Experimental determination and modelling of trace metal-humate interactions: a pragmatic approach for applications in groundwater

摘要

Complexation of radionuclides by humic substances and the concomitant remobilisation of sorbed radionuclides is a source of uncertainty in performance assessment of radioactive waste repositories. Despite more than 30 years of world-wide intensive research in this field, only very few datasets are available which are relevant for performance assessment. The reason for this unusual situation is found in the poor understanding of chemical structures of humic substances, which is a label for a most complex, heterogeneous mixture of organic molecules. Because of the ignorance of the 'real' structures of the complexes formed between radionuclides and humic substances, no binding model was developed up to now, which is firmly based on thermodynamics and which would allow extrapolations outside the chemical parameter space at which it has been calibrated. It is therefore the main purpose of the present work to develop means for performance assessment to conservatively bound the effect of humic substances on radionuclide speciation in solution at relevant chemical conditions. (author) 70 figs., tabs., refs.