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.
Highlights
The last 10 years consolidated the position of steelmaking slag as a suitable technical alternative to natural stones for several engineering applications, such as road construction and concrete production [1,2,3,4].After an initial stationary consumption of steelmaking slag by employing the whole amount of produced material, since 2010 the production of slag has increased by about 25% and its use has overcome the stocks of about 3%, reaching is maximum in 2008 (25 Mt/y of recycled slag)
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
The successful conversion of steelmaking slag into a valuable product is due to the development of several stabilization treatments able to solve some of the issues concerning this material: volume expansion, self-dusting, and toxic metal leaching
Summary
The last 10 years consolidated the position of steelmaking slag as a suitable technical alternative to natural stones for several engineering applications, such as road construction and concrete production [1,2,3,4].After an initial stationary consumption of steelmaking slag by employing the whole amount of produced material, since 2010 the production of slag has increased by about 25% and its use has overcome the stocks of about 3%, reaching is maximum in 2008 (25 Mt/y of recycled slag). The last 10 years consolidated the position of steelmaking slag as a suitable technical alternative to natural stones for several engineering applications, such as road construction and concrete production [1,2,3,4]. Minerals 2019, 9, 706 whole amount of the recycled slag In this scenario, electric arc furnace carbon steel slag (EAF-C slag) production oscillates around 5 Mt/y (Figure 1). The successful conversion of steelmaking slag into a valuable product is due to the development of several stabilization treatments able to solve some of the issues concerning this material: volume expansion, self-dusting, and toxic metal leaching. Stabilization treatments have been applied to all the different types of steelmaking slag, such as basic oxygen furnace (BOF) slag, electric arc furnace (EAF)
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