Rothmund–Kornfeld selectivity coefficient (K_RK) and regular solution model are rarely used to describe soil exchange data but it seems to be able to satisfactorily predict the true thermodynamic equilibrium constant (K_ex). We tested the ability of Rothmund–Kornfeld and regular solution models to predict K_ex in binary (K–NH₄, Ca–Mg, and K–Ca) and ternary (Na–Ca–Mg) cation exchange systems in clays and soils with different dominant mineralogies. Applying the Rothmud–Kornfeld model to the exchange data indicated the preference of K over Ca and NH₄, and Ca over Mg in binary, and Ca over Mg in ternary exchange systems. Similar results were obtained on the preference of cations by different exchangers when the regular solution model was applied to describe the exchange data. Despite the different assumptions of Rothmund–Kornfeld and regular solution models to approximate the activity coefficient of the ions on the exchange phase, similarity between the value of selectivity coefficients obtained by these two models was observed in homovalent cation exchange reactions. Also, a close agreement was observed between the value of selectivity coefficients obtained by these two models and K_ex. However, in heterovalent cation exchange reactions, Rothmund–Kornfeld and regular solution models did not provide accurate estimation of the K_ex. But these models can correctly indicate the overall preference of one ion to another as K_ex. The results suggested Rothmund–Kornfeld and regular solution models can be applied satisfactorily in clay and soil systems as a rapid method to estimate K_ex, especially in homovalent exchange reactions.

Abbreviation: K_RK : Rothmund–Kornfeld selectivity coefficient; K_ex: True thermodynamic equilibrium constant; ƒ: Exchange-phase activity coefficients; NP: Thermodynamic non-preference; E: Equivalent fractions of ion in exchange phases; Ẽ: Equivalent fractions of ion in solution phases; K_RS: Regular solution selectivity coefficient; K_v: Vanselow selectivity coefficient; ∆G_ex: Gibbs free energy change

Rothmund-Kornfeld选择性系数（K _RK）和常规溶液模型很少用于描述土壤交换数据，但似乎能够令人满意地预测真实的热力学平衡常数（K _ex）。我们测试了Rothmund-Kornfeld模型和常规溶液模型预测粘土和土壤中二元（K-NH ₄，Ca-Mg和K-Ca）和三元（Na-Ca-Mg）阳离子交换体系中K _ex的能力。不同的主要矿物学。将Rothmud-Kornfeld模型应用于交换数据表明，钾比钙和NH ₄的优先性在二元交换系统中，Ca超过Mg，在三元交换系统中Ca超过Mg。当使用常规溶液模型描述交换数据时，不同交换者对阳离子的偏爱获得了相似的结果。尽管Rothmund-Kornfeld模型和常规溶液模型的假设不同，以近似离子在交换相上的活度系数，但在同价阳离子交换反应中，观察到了这两种模型获得的选择性系数值之间的相似性。同样，在通过这两个模型获得的选择性系数的值与K _ex之间观察到了密切的一致性。但是，在异价阳离子交换反应中，Rohthmund-Kornfeld模型和常规溶液模型无法准确估算K _ex。但是这些模型可以正确地表明一个离子对另一个离子的总体偏好为K _ex。结果表明，Rothmund-Kornfeld模型和常规溶液模型可以令人满意地应用于粘土和土壤系统中，作为估算K _ex的快速方法，尤其是在同价交换反应中。

缩写：K _RK：Rothmund-Kornfeld选择性系数；K _ex：真热力学平衡常数；ƒ：交换阶段活度系数；NP：热力学非偏好；E：离子在交换相中的当量分数；Ẽ：溶液相中的离子当量分数；K _RS：规则溶液的选择系数；K _v：Vanselow选择性系数；∆G _ex：吉布斯自由能变化