As a market professional for EPIC Powder, I understand the importance of staying at the forefront of material processing technology. For clients in the high-purity quartz industry, understanding the latest purification methods is crucial for producing superior products. Today, we will introduce seven advanced quartz purification techniques that are shaping the future of the industry.
1. High-Temperature Vacuum Treatment
This process involves heating quartz to over 1000°C in a vacuum state at 0.01 Mpa. The significant pressure difference between the inside and outside of gas-liquid inclusions causes them to burst. Simultaneously, the high-temperature vacuum environment is highly effective at removing hydroxyl groups from the quartz sand.
During high-temperature roasting, the quartz crystal lattice undergoes transformation. It changes from α-quartz to β-quartz at lower temperatures, and with further temperature increases, it can transform into cristobalite. This lattice transformation occurs through changes in the Si-O bond angles. When the lattice deforms, its volume changes, disrupting the original structural balance within the quartz crystal. Impurity metal elements within the lattice become unstable, undergo thermal movement, diffuse to the crystal surface, and eventually vaporize.
Furthermore, under these conditions, the gas-liquid inclusions expand thermally. As the quartz lattice deforms and its volume changes, these inclusions rupture, exposing the impurities inside. Driven by the concentration difference, these impurities are then vaporized and removed, achieving the goal of purification.
2. Chlorination Roasting
Chlorination roasting, also known as chlorination degassing, utilizes the chemical potential gradient created by high-concentration chlorine gas between the particle surface and its interior to drive out gas-liquid inclusions. Impurities like alkali metals, alkaline earth metals, and residual inclusions on the surface of quartz particles react with chlorine gas at high temperatures to form gaseous chlorides. Compared to other metal ions, Al and B have lower reactivity. The high-temperature airflow carries these volatile chlorides away, achieving deep purification.
This is a deep purification process characterized by high costs, limited processing capacity, and certain safety risks. Currently, only a few companies globally, such as US-based Sibelco, have achieved industrial application of this technology.
The feed material for this process must meet strict requirements. Typically, it requires quartz sand that has been purified by traditional methods to a SiO₂ purity of 99.99% with total impurities less than 100×10⁻⁶. The equipment for chlorination roasting is often custom-designed, as no unified standard equipment exists yet, and the technology is continuously being developed and refined.
Based on the type of chlorinating agent, this process can be divided into:
- Solid Chlorination Roasting: Uses solid chlorinating agents like NaCl, CaCl₂, and NH₄Cl.
- Gas Chlorination Roasting: Uses gaseous chlorinating agents like Cl₂ and HCl.
3. Superconducting Magnetic Separation
The superconducting magnetic separation is a novel mineral purification method that introduces superconducting technology into mineral processing. Superconducting materials can generate extremely powerful magnetic fields, capable of magnetizing and removing even the finest impurities and solid inclusions within quartz. This plays a vital role in removing foreign minerals and solid inclusions, making it a key process and piece of equipment in the production of high-purity quartz raw materials.
As a high-end piece of mineral processing equipment, the core technology of a superconducting magnetic separator lies in using cryogenic technology to cool the coil to a superconducting state, dramatically increasing the background field strength generated by the magnet.
The working principle involves using superconducting wires made from materials like niobium-titanium or niobium-tin. We wind these wires into special coils and place them in a well-sealed cryostat. Using liquid helium immersion and a conduction-cooling refrigeration system, we maintain the operating environment for the superconducting coil at around -268.8°C. At this temperature, the coil’s electrical resistance becomes zero. With zero resistance and infinite conductivity, the coil can carry a much higher current, and we can increase the number of coil turns. By winding it in a solenoid configuration, we achieve an extremely high background magnetic field.
4. Electrostatic Separation
Electrostatic separation uses high-voltage electricity to separate materials. This physical beneficiation method exploits differences in the electrical conductivity and dielectric constants of materials. Particles become charged in an electric field, and due to differences in the electrostatic forces, gravity, and centrifugal forces acting on them, their trajectories in the field vary, enabling separation.
This technology offers a simple process and is a dry operation, eliminating issues related to wastewater pollution and treatment. It holds significant development potential and broad application prospects.
In recent decades, electrostatic separation has been widely used not only in the concentration of rare metal ores but also in the beneficiation of non-ferrous metals, non-metallic minerals, and even ferrous metals. It is also extensively applied in the recycling of municipal solid waste, focusing on areas like de-carbonization of fly ash, separation of waste plastics, and recycling of waste household appliances. Other applications include recovering valuable resources from industrial wastes, such as processing metallurgical silicon slag and metal grinding swarf.
As a mature physical separation technology, electrostatic separation equipment is known for its reliability, simple control, and stable performance. It can effectively reduce metal impurities in high-purity quartz, lessening the burden on subsequent purification processes and playing a unique role in quartz impurity removal.
5. Ultrasonic Treatment
Ultrasonic treatment is safe, efficient, and stable. Ultrasound refers to sound waves with frequencies between 2×10⁴ and 10⁹ Hz. When ultrasound waves propagate through water (or a solution), they create numerous compression and rarefaction zones. This leads to the formation and violent collapse of countless microbubbles (cavitation bubbles), a phenomenon known as cavitation.
When these cavitation bubbles implode, they generate extremely high temperatures exceeding 5000 K and high pressures around 5×10⁷ Pa within an incredibly short time and minute space. The temperature change rate can reach up to 10⁹ K/s. This implosion is accompanied by intense shockwaves and micro-jets traveling at speeds up to 400 km/h. These forces violently impact the quartz sand particles suspended in the liquid, causing trace impurities on the particle surfaces to detach rapidly, thus achieving purification.
6. Microwave Roasting
Microwave roasting leverages the difference in dielectric constants between various materials. When quartz containing gas-liquid inclusions is subjected to microwave radiation, the inclusions heat up and vaporize much faster than the quartz matrix. This creates immense internal pressure, causing the quartz particles to fracture and effectively releasing the gas-liquid inclusions.
7. Doping Purification
Doping purification involves adding specific elements to quartz at high temperatures. These dopants react with impurity elements to form compounds that are readily soluble in water or acid. These soluble compounds can then be removed by subsequent washing or acid leaching.
In one study, researchers started with quartz powder having a total impurity content of 41.94×10⁻⁶. They successively doped it with NaNO₃ and Al(NO₃)₃·9H₂O and then calcined it at 900°C. The resulting purified quartz sand had total impurities reduced to less than 25×10⁻⁶, meeting the IOTA-Std standard.
At EPIC Powder, we are committed to providing advanced solutions for the powder processing industry. Understanding these purification technologies is the first step in optimizing your production line for the highest quality output. For more information on our equipment and how it can support your purification processes, please contact our team today.
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