Alkali-hydrothermal activation of mine tailings to prepare one-part geopolymer: Activation mechanism, workability, strength, and hydration reaction

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing CO2 emissions. Mine tailings (MTs) rich in Si and Al can be served as a promising precursor for geompolymer preparation only when the severe defect in the low reactivity is overcame. Alkali-hydrothermal activation technology was used to enhance the reactivity of MTs, and then activated tailings (ATs) and slag served as the precursors for the one-part geopolymer (OPG) preparation. Activation mechanism of MTs, workability, compressive strength, and hydration reactions of OPG samples were studied. The crystalline mineral phases in the MTs reacted with NaOH to form the amorphous sodium aluminosilicate, thus increasing the amorphization degree. High NaOH content favored the MTs activation, and the ATs with high NaOH content tended to create a higher initial pH and release more active species (Si and Al) for the slag hydration. The increase of NaOH content shortened the setting time, decreased the fluidity, and increased the strength of OPG samples. This was because the duration of the induction period was shortened and the hydration rate in the acceleration period of OPG samples was improved with increasing NaOH content, which generated large amounts of calcium–sodium aluminosilicate hydrate (C(N)-A-S-H) gel and yield the compact microstructure. However, excessive NaOH content resulted in a poor microstructure, and it is likely responsible for the reduction in strength.