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Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing CO 2 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. [ABSTRACT FROM AUTHOR]

Environmental and economic issues caused by several tailings storages have attracted worldwide attention; therefore, these urgently need to be solved cost-effectively. In this study, gold mine tailings rich in Si and Al oxides were activated by an alkaline hydrothermal method for use as precursors to produce a one-part geopolymer. The results indicated that the crystalline mineral phases in tailings were partially or completely decomposed by alkaline hydrothermal activation. However, this decomposition depended heavily on the alkali content, temperature, and time. The decomposed tailings were converted to the amorphous sodium aluminosilicate reactant, thereby making tailings a reactive starting material. Subsequently, the one-part geopolymer was prepared from the activated tailings and slag by just adding water without adding any extra alkaline activator. By adding 60 wt% of slag, the one-part geopolymer with an optimum compressive strength value of 33.5 MPa at 28 days was obtained. This was much higher than that of the control sample containing raw tailings without any pretreatment. The high strength could have been because of the amorphous sodium aluminosilicate formed in the activated tailings that could dissolve in water to create alkaline conditions, which could effectively activate the pozzolanic activity of the slag. The main geopolymerization product was the glassy calcium-sodium aluminosilicate hydrate (C(N)-A-S-H) gel, which acted as a binder to closely connect the residual solid particles and form a hardened geopolymer material. [Display omitted] • NaOH hydrothermally activated tailings were used as a reactive precursor. • Mineral phases in tailings were converted into the amorphous sodium aluminosilicate. • Soluble activation product could create alkaline conditions for the slag activation. • Hardened one-part geopolymer was prepared due to the formation of C(N)-A-S-H gel. [ABSTRACT FROM AUTHOR]