Activation effect of lead ions on scheelite flotation: Adsorption mechanism, AFM imaging and adsorption model

This paper systematically studied the effect of lead ions on floatability of scheelite under sodium oleate (NaOL) system, and the deep adsorption mechanism was revealed by a series of mechanism experiments and the adsorption morphology of NaOL was observed by atomic force microscope (AFM). Micro-flotation test indicated that the floatability of scheelite increased sharply from 47.25% to 80.12% in the presence of lead ions at pH 7. Zeta potential results revealed the positively charged lead ions species (Pb2+ and PbOH+) positively changed the zeta potential of scheelite, which favored the adsorption of negatively charged NaOL species (RCOO-, RCOOH.RCOO- etc.). XPS and FTIR analysis confirmed that NaOL was chemisorbed on scheelite surface and the adsorption was more severe in the presence of lead ions. Lead ions were chemisorbed on scheelite surface in the form of W-O-Pb2+, which facilitated the further adsorption of NaOL. This increased the active sites on scheelite surface for NaOL adsorption. AFM images intuitively showed the presence of lead ions increased the adsorption coverage of NaOL but did not affect the thickness of the adsorption layer. The adsorption thickness was still 6 nm-7 nm and the adsorption was multilayer adsorption. Based on these studies, an adsorption model was finally obtained.