The role of pH and of dissolved mineral species on the separation of pyrite and nonpyritic minerals from Pittsburgh No. 8 coal by flotation was investigated. In the pH range of 4 to 8, enhanced pyrite rejection was obtained at higher pH. However, pH itself had no measurable effect on the separation of non-pyritic minerals from coal in the pH range of 4 to 10. The precipitation/adsorption of the dissolved mineral ions resulted in a measurable decrease in the selectivity for non-pyritic minerals separation. Increased pyrite rejection with pH increase was shown, by induction time measurements, to be mainly due to the decrease of the pyrite hydrophobicity. The adsorption of Ca ions in the coal flotation systems had a positive effect on the pyrite separation, although it did not affect coal recovery to a measurable extent. This could be due to the selective precipitation/adsorption of Ca species on the pyrite surface. The precipitation/adsorption of Fe species had no measurable effect on the selectivity, even though it depressed coal flotation considerably. This is attributed to the non-selective precipitation of Fe species between the surfaces of coal and pyrite.