Separation of thorium by anion-exchange chromatography in malic acid media

Summary Systematic studies on the anion-exchange behaviour of thorium in malic acid solution on Amberlite IRA-401 have been carried out. Acids such as HNO₃, HCl, H₂SO₄, HClO₄ and salts such as NH₄Cl, (NH₄)₂SO₄, NaClO₄, NaCl and NaNO₃ have been tested as eluants for thorium, their efficiency being evaluated in terms of their distribution coefficients. HNO₃ is the best eluent for thorium. Methods have been developed for the separation of thorium from several elements in malic acid media using selective adsorption or selective elution. The proposed method is applied to the analysis of thorium in monazite where HClO₄ is a better eluant than HNO₃. The method is simple and the accuracy about ±3%.     

Extraction chromatographic separation of thorium (IV) with tri-n-octylphosphine oxide (TOPO)

Thorium was extracted from a mixture of nitric acid and NaNO₃ of 0.01M each at pH 2.2 on a column of silica gel coated with TOPO. Thorium was separated from alkalis, alkaline earths, chromium, iron, cobalt, nickel, zinc, cadmium, mercury, lead, trivalent rare earths, platinum group metals, chloride, phosphate and acetate in binary mixtures by selective extraction of thorium. Thorium was separated from cerium (IV), zirconium, uranium and molybdenum by selective elution of thorium with 0.01M H₂SO₄. The method was extended for the analysis of thorium in monozite ore.     

Radiochemical separation of rhenium(VII) from tungsten(VI)

The absorption of rhenium(VII) and tungsten(VI) ions on Al₂O₃ from HCl, HClO₄, HNO₃, H₂SO₄, H₃PO₄, NaOH, NH₄OH, NaCl, NaF, and Na-tartarate solutions by batch equilibration, as well as by passage through a chromatographic column, has been studied. The results show that rhenium(VII) can be effectively separated from tungsten(VI) using any of the acid or salt solutions investigated. The experimental data allowed to develop a simple procedure for the radiochemical separation of rhenium isotopes from an irradiated WO₃ sample.     

Study on multistage anodization for high-modulus carbon fiber

Because of the strong chemical inertness of high-modulus carbon fiber (HMCF), the surface treatment of HMCF becomes less effective. In this work, multistage anodization method was applied to modify HMCF. NH₄HCO₃ and (NH₄)₂SO₄ were used as electrolytes to study the influence of electrolyte type on the oxidation effect in the multistage oxidation process. The HMCF was treated by multistage anodization in the following three ways: NH₄HCO₃ → NH₄HCO₃, (NH₄)₂SO₄ → (NH₄)₂SO₄, and NH₄HCO₃ → (NH₄)₂SO₄. In order to compare with the multistage anodization methods, HMCF was also anodized by NH₄HCO₃ and (NH₄)₂SO₄ using single anodization method, respectively. The treated HMCFs were characterized in detail using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM), and dynamic contact angle analysis, respectively. The results of XPS exhibited that HMCF modified by multistage anodization showed more functional groups on its surface. More sp2 hybridized bonds were converted into sp3 hybridized bonds after modification by multistage anodization, especially when (NH₄)₂SO₄ was used as electrolyte. The results of SEM/AFM indicated that HMCF modified by multistage showed a greater surface roughness. Interlaminar shear strength (ILSS) was used to observe the interfacial properties of HMCF between epoxy resin. The results showed that ILSS of untreated carbon fiber composite was only 27.3 MPa; it was increased to 71.8 and 78.6 MPa after treated with single anodization by NH₄HCO₃ and (NH₄)₂SO₄, respectively. After modification by multistage anodization, the ILSS increased in different degrees compared with single anodization method. Especially, the ILSS reached 93.1 MPa when the method of using NH₄HCO₃ followed by (NH₄)₂SO₄ was used to treat HMCF.     

