Sorption data analysis was carried out using the Freundlich, Langmuir, and Modified Freundlich isotherms for the uptake of sodium and potassium in an initial concentration range of 10-100 mg/L on backfill materials, viz., bentonite, vermiculite, and soil samples. The soil samples were collected from a shallow land disposal facility at Kalpakkam. The Freundlich isotherm equation is validated as a preferred general mathematical tool for representing the sorption of K+ by all the selected backfill materials. The Modified Freundlich isotherm equation is validated as a preferred mathematical tool for representing the sorption of Na+ by the soil samples. Since a negative sorption was observed for the uptake of Na+ by commercial clay minerals (vermiculite and bentonite clay in the laboratory experiments), sorption analysis could not be carried out using the above-mentioned isotherm equations. Hill plots of the sorption data suggest that in the region of low saturation (10-40 mg/L), sorption of K+ by vermiculite is impeded by interaction among sorption sites whereas sorption by soil and bentonite clay is enhanced by interaction among sorption sites. In the region of higher saturation (60-100 mg/L), sorption of K+ by all three backfill materials is enhanced by interaction among sorption sites. The Hill plot of the sorption data for Na+ by soil suggests that irrespective of Na+ concentration, sorption of Na+ at one exchange site enhances sorption at other exchange sites.