Towards a more comprehensive modelling of the behaviour of transuranic elements in agricultural soils: Experimental procedure for the study of the sorption/desorption parameters and speciation of transuranic actinides in the rhizosphere

The present paper describes the experimental on-going program on the biogeochemical behaviour of americium and neptunium in the rhizosphere of agricultural soils. Investigation is made by column experiments under close-to-natural conditions, supported by complementary batch experiments. Columns filled with 2mm-sieved soil, contaminated with 241Am or 237Np, are leached by soil solutions of varying compositions including citric acid and/or glucose. The outlet solution is analyzed (pH, Eh, conductivity, major ions, low molecular weight organic acids, radionuclides) and ultrafiltration is used to determine the relation between particle size and α activity. The objective of the study is to ascertain quantitative information on the effects of root exudates, of the physico-chemical parameters of the soil solution as well as the potential role of microorganisms, on the sorption/desorption processes and the speciation in solution 241Am and 237Np