Cesium Incorporation and Diffusion in Cancrinite, Soalite, Zeolite, and Allophane

Journal Article · Mon Nov 28 04:00:00 EST 2005 · Microporous and Mesoporous Materials

DOI:https://doi.org/10.1016/j.micromeso.2005.07.030· OSTI ID:889080

Mon, Jarai; Deng, Youjun; Flury, Markus; Harsh, James B

At the US Department of Energy?s Hanford site, high level nuclear waste has leaked from under4 ground storage tanks. The waste consists of hyperalkaline solutions, which upon contact with the 5 sediments, caused dissolution of silicate minerals and precipitation of secondary aluminosilicate minerals. Cancrinite, sodalite, LTA zeolite, and allophane have been identified as the new mineral phases 7 in laboratory simulations. Cesium, the major radionuclide in the waste solutions, may be incorporated 8 into the structural framework of the precipitates. The objectives of this study were to determine the 9 resistance of incorporated Cs to ion exchange and the mobility and diffusion coefficient of Cs in the 10 minerals. The minerals were synthesized in solutions mimicking the tank waste and were washed with 11 deionized water. Two sets of experiments were conducted to test the resistance of Cs to ion exchange. 12 In the first set, Cs was exchanged three times at 80 C by 0.5 N Na, K, or Ca. The Cs remaining in 13 minerals was quantified after acid digestion. In the second set, we studied the Cs desorption kinetics 14 by using 0.1 M Na as ion exchanger. Cesium concentration in the solution phase was measured as a 15 function of time for 23 days. Cesium incorporated in sodalite and cancrinite was far more difficult to 16 replace than that in LTA zeolite and allophane. Most of the incorporated Cs (94?99%) in LTA zeolite 17 and allophane was readily exchangeable with Na or K; less than 20% of Cs in sodalite and <55% of 2 Cs in cancrinite could be exchanged. The fraction of desorbed Cs was also affected by the exchanging 19 ions; the ion with lowest dehydration energy (K) was the most effective in replacing Cs. The results 20 of the desorption kinetics experiments showed that Cs desorbed quickly from LTA zeolite and the Cs 21 diffusion coefficient was close to that in solution; i.e., about 10?9 m2/s. Solid-state NMR analysis 22 supported the high mobility of Cs in LTA zeolite. Cesium desorption from cancrinite, sodalite, and 23 allophane, however, was slow, suggesting that Cs was trapped in cages and channels of these minerals. 24 Effective diffusion coefficients for Cs in cancrinite and sodalite were near 10?14 m2/s.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 889080
• Journal Information: Microporous and Mesoporous Materials, Journal Name: Microporous and Mesoporous Materials Journal Issue: 1-3 Vol. 86
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
CESIUM
DEHYDRATION
DESORPTION
DIFFUSION
DIGESTION
DISSOLUTION
Environmental Molecular Sciences Laboratory
ION EXCHANGE
KINETICS
LIQUID WASTES
PRECIPITATION
RADIOACTIVE WASTES
RADIOISOTOPES
SEDIMENTS
SILICATE MINERALS
STORAGE
TANKS
WASTES
WATER
ZEOLITES