Abstract: An apparatus is provided for the wet-mechanical separation of solids within a parting liquid into floats and sinks according to their density which includes a container rotatable about an axis provided with at least one opening for the admission of said solids to be separated and at least one separate opening for the discharge of the sinks, the floats and the parting liquid. A screw conveyor for separating the solids is arranged in the container. The screw conveyor is rotatable about the container axis with one set of helices for engaging the floats and another set of helices for engaging the sinks. A diaphragm plate is arranged axially on the screw conveyor between the admission opening for the solids to be separated and the discharge opening for the sinks such that one part of the screw conveyor conveys the sinks to the sinks discharge opening with its helices and another part of the screw conveyor conveys the floats to the floats discharge opening with its helices.