Solidification/stabilization of red mud with natural radionuclides in granular blast furnace slag based geopolymers

Red mud is a NORM residue of aluminum industry, and its large storage endangers environmental safety. In this study, red mud was used to prepare geopolymers to dilute its radioactivity. The activity concentrations of 226Ra, 232Th and 40K of geopolymers with different contents of red mud (0, 30, 50, 70 wt%) were investigated, and the activity concentration index, annual effective dose and shielding rate were calculated to evaluate the radiological safety and solidification effect of geopolymers. The solidification/stabilization mechanism of geopolymers was discussed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that the hydration process of geopolymers had a solidification effect on the radionuclides contained in red mud. When the red mud content was 30 wt%, the radioactivity was within the safety threshold as a building material, and the compressive strength of the geopolymers reached 72.19 MPa. The maximum red mud content in geopolymers was 40.81 wt% by fitting. The adsorption effect and the encapsulation effect of C-S-H gel could promote the solidification/stabilization of radionuclides of red mud in geopolymers. This research provides a perspective for the radiological safety of the red mud based geopolymers in construction materials.