Current Status and Advances in Quartz Sand Purification Technologies

Quartz sand, a core raw material for high-tech industries such as photovoltaics and semiconductors, requires ultra-high purity (SiO₂≥99.995%) to meet performance demands. Purification technologies are critical to overcoming supply chain bottlenecks. This article focuses on advanced purification methods and their innovations.

1. Conventional Purification Processes

Traditional methods combine physical and chemical approaches:

1.    Magnetic Separation: Removes Fe and Ti via magnetism but ineffective against isomorphous impurities (e.g., Al³⁺, Li⁺).

2.    Flotation: Uses reagents to separate gangue minerals (e.g., feldspar), yet limited for submicron inclusions and lattice-bound impurities.

3.    Acid Leaching: Dissolves metal oxides with HCl/HF but weak against fluid inclusions.

4.    Oxidative Roasting: Eliminates organic impurities at high temperatures but energy-intensive and causes microcracks.

2. Innovative Purification Technologies

1. Chlorination Roasting

NH₄Cl decomposes into Cl⁻ at high temperatures, reacting with metal impurities (e.g., Al³⁺) to form volatile chlorides. This reduces total metallic impurities (Σ) from 21.36 ppm to 9.24 ppm, achieving 99.999% SiO₂ purity.

2. Pressure Leaching

Under high temperature (200–300°C) and pressure (1–5 MPa), acid penetration is enhanced, dissolving inclusions effectively. Pressure leaching increases Al removal from 64.21% to 94.51% and Fe removal from 81.65% to 85.32%.

3. Optimized Secondary Flotation

Targets residual isomorphous impurities (e.g., Al, Ti) using selective collectors (e.g., sulfonated oleic acid). Post-treatment, Al content drops from 9.19 ppm to 7.31 ppm, and Ti from 4.14 ppm to 3.70 ppm.

4. Microwave Roasting

Microwave selectively heats fluid inclusions, inducing rapid vaporization and internal pressure buildup to fracture quartz sand. This reduces inclusion density by 80%, improving transparency for crucible applications.

3. Challenges and Future Directions

1.    Deep Removal of Isomorphous Impurities: Novel techniques like ion exchange or supercritical fluid extraction are needed for Al/Ti removal.

2.    Fluid Inclusion Control: Integration of vacuum degassing and dynamic pressure regulation can eliminate nano-scale inclusions.

3.    Green Process Development: Replace hazardous chemicals (e.g., HF) with bioleaching or electrochemical methods.

Conclusion

Current technologies (e.g., chlorination roasting, microwave roasting) have improved purity, yet isomorphous impurities and fluid inclusions remain barriers to domestic 5N-grade quartz sand production. Future efforts should focus on multi-technology integration and eco-friendly innovations to achieve sustainable and autonomous manufacturing.