Types of goethite from Quadrilátero Ferrífero's iron ores and their implications in the sintering process

Abstract

Quadrilátero Ferrífero's iron ores used in the sintering process correspond to mixes of hematitic and goethitic ore typologies. The ores have particle size mainly distributed in the range from 6·35 to 0·105 mm. The goethitic typology comprises a low amount in these ore blends; however, it can be relevant in the reactivity during sintering. This research involved techniques such as reflected light optical microscopy (RLOM) and scanning electron microscopy-backscattered electron (SEM-BSE) images for microstructure evaluation, and energy dispersive X-ray spectrometry (SEM-EDS) for microanalytical study. Many morphologies of goethite were identified considering the three ore blends: colloform type, massive, thin (granular and lamellae/fibrous) and earth-like. They have variable degrees of microporosity. Some microanalytical differences among these morphologies were observed as Si–Al–P bearing Gt, which corresponds to the common type, Al₂O₃-rich Gt and MnO bearing Gt. The latter two types have also Si, Al and P in their compositions. Although goethite is completely consumed during the sintering processes, its control in the sintering burden is very important owing to its morphologies with different degrees of porosity and with variable elements for Fe substitution. These factors can affect in different ways the composition of the sinter phases. Therefore, the identification of the goethite types and their amounts in the iron ore mixes, as well as their chemical constitution, can avoid the increase in deleterious elements during the sintering stage.