Abstract: An improvement in a mixture concentrator on the one hand, or a fluid medium separator on the other, that is usable, for example, for significantly increasing the amount of proppant in a formation fracturing foam is disclosed. The concentrator is comprised of an elongate vessel, a rotor rotatably mounted inside the vessel on a shaft and a motor for rotating the shaft. The vessel has a mixture intake at a forward end and a concentrated mixture outlet and a fluid medium outlet at the rearward end. Mounted on the shaft near the mixture intake is a cylindrical stabilizer which imparts a spin to the incoming mixture. Also mounted on the shaft, downstream of the stabilizer and of the mixture intake is a intake impeller means for removing substantially only the fluid medium from the mixture which is located in the annular channel between the vessel and the rotor to an internal passageway located inside the rotor.