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Project Caesium - An ion exchange model for the prediction of distribution coefficients of caesium in bentonite

Technical Report:

Abstract

A surface chemical model is established to thermodynamically describe caesium sorption on bentonite. Caesium sorption is studied on Wyoming bentonite MX-80 in solutions of NaCl, KCl, MgCl{sub 2}, CaCl{sub 2}, NaNO{sub 3} and Ca(NO{sub 3}){sub 2} of concentrations varying between 0.025M and 1M, as well as in the weakly saline Allard groundwater and the strongly saline Aespoe groundwater. Based on these experiments it is shown that the sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant for the replacement of Na{sup +} on montmorillonite by Cs{sup +} is logK{sub ex} degrees = 1.6. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. For the analysis of diffusion experiments in compacted bentonite, the apparent diffusivity of tritiated water, HTO, is used as an analogue to estimate the pore diffusivity of Cs{sup +}. Since insufficient information is available at present to estimate the porosity actually available for diffusion in compacted bentonite, it is assumed that the diffusion porosity can be approximated by using the value of the bulk porosity. Under  More>>
Authors:
Wanner, H; Wieland, E; [1]  Albinsson, Y [2] 
  1. MBT Umwelttechnik AG, Zuerich (Switzerland)
  2. Chalmers Univ. of Technology, Goeteborg (Sweden). Dept. of Nuclear Chemistry
Publication Date:
Jun 01, 1994
Product Type:
Technical Report
Report Number:
SKB-TR-94-10
Reference Number:
SCA: 400201; 052002; PA: AIX-26:009398; EDB-95:030288; SN: 95001323016
Resource Relation:
Other Information: PBD: Jun 1994
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; CESIUM; DISTRIBUTION FUNCTIONS; SORPTION; BENTONITE; CHEMICAL REACTIONS; DIFFUSION; GROUND WATER; ION EXCHANGE; RADIOACTIVE WASTE DISPOSAL; THERMODYNAMIC ACTIVITY; UNDERGROUND DISPOSAL; 400201; 052002; CHEMICAL AND PHYSICOCHEMICAL PROPERTIES; WASTE DISPOSAL AND STORAGE
OSTI ID:
10111250
Research Organizations:
Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden)
Country of Origin:
Sweden
Language:
English
Other Identifying Numbers:
Journal ID: ISSN 0284-3757; Other: ON: DE95611797; TRN: SE9400191009398
Availability:
OSTI; NTIS; INIS
Submitting Site:
SWDN
Size:
44 p.
Announcement Date:
Jun 30, 2005

Technical Report:

Citation Formats

Wanner, H, Wieland, E, and Albinsson, Y. Project Caesium - An ion exchange model for the prediction of distribution coefficients of caesium in bentonite. Sweden: N. p., 1994. Web.
Wanner, H, Wieland, E, & Albinsson, Y. Project Caesium - An ion exchange model for the prediction of distribution coefficients of caesium in bentonite. Sweden.
Wanner, H, Wieland, E, and Albinsson, Y. 1994. "Project Caesium - An ion exchange model for the prediction of distribution coefficients of caesium in bentonite." Sweden.
@misc{etde_10111250,
title = {Project Caesium - An ion exchange model for the prediction of distribution coefficients of caesium in bentonite}
author = {Wanner, H, Wieland, E, and Albinsson, Y}
abstractNote = {A surface chemical model is established to thermodynamically describe caesium sorption on bentonite. Caesium sorption is studied on Wyoming bentonite MX-80 in solutions of NaCl, KCl, MgCl{sub 2}, CaCl{sub 2}, NaNO{sub 3} and Ca(NO{sub 3}){sub 2} of concentrations varying between 0.025M and 1M, as well as in the weakly saline Allard groundwater and the strongly saline Aespoe groundwater. Based on these experiments it is shown that the sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant for the replacement of Na{sup +} on montmorillonite by Cs{sup +} is logK{sub ex} degrees = 1.6. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. For the analysis of diffusion experiments in compacted bentonite, the apparent diffusivity of tritiated water, HTO, is used as an analogue to estimate the pore diffusivity of Cs{sup +}. Since insufficient information is available at present to estimate the porosity actually available for diffusion in compacted bentonite, it is assumed that the diffusion porosity can be approximated by using the value of the bulk porosity. Under these circumstances, the cation ex change capacity (CEC) found to be available for the diffusing species in compacted bentonite corresponds to about 12% of the total CEC of bentonite. It is recognised that the errors made in the estimation of the pore diffusivity and of the diffusion porosity are contained in the reduction factor of the CEC. A discussion of the factors affecting the diffusivities of radionuclides and the problem of establishing consistent sets of diffusivity data is given in the Appendix. 33 refs, 7 figs, 12 tabs.}
place = {Sweden}
year = {1994}
month = {Jun}
}