Fayalitic Minerals and Slags (Part I): A Survey on Composition and Potential for Phases Design

Abstract Fayalitic slag, primarily formed by FeO and SiO 2 , is a significant byproduct from nonferrous metallurgy, mainly copper, lead, and zinc industries. It is estimated that circa 2.2 tons of fayalitic slag are generated per ton of copper produced. This slag contains many other valuable chemical elements, but often in low concentrations. This work is the first of two parts: a literature review of the composition and mineralogy (Part I) and a thermodynamic modeling of the physical properties (Part II) of such slags. Part I analyzes 104 literature sources regarding chemical composition, mineralogical phases, and phase transformations of fayalitic slags. The aim is to identify trends, understand behaviors, and guide future research. Fayalitic slags average 44.16 mass% FeO eq and 32.56 mass% SiO 2 , showing significant compositional variability, with CaO, Al 2 O 3 , and MgO as key minor constituents. Global composition analysis revealed regional differences, where Asia and Europe contributed with most citations. Mineralogically, phase transformations influenced by cooling rates and oxygen partial pressure often involve the oxidation of fayalite into magnetite and hematite as well as the liberation of SiO 2 . Minor key components such as Pb and Cu were also mentioned significantly. Ternary phases diagrams (CaO–FeO–SiO 2 ) were assessed, showing mineralogy phases consistent with the available literature. This understanding highlights patterns and tendencies in the nonferrous metallurgical industry that emphasize the valorization of fayalitic slags. This opens possibilities for targeted mineral enrichment and metal recovery by addressing metallurgical process windows and mineralogical characteristics, thereby supporting circular economy principles. Graphical Abstract