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 min6
erals. Cancrinite, sodalite, LTA zeolite, and allophane have been identified as the new mineral phases
7 in laboratory simulations. Cesium, the major radionulide 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
Revised: August 4, 2006 |
Published: November 28, 2005
Citation
Mon J., Y. Deng, M. Flury, and J.B. Harsh. 2005.Cesium Incorporation and Diffusion in Cancrinite, Soalite, Zeolite, and Allophane.Microporous and Mesoporous Materials 86, no. 1-3:277-286.