SORPTION-DESORPTION DYNAMICS OF RADIOCESIUM IN ORGANIC-MATTER SOILS

A systematic study has been carried out on the radiocaesium sorption p roperties of 25 soils (forest, peat) covering organic matter (OM) cont ents in the range of 10-97%. Predictions are made for radiocaesium par titioning between micaceous Frayed Edge Sites (FES) and regular exchan ge sites (RES) on the basis of specific radiocaesium interception pote ntials 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 th e OM exchange complex. Experimental findings, based on a desorption sc reening with a variety of desorption agents are in agreement with thes e predictions. On the basis of a study of sorption kinetics, some addi tional tools are available for identifying problem soils. In cases of very high OM content, radiocaesium adsorption is completed within hour s demonstrating the involvement of the OM sites. In soils for which in terception occurs in the FES, sorption continues to proceed for period s of 2-3 weeks. In conclusion, some examples are presented on radiocae sium desorption using ion exchangers as radiocaesium sinks in promotin g desorption. For a peaty soil, near quantitative desorption is accomp lished. For forest soils with OM contents in a range of 10-40%, fixati on levels of 30-50% are demonstrated.