Mechanochemical activation of kaolinite and muscovite: Reactivity, gel formation, and reaction competition in kaolinite–muscovite geopolymers

Abstract

Layered aluminosilicate minerals are promising precursors for alkali-activated materials, but their stable lamellar structures can restrict dissolution and gel formation. This study investigated the effects of mechanochemical activation (MCA) on muscovite, kaolinite, and an equal-mass muscovite–kaolinite mixture, focusing on structural evolution, alkaline reaction behavior, gel formation, and mechanical performance. Under identical milling conditions, muscovite underwent more pronounced structural disordering and exhibited faster ionic release and more sustained late-stage polymerization than kaolinite. Accordingly, the muscovite-derived geopolymer achieved the highest 28 d compressive strength of 22.22 MPa. Fourier transform infrared (FTIR) spectral deconvolution showed that the Q4/(Q3 + Q4) area ratio reached 42.3% in the muscovite-derived geopolymer, compared with 29.9% and 28.4% in the mixture- and kaolinite-derived systems, respectively, indicating a greater contribution from highly connected SiOT environments. Point-based backscattered electron imaging coupled with energy-dispersive X-ray spectroscopy (BSE–EDS) further showed that 67% of the analyzed points in the muscovite-derived geopolymer fell within the Al/(Na + K) <1. The equal-mass mixture showed no synergistic enhancement, exhibiting weaker dissolution–polymerization coupling and lower strength than the muscovite-derived system. The amorphous fraction determined by X-ray diffraction (XRD) cannot be directly equated with reacted gel content because it includes both newly formed products and mechanically disordered precursors. These findings highlight the importance of mineral-specific structural disordering and reaction competition in MCA-activated clay geopolymers.