Volume 95, Issue 5

Sorption of uranyl ion, UO 2 2+ , on silicate particles (3.00g/L) was studied in sodium perchlorate solution as a function of pcH and ionic strength at 298 K. The effects of different ligands ( e.g. , N -donors, carboxylic acids) on the uranyl sorption were investigated. At I = 0.20 M (NaClO 4 ), uranyl sorption on silicate increased from ca. 6% (pcH 3.0) to ca. 99% (at pcH 6.5), above which a small decrease was observed. A synergistic enhancement in uranyl sorption was observed in the presence of N -donor ligands such as 1,10-phenanthroline and ethylenediamine in the pcH range 3 to 4.5 as compared to that in the absence of ligands. Carboxylic acids inhibited the sorption in the order: citric acid > malonic acid > nitrilotriacetic acid > iminodiacetic acid > sulfosalicylic acid > succinic acid > glycolic acid. The presence of organic cosolvents such as dimethylsulfoxide, glycerol and tetrahydrofuran had no significant influence on the uranyl sorption profile. Uranyl sorption decreased marginally in the presence of 1.00 × 10 −3 M Eu(III).

Previous published data for the adsorption of U(VI) and/or phosphate onto amorphous Fe(III) oxides (hydrous ferric oxide, HFO) and crystalline Fe(III) oxides (goethite) was examined. These data were then used to test the ability of a commonly-used surface complexation model (SCM) to describe the adsorption of U(VI) and phosphate onto pure amorphous and crystalline Fe(III) oxides and synthetic goethite-coated sand, a surrogate for a natural Fe(III)-coated material, using the component additivity (CA) approach. Our modeling results show that this model was able to describe U(VI) adsorption onto both amorphous and crystalline Fe(III) oxides and also goethite-coated sand quite well in the absence of phosphate. However, because phosphate adsorption exhibits a stronger dependence on Fe(III) oxide type than U(VI) adsorption, we could not use this model to consistently describe phosphate adsorption onto both amorphous and crystalline Fe(III) oxides and goethite-coated sand. However, the effects of phosphate on U(VI) adsorption could be incorporated into the model to describe U(VI) adsorption to both amorphous and crystalline Fe(III) oxides and goethite-coated sand, at least for an initial approximation. These results illustrate both the potential and limitations of using surface complexation models developed from pure systems to describe metal/radionuclide adsorption under more complex conditions.

Th(IV) adsorption onto oxidized multi-wall carbon nanotubes (MWCNTs) was carried out at 293±2K. The effects of MWCNT concentration, pH, and ionic strength were studied. The results showed that Th(IV) adsorption onto oxidized MWCNTs strongly depended on MWCNT concentration and pH, and was weakly dependent on ionic strength. Oxidized MWCNTs showed a higher Th(IV) adsorption capacity than as-grown MWCNTs. The adsorption process followed pseudo second order kinetics. The Freundlich isotherm model described the data better than the Langmuir model. The adsorption mechanism of Th(IV) may be surface complexation. Oxidized MWCNTs may be a promising candidate for the concentration of Th(IV), or its analogue actinides from large volumes.

The sorption of europium, Eu(III), on suspended silica was studied in perchlorate media under varying concentrations of Eu(III) and silica, at pH 4 to 8, and ionic strength from 0.20 to 1.40 M NaClO 4 at 298 K. The complexing anions, carbonate, acetate, citrate, oxalate, phosphate and EDTA, affected the sorption of Eu(III). A synergistic enhancement in the sorption of Eu(III) was observed for oxalate and phosphate ligands. Other anions suppressed the sorption in the order: acetate < carbonate < citrate < EDTA. The results of TRLFS studies were consistent with ternary Eu/silica/ligand complexation for oxalate and phosphate anions.

