Scheelite beneficiation process improves beneficiation efficiency by 20%

 Introduction

Scheelite (CaWO₄) is one of the most critical tungsten resources, accounting for over 60% of global tungsten reserves. In China, scheelite deposits are mainly skarn-type or composite-type, often associated with molybdenum, bismuth, and copper. Due to its finer grain size and complex mineralogy, scheelite beneficiation predominantly relies on flotation. However, challenges such as separation from calcium-bearing minerals (e.g., fluorite, calcite) and low recovery of fine particles persist. This article systematically reviews the process flow, key technologies, and future directions of scheelite processing in China.

1. Main Process Flow of Scheelite Beneficiation

The scheelite beneficiation process generally includes pre-treatment, sulfide flotation, tungsten roughing, and cleaning:

1. Pre-treatment and Grinding

·         Crushing: Three-stage crushing (jaw crusher, cone crusher) reduces ore size to 10-15 mm.

·         Grinding: Rod or ball mills grind ore to 80% passing 200 mesh, ensuring liberation of scheelite.

2. Sulfide Flotation

Scheelite is often associated with sulfides (e.g., chalcopyrite, galena), which are removed first:

·         Regulators: Lime (pH 9-10) to depress pyrite; zinc sulfate for sphalerite suppression.

·         Collectors: Xanthates (e.g., butyl xanthate) or dithiophosphates.

·         Example: A one roughing-two scavenging-three cleaning circuit achieves 85% sulfide recovery and 20% Cu concentrate grade.

3. Tungsten Roughing

Sulfide tailings undergo scheelite roughing:

·         Regulators: Sodium carbonate (pH 9.5-10.5) and sodium silicate to depress quartz.

·         Collectors: Fatty acids (e.g., oleic acid) or chelating agents (e.g., 733, GYB).

·         Process: A one roughing-three scavenging circuit yields rough concentrate with 5%-10% WO₃.

4. Cleaning Process

The rough concentrate is upgraded to >65% WO₃ via:

·         Hot Flotation (Petrov Process):
Concentrate is thickened to 60%-70% solids, heated to 80-90°C with sodium silicate, and stirred for 30-60 minutes to depress calcium minerals. Subsequent flotation at ambient temperature enhances selectivity.

·         Cold Flotation:
Combined depressants (sodium silicate + sodium hexametaphosphate) and chelating collectors (e.g., GYB) achieve separation. For instance, Dangping Tungsten Mine’s Baoshan Plant attains 68% WO₃ grade and 82% recovery via a one roughing-two scavenging-five cleaning circuit.

2. Key Technologies and Equipment

1. Advanced Reagent Systems

·         Chelating Collectors: Agents like 733 (hydroxamic acid) and GYB (phosphonic acid) selectively adsorb on scheelite surfaces.

·         Composite Depressants: Sodium silicate + sodium carbonate for fluorite suppression; sodium hexametaphosphate for slime dispersion.

2. Optimized Flotation Equipment

·         Air-forced Flotation Cells: KYF-type for high-throughput roughing.

·         Mechanical Agitation Cells: XCF-type for precise cleaning.

3. Fine Particle Recovery

·         Centrifugal Concentrators: Enrich -20μm particles via enhanced centrifugal forces.

·         High-Gradient Magnetic Separators (HGMS): Remove weakly magnetic impurities.

3. Case Studies

Case 1: Dangping Tungsten Mine, Baoshan Plant

·         Ore Characteristics: Skarn-type scheelite with fine grains (10-50μm), intergrown with fluorite and calcite.

·         Process Flow:

1.    Sulfide flotation: One roughing-two scavenging-three cleaning for Cu, Pb, Zn recovery.

2.    Scheelite roughing: Collector 733 with Na₂CO₃/Na₂SiO₃, one roughing-three scavenging.

3.    Cold cleaning: Five-stage cleaning after 45-minute conditioning with sodium silicate.

·         Performance: 68% WO₃ grade, 82% recovery, fluorite content <3%.

Case 2: Xianglushan Tungsten Mine Retrofit

·         Issues: Low recovery (50%) via gravity separation; fine particle losses.

·         Solutions:

1.    Introduced flotation with chelating collector GYB.

2.    Added centrifugal concentrators for slime recovery.

·         Results: Overall recovery increased to 75%, generating over CNY 10 million annually.

4. Challenges and Future Directions

1. Current Limitations

·         Separation from Calcium Minerals: Fluorite and scheelite show similar floatability.

·         Low Fine Particle Recovery: <40% efficiency for -10μm particles.

·         High Energy Consumption: Hot flotation accounts for 30% of total costs.

2. Innovation Pathways

·         Novel Reagents: Targeted chelating collectors and eco-friendly depressants.

·         Advanced Equipment: Hybrid force-field flotation cells (e.g., ultrasound-enhanced).

·         Hydrometallurgical Integration: Alkali leaching of low-grade concentrates (15%-30% WO₃).

3. Sustainability and Intelligence

·         AI-driven Optimization: Machine learning for real-time reagent and parameter adjustment.

·         Water Recycling: Closed-loop water systems to minimize freshwater use and wastewater discharge.

5. Conclusion

Scheelite beneficiation, centered on flotation, has achieved high recovery and concentrate grades through reagent innovation and process optimization. However, challenges in calcium mineral separation, fine particle recovery, and energy consumption demand breakthroughs. Future advancements in chelating agents, intelligent sorting, and sustainable practices will drive the industry toward higher efficiency and lower carbon footprints, ensuring the sustainable utilization of tungsten resources.