Volatilization rate of free particles in a d.c. arc plasma,burning in air under atmospheric pressure

The volatilization rate (Q) of free particles (atom, ions and molecules) from the anode cavity into the discharge zone of d.c. arcs burning in air under atmospheric pressure was studied. In volatilization rate of particles of uranium, thorium and zirconium matrices was measured by two methods. The first is an indirect method, in which the residue in the anode cavity after the arcing period was chemically analysed (Q_ch and corrections for side losses of particles were applied. The second method is a direct one, in which aluminium wires were passed at uniform velocity through the plasma, in the vicinity of the anode. The wires coated by the free particles were analysed (Q_w) by neutron activation for uranium and spectrochemically for thorium and zirconium content. The two methods are compared.     

Electron density calculations derived from the energy balance equation in a d.c. arc plasma burning in air

The Elenbaas-Heller equation was used to calculate the spatial distribution of electron densities ($\text{n}$_e(itR.z)) in a d.c. arc plasma burning in air at atmospheric pressure. Uranium, thorium, zirconium and a number of rare-earths were introduced as oxides into the plasma. The temperature and the electric field gradients were measured axially and radially. Electron densities were then derived from the calculated mean electrical conductivity ($\text{σ}$_(R.z)). The resulting electron density values were compared with values derived from Saha's equation for ionization processes.     

Some analytical characteristics of an argon—nitrogen d.c. plasma arc for emission spectrometry

A low-power d.c. plasma arc device was used to estimate the analytical characteristics of an Ar—N₂ plasma arc compared to those of an argon plasma arc. When the flow rate of added nitrogen was varied from 0 to 1 l min^-1, the Cd I 228.802-nm line showed a maximum signal-to-background ratio at a nitrogen flow rate of approximately 0.3 1 min^-1 which corresponds to 0.23% of the total argon flow rate. Ratios of the signal intensities with the Ar—0.23%N₂ and argon plasma arcs are given for the spectral lines of seventeen elements. Relatively higher ratios were found for the atom lines of the group VIII through IIIA elements in the periodic table. Better precision and lower detection limits were attained for aluminium and cadmium with the Ar—0.23%N₂ plasma arc than with the argon plasma arc.     

Redistribution of uranium and thorium by soil/plant interaction in a recultivated mining area

During the recultivation of the uranium mining area of K?vágósz?l?s (Hungary), the tailings were covered with clay and loess soil layers having a thickness of 30 cm and 100 cm, respectively. In the loess covering layer, acacia (Robinia pseudoacacia), poplars (Populus × albus, Populus × canescens), oak (Quercus pubescens), silver tree (Eleagnus angustifolia) were planted between 1996 and 2004. In order to establish the extent of the uranium and thorium transport from the sludge to the leaves by uptake and translocation processes through roots with a length higher than 1.3 m results in a remarkable redistribution of these pollutants, a gray poplar tree, growing spontaneously in the last uncovered tailing, being selected as reference tree. The U and Th concentrations in the leaves of the above-mentioned trees, in the covering layers as well as in the original sludge were determined by inductively coupled plasma sector field mass spectrometry (ICP-SF-MS). Generally, the Th concentration of the soils was about 4 times higher than that of uranium, while uranium concentration was about 10-130 times higher than that of thorium in the leaf samples and its concentration ranged from 28 to 1045 ng g^− 1, the last value belonging to the poplar tree growing on the last uncovered tailing. In order to assume the mobility and bioavailability of uranium if the dry leaves fall down, the uranium species in the leaves of the poplar tree growing in the uncovered reservoir were determined applying ultrasound-assisted extraction with distilled water and ammonium acetate as well as high performance liquid chromatographic (HPLC)-ICP-SF-MS technique. About 20% of total uranium could be extracted in form of uranyl cations and a presumably negatively charged uranium compound. Estimations revealed that the annual increment of U in the soil surface layer due to the dead fallen leaves in case of the investigated gray poplar (Populus × canescens) is about 1.2%.     