The characterization of technetium (Tc) environments in borosilicate glasses is important with regard to the long-term isolation of Tc in nuclear wastes from the environment by waste vitrification. In this study, Raman spectroscopy was used to detect Tc in various borosilicate waste glass formulations in which Tc valence and average coordination environment were previously characterized by X-ray absorption spectroscopy. Raman spectral comparisons between chemically equivalent Tc-containing and Tc-free borosilicate glass pairs indicate Tc-dependent features near 320 and 910 cm −1 resulting from internal vibrational modes of pertechnetate tetrahedral (Tc 7+ in TcO 4 − ), similar to those observed for pertechnetate aqueous solutions. Initial observations of the pertechnetate Tc–O symmetric stretch mode near 910cm −1 indicate a peak area dependence on pertechnetate concentration and a detection limit near 50 ppm Tc 7+ in borosilicate glass. Pertechnetate Tc–O symmetric stretch mode frequency versus composition relationships for the borosilicate waste glasses suggest that pertechnetate tetrahedra are surrounded by network-modifying cations. However, Raman spectroscopy is insensitive to six-coordinated Tc 4+ species in borosilicate glasses.

The sorption of mercury ions from aqueous solutions on styrene-divinylbenzene copolymer beads (St-DVB) has been investigated for the decontamination of mercury from aqueous media. Various physico-chemical parameters, such as selection of appropriate electrolyte, contact time, amount of adsorbent, concentration of adsorbate, effect of diverse ions and temperature were optimized to simulate the best conditions which can be used to decontaminate mercury from aqueous media using St-DVB beads as an adsorbent. The radiotracer technique was used to determine the distribution of mercury. The highest adsorption was observed at 0.001 mol L −1 acid solutions (HNO 3 , H 2 SO 4 and HClO 4 ) using 0.2 g of adsorbent for 5.14×10 −5 mol L −1 mercury concentration in five minutes equilibration time. Studies show that the adsorption decreases with the increase in the concentrations of all the acids. The adsorption data follows the Freundlich isotherm over the mercury concentration range of 2.19×10 −4 to 5.90×10 −3 mol L −1 . The characteristic Freundlich constants, i.e. 1/ n = 0.42±0.01 and A = (1.54±0.03)×10 −3 mol g −1 have been computed for the sorption system. The sorption mean free energy from Dubinin–Radushkevich isotherm is 11.9±0.1 kJ mol −1 indicating ion-exchange mechanism of chemisorption. The uptake of mercury increases with the rise in temperature. Thermodynamic parameters, i.e. Δ G , Δ S and Δ H have also been calculated for the system.

Various 3-phenyl-4-aroyl-5-isoxazolones, namely, 3-phenyl-4-benzoyl-5-isoxazolone (HPBI), 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI) were synthesized and examined with regard to the solvent extraction behavior of Zr(IV) and Hf(IV) from hydrochloric acid solutions. The results demonstrated that Zr(IV) and Hf(IV) extracted into chloroform with 3-phenyl-4-aroyl-5-isoxazolones (HA), as ZrOA 2 and HfOA 2 , respectively. The equilibrium constants of the extracted complexes follow an order HFBPI > HPBI > HTPI, which is in accordance with their p K a values. The synergistic extraction of Zr(IV) and Hf(IV) was also investigated with mixtures of HPBI and tri- n -octylphosphine oxide (TOPO), trialkylphosphine oxide (TRPO), and tri- n -butylphosphate (TBP), where the complexation strength follows the order TOPO > TRPO > TBP. The equilibrium constants of the synergistically extracted complexes have been correlated with the donor ability of phosphoryl oxygen of the neutral organophosphorus extractants in terms of their 31 P NMR chemical shifts and their basicity values. The addition of neutral organophosphorus extractant to the metal chelate system not only enhances the extraction efficiency but also improves the selectivity between these metal ions.

A new polyoxometalate of chemical formula, Na 2 (H 2 O) 4 (H 3 O)[Al(OH) 6 Mo 6 O 18 ] (1) containing Anderson type large anion has been synthesized and characterized by single-crystal X-ray structure determination and IR spectroscopic studies. The crystal of 1 is triclinic, spacegroup P−1 with cell dimensions, a = 6.365(9)Å, b = 10.37(1)Å, c = 10.44(1)Å and α = 65.41(1), β = 77.18(1), γ = 86.58(1) and Z = 1. The compound 1 behaves as an ion exchanger and is stable in thermal, radiation and chemical environments. Radiochemical separation of the short-lived daughter 137m Ba ( t 1/2 = 2.50 min) from its long-lived parent 137 Cs using this newly designed and synthesized ion exchanger has been developed.