Beneficiation and Lithium Extraction from Lepidolite: Current Status, Challenges, and Future Directions

Introduction: The Significance of Lithium and the Role of Lepidolite

Lithium, hailed as the "Energy Metal of the 21st Century," is witnessing surging demand driven by electric vehicles, energy storage systems, and consumer electronics. Approximately 60% of global lithium salts are produced from hard-rock lithium ores, with lepidolite contributing around 15% of global lithium salt output. However, low-grade lepidolite ore (0.1%-0.7% Li₂O) and its association with gangue minerals like feldspar and quartz complicate its beneficiation and extraction processes. This article reviews advances in lepidolite beneficiation and lithium extraction technologies while exploring future trends.

I. Physical Beneficiation of Lepidolite

Physical beneficiation aims to separate gangue minerals and concentrate lepidolite through differences in surface properties or physical characteristics. Key methods include gravity separation, magnetic separation, and flotation, with flotation being the most efficient.

1. Flotation: Collector Optimization

Flotation relies on selective collectors. Lepidolite’s negatively charged surface traditionally interacts with cationic collectors (e.g., dodecylamine (DDA) or coconut amine) under acidic conditions. However, conventional cationic collectors face challenges such as pH sensitivity and high foam viscosity.

Innovations:

• Combined Collectors:      Anionic-cationic hybrid collectors (e.g., DDA with oxidized paraffin soap)      improve efficiency, elevating Li₂O grade from 3.77% to      4.4%.

• Novel Collectors: Surfactants like      dodecyl dimethyl ammonium bromide (HBDB) reduce dosage by 50% while      boosting lithium recovery by 16%.

• Magnetic-Flotation Integration:      Post-flotation high-intensity magnetic separation removes iron-bearing      micas, increasing Li₂O grade from 2.6% to 3.03%.

2. Auxiliary Techniques: Gravity and Magnetic Separation

• Gravity Separation:      Pre-concentrates tantalum-niobium minerals using density differences      (72.39% recovery at 2.7 specific gravity).

• Magnetic Separation: Weak magnetic      separation removes magnetite, while high-intensity separation eliminates      iron-rich micas.

II. Chemical Lithium Extraction from Lepidolite Concentrate

Lepidolite concentrate (1.7%-3.5% Li₂O) undergoes chemical processing to break its mineral structure. Dominant methods include sulfate roasting, chlorination roasting, sulfuric acid leaching, and pressure digestion.

1. Sulfate Roasting: Mature but Energy-Intensive

Lepidolite reacts with sulfates (e.g., Na₂SO₄, FeSO₄) at 700-1000°C, converting lithium into soluble sulfates.

• Advantages: High adaptability (96%      Li recovery) for low-grade ores.

• Challenges: High energy consumption      (e.g., 675°C for FeSO₄), hazardous gas emissions (HF, SO₂),      and alkaline slag disposal.

2. Sulfuric Acid Method: Efficiency vs. Waste Management

• Acid Curing: Concentrated H₂SO₄ reacts with lepidolite at 150-350°C, achieving >95%      Li extraction but requiring alkali neutralization.

• Direct Leaching: Simpler process      but lower recovery (62%-76.7%).

3. Chlorination Roasting: Short Process with Equipment Demands

Using CaCl₂ or NaCl at 800-1000°C, lithium converts to soluble chlorides.

• Advantages: Co-recovery of Rb and      Cs with minimal residue.

• Limitations: Corrosive agents      demand anti-corrosion equipment, and Ca(OH)₂ is      needed to suppress side reactions.

4. Pressure Digestion: High Efficiency Under Pressure

• Lime Digestion: Defluorinated      lepidolite reacts with lime milk under high pressure, yielding 98.9% Li      extraction and 99.9% purity Li₂CO₃, albeit with high capital costs.

• Alkaline Leaching: NaOH pressure      leaching recovers Li and Rb (>96%), but impurities co-precipitate.

5. Fluoride-Based Methods: High Efficiency with Environmental Risks

HF or H₂SiF₆ dissolves lithium (＞97% recovery), but HF emissions require closed-loop treatment.

III. Challenges and Future Prospects

Current challenges include low resource utilization, high energy costs, and environmental pressures. Future directions focus on:

1. Collector Innovation: Developing      cost-effective, selective collectors (e.g., bio-engineered surfactants).

2. Co-Extraction of Metals: Enhancing      recovery of Li, Rb, Cs, and K.

3. Process Integration: Combining      sulfate roasting with pressure digestion and using low-cost additives      (e.g., FeSO₄·7H₂O).

4. Waste Valorization: Converting      lithium slag into construction materials or extracting Si/Al.

5. Green Technologies: Optimizing gas      (HF, SO₂) capture and exploring low-toxicity alternatives to HF.

Conclusion

As a strategic resource, lepidolite’s efficient utilization is vital for lithium supply chains. Through optimized flotation, innovative extraction, and resource recycling, lepidolite processing is transitioning toward sustainability. Collaborative R&D and policy support will accelerate technological breakthroughs, fostering a greener lithium industry.