The effect of Cu2+, Fe2+ and Ca2+ ions on pyrite floatability with xanthate as a function of pH in the presence and absence of sphalerite was studied. in the alkaline pH region, these ions activated the pyrite when alone but not when sphalerite was present. Zeta-potential measurements and infrared surface characterization confirmed the different interaction with xanthate depending whether the pyrite was alone or with sphalerite.