Electrostatic separation of metals and plastics from granular industrial wastes

Recycling of metals and plastics from wastes is one of the major applications of the electrostatic separation technologies. The paper analyses the multitude of factors that affect the efficiency of this technique, to establish design principles and formulate operation recommendations. The theoretical analysis of corona and induction charging of, respectively, insulating and conducting particles allows a crude evaluation of the role of the various factors involved, including the electric field strength E-0, and the current density J in the active zone of the separator. A first set of experiments has been carried out for estimating E-0, J and the charging time constant tau, based on the measurement of the current-voltage characteristic of a standard electrode arrangement. A second set of experiments consisted of three series of separation tests performed on samples of millimetre-sized granulated electric wire scrap (62.5% copper, 37.5% PVC). By using a combined corona-electrostatic field and a three-stage separation scheme? a PVC concentrate containing less than 0.04% copper (recovery: 92.2%) and a copper product with less than 0.1% PVC (recovery: 90.8%) were obtained. Design and operation recommendations were formulated regarding the optimum electrode arrangement, high-voltage level, roll speed and feed rate for typical industrial applications.