Re-examining the suitability of high magnesium nickel slag as precursors for alkali-activated materials

High-magnesium nickel slag (HMNS) has shown the potential as precursor in the production of alkali activated materials (AAMs). This study re-examines the suitability of HMNS by comparatively investigating the reactivity of four different sourced HMNSs and analyzing impacts of the magnesium sources in HMNS on the reaction products of AAMs. Results show that the cooling way plays a determinant role of their mineral compositions. The air-cooled HMNSs contain only similar to 30 wt% glassy phases, while the water-quenched one is dominantly amorphous. The reactivity of HMNS determined by the dissolution tests correlates well with the calculated depolymerization degree of glasses. HMNS indeed exhibits lower reactivity than the precursors commonly used for AAMs production, such as fly ash and blast furnace slag. In the HMNS samples in the sodium hydroxide solution, M-S-H, C-S-H and hydrotalcite are the main reaction products. The OH- ions in the aqueous system react with Mg2+ to form the brucite, indicating that there is still a volume expansion risk if sodium hydroxide is used as activator. In comparison, only M-S-H and C-S-H gels are coexistent in the samples leached in the sodium silicate solution, because of the kinetic hindrance of soluble silicates for the formation of hydrotalcite and brucite. (C) 2019 Elsevier Ltd. All rights reserved.