An effective strategy for converter slag and blast furnace dust by a deep self-reduction technology: Synergetic reaction and phase evolution behavior

Advanced self-reduction roasting technology is a simple route for realizing the clean and synergetic utilization of hazardous blast furnaces and converter slag. However, the correlation between the crushing strength and metallization ratio of flux-metalized pellets has not been elucidated. This work clarified the consolidation behavior and synergetic mechanism in the preparation process of flux-metalized pellets. Through comprehensive optimization of process parameters, fluxed metalized pellets with a crushing strength of 3924 N/P, a metallization ratio of 86.54 % and a zinc recovery ratio of 90.35 % were successfully produced under the following optimal conditions: a reduction temperature of 1200 °C, a reduction time of 60 min, a basicity of 1.25 and an FC/O of 0.9, which meets the requirements for raw materials in blast furnace production. The reduction behavior of zinc ferrite Zn_xFe_3-xO₄ and stirlingite ZnFeSiO₄ played a crucial role in the preparation of pellets. During the reduction process of Zn_xFe_3-xO₄, Zn_xFe_3-xO₄ was initially reduced to wustite Zn_yFe_1-yO and then further reduced to metallic iron and zinc. During the reduction process of ZnFeSiO₄, olivine-type Zn_xFe_2-xSiO₄ could combine with CaO to form stable olivine CaSiO₄ under the action of CaO flux, in which the participation of CaO could effectively decrease the reduction activation energy of FeZnSiO₄. In addition, Ca_yFe_2-ySiAl₂O₇ originated from the displacement reaction between Ca_xFe_1-xAl₂O₄, which has a spinel crystal structure, and Ca_xFe_2-xSiO₄, which has an olivine crystal structure. A deep self-reduction roasting technology was developed to provide technical support and theoretical guidance for the clean utilization of metallurgical solid waste resources.