Characterisation and reduction of ironstone ore by CO gas

Abstract

Ironstone ore can be a valuable source of iron and silicon for the production of silicomanganese and other alloys. This paper provides analyses of the chemical and phase composition of ironstone and information on the reduction of ironstone by carbon monoxide at temperatures in the range 800–1150°C. Ironstone was provided as crushed and a lumpy ore. Crushed ironstone ore contained higher Fe₂O₃ concentration (40.6 wt-%) and lower SiO₂ content (44.3 wt-%) compared to the lumpy one (21.2 wt-% Fe₂O₃, 68.9 wt-% SiO₂). The main phases in the ore detected by XRD and SEM/EDS analyses were haematite and quartz. Two major reactions were observed upon heating ironstone in CO atmosphere, namely; partial reduction of iron oxides and formation of fayalite. The rate of fayalite formation increased with increasing temperature. Ore porosity significantly decreased upon heating. Ore softening and partial melting started at 1100–1150°C with a significant negative effect on iron oxide reduction. The weight loss of the crushed ore increased with increasing temperature to 1000°C and decreased when the temperature increased further to 1150°C. The weight loss of lumpy ore decreased with increasing temperature from 1100 to 1150°C. Based on the analysis using LECO oxygen analyser, the degree of iron oxide reduction in the crushed ore was estimated to be 82.4% at 1000°C, 68.8% at 1100°C and 33.1% at 1150°C. The degree of iron oxide reduction in the lumpy ore was 79.5% at 1000°C, 82.7% at 1100°C and 47.2% at 1150°C. No metallic iron was detected by XRD in samples heated in CO atmosphere at 1150°C, although a small amount of metallic iron was observed in SEM/EDS analysis. Equilibrium phases in the reduction of ironstone ores by CO were calculated using MPE model and compared with experimental data, these calculations also provided useful data on behaviour of ironstone during reduction at different temperatures.