[en] The possibility of quantifying the sorption properties of soils and sediments for radiocaesium allows to make predictions on soil chemical availability and geochemical mobility. Consequently, counter measurements in view of the prevention of the transfer of radiocaesium to plants and the food chain in contaminated soils can be selected on a rational basis. The efficiency of these counter measurements dependents on the relative Cs-sorption selectivity of soil and amendments. A set of examples, relating to Cs-selective zeolites is presented and their efficiency for reducing soil-chemical availability of radiocaesium is demonstrated

[en] Among the possible remedial actions to reduce the soil-to-plant transfer of radiocaesium and radiostrontium, the addition of clay minerals or zeolites aims at increasing permanently the radionuclide fraction adsorbed on the solid phase, thus lowering the radionuclide solution level available for root uptake. The traditional procedure to test the effectiveness of such amendments is rather empirical: the amendments are applied to the soil and the effect is expressed in terms of the change of the transfer factor, defined as the ratio of Bq per kilogram plant and soil. This procedure yields no insight in the processes responsible for the observed effect and does not allow predictions for other scenarios. Based on the knowledge that soil-to-plant transfer essentially depends on soil type, the use of soil amendments was investigated by quantitatively addressing the physico-chemical parameters which govern solid/liquid partitioning of radionuclides in soils and soil amendments. It is shown that this approach allows to identify the potential soil/amendment combinations to estimate the effects to be expected

[en] A survey is given of some of the important processes involved in the solid-liquid distribution behaviour of radionuclides in both well-defined adsorbents and multicomponent natural systems. The thermodynamic significance of distribution coefficients is analyzed and the various parameters affecting partition behaviour are discussed in relation to possible retention mechanisms. Attention is being given to factors such as solid/liquid ratio, pH-Eh, reversibility, liquid phase composition and speciation effects. Various processes are discussed such as ion exchange and complex formation involving clays, oxides, humic acids. It is shown that, only in rare cases, Ksub(D) values can be rationalized in terms of process mechanistics. In addition, it is indicated that, in general, radionuclide distribution coefficients cannot be considered as constants unless the conditions are restricted to very small loading intervals. It is furthermore suggested that, in order to produce meaningful data on radionuclide partitioning behaviour, efforts should be made to operate under conditions which are representative for the 'in situ' situation. (author)

[en] The purpose of this paper is to show that the factor by which the mobility of ions is reduced in clay gels imbibed with an electrolyte solution can be predicted from the relationship which has been found to describe tortuosity effects in porous media formed by the random packing of particles less anisometric and coarser than clay plates. Estimating these tortuosity effects in a wide range of porosity by means of self-diffusion experiments would involve an almost prohibitive expense of labour. Electrical conductivity measurements provide an easy and rapid method for achieving the same result

[en] The key parameters for the experimental determination of the interaction constants of transition metal ions and radionuclides with humic substances are discussed. A number of factors affecting the widely diverging literature results on Eu³⁺ and Am³⁺ humic acid complexation are considered. The influence of pH, ionic strength, origin and nature of humic substances on the interaction constants is extensively discussed using literature data and new results. (orig.)

[en] A quantitative study is presented on the effects of sulphate complex formation in the liquid phase on the solid-liquid trace distribution of europium in montmorillonite and Boom clay. Equilibria are carried out at a pH of 3 in the presence of either Na or Mg at a total concentration of 0.1, 0.25 and 0.4 N (montmorillonite) and 0.1 N (Boom clay) in nitrate sulphate mixtures of various compositions. It is shown that the effects can be reasonably well described on the basis of Eu-sulphate complex formation, involving the ionic strength-dependent formation of Eu(SO₄)⁺ and Eu(SO₄)^- species and assuming that the trivalent Eu⁺⁺⁺ is the only species being adsorbed. It is furthermore shown that in montmorillonite, we are dealing with a reversible ion exchange process involving the permanent lattice charge whereas in Boom clay, the humic acid fraction appears to be the sink responsible for Eu sorption. (author)

[en] This paper deals with the speciation of europium in the solid phase and liquid phase extracts of Boom Clay under in situ conditions. Using a new method for measuring the europium-humic acid complex stability constant at high pH, it is shown that carbonate complexation is poorly competitive with humic acid, europium being quantitatively present as humic acid complex, its stability constant being of the order of 10¹²-10¹³. It is furthermore shown that partial oxidation of the sediment, which is strongly reducing under in situ conditions, leads to a significant increase in Ksub(D) values, whatever the liquid/solid ratio used. This effect is ascribed to the involvement of ferric oxides which are generated in the solid phase and which lead to a displacement of the metal from the humic acid sink. Some examples are presented which demonstrate that at high pH, around 9, ferric oxides may be competitive with humic acids for metal sorption and that this effect increases with pH. (author)

[en] Published in summary form only

[en] A model describing the uptake of TcO-4 by spinach plants was developed. The equation relates both plant and soil parameters (e.g., growth, metabolism, concentration of TcO-4 and composition of the growth medium) to the concentration of Tc in the shoot of the plant. As the soil solution is the medium from which plants obtain nutrients and non-nutrients, the modeling parameters have been obtained from uptake experiments using nutrient solutions (= simulated soil solutions) as the growth medium. Two important model assumptions are: (1) that an equilibrium exists between TcO-4 in the plant and the growth medium and (2) that the leaf TcO-4 metabolism is a pseudofirst order reaction occurring in a non-constant volume

[en] Published in summary form only