Determination of rare-earth elements in a limestone geological standard reference material by ICP-MS following solvent extraction.

Rare-earth elements in a limestone geological standard (JLs-1) were determined by inductively coupled plasma mass spectroscopy (ICP-MS) using phosphoric acid 2-ethylhexyl ester solvent extraction, which had been established for seawater analysis. First, the limestone sample was divided into two fractions: acetic acid soluble (carbonate fraction) and insoluble (residue). A modification of the method was undertaken to achieve quantitative recovery. With this method most of the REEs in the carbonate fraction were quantitatively recovered, except for the heaviest three REEs (Tm, Tb and Lu). The reason for the poor recoveries of the three elements was investigated, but still remained unclear. The mass-spectroscopic interference of BaO with Eu made an accurate determination of both lighter REEs and Eu at the same time impossible. The precision of this method was better than 20%. The data adopted after analytical consideration were consistent with those previously reported.     

Selective extraction of the transplutonium and rare-earth elements by trioctylphosphine oxide

In the studies of nuclear reactions of heavy ions with heavy nuclei it is often necessary to determine the yields of TPE. Trioctylphosphine oxide (TOPO) has high selectivity with respect to trivalent TPE and rare earths. The possibility of using target or catcher materials as salting-out agents in the extraction of TPE with TOPO from solutions containing DTPA and lactic acid was investigated. The influence of the concentration of Pb, Bi, Cu, Ni, nitric acid and TOPO on the distribution coefficients was established. The advantages of application of the method for the extraction chromatographic separation of TPE and rare earths from the other elements produced in the interaction of ions with heavy elements are shown.     

Microviscosity of ions and salting-out in the extraction of rare-earth and transplutonium elements

A chemical procedure has been developed for the separation of U, Th, Fe, Sc, Na, Ta and Mo, which interfere in neutron activation analysis of the lanthanide elements in rocks. This methods in based on the extraction of interferents, before irradiation of the samples, using a solution of tetracycline in benzyl alcohol. The lanthanide elements remain in the aqueous phase and are coprecipitated with calcium oxlate or ferric hydroxide for irradiation and subsequent determination by gamma-ray spectrometry. Conditions for the separation of these interferences are examined determining the extraction curves. The chemical separation procedure was applied in the analysis of lanthanides in geological materials and the results showing the accuracy and the reproducibility of the method are presented. The sensitivity for all the lanthanides was determined.     

On sorption extraction of rare-earth elements in the nitric acid processing of Khibiny apatite concentrate

Fundamental aspects of the sorption recovery of rare-earth elements with a sulfocationite from a nitric-phosphoric acid solution formed as intermediate product in the nitric acid processing of Khibiny apatite concentrate were studied. It was confirmed that rare-earth elements can be effectively sorbed from a nitric-phosphoric acid solution without its preliminary neutralization. It was found that polyvalent metals can be sorbed from a nitric-phosphoric acid solution in the form of positively charged (possibly, single-charged) complexes containing nitrate and(or) phosphate ligands.     

Properties of PAN-TBP extraction chromatographic material

Three production routes of the preparation of a solid extractant based on tributylphosphate (TBP) embedded in the polyacrylonitrile matrix (PAN) have been studied. The method of direct PAN coagulation with TBP was found to be not viable due to the significant TBP solubility in the coagulation bath. The most suitable PAN-TBP solid extractant was prepared by the well-known impregnation method of ready-made neat PAN beads. The kinetics of uranium extraction from 3 mol L^?1 HNO₃, the effect of nitrate and nitric acids concentrations on the value of weight distribution coefficients D _g as well as the uranium “extraction isotherm” were determined for this material. Uranium extraction was rather fast, approximately 1 h was sufficient for the equilibrium achievement. Capacity for the uranium uptake, measured in batch experiments on PAN-TBP for 0.048 mol L^?1 of uranium in 3 mol L^?1 nitric acid, was found to be q = 0.363 mmol g^?1 (58 % of the theoretical capacity). It was concluded that PAN-TBP material behaves like TBP in liquid–liquid extraction. Extraction capacity determined in column experiments was lower (by about 23 %) than expected from the “extraction isotherm” due to the TBP leaching out of the column. The thus prepared material is therefore not very suitable for multicycle extraction and stripping and can be used once, particularly for the analytical purposes.     

Separation of transplutonium and rare-earth elements by extraction with HDEHP from DTPA solutions

The extraction behaviour of Am, Cm, Bk, Cf, Es, La, Ce, Pr, Pm, Sm, Eu, Gd, Ho, Yb and Lu in the system HDEHP—DTPA in lactic acid has been studied from the point of view of group separation of the transplutonium and rare-earth elements. Optimum separation conditions have been found on the basis of the results obtained. Some test separations of transplutonium elements from rare-earth fission products have been carried out in real solutions by extraction chromatography. It has been shown that this method can be used successfully for the analytical determination of transplutonium elements as well as for recovery of the latter from irradiated samples.     

