Abstract: A rotary drum separator is provided having a plurality of elongated pockets that extend in the direction of pocket movement, wherein more than one kind of particle in a bulk mixture in the drum longitudinally may lodge in the pockets; wherein each of the pockets includes a generally flat upstream surface so that a particle longitudinally lodged therein partly rests or stands upon the generally flat surface when elevated above the bulk mixture. Diverse particles having about the same width and depth, but a different length, are able to be lifted by the pockets, but the longer ones are lifted higher above the bulk mixture. If the shorter particles also have a different shape than the longer ones so that the shorter ones are lodged less stably in the pockets than the longer ones, this difference will contribute to an earlier departure of the shorter particles from the pockets.