The effect of pulp oxidation potential, Eh, on the flotation of copper-activated pyrite at pH 9.0 in the presence of xanthate was investigated. It was found that pyrite recovery is at a maximum value when the Eh during conditioning is approximately 35 mV (SHE), but decreases at lower and higher Eh values. Solution and surface analytical techniques (EDTA extraction, and UV-visible and X-ray photoelectron spectroscopies) were used to explain the trends observed in the pyrite recovery with Eh. The increase in pyrite recovery with increasing Eh values has been attributed to an increase in xanthate adsorption at the pyrite surface while the decrease in recovery at high Eh values is the result of an increase in the proportion of surface iron oxidation species covering the hydrophobic species. (c) 2005 Elsevier Ltd. All rights reserved.