## 3 Textural Segmentation in OIA of Iron Ore Sinter  
Together with coke, iron ore sinter is the one of the major blast furnace loads. It can constitute up to 70-85% of the total ferrous burden fed to the blast furnace and its quality is also very important for stable blast furnace operation. The quality of sinter (e.g., its strength and reducibility) mainly depends on its petrology and texture, which in turn are determined by the initial ore blend, the fluxes added to the blend, and the sintering conditions. To optimize sinter quality and productivity the relationships between the initial sinter mix, sintering conditions and sinter structure, petrology and porosity must be understood [23; 24; 25; 26]. One of the important characteristics of iron ore sinter is the quantity of primary and secondary hematite, which can provide insights into the presence of large grains of hematite in the initial iron ore blend, the degree of reaction and sintering conditions. The two types of hematite have very similar, or the same, mineral chemistry and reflectivity, so they cannot be segmented by standard scanning electron microscopy or optical image analysis methods. However, they have different morphology and phase associations which can be discriminated by OIA. Primary hematite generally does not contain inclusions of melt-precipitated phases and often preserves the morphology of the original ore particle. Secondary hematite, which mostly precipitates during cooling from the sinter melt, has crystals fully surrounded by, and/or including, other melt-precipitated sinter phases, such as Silico-Ferrites of Calcium and Aluminium (SFCA), undifferentiated glass, and larnite (di-calcium silicate). The presence  
Figure 7: Segmentation of partially reacted IMDC: (**a**) bulk IMDC identification of PR IMDC; (**b**) porous IMDC identification of PR IMDC; (**c**) the combination of (**a**) and (**b**) with not reacted IMDC removed (blue); (**d**) PR IMDC areas (blue). or absence of these spatially associated phases is the key feature used by Mineral4 for textural segmentation of the two types of hematite. As a starting point for OIA processing, a map of all hematite in the sinter image is obtained by standard thresholding (Figure 1a,c and Figure 8a). A combined map of all phases which are typically associated with secondary hematite, such as SFCA, glass and larnite, is also prepared (Figure 8b). This second map is scrapped of its finest elements (to exclude the effect of imaging artefacts) and then strongly dilated to create a map of areas associated with the melt-precipitated phases (Figure 8c). Next, these areas are removed from the overall map of hematite. After additional scrap, removing undersized regions, only the areas of primary hematite are left in the map (Figure 8d). More dilation follows to compensate for loss during strong dilation of SFCA/glass areas (Figure 8e). Finally the map is masked with the original hematite map (Figure 8f) and fine/undersized objects are removed from it. The resulting identification of primary and, by exclusion, secondary hematite is shown in Figure 9.  
Figure 8: Textural segmentation of primary hematite in iron ore sinter: (**a**) map of all hematite in the image; (**b**) map of SFCA and all phases darker than SFCA; (**c**) map of areas associated with glass and SFCA; (**d**) hematite map without areas associated with melt-precipitated phases; (**e**) map of possible areas for primary hematite; (**f**) identified areas of primary hematite including smaller grains to be removed later based on size. Figure 9 demonstrates the false color map of all sinter phases identified by Mineral4 software during automated image analysis of the crushed sinter shown in Figure 1a. Note that the large grain of primary hematite in the bottom right corner includes some remnant kenomagnetite. Magnetic may still be present in stable ore nuclei remaining after sintering, not just as one of melt-precipitated sinter phases. Therefore, it is not included as part of the melt-precipitated phases in the map (Figure 8b).