Carrier distillation method

Radwan Z., Strzyzewska B. and Minczewski J. (1963) Spectrographic determination of trace amounts of rare earths. II. Analysis of lanthanum, yttrium, europium, praesodymium neodymium and samarium by the carrier distillation method, Appl Spectrosc 17 60-62. 

Due to the large number of lines, spectral analysis of trace impurities in a tungsten matrix is only possible in a reducing atmosphere after conversion into tungsten carbide and when using a carrier distillation method. 

Statistical Results from the Analysis Methods. Continuous time vs. relative intensity curves were made spectrometrically for each of 11 elements in seven different coal ash samples. The results showed that peak intensities for all the elements in each sample were generally reached between 50 and 60 sec after initiation of the arc. This behavior helps to explain why using iron as the variable internal standard was successful for the normally wide range of volatilities represented. The large dilution factor involved or a possible carrier distillation effect of barium nitrate might explain the almost complete absence of fractional volatilization. 

Impurities in zirconium and zirconium alloys and compounds are often determined by emission spectroscopy. Both carrier distillation techniques and poiat-to-plane methods are available (91,92). Several metaUic impurities can be determined instantaneously by this method. Atomic absorption analysis has been used for iron, chromium, tin, copper, nickel, and magnesium (93). The interstitial gases, hydrogen, nitrogen, and oxygen are most often determiaed by chromatography (81). Procedures for carbon, chloride, fluoride, phosphorus, siUcon, sulfur, titanium, and uranium in zirconium are given in the hteiatuie (81,94—96). 

Distillation Methods Distillation methods have been widely used in iodine isotope production. Since iodine may be converted to a volatile form (I2), either wet distillation or dry distillation has been employed. A general distillation procedure for carrier-free purification has been reported earlier by Kahn and Freedman (1954). In a wet distillation method (IAEA, 1966), irradiated Te metal is dissolved in a chromic acid-H2S04 mixture. After complete dissolution, the iodate (IO3) formed is reduced to elemental iodine (I2) with oxalic acid and then distilled off from the solution. The distillate is trapped in alkaline sulfite solution. This solution is then purified by an oxidation-reduction cycle and finally redistilled into dilute alkaline solution. In another wet distillation method, irradiated Te02 is dissolved in NaOH and the sodium tellurite is oxidized with H2O2 in the presence of a catalyst, sodium molybdate. The mixture is then acidified with H2SO4 and the iodine is distilled off and trapped in ice-cold water. 

In the distillation method, iodide carrier was added to the sample, an oxidation-reduction cycle was carried out, and molecular iodine was distilled into carbon tetrachloride. (In the oxidation-reduction cycle, iodide was oxidized to iodate by permanganate in sulfuric acid solution and any elemental bromine and chlorine activities formed were distilled off.) Iodine was back-extracted as iodide into water from the carbon tetrachloride by means of acid sulfite and silver iodide was precipitated. 

In contrast to other organothallium(I) compounds, cyclopentadienyl-thallium(I) is a remarkably stable compound. Samples can be stored in sealed bottles for months without appreciable decomposition occurring it is unaffected by water and dilute alkali and it is only slowly oxidized by air at room temperature. Cyclopentadienyltballium(I) was first prepared by Meister in 1956 by addition of freshly distilled cyclopentadiene to a suspension of thallium(I) sulfate in dilute potassium hydroxide solution 101, 102). A number of variations of this procedure have been described (5, 25, 34, 56), and the compound has been made in other ways 35, 56,110, 164), but Meister s preparation, in which the yield of crude product is greater than 90%, remains the method of choice. Purification of crude cyclopenta-dienylthallium(I) is best accomplished by vacuum sublimation, and purity of samples can readily be assessed by gas-liquid chromatography on silicone oil at 170° C using hydrogen as carrier gas (7). 

The distillation separation procedure was the principal method used for the arsenic determinations, but more recently Santoliquido (24) has developed a method for the carrier-free separation of arsenic from low-temperature coal ash involving retention on an inorganic exchanger column. 

The mixture to be separated and analyzed may be either a gas, liquid, or a solid in some instances. All that is required is that the materials be stable, have a vapor pressure of 0.1 torr at the operating temperature and interact with the column material (either a solid adsorbent or a liquid stationary phase) and the mobile phase (carrier gas). The result of this interaction is the differing distribution of the sample components between the two phases, resulting in the separation of the sample components into zones or bands. The principle that governs the chromatographic separation is the foundation of most physical methods of separation, for example, distillation and liquid-liquid extraction. 

Friedrich et al. [28] describes a method of recycling a rhodium catalyst via thermal separation. The rhodium, which is fixed on a layer, is dissolved into the solution, in which triphenylphosphine stabilizes the rhodium. The reaction is carried out in a reactor with a synthesis gas pressure of 60 bar and at 120°C. After the reaction, the carrier is filtered before the product, methyl formylstearate, is separated by distillation. The rhodium-containing residue is united with the carrier before the organic... 

Short-lived antimony Isotopes, such as 19-mlnute Sb12 , 10.3-mlnute Sb12 , and 1.9-minute Sb1 2 produced In Te(d,a) and Te(n,p) reactions or In the fission process, can be separated rapidly as stibine (1,87,88). More recently, 10-second separations of the antimony activities In fission products have been made (l64). For this method Sb+ carrier with the fission products and 300 sulfuric acid was dropped onto metallic zinc held In a distillation flask at 100° C. 

The ideal solvent would be easily recovered from the extract. For example, if distillation is the method of recovery, the solvent-solute mixture should have a high relative volatility, low heat of vaporization of the solute, and a high equilibrium distribution coefficient. A high distribution coefficient will translate to a low solvent requirement and a low extract rate fed to the solvent recovery column. These factors will minimize the capital and operating costs associated with the distillation system. In addition to the recovery aspects, the solvent should have a high selectivity (ratio of distribution coefficients), be immiscible with the carrier, have a low viscosity, and have a high density difference (compared to the carrier) and a moderately low interfacial tension. 

Membrane distillation (MD) is a separation method that employs porous liophobic membrane, non-wettable by the liquid. Because of liophobicity of the polymer, only vapor is transported through membrane pores. The condensation takes place on the other side of the membrane in air gap, cooling liquid or inert carrier gas. Usually MD is employed to treat water solutions, therefore hydrophobic membranes manufactured from polymers such as polypropylene (PP), polytetrafluoroehtylene (PTFE),... 

Radiochemical purification of the induced activity in the presence of carrier involves chemical operations such as precipitation, distillation, solvent extraction, chromatography, and ion exchange. While the chemistry performed on the carrier and sample should be designed to isolate the material in a pure state, a useful operation frequently carried out is scavenging. Strongly adsorptive precipitates such as ferric hydroxide, lanthanum fluoride, and antimony sulfide may be formed in the solution. These precipitates, by coprecipitation, occlusion, and surface adsorption can be used to remove unwanted traces of activity. A scavenging agent should be chosen that wdll not carry down appreciable amounts of the carrier from solution. An alternative method is to add hold-back carriers for the unwanted traces of activity and precipitate the required element in their presence. 

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