Volume 98, Issue 1

The neutron capture cross section for the 139 La( n , γ) 140 La reaction at 0.0536 eV was measured for the first time using monochromatic neutrons coming from a Triple Axis Spectrometer at the TRIGA Mark-II reactor. The neutron beam intensity was determined by irradiating Au-monitor foil together La 2 O 3 target. The radioactivity of the products was determined via high resolution γ-ray spectrometry. The obtained cross section value is 6.13±0.3 b, which is 1.34% and 0.21% lower than that in the ENDF/B-VII and JENDL-3.3 data library, respectively.

The ion-exchange behavior of Zr and Hf in H 2 SO 4 and H 2 SO 4 /HClO 4 mixed solutions has been studied by a batch method using the carrier-free radiotracers 88 Zr and 175 Hf. It is found that the ion-exchange behavior of Zr and Hf is basically similar to each other, and that Zr and Hf are adsorbed on the cation-exchange resin as well as on an anion-exchange one in H 2 SO 4 . In 0.11−0.99 M H 2 SO 4 , the logarithmic values of distribution coefficients ( K d ) of Zr and Hf on the cation- and anion-exchange resins linearly decrease with log[H + ] eq and log[HSO 4 - ] eq , respectively, indicating that M 4+ and M(SO 4 ) 3 2- (M=Zr and Hf) are the predominant cationic and anionic species adsorbed on the resins, respectively. The K d values of Zr and Hf on the cation-exchange resin in H 2 SO 4 /HClO 4 at [H + ] eq =1.0 M also decrease with an increase of [HSO 4 - ] eq , reflecting successive formation of sulfate complexes. The slope analysis demonstrates that Zr and Hf are coordinated by one SO 4 2- ion at 0.011 and 0.020 M [HSO 4 - ] eq , respectively, and by two SO 4 2- ions at 0.079 and 0.20 M [HSO 4 - ] eq , respectively.

Successful geochemical modelling of the migration of radioactive materials, such as the transuranic elements, from nuclear waste repositories is dependent upon an understanding of their interaction with biogeopolymers such as humic acids, the most likely complexing agents in groundwaters. An established silica/humic acid composite has been evaluated as a model substrate for naturally occurring humate-coated minerals that are likely to be present in the vicinity of the repositories. The binding of Pu(IV), the highly likely oxidation station, by the silica/humic substrate was examined at pH 4 in the range 0.02 to 3.00 M NaClO 4 by the titration method. Pu(IV)-humate conditional stability constants have been evaluated from data obtained from these experiments by using non-linear regression of binding isotherms. The results have been interpreted in terms of complexes of 1:1 stoichiometry. Analysis of the complex formation dependency with ionic strength shows that the effect of ionic strength on humate complexation of Pu(IV) is not dramatically pronounced. The complexation constants are evaluated for the humate interaction with Pu 4+ and Pu(OH) 3 + at pH 4. The complexation constants are found, respectively, to be log HA β 0 (Pu 4+ )=16.6±0.3 and logβ 0 1.3.1 =46.6±2.3. The estimations through analogy from previous results are in agreement with these new experimental data.

Sorption of Eu(III) and Am(III) on attapulgite were studied as a function of pH, ionic strength, the liquid-to-solid ratio ( V / m ), and Eu(III) and Am(III) concentrations under ambient conditions using batch technique. The sorption of Eu(III) and Am(III) was quickly and ∼4 hours were enough to achieve the sorption equilibrium. The K ′ values were 6.57×10 6  g mg -1 h -1 for Eu(III) and 6.67×10 6  g mg -1 h -1 for Am(III), respectively; and q e values were 4.46×10 -7  mg/g for Eu(III) and 1.0×10 -6  mg/g for Am(III), respectively. Sorption of Eu(III) and Am(III) on attapulgite were strongly affected by pH values, and weakly dependent on ionic strength. Sorption of Eu(III) and Am(III) were mainly dominated by surface complexation, although ion exchange also contributed to Eu(III) and Am(III) sorption. In the presence of fulvic acid (FA), the sorption edge of Eu(III) and Am(III) was obviously shifted to lower pH. The results showed that the sorption of Eu(III) and Am(III) to attapulgite was enhanced significantly in the range of pH 0.5 to 6.

