Quartz sand beneficiation and deep processing technology

 Introduction

Quartz sand, a critical non-metallic mineral resource with SiO₂ content exceeding 99.9%, is widely used in high-end industries such as semiconductors, photovoltaics, and optical glass. However, natural quartz sand contains impurities like iron, aluminum, and feldspar, necessitating advanced beneficiation and deep processing to meet industrial standards. This article systematically analyzes the key processes in quartz sand purification and modification, providing insights for industrial production.

1. Quartz Sand Beneficiation Process

The beneficiation process involves crushing, magnetic separation, flotation, and dehydration to remove impurities and obtain high-grade concentrates.

1.1 Crushing and Screening

The primary step is multi-stage crushing and screening:

·         Primary Crushing: Jaw crushers reduce raw ore (300–500 mm) to 50–100 mm.

·         Secondary Crushing: Cone or impact crushers further break particles to 20–50 mm.

·         Screening: Vibrating screens classify particles into 0.074–4.75 mm.

Parameters such as crushing ratio (4–6) and feed rate are optimized to avoid over-grinding. Dust control systems (e.g., bag filters) ensure workplace safety.

1.2 Magnetic Separation and Flotation

·         Magnetic Separation: Wet magnetic separators (0.1–0.3 T) remove iron oxides. pH adjustment (8.5–9.0) and FeSO₄ activation enhance efficiency, reducing Fe₂O₃ to <0.05%.

·         Flotation: Using cationic collectors (e.g., octadecylamine) and frothers (pine oil), feldspar and mica are separated in alkaline conditions (pH 8–9). Multi-tank and column flotation cells achieve Fe₂O₃ ≤0.02% and Al₂O₃ ≤0.15%.

1.3 Washing and Dewatering

·         Washing: Hydrocyclones remove micron-sized impurities via centrifugal force. The cut size ds is determined by ds= KΔpVDμ..

·         Dewatering: High-frequency screens (40–50 Hz) reduce moisture content to <1%, with residual impurities <0.1%.

2. Deep Processing Technologies

2.1 Chemical Purification

·         Acid Leaching: HCl (10%–20%) at 90–100°C dissolves metal impurities, achieving >95% removal.

·         Alkali Fusion: NaOH/Na₂CO₃ melting (800–1000°C) forms soluble silicates, yielding 99.999% purity after washing.

2.2 Heat Treatment

Phase transformations under controlled conditions:

·         α-Quartz (<573°C): Enhanced hardness.

·         β-Quartz (573–870°C): Microcracks improve interfacial bonding.

·         β-Tridymite (>870°C): Particle refinement.

Inert gas protection and precise cooling rates prevent defects.

2.3 Precision Classification and Surface Modification

·         Electrostatic Classification: High-voltage fields separate 1–100 μm particles based on surface charge.

·         Surface Modification: Silane coupling agents (e.g., γ-APS) or ball milling (energy E =1/2m(ωR)2)enhance hydrophobicity and reactivity.

3. Conclusion and Prospects

China has mastered core technologies for high-purity quartz sand production, yet challenges remain in cost reduction and equipment innovation. Future efforts should focus on:

1.    Process Optimization: Developing eco-friendly methods like bioleaching.

2.    Equipment Advancements: High-precision separators and AI-driven control systems.

3.    Application Expansion: Tailoring products for 5G and quantum computing.

Collaborative R&D will strengthen China’s position in the global quartz sand industry.