Abstract: Clarifier sludge is dewatered to a relatively low residual moisture content by passing it axially in one direction through an inner centrifuge drum in which initial dewatering takes place in a first centrifugal force field. Immediately thereafter the solids phase is introduced into an outer second drum having a diameter approximately twice that of the first and in which the solids are subjected to a centrifugal force field about twice as great as the first force field. In each drum the solids are displaced by wipers or scrapers (strippers) preferably of the worm type and the liquid is drawn from the drum at the opposite axial end from that at which the solids are removed.

Abstract: A slurry, such as of sulfide-type copper ore, is separated into a coarse suspension and a fine suspension. The coarse suspension is centrifuged to separate the solid and liquid phases thereof. The fine suspension may be centrifuged or filtered separately from the coarse suspension similarly to separate its solid and liquid phases. The solid phases of both of these separation operations are then mixed together and can be used for further smelting. It is also possible according to this invention to use a drum centrifuge both for the initial separation into fine and coarse suspensions and for the dewatering for the coarse suspension.