Ion exchange model for reversible sorption of divalent metals on calcite: implications for natural environments.

Most of the thermodynamic models available in the literature describing the speciation of the calcite surface do not predict a significant concentration of sorbed Ca(II), whereas previous electrokinetics studies clearly show that Ca(2+) is the main cation determining the potential of the calcite surface. This study proposes a new thermodynamic model based on ion-exchange theory that is able to describe the reversible sorption of Ca(2+) on calcite. To constrain the model, concentrations of Ca(II) sorbed reversibly on the mineral surface were obtained as a function of pH.

New experimental approach for studying diffusion through an intact and unsaturated medium: a case study with Callovo-Oxfordian argillite.

The diffusion of tritiated water and anionic species was studied in an unsaturated core of Callovo-Oxfordian claystone, which is a potential host-rock for disposal of high-level radioactive wastes. The diffusion parameters in such conditions were determined using modified through-diffusion cells in which the suction is generated by the osmosis process. This specific device leads to values of saturation degree ranging from 81% to 100%.