Selective volatilisation of trace metals from refractory solids into an inductively coupled plasma

Feasibility studies have been carried out on the use of a graphite electrode assembly for the introduction of U₃O₈ solid samples into a continuously running low-powered argon inductively coupled plasma for the assay of trace metallic elements in uranium. The d.c. arc carrier distillation procedure has been adopted here for the selective volatilisation of analyte elements from the refractory matrix by injecting analyte vapours into the central zone of the plasma using Scribner-Mullin electrodes covered with a graphite lid having a central opening. The experimental parameters have been optimised for the direct determination of B, Be, Cd, Co, Cr, Cu, Fe, K, Li, Mn, Na, Ni and Pb in U₃O₈ powders. The analytical performance of the method has been checked by analysing spiked U₃O₈ samples and is seen to be comparable to or better than d.c. arc methods for these analytes. These results indicate that the carrier-distillation-ICP combination shows promise as a sensitive and precise method for analysis of trace metallic elements in a refractory matrix with a complex spectrum.     

Kinetic studies on the extraction of uranium(VI) from phosphoric acid medium by bulk liquid membrane containing di-2-ethylhexyl phosphoric acid

To go through the first stage of industrial solvent extraction process in order to recover uranium from phosphate rocks by liquid membrane techniques, as a simple model, the kinetics of facilitated transport of uranium(VI) from a dilute phosphoric acid medium into more concentrated phosphoric acid media as a receiving phase through a bulk liquid membrane containing di-2-ethylhexyl phosphoric acid as a carrier was studied. The influence of phosphoric acid concentration in the source and receiving phases, carrier concentration, type of solvent, stirring speed and temperature were investigated. The kinetic parameters (k _e, k _s, t _max, J _max) were calculated for the interface reactions assuming two consecutive, irreversible first-order reactions. The activation energy values were calculated as 29.40 and 19.51 kJ mol^?1 for extraction and stripping, respectively. The values of calculated activation energy indicated that both the extraction and stripping processes were controlled by mixed regime (both kinetic and diffusion). In addition, the influence of adding trioctyl-phosphine oxide into the membrane phase as a synergic agent on the transport kinetics was determined.     

Determination of arsenic in sediments by chloride formation and d.c. plasma arc emission spectrometry

The sediment sample is heated in an induction furnace in hydrogen chloride—argon; arsenic trichloride evolved is trapped and then swept into a d.c. plasma arc. Calcium sulfate addition enhances the signals and suppresses interference from organic matter. The limit of detection is 15 ng As; the relative standard deviation is 3.4% (n = 10) for 1.5μg As₂0₃.     

Assessment of the natural radioactivity using two techniques for the measurement of radionuclide concentration in building materials used in Japan

The specific activities of ²³⁸U, ²³²Th, and ⁴⁰K in selected building materials used in Japan were measured using a high-purity germanium detector. The uranium and thorium concentrations were determined from same samples using inductively coupled plasma mass spectrometry. There was a good agreement between the measurement of uranium and thorium with both methods (R ² = 0.94, and 0.97, respectively). Based on the specific activities, we have estimated some hazard indexes such as radium equivalent activities (Ra _eq), external hazard index (H _ex), internal hazard index (H _in), annual gonadal equivalent dose (AGED), internal alpha dose, mass exhalation rate and emanation coefficient of radon.     

Characteristics and electrode erosion rates of a D.C. plasma torch operating with TiCl4 plasma gas

A stable TiCl₄ plasma was produced using a simplified d.c. torch. The arc was struck between two concentric ring electrodes, d mm apart, and rotated using a magnetic coil. The electrode material was a new TaC composite. The arc was operated at 100 A for up to I h using plasma gas containing 0–30% TiCl₄. The voltage was 24–60 V, depending on the TiCl₄ concentration. The electrode erosion rate was of the order of 20g/C. It is shown that the erosion rate is a function of the aerodynamic drag of the are column.     

Synthesis, characterization, thermodynamic and kinetic investigations on uranium (VI) adsorption using organic-inorganic composites: Zirconyl-molybdopyrophosphate-tributyl phosphate

Zirconyl-molybdopyrophosphate-tributyl phosphate (ZMPP-TBP) was a novel organic-inorganic composite adsorbent prepared by co-precipitation method and used in the adsorption of uranium from aqueous solution in batch adsorption experiments. The as-obtained product was characterized using SEM, energy dispersive X-ray spectroscopy (EDX), XRD and BET-N₂ adsorption measurements. The study had been conducted to investigate the effects of solution pH, temperature, contact time, initial concentration and coexisting ions. A maximum removal of 99.31% was observed for an initial concentration 5 mg/L, at pH 6.0 and an adsorbent dose of 1.0 g/L. The isothermal data were fitted with both Langmuir and Freundlich equations, but the data fitted the former better than the latter. According to the evaluation using the Langmuir equation, the maximum adsorption capacity of uranium (VI) was 196.08 mg/g at 293 K and pH 6.0. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the kinetic data, and the pseudo-second-order kinetic model was better. The thermodynamic parameter ΔG was calculated, the negative ΔG values of uranium (VI) at different temperature showed that the adsorption process was spontaneous. The good reusability of ZMPP-TBP also indicated that the ZMPP-TBP was a very promising adsorbent for uranium adsorption from aqueous solution.     

