The change in collectorless flotation of sphalerite with pH and Cu(II) concentration was correlated with the type and proportion of species present on the sphalerite surface. The solution and surface species were determined using a combination of analytical techniques including zeta potential measurement and X-ray photoelectron spectroscopy. An optimum copper concentration for maximum sphalerite flotation was identified, beyond which flotation decreased. This decrease in flotation coincided with the precipitation of copper hydroxide in neutral to mildly alkaline pH conditions, The hydrophobic polysulfide and hydrophilic copper hydroxide species were the main surface species influencing splialerite flotation. (c) 2005 Elsevier B.V. All rights reserved.