Co‐Calcination of Silicate or Aluminosilicate Network of Clay and Non‐Clay Minerals With NaOH: Physicochemical Insights

ABSTRACT

This study investigates the physicochemical role of NaOH during co‐calcination of representative minerals commonly present in natural clay deposits, namely, kaolinite, montmorillonite, quartz, and feldspar, with 0–20 wt.% NaOH at 600°C. Spectroscopic and diffraction analyses (Fourier transform infrared [FTIR], solid‐state nuclear magnetic resonance [NMR], and x‐ray diffraction [XRD]) reveal that NaOH promotes depolymerization of Si–O–T (T = Si, Al) networks, induces redistribution of Al coordination environments, and facilitates partial amorphization or alkali‐stabilized phase formation depending on mineralogy. These physicochemical changes translate into distinct dissolution behaviors, as quantified by inductively coupled plasma‐mass spectroscopy (ICP‐MS), and corresponding variations in pozzolanic reactivity, measured by the R ³ test. The results demonstrate that the efficiency of co‐calcination is strongly mineral‐dependent and correlates with framework composition and Al ₂ O ₃ content. Co‐calcination with NaOH enhances the reactivity of montmorillonite and quartz through network depolymerization and the formation of reactive silicate environments, whereas excessive alkali addition to kaolinite promotes the formation of crystalline nepheline and reduces the availability of reactive Al ^v sites.