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Application of A Monte Carlo Approach to Surface Complexation Modelling

Published online by Cambridge University Press:  17 March 2011

M.M. Askarieh ,
T.G. Heath  and
W.M. Tearle
M.M. Askarieh
Affiliation:
United Kingdom Nirex Limited, Curie Avenue, Harwell, Didcot, Oxfordshire OX11 0RH, UK
T.G. Heath
Affiliation:
Serco Assurance, B150 Harwell, Didcot, Oxfordshire OX11 0QJ, UK
W.M. Tearle
Affiliation:
formerly Serco Assurance, present address Ghyll Mount, Gillan Way, Penrith 40 Business Park, Penrith, Cumbria CA11 9BP, UK
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Abstract

A Monte Carlo-based approach has been adopted for development of a chemical thermodynamic model to describe the goethite surface in contact with sodium nitrate solutions. The technique involves the calculation of the goethite surface properties for the chemical conditions corresponding to each experimental data point. The representation of the surface was based on a set of model parameters, each of which was either fixed or was randomly sampled from a specified range of values. Thousands of such model representations were generated for different selected sets of parameter values with the use of the standard geochemical speciation computer program, HARPHRQ. The method allowed many combinations of parameter values to be sampled that might not be achieved with a simple least-squares fitting approach. It also allowed the dependence of the quality of fit on each parameter to be analysed. The Monte Carlo approach is most appropriate in the development of complex models involving the fitting of several datasets with several fitting parameters.

Introduction of selenate surface complexes allowed the model to be extended to represent selenate ion sorption, selenium being an important radioelement in evaluation of the long-term safety of ILW disposal. The sorption model gave good agreement with a wide range of experimental sorption datasets for selenate.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 824: Symposium CC – Scientific Basis for Nuclear Waste Management XXVIII , 2004 , CC7.1
Copyright
Copyright © Materials Research Society 2004

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