Volume 102, Issue 9

Sorption of Cm(III) on silica surface from aqueous solutions of varying pH was investigated in absence and presence of alpha hydroxy isobutyric acid (HIBA) by employing batch sorption and surface complexation modeling (SCM). Cm(III) sorption on silica increased with the pH of the suspension and remained constant above pH∼6. With increase in HIBA concentration, the sorption edge shifted to higher pH. The effect of addition order of HIBA and Cm(III) on the sorption was studied and higher shift in sorption edge, as compared to binary system, was observed when HIBA was added to silica suspension prior to Cm(III). The sorption data could be satisfactorily explained by SCM in all the systems. The results have been compared with that reported earlier on the effect of HIBA on sorption behaviour of Eu(III) by silica. Further, the use of small organic molecules as model compounds of humic acid (HA) has been evaluated by comparing the influence of HA and HIBA on sorption of Cm(III) on to silica.

Optical absorption spectra of Np in 3 mol/dm 3 nitric acid at elevated temperatures were measured using an optical glass cell with a water jacket having a light path of 1 cm. Molar extinction coefficients of Np(VI), ε T M – 1  cm – 1 , were obtained at various temperatures (297, 313, 334, 352, and 372 K). The values of ε T were found to decrease with increasing temperature and could be described by the equation ε T  =− 0.14 T  + 85.5, where T is the temperature. Oxidation of Np(V) to Np(VI) in 3 M nitric acid at elevated temperatures (336, 342, 354, and 362 K) was observed using the optical glass cell. Oxidation of Np(V) was promoted by increasing the temperature and proceeded as a pseudo-first order reaction with respect to Np(V) concentration. The rate equation in the temperature range of 336–362 K was obtained as follows: − d[Np(V)] t /d t  = 2.2 × 10 7  exp [− 65 × 10 3 /( RT )][Np(V)] t , where R , T , and [Np(V)] t indicate the gas constant, temperature, and Np(V) concentration at time t , respectively.

The complex formation of NpO 2 + with carboxylates: oxalic acid (Ox), malonic acid (Mal) succinic acid (Suc); glutaric acid (Glu), methylmalonic acid (Memal), oxydiacetic acid (ODA), TDA (thiodiacetic acid) and citric acid (Cit) and aminocarboxylates: iminodiacetic acid (IDA), methyliminodiacetic acid (MIDA),nitrilotriacetic acid (NTA), 2-hydroxyethylethylenediamine triacetic acid (HEDTA),ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) was studied by solvent extraction in 6.60 m NaClO 4 at 25 ℃. The formation of only the 1:1 NpO 2 + complex was observed with the ligands under investigation. The complexation of NpO 2 + with Ox, IDA, ODA and TDA was also measured at variable temperatures ranging from 25–60 ℃ in 6.60 m NaClO 4 . Results show that the complexation of NpO 2 + with these ligands increases with increasing temperature. The enthalpy and entropy of complexation of NpO 2 + were calculated from the temperature dependence of the stability constants using the Van't Hoff equation. Additionally, the formation of an aqueous ternary complex of the form NpO 2 (X)(L) (X = EDTA or HEDTA; L = Ox or ODA) was identified for NpO 2 + at 25 ℃. Stabilities of these complexes are measured and discussed in term of their structures and basicities.

Aluminum co-precipitated with goethites (Al-FeOOHs) are ubiquitous within (sub)-surface environments, which are considered one of the most important sinks for radionuclide pollution management. Accordingly, various mole ratios Al-FeOOH were synthesized and characterized by XRD, FT-IR, TEM, specific surface area and potentiometric acid-base titration. According to XRD and TEM images, the morphology of Al-FeOOH was transformed from acicular-like goethite to cotton-like gibbsite with increasing Al content. The adsorption and sequential desorption of U(VI) on Al-FeOOHs were conducted by batch techniques under N 2 conditions. The batch adsorption results showed that the adsorption of U(VI) on Al-FeOOHs slightly increased at pH < 4.0, then the significant increase of U(VI) adsorption was observed at pH from 4.0 to 7.0, whereas the suppressed adsorption at pH > 8.0 was due to the electrostatic repulsion between negative charge surface and negative carbonato-complexes. The adsorption of U(VI) on Al-FeOOHs was independent of ionic strength at pH > 5.0, indicating that the inner-sphere surface complexation predominated their adsorption behaviors, whereas U(VI) adsorption on Al-FeOOH could be the outer-sphere surface/cation exchange reaction. The sequential extraction texts showed that the desorption of U(VI) from Al-FeOOHs decreased with increasing Al content. These findings highlighted the effect of Al content on the sequestration and immobilization of U(VI) onto Al-FeOOHs from (sub)-surface environments in pollution management.

In this paper, an attempt to explore the use of laser induced breakdown spectroscopy (LIBS) technique for determination of uranium in the vitrified simulated high level barium borosilicate waste glass matrix was made with a commercial portable LIBS system. The emission spectrum of the waste glass being very complex, detailed study was done for proper choice of the emission lines. Investigations were carried out to optimize the experimental parameters like laser energy and acquisition delay time for the analysis. Calibration curves were obtained for two emission lines of U in these glasses. Effect of Ar atmosphere was also studied and the signal intensity was found to be ∼5 times higher than in air atmosphere The emission lines used for normalization with vast difference in the upper energy level compared to the line of interest were found to give poor precision in air. In the Ar atmosphere, this effect was found to be much less significant and such emission lines can be used as an internal standard to achieve precise calibration curves. LIBS approach will be useful for real time determination of U in such samples, eliminating quantitative dissolution step required in many other analytical techniques like solution based ICP-MS/OES.

