collected by the extraction unit 22 are pumped through a pipe 24 to a centrifugal cleaning device 26 to remove relatively high specific gravity contraries such as staples sand grit and glass from the fiber in a preferred embodiment of the invention a high consistency centrifugal cleaner for example the liquid cyclone from black clawson co is suitable as the centrifugal cleaning device cleaned fiber from the centrifugal cleaning device 26 is then pressured through a pipe 28 to a low consistency forward centrifugal cleaner 30 to remove small grit and similar material not removed in the high consistency centrifugal cleaner 26 a suitable device for the forward centrifugal cleaner 22 is the rb 90 manufactured by ahlstrom having a 3 to 4 inch diameter cone the centri cleaner u00ae from c e bauer has also been found to be suitable preferably the forward centrifugal cleaner may comprise a bank of cleaners in series in the illustrated embodiment reject from the forward centrifugal cleaner 30 is sent through a pipe 50 to a secondary forward centrifugal cleaner 31 the secondary forward centrifugal cleaner 31 is similar to the forward centrifugal cleaner 30 and removes very fine high density particles such as glass fragments from the material additional forward centrifugal cleaner stages may be provided to minimize fiber loss by additional reprocessing of the reject material accept material is fed from the secondary forward centrifugal cleaner 31 through a pipe 48 to the primary process immediately upstream of the forward centrifugal cleaner 30.