Tannin vs. Starch in Green Hematite Reverse Cationic Flotation Separation from Micaceous Minerals

Reverse cationic flotation remains the principal technique for upgrading hematite from silicate minerals. Micaceous phyllosilicates, such as biotite and phlogopite, pose significant challenges because their surface properties often resemble those of hematite. Limited investigations address the potential interactions between these silicates and hematite depressants. To address this gap, this study comprehensively evaluated two biodegradable depressants, corn starch (CS) and tannin (TA), assessing their effects on the floatability of biotite and phlogopite. An integrated approach was employed, combining mineral characterization (XRD and XRF), surface chemistry analyses (contact angle, zeta potential, turbidity, adsorption, and FTIR), and micro-flotation experiments (single and mixed minerals) to reveal the molecular interactions of these green reagents with mineral surfaces under industrially relevant alkaline conditions. Experimental results revealed distinct adsorption mechanisms of CS and TA on the mineral surfaces studied, leading to different flotation responses. At an optimum depressant dosage of 100 mg/L, hematite flotation recovery decreased to ∼1.9-8.8% with TA and ∼2.5-12.7% with CS over the examined EDA range (0-30 mg/L). TA exhibited broader depression, affecting both hematite and micaceous gangue minerals. It forms strong chemical bonds with Fe-rich surfaces via complexation, making it suitable for bulk gangue rejection but limiting selective separation. CS was selective because it preferentially adsorbed onto hematite via acid-base/H-bond interactions with hydroxylated Fe sites, thereby limiting amine adsorption, whereas its weaker interaction with micaceous minerals (limited accessible metal sites; siloxane/silanol-dominated surfaces) preserved biotite/phlogopite floatability. Its adsorption occurred primarily via acid-base interactions and hydrogen bonding, yielding higher-grade iron concentrates with lower SiO 2 contamination (SiO 2 reduced from 16.74% to 4.09% in hematite concentrate). Flotation tests on single and mixed minerals confirmed that selecting an appropriate depressant can significantly improve hematite recovery while reducing silica in the concentrate. Overall, CS proved more selective and effective for high-quality separation. The mechanistic understanding and development of sustainable depressants are thus essential for enhancing beneficiation efficiency, meeting quality standards in steel production, and promoting mineral processing.