THE PRESENCE OF NATURAL ORGANIC LIGANDS (HUMID-FULVIC ACIDS) AS COMPLEXING AGENTS OF CATIONS IN THE DEEP OR SHALLOW AQUIFERS COULD HAVE A GREAT INFLUENCE ON THE MOBILITY OF RADIONUCLIDES IN THE GEOSPHERE /1/.

THE STUDY OF RADIONUCLIDES INTERACTIONS WITH HUMIC MATERIALS CONSTITUTES A RESEARCH AREA OF MAJOR IMPORTANCE : UP TO NOW THE SYSTEMS CATIONS-HUMIC SUBSTANCES ARE NOT WELL KNOWN PARTLY DUE TO A LACK OF KNOWLEDGE IN THE HUMIC SUBSTANCES FIELD (STRUCTURE, PROPERTIES,...). THE PURPOSE OF THE PRESENT RESEARCH IS TO DEFINE IN THE MOST COMPLETE WAY : FIRSTLY, THE PROPERTIES AND CHARACTERISTICS OF HUMIC MATERIALS, SECONDLY THE FORMATION CONDITIONS AND BINDING STRENGTHES OF HUMIC-RADIONUCLIDES SPECIES.

A CHROMATOGRAPHIC TECHNIQUE /2/ IS RETAINED TO STUDY THE ASSOCIATIONS OCCURRING BETWEEN TRANSURANIC ELEMENTS AND HUMIC MATERIALS WHICH WILL BE WELL CHARACTERISED BY DIFFERENT PHYSICAL AND CHEMICAL METHODS.
DEVELOPMENT IN HUMIC SUBSTANCES ANALYSIS (POTENTIOMETRY, SIZE EXCLUSION CHROMATOGRAPHY) AND ON THE CHROMATOGRAPHIC METHOD (CHROMATOGRAPHIC SUPPORT, DETECTION...) WILL BE PERFORMED.

THE FINAL OBJECTIVE OF THE PROGRAMME IS TO CONCLUDE ON THE CONTRIBUTION OF HUMIC SUBSTANCES TO THE POSSIBLE TRANSPORT OF RADIOACTIVE IN THE GEOSPHERE VIA GROUNDWATER.

A COLLABORATION WITH THE KBS IS UNDERTAKEN IS THIS RESEARCH AREA.
The first part of the research was concerned with the description of the selected aquifer (representative of a granitic geological formation, Fanay-Augeres), the method for the collection and concentration of the humic substances (a sorption technique), and their characterisation by different physicochemical techniques (elementary and mineral composition, spectroscopic properties, size, proton capacity, datation). The results show that Fanay-Augeres humic substances (considered as site specific humic substances) represent 41% of the total organic carbon (TOC) present in the aquifer (2 ppm) and have properties similar to other aquatic humic substances. The second part describes the study of the interactions occurring between these humic substances and trivalent cations (europium and americium). 2 different analytical methods were developed to perform these investigations, namely spectrophotometry and size exclusion chromatography. Interaction constants and complexing capacities were determined and are shown to agree with literature data.
B.1. ISOLATION AND CHARACTERISATION OF HUMIC SUBSTANCES
B.1.1. CONCENTRATION OF HUMIC MATERIALS FROM NATURAL GROUNDWATERS : SAMPLING, CONCENTRATION.
B.1.2. CHARACTERISATION OF HUMIC MATERIALS BY DIFFERENT PYSICAL AND CHEMICAL METHODS : ELEMENTARY, MINERAL, FUNCTIONNAL, POTENTIOMETRIC AND MOLECULAR WEIGHT (SIZE) ANALYSES.

B.2. INTERACTIONS BETWEEN HUMIC COUMPOUNDS AND TRANSURANIC ELEMENTS
B.2.1. DEVELOPMENT OF THE CHROMATOGRAPHIC METHOD CHOSEN FOR THE COMPLEXATION STUDIES (CHOICE OF CHROMATOGRAPHIC SUPPORT, SYSTEM OF DETECTION).
B.2.2. MEASUREMENT OF INTERACTION CONSTANTS WITH THIS CHROMATOGRAPHIC METHOD AS A FUNCTION OF VARIOUS CHEMICAL PARAMETERS (PH, IONIC STRENGTH, METAL AND LIGAND CONCENTRATIONBS).

B.3. INTER-LABORATORY COMPARISON EXERCISE ON CHARACTERISATION OF HUMIC MATERIALS AND ON COMPLEXATION OF RADIONUCLIDES WITH THESE SUBSTANCES.