Two-site equilibrium model for ion exchange between multi-valent cations and zeolite-A in a molten salt

A model has been developed and tested for its ability to describe the ion exchange of fission product species between zeolite and a molten salt bath used for pyroprocessing of spent nuclear fuel. The model is based on a system at equilibrium and assumes species interacting with zeolite are chemically independent of each other. This assumption was tested via a set of salt-zeolite contact experiments. Zeolite 4A was batch contacted with Cs ternary salt (CsCl-LiCl-KCl), Nd ternary salt (NdCl3-LiCl-KCl) or Cs-Nd quaternary salt (CsCl-NdCl3-LiCl-KCl) until ion exchange steady state was reached. Results from ternary salt and zeolite chemical analyses were used to determine model parameters for all species present. These parameters, in turn, were applied to compute estimated compositions of zeolite contacted with quaternary salt. The estimated compositions compare favorably with results from chemical analyses of the zeolite-quaternary salt experiment samples. Based on the data collected, the model is modified for predictive capability for a range of salt compositions.