An apparatus (10) for surface treating particulate material (M) with surface treatment particles (S) includes a substantially cylindrical body (12) having a top (18), bottom (16) and sidewall (14). A mixing chamber (42) is defined within the body (12). At least one injector inlet (36) and at least one process air inlet (32) are in communication with the mixing chamber (42). At least one outlet (34) is in fluid communication with the mixing chamber (42).