title: Thermodynamic parameters of U (VI) sorption onto soils in aquatic systems.
abstract: The thermodynamic parameters viz. the standard free energy (∆Gº), Standard enthalpy change (∆Hº) and standard entropy change (∆Sº) were determined using the obtained values of distribution coefficient (kd) of U (VI) in two different types of soils (agricultural and undisturbed) by conducting a batch equilibrium experiment with aqueous media (groundwater and deionised water) at two different temperatures 25°C and 50°C. The obtained distribution coefficients (kd) values of U for undisturbed soil in groundwater showed about 75% higher than in agricultural soil at 25°C while in deionised water, these values were highly insignificant for both soils indicating that groundwater was observed to be more favorable for high surface sorption. At 50°C, the increased kd values in both soils revealed that solubility of U decreased with increasing temperature. Batch adsorption results indicated that U sorption onto soils was promoted at higher temperature and an endothermic and spontaneous interfacial process. The high positive values of ∆Sº for agricultural soil suggested a decrease in sorption capacity of U in that soil due to increased randomness at solid-solution interface. The low sorption onto agricultural soil may be due to presence of high amount of coarse particles in the form of sand (56%). Geochemical modeling predicted that mixed hydroxo-carbonato complexes of uranium were the most stable and abundant complexes in equilibrium solution during experimental.
authors.affiliation: Health Physics Division, Bhabha Atomic Research Centre, Mumbai, India.
authors.forename: Ajay
authors.initials: A
authors.lastname: Kumar
authors.forename: Sabyasachi
authors.initials: S
authors.lastname: Rout
authors.forename: Malay
authors.initials: M
authors.lastname: Ghosh
authors.forename: Rakesh Kumar
authors.initials: RK
authors.lastname: Singhal
authors.forename: Pazhayath Mana
authors.initials: PM
authors.lastname: Ravi
keywords: Deionised water; Distribution coefficients; Groundwater; Soil; Uranium