Unraveling roles of lead ions in selective flotation of scheelite and fluorite from atomic force microscopy and first-principles calculations

•Pb(II) played as an inhibitor for fluorite flotation and an on-off switch for scheelite flotation.•The adhesion force between BHA and the scheelite surface was stronger than that between BHA and fluorite without Pb(II).•BHA-Pb complexes demonstrated repulsive interactions on fluorite surfaces but attractions on scheelite surfaces.•AFM and first-principles calculations have shown great potential in the analysis of the complicated interface interactions.