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This article in SSSAJ

  1. Vol. 52 No. 5, p. 1289-1292
    Received: Oct 16, 1987

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Sorption of Cadmium, Nickel, and Zinc by Kaolinite and Montmorillonite Suspensions1

  1. Robert W. Puls * and
  2. Hinrich L. Bohn
  1. R.S. Kerr Environmental Research Lab., Ada, OK 74820
    Dep. of Soil and Water Sciences, Univ. of Arizona, Tucson, AZ 85721



Sorption is the predominant process governing metal ion movement in soils and includes the following physical and chemical mechanisms: adsorption, precipitation and absorption. This research attempts to use the hard-soft-acid-base principle to explain sorption selectivity of the metal cations Cd, Ni and Zn by kaolinite and montmorillonite clays. The hard-soft character of the clay surfaces, which is due to their surface functional groups, may be inferred by cation sorption selectivity experiments where pH and complex ion formation are controlled and monitored. Calcium saturated clays were suspended in Ca(ClO4)2, CaCl2 or CaSO4 and spikes of the above metals as divalent cations were added and their reactivity assessed within the framework of the HSAB Principle. For kaolinite in Ca(ClO4)2, metal sorption followed the sequence Cd > Zn > Ni. For montmorillonite in Ca(ClO4)2, metal sorption followed the sequence Cd ≈ Zn > Ni. In CaCl2 and CaSO4, the selectivity was different due to the presence of Cl and SO2−4 which competed with the mineral surfaces for the divalent metal cations.

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