Abstract
Cation exchange capacity and selectivity coefficients are essential parameters that influence cation distribution between sorbed and solution phases and their mobility in the soil profile. We propose a rapid method for the determination of cation exchange isotherms using short soil columns or thin disks. The method is based on continuous flow through a thin soil layer (1 mm) where concentration of cations in the effluent solution is collected in fractions over time. Binary exchange isotherms for Ca-Mg, Ca-K, and Mg-K were derived for two soils; Mahan (kaolinitic, thermic Typic Hapludult) and Sharkey (montmorillonitic, non-acidic, thermic, Vertic, Haplaquept). Chloride and percholate were used as the background anions. Selectivity coefficients from the thin disk method were consistent with values derived earlier from laborious batch methods. We conclude that the proposed method allows easy determination of selectivity coefficients for different ionic strengths.
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