Recovery of zinc from zinc ferrite and electric arc furnace dust

This thesis research project addresses a very practical and troublesome problem which has been vexing Electric Arc Furnace (EAF) steelmakers and environmentalists for many years. EAF dust is generated during the EAF steelmaking process and it is designated as a hazardous waste in most industrialized countries. A suitable treatment process which is both economic and environmentally safe has not yet been found.; The major EAF dust treatment processes are pyrometallurgical at this time. However, there is an increased interest in hydrometallurgical treatment processes, because small scale on-site hydrometallurgical processes could be economic and these processes have potential environmental benefits. The major problem with the hydrometallurgical treatment processes is the low zinc recovery, since the zinc ferrite (ZnFe₂O₄) in EAF dust is insoluble and thus the zinc which is present in the zinc ferrite can not be recovered in the leaching process. In the present work, research on the kinetics of zinc ferrite formation, the leaching of zinc ferrite and EAF dust in caustic media were performed and evaluated. The experimental results indicated that decomposition of zinc ferrite was mainly dependent on temperature.; The major constituents of EAF dust, zincite (ZnO) and zinc ferrite (ZnFe ₂O₄) are good microwave absorbers. Microwaves as an energy source have many advantages over the conventional heating processes and thus the microwave leaching of the dust was studied. The results showed that the microwave leaching of the electric arc furnace dust resulted in improved decomposition of the zinc ferrite as compared to that observed in the conventional leaching process. However, the majority of the zinc ferrite in the EAF dust was still insoluble. Thus, in order to further decompose the zinc ferrite, other options were considered.; Research on the low temperature roasting of both synthetic zinc ferrite and EAF dust was performed. By adding caustic soda with EAF dust, the zinc ferrite was decomposed and formed a soluble compound during roasting at low temperatures. About 95% of the zinc was recovered in the subsequent dilute caustic leaching process. Based on the experimental findings, a hybrid low temperature pyrometallurgical and hydrometallurgical process was proposed for the treatment of EAF dust. This process has considerable commercial potential.