Study on the synergistic preparation of supplementary cementitious materials from multiple solid wastes: Bayer red mud and gold tailings

Abstract

This research proposed a novel method for the preparation of sustainable supplementary cementitious materials with low carbon emissions, utilizing Bayer red mud (RM) and gold tailings (GOT) as raw materials. Based on the Box-Behnken design of the response surface methodology (RSM), a regression model was established to assess the impact of individual influencing factors and their interactions on the 28 d strength activity index (SAI) of RM and GOT mixtures (RGM). Finally, the hydration properties of RGM were studied by observing the phase composition, combined water content, and micromorphology of the cement hardened paste mixed with RGM. The results showed that high-temperature calcination did not significantly improve the 28 d strength activity index of RM and GOT. Through the RSM optimization test, the 28 d SAI of RGM reached 87.11%. At a calcination temperature of 630 ℃, the mineral phases in the RGM decomposed and promoted mutual reactions, generating a large amount of active silicon, active aluminum and soluble salts, thereby enhancing the reactivity of the RGM. The incorporation of RGM6 changed the growth mode of calcium hydroxide (CH) and increased the content of prismatic CH. In the alkaline environment generated by cement hydration, the active silicon and active aluminum in RGM were ionized, and the generated SiO44-, AlO2- and active M2O·xSiO2 (aq) reacted with CH to generate calcium aluminate hydrate, C-S-H gel and C-S-A-H gel. The addition of RGM6 increased the concentration of CO32- in the solution, which inhibited the conversion of ettringite to monosulfate, thereby reducing the formation of pores due to volume contraction during the conversion process. The hydration products in the paste were intertwined, and the unreacted particles were bound together to create a denser internal microstructure, thereby enhancing the compressive strength of the mortar. The proposed method reduced the impact of RM and GOT on the environment and provided a sustainable and environmentally friendly solution for the development of the low-carbon construction industry.