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A Novel Equation for Prediction of Intrinsic Sorption Constants of Metal Cations at Mineral-Water Interfaces

Published online by Cambridge University Press:  17 March 2011

Huifang Xu  and
Yifeng Wang
Huifang Xu
Affiliation:
Department of Earth and Planetary Sciences, The University of New Mexico, Albuquerque, New Mexico 87131, hfxu@unm.edu
Yifeng Wang
Affiliation:
Sandia National Laboratories, Albuquerque, New Mexico 87185, ywang@sandia.gov
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Abstract

The sorption of radionuclides onto mineral-water interfaces is an important mechanism of radionuclide retardation in subsurface environments. Although a large body of data on metal sorption has been accumulated, the interaction of radionuclides at the mineral-water interface is still not well quantified. In this paper, we establish a linear free energy relationship that can correlate intrinsic metal sorption constants to the known thermodynamic properties of metal cations and mineral phases. This relationship can be used to predict the intrinsic sorption constants of metal cations adsorption on various mineral-water interfaces. Based on a surface complexation model, an adsorption constant of a cation Mn+ onto a mineral surface can be represented by the sum of “intrinsic” and coulombic terms, that is logKads, Mn+ = logKint, Mn+ - (nF/2.303RT)0. To construct our linear free energy relationship, we further decompose an intrinsic sorption constant into the solvation contribution, which characterizes the work to be done to move a cation from one dielectric medium (solution) to another (interface), and the chemical contribution, which characterizes the chemical bonding abilities of cations to mineral surface sites. The overall intrinsic sorption constant can be calculated by the equation of:

2.303RTlogKint, Mn+ = -ΩMn+ (1/εk) - a* δG0n, Mn+ - b* - β*rMn+ + δG0f, Mn+, or

2.303 RT logKint, Mn+ = -ΩMn+ (1/εk) + a* δG0s, Mn+ + (1 - a*)δG0f, Mn+ - b* - β* rMn+,

where, ΩMn+ is interfacial Born solvation coefficient of cation M, εk is the dielectric constant of a mineral; δG0n, Mn+, δG0s, Mn+ and δG0f, Mn+ are the non-solvation energy, solvation energy and the Gibbs free energy formation of a cation, respectively; rMn+ is the ionic radius of a cation; and a*, β*, and b* are constants, which can be determined by fitting the equation to the existing experimental data. We have applied the equation to the sorption of divalent cations on oxide, hydroxide, and silicate minerals. In particular, based on additivity of molecular polarizabilities, we have used the equation to calculate the intrinsic sorption constants of divalent metals and radionuclides on interstratified clay minerals that are commonly found in the nature or are proposed as backfills for nuclear waste geologic repositories. The discrepancies between calculated and measured values are generally within 0.8 log unit.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 824: Symposium CC – Scientific Basis for Nuclear Waste Management XXVIII , 2004 , CC7.10
Copyright
Copyright © Materials Research Society 2004

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References

References Cited

1. Dzombak, D. A. and Morel, F. M. M., Surface Complexation Modeling: Hydrous Ferric Oxide. John Wiley, New York (1990).Google Scholar
2. Davis, J. A. and Kent, D. B., In Hochella, Michael F. Jr, and White, Art F. eds., Reviews in Mineralogy, 23, 177–260 (1990).Google Scholar
3. Davis, J. A. and Leckie, J. O., J. Colloid and Interface Sci., 67, 90–107 (1978).Google Scholar
4. Sverjensky, D. A., Nature, 364, 776–780 (1993).Google Scholar
5. Xu, H. and Wang, Y., In Pillary, K. K. S. and Kim, K.C. Eds. Plutonium Futures – The Science. (AIP Conference Proceedings # 532), Page 402. American Institute of Physics, Melville, New York (2000).Google Scholar
6. James, R. O. and Healy, T. W., J. Colloid and Interface Sci., 10, 65–81 (1972).Google Scholar
7. Sverjensky, D. A. and Molling, P. A., Nature, 356, 231–234 (1992).Google Scholar
8. Shock, E. L. and Helgeson, H. C., Geochim. Cosmochim. Acta, 52, 2009–2036 (1988).Google Scholar
9. Shannon, R. D. and Prewitt, C. T., Acta Crystallogr., B25, 925–946 (1969).Google Scholar
10. Schindler, P. W., and Stumm, W., In Stumm, W. ed. Aquatic Surface Chemistry. John Wiley, New York, p. 83–110 (1987).Google Scholar
11. Wang, Y. and Xu, H., Geochim. Cosmochim. Acta, 65, 1529–1543 (2001).Google Scholar
12. Balistrieri, L. S. and Murray, J. W., Amer. J. Sci., 281, 788–806 (1981).Google Scholar
13. Olhoeft, G. R., In Touloukian, Y. S. ed. Physical Properties of Rocks and Minerals. McGraw-Hill, New York, pp 257–329 (1981).Google Scholar
14. Shannon, R. D., Dickinson, J E. and Rossman, G. R., Phys. Chem. Minerals, 19, 148–156 (1992).Google Scholar
15. Ahn, J. H., Xu, H. and Buseck, P. R., Clays and Clay Minerals, 45, 295–297 (1997).Google Scholar
16. Banfield, J. F., Bailey, S. W. and Barker, W. W., Contrib. Mineral. Petrol., 117, 137–150 (1994).Google Scholar
17. Bish, D. L. and Aronson, J. L., Clays and Clay Minerals, 41, 148–161 (1993).Google Scholar
18. Veblen, D. R., Guthrie, G. D. Jr, Livi, K. J. T. and Reynolds, R. C., Clay & Clay Minerals, 38, 1–13 (1990).Google Scholar
19. Veblen, D. R. and Ferry, J. M., Amer. Mineral., 68, 1160–1168 (1983).Google Scholar
20. Xu, H., Zhang, Y. and Veblen, D. R., American. Mineral., 81, 1396–1404 (1996).Google Scholar
21. Xu, H. and Veblen, D. R., Contrib. Mineral. Petrol., 124, 291–301 (1996).Google Scholar
22. Shibata, M., Shiotsuki, M. and Umeki, H., Overview of R&D on backfill materials for the HLW/TRU disposal concepts in Japan. In: Bennett, D. G., Papenguth, H. W., Chu, M. S., Galson, D. A., Duerden, S. L. and Matthews, M. L. (eds.) International Workshop on the Uses of Backfill in Nuclear Waste Repositories, Carlsbad, New Mexico, US, May, 1998.Google Scholar
23. Roberts, R., Dielectric constants and polarization of ions in simple crystals and barium titanates. Phys. Rev., 76, 1215–1220 (1949).Google Scholar
24. Roberts, R., Polarizabilities of ions in perovskite-type crystals. Phys. Rev., 81, 865–868 (1951).Google Scholar
25. Lasaga, A. C. and Cygan, R. T., Amer. Mineral., 67, 328–334 (1982).Google Scholar
26. Schlegel, M. L., Manceau, A., Chateigner, D. and Charlet, L., J. Colloid and Interface Sci., 215, 140–158 (1999).Google Scholar