Volume 97, Issue 11

The reducing properties of humic substances (humic acid (HA) and fulvic acid (FA)) of varying functionality towards Np(V) have been studied under anaerobic conditions between pH 3.5 and pH 9.0 in batch experiments. For Np redox speciation in solution solvent extraction, NIR absorption spectroscopy and ultrafiltration were applied. The reduction rate varied with type of humic substances, solution pH, HA to Np concentration ratio, and equilibration time. In comparison to natural humic substances, synthetic HA with designed redox properties lead to a stronger reduction of Np(V) to Np(IV). The reducing capacities of humic substances towards Np(V) could be correlated to their phenolic/acidic OH group content, which includes both hydroquinone-like moieties and non-quinoid phenols. By applying a synthetic HA with blocked phenolic/acidic OH groups, the dominance of phenolic/acidic OH groups as the redox-active moieties of humic substances was verified. The Np(IV) formed in the course of the experiments is predominantly humic colloid-bound. Np(IV) oxo/hydroxide colloids, that might be formed in addition, are stabilized by adsorbed humic substances. The remaining Np(V) occurs as NpO 2 + ion or Np(V) humate depending on pH. The ability of synthetic HA to effectively maintain Np in the tetravalent state during humate complexation experiments could be shown.

An accurate, inexpensive and less laborious controlled adsorptive accumulation of uranium(VI)-arsenazo-III on a hanging mercury drop electrode (HMDE) has been developed for uranium(VI) determination. The method is based upon the collection of uranium(VI)-arsenazo-III complex at pH 5–6 at the HMDE and subsequent direct stripping measurement of the element in the nanomolar concentration level. The cathodic peak current ( i p,c ) of the adsorbed complex ions of uranium(VI) was measured at −0.35 V vs. Ag/AgCl reference electrode by differential pulse cathodic stripping voltammetry (DP-CSV), proceeded by an accumulation period of 150s2.5 in Britton–Robinson buffer of pH 5. The plot of the resulting i p,c vs. uranium(VI) concentration was linear in the range 2.1×10 −9 to 9.60×10 −7  mol L −1 uranium(VI) and tended to level off at above 9.6×10 −7  mol L −1 . The limits of detection and quantification of uranium(VI) were found to be 4.7×10 −10 and 1.5×10 −9  mol L −1 , respectively. A relative standard deviation of ±2.39% ( n =5) at 8.5×10 −7  mol L −1 uranium(VI) was obtained. The method was validated by comparing the results with that obtained by ICP–MS method with RSD less than ±3.3%. The method was applied successfully for the analysis of uranium in certified reference material (IAEA soil-7), and in phosphate fertilizers.

Sorption of radionuclides on MX-80 bentonite has been studied extensively because of its high sorption capacity and low penetrability. Herein, MX-80 bentonite was characterized by acid–base titration, XRD and FTIR in detail. The sorption of Eu(III) from aqueous solution to MX-80 bentonite was investigated as a function of contact time, solid content, ionic strength and pH under N 2 conditions. The experimental data was performed with the diffuse layer model (DLM) with the aid of FITEQL 3.1 code. The site densities are 2.52×10 −4  mol/g for [≡XOH] and 1.54×10 −4  mol/g for [≡YOH], and acidity constants as p K a are p K XO − =6.772, p K YOH 2 + =−1.68, and p K YO − =4.145. The sorption of Eu(III) on MX-80 bentonite consists of ≡YOEu 2+ species at low pH values and ≡XOEu(OH) + species at high pH values. The sorption isotherms were simulated by Langmuir, Freundlich and Dubini–Radushkevich (D–R) models, respectively, and the results indicated that Langmuir model fitted the sorption data better than the Langmuir and D–R models. XAFS technique was applied to characterize the local structural environment of the adsorbed Eu(III), and the results indicated that Eu(III) was bond to O atoms at a distance of about 2.43 Å as ≡Y/XO-Eu 2+ at low pH values.

For estimation of the activity of the long-lived 41 Ca isotope in seven concrete samples exposed to a varying neutron flux, 45 Ca activities in the samples were determined. Instead of total dissolution the concrete samples were treated with 8 M HCl and HNO 3 for partial dissolution of calcium. From the leachate, stable calcium was determined by AAS and 45 Ca activity with LSC after radiochemical separation while the total stable calcium in the concrete samples was determined by XRF. Calcium was separated from the leachates using cycles of precipitation and ion exchange. In addition to 45 Ca, seventeen γ-emitting radionuclides were detected directly in the concrete samples by γ-spectrometry. Ratios of 45 Ca activity concentrations to those of γ-emitting nuclides in the concrete samples with varying dose were more or less identical. Determination of 63 Ni activity in the concrete samples failed because activity levels were below the detection limit.

A polyethylene glycol based aqueous biphasic system has been studied for the extraction and separation of long-lived radionuclides, 152,154 Eu and 134 Cs. The effects of pH variation of the salt rich phases on the extraction properties of these radionuclides were studied and the experimental results were found to be supported by theoretical calculations. It has been observed that at neutral pH of sodium sulphite and at pH 11 of sodium phosphate salt rich phase 134 Cs could be separated from 152,154 Eu radionuclides. The exact phase forming concentrations of the salt rich phases were determined by measuring the volume of salt rich phase after equilibration.

The major and trace element contents in three iron-based ore reference materials were investigated using two methods of k 0 -based neutron activation analysis ( k 0 -NAA): instrumental ( k 0 -INAA) and radiochemical ( k 0 -RNAA). To avoid interferences from iron in the determination of elements present at trace levels, a method using radiochemical separation was applied ( k 0 -RNAA). Determination of the investigated elements by k 0 -RNAA in the aqueous phase from hydrochloric acid solution was performed after extraction of iron by diisopropyl ether (DIPE). It was found that Fe elimination lowered the limit of detection for some elements, thus enabling the determination of their content. The distribution of 39 elements (with intermediate/medium and long half-life radionuclides) present in the studied materials after Fe removal was investigated.

The k 0 -method has been developed for 10 MW Pakistan Research Reactor (PARR-1). It involved the full energy peak efficiency calibration of HPGe detector for different counting geometries and characterization of neutron flux at three irradiation channels. Neutron flux was characterized for thermal to epithermal flux ratio, epithermal flux shape factor, modified spectral index, Westcott´s g-factor and fast flux. The method was validated by analyzing IAEA-SL1 (lake sediment) and NIST-SRM-1572 (citrus leaves). All calculations were performed in Excel. The results revealed most of the elements with good accuracy.

The effects of reactants molar ratio, absorbed dose, and absorbed dose rate were studied on benzaldehyde–chlorobenzene system. Irradiation products were identified by GC/MS analysis and their quantities were determined by GC analysis. Study of the reactants molar ratio effect indicates important aspects of the radiation chemistry of this system. It was observed that the yields of the major products increase as absorbed dose increase. On the other hand, these yields decrease as dose rate increases. Which reflects that the major products are formed via inter-spur reactions i.e. in the bulk of the medium. The mechanisms of the formation of the products were suggested. Benzophenone is one of the main products of this system. Therefore, this study gives a spot of light on a novel radiation chemical route for benzophenone formation. The radiation chemical yield ( G -value) of benzophenone was determined at different dose rates.