Study on the role of a hydroxamic acid derivative in wolframite flotation: Selective separation and adsorption mechanism

• A hydroxamic acid derivative (NPOHA) was synthesized and first introduced as wolframite collector. • The chemical reactivity and surface activity of NPOHA were stronger than BHA and OHA. • NPOHA could efficiently separate wolframite from fluorite and quartz, with no activator or frother applied. • NPOHA chemisorbed onto wolframite surfaces by bonding two oxygen atoms of CONOH group with Fe atom. Wolframite, as the main mineral for extracting tungsten, is usually separated and enriched by flotation in mineral processing, thus the construction of efficient flotation collector is of great concern to the effective utilization of tungsten resources. In this study, by introducing a phenyl group into octyl hydroxamic acid (OHA) structure, we design and synthesize a hydroxamic acid derivative N-substituted phenyl octyl hydroxamic acid (NPOHA), and report its first employment as a collector in wolframite flotation. Density functional theory (DFT) calculations and surface activity characterization revealed that compared to OHA and benzohydroxamic acid (BHA), NPOHA possessed not only superior electron-donating ability and chemical reactivity, but also stronger hydrophobicity, which contributed to its application in wolframite flotation. Micro-flotation tests proved that NPOHA possessed much stronger collecting ability to wolframite than BHA and OHA, with superb flotation selectivity against quartz and fluorite, which was regarded as an appropriate collector for wolframite flotation. Zeta potential, Fourier Transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements indicated that NPOHA chemisorbed onto wolframite surfaces through the formation of N-O-Fe and C-O-Fe bonds, which was further verified and explained by binding ability evaluations.