A Quantitative Model for Ion Diffusion in Compacted Bentonite

Michael Ochs, Maarten Boonekamp, Hans Wanner, Haruo Sato, Mikazu Yui

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


Compacted bentonite is a candidate backfill material for the disposal of radioactive waste. A correct understanding of the processes affecting diffusion in compacted bentonite is needed to predict radionuclide migration. Using distribution coefficients (Kd) obtained in batch experiments and geometric factors relevant for compacted bentonite, it is not possible to predict or explain the apparent diffusivities (Da) typically observed. Here, an approach is presented that integrates mechanistic sorption and diffusion models in combination with thermodynamic data and bentonite characteristics in order to predict Da for cesium. Key features of this approach are (i) to calculate the correct Kd value at high dry densities of the bentonite, and (ii) to calculate the correct constrictivity based on an electric double layer model. The integrated sorption-diffusion model present in this paper assigns exchangeable, immobile ions to the Stern layer, whereas ions located in the diffuse layer are considered mobile. Constrictivity is interpreted as the ratio of the average concentration of an ion in the diffuse layer to its concentration in the bulk solution. We show that in this way, the diffusion of Cs in Kunigel-V1 as well as Kunipia-F bentonite can be modeled successfully for a wide range of dry densities. Stern plane potentials calculated for these conditions also agree with measured zeta-potentials.

Original languageEnglish
Pages (from-to)437-443
Number of pages7
JournalRadiochimica Acta
Issue number1
Publication statusPublished - Dec 1 1998
Externally publishedYes


  • Bentonite
  • Cesium
  • Diffusion
  • Models
  • Sorption

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


Dive into the research topics of 'A Quantitative Model for Ion Diffusion in Compacted Bentonite'. Together they form a unique fingerprint.

Cite this