PHASE RELATIONS IN THE SYSTEM OF ZnO-Fe_2O_3-CaO AND ITS IMPORTANCE FOR ELIMINATION OF ZINC FERRITE IN EAF DUST

摘要

Electric Arc Furnace Dust (EAFD) is a hazardous waste from the steel industry. It has a high content of both Fe_2O_3 and ZnO. Much of ZnO in EAFD exists as ZnOFe_2O_3 and the rest as free ZnO. For most of the hydrometallurgical processes for EAFD treatment that have been proposed and tested only free ZnO could be recovered. This means low yield of Zn-recovery. Based on detailed studies of the phase relations in the system of ZnO-Fe_2O_3-CaO_3 a process concept for elimination of ZnOFe_2O_3 by CaO treatment has been proposed and preliminary tested in small scale. It has been shown that by proper CaO-control most of the ZnO in EAFD could be transferred to free ZnO. XRD and SEM investigations on leaching residue reveal that all converted free ZnO could be recovered and the leaching residue consists mainly of Ca_2Fe_2O_5, which is a good slag former for steelmaking processes.