Hydration of Na+, Ni2+, and Sm3+ in the Interlayer of Hectorite: A Quasielastic Neutron Scattering Study

Oleg S. Sobolev (1) , Lydie Le Forestier (2) , Miguel A. Gonzales (3) , Laurent Charlet (1)

1 LGIT - Laboratoire de Géophysique Interne et Tectonophysique
2 ISTO - Institut des Sciences de la Terre d'Orléans
3 ILL - Institut Laue-Langevin

Quasielastic neutron scattering experiments were performed with Na−hectorite, Ni−hectorite, and Sm−hectorite samples in order to find out whether Sm3+ is present in the clay interlayer as a fully hydrated cation (outer-sphere complex), or, as it follows from neutron diffraction data analysis, it is dehydrated and bound to the clay surface (inner-sphere complex). The results obtained for the Sm−hectorite were compared with other interlayer cations: strongly hydrated Ni2+ and relatively weakly hydrated Na+. It was found that water mobility in the Sm−hectorite sample is very close to the water mobility in Ni−hectorite. This is only possible if the Sm3+ ion is fully hydrated. It was shown that water molecules hydrating Ni2+ and Sm3+ exhibit diffusion mobility measurable with backscattering spectrometers. The diffusion coefficients of the exchangeable cations were found using the slow exchange approximations DNi = (0.05 − 0.14) × 10−9 m2/s and DSm = (0.04 − 0.18) × 10−9 m2/s.

Domains: Continental interfaces, environment; Global Changes

Oleg S. Sobolev, Lydie Le Forestier, Miguel A. Gonzales, Laurent Charlet. Hydration of Na+, Ni2+, and Sm3+ in the Interlayer of Hectorite: A Quasielastic Neutron Scattering Study. Journal of Physical Chemistry C, 2009, 113, pp.13801-13812. ⟨10.1021/jp903179g⟩. ⟨insu-00413847⟩