The effect of chemical composition and burning temperature on pellet quality

The effect of pellet chemical composition and burning temperature on pellets’ properties of the Gol-e-Gohar hematite recovery plant was investigated in this study. Green pellets of different sodium hydroxide ratio and hydrated lime were prepared as well. Then the pellets were burnt in a muffle kiln under different temperature conditions. The Design Expert software was employed to explore the optimized conditions and to model the effective parameters in the pelletizing process. The wet compressive strength of green pellets was determined to be 1.4-1.5 kilograms per pellet. The porosity of burnt pellets at different temperatures was determined between 16% to 38%. The firing process of green pellets provided discrimination between the outer layer and the central part of individual pellets. The model developed by the experiment design software showed that the temperature was the most effective parameter on increasing the compressive strength. While the burn temperature increased the cold compressive strength, it reduced the porosity of pellets. The cold compressive strength of burnt pellets was improved through increasing the temperature. However, a further increase in temperature led to a decrease in the cold compressive strength, because of hematite decomposition into secondary magnetite.