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Smectite Dissolution Kinetics in High-Alkaline Conditions

Published online by Cambridge University Press:  01 February 2011

Hiroshi Ohmoto ,
Kathryn R. Spangler ,
Yumiko Watanabe  and
Gento Kamei
Hiroshi Ohmoto
Affiliation:
Astrobiology Research Center and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, U.S.A.
Kathryn R. Spangler
Affiliation:
Astrobiology Research Center and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, U.S.A.
Yumiko Watanabe
Affiliation:
Astrobiology Research Center and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, U.S.A.
Gento Kamei
Affiliation:
Japan Nuclear Cycle Development Institute, Tokai, Ibaraki, 319–1194, Japan
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Abstract

To determine the initial rates and effects of silica in solution on the dissolution kinetics of smectite, short- and long-term batch experiments (0.5 hour to 30 days) were completed at three temperatures (T = 25, 50, and 75°C) using stock solutions pH adjusted by NaOH (pH = 12, 13, and 13.5) with varying initial silica concentrations (0, 30, 60, and 100 ppm). The following important characteristics were observed at pH = 12: (1) The concentrations of Al, Si, Mg, Fe, and Ti in solutions increase rapidly during the first ∼2 hours and reach steady state (equilibrium) within ∼5 days. (2) The concentration ratios of Al, Si, Fe, Mg, and Ti in solutions during the early (<2 hours) reaction phase differ significantly from those of smectite, indicating initial dissolution proceeds non-stoichiometrically; Al dissolves much faster than Si, Mg, Fe, and Ti. (3) Further dissolution of smectite proceeds nearly stoichiometrically, including Fe and Ti. (4) The high solubility of Ti in highly alkaline solutions may be due to the formation of aqueous complexes, such as TiO(OH)3− and TiO2(OH)22−, similar to aqueous silica species. (5) The initial rate of smectite dissolution increases with increasing pH, T, and initial silica content of solution. (6) The silica in solution acts as a promoter and a catalyst, rather than an inhibitor, of smectite dissolution in high-alkaline solutions. This role is easily recognizable when the solubility of smectite and amorphous silica are very high, i.e., at pH >∼9.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 807: Symposium Scientific Basis for Nuclear Waste Management XXVII , 2003 , 723
Copyright
Copyright © Materials Research Society 2004

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References

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