Dissolution behavior and mineralogical changes of mine tailings subjected to NaOH solution

Due to the low reactivity of mine tailings in cementitious systems, increasing the pH with alkaline solutions, a process known as alkaline activation, was investigated to enhance their reactivity. This study, therefore, screened the dissolution behavior and mineralogical alteration of nine distinct mine tailings exposed to an alkaline solution (6 M NaOH) to assess their reaction potential as high-pH binder material. The investigations primarily focused on aluminum (Al) and silicon (Si) due to their role in gel formation in addition to calcium (Ca) and sulfur (S), because of the potentially high carbonate and sulfide content in mine tailings. Alkaline dissolution extents of Al (0.02–4.3 %), Ca (0.01–3.0 %), and Si (0.5–2.5 %), as measured by inductively coupled plasma-optical emission spectroscopy, demonstrated limited dissolution compared to commonly used materials for alkali activation. The highest dissolution extent was from S (13–127 %). The dissolution extent was not controlled by initial bulk elemental content but by mineralogical composition. Material characterization (X-ray diffraction, thermogravimetric analysis, automated mineral analysis) of the solids before and after dissolution showed tectosilicates to have greater resistance towards alkaline dissolution. In contrast, soro-, inosilicates, and sulfates showed total alkaline dissolution, while phyllosilicates and carbonates were less reactive. These trends correlated with the mineral-specific average particle size, where reactive minerals displayed a reduction, while the size of minerals with low solubility remained unchanged. Despite a low dissolution extent, the screening enabled a better understanding of the impact of mineralogy, warranting further investigations. • Study used alkaline dissolution as screening tool for reactivity assessment of low-reactivity mine tailings. • Alkaline solution assessed nine mine tailings activation potential. • Al, Ca, and Si showed limited alkaline dissolution; S showed higher extents. • Mineralogy, not bulk composition, controlled dissolution. • Tectosilicates showed high resistance to alkaline dissolution.