Hydrogen adsorption and diffusion in synthetic Na-montmorillonites at high pressures and temperature

Sodium montmorillonite (Na-Mt) was synthesized with the aim to investigate the adsorption and diffusion of hydrogen gas in a model smectite at high pressures (up to 90 bar) and non-cryogenic temperature (363 K). Na-Mt samples were synthesized from hydrogels in mild conditions (493 K and autogenous pressure). Two further Na-Mt samples with different levels of structural iron were prepared to investigate the effect of iron on the textural and hydrogen adsorption properties. Structural and elemental analyses confirmed that well crystalline smectite samples were obtained according to the nominal chemical formulae. Nitrogen adsorption-desorption isotherms revealed that the synthesized materials have specific areas in the range 90-120 m(2)/g and are mainly mesoporous. High pressure volumetric measurements showed that hydrogen absorption at 363 K saturated between 40 and 60 bar, reaching 0.2 +/- 0.02 wt% (i.e. similar to 1.0 mmol/g) at the plateau. Quasielastic neutron scattering revealed ' that hydrogen diffuses inside the clay porous network according to the Fick's law (continuous diffusion), while jump diffusion cannot be excluded at distances lower than 6.3 angstrom, i.e. less than the one between two Na+ exchangeable ions. The hydrogen self-diffusion coefficients in the temperature range 25-300 K were determined to fall in the interval 0.1-1.0 10(-7) m(2) s(-1). The results are compared with H-2(g) adsorption and diffusion in other systems. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Hydrogen uptake and diffusion in Callovo-Oxfordian clay rock for nuclear waste disposal technology

The Callovo-Oxfordian clay-rich rock formation is currently considered as host rock barrier in the French geological repository facility for radioactive waste (Meuse/Haute-Marne). After the closure of the facility, hydrogen gas is expected to develop mainly from anaerobic corrosion of steel containers and other ironcontaining structures. Gas pressure build-up could impact the safety of the repository. It is therefore important to acquire in-depth knowledge on the interaction between hydrogen gas and surrounding clay rock in terms of uptake ability and diffusion. Hydrogen uptake capacity was evaluated on dried clay rock samples: (i) at 20K, to allow for hydrogen liquefaction and determine the maximal Hy uptake of the clay, and (ii) at typical pressure and temperature conditions expected to develop in the repository (up to 363 K and a hydrogen pressure of 40-60 bar). H-2 absorption on the dried raw Callovo-Oxfordian start to saturate at about 30-40 bar, and the average adsorption above 40 bar is about 0.1% in weight. Quasi-elastic neutron scattering spectroscopy was used to study the diffusion mechanism of hydrogen gas in the clay rock at the microscopic scale and to determine hydrogen self-diffusion coefficients in the dry samples in the temperature range 25-300 K. Neutron data suggested that hydrogen diffuses in the dry clay rock according to Fick's law. The findings reported in this work can help to better understand the behavior of H-2 in clay rock samples. (c) 2014 Elsevier Ltd. All rights reserved