# A Comprehensive Review on Mine Tailings as a Raw Material in the Alkali Activation Process
## 3 Alkali Activation
### Mine Tailings as a Filler Material in Alkali Activation  
Using mine tailings as a filler material in alkali activation is a sustainable approach to repurposing mining waste. Mine tailings with low levels of reactivity can find a valuable role as inert fillers in alkali activation when combined with an appropriate co-binder material [105]. This approach helps us use tailings that might otherwise have limited levels of reactivity. Different studies demonstrate the potential of alkali activation as a stabilizing method for a range of mine tailings, including those from base metal, coal, uranium, and potash mining sites, and the crucial role of metakaolin as a co-binder [106; 107; 108]. Alkali activation, as a versatile process, not only has a great capacity to immobilize hazardous elements but also results in a final matrix with a robust mechanical performance, making alkali activation a sustainable solution for repurposing mine tailings. Analyzing the geochemistry of Kaltails tailings produced under different conditions is crucial before utilizing them in alkali-activated materials, which provides critical insights into the chemical composition, mineralogy, and potential reactivity of the tailings [109]. The material composition, rich in Si (silicon), Al (aluminum), Mg (magnesium), Fe (iron), Na (sodium), and SO\({}_{3}\) (sulfate), suggests a potentially reactive mixture when combined with fly ash or blast furnace slag, demonstrates excellent mechanical properties, and good levels of durability and permeability. Notably, these positive outcomes were achieved when the mixture had a low proportion of tailings (less than 70 wt%), indicating that even with a relatively low proportion of tailings, they could contribute to the desirable properties of the final material significantly, demonstrating the potential for effectively utilizing mine tailings as a valuable component in construction materials [110]. Studies provide valuable insights into the alkali activation of copper mine tailings, which consist of minerals like quartz, albite, potassium aluminum silicate, and gypsum, contributing to the reactivity of the tailings. Sodium hydroxide (NaOH) was employed as the activator to initiate the polycondensation reactions necessary for forming a 3D structure in a material [111; 112]. Studies have also highlighted the essential role of a co-binder in achieving good mechanical properties and levels of durability in the final material, suggesting that the inherent reactivity of copper mine tailings alone may not be sufficient to achieve the desired properties [113]. Adding fly ash to the mixture further enhanced the final strength of the alkali-activated copper mine tailings. The successful alkali activation of copper mine tailings and the essential role of co-binders underscore the potential for repurposing mining waste in sustainable construction materials [114]. Moreover, optimizing the curing conditions can substantially impact the mechanical properties of alkali-activated materials. Specifically, a study demonstrated that better mechanical properties were achieved by carefully controlling the curing conditions. This involved either controlling the pressure or using an elevated curing temperature of 90 \({}^{\circ}\)C [115]. The composition of the mine tailings, including dolomite, kaolinite calcite, and quartz, from the vanadium mining site in China provides insight into the potential reactivity and properties of these materials. The tailings were used as a raw material in alkali activation, with metakaolin as a co-binder and sodium silicate as an activator [116]. Another study used metakaolin, a thermally activated form of kaolinite clay, as a co-binder for molybdenum mine tailings, with the potential for the use of mining waste. The molybdenum mining site was rich in minerals like quartz and calcite and phases containing calcium, aluminum, and iron [117].