Disintegration of Northern Cape iron ores under reducing conditions

Cracking occurs in the first step of gaseous reduction of hematite iron ore, to magnetite, and can lead to the formation of fine material, with deleterious effects on operation of shaft furnaces. To study this, samples of three ore types from the Northern Cape iron ore field in South Africa, and one blended ore from this region, were studied. The methods were high temperature microscopy (during reduction) and quantification of fines formation following reduction disintegration tests. The ore types do differ significantly with regards to their propensity to form fines. Although disintegration is clearly triggered by reduction, no direct correlation could be established between the degree of reduction and the amount of fines generated. Reduction disintegration increased with higher hydrogen percentages (>5%) in the reduction gas, and at higher temperatures (in the 500–700°C range). Disintegration of the samples decreased at temperatures >750°C. There was no correlation between the presence of gangue minerals and fines formation.