Workreport 2008-62



Sorption of Cesium on Olkiluoto Mica Gneiss and Granodiorite in Saline Groundwater; Retardation of Cesium Transport in Rock Fracture Columns


Kyllönen, J., Hakanen, M. & Lindberg, A.



Page count:



Sorption of cesium on Olkiluoto mica gneiss and granodiorite rock types has been studied earlier by batch experiments using crushed rocks and rock slices (Huitti et al., 2000, Huitti et al., 1998). The sorption distribution ratios (Rd) of cesium on the rocks are strongly reduced with increases in salinity and increases in cesium concentration in the solution. In addition, highly nonlinear sorption at elevated cesium concentrations in saline solutions has been found and also very slow desorption of cesium at trace concentrations.

In this work the sorption of cesium on Olkiluoto rocks is studied and a mechanistic cation exchange model is applied for sorption of cesium on Olkiluoto mica gneiss and granodiorite. The sorption of cesium on rock was in accordance with charge balances of cations in a low-salinity groundwater stimulant. Earlier studies have indicated that biotite is the dominating cesium-sorption mineral in fresh mica gneiss, granodiorite and granite. This suggested that a composite additive sorption model for cesium on rocks could be constructed based on the sorption on biotite.

Biotites were separated from the Olkiluoto mica gneiss and granodiorite for biotite specific sorption studies of cesium. The cation exchange capacities of the separated Olkiluoto biotites were almost the same for all the exchangeable cations. The selectivity coefficients of Cs-Na, Cs-K and Cs-Ca cation exchange reactions were determined for the Na-, K- and Ca-conditioned biotites by modelling of the cesium sorption isotherms in the electrolyte solutions. A three-site model is needed to model the sorption over cesium concentration range 1*10-8 M to 1*10-3 M isotherms.

Selectivity coefficients determined for the exchange reactions were used in a reactive transport model for migration of cesium in rock fractures at the laboratory scale. The PhreeqC programme was applied. The model was calibrated for migration of cesium in a mica gneiss fracture under constant chemical conditions. The model was applied to modelling of migration of cesium in granodiorite fractures under constant chemical conditions. In this case the sorption site concentrations were reduced owing to the lower biotite content of granodiorite. Modelling of cesium breakthrough during constant concentration inflow in saline groundwater-conditioned mica gneiss and granodiorite was made using the sorption site concentrations for the rock types.

Cesium breakthrough in mica gneiss for 1*10-6 M Cs in OL-SO was calculated by PhreeqC omitting the sorption on fracture surfaces. The results indicate that in the long run matrix diffusion dominates the breakthrough, but the time of the start of breakthrough is determined by surface sorption. An analytical approach for the same situation with a Kd for sorption and De for matrix diffusion was used for comparison. High sorption, a De value in accordance with 2% porosity, and omitting the formation factors for the rock porosity were needed to reproduce the long term breakthrough of cesium in an OL-SO-conditioned fracture


Sorption of Cesium, Mica Gneiss, Granodiorite, Olkiluoto


Sorption of Cesium on Olkiluoto Mica Gneiss and Granodiorite in Saline Groundwater; Retardation of Cesium Transport in Rock Fracture Columns (pdf) (602.2 KB)


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.


To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.