The interaction of the sphalerite (ZnS) mineral with ferrous, ferric, and xanthate ions at pH 10 has been studied by using ex situ X-ray photoelectron (XPS) and ex situ and in situ infrared (DRIFTS and ATR, respectively) spectroscopy. Interaction occurs with Fe2+ but not with Fe3+. The mechanism involves initial adsorption of Fe2+, followed by oxidation to Fe3+, and subsequent reaction with xanthate. The final surface product is hydrophobic and may be a factor in the notation of sphalerite.