# A Comprehensive Review on Mine Tailings as a Raw Material in the Alkali Activation Process
## 4 Pre-Treatment Methods
### Alkaline Fusion  
Alkaline fusion is a chemical process that involves heating a material, typically in the presence of an alkaline substance like sodium hydroxide (NaOH) or potassium hydroxide (KOH), to create a fusion or reaction. This process is used to alter the composition and properties of the material and increase the reactivity of the material prior to alkali activation [145]. In the context of mine tailings, alkaline fusion refers to subjecting the tailings to high temperatures in the presence of an alkaline substance. The high temperatures and alkaline environment cause chemical reactions within the tailings, leading to the transformation of the minerals into different phases or forms. The process involves elevating the temperature beyond the melting point of the alkali source present in the mixture. Following this heat treatment, the processed material is subjected to alkali activation using an alkaline solution. Alkaline fusion can facilitate the removal of impurities or unwanted components from the tailings, making them more suitable for specific applications [146].  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mine** **Tailings** & **Main Minerals** & **Calcination** & **Mineralogy Changes** & **Other Comments** & **Ref.** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Tungsten \\ tailings \\ \end{tabular} } & \multirow{3}{*}{Muscovite and quartz} & \multirow{3}{*}{950 \({}^{\circ}\)C} & High thermal resistance & Increased amount of \\  & & & & amorphous phase; \\  & & & for muscovite & thermal behavior similar \\  & & & & to that of phylosilicate \\  & & & & minerals \\ \hline \multirow{3}{*}{\begin{tabular}{c} Boron \\ tailings \\ \end{tabular} } & \multirow{3}{*}{Colemanite (Ca\({}_{2}\)B\({}_{6}\)O\({}_{11}\)5H\({}_{2}\)O), \\  & & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\ \hline \multirow{3}{*}{\begin{tabular}{c} Phosphate \\ tailings \\ \end{tabular} } & \multirow{3}{*}{Quartz, calcite, fluorapatite, \\  & & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Kaolinite \\ tailings \\ \end{tabular} } & \multirow{3}{*}{Muscovite, kaolinite, \\  & and quartz \\  & & & & metakaolin \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Copper \\ tailings \\ \end{tabular} } & \multirow{3}{*}{Quartz, albite, chlorite, \\  & and dolomite \\ \end{tabular} } & \multirow{3}{*}{400–600 \({}^{\circ}\)C} & Quartz, fluorapatite, and multite \\  & & & & remained constant; \\  & & & & achieved with \\  & & & & \\  & & & & \\  & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Summary of studies regarding heat-treated mine tailings.  
A study investigated alkaline fusion in conjunction with poorly reactive volcanic ash. This process resulted in a greater quantity of soluble aluminosilicates due to the conversion of minerals like muscovite, anorthoclase, and diopside. Consequently, this led to an enhancement in the reactivity of the ash [147].  
Alkaline fusion has been explored as a method for treating gold mine tailings. In this process, an Al\({}_{2}\)O\({}_{3}\) additive was blended with the tailings at different concentrations, and NaOH pellets were introduced to the mixture. The fusion process was carried out at 550 \({}^{\circ}\)C for 1 h, with the temperature increasing at a rate of 10 \({}^{\circ}\)C per minute. Following the heating process, the mixture was combined with Na\({}_{2}\)SiO\({}_{3}\). It was observed that the primary factor influencing the reactivity was the content of Al\({}_{2}\)O\({}_{3}\) rather than the curing temperature [52].  
A study on alkaline fusion with granite waste was also conducted, and it was found that the crucial factor influencing the reactivity of the material was the quantity of alkaline reagent applied [148]. Moreover, when alkaline fusion was employed with phosphate tailings, notable changes were observed [149]. This included the decomposition of illite, palygorskite, and dolomite phases alongside an augmentation in the content of Na-rich crystalline phases [150].