Low- and high-temperature reoxidation of direct reduced iron: a relative assessment

Sponge iron or direct reduced iron (DRI) is known to be very susceptible to loss of metallization by reoxidation in moist oxygen-containing atmospheres, even resulting in spontaneous ignition under specific situations. Different mechanisms have been put forward so far for such this phenomenon. On the basis of experimental investigations carried out extensively with coal-based DRI produced through a pilot kiln, it has been brought to light that the reoxidation process follows a logarithmic law at low temperatures and a first-order law at high temperatures. It is also shown that both laws may be derived from similar expressions for a porous material such as DRI.