Clays and Clay Minerals

, Volume 43, Issue 2, pp 237–245 | Cite as

The Problem of Expressing the Specific Surface Areas of Clay Fractions

  • E. Padmanabhan
  • A. R. Mermut


Estimations of the external specific surface areas (S.S.A.) by the N2-BET method of clay separates that were further fractionated by the high gradient magnetic separation technique revealed that the magnetic fractions had consistently lower S.S.A. compared to non-magnetic fractions. This phenomenon has been attributed, in the past, to the intimate association of Fe-oxides with silicate clays. It is the contention of this study that this reasoning is insufficient due to the following reasons. X-ray diffractograms (XRD) confirmed that heavy minerals were abundant in the magnetic fractions of these clays. Total chemical analyses and energy dispersive X-ray analyses showed that these heavy minerals contained Fe and Ti, which were not completely extracted by the dithionite-citrate bicarbonate (DCB) treatments. Crystallinity and quantity of these oxides in the different fractions did not show any relationships with the S.S.A. Lower S.S.A. were found in the magnetic fractions of both coarse and fine clays in the untreated as well as DCB-treated samples. The average particle density of the magnetic fractions was found to be higher than the non-magnetic fractions, resulting in an underestimation of the S.S.A. This underestimation was further proven when clay-sized illmenite (density = 4.79 Mg m−3) was found to have lower S.S.A. than quartz (density = 2.65 Mg m−3) and well-crystallized Georgia kaolinite (density = 2.61 Mg m−3), even though the illmenite particles were smaller in size compared to the kaolinite particles and similar in size compared to the quartz particles. It is, therefore, proposed that the specific surface areas should be expressed either on a volumetric basis or corrected for differences in density to avoid underestimations when heavy minerals are present in the samples.

Key Words

Density Fe and Ti oxides Magnetic and non-magnetic fractions Specific surface area 


