Abstract:
Every year, thousands of tons of waste scales are produced during rolling mill steel processing
worldwide. The scales are rich in hematite and magnetite, and different ways of reduction and
oxidation have been proposed for recycling the iron oxides. Modern methods for removing
and processing steel scales fall into three classes: mechanical, chemical, and electrochemical
approaches. Each method has its advantages and disadvantages, and the choice of method
depends on cost and users’ need for the final product. The present work reports the
reduction of the mill scales by their precipitation in a mixture of HCl and HNO3 acids to
form α-FeOOH nanopowder, followed by thermal oxidation in a hydrogen atmosphere at
400°C and 375°C. This approach combines chemical and physical processes and it is known
as chemical metallurgical method. Sodium dodecyl sulphate is used as a surfactant to
obtain Fe and Fe3O4 powders. X-ray diffraction analysis shows that thermal treatment results
in the formation of γ-Fe2O3 phase. It also causes a transition from magnetite (Fe3O4) to γFe2O3, with a preferential crystallite orientation of the γ-Fe2O3 phase to the (220) texture
plane. Eventually, longer thermal treatment time increases the crystallite size for the γ-Fe2O3
phase and decreases it for the Fe3O4 phase.
