pH-driven selective flotation of scheelite using a tailored hydroxamate collector: mechanistic insights from surface coordination and dissolution

The efficient separation of scheelite from calcium-bearing gangue minerals remains a critical challenge in mineral processing due to their similar surface properties. This study introduces N-dodecanoyl-N-phenylhydroxylamine (DPHA), a structurally tailored hydroxamate collector, to address this long-standing selectivity issue. Systematic flotation experiments demonstrate DPHA’s superior performance over conventional collectors (benzohydroxamic acid and sodium oleate), achieving effective scheelite recovery at low concentrations under alkaline conditions (pH ≥ 12) without auxiliary reagents. Mechanistic investigations through contact angle measurements, Zeta potential tests, X-ray photoelectron spectroscopy (XPS) analyses reveal that DPHA’s ionic speciation at high pH facilitates selective chemisorption with calcium active sites on scheelite surfaces. Crucially, the reduced calcium dissolution from scheelite compared to calcite minimizes hydroxide competition for surface sites, enabling DPHA to overcome the inherent adsorption barriers in Ca-rich systems. The collector’s molecular architecture, featuring a hydroxamate headgroup for calcium coordination and a branched alkyl chain for enhanced hydrophobicity, synergistically promotes both selectivity and floatability. This work not only advances the flotation of tungsten resources but also provides a framework for designing surface-specific reagents in critical mineral recovery.