Sulfur anions separation

Fig. 5 Electropherogram of six sulfur anions illustrating peak fronting [thiosulfate (S2Ol-)] and peak tailing [tetrathionate (S4Ol-)] for better visibility of peak asymmetry, the perpendicular peak axis is drawn as a solid line. Separation in 20 mM chromate run buffer at pH 8.3.

High-performance ion chromatography was used by Biemer (17) to separate acesulfame-K from saccharin and cyclamate. A Dionex AS4A anion separator column and a mobile phase of 300 mg Na2C03/L were used for the separation of the sweeteners. The regenerate solution consisted of 25 mM sulfuric acid solution. Wu et al. (63) determined acesulfame-K on Dionex AS4A-SC and 0.5 mM Na2C03 mobile phase. 

As can be expected, sulfuric acid separates well from hydrochloric acid, because the size of the two anions differs noticeably, rhydr = 3.79 and 3.32A, respectively. Similarly, K2SO4 will separate from KCl with almost the same selectivity, since the K ion, being the smallest in the mixture (3.31 A), does not influence significantly the situation in the system. 

Systematic studies compared the effect of eluent composition on the separation of six sulfur anions. Tetraethylammonium (TEA) salts did not resolve the peak tetrabutylammonium (TEA) gave very long retention times, but tetrapropylammo-nium (TPA) acetate resolved aU peaks in 22 min. 

The effect of varying TPA concentrations from 3-11 mM at a fixed 20% acetonitrile in water and pH 5.0 was studied. Increasing the TPA concentration slowed the elution rate of the sulfur anions. At TPA concentrations of 3 and 4 mM, all six anions eluted rapidly but thiosulfate was not separated from thiocyanate. TPA concentrations above 9 mM hexathionate required an elution time of >25 min. Good resolution of all peaks was obtained at 6 mM TPA. 

Nickel and Cobalt. Often present with copper in sulfuric acid leach Hquors are nickel [7440-02-0] and cobalt [7440-48-4]. Extraction using an organophosphoric acid such as D2EHPA at a moderate (3 to 4) pH can readily take out the nickel and cobalt together, leaving the copper in the aqueous phase, but the cobalt—nickel separation is more difficult (274). In the case of chloride leach Hquors, separation of cobalt from nickel is inherently simpler because cobalt, unlike nickel, has a strong tendency to form anionic chloro-complexes. Thus cobalt can be separated by amine extractants, provided the chloride content of the aqueous phase is carefully controUed. A successhil example of this approach is the Falcon-bridge process developed in Norway (274). 

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S0 3, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach Hquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH NO, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and cosdy ore particle/leach hquor separation step. 

Dilution with water reverses the reaction, and heating the solution Hberates sulfur dioxide. Upon being added to a solution of teUurides, teUurium forms colored polyteUurides. Unlike selenium, teUurium is not soluble in aqueous sodium sulfite. This difference offers a method of separating the two elements. Like selenium, teUurium is soluble in hot alkaline solutions except for ammonium hydroxide solutions. Cooling reverses the reaction. Because teUurium forms solutions of anions, Te , and cations, Te" ", teUurium films can be deposited on inert electrodes of either sign. 

The liquid membrane (thickness 0.2 cm) was separated from the aqueous solutions by two vertical cellophane films.The electrode compartments were filled with 0.05 M sulfuric acid solutions and were separated by the solid anion-exchange membranes MA-40. Binary mixtures contained, as a mle, 0.04 M Cu(II) and 0.018 M Pt(IV) in 0.01 M HCl. 0.1 M HCl was used usually as the strip solution. 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

Active fractions are combined and concentrated in vacuo to about 5 liters. The concentrate is then adjusted to a pH of 8.0 with 6N sulfuric acid and passed through a column packed with 1 liter of an anion exchange resin, Dowex 1X2 (OH form). The column is washed with about 5 liters of water and the effluent and the washings containing active substance are combined and are concentrated to 1/15 by volume. The concentrate is adjusted to a pH of 10.5 with 6N sodium hydroxide and 5 volumes of acetone is added thereto. The resultant precipitate is removed by filtration and the filtrate is concentrated to 500 ml. The concentrate is adjusted to a pH of 4.5 with 6N sulfuric acid and 2.5 liters of methanol is added thereto. After cooling, a white precipitate Is obtained. The precipitate is separated by filtration and washed with methanol. After drying in vacuo, about 300 g of white powder is obtained. 

A number of radical anions of sulfur-containing aromatic compounds have been studied essentially by means of ESR spectroscopy and sometimes by electronic spectroscopy. The studied compounds include aromatic rings separated by the oxidized sulfur functionality. The effects caused by the latter depend on the geometry and topology of the aromatic systems as well as on the electron-withdrawing ability of the other substituents. 

The analysis of phosphates and phosphonates is a considerably complex task due to the great variety of possible molecular structures. Phosphorus-containing anionics are nearly always available as mixtures dependent on the kind of synthesis carried out. For analytical separation the total amount of phosphorus in the molecule has to be ascertained. Thus, the organic and inorganic phosphorus is transformed to orthophosphoric acid by oxidation. The fusion of the substance is performed by the addition of 2 ml of concentrated sulfuric acid to — 100 mg of the substance. The black residue is then oxidized by a mixture of nitric acid and perchloric acid. The resulting orthophosphate can be determined at 8000 K by atom emission spectroscopy. The thermally excited phosphorus atoms emit a characteristic line at a wavelength of 178.23 nm. The extensity of the radiation is used for quantitative determination of the phosphorus content. 

The thiazolecarboxylic acid structure (40) was also guessed in a similar way, from tracer experiments. The unknown compound was converted into the thiamine thiazole by heating at 100°C and pH 2. On paper electrophoresis, it migrated as an anion at pH 4. Tracer experiments indicated that it incorporated C-l and C-2 of L-tyrosine, and the sulfur of sulfate. The synthetic acid was prepared by carboxylation of the lithium derivative of the thiamine thiazole, and the derivatives shown in Scheme 19 were obtained by conventional methods. Again, the radioactivity of the unknown, labeled with 35S could not be separated from structure 40, added as carrier, and the molar radioactivity remained constant through several recrystallizations and the derivatizations of Scheme 17. 

Chlorinating the aqueous waste sludge suspension (to oxidize the chromium) at temperatures of 20 to 80°C and pH values between 4 and 13. The chlorinated sludge is then acidified with sulfuric acid to a pH of 1.0 to 3.0. The insoluble components are then separated, followed by the separation of the chromium(VI) from the solution using a fixed-bed anion exchanger (at pH values of <3). 

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