Anion exchange studies of aluminium and iron(III) in malonate solutions: Separation from mixtures

Summary Systematic anion exchange studies of aluminium and iron(III) in malonate solutions were carried out. Aluminium and iron form negatively charged complexes with malonic acid at pH 4.5. The malonate complexes can be adsorbed on a column (1.4×20 cm) of Dowex 21K. Various reagents (hydrochloric, sulfuric and nitric acids; ammonium chloride, bromide, sulfate and nitrate; and sodium chloride and nitrate) were tested as eluants. The efficiency of the eluants was evaluated in terms of elution constant, volume distribution coefficient and peak elution volume. Methods were developed for the separation of aluminium or iron from a large number of elements by taking advantage of the fact that certain elements form weaker or stronger malonate complexes as compared to those of aluminium or iron. The method was applied to the analysis of aluminiumbased alloy.

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Zusammenfassung Systematische Untersuchungen des Verhaltens von Al(III) und Eisen(III) in Malonatlösungen gegenüber Anionenaustauschern wurden durchgeführt. Beide Metalle bilden mit Malonsäure negativ geladene Komplexe bei pH 4,5. Diese werden in einer Säule (1,4×20 cm) von Dowex 21K adsorbiert. Verschiedene Reagenzien (HCl, H₂SO₄, HNO₃; NH₄Cl, NH₄Br, (NH₄)₂SO₄, NH₄NO₃; NaCl und NaNO₃) wurden als Elutionsmittel geprüft. Deren Wirksamkeit wurde mit der Elutionskonstante, dem Verteilungskoeffizienten und der Peakhöhe des Elutionsvolumens gekennzeichnet. Trennungsmethoden für Al oder Fe von vielen anderen Elementen ergaben sich daraus, daß manche Elemente vergleichsweise schwächere bzw. stärkere Malonatkomplexe bilden. Die Methode wurde zur Analyse von Aluminiumlegierungen verwendet.

     

The effects of ammonium sulfate and sulfamic acid on the surface acidity of sulfated zirconia

In this work, sulfated zirconia (SZ) was prepared by a solvent-free method, ammonium sulfate ((NH₄)₂SO₄) and sulfamic acid (NH₂SO₃H) were as sulfur sources, respectively. The resulting catalysts were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), N₂ adsorption–desorption isotherms, inductively coupled plasma (ICP) and pyridine-FTIR. The characterization of the catalysts revealed that SZ prepared with (NH₄)₂SO₄ as sulfur source contained more Lewis acid sites and less Brønsted acid sites. The effects of sulfur sources on the catalytic activity of catalysts were studied. Catalytic testing showed that SZ prepared with (NH₄)₂SO₄ as sulfur source had a better catalytic performance for removing trace olefins from aromatics.     

Repeated use of a hydrophobic ligand-containing porous membrane for protein recovery

A porous hollow-fiber membrane containing a phenyl group as a hydrophobic ligand was prepared by radiation-induced graft polymerization of glycidyl methacrylate, followed by successive ring-opening reactions with phenol and water. Bovine serum albumin (BSA) was bound to the ligand during permeation of a BSA solution in phosphate buffer containing 2M (NH₄)₂SO₄ through the pores of the hollow fiber. Subsequent elution with an (NH₄)₂SO₄-free buffer exhibited an elution percentage of 82%. Repeated cycles of adsorption and elution caused the accumulation of BSA on the pore surface, resulting in a decrease in the binding capacity of BSA with increasing number of cycles. In contrast, by permeating 1 M NaOH after each elution, the binding capacity of BSA was maintained even after ten cycles. This alkaline regeneration was found to be effective in ensuring repeated use of the phenyl-group-containing porous membrane for recovery of proteins.     

Anion-exchange separation of Pt and Pd using perchloric and hydrochloric acid solutions

On Biorad Ag-1X8 anion-exchange resin (200–400 mesh), Pd and Pt may be separated from one another by elution with 0.2M HClO₄, and 5M HClO₄, respectively. If present, Au may be retained by making the elutriants 0.003M in HCl. Alternatively, reduction by H₂SO₃ enables elution of Pt²⁺ with 6M HCl before recovery of Pd²⁺ with 0.2M HClO₄·Ir⁴⁺ is reduced to Ir³⁺ by H₂SO₃ and may be eluted ahead of Pt²⁺ by 2M HCl.     

