This paper studies several kinetic aspects of flotation of celestite and calcite in a mechanical cell with sodium dodecylsulphate as the collector agent, using pure minerals ranging in average particle size between 137 and 74 mum, respectively, with a constant pH 3 in the flotation bath in all experiments. The results obtained indicate that both minerals float rapidly and that the flotation rate constant responds to a non-integral order equation. Likewise, a linear relationship exists between flotation rate and particle diameter.