Optimizing activating solution and environmental leaching characteristics of Fe-rich alkali-activated Zn slag

In this work, slag from Zn processing was used to produce Fe-rich alkali-activated materials (AAMs) with low environmental impact. The interconnection between activating solution composition, compressive strength, and environmental leaching characteristics was assessed. The reaction products characterised with FT-IR, XRD, and SEM-WDS were represented by Fe-rich C-S-H gel of tobermorite-related structure. The local aggregation of Na and Mg suggests the minor role of these elements in the reaction product. The reaction product seems to be undependable on the alkali cation used in the solution. Besides, the hardening reaction took place fast, and the maximum compressive strength of 70 MPa was determined only after 1 day after mixing with silicate solutions. To decrease the economic and environmental impact, 1) simultaneous decreasing Na₂O/slag and SiO₂/slag ratios or 2) decreasing SiO₂/Na₂O ratio can be applied without prominent deterioration of the strength. Environmental leaching results showed an increase in the leached content of several metal(loid)s (e.g., As, Mo, Cr, Sb, Se, V) as a results of alkali activation, but also some immobilization effect for Ba, Pb and Zn. Also, the presence of liquid silica in the activating solutions or higher water content reduced the leaching of some elements.