The effects of cations and concentration on reaction mechanism of alkali-activated blast furnace ferronickel slag

The effects of ion species and alkalinity on the alkali activated furnace ferronickel slag (FNS) were studied in this paper. NaOH and KOH with different concentration (2 M & 6 M) were used as activator. XRD, FT-IR and BET results show that more C-A-S-H gels were produced than the crystalline phases at lower activator concentration, while more crystalline phases formed at high concentration. Isothermal calorimetry and ICP results show that the effects of cations are different at different concentration. At lower concentration, higher reaction rate and higher concentrations of Si and Al were found in NaOH activated FNS although the alkalinity of NaOH is lower. This is due to the stronger polarization ability of Na+ than K+ can stabilize Si and Al anions in the solution and improve the reaction rate. At higher concentration, isothermal calorimetry shows large differences between NaOH and KOH while only small differences was found in ICP data. This indicates that cations have greater impact on the reaction process at higher concentration. A hypothesis was proposed to explain the anomalous phenomenon at higher concentration. At high concentration, there are not enough water molecules in the solution for ion hydration. Na+ with higher ionic polarization and hydration heat will strongly bind to dissolved anions and accelerate the reaction near the FNS particle. While K+ bind to less water molecules which enable faster diffusion of anionic species and promote the later reaction.