ABSTRACT
It is well established that a solid-solid reaction is always slower than a reaction between a gas and a solid, for two reasons. First, the solid–solid contact area is limited, while when a gas reacts with a solid, the gas envelopes the entire surface of the solid particles; and second, solid state diffusion is much slower compared with mass transfer to/from gases. The porosity of the iron oxide particles is one of the most important factors affecting its reducibility. Solid state reduction of iron oxide is a heterogeneous reaction involving solid and gas phases separated by an interface. The rate at which the iron oxide can be reduced to metallic iron is the primary determinant of the rate of production in any Direct reduction (DR) process. The supply of the reducing agent to the surface of iron oxide is controlled by diffusion through a stagnant gas film around the oxide particle, which is determined by the gas flow rate.