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  1. Barberis, E., F. Ajmore Marsan, V. Boero, and E. Arduino. 1991. Aggregation of soil particles by iron oxides in various size fractions of soil B horizons. J. Soil Sci. 42: 535–542.CrossRefGoogle Scholar
  2. Bigham, J. M., D. C. Golden, S. W. Buol, S. B. Weed, and L. H. Bowen. 1978. Iron oxide mineralogy of well-drained Ultisols and Oxisols. II Influence on color, surface area and phosphate retention. Soil Sci. Soc. Am. J. 42: 825–830.CrossRefGoogle Scholar
  3. Borggaard, O. K. 1982. The influence of iron oxides on the surface area of soil. J. Soil Sci. 33: 443–449.CrossRefGoogle Scholar
  4. Buol, S. W. 1985. Mineralogy classes in soil families with Low Activity Clays. In Mineral Classification of Soils. J. A. Kittrick, ed. Soil Sci. Soc. Am. Special Pub. No. 16. Soil Sci. Soc. Am. Inc. Madison, Wisconsin: American Soc. of Agron. Inc., 169–178.Google Scholar
  5. Churchman, G. J., and C. M. Burke. 1991. Properties of subsoils in relation to various measures of surface area and water content. J. Soil Sci. 42: 463–478.CrossRefGoogle Scholar
  6. Dasog, G. S., D. F. Acton, A. R. Mermut, and E. De Jong. 1988. Shrink-swell potential and cracking in clay soils of Saskatchewan. Can. J. Soil Sci. 68: 251–260.CrossRefGoogle Scholar
  7. Deer, W. A., R. A. Howie, and J. Zussman. 1967. An introduction to the rock-forming minerals. London: Longmans, Green and Co. Ltd. 528 pp.Google Scholar
  8. De Kimpe, C. R., M. R. Laverdiere, and Y. A. Martel. 1979. Surface area and exchange capacity of clay in relation to the mineralogical composition of gleysolic soils. Can. J. Soil Sci. 59: 341–347.CrossRefGoogle Scholar
  9. Desphande, T. L., D. J. Greenland, and J. P. Quirk. 1968. Changes in soil properties associated with the removal of iron and aluminium oxides. J. Soil Sci. 19: 108–122.CrossRefGoogle Scholar
  10. Feller, C., E. Schouller, F. Thomas, J. Rouller, and A. J. Herbillon. 1992. N2-BET specific surface areas of some Low Activity Clay soils and their relationships with secondary constituents and organic matter contents. Soil Sci. 153: 293–299.CrossRefGoogle Scholar
  11. Fontes, M. P. F. 1992. Iron oxide-clay mineral association in Brazilian Oxisols: A magnetic separation study. Clays & Clay Miner. 40: 175–179.CrossRefGoogle Scholar
  12. Gallez, A., A. S. R. Juo, and A. J. Herbillon. 1976. Surface and charge characteristics of selected soils in the tropics. Soil Sci. Soc. Am. J. 40: 601–608.CrossRefGoogle Scholar
  13. Ghabru, S. K., R. J. St. Arnaud, and A. R. Mermut. 1987. Liquid magnetic separation of iron-bearing minerals from sand fractions of soils. Can. J. Soil Sci. 67: 561–569.CrossRefGoogle Scholar
  14. Greenland, D. J., J. M. Oades, and T. W. Sherwin. 1968. Electron microscope observations of iron oxides in some red soils. J. Soil Sci. 19: 123–196.CrossRefGoogle Scholar
  15. Harsh, J. B., and H. E. Doner. 1985. The nature and stability of aluminium hydroxide precipitated on Wyoming Montmorillonite. Geoderma 36: 45–56.CrossRefGoogle Scholar
  16. Hillel, D. 1982. Introduction to soil physics. New York: Academic Press Inc. 364 pp.Google Scholar
  17. Hughes, J. C. 1982. High gradient magnetic separation of some soil clays from Nigeria, Brazil and Colombia. I. The inter relationships of iron and aluminium extracted by acid ammonium oxalate and carbon. J. Soil Sci. 33: 509–519.CrossRefGoogle Scholar
  18. Jackson, M. L. 1969. Soil chemical analysis—Advanced course. 2nd. Edition, 8th. Printing, 1973. Published by M. L. Jackson. Dept of Soil Science, Univ. of Wisconsin, Madison, Wis.Google Scholar
  19. Jones, R. C., W. H. Hudnall, and W. S. Sakai. 1982. Some highly weathered soils of Puerto Rico 2. Mineralogy. Geoderma 27: 75–137.CrossRefGoogle Scholar
  20. McKeague, J. A. Ed. 1978. Manual on sampling and methods of analysis. 2nd. Edition. Can. Soc. of Soil Sci., Ottawa. Canada.Google Scholar
  21. McKeague, J. A., and J. H. Day. 1966. Dithionite- and oxalate-extractable Fe and Al as aids in differentiating various classes of soils. Can. J. Soil Sci. 46: 13–22.CrossRefGoogle Scholar
  22. Mehra, O. P., and M. L. Jackson. 1960. Iron oxides removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clays & Clay Miner. 7:317–327.CrossRefGoogle Scholar
  23. Newman, A. C. D. 1983. The specific surface of soils determined by water sorption. J. Soil Sci. 34: 23–32.CrossRefGoogle Scholar
  24. Peter, C. J., and J. B. Weber. 1985. Adsorption, mobility and efficacy of metribuzin as influenced by soil properties. Weed Sci. 33: 868–873.CrossRefGoogle Scholar
  25. Rieke, R. D., T. S. Vinson, and D. W. Mageau. 1983. The role of specific surface area and related index properties in the frost heave susceptibility of soils. Permafrost: Fourth Int. Conf., Proc. (National Academy of Sciences), Washington, D.C.: National Academy Press, 1066–1071.Google Scholar
  26. Saleh, A. M., and A. A. Jones. 1984. The crystallinity and surface characteristics of synthetic ferrihydrite and its relationship to kaolinite surface. Clay Miner. 19: 745–755.CrossRefGoogle Scholar
  27. Schulze, D. G., and U. Schwertmann. 1984. The influence of aluminium on iron oxides: X. Properties of Al-substi-tuted goethites. Clay Miner. 19: 521–539.CrossRefGoogle Scholar
  28. Schwertmann, U., and N. Kämpf. 1985. Properties of Goethite and hematite in kaolinitic soils of Southern and Central Brazil. Soil Sci. 139: 344–350.CrossRefGoogle Scholar
  29. Smith, C. W., A. Hadas, J. Dan, and H. Koyumdjisky. 1985. Shrinkage and Atterberg limits in relation to other properties of principal soil types in Israel. Geoderma 35: 47–65.CrossRefGoogle Scholar
  30. Sposito, G. 1984. The surface chemistry of soils. N.Y.: Oxford Univ. Press., Oxford: Clarendon Press. 234 pp.Google Scholar
  31. Tiller, K. G., and L. H. Smith. 1990. Limitations of EGME retention to estimate the surface area of soils. Aust. J. Soil Res. 28: 1–26.CrossRefGoogle Scholar
  32. Van Olphen, H., and J. J. Fripiat Ed. 1979. Data handbook for clay materials and other non-metallic minerals. Oxford, New York, Toronto, Sydney, Paris, Frankfurt: Pergamon Press Inc., 346 pp.Google Scholar
  33. Wann, S. S., and T. C. Juang. 1985. Grouping soils for management practice. FFTC Book series No. 29: 41–54.Google Scholar

Copyright information

© The Clay Minerals Society 1995

Authors and Affiliations

  • E. Padmanabhan
    • 1
  • A. R. Mermut
    • 1
  1. 1.Department of Soil ScienceUniversity of SaskatchewanSaskatoonCanada

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