Mechanical properties of interfacial films formed by lysozyme self-assembly at the air-water interface

We present the first characterization of the mechanical properties of lysozyme films formed by self-assembly at the air-water interface using the Cambridge interfacial tensiometer (CIT), an apparatus capable of subjecting protein films to a much higher level of extensional strain than traditional dilatational techniques. CIT analysis, which is insensitive to surface pressure, provides a direct measure of the extensional stress-strain behavior of an interfacial film without the need to assume a mechanical model (e.g., viscoelastic), and without requiring difficult-to-test assumptions regarding low-strain material linearity. This testing method has revealed that the bulk solution pH from which assembly of an interfacial lysozyme film occurs influences the mechanical properties of the film more significantly than is suggested by the observed differences in elastic moduli or surface pressure. We have also identified a previously undescribed pH dependency in the effect of solution ionic strength on the mechanical strength of the lysozyme films formed at the air-water interface. Increasing solution ionic strength was found to increase lysozyme film strength when assembly occurred at pH 7, but it caused a decrease in film strength at pH 11, close to the pI of lysozyme. This result is discussed in terms of the significant contribution made to protein film strength by both electrostatic interactions and the hydrophobic effect. Washout experiments to remove protein from the bulk phase have shown that a small percentage of the interfacially adsorbed lysozyme molecules are reversibly adsorbed. Finally, the washout tests have probed the role played by additional adsorption to the fresh interface formed by the application of a large strain to the lysozyme film and have suggested the movement of reversibly bound lysozyme molecules from a subinterfacial layer to the interface.     

Determination of rare-earth elements in environmental samples

A procedure is suggested of extraction-chromatographic pre-separation of REE's for the next activation determination. This method was applied for analyzing geological samples, underground and surface water, some technological materials.     

Properties and structure of interfacial layers formed by hydrophilic silica dispersions and palmitic acid

The properties and structure of different types of interfacial layers obtained from aqueous dispersions of nanometric silica and palmitic acid (PA) have been studied and characterized by different diagnostics and measurements. The investigations concern PA monolayers spread on the silica dispersions, dispersions in contact with PA solutions in oil and silica dispersions containing PA, aiming at elucidating the role of the PA interaction with the particles and investigating the surface-activity of the originated silica-PA complexes. Drop shape tensiometry was utilized to measure the dynamic surface and interfacial tension while a Langmuir trough apparatus was used to obtain compression isotherms of the spread PA layers and to measure the dilational viscoelasticity according to the oscillating barrier method. Brewster angle microscopy and ellipsometry were utilized to investigate the lateral and vertical structure of the interfacial layers. From this multifold approach emerges a complex picture of the features of these interfacial layers that can be rationalized on the basis of the adsorption of PA on the particle surface. The results evidence a threshold in PA adsorption above which particles change from hydrophilic to partially hydrophobic, promoting their incorporation into the interfacial layer.     

Effect of ionic liquids on the extraction of rare-earth elements by bidentate neutral organophosphorus compounds from chloride solutions

The partition of microamounts of lanthanide chlorides (Ln = La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) between aqueous HCl and organic solutions of tetraphenylmethylenediphosphine dioxide, diphenyl(diethylcarbamoylmethyl)phosphine oxide, and dibutyl(diethylcarbamoylmethyl)phosphine oxide was studied in the presence of ionic liquids (ILs): 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The stoichiometry of extracted complexes was determined. The effect of the aqueous HCl concentration, the nature of the extractant, and the organic diluent on the efficiency of lanthanide extraction was studied.     

Effect of external factors on the increase in the extraction rate in a vibration treatment on the dynamic interfacial layer

Vibration treatment of a dynamic interfacial layer in the extraction system constituted by an aqueous solution of a salt of a rare-earth element and a solution of di-(2-ethylhexyl)phosphoric acid in heptane (toluene) results in an increase in the process rate. This increase is characterized by an acceleration coefficient defined as the ratio between the lanthanide concentrations in the organic phase after equal intervals of time in systems with and without vibrations. It is shown that the acceleration coefficient depends on the concentration of the extractive agent, initial concentration of an element being extracted, solution pH, and phase contact duration. The observed behavior is explained in terms of the process model suggested by the authors. According to this model, the effect depends on the relative contributions made by a number of interfacial phenomena accompanying the extraction of a lanthanide with solutions of di-(2-ethylhexyl)phosphoric acid in diluents and, in particular, by the spontaneous surface convection and structuring in the interfacial layer.     

Thermodynamics of the formation of oxosulfides of rare-earth elements

The enthalpies of solution of several oxosulfides of rare-earth elements and the high-temperature enthalpies of oxosulfides and oxosulfates of lanthanum and yttrium were measured using solution calorimetry and high-temperature microcalorimetry techniques. Standard enthalpies of formation and some thermodynamic properties of oxosulfides and oxosulfates were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2 pp. 294–297, February, 1997.     

Thermophysical properties of interfacial layer in nanofluids

Although recent experiments have revealed that nanofluids have superior thermal conductivities to base fluids, the inherent physics are not fully understood. In this study, an interfacial layer, competing with Brownian motion as a corresponding mechanism, is conceptually connected with the surface-charge-induced electrical double layer. By applying colloidal science, the first explicit equations for the thickness and thermal conductivity of the layer are obtained. A fractal model including the new concept of the layer is developed. The model predictions are compared with experimental data for effects of pH, temperature, volume fraction, and primary particle size of CuO-water nanofluids.