AFFINITY OF FINELY DISPERSED MONTMORILLONITE COLLOIDAL PARTICLES FOR AMERICIUM AND LANTHANIDES

We studied (i) the affinity of the finely dispersed montmorillonite co lloidal particles (< 0.45 mu m), which originated from Japan, for trac e amounts of Am3+ and lanthanide ions (Ln(3+): Nd3+, Eu3+, Gd3+), and (ii) the differences between the sorption behavior of Am3+ and Ln(3+) onto the colloidal particles and that onto the massive montmorillonite solids. The ion-exchange stoichiometry of sorption reaction of Am3+ a nd Ln(3+) onto the colloidal particles was 1:3 in the low Na+ concentr ation region. In the high Na+ concentration region, the sorption ratio was constant, and specific for Am3+ and each Ln(3+). The influence of Na+ and Ca2+ on the sorption of Ln(3+) onto the finely dispersed Na- and Ca-montmorillonite colloidal particles at different NaCl and CaCl2 concentrations was examined. It was found that the coverage of the so rption sites increased with the Ln(3+) concentration. The affinity for Ln(3+) was discussed by selectivity and a Langmuir-type isotherm.