This paper presents an initial part of a project devoted to the recycling of mill scale in the form of selfreducing briquettes. First chemical and morphological characteristics of mill scale were investigated and next its gaseous reduction behavior was studied by thermogravimetry. The chemical characterization showed that wustite is the major constituent of this waste matter, with small amounts of magnetite, hematite and metallic iron. The microscopic examination of the scale revealed its complex and layered microstructure with three distinct zones. The outer layer is relatively thin and porous. It is mainly composed of hematite and magnetite. The intermediate layer is made of the dense, columnar grains of wustite. The inner layer is a very porous wustite. The gaseous reduction by carbon monoxide has a topochemical character regardless of initial morphology of scale and, depending on temperature and reducing gas composition it produces a porous iron or the iron whiskers. The unreacted shrinking core model with one interface fits quite well the kinetic data and the activation energy of reduction is about 80 kJ/mol.

Self-reduction experiments of mill scale with four potential carbonaceous reductants (charcoal, coal char, blast furnace coke and petroleum coke) were carried out by thermogravimetry (TG) in order to choose one allowing the highest reduction rate and overall conversion. The fastest rate of self-reduction was measured for the charcoal and the slowest for the petroleum coke. The Friedman method of kinetics data analysis was used to calculate apparent activation energy at different conversion rates. Based on these values it can be concluded that the Boudouard reaction controls the rate of self-reduction with charcoal up to about 60% of conversion and even more for others reductants. It has also been demonstrated that the morphology of the iron produced strongly depends on reactivity of carbonaceous reductant.

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