Preparation and characterization of phosphoric acid activation of granite powder and metakaolin-based geopolymer

The massive stockpile of granite powder (GP) not only occupies the land, but also poses a threat to the environment and human health. The active silica-alumina content in GP is low. Most prepared geopolymers need alkali pretreatment at high temperatures for good compressive strength. Activation of GP with phosphoric acid and synthesis of acid-activated geopolymers is a cost-reducing alternative. In this study, a new green phosphate-based geopolymer was successfully prepared from GP and metakaolin (MK). The optimal preparation conditions were determined by orthogonal tests to be a GP:MK ratio of 4:6, a phosphoric acid concentration of 10 M, and a liquid–solid ratio of 0.6. The compressive strength of the prepared geopolymer was 37.48 MPa. The microstructure and mechanism of the geopolymer were investigated by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive spectrometer (EDS). It was shown that phosphate-based geopolymers prepared from both GP and MK have higher mechanical properties than those prepared from single GP or MK. “The GP-MK base geopolymer matrix is mainly AlPO₄ and comprises Si–O–P, Si–O–Al–O–P, Al–O–P, and Si–O–Si units”. This study provides a new idea for the comprehensive utilization of GP.