High temperature properties of by-product cold bonded pellets containing blast furnace flue dust

Abstract

In this investigation, the fundamental reactions occurring during the heat treatment of cold bonded pellets (CBP) comprised of iron and steelmaking by-products have been studied. Blast furnace (BF) flue dust, which contains fractions of coal and coke particles, has been included in the CBP blend as a source of solid reductant. Thermal analysis was performed on CBP samples in inert atmosphere at a heating rate of 10 °C/min in order to observe their high temperature properties, specifically, the mechanisms of self-reduction within CBPs. Both endothermic and exothermic reactions were observed during heating. The gases generated during thermal analysis were analyzed using a quadropole mass spectrometer (QMS). Furthermore, CBP samples heated to several different temperatures and quenched in argon were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results from this investigation demonstrate that the decomposition of hydrates and carbonates in CBP samples contribute, as gaseous intermediates, to an earlier reduction of contained iron oxides. The gaseous intermediates are responsible for an initial gasification of carbon contained in blast furnace flue dust leading to low temperature iron oxide reduction. The step-wise reduction of iron oxides in CBPs at the given conditions begins at ∼500 °C and is nearly completed at 1200 °C. This work can help to provide a fundamental understanding of the reduction characteristics of iron and steelmaking by-product agglomerates.