Removal of uranium (VI) from nuclear effluents onto aluminophosphate and silicoaluminophosphate molecular sieves

Aluminophosphate and silicoaluminophosphate molecular sieves with both five (AFI) and eleven (AEL) type structures are synthesized by hydrothermal crystallization at 473 K, using tripropylamine and dipropylamine as a structure-directing template. The as-prepared AFI and AEL sieves are characterized and then assessed as sorbents for uranium (VI) from radioactive effluents. The sorption process is used to reduce the volumes of effluents and convert them into a stable solid waste. The batch experimental studies are carried out to evaluate the AEL and AFI structure effect on the removal of uranium. The AlPO₄-5, SAPO-5, AlPO₄-11 and SAPO-11 are applied to radioactive effluents with different activities obtained from Nuclear Research Center of Draria, Algeria. Important decontamination factor values are obtained for AFI sorbents. Thermodynamic parameters, namely, the enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) for each sorption process are calculated. The collected results indicated that sorbents are effective materials for the removal of uranium (VI) ions, the sorbent with AFI structure being a highly effective material for the removal of uranium (VI) ions from nuclear effluents.     

Transport velocities of particles in the plasma of a d.c. arc in air

Axial transport velocities of materials injected into a d.c. arc plasma by a liquid jet method have been determined on the assumption that the motion is influenced by diffusion (due to gradients in the number density of particles), axial electric field and convection. The velocities were measured using both high speed cinematography and cross-correlated photomultiplier signal techniques. In the interpretation of the measurements, with both methods use had to be made of the motion of the constant concentration boundary of the injected material in the frames of reference relative to both the arc electrodes and the point of maximum material density. Particular attention was given to convection effects.     

Ultrasonic Speed and Thermodynamic Parameters of Novel Epoxy Resin Solutions Based on Cardo Symmetric Double Schiff Bases at 308.15 K

The density, viscosity and ultrasonic speed (2?MHz) of several pure solvents: chloroform, THF, and 1,4-dioxane, along with epoxy resin solutions, have been investigated in order to understand the effect of solvents on molecular interactions in these systems at 308.15?K. Various thermodynamic parameters such as the ultrasonic speed (U), adiabatic compressibility (?? _?? ), Van der Waals constant (b), internal pressure (??), intermolecular free path length (L _f), and viscous relaxation time (??) have been determined and correlated with the concentration (C). Good-to-excellent correlations are observed between a given parameter and the concentration. Linear or nonlinear increases or decreases of thermodynamic parameters with concentration indicated the existence of strong molecular interactions in the solutions. Gibb??s energy of activation was found to be dependent on the concentration, nature of the solutes, and the solvents used.     

Determination of refractory elements in U(3)O(8) by carrier distillation emission spectrography

An emission spectrographic method using carrier distillation for the determination of the refractory impurities Ta, Hf, Nb, Th, and W in uranium is described. Different carriers, such as Ga₂O₃, AgCl, AgCl + LiF, and AgCl + NaF in various proportions, were investigated: a 1% NaF + 9% AgCl mixture as carrier at 10% of total charge arced was found to be the most suitable. Spectra were excited in a d.c. arc at 12 A and were photographed with 35-sec exposures. Palladium was used as an internal standard. The lowest limits of determination lie in the range 1–10 ppm for a 100-mg charge. The precision of the method is about 16% or better.     

Äquidensitometrie-eine Methode zur Beurteilung von Plasmen—XI: Untersuchung des Einflusses von NaCl und Ba(NO3)2 auf die Intensität von Linien und die Verteilung von Teilchen im Gleichstrombogenplasma der Silberstein-Methode

The influence of NaCl and Ba(NO₃)₂ on the intensities of atomic lines of Al, Sn and Be and on the axial particle distribution of these elements in the d.c. arc plasma was investigated. As the analytical method we used the procedure of Silberstein in which micro-amounts of solutions were added to the cathode and also to the anode. The time of evaporation, the temperature, the electron pressure, and the intensities of lines were investigated. We used the combination of spectral photography and photographic equidensitometry to derive particle distribution. The results of these investigations were: (1) NaCl and Ba(NO₃)₂ reduced the temperature of the plasma. The electron pressure was constant both in the presence of fairly large amounts of NaCl or Ba(NO₃)₂ and in the hotter arc without additive. (2) The enhancement of the intensities was best in presence of rather large amounts of Ba(NO₃)₂. (3) The maximum of the particle concentration was shifted, by additives from the cathode, towards the middle of the arc. We found a correlation between intensity and this shifting. In the arc with Ba(NO₃)₂ the most homogeneous plasma was obtained.     

