Carbothermic Kinetics and Reaction Mechanism of Carbon-Containing Pellets: A Combined Treatment of Chromium-Containing Sludge and Zinc-Bearing Dust

The present work focuses on the co-processing and resource recycling of solid wastes with various valuable metallic resources generated by the steel-making process. The carbon-containing pellets were prepared using zinc-bearing dust and chromium-containing sludge as the main raw materials. Then the pellets were reduced in a tube furnace with different roasting temperatures (800–1300 °C), roasting time (10–60 min), and carbon contents (9–17 wt%). The reduction mechanism of the carbothermic reduction was characterized based on thermodynamic analysis and XRD. In addition, based on the non-isothermal thermogravimetric method, the kinetics of the reducing process was investigated at heating rates of 15, 20, and 25 °C/min. The results show that mixture pellets composed of zinc-bearing dust and chromium-containing sludge can contribute to a fine integrated system. The ZnFe2O4 and FeCr2O4 phases can effectively be decomposed into iron oxide and chromium oxide at 1000 °C. As the temperature rises, iron oxide followed the law of stepwise reduction and was reduced to pure iron. Compared with iron oxide, chromium oxide can be reduced to pure chromium at a higher temperature. The kinetics results show that the reaction process can be divided into five stages and the main three stages follow the three-dimensional diffusion model. This study provides a new method and insight into the feasibility of the co-processing of various wastes with different valuable resources.Graphical Abstract