Research on Bentonite Ore Dressing and Purification Technology

Introduction

Bentonite, a layered silicate mineral primarily composed of montmorillonite, is renowned as the universal clay due to its unique physicochemical properties (e.g., adsorption, swelling, ion exchange). It is widely used in metallurgy, environmental protection, chemicals, and pharmaceuticals. However, natural bentonite typically has low montmorillonite content (often around 50%) and contains impurities such as quartz, feldspar, and cristobalite, limiting its direct application in high-end products. Thus, beneficiation and purification are critical to enhancing its value. This article reviews global research progress on bentonite purification methods and their practical applications.

 Major Purification Methods for Bentonite

Bentonite purification techniques include physical (dry and wet) and chemical methods, with selection depending on ore grade, impurity types, and target applications.

1. Dry Purification

Dry purification is a physical separation method based on density and particle size differences, suitable for high-grade bentonite (montmorillonite >80%), especially in arid regions. Key steps include crushing, air classification, and cyclone separation.

· Process Flow: Drying → Crushing → Air Classification → Fine Particle Collection.

· Advantages: Water-free, low cost, eco-friendly, high recovery. For instance, Yang Qifan et al. achieved a 32% increase in montmorillonite content in Xinjiang sodium-based bentonite, while Wang Zhiqiang reported 24% cost savings.

· Limitations: Ineffective for low-grade ores and ultrafine impurities (e.g., cristobalite).

2. Wet Purification

Wet purification, the mainstream method in China, separates impurities via hydraulic forces and includes sub-techniques:

（1）Natural Sedimentation

Montmorillonite and impurities are separated by settling velocity. Xie Jingli et al. improved montmorillonite content from 75% to 96.4% using stirring-sedimentation-filtration. However, this method is time-consuming and low-yield, often used as a pretreatment.

（2）Centrifugation

Centrifugal force accelerates particle settling. OZOLA-DAVIDANE et al. optimized parameters (700 r/min, 2 min) to increase montmorillonite content from 44% to 96.5%. Fu Jiacheng combined sodium modification and ultrasonic exfoliation to remove cristobalite, though energy consumption remains a challenge.

（3）Flocculation

Flocculants (e.g., organic polymers) induce montmorillonite aggregation. Li Yuling et al. used chitosan acetate to boost montmorillonite content from 46.7% to 90.1%, but flocculants may reduce adsorption performance.

（4）Ultrasonic Method

Ultrasonic cavitation disrupts montmorillonite-impurity bonds. Zhao Zihao et al. achieved >90% montmorillonite purity using ultrasonic-centrifugal synergy, while Wang Fuping efficiently removed hematite via ultrasound pretreatment.

（5）Hydrocyclone Separation

This technique leverages density and size differences for efficient grading. Yin Hang et al. applied a three-stage hydrocyclone system to increase montmorillonite content from 75% to 97.59%, while Ren Ruichen optimized slurry concentration and pressure for >95% purity.

3. Chemical Purification

Chemical methods target ultrafine impurities (e.g., cristobalite, lattice iron). NaOH dissolves quartz, while sodium dithionite removes iron oxides. QIAO et al. demonstrated that chemical-physical hybrid methods achieve ~99% purity but require strict condition control to preserve montmorillonite structure.

 Selection and Optimization of Purification Processes

1.        Impurity Analysis: Quartz and feldspar are removable via physical methods, while cristobalite (<2 μm) requires chemical treatment.

2.        Application Requirements: Medical-grade montmorillonite demands >99% purity, whereas foundry binders need moderate levels.

3.        Cost-Effectiveness: Dry methods suit water-scarce regions, wet methods for large-scale production, and chemical methods for high-value products.

4.        Hybrid Processes: Combined techniques (e.g., centrifugation-ultrasonic-chemical) enhance efficiency and purity.

  Challenges and Future Perspectives

1.        Technical Barriers: Separation of ultrafine impurities and structural preservation during chemical purification need breakthroughs.

2.        Green Development: Low-energy, non-polluting methods (e.g., bio-flocculants) are emerging.

3.        Intelligent Systems: AI-driven parameter optimization enables precise control.

 Conclusion

Bentonite purification is pivotal for resource utilization. With advancements in dry, wet, and chemical methods, the integration of multi-technology synergies and green innovations will drive the bentonite industry toward high-end and sustainable development.