Dispersion of Chloride, Sodium, and Calcium Ions in Soils as Affected by Exchangeable Sodium
1982
Dufey, Joseph E. | Sheta, Tarek H. | Gobran, Georges R. | Laudelout, Henri
A sand-clay soil mixture was equilibrated in a column with various NaCl-CaCl₂ solutions at constant normality (0.03N). After each equilibration, the percolating solution was labeled successively with ³⁶Cl, ²²Na, and ⁴⁵Ca. The breakthrough curves of the radioactive species made it possible to calculate both effective pore volume and, at a given Darcy velocity, the Peclet number (P) for each ion. PCₗ was found to decrease markedly when the exchangeable sodium percentage (ESP) increased from 0 to about 20%. PNₐ and PCₐ were almost not affected by changing ESP. The following sequence was observed: PCₐ < PNₐ < PCₗ. The discriminatory mixing power of soil towards the three ions likely results from changing size of montmorillonite tactoids and from demixing of adsorbed Na and Ca cations.
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