Abstract: The oxidation rate of magnetite concentrate is ery quick at the reaction beginning, but it becomes much slower when the reaction is conducted to a certain level because the product layer on the micro particles resists the oxygen diffusion greatly. This phenomena are proved through experiments. And a function is put forward to calculating the quivalent osmosing thickness of the product layer. Based on the function, a mathematical model is established for the whole range reaction process of magnetite in pellets. It is proved that this model fits the real process very well under any condition.

Key words: Magnetite, kinetics, mathematical model