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

摘要

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 degrees 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 degrees 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 degrees 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. GRAPHICS .