Geopolymer prepared with high-magnesium nickel slag: Characterization of properties and microstructure

High-magnesium nickel slag (HMNS) is a hazardous waste that is generated in nickel pyrometallurgical production. The present work investigates the feasibility of using this slag in geopolymer manufacturing. The effects of HMNS addition on the reaction, mechanical properties and microstructure of fly ash-based geopolymers are studied through isothermal conduction calorimetry (ICC), compressive strength testing, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), X-ray diffractometry (XRD) and drying shrinkage testing. The results showed that the major phase in fly ash-HMNS geopolymers was a type of sodium magnesium aluminosilicate gel (N–M–A–S) with amorphous features. The Si/Al ratio of the gel phase increased with HMNS content due to the high silica supplied by HMNS. In terms of compressive strength, the maximal strength of fly ash-based geopolymers was achieved by 20% HMNS substitution. At this optimal content, the sample possessed a refiner pore structure and lower linear drying shrinkage compared with the other samples containing 0%, 40% and 60% HMNS contents. This study shows the potential of incorporating HMNS as value source material for geopolymer production.