Release of long-lived radioactivity to the aquatic bodies from various nuclear fuel cycle related operations is of great environmental
concern in view of their possible migration into biosphere. This migration is significantly influenced by various factors
such as pH, complexing ions present in aquatic environment and sorption of species involving radionuclides on the sediments
around the water bodies. 241/243Am are two major radionuclides which can contribute a great deal to radioactivity for several thousand years. In the present
study, 241Am sorption on natural sediment collected from site near a nuclear installation in India, has been investigated under the
varying conditions of pH (3–10) and ionic strength [I = 0.01–1 M (NaClO4)]. The sorption of Am increased with pH of the aqueous medium [10% (pH 2) to ~100% (pH 10)], which was explained in terms
of the increased negative surface charge on the sediment particles. There was marginal variation in Am(III) sorption with
increased ionic strength (within error limits) of the aqueous medium suggesting inner-sphere complexation/sorption process.
Sediment was characterized for its elemental composition and structural phases using Energy Dispersive X-Ray (SEM-EDX) and
X-Ray Diffraction (XRD) techniques. Zeta-potential measurement at I = 0.1 M (NaClO4) suggested that Point of Zero Charge (pHPZC) was ~2, indicating the presence of silica as major component in the sediment. Kurabtov plot using sorption data as a function
of pH at fixed I = 0.1 M (NaClO4) indicated the presence of multiple Am(III) species present on the surface. Potentiometric titration of the suspension indicated
the presence of mineral oxide like behavior and assuming a generic nature (≡XOH) for all types of surface sites, protonation–deprotonation
constants and total number of sites have been obtained. The sorption data has been modeled using 2-pK Diffuse Double Layer
Surface Complexation Model (DDL-SCM). ≡XOAm2+ has been identified as the main species responsible for the sorption profile.
The amphoteric acid-base behavior of hydrous zirconium oxide (HZO) was investigated by titrating HZO with 0.05M HNO3 and NaOH at constant ionic strength. The sorption of strontium from 0.05M NaNO3 solution was measured as a function of pH. Abrupt increase in sorption was observed at the equilibrium pH of 9. The experimental titration and strontium sorption data on HZO were evaluated using the constant capacitance model (CCM) and diffuse double layer model (DLM). Various model parameters of Surface Complexation Models (SCM) were estimated, numerically, by non-linear regression. Modeling the sorption and speciation of Sr2+ on HZO indicated that the hydrolysis of Sr2+ to lower charged SrOH+ is the pre-requisite for the abrupt sorption behavior at pH 9.
A surface complexation model, the so-called diffuse double layer model (DLM), was used in the description of the multicomponent
system consisting of Czech sodium bentonite SABENYL and synthetic granitic water spiked with233U(VI). The experimental data were evaluated and the characteristic parameters, e.g., the equilibrium constants of all the
reactions considered, were obtained and used for the numerical simulation of sorption selectivity of the uranium in relation
to the total carbonate concentration. The values of separation factors indicate that the selectivity of uranium sorption in
such multicomponent systems can depend not only on the pH and composition of both phases, but also on the phase ratio and
starting concentrations of participating components.
Dzombak, D. A. & Morel, F. M. M., 1990. SurfaceComplexationModeling: Hydrous Ferric Oxide. Wiley. New York.
Fiedler, S. & Sommer, M., 2004. Water and redox conditions in wetland soils – their influence on pedogenic oxides and
reaction is accompanied by enthalpy changes, which are valuable information for characterizing the interfacial chemical and physical processes. According to the surfacecomplexationmodel, the mechanism of surface charging will be interpreted by the 2-pK