New strategies for trace analyses of ZrO2, SiC and Al2O3 ceramic powders

The progress possible in the analysis of refractory powders such as ZrO₂, SiC and Al₂O₃ by the use of new sample preparation, processing and introduction techniques elaborated for AAS, ICP-OES and ICP-MS with low and high mass resolution is demonstrated. For optimized sample preparation techniques based on dissolution of ZrO₂, e.g. fusion with (NH₄)₂SO₄, it is shown to what extent impurities present in (NH₄)₂SO₄ determine the detection limit. Hydraulic high pressure nebulization with and without matrix removal by complexing the impurities with dithiocarbamates (Cu, Co, Cr and Ni) or oxine (Fe, Mn and Mo) and fixing them on a C₁₈ solid phase for subsequent solid phase extraction coupled with flame atomic absorption was used to determine Fe, Cu, Cr, Mn, Ni, Co and Mo impurities in (NH₄)₂SO₄ in the 10–100 ng/g range. Further a method to synthesize (NH₄)₂SO₄ with higher purity than some commercially available high-purity (NH₄)₂SO₄ with respect to Fe, Cu, Cr and Mn using high-purity NH₃ and chlorosulphonic acid is shown. Reliable determinations of Fe and Al at the 100 μg/g level in ZrO₂ with ICP-OES with matrix removal as well as with ICP-MS without matrix removal are reported. For the direct analysis of Al₂O₃ powders, slurry nebulization ICP-MS sample introduction is shown to improve detection limits and to reduce sample preparation, if the leachable and non-leachable fractions are analyzed separately. For powders such as SiC, the matrix or solvents can cause spectral interferences. Matrix removal is shown to be useful to improve detection limits for the interfered elements. High resolution ICP-MS can be used to control the completeness of matrix removal techniques and to overcome limitations due to spectral interferences even in case of complex materials.     

Studies on the determination of trace elements in high-purity Sb using GFAAS and ICP-QMS

Trace element impurities in high-purity antimony were determined employing three different methods for the removal of matrix; on Dowex 50WX 8 by adsorption from 0.1 mol/L HF and elution with 4 mol/L HNO₃; on Chelex-100 resin (in NH₄ ⁺ form) Bi, Cd, Co, Cu, and Pb were separated in the presence of tartaric acid at a pH of 9.0 ± 0.1 with subsequent elution with 2 mol/L HCl; these determinations were carried out by GFAAS. The separation of trace impurities from Sb by volatilization of the matrix from H₂SO₄ and HBr medium was also investigated. ICP-MS was used for the determination in these cases. All the three procedures showed that the removal of the antimony matrix was nearly quantitative (> 99.99%). The recoveries of trace elements were found to be > 95%. The relative standard deviations were in the range 2–7%. Standard addition calibrations were used. The levels of process blanks indicate that with careful optimization, the volatilization procedure coupled with ICP-QMS can be used for trace impurity characterization of 6N+ Sb.     

A theoretical investigation on the structures of (NH3)·(H2SO4)·(H2O)0-14 clusters

Ternary clusters (NH₃)·(H₂SO₄)·(H₂O)_n have been widely studied. However, the structures and binding energies of relatively larger cluster (n > 6) remain unclear, which hinders the study of other interesting properties. Ternary clusters of (NH₃)·(H₂SO₄)·(H₂O)_n, n = 0-14, were investigated using MD simulations and quantum chemical calculations. For n = 1, a proton was transferred from H₂SO₄ to NH₃. For n = 10, both protons of H₂SO₄ were transferred to NH₃ and H₂O, respectively. The NH₄⁺ and HSO₄⁻ formed a contact ion-pair [NH₄⁺-HSO₄⁻] for n = 1-6 and a solvent separated ion-pair [NH₄⁺-H₂O-HSO₄⁻] for n = 7-9. Therefore, we observed two obvious transitions from neutral to single protonation (from H₂SO₄ to NH₃) to double protonation (from H₂SO₄ to NH₃ and H₂O) with increasing n. In general, the structures with single protonation and solvated ion-pair were higher in entropy than those with double protonation and contact ion-pair of single protonation and were thus preferred at higher temperature. As a result, the inversion between single and double protonated clusters was postponed until n = 12 according to the average binding Gibbs free energy at the normal condition. These results can serve as a good start point for studies of the other properties of these clusters and as a model for the solvation of the [H₂SO₄-NH₃] complex in bulk water.     

