Effect of Addition of Mill Scale on Sintering of Iron Ores

Abstract

Iron-rich (65 to 70 pct total Fe) mill scale generated during processing by steel mills can be recycled by using it as a ferrous raw material in the sintering process. The effect of mill scale addition on the phase formation of sintered specimens from an industrial sinter blend containing 0 to 15 wt pct mill scale was examined, and the mineral phases formed during sintering under various conditions (T = 1523 K to 1598 K [1250°C to 1325°C] and gas compositions of pO 2 = 0.5, 5 and 21 kPa) were quantitatively measured. For samples sintered in air (pO 2 = 21 kPa), there was negligible effect of mill scale addition on the phases formed. The oxidation of the mill scale was complete, and phases such as Silico-Ferrite of Calcium and Aluminum (SFCA), SFCA-I, and hematite dominated. Under lower oxygen partial pressures (pO 2 = 0.5 or 5 kPa), and throughout the temperature range examined, the mill scale was converted to magnetite, with the extent of reaction controlled by the hematite-magnetite conversion kinetics. When sintered in the gas mixture with pO 2 = 5 kPa, an increase in the mill scale content from 0 to 15 wt pct resulted in a decrease of hematite and total SFCA phases and a corresponding increase in the amount of magnetite which formed. The oxidation of wustite in mill scale to magnetite decreased the local partial pressure of O 2 and increased sintering temperature, which promoted the decomposition of hematite.

Fundamentals of silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phase formation: effects of mill scale addition

“…Secondly, any Fe 2 O 3 which forms through oxidation of the FeO and Fe 3 O 4 in the mill scale only begins to convert to Fe 3 O 4 above ∼1150°C (see Figures 1 and 2) and so no appreciable conversion of Fe 2 O 3 to Fe 3 O 4 , which is unreactive in the context of SFCA-I and SFCA phase formation (Webster et al, 2013a), can occur before formation of SFCA-I and SFCA and the Fe 2 O 3 is available for reaction to form the SFCA phases. If the pO 2 the experiments were conducted under was more reducing, then the effect of mill scale addition would likely become significant, in accordance with the results of Wang et al (2016b).…”

“…The results of the internal standard-based determination outlined in the section IID confirm this. Since the mill scale sample exhibited negligible loss on ignition (Wang et al , 2016b) this amorphous material is considered likely to be amorphous/nanocrystalline Fe-oxide material, rather than hydrated mineral(s). This work demonstrates the power of in situ XRD, combined with the external standard approach to QPA, for gaining insights into the quantity and nature of amorphous material in mineral mixtures.…”

“…If the pO 2 the experiments were conducted under was more reducing, then the effect of mill scale addition would likely become significant, in accordance with the results of Wang et al . (2016b).

Figure 4. Stack plots of the in situ XRD collected for the (a) 2.6, (b) 10.6, and (c) 21.2 wt% mixtures in the range 1100–1310 °C.

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“…The mill scale has previously been characterised (Wang et al , 2016b). In summary, its bulk composition is 71.0 wt% total Fe, 0.2 wt% CaO, 0.1 wt% Al 2 O 3 , 0.9 wt% SiO 2 , 0.2 wt% MgO, and 0.6 wt% Mn.…”

Alüminotermik Yöntem Yoluyla Tufalden Ferromolibden Üretimi

“…Also, it is employed in the adsorbing of lead ions in aqueous solutions [6]. Besides, it is used as an iron oxide source in sintering applications [7].…”