Sorption of Sr on montmorillonite clays: Theoretical and experimental study

Montmorillonite is a clay mineral widely used to remove pollutants from wastewater. The Sr sorption on montmorillonite was analyzed combining an experimental - theoretical approach. Sr sorption on natural and synthetic Na-montmorillonite was studied, characterizing the materials before and after Sr incorporation by Xray diffraction and Zeta potential. The total specific surface area was also determined. Besides, ab-initio calculations were performed in order to investigate the sorption stability of the clay. The effect of the hydration of Sr atoms and the influence of the van der Waals interaction were evaluated. The experimental results indicated that Sr was sorbed on both, external and internal surfaces and that the total specific surface area seems to be relevant for the sorption process. The increasing in the interlayer space by Sr incorporation was associated with the cationic exchange, the hydration of the Sr atom and the relative humidity. Nuclear magnetic resonance parameters were calculated and compared with the experimental chemical shift and electric field gradient. The calculated Sr-chemical shift corresponds to the range for atomic coordination n = 6. Since there is no experimental data available for the principal component of the electric field gradient at Sr site, the obtained theoretical value stands as a prediction.