Rings growth behavior within a pre-reduction rotary kiln: The layered structure and formation mechanism

摘要

An in-depth understanding of the rings growth behaviors and formation mechanism is helpful for process parameters optimization to control the growth of rings and reduce breakdown ratio of the rotary kiln. This study quantitatively characterized the mineralogical characteristics of the rings within an ore pre-reduction rotary kiln through X-ray diffraction (XRD-Rietveld) and field emission scanning electron microscope (FESEM) coupled to an energy dispersive X-Ray spectrometer (EDS). The results indicated that the rings in the kiln have a distinct layered structure which can be divided into the dense layer and the loose layer. The mineral composition of the rings is hematite (16.6%), magnetite (29.6%), spinel (33.6%), and diopside (20.2%). Mineral evolution and consolidation mechanism of the dense layer and the loose layer were further studied through a series of experiments with various roasting temperature, roasting time and alkali metal contents. Research findings showed that the mass of the liquid phase increased as the roasting temperatures rise, and the roasting temperature was deemed to the main factor of solidification strength. The results also confirmed that the addition of Na2O contents in the raw material will not only help to increase the liquid contents and the compressive strength, but also improve the fluidity of the liquid phase. In all, a "layer-by-layer" formation mechanism of the rotary kiln for pre-reduction was proposed based on the experimental results and theoretical analysis. (C) 2019 Elsevier B.V. All rights reserved.