Fixation of Caesium, Strontium and Thorium Ions in Commercial Synthetic Zeolite Matrices by Thermal Treatment.

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Abstract
Synthetic zeolites AR-1 (a mordenite), 4A and 13X, all in their Na-forms, have been found to be suitable for the uptake of Cs, Sr and Th ions, respectively. Samples of Cs-loaded AR-1, Sr-loaded 4A and Th-loaded 13X were prepared and heated in a furnace to various temperatures (up to 1,200°C), for fixing the exchanged ions in the host zeolite matrix. X-ray diffraction patterns of the products indicated that the crystallinity of Cs-AR-1 and Sr-4A was intact till 500°C, partially lost between 500°C and 1,000°C, and improved again at 1,200°C. For Th-13X, the crystallinity was gradually lost after 500°C. Thermogravimetric-differential scanning calorimetrie (TG-DSC) studies indicated the occurrence of phase transformations at around 890–1,020°C, for Na-4A, Sr-4A, Na-13X and Th-13X. For Na-AR-1 and Cs-AR-1, no clear inference of change of phase could be drawn. Above 1,300°C, all the zeolites converted to a glassy mass. Desorption studies in vigorously stirred liquid media, viz. demineralized (DM) water, 10mMNaNO3, 1M NaNO3 and 2.8 M HNO3, and Static leach tests in DM water and tap water media, with fresh replacement of the water after preset time durations, were carried out with the zeolite samples heated to 1,000°C. The leach rates at equilibrium were found to be low, of the order of 10−7 g/cm2-d for Cs and Sr and still smaller for Th.

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