Complexation behaviour of humic substances from granitic groundwater towards Am(III)

The role of humic substances in the transport of radioelements in natural aquifers is widely recognized. Complexation with humic materials is of particular interest when assessing the speciation of actinides in natural waters for the safety evaluation of nuclear waste storage policies. The interaction between Am(III), a trivalent actinide, and humic/fulvic acids of aquatic origin (granitic groundwater) was investigated by two different techniques: spectrophotometry and size exclusion chromatography. Stability constants were calculated assuming the formation of complexes of 1:1 stoichiometry. The unit systems of these constants are discussed. Results when using these two techniques on Am(III) and Eu(III) are compared.