Evaluation of iron ore concentrate and micropellets as potential feed for sinter production

Abstract

The use of iron ore concentrate has become of interest as the demand for higher grade sinter feed is increasing. The fine nature of the concentrate however raises concerns as it can affect permeability during sintering which could have a drastic impact on sinter productivity. In this study the use of iron ore concentrate and micropellets as sinter feed was evaluated. Five mixtures containing different proportions of iron ore concentrate and micropellets, together with iron ore fines, were prepared. These mixtures were agglomerated through pilot scale sinter pot tests, followed by measuring the sinter strength, reduction disintegration and reducibility. Samples of the produced sinters were also subjected to XRF, XRD and SEM-EDS analyses for mineralogical analysis, and MF-XRT for sinter structure analysis. Granulation results revealed that the mixture containing 0% micropellets – 40% concentrate showed superiority in material transfer efficiency while the mixture containing 30% micropellets – 10% concentrate showed superiority in permeability. X-ray diffraction analysis (XRD) revealed an increase in hematite as micropellet content increased. The analysis also revealed high SFCA content for the 0% micropellet – 40% concentrate which decreased as micropellet content increased. This was mainly associated with a decrease in reactivity. Optical microscopy confirmed a large presence of SFCA and also revealed significant precipitation of magnetite and SFCA in the bonding phase structures of the high concentrate containing sinters. It also revealed a pronounced presence of acicular SFCA in the high micropellet containing mixtures. Scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS) revealed a slight consistency in phase chemistry across the different sinter mixtures. This was mainly associated to similar chemical compositions of the starting mixtures. It also revealed that the micropellets maintained a hematite-silica core surrounded by a Fe-rich sintered matrix. It was further determined that the introduction of iron ore concentrate and micropellets did not significantly impact mechanical properties of sinter as similar tumble indices (TI) were observed. A slight variation in reduction disintegration index (RDI) was however seen with high micropellet sinters showing a larger degree of degradation compared to high concentrate containing sinters. Sinter reducibility (RI) also decreased slightly as micropellets increased and this was associated with the inability of micropellets to assimilate during sintering. It was therefore concluded that although micropellets and concentrate can be used as sinter feed, the optimum amount thereof was not yet determined.