Alkali-hydrothermal activation of tailings with red mud as a supplementary alkali source to synthesize one-part geopolymer

Utilization of mine tailings via geopolymerization is a promising approach to convert them into value-added products. In this method, development an affordable and effective activation technology for enhancing the reactivity of tailings is necessary. In this study, an alkali-hydrothermal method was used for the tailings activation, with the high-alkaline red mud as a supplementary alkali source. Two different types of activated tailings were prepared: the activated tailings without adding red mud (ATs) and the activated tailings with adding red mud (ARTs). Subsequently, the one-part geopolymer was prepared from the activated tailings and slag. The results demonstrated that the addition of red mud contributed to the activation of tailings because of the increased alkali concentration. ARTs had lower relative crystallinity, higher initial pH, and higher solubility of Si and Al than these of ATs under the same NaOH content. As a result, geopolymer samples from ARTs exhibited a shorter induction period, a faster rate of hydration reactions, larger amounts of hydration reactants, and a more compact microstructure compared to control samples from ATs, resulting in the excellent mechanical strength. The geopolymer sample possessed the optimum strength of 21.50 and 52.65 MPa at 1 and 28 days, respectively, when the NaOH content was controlled at 15 wt.% during the alkali-hydrothermal process. This value was even higher than that of control samples with the addition of 20 wt.% NaOH.