Impact of altered quartz surface chemistry on mechanical properties and microstructure of geopolymers

The preparation of geopolymers from tailings rich in quartz typically requires activation to enhance final strength, though the underlying mechanism remains unclear. Quartz, as a common inert gangue mineral in tailings, was selected as the research subject. Quartz with varying reactivity was prepared through mechanical activation of different particle sizes and used for geopolymer synthesis, aiming to elucidate the strengthening mechanism of activated quartz on geopolymers. When the activation time was identical, quartz particles of different sizes exhibited the same soluble silicon content. However, due to the increased surface-active groups after activation, geopolymers derived from larger quartz particles (5–8 mm) achieved compressive strengths of 57.24–64.73 MPa, while those from smaller particles (0.08–0.12 mm) only reached 43.83–50.42 MPa. After activation, the main active groups on the quartz surface were the Q n (n = 1, 2, 3) structures containing non-bridging oxygens and silicon radicals. The Q 1 and Q 2 structures mainly provide soluble silicon in geopolymerization and have little effect on the strength of the geopolymer. While the Q 3 structure can combine with the geopolymer gel through Si-O-Si bonds, reducing the porosity at the interface between quartz and geopolymer, significantly enhancing the strength of geopolymer. The results indicate that, compared to soluble silicon content of quartz, the content of active groups on its surface is the main factor influencing the performance of geopolymer. For the activation of tailings, increasing the reactivity of their surface is more effective in improving geopolymer strength than enhancing the leaching of soluble silicon and aluminum through overall activation.