Analysis of barium retention mechanisms on calcium silicate hydrate phases

Abstract

Calcium silicate hydrate (C-S-H) phases mostly contribute to contaminant retention in cement. The adsorption mechanisms of Ba on C-S-H phases with four different Ca/Si ratios were investigated by batch sorption experiments. The sorption kinetics, the effects of the solid to liquid ratio and the presence of alkalis in solution were analysed. Sorption isotherms in a wide range of Ba concentrations (from 10−10 to 1 · 10−1 M) were performed. To understand the underlying retention mechanisms, the effects of Ba adsorption on surface potentials were additionally examined. The main objective of this studywas to develop a sorptionmodel able reproducing not only the Ba sorption behaviour, but also the C-S-H surface potential before and after Ba uptake. The reactions and model parameters selected for satisfying these conditions are discussed in the paper. A three-site model, with weak and strong silanol sites and one exchange site, which satisfactorily fulfils the initial aims, is proposed.