Comparison of high temperature behavior of self-reducing pellets produced from iron ore with that of dust from sintering plant

The main advantage of the self-reducing pellets is related to the reaction rate: due to the closeness of the reactants, their small size and nitrogen free environment, almost complete reduction can be achieved with reaction times ranging from 5 to less than 10 minutes for temperatures between 1000 degreesC and 1200 degreesC. These reaction times depend on the nature of the iron bearing material. This paper presents the comparison of experimental results when compact hematite iron ore and dust from sintering plant were used. Self-reducing pellets with 18 mm diameter were made with these materials composing with coal plus binder (4% Portland cement plus 4% Blast Furnace slag). The pellets were submitted to 8 different thermal paths for evaluating the high temperature behavior, that is: decrepitating, swelling, strength and reducing. The results showed that none of the pellets presented decrepitating and that the pellet with dust from sintering plant does not present any tendency for swelling. The abnormal swelling of the pellets containing hematite iron ore can be minimized or avoided by designing a self-reducing process with controlled heating rate and completing the reduction at temperature higher than 1100 degreesC. The strength of 200 similar to 400 N/pellet, at room temperature, decreased to a minimum of 20 similar to 40 N/pellet after submitted to 900-950 degreesC. The dust from sintering plant, to achieve high degree of reduction, is less dependent of the heat intensity supply and temperature than iron ore.