Decontamination treatment of uranium in tricarbonated solutions

It has been established that the coexistence of chemical species structurally different from cerium, is a direct consequence of the time taken for its preparation. Its practical applications, within the scope of purifying uranium, may constitute the most important technological aspect in the process of ionic exchange, to separate¹⁴¹Ce from uranium.     

Nuclear interferences of uranium and thorium in a reactor neutron activation analysis determination of cerium using the radionuclides141Ce and143Ce

The interference contributions of uranium and thorium to the determination of cerium based on radionuclides¹⁴¹Ce and¹⁴³Ce produced by irradiation in a reactor core was determined. The values of the interference contributions for¹⁴¹Ce were 0.28±0.01 g Ce/g U and /2.01±0.05/x10^–3 g Ce/g Th, and for¹⁴³Ce 1.33±0.03 g Ce/g U and /9.0±0.2/x10^–3 g Ce/g Th.     

Positively charged colloidal species in aqueous anionic surfactant solutions

The solution chemistry of fatty acids was reassessed. Transmittance measurements confirmed the existence of a colloidal precipitate in accordance with the constructed thermodynamic diagram. The electrokinetic potential of the precipitate and its dependence on pH was examined and an i.e.p. was found around pH 3. It results then that positively charged species exist below pH 3 in the broad range of fatty acid aqueous solution concentrations.     

Determination of low uranium concentration in carbonate-bicarbonate solutions by X-ray fluorescence

A method has been developed for the direct determination of uranium in carbonate solutions by X-ray fluorescence. Uranium, in the concentration range 0.2–50 ppm, is first absorbed as the carbonate complex on an anion exchange resin and then determined by X-ray fluorescence. A sensitivity corresponding to 20 ppb in 250 ml solution and a precision of ±6.5% was obtained. The sensitivity was 100-fold greater than that obtained by the direct determination in solution by X-ray fluorescence.     

Critical aggregation concentration in mixed solutions of anionic polyelectrolytes and cationic surfactants

We have examined the polymer/surfactant interaction in mixed aqueous solutions of cationic surfactants and anionic polyelectrolytes combining various techniques: tensiometry, potentiometry with surfactant-selective electrodes, and viscosimetry. We have investigated the role of varying polymer charge density, polymer concentration, surfactant chain length, polymer backbone rigidity, and molecular weight on the critical aggregation concentration (Cac) of mixed polymer/surfactant systems. The Cac of these systems, estimated from tensiometry and potentiometry, is found to be in close agreement. Different Cac variations with polymer charge density and surfactant chain length were observed with polymers having persistence lengths either smaller or larger than surfactant micelle size, which might reflect a different type of molecular organization in the polymer/surfactant complexes. The surfactant concentration at which the viscosity starts to decrease sharply is different from the Cac and probably reflects the polymer chain shrinkage due to surfactant binding.     

Verification of the long term stability of uranium reference solutions of low concentration

The evolution of trace concentrations (sub ng·g^–1) of uranium in aqueous reference solutions was followed over time by isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). Blank levels and detection limits needed to be determined prior to the actual investigations. Accuracy and precision of the method were determined on the basis of results obtained for uranium reference materials under similar experimental conditions. Reference solutions, certified for uranium concentration were prepared on gravimetrical basis. Analyses were performed over a period of 2 years. Taking into account the accuracy and the precision achieved, no significant change of the concentration is observed with time. Therefore, the mid and long term stability of the concentration of such reference materials was successfully demonstrated.     

Hydrous oxides in the concentration and removal of fission products from alkaline solutions of uranium

A great variety in retention properties occurs as a result of different methods of preparation of the sorbents. Specific surfaces and porosities, which are mostly connected with the sorption activities, may vary widely. The activation of Al₂O₃, SnO₂ and silica gel, to produce highly active sorbents occurs only if the oxide is contacted with acid immediately after thermal treatment. The efficiency of the separation scheme has been tested using uranium and fission products under static conditions from strongly alkaline aqueous solutions.     

