Mobility of radionuclides in soil/groundwater system: Comparing the influence of EDTA and four of its degradation products

The adsorption behavior of 241Am, 60Co, 137Cs and 85Sr in the presence and absence of chelating ligands (ethylenediaminetetraacetic acid, ethylenediaminediacetic acid, hydroxyethyliminodiacetic acid, iminodiaceiticacid and methyliminodiacetic acid) was investigated. Sorption affinity in the absence of chelating ligands followed: Am(III) > Co(II) > Cs(I) > Sr(II). The presence of chelating ligands generally had little effect on sorption of 85Sr and 137Cs with Kd values 110 and 690 mL g−1, respectively. But at 0.02 M of ethylenediaminetetraacetic or hydroxyethyliminodiacetic, the Kd decreased to 5 or 63 mL g−1, respectively, where thermochemical modeling indicated almost all 85Sr is complexed with these ligands. The Kd values for 241Am and 60Co generally decreased with increasing chelating agent concentrations. In notable cases, the Kd values for Am increased at specific concentrations of 10−3 M for IDA, MIDA and 10−4 M for EDDA. This is proposed to be due to formation of a ternary surface complex.