Hydration of zirconium diphosphate (ZrP2O7) conduced to formation of active sites in solid/liquid interface. In ZrP2O7/NaClO4 0.5 M suspensions, active sites and their acidity constants are quite determined but the presence of some impurities is now studied. This work was conducted to determine the surface properties changes produced by oxalic and citric acid during the hydration process. Moreover the presence of organic acids with ZrP2O7 modified reveals an increase in uranium sorption constants. The zirconium diphosphate has been characterized using X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Particle induced X-ray emission and Neutron (PIXE). Furthermore, the specific surface area, measured by the BET method, was 3.5 m2/g. The pH corresponding to the isoelectric point, determined by Zeta Potential measurements and mass titration was 3.6. The sites density calculated using titration curves was around of 5.37 s/nm2 for NaClO4 0.5 M, 13.71 s/nm2 for NaClO4 0.5 M/citric acid 0.1 M and 7.33 s/nm2 NaClO4 0.5 M/oxalic acid 0.1 M. The surface acidity constants and species distribution in surface were calculated by means of simulation of the titration curves with the FITEQL code (constant capacitance model), for ZrO and PO amphoteric sites of ZrP2O7. The uranyl sorption edge was determined for NaClO4 0.5 M. It spreads between pH 3 and 4.5 for complete sorption according to the previously published results. In the ZrP2O7–citrate modified surface, the uranyl sorption edge begin at pH 2 and was almost complete at pH 3.2 while ZrP2O7–oxalate modified surface edge started at 50% of sorption at pH of 1.5 and was complete at pH 3
In the field of nuclear waste management, prediction of radionuclide migration through the geosphere has to take into account the effects of organic matter. This work deals with the effects of organic acids (citric and oxalic acid) on speciation of uranium(VI) sorbed onto zirconium diphosphate (ZrP 2 O 7 ). Surface properties of zirconium diphosphate and its uranium(VI) sorption capability in the presence and absence of organic acids were previously studied. The preliminary study suggested that organic acids take part in the sorption equilibria. In order to understand the interactions between organic ligands (citrate or oxalate), uranium(VI) and zirconium diphosphate, a luminescence spectroscopy study was carried out. Luminescence measurements indicated that only one uranium(VI) surface complex is formed when citric or oxalic acid is present. Moreover, the total carbon content in the studied samples indicated that organic ligands remain on the surface when uranium(VI) sorption is carried out. Uranium sorption edges were then fitted with the FITEQL4.0 code [15] and the Constant Capacitance Model (CCM). Spectroscopy information was used to constraint the modeling. The best fit for the U(VI)/citrate/ZrP 2 O 7 and U(VI)/oxalate/ZrP 2 O 7 systems considered the formation of a ternary surface complex.
An analysis of the sorption process allowed to establish that Fe3+ sorption into montmorillonite is a chemical process that involves an exchange of cations from the montmorillonite interstitial space between layers.
When a mineral surface is immersed in an aqueous solution, it develops an electric charge produced by the amphoteric dissociation of hydroxyl groups created by the hydration of the solid surface. This is one influential surface property. The complete hydration process takes a time which is specific for each mineral species. The knowledge of the aqueous solution contact time for complete surface hydration is mandatory for further surface phenomena studies. This study deals with the optimal hydration time of the raw zircon (ZrSiO4) surface comparing the classical potentiometric titrations with a fluorescence spectroscopy technique. The latter is easy and reliable as it demands only one sample batch to determine the optimal time to ensure a total hydration of the zircon surface. The analytical results of neutron activation analysis (NAA) showed the presence of trace quantities of Dy3+, Eu3+ and Er3 in the bulk of zircon. The Dy3+ is structured in the zircon crystalline lattice and undergoes the same chemical reactions as zircon. Furthermore, the Dy3+ has a good fluorescent response whose intensity is enhanced by hydration molecules. The results show that, according to the potentiometric analysis, the hydration process for each batch (at least 8 sample batches) takes around 2 h, while the spectrometric method indicates only 5 min from only one batch. Both methods showed that the zircon surface have a 16h optimal hydration time.
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