Influence of the structure of amphiphilic anions on the Krafft temperature of micellar solutions of anionic surfactants

The influence of the structure of surfactants on the Krafft temperature T _k was studied for aqueous solutions of anionic surfactants containing the sulfate and sulfonate head groups, the hydrophilic (H) and lipophilic (L) fragments in amphiphilic anions, and various polar and C₈—C₁₈ hydrocarbon groups. The best statistical quality was obtained for the model with separate account of the effect of the H and L structural fragments on the T _k value.     

Complexation studies of iodides of trivalent uranium and lanthanides (Ce and Nd) with 2,2'-bipyridine in anhydrous pyridine solutions

In anhydrous pyridine solution at 294 K, U(III) and Ce(III) triiodides were found to form both 1:1 (ML) and 1:2 (ML(2)) complexes with bipyridine (bipy = L) while Nd(III) triodide formed only a 1:2 complex. The 1:3 (ML(3)) complexes were identified at low temperature with a large excess of L. Conductometry measurements showed for U(III) a large increase in the conductivity when increasing the molar ratio L:U. The complex UL(2) was found to be a 1:1 electrolyte and the species UI(2)(+) was more reactive toward L in comparison with UI(3). For Ce(III) and Nd(III), MI(2)(+) and MI(3) present about the same affinity for L. The stability of the complexes is limited, and U(III) possesses a slightly higher affinity for bipy than the trivalent lanthanides. Interestingly, a preference for the formation of ML(2) complex was shown for all the studied M(III) ions. The driving force for complex formation was always the enthalpy, and, surprisingly for a bidendate ligand (bipy), no favorable entropy contribution to complex formation was observed. The X-ray crystal structures of [CeI(3)(bipy)(2)(py)](4).5py.bipy and UI(3)(bipy)(2)(py).2py were determined. The structures of the molecules MI(3)(bipy)(2)(py) are almost identical for U and Ce. The mean M(III)-N(bipy) bond distances are equal to 2.67(3) A for Ce(III) and 2.65(4) A for U(III). The slightly smaller M(III)-N(bipy) distances observed for U(III) would reflect a slightly more important covalent character of the U(III)-N(bipy) bonds, in agreement with the slightly better affinity of U(III) than Ce(III) or Nd(III) toward bipy observed in solution and with the fact that the enthalpy is the driving force for complex formation.     

At the surface of non-aqueous solutions of anionic surfactants

We have determined the concentration–depth profiles of sodium dodecyl sulfate (SDS) and cesium dodecyl sulfate (CDS) in their pure solutions, by which the surface structure of those solutions are characterized. With the identical bulk concentration, more Cs ions than sodium ions are present at the topmost layer and they penetrate deeper than sodium ions into the layer formed by the heads of the anions, shielding the electrostatic repulsion among those negatively charged anions more efficiently. The distributions of the charge at the surface of each studied solution were determined from those concentration–depth profiles of surfactant ions. The charge density varies more drastically in SDS solutions than in CDS solutions when their bulk concentrations are identical. These charge density profiles exhibit a visible and direct insight into the electric charge structure of the surface of ionic surfactant solutions. The experimental findings might be helpful to the investigations on the surface structures of aqueous solutions of ionic surfactants.     

Activity concentration of uranium in groundwater from uranium mineralized areas and its neighborhood

Uranium mineralization in parts of northeastern Nigeria necessitated its exploration during early eighties by the Nigeria Uranium Mining Company (NUMCO) which was later abandoned. During their course of decay, uranium isotopes pass through radioactive decay stage and eventually into stable isotope of lead. The course of concern for soluble uranium in groundwater especially from the mineralized areas include ionizing radiation, chemical toxicity and reproductive defects for which ingested uranium has been implicated to have caused. This study is aimed at assessing the levels of concentration of uranium in groundwater to ascertain its compliance with the World Health Organization’s (WHO) and the United State Environmental Protection Agency’s (EPA) guideline for uranium in drinking water. Thirty five groundwater samples were collected using EPA’s groundwater sampling protocol and analyzed at the Department of Geology, University of Cape Town using an Inductively Coupled Plasma Mass Spectrometric (ICP-MS) technique. Significant finding of this work was that there is radiological contamination of groundwater in the area. There is also an indication that the extent of radiological contamination is not much within the mineralized zones, therefore, there is likelihood that groundwater has acted as a medium of transporting and enhancing uranium in groundwater in an environment away from that of origin. About 5.7 % of the samples studied had uranium concentration above WHO and EPA’s maximum contaminant level of 30 μg/L which is a major concern for inhabitants of the area. It was also apparent that radiological contamination at the southwestern part of the study area extends into the adjacent sheet (sheet 152). Uranium concentration above set standards in those areas might have originated from rocks around established mineralized zones but was transported to those contaminated areas by groundwater that leaches across the host rock and subsequently mobilizing soluble uranium along with it.     

