Reduction Behavior of Dolomite-Fluxed Magnetite: Coke Composite Pellets at 1573\xa0K (1300\xa0\xb0C)

Hyunsik Park,Il Sohn,John Tsalapatis,Veena Sahajwalla

doi:10.1007/s11663-018-1208-9

Abstract

High-temperature behavior of magnetite—coke composite pellet fluxed with dolomite was investigated by customized thermogravimetric analyzer (TGA) at 1573 K (1300 °C). The overall reaction was influenced by C/O ratio and dolomite content. The reduction was accelerated by increased amount of dolomite, while the samples with higher C/O ratio showed the improved reduction degree. X-ray diffraction (XRD) pattern of reduced pellet showed the phase changes of the iron oxides. Noticeable iron peaks were observed when the sample reached the final stage of reduction. CO and CO2 gases released from the reaction were measured by Infrared (IR) gas analyzer. Relation between enhanced reducibility of pellets and larger CO gas evolution from the Boudouard reaction was confirmed from the analysis. Compressive strengths were studied for the practical assessment of reduced pellets. Samples with low-reduction degree showed better physical property. Excessive amount of dolomite also deteriorated the integrity of pellets.

Highlights

AS the quality of highly reducible hematite ores decreases worldwide, there has been significant interest in the broader use of magnetite ores, which are comparatively difficult to reduce than hematite
High-temperature behavior of dolomite-fluxed magnetite-coke composite pellet was investigated at 1573 K
Significant discrepancies between samples according to the carbon and oxygen (C/O) ratio occurs during this stage due to the different supply of reducing CO gases produced from the Boudouard reaction and subsequent acceleration of the reduction by the intermediate gaseous reactions

Summary

INTRODUCTION

AS the quality of highly reducible hematite ores decreases worldwide, there has been significant interest in the broader use of magnetite ores, which are comparatively difficult to reduce than hematite. OneSteel Whyalla Steelworks has operated a grate-kiln pellet plant since the late 1960s This plant was originally designed to use 100 pct hematite ore to make acid pellets and later modified to make highly fluxed pellets as the prime ferrous feed for the Whyalla Blast Furnace. MgO is reported to be concentrated in magnetite and calcium ferrite during reduction that forms higher melting solid solution ‘magnesiowustite.’[4] dolomite was considered to be an excellent fluxing material for non-indurated pellets to improve high-temperature reduction properties of iron ore pellets by increasing its softening point and reducibility.[18] The compressive strengths of the reduced composite pellets at varying carbon and dolomite contents were evaluated. The coke breeze and waste dolomite combination is assumed to be a suitable combination for the improvement of magnetite ore reduction and increasing the sustainability of the ironmaking process route

EXPERIMENTAL

Reduction Behavior of Composite Pellet

Physical Property of Reduced Pellets

CONCLUSIONS