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Studies of the Reactivity of the Ferrihydrite Surface by Iron Isotopic Exchange and Mössbauer Spectroscopy

Published online by Cambridge University Press:  28 February 2024

Brigid A. Rea
Affiliation:
Water Resources Division, U. S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303
James A. Davis
Affiliation:
Water Resources Division, U. S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025
Glenn A. Waychunas
Affiliation:
Center for Materials Research, Stanford University, Stanford, California 94305
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Abstract

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Two-line ferrihydrite is an important adsorbent of many toxics in natural and anthropogenic systems; however, the specific structural sites responsible for the high adsorption capacity are not well understood. A combination of chemical and spectroscopic techniques have been employed in this study to gain further insight into the structural nature of sites at the ferrihydrite surface. The kinetics of iron isotopic exchange demonstrated that there are at least two types of iron sites in ferrihydrite. One population of sites, referred to as labile sites, approached iron isotopic equilibrium within 24 hr in 59Fe-NTA solutions, while the second population of sites, referred to as non-labile, exhibited a much slower rate of isotopic exchange. Adsorbed arsenate reduced the degree of exchange by labile sites, indicating that the anion blocked or greatly inhibited the rate of exchange of these sites. Mössbauer spectra were collected from a variety of samples including 56Fe-ferrihydrite samples with 57Fe in labile sites, samples containing 57Fe throughout the structure, and samples with 57Fe in non-labile sites. The spectra showed characteristic broad doublets signifying poor structural order. Refined fits of the spectra indicated that labile sites have larger quadrupole splitting, hence more local distortion, than non-labile sites. In all cases, the spectra demonstrated some degree of asymmetry, indicating a distribution of Fe environments in ferrihydrite. Overall spectral findings, combined with recent EXAFS results (Waychunas et al., 1993), indicate that labile sites likely are more reactive (with respect to iron isotopic exchange) because they have fewer neighboring Fe octahedra and are therefore bound less strongly to the ferrihydrite structure. The labile population of sites probably is composed of end sites of the dioctahedral chain structure of 2-line ferrihydrite, which is a subset of the entire population of surface sites. Mössbauer spectra of samples containing adsorbed arsenate indicated that the anion may slightly decrease the distortion of labile sites and stabilized the structure as a whole by bidentate bonding.

