XAS was employed to determine the nature of lead speciation on the surface of ZnS with relevance to sphalerite flotation. Lead sorbed onto the ZnS surface from mildly acidic solutions is present in a very disordered environment bonded to oxygen. On the addition of xanthate, bonds are formed between the surface lead and the xanthate sulfur, creating a more ordered structural environment for the lead. Atomistic computer simulations demonstrated that direct sorption of Pb onto the ZnS surface is energetically unfavourable. Thus, XAS has provided direct structural information for the processes involved in the activation of sphalerite during galena flotation.