Separation of trace impurities of131I from99Mo obtained by extraction from fission products of uranium

The radioisotope⁹⁹Mo was separated from a mixture of²³⁵U fission products in the presence of Hg²⁺ by sorption on a chromatographic column filled with Al₂O₃ and elution with 1M NH₄OH. Trace impurities of¹³¹I in the molybdenum fraction were eliminated by selective sorption on silver iodide or by repeated sorption of⁹⁹Mo on Al₂O₃.     

Solid-state detection of gases by use of thin films based on pyrazole units, and morphological characterization of the films by AFM

Synthesis of a series of heterocyclic compounds based on pyrazole units is reported. The possibility of using these compounds, as solid-state thin layers deposited on quartz substrates, for optical recognition of hazardous pollutant gases was investigated. The gases SO₂, NO₂, CO, CH₄, and NH₃ were studied. Two of the ligand layers had reversible sensitivity toward SO₂, with good reaction time. The presence of CO, CH₄ NO₂, and NH₃ had no effect on the optical properties. Morphological characterization by use of AFM microscopy was also investigated.     

Separations of platinum metals by ion exchange : The separation of palladium from iridium

Palladium and iridium are separated by passing an ammoniacal solution of the chlorides over Amberlite IR-100 resin. Palladium is retained as Pd(NH₃)₄⁺² while iridium, as IrCl₆^-3, passes through the column quantitatively. Palladium is then removed from the column by elution with 1 M hydrochloric acid.     

Electrochemical oxidative modification of nanocarbon materials in aqueous electrolyte solutions

The effect exerted by electrochemical oxidative modification of carbon nanofibers and nanotubes by anodic and successive cathodic and anodic polarization in aqueous solutions of electrolytes H₂SO₄, CH₃COONH₄, HNO₃, (NH₄)₂SO₄, [H₂SO₄ + (NH₄)₂SO₄] on the structure and morphology of the fibers constituting the nanomaterials, on the composition of surface groups, on the stationary electrode potential of carbon nanofibers, and on properties of epoxy–carbon composites was studied. The results of the electrochemical modification were compared to the results of chemical modification of carbon nanofibers in a 6.0 M HNO₃ solution and of carbon nanotubes in a mixture of concentrated acids H₂SO₄ + HNO₃.     

Column chromatographic separation of thorium(IV) from ascorbic acid medium using poly-(dibenzo-18-crown-6)

A simple separation method has been developed for thorium(IV) using poly-(dibenzo-18-crown-6) and column chromatography. The separation was carried out from ascorbic acid medium. The adsorption of thorium(IV) was quantitative from 0.001-0.01M ascorbic acid. The elution of thorium(IV) was quantitative with 4.0-8.0M HCl, 3.0-6.0M HClO₄, 4.0-8.0M H₂SO₄ and 1.0-8.0M HBr. The capacity of poly-(dibenzo-18-crown-6) for thorium(IV) was found to be 1.379±0.01 m^.mol/g of crown polymer. Thorium(IV) was separated from a number of cations in binary as well as in multicomponent mixtures. The method was extended to the determination of thorium in monazite sand. It is possible to separate and determine 5 ppm of thorium(IV) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately ±2%).     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—I. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE, 4-AMINOBENZOIC ACID AND RELATED COMPOUNDS

