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The effect of cellulose degradation products on thorium sorption onto hematite: studies of a model ternary system

Published online by Cambridge University Press:  05 July 2018

G. M. N. Baston ,
M. M. Cowper ,
T. G. Heath ,
T. A. Marshall  and
S. W. Swanton
G. M. N. Baston
Affiliation:
AMEC †, B150, Thomson Avenue, Harwell, Didcot, Oxfordshire OX11 0QB, UK
M. M. Cowper
Affiliation:
AMEC †, B150, Thomson Avenue, Harwell, Didcot, Oxfordshire OX11 0QB, UK
T. G. Heath
Affiliation:
AMEC †, B150, Thomson Avenue, Harwell, Didcot, Oxfordshire OX11 0QB, UK
T. A. Marshall
Affiliation:
AMEC †, B150, Thomson Avenue, Harwell, Didcot, Oxfordshire OX11 0QB, UK
S. W. Swanton*
Affiliation:
AMEC †, B150, Thomson Avenue, Harwell, Didcot, Oxfordshire OX11 0QB, UK
*
*E-mail: steve.swanton@amec.com
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Abstract

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Cellulose degradation products (CDPs) can complex with radioelements causing solubility enhancement and sorption reduction, effects which are detrimental to the containment of radionuclides in the near field of a geological disposal facility and surrounding geosphere. Isosaccharinic acid (ISA) is the principal component of CDPs formed under the alkaline anaerobic conditions of a cement-based near field and appears to be largely responsible for the impact of CDPs on radionuclide solubility and sorption under near-field conditions. However, the situation appears to be more complicated under near-neutral pH geosphere conditions.

A combined experimental and modelling study was undertaken to compare the impact of a CDP leachate to ISA in a simple model ternary sorption system consisting of hematite as a single mineral substrate, thorium as the radioelement and ISA or a CDP leachate as the complexant. Thorium sorbs strongly to hematite. A triple layer model for thorium sorption to hematite was refined to fit to the experimental data in the absence of ISA or CDP leachate; the effect of ISA on thorium sorption was then predicted.

In the presence of CDP leachate, a significant reduction in thorium sorption was observed from pH 6 to 12 in good agreement with model predictions based on a high concentration of ISA. However, only a limited impact of ISA on thorium sorption was observed at pH 6 to 12, in contrast to predictions. The effects of ISA could be accounted for by assuming the formation of a ternary thorium–ISA–surface complex. The model has yet to be extended to the more complex CDP systems. Differences in the thorium speciation in solution due to the formation of a ternary calcium–thorium–ISA complex in the CDP leachate, which is absent from solutions with ISA only, provides the most likely explanation for the differences observed experimentally.

Keywords

cellulose degradation productshematiteisosaccharinic acidorganic complexantssorptionsurface complexation modelthorium
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 8 , December 2012 , pp. 3381 - 3390
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2012] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

Footnotes

†

Formerly Serco

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