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This article in SSSAJ

  1. Vol. 31 No. 5, p. 614-619
    Received: Jan 9, 1967
    Accepted: June 22, 1967

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Aluminous Chlorite Origin of pH-Dependent Cation Exchange Capacity Variations1

  1. J. M. de Villiers and
  2. M. L. Jackson2



Cation exchange capacity (CEC) and K-fixing power of a micaceous vermiculite were markedly reduced following treatment with solutions of polymeric hydroxy alumina. The partially chloritized product exhibited linear increase in CEC (measured with KCl) from 48 to 95 meq/100 g as the pH of the NaOAc buffer and then KCl washings increased from pH 4 to 8.5; the CEC increased further to 117 meq/100 g upon brief exposure 2 alkali (2% Na2CO3, pH 11) at 25C. The pH-dependent CEC appeared to arise from isomorphous substitutional charge (permanent negative charge), blocked by hydroxy Al charged positively by edge — AlOH2 groups, and restored by deprotonation of the latter on addition of base. The present findings with chloritized vermiculite further establish the mechanism of pH-dependent CEC of soils since the behavior found is essentially identical to that reported earlier for soil clays containing aluminous, pedogenically formed chlorite, the constituent responsible for pH-functional variations in CEC in crystalline clays.

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