The photodecomposition of sulfanilamide, 4-aminobenzoic acid and other related analogs has been studied with the aid of the spin trap 2-methyl-2-nitrosopropane. UV photolysis of an aqueous solution of sulfanilamide yielded the following radicals C˙₆H₄SO₂NH₂, C₆H₅SO_2˙, S˙O₂NH₂ and SO^-_#˙ (or SO^-_2dot;). Under the same conditions 4-aminobenzoic acid gave C˙₆H₄COOH. In addition both sulfanilamide and 4-aminobenzoic acid, but not 4-dimethylaminobenzoic acid, generated e^-_aq or hydrogen atoms during UV irradiation. The C₆H₄SO₂NH₂ radical was also produced by photolysis of 4-iodobenzenesul-fonamide and 4-nitrobenzenesulfonamide. The C₆H₄COOH radical was generated by photolysis of 4-nitrobenzoic acid and 4-iodobenzoic acid. Finally the C₆H₄NO₂ radical was formed during the irradiation of 4-nitroaniline, 1,4-dinitrobenzene and 4-iodonitrobenzene. The free radicals generated by sulfanilamide and 4-aminobenzoic acid may play an important role in the phototoxic and photoallergic responses elicited by these drugs in certain individuals.     

Studies on the determination of trace elements in high-purity Sb using GFAAS and ICP-QMS

Trace element impurities in high-purity antimony were determined employing three different methods for the removal of matrix; on Dowex 50WX 8 by adsorption from 0.1 mol/L HF and elution with 4 mol/L HNO₃; on Chelex-100 resin (in NH₄ ⁺ form) Bi, Cd, Co, Cu, and Pb were separated in the presence of tartaric acid at a pH of 9.0 ± 0.1 with subsequent elution with 2 mol/L HCl; these determinations were carried out by GFAAS. The separation of trace impurities from Sb by volatilization of the matrix from H₂SO₄ and HBr medium was also investigated. ICP-MS was used for the determination in these cases. All the three procedures showed that the removal of the antimony matrix was nearly quantitative (> 99.99%). The recoveries of trace elements were found to be > 95%. The relative standard deviations were in the range 2–7%. Standard addition calibrations were used. The levels of process blanks indicate that with careful optimization, the volatilization procedure coupled with ICP-QMS can be used for trace impurity characterization of 6N+ Sb. Received: 25 May 1998 / Revised: 23 September 1998 / Accepted: 26 September 1998     

Peak parking technique for the simultaneous determination of anions and cations

An ion chromatography method is described for the simultaneous determination of anions (Cl^–, NO₃^–, and SO₄^2–) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) using a single pump, a single eluent and a single detector. An anion-exchange column modified with chondroitin sulfate C facilitated the elution of the above three anions using 5 mM tartaric acid as the eluent in isocratic mode, whereas the same eluent facilitated the separation of the above five cations on a commercially-available cation-exchange column. The separation columns were connected in series via two six-port switching valves, so the required cation-exchange or anion-exchange separation could be carried out by selecting the appropriate positions for the switching valves. The separations were completed in 30 min.     

DSC studies of binary inorganic ammonium compound systems

The thermal behaviour of the binary systems HNH₂SO₃-NH₄NH₂SO₃ (I), HNH₂SO₃-(NH₄)₂SO₄ (II), HNH₂SO₃-NH₄HSO₄ (III), NH₄NH₂SO₃-(NH₄)₂SO₄ (IV), NH₄NH₂SO₃-NH₄HSO₄ (V), (NH₄)₂SO₄-NH₄HSO₄ (VI) was investigated with a Du Pont Thermal Analyzer supplied with a DSC module. The corresponding single compounds and freshly prepared (NH₄)₂S₂O₇ were examined under the same conditions in preliminary experiments. The ΔH _f values of HNH₂SO₃, NH₄NH₂SO₃, (NH₄)₂S₂O₇ and (NH₄)₂SO₄ · NH₄HSO₄ determined in the absence of air were 11.9, 16.8, 11.7 and 11.7 kJ/mole. Due to the moisture content of the atmosphere, an repeated heating in air the DSC curves showed more endothermic peaks than under air-free conditions. Exothermic additive reactions took place for binary systems (I) and (III), resulting in the formation of (NH₄SO₃)₂NH and (NH₄)₂S₂O₇, respectively, and for systems (II) and (VI), producing a new compound on melting.