The Influence of Slag Tapping Method on the Efficiency of Stabilization Treatment of Electric Arc Furnace Carbon Steel Slag (EAF-C)

Abstract

Studies conducted over the past 10 years have demonstrated the technical suitability of the electric arc furnace slag as an alternative to natural stone in several applications. Steel slag can be profitably used as a road surface layer, for foundations and embankments, or for concrete aggregates. However, a strong limitation to their use is due to the presence of toxic metals (Ba, Cr, V, Mo, etc.) that can be released into the environment in particular conditions, especially for unbound products in which the slag can come into contact with water. Recent studies have investigated the role of chemical composition and microstructure of slag on toxic metal leaching, allowing for the design of suitable stabilization treatments for hindering such leaching. In this work, four batches of electric arc furnace carbon steel slag underwent a stabilization treatment and the obtained results were compared. In two batches, the stabilizer was added directly in the slag pot and the slag was cooled down in the same pot. The other two batches were stabilized during the downfall from slag door to slag pit. Several slag samples were collected before and after the stabilization treatment and were characterized by means of ED-XRF, XRD, and SEM analysis. Leaching tests were carried out in agreement with EN 12457-2 standard on 4 mm granulated slag, and the leachate concentration was compared with the current Italian limits listed in D.M. 3 August 2005 N. 201 and D.M. 5 April 2006 N. 186. The results clearly indicated that the cooling in the slag pot improved the efficiency of the stabilization treatment, leading to a complete transformation of the microstructure by a full development of homogeneous gehlenite matrix and a coarsening of Cr-spinels, assuring better toxic metal retention behavior. On the contrary, stabilization in the slag-pit was rapid and reduced the interaction between slag and stabilizer, leading only to partial transformation of larnite into gehlenite, and also reducing the coarsening of Cr-spinel. In addition, a layering effect was observed, resulting in an inhomogeneous product from top to bottom in terms of chemical composition, microstructure, and leaching behavior.

Leaching and Geochemical Modelling of an Electric Arc Furnace (EAF) and Ladle Slag Heap

“…Spinels ((Mg, Al, Fe, Cr)2O4), larnite, periclase, and brownmillerite are minerals The mineral phases identified are in line with the mineral phases reported in the literature. Spinels ((Mg, Al, Fe, Cr) 2 O 4 ), larnite, periclase, and brownmillerite are minerals commonly found in EAF C slag [36][37][38][39]. In ladle slag dicalcium silicate (γ-C2S), larnite, mayenite and tricalcium aluminate are more frequently observed [38,[40][41][42].…”

“…In ladle slag dicalcium silicate (γ-C2S), larnite, mayenite and tricalcium aluminate are more frequently observed [38,[40][41][42]. Larnite and mayenite, however, may also be found in EAF slag [35,36,43]. The quartz most likely originates from other materials (sand, refractory brackets) that were probably also dumped on the metallurgical slag heap.…”

“…In the "fresh" EAF S slag and ladle slag the brownmillerite was not, however, observed, due to the fact that EAF C slag was not investigated in those studies. It is well known that brownmillerite is a constituent of EAF C slag [36].…”

Innovative Reuse of Electric Arc Furnace Slag as Filler for Different Polymer Matrixes

“…The knowledge of the chemical and physical characteristics is fundamental to in-crease the reuse of the slag both internally and in different fields of application. In particular, the knowledge of the composition of the various phases allows the development of ad hoc stabilization methods making the slag suitable for its reuse [16][17][18][19]. EAF slag is named also "black" slag when it is derived by the smelting of the scrap metals, while it is known as "white" slag when it is derived by the following refining process in the ladle, out-side the furnace.…”

Editorial for Special Issue “Metallurgical Slags”

“…The contribution of Mombelli et al [12] investigates the impact of the tapping method on the stabilization treatment of electric arc furnace carbon steel slags. It was noted that cooling in the slag pot improved the stabilization efficiency through the formation of coarse-grained texture.…”