Removal behavior of Zn, Pb, K and Na from cold bonded briquettes of metallurgical dust in simulated RHF

Abstract

Removal behavior of Zn, Pb, K and Na from cold bonded briquettes made by mixing four typical metallurgical wastes, as blast furnace dust, converter dust, electric arc furnace dust and converter sludge with proper proportions, in a simulated RHF (Rotary Hearth Furnace) were investigated in this paper. Effects of temperature and C/O molar ratio on metallization rate of iron oxides, and effect of temperature on removal rate of elements Zn, Pb, K and Na were checked respectively. The results show that when reduction temperature, C/O molar ratio, reduction time are 1 300°C, 1 and 15 min respectively, removal rates of Zn, Pb, K and Na are 97.1 %, 99.4%, 94.5% and 89.6% respectively, at the same time the metallization rate is 80.6%, which can meet demands of the blast furnace. X-ray mapping analysis via scanning electron micrograph (SEM) for Zn, Pb, K and Na in the cold bonded briquettes at different reduction time and different selected areas tells that Zn, Pb, K and Na located in edge of the briquettes remove faster than those located in the center of briquettes. The dust arrested in the reduction process, called as secondary dust, is proved to be mixture of mainly Zn, ZnO, KCl and NaCl by X-ray diffraction (XRD) analysis and SEM EDS (energy-dispersive spectrometry), and contents of Zn and KCl are obtained as over 60% and nearly 20% respectively, while Pb is probably in an insufficient amount to be detected. Water leaching tests arrive at a conclusion that primary separation of Zn and Pb from K and Na is obtained as expected, meanwhile content of element Zn increases from 57.9% in the initial secondary dust to 73.6% as ZnO in the leaching residual. © 2009 ISIJ.