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Effect of Humic Substances on the Migration of Radionuclides: Complexation of Actinides with Humic Substances in Natural Aquatic Systems

Objective

The aim of the present research programme is to study the complexation behaviour of actinide ions with humic substances in natural aquifer systems and hence to quantify the commonly found in all groundwaters in different concentrations have a strong tendency towards complexation with actinide ions. This in one of the major geochemical reactions but hitherto least quantified. Therefore, the effect of humic substances on the actinide migration is poorly understood. In the present research programme the complexation of actinide ions with humic substances will be described thermodynamically. This description will be based on a model being as simple as possible to allow an easy introduction of the resulting reaction constants into geochemical modelling of the actinide migration.
The aim of the present research programme is to study the complexation behaviour of actinide ions with humic substances in natural aquifer systems and hence to quantify the effect of humic substances on the actinide migration. Aquatic humic substances commonly found in all groundwaters in different concentrations have a strong tendency towards complexation with actinide ions. This is one of the major geochemical reactions but hitherto least quantified. Therefore, the effect of humic substances on the actinide migration is poorly understood. In the present research programme the complexation of actinide ions with humic substances will be described thermodynamically. This description will be based on a model being as simple as possible to allow an easy introduction of the resulting constants into geochemical modelling of the actinide migration.

A study has been conducted to determine an effective ligand concentration of a given humic acid. This is a parameter being used for the evaluation of the complexation constant of a metal ion for bulk polyelectrolytes like humic or fulvic acid. Time resolved laser fluorescent spectroscopy (TRLFS) is further developed for its application to the humate complexation study of trivalent metal ions. The effect of humic acid on the interaction of metal ions with inorganic colloids is examined systematically, together with the humate complexation of neptunium(V). This study is of experimental significance for understanding the effect of metal ion concentration on the humate complexation.
Work programme:

The programme consists of the following three main tasks:

Task 1: Complexation reactions of actinide ions with well characterized reference and site-specific humic and fulvic acids.
Task 2: Competition reactions with major cations in natural groundwaters.
Task 3: Validation of the complexation data in natural aquatic systems by comparison of calculation with spectroscopic experiment.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

TECHNICAL UNIVERSITY OF MUNICH
Address
Walther-meissner-strasse 3
85748 Garching
Germany

Participants (3)

Commissariat à l'Energie Atomique (CEA)
France
Address
Centre D'études De Fontenay-aux-roses
92265 Fontenay-aux-roses
JOHANNES GUTENBERG UNIVERSITAET MAINZ
Germany
Address
Fritz-strassmann-weg 2
55128 Mainz
KATHOLIEKE UNIVERSITEIT LEUVEN
Belgium
Address
92,Kardinaal Mercierlaan 92
3001 Heverlee