Sorption-desorption dynamics of radiocaesium in organic matter soils

A systematic study has been carried out on the radiocaesium sorption properties of 25 soils (forest, peat) covering organic matter (OM) contents in the range of 10–97%. Predictions are made for radiocaesium partitioning between micaceous Frayed Edge Sites (FES) and regular exchange sites (RES) on the basis of specific radiocaesium interception potentials of the soil and overall exchange capacity. It is shown that for soils with a very high OM content (> 80%), significant fractions are present in a readily reversible form in the OM phase. In soils of low-medium OM content (< 40%), only a very minor fraction is present in the OM exchange complex. Experimental findings, based on a desorption screening with a variety of desorption agents are in agreement with these predictions. On the basis of a study of sorption kinetics, some additional tools are available for identifying problem soils. In cases of very high OM content, radiocaesium adsorption is completed within hours demonstrating the involvement of the OM sites. In soils for which interception occurs in the FES, sorption continues to proceed for periods of 2–3 weeks. In conclusion, some examples are presented on radiocaesium desorption using ion exchangers as radiocaesium sinks in promoting desorption. For a peaty soil, near quantitative desorption is accomplished. For forest soils with OM contents in a range of 10–40%, fixation levels of 30–50% are demonstrated.