Sintering and heating reduction processes of alumina containing iron ore samples

Abstract

Alumina containing iron ore samples (0·7–5·5%Al2O3) were sintered in a down draft sinter pot. The structures of the produced sinters were microscopically examined and the different phases developed were identified. Electron probe micro analyser (EPMA) was used for the quantitative analysis of Fe, Ca, Si, Mn and Al in different phases. Silico ferrite of calcium and alumina (SFCA) phase sinter was identified and its stability was Al2O3 content dependent. In sinter containing ≤1·5%Al2O3, SFCA was dissociated at higher temperatures to porous magnetite and silicate melt. In samples containing ≥2·5%Al2O3, SFCA was stable and its quantity increased with increasing alumina content. The non-isothermal reduction of sinter samples was carried out using a heating reduction technique with the facility of following up the high temperature phenomena during reduction process. X-ray observations, reduction rate profile and the gasification rate were used for the determination of high temperature properties of samples. In the gas–solid reduction region, Al2O3 increased the reduction rate (RDR) at the initial stage up to 1073 K and the RDR increases with increasing Al2O3 content up to 2·5%. At >1073 K, the RDR was relatively slower due to the presence of primary low melt slag containing alumina. For sinter containing >2·5%Al2O3, the lowering in RDR and total reduction degree (TRD) starts to decrease with increasing Al2O3 content as a result of the formation of SFCA phase which has a good reducibility and as a consequence of the decrease in the quantity of the primary low melt slag containing alumina. No more than 2·5%Al2O3 in the slag results in a harmful effect on the high temperature properties while higher alumina content in sinter leads to the formation of SFCA which improves the high temperature reduction properties.