Extraction preconcentration with anionic surfactants in acidic solutions

Extraction preconcentration with anionic surfactants in acidic solutions on the basis of the cloud point was studied. Advantages and disadvantages of this method were considered. Conditions of the phase separation of some anionic surfactants (sodium decyl sulfate, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate) in acidic solutions were studied. With the example of pyrene and its derivatives, it was demonstrated that these surfactants can be used for extraction preconcentration. Analytical characteristics of the determination of pyrene and its derivatives in model aqueous solutions by the fluorimetric method in combination with extraction preconcentration with sodium dodecyl sulfate were obtained     

Physicochemical properties of anionic triple-chain surfactants in alkaline solutions

A series of novel gemini cationic surfactants alkanediyl-alpha,omega-bis (hydroxyethylmethylhexadecylammonium bromide) with polymethylene spacer chain length of 4, 6, 8, and 10 carbon atoms was synthesized and characterized. Critical micellar concentrations of the gemini surfactants in aqueous solutions as determined by the surface tension and conductance measurements were observed to be in the range 1.39-3.63 microM. The critical micellar concentration was observed to increase initially with spacer length up to 6 methylene groups and to decrease thereafter with the increase in spacer length. The micellar microstructure in aqueous solutions examined through small angle neutron scattering (SANS) revealed that the extent of aggregation growth and variation in shapes of micelles strongly depend on head group polarity, spacer chain length, and temperature. The propensity to micellar growth with spacer chain length 4 was found to be much higher than with the longer spacer lengths. The fractional charge on the micelle increases with increased spacer chain length and temperature.     

Interaction between anionic surfactants and oil dye in the aqueous solutions

The interactions between 4-phenylazo-1-naphthylamine and 6 sodium alkyl sulfates have been studied by a spectrophotometer. At lower concentrations than each CMC, 3 surfactants (octyl, decyl and dodecyl sulfate) and the dye formed hydrophobic complexes with a binding molar ratio of 11, while the others (tetradecyl, hexadecyl, and octadecyl sulfate) and the dye made 21 complexes. The wavelength of the maximal absorption is 440 nm in the former, and 520 nm in the latter. In the neighborhood of each CMC region, thermochromism occurred in every surfactant solution. The temperature at which the maximal absorption moved from 520 nm to 440 nm increased with an increase in the number of carbon atoms in the surfactant molecules. At higher concentrations than each CMC, in the case of the octyl and decyl sulfate, the maximal absorption occurred at the 440 nm band above room temperature; in the case of the dodecyl, tetradecyl, and hexadecyl sulfates, the maximal absorption occurred at the 520 nm band, regardless of temperature. In the case of octadecyl sulfate, the maximal absorption moved from 610 nm to 520 nm with increase in temperature. It is found that the protonation equilibrium of the dye is dependent on the micellar structure through the differences in the alkyl chain lengths of the surfactants, and the differences in interaction with surfactant crystals.     

