Micro-structural evolution of high aluminium fly ash enhanced by microwave heating to accelerate activation reaction process

In this study, Na2CO3 was used as an activator to roast and activate high aluminium fly ash (HAFA) via conventional heating. Microwave roasting technology was then used to strengthen the activation process and the reaction mechanism was discussed and compared with that of conventional heating. Microwave heating had an obvious effect on the HAFA activation process: with an aluminium leaching rate of approximately 93.00%, both the roasting time (30 min) and temperature (700 °C) were comparatively reduced, and the mass ratio of HAFA to Na2CO3 employed was 1:0.8. XRD analysis showed that the phase evolution of HAFA was not changed during microwave heating, but the Na2CO3-HAFA activation reaction was promoted. And SEM analysis showed that the micro-structure of roasted materials varied greatly with respect to the different heating methods. With microwave heating, overall breakage of mullite particles occurs and there is higher degree of breakage than conventional heating. [Display omitted] •Microwave is employed to enhance the activation process of high aluminium fly ash.•After microwave heating high aluminium fly ash, the content of NaAlSiO4 increased.•The selective heating by microwave heating increases the reaction interface.•The effect of microwave on accelerating the activation is obvious.