Kinetic sorption in the transport of species in a cement based composite

Cement based composites are considered to be a very important part of the present multi-barrier concepts in nuclear waste management. To assess their suitability in this respect, it is necessary to understand in detail the transport of radionuclides in such composites. One of the tasks is a proper description of adsorption into the pore walls. Usually, an equilibrium isotherm is assumed to well describe the sorption. However, in this paper we introduce a first-order kinetic sorption model to show that it could plausibly interpret experimental data on the transport of gadolinium in a dry cement composite. The data are measured by neutron imaging, and the optimization of model parameters in order to fit the data is based on the Levenberg-Marquardt method.