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Abstract  

A novel sorbent resin consisting of a Phosphonic Acid grafted on Merrifield Resin (PA-MR) for the extraction of uranyl from nitrate media is described. The sorption behaviour of uranyl cation on PA-MR was investigated using batch equilibrium technique. The effects of parameters such as shaking speed, pH levels, contact time, metal concentrations, ionic strength and temperature were reported. The results show that the sorption capacity increases with increasing both initial uranyl ion concentration and temperature and decreases with increasing ionic strength. Therefore, the optimum condition for the present study should be using 6.6 mg adsorbent per 1.0 mg uranyl in solution with pH 3.6 and shaking at 250 rpm for 180 min. The adsorption behavior of the system was also investigated and found to be in line with Langmuir isotherm. The kinetic data was well described by the pseudo second-order. Thermodynamics data leads to endothermic process ∆H = + 31.03 kJ−1 mol−1, ∆S = + 146.64 J mol−1 K−1 and ∆G = −11.96 kJ mol−1 at 20 K. ∆G decreased to negatives values with increasing temperature indicating that the process was more favoured at high temperature.

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Abstract  

We have performed a large number of batch sorption experiments of uranyl onto SiO2 and examined the effects of nitrate or ionic strength, phosphate, fulvic acid(FA), phthalic acid (PH), salicylic acid (SA), and catechol (CA) on the uranyl sorption onto SiO2. Three sorption edges and three sorption isotherms at ionic strengths 0.05, 0.1, and 0.5 mol/L KNO3 were used to investigate the effect of ionic strength or nitrate on the sorption and the Langmuir, Freundlich, and Dubinin-Radushkevich models are used to simulate the sorption isotherms, respectively. Five sorption edges in the presence of phosphate, FA, PH, SA, and CA were compared with that in the absence of complexing ligand. The results suggest that the effect of complexation of uranyl with nitrate on the uranyl sorption can be negligible and the sorption can be described Freundlich and D-R model very well. The positive effect of phosphate on the uranyl sorption was found, though the extent of effect was decreased with increasing pH. The positive effect and the negative effect of FA on the uranyl sorption were found at low pH and high pH ranges, respectively. The sorption edge of uranyl sorption remained unaffected in the presence of PH in the pH 2–10. In the presence of SA, the no effect and the negative effect on the uranyl sorption were, respectively, found at low pH and high pH ranges. The negative effect of CA on the uranyl sorption was found in the pH 2–10.

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Abstract  

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.

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