removes independent gangue minerals like feldspar and mica. Although quartz shares similar physical and chemical properties with feldspar, flotation effectively separates them. Common equipment includes agitation flotation machines and bar flotation machines.
Separación magnética
In a magnetic field, non-magnetic quartz remains unaffected, while magnetic impurities are attracted. Separation is achieved based on this difference in magnetism. Typical equipment includes electromagnetic dry powder separators, permanent magnetic drum separators, high-intensity magnetic plate separators, vertical ring high-gradient magnetic separators, electromagnetic slurry separators, and superconducting magnetic separators.
Electrostatic Separation
This technique separates minerals by applying an electric field, where particles with different charges or polarities move in distinct trajectories. As a mature physical beneficiation method, it offers reliable performance, simple operation, and effectively reduces metallic impurities in high-purity quartz, thereby simplifying downstream processing.
Acid Leaching
Metal oxide impurities in quartz sand react with mixed acids to form insoluble residues, which are then removed. This process is typically conducted in sealed acid reaction vessels.
Heat Treatment
Methods such as thermal shock (high-temperature bursting) and chlorination roasting are performed using specialized equipment like high-temperature chlorination furnaces or roasting furnaces.
IV. Quality Detection Technology
Research on deposit genesis, classification of siliceous raw materials, and product quality control require analytical testing support. While unified standards are lacking, detection methods for main component SiO2 fall into two categories:
Chemical Analysis Methods
Include gravimetric methods (animal glue coagulation, polyoxyethylene coagulation, perchloric acid dehydration, silicon tetrafluoride direct volatilization), potassium fluorosilicate titration, silicon molybdenum blue spectrophotometry, potassium fluorosilicate volumetric method. Polyoxyethylene coagulation and animal glue coagulation are national standard methods due to high accuracy.
Instrumental Analysis Methods
Include X-ray Fluorescence Spectrometry (XRF), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
Application of Jet Mills in High-Purity Quartz Processing
The jet mill, particularly the fluidized-bed jet mill, is a core piece of equipment for the ultrafine grinding of high-purity quartz. It utilizes high-speed gas streams to cause quartz particles to collide and abrade against each other, achieving pulverization without mechanical wear. This process entirely avoids metallic contamination, perfectly aligning with the stringent low-impurity requirements of high-purity quartz. Its integrated classification system can separate qualified fine powder in real time, ensuring a concentrated particle size distribution (PSD), which is critical for subsequent chemical purification and high-end applications. By precisely controlling parameters such as air pressure and classifier wheel speed, an adjustable ultrafine powder with a D50 ranging between 5 and 20 microns can be obtained, meeting the specific needs of fields like semiconductor packaging and high-end quartz crucible manufacturing.
The Crucial Role of Air Classifiers
In the precision classification of high-purity quartz, air classifiers—especially high-efficiency turbo classifiers—play an irreplaceable role. They operate not by simple screening but by leveraging the precise balance between centrifugal force and aerodynamic drag to achieve efficient and accurate classification of micron and even sub-micron quartz powders. This equipment effectively removes coarse particles and ultrafine fines generated by over-grinding, strictly controlling the product’s top and bottom size limits. This enhances the powder’s flowability and packing density. When integrated with a jet mill to form a closed-circuit system, it creates an efficient integrated “grinding-classification” process, significantly improving production efficiency and product consistency. This combination is a key link in achieving scalable, high-quality production of high-purity quartz.
The combination of jet mills and air classifiers not only addresses the precision of physical comminution but also creates favorable conditions for subsequent chemical purification. Uniform and refined particles increase the specific surface area, allowing acid solutions to penetrate more easily. This dramatically improves the efficiency of acid leaching in removing inclusions and surface impurities. Simultaneously, precise particle size control avoids process challenges caused by excessively fine powder in downstream steps (e.g., overly dense filter cakes, difficult washing). Therefore, this system is not merely a physical processing tool but a strategic link in optimizing the overall purification process and enhancing the final product’s purity and performance.
Conclusión
With the rapid development of high-tech fields, the strategic importance of high-purity quartz is increasingly prominent, driving ever-stricter quality requirements.
High-purity quartz production is a systematic engineering project reliant on integrated technologies—encompassing resource selection, processing/purification techniques, production equipment level, and inspection/analysis capabilities. It’s an interconnected whole. Evaluating raw materials cannot rely solely on SiO2 content. Considerations must include mineral dissemination characteristics, associated gangue types, inclusion content/size, and isomorphous impurity distribution. These characteristics then guide the selection of appropriate purification processes and processing equipment.
Polvo épico
Polvo épico has more than 20 years experience in various powders processing. We offer a wide range of equipment models and tailor solutions to meet your specific needs. Our team has more than 20 years experience in various powders processing. Epic Powder is specialized in fine powder processing technology for mineral industry, chemical industry, food industry, pharama industry, etc. Contact us today for a free consultation and customized solutions!
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