PHILLIPSITE IN Cs DECONTAMINATION AND IMMOBILIZATION

Abstract--The Cs selectivity of several natural zeolitic tufts and synthetic zeolites was measured. Phil-lipsite-rich tufts from California and Nevada exchanged 13.5 and 23.7%, respectively, ofthe Cs present in simulated alkaline defense waste containing 0.00025 M CsCl in 5.5 M NaC1-NaOH solution from the Savannah River Plant, Aiken, South Carolina; whereas mordenite-rich tufts from Arizona and Nevada exchanged less than 12.7%. The immobilization r fixation of Cs in phillipsite unlike other zeolites can be achieved by heating the zeolite at 600 ~ for 4 hr in air and collapsing the silicate (aluminate) tetrahedral tings around the Cs ions to produce aCs-feldspar-type hase. Treatment ofthe Cs-exchanged phillipsite-rich tuft at 800 ~ to 1000 ~ resulted in pollucite, CsA1Si206, which also "locks in " the Cs ions in its structure. The fixation of Cs exchanged inphillipsite can also be achieved by the formation of pollucite upon hydrothermal treatment a 300 ~ and 30 MPa pressure within 12 hr. These results uggest that phillipsite-rich tufts are good candidates for Cs immobilization byheat treatment a low temperatures after they have been used as sorbents in waste decontamination