Effect of CaO on hydration properties of one-part alkali-activated material prepared from tailings through alkaline hydrothermal activation

Enhancing the reactivity of mine tailings through the efficient and economical technology and using them as active precursors for alkali-activated materials is essential to effectively alleviate environmental issues caused by huge tailings emissions. In this study, an alkaline hydrothermal technology was proposed for increasing the reactivity of gold mine tailings. X-ray diffraction (XRD) analysis and leaching tests indicated that the crystalline structures of tailings were significantly destroyed and amorphous sodium aluminosilicate was identified as the major hydrothermal activation product, which dissolved in water, released large quantities of active Si and Al species, and created an alkaline environment for the slag activation. Subsequently, one-part alkali-activated materials (OPM) were prepared from activated tailings and slag. To improve the hydration properties of these materials, quicklime (CaO) was employed as an additive. OPM sample exhibited the optimum strengths of 8.4, 28.7, 39.5, and 42.5 MPa at 1, 3, 7, 28 days, respectively, when CaO content was controlled at ∼ 6 wt%. pH tests, XRD, thermogravimetric (TG), and scanning electron microscopy (SEM) analyses revealed that the addition of CaO improved the pH of the pore solution, increased the quantity of calcium-sodium aluminosilicate hydrate gel (C(N)-A-S-H, the main hydration reactant), and generated the compact microstructure, thereby enhancing the strength of the OPM samples. However, the strength was dramatically reduced when CaO content exceeded 6 wt% at later stages, mainly because of the severe carbonation of the sample.