Research Progress on Flotation Separation of Fluorite and Calcite

Fluorite (CaF₂), a strategic mineral resource, plays a critical role in industries such as chemicals, metallurgy, and new energy. However, China's fluorite resources are predominantly low-grade and associated with calcite (CaCO₃), which are finely disseminated and complexly intergrown, making conventional physical separation inefficient. Flotation, the core technique for fine-grained minerals, faces significant challenges in separating fluorite from calcite.

Separation Challenges

1.    Similar Surface Properties: Both minerals exhibit Ca²⁺ as active sites, leading to comparable adsorption of fatty acid collectors and poor selectivity.

2.    Homogenization Effect: Dissolution of fluorite and calcite releases F⁻ and CO₃²⁻, which re-adsorb on mineral surfaces, reducing their floatability differences.

3.    Sensitivity to Slurry Environment: pH significantly impacts dissolution and surface conversion. For instance, calcite solubility increases under alkaline conditions, intensifying competitive adsorption.

Floation Technologies and Reagent Development
Current research focuses on direct flotation (depressing calcite and collecting fluorite), with key advancements in collectors, depressants, and their combinations:

1. Collector Optimization

·         Anionic Collectors: Oleic acid is widely used but modified via acidification or halogenation to enhance selectivity. Acidified oleic acid achieved 98.8% CaF₂ grade and 97.1% recovery.

·         Combined Collectors: Synergistic effects from cationic-anionic mixtures (e.g., CTAB and SPA) expand hydrophobicity differences, increasing contact angle disparity to 26.7°.

·         Novel Collectors: Sodium N-lauroylsarcosinate (SNLS) and propyl gallate (PG) enable selective adsorption. SNLS showed a 54.59% recovery gap between fluorite and calcite at pH=9.

2. Depressant Innovation

·         Inorganic Depressants: Acidified sodium silicate forms hydrophilic silica gels on calcite, while sodium hexametaphosphate chelates Ca²⁺.

·         Organic Depressants: Tannic acid and humate bind to calcite via chemical/hydrogen bonds. Myrica tannin reduced calcite recovery from 66.9% to 9.8%.

·         Combined Depressants: Acidified sodium silicate mixed with humate synergistically depresses calcite, yielding 98.07% fluorite concentrate.

·         Metal Ion Assistance: Pb²⁺ and Al³⁺ enhance depressant selectivity. Pb²⁺ forms lead silicate polymers to strengthen calcite depression.

3. Reverse Flotation Exploration
Reverse flotation (depressing fluorite) is less studied but shows promise. For example, diethylenetriamine pentamethylene phosphonic acid (DTPMP) selectively depresses fluorite at low dosages.

Future Directions

·         Develop cost-effective, selective depressants (e.g., polyhydroxy compounds);

·         Investigate metal ion-reagent interactions;

·         Optimize reagent combinations for complex ores.

Efficient fluorite-calcite separation is vital for sustainable resource utilization. Breakthroughs in reagent innovation and process optimization could overcome current limitations, providing technical support for strategic mineral exploitation.