Studies conducted over the past 10 years have demonstrated the technical suitability of the\nelectric arc furnace slag as an alternative to natural stone in several applications. Steel slag can be\nprofitably used as a road surface layer, for foundations and embankments, or for concrete aggregates.\nHowever, a strong limitation to their use is due to the presence of toxic metals (Ba, Cr, V, Mo, etc.) that\ncan be released into the environment in particular conditions, especially for unbound products in\nwhich the slag can come into contact with water. Recent studies have investigated the role of chemical\ncomposition and microstructure of slag on toxic metal leaching, allowing for the design of suitable\nstabilization treatments for hindering such leaching. In this work, four batches of electric arc furnace\ncarbon steel slag underwent a stabilization treatment and the obtained results were compared. In two\nbatches, the stabilizer was added directly in the slag pot and the slag was cooled down in the same\npot. The other two batches were stabilized during the downfall from slag door to slag pit. Several\nslag samples were collected before and after the stabilization treatment and were characterized by\nmeans of ED-XRF, XRD, and SEM analysis. Leaching tests were carried out in agreement with EN\n12457-2 standard on 4 mm granulated slag, and the leachate concentration was compared with the\ncurrent Italian limits listed in D.M. 3 August 2005 N. 201 and D.M. 5 April 2006 N. 186. The results\nclearly indicated that the cooling in the slag pot improved the efficiency of the stabilization treatment,\nleading to a complete transformation of the microstructure by a full development of homogeneous\ngehlenite matrix and a coarsening of Cr-spinels, assuring better toxic metal retention behavior. On the\ncontrary, stabilization in the slag-pit was rapid and reduced the interaction between slag and stabilizer,\nleading only to partial transformation of larnite into gehlenite, and also reducing the coarsening of\nCr-spinel. In addition, a layering effect was observed, resulting in an inhomogeneous product from\ntop to bottom in terms of chemical composition, microstructure, and leaching behavior.
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