Pyrometallurgical recovery of zinc and valuable metals from hazardous blast furnace dust via self-reduction roasting: Phase transformations and morphological evolution

Blast furnace dust (Zn–Fe dust) containing high heavy metal contents is a hazardous waste, and it is derived from the gravity dust removal system and bag dust removal system of a blast furnace. This study elucidated the underlying reasons for the poor separation of Zn and Fe and recommended conditions for the carbothermic reduction roasting process. The results indicated that the poor efficiencies for Zn and Fe separation from Zn–Fe dust were caused by the formation and gradient reduction of wustite (Fe y Zn 1-y O). A higher reduction temperature, longer reduction time and basicity created an advantageous environment for reduction of the wustite intermediate phase and enabled synergistic catalytic reduction of the wustite phase (Fe y Zn 1-y O and Fe y Ca 1-y O). The formation and reduction of the wustite phase (Fe y Zn 1-y O and Fe y Ca 1-y O) are crucial steps in reduction roasting of olivine (Zn y Fe 2-y SiO 4 ) and Zn x Fe 3−x O 4 with a spinel crystal structure. After adjusting the experimental parameters, the efficiencies for recovery of Zn and Fe from the Zn–Fe dust reached 95.12 % and 96.55 %, respectively.