Modeling the alkaline dissolution of metakaolinite

The alkaline dissolution of metakaolinite (Al2[jls-end-space/]Si2[jls-end-space/]O7[jls-end-space/]) in NaOH solutions was monitored by in-situ 27Al NMR spectroscopy. A population balance model, combined with geochemical equilibrium calculations, was used to fit the time-dependent concentration of the Al(OH)4− species in solution and calculate the Al2[jls-end-space/]Si2[jls-end-space/]O7 dissolution rate. To this aim, a critically revised dissolution equation for metakaolinite was provided. By estimation of the equation parameters, a generalized dissolution rate was obtained as a function of pH. Therefore, these results are suitable for cement systems reacting at different pH ranges, from blended to alkali-activated ones. Specifically, the results presented in this paper constitute a basis on which more sophisticated kinetic models of binders based on metakaolin, or kaolinitic calcined clays, could be set up, with the aim of predicting their dissolution-precipitation kinetics and associated properties.