ACTIVATOR (from the Latin word "activus", which means "active" * EN: activator, activating agent, promoter; DE: Aktivator, Beieber; FR: activateur; ES: activador; RU: активатор) is the flotation reagent, which is used for the selective amplification of the flotability of the minerals under the conditions of the selective flotation.

The activators are usually water soluble ionogenic inorganic substances, which form the stable compounds on the surface of the mineral, which ensures the effective flotation. For example, the copper sulfate (or other water soluble compounds of copper) is the activator of the sphalerite (ZnS): the copper ions replace zinc on the surface of the sphalerite, thus forming the CuS, which is actively interacting with the collector, which enforces the flotation of the particles of the sphalerite. The reagent, which is activating one mineral, may be the depressor of the other mineral; the same reagent at the low concentrations may activate the mineral, while at the high concentrations it may become its depressor.