During the induration of pellets, temperature and oxygen partial pressure influence the formation of different phases and microstructure. With increasing the pellet size, these thermo-chemical conditions vary across its cross section. The time difference between the oxidation of the pellet surface and the core increases with increasing pellet size, i.e. the oxidation takes place under different conditions resulting in different phases and microstructure. In this study commercial pellets of different sizes (8-16 mm) were studied for their physical, mechanical and metallurgical properties. Pellets in the size range of 10-12.5 mm showed superior properties. Electron and optical micro structural studies with image analysis revealed that hematite content, pore density, amount and distribution of silicate melt of different sized pellets are different and distinctly affect the pellet quality. SEM-EDX analysis and X-ray mapping techniques revealed that Mg has a specific distribution pattern across the cross section of the pellet.KEY WORDS: iron ore pelletisation; pore density; silicate melt; iron oxides; pellet size; FeO; MgO. phases. An attempt was made to correlate pellet quality to its microstructure. Pelletisation ProcessPellets required for the present study were collected from a commercial straight-grate pellet plant of 3 Mt/year capacity. Production of iron oxide pellets from iron ore fines involves different operations like drying of ore fines to remove the moisture and grinding to get the required fineness. After mixing these ground ore fines with other additives like bentonite, limestone and coke breeze, green pellets are prepared using pelletising discs. These green pellets are fired in straight-grate indurating machine to get the required physical, mechanical and metallurgical properties making them suitable feed to iron making units. Pellets are transported through the furnace by a traveling grate, which retains the pellets while allowing the air to flow through. The traveling grate is loaded with approximately 0.05 m height of fired pellets as hearth layer to protect the grate and then 0.50 m of green pellets. The induration process consists of three main steps; 1) Drying for green pellets 2) Firing of pellets at 1250-1300°C to sinter the iron oxide particles 3) Cooling of hot pellets before discharging them on to the conveyors leading to the stockpiles. Figure 1 shows a simplified flow sheet of straight-grate indurating machine. It consists of seven different zones, viz., up-draft drying (UDD), down-draft drying (DDD), preheating (PH), firing (FZ), after-firing (AFZ), primary cooling (CZ1) and secondary cooling zone (CZ2). Process air is circulated through these different zones with the help of five interconnected process fans. ExperimentalAround 1 t of fired pellets were collected from the product conveyor of the plant in one shift at an interval of 1 h. Sample collecting shift was decided in such a way that there was no production interruption in the preceding 3 shifts to ensure stable operating cond...

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The twenty-first century is bringing radical changes in mineral industry. High speed and low cost computational and sensing devices make it possible to reach at remote location and instantaneous control on the processes. Image processing which was very useful for some selected applications is getting popularity in mineral industry in changed scenario. In the present article image processing technique is explained briefly and its application in mineral industry has been summarised. A case study of ferruginous Indian manganese ore is presented. These ores show variation in their colour owing to variation in chemical composition. These ores were studied in red, green and blue colour space, histogram analysis; textural analysis and edge detection technique were used for separation of alumina lumps and to distinguish different ores. It shows acceptable results to carry out further studies for developing new cost effective ore blending and ore sorting methodologies for mineral industry. MATLAB 7 . 0 was used for image processing studies.