HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Evangelou, V. P. Articles by Phillips, R. E. Search for Related Content PubMed Articles by Evangelou, V. P. Articles by Phillips, R. E. Agricola Articles by Evangelou, V. P. Articles by Phillips, R. E.

Comparison Between the Gapon and Vanselow Exchange Selectivity Coefficients

Department of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091

* Corresponding author.

ABSTRACT

The Gapon exchange equation is commonly employed in the literature to study binary heterovalent exchange reactions. However, the Gapon equation is not consistent with thermodynamics of exchange reactions. The Vanselow exchange equation, on the other hand, is consistent with thermodynamics of exchange reactions. Algebraic analysis on the interrelationship between the Vanselow (K_V) and the Gapon (K_G) exchange selectivity coefficients for monovalent-bivalent exchange (Na⁺-M²⁺; M = Ca²⁺ or Mg²⁺), K_G = K_V (1 + E_Na)^1/2/[2(1 – E^Na)^1/2], has shown that K_G = 0.5 K_V when E_Na 0, and K_G = when E_Na 1 (E_Na = charge fraction of Na on the exchanger). Also, K_V and K_G are equal at a sodium equivalent fraction of the exchanger (E_Na) = 0.60. These K_V-K_G interrelationships as a function of E_Na are independent of the magnitude of the cation exchange capacity (CEC). This study was conducted to test whether experimental data of monovalent-bivalent binary exchange on soil clay minerals conform to the algebraic interrelationships between K_V and K_G. This was tested by estimating values of K_V and K_G with previously reported experimental data for Na-Ca and Na-Mg exchange of clay minerals and a soil, carried out in perchlorate background media. The results of the experimental data confirm that these interrelationships are met.

Contribution from the Dep. of Agronomy, Univ. of Kentucky Agric. Exp. Stn. The investigation reported in this paper (no. 87-3-27) is in connection with a project of the Kentucky Agric. Exp. Stn. and is published with the approval of the director.

Received for publication June 4, 1987.