Abstract
Ferrihydrite, prepared in the presence of 0 to 20 mole % Cd in the solution, was used to study the transformation of ferrihydrite into crystalline products. The result showed that the presence of Cd strongly retards the transformation of ferrihydrite into crystalline products, suppressing the formation of goethite and leading to a product which eventually consists entirely of hematite at pH 8 and at 70 °C. The fraction of hematite in the transformation products increased with increasing level of Cd in the system. When 9 mole % Cd was present, the transformation product consisted entirely of hematite. The chemical analysis and XRD data showed that Cd was incorporated into the lattice of iron oxides, Cd-hematite and Cd-goethite being formed. The mole % Cd which replaced iron in the iron oxides increased with increasing level of Cd in the system below 9 mole % Cd. Above this value, but below 20 mole % the mole % of Cd incorporated in the lattice of iron oxides was constant at about 2.9 mole %. The volume of the unit cell of Cd-goethite increased with increasing level of Cd in the system until the goethite production was entirely suppressed. The volume of the unit cell of Cd-hematite also increased with increasing level of Cd, below 9 mole % of Cd in the system. Above this value, it was constant. Scanning electron microscopic examination showed that the presence of Cd affected the morphology of hematite more than that of goethite. The goethite grew from ferrihydrite as acicular crystals independent of the amount of Cd in the system. The shape of hematite particles varied from irregular platelets with lower Cd level, to ellipsoids, with higher Cd level in the system, and it also suggested that Cd prevented the formation of goethite by hindering the dissolution of ferrihydrite rather than by interfering with nucleation and growth of goethite from solution. The rate of transformation was studied at pH 8, 50 °C and 70 °C. The transformations were first order reactions at both temperatures.
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References
Bertine, K. K. and Goldberg, E. D.: 1971,Science 173, 233.
Bradshaw, A. D. and Chadwick, M. J.: 1980,The Restoration of Land, Blackwell Scientific Publications, Oxford.
Canadian Council of Resource and Environment Ministers: 1987,Canadian Water Quality Guidelines, Prepared by the Task Force on Water Quality Guidelines. Ottawa: Environment Canada, Water Quality Branch.
Cornell, R. M.: 1988,Clay Minerals 23, 329.
Cornell, R. M. and Giovanoli, R.: 1985,Clays and Clay Minerals 33, 219.
Cornell, R. M. and Giovanoli, R.: 1987,Clays and Clay Minerals 35, 11.
Cornell, R. M. and Giovanoli, R.: 1988,Polyhedron 7, 385
Cornell, R. M. and Giovanoli, R.: 1989,Clays and Clay Minerals 37, 65.
Cornell, R. M., Giovanoli, R. and Schneider, W.: 1990,Clays and Clay Minerals 38, 21.
Duffus, J. H.: 1980,Environmental Toxicology, Resource and Environmental Sciences Series, Edward Arnold, London.
Fischer, W. R. and Schwertmann, U.: 1975,Clays and Clay Minerals 23, 33.
Gerth, J.: 1990,Geochim. et Cosmo. Acta 54, 363.
Giovanoli, R. and Cornell, R. M.: 1992,Z. Pflanzenernaehr. Bodenk. 155, 455.
Goldschmidt, V M.: 1937,J. Chem. Soc. 655.
Hiatt, V. and Huff, J. E.: 1975,Int. J. of Env. Studies 7, No. 4, 277.
Kruus, P., Demmer, M. and McCaw, K.: 1991, Chemicals in the Environment,Polyscience, Publications Inc., Quebec, Canada.
Leckie, J. O., Merrill, D. T. and Chow, W.: 1985, A. I. Ch. E. Symposium series 243,81, p. 28.
Nobbs, C. L. and Pierce, D. W.: 1976,Int. J. of Env. Stud. 8, p. 245.
Paige, C. R., Snodgrass, W. J., Nicholson, R. V. and Scharer, J. M.: 1994,Water Poll. Res. J. Canada,29, No. 4, 507.
Schwertmann, U., Fitzpatrick, R. W., Taylor, R. M. and Lewis, D. G.: 1979,Clays and Clay Minerals 27, 105.
Schwertmann, U. and Murad, E.: 1983,Clays and Clay Minerals 31, 277.
Sorum, C. H. and Lagowski, J. J.: 1983,Introduction to Semimicro Qualitative Analysis, Sixth edition, Prentice-Hall, Inc., Englewood Cliffs, N.J. 07632.
Vempati, R. K. and Loeppert, R. H.: 1989,Clays and Clay Minerals 37, 273.
Weast, R. C.et al: 1974,Handbook of Chemistry and Physics, C.R.C. Press, U.S.A., F198.
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Sun, T., Paige, C.R. & Snodgrass, W.J. The effect of cadmium on the transformation of ferrihydrite into crystalline products at pH 8. Water Air Soil Pollut 91, 307–325 (1996). https://doi.org/10.1007/BF00666266
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DOI: https://doi.org/10.1007/BF00666266