Ordered mesoporous U 3 O 8 has been synthesized by a nanocasting route using mesoporous silica (KIT-6 and SBA-15) as templates and characterized by using XRD, SEM and nitrogen adsorption/desorption techniques.

The aqueous solubility of BaSeO 4 (cr) was studied at 23 ± 2 ℃ as a function of Na 2 SeO 4 concentrations (0.0001 to 4.1 mol kg – 1 ) and equilibration periods (3 to 596 d). The equilibrium, approached from both the under- and over-saturation directions, in this system was reached rather rapidly (≤3 d). The SIT and Pitzer's ion-interaction models were used to interpret these data and the predictions based on both of these models agreed closely with the experimental data. Thermodynamic analyses of the data show that BaSeO 4 (cr) is the solubility-controlling phase for Na 2 SeO 4 concentrations <0.59 mol kg – 1 . The log  10 K 0 value for the BaSeO 4 (cr) solubility product (BaSeO 4 (cr) ⇌ Ba 2+ + SeO 4 2 – ) calculated by the SIT and Pitzer models were very similar (− 7.32 ± 0.07 with Pitzer and − 7.25 ± 0.11 with SIT). Although the BaSeO 4 (cr) solubility product and Ba concentrations as a function of Na 2 SeO 4 concentrations predicted by both the SIT and Pitzer models are similar, the models required different sets of fitting parameters. For examples, 1) interpretations using the SIT model required the inclusion of Ba(SeO 4 ) 2 2 – species with log  10 K 0  = 3.44 ± 0.12 for the reaction (Ba 2+ + 2SeO 4 2 –  ⇌ Ba(SeO 4 ) 2 2 – ), whereas these species are not needed for Pitzer model, and 2) at Na 2 SeO 4 concentrations >0.59 mol kg – 1 it was also possible to calculate the value for log  10 K 0 for the solubility product of a proposed double salt (Na 2 Ba(SeO 4 ) 2 (s) ⇌ 2Na + + Ba 2+ + 2SeO 4 2 – ) which for the SIT model is − (8.70 ± 0.29) whereas for the Pitzer model it is − (9.19 ± 0.19). The ion-interaction/ion-association parameters hitherto unavailable for both the SIT and Pitzer models required to fit these extensive data extending to as high ionic strengths as 12.3 mol kg – 1 were determined. The model developed in this study is consistent with all of the reliable literature data, which was also used to extend the model to barium concentrations as high as 0.22 mol kg – 1 and pH ranging from 1.4 to 13.8, in addition to selenium concentrations as high as 4.1 mol kg – 1 .

A novel solvent system containing chlorinated cobalt dicarbollide (CCD) in a diluent mixture containing 2-nitrophenyloctyl ether (NPOE) and n -dodecane was found to be highly efficient for the extraction of radio-cesium from acidic feed conditions. When PEG-400 (polyethylene glycol with average molecular weight of 400) was added to the solvent system, it was found to extract radio-strontium as well similar to that reported with the UNEX (Universal Extractant) solvent. The solvent system was found to be superior as compared to analogous solvent systems reported previously using CCD in either nitrobenzene or PTMS (phenyltrifluoromethyl sulphone, a fluorinated diluent). The present work deals with less toxic solvent formulation which can be used as an alternative to these hazardous/toxic chemicals for simultaneous recovery of Cs(I) and Sr(II) from acidic solutions. Batch co-current extraction data are also presented for the simultaneous recovery of Cs and Sr which indicated near quantitative extraction (>99.5%) of the metal ions in 4 and 3 stages, respectively. The reusability and radiolytic stability studies were also carried out which suggested highly encouraging results.

The sorption behaviour of niobium on kaolinite and illite minerals in sodium and calcium perchlorate solutions was evaluated with use of the mass distribution coefficient, R d , obtained in batch sorption experiments. Very high distribution coefficient values, about 100 m 3 /kg, were obtained for both minerals in the neutral pH range between 6 and 8. Values were somewhat lower at pH 5. In NaClO 4 solution, the sorption of niobium starts to decrease at pH higher than 8. This is in agreement with the increase, with pH, in the proportion of anionic niobate species, which are presumed to be low or non-sorbing. A similar decrease was not observed in Ca(ClO 4 ) 2 solution, probably owing to the influence of Ca on niobium solution speciation and surface species. The surface complexation model was applied to model the R d values. The model fitted well for the NaClO 4 solution but only at pH below 9 for the Ca(ClO 4 ) 2 solution. The discrepancy between the strong sorption of niobium in calcium-bearing solution at high pH and the calculated speciation is due in part to the non-inclusion of calcium niobate solution species and Ca-Nb compounds in the present NEA and other similar thermodynamic databases.

CdSe/CdS quantum dots (QD) were synthesized and bioconjugated with Sambucus nigra agglutinin (SNA) lectin (Lec). Mannose triflate and cysteamine molecules (MTC) were also utilized to prepare MTC-QDs and MTC-QDs-Lec probes as well as Lec bound QDs. Afterwards; potential use of these nanoparticles as radiolabeled fluorescence nano-probes for the cell imaging studies has been investigated. Biological activities of 125 I – , 125 I-MTC-QDs, MTC-QDs- Lec- 125 I, QDs-Lec- 125 I and Lec- 125 I were examined on various cancer cell lines such as Caco-2, MCF-7 and A-549 in terms of cell incorporation. QDs-Lec- 125 I exhibited the highest cell incorporation on whole cell lines. In addition, the QDs-Lec- 131 I, was used for in vivo imaging. The whole body distribution of the radiolabeled QDs on New Zealand rabbits and Balb C mice were examined by taking dynamic and static images. Radioactivity cleared from the kidneys and the bladder, while significant amount radioactivity was retained in the heart and liver within 24 h.