Electrostatic separation of non-conductive materials can be accomplished by triboelectric charging. The efficiency of convential separators becomes worse in the size range below about 100 m. These problems are solved by developing a new double-drum-separator. The investigations have shown the possibility of separating very fine mineral mixtures (eg quartz/calcite) in a strong electric field after tribo-charging in a special dust-feeder. The paper reports about the influence of particle size and field intensity on the separation and deals furthermore with the problem of desagglomeration.