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This article in SSSAJ

  1. Vol. 33 No. 3, p. 388-392
    Received: Dec 2, 1968
    Accepted: Jan 16, 1969

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Interactions of pH-Dependent and Permanent Charges of Clays: I. Use of Specific Ion Electrodes for Measuring Ca and Rb Activities in Bentonite and Illite Suspensions1

  1. E. O. McLean and
  2. G. H. Snyder2



Recent development of selective electrodes for many ions is revitalizing analytical potentiometry. Examination of recent evidence appeared to justify their use for measuring ionic activities in clay suspensions. Calcium and Rb ion activities in Fithian illite and Panther Creek bentonite were measured with the Orion divalent and the Beckman monovalent ion electrodes. The clays were saturated reciprocally with Ca-Rb, Ca-H, and Rb-H. Electrode-measured Ca and Rb activities were generally valid indexes of tracer-measured root uptake and clay retention of cations, details of which are given in companion reports. Activities and fractions active of Ca and Rb reached minimal or near minimal values when sufficient H was added to equal the pH-dependent CEC of each clay, a fact which suggested interaction of pH-dependent and permanent charges.

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