Survey about Safe and Reliable Use of EAF Slag

Abstract

The demand of green and recycling technology has become, nowadays, a crucial issue for the scientific community. In this work, a preliminary approach for safe and reliable "black slag" use is discussed on chemical and microstructural characterization basis. Different EAF slag types, coming from several steelmaking plants, are analyzed. The characterization is aimed to explain the diffusion, dissolution and releasing mechanisms of the polluting elements that affect the black slags and avoid their recycle as alternative filler materials. Furthermore, the work focuses on the leaching inhibition of these dangerous species in the environment.Experiments involve SEM-EDS and SEM-EBS analysis and elution tests, according to the UNI EN 12457 standard, on high FeO content slag, on slag featured by chromium high content and on slag with low FeO content. The analysis allows to recognize the phases responsible for the polluting elements releasing and to identify the phases to be promoted in order to obtain a safe and inert by-product.

The effect of chemical composition on the leaching behaviour of electric arc furnace (EAF) carbon steel slag during a standard leaching test

“…and a small quantity of FeO the other species were always under the regulatory limits [37]. 178 These results were observed also in previous experiments [38][39][40] 179 and for this reason only Ba, Cr and V behaviour were discussed. The Vanadium oxide is considered an amphoteric species [43,44] 226 and in alkaline solutions tends to behave as acid oxide [45].…”

“…The limits on Cd and Se in Spain are the most strictly 36 (less than 1 mg/l) amongst the considered European countries. 37 Moreover, German legislation does not require any control on Ba 38 leaching, whereas the Ba limits in France and Spain are twice the 39 level of Italian limits. Also the V is considered differently in the 40 various EU countries: severe limits are set in Italy, Germany and 41 Spain, but not in France [10][11][12][13][14][15].…”

EAF Slag Treatment for Inert Materials’ Production

“…As indicated in the ternary diagrams reported in Fig. 6, the slag composition moved from high melting point area, associated with unstable and leachable microstructure, to low melting temperature area, leading to the formation of more stable microstructure [23][24][25].…”

“…The addition, preferably of quartzite, seems to promote the demixing of chromium that tends to bind with Mg-wüstite forming stable Cr-Mgspinels that also act as the nuclei where the silicate crystals start to nucleate and to grow. These structures are stable [25], and, as a consequence, Cr can be considered irreversibly captured. Similar microstructures have been obtained by adding SiO 2 -MgO or SiO 2 -FeO mix.…”

“…The designed treatment plant transforms the slag microstructure promoting the formation of low-hydraulic properties phases (i.e., gehlenite) [23][24][25] and forming complexes that avoid the free lime exceeding fraction.…”