The extent and factors influencing sorption of plutonium (Pu) in shale media have been studied in batch-type experiments. The equilibrium time and isotherm of Pu sorption have been firstly determined. The effect of shale grain size, aqueous pH, water/solid ratio, co-existing ions (cations and anions) and temperature were studied as the factors likely to influence Pu sorption. The experimental variables included the following: grain sizes in five ranges, 0.12 to 0.15 mm, 0.15 to 0.18 mm, 0.18 to 0.25 mm, 0.25 to 0.38 mm, and 0.38 to 0.83 mm; solution pH values of 4, 6, 8, and 10; water/solid ratios of 10:0.25, 10:0.5, 10:0.75, and 10:1; temperatures of 20 °C, 40 °C, and 60 °C); and selected co-existing conventional cations including Na + , Fe + , Al 3+ , Ca 2+ , and K + and anions including SO 4 2- , CO 3 2- , NO 3 - , and Cl - in each case in solutions of the same total ionic strength. The experimental results demonstrate that the equilibrium time of Pu sorption is 9 d, that the sorption behavior of Pu in the solution is well described by the Freundlich sorption isotherm ( C s = k C eq N ), and that Pu is strongly sorbed on shale media. The extent of Pu sorption increased with decreasing grain size, apparently in response to the increase in specific surface area and total pore volume. The results also show that Pu sorption increases with increasing solution pH and with increasing water/solid ratio. The influence of co-existing anions on Pu sorption was much stronger, under the same conditions, than that of the cations; this was attributed to Pu complexation in solution, i.e. , the complexing apparently weakened the sorption of Pu on shale particles in the solution. Finally, the influence of varying temperature on Pu sorption is found to be less important than that of other factors, but should never be ignored.

The reduction of Np(VI) and Np(V) by Dihydroxyurea (DHU) was studied by spectrophotometry. The results show that the reduction of Np(VI) to Np(V) by DHU is particularly fast. The apparent rate constant is 1.86 s -1 at 4 °C as [HNO 3 ]=0.44 M and [DHU]=7.5×10 -2  M. While further reduction of Np(V) to Np(IV) is so slow that no Np(IV) is observed in 2 h. The reduction back-extraction behavior of Np(VI) in 30% tri-butyl phosphate/kerosene was firstly investigated under conditions of different temperature, different concentrations of DHU and HNO 3 and various phase contact time, respectively. The results show that 98% of Np(VI) in the organic phase can be stripped rapidly to the aqueous phase by DHU under the given experimental conditions. As the concentration of HNO 3 in the aqueous phase increases, the stripping efficiency decreases. While the stripping efficiency increases with the increase of the concentration of DHU. Simulating the 1B contactor of the PUREX process using DHU as the stripping agent, the SF U /Np equals to 183 under the given experimental conditions. It indicates that Np will follow with Pu in the U/Pu separation stage in the reprocessing of spent fuels.

A new Cs + adsorbent, activated carbon loaded ammonium molybdophosphate (AMP-AC) was prepared by repeating batch reaction of H 3 PO 4 and (NH 4 ) 6 Mo 7 O 24 . The surface of the activated carbon particles was coated with AMP microcrystals through a controlled crystallization process. The X-ray diffraction (XRD) analysis identified the AMP loaded on AC with the formula of (NH 4 ) 3 PO 4 (MoO 3 ) 12 ·4H 2 O. Scanning electron microscope images demonstrated that the fine AMP crystals was successfully immobilized and uniformly distributed on the porous carbon substrate. The effects of medium acidity, contact time, temperature and competing ions on Cs + uptake by the composite were investigated. The results show that the as-prepared adsorbent keeps high selectivity and adsorption capacity (∼0.75 mmol/g) for Cs + in acidic feed solution (0.1 M HNO 3 ), even in the presence of plentiful competing cations, Na + , Zn 2+ , Sr 2+ , Cr 3+ and La 3+ , while activated carbon itself has no specific affinity for Cs + . The adsorption process could be described by Langmuir adsorption equations. There is no significant difference (9.4%) on Cs + adsorption by the composite during system temperature changing from 298 to 348 K.

Species dependent studies of no-carrier-added (nca) mercury were carried out using radioanalytical technique coupled with two greener analytical methodologies. The adsorption of nca 195m,g Hg and 197m Hg radionuclides on chitosan biopolymer and cloud point extraction (CPE) was studied to develop environmentally sustainable speciation methodologies at ultra trace level. Species information was obtained by comparing the adsorption profile of nca radiomercury on chitosan biopolymer with the software code CHEAQS PRO. Results obtained from the adsorption study were validated by CPE technique using non ionic surfactant and mixed micelle. Both the experiments established that nca Hg existed as Hg(II). The experimental results support the presence of HgCl 2 species over the pH range 2–4, whereas Hg(OH) 2 is the main species over the pH range 6–8. Chitosan biopolymer and mixed micelle [Triton-X-114 and cetyltrimethylammonium bromide (CTAB)] constitute an efficient reagent for the preconcentration of ultra trace level mercury.

In this work instrumental neutron activation analysis (INAA) was applied to investigate a total of 30 samples of metallurgical raw materials (sinter, pellets, coke) and related finished products (pig iron, slag, blast-furnace flue dust) sampled from the same blast furnace discharge in the ironmaking process in the Integrated Iron and Steel Works of Galati (Romania). The transfer efficiencies of minor elements As, Cu, K, Na, V and W from raw materials — iron-bearing components (sinter, pellets) and coke — to pig iron and their losses in slag and flue dust have been determined and a discussion of the behaviour of each element during the blast furnace process was done.