Dual role of environmentally friendly tannin extract in lead−zinc separation: Elimination of Pb2+ activation and enhancement of sphalerite hydrophilicity

This study introduces tannin extract (TE) as a novel organic depressant for the highly selective separation of galena from sphalerite under weak alkaline conditions (pH 8) without lime. Although the collector aniline aerofloat (AAF) exhibits excellent selectivity in single-mineral flotation, its performance is severely compromised in mixed-ore systems due to Pb²⁺ activation of sphalerite, significantly reducing separation efficiency. The introduction of TE effectively addressed this challenge, achieving 80 % galena recovery while suppressing sphalerite recovery to 24 % in mixed-ore flotation. XPS analysis revealed that TE eliminates Pb²⁺ activation on sphalerite surfaces, as indicated by the shift in Zn 2p₃/₂ binding energy from 1022.37 eV (Pb²⁺-activated state) to 1021.12 eV (near-native state), preserving the inherent surface properties of sphalerite. Furthermore, TE chemically interacts with Zn atoms in the sphalerite lattice through its active functional groups (–OH and –COOH), forming stable surface complexes that significantly enhance mineral hydrophilicity. Zeta potential measurements, FTIR spectroscopy, and contact angle analyses confirmed that TE adsorption substantially increases sphalerite surface hydrophilicity, thereby effectively regulating its flotation behavior. These findings demonstrate that TE achieves selective sphalerite depression through a dual mechanism: eliminating Pb²⁺ activation and enhancing surface hydrophilicity via chemisorption.