Preparation and Properties of Fayalite (Fe2SiO4) Synthetic Copper Slags with Fe/SiO2 Ratios from 1.5 to 2.3

Abstract Industrial fayalite slags have complex chemistry, but understanding the properties of slags representing fundamental FeO x -SiO 2 system is important for advancing slag engineering, developing freeze-lining concepts and next-generation Cr-free refractories, and in slag valorization. In this work, synthetic copper slags with Fe/SiO 2 ratios of 1.5, 2.0 and 2.3 were produced using the method of melting the Fe 2 O 3 +SiO 2 mixture in a graphite crucible at 1280 °C. The produced slags consisted of Fe 2 SiO 4 (82.4–100 pct) and Fe 3 O 4 (13.9–17.6 pct) as confirmed by XRD which well represented industrial slags. SEM/EDS analysis conducted on panoramic images of slags revealed best developed large, columnar fayalite grains with their average size of 366 µ m and highest aspect ratio of 7, without free SiO 2 and Fe 3 O 4 , for slag with Fe/SiO 2 of 2.0. Whereas slag with Fe/SiO 2 ~1.5 and ~2.3 additionally form free silica and free magnetite in slag volume, respectively, which would diminish freeze-lining integrity or cause silica penetration to refractory easier. All slags showed partial fayalite oxidation from SEM images. Increased oxygen activity during slag cooling also produced Fe 3 O 4 layer at slag surfaces, with its thickness increased with higher Fe/SiO 2 in slag. Fe 2+ /Fe 3+ in slags were reduced with higher Fe/SiO 2 of 32.3 (S1.5), 4.3 (S2.0), 3.5 (S2.3). The peak shift in energy scale for Si K edge XAS spectra of SiO 2 in fayalite slags indicated reduced polymerization degree with higher Fe/SiO 2 .