Characterisation of sinter mineralogy through image analysis under reflected light optical microscope with focus on primary and secondary hematite distinction (Université de Liège)

Abstract

The demand for iron ore products is continuously increasing by the steel production industry worldwide. Among these products, there is the sinter, one of the burden components that feed a blast furnace for pig iron production. A good quality sinter is the key element for stable and efficient blast furnace operation, and the mineralogical composition of a sinter directly influences its quality. Secondary hematite for example, is detrimental to the reduction degradation of sinter, which justifies the need to control it. For this reason, it is crucial to have characterization methods that allow the evaluation of this mineralogy in an economically viable way and the optical image analysis appears as a simple, but powerful tool for such characterization. Therefore, an automated optical image analysis method has been developed, which is capable of quantifying not only the major sinter phases, but also distinguishing different morphologies of the same mineral, such as primary and the above mentioned, secondary hematite. Such distinction is a challenging task, since the two hematite forms present similar chemistry and the same optical properties. The algorithm performance has been evaluated by another optical analysis technique, manual point counting, which demonstrated that the majority of the primary/secondary hematite measurements performed by the automated method were within the interval of +/- 5% the actual value, a promising performance. Subsequently, three sinters produced from different amounts of solid fuel had their mineralogies related to quality indexes (reducibility, cold strength and reduction degradation), to evaluate the influence that each sinter phase has on the quality of the sinter. Finally, in an attempt to observe the transformation of hematite with increasing temperature, tests in a quenching furnace have been conducted, allowing the visualization of interesting intermediary stages of this transformation, part of this thermal-chemical process that is the sintering process.