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This article in SSSAJ

  1. Vol. 40 No. 3, p. 359-364
    Received: Aug 13, 1975
    Accepted: Jan 29, 1976

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Electric Charges on Sesquioxidic Soil Clays1

  1. M. V. Fey and
  2. J. le Roux2



The effects of pH, phosphate, oxalate, pyrophosphate, citratedithionite-bicarbonate and Na2CO3 pretreatments on the positive and negative exchange charges of sesquioxidic clays from soils of South Africa, Australia, Brazil, Japan, and New Zealand were measured using 0.05N KCl as index electrolyte according to a method which obviates a washing step for removal of excess salt prior to replacement of the index ions, Behavior of clays rich in allophane was compared to that of three synthetic amorphous, aluminosilica gels.

Hysteretic, pH-dependent net negative exchange charge appears to arise from positive exchange charge hysteresis only, CEC being fully reversible by titration with strong acid.

The methodology of cation and anion exchange capacity determinations is discussed with special reference to the problem of surface charge density variations encountered in different materials.

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