Sorption of selected radionuclides to clay in the presence of humic acid

Within the framework of the FUNMIG programme, Loughborough University is performing work to increase understanding of the sorption behaviour of selected radionuclides with various minerals in the absence and presence of competing complexing ligands, such as humic acid (HA). The determination of the distribution ratios (Rd) of binary (metal- and humic-solid), and ternary (metal-solid-humic) systems using a batch adsorption technique is reported. Four radionuclides have been used; 137Cs, 63Ni, 152Eu and 109Cd, to facilitate modelling. Montmorillonite, kaolinite and α-goethite have been used as solids. Humic acid concentrations (2 - 300 ppm (w/v)) were determined using UV spectrophotometry. Radiometric analysis was used for radionuclide measurement. Construction of sorption isotherms using the Langmuir and Freundlich Equations has allowed characterisation of sorption types, and has provided maximum sorption capacities of the solid surfaces for each of the metals in the binary systems. Distribution relationships between metal and humic acid for each ternary system have been established and correlated.