Soil sorption of caesium modelled by the Langmuir and Freundlich isotherm equations

The Langmuir and Freundlich adsorption isotherm equations were used to model Cs sorption in 6 Welsh soils. The pH (in water), of the soils ranged from 3.5 to 6.5, and the estimated organic matter (determined by loss-on-ignition) ranged from 4.8% to 46%. According to the Langmuir adsorption isotherm, highest sorption maxima, b, were displayed by the loams at 102-204 mg kg(-1), compared with organic soils at 37-86 mg kg(-1). Subsoil horizons (15-30 cm depth) did not always display higher sorption maxima than their topsoil (0-15 cm depth) counterparts. Where an improved fit to the Freundlich model was found over the Langmuir model, it was assumed that either concurrent desorption of other species, or bond-energy heterogeneity in the substrate, were significant for these soils.