The removal of thorium from aqueous solutions using zeolites

The ability of zeolites to remove thorium-232 from naturally radioactive thorium nitrate solutions was studied by ion exchange, adsorption and surface phenomena. The best zeolites were a clinoptilolite from Mudhills, California, USA and a mordenite rich tuff from Eastgate, Nevada, USA. As the concentration of thorium in solution was increased the mechanism of thorium removal switches from that of partial ion-exchange to a surface precipitation. This was confirmed by electron probe microanalysis (EPMA) in conjunction with XRD and Energy Dispersive X-ray analysis (EDX). A Langmuir-type of adsorption occured with the thorium-232 daughter isotopes at the same time as partial exchange/precipitation of the thorium parent which is in regular equilibrium with its natural daughters. Some experiments with 234Th were carried out to confirm this hypothesis as well as column experiments to confirm the usefulness of the Th removal. (author) 15 refs.; 19 figs.; 2 tabs