Caustic roasting and leaching of electric arc furnace dust

Electric arc furnace (EAF) dust is produced when iron and steel scrap is remelted in an electric arc furnace. There are still significant problems associated with the pyrometallurgical and/or hydrometallurgical processes for the treatment of this dust. In the present research, the dust was roasted with caustic soda at low temperatures. It was found that the zinc ferrite (ZnFe₂O₄) in the dust was converted into sodium zincate (Na₂ZnO₂) and iron oxide (Fe₂O₃). In the subsequent dilute caustic leaching process both the zincite (ZnO) and the sodium zincate were soluble and the hematite was relatively insoluble. After roasting and leaching, the zinc recovery was found to be about 95%, while the majority of the iron oxide remained in the leach residue. The lead, cadmium and chromium recoveries were approximately 85, 89 and 37%, respectively, for roasting tests in which moisture was added. Without a moisture addition in roasting, the lead recovery decreased to 63% while the chromium recovery increased to 81%. Based on the experimental results, a hybrid low temperature roasting and dilute caustic leaching process followed by zinc cementation and electrowinning is proposed and discussed. This proposed hybrid EAF dust treatment process provides some potential advantages in comparison to the other hybrid processes which have been described in the literature.