Environmental Impact of Steel Slag Reused as Aggregates in Road Manufacturing: Molecular Mechanisms of Chromium and Vanadium Release

摘要

The speciation of chromium (Cr) and vanadium (V), two potential pollutants, present as traces in a residue from steel-making operations (BOF slag) and their leaching behavior were studied to assess the environmental compatibility of this waste as a recycled material for road making. A multi techniques approach (XAS, XANES, micro-XANES, micro-XRF and micro-XRD) was required to assess the molecular mechanisms of Cr and V release. Leaching tests have shown that Cr is little released and moreover remains at its initial trivalent form, less toxic, even during leaching. One part of octahedral Cr(III) ions replaces structurally the octahedral Fe(III) in a dicalcium aluminoferrite phase and the other part is associated to a solid solution (Fe, Mn, Mg)O. Spatially resolved techniques allowed showing that Cr is tightly bound to a secondary phase formed during leaching which controls its solubility. V present in BOF slag is environmentally more critical because its release is relatively high and it is oxidized to its most toxic form (V(V)) during leaching. Micro-XRF coupled with chemometric analysis (SIMPLISMA) indicates that V is also associated to a dicalcium aluminoferrite.