Why Clays Swell

Abstract

The particularly difficult subject of predicting the swelling behavior of clay minerals is addressed by a combination of molecular dynamics and Monte Carlo sampling techniques. The introduced algorithm essentially mimics the experimental determination of the water adsorption isotherm and quantitatively predicts clay swelling for a montmorillonite-type clay including such details as the occurrence of hydrated states and hysteresis. Furthermore, important insights into the underlying mechanism of clay swelling from the one-layer to the two-layer hydrate are derived. It turns out that, for this case, clay swelling proceeds via the migration of counterions that are initially bound to the mineral surface to the central interlayer plane where they become fully hydrated. The extent of clay swelling strongly depends on the charge locus. This information appears to be transferable to other clay types.