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Clays and Clay Minerals

, Volume 33, Issue 2, pp 145–151 | Cite as

Phillipsite in Cs Decontamination and Immobilization

  • Sridhar Komarneni
Article

Abstract

The Cs selectivity of several natural zeolitic tuffs and synthetic zeolites was measured. Phillipsite-rich tuffs from California and Nevada exchanged 13.5 and 23.7%, respectively, of the Cs present in simulated alkaline defense waste containing 0.00025 M CsCl in 5.5 M NaCl-NaOH solution from the Savannah River Plant, Aiken, South Carolina; whereas mordenite-rich tuffs from Arizona and Nevada exchanged less than 12.7%. The immobilization or fixation of Cs in phillipsite unlike other zeolites can be achieved by heating the zeolite at 600°C for 4 hr in air and collapsing the silicate (aluminate) tetrahedral rings around the Cs ions to produce a Cs-feldspar-type phase. Treatment of the Cs-exchanged phillipsite-rich tuff at 800° to 1000°C resulted in pollucite, CsAlSi2O6, which also “locks in” the Cs ions in its structure. The fixation of Cs exchanged in phillipsite can also be achieved by the formation of pollucite upon hydrothermal treatment at 300°C and 30 MPa pressure within 12 hr. These results suggest that phillipsite-rich tuffs are good candidates for Cs immobilization by heat treatment at low temperatures after they have been used as sorbents in waste decontamination.

Key Words

Cation exchange Cesium Cs-feldspar Nuclear waste disposal Phillipsite Pollucite Thermal treatment Zeolite 

Резюме

Измерялась Сѕ селективность нескольких природных цеолитовых туфов и синтетических туфов. Обогащенные филлипситом туфы из Калифорнии и Невады обменивали соответственно 13,5 и 23,7% Се, присутствующега в 5,5 М №С1-МаОН растворе, содержащем количество 0,00025 М СвС1, имитирующем щелочные отходы фабрики Савана Ривер в Аикен, Южная Каролина. В то же самое время обогащенные морденитом туфы из Аризоны и Невады обменивали менее 12.7%. Неподвижность или фиксация Сз в филлипсите в противоположность к другим цеолитом достигается путем обогрева цеолита при 600°С в течение 4 часов в воздухе и разрушения силикатных (алюминатных) тетраэдрических колец вокруг ионов Сз для образования фазы типа Св-полевой шпат. Обработка С8-обменного обогащенного филлипситом туфа при температуре от 800° до 1000°С приводила к образованию поллуцита, С$А1$1206, который также “закупоривал” ионы Ск в своей структуре. Фиксация обменного Св в филлипсите могла также быть достигнута путем образования поллуцита в результате гидротермической обработки при температуре 300°С и давлении ЗОМПа в течение 12 часов. Эти результаты указывают на то, что обогащенные филлипситом туфы являются хорошим материалом для “нейтрализации” Св путем термической обработки при низких температурах после того, как они использовались в качестве сорбентов при очищении отходов. [Е.G.]

Resümee

Es wurde die Cs-Selektivität von verschiedenen natürlichen Zeolith-Tuffen und synthetischen Zeolithen gemessen. Phillipsit-reiche Tuffe von Kalifornien und Nevada tauschten 13,5 bzw. 23,7% des in simuliertem alkalischem Abfall vorhandenen Cs aus, der 0,00025 m CsCl in einer 5,5 m NaCl-NaOH-Lösung von der Savannah River Plant, Aiken, South Carolina, enthielt. Mordenit-reiche Tuffe von Arizona und Nevada tauschen dagegen weniger als 12,7% aus. Die Immobilisierung oder Fixierung von Cs in Phillipsit kann anders als bei anderen Zeolithen dutch Erhitzen des Zeolithes auf 600°C in Luft für 4 Stunden erreicht werden, wodurch die Silikat- (Aluminat-) Tetraederringe um das Cs-Ion kollabieren und eine feldspatartige Cs-Phase entsteht. Eine Behandlung der Cs-ausgetauschten Phillipsit-reichen Tuffe bei 800°−100°C führt zur Bildung von Pollucit CsAlSi2O6, der ebenfalls die Cs-Ionen in seiner Struktur “einsperrt.” Die fixierung von durch Phillipsit ausgetauschtem Cs kann auch durch die Bildung von Pollucit aufgrund hydrothermaler Behandlung bei 300°C und 30 MPa Druck über 12 Stunden erreicht werden. Diese Ergebnisse deuten darauf hin, daß Phillipsit-reiche Tuffe gute Anwärter für die Cs-Immobilisierung dutch Behandlung bei niedrigen Temperaturen sind, nachdem sie als Sorbenten bei der Abfalldekontamination verwendet wurden. [U.W.]

Résumé

On a mesuré la sélectivité Cs de plusieurs tufts zéolitiques naturels et de zéolites synthétiques. Des tuffs riches en phillipsite de Californie et du Nevada ont échangé 13,5 et 23,7% respectivement du Cs présent dans un déchet de dàfense alkalin simulé contenant 0,00025 M CsCl dans une solution 5,5 M NaCl-NaOH provenant du Savannah River Plant, Aiken, Caroline du Sud; tandis que des tuffs riches en mordénite d’Arizona et du Nevada ont echangé moins que 12,7%. L’immobilisation ou la fixation de Cs dans la phillipsite, dissimilairement aux autres zéolites, peuvent être atteintes par échauffement de la zéolite à 600°C pendant 4 heures à l’air et en fermant les anneaux silicates (aluminate) tetraédriques autour des ions Cs pour produire une phase du type Cs-feldspar. Le traitement du tuff riche en phillipsite échangé au Cs de 800° à 1000°C a resulté en de la pollucite, CsAlSi2O6, qui enferme aussi les ions Cs dans sa structure. La fixation de Cs échangé dans la phillipsite peut aussi être atteinte par la formation de pollucite lors du traitement hydrothermique à 300°C et 30 MPa de pression endéans 12 heures. Ces résultats suggèrent que les tuffs riches en phillipsite sont de bons candidats pour l’immobilisation de Cs par traitement à la chaleur à de basses températures après qu’ils aient été employés comme solvants dans la décontamination de déchets. [D.J.]

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Copyright information

© The Clay Minerals Society 1985

Authors and Affiliations

  • Sridhar Komarneni
    • 1
  1. 1.Materials Research Laboratory and Department of AgronomyThe Pennsylvania State UniversityUniversity ParkUSA

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