Hydration properties of bentonites from Cabo de Gata (SE, Spain). Isotopic study (18O/16O; 2H/H) of the hydration water

The aim of this study is to determine the isotopic composition (δ18O and δ2H) of interstitial water in bentonites. The study had been carried out from adsorbed vapour in homoionic bentonites. We have worked with the fraction <20μm of a bentonite from Serrata de Níjar (Almería, Spain). Homoionic sodium and calcium bentonites were prepared as well as variable quantities of exchangeable Na/Ca (75Ca/25Na; 50Ca/50Na; 25Ca/75Na), by mixing pure sodium and calcium suspensions in the appropriate quantities. To carry out the hydration of the samples, every one of them was previously dried at 300°C overnight, they were subjected to controlled saturation conditions in an atmosphere of different relative humidity and at a constant temperature of 20°C, until equilibrium was achieved. The different vapour pressures were: P/Po=0.05; P/Po=0.078; P/Po=0.15; P/Po=0.32; P/Po=0.45; P/Po=0.63; P/Po=0.8; P/Po=1, obtained from the saturated solutions of different salts or sulphuric acid.