Mechanistic insights into Pb2+-mediated benzohydroxamic acid adsorption and bubble attachment on rutile

Functionalized AFM directly quantified Pb 2+ -mediated BHA–rutile interactions. • Pre-mixed Pb–BHA maintained ~90% rutile recovery over pH 3.5–10.0. • Pre-formed Pb–BHA species strengthened interfacial adhesion on rutile. • Bubble-probe AFM showed that Pb–BHA weakened hydration-film resistance and facilitated bubble–rutile attachment. Understanding metal-ion-mediated interfacial interactions is critical for regulating hydroxamate adsorption on oxide surfaces. However, the molecular mechanism by which Pb 2+ promotes benzohydroxamic acid (BHA) adsorption on rutile (TiO₂), as well as its influence on bubble–rutile attachment, remains insufficiently understood. Herein, an integrated interfacial analysis combining functionalized atomic force microscopy (AFM) force spectroscopy and AFM bubble-probe measurements was employed to elucidate the Pb 2+ -assisted adsorption mechanism at the molecular level. Macroscopic flotation and wettability measurements revealed that pre-formed Pb–BHA complexes improved flotation stability and promoted rutile surface hydrophobization compared with untreated rutile, outperforming sequential reagent addition over a broad pH range. Functionalized AFM force spectroscopy provided direct evidence of strengthened collector–rutile interaction forces in the presence of Pb 2+ , confirming the formation of a stronger interfacial coordination structure. In addition, AFM bubble-probe measurements revealed that Pb 2+ –BHA adsorption weakened the hydration repulsion between air bubbles and rutile surfaces, promoted short-range attractive interactions, and facilitated bubble–mineral attachment. These results demonstrate that Pb 2+ functions as an interfacial coordination mediator by forming a metal–ligand–surface bridging structure, thereby enhancing both collector adsorption strength and bubble attachment efficiency. This study provides direct molecular- and interface-scale evidence for metal-ion-regulated hydroxamate adsorption, hydration-layer modulation, and bubble attachment enhancement on oxide mineral interfaces.