Abstract
The dissolution behavior of smectite under alkaline conditions at 25° to 50°Cwas investigated using in-situ Contact mode atomic force microscopy (CMAFM) and Tapping mode AFM (TMAFM). Smectite particles dissolved via the retreat of the edge surfaces without the affect of the AFM tip, except in some series of the dissolution experiment in CMAFM. No etch pits were observed forming on the basal surface within the experimental durations. The edge surface area (ESA)-normalized dissolution rates of smectite at a certain pH and temperature condition, therefore, have a constant value independent of the particle size, indicating the essential dissolution rate. In contrast, the dissolution rates normalized to the total surface area (TSA) of smectite varied with the particle size. The activation energy of smectite dissolution under alkaline conditions appears to be dependent on pH, like as kaolinite. A model dissolution rate equation which includes simultaneously the effect of pH and temperature was deduced from the effect of the activation energy on pH, the rate equation of smectite dissolution at 25°C, and the Arrhenius equation. The rates estimated using the model are in good agreement with experimental dissolution rates between 20°and 60°C.
