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This article in SSSAJ

  1. Vol. 70 No. 2, p. 550-554
    Received: Mar 1, 2005

    * Corresponding author(s): desutter@nstl.gov
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Flow-Through and Batch Methods for Determining Calcium-Magnesium and Magnesium-Calcium Selectivity

  1. Tom M. DeSutter *a,
  2. Gary M. Pierzynskib and
  3. Luke R. Bakerb
  1. a USDA-ARS, National Soil Tilth Lab., Ames, IA, 50011, formerly with Dep. of Agronomy, Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506
    b Dep. of Agronomy, Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506


Conducting binary-exchange experiments is a common way to identify cationic preferences of exchanger phases and the two most common approaches are the flow-through and batch methods. The objectives of this research were to provide the materials and methods for both flow-through and batch equilibration techniques and to compare Ca-Mg and Mg-Ca selectivity when using these two methods on a montmorillonitic soil. The methods were evaluated by comparing both the Gibbs free energy values (ΔGex) and selectivity diagrams derived from the flow-through and batch exchange reactions. The ΔGex values for the Ca-Mg reaction were 634 and 444 J mol−1 as determined by the flow-through and batch methods, respectively, indicating an exchanger preference for Ca. Exchanger preference for Ca was also evident in the Mg-Ca reaction with ΔGex values of −882 and −784 J mol−1 for the flow-through and batch methods, respectively. The flow-through and batch methods worked very well for determining cation selectivity and results indicate no significant differences existed between the two methods.

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