Type
Research Article
Copyright
Copyright © 1994, Clay Minerals Society

References

Atkinson, R. J., Posner, A. M., and Quirk, J. P., (1968) Crystal nucleation in Fe(III) solutions and hydroxide gels: J. Inorganic Nuclear Chem. 30, 23712381.CrossRefGoogle Scholar
Bancroft, G. M., (1973) Mössbauer Spectroscopy: An Introduction for Inorganic Chemists and Geochemists: Halsted Press, New York, 252 pp.Google Scholar
Cardile, C. M., (1988) Tetrahedral Fe3+ in ferrihydrite: 57Fe Mössbauer spectroscopic evidence: Clays & Clay Minerals 36, 537539.CrossRefGoogle Scholar
Carlson, L., and Schwertmann, U., (1981) Natural ferrihydrites in surface deposits from Finland and their association with silica: Geochim. Cosmochim. Acta 45, 421429.CrossRefGoogle Scholar
Childs, C. W., and Johnston, J. H., (1980) Mössbauer spectra of protoferrihydrite at 77 K and 295 K, and a reappraisal of the possible presence of akaganeite in New Zealand soils: Aust. J. Soil Res. 18, 245250.CrossRefGoogle Scholar
Combes, J. M., Manceau, A., Calas, G., and Bottero, J. Y., (1989) Formation of ferric oxides from aqueous solutions: A polyhedral approach by X-ray absorption spectroscopy: I. Hydrolysis and formation of ferric gels: Geochim. Cosmochim. Acta 53, 583594.CrossRefGoogle Scholar
Crank, J., (1975) The Mathematics of Diffusion, Oxford University Press, Ely House, London, 347 pp.Google Scholar
Eggleton, R. A., and Fitzpatrick, R. W., (1988) New data and a revised structural model for ferrihydrite: Clays & Clay Minerals 36, 111124.CrossRefGoogle Scholar
Fitzpatrick, R. W., (1988) Iron compounds as indicators of pedogenic processes: Examples from the southern hemisphere: in Iron in Soils and Clay Minerals. NATO ASI Series, Series C: Mathematical and Physical Sciences, Stucki, J. W., Goodman, B. A., and Schwertmann, U., eds., D. Reidel Publishing Company, Boston, 351396.Google Scholar
Fuller, C., Davis, J. A., and Waychunas, G. A., (1993) Surface chemistry of ferrihydrite: 2. Kinetics of arsenate adsorption and coprecipitation: Geochim. Cosmochim. Acta 57, 22712282.CrossRefGoogle Scholar
Fuller, C., and Davis, J. A., (1989) Diel cycles of pH and trace elements in surface waters: Coupling of sorption and photosynthetic processes: Nature 340, 5254.CrossRefGoogle Scholar
Hawthorne, F. C., (1988) Mössbauer spectroscopy: Spectroscopic Methods in Mineralogy and Geology, Reviews in Mineralogy, Vol. 18, Hawthorne, F. C., ed., Mineralogical Society of America, Washington, D.C., 255340.CrossRefGoogle Scholar
Hawthorne, F. C., and Waychunas, G. A., (1988) Spectrum fitting methods: Spectroscopic Methods in Mineralogy and Geology, Reviews in Mineralogy, Vol. 18, Hawthorne, F. C., ed., Mineralogical Society of America, Washington, D.C., 6398.CrossRefGoogle Scholar
Hingston, F. J., (1981) A review of anion adsorption: Adsorption of Inorganics at Solid-Liquid Interfaces, Anderson, M. A., and Rubin, A. J., eds., Ann Arbor Science, Ann Arbor, Michigan, 5190.Google Scholar
Johnston, J. H., and Lewis, D. G., (1983) A detailed study of the transformation of ferrihydrite to hematite in an aqueous medium at 92°C: Geochim. Cosmochim. Acta 47, 18231831.CrossRefGoogle Scholar
Langmuir, D., and Whittemore, D. O., (1971) Variations in the stability of precipitated ferric oxyhydroxides: Non-Equilibrium Systems in Natural Water Chemistry, Advances in Chemistry Series 106, Gould, R. F., ed., American Chemical Society, Washington, D.C., 209234.Google Scholar
Leckie, J. O., Merrill, D. T., and Chow, W., (1985) Trace element removal from power plant wastestreams by adsorption/coprecipitation with amorphous iron oxyhydroxide: Separation of heavy metals and other trace contaminants: AIChE Symposium Series #243, Vol. 81, Peters, P. W., and Kim, B. M., eds., 2842.Google Scholar
Manceau, A., Combes, J.-M., and Calas, G., (1990) New data and a revised structural model for ferrihydrite: Comment: Clays & Clay Minerals 38, 331334.CrossRefGoogle Scholar
Martell, A. E., and Smith, R. M., (1974) Critical Stability Constants, I: Amino Acids, Plenum Press, New York, 469 pp.Google Scholar
Murad, E., (1988) The Mössbauer spectrum of “well”-crystallized ferrihydrite: J. of Magnetism and Magnetic Mater. 74, 153157.CrossRefGoogle Scholar
Murad, E., Bowen, L. H., Long, G. J., and Quin, T. G., (1988) The influence of crystallinity on magnetic ordering in natural ferrihydrites: Clay Miner. 23, 161173.CrossRefGoogle Scholar
Murad, E., and Johnston, J. H., (1987) Iron oxides and oxyhydroxides: in Mössbauer Spectroscopy Applied to Inorganic Chemistry, Vol. 2, Long, G. J., ed., Plenum Press, New York, 542547.Google Scholar
Murad, E., and Schwertmann, U., (1980) The Mössbauer spectrum of ferrihydrite and its relation to those of other iron oxides: Amer. Mineral. 65, 10441049.Google Scholar
Papelis, C., Hayes, K. F., and Leckie, J. O., (1988) HYDRAQL: A program for the computation of aqueous batch systems including surface-complexation modeling of ion adsorption at the oxide/solution interface: Tech. Rept. 306, Department of Civil Engineering, Stanford University, 130 pp.Google Scholar
Parfitt, R. L., Atkinson, R. J., and Smart, R. St. C., (1975) The mechanism of phosphate fixation by iron oxides: SSSA Proc. 39, 837841.Google Scholar
Ruby, S. L., (1973) Why MISFIT when you already have χ2?: Mössbauer Effect Methodology, Vol. 8, Gruverman, I. J., ed., 263276.CrossRefGoogle Scholar
Schultz, M. F., Benjamin, M. M., and Ferguson, J. F., (1987) Adsorption and desorption of metals on ferrihydrite: Reversibility of the reaction and sorption properties of the regenerated solid: Environ. Sci. Technol. 21, p. 863.CrossRefGoogle Scholar
Schwertmann, U., and Fischer, W. R., (1973) Natural “amorphous” ferric hydroxide: Geoderma 10, 237247.CrossRefGoogle Scholar
Schwertmann, U., and Taylor, R. M., (1977) Iron Oxides: in Minerals in Soil Environments, Dixon, J. B., and Weed, S. B., eds., Soil Science Society of America, Madison, Wisconsin, 145180.Google Scholar
Towe, K. M., and Bradley, W. F., (1967) Mineralogical constitution of colloidal “hydrous ferric oxides”: J. of Coll. and Inter. Sci. 24, 384392.CrossRefGoogle Scholar
Van der Kraan, A. M., (1973) Mössbauer effect studies of surface ions of ultrafine α-Fe2O3 particles: Phys. Stat. Sol. A 18, 215226.CrossRefGoogle Scholar
Waychunas, G. A., Rea, B. A., Davis, J. A., and Fuller, C. C., (1993) Surface chemistry of ferrihydrite: I. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate: Geochim. Cosmochim. Acta 57, 22512269.CrossRefGoogle Scholar
Waychunas, G. A., Brown, G. E., Ponader, C. W., and Jackson, W. E., (1988) Evidence from X-ray absorption for network-forming Fe2+ in molten alkali silicates: Nature 332, 251253.CrossRefGoogle Scholar
Waychunas, G. A., (1979) Mössbauer, X-ray, optical and chemical study of cation arrangements and defect association in Fm3m solid solutions in the system periclase-wustite-lithium ferrite: Ph.D. dissertation, University of California, Los Angeles, 456 pp.Google Scholar