Samson et al.(2005)による〔『Transient and quasi-steady-state dissolution of biotite at 22-25℃ in high pH, sodium, nitrate, and aluminate solutions』(399p)から〕

『高いpH・ナトリウム・硝酸塩・アルミン酸塩溶液における22-25℃での黒雲母の一時的および準定常状態の溶解』


Abstract
 Biotite dissolution under conditions of high pH and high aluminum, sodium, and nitrate concentrations analogous to those found in tank wastes at the Hanford Site was investigated using continuously stirred flow-through reactions at 22 to 25℃. Experiments were designed to simulate tank leaks into the Hanford vadose zone where Fe(II) from biotite is the dominant reducing agent available to immobilize certain contaminants. Both non-steady-state and steady-state dissolution kinetics were quantified; interest in non-steady-state kinetics derives from the inherently transitory nature of tank leaks. Biotite was conditioned in pH 8 solutions to simulate the alkaline environment of the Hanford sediment, and then reacted in pH 10-14 solutions, some including 0.055 M Al(NO3)3 and/or 2 M or 6 M NaNO3. Initial dissolution transients (intervals of rapid release rates that decay to slower steady-state rates) showed fast preferential release of K followed by near-stoichiometric release of Si, Al, and Mg, and slower release of Fe. Each increase in pH resulted in a second transient with the greatest amounts of Si, Al, and K released at pH 14, followed by pHs 13, 12, 11, and 10. Fe release also was highest at pH 14, but unchanging at pHs 10-13 within experimental error. Transient releases at high pH are attributed to dissolution of amphoteric secondary phases such as ferrihydrite that are inferred from saturation calculations and solid analyses to form during the conditioning interval. Transient release of Si was inhibited by the presence of 0.055 M Al(NO3)3; the effects of Al(NO3)3 and NaNO3 on the release rates of Al, Fe, Mg, and K were variable and generally outweighed by the effect of pH. Quasi-steady-state release rates were slowest at pH 11-12 (10-12.2 mol biotite m-1 s-1 for Si) and increased i either direction in pH away from this minimum (to 10-11.5 at pHs 8 and 14 for Si). Fe release rates at high pH were sufficient to account for observed Cr(VI) reduction at Hanford. The net release rates of the major framework cations, from which the biotite dissolution rate is inferred, may reflect the precipitation of secondary phases or the alteration of biotite to vermiculite. The most extensive solid-phase alterations were observed in Na-enriched solutions.』

1. Introduction
2. Experimental
 2.1. Pretreatment and characterization of solid
 2.2. Experimental procedure
 2.3. Calculation of release rates
 2.4. Analyses
3. Results
 3.1. Elemental release
 3.2. Solids characterization
4. Discussion
 4.1. Solid phase alteration
 4.2. Dissolution transients following changes in pH
  4.2.1. Non-stoichiometry and sources of transient release
  4.2.2. Magnitude of transient releases
 4.3. Steady-state dissolution rates
 4.4. Implications for the Hanford Site and weathering
5. Conclusions
Acknowledgments
References
Appendix



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