Beyond Peak Matching: X-Ray Diffraction, Phase Identification, and Mineralogical Uncertainty in Electric Arc Furnace Dust — A Critical Review

Abstract

Electric arc furnace dust (EAFD) is a heterogeneous metallurgical residue in which bulk chemistry alone cannot resolve the chemical form, crystal structure, substitution state, or accessibility of Zn, Fe, and minor elements. X-ray diffraction (XRD) is therefore central to EAFD characterization, but the apparent simplicity of phase search–match can conceal substantial uncertainty arising from peak overlap, solid solutions, nanocrystallinity, microabsorption, preferred orientation, poorly crystalline material, and incomplete structural models. This critical review evaluates the reliability of qualitative and quantitative XRD for EAFD, with emphasis on zincite, zinc ferrite/franklinite-type spinels, magnetite–maghemite discrimination, XRD-amorphous/unmodeled material, and phase evolution during thermal and hydrometallurgical treatment. Particular attention is given to Rietveld-based quantitative phase analysis, the meaning of fit quality and uncertainty, and the role of SEM–EDS, EPMA/WDS, Mössbauer spectroscopy, Raman spectroscopy, X-ray absorption methods, and automated mineralogy in validating phase assignments. The review argues that a diffraction peak compatible with ZnFe₂O₄ does not, by itself, demonstrate stoichiometric zinc ferrite, and that process predictions are only as defensible as the mineralogical assignments they are based on. We propose a practical evidence hierarchy and multimethod workflow to connect phase identification with reagent demand, zinc recovery, ferrite refractoriness, thermal transformation, and residue behavior. The resulting framework supports more transparent reporting, uncertainty-aware mineralogical mass balances, and stronger translation from XRD patterns to metallurgical decisions.