Effect of dissolved oxygen on the sulfidization flotation of smithsonite

•Sulfidization favors the floatability of smithsonite, and the presence of dissolved oxygen deteriorates it.•In the absence of dissolved oxygen, the stable sulfidization products (zinc monosulfide) formed rapidly on the smithsonite surfaces.•Dissolved oxygen frustrates the formation of the sulfidization products.•The newly unstable sulfidization products could be oxidized to sulfate.