Characterization of the Origin and Distribution of the Minerals and Phases in Metallurgical Cokes

Abstract

Three industrial metallurgical cokes were examined using X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray analysis (SEM/EDS). The study highlighted the difficulties and implications of identifying the inherent crystalline mineral phases in cokes using XRD such that increasing the ashing temperature led to the formation of anhydrite and destruction of metallic iron: microwave plasma ashing resulted in minimal alteration of the original coke mineralogy apart from the formation of bassanite and possibly jarosite. A preliminary scheme to characterize coke minerals is presented such that, physically, minerals can be classified as fine (<50 μm), coarse (50−100 μm), and agglomerate (>1000 μm); chemically, minerals can be grouped as refractory, semirefractory, and reactive, while on the basis of distribution they can be described as discrete, disseminated, or pore inclusions. Quartz, cristobalite, mullite, and high melting point Al-silicates were found to be the predominant refractory phases while low melting point Al-silicates, e.g., containing high fluxing elements such as K, and Fe were the main semirefractory phases present in all cokes. A variety of iron containing phases including pyrrhotite, troilite, iron oxides, metallic iron, and iron silicates were also invariably present in all cokes while calcium phases were found to occur as sulfide, silicates, and phosphates. In general, iron and calcium phases can be categorized as reactive phases with few exceptions such as oldhamite (CaS). The study highlighted that most of the cokes possess a similar mineralogy, with the main distinction being in their relative abundance, particle size, and nature of distribution in the coke matrix. The study provides a basis to develop a mechanistic understanding of the influence of minerals on coke reactivity and strength at high temperatures.