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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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Global iron and steel making industries generate immense number of by-products, among which few are already being utilized for the generation of high value products, while few are still struggling to gather a good market space. Waste utilization is the major concern for every industrial maker. In this context, iron powder which holds immense market in applications like powder metallurgy (PM) parts, welding electrodes, advanced oxidative agents for water treatment, food fortifying agents, metal injection moulding, catalysts, fuels etc., can now be a novel outcome from steel industry by-products. Iron powder can be manufactured by various techniques like reduction, atomization, electrolysis, etc., resulting in fine particles of various morphologies ranging from spherical to irregular shapes and low to high purity. The application of these iron powders is depended on the process, quality and purity of the desired product.

Pelletizing of Indian chromite ores is more challenging due to their high refractory nature. High Cr/Fe ratio and high MgO content in these ores demand high firing temperatures and longer firing cycles but often result in low strength fired pellets. Aim of this study was to develop cold bonded chromite pellets for smelting in submerged arc furnace (SAF) from chromite fines using suitable binder that induce less gangue into the pellets but cures quickly. Different binders were studied through laboratory pelletizing experiments for their suitability for cold bonding the pellets. As result, a composite binder comprising dextrin and bentonite, was found to be suitable and pellets made from the same were tested for their low and high temperature behavior. Electron and optical micro structural studies with image analysis were carried out to find out the type and amount of phases formed in the chromite pellets during high temperature reduction. High temperature reduction studies revealed that pellets were resistant to disintegration up to 1 200°C. Pilot scale arc furnace trials were also carried out to compare the performance of cold bonded pellets (CBPs) with sintered chromite pellets and found that for a constant power input, smelting rate was faster for CBPs than sintered pellets. Loss of Cr to slag was reduced in case of cold bonded pellets usage.