铀在地下水中的化学形态模拟研究

用EQ3/6程序模拟研究了某场址地下水中U的化学形态,并模拟了在不同的pH、温度T、总碳?∑C?浓度、U的浓度ρ(UO22 )等条件下U的化学形态,分析了其化学形态变化规律。结果表明,在该场址地下水中,铀主要以碳酸铀酰络合物形式存在。pH、T、∑C浓度变化对铀的化学形态影响较大。     

Tautomeric equilibria of 5-fluorouracil anionic species in water

It has long been postulated that rare tautomeric or ionized forms of nucleic acid bases may play a role in mispair formation. Therefore, ab initio quantum chemical investigations on the tautomeric equilibrium in 5-fluorouracil (5FU) and its anions (deprotonated from N1, AN1, and from N3, AN3) and their tautomeric forms in water were performed. The effect of the water as solvent was introduced using solute-solvent clusters (four water molecules). The influence of the water molecules on the tautomeric reactions between different forms was considered by multiple proton transfer mechanisms. We show that when a water dimer is located in the reaction site between the two pairs of N-H and C═O groups, the assistive effect of the water molecules is strengthened. All calculations of the solute-water complexes were carried out at an MP2 level of theory and supplemented with correction for higher order correlation terms at CCSD(T) level, using the 6-31+G(d,p) basis set. The ab initio calculated frequencies and Raman intensities of 5FU and its anions AN1, AN3, and dianion are in good agreement with the experimental Raman frequencies in aqueous solution at different pH. In order to establish the pH-induced structural transformation in the molecule of 5FU, further (1)H, (19)F, and (13)C NMR spectra in water solution for pH = 6.9-13.8 were acquired and the chemical shift alterations were determined as a function of pH. On the basis of NMR spectroscopic data obtained for 5FU in aqueous solution at alkaline pH, we suggest the existence of a mixture of the anionic tautomeric forms predicted by our theoretical calculations.     

Association of chitosan in the presence of an anionic surfactant in aqueous-glycerol solutions

Russian Journal of Applied Chemistry - The effect of additions of sodium tetradecyl sulfate as an anionic surfactant on the association of chitosan macromolecules in aqueous-glycerol solutions was...     

Voltamperometric determination of uranium and plutonium in alkaline solutions

The simultaneous determination of U(VI), Pu(VI), Pu(V) in 0.5–4.0 M NaOH has been elaborated by means of classical and differential pulse voltamperometry. U(VI) is determined with a dropping mercury electrode (DME) at the half-wave potential of E_1/2=–0.89 V vs. Ag/AgCl reference electrode due to reduction to U(V). The limiting current or peak heights are proportional to uranium(VI) concentration in the range of 1.3.10^–7–3·10^–4 M U(VI). Deviation from proportionality is observed for higher concentrations due to polymerization of uranates. Pu(VI) and Pu(V) are determined with a platinum rotating electrode at E_1/2=–0.02 V due to the reaction Pu(VI)+e^–»Pu(V) and with DME at E_1/2=–1.1 V due to the reduction to Pu(III). The limiting currents of both Pu(VI) and Pu(V) are proportional to their concentrations in the range of 4·10^–6–1.2·10^–3 M Pu. The determination of U(VI), Pu(VI), Pu(V) is not interfered by the presence of the following salts: 2M NaNO₃, 2M NaNO₂, 1.5M NaAlO₂, 0.5M NaF and ions of Mo(VI), W(VI), V(V), Cu(II). The presence of CrO ₄ ^2– and FeO ₂ ^– ions disturbs the determination of U(VI) in 1–4M NaOH, however, contribution of the reaction Fe(III)+e^–»Fe(II) to uranium reduction peak can be calculated from the height of the second peak Fe(II)+2 e^–»Fe(0).     

Micellization in solutions of anionic surfactants with two ionogenic groups

Conductometry is employed to measure the critical micellization concentrations of homologous sodium monoalkyl sulfosuccinates with double-charged surface-active anions and alkyl radicals R containing 10–14 carbon atoms (ROOCCH₂CH(SO₃Na)COONa). The degrees of counterion binding with micelles and the Gibbs energy ΔG ^m of micellization are calculated. The incorporation of an additional ionogenic group into a surfactant molecule somewhat decreases ΔG ^m. For the examined series of surfactants, the increment of ΔG ^m due to one methylene group is ?4.44 kJ/mol.