Electrostatic separation of metals and plastics from granular industrial wastes

Recycling of metals and plastics from wastes is one of the major applicatio ns of the electrostatic separation technologies. The paper analyses the mul titude of factors that affect the efficiency of this technique, to establis h design principles and formulate operation recommendations. The theoretica l analysis of corona and induction charging of, respectively, insulating an d conducting particles allows a crude evaluation of the role of the various factors involved, including the electric field strength E-0, and the curre nt density J in the active zone of the separator. A first set of experiment s 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 s tandard electrode arrangement. A second set of experiments consisted of thr ee series of separation tests performed on samples of millimetre-sized gran ulated electric wire scrap (62.5% copper, 37.5% PVC). By using a combined c orona-electrostatic field and a three-stage separation scheme? a PVC concen trate containing less than 0.04% copper (recovery: 92.2%) and a copper prod uct with less than 0.1% PVC (recovery: 90.8%) were obtained. Design and ope ration recommendations were formulated regarding the optimum electrode arra ngement, high-voltage level, roll speed and feed rate for typical industria l applications.