HPLC Determination and Pharmacokinetic Study of Valdecoxib in Human Plasma

A sensitive, simple, and accurate high-performance liquid chromatographic method has been developed for determination of valdecoxib and the internal standard rofecoxib in human plasma. Protein was precipitated from plasma samples by addition of perchloric acid (HClO₄); the drug was then extracted with diethyl ether. Separation was performed on a Cosmosil C₁₈ column (150 mm × 4.6 mm i.d., 5 m particles) with ammonium acetate buffer-acetonitrile, 60:40 (v/v), containing 0.1% TEA, pH 6.5, as mobile phase. Detection and quantification were performed by UV-visible detection at 239 nm. Detection and quantification limits were 3 and 5 ng mL^–1, respectively. The linear concentration range for valdecoxib was 5–400 ng mL^–1. The validated RP HPLC method was used for determination of the pharmacokinetic data for the drug in humans.     

Arc plasma in air with calcium and fluorine—II. Effect of fluorine on radial distribution of calcium particles

The radial distributions of temperature, Ca and Ca⁺ spectral line intensities, and CaO and CaF bands intensities were determined in a d.c. arc. The results, when combined with the calculation of the plasma composition, made it possible to determine the radial distribution of the total calcium in the plasma without and with fluorine. The addition of F caused a higher gradient in the radial density distribution of Ca in the plasma. This might have been caused by chemical reactions between Ca and F which occurred at the arc periphery and probably induced a change in the mass transport parameters.     

Adsorption thermodynamic and desorption studies of U(VI) on modified silica gel (SiAPMS-HL)

In this study, the adsorption process was examined by various isotherm models Langmuir, Freundlich and Dubinin–Radushkevich and equilibrium data were successfully described by Langmuir model. Adsorption thermodynamics of uranium (VI) on modified silica gel (SiAPMS-HL) has been studied within a temperature range from 293 to 333 K and the thermodynamic parameters, such as equilibrium constant (K _D), standard free energy changes (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°), have been obtained. The desorption studies were conducted in batch system to investigate the kind, concentration and volume of the eluent.     

Sorption of uranium on lead hydroxyapatite

The uranium sorption from diluted aqueous solution onto lead hydroxyapatite was studied by using a batch-mode technique and the fluorimetric determination of uranium mass concentration. Partially crystallised lead hydroxyapatite [Pb₁₀(PO₄)₆(OH)₂] was obtained by direct precipitation and mild heating. This material presents very high specific surface, which is the key factor in the sorption of uranium from diluted solution. This material has a high ability to remove uranium (K _d,max from 5,661 to 18,833 ml/g, at 4 and 60 °C, respectively) in the chosen setup conditions (initial concentration of uranium 5 × 10^?6 M and pH 5.65).     

Detection of uranium in industrial and mines samples by microwave plasma torch mass spectrometry

Microwave plasma torch (MPT), traditionally used as the light source for atomic emission spectrophotometry, has been employed as the ambient ionization source for sensitive detection of uranium in various ground water samples with widely available ion trap mass spectrometer. In the full‐scan mass spectra obtained in the negative ion detection mode, uranium signal was featured by the uranyl nitrate complexes (e.g. [UO₂(NO₃)₃]^?), which yielded characteristic fragments in the tandem mass spectrometry experiments, allowing confident detection of trace uranium in water samples without sample pretreatment. Under the optimal experimental conditions, the calibration curves were linearly responded within the concentration levels ranged in 10–1000 µg·l^?1, with the limit of detection (LOD) of 31.03 ng·l^?1. The relative standard deviations (RSD) values were 2.1–5.8% for the given samples at 100 µg·l^?1. The newly established method has been applied to direct detection of uranium in practical mine water samples, providing reasonable recoveries 90.94–112.36% for all the samples tested. The analysis of a single sample was completed within 30 s, showing a promising potential of the method for sensitive detection of trace uranium with improved throughput. Copyright © 2016 John Wiley & Sons, Ltd.