Properties and mechanism of high-magnesium nickel slag-fly ash based geopolymer activated by phosphoric acid

A series of geopolymers were prepared by using phosphoric acid as activator to stimulate high-magnesium nickel slag (HMNS) and fly ash (FA). The effects of amount of phosphoric acid, the ratio of HMNS:FA and water-binder ratio, on the mechanical properties of HMNS-FA-phosphate based geopolymers were studied through compressive strength testing, X-ray diffractometry (XRD), Fourier transform infrared spectrometer (FT-IR) and scanning electron microscopy (SEM), energy dispersive spectrometer (EDS). The results showed that the most convenient amount of phosphoric acid, the ratio of HMNS:FA and water-binder ratio required for producing HMNS-FAphosphate based geopolymers with better mechanical properties was that phosphoric acid amount was 25%, the ratio of HMNS:FA was 0.7:0.3 and the water-binder ratio was 0.24. The major phase in HMNS-FA-phosphate based geopolymers was newberyite (MgHPO4 center dot 3H2O) with crystal structure and amorphous features. The HMNSFA-phosphate based geopolymers formed a gel-crystal phase structure, which was more reasonable than the gelbased structure, because it used crystals as the framework and colloids as the bonding medium to increase the density of geopolymers and formed a more compact hardened body. The geopolymerization mechanism of HMNS-FA-phosphate based geopolymer was also discussed. This study shows the potential of using HMNS as value source material for geopolymer production activated by phosphoric acid.

Automated summary

This study prepared HMNS-FA-phosphate based geopolymers by using phosphoric acid as activator and investigated the effects of phosphoric acid amount, HMNS:FA ratio, and water-binder ratio on the mechanical properties. The optimal conditions were found to be phosphoric acid amount of 25%, HMNS:FA ratio of 0.7:0.3, and water-binder ratio of 0.24.