Effect of Temperature, Time, and Cooling Rate on the Mineralogy, Morphology, and Reducibility of Iron Ore Sinter Analogues

Tobin Harvey,Jeff Chen,Nathan A S Webster,Leanne Matthews,Tom Honeyands,Thi Bang Tuyen Nguyen,Mark I Pownceby,Damien O’Dea

doi:10.1007/s11837-020-04452-6

Abstract

Analogue sinter tablets were produced at temperatures between 1250°C and 1320°C, with a range of hold times and cooling rates. Platy silico-ferrite of calcium and aluminum (SFCA) morphology was identified in samples produced at 1250°C using reflected light microscopy; however, quantitative x-ray diffraction (XRD) identified the presence of the SFCA phase, with no SFCA-I detected. This proves that the platy SFCA morphology common in analysis by reflected light microscopy cannot be attributed to the SFCA-I mineral without further analysis. Micro-XRD and electron probe micro-analysis (EPMA) were carried out on an area of platy SFCA confirming this result. The sinter analogue tablets were reduced in a 30% CO, 70% N2 gas mixture at 900°C in a tube furnace thermo-gravimetric analyzer. The degree of reduction of the tablets in this study was found to be controlled by the porosity of the samples, rather than by the morphology or mineralogy of the bonding phase.

Highlights

The continued growth of iron and steelmaking, combined with environmental pressure to reduce greenhouse gas emissions, makes the optimization of the iron ore sintering process more important than ever
The primary hematite content of the analogues generally decreases with increasing maximum temperature and hold time, as more assimilation of the iron ore particles occurs into the calcium ferrite melt.[31]
These results are aligned with the temperature stability ranges for silico-ferrite of calcium and aluminum (SFCA)-I and SFCA,[5] which tempts the researcher to assume that the platy SFCA morphology is identical to the SFCA-I mineral

Summary

Introduction

The continued growth of iron and steelmaking, combined with environmental pressure to reduce greenhouse gas emissions, makes the optimization of the iron ore sintering process more important than ever. Sintering is a process by which a mixture of fine-grained iron ores (< 6.3 mm), fluxes, and coke are agglomerated in a sinter plant to manufacture a sinter product of a suitable composition, quality, and granulometry to be used as burden material in the blast furnace. Key quality parameters important for producing a good sinter include high strength, low impurities, high porosity and permeability, and high reducibility. All of these are influenced in some way by the mineralogy of the sinter, which in turn is dependent on variables such as temperature, composition, and fuel. In order to generate a suitable sinter for ironmaking, the bonding phase must be physically strong, permeable to reducing gases in the blast furnace and reduced. Over the past 50 years, a significant body of work has demonstrated that the bonding phase that develops in fluxed iron ore sinters is composed of a complex solid solution phase related to calcium ferrites, but given the general acronym SFCA (silico-ferrite of calcium and aluminum).[1,2]

Objectives

Results

Conclusion