Much work has so far been done for modelling the magnetic deflecting (repulsive) force of eddy current separators. However, selective separation of various materials by eddy current separation depends not only on magnetic deflecting forces but also on competing forces like the gravitational force and the centrifugal force. Co-acting forces on a particle leaving the external drum are analyzed and evaluated in this study. Separation mechanisms of metal/non-metal and metal/metal separation systems have been investigated by a newly-developed High-Force® eddy-current separator. Further, a separation model governing an effective separation among various materials is presented. Based on this separation model, four practical separation criteria for metal/metal separation systems are put forward and have been substantiated experimentally.