The U.S. steel industry produces approximately 500,000 tons/year of electric arc furnace (EAF) dust, which is classified as a hazardous waste. Increasing disposal costs of these dusts have encouraged studies to investigate treatment processes to render the material non-hazardous, and to possibly recover metal values. This research project was designed to examine the hydrometallurgical recovery of zinc from EAF dusts that have been treated by a double-kiln fuming process. The test work consisted essentially of acidified brine leaching of the pelletized calcine to determine the influence of traditional conditions, such as acid concentration, temperature and agitation, plus the application of ultrasound, on the zinc dissolution efficiency and selectivity. Preliminary leaching tests using acidified calcium chloride indicated that selective leaching of zinc over iron could be attained if ultrasound was employed. The effect of air and nitrogen on the leaching process was investigated and it was established that selective leaching with ultrasound was not dependent upon external agitation or on the availability of oxygen. Without ultrasound, zinc dissolution was enhanced by the presence of oxygen, while iron dissolution was greatly retarded by the absence of oxygen. The role of surface area was examined by pellet grinding and it was demonstrated that selectivity was strongly lime dependent and that zinc recovery and iron rejection were enhanced al finer particle sizes. The results of the lest work permitted possible mechanisms to be established for the acidified brine leaching process, and it is apparent from the results that ultrasound leaching can significantly improve the selective leaching of zinc from double-kiln treated EAF calcine.
