Floating sulfides: activating and poisoning surfaces

Froth flotation is the established method of mineral separation in mineral processing. The flotation behaviour of sulfide minerals can be radically mo dified by surface sorption of metals from complex sulfide ore pulps; this c an be both beneficial (activation) and problematic (poisoning). Using XAS ( REFLEXAFS), the Pb species that "poison" and the Cu species that "activate" the surface of ZnS have been determined. The Cu activation, which is vital to successful ZnS flotation, involves Cu-Zn exchange at the ZnS surface an d the development of an oxidised CuS species xanthate attaches to this spec ies forming covellite. Pb sorbs onto the ZnS surface as an Pb-O species whi ch subsequently reacts with xanthate to form a PbS-like species. With chalc opyrite, both Zn and Pb can poison the surface; the Pb reacts with the CuS species which develops on the oxidised CuFeS2 surface while Zn sorbs onto t he FeOOH component present on the surface.