A New Method To Estimate Adsorption Energies between Cations and Soil Particles via Wien Effect Measurements in Dilute Suspensions and an Approximate Conductivity−Activity Analogy

Abstract

Measurement of the Wien effect (increased electrical conductivity at strong electrical fields) in soil suspensions is proposed as the basis of a new method to characterize energy relationships between cations and soil particles. The simplified theory behind the method, the working principle of the short high-voltage pulse apparatus, and the measuring procedure are outlined briefly. The new method was used to evaluate the adsorption energies of two monovalent (Na, K) and two divalent (Ca, Cd) cations on yellow-brown soil and black soil particles, assuming an analogy between the activity of the cations and their contribution to the electrical conductivity of the suspension. Both the mean free bonding energies, deltaGbo, and the adsorption energies, deltaGad, of the cations for these two soils increased in the order: Na < K < Ca < Cd. Under the conditions of our experiments, estimated deltaGbo ranged from 4.7 to 6.4 kJ mol(-1) and from 7.0 to 8.2 kJ mol(-1) for mono- and divalent cations, respectively. The bonding energies obtained with the new method were similar to those determined previously by ionic activity measurement. The determined mean adsorption energies of cations desorbed at a field strength of 100 kV cm(-1), for example, ranged from 0.7 to 1.2 kJ mol(-1) and from 1.9 to 2.3 kJ mol(-1) for mono- and divalent cations, respectively.