# A Comprehensive Review on Mine Tailings as a Raw Material in the Alkali Activation Process
## 4 Pre-Treatment Methods
### Mechanical Activation  
Mechanical activation is a crucial pre-treatment step in maximizing the potential of mine tailings for use in alkali activation technology. The primary goal of mechanical activation is to enhance the reactivity of specific components within the mine tailings. This is achieved by subjecting the material to grinding or milling processes, including reducing the particle size, increasing the surface area, and disrupting crystalline structures [124]. The increased reactivity observed after milling is attributed to the higher amorphous content of the reactive elements. As the particle size of the mine tailings is reduced through milling, the total surface area of the material increases significantly since smaller particles have a more exposed surface area relative to their volume. This increased surface area means that a larger proportion of the material is now available for chemical reactions, allowing for a greater number of reactive sites to participate in the formation of the 3D structure [125]. The larger surface area facilitates faster reaction kinetics, meaning that chemical reactions can occur more quickly, leading to a more efficient alkali activation process [126]. A study focused on investigating mechanical treatments with the aim of enhancing the ultimate properties of alkali-activated mine tailings originating from a vanadium mining site that were primarily composed of quartz, feldspar, diopside, mullite, and hematite. After a 60 min grinding process, the particles exhibited a more uniform shape, and the average particle size was reduced from 31 to 2 \(\upmu\)m, resulting in a higher mechanical strength in the final alkali-activated material [127]. Furthermore, the grinding process led to the increased solubility of silicon (Si) and aluminum (Al) in the material [128]. The ultimate alkali-activated materials were created by blending mine tailings, fly ash, and solid sodium silicate powder. This dry mixture was subsequently combined with water, exhibiting superior thermal resistance properties compared to those of composites made with Portland cement [127; 129]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mine Tailings** & **Procedure** & **Main** & **Mineralogy** & **Final Properties** & **Ref.** \\ \hline \multirow{4}{*}{Molybdenum tailings} & Metakaolin as a co-binder; curing at room temperature & & Calcite, andradite, quartz, dolomite, and calcium aluminum silicate & The improved strength of the final material with metakaolin & [116; 117; 118] \\ \cline{2-6}  & Blast furnace slag & & Dolomite, quartz, diloncolore, muscovite, alpine, and gypsum & Metakaolin used for adjusting the scarce Al content in the mixture; the effect of co-binder content on the final material & [119] \\ \cline{2-6} Gold tailings & & & & & \\ \cline{2-6}  & & & & & \\ \cline{2-6}  & & & & & \\ \cline{2-6}  & & & & & \\ \hline Gold tailings & Slag, gypsum, cement, lime, and silica fume as co-binders & - & Quartz, albite, mica, sanidine, and microcline & Appropriate material to utilize for paste backfill technology & [120; 121] \\ \hline Sulfidic mine waste rock & Fly ash as a co-binder & - & Chlorite, quartz, dilute, and pyrite & Suitable to utilize sulfidic mining waste rock as aggregate in alkali activation & [122] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._Copper mine tailings that were rich in quartz, albite, dolomite, and chlorite were studied. After grinding copper mine tailings for 3 h, a remarkable increase in solubility was observed. Specifically, there was a 93% higher solubility of aluminum (Al) and a 23% higher solubility of silicon (Si) compared to a mine tailing material that was not ground [130]. Antigorite (Mg\({}_{3}\)Si\({}_{2}\)O\({}_{5}\)(OH)\({}_{4}\))-rich mining waste was also mechanically activated. The tailings were milled with a planetary mill (0.5-10 min). According to that study, the process of dehydroxylation was evidently linked to the generation of a greater amount of amorphous material during the milling process.