High-Purity Quartz Sand Purification: From Ore to Critical Advanced Material

Quartz sand, particularly high-purity quartz with SiO₂ content ≥99.99%, is a strategic material for semiconductors, photovoltaics, and aerospace. Its purification integrates physical, chemical, and thermodynamic technologies. Here are the core processes and breakthroughs:

 I. Four-Stage Purification: Stepwise Impurity Removal

1.        Preprocessing

o  Crushing & Washing: Raw ore is crushed to 20–40mm via jaw/cone crushers, then pulverized into 0–5mm particles. Clay and dust are removed by hydrocyclones or scrubbers, reducing Fe/Al content significantly17.

o  Desliming & Classification: Removes >80% of iron and aluminum impurities from fine-grained sand7.

2.        Physical Purification

o  Magnetic Separation: Wet high-intensity magnetic separators (≥10,000 Oe) target weakly magnetic minerals (e.g., hematite). Finer particles yield better results14.

o  Flotation: Cationic/anionic collectors (e.g., dodecylamine-PS blend at 6:1 ratio) float feldspar and mica, achieving 99.3%–99.9% SiO₂. Fluorine-free methods now replace toxic HF-based processes36.

3.        Chemical Refinement

o  Acid Leaching: Sulfuric acid (15%–20%) or dilute HF (≤10%) dissolves metal oxides at 60–80°C for 2–4 hours. In Algerian high-iron desert sand, H₂SO₄ leaching achieved >88% iron removal12.

o  Hybrid Enhancement: Calcination (900°C) cracks fluid inclusions; water quenching expands fractures, boosting acid penetration. Fe/Al removal rates reach 88.71% and 36.79%10.

4.        Deep Purification

o  Chlorination Roasting: At 1000–1200°C, dry HCl or Cl₂ gas volatilizes lattice-bound alkali metals (K, Na). Tests by Hubei Feilihua show Na/K content drops below 0.5ppm after 2 hours, meeting demands for 12-inch silicon wafers49.

 II. Game-Changer: Chlorination Roasting

This technique uniquely eliminates lattice impurities. U.S.-based Unimin leads its industrial application, with critical insights:

· Precision Control: Temperatures >1200°C cause quartz melting, blocking impurity diffusion paths.

· Optimized Agents: Dry HCl outperforms Cl₂ in removing Na, Fe, and K94.

III. Customized Process Flows

Solutions adapt to ore characteristics:

· Glass-Grade Sand: Scrubbing–magnetic separation–flotation (SiO₂≥99.5%)7.

· Semiconductor-Grade: Rod-mill scrubbing–flotation–acid leaching–chlorination (SiO₂≥99.99%, Fe≤5ppm)16.

· Green Innovations: Microbial leaching (e.g., Aspergillus niger) and microwave-assisted acid treatment reduce energy use and pollution13.

 Conclusion: Strategic Imperatives

Purification technology transforms industrial sand (¥30,000/ton) into photovoltaic-grade material (¥200,000/ton). With advances like fluorine-free flotation and low-temperature chlorination, China is poised to break foreign monopolies and underpin its semiconductor and renewable energy ambitions