NEPTUNIUM UPTAKE ON BOOM CLAY - TIME-DEPENDENCE AND ASSOCIATION OF NPWITH FINE PARTICLES

Boom clay was contacted with solutions containing Np-237 in a glove-bo x under a N-2 atmosphere. The kinetics of Np sorption and the associat ion of Np with colloids (particles <1 mu m) were studied in experiment s at two Np concentrations. The solid and liquid phases were separated in the glove-box using filters with pore-sizes of 0.45 mu m, 0.1 mu m , 100000 NMWL and 10000 NMWL. Over 99.5% of the Np was adsorbed by the clay within 24 hours, with Np uptake continuing for at least two week s. The sorption kinetics appeared to be related to initial Np concentr ation. In some experiments, the amount of Np which passed through a 0. 45 mu m filter was more than a hundred times greater than the Np level in the filtrate of a 10000 NMWL filter. This suggested an association of Np with colloids or organic matter in these experiments. However, in other experiments with a greater amount of Np, filter pore-size had no effect on Np levels in the filtrates. The data suggest potential d ifficulties in calculating R(d) values for Np, since these values are a